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ALUMINIUM EXTRUSIONS
— a technical design guide
i ; c
For free, objective advice on all matters relating to aluminium extrusions contact:
The Shapemakers Information Service Broadway House Calthorpe Road Birmingham B151TN
Tel: 021 4562276 Fax: 021 4562274
ALUMINIUM EXTRUSIONS — a technical design guide
PUBLISHED BY THE SHAPEMAKERS — the information arm of the UK Aluminium Extruders Association
'I
© The Shapemakers
Broadway House Calthorpe Road Birmingham B151TN
DISCLAIMER
This book is intended for use by technically skilled personnel. The use of the information contained herein by such technically skilled personnel, is at the risk of the user. While all reasonable skill and care has been exercised in the preparation of this book, there are no warranties, express or implied, as to the accuracy or completeness of this work, either by the author or the publisher, both of whom deny responsibility or liability for any results obtained or damages caused as a consequ- ence of the use thereof .The publisher and the author hereof grant no licence with this book and disclaim all liability for suitability, practicability, infringement of property rights of third parties or non-conformance with any codes, standards or regulations.
ACKNOWLEDGEMENT TO BSI
Extracts from British Standards are reproduced with the permission of BSI. Com- plete copies of the Standards can be obtained by post from BSI Sales, Linford Wood, Milton Keynes, MK1 4 6LE.
First published October 1989 Reprinted July 1991 Reprinted August 1994
Printed in Great Britain by St Edmundsbury Press Ltd Bury St Edmunds, Suffolk
VI
PREFACE to the 1994 reprint — by Howard Spencer
Since this manual was originally published, British Standards have published a new aluminium structural code, BS 8118 1991, which supersedes BS CP118 1969:
— Part 1: Code of Practice for Design — Part 2: Specification for Materials, Workmanship and Protection
There is at present a change-over period where both design codes are valid, but at some time in the future BS CP118 will be withdrawn. This new code is intended to
bring aluminium structural design into line with other metals and also with European standard codes, which will simplify future preparation of an overall European structural code for aluminium.
I intend here to give users of the manual a very brief outline of how the new codes will
affect the use of aluminium. It is impossible to go into too much detail. Those
requiring additional information should refer to the codes themselves, available from British Standards (see address below).
The New Code
The new code is based around a new design approach, based on the principle of 'limit state design'. This principle is concerned with ensuring that any given structure can carry the loads and forces placed upon it without failure, up to a pre-determined limit. The factored resistance of a structure must therefore never be less than the factored loading. The following equation can be applied:
Y12R = Y4S
= overall resistance factor R = calculated resistance
= overall loading factor S = maximum design load
The resistance is calculated from the effective sectional properties, the limiting stress and a material and connection factor. The loading effect is factored for type of load, i.e. dead load, imposed load, wind load and temperature induced forces.
The new code also covers the calculation of elastic instabilities. Aluminium sections with very wide, thin elements are susceptible to local buckling under high compres- sive stresses. The relevant calculations have been simplified in the new code by adopting a classification system based upon a factored relationship between the width or depth of the element and the thickness. Three categories are listed for moment resistance — compact, semi-compact and slender. For compact sections,
I
no further check is required as they will not suffer from local buckling. (For example, afl the sections listed in BS 1161 "Aluminium Structural Sections" are compact.) Semi-compact resistance is obtained by using the quoted limiting stress of the material. Sections defined as slender, however, are assessed on the basis of a reduced effective wall thickness and the extent of the reduction can be obtained from a series of curves. Only the compact and slender categories are allowed when calculating the axial resistance of struts.
The recommendation for deflection levels has not changed, but a word of caution is included in the specification against imposing too tight a standard on aluminium structures when the particular application does not merit it.
The section on welding has been greatly extended from that in the original code. Guidance is provided on the design of welds taking into account the strength of the weld metal and a partial reduction in strength in the heat affected zone of the parent metal. The limiting stresses for both filler and parent metal are given with factors for designing butt and lap joints for both traverse and longitudinal welds.
Adhesively bonded joints are only recommended for secondary stressed connec- tions. The factored resistance of a bonded joint can be calculated from an expres- sion containing a failing standard, obtained from testing, and a material connection factor for bonded joints, If validated test data is available, it can be used in the joint resistance expression.
The section on fatigue has also been greatly extended, incorporating information from both UK and European research. The tables for both welded and non-welded structures contain detailed sketches illustrating the type of construction, direction of stress, fluctuation and possible crack locations. The tables are based upon BS 5400 Part 10: Bridges and give the classification for a range of structural detail.
Full supporting data including mathematical formulae relevant to the design calcula- tions and curves used in the code are set out in the appendices of the new code and can be used to assist computer aided design.
All references in the manual to BS CP1 18 now apply to BS 8118 and, as the new code does not cover permissible stress levels, table 3.2 and figure 3.3 are not applicable. Tables 3.4 and 6.11 have also been modified as the standard elastic modulus for all wrought aluminium alloys is now 70,000 N/mm2
Reviewing the worked examples given in the manual, the pedestrian balustrade (pages 113—122) results in marginal modifications to some sections when worked to the new code but gives similar overall results. In the case of the unloading ramp, however (pages 111—112) there could be a slight saving in the thickness of the section when meeting the new code. The column example (pages 123—125) refers to alloy 2014 AT6 which is no longer a standard material in the new code. Although it can be used, the limit state stresses would have to be established and, in this case, the section thickness would have to be slightly increased.
VIII
Competently used, the old code should still give an acceptable level of design. It should be noted, however, that if the calculations are to be officially approved then only the new code is valid. Furthermore, the up-dated information in the new code can result in a more economical structural use of the material.
Codes referred to: BS 8118 Part 1: 1991 Code of Practice for Design BS 8118 Part 2: 1991 Specification for Materials,
Workmanship and Protection
These are available from: Sales Dept, BSI, Linford Wood, Milton Keynes, MK14 6LE, or any HMSO.
ix
INTRODUCTION
Aluminium is a highly versatile, light and strong material which can be produced in a variety of alloys and extruded into an almost infinite number of shapes. This powerful combination of factors enables the user to be more innovative and facilitates cost- effective design.
Comprising 8% of the earth's crust, aluminium is a plentiful resource. It is a modern material, first used in commercial production in 1886. Since then, the list of applications has grown immensely. Now, designers working in a whole range of different sectors, including general engineering, construction, transport, packaging and consumer products, are reaping the benefits gained by using aluminium extrusions.
The Shapemakers was established by the Aluminium Extruders Association (AEA) in 1984 to provide independent guidance on all matters relating to extruded aluminium. Representing the UK's top extrusion companies, The Shapemakers is able to draw upon these companies' considerable resources and expertise.
This technical design guide contains a wealth of information on aluminium itself, as well as giving details on the extrusion process, fabrication and finishing. Also included is a comprehensive design section, which outlines the important design considerations and shows a number of worked examples.
For reasons of clarity, only six alloys have been incorporated into the main body of the manual. These have been carefully selected to illustrate the various uses of alloys — from general purpose to high strength. Additional alloys are listed in the appendices. For details of the availability of any alloy listed in this manual, please contact the Shapemakers Information Service in Birmingham, Tel: 021 456 2276.
The AEA would like to thank The Shapemakers' technical consultant, Howard Spencer, for all his work in compiling this design guide. A special thanks also goes to The Shapemakers' members, Hugo Ravesloot, Jim Peach and Chris Forman.
Derek Phillips
Chairman of The Shapemakers
CONTENTS
PRINCIPLES OF EXTRUSION 1
MATERIAL SPECIFICATIONS 25
MECHANICAL PROPERTIES 33
DURABILITY 45
SURFACE FINISHING 55
FABRICATION 63
CONDUCTIVITY 87
TEMPERATURE 93
FIRE 97
CARE AND CONTROL 101
DESIGN 105
GLOSSARY OF TERMS 127
APPENDICES 133
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 1 - PRINCIPLES OF EXTRUSION
CONTENTS
Title Page No.
EXTRUSION PROCESS 4 Direct Extrusion 4 Indirect Extrusion 5 Hollow Sections 6
EXTRUDABILITY 7 Extrusion Ratio 7 Shape Factor 7
SIZE 8
THICKNESS 8
SLOTS 10
SECTION CLASSIFICATION 11
CORNERS 11
TOLERANCES 12
List of Figures
Fig No. Title Page No.
1.1 The Direct Extrusion Process 4
1.2 The Differing Operating Principles of Direct and Indirect Extrusion 5
1.3 Extrusion of a Hollow Section 6
1 .4 Thick to Thin Transitions in Extrusion Cross Section 10
1.5 Pressure Hinge 10
1.6 Slot Aspect Ratios 10
1.7 Standard Section Types 11
List of Tables
No. Title Page No.
1.1 Shape Factor Value 8
1.2 A Guide to Minimum Thickness 9
1.3 Tolerances on Diameter of Round Bar Intended for use on Automatic Lathes 12
1.4 Tolerances on Widths Across Flats of Hexagonal Bar for the Manufacture of Nut & Bolts 13
1.5 Tolerances on Diameter of Round Bar in the Controlled Stretched Condition 13
2
List of Tables (contd.)
No Title Page No.
1.6 Tolerances on Diameter or Width Across Flats of Bars for General Purposes and on Width of Solid or Hollow Regular Sections 14
1 .7 Angular Tolerances for Extruded Regul& Sections 15
1.8 Permitted Corner Radii 15
1 .9 Tolerances on Wall Thicknesses of Extruded Round Tube (classes A, B and C). 16
1.10 Tolerances on Thickness of Bars and Regular Sections 17
1.11 Tolerances on Open End of Channels and L Beams 18/19
1.12 Tolerances on the Outside Diameter of All Extruded Round Tube and on the Inside Diameter of Class A and Class B Extruded Round Tube 20
1.13 Tolerances on Thickness of Hollow Sections (classes A and B) 21
1 .14 Tolerances on Straightness for Extruded Bar, Regular Sections and Extruded Round Tubes 22
1.15 Tolerances on Length for All Materials Supplied in Fixed Cut Lengths 23
1 .16 Tolerances on Concavity and Convexity for Extruded Solid and Hollow Sections 23
1 .17 Tolerance on Twist for Extruded Solid and Hollow Sections 24
3
EXTRUSION PROCESS
Direct Extrusion
The direct extrusion process can be clearly seen in the schematic diagram in Fig. 1.1. Cylindrical aluminium alloy billets of cast or extruded manufacture are heated to between 4500 and 500° before being loaded into a container and the billet squeezed through a die orifice using ram pressures of up to 68OMPa. The die is supported by a series of back dies and bolsters so that the main press load is transferred to a front platen.
Fig. 1.1 - The Direct Extrusion Process
4
Platen
Ram cross head
Stem
Liner Die slide
Dummy block
Container
Billet
Die
Backer
Sub bolster
Extruded section
On leaving the die the temperature of the section is more than 500°C and with heat
treatable afloys the quenching, or solution heat treatment, takes place in the production line. This can be by water bath, water spray or forced-draught air, with the latter being particularly useful for thin sections. The approximate temperature drop during the traverse of the quench box is 250°C. To avoid distortion care has to be exercised in handling sections with extreme aspect ratios and large variations in thickness.
After extrusion the section is guided down the table by a puller on to a slatted moving belt. Modern Pullers are based on linear motor s,stems and operate on tables up to 40 metres long. On completion of an extruded length, the section is sheared at the
press end and lifted from the slatted table by eccentric pivoted arms. It is then transferred by a walking beam or multi-belt transfer table to the stretcher bay where it is given a controlled stretch to straighten and remove minor mis-alignments. The section is then taken and cut to ordered lengths on high speed tungsten carbide tipped saws.
If the material is required in the solution heat treated condition (T4) it is released at this stage. If the full strength aged material (T6) is required, it is given a precipitation treatment before release. In the case of the T5 temper, there is limited cooling at the press exit and the material goes directly to precipitation treatment.
Indirect Extrusion
In the traditional direct method of extrusion, as described above, the die is stationary and the press ram applies pressure on to the billet. In the indirect method, the ram carries the die and applies pressure on to the stationary billet, in the opposite direction of extrusion. There can be variation to this basic concept, but in every case the billet remains stationary in relation to the container, thereby keeping friction loss to a bare minimum. See Fig. 1.2. Die
Fig. 1.2 - The Differing Operating Principles of Direct and Indirect Extrusion
5
Extrusion
Die Billet
Extrusion Indirect extrusion
Die Billet
Hollow Sections
A bridge or 'port-hole die' is usually used to make hollow sections. A solid billet is forced, under pressure, through a composite die tool that first divides the metal into two or more separate streams which then flows down under the bridge to be pressure welded together and emerge, as an extruded section, through the orifice formed between the mandrel nose and the outer section shape which has been cut in the die. See Fig. 1.3.
Any sample taken across the section would show an integral material quality with no reduction of strength in the weld areas. Inspection methods are usually by destructive test sampling in line with that laid down by the British Standards for scaffold tubing in specification BS 1139. Production methods for this kind of section are well established and extruders will be pleased to advise on the feasibility of producing any hollow section.
Some caution must be exercised, however where thin hollow sections are required in the stronger alloys, particularly from the bridge or port-hole production methods. Hollow sections are usually produced in these alloys by using centre mandrels that are not connected to the die but are passed through a bored or pierced hole in the centre of the billet and either connected or supported by the press rod. In this type of production, the metal flow around the mandrel is not interrupted and there are no extrusion weld planes in the section. There may be some restriction in the availability of this type of production and in the range of sections obtainable from it. As the standard of tolerances may also be wider further information and advice should be sought from the extruder for strong alloy hollow sections.
Pressure
Fig. 1.3 - Extrusion of a Hollow Section
6
area
Bridge Mandrel nose
EXTRUDABILITY
Aluminium alloys offer a wide range of performance characteristics and important amongst these is its extrudability. Linked with modern die-making facilities and traditional expertise the metal offers a virtually unlimited variety of section shapes. The feasibility of any extrusion has both technical and commercial considerations and most extruders use a number of methods to evaluate extrusion complexity. These methods are usually based upon a combination of extrusion theory and experience.
Extrusion Ratio
Extrusion ratio is the value obtained by dividing the cross-section area of the extrusion billet by the cross-section area of the extrusion to be produced. It depends very much on the size and type of press available and is a factor that can only be considered by the extruder. Optimum extrusion ratios for direct extrusion are usually between 30 and 50.
With low values of 7 or under, there is very little working of the material during extrusion. This gives a corresponding drop in mechanical properties and the possibility of coarse
grain bands. Values of 80 and above require high breakthrough pressures which are likely to cause die distortion and possible breakage.
In some cases the extrusion ratio can be improved by using a multi-hole die. In the case of indirect extrusion much higher extrusion ratios are possible because of the relatively low frictional force developed in the system.
Shape Factor
The resistance of a section to extrusion can be influenced by the shape factor. This is the relationship between the periphery and cross-section area of the section being extruded. It is usual for extruders to modify the shape factor value, in terms of extrusion weight, by dividing the periphery by the cross sectional area and multiplying by .0027. The shape factor of a proposed extrusion is usually compared with that of a similar existing extrusion to obtain a measure of extrudability. This is not a precise method, however, as any large difference in wall thickness can alter the ratio substantially. In
general, the higher the value the more difficult the extrusion and the more limited the alloy choice thereby restricting some high strength alloys. Table 1 .1 sets out some general values which can be used for reference.
7
Table 1.1 - Shape Factor Values
Section Type CCD Thickness Shape Factor mm mm
L 142 2.5 300
L 70 1.5 500 I 112 5.0 152
O 142 solid 15
O 70 solid 30
© 50 3.0 247
© 50 1.5 494
ltiiiiiil 210 3.0 190
210 2.0 285
Iii 11J 140 2.0/6.0 183
I- I 40 2.0/1.5 430
SIZE
The size of an extruded shape is determined by the diameterof the circumscribing circle (CCD) required to enclose the cross-section. The maximum CCD for any die size is
governed by the need to keep an unbroken structural ring around the die orifice.The minimum width of that ring can vary from 20 mm on an average size solid die to 60 mm or more on dies for large hollow sections. Most average sections fit into CCDs below 155 mm with a medium range of 250 mm and very large sections up to 400 mm.
The section, should, as far as possible, be distributed around the centre of the CCD. In any extrusion, metal flow is slower towards the outside edge of the die so the placing of thicker parts of the section away from the centre results in a more even metal flow.
THICKNESS
Factors that dictate thickness are influenced by section shape, alloy, die face pressure, extrusion speed and section stability during solution heat treatment and post-extrusion handling. A general guide to minimum thickness is given in Table 1.2 which is based on 6063 material.
8
E E
I- 0) 0)
C-) r 0)
0)
Table 1.2 - A Guide to Minimum Thickness
C C D in mm
a) Values for 6082 should be increased by 25% b) These thickness - GCD ratios represent average values based upon good working
practice. c) The values up to 1 .25 mm thick are for small specialised presses with very high
die face pressure levels. d) When ratios below those shown are required contact extruders.
The extrusion process will tolerate variations in section thickness but it is important to avoid abrupt change. Acceptable transition between thicknesses can be obtained by using radii or blending curves, see Fig. 1 .4. Short spans of local thinning can also be
incorporated in most sections. This is a useful method of introducing pressure hinges in section elements which will be deformed during subsequent fabrication, see Fig. 1 .5.
9
50 200 250 300
p
p I Thin hinge Radius / —
Fig. 1.4 - Thick to Thin Transitions in Fig. 1.5 - Pressure Hinge Extrusion Cross-Section
SLOTS
The formation of slots, or open box channels, in a section requires a finger or box spigot to be retained on the die. As it is not possible to reinforce these spigots, which act as local cantilevers under extrusion pressure, a practical limit must be placed on the size and type of slots available. Fig. 1.6 details the normal method of calculating slot aspect ratios although where gaps are below 3 mm these ratios are even further reduced. The maximum ratios are 3:1. Higher values are possible, particularly in 6063 alloy. Screw ports and bolt slots are detailed under these headings in section 6 Fabrication.
— Gap — Depth
___ _____ Width
Area Depth Aspect Ratio = — Aspect Ratio = — Gap2 Width
Fig. 1.6 - Slot Aspect Ratios.
10
SECTION CLASSIFICATION
There are three standard types of section - solid, semi-hollow and hollow. The first and last are self-explanatory. Semi-hollow describes those solid sections which have open box recesses with aspect ratios (depth/width) less than three. In general, the tooling and production costs increase with section categories from solid to semi-hollow and then hollow.
Solid Semi-hollow Hollow
Fig. 1.7 - Standard Section Types
CORNERS
All corners are normally broken by a radius but where absolutely necessary, sharp corners can be incorporated in a section either internally or externally but the life of the die and the speed of extrusion are both markedly reduced. Such corners also introduce problems where painted finishes are specified, introducing obvious sight lines. The
breaking of the corners, even by 0.5 mm radii is helpful in overcoming these problems but for ideal extrusion conditions, radii should be related to the overall size of the section. Table 1.8 sets out preferred values.
11
TOLERANCES
Tolerance levels for regular sections are laid down in BS 1474, however as the bulk of extrusions are non-standard they are not covered in the standard. The extrusion industry regards BS 1474 as a target level and is prepared to accept if for all general business, apart from very thin or complex sections which will be the subject of special enquiry. Closertolerances can be obtained for some sections but, again, this is a matter between customer and extruder.
In line with most production methods, tolerances are necessary to cover variations in the actual process and wearing of tools and dies.
Most tolerances are quoted as plus or minus around a datum value but, if required, unilateral tolerance can be obtained, either all positive or all negative. It is essential, however, to agree this requirement before die manufacture is commenced as the dimensional datum of the die will be altered.
All tolerances should be measured at 160G. This is particularly significant forthe length tolerances of long bars.
There is no laid-down standard for the surface smoothness or texture of mill finished extruded sections.
Table 1.3 - Tolerances on Diameter of Round Bar Intended for use on Automatic Lathes
Diameter Plus and minimum tolerances on
diameter Over Up to and including
mm 10 18 30 40 60 80
100
mm 18 30 40 60 80
100 160
+mm -mm 0.05 0.10 0.08 0.13 0.14 0.14 0.20 0.20 0.30 0.30 0.40 0.40
± 0.5% of specified diameter
12
Table 1.4 - Tolerances on Width Across Flats of Hexagonal Bar for the Manufacture of Nuts & Bolts
Width across flats Tolerance on width across flats
(all minus) Over Up to and Including
mm mm mm - 4.0 0.08 4.0 19.0 0.10
19.0 36.0 0.13 36.0 46.0 0.15 46.0 80.0 0.20
Table 1.5 - Tolerances on Diameter of Round Bar in the Controlled Stretched Condition*
Diameter Tolerances on diameter
(plus and minus) Over Up to and including
mm mm +mm -mm 10 18 0.05 0.20 18 30 0.08 0.26 30 40 0.14 0.28 40 60 0.20 0.40 60 80 0.30 0.60 80 100 0.40 0.80
100 180 0.5% of 1.0 % of specified specified diameter diameter
* The controlled stretch procedure reduces the level of any residual stresses in a bar and is ideal for machining stock. Special Tempers T6510 and T6511 refers.
13
Table 1.6 - Tolerances on Diameter or Width Across Flats of Bars for General Purposes and on Width of Solid
or Hollow Regular Sections
Diameter, width or width across flats
Tolerances (see notes 1 and 2) Over Up to and
including
mm mm ±mm - 3 0.16 3 10 0.20
10 18 0.26 18 30 0.32
30 40 0.40 40 60 0.45 60 80 0.50 80 100 0.65
100 120 0.80 120 140 0.90 140 160 1.00 160 180 1.10
180 200 1.20 200 240 1.30 240 280 1.50 280 320 1.70
NOTE 1: Tolerances in this table apply to solid materials other than: (a) round bar for use on automatic lathes (see table 1.4) (b) controlled stretched bar (see table 1.6) (c) hexagonal bars for the manufacture of nuts and bolts (see table
1.5)
NOTE 2: Tolerances in this table apply to hollow regular sections
having a wall thickness not less than 1.6mm or 3% of the overall width, whichever is the greater. In the case of non-heat-treated material or 1.6mm or 4% of the overall width, whichever is the greater, in the case of heat treated material. The tolerance should be applied to the width measured at the corners.
14
Table 1.7 - Angular Tolerances for Extruded Regular Sections
Nominal thickness of thinnest leg Allowable deviation from angle
specified (measured at the ex- tremitles of the section)
j-
Over Up to and including
mm mm - 1.6 2°
1.6 5.0 1.5° 5.0 - 1°
Table 1.8- Permitted Corner Radii
For square and rectangular sections
Minor dimension Radius on corner (max.)
Over Up to and Including
mm mm mm - 5 0.4 5 10 0.8
10 25 1.6 25 50 2.5 50 120 3.0
120 - 5.0
For regular sections (e.g. angle, channel, I- and I - sec-
tions)
Thickness of section
Radius on corner (max.)
mm Up to and including 5
Over5
mm
0.8
1.5
15
Table 1.9 - Tolerances on Wall Thickness of Extruded Round Tube (classes A, B and C) (see note 1)
Nominal wall thickness of tube
Class A Class B Class C
Toleranc on mean wall thickness
Wall thickness at any point
(Max.) (Mm.)
Tolerano on mean wall thickness
Wall thickness at any point
Tolerance on mean
Wall thickness at any point
.
(Max.) (Mm.) (Max.) .
(Mm.)
wall thickness
mm
1.0 1.5 2.0
2.5 3.0 4.0
5.0 6.0 7.0
8.0 10.0 12.0
14.0 16.0 18.0
20.0 22.0 25.0
±mm
0.15 0.16 0.17
0.18 0.20 0.23
0.26 0.28 0.31
0.34 0.40 0.46
0.53 0.58 0.63
0.68 0.74 0.81
mm
1.20 1.71 2.23
2.74 3.27 4.30
5.34 6.38 7.43
8.47 10.52 12.61
14.71 16.76 18.82
20.90 23.00 26.10
mm
0.80 1.29 1.77
2.26 2.73 3.70
4.66 5.62 6.57
7.53 9.48
11.39
13.29 15.24 17.18
19.10 21.00 23.90
±mm
-
0.18 0.20
0.22 0.27 0.31
0.37 0.43 0.51
0.56 0.65 0.77
0.88 1.00 1.13
1.22 1.35 1.49
mm
- 1.74 2.27
2.80 3.36 4.42
5.49 6.58 7.67
8.76 10.85 13.03
15.24 17.34 19.44
21.63 23.81 27.00
mm
- 1.26 1.73
2.20 2.64 3.58
4.51 5.42 6.33
7.24 9.15
10.97
12.76 14.66 16.56
18.38 20.19 23.00
±mm
- - -
- 0.65 0.70
0.75 0.82 0.89
0.94 1.03 1.15
1.30 1.40 1.50
1.60 1.73 1.88
mm
-
-
- 3.87 4.93
6.00 7.09 8.18
9.27 11.36 13.54
15.75 17.88 20.00
22.13 24.32 27.50
mm
- -
-
-
2.13 3.09
4.00 4.91 5.82
6.73 8.64
10.46
12.25 14.12 16.00
17.88 19.68 22.50
NOTE 1: BS tolerance classes A,B and C for round tube denote a descending order of tolerance standard. All classes applicable to 6063, 6063A, 6082, 6101A, 6463, Only Classes B & C are applicable to 2014A
NOTE 2: The tolerances given in this table apply to non-heat-treated tube of wall thickness not less than 1.6mm or 3% of the outside diameter, whichever is the greater and to heat treated tube of wall thickness not less than 1.6mm or 4% of the outside diameter, whichever is the greater.
NOTE 3: These tolerances on wall thickness do not apply where tolerances on both outside and inside diameter are required in which case the eccentricity tolerance on the resultant wall should be agreed between the purchaser and the supplier at the time of the enquiry and order.
NOTE 4: Mean thickness is defined as the sum of the wall thicknesses measured at the ends of any two diameters at right angles, divided by four.
NOTE 5: The tolerance on the wall thickness of intermediate nominal wall thickness should be taken as those of the next lower size.
16
—4
Tab
le 1
.10-
Tol
eran
ces
on T
hick
ness
of
Bar
s an
d R
egul
ar S
ectio
ns
Wid
th ac
ross
fla
ts o
f bar
or
wid
th o
f se
ctio
n
Ove
r U
p to
and
In
clud
ing
Tol
eran
ces
on s
peci
fied t
hick
ness
(plu
s an
d m
inus
)
Up
to a
nd O
ver
Incl
udin
g 1.
6mm
1.
6mm
up
to a
nd
thic
k in
clud
ing
3mm
th
ick
Ove
r 3m
m
up t
o an
d in
clud
ing
6mm
th
ick
Ove
r 6m
m
up t
o an
d in
clud
ing
10m
m
thic
k
Ove
r 10
mm
up
to a
nd
incl
udin
g 18
mm
th
ick
Ove
r 18
mm
up
to a
nd
incl
udin
g 30
mm
th
ick
Ove
r 30
mm
up t
o an
d
incl
udin
g 40
mm
th
ick
Ove
r 40
mm
up
to a
nd
incl
udin
g 60
mm
th
ick
Ove
r 60
mm
up
to a
nd
incl
udin
g 80
mm
th
ick
Ove
r 80
mm
up
to
and
incl
udin
g 10
0mm
th
ick
Ove
r 10
0mm
up
to a
nd
incl
udin
g 12
0mm
th
ick
Ove
r 12
0mm
up
to
and
incl
udin
g 14
0mm
th
ick
Ove
r 14
0mm
up
to
and
incl
udin
g 16
0mm
th
ick
mm
-
mm
10
mm
016
± m
m
018
± m
m
020
± m
m
022
± m
m
-
+ m
m
-
+ m
m
- +
mm
-
+ m
m
-
± m
m
mm
-
+ m
m
-
mm
-
10
18
018
020
022
024
026
.
18
30
022
024
026
028
030
032
- -
- -
- -
.
30
60
0 24
0
26
0 28
0
30
0 33
0
36
0 40
-
- .
.
60
80
0 28
0
30
0 32
03
4 0
37
0 40
04
3 0
45
0 50
-
- -
-
80
120
032
034
036
039
042
045
048
052
057
065
080
- -
120
180
- 03
6 04
0 04
5 05
0 05
5 06
0 06
5 07
0 07
5 08
2 09
0 10
0
180
240
- -
050
055
060
065
070
075
080
085
090
095
105
240
320
- -
060
065
070
075
080
085
090
095
100
105
1 10
NO
TE
:-
For
sec
tions
over
160
mm
thic
k, th
e to
lera
nces
on t
hick
ness
are
tho
se sh
own
for c
ompa
rabl
e wid
ths
(see
Tab
le 1
.6)
Tab
le 1
.11
Tol
eran
ces
on O
pen
End
Cha
nnel
s an
d L
Bea
ms
Ove
rall
wid
th
Wof
ch
anne
l or i
-bea
m
Min
imum
th
ickn
ess
of w
eb or
flang
e In
lern
al or
exte
,nai
tol
eran
ce o
n op
en e
nd d
imen
sion
for v
ario
us d
eplh
s of
open
ing
D(p
ius
and
min
us)
For
0
For
0
For
0
For
D
For
D
For
0
For
0
For
0
For
0
For
0
For
0
up t
o an
d ov
er
over
ov
er
over
ov
er
over
ov
er
over
ov
er
over
in
clud
ing
10m
m
18m
m
30m
m
40m
m
60m
m
80m
m
100m
m
120m
m
140m
m
160m
m
10m
m
up to
and
up
to
and
up to
and
up
to a
nd u
p to
and
up
to
and
up to
and
up
to a
nd u
p to
and
up
to a
nd
deep
in
clud
ing
incl
udin
g in
clud
ing
incl
udin
g in
clud
ing
incl
udin
g In
clud
ing
incl
udin
g in
clud
ing
incl
udin
g 18
mm
30
mm
40
mm
60
mm
80
mm
10
0mm
12
0mm
14
0mm
16
0mm
18
0mm
de
ep
deep
de
ep
deep
de
ep
deep
de
ep
deep
de
ep
deep
Ove
r U
p to
and
in
clud
ing
Ove
r U
p to
and
in
clud
ing
mm
-
mm
10
mm
- 1.5
3.0
mm
1.5
3.0
-
* mm
026
0.23
0
22
+ m
m
032
0.28
0.
26
÷ m
m
0.41
0.
34
0.30
+ m
m
- • -
* m
m
- • -
+ m
m
- • -
+ m
m
- - -
* m
m
- - -
+ m
m
- - -
+ m
m
- - -
+ m
m
- - -
10
18
- 1.5
3.0
1.5
3 0
-
0.31
0
29
0.28
038
0.34
0.
32
0.47
0
40
0.36
0.56
0.
46
0.41
070
0.55
0.
47
- - -
- - -
- - - - - -'
- - -
- - -
18
30
- 3.0
6.0
3.0
6.0
-
037
0.37
0.
35
047
044
0.41
0.57
05
3 04
8
0.68
0.
62
055
0.84
07
6 0.
64
1.05
09
3 0
78
126
1.11
09
1
- - -
- - -
- - -
- - -
30
40
- 3.0
6 0
3.0
6.0
-
0.45
0.
45
0 43
0.55
0.
52
0.49
0.65
0.
61
0 56
0 76
0.
70
0 63
0 92
0.
84
0.72
1.13
1.
01
0 86
1 34
1.
19
0.99
1.55
1.
36
1.12
1 76
1,
54
1.26
- - -
- - -
40
60
- 3 0
6.0
3.0
6 0
-
- - -
060
0.57
0.
54
0.70
0
66
061
081
0.75
0.
68
097
0 89
0,
77
1.18
1
06
0.91
1.39
1
24
1.04
1.60
1.
41
117
181
1 59
1.
30
2.02
1.
76
1 43
- - -
60
80
- 3.0
6.0
3.0
6.0
-
- - -
0.65
0.
62
0.59
0 75
0.
71
0.66
0.86
0.
80
073
1.02
0.
94
0.82
1 23
1.
11
0.96
1 44
1.
29
1.09
165
1.46
1.
22
1.86
16
4 1.
35
2.07
1.
81
148
2.28
1.
99
161
80
100
- 6 6 -
- - - -
0.90
08
6 1.
01
095
1.17
1.
09
1.38
1.
26
1 59
1.
44
1.80
1.
61
2.01
1
79
2.22
1.
96
2.43
2.
14
100
120
- 6 6 -
- - - -
1.05
1.
01
1.16
1.
10
1 32
1.
24
1.53
1.
41
1 74
1
59
1.95
1.
76
2.16
1.
94
2.37
2.
11
2.58
2.
29
120
140
- 6 6 -
- - - -
1.15
1.
11
126
120
1,42
13
4 1.
63
1,51
1.
84
1.69
20
6 1.
86
2.26
2.
04
247
221
265
2.39
140
160
- 6 6 -
- - - -
1.25
1.
21
1 36
1.
30
1.52
1.
44
1 73
1.
61
1.94
1.
79
2.15
1.
95
2.36
2.
14
2.57
2.
31
2.78
2.
49
-L
(0
Tab
le 1
.11
(con
tinue
d)
Dep
th o
f
Ope
n en
d dl
men
s!on
Flo
nqe
Web
Ope
n
0 D
epth
of
opee
ng
Ove
rall w
idth
Wof
M
inim
um th
ickn
ess
inte
rnal
or
exte
rnal
tol
eran
ce o
n op
en e
nd d
imen
sion
fo
r va
rious
dept
hs o
f ope
ning
D
(plu
s an
d m
inus
) ch
anne
l or I
-bea
m
of w
eb o
r fla
nge
or D
F
or D
F
or D
F
or D
F
or 0
F
or 0
F
or D
F
or D
F
or 0
F
or 0
F
or 0
O
ver
Up
to a
nd
Ove
r U
p to
and
up
to a
nd
over
ov
er
over
ov
er
over
ov
er
over
ov
er
over
ov
er
Incl
udin
g in
clud
ing
Incl
udIn
g 10
mm
18
mm
30
mm
40
mm
60
mm
80
mm
10
0mm
12
0mm
14
0mm
16
0mm
10
mm
up
to
and
up t
o an
d up
to a
nd u
p to
and
up
to
and
up t
o an
d up
to
and
up t
o an
d up
to a
nd
up to
and
de
ep
Incl
udin
g In
clud
ing
incl
udin
g in
clud
ing
incl
udin
g in
clud
ing
incl
udin
g in
clud
ing
incl
udin
g in
clud
ing
18m
m
30m
m
40m
m
60m
m
80m
m
100m
m
120m
m
140m
m
160m
m
180m
m
deep
de
ep
deep
de
ep
deep
de
ep
deep
de
ep
deep
de
ep
mm
160
mm
180
mm
- 6
mm
6 -
mm
- -
+ m
m
- -
+ m
m
1.35
1
31
+ m
m
146
1.40
+ m
m
162
1.54
+ m
m
183
1 71
+ m
m
204
1.89
+ m
m
225
2.06
+ m
m
246
2.24
+ m
m
2.67
24
1
+ m
m
288
259
180
200
- 6 6 -
- - - -
1.45
14
1 1
56
150
1.72
1.
64
1.93
18
1 21
4 19
9 2.
35
2.16
25
6 2.
34
277
251
298
269
200
240
- 6 6 -
- - - -
1 55
15
1 1
66
160
1 82
1.
74
2 03
19
1 2,
24
209
2 45
2.
26
2 66
2.
44
2 87
26
1 3
08
279
240
280
6 -
- -
1 71
18
0 19
4 21
1 22
9 24
6 26
4 28
1 29
9
280
320
6 -
- -
1.91
2.
00
2 14
23
2 2.
40
2.66
28
4 3.
01
3.19
Table 1.12 - Tolerances on the Outside Diameter of All Extruded Round Tube and on the Inside Diameter of Class A and class B
Extruded Round Tube (see note 1)
Outside diameter, or inside diameter
Tolerance on the actual diameter (see notes 5 and 6)
Tolerance on the mean diameter (see notes 5 and 6)
Over Up to and Including
mm 12 18 30
40 50 60 80
mm 18
30 40
50 60 80
300
±mm 0.25 0.30 0.36
0.45 0.54 0.60
1%of diameter
±mm 0.19 0.23 0.27
0.34 0.40 0.45
314%of diameter
NOTE 1. For details concerning the applicability of tolerance class (A or B) to alloy, see 1.9.
NOTE 2. The tolerances are applicable to non-heat-treated tubing of wall thickness not Iessthan 1.6mm or 3% ofthe out- side diameter, whichever is the greater, and to heat-treated tubing of wall thickness not less than 1.6 mm or 4 % of the outside diameter, whichever Is the greater.
NOTE 3. In the case of tubing in straight lengths, the above tolerance limits are Inclusive of ovality.
NOTE 4. Where a tolerance on wall thickness is required, the tolerances on diameter are to be applied either to the outside diameter or to the Inside diameter, but not to both.
NOTE 5. Tolerances on the actual diameter Indicate the amount by which the diameter (inside or outside, as appro- priate measured in any direction may depart from the speci- fied diameter. Tolerances on the mean diameter (inside or outside, as appropriate) Indicate the amount by which the mean of two diameters measured In two directions at right angles in the same plane may depart from the specified diameter.
NOTE 6. The given tolerances on the actual diameter do not apply to annealed tube, coiled tube, or tube having a wall thickness less than 2.5 % of outside diameter. The toler- ances of these products and of controlled stretched tube are subject to agreement between purchaser and supplier.
20
Tab
le 1
.13-
Tol
eran
ces
on T
hick
ness
of
Hol
low
Sec
tions
(cla
sses
A a
nd B
(
Wid
th o
r w
idlh
ac
ross
fla
ts
Tol
eran
ces
on s
peci
fied
thic
knes
s
Cla
ss A
C
lass
B
Ove
r U
p to
and
In
clud
ing
Up
to a
nd
incl
udin
g 1.
6 m
m
thic
k
Ove
r 1.
6mm
up
to
and
incl
udin
g 3.
0mm
th
ick
Ove
r 3.
0mm
up
to a
nd
Incl
udin
g 6.
0mm
th
ick
Ove
r 6.
0mm
up
to a
nd
incl
udin
g 10
mm
th
ick
Ove
r 10
mm
up
to
and
incl
udin
g 18
mm
th
ick
Ove
r 18
mm
up
to
and
Incl
udin
g 30
mm
th
ick
Up
to a
nd
incl
udin
g 1.
6mm
th
ick
Ove
r 1.
6mm
up
to a
nd
incl
udin
g 3.
0mm
th
ick
Ove
r 3.
0mm
up
to
and
incl
udin
g 6.
0mm
th
ick
Ove
r 6m
m
up t
o an
d
incl
udin
g 10
mm
th
ick
Ove
r 10
mm
up t
o an
d
incl
udin
g 18
mm
th
ick
Ove
r 18
mm
up
to
and
incl
udin
g 30
mm
th
ick
mm
m
m
10
10
18
18
30
+ m
m
- 0.20
02
6
* m
m
. 0.22
0.
28
* m
m
. - 032
+ m
m
. . -
* m
m
- - .
mm
- - -
* m
m
- 022
0.28
+ m
m
- 0.28
03
6
* m
m
- - 0.54
mm
- . -
mm
- .
+
nm
-
30
60
60
80
80
120
032
0,36
.
036
041
0.48
0.41
04
8 0
58
048
058
0.68
. 062
0 82
- - 1 00
036
045
-
0.45
05
5 0.
65
065
075
0 80
090
095
1 00
1 40
14
5 1.
50
- - 2 00
120
180
180
240
240
320
. - -
0.65
- -
075
095
-
0.85
1
05
1 25
0.95
1
20
1 45
110
1 40
1
80
. - - 07
5 - -
0.85
1
00
- 11
0 1
20
1 40
1 60
1
80
2 00
2.20
24
0 2
60
NO
TE
1.
For
det
ails
conc
erni
ng th
e ap
plic
abili
ty of
tole
ranc
e cl
ass
(A to
B) t
o al
loy,
see
Not
e 1
of T
able
1,9
NO
TE
2.
The
tole
ranc
es ap
ply t
o no
n-he
at-t
reat
ed se
ctio
ns o
f wal
l th
ickn
ess
not
less
tha
n 1.
6 m
m o
r 3%
of
the
over
al w
idth
, whi
chev
er
is th
e gr
eate
r, a
nd
to h
eat-
trea
ted
sect
ions
of w
all
thic
knes
s no
t le
ss t
han
1.6m
m o
r 4%
of
the
over
all w
idth
, whi
chev
er is
the
grea
ter.
N) -'
Table 1.14 - Tolerances on Straightness for Extruded Bar, Regular Sections and Extruded Round Tubes (see below)
For bars, tubes or sections within a
circumscribing circle
Temper Nominal length of bar, tube or section L
Maximum derivation S from straightness of length L (metres) (see below)
Maximum localized kink in any 300 mm
portion
mm Up to and including 100
All tempers m
over 0.4 mm 1.5 L
mm 0.6
Over 100 F
All other tempers
over 0.4
over 0.4
2.0 L
2.5 L
0.8
1.0
NOTE 1. The straightness is measured by determining the maximum deviation from straightness S over length 1, when the bar, section or tube is supported on a flat table such that the deviation is minimized by Its own mass.
NOTE 2. Kink Is measured using a straight edge 300 mm in length (see below).
NOTE 3. Tolerances on straightness for annealed and controlled stretched materials should be subject to agreement between the purchaser and the supplier at the time of the enquiry and order.
Localized kink 300mm straightedge Bar, tube or section ot length L
V 7/ / / / ///V/ ////4// // /// // / //
Maximum Section through - deviation S
tiatness measuring table
Length L
22
Table 1.15 - Tolerances on Length for All Materials Supplied in Fixed Cut Lengths
Diameter, width across flats or overall width
Tolerances on length for given length (plus and minus) (see notes 1 and 2)
Over Up to and including
Over 300 mm up to and including 1000 mm long
Over 1000 mm up to and including 1500 mm long
Over 1500 mm up to and including 5000 mm long
Over 5000 mm up to and including 7000 mm
long
Over 7000 mm up to and including 10000 mm
long
Over 10000 mm long
mm
- 60
100 140 180
mm
60 100 140 180 240
jmm
2.0 2.0 3.0 3.5 4.5
jmm
2.5 2.5 3.5 4.0 5.0
jmm
2.5 3.5 4.0 5.0 6.5
jmm
3.5 4.0 5.0 6.5 8.0
jmm
4.0 5.5 6.5 8.0 9.5
jmm
6.5 7.5 8.0 9.5
11.0
NOTE 1. Tolerances on length are measured at a temperature of 16 5 C. They provide for out-of-squareness of cut to the extent of 10.
NOTE 2. Total tolerances (i.e. the sum of the plus and minus limits) may be applied unilaterally by agreement between the supplier and the purchaser.
Table 1.16 - Tolerances on Concavity and Convexity for Extruded Solid
and Hollow Sections
Width of section W Maximum allowable deviation D (see figure)
mm mm
Up to and including 25 0.125
Over25 0.l2Sper2Smm increment in width (e.g. for 150 mm width maximum deviation D permitted is 0.75 mm)
23
Coo cool ty
Under 20
20 up to and including 40
Over 40 up to and including 80
Over 80:
Lengths upto and including 8000 mm
Lengths over 8000 mm
degrees
3
0.5
degrees
7
5
3
Table 1.17- Tolerances on Twist for Extruded Solid and Hollow Sections
Twist T
24
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 2- MATERIAL SPECIFICATIONS
CONTENTS
Title Page No.
ALLOYS 27
TEMPER 29 Solution Heat Treatment 30 Precipitation Heat Treatment 30
25
List of Figures
Fig No. Title Page No.
2.1 Temper Cycles 29
2.2 Solubility Diagram 31
List of Tables
No. Title Page No.
2.1 Chemical Composition 27
2.2 Alloy Characteristics and Uses 28
26
ALLOYS
High purity aluminium, 99.00% and above, has excellent durability together with high thermal and electrical conductivity. It is easily worked and afthough it can be strengthend by cold working it remains a low stength material.
For more general use, alloying elements are introduced, producing materials that retain the general characteristics of pure aluminium but have greater structure strength (refer to Table 2.2). In the extrusion industry, the alloys most widely used
throughout the world are in the International Standards 6000 series, to which the British Standards alloys also conform. The main alloying constituents in this series are silicon and magnesium (refer to Table 2.1).
Table 2.1 - Chemical Composition
COMPOSITION (%) ALLOY BS 1474 Others (1987) SI Fe Cu Mn Mg Cr NI Zn TI Each Total Al
0.20- 0.45- 6063 0.60 0.35 0.10 0.10 0.90 0.10 - 0.10 0.10 0.05 0.15 REM
0.30- 0.15- 0.60- 6063A 0.60 0.35 0.10 0.15 0.90 0.05 - 0.15 0.10 0.05 0.15 REM
0.70- 0.40- 0.60- 6082 1.30 0.50 0.10 1.00 1.20 0.25 - 0.20 0.10 0.05 0.15 REM
* 0.30- 0.40- 6101A 0.70 0.40 0.05 - 0.90 - - - - 0.03 0.10 REM
0.20- 0.45- 6463 0.60 0.15 0.20 0.05 0.90 - - 0.05 - 0.05 0.15 REM
0.50- 3.90- 0.40- 0.20- 0.15-
2014A 0.90 0.50 5.00 1.20 0.80 0.10 0.40 0.25 0.20 0.05 0.15 REM
* 6101A comforms to BS 2898 ** T + Zr
27
Table 2.2 - Alloy CharacteristIcs and Uses
BS CHARACTERISTICS TYPICAL USES
6063 Suitable for intricate extruded sections of mid-strength. Forms well in T4 condition. High corrosion resistance. Good surface finish.
6063A A stronger version of 6063 but retaining most of that alloy's good surface finish and formability.
6082 The recommended alloy for structural purposes with good strength and general corrosion resistance.
6101A The best combination of electrical and mechanical conductor properties with conductivity of 55% of the International Annealed Copper Standard.
6463 Based on high purity (99.8%) aluminium, this alloy was developed to respond well to chemical or electro-chemical brightening or anodizing. It has excellent formability.
2014A A high strength alloy with moderate corrosion resistance.
28
The most widely used alloy. Architectural members i.e. glazing bars and window frames; windscreen sections, road trans- port.
Road and rail transport, general engi- neering, ladders and light structures.
Road and rail transport, scaffolding, bridges, cranes and heavy structures.
Busbar, electrical conductors and fittings
Motor car trim and other applications requiring a bright finish.
Structures, aerospace, general engineering.
TEMPER
The properties of alloys in the 6000 and 2000 range can be improved by heat treatments after extrusion.
These alloys, although available in the F, "as manufactured", condition, are more
usually produced in one of the following three tempers:-
T4 - solution heat treated
T5 - precipitation treated (artificially aged)
T6 - solution heat treated and precipitation treated (fully heat treated)
T5 PRECIPITATION
HEAT ___________ SOLUTION TREATMENT
EXTRUSION_F (QUENCHING)
(AGEING)
:
F
Fig. 2.1 - Temper Cycles
The current procedure for producing the T4 temper is usually 'on-line". An extrusion, emerging from the die at about 500°C, is rapidly cooled by air, water spray or water immersion, depending upon the section shape and extrusion speed. The temper, although stronger than in the F condition, is still of relatively low strength and, with its high elongation value, it is an excellent choice where severe forming is required. Some natural ageing or hardening will occur which will, in some alloys, curtail the time available for forming.
For thin sections a stronger temper, T5, is available. T5 is given greater strength by carrying out precipitation treatment without any solution heat treatment. This is
provided by heating the material up to about 180°C and soaking for several hours in an oven.
29
The final and strongest temper available (without the application of cold work) is T6 which combines both the solution heat treatment and the precipitation treatment.
The relationship between mechanical properties and heat treatment of a range of aluminium alloys was first discovered by Wilm in 1906. Overthe years, the process has been developed with improvements and innovations being introduced which have
helped to make the "heat treated" alloys the most widely used extrusion materials in the world.
in recent years, much greater use has been made of reheat treatment following low temper or heat induced fabrication operations such as bending and welding. This is
a property of aluminium that is well worth considering at the design and material selection stage of fabricated components.
It is not the purpose of this manual to deal with detailed metallurgical aspects of aluminium and its alloys, but the following simplified explanation of heat treatment may be of background interest:-
The thermal treatment consists of two phases:
a) solution heat treatment b) precipitation heat treatment
Solution Heat Treatment
The chemical constituents of aluminium alloys are to a greater or lesser extent soluble in aluminium. The degree of absorption varies with the amount and type of constituent and temperature. The higher the temperature, the greater the amount dissolved. Fig. 2.2 shows a typical solubility diagram where, at temperatures above point A , (the Solvus temperature) the atoms are in solid solution and designated by the prefix "solute". These atom phases of constituents are thus dissolved in solid solution and a rapid temperature drop, through quenching, will prevent the solute atoms from diffusing out of solution. This condition, however, is not totally stable and a natural ageing will take place, varying from several days to several weeks depending upon the alloy. During the ageing process a fine dispersion of clusters of solute atoms will occur. The final stable condition is defined as T4 temper.
Precipitation Heat Treatment
The precipitation heat treatment process, also known as artificial ageing, speeds up and greatly increases the rate of precipitation and fine dispersion of the constituent atoms, which are distributed in clusters over the whole matrix. The alloy will now tend to resist material dislocation, resulting in a marked improvement in both strength and hardness, usually to a level well above that obtained by natural ageing.
30
0 U)
CU
U) 0 E U)
I—
Liquid
% Constituent
Figure 2.2 - Solubility Diagram
31
Liquid - solid
5
Solid
Page blank in original
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 3- MECHANICAL PROPERTIES
CONTENTS
Title Page No.
INTRODUCTION 35
STRESS 36 Axial Loading 38
STIFFNESS 41
HARDNESS 43
FATIGUE 43
33
List of Figures
Fig No. Title Page No.
3.1 Yield Point 36
3.2 Typical Stress Strain Curves 37
3.3 Permissible Compressive Stresses in Struts 39
3.4 Relationship Between Hardness Number and Tensile, Yield Strengths 42
3.5 Fatigue Curves For Some Aluminium Alloys (Rotating Cantilever Tests) 44
List of Tables
No. Title Page No.
3.1 Properties to BS 1474 35 (1987)
3.2 Permissible Stresses 38
3.3 Effective Lengths of Struts 40
3.4 Moduli of Elasticity 41
34
INTRODUCTION
A wide range of mechanical properties is available from aluminium and its alloys with the level of performance varying with the degree of alloying and temper. The property range for the more generally available commercial alloys is given in Table 3.1.
Table 3.1 - Properties to BS 1474(1987)
ALLOY TEMPER MAX THICKNESS
mm 0.2% Ps N/mm2
ULT. STRESS N/mm2
%ELONGATION b)
5.65y' 50 mm
6063
Fe) T4 T5 16
200 150 25
150
- 70 110 160
100 130 150 195
13 16 8 8
12 14 7 7
6063A T4 15 T6
25 25 25
90 160 190
150
200 230
14 8 8
12 7
7
6082
Fe) T4 15 T6
200 150
6
20a)
- 120 230 255
110 190 270 295
13 16 -
8
12 14
8 7
6lOlAd) T6 - 170 200 10 8
6463 T4 T6
50 50
75
160
125 185
16 10
- -
2014A 14 T6
20a) 20a)
230 370
370 435
11
7 10 6
a) Thicker sections are possible and give higher mechanical properties. For details contact extruder.
b) The elongation is obtained from a tensile test sample on which a gauge length is marked prior to testing. The gauge length is specified, being either 50 mm
long or 5.65 / cross-sectional area. (So) C) The properties of aluminium vary with temperature outside an approximate
range of -50°C to +80°C. They will increase at low temperatures and decrease at high temperatures. The values vary with the alloy, see Table 8.2.
d) Alloy 6101A conforms to BS 2898. e) Values given for F condition are not specified properties in British Standards
and are given for information only.
35
STRESS
Aluminium does not exhibit a yield point. Stress/strain behaviour is similar to that of a numberof other metals, including some alloy steels. It is necessary, therefore, to advise a recognisable point of departure from elastic to plastic behaviour. In the method chosen, the stress level registered at 0.2%. Permanent strain is regarded as the yield point. The yield point can be obtained from the stress/strain curve by drawing the offset of O.2% strain parallel to the elastic line for the alloy under consideration. The 0.2% proof stress can be read at the point of intersection of the two lines, see Fig. 3.1. Alloy curves will have a different point of departure for each temper condition.
E E
z 0, CO
U)
Fig. 3.1 - Yield Point
36
0.70
200
/ /
0.2 Ordinate
NB. for reasons of clarity the alloy curve is exaggerated
/ / /
20 / 0.50 0.60
% Strain
500- 2014A T6
Mild Steel
400 —— / / /
E 300- //'7 6082 T6
z a, / ci) /
'—'—I
(I)
200-
100-
I I I
0 5 10 15 20
% Strain
Fig. 3.2 - Typical Stress Strain Curves
37
Table 3.2 - Permissible Stresses
ALLOY TEMPER AXIAL e) N/mm2 Pt Pc
BENDING N/mm2 Pbt Pbc
SHEAR N/mm2
BEARING N/mm2
s
6063
6063
6082
2014A
2014A
15
T6
16
T4
16
62
87
139
135 124
154d) 20
69
96
154
153 142
154d) 224
37
52
83
81
108
117
139
222
239
278
106
81
61
71
49
Pt AXIAL TENSION Pc AXIAL COMPRESSION Pbt BENDING TENSION Pbc BENDING COMPRESSION s SLENDERNESS RATIO AT EULER BLEND POINT SEE FIG. 3.3
a) Permissible stress levels are laid down in BS CP1 18 The Structural Use of Aluminium".
b) 6063 values are applicable to 6101A and 6463.
C) 6063A is a new alloy, not yet allocated a value but from experience it should be slightly in excess of 6063 values (8%).
d) Arbitrarily reduced values to allow for inferior crack-propagation resistance. e) Applies only when buckling is not the criterion.
AxIal Loading
For axial loading, in columns and struts, the permissible compressive stress is obtained by inserting the appropriate slenderness ratio into the alloy/temper curves given in
Fig. 3.3, and using the effective length factor from Table 3.3.
38
CM
E E z 'a CM a)
(1)
a) > U) (a a) 0. E 0 0 a) .0 0) 0) E a)
Fig. 3.3 - Permissible Compressive Stresses in Struts
= K!.
whore = slenderness ratio K = end fixity factor (effective length) L = spaninmm r = radius of gyration of section in mm
also r =
= inertia A = cross sectional area
39
100 1 A Slenderness Ratio
Table 3.3 - Effective Lengths of Struts
End Condition Effective Length of Strut
Effectively held in position and restrained in direction at both ends 0.7 L
Effectively held in position at both ends and restrained in direction at one end 0.85 L
Effectively held in position at both ends, but not restrained in direction L
Effectively held in position and restrained in direction at one end and partially restrained in direction but not held in position at the other end
1.5 L
Effectively held in position and restrained in direction at one end, but not held in
position or restrained at other end 2.0 L
NOTE. L is the length of strut between points of lateral support.
The extensive range of shapes and, over the last few years, the ability of the industry to produce thinner extrusions has encouraged the use of slender sections. Because of low aspect ratios (width/depth) and high element thickness ratios (width/thickness) of the thinner extrusions they require examination for possible modes of elastic instability. The modes of failure listed below are particularly relevanttothin-walled open sections of asymmetrical shape in aluminium alloys.
a) Torsional warping b) Lateral instability C) Local buckling
All the factors are influenced by the shape and dimensions of the section and, whilst (a) and (b) are also relevant to span, (C) is not.
Although safe values are often quoted in simple terms for aspect and element thickness ratios, they are not entirely reliable and should not be used. If there is any doubt about the robustness of a section in the form of failures list above, it should be checked, using appendices F, G, H and Kin BS CP 118- The Structural Use of Aluminium". The design approach uses equivalent slenderness ratios in conjunction with alloy compression curves. The strut curves in Fig. 3.3 can be used for torsional warping but will give pessimistic values for lateral instability and local buckling, where the equivalent slenderness ratio falls on the straight line parts of the graphs: See BS CP1 18 Fig. 2 for modified compression curves suitable for solving lateral instability and local buckling.
40
STIFFNESS
The stress/strain relationship is given by Hooke's Law which states that intensity of stress is proportional to strain. This is applicable to aluminium alloys to a level just below the 0.2% proof stress, the slope of the line being obtained from:
Table 3.4 - Modull of Elasticity
E = Stress where E is the modulus of elasticity Strain
ALLOY MODULUS OF ELASTICITY E N/mm2
6063 65,500 6063A 65,500 6082 68,500 6101A 65,500 6463 65,500 2014A 72,000
These values are approximately one third of that of mild steel, 210,000 N/mm2. Aluminium under elastic bending will therefore give deflections three times greater than those obtained from mild steel under similar loading conditions. This is not true for self weight loading where the light weight of aluminium counteracts the effect of the lower elastic modulus of aluminium. The advantage to be obtained from a low modulus are greater impact absorption with shock loads and lower imposed stress levels from movement in static structures caused by temperature variation or support settlement. The modulus of elasticity will vary with temperature, see Table 8.2.
In applications where deflection is the controlling design factor, the performance of aluminium can be dramatically improved by utilising the advantages of the extrusion
process to position materials strategically around the section. The geometric proper- ties can also be increased by small additions to section depth.
This modification applies to all materials but can be more readily incorporated into extruded aluminium sections. Examples are given in Section 11, Design.
The relationship between lateral and longitudinal strain, within the elastic limit, is given by Poisson's Ratio which, for aluminium alloys, is usually 0.34.
41
30 x E E 25 z -c 0) c 20 )2)
(0 D .; 15-
(0 C 10 a I-
HARDNESS TESTER SETTINGS Brinell
lOmm.Steel ball penetrator - 500kg.load Vickers
Diamond penetrator - various loadings Rockwell 'F'
1.6mm Steel ball penetrator - 6Okg.load Rockwell 'E'
3.2mm, Steel ball penetrator - lOOkg.load
Rockwell 'B' 1.6mm Steel ball penetrator - lOOkg.load
Rockwell 'K' 3.2mm Steel ball penetrator - l5Okg.load
Webster Model 'B'
Note: As this table shows, a hardness value covers a range of stress levels and must not therefore be used to give precise measurements of strength.
Fig. 3.4 - Relationship Between Hardness Number and Tensile, Yield Strengths
42
35
Tensile
Relationship between hardness number and tensile strength for magnesium - silicide alloy extrusions in the artificially aged condition
Yield
(1/6063 T5 & T6 6082 T6 F
j"1 i'• •1
Brinell 6063A
T6 Vickers 45 055 6065 707580 85 9095100105110
46 51 56 61 66 71 76 82 87 92 98103 109115 Rockwell 'F' Rockwell 'E' 54 61 67 71 76 79 82 85 87 89 91 -
Rockwell 'B' 47 55 62 68 72 77 80 83 86 88 90 92 94 96 I I I
Rockwell 'K' - - - - 12 23 32 39 45 50 55 60 63 66
— 15253441485358826670737678 Webster 5 7 9 10 11 12 13131414—151515161616—1717
Hardness number
HARDNESS
The surfaces hardness of aluminium alloys can be assessed by most of the general methods of measurement, Brinell, Vickers and Webster etc. The accuracy of the results can vary, particularly with those methods that use manual pressure to obtain the surface indentation.
The trend to relate mechanical properties to hardness values is not to be recommended as there is no accurate constant relationship. The curves shown in Fig. 3.4 are for general guidance only and indicate that there are given ranges of stress levels for each hardness value.
FATIGUE
Aluminium is similar in its fatigue behaviour to other non-ferrous metals in that the stress/cycle curves never totally flatten out. An arbitrary maximum endurance level is therefore imposed,. usually 50 million cycles. Curves are drawn up for alloy and temper groups against semi-range of stress levels (see Fig. 3.5). Fatigue curves are usually based upon actual test results from Wohler type beam machines which subject the specimens to sinusoidal reversed bending. The results are generally plotted for high cycle applications, above 1 O cycles, and any high strain/low cycle applications should be discussed with the extruder.
The surface finish and geometric aspects of components, particularly joints, can influence performance. Shot blasting of the surface can improve fatigue resistance, whilst notches can reduce it. With welded connections, it is usual to obtain better results from butt joints than those which are lapped and continuous welds give a superior performance to that of intermittent welds. Some data based upon nine different classifications of structural components is given in BS CP1 18.
43
300-
270-
240-
210- E E
z 180-
a
a
0 a a, 150- C C,,
E
120-
90-
60 -
i0 106 i07 108
Endurance (cycles)
Similar results are obtained for alloy 6082T6
Fig. 3.5- Fatigue Curves for Some Aluminium Alloys (Rotating Cantilever Tests)
44
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 4- DURABILITY
CONTENTS
Title Page No.
INTRODUCTION 47
ATMOSPHERIC 47
CHEMICAL 49
MATERIALS 49 Bi-MetaIlic 49 Wood 53 Insulating Materials 53 Concrete 53
45
List of Figures
Fig No. Title Page No.
4.1 6082 T6 Alloy (Mill Finish) Exposure Graph (1) 48
4.2 6082 T6 Alloy (Mill Finish) Exposure Graph (2) 48
4.3 Principle of Galvanic Reaction 49
4.4 Typical Bi-metallic Connections Between Aluminium and Steel 52
List of Tables
4.1 Electro-Chemical Series 50
4.2 Guide to Bi-metallic Corrosion Effects at Junction of Aluminium and Other Metals 51
46
INTRODUCTION
Aluminium and its alloys have, in general, excellent durability and corrosion resistance. Like most materials, however, their behaviour can be influenced by the way in which
they are used. In this section the manner in which aluminium responds to various environments and design situations is reviewed with advice on use in specific applications.
ATMOSPHERIC
Aluminium's natural affinity with oxygen results in the formation of an oxide layer when exposed to air. The resulting film is generally 50 Ang thick, extremely hard, chemically stable, corrosion resistant and adheres strongly to the parent metal surface, produc- ing an integrated material. Once formed, it prevents further oxidisation and, if
damaged in any way, will reform, oxygen availability permitting. The only practical reason for removing this film is to facilitate anodizing or welding. In the first instance, a thicker, more controlled deposition of the oxide layer can be carried out and in the latter case, the oxide film would be a deterrent to good metal fusion.
The behaviour under atmospheric exposure can therefore be described as self- stifling. If the surface layer is pitted by any of the air-borne pollutants usually found in industrial or marine atmospheres, such as sulphuric acid and sodium chloride, the resulting chemical reaction produces a larger volume of powdered corrosion product than the volume of the original pit, thereby sealing off the surface of the aluminium and inhibiting any further corrosive reaction. In general, the ratio of corrosion product to pit volume is 240:1.
With time, existing pits, which are usually of a shallow hemispherical shape, are sealed and the rate of formation of new pits is reduced so that eventually all reaction can be assumed to have ceased. This process can be described as weathering, for the depth of pitting is extremely small. The level of pollution of course will determine the general appearance, which will appear to be a soft blueish-grey colour in rural areas and dark grey to black in industrial areas. Regular maintenance and washing down should prevent the permanent discolouration from industrial pollutants. Anodized surfaces, however, will retain their original appearance for a much longer period, providing that regular maintenance is carried out. See Section 10.
For the purposes of assessment, the various types of environmental conditions are divided into 3 categories:
a) RURAL b) MARINE
c) INDUSTRIAL
47
E E
1) 0. D
3-
Fig. 4.2- 6082 T6 Alloy (Mill Finish) Exposure Graph (2)
48
6
Exposure time - years
Marine Industrial
Rural
Fig. 4.1 - 6082 T6 Alloy (Mill Finish) Exposure Graph (1)
The exposure trials on which Fig. 4.1 is based also provided samples for testing the mechanical properties of the materials. As can be seen in Fig. 4.2 there is very little drop in these properties, even after prolonged exposure of 12 years. In both figures, the graph line is virtually horizontal and therefore durability and mechanical properties can be assumed to have reached stable conditions.
i:: stri:l 0 6 8 10 12
Exposure time - years
CHEMICAL
The behaviour of aluminium alloys in contact with a wide range of chemicals is well- documented arid requests for specific information can usually be dealt with by your material supplier. In general, corrosion of aluminium only occurs to any great degree where the ph is be'ow 3 or above 9, i.e. under strong acidic or alkaline conditions. t is
therefore necessary to know the concentration of the chemical underconsideration and
also the temperature at which it will operate, as in some cases the temperature can be
the major consideration by altering the normal behaviour pattern.
MATERIALS
When aluminium will be in contact with other materials under wet or moist conditions, it is necessary to check whether some form of protection is required.
Bi-Metallic
When dissimilar metals are coupled together in the presence of moisture, there is a likelihood of a galvanic reaction in which one metal will corrode see, (Fig. 4.3). In this
situation an electrolytic couple is formed in which a current flows from the less noble
metal, acting as an anode, to the more noble metal, acting as a cathode, with corrosion concentrated on the less noble metal. This behaviour is usually consistent with the relative placings in the electro chemical series, see Table 4.1.
Corrosion Electrons
— ri Positive + Base or less noble metal
1 ions 2
Electrolyte Noble metal Anode Cathode
Corrosion cell
Fig. 4.3 - Principle of Galvanic Reaction
49
The severity of the galvanic action also depends on the degree of separation, electrical resistance of the metal path, conductivity of the solution and the area ratio between the two dis-similar metals. In practice, however, reaction between the metals can be avoided by insulating them from each other with an electrically inert non-abosrbent barrier. An excellent example of this kind of connection is between the aluminium super-structure and steel decking on ships. Reference can be made to B.S. publication PD 6484 - 1984.
Table 4.1 - Electro-Chemical Series
BASE Magnesium Zinc Aluminium Cadmium Mild Steel Cast Iron Lead Tin Nickel Brasses Copper Bronze Monel Silver solders (70% Ag. 30% Cu) Nickel Stainless Steel (Type 304) PASSIVE Silver Titanium Graphite Gold
NOBLE Platinum
50
Table 4.2 - Guide to Bi-metallic Corrosion Effects at Junction of Aluminium and Other Metals
Metals Coupled With Aluminium Of Aluminium Alloy
Bi-metallic Effect
Gold.platinum, rhodium,silver.
Attack accelerated in most environments
These metals, and especially those at the top of the list are generally cathodic to aluminium and its alloys, which therefore suffer preferential attack when corrosion occurs.
Copper, copper afloys. irwnersion. silver solder
Attack accelerated in most atmospheres to aluminium and its and conditions of total
Solder coatings on steel or copper
Attack accelerated at the interface in severe or moderate atmospheres and under conditions of total immersion,
Nickel, nickel alloys
—_____________
Attack accelerated in marine and industrial
atmospheres and conditions of total irmtersion but not in mild environments, —---
Steel, cast iron Attack accelerated in marine and industrial atmospheres and conditions of total immersion but not in mild environments.
Lead, tin Attack accelerated only in severe environments, such as marine and some indiatrial.
Tin I zinc plating (80 /20) on steel
Attack accelerated only in severe atrrspheres and condtions of total Immersion.
Pure aluminium and
alloys not containing si,stantial additions of copper or zinc
When aluninium is alloyed with appreciable amounts of copper becomes moe noble and when alloyed with appreciable
amounts of zinc it becomes less noble. In marine or industrial
atmospheres or when totally immersed, alunnium alloy suffers accelerated attack when In good electrical contact with another aluminium alloy that contains substantial copper, such ax wrought alloys 2024 and 2014 and cast alloys LM 4-M and BS L92. The aluminium-zinc alloys, being less noble, are used as cladding for the protection of the stronger aluminuim alloys,
Cadmium No acceleration of attack on cadmium except in fairly severe atmospheres in contact with an aluminium alloy containing copper and under conditions of total immersion,
Attack on zinc accelerated in severe environments such as marine and industrial and under conditions of total immersion,
These metals are generally anodic to aluminium and suffer attack when corrosion occurs, thereby protecting the aluminium,
Zinc and zinc alloys
Magnesium and magnesium- base alloys
Attack on magnesium accelerated in severe environments such as marine and industrial and under conditions of total immersion,
Attack on alurntnium may also be accelerated.
Titanium Not many data available, but attack on alurTinium is known to be accelerated in severe marine and industrial conditions and when immersed in seawater.
These metals form protective films that tend to reduce bi-metallic effects. Where attack occurs the aluminium base material suffers.
Stainless steel
(18 / 8. 18/8/2 and 13%, Cr)
No acceleration of attack on aluminium in mode- rate atmospheres, but attack may be accelerated in severe marine and industrial atmospheres and under conditions of total irrynertion. —- No acceleration of attack on aluminium when plating is not less than 0.0025 mm thick. except in severe atmospheres; also provlded the
preliminary nickel costing us in accordance with requirements of BS 1224.
Chromium plate
51
Steel bracket and 150mm mm. Steel foundation bar
Treatment as for A but with plate lapped to inside of foundation bar. Steel rivets
Outside
Aluminium plate lapped to joggled steel flat bar.
) Galvanised steel bolts with insulating washers and ferrules. Treatment otherwise as for A.
Figure 4.4 - Typical Bi-metallic Connections Between Aluminium and Steel
52
Bulb plate stiffener
Aluminium plating
between
A
Outside Inside
C
Inside
B C
Wood
In dry conditions there is usually no reaction on the aluminium but if the wood is unseasoned or in damp conditions, it should be coated with aluminium or bituminous paint. In very aggressive environments (immersion) a non-absorbent insulating gasket should be fitted as with bi-metallic joints. Where timber is treated with preservative advice should be obtained from your aluminium supplier.
Insulating Materials
In the unusual event of insulating materials becoming saturated, some protection of the aluminium would be necessary for, apart from the possibility of attack from leached-out chemicals, some poultice corrosion could occur, activated mainly by the reduced availability of oxygen. Protection can be afforded by using an inert barrier.
Concrete
Under perfectly dry conditions, aluminium buried in concrete would need no protec- tion. In practice, however, such conditions are rarely achieved therefore it is recom- mended that in all cases the contact area of the aluminium is coated with a bituminous paint. In no circumstances should the steel reinforcement used in concrete be allowed to come in direct contact with the aluminium as this will result in a bi-metallic reaction which in turn could cause spalling of the concrete.
53
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ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 5- SURFACE FINISHING
CONTENTS
Title Page No.
INTRODUCTION 57
PRE-TREATMENT 57
ANODIZING 57 Specification Factors for Architectural Type Anodizing 59 Chromic Acid Anodizing 61 Hard Anodizing 61
PAINTING 61
Electrophoretic 61 Electrostatic 61
Paint Performance 62
55
List of Figures
Fig No.Titie Page No.
5.1 Anodizing Programme 58
5.2 Deposition of Colouring 59
List of Tables
5.1 Suitability for Anodizing 60
5.2 Paint Performances 62
56
INTRODUCTION
One of the most important considerations relating to surface finish is the need to have a sound and permanent bond between any applied film or coating and the parent material. In this respect aluminium and its alloys are particularly suitable, providing as they do integral bonding with anodizing and excellent paint keys when suitably etched and de-greased.
PRE-TREATMENT
The surface textures on aluminium, like those on other metals, will be visible through all but the thickest coating so it is as well to consider this aspect before deciding on the final surface treatment. Where positive relief features are required, like ribbing or serrations, these can be easily incorporated into the extrusion shape. The usual cycle for pre-treatment incorporates a de-greasing dip, followed by a rinse and then an etch dip. The make-up and chemical concentration of this etch can be varied to produce a range of surfaces that will affect the final appearance of an anodized finish. These can be graded from the natural metal appearance, through a light grey satin finish to a darker grey frosted appearance.
Specialised surface finishes can be applied, such as chemical brightening, mechani- cal polishing, scratch brushing and shot or vapour blasting. The special finishes extend from bright reflective polished surfaces, through to heavy peened rough textures.
Aluminium provides an excellent surface for paint. After degreasing, a light etch is used followed, when necessary, by a chemical conversion coating to improve the paint key even further.
All of these services are available directly or indirectly through extrusion suppliers. In
general the level of concentration of pre-treatment chemicals makes them unsuitable for manual non-dip application.
ANODIZING
Anodizing is a controlled surface oxidisation by immersion in an electrolyte, usually dilute sulphuric acid. A low voltage, high amperage direct current is passed through the metal, using the aluminium as the anode and a hard, non-corroding oxide film builds
up on the surface of the aluminium. A less dense layer is subsequently formed in which there are capillary pores. These pores provide the means for further oxidisa- tion, building up the thickness from the base. This film is an integral part of the metal and is not an applied coating.
57
Pro- OPTIONAL TREATMENTS Treatment
Mechanically Chemically Metallic Polish Brighten Colour
Organic Colour
Degrease Scratch Brush
Vapour Blast
Rinse r r
Shot Blast
Light Etch Natural Etch Rinse Anodize Finish Seal
I I I I
FIg. 5.1 - Anodizing Programme
After the actual anodizing operation, the surface film is porous and in a condition to accept colouring agents, if required. If a natural aluminium finish is desired then the material proceeds directly to the final tank which is usually boiling water. The chemical reaction of immersion seals the pores against further moisture penetration, giving a hard, weather resisting surface.
Where colour is required, the choice lies between those obtained from organic dies, as used with textiles, and those obtained from metallic salts. The former gives a range of primary colours, whilst the latter offers colours varying from grey through umber to dark brown and black. As will be seen from Fig. 5.2 the organic dies tend to remain at the top and the metallic salts at the bottom of the surface pores.
58
H Ratio d
= 1500:1
Fig. 5.2 Deposition of Colouring
Specification Factors for Architectural Type Anodizing
M
l7nm
25 micron (25,000nm)
British Standards lay down specifications to govern the quality of anodizing. BS 1615 covers general anodized coatings in aluminium and BS 3987 covers external architectural applications. European standards are covered by the Qualanod quality control scheme.
The average thicknesses readily available are usually designated in AA values, the figures conforming directly to the film thickness in microns.
Applications
5 Furniture and other indoor products. Also used with chemically brightened material where a thicker coating would tend to reduce reflectivity.
101 Internal applications likely to have more robust
155 handling such as hand-railing and internal partitions.
25 All external applications such as window frames etc.
59
Natural Organic Metallic dies salts
c) The most appropriate extrusion alloys fordecorative and architectural anodizing are in the 6063 range. Other alloys can be anodized but the finish cannot be guaranteed to meet the requirements of British Standards architectural specifications.
Table 5.1 - Suitability For Anodizing
Alloy Natural Colour Brightened Protective *
6063 V V G-V V
6063A V V G-V V
6082 F F F G
6463 V V E V
2014A F F U G
*This also includes "hard" anodizing
E = excellent V = very good G = good F = fair U = unsuitable
d) In component anodizing, the heat affected zone of welded or brazed joints will show some colour variation from that on the rest of the section. This can vary from slightly darker tone to a very dark grey or even black if a silicon filler wire is used in brazing.
e) There can be slight variation in colour between production batches, so top and bottom colour limits should be agreed with the anodizer. This is particularly so where cast and wrought components are concerned, because an exact colour match is rarely possible due to the marked difference in the chemical composition of the two materials.
f) Electrical contact is extremely important between the loading bars and the aluminium section during anodizing. It is obtained by jigging with non- metallic clamps. The contact areas, however, do not anodize or colour and will therefore leave a light-coloured area even on naturally anodized material. Non-visible surfaces should be shown on drawings so that the clamps can be placed in the best possible position. If all surfaces are visible, then an extra 50 mm should be allowed at each end of the bar for clampings, which can be cut off after anodizing.
60
Chromic Acid Anodizing
The original commercially developed anodizing process used chromic acid as the electrolyte. The procedure is similar to that employed with sulphuric acid but the bath
temperature is higher. The resultant film is softer and thinner (max. 10 microns) but for equal thicknesses it offers more corrosion resistance which makes it ideal for aggressive industrial environments where the relatively soft surface is no disadvantage. As the chromic acid is passive with aluminium, it is also recommended lorfinished components where there are laps or crevices which could retain electrolyte.
Hard Anodizing
Hard anodizing is a low temperature operation, using considerably higher voltage than other anodizing processes. The relatively rough surface produced is extremely dense and hard and is available up to 125 microns thick. The film is normally left unsealed but can be waxed or treated with mineral oil. In either case, the abrasion resistance is very high, comparing favourably with that of tooled steel and chromium plate. Hard anodized films have good electrical insulation properties and their excellent corrosion resistance and durability make them ideal for use even in aggressive environments.
PAIN11NG
Aluminium rarely needs to be painted for protection but where colour is necessary on aesthetic grounds a number of high-quality paints and methods of application are available. The surface presented by aluminium is ideal for coating when the correct pre- treatment is carried out. As most coatings are applied by commercial coating companies, the basic pre-treatments are usually varied to suit their particular paint formulations and methods of application. In general, the oxide film is removed and the material de- greased, etched and rinsed. This is adequate preparation for electrophoretic paints but there is an additional chemical conversion coating which is then applied for electrostatic application.
Electrophoretic
The pre-treated workpieces are made anodic and dipped into electrically charged paint tanks. This ensures that the paint is attracted to the metal surface and deposited in an even coating. After rinsing, the material passes through stoving ovens at approximately 160°C for a duration of 15 minutes. During this operation the paint is fused and strongly bonded to the aluminium.
Electrostatic
After pre-treatment, the workpieces are passed through an electrostatic field during which time paint, in the form of wet or powder particles, is sprayed on to the surfaces. The workpieces are then transferred to a tunnel oven where they are stoved at 200°C for 10 minutes.
61
Paint Performance
Comparing paint surfaces and their respective performance is always somewhat subjective, nevertheless Table 5.2 attempts to provide generalised information. Paint and coating companies are always pleased to advise on the best system of application. For all paints and systems, sharp corners provide a challenge in that either a metal or a shadow line appears, depending upon the thickness of the paint. This can be avoided by following good extrusion design although for paint the minimum recommended corner radius is 1mm.
Table 5.2 - Paint Performances
PAINT Method Mean Colour Surface Gloss Colour Hardness Inside Post of Thickness Range Texture Level Fastness Groove Painting Application (Microns) Coating Fabrication
Acrylic Electro-
Poly- phorec urethane (Wet Bath)
25 White Smooth 70% Moderate Hard V. good Good
Poly- Electro- ester static
(Powder Spray)
60-80 Wide
Range Slightly Textured
20%-
93% Good Moderate Shallow
Channels
Only
Excellent
PVF2 Electro- static
(Powder Spray)
30-100
(a)
Small
Range V.good
Fluoro- Electro- Carbon static
(Wet Spray)
25(a) Wide
Range
Smooth 9%- 70%
Excellent Moderate Moderate
Acrylic Electro-
Polyesterstatic (Wet Spray)
25 Full
Range
Smooth 9%- 90%
Good Hard V. good
(a) Suitable for multi-coat applications
Further information is available from: Aluminium Coating Association
Broadway House
Calthorpe Road
Birmingham B15 1TN
62
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 6- FABRICATION
CONTENTS
Titles Page No.
BENDING 65 Machine Types 65 Alloy/Temper 67 Shape Factors 67 Tube Bending 69
Springback 70 Lubrication 70
MACHINING 70 Routing 72 Drilling 73 Sawing 74
JOINING 75 Welding 75 Joint Design 79 Screwing 81
Crimping 82 Riveting 83 Bolting 85 Adhesives 86
63
List of Figures
Fig No. Title Page No.
6.1 Bending Methods 65/66 6.2 Routing (Profiling and
Facing) 72 6.3 Drills 73 6.4 Types of Saw 74 6.5 TIG Welding 77 6.6 MIG Welding 78 6.7 Recommended Diameters
of Screw Grooves 81 6.8 Longitudinal Screw
Grooves 82 6.9 Crimping 82 6.10 Blind Rivets 83 6.11 Self-Piercing Rivets 84 6.12 Clench Rivets 84
List of Tables
No. Title Page No.
6.1 Bending Characteristics 67 6.2 Minimum Bend Radii (1) 68 6.3 Minimum Bend Radii (2) 68 6.4 Minimum Bend Radii (3) 69 6.5 Minimum Bend Radii (4) 69 6.6 Minimum Root Radii R in
Terms of Tube Diameter 71
6.7 Basic Saw Tool Data 74 6.8 Process Capacity 76 6.9 Recommended Filler Alloys
for Welding Parent Metal Combinations 79
6.10 Edge Preparation and Fit Up forTiG and MIG 80
6.11 Permissible Stress Levels 81
64
BENDING
There are several types of torming machine suitable for bending aluminium sections. The choice depends upon the class of section, whether solid open or hollow; the range of support tooling available; the alloy and the temper.
Machine Types
Bending may be carried out by four main methods, as shown in Fig. 6.1. The three roll bender has a central moveable roller which is gradually depressed until the desired radius is obtained. The point bender has a similar method of operation, the load either
being applied gradually or impacted. The roll and point methods of bending are usually applied to robust sections.
In the wrap and the mandrel benders, it is possible to provide formers and other support tools which enable tighter radii to be obtained and minimise the amount of buckling.
As the name implies, the stretch former puts the section into tension and then, moving laterally, wraps it around a former: this method reduces the likelihood of compression failure.
As well as the above basic machines, a number of specialist benders are available, such as the rotating disc, which is suitable for tube bending.
I Wrap Bender
Former Moves Around Section Draw Mandrel Bender
Section Moves Around Former
Fig. 6.1 - Bending Methods
65
-Former
Clamp Guide
FIg. 6.1 - Bending Methods (continued)
66
Section
Fixed Position Drive Rolls
Three Roll Bender
Bending Roll
Bending Point Fixed Position Drive Points
Three Point Bender
L Stretch Former
Alloy/Temper
Heat treated aluminium alloys in the T6 condition have relatively short plastic ranges with proof-stress/ultimate-stress ratios of 0/86: 1 and minimum elongation values of 7% - 10%. Although these values do not provide the whole picture of ductile performance, they give a reliable indication of bendability. Where bending is a primary requirement, it is usual to use material in the T4 solution treated condition. The plastic stress range ratios are then improved to 0.6:1 with minimum elongation values of between 14% and 16%. The slow rate of natural ageing in the 6000 series alloys does not appreciably affect the bending characteristics, except in the most severe bending cases.
Bending at raised temperatures is not usually recommended as the mechanical properties would be affected. It is possible to carry out post-bending heat treatment on T4 temper material that will increase its properties towards those of the T6 condition. Care should be exercised with thin sections as some distortion could occur under this treatment.
Table 6.1 - Bending Characteristics
Alloy Temper Bending Index
6063 T4 T6
V G
6063A 14 T6
V G
V=very good
6082 T4 T6
G F
G = good
6101A T6 G F=fair
6463 T4 T6
V G
2014A 14 T6
G F
Shape Factors
The complexity of shapes available in aluminium alloys makes it very difficult to provide information to cover every situation. By considering the behaviour of the various elements of the shape in relation to the bending axis it is possible to predict the most likely mode of failure when bent through too tight a radius. In most cases, the neutral axis of the section and the bending axis almost coincide but this is not true for stretch- forming where, because of longitudinal tension, the bending axis is assumed to move outside of the section.
67
The following tables give minimum bend radii for section elements under the various forms of bending stresses.
Radii values are to the neutral axis and are given in multiples of y.
y is the maximum distance from outer fibres of the element to the neutral axis of whole section. t is thickness of element.
Flange denotes shaded element parallel to the plane of bending.
Web denotes shaded element vertical to the plane of bending.
The use of support tooling in the buckling modes can reduce the minimum radii below the levels shown in the tables. The extent of the reduction depends upon the type of tooling used.
Table 6.2 - Minimum Bend Radii (1) y t 1 2 4 8 12
WEB TENSILE
Alloy Temper =1
6063 T4 O.7y 0.7y O.8y 2.Oy 3.5y L T6 O.8y 0.By l.4y 3.Sy 7.Oy L
6082 T4 2.5y 2.5y 2.5y 3.Oy 5.Oy
T6 2.5y 2.5y 2.5y 3.5y 7.Oy
Table 6.3 - Minimum Bend Radii (2) y WEB t 2 3 4 6 BUCKLING
Alloy Temper C1
6063 T4 l.Oy 3.5y 8.Oy 20.Oy
T6 l.Oy 4.Oy 1O.Oy 20.Oy
6082 T4 l.8y 4.Oy 1O.Oy 20.Oy F1 T6 l.8y 5.Oy 1O.Oy 25.Oy
68
Table 6.4 - Minimum Bend Radii (3) FLANGE WIDTH
THICKNESS 4 8 FLANGE TENSILE
Alloy Temper
6063 14
T6
7.Oy 8.Oy
10.Oy lO.Oy
6082 14 8.Oy Boy
T6 10.Oy lO.Oy
Table 6.5 - Minimum Bend Radii (4) FLANGE WIDTH
THICKNESS 4 8 FLANGE
BUCKLING
Alloy Temper
6063 T4
T6
6082 T4
5.Oy 8.OY
8.Oy 20.OY
7.Oy l2.Oy
J
16 8.Oy 2O.Oy
N.B. Where flanges have bulbs greater than 3t thick they can be bent to radii 60% of those shown in the table.
Tube Bending
The recommended methods of tube bending are wrap and draw mandrel. Although three point bending can be used, there is less control particularly with thin-walled tubes in the stronger alloys and tempers. Aluminium tubes can be readily bent but, like all materials, there are limits and the key to successful bending is to understand them and take appropriate action at both the design and fabrication stages.
Failure modes are, once again, tensile tearing and compression buckling but there are in-between situations where wrinkling, necking and flattening can occur without causing fracture of the tube. To prevent these surface defects or to restrict them to an acceptable level, the tubes can be filled with sand, springs or low melting materials such as Wood's metal.
69
These are all established methods of providing internal support which, together with the use of external groove formers and followers, provide the maximum level of bending control.
Table 6.6 shows the minimum root radii for a range of tube sizes based upon diameter! wall thickness ratios, alloys and tempers but ignoring flattening.
Sprlngback
Although the degree of springback can be calculated for a specific section that has been bent around a given radius, it involves a lengthy process. The more usual method of establishing springback is to carry out trials prior to a production run. Generally, sections which are symmetrical and have the major portion of their material away from the neutral axis exhibit less springback than a heavy centred cruciform section or an asymmetrical T-bar.
Lubrication
Friction between the surfaces of steel forming tools and the natural surface oxide of the aluminium creates the need to lubricate both work and tools. This helps to reduce tool wear and prevent damage to the surface finish of the formed parts. Depending upon tool shape, section size and alloy, the lubricants commonly used include mineral oil, lard oil, proprietary water soluble compounds and waxes.
MACHINING
Aluminium alloys are amongst the most machinable metals and can be cut at high speeds. Two basic properties influence the machining operation:
a) the high co-efficient of linear expansion of aluminium.
b) the friction generated between small tools and aluminium.
The problems associated with the above characteristics can easily be overcome by using a combined lubricant and coolant.
Machines normally found in a workshop are suitable for use on aluminium. The best results are obtained with relatively high speeds and it is frequently found that woodworking machines can be employed for machining, providing they have sufficient power and rigidity. High speed steel tools may be used on all the aluminium alloys. Plain carbon steels may also be used for short runs but they do not have sufficient life for quantity production. For long production runs tungsten carbide tips are recom- mended but even these tools would require regular resharpening particularly when used with anodized material. A chip breaker should be used on alloy 6082 for high speed operations to avoid the formation of long spiral swart.
70
Table 6.6 - Minimum Root Radii R In Terms of Tube Diameter
30
tr
o 20
Ill S - ——--———- ———-
lEt 2D 3D 4D 50
Minimum Root RodS In Terms Of lobe Diomneter
Wrap Bends
MATERIAL CHARACTERISTIC CURVE DESIGNATION AND TEMPER WRAP MANDREL
6063 F B B T4 B B T6 C C
6082 F B B T4 C C T6 D D
6101A T6 C C
4U -
30
C
o 20
10
S
15 5
lD 2D 3D 4D 5D
Minimum Rout Rods In Terms Of Tube Diameter
Mandrel Bend
71
Where extensive removal of metal is to be carried out, there is always the possibility of distortion occurring. Machining practices will also affect the amount of distortion that takes place. Cooling and lubrication should be generous but even so, over-tightened chucks could add to other stresses occurring through thermal expansion. If there is any doubt, the material supplier should be consulted.
Routing
One of the best methods of machining aluminium is by routing. This resembles a milling operation, giving a good surface finish, as fine as 0.75 micron, and can be used with spindle speeds up to 24,000 rpm. The high operating speed, in conjunction with low loading, ensures smooth, easy control which is essential when following the contours of a complex template. See Fig 6.2.
Helix angle
Radial rake Primary
clearance
Fig. 6.2 - Routing (Profiling and Facing)
72
CUlliNG SPEED FEED HELIX RADIAL CLEARANCE rn/mm rn/mm ANGLE RAKE
Profiling Up to 6 600-2100 Reduced
speeds Facing: necessary Upto with 25° 5-7° 5-10° 6000 increase
in work thickness
Drilling
As with other aluminium machining operations, drilling can be carried out at very high speeds. Special machines for use with small diameter drills work at 80,000 rpm, most
drilling operations, however, are carried out at more modest speeds. The cutting performance ot a drill is influenced by its peripheral speed and this should be taken into
account when deciding upon the spindle speed for a given drill diameter.
Drills should be inspected regularly to ensure that they keep their bright finish and
polished flutes to ensure rapid chip removal and prevent build-up. When necessary, the drills should be reground with care being taken to ensure thatthe chisel edge retains its correct length and the web atthe drill point does not thicken. Should thickening occur there will be increased end pressure on the drill with the possibility of drill breakage.
When drilling deep holes, particularly of large diameter,excessive heat is generated and if not dissipated by the coolant, hole contraction could take place.
DRILL ELEMENT TOOL ANGLE
PointAngle,H 118°
Helix AngIe 20 - 25°
Clearance Angle, 0 12 - 20°
Flutes Polished
Web Thickness Thiner than that used for other metals
Fig. 6.3 - Drills
73
Sawing
Modern saws used in the fabrication of aluminium sections give clean, virtually burr-free cuts provided that the correct tooth size and rotation speed are used and the teeth kept sharp. This is particularly so for tungsten carbide tipped blades which are in general use for aluminium. This type of blade gives excellent results on the hard surface of pre- anodized sections. Feed will vary with the type of saw, section size, alloy and temper but should never be below 0.05mm per tooth. When cutting thin sections, it is advisable to have two or more teeth engaging at the same time.
Table 6.7 sets out basic tool data. The lower speed range is recommended for high speed steel blades and the higher range for tungsten carbide tipped blades. It is always advisable to use a cutting fluid.
High speed steel Segmental teeth
Top clearance
Th Fig. 6.4 - Types of Saw
Table 6.7 - Basic Saw Tool Data
74
Top clearance
Depth of Top rake gullet
Depth of gullet
Type of Blade Cutting Teeth Angles Saw & Size Speed Pitch Gullet Top Clearances Blade Depth Rake Top Side Material mm m/min mm mm
Circular 250-460 8.5-13 Handfeed: High dia 1500 6.4 12-18° 20-30° Speed x to Hollow to Powerfeed: 1-2° Steel 2.3-3.7 2400 Ground 12.7 15-24° 25-35°
thick Circular 560- 1200 coarse Handfeed: Seg- 1220 to 25-50 5-12° 7-9° mental dia 4500 Chip- 12.7- Powerfeed: 1.2° Inserted x breaker 57 10-20° 5-7° Carbide 64-12.7 teeth Tips thick
JOINING
Aluminium alloys can be connected in a variety of ways. The usual methods, all well- established, are welding, riveting, bolting, screwing, corner crimping and glueing (but aluminium alloys have also been explosively bonded to other materials)..
The combination of material flexibility and the extrusion process enables mating sections to be manufactured in a range covering both permanent and releasable types of sliding, rolling or straight clip connections. Details of this type of joining are given under Section 11, Design.
Welding
Aluminium welding is a widely accepted method of fabrication, with no shortage of competent personnel in the engineering and manufacturing industries. There are several methods available, the basic ones being Tungsten Inert Gas (hG) and Metal Inert Gas (MIG). As the titles suggest, both are inert gas shielded systems where the weld area is shrouded from the air to prevent the reformation of an oxide film.
Preparation
Cleanliness and the removal of the oxide film are most important. The proposed weld areas has to be de-greased, using white spirit or acetone and the joints wiped dry. Adequate ventilation must be provided for any solvents used but is particularly applicable to industrial cleaning solvents, such as carbontetrachloride etc. After de- greasing the joint is deaned, using stainless steel wire brushes or a chemical etch cleaner to remove the oxide film. Welding should be carried out as soon as possible afterwards. Carborundum wheels are not recommended as grit particles can become embedded in the surface causing contamination of the completed weld. Filler wire is cleaned by wiping with wire wool; pre-packed spool wire is supplied in a clean condition.
Tungsten Inert Gas
In the tungsten inert gas (TIG) process, the arc is struck between the workpiece and a non-consumable tungsten electrode. The filler wire is fed independently. Although mechanised TIG is available the process is more widely used as a manual system where close control of the welding conditions can be readily maintained. The resulting welds are usually of good appearance and penetration, particularly where no backing plate is available. Fig. 6.5 shows a schematic layout of a typical TIG system and Table 6.8 shows the thickness range.
75
Metal Inert Gas
In the metal inert gas (MIG) process, the arc is struck between the workpiece and a consumable electrode which is constantly fed from a wire spool. The arc is self- adjusting and takes into account small movements of the torch. Penetration and appearance are not so easy to control as in the TIG system, although the addition of pulsed arc equipment will improve the penetration and reduce the need for backing plates. Fig. 6.6 shows a schematic layout of a typical MIG system and Table 6.8 shows the thickness range. Small spool hand guns, sometimes called fine wire, are also available with MIG systems. These dispense with the need for long wire feed leads thereby increasing the area of work accessible from the base unit.
Table 6.8 - Process Capacity
PROCESS
PARENT METAL THICKNESS
EQUIPMENT
Mm I Max. (mm) (mm)
Item
TIG 1.2 9.5 (1)
Composite unit (350 A) Transformer (350 A) H.F. or Surge Injector unit Suppressor Welding Torches
MIG 0.5 kg 1.6 8.0 (2)
Composite unit (250 A) with Wire Feed unit and
Welding Gun for 1 lb Spool
MIG 5kg
4.8 None Composite unit (350 A) with Wire Feed unit and Welding Gun for 10 lb spool
NOTES: (1) Although the TIG process can weld thicker material, for economic reasons it is not normally used for aluminium over 9.5 mm thick.
(2) In theory there is no upper limit for 'one-pound 'MIG, but it is more economical to use 'ten-pound
' MIG for material over 8.0 mm thick.
76
NOTES
1 Composite TIG welding units include all the necessary auxiliaries: argon and water shut-off valves are usually controlled by solenoids, although they may be manually operated.
2 The main power cable, fuse and torch can be air-or water-cooled.
Fig. 6.5 - TIG Welding
77
NOTES
1 The a.c. supply is 11OV for 'one
pound' MIG and 220V tot 'ten-pound' MPG welding.
2 Composite MIG welding units have the contactor and control box built in.
3 The filler wire feed unit is integral with the gun in 'one-pound' MIG and
independent of it in 'ten-pound MIG
Systems.
Dry Bobbin Flowmeter Pressure Reducing Valve Pressure Gauge
4 Voltage pick-up lead for 'one-pound' MIG.
5 The main power cable and gun of 'ten-pound MIG can be water cooled.
6 Arc Voltage in MIG Welding Procedures is measured with a voltmeter connected between the contact tube and the workpiece.
Fig. 6.6 - MPG Welding
78
Wire Feed Unit
Workpiece
Filler Wire
6063 and 6082 alloys can be readily welded to a wide range of other aluminium alloys. Table 6.9 shows the preferred weld filler wire in bold print. An alternative, where given can be used when the finished component is to be anodized and a close colour match is required between the weld area and the parent metal. Alloy 2014A is not shown in the table as this alloy is not recommended for welding using the TIG and MIG
processes.
Table 6.9 - Recommended Filler Alloys for Welding Parent Metal Combinations
PARENT ALLOY
6063 6082
1050a 4043 5356
3103 4043 5356
5083 5356
5251 5356
5454 5356
6061 6063 6082
4043 5356
Alloy 2014A is Not Recommended for Fusion Welding
Joint Design
Good joint design encompasses both the practicalities of the welding process and the structural requirements of the joints in service. The edge preparation will depend upon the type of joint, butt or lap, thickness of material to be joined and the welding process to be employed. Table 6.10 shows typical edge preparation for both TIG and MIG
processes.
The strength of welds is covered by BS CP1 18 which gives permissible stress levels for both 6063 and 6082 alloys in both butt and filled applications see Table 6.11. The reduction in strength from the 0.2% proof stress levels is very marked, allowing for
79
Table 6.10 - Edge Preparation and Fit Up for Tig and Mig
p= Permanent Backing Plate c= Temporary Backing Plate
THICKNESSt (1) g n a NOMINAL MAXIMUM ROOT INCLUDED JOINT
GAP GAP FACE ANGLE DETAIL (mm) (mm) (mm) (deg.)
MIG TIG
- 0.8c Nil Nil - - $
- - -
3.2c 4.8c 3.2p
1.2c 1.6c 4.8c
- - -
Nil Nil - - Nil 0.8 - -
Nil 1.6 - -
1.6 2.4 - - g 2.4 3.2 - -
4.8 6.4 - - 8.0 6.4c 4.8P
-
- -
6.4c
Nil 0.8 1.6 60 1.6 2.4 1.6 60 4iit 3.2 4.8 Nil 60 Nil 1.6 1.6 75
12.7 15.9
- -
Nil 0.8 1.6 90 Nil 0.8 1.6 90
-
3.2 4.8
1.6 2.4 6.4
Nil Nil - - I Nil 0.8 - -
Nil 1.6 - - jj 6.4p - 1.6 3.2 0.8 60
9.5 - Nil 0.8 0.8 60 HL -
3.2 4.8
1.6 -
8.9
Nil Nil - -
Nil 0.8 - - g
Nil 1.6 - -
12.7 19.0 25.4
- - -
Nil 1.6 3.2 60 r Nil 1.6 4.8 60 Nil 1.6 6.4 60
Li - 0.8 Nil Nil - -
[JJ - -
- -
1.2c 2.4c
1.6 3.2c
Nil Nil - - Nil 0.8 - -
flu
Nil Nil - - Nil 0.8 - - g n
1) Minimum Thickness of Parent Metal 80
contingencies in the welding process and the reduced property levels of the weld heat affected zones. The most cost effective way of designing welded structures, therefore, is to keep the welded connections clear of maximum stress points, as far as possible.
Table 6.11- Permissible Stress Levels
Screwing
ALLOY
BUTT WELDED JOINTS &
REDUCED HAZ.
FILLET JOINTS (WELD METAL)
TENSION COMPN TRANSVSL LONGITL
6063
6082
31
51
19
31
54
54
31
31
Permissible Stresses for Table Welded Joints in N/mm2 HAZ = Heat affected zone
The ease with which aluminium alloys can be drilled or punched and the incorporation of screws ports or channels in extrusions has encouraged the use of stainless steel self-tapping screws as the standard method of joining, particularly in the window and door industries. The stainless steel threads bite into the aluminium to give a very positive connection. A typical patio door will use two self-tapping screws per kilogram of aluminium section used.
Screw ports are rarely fully closed as the use of 300 degree ports, (Fig. 6.8), gives a very marked improvement in extrudability with very little loss in pullout strength. The dimensional accuracy of the port diameter is very important and all extruders have standard bore dimensions for each screw size. It is advisable to contact extruders at the die design stage and where possible provide sample screws.
— \ — \
__ \ 1.78mm (mm) 60°
/ I
N / .. / .... /
Screw Size
Screw Dia. (mm)
Screw Groove Int. Dia. (mm)
6 3.45 3.20 8 4.17 3.56
10 4.88 4.32
12 5.59 5.03
14 6.25 5.74
FIg 6.7 - Recommended Diameters of Screw Grooves
81
The use of longitudinal screw grooves, (Fig. 6.8), is not so widespread but the correct combination of slot width and screw size can ensure high pullout values. Some care is necessary if self-tapping screws of triangulated cross-section are used as full engagement of threads may not be possible on both sides of the groove. Advice from the extruder is recommended.
Crimping
Li
Fig. 6.8 - Longitudinal Screw Grooves
In this method of corner connection, the extrusion has a built-in channel recess and afterthe sections have been mitred, the crimping angle is fitted and the joint assembled and held in a rigid jig. Two pressure prongs then upset the section flange into the corner angle, producing a very stable frame assembly, see Fig 6.9. Most crimped corners rely on mechanical connections, but, if required, a slow setting adhesive can be used to seal the corners and provide some extra strength.
Crimping is most likely to be found in the door and window industry but is applicable to any component or form of construction where mitred corners are used.
Fig. 6.9 - Crimping
82
Crimping flange
Riveting
Aluminium can be riveted with aluminium rivets, which are usually driven cold. As there is a tendency for these to work harden during the process they should be closed with the minimum number of blows. It is advantageous to use a long stroke hammer, a size larger than would be used with equivalent diameter hot steel rivets. The rivets should be driven square, not rolled round the edges. Larger diameter rivets (over 12 mm.) can have pre-formed end recess points to assist initial forming. Power operated squeeze riveters are ideal for aluminium as the heads are formed in a single stroke.
Where aluminium is to be riveted to steel structures, the faying (contact) surfaces should be treated with a zinc-chromate primer and brought together while still wet. Hot driven steel rivets should be used but these must be given at least one coat of primer in way of the aluminium, after driving and cooling.
Blind Riveting
This form of joining is well established and uses rivets of tubular construction which enable the workto be carried outfrom one side only. This is particularly attractive where access to the reverse side is difficult. Only one operator is required and there is choice of setting tools - pneumatic, hydraulic or hand held. There are a number of proprietary systems available, in diameters upto 6.5 mm. Rivet lengths are available for combined joint thickness of up to 13 mm. Further details are available from rivet manufacturers.
ELE Mandrel breaks and falls free
Setting tool Clinching mandrel
Fig. 6.10 - Blind Rivets
83
Self-Piercing Riveting
This is a relatively new development which can be used on combined thicknesses of up to 6.5 mm.
T
Clench Riveting
L = 9.5mm
1=6.5mm S = 5.0mm
Fig. 6.11 - Self-Piercing Rivets
A numberof proprietary fastening systems use the gripof threaded bolts with the closing mechanism of clench riveting. Fig. 6.12 shows atypical pin and collet assembly. The bolts are closed from one side in a similar manner to blind riveting, although access to the non-closing side is necessary to install the rivet. The collet deforms around the threaded pin before the pin breaks off at the waisted neck under a pre-determined load. As well as the advantage of ease of installation, these fastenings have excellent vibration resistance.
Fig. 6.12 - Clench Rivets
84
Max.
Countersunk
Bolting
In this method o construction stainless steel, aluminium or mild steel bolts can be used. If stainless steel to 18/8 specification is used, no extra protection is used and the bolts can be used in the conventional manner. The best aluminium materials are 6082 and 2014A but the latter will need painted protection in heavy industrial and marine environments. Alloy 2011 is a widely used and available bolt material but would certainly need protection in any external application. In the case of mild steel bolts, galvanized steel washers MUST be fitted.
All bolts are best used in close-fitting holes and the appropriate tolerance levels will be found in BS CP118.
Where possib'e, control torque levels shoud be specified for aluminium bolts and the indiscriminate use of "tommy bars' is an unacceptable practice. In line with good bolting practice, no part of the threaded portion should be within the thickness of the joint flanges.
The extrusion process allows captive bolt head slots to be built into the extrusion. The bolt can be positioned anywhere along the slot, thus requiring hole accuracy in one dimension only. The internal width of the slot should be dimensioned to suit the maximum width of the boithead across flats thereby locking the bolthead against turning when tightening up the nut. See Fig. 11.3
85
Adhesives
This method of joining has found favour in the high-tech industries, i.e. electronics and aero-space where product cleanliness and close fabrication control were already well- established practices. In more recent years, adhesives tolerant of imperfect joint conditions have been developed and have been taken up, particularly by transport, engineering and even structural industries.
In general, bonding systems still require clean etched surfaces; some respond to unsealed, anodized or conversion coated surfaces. The range of adhesives available covers cold, impact or heat curing together with single or two-part mixes. Each has its own characteristic and therefore advice on suitability for any specific application should be sought from adhesive manufacturers.
86
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 7- CONDUCTIVITY
CONTENTS
Title Page No.
THERMAL 89 Thermal Barriers 89
ELECTRICAL 90
87
List of Figures
Fig No. Title Page No.
7.1 Mechanically Closed Insulating Web 90
7.2 Poured Resin
Insulating Web 90
List of Tables
No. Title Page No.
7.1 Thermal Conductivity 90 0-100°C
7.2 Electrical Conductivity 91
88
THERMAL
Aluminium has a high co-efficient of conductivity. It varies with the different alloys but the value for pure aluminium is 244 W/m0C. See Table 7.1. This property is extremely useful when designing heat transfer products, such as radiators and electrical heat sink units. It is obviously less attractive in those applications where low heat transfer is
required and it is then often necessary to in-corporate components to improve the thermal resistance, e.g. thermally broken window sections.
Thermal Barriers
This solution to the therma transfer problem has been used in the building and construction industries for nearly thirty years. During this time, design and manufac- ture has been refined so that now two major types of systems are in general use.
In the first, Fig. 7.1, the thermal insulating web, or webs, is made from strip material -
nylon, polyamide etc. - fixed into position by mechanical closing of dovetail type channels in the aluminium sections. Two separate sections are used enabling different surface finishes or colours to be used. The closing methods vary between rolling, pressing and broaching, depending upon individual manufacturers. Internal broaching, can only be used in the case of double web sections.
The second system is frequently referred to as the "pour and cut" method, Fig. 7.2. A specially formulated liquid resin is poured into a semi-closed channel in the single aluminium section. After the resin has solidified, the connecting aluminium strip "a" is cut away leaving the thermal barrier or barriers. As with the first system, a double web section can be produced, in this case by using either a proprietary instantaneous double pour machine or by a two pass procedure on conventional machines.
The structural properties of thermal barrier materials will generally be below those of aluminium and will vary not only between different materials but also over atemperature range of -20°C to +80°C. It is good design procedure, therefore, to keep the thermal barrier material as close as possible to the neutral axis of the final composite section. In practice, this is not always possible and examples can be seen in existing window systems where the thermal barrier is offset. In these cases it is essential that extensive laboratory proving tests are carried out to confirm that the composite section has sufficient strength and stiffness as well as thermal performance.
89
Lips Mechanically Closed On Insert
Solid Insulating Inserts
Aluminium Holding Web
Cut Out "a"
Table 7.1 - Thermal Conductivity 0- 1000C
* International Annealed Copper Standard
ELECTRICAL
Materials that are good thermal conductors are in general also good electrical conductors and this is certainly true of aluminium. The copper/aluminium ratio values for thermal conductivity run virtually parallel to those for electrical conductivity. A special alloy has been developed for electrical use -6101 A. This medium strength alloy has excellent electrical conductivity and good fabricating characteristics. It is available in the T6 temper only.
Compared with copper, an aluminium conductor of equal current-carrying capacity will have cross-sectional area 84% larger but will be only 54% of the weight of the copper bar.
90
Resin Webs
Mechanically Closed
Fig. 7.1 - Mechanically Closed Insulating Web
Poured Resin
Fig. 7.2 - Poured Resin Insulating Web
ALLOY TEMPER W/m°C % IACS
6063 T4 197 50 T6 201 51.1
6063A T4 197 50 T6 201 51
6082 14 172 43.7 T6 184 46.7
2014A T4 142 36.1 T6 159 39.8
Table 7.2 - Electrical Conductivity
Electrical Temperature Resistivity Conductivy Coefficient of (20°C) (200C) Resistance
ALLOY Microhm %IACS per°C
6101AT6 3.133 max. 55.1 mm. 0.00364
91
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ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 8- TEMPERATURE
CONTENTS
Title Page No.
EXPANSION 95
MECHANICAL PROPERTIES 95
Creep 96 Melting Point 96
93
List of Tables
No. Title Page No.
8.1 Coefficient of Linear
Expansion (200 C - 1000 C) 95
8.2 Influence of Temperature on Properties as % of 25° C Values 96
94
EXPANSION
Although aluminium has a relatively high co-efficient of linear expansion, 24 x 10-6 per degree C in its pure form, the low modulus of elasticity enablesthetemperature induced stresses to be held at a low level. These are usually two thirds of those induced in a similar steel structure. It is still recommended, however, that all long restrained struc- tures likely to be subjected to temperature variation and particularly those in dark colours are checked out in the design stage. Any excessive stresses can be reduced
by fitting simple expansion joints. The general effect of alloying is to reduce the co- efficient of expansion and relevant values for the more common aluminium alloys are shown in Table 8.1.
Table 8.1 - Coefficient of LInear Expansion (20°C - 100°C)
ALLOY TEMPER 106/0C
6063 T4 24 T6 23.5
6063A T4 24
16 23.5
6082 T4 23
T6 23
6101A T6 23.5 6463 T4 24
16 23.5
2014A T4 22
T6 22
MECHANICAL PROPERTIES
Variation in temperature also directly affects the mechanical properties of aluminium alloys. At low temperatures the structural strength and elastic modulus values are actually increased, whilst at higher temperatures they are reduced. A further important characteristic is that at low temperatures aluminium and its alloys show no brittleness which makes them extremely useful in cryogenic applications such as containers for low temperatures liquid gases. The more important properties are given for each of the alloys in Table 8.2. The dotted line inTable 8.2 signifies the maximum temperature at which it is recomended each alloy can continuously be used. Some official codes will accept higher temperatures in specific applications - BS5222 "Aluminium Pressure Piping" sanctions temperatures up to 2000C.
Note: special alloys have been developed for high temperatures applications, contact extruders for performance data and availability.
95
Table 8.2 - Influence of Temperature on Properties as % of 25°C Values
Alloy Temoerature Temper Stress -200 -100 25 100 150 200 300
606316 Ult 130 110 100 95 65 20 10 0.2% PS 115 105 100 95 65 I 20 10
608216 Ult 130 110 100 95 70 I 40 10
0.2% PS 115 105 100 95 L40 5 2014AT6 Ult 124 108 100 85 44 191 11
0.2% PS 125 109 100 87 41 17 10
Modulus I
of Elasticity 110 105 100 100 95 90 70
Creep
At elevated temperatures under the prolonged application of a stress of sufficient magnitude, metal will "creep" and may eventually rupture. This behaviour, the progres- sive deformation without increase in load, does not enter into the design considerations for structures operating below 100°C but may require study in high temperature applications. When creep is considered to be a design factor, more information should be obtained from the material supplier.
Melting Point
As aluminium approaches its melting point it does not change colour, so other means such as temperature sensitive crayons, must be employed if a visual check on the temperature is required. While pure aluminium has a well-defined melting point of 660°C, aluminium alloys have a melting range which, for the alloys listed in the Table 8.2, varies from 570°C to 660°C.
96
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 9- FIRE
CONTENTS
Title Page No.
ALUMINIUM AND FIRE 99
97
List of Tables
No. Title Page No.
9.1 BS 476 Fire Test Series 99
98
ALUMINIUM AND FIRE
ALUMINIUM DOES NOT BURN. It will not ignite. It will not add to the fire load. It will not spread surface flame.
Although aluminium melts at around 620°C, it has a thermal conductivity of four times that of steel and a specific heat twice that of steel. Heat is conducted away faster and therefore a greater heat input is necessary to bring aluminium upto a given temperature than required for steel.
In any application requiring a structural fire resistance measured against time, a test certificate is usually necessary. Although aluminium components have obtained ap- provals above 30 minutes in tests it is not possible to make accurate predictions. It is necessary, therefore, to obtain a test approval for each type of application. Where
higher time ratings are required, aluminium must be used in conjunction with other conventional fire-resisting materials.
The more usual fire performance requirements for aluminium extrusions can be obtained from the results of the British Standards tests shown in Table 9.1.
Table 9.1 - BS 476 Fire Test Series
Part No. Title Aluminium Results
* 4 Non-Combustibility Test Non-Combustible
* 5 ignitibility Test P, not easily ignited
* 6 Fire Propagation Test P. actual index will
vary with thickness
* 7 Surface Spread of Flame Test Class 1. Painted surfaces will reduce performance rating
21 1 Time/Structural 22 Resistance & Insulation ** individual 23 Test component testing
required
99
The British Standard fire tests are laid down in BS 476 and define results irrespective of materials. Aluminium and its alloys achieve the highest possible ratings for parts 4, 5, 6 and 7 and are therefore widely used throughout the construction and other industries where the highest standards of performance are required. Painted surfaces could, however, reduce the levels of performance.
Tests 21, 22 and 23 are used to obtain the performance of a component or unit for strength, integrity and insulation, all compared to time against closely calibrated temperature levels.
** It is usual for aluminium extrusions, in these instances, to be used in conjunction with other materials to obtain resistance times in excess of 30 minutes.
* Indicated highest possible rating.
100
ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 10- CARE AND CONTROL
CONTENTS
Title Pag No.
INTRODUCTION 102
HANDLING 102
STORAGE 102
MAINTENANCE 103
101
INTRODUC11ON
In post-extrusion handling, every care is taken by extruders to minimise damage. It is essential that this "good house-keeping" is continued in customers' works and ware- houses. As with other high quality materials, carelessness can cause unnecessary rejection, resulting in higher production costs.
HANDLING
The following recommended practices should be followed:-
(1) Single lengths should never be pulled longitudinally from the middle of a bundle of aluminium sections as the entrapped end will score adjacent sections.
(2) Cleanliness is very important, particularly with sections to be anodised. Gloves should be worn whenever dealing with this type of section as the natural oil from the hands can cause finger print corrosion which will become apparent at the etching stage of the process.
(3) When lifting by crane, double slings should be used as single slings can cause bending damage particularly with bundles of long, light sections.
(4) The sections should always have adequate support when lifted by a fork-lift truck.
STORAGE
Although aluminium alloys are very resistant to atmospheric corrosion, certain simple precautions should be taken during their storage. All materials should be stored away from excessive dust or fumes; particularly when portable gas or oil heaters are used, for as well as pollutants these heaters also produce moisture. Storage spaces should be dry and well ventilated and kept at a constant temperature above 16°C. Any superficial corrosion that occurs on extrusions is usually easily removed by hand cleaning with white spirit. Even the most severe superficial corrosion responds to cleaning with fine wire wool and white spirit.
The more troublesome form of staining is water marking, caused by moisture ingress between sections that are closely nested, e.g. angle bars. This can occur directly or by condensation. In the latter case, it is possible for the moisture to work upwards by capillary action. Stacking in a self-draining position is therefore no solution. It is, however, easily avoided by spacing the sections and ensuring that moisture can not bridge the gap. The stain can be removed by wire-brushing and chemical treatment.
Storage staining and corrosion will not usually have any detrimental effect on the mechanical properties of the material.
102
Vertical racks are preferred for storage. If horizontal storage is unavoidable, care should be taken not to overload racks and to support light sections adequately to avoid local damage at the points ot support. Timber rubbing bars should be fitted to steel racks to minimise abrasion and to avoid spots which could cause condensation under adverse storage conditions.
Racking should be arranged to facilitate easy inspection which should be carried out at regular intervals. As most aluminium alloys look alike, materials should be stamped or colour-coded so that different alloys and tempers can easily be identified. This would not be necessary where an alloy or temper is consistent with a special shape. It is also useful to mark batches on arrival in store to ensure that they are used in the
original delivery sequence.
MAINTENANCE
Aluminium alloys require little or no maintenance to retain their original mechanical properties. Without regular cleaning, however, surfaces can become stained particu- larly under prolonged exposure on industrial sites. Mill-finished aluminium can be cleaned by rubbing down with fine wire wool and white spirit. Anodised surfaces are more resistant to staining but, nevertheless, benefit from regular washing down with soapy water. Proprietary cleaners are available for both mill finished and anodised surfaces but should they be used, it is absolutely essential that the manufacturer's instructions are strictly adhered to.
103
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ALUMINIUM EXTRUSIONS — a technical design guide
SECTION 11 - DESIGN
CONTENTS
Title Page No.
DESIGN PROCEDURE 107
VALUE ANALYSIS 107
PRACTICAL DESIGN FEATURES 109
WORKED EXAMPLES 111
Unloading Ramps 111
Pedestrian Balustrade 113 Columns 123
105
List of Figures
Fig No. Title Page No.
11.1 Steel and Aluminium Beams 108
11.2 Examples of Solid Section Aluminium 108
11.3 Built-in Mechanical Fastener 110
11.4 Advantages of Aluminium Versus Steel 110
11.5 Various Snap Fit Connections 110
106
DESIGN PROCEDURE
In designing a section, it is usualto have a performance specification setting out the total requirements of both section and material. This could be part of a much wider
specification for a complete finished product of which the aluminium extrusion is only one of the components. The extent and detail required for such a specification will vary with the application and also within different industries. It is good design practice to have such a "check list" providing, as it does, a target of what needs to be achieved and a logical procedure for assessing different ideas. A comprehensive list of design considerations is set out in Appendix 1.
Rarely will all these factors need to assessed and a more general approach is given in the following flow chart.
Idea
Performance Specification
I I I I•• I. I. .1.. Material Fabrication Appearance Mechanical Durability Special Unit Availability Selection Properties Requirements Cost
4 Machining Shape Strength Atmospheric Electrical
I Conductivity
Forming Surface Stiffness Chemical Unit Weight Finish
Jointing Hardness Fatigue
VALUE ANALYSIS
Although basic material cost is important, it should be balanced against the overall cost of fabrication and subsequent service performance. This is particularly relevant to aluminium extrusions where shapes can be produced that require little or no further fabrication and the aluminium alloys available have characteristics suitable for a wide range of applications.
Aluminium extrusions are usually sold by weight which tends to encourage compari- son with other materials on a straight weight/cost basis. This in unrealistic as compared with steel, allowing for the lower elastic modulus, aluminium/steel weight ratios of 1 : 2 are easily attained to equal performance specifications.
107
Ag. 11.1 - Steel and Aluminium Beams
The two beams in Fig. 11.1 have been designed for equal stiffness in both xx and yy axes. The strength of the aluminium beam is well over twice that of mild steel if alloys 2014A 16 or 6082 T6 are used.
It is important always to check the actual deflection requirement as in many cases the steel design has been stress based and the corresponding level of deflection is
automatically accepted without consideration of the real level required.
The economic use of aluminium alloys is not just confined to comparisons with steel and other materials. The proficient use of extrusions can frequently result in comparisons with other aluminium profiles to obtain the optimum shape. Fig. 11.2 illustrates the design of solid sections to give good strength and stiffness in both major axes instead of a more expensive hollow section.
[1 ii
ft_ 11
Fig. 11.2- Examples of Solid Section AluminIum
108
145 .. 100
Steel 21.7 kg/M
0L 150
Aluminium 10.6 kg/M
In other cases, the use of standard structural sections is more appropriate. Two ranges of I beams, channels, T bars and angles are available, namely the specially designed lipped sections conforming to BS 1161 and the range covering structural sections similar to the universal sections used in the steel industry.
in manufacture, the availability of sections that require little or no fabrication can be a major factor in reducing final component costs. This equally applies to site erection
where, apart from light weight, the ability to use hidden fixings can simplify procedure.
PRACTICAL DESIGN FEATURES
Replace several parts
One extrusion can often do the work of several structural shapes joined together and produce a neater, sounder
design, at less cost.
Place metal where It is most effective
Thus, bulbs, fillets and variations in thickness can easily be incorporated for structural advantage and local increases of thickness can be introduced to counter wear and abrasion or permit tapping of screws.
The two bulbs, and root buteress improve inertia and section modulus values as well as increasing torsional resistance.
Hinge Fits
Continuous hinges with built in stop bars plus screw groove for end stops.
A slide fit which allows one shape to move in a circular arc with respect to the other.
109
Slots, holes and threads for mechanical fasteners can be extruded as integral features.
Typical early steel frame section. Typical aluminium frame section.
FIg. 11.4- Advantages of Aluminium Versus Steel
Locking Cover
Fig. 11.5 - Various Snap Fit Conections
110
Adjustable locking connection.
FIg. 11.3 - Built-in Mechanical Fastener
Retractable Cover Adjustable Locking
WORKED EXAMPLES
Unloading Ramps
Single lengths of channel bar are frequently used in tandem to unload wheeled vehicles. In the interests of good working practice, they should always be longitudinally and
transversely restrained.
There are several ways of calculating the size required. The following method is based upon simple point load bending without any axial component. it is assumed that unloading is always controlled and no unusual dynamic loads will occur.
Specification. The ramps should be a maximum weight of 50 kg each. Span 2.5 metres. Operating angle up to 30 degrees. Maximum vehicle load 2.0 tonnes equally shared on four wheels. Maximum tyre width 200 mm with 25 mm clearance.
The initial choice of section size is governed by the final specification requirement, that of type width and clearance.
Channel Section : 254 x 88 x 11 web x 14 flanges (all in mm)
Section properties:
Area 5030 mm2
Modulus Zxx 54620 mm3
Inertia
Radius of Gyration Weight/metre Alloy
lxx 3459100 mm4- Note: as section is used in
this plane check with
property tables to confirm
26.2 mm the way x & y axes are given 13.39 kg/m 6082 T6
111
Slope Q in degrees
Loading. As the vehicle is unloaded it moves out of the horizontal with a considerable shift in its neutral axis and the loading on the first set of wheels increasing. This will be a feature of the individual vehicle. For the purposes of this calculation it is assumed to be 10%, hence -
Maximum individual wheel load = 1 9640N (2 tonnes) x 1 10 = 5400N 4 100
Bending Stresses. The ramp acts as a simply supported beam and with normal wheelbased vehicles will have a central load as the worst condition. (Load Case 2.)
M = WL = 5400N x 2500mm 4 4
Maximum bending moment = 3375000 Nmm
Maximum Stress = 3375000= fbc= 61.8N/mm2 54620
Allowable Stress Levels. See Table 3.2 (From British Standards CP1 18)
6082 T6 alloy
Bending p, 154N/mm2
Deflection
8 = For 6082 E = 68,900N/mm2 48El
8 = 5400x 2500 48 x 68900 x 3459100
8 = 7.45mm
The deflection/span factor = 336
which is well inside the recommended value of 200
Lateral Instability. It is usually advisable to check the ramp for lateral instability. The method for calculating this can be found in BS CP1 18. The cross-tying of the two ramps together with lateral ties will dramatically increase the resistance to lateral instability, but in this case, with the stronger axis of the section acting transversally, instability will not occur.
112
Pedestrian Balustrade
Specification. To enclose an external paved area within the confines of an office block. The railings must meet the requirements of the appropriate British Standards and whilst being functional should have an attractive appearance. Low maintenance is also essential.
BS 3049 Pedestrian guardrail BS 6180 Protective barriers in and around buildings. In this instance BS 6180 applies.
As it is a possible area of assembly, although in an office development, two categories of use are applicable.
From BS 6180 Table 1
Type 4 Office building Type 7b Place of assembly
LOAD FACTORS Tables 2 and 3 from BS 6180
TYPE HORIZONTAL INFILL INFILL MINIMUM U.D.L. IJ.D.L. POINT LOAD BARRIER HEIGHT kN/M kN/M2 kN mm
4 0.74 1.0 0.50 1100 7b 1.5 1.5 1.50 800
Access will be controlled and private so that type 4 will apply.
Material. Aluminium alloy 6063 T6 will meet all the requirements of -
surface finish durability low maintenance
It is also an approved material in BS 6180 and its structural characteristics are set out in BSCP 118.
113
Fabrication Details
76x50 Top rail 70x70x2.5 Posts
1lOOmm
1500mm
E E 0 0
Main stanchions: These are to be set directly into concrete foundations. The stanchion base over the area to be bedded into the ground is to be given two coats of bituminous paint.
Top and bottom rails: These are to be connected to the stanchions using bolted lugs. Bolts to be stainless steel to 18/8 specification.
Balusters: These are to be slotted into the top rail and into punched slots in the bottom rail, then welded into position on both top and bottom rails.
Surface finish: A natural anodized finish is required to AA 25 suitable for external application. This will necessitate the infill panels being anodized as single units. Check availability of suitable facilities.
114
.r 50 x 54
—30x30x2 Balusters
—100mm Max Gap
1500mm
Section Design
The following sections have been drawn up to meet the requirements of the perform- ance specification.
2mm
Stanchion
Baluster
STANCH ION
BALUSTER
Area CCD
Shape factor
—I
215 mm2 43mm 370
76
lop rail
TOP RAIL
54
BOTTOM RAIL
Area CCD Shape factor
300 mm2 74mm 370
50
:: Rad.:
70
70 Overall thickness 2.5mm
Bottom rail
Area 661 mm2 Area 585 mm2 CCD 99mm CCD 89mm Shape factor 298 Shape factor 334
115
The CCDs are well within the capacity of most medium sized presses with container diameters of 150 mm.
The shape factors are slightly above average, but still acceptable.
The thicknesses have been checked out against Table 1.2 and are within the level
required for 6063 material.
A further check is necessary on the top rail for both the extrudability ratios of the semi- enclosed area and the depth/width ratio of the side channels.
Large recess = 59 mm x 45 mm = 2655 mm2
Gap = 31 mm Gap2 = 961 mm2
Area/gap2 ratio = 2.76: 1
The section can be classed as a solid and the extrudability is acceptable.
Side channels Depth 17.5 mm
Gap = 3.5 mm
Depth/gap ratio = 5:1
This is not acceptable so it is necessary to reduce the outer flange from 20 mm to 13 mm.
The internal depth of the channel is now 10.5 mm The depth/gap ratio is now 3 : 1
This is now acceptable and the new top rail section details are as follows:
Area = 550 mm2 CCD = 89mm Shape factor = 314
Section Properties
STANCHION - Area 661 mm2 Modulus Z 14190 mm3 Inertia I 496680 mm4
TOP RAIL - Area 550 mm2
(modified) Modulus Zy 11150 mm3 Inertia ly 423740 mm4
BOTTOM RAIL - Area 300 mm2 Modulus Zy* 5650 mm3 Inertia ly * 152500 mm4
*effective area values (less slot area)
116
BALUSTERS - Area 215 mm2 Modulus Z 1838 mm3 Inertia I 27600 mm4
Loading
STANCHIONS The load is applied to the stanchion through the top rail.
Hence load 740N1M x 1.5M = 111ON
RAILS The load for the top and bottom rails is the same as that for the stanchions.
Hence load = 111ON
BALUSTERS Central point load 500N
STANCH IONS Load Case Cantilever
f = ..WL = lllQNxllQOmm = 86.OON/mm2 Z 14190 mm3
TOP RAIL Load Case Two span, simply supported UDL
f = - YL. = lllONxl500mm =1886N/mm2 8Z 8 x11150 mm3
BOTTOM RAIL Load Case Simply supported UDL
f = WI. = lllONxl500mm = 36.BON/mm2 8Z 8x5650mm3
BALUSTERS Load Case Simply supported central point load
f = Y.L. = 500N x 100mm = 68.OON/mm2 4Z 4x1838mm3
117
From CP 118 "Structural Use of Aluminium", the allowable stress levels for 6063 T6 are as follows (see Tables 3.2 and 6.11)
Bending 96N/mm2
Shear 52N/mm2
Welded areas
Heat affected zones Bending 31N/mm2
Shear 19N/mm2
Welds (throat area) 31 N/mm2
Assessment of bending stresses.
STANCH IONS No welding. Allowable bending stress 96N/mm2 Section acceptable
TOP RAIL Heat affected zone is in maximum bending position. Allowable stress level 31 N/mm2. Section acceptable.
BOTTOM RAIL Heat affected zone in maximum bending position. Allowable stress level 31 N/mm2. Section not acceptable - re-design
BALUSTER Heat affected zone clear of maximum bending position. Allowable stress level 96N/mm2. Section acceptable.
Redesign of Bottom Rail.
Large bulbs placed at toes of flanges and merged into 2 mm thickness by 45 degrees fillet to ease transition.
New extrudability factors
Area = 350 mm2 CCD = 74mm Shape factor = 335
118
54
New geometric properties (effective less slot area)
ModulusZy = 6830mm3 Inertialy = 184410 mm4
Re-check bending stress
= = lllONxl500mm =30.5Nfmm2 8Z 8 x6830
Allowable stress for heat affected zone material from Table 6.11
= 31N/mm2
New section acceptable. Weld
Weld Strenath
The balusters are slotted into the top channel and welded B a luster in position. They stand on the top of the bottom channel web and are welded into position. The top welds hold the baluster in the line of the top rail and do not directly take Weld 25mm each side the full load. This is also the case at the bottom of the (no transverse welds) baluster and it is reasonable, therefore, to consider only the bottom rail.
Consider aweld leg length of 3 mm. The critical dimension weld design is the throat width. It is usual to define this Throat dimension as a fraction of the leg length.
Leg I For 90 degrees angle throat factor = 0.7.
Weld Throat width = 0.7 leg length = 2.1
Effective weld area = length of weld x throat width 5Ommx2.1 mm=105mm2
Shear load on weld = QQII = 250N/mm 2
Stress in weld = QJ = 2.3NImm2 105 mm2
Allowable stress in weld material = 19N/mm2
With such a high safety factor, the baluster can be welded to the bottom rail in a similar manner to that at the top, on the longitudinal sides only.
Weld strength acceptable, top and bottom welds resisting downward load with top weld also resisting sideways load.
119
TIG WELDING
Electrode Filler Nozzle Argon Alt. Weld Weld dia. rod dia. Bore flow current speed passes mm mm mm Llmin A mm/mm
2.4 2.4 9.5 5.7 110 190 1
No edge preparation and no gap between sections.
Filler rod material - 4043 or 5356 This material would give better colour match after
anodising
Deflections.
STANCHIONS Load Case Cantilever
6 = WL3 = 1110x11003 = 15.14mm 3E1 3 x 65500 x 496680
TOP RAIL Load Case Two span, simply supported UDL
8 = WL3 = lllOx 1500 = 0.73 mm 1 85E1 185 x 65500 x 423740
BOTTOM RAIL Load Case Simply supported UDL
8 = = 5x1110x15003 = 3.93mm 384EI 384x65500x 184410
BALUSTERS Load Case Simply supported central load
8 = 1.3 = 500x l000 = 5.70 mm 48E1 48 x 65500 x 27600
Allowable Deflection.
BS6180 sets out a maximum deflection standard of 12 mm but calculated on the basis of:
Aoolied load + wind load 2
120
This requires a wind load assessment to be made using BS CP3 chapter V "Wind
Loading". It is necessary to know where the installation is to be, as the wind code lays down a map of basic wind speeds related to area and on which the dynamic wind pressure is based.
Birmingham and the West Midlands are in the 44m/sec area.
This value is, however, factored for there are other considerations:
Si Topography (site exposure) For urban areas the value is i .00.
S2 Ground roughness and height For urban areas the value is 0.56 in this case.
S3 Probability levels The probability of the maximum design wind speed being exceeded. The usual factor is once in 50 years and the value is 1.00.
Wind speed is therefore:
44 x 1.00 x 0.56 x 1.00 = 25 m/s.
Dynamic Pressure = 383N/m2
Total area per panel span of balustrading
= 0.59m2
Wind load = 383 x 0.59 = 226N
The worst case is the stanchion with an actual deflection of 15.14 mm.
Therefore consider the stanchion.
Code BS61 80 requires the deflection to be considered using an equivalent total load which equals:
Basic load + Wind load 2
121
And where the resulting deflection should not exceed:
Span between stanchions 125
Equivalent design load = 111ON + 226N = 668N 2
Stanchion deflection with load 668N = 9.20 mm
Permissible deflection = j.QQ = 12mm 125
Stanchion is acceptable.
It is obvious that all the other sections will meet the deflection standard.
Temperature.
In hot sheltered sites thermal expansion should be considered and in general it is preferable to fit expansion joints in long runs of balustrading.
Assumed erection temperature 16°C
*Max surface temp. on aluminium 36°C
Temperature rise 20°C
*This will vary on the degree of sun and wind as well as on the colour of the aluminium.
Thermal expansion of 6063 = 23.5 x 1 061°C
Fit expansion joints at 15 metre intervals
Expansion = 23.5 x 10-6 x 20°C x 15000 mm
= 7.1 mm
Stress induced in the rails if this expansion is not relieved can be obtained from:
Stress = E Strain
= 69000M/mm2 x 7.1 mm = 32.4N/mm2 15000mm
If expansion joints are not fitted, the 32.4N/mm2 stress will be absorbed axially down the rail. To check the ability of the rail to withstand this stress it will be necessary to calculate the combined bending and axial compression in a similar mannerto that given
122
in the column example page 11.20. The bottom rail, however, is performing very close to its allowable stress level e.g. 30.5N/mm2 to 31.ON/mm2. Therefore it will not withstand the extra temperature induced stress. Expansion joints at 15 metre intervals are therefore necessary. The above proposed design meets all the requirements of BS 6108 and is therefore
acceptable.
Columns
a) An aluminium alloy column, 1 metre long, is fixed and restrained at both ends. The cross section is a 50 mm x 50 mm x 2 mm hollow box and subjected to a 62 kN concentric load. It is necessary to confirm the most appropriate alloy and
temper.
Section Properties
Section Area 384 mm2 Section Modulus 5910 mm3 Radius of gyration 19.6 mm
Actual axial stress f = Load Cross sectional area
= 62000 = 161.5N/mm2 384
As the column is rigidly held at both ends the effective length from Table 3.3
= o.7L = 700 mm
X = Effective Lenath = 700 mm = 35.7 Radius of gyration 19.6 mm
Using this value in the strut curve Fig 3.3 the 35.7 vertical ordinate gives the
permissible axial stress for a number of alloys and tempers.
Pc = 163N/mm2 for 2014A T6
A 50 x 50 x 2 mm box hollow in 2014A T6 is acceptable.
b) If the load in the above column is offset by 10 mm, will the column still be strong enough?
The load eccentricity will induce bending stresses as well as axial stresses into the column.
123
The simplest way to check is to considerthe axial and bending stresses individually and then check against the requirements of the combined stresses.
The axial stress at 161 .5N/mm2 is 99% or the permissible stress of 1 63N/mm2 so there is obviously no allowance left for bending in the original section.
Increase section size to 70 x 70 x 2.5 mm box alloy 2014A T6.
Section properties
Section Area 675 mm2 Section Modulus 14670 mm3 Radius of gyration 27.6 mm
= 700mm = 25.4 27.6 mm
From Fig. 3.3 25.4 ordinate for 201 4A T6 Gives the permissible stress = 1 77N/mm2
Actual axial stress from concentric load
f c Load = 62.000mm Cross sectional area 675mm2
f c = 92N/mm2
Induced bending stress = f bc
Moment = 62,000N x 10mm = 620,000 N mm
f bc Moment = 620.000N mm Section modulus 14,670 mm3
f bc = 42.3N/mm2
Permissible compressive bending, stress for 2014A 16 from Table 3.2
= 202N/mm2
Individually the bending and axial stress levels are within the permissible stresses laid down in BS CP 118, but the should be checked against combined stress allowances.
124
For combined bending and axial compression
+ I bc must not exceed 1
Pc Pbc(1-J Pe
Where f c axial compressive stress Pc permissible axial compressive stress
5 bc compressive stresses due to bending Pbc permissible bending compressive stress Pe Euler critical stress for buckling
where Pe =
Pe it2 x 72.400 = 1108N!mm2 25.42
fc = 92N/mm2 Pc = 177N/mm2
5 bc = 42.3N/mm2 Pbc = 202N/mm2
Combined stresses = .52 + .23 < 1
= .75 < 1
New 70 x 70 x 2.5 mm box section in 2014A T6 is within combined stress
requirements in BS CP 118.
Further modifications could be carried out by reducing the size of the section in order to obtain a more efficient solution and thereby approximating the combined stress ratios towards unity.
125
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ALUMINIUM EXTRUSIONS — a technical design guide
GLOSSARY OF TERMS
Term Definition
Ageing Precipitation from solid solution resulting in a change in properties of an alloy, usually occurring slowly at room temperature (natural ageing) and more rapidly at elevated temperatures (artificial ageing).
Angularity Conformity to, or deviation from, specified angular dimensions in the cross section of a shape or bar.
Annealing Thermal treatment intended to soften a metal or alloy hardened by cold work or artificial ageing.
Anodizing An electrochemical method of producing an integral oxide film on aluminium surfaces. See Section 5.
Anodizing Describes material with characteristics that make it suitable for Quality decorative anodizing after suitable preliminary treatment.
Billet A cast aluminium product suitable for subsequent extruding. Usually of circular cross-section but also may be rectangular.
Bow The deviation, in the form of an arc, of the longitudinal axis of a product.
Bright A process used to obtain highly reflective and bright anodized anodizing surfaces using alloy 6463.
Buffing A mechanical finishing operations in which fine abrasives are applied to a metal surface by rotating fabric wheels for the purpose of developing a lustrous finish.
Burr A thin ridge or roughness left by a cutting operation such as routing, punching, drilling and sawing.
Chemical Treatment to improve the reflectivity of a surface. brightening
Circumscribing (CCD) A circle that will just contain the cross section of an extrusion, circle diameter usually designated by its diameter.
127
Cold work Plastic deformation of metal at such temperature and rate that strain hardening occurs.
Concavity A concave departure from flat.
Concentricity Conformity to a common centre as, for example, the inner and outer walls of round tube.
Container A hollow cylinder in an extrusion press from which the billet is extruded.
Conversion Treatment of material with chemical solutions by dipping or spraying coating to increase the surface adhesion of paint. See Section 5.
Corrosion The deterioration of a metal by chemical or electrochemical reaction with its environment. See Section 4.
Direct extrusion A process in which a billet in the container is forced under pressure through an aperture in a stationary die.
Drift test A routine sampling test carried out on hollow sections produced by bridge or porthole methods, in which a tapered mandrel is driven into the end of the section until it tears or splits.
Drawing The process of pulling material through a die to reduce the size, change the cross section or shape, or work harden the material.
Etching The production of a uniform mafl finish by controlled chemical (acid or alkali), treatment.
Etching test The treatment of a sample using a chemical reagent to reveal the macro-structure of the material.
Extrusion ratio The ratio of the cross-sectional area of the extrusion container to that of the extruded section (or sections in the case of multi-cavity dies).
Fillet A concave junction between two surfaces.
Flutes Longitudinal concave corrugations with sharp cusps between them used to break up the surface decoratively.
Free machining An alloy designed to give small broken chips, superior finish and/or alloy longer tool life.
Full heat Solution treatment followed by artificial ageing. treatment
128
Grain growth The coarsening of the grain structure occurring under certain conditions of heating.
Grain size The mean size of the grain structure usually expressed in terms of the number of grains per unit area or as the mean grain diameter.
Hardness The resistance of a metal to plastic deformation usually by controlled indentation.
Heat treatable An alloy capable of being strengthened by suitable heat treatment. alloy
Homogenization A high temperature soaking treatment to eliminate or reduce segregation by diffusion.
Indirect extrusion A process whereby a moving die located at the end of a hollow ram is forced against a stationary billet.
Mean diameter The sum of any two diameters at right angles divided by two.
Mean wall The sum of the wall thickness of tube measure at the ends of any thickness two diameters at right angles, divided by four.
Mechanical Those properties of a material that are associated with elastic and properties inelastic reaction when force is applied, orthat involve the relationship
between stress and strain. These properties are often incorrectly referred to as physical" properties.
Modulus of The ratio of stress to corresponding strain throughout the range Elasticity where they are proportional. Also referred to as "Young's Modulus".
Modulus of The ratio of the unit shear stress, in atorsion test, to the displacement Rigidity caused by it per unit length in the elastic range.
Non-heat An alloy incapable of being strengthened by thermal treatment. treatable
Ovality The departure of the cross section of a round tube, bar or wire from a true circle.
Percentage The increase in distance between two gauge marks that results
elongation from stressing the specimen in tension to fracture.
Physical The properties, other than mechanical, that pertain to the physics properties of a material; for example, density, electrical conductivity, thermal
expansion.
129
Pitting Localised corrosion resulting in small pits or craters in the metal corrosion surface. See Section 4.
Porthole die An extrusion die that incorporates a mandrel as an integral part of its assembly. Bridge and spider are special forms of this type of die, which are used to produce extruded hollow products from solid extrusion billets.
Proof stress The level of stress used to signify the limit of proportionality designated at the point of 0.2% strain for aluminium and it alloys. See Section 3.
Quenching Controlled rapid cooling of a metal from an elevated temperature by contact with a liquid, gas or solid.
Residual stress That internal stress which is left in afinished product afterfabrication.
Sealing A treatment applied after anodizing to reduce the porosity of the surface.
Segregation Non-uniform distribution or concentration of impurities or alloying constituents that arises during the solidification of a billet.
Solution heat A thermal treatment in which an alloy is heated to a suitable treatment temperature and held for sufficient time to allow soluble constituents
to enter into solid solution wherethey are retained in a supersaturated state after quenching. See Section 2.
Stabilizing A thermal treatment to reduce internal stresses in order to promote dimensional and mechanical property stability.
Stepped An extruded shape whose cross section changes abruptly in area at extrusion intervals along its length.
Stretching The straightening of extruded and drawn materials by imparting sufficient permanent extension to remove distortion. Specific levels of stretching (permanent set) can be imparted to relieve internal stresses.
Tempers Stable levels of mechanical properties produced in a metal or alloy by mechanical or thermal treatments.
Twist A winding departure from flatness.
Ultimate tensile The maximum stress which a material is capable of sustaining in strength tension under a gradual and uniformly applied load.
130
Waterstains Superficial surface oxidization due to the reaction of water films held between closely adjacent metal surfaces such as nested angle sections. The appearance varies from iridescent in mild cases, to white, grey or black in more severe instances.
ABBREVIATIONS
E = Young's modulus of elasticity * N = Newton = kiloaramme
G = Torsion modulus gravity r = Radius of gyration k = End fixity co-efficient
* P = Pascal = N/m2 = Slenderness ratio = Micron
8 = Deflection P = Stress suffix - t - tension c - compression * iN/mm2 = 1MPa
both terms are used to define stress levels
131
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ALUMINIUM EXTRUSIONS — a technical design guide
LIST OF APPENDICES
No. Title Page No.
APPENDIX 1 DESIGN CONSIDERATIONS 135
APPENDIX 2 BEAM STRESS AND DEFLECTION TABLES 139
APPENDIX 3 PREVIOUS B.S. DESIGNATIONS 153
APPENDIX 4 COMPARISON OF NATIONAL SPECIFICATIONS- WROUGHT ALLOYS 155
APPENDIX 5 CHEMICAL COMPOSITION LIMITS AND MECHANICAL PROPERTIES 159
133
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ALUMINIUM EXTRUSIONS — a technical design guide
APPENDIX 1 - DESIGN CONSIDERATiONS
135
The following list contains most potential considerations likely to arise in the design of aluminium extruded products.
ALLOY
TEMPER
MECHANICAL PROPERTIES - 0.2% proof stress Ultimate stress % elongation Compressive strength
Axial loading - column length end fixing load eccentricity
Shear stress Bearing stress (jointing) Surface hardness Torsion Fatigue Stiffness
SECTION DESIGN - Size, shape and thickness Production availability and section extrudability Geometric properties Weight Tolerance Value engineering
SURFACE FINISH - Mill Etched Shot blasted Anodised - Natural
Colour (organic) Colour (metallic) AA thickness Protective anodizing
Paint - Colour Electrostatic (Powder Spray
or Wet Spray) Electrophoretic (Wet Dip)
136
JOINING - Welding - TIG Filler wire MIGJ
Gas Welding Brazing Rivetingi Bearing strength Bolting I Choice of fastening material
Screwing - Screw material and size Pull out strengths
Corner crimping Adhesives - Type
Strength Application details
FABRICATION - Bending - Alloy and temper Tooling Twisting Necking Springback
Machir;ing - Routing Drilling Sawing
TEMPERATURE - Expansion/Contraction Effect on mechanical properties
CONDUCTIVITY - Heat transfer Electrical
DURABILITY - Atmospheric - Environment - Rural Marine Industrial
Chemical - Substance Concentration Temperature
Compatibility - Design of Bi-metallic connections
FIRE - Melting point Non-combusibility Non-ignitability Fire propogation Surface spread of flame Structural resistance
137
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ALUMINIUM EXTRUSIONS — a technical design guide
APPENDIX 2- BEAM STRESS AND DEFLECTION TABLES
139
Type of Beam
Stresses
General Formula for Stress at any Point
Stresses at Critical Points
Case 1.- Supported at Both Ends, Uniform Load
TOTAL LOAD W
fjfjjfijf4 2 2
s=-
Stress at centre, - If cross-section is
constant, this is the maximum stress.
Case 2.- SupportedatBoth Ends, Load at Center
2 2
Betweeneachsupport and load,
2Z S = -
Stress at centre, - If cross-section is
constant, this is the maximum stress.
Case 3.- Supported at Both Ends, Load at any Point
I I ab1
For segment of length a,
5=-x ZI
For segment of length b,
Way S —-
- wa Stress at load
If cross-section is constant, this is the maximum stress.
Case 4.- Supported at Both Ends, Two Symmetrical Loads
w w TId w w
Between each support and adjacent load,
s = -- z Between loads,
z
Stress at each load, andatallpointsbetween,
Wa
140
Deflections
General Formula for Deflection at any Point Deflections at Critical Points
W(I-) '12÷x(I-x)J 24E11
Maximum deflection, at centre,
—— V3 384 El
Between each support and load,
(312-4x2) 4BEl Maximumdeflection,atload, WI3 4E7
For segment of length a,
(I2--b) — 6E11
For segment of length b,
Way y= (12-v2-a2)
Deflection at load, Wa 2b2 3E II
Let a be the length of the shorter segment and b of the longer one. The maximum deflection is in the longer segment, at
v = bv'jj = v1, and is
Between each support and adjacent load,
f3a (I - a) - x 2) = 6E I
Between loads,
Wa " 6E1 (3v(I-v)-a21
Maximum deflection at centre,
Wa '312-4a2)
Deflection at loads (3/- 4a)
141
Type of Beam
Stresses
General Formula for Stress at any Point
Stresses at Critical Points
Case 5.- Both Ends Overhanging Supports Unsymmetrically,
UniformLoad
TOTAL LOADW
2(/-d-c) w ÷d-c) 2!
Foroverhanging end of
length c,
w s— X(c-u)2
Between supports,
C2Lx L2ZL
÷d2X(!X)} Foroverhangingendof
lengthd,
W S= 2ZL
Stress at support next end of length c,
Wc2 2ZL
Critical stress between
supports is at /2÷ c2- d2
X 2/ =1 andis (C2- 2)
2ZL X7
Stress at support next endoflengthd,
Ld2 2ZL
If cross-section is constant, the greatest of these three is the maximum stress.
If x,>' the stress is zero at points .f 2 - c2 on both sides of x = Xr
Case 6..- Both Ends Overhanging Supports, Load at any Point
Between
ba I
(a+b=I)
Between supports: For segment of length
a, s=_x
ZI
For segment of length b,
Way S7f Beyond supports s=o.
Stress at load,
Wa!) 7i If cross-section is
constant, this is the maximum stress.
142
Deflection at end c,
24E1L (21(d2÷ 2c2)÷3c3-13J
Deflection at end d,
24E1L (21(c2÷ 2d2)÷3d3-131
This case is so complicated that convenient
general expressions for the critical deflections between supports cannot be obtained.
General Formula for Deflection at any Point
Defiections
Deflections at Critical Points
For overhanging end of length c,
Wv 24E1L (21(d2÷ 2c2)
i-6c2u-u2(4c-u)-13J
Between supports,
Wx (I - x) I' 24E1L x(I-9+I2--2(d2÷c2)
- fd÷ c2(Ix)J}
For overhanging end of length d,
)24EILt2+2c) ÷6d2w-w2(4d-w)-13J
Between supports, same as Case 3. For overhanging end of length c,
Wabu y=
For overhanging end of length d,
WaLw y = - (1÷ a)
Between supports, same as Case 3.
Deflection at end c, Wabc
Deflection at end d,
(I + a) 6E II
143
Type of Beam
Stresses
General Formula for Stress at any Point
Stresses at Critical Points
Case 7.- Both Ends Overhanging Supports, Single Overhanging
Load
Between load and adjacent support,
W(c U) -
Between supports, Wc S = - (I - x)
Between unloaded end and adjacent support, s = 0.
Stress at support adjacent to load,
WC z
If cross-section is constant, this is the maximum stress.
Stress is zero at other support.
Case 8.- Both Ends Overhanging Supports, Symmetrical Overhanging
Loads
w w
W W
Between each load and adjacent support,
W s= --(c-u)
Between supports
S = - Wc
Stress at supports and at all points between,
Wc 1
constant, this is the If cross-section is
maximum stress.
Case 9.- Fixed at One End, Uniform Load
TOTAL LOAD W
W thi-2 Stress at support,
WI -- If cross-section is
constant, this is the maximum stress.
144
Deflections
General Formula for Deflection at any Point Deflections at Critical Points
Between load and adjacent support,
Wu (3cu-u2÷2c!) all
Between supports,
Wcx Y= —y (I-x)(2I-x)
Betweenunloadedendandadjacentsupport, Wc/w y=
Deflection at load, !.1 (a + I) 3E I
Maximum upward deflection is at
Wc12 x=042265 I, and 5 15.55E1
WcId Deflection at unloaded end,
Between each load and adjacent support,
= (3c (I + U) - u 2]
(I-x) Between supports,y 2E1
Deflections at loads, -W- (2c + 3/) 6E I Deflection at center, — Wa!2 7
The above expressions involve the usual approximations of the theory of flexure, and hold only for small deflections. Exact expressions for deflections of any magnitude are as follows:
Between supports the curve is a circle of radius r =E y = V'r2 1/412 /2 (l/2 I- x)2 __________ Wc
Deflection at centre, /r 2 - / 2 -
y = -'--—f2! + (2!- x) 2] 24E1! Maximum deflection, at end, WI3
8E1
145
146
wI
Type of Beam
Stresses
General Formula for Stress at any Point
Stresses at Critical Points
Case 10. - Fixed at One End, Load at Other
wI( w W s= -y (i-x)
Stress at support,
If cross-section is constant, this is the maximum stress.
Case 11. - Fixed at One End, Intermediate Load
Between support and load,
W S = Z
Beyond load, s = o.
Stress at support,
If cross-section is constant, this is the maximum stress.
Case 12. - Fixed at One End, Supported at the Other, Uniform Load
TOTAL LOAD W
5
S1)r/4Ix) 2Z1
Maximum stress at wi
point of fixture,y Stress is zero at
=V4L Greatest negative
stress isatx=6/.Iand 9 WI r
Deflections
General Formula for Deflection at any Point Deflections at Critical Points
y (3!- x) Maximum deflection, at end,
Between support and load,
Y= - (31-x)
Between unloaded end and adjacent support,
y = (3v -I)
WI3 Deflections at load,
Maximum deflection, at end,
WI2 (2! ÷ 3b)
W2 (I - x) = 48E (31- 2x)
Maximum deflection is at x = 05785 I,
and is Y?I_ 185E I
Deflection at center, 192E I
Deflection at point of greatest negative
stress, atX= — us WI3 8 187E1
147
148
w
Type of Beam
Stresses
General Formula for Stress at any Point
Stresses at Critical Points
Case 13. - Fixed at One End, Supported at the Other, Load at Center
I 16
Between point of fixture and load,
w s= -(3I- lix) Between support and
load,
5 Wv s=_T Z
Maximum stress at
point of fixture, 3 14'!
16 Z Stress is zero at
3 x = - I Greatest negative
stress at center, 5 Wi 32Z
Case 14. - Fixed at One End, Supported at the Other, Load at
any Point m_—(I÷a)(I+b)+a/
n=aI(I÷b)
Wab(/÷b) 2/2
a2 wa2(31-a) w[i--(sI-a)] 2I
Between point of fixture and load,
Wb s= 2(n-mx) Between support and
load,
-Wa 2v s = 2(3I a)
Greatest positive stress, at point of fixture,
V.P(J÷) /2 Greatest negative
stress, at load, Wa2b (3!- a) 2Z13
If a <0.5858 I, the first is the maximum stress. If a = 0.5858!, the two are equal and are
5.83Z If a 0.5858 I, the
second is the maximum stress. n
Stress is zero atX = Case 15. - Fixed at Both Ends,
Uniform Load
TOTAL LOAD W
2 2
Will x x 21 s=
Maximum stress at ends, WI
Stress is zero at x=0-78871 and at x=O.2li31
Greatest flegative wi stress, at centre, -
Deflections
General Formula for Deflection at any Point Deflections at Critical Points
Between support and load,
W2 = 96E (9!- lix)
Between support and load,
Wv 96E1 (312-5v2)
Maximum deflection is at v=0.4472 I, and is WI3
107.33E I
Deflection at load, i_ !tV 768 El
Between point of fixture and load,
Wx2b 12E1/3 (3n-mx)
Between support and load,
Wa 2v 12E1/3 1312b-v2(3!-a)J
Deflection at load, Wa3b2 (3! + b) 12E113
If a < 0.5858 1, maximum deflection is between load and support, at
v=!/andis 6E1 21÷b
If a = 0.58581, maximum deflection is at load and is WI3
1Oi.9E I If a >0.5858!, maximum deflection is between
load and point of fixture, at
2n Wbn3 and '53EIm2I3
Wx2 (/-x)2 24E1!
Maximum deflection, at centre,
— 384E1
149
Type of Beam
Stresses
General Formula for Stress at any Point
Stresses at Critical Points
Case 16.- Fixed at Both Ends, Load at any Point
Wab2 Wab /2
Tb2(/2) Wa2(/2;f fT
For segment of length a,
s= 3(aI-x(I÷2a)] Forsegmentof length
b,
S 32(bI - V (I + 2b)j
Stress at end next segmentof length a,
Wab2 r2
Stress at end next segment of length b,
Wa2b Z12
Maximum stress is at end next shorter segment.
Stress is zero for
a! = I÷2b
Greatest negative stress, at load
2Wa2b2 ---p-
Case 17. - Continuous Beam,with Two Equal Spans, Equal Loads
at Center of Each TOTAL LOAD ON EACH SPAN,W J'I-j) (I/i) -
2Z!
Maximum stress at point A, WI -
Stress is zero at x=4I
Greatest negative stress isatx=5/5! and
is,_ 9 WI -- Case 18. - Continuous Beam,with
Two Equal Spans, Equal Loads at Center of Each
w
-_____ Between point A and
load, w s= j-(3I-llx)
Between point B and load,
5 Wv 5iT
Maximum stress at
point A, 3 WI 16 Z
Stress is zero at 3
X
Greatest negative stress at center of span
5 WI ----r
150
Deflections
General Formula for Deflection at any Point Deflections at Critical Points
For segment of length a,
2b2 (2a(I-x)÷I(a-x)]
For segment of length b,
Wv2a2 = 6E J/3 (2b (I - v) + I(b - v)J
Deflection at load, Wa
Let b be the length of the longer segment and aoftheshorterone.
The maximum deflection is in the longer segment, at
2N V1 and is
2Wa2b3 3E I (I ÷ 2b)2
— Wv2(I-) '3/ 2 - 48E II - Xi
Maximum deflection is at x = 0.5785!, and is
WI3 185E1
Deflectionatcenterof span, WI3 192E I
Deflection at point of greatest negative
stress, atx £ I is WI3 8 187E1
Between point A and load,
W y= -j.(9I-11x) Between point Band load,
wv = 9J(3I 2-5v2)
Maximum deflection is at v= 0.4472!, and is WI3
107.33E1
Deflection at load, L !! 768 El
151
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ALUMINIUM EXTRUSIONS — a technical design guide
APPENDIX 3- PREVIOUS BS DESIGNATIONS
153
PREVIOUS B.S. DESIGNATIONS (PROPERTIES IN IMPERIAL UNITS)
OLD B.S.
NUMBER
NEW B.S.
NUMBER TEMPER
OLD NEW
0.2 % PROOF STRESS
TONS/IN2
ULT. STRESS
TONS/IN2
% ELONG ON
50 MM
HE9 M F 6.5 12
HE9 -
6063 TB T4 4.5 8.5 14
HE9 TE T5 7.1 9.7 7
HE9 IF T6 10.4 12.0 7
HE3O 1 M F 7.5 12
HE3O 6082 TB 14 7.8 12.4 14
HE3O TF 16 16.5 19.1 7
E91E 6101A TF T6 11.3 13.3 8
BTRE6 6463 TF T6 10.4 12.0 9
HE15 2014A TB 14 15.3 24.7 10
HE15 TF T6 24.7 29 6
6063A TB T4 6.0 10.0 12
6063A TE 15 10.4 13.3 7
6063A IF 16 12.6 15.3 7
These designations and properties are for guidance only. All orders are manufactured to the existing British Standards alloy numbers and tested in metric units.
154
ALUMINIUM EXTRUSIONS — a technical design guide
APPENDIX 4- COMPARISON OF NATIONAL SPECIFICA11ONS
155
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-U 5
Pb
Bi
3.16
55
Al C
u S
i Pb
UN
1636
2 14
4355
A
l Cu
6 B
i P
b 20
11
2014
A
Al C
u 4 S
i Mg
H15
A
-U4S
G
3,12
55
Al C
u S
i Mn
UN
13S
O1
1443
38
Al C
u 45
1 M
n A
K8
2014
5
2017
A
2017
5 A
ICu
4Mg
Si
A-U
4G
3.13
25
AlC
u Mgi
.
2024
A
l Cu
4Mg
1 2L
97,
2L 9
8, L
109
, Li 1
0 D
TO
510
0A
A-U
4GI
3,13
55
Al C
u M
g2
LJN
1358
3 A
l Cu
4Mg
1.5
1316
20
24
2031
—
H
12
A-U
2N
2031
2117
A
l C
u 2
Mg
3L86
A
-U 2
0 3.
1305
A
l Cu
Mg
0.5
UN
1357
7 13
18
2117
2218
7L
25
2218
2618
5 H
16
A-U
2GN
A
K4-
1 26
185
3103
A
l Mn
1 N
3 3,
0515
A
l M
n U
N13
568
1440
54
Al M
n 31
03
3105
N
31
3.05
05
Al M
n 0.
5 M
g 0,
5 31
05
4043
N
21
A-S
5
4043
4047
14
2 A
-S 1
2 45
47
5005
A
l Mg
1 14
41.
A-C
0.6
U
N15
764
1441
06
Al M
gi
5005
5056
5 51
Mg
5 N
6 3.
3555
A
l Mg
5 U
14l1
3576
50
585
5083
50
83
Al M
g 4.
5 M
n N
8 A
-C 4
.5 M
C
3354
7 A
l M
g 4.
5 M
n U
N17
790
1441
40
Al M
g 5
5154
A
145
UN
1357
5 A
MG
3 51
54A
5251
A
l Mg 2
N4
A-G
2 M
3.
3525
A
l M
g 2
Mn
0.3
Al M
g 2
0201
5454
A
l Mg
3.6
1451
—
A
-G 2
,5 M
C
3.35
37
Al
Mg 21
Mn
UN
1778
9 A
l M
g 2.
7 M
n 54
54
5554
14
52
5554
5556
5
6061
N61
55
565
AIM
5IS
1Cu
H20
A
-CS
UC
U
N16
170
AD
3 60
61
6063
A
l Mg
0.5
Si
H9
UN
1356
9 14
4104
A
D3I
60
63
6082
A
ISi I
Mg
Mn
H30
A
-S G
M0.
7 3.
2315
A
l Mg
Si
1 U
N13
571
1442
12
Al
Mg S
il M
n 60
82
6101
A
916
Al M
g S
i 0.
5 61
01A
6463
E
6 64
63
7010
D
TD
0I3O
:512
0A
7010
7014
D
TD
502
5: 5
104A
: 509
45
—
7014
7020
A
l Zn
4.5
Mg
Hi7
A
-Z 5
G
3.43
35
Al Z
n M
gi
UN
1779
1 A
l Z
n 45
Mg
1
—
7020
7075
A
l Zn
6Mg
Cu
2L95
; L16
0;L1
61;
L162
A
-Z 5
G U
3.
4365
A
l Zn
Mg
Cu
1.5
UN
1373
5 G
rang
es
SM
695
8 A
l Z
n 6M
g C
u 1
5 V
95
7075
Page blank in original
ALUMINIUM EXTRUSIONS — a technical design guide
APPENDIX 5- CHEMICAL COMPOSITION LIMITS AND MECHANICAL PROPERTIES
159
Page blank in original
Che
mic
al c
ompo
sitio
n lim
its
'1 a
nd m
echa
nica
l pr
oper
ties
°1 o
f he
at-t
reat
able
Alu
min
ium
al
loy
bars
, ex
trud
ed r
ound
tub
e an
d se
ctio
ns
(Fig
ures
in p
aren
thes
es re
fer t
o th
e no
tes
at th
e en
d of
this
tab
le)
____
____
Mat
eria
l de
sign
atio
n S
mlio
on
iron
Cop
pe
Man
gane
se
Mag
nesi
um
Chr
omiu
m
Nic
kel
Zin
c O
ther
re
stric
tions
T
itani
um
—
Eac
h T
otal
Alu
min
ium
(bar
) or
th
ickn
ess
(tub
e!
sect
ion)
—
— pr
oof
stre
ss
(mm
.)
stre
ngth
Mm
. M
ax,
On
On
5.65
'JS
o (r
rrin
.(
50 m
m
(mn.
)
6060
%
0.30
- 06
0
%
0.10
- 03
0
¾
0.10
¾
0.10
%
0.35
- 0.
60
¾
0.05
¾
-
%
0_is
¾
¾
0_to
¾
005
¾
0.15
¾
Ren
t. T
4 T
5 T
6
mm
- -
mm
150
150
150
N/m
m'
60
100
150
N/m
m'
120
145
190
N/m
m'
- - -
%
16
8 8
¾
- - -
6061
0,40-
080
0.70
0.15-
0.40
0.15
0.80-
120
0.04-
035
-
0.25
- 0.15
0.05
0.15
Rem.
T4
T6
T65i0
- -
150
iSO
itS
240
190
280
- -
16
8
14
7
6063
0.20-
0.60
0.35
0_to
0.10
0.
45-
0.90
0.
10
- 0_
ia
- 0.
10
0.05
0.
15
Ren
t. 0 F
T4
5
T5
T6
I
l,
- - 150
- - iSO
200
200
150
200 25
15
0 20
5
. - 70
70
110
160
130
- (100
) 13
0 12
0 15
0 19
5 15
0
140
- - - - - -
15
(13)
16
13
8
8
6
13
(12)
14
- 7 7 -
6063
A
0.30-
060
0.15-
035
atO
075
0,50-
090
005
-
015
' 0.
10
0,05
0.
15
Ren
t T
4 T
5 T
6
- - -
25
25
25
90
160
190
150
200
230
- - -
14
8 8
12
7 7
6082
0.
70-
130
0.50
0.
10
0.40
- 1.
00
0.60
- 1.
20
025
- 0.
20
- 0.
15
0.05
0.
15
Rem
. 0 F
T
4
T5
T6
T65
t0
- - - 150
- - 20
150
205
200
150
200 6 20
ISO
200
' - 120
100
230
255
270
240
- (100
) 19
0 17
0 27
0 29
5 31
0 28
0
170
- - - - - - -
16
(13)
16
13
8 8 S
14
(12)
14
- 8 7 - -
6101A
030-
070
0.40
0.05
- 0,40-
090
-
-
-
. -
0.03
0.10
Rem.
T6
- .
170
200
- 10
8
6463
0,20-
060
0.15
0.20
005
0.45-
0.90
- -
005
-
-
0.05
0,15
Rent.
T4
T6
- - 50
50 78
150
125
185
- - 16
tO
14
9
20i4A
0.50-
0.90
0,50
3.90-
5 00
0.40-
1.20
0.20-
0.60
0.10
0.10
0,25
0.20
Zr e
Ti
0.15
0.05
0,15
Rem.
T4
T6
T65i0
- 20
75
150
- 20
7S
150
20
75
150
200
20
75
150
200
230
250
250
230
370
435
420
390
370
390
390
370
435
480
465
435
- - - - - - - - -— ii ii 8 8 7 7 7 7
10
- - - 6 - - -
7020
0.35
0.40
0.20
0.05-
0.50
1.00-
1.40
0,10-
0.35
- 4.00-
5.00
008-0.25
Zr
Ti
- 0.05
0.15
Rent
T4
T6
- -
25
25
190
280
300
340
- 12
10
10
8
( IN
DIV
IDU
AL PERCENTAGE VALUES OF CONSTITUANTS ARE M
AX
IMU
M
(2) ALL MECHANICAL PROPERTIES ARE TYPICAL.
(3) TEMPER T6510 APPLIES ONLY TO CONTROLLED STRETCHING OF SO
LID BARS
a)
Page blank in original
Aluminium extrusions are used in a wide variety of engineering
and architectural applications. As a strong, light, non-corrosive
material which can be extruded into complex shapes, aluminium
provides the solution to a whole range of design problems.
This concise technical guide provides the reader with the
information necessary to design effectively with aluminium
extrusions. It presents brief details on the extrusion process,
outlines aluminium's material specifications and mechanical
properties and covers such design considerations as conductivity,
temperature, fabrication and finishing. The book also contains
specific guidance on design procedure, including worked
examples, and concludes with an extensive glossary.
"It's a true working manual...a must for every
drawing office which uses or might use
aluminium extrusions"
Chris Rand, Industrial Technology magazine
"A valuable document...four star rating out of
fve" Andy Pye, Design Engineering magazine
"A much needed source of reference"
Roy Woodwarci, Aluminium Industry magazine
Published by The Shapemakers — the information arm of the UK
Aluminium Exfruders Association
Aluminium