Joining Techniques Design Guide - Covestro · 2020. 9. 9. · 11 Spring-Steel Fasteners 12 Joining...

Engineering PolymersJoining TechniquesDesign Guide

This manual is intended to help yousuccessfully design and manufactureassembled parts made of:

• Makrolon® polycarbonate;

• Apec® high-heat polycarbonate;

• Bayblend® polycarbonate/ABS blend;

• Makroblend® polycarbonate blend;

• Texin®and Desmopan® TPUs

• ABS

• SAN;

• SMA;

• ASA, AES and ASA/AESweatherable polymers;

• Polyamide 6; and

• Texin® and Desmopan®

thermoplastic polyurethanes.

Thermoplastics can be joined success-fully in a number of different ways,including mechanical fastenings, ultra-sonic assembly, metal inserts, snap fits,electromagnetic and heat welding andsolvent/adhesive bonding.

DESIGNING FORASSEMBLY AND DISASSEMBLY

1

Thousands of partsare joined togetherin each automobile,such as the plasticcomponents in thisDodge Viper.

To design good assemblies you musthave:

• A working knowledge of the plasticresin you have selected;

• A fundamental knowledge of goodjoint design; and

• A thorough understanding of the purpose, geometry, ambient environ-ment, chemicals, and mechanicalloading which your assembly willencounter.

Additionally, a designer should designfor disassembly, an important factor forserviceability that has gained increasedemphasis because of plastics recyclingconsiderations. Involving the designer,end user, materials supplier and molderor processor throughout a project willmake the transition from concept tofinished part much easier.

The techniques referenced in thisbrochure for joining parts made ofCovestro engineering thermoplastic resinsare those generally used in the industry.In those special cases where a techniqueshould be modified for a specific Covestroresin, a note will be included in the text. For property and applicationsinformation, please go to our website:www.plastics.covestro.com.

Sometimes you will have to assemble two or morecomponent parts to produce a complex part.Early in the development stage, designers need to consider how they will effectively join matingcomponents into a functional unit. Joining tech-niques can offer a cost-effective, aestheticallypleasing, and structurally sound solution fordesigning and manufacturing intricate parts.

The following guidelines are rules of thumb forpart assembly. Naturally, there are exceptions toall rules of thumb or times when two of themconflict. If this happens, talk with your joiningequipment supplier and Covestro personnel forassistance before proceeding. Prototyping andpart testing are always required before going tofull commercial production.

2

GUIDELINES FORJOINING TECHNIQUES

TABLE OF CONTENTS

MECHANICAL FASTENING

5 Screws, Bolts and Rivets

6 Molded-In Threads

7 Self-Threading or Self-Tapping Screws

7 Thread-Cutting7 Thread-Forming8 Screw Bosses10 Tightening Torque10 Self-Piercing/Self-Drilling Screws10 Boss Caps11 Thread Lockers

11 Rivets

11 Spring-Steel Fasteners

12 Joining Dissimilar Materials

14 Worked Example

ULTRASONIC ASSEMBLY

17 Ultrasonic Welding

17 Ultrasonic Staking

18 Ultrasonic Spot Welding

18 Ultrasonic Inserts/Heat Inserts

METAL INSERTS

22 Molded-In Metal Inserts

22 Coil-Threaded Inserts

22 Thread-Cutting Inserts

23 Expansion Inserts

SNAP AND PRESS FITS

24 Snap Fits

25 Press Fits

HEAT WELDING AND SEALING

26 Heat or Hot-Plate Welding

26 Bar Sealing

27 Hot-Knife Sealing

27 Electromagnetic or Induction Welding

28 Vibration Welding

28 Spin Welding

SOLVENT AND ADHESIVE BONDING

29 Solvents

29 Polycarbonate and Polycarbonate Blends30 Makroblend Resins30 Polyamide and PA Blends30 Thermoplastic Elastomers30 Safe Solvent Handling30 Bonding Procedures

30 Curing Solvent-Bonded Parts

31 Adhesive Bonding Systems

31 Safe Adhesive Handling

TECHNICAL SUPPORT

34 Design and Engineering Expertise

34 Technical Support

35 Regulatory Compliance

35 Health and Safety Information

35 For More Information

36 Notes

3

MECHANICAL FASTENING

SCREWS, BOLTS AND RIVETS

When using common mechanical meth-ods for securing parts, pay special atten-tion to the fastener’s head. Conicalheads, called flat heads, produce unde-sirable tensile stress in the mating partsand should be avoided (see figure 1).Bolt or screw heads that have a flatunderside, called pan or round heads,produce less harmful, compressivestress. Use flat washers under both nutand fastener heads, because they helpdistribute the assembly force over largerareas (see figure 2).

Mechanical fasteners — screws, boltsand rivets — offer one of the leastexpensive, most reliable and commonlyused joining methods for assembliesthat must be taken apart a limited number of times. Common practices for using mechanical fasteners are discussed in this section.

Always make sure that there is suffi-cient distance between the edge of thefastener’s hole and the part’s edge. As a rule of thumb, this distance shouldbe at least the diameter of the hole ortwice the part’s thickness, whichever is greater.

Additional clearance may be needed ifyour part has slotted holes for attachinglarge plastic panels to metal or woodframes to account for the differing coefficients of thermal expansion. Seepage 12 for a discussion of this topic.

5

1-64 0.073 M1.8x0.35 0.071

2-56 0.086 M2.2x0.45 0.087

3-48 0.099 M2.5x0.45 0.098

4-40 0.112 M2.6x0.45 0.102

5-40 0.125 M3x0.5 0.118

6-32 0.138 M3.5x0.6 0.138

8-32 0.164 M4x0.7 0.157

10-24 0.190 M5x0.8 0.197

12-24 0.216 — —

1/4-20 0.250 M6x1 0.236

5/16-18 0.313 M8x1.25 0.315

3/8-16 0.375 M10x1.5 0.394

7/16-14 0.438 M11x1.5 0.433

1/2-13 0.500 M12x1.75 0.472

9/16-12 0.563 M14x2 0.551

5/8-11 0.625 M16x2 0.630

3/4-10 0.750 M20x2.5 0.787

7/8-9 0.875 M22x2.5 0.866

Figure 1

Common head styles of screws and bolts.

Oval

Flat

Pan

Truss

Fillister

Hex andSquare

Washer

Incorrect

Correct

Table 1 U.S. & Metric Threads

Unified National Outer Nearest ISO OuterCoarse(UNC) Diameter, US Equivalent Diameter, ISO(Size) (in) (mm) (in)

If possible, avoid molded-in threadswhen mating thermoplastics to metal.These materials have large differencesin both stiffness and thermal expansion,and sharp edges of metal threads canalso result in high stress in the thermo-plastic part. Initial engagement andtightening will cause some stress andshould be checked to prevent tensilecrazing or breaking. Stress relaxation ofplastic threads can lead to loosening ofa connection, and possibly part failure.

MOLDED-IN THREADS

When your application requires infre-quent assembly and disassembly, youcan use molded-in threads for matingthermoplastic to thermoplastic parts(see figure 3). For easier mold fillingand better part tolerances, avoid design-ing parts with threads of 32 or finerpitch. Do not use tapered threads, suchas pipe threads, unless you provide apositive stop. Overtightening can causeexcessive stress following assembly thatcan lead to part failure.

When designing parts with molded-inthreads, consider the following factors.

• Thread Damage: Avoid feather edgeson thread runouts to prevent cross threading and thread damage.

• Roots and Crests: Avoid sharp roots and crests on threads to reduce stress concentrations and make filling the mold easier.

• Mold Cost: Internal threads, formed by collapsible or unscrewing cores, and external threads, formed by split cores or unscrewing devices, increase mold cost.

6

Mechanical Fasteningswith Self-Tapping Screws

Figure 2

Mechanical Fastenings withBolts, Nuts, and Washers

Incorrect Incorrect Incorrect

Correct Correct Correct

UseStandoffs

UseWashers

Mechanical Fastenings

1/32 in (0.8 mm) min.

Roots

Rounded

Crests

Molded-In ThreadsFigure 3

TypicalRadius0.015 in(0.381 mm)

1/32 in (0.8 mm) min.

MECHANICAL FASTENING continued

Thread-Cutting

Thread-cutting screws cut away materi-al from the boss inner diameter to forma mating thread. Compared to thread-forming screws, the radial and hoopstresses in the boss wall are lower afterinstallation, resulting in better long-termperformance. Typically, thread-cuttingscrews are classified as ANSI BT (Type 25), ANSI T (Type 23) and theHi-Lo* screw with a cutting edge on itstip (see figure 4).

In multiple assembly/disassembly oper-ations, thread-cutting screws must bereinstalled carefully to avoid damagingthe previously cut threads. Alternatively,replace Type 23 thread-cutting screwswith standard machine screws. BecauseType 25 and Hi-Lo* screws have non-standard thread pitches, you cannot substitute a standard machine screw forthese types.

SELF-THREADING ORSELF-TAPPING SCREWS

Self-threading screws, classified intotwo categories for plastic parts —thread-cutting or thread-forming, aremade in accordance with AmericanNational Standard ANSI B18.6.4.Various DIN and ISO specificationscover metric self-threading screws.

Mechanical fasteners give you detach-able connections that are both reliableand cost-effective. Driving the properscrew directly into a thermoplastic partresults in pullout force levels compara-ble to those using threaded metalinserts.

Thread-Forming

Thread-forming screws do not have acutting tip. They displace material in theplastic boss to create a mating thread.Because this process generates high levels of radial and hoop stress, avoidusing these screws with less-compliantmaterials, such as Makrolon polycar-bonate resins or polycarbonate blends.As an alternative, use thread-cuttingscrews for these materials.

Stress caused during installation ofthread-forming screws can be reduced ifsufficient frictional heat is generated inthe contact area. Use an installationspeed of 300 – 500 rpm for most screw sizes.

7

Type 23Thread-Cutting

Screw

Type 25Thread-Cutting

Screw

Hi-Lo*Thread-Cutting

Screw

Figure 4

Thread-cutting screws can be used for Covestro thermoplastic resins.

Single-use, medical device with molded-inthreads for catheter couplings.

* Hi-Lo is a trademark of Shakeproof Division of Illinois Tool Works Inc.

For more information on self-threadingscrews and their availability, contact:

ShakeproofElgin, IL 60120(847) 741-7900

Camcar/TextronRockford, IL 61104(815) 961-5305

ATFLincolnwood, IL 60645(847) 677-1300

Continental/Midland, Inc.Park Forest, IL 60466(847) 747-1200

Screw Bosses

Design screw bosses with care. Whilesmall boss diameters reduce the tenden-cy for sinks and/or voids because theyhave thin side walls, they may not pro-vide sufficient structural strength towithstand assembly hoop stress. Seefigure 5 for suggested boss design. A counterbore, provided as a lead-in,helps align the screw and reduces hoopstresses at the top of the boss, wherestress-cracking generally starts. Tables2A through 2D list some average pull-out forces and various torque data forthread-cutting screws tested in selectedCovestro resins. For this data, the screwswere installed in the manufacturers’suggested hole diameters. The screwboss outer diameter was approximatelytwice the screw outer diameter.

8

Figure 5

These boss designs for thread-cutting screws are based upon structural considerations.Other design details addressing aesthetic considerations are available.

D

0.3T max.

T

0.060 in(1.5 mm)

D

2.0 to2.4D

d

DiameterScrew ±0.002 in ±0.002 inSize D(±0.0005 mm) d(±0.0005 mm)

#6 0.140 in (3.6 mm) 0.123 in (3.1 mm)

#8 0.166 in (4.2 mm) 0.145 in (3.7 mm)

#10 0.189 in (4.8 mm) 0.167 in (4.2 mm)

#12 0.219 in (5.6 mm) 0.191 in (4.9 mm)

1/4" 0.250 in (6.4 mm) 0.220 in (5.6 mm)

Screw Length Minimum: 2.3 x Diameter (D)

Suggested Boss Inner Diameter (d): 0.88 x Diameter (D)


9

#6, Type 23 0.375 (9.5) 0.120 (3.0) 8 (0.9) 14 (1.6) 25 (2.8) 360 (1600)

#6, Type 25 0.500 (12.7) 0.120 (3.0) 6 (0.68) 16 (1.8) 30 (3.4) 568 (2528)

#6, Hi-Lo 0.750 (19.0) 0.115 (2.9) 5 (0.56) 14 (1.6) 30 (3.4) 668 (2973)

#8, Type 23 0.500 (12.7) 0.146 (3.7) 9 (1.0) 21 (2.4) 38 (4.3) 556 (2474)

#8, Type 25 0.562 (14.3) 0.146 (3.7) 18 (2.0) 28 (3.0) 50 (5.6) 884 (3934)

Screw Screw Hole Drive Recommended Stripping ScrewSize Length Diameter Torque Tightening Torque Torque PulloutType in (mm) in (mm) Td lb-in (N•m) Tt lb-in (N•m) Ts lb-in (N•m) lb (N)

Table 2A Thread-Cutting Screw Data for Makrolon 3200 Polycarbonate Resin

#6, Type 23 0.375 (9.5) 0.120 (3.0) 2.4 (0.28) 4.7 (0.53) 9.1 (1.02) 210 (936)

#6, Type 25 0.500 (12.7) 0.120 (3.0) 2.0 (0.23) 5.6 (0.63) 12.7 (1.44) 193 (856)

#6, Hi-Lo 0.750 (19.0) 0.120 (3.0) 3.0 (0.34) 8.3 (0.94) 19.0 (2.14) 216 (961)

#8, Type 23 0.500 (12.7) 0.136 (3.5) 4.0 (0.45) 6.7 (0.75) 12.0 (1.36) 363 (1616)

#8, Type 25 0.562 (14.3) 0.146 (3.7) 3.8 (0.43) 10.3 (1.16) 23.2 (2.62) 487 (2168)


Table 2C Thread-Cutting Screw Data for a General Purpose ABS Resin

#6, Type 23 0.375 (9.5) 0.120 (3.0) 3.1 (0.35) 4.8 (0.54) 8.1 (0.92) 171 (760)

#6, Type 25 0.500 (12.7) 0.120 (3.0) 2.5 (0.29) 6.1 (0.69) 13.3 (1.51) 181 (803)

#6, Hi-Lo 0.750 (19.0) 0.120 (3.0) 2.8 (0.31) 8.0 (0.91) 18.5 (2.1) 279 (1242)

#8, Type 23 0.500 (12.7) 0.136 (3.5) 5.2 (0.59) 6.5 (0.74) 9.2 (1.03) 272 (1209)

#8, Type 25 0.562 (14.3) 0.146 (3.7) 3.6 (0.41) 9.0 (1.01) 19.7 (2.22) 405 (1800)


Table 2D Thread-Cutting Screw Data for Weatherable ASA Resin

#6, Type 23 0.375 (9.5) 0.120 (3.0) 3.3 (0.37) 5.6 (0.63) 10.15 (1.14) 349 (1552)

#6, Type 25 0.500 (12.7) 0.120 (3.0) 3.3 (0.37) 7.9 (0.89) 17.16 (1.93) 308 (1370)

#8, Type 23 0.500 (12.7) 0.136 (3.5) 4.9 (0.55) 8.4 (0.95) 15.5 (1.75) 479 (2130)

#8, Type 25 0.562 (14.3) 0.146 (3.7) 4.2 (0.47) 11.5 (1.3) 26.2 (2.96) 512 (2277)


Table 2B Thread-Cutting Screw Data for Bayblend FR-110 PC ABS Resin

Use a thread engagement of at least 2.3 times the screw diameter forself-threading screws.

Tightening Torque

The torque required to tighten a screwshould be at least 1.2 times the drivingtorque (Td), but should not exceed one-half the maximum, or stripping torque(Ts) (see figure 6). Actual test datadetermines driving and maximumtorques.

Self-Piercing/Self-Drilling Screws

Generally, self-piercing or self-drillingscrews that do not need a pilot hole, orscrews that are force-fit into a receivinghole should not be used with parts madeof Covestro thermoplastics; these producehigh hoop stresses.

Boss Caps

Boss caps, such as On-sert* caps, mayhelp when higher tightening torques andpositive screw alignment are necessary(see figure 7). Carefully select theproper screw type for the plastic materi-al used because the wrong screw maystill crack a part even with the use of aboss cap.

10

25

20

15

10

5

0TOR

QU

E (l

b-in

)

0 2 4 6 8 10

SCREW TURNS

Figure 6

ScrewOD = 0.164" (M4x0.7)

Td = Driving TorqueTs = Stripping Torque

Suggested Tightening Torque

mN

2.8

2.2

1.7

1.1

0.6

0

Ts

Td

Suggested Tightening Torque Range

0.5 x Ts

1.2 x Td

Figure 7

On-sert* fasteners fit over plastic bossesproviding additional support.

* On-sert is a trademark of the Palnut Company


THREAD LOCKERS

Generally, thread lockers can be chemi-cally aggressive to plastics. If you areusing a thread-locking liquid to securemetal fasteners, fully test the liquid forchemical compatibility with the thermo-plastic material before production use.Request a copy of ChemicalCompatibility Test for UnreinforcedThermoplastic Resins from Covestrofor further information.

RIVETS

Rivets provide a low-cost, simple instal-lation process that can be easily auto-mated. Use them to join thin sections ofplastics, plastic to sheet metal or plas-tics to fabric. To minimize stresses, userivets with large heads — three timesthe shank diameter is suggested — andwashers under the flared end. Never use countersunk rivets (see figure 8).Calibrate the rivet-setting tools to thecorrect length to minimize compressivestress and shear in the joint area.

SPRING-STEEL FASTENERS

Self-locking steel fasteners and push-on spring-steel fasteners, such asTinnerman* clips (see figure 9), offeranother option for assemblies subjectedto light loads. Usually pushed over a molded stud, these fasteners arefrequently used in applications such ascircuit boards. The plastic stud shouldhave a minimum 0.015 inch (0.38 mm)radius at its base.

Slotted tubular spring pins and

spiral-wrapped (roll) pins (see figure10) are typically used in shear-loadingapplications. Pressed into preformedholes with an Arbor press or drill/ham-mer machine, these pins can cause highhoop stress similar to those in press fits (see page 24). This may result inpart crazing or cracking in some plastics.

11

Four standard rivet heads for use with Covestro thermoplastic resins.

Figure 8

CountersunkPanTruss FlatButton

Correct Incorrect

Figure 9

Spring steel fasteners.

Tinnerman* Clip ThermoplasticStud

Figure 10

SlottedTubular Pin

Spiral-Wrapped Pin

* Tinnerman is a trademark of the Eaton Corporation

Where:αm = Coefficient of linear thermal

expansion of the metalαp = Coefficient of linear thermal

expansion of the plastic resinEp = Young’s modulus of elasticity for

the plastic resin∆T = Change in temperature

(When performing these calculations, aconsistent system of units is essential.Use the temperature units specified in “α.”)

JOINING DISSIMILARMATERIALS

In a typical, large plastic and metalassembly where movement is restricted,high compressive or tensile stresses candevelop. Figure 10A shows a large plastic part fastened to a metal base orbracket. As the ambient temperaturerises, the plastic will expand more thanthe metal because the plastic has a higher coefficient of linear thermalexpansion. In this example, the plastic’sexpansion coefficient is four to sixtimes higher.

Because the plastic part expands more,it develops a strain-induced compres-sive stress. An equal tensile stressdevelops in the metal part. In mostcases, these stresses are more harmfulfor the plastic part than the metal part.An approximation for thermallyinduced stress in the plastic is:

σT = (αm - αp) • Ep • ∆T

Typically, as the temperature rises, thestiffness of the plastic part decreases.With even higher temperatures, theplastic part will eventually buckle. Theopposite occurs when the temperaturedecreases: The plastic part shrinks,developing strain-induced tensile stress. With much lower temperatures,stiffness increases even more and thestrain-induced stress approaches criticallevels, leading to part failure.

12

Restricted fabrication technique is not recommended.

Figure 10A Xxxxxx Xxxxx

MetalBracketStiffener

PlasticPanel

Incorrect


To avoid these problems, use slottedscrew holes in the plastic part for temperature-sensitive designs, such as a large automotive cowl vent panel.Figures 10B through 10D illustrate this concept. As shown in these figures,the slotted holes allow differential thermal expansion and contraction ofthe assembly’s plastic and metal parts.

When joining plastic and metal parts,tightening torque for the inserted screwhas important implications. Do nottighten fasteners to the point where jointfriction and compressive loads preventrelative movement. If the fasteners aretoo tight, the effect of the slotted holeswill be negated, leading to possible partfailure.

13

Other factors to consider when joiningplastic and metal parts include:

• The span between mounting points;

• The magnitude of the temperaturerange; and

• The relative thermal expansion coefficients of the materials used inthe assembly.

Consult the Covestro data sheet for thespecific grade you’re using if it does notappear in table 3.

The slotted hole and sliding attachment at one end of the plastic cover in the lowerassembly enables it to accommodate the thermal expansion difference with the metal base.

Figure 10B

BadResult

BetterResult

Worked Example

(Note: Bayblend T-85 resin is used as an example. Please substitute values foryour Covestro material for proper results.)

Assume that an assembly is made ofBayblend T-85 resin and an attachedaluminum stiffener, and will be exposedto a temperature range of -20 to 120°F.The outboard assembly fasteners are48 inches apart and the part wasassembled in an ambient temperature of 70°F. To determine the change in length start with the basic formula:

Then substitute the difference of coefficients for α in the formula:

α for Aluminum is 1.3 x 10-5 in/in/°Fα for Bayblend T-85 is 4.0 x 10-5 in/in/°F∆L = (α plastic - α metal) • ∆T • L∆L = (4.0 x 10-5 - 1.3 x 10-5) x

(120 - (-20)) x 48∆L = 0.181 inch

∆L = α • L • ∆T

14

Table 3Coefficient of Linear Thermal Expansion (CLTE) Values for Common Materials

CLTE CLTEMaterial (10-5 • in/in/°F) (10-5 • mm/mm/°C)Bayblend T-85 4.0 7.2

Bayblend T-65 4.3 7.7

Bayblend T-45 4.6 8.3

Makrolon (Most) 3.9 7.0

Aluminum 1.3 2.3

Brass 0.95 1.7

Magnesium Alloys 1.5 2.2

Steel 0.80 1.4

Wood (W/Grain) 0.36 0.65

Wood (Acc/Grain) 2.9 5.2

Zinc Alloys 1.5 2.7

Glass 0.5 0.9


The total difference in thermal expan-sion is 0.276 inch. Because we have twoassembly points, the movement betweenfasteners is 0.276/2 or 0.138 inch. Inthis example, you would have to planfor a range of movement of 0.138 inchat each fastening site. You must allowfor this expansion in your design to pre-vent stresses that could jeopardize theassembly, which can be estimated usingthe following formula:

Where:αm = Coefficient of linear thermal

expansion of the metalαp = Coefficient of linear thermal

expansion of the plastic resinEp = Young’s modulus of elasticity for

the plastic resin∆T = Change in temperature

(When performing these calculations, aconsistent system of units is essential.Use the temperature units specified in “α.”)

σ = (αp - αm) • Ep • ∆T

15

Figure 10C Joining Dissimilar Materials

There are many “J” clipsand fasteners that willallow relative movementin assemblies.

MetalPart

SlottedHole

Soft Washer

PlasticPart

Fastener

The slotted hole couldbe in either piece, aslong as relativemovement is allowed.

Allow for relative movement in assemblies of dissimilar materials.

Figure 10D Xxxxxx Xxxxx

Bayblend T-85Panel

AluminumStiffener

24 in

48 in

24 in

ULTRASONIC WELDING

Ultrasonic welding is an excellentbonding method for thermoplastics.Generally, small amounts of fillers,such as fiberglass, will not inhibit weld-ing. If glass content in the resin exceeds10%, some horn wear on the weldingdevice may occur. If glass contentexceeds 30%, the bond may be poor.Additionally, some external mold-release agents, lubricants and flameretardants may affect weld qualityadversely.

The most important design feature in anultrasonically welded joint, the triangu-lar-shaped energy director, minimizesinitial contact between the parts. Duringwelding, the energy director tip meltsrapidly, filling the joint with molten

Ultrasonic assembly, one of the mostwidely used joining techniques for ther-moplastics, makes permanent, aestheti-cally pleasing joints. Four commonultrasonic assembly techniques — welding, staking, spot welding, ultra-sonic inserts — use high-frequencymechanical vibration to melt matingsurfaces. This section discusses variousultrasonic assembling techniques.

An ultrasonic plastic assembly systemconverts standard electrical energyfrom 50/60 Hz to 20 to 40 kHz and theninto mechanical vibratory energy. A 40-kHz machine produces an amplitude ofone-half that of a 20-kHz unit, allowingfor a more gentle action.

resin and melting the surrounding areasslightly. The melted material from bothparts solidifies to create a permanentbond.

Design energy directors with an apexangle from 60 to 90° (see figure 14).For thin-walled parts, a 60° energydirector may be more practical.Generally, the base width of the energydirector should not be more than 20 to25% of the wall thickness supporting it.Figures 13 through 15 show a variety ofjoint designs using energy directors.(An energy director with a 90° apexangle creates more melt and willimprove joint strength marginally forsome semi-crystalline resins, such asMakroblend and Polyamides)

16

ULTRASONIC ASSEMBLY

Figure 11

***Depthof Weld

Min.Lead-In0.030 in 30 – 45°

Prior to Ultrasonic Welding

Fixture

Finished Sealed Part

Melt

Shear Joint

Melt

Interference

Maximum InterferencePart Per Dimensions Side

0.75 in or less 0.008 – 0.012 in

0.75 – 0.150 in 0.012 – 0.016 in

1.50 in or larger 0.016 – 0.020 in***Minimum Depth of Weld: 1.1 x Wall Thickness

ULTRASONIC ASSEMBLY

For optimum welding:

• The horn, fixture and parts must bealigned properly;

• The stationary part should fit snuglyin the nest or fixture;

• The height of the energy directorshould be approximately 0.020 inch(0.51 mm); and

• Nylon parts should be welded imme-diately after molding, while still dry.

If your parts are made of polyamideresins or polyamide blends andwelded at a later time, store them insealed, airtight bags so that they do notabsorb water.

ULTRASONIC STAKING

In ultrasonic staking, high-frequencyvibrations from a specially contouredhorn melt the top of a thermoplasticstud which protrudes through a hole inthe mating part of the assembly (seefigure 16). Mating material can be adissimilar plastic or even metal. Whenthe top of the stud melts, it forms a headthat locks the two components together.The base of the stud must be rounded to help reduce stress concentration.Additionally, the through hole on themating part should be a close fit to pre-vent melt from flowing into the gapbetween the stud and the mating part.

17

0.020 in(0.50 mm)

Butt joint with energy director.

Figure 12

1/4 W

Apex angle 60 – 90°.

Figure 14

60 – 90°

W

Figure 13

Tongue and groove joint.

3 – 5°

xClearanceFit

x

Figure 15

Step joint.

W

1/3 WSlip Fit

1/3 W

For optimum ultrasonic welds, joinparts made of the same resin. Partsmolded from dissimilar resins can bewelded ultrasonically if they share acommon polymer component, such asPC welded to PC/ABS. Additionally,testing at Covestro shows some grades ofMakrolon polycarbonate resins can bewelded to select grades of ABSresin.

In applications requiring a water-tightor hermetic seal, a shear-joint designusually performs better than an energydirector design (see figure 11). Shearjoints require more energy to weld thanenergy director joints. Do not exceedthe machine energy limits because ofpart size.

ULTRASONIC INSERTS/HEAT INSERTS

For installing inserts, both of the pre-ferred bonding techniques — ultrasonicenergy and heat — provide a solid bondwithout the high stresses found in pressfits and expansion inserts. As shown infigure 18, the boss OD should be 2 to2.5 times the insert diameter for opti-mum insert performance. The receivinghole can be either straight or with an 8°taper depending upon the type of insertused. As a general rule, the receivinghole diameter can be approximately0.015 to 0.020 inch (0.38 to 0.51 mm)smaller than the insert OD. For yourspecific application, use the insertmanufacturer’s recommendation for thereceiving hole size for the particularinsert that will be used. Also, the receiv-ing hole should be deeper than the insertlength to prevent the insert from bot-toming out and to provide a well forexcess plastic melt.

18

Figure 16

Ultrasonic staking designs for Covestro thermoplastics.

Typical Stud and Staking Horn

Radius (Preferred)

D

D 1.6D

0.5DRadius

Used when D = < 0.125 in (< 3.2 mm)

0.5D2.1D

Dome Stake

Used when D = 0.125 – 0.156 in (3.2 – 4.0 mm)

2D0.5D

Standard Profile Stake

Used when D = > 0.187 in (> 4.8 mm)

0.5D0.5D

D

Hollow Stake

ULTRASONIC SPOT WELDING

Requiring no preformed holes or energydirectors, ultrasonic spot welding joinstwo layers of thermoplastic resins withsimilar melting temperatures in a singlelocation, forming a permanent bond.

In ultrasonic spot welding, the pilot tipmelts through the first surface. As the

tip penetrates the second or bottomsurface, displaced molten plastic flowsbetween the two surfaces, forming abond (see figure 17).

Generally used for large parts or sheets,ultrasonic spot welding can be donewith a portable, hand-held device andpower supply.

Figure 17

Ultrasonic spot welding.

ULTRASONIC ASSEMBLY continued

When installed, the insert’s top shouldbe flush with or slightly above theboss’s top surface, but no more than0.010 inch (0.003 mm). If the insert isbelow the top surface, the embeddedinsert could pull out of the parent mater-ial as the screw is tightened, a conditionsometimes referred to as “jackout.”

Figures 19A and 19B show pulloutstrength and stripping torque values for a variety of ultrasonic inserts testedat Covestro. These values represent an average for various insert types and should be used only for general guidance.

19

Figure 18

Horn,Titanium

SteelInsert,Brass

ThermoplasticBoss

Tapered Hole Straight Hole

D

2D to 2.5D8°

Ultrasonic Inserts

RE

SIN

GR

AD

E

Figure 19AAverage Stripping Torque

STRIPPING TORQUE (lb-in)

Apec9350 Resin

BayblendFR-110 Resin

GP ASA

GP ABS

MakroblendUT-1018

MakrolonFCR 2400 PC

MakrolonT-7855 PC

10 20 30 40 50 60 70

Insert Size

#4

#6

#8

0

Spirol® Heat/Ultrasonic InsertSpirol International CorporationDanielson, CT 06239(860) 774-8571

Yardley Type H Intro Sert®

Yardley Products CorporationYardley, PA 19067(215) 493-2723

Barb-Sert® InsertGroove Pin CorporationRidgefield, NJ 07657(201) 945-6780

Inserts were supplied by:

Dodge Ultrasert II®

HeliCoil ProductsShelton, CT 06484(203) 743-7651

P.S.M. Sonic-Lok 86 SeriesP.S.M. Fastener CorporationFairfield, NJ 07004(201) 882-7887

An alternate way to install insertsinstead of using ultrasonic energy isheat insertion. In this method, insertsare heated to a pre-determined tempera-ture, derived empirically for each insertand part. Much like ultrasonic inserts,heat inserts are positioned via air pres-sure. The plastic around the insertmelts, causing a bond. Use the samebasic guidelines for boss design andinstallation as for inserts that are ultra-sonically installed. Figures 20 and 21show pullout strength and strippingtorque values for heat inserts.

20

RE

SIN

GR

AD

E

Figure 19BAverage Pullout Force

PULLOUT FORCE (lb)

Apec9350 Resin

BayblendFR-110 Resin

GPASA

GP ABS

MakroblendUT-1018

MakrolonFCR 2400 PC

MakrolonT-7855 PC

100 200 300 400 500 600 700 800 900

Insert Size

#4

#6

#8

0

ULTRASONIC ASSEMBLY continued

21

PU

LLO

UT

FOR

CE

(lb)

ABS

900

800

700

600

500

400

300

200

100

0#4 #6 #8

Makrolon PC

Figure 20

Pull-out strength of heat inserts in Makrolon 3200 PC and an ABS resin.

Pullout Force vs. Insert Size

INSERT SIZE

Figure 2180

70

60

50

40

30

20

10

0

ABS

Makrolon PC

Stripping Torque vs. Insert Size

#4 #6 #8

STR

IPP

ING

TO

RQ

UE

(lb-

in)

INSERT SIZE

Stripping torque of heat inserts in Makrolon 3200 PC and an ABS resin.

For more information on ultrasonic

joining techniques, contact:

Branson Ultrasonics Corporation41 Eagle RoadDanbury, CT 06813-1961(203) 796-0400

Dukane Corporation2900 Dukane DriveSt. Charles, IL 60174(630) 584-2300

Forward Technology Industries, Inc.13500 County Road 6Minneapolis, MN 55441(612) 559-1785

Herrmann Ultrasonics, Inc.620 Estes AvenueSchaumburg, IL 60193(847) 985-7344

UltraSonic Seal Co.368 Turner Industrial WayAston, PA 19014(610) 497-5150

METAL INSERTS

Before inserts are placed in a mold, theyshould be cleaned to remove foreignmatter, including any oils or lubricants.Inserts should seat securely in the moldto prevent floating and possible damageto the mold.

Avoid inserts with sharp knurls or pro-trusions. Although they can have highpullout values, the sharp points cause anotch effect in plastics which can leadto early failure.

Inserts larger than 0.25-inch (6.35-mm)diameter may induce excessive thermalstresses, which can be partially reducedby preheating the insert prior to placingit in the mold. Preheat inserts used inpolycarbonate parts to 350°F to 400°F(177°C to 204°C).

If your part is going to be disassembledregularly, consider using metal insertsfor joining. Most inserts should beinstalled ultrasonically or with heat tominimize residual stresses (see page18). Use and installation suggestionsfor other types of metal inserts appearin this section.

MOLDED-IN METAL INSERTS

Molded-in metal inserts can cause highresidual stresses in plastic bosses.Avoid inserts in parts made of polycar-bonate resins and blends, because theresidual stress may result in crazing,cracking and eventual part failure.Plastic, having much higher coefficientsof thermal expansion than metal,shrinks around the insert and becomesstressed at the interface because theinsert imposes a restriction. Becauseglass-reinforced resins have thermalexpansion coefficients closer to those of metals, problems with metal insertsoccur less frequently in these resins.Molded-in metal inserts have also beenused successfully in some nylons, vari-ous grades of thermoplastic urethanes,and styrenic polymers, such as ABS and ASA resins. Always thoroughly test all molded-in inserts inend-use conditions prior to beginningfull production runs.

COIL-THREADED INSERTS

Made into a coil of wire, coil-threadedinserts provide greater wear resistanceand strength than the parent material(see figure 22). However, they can alsoproduce high stress in the boss orreceiving hole, which may lead to boss failure.

THREAD-CUTTING INSERTS

With external cutting edges similar to atap, thread-cutting inserts (see figure23) cut a clean, even thread wheninserted into a molded or drilled hole.These inserts are usually installed witha tap wrench or a drill press and tappinghead. Never use lubricants or cuttingfluids when tapping holes in plastic.

22

Notch

Figure 22

Coiled threaded inserts.

METAL INSERTS

EXPANSION INSERTS

Installed into slip-fit, molded or drilledholes, expansion inserts have signifi-cantly reduced mechanical performancecompared to those installed with ultra-sonic energy or heat. When a screw isinstalled, the insert expands against thewalls of the hole, which can result inexcessive hoop stress that can lead toboss or part failure in polycarbonatematerials. Expansion inserts have beenused successfully with more compliantresins such as Polyamides and ABS.See figure 24 for typical pullout valuesfor expansion inserts in nylon.

23

4-40 M3x0.5 0.171 0.234 0.152 – 0.149

6-32 M3.5x0.6 0.218 0.281 0.194 – 0.190

8-32 M4x0.7 0.250 0.328 0.226 – 0.222

10-32 M5x0.8 0.296 0.375 0.264 – 0.259

Tap-Lok® C-Series self tapping insert. Courtesy of Groov-Pin Corporation, Ridgefield, NJ 07657, (201) 945-6780

Figure 23

L

D

H

2°

1.25TimesInsertLength

Before InstallingScrew

After ScrewInsertion

Pullout force for Dodge expansion inserts.

Figure 24

Nylon

1.6

1.4

1.2

1.0

0.8

0.6

PU

LLO

UT

FOR

CE

(lb)

M3 M4 M56-32 8-32 10-24

360

315

270

225

180

135

kN

INSERT SIZE

RecommendedInch Sizes Metric Sizes Diameter Length Hole Size

Internal InternalThread Size Thread Size D (in) L (in) H (in)

SNAP AND PRESS FITS

Designed into the geometry of matingparts, snap fits offer a very inexpensive,quick and efficient joining method.Press fits must be designed with greatcare to avoid excessive hoop stress inthe assembly. This section discussessnap and press fits, giving commondesign parameters for their use.

SNAP FITS

Used commonly to join plastic parts,snap fits offer a simple, economical andefficient joining method. Using snap fitsmay enhance your part’s recyclabilitybecause they may reduce or eliminatemetal fasteners and allow for easy

disassembly (see figure 25 for an example of a cantilever-arm snap fit).

Although the suitability of any givenresin varies with part design and use,most plastics can be used for snap fits,particularly if the design calls for a one-time assembly. If the end use calls forrepeated assembly and disassembly,reduce the maximum strain to which thepart is exposed.

For a comprehensive discussion of andcomplete design guide for snap fits,please contact your sales representativefor a copy of Covestro’s Snap-FitJoints in Plastics brochure.

24

εL2

h

Figure 25

Simple cantilever snap arm.

L

yh

y = Deflectionε = Strain

y = 0.67 •

INTE

RFER

ENCE

(in/

in o

r m/m

Sha

ft Di

a.)

SHAFT OD/HUB OD

Figure 26 Maximumdiametricalinterference forMakrolonpolycarbonate andsteel press fits(solid shafts).

0.013

0.012

0.011

0.010

0.009

0.008

0.007

0.006

Example:Shaft OD = 0.250 inHub OD = 0.450 in0.250 in ÷ 0.450 in = 0.55Interference = 0.0093 in/in0.0093 in/in x 0.250 in =

0 0.2 0.4 0.6 0.8 1

Makrolon PC shaft into Makrolon PC hubSteel shaft into Makrolon PC hub

0.002 in Max. Dia. Interference

SNAP AND PRESS FITS

The example shown in figure 26 per-mits only 0.002-inch diametrical inter-ference on the 0.250-inch shaft. Actualproduction tolerances of the shaft andhub may vary enough to cause a slip fit— such that the part will not function asdesigned — or excessive interference,leading to high hoop stresses in theplastic hub. For these reasons, press fitsare used only rarely in Markolon poly-carbonate resin. Other resins, such asABS, nylon and TPU, can better toler-ate excessive interference; but mayexhibit stress relaxation, leading to a looser fit over time. We suggest prototyping and thorough testing of allpress-fit assemblies.

PRESS FITS

Because press fits can result in highstresses, use caution when choosing this assembly method. Generally, do not use press fits as a primary joiningmethod for parts made of Covestro resins.Figures 26 and 27 show the maximumdiametrical interference recommendedfor hubs made of Makrolon resin whenpressed onto either shafts of Makrolonpolycarbonate resin or steel.

When using press fits:

• Clean all parts to ensure that they arefree of any foreign substance, such aslubricants or degreasers;

• Avoid press fits when the matingparts are made of two different mate-rials and the part will be subjected tothermal cycling; and

• Avoid press fits if the assembly willbe subjected to harsh environmentsduring manufacturing, assembly,transportation or end use.

25

Figure 27 Maximumdiametricalinterferencefor Makrolonpolycarbonatepress fits(hollow shafts).

*These curves are for shafts made of Makrolon polycarbonate.

INTE

RFER

ENCE

(in/

in o

r m/m

Sha

ft Di

a.)

SHAFT OD/HUB OD

0.034

0.032

0.030

0.028

0.026

0.024

0.022

0.020

0.018

0.016

0.014

0.012

0.010

0.008

0.0060 0.2 0.4 0.6 0.8 1

Hollow ds/Ds = 0.8*

Hollow ds/Ds = 0.6*

Hollow ds/Ds = 0.4*

Hollow ds/Ds = 0.2*

Solid ds/Ds = 0*

Solid Steel Shafts

ds = Inside Shaft DiameterDs = Outside Shaft Diameter

To ensure operator’s safety, follow themanufacturer’s instructions regardingoperation of their equipment.

HEAT OR HOT-PLATE WELDING

In heat welding, a heated platen, usuallycoated with polytetrafluoroethylene(PTFE), contacts two plastic parts untilthe joint area melts. The parts are thenpressed together under slight pressureuntil the bond is set (see figure 28).

For permanent, inexpensive joints,consider heat welding and sealing.Although some residual plastic —called “flash” — may detract from thepart’s appearance, heat welding can beused on parts where aesthetics are notimportant. As with all bonded joints,increased fillers and fibers may reducebond strength.

BAR SEALING

A common and practical joining tech-nique, bar sealing involves holding filmbetween a double-heater element for ashort period of time at a given tempera-ture and pressure, depending upon resintype and film thickness. Makrolon poly-carbonate films up to 0.010 inch (0.25mm) thick can be bar sealed. Do notseal thicker sheets in this manner,because bond dimensions may distort.

26


Figure 28 Hot Plate Welding

1. Parts are held and aligned by holding fixtures.

3. Parts are pressed against the platen to melt edges.

5. Parts are compressed so edges fuse together as the plastic cools.

2. Heating platen is inserted.

4. Heating platen is withdrawn.

6. Holding fixtures are opened, leaving the bonded part in the lower fixture.

Courtesy of Forward Technology Industries, Inc.,13500 County Road 6, Minneapolis, MN 55441, Telephone: (612) 559-1785

Part

Seal Stop

Heating Platen

Holding Fixture

MeltStop

PolycarbonatePart Thickness, Timein (mm) (Approx.)

Table 4

Drying Times for Parts to be Joined by Heat Welding and Sealing for Polycarbonateat 250°F (120°C)

0.020 (0.5) 20 min

0.031 (0.8) 30 min

0.040 (1.0) 40 min

0.062 (1.6) 2 hr

0.080 (2.0) 3.5 hr

0.093 (2.4) 4 hr

0.125 (3.2) 6 hr

0.187 (4.7) 14 hr

For maximum bonding strength, dry both components before bonding.For example, if you are heat weldingMakrolon polycarbonate parts, pre-dryparts at 250°F (120°C) for maximumbond strengths. Drying time and temperature depend upon part thicknessand material selected. (see table 4). Besure that items made of polyamide 6are kept dry. See handling and storagesuggestions under ultrasonic welding.


ELECTROMAGNETIC OR INDUCTION WELDING

Using the principles of inductive heat-ing to create fusion temperatures in ajoint area, electromagnetic welding cre-ates excellent hermetic or high-pressureseals. This process requires bondingmaterial, usually supplied as extrudedprofiles such as strands (beads), tape or sheet, or special injection-moldedprofiles conforming to a particular jointcontour.

In this welding process, ferromagneticparticles are mixed with a thermoplasticmatrix to form a magnetically activematerial for bonding. Bonding materialis placed at the interface of the twoplastic parts, which are then brieflyexposed to an oscillating electromagnet-ic field. A high-frequency alternatingcurrent (5 to 7 MHz) flows through aset of conductive work coils to createthe electromagnetic field. Within sec-onds, the parts reach fusion tempera-ture, melting the binder and interface(see figure 29).

For bar sealing polycarbonate film, thesurface temperature of the heater ele-ments should be between 450 and500°F (230 and 260°C). Typically, youwill need a contact pressure of approxi-mately 100 psi (690 kPA) which usuallyresults in a cycle time of 0.5 to 2 sec-onds, depending upon the thickness ofthe film to be sealed. Polyamide 6films also have excellent bar-sealingcharacteristics.

HOT-KNIFE SEALING

For plastic films that are too thick forconventional bar sealing, hot-knife seal-ing offers an alternative joining method.In hot-knife sealing, a heated “blade”passes between the parts and appliesheat from the seal side. Knife tempera-ture and speed depend upon the resintype and thickness. After adequate heat-ing, surfaces are pressed together andheld at a specified contact pressure untilthe bond solidifies. If you apply exces-sive pressure during curing, the plasticfilm may develop a localized strain.Additionally, as sheet thickness increas-es, its stiffness may prevent the success-ful use of this bonding method.

For polycarbonate sheet sealing, thesurface temperature of the blade shouldbe about 550 to 650°F (290 to 345°C).You need to regulate the speed of theheated element so that the surfaces to bejoined reach a temperature of about450°F (230°C). Then, they are immedi-ately pressed together at a contact pres-sure of about 100 psi (690 kPa) andheld together for a few seconds until thebond solidifies.

Fusion times range from a fraction of asecond for small assemblies to 30 sec-onds for large assemblies — those withbond lines of as much as 20 feet. Forfurther information on this weldingtechnique, contact:

Emabond SystemsSpecialty Polymers & Adhesives

DivisionAshland Chemical Company49 Walnut StreetNorwood, NJ 07648(201) 767-7400

HellerbondP.O. Box 20156Columbus, OH 43220(614) 527-0627

27

Figure 22

Figure 29

Electromagnetic or induction welding.

Tongue and Groove Joint

Shear Joint

In this process, one part is fixed in astationary head, while the second part,attached to a welding head, vibrates onthe joint plane. Pressing the two parts’surfaces together at a pressure of 200 to245 psi (1.4 to 1.7 MPa) and vibratingone against the other generates heat.

VIBRATION WELDING

A friction-welding technique, vibrationwelding uses a machine that operates ata frequency of either 120 or 240 Hzwith a small displacement of 0.030 to0.140 inch (0.7 to 3.5 mm).

When the joint interface reaches amolten state, the vibrating action isstopped, parts are aligned, and clamppressure is briefly applied. Overallcycle times for vibration welding areusually 4 to 15 seconds (see figures 30,31, 32 and 33 for joint designs).

SPIN WELDING

You can weld round parts using spin welding. Often a tongue-and-groovejoint design is used to align the two partsand provide a uniform bearing surface.

In spin welding, one part remainsstationary, while the other rotates at 300 to 500 rpm. Pressure applied during the welding cycle keeps the partsin contact with each other. Friction-generated heat brings the surfaces tosealing temperature, which varies witheach resin. For example, this tempera-ture is approximately 425°F (220°C) forMakrolon polycarbonate resins. Aftergetting sufficient melt, the rotation isstopped and the pressure is increased todistribute melted material and completethe bonding process.

To counteract inertial forces in somecases, the stationary part is allowed torotate with the moving part after themating surfaces have melted.

28

Figure 30

Butt joint.

Before After

Figure 31

Flanged joint, for thin or long, unsupportedwalls.

Before After

Figure 32

Butt joint with flash trap.

Weld Surface

Wall Thickness

Melt Down,0.015 – 0.030 in(0.4 – 0.8 mm)

0.020 in(0.5 mm) Min.

a2 = 1.3 a1

a2

a1

Figure 33

Variations with flash traps.

SOLVENT AND ADHESIVE BONDING

SOLVENTSPolycarbonate and Polycarbonate Blends

Suitable bonding solvents vary withresin. You can bond parts made ofMakrolon polycarbonate and/orBayblend resins using methylene chlo-ride or ethylene dichloride. Methylenechloride’s fast evaporation rate helps toprevent solvent-vapor entrapment forsimple assemblies (see figure 34). Forcomplex assemblies that require morecuring time, use ethylene dichloride,

Solvent and adhesive bonding are prob-ably the least expensive joining methodsfor permanent bonds. Solvent bondingjoins one plastic to itself or another typeof plastic that dissolves in the same sol-vent. Typically, this process involvestreating the bonding area with the mini-mum amount of solvent needed to softenthe surfaces, then clamping the partstogether until they bond. Adhesivebonding uses commercially availablematerials that are specifically formulat-ed to bond plastic parts to themselves orother substrates. This section discussescommon bonding methods and practicesassociated with these joining techniques.

Safe Solvent Handling

Be careful when using any of these

solvents. You must refer to your

solvent supplier’s Material Safety

Data Sheet for health and safety

information and appropriate handling

recommendations, including the use of

proper protective equipment, for all of

the solvents discussed in this section.

because it has a slower evaporation rate,allowing for longer assembly times.Mixing methylene chloride and ethyl-ene dichloride in a 60/40 solution, acommonly used mixture, will give you alonger time to assemble parts than puremethylene chloride because of thereduced evaporation rate.

When using solvent-bonding techniqueswith these resins, some embrittlementmay occur. Parts can lose some of theirexcellent impact strength at the weld joint.

29

100

90

80

70

60

50

40

30

0 20 40 60 80 100 120 140 160 180 200

Methylene Chloride

Figure 34

BO

ND

STR

EN

GTH

(% o

f par

ent s

treng

th)*

Cure curves for Makrolon 2608 resin @ 10/60 sec setup/clamp, 100 psi, lap-shear test.*Parent strength is yield strength of the base resin.

CURE TIME (hours)

Ethylene Dichloride

Bond Strength vs. Cure Time

Thermoplastic Elastomers

Parts made of Texin or Desmopan thermoplastic polyurethanes can bebonded to themselves and other substrates with dimethyl formamide(DMF) or tetrahydrofuran (THF).

Styrenics

Parts made of ABS, SAN and ASA polymers can be solventbonded using similar procedures anddifferent solvents. Typically, usemethylethylketone (MEK), acetone, or a mixture of the two. Additionally, apaste made of MEK and the base resincan be used to fill small gaps in a partor assembly.

Safe Solvent Handling

Be careful when using any of these

solvents. You must refer to your

solvent supplier’s Material Safety

Data Sheet for health and safety

information and appropriate handling

recommendations, including the use of

proper protective equipment, for all of

the solvents discussed in this section.

BONDING PROCEDURES

Mating surfaces should be cleaned andfree of grease, dirt or foreign matterbefore bonding. For optimum bonding,parts should be well mated with nostrains to ensure uniform pressure distribution across the entire bond area.

A five to ten percent solution of poly-carbonate in methylene chloride helpsto produce a smooth, filled joint whenthe mating parts made of Makrolonresin or Bayblend PC/ABS resin do notfit perfectly. Do not use this mixture tocompensate for severely mismatchedjoints. Increasing the concentration canresult in bubbles at the joint.

Makroblend Resins

Do not use solvent bonding with partsmade of Makroblend resins. Because ofMakroblend’s polyester component andthe resulting high chemical resistance,aggressive solvents must be used forbonding. These solvents can cause lowbond strength.

Polyamide and PA Blends

Parts made of polyamide 6 resinscan be solvent bonded using solutionsof concentrated formic acid, alcoholiccalcium chloride, concentrated aqueouschloral hydrate, or concentrated alco-holic phenol and resorcinol. Addingfive to ten percent by weight of unrein-forced polyamide resin makes the sol-vents easier to use. In optimum bondingconditions, the bond strength afterbonding approaches the resin’s normalstrength.

Use a minimum amount of solvent. Forbest results, only one surface needs tobe wet. Excessive solvent can causebubbling and “squeeze out,” decreasingthe bond strength.

Apply a thin film of solvent to one partonly. Within a few seconds after apply-ing the solvent, clamp parts together ina pressure fixture applying between 100 and 500 psi for a minimum of 60 seconds.

Because ultimate bond strength is pri-marily a function of solvent concentra-tion on mating surfaces, control theelapsed time between application andclamping carefully. If too much evapo-ration occurs before clamping, poorbonding will result. For critical applica-tions needing more durability, consideradhesive bonding.

CURING SOLVENT-BONDED PARTS

Cure parts molded from Makrolon resinbonded with methylene chloride that are ultimately intended for room-temperature service for 24 to 48 hoursin a well-ventilated area at room tem-perature. Never cure these parts in anair-tight enclosure where solvent vaporsmay be trapped. These vapors couldattack parts and embrittle them.

Tests done at Covestro indicate that meth-ylene-chloride-bonded parts had 80 to90 percent of the ultimate bond strengthafter curing for one to two days (see figure 34).

30

31

ADHESIVE BONDING SYSTEMS

Adhesive bonding systems are amongthe most versatile for joining plasticparts to parts made of the same plastic,a different plastic or a non-polymericsubstrate. Generally, adhesives producemore consistent and predictable resultsin joints requiring strength and durabili-ty than other joining methods. The widevariety of modern adhesives ensuresthat you can find an optimum systemfor your application.

A number of variables must be consid-ered when selecting adhesive bondingmaterials, including:

• Chemical compatibility with the plastic substrate;

• Flexibility/rigidity requirements;

• Environmental and temperaturerequirements; and

• Aesthetics.

Generally, two-part epoxy and urethaneadhesives impart excellent bondstrength for thermoplastic materials.Cyanoacrylate-based adhesives can produce quick bonds; however, cyano-acrylates can be aggressive when usedwith polycarbonate resins, especially ifparts have high levels of molded-inand/or applied stresses. Additionally,cyanoacrylic adhesive can be brittle. Ifyour part will be subjected to bendingloads at the joint, you may want toselect a more ductile system.

When working with polycarbonateresins and blends, curing parts for ele-vated-service use and maximum bondstrength is much more complicated.You may have to use a complicatedtreatment schedule of gradually increas-ing temperatures for these applications(see table 5). For example, if an assem-bly is going to operate in an ambienttemperature of 200°F (93°C), the bond-ed parts should be cured at 73°F (23°C)for eight hours; then at 100°F (38°C)for 12 hours, 150°F (65°C) for 12hours, and finally 200°F (93°C) for 12 hours. Smaller bond areas can curein shorter times, while large areas usually require longer times or smallertemperature intervals.

Uncured parts suddenly exposed toelevated-temperature service can suffercomplete joint failure. Generally, thehighest cure temperature should beequal to or slightly higher than thehighest expected service temperature.

UV-cured adhesives, excellent for trans-parent materials such as Makrolon poly-carbonate and SAN, cure inseconds and typically have high bondstrength. Two-part acrylic adhesivesusually show high bond strength. Usecare in selecting these adhesives, assome of their accelerators can be veryaggressive to Makrolon polycarbonateand Bayblend resins (see table 6).

Table 7 lists the relative bond strengthsfor four commercially available adhe-sives and one solvent for medical-gradeTexin 5000-series thermoplasticpolyurethanes (TPU) bonded to variousplastics. Mating substrates includedflexible and rigid PVCs, thermoplasticpolyurethanes, acrylic, and polycarbon-ate resins.

Prototype-test all parts to determine a given adhesive’s suitability.

Safe Adhesive Handling

You must refer to your adhesive

supplier’s Material Safety Data Sheet

for health and safety information and

appropriate handling recommenda-

tions, including the use of proper

protective equipment, for any

bonding system that you use.

8 hr 73°F (23°C)

12 hr 100°F (40°C)

12 hr 150°F (65°C)

12 hr 200°F (93°C)

12 hr 225°F (110°C)

Sequential Part orHolding BondTime Temperature

Table 5 Solvent Bond Curing Schedule

SOLVENT AND ADHESIVE BONDING continued

32

Epoxy (Two-Part) A, B ● ● ● ● ● ● ● ● N/A ●

Urethane (Two-Part) C, D, E, H, K ● ● ● ● ● ● ● ● ● ●

Cyanoacrylate B, F ■ ■ ● ● ● ● ■ ■ ● ●

Acrylic H ● ● ● N/A ● ● ● ● ● ●

Methacrylic M ● ● ● N/A ● ● ● ● ● ●

Silicone G ● ◆ ◆ ● ◆ ◆ ● ● ● ◆

UV Cure B, I ● N/A N/A N/A N/A ● N/A ● ● N/A

Hot Melt F, N ● ● ● ● ● ● ● ● ● ●

LIQUID NAILS® L X X ● ● ● ● X X X ●

Vinyl J ● ● ● ● ● ● ● ● ● N/A

Contact Tape A ● ● ● ● ● ● ● ● ● ●

Resins

Type of Adhesive Suppliers

Table 6 Adhesive Systems Suitable for Bonding Covestro Thermoplastics

ABS

Polya

mid

es

ASA

Bayb

lend

Apec

SAN

Makr

oblen

d

Makr

olon

Texin

PA/A

BS B

lend

● Suitable adhesives

■ Some cyano-acrylates can beaggressive to poly-carbonate and PCblends, and somecure to a brittlelayer which cansignificantly lowerthe flexural andimpact propertiesof the substrate

◆ Acetoxy-cure silicones can beaggressive tostyrenics andstyrenic blends ifthe acetic acidfumes are trappedin the joint

X Cannot be usedwith resins contain-ing polycarbonate

A. 3M Industrial SpecialtiesSt. Paul, MN 55144(612) 733-1110Epoxies, Contact Tape,

Contact Adhesives

B. Loctite CorporationRocky Hill, CT 06067(860) 571-5100Epoxies, Cyanoacrylates,

UV Cure

C. Ciba-Geigy CorporationEast Lansing, MI 48823(800) 875-1363Urethanes

D. Ashland ChemicalsColumbus, OH 43216(614) 790-3639Urethanes

E. Lord CorporationErie, PA 16514(814) 868-3611Urethanes

F. BostikMiddleton, MA 01949(508) 777-0100Hot Melts,

Cyanoacrylates

G. GE SiliconesWaterford, NY 12188(518) 237-3330Silicones

H. Ciba Furane ProductsLos Angeles, CA 90039(818) 247-6210Acrylics, Urethanes

I. Dymax CorporationTorrington, CT 06790(203) 482-1010UV Cures

J. King AdhesiveCorporationSt. Louis, MO 63110(314) 772-9953Vinyls

K. Morton International Inc.Chicago, IL 60606-1598(312) 807-3218Urethanes

L. The Glidden CompanyCleveland, OH 44115(216) 344-8000LIQUID NAILS®

M. ITW Adhesives SystemsDanvers, MA 01923(800) 851-6692Methacrylics

N. Henkel AdhesivesLaGrange, IL 60525-3602(708) 579-6150Hot Melts

SOLVENT AND ADHESIVE BONDING continued

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Solvent or Adhesive Material (from highest to moderate bond strength)

For more information on these products,please contact the following suppliers:

Dimethyl Formamide Solvent (DMF)Fisher Scientific585 Alpha DrivePittsburgh, PA 15222(412) 963-3300

Solvent-Based Urethane Adhesive (B-7133)Bostik, Inc.211 Boston StreetMiddleton, MA 01949(508) 777-0100

Prism Cyanoacrylate Adhesive (P-454)Loctite Corporation705 N. Mountain RoadRocky Hill, CT 06067(860) 571-5100

UV-Curable Adhesive (181-M) and (190-M)Dymax Corporation51 Greenswood RoadTorrington, CT 06790(860) 482-1010

Dimethyl Formamide (DMF Solvent)

Solvent-Based Urethane (Bostik 7133 Adhesive)

UV-Curable (Dymax 190-M Adhesive)

Cyanoacrylate (Loctite P-454 Adhesive)


























Flexible PVC to Texin TPU resin

Rigid PVC to Texin TPU resin

Acrylic to Texin TPU resin

Polycarbonate to Texin TPU resin

Texin TPU toTexin TPU resin

Polycarbonate to Polycarbonate

Table 7Relative Bond Strength of Several Thermoplastic Materials to MedicalGrade Texin Thermoplastic Polyurethanes

TECHNICAL SERVICES

• Applicable government or regulatoryagency test standards

• Tolerances that must be held in the functioning environment of the part(s)

• Any other restrictive factors or pertinent information of which we should be aware

Upon request, Covestro will furnish suchtechnical advice or assistance it deemsto be appropriate in reference to youruse of our products. It is expresslyunderstood and agreed that because allsuch technical advice or assistance isrendered without compensation and isbased upon information believed to bereliable, the customer assumes andhereby releases Covestro fromall liability and obligation for any

DESIGN AND ENGINEERING EXPERTISE

To get material selection and/or designassistance, contact your Covestrorepresentative. .To better help you, we will need toknow the following information:

• Physical description of your part(s) and engineering drawings, if possible

• Current material being used

• Service requirements, such as mechanical loading and/or strain, peak and continuous service temp-eratures, types of chemicals to which the part(s) may be exposed, stiffness required to support the part itself or another item, impact resistance, and assembly techniques

advice or assistance given or results obtained. Moreover, it is your respo-nsibility toconduct end-use testing and to otherwise determine to your own satisfaction whether Covestro’s products and information are suitable for your intended uses and applications.

TECHNICAL SUPPORT

We provide our customers with designand engineering information in severalways: Applications advice, available through your Covestro representative; processing assistance, through a nationwidenetwork of regional field technical servicerepresentatives; technical productliterature; presentations and seminars.

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TECHNICAL SERVICES

REGULATORY COMPLIANCE

Some of the end uses of the productsdescribed in this publication mustcomply with applicable regulations,such as the FDA, USDA, NSF, andCPSC. If you have any questions on theregulatory status of these products,contact your Covestro representative or the Regulatory Affairs Manager inPittsburgh, Pa.

HEALTH AND SAFETYINFORMATION

Appropriate literature has beenassembled which provides informationconcerning the health and safety pre-cautions that must be observed whenhandling Covestro thermoplastic resinsmentioned in this publication. Beforeworking with any of these products, youmust read and become familiar with theavailable information on their hazards,proper use, and handling. This can notbe overemphasized. Information isavailable in several forms, e.g., materialsafety data sheets and product labels.Consult your Covestro representative orcontact the Product Safety Manager forPolymers Division products inPittsburgh, Pa.

The types of expertise you can obtainfrom Covestro include:

Design Review Assistance

• Concept development• Product/part review• Tooling review• Material selection• Finite element analysis• Mold filling analysis• Structural stress analysis

Application Development Assistance

• Product development• Color matching• Prototyping• Part failure analysis• Molding trials• Physical testing• Secondary operation advice

Product Support Assistance

• Dryer audits• On-site processing audits• Start-up assistance• On-time material delivery• Troubleshooting• Processing/SPC Seminars• Productivity audits

FOR MORE INFORMATION

The data presented in this brochure arefor general information only. They areapproximate values and do not neces-sarily represent the performance of anyof our materials in your specific appli-cation. For more detailed information,go to www.plastics.covestro.comor contact your Covestro salesrepresentative.

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The conditions of your use and application of our products, technical assistance and information (whether verbal, written or by way of production evaluations), including any suggested formulations and recommendations, are beyond our control. Therefore, it is imperative that you test our products,technical assistance and information to determine to your own satisfaction whether they are suitable for your intended uses and applications. This application-specific analysis at least must include testing to determine suitability from a technical as well as health, safety, and environmental standpoint.Such testing has not necessarily been done by Covestro LLC. All information is given without warranty or guarantee. It is expressly understood andagreed that customer assumes and hereby expressly releases Covestro LLC from all liability, in tort, contract or otherwise, incurred in connectionwith the use of our products, technical assistance and information. Any statement or recommendation not contained herein is unauthorized and shall not bind Covestro LLC. Nothing herein shall be construed as a recommendation to use any product in conflict with patents covering any material or its use. No license is implied or in fact granted under the claims of any patent.

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NOTES

The manner in which you use and the purpose to which you put and utilize our products, technical assistance and information (whether verbal, written or by way of production evaluations), including any suggested formulations and recommendations, are beyond our control. Therefore, it is imperative that you test our products, technical assistance, information and recommendations to determine to your own satisfaction whether our products, technical assistance and information are suitable for your intended uses and applications. This application-specific analysis must at least include testing to determine suitability from a technical as well as health, safety, and environmental standpoint. Such testing has not necessarily been done by Covestro. Unless we otherwise agree in writing, all products are sold strictly pursuant to the terms of our standard conditions of sale which are available upon request. All information and technical assistance is given without warranty or guarantee and is subject to change without notice. It is expressly understood and agreed that you assume and hereby expressly release us from all liability, in tort, contract or otherwise, incurred in connection with the use of our products, technical assistance, and information. Any statement or recommendation not contained herein is unauthorized and shall not bind us. Nothing herein shall be construed as a recommendation to use any product in conflict with any claim of any patent relative to any material or its use. No license is implied or in fact granted under the claims of any patent.

Covestro LLC1 Covestro CirclePittsburgh, PA 15205

[email protected]

2015© Covestro LLC COV-031 10/2015

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