Manual de engranes

129

5

TYPICAL APPLICATIONS

Roller chain drives perform efficiently and economically in a wide range of applications. Rollerchain drives are commonly used in drives in industrial conveyors and processing equipment, inconstruction and agricultural equipment, on bicycles and motorcycles, in oil well drilling rigs, andin large stationary engines. Some typical drives using single-strand and multiple-strand roller chainsare shown in Figure 5-1.

SCOPE

This chapter covers selecting roller chain drives with only one driver and one driven sprocket usingAmerican National Standards (ANS) roller chains conforming to ASME B29.1, “Precision Power

chains covered in ASME B29.1. Many manufacturers also make double-pitch drive chain coveredin ASME B29.3. Although not covered by any ASME standard, many manufacturers also makehigh-strength, sealed joint, and corrosion-resistant chains that run on standard ASME B29.1 sprock-ets. Double-pitch and nonstandard drive chains are beyond the scope of this chapter, so the designershould consult an ACA roller chain manufacturer for help in selecting drives using chains notcovered by ASME B29.1.

The following guidelines and procedures are intended to help a drive designer manuallyselect a suitable roller chain drive as quickly and efficiently as possible. Some manufacturersoffer roller chain drive selection software. These programs eliminate much of the work in selectinga roller chain drive, but be sure to read and follow all of the cautions and restrictions that comewith such software.

GENERAL ROLLER CHAIN DRIVE SELECTION GUIDELINES

S

ELECTION

O

PTIONS

Several different chain and sprocket combinations usually can be found for a particular application.It is good practice to make two or three alternative selections and then make a final selection basedon cost, space, and weight constraints, required life, or other important factors.

The chain normally should be the weakest component in a chain drive because the chain usuallyis the least costly component to replace. Be careful not to select a chain and sprocket combinationwith too much capacity. The more expensive bearings and shafting may then become the weakestcomponents in the drive.

C

HAIN

P

ITCH

The smallest pitch, single-strand chain that will transmit the required power at the specified speedusually is the best selection. Higher speed generally requires a smaller pitch chain.

DK4023_C005.fm 29 Wednesday, August 17, 2005 10:23 AM

© 2006 by American Chain Association

Transmission Roller Chains, Attachments, and Sprockets.” Table 2-6 lists general dimensions of

Roller Chain Drives

130

Standard Handbook of Chains

N

UMBER

OF

S

PROCKET

T

EETH

Small Sprocket

The small sprocket must be large enough to accept the specified shaft diameter and keyway. Table 4-7 gives maximum recommended bore and hub diameters for roller chain sprockets with up to 25 teeth.

A sprocket is essentially a polygon, and the chain strand rises and falls as each roller engagesa sprocket tooth, as shown in Figure 5-2. This oscillation is called chordal action and causes cyclicchain velocity variation and roller impact on each sprocket tooth. Velocity fluctuation from chordalaction decreases as the number of teeth on the sprocket increases, as shown in Figure 5-3. Therefore,a small sprocket should have more teeth as the speed increases. A suggested minimum number ofteeth on a small sprocket for a given chain pitch and shaft speed may be obtained from Table 5-1.

The small sprocket, or any sprocket with fewer than 25 teeth, should have an odd number ofteeth. In a roller chain, the pin link elongates with wear, but the roller link does not. Pin links androller links engage the sprocket teeth differently as the chain wears. A given tooth on a sprocketwith an even number of teeth engages the same type of link on every revolution and the wear onalternate teeth is noticeably different. However, a given tooth on a sprocket with an odd numberof teeth engages a pin link on one revolution and a roller link on the next revolution and the wearon all of the teeth will be more nearly equal.

FIGURE 5-1

Typical drives with single- and multiple-strand roller chains.

FIGURE 5-2

Chain rise and fall as it engages a sprocket.

R - r

R r

DK4023_C005.fm Page 130 Wednesday, August 17, 2005 10:23 AM


Roller Chain Drives

131

The small sprocket in a roller chain drive should have at least 11 teeth. The chain and sprocketwith fewer than 11 teeth has more power capacity than the cold rolled shafting that will fit intothe sprocket. That combination can cause the more costly shafting to fail before the chain.

The largest sprockets practical should be chosen for a low speed ratio (1:1 to 2:1) drive thathas the chain slack span on top. This will reduce the possibility of contact between the chain strandsas the chain wears.

Large Sprocket

The number of teeth on the large sprocket limits the maximum allowable chain wear elongation.The chain elongates with wear and when chain elongation, over the arc of engagement, nears one-half pitch, the chain can jump teeth and damage the chain or sprocket. The ACA recommends thatmaximum permissible chain wear elongation be no more than 3%. The maximum elongation, inpercent, that a large sprocket will accept is 200/(number of teeth on the large sprocket). So asprocket with 67 teeth is the largest that can utilize the maximum allowable chain wear elongationof 3%. The large sprocket normally should have 120 teeth or less because it is difficult, andexpensive, to manufacture sprockets with more than 120 teeth.

H

ARDENED

S

PROCKET

T

EETH

Tooth loads and engagement frequency increase with fewer teeth on the sprocket. Sprocket teethshould be hardened when the number of teeth is 25 or less and the sprocket is used in:

• heavily loaded drives • abrasive conditions • high-speed drives • drives that require extremely long life

C

HAIN

W

RAP

ON

S

MALL

S

PROCKET

The chain should wrap at least 120 degrees, or three teeth, on the small sprocket. The wrap maybe as little as 90 degrees only if excellent chain adjustment is maintained. The chain can jump

FIGURE 5-3

Velocity variation from chordal action.

0%

2%

4%

6%

8%

10%

12%

14%

5 10 15 20 25 30

Number of Teeth on Sprocket

Vel

oci

ty V

aria

tio

n, %



132


teeth and damage the chain or sprocket if chain adjustment is not closely maintained with a wrapof less than 120 degrees. The wrap on the small sprocket will always be 120 degrees or more whenthe drive ratio is 3:1 or less.

D

RIVE

R

ATIO

The drive ratio is the speed of the faster shaft divided by the speed of the slower shaft. The driveratio normally should not be more than 7:1 in a single-stage drive (Figure 5-4a), but may be as

TABLE 5-1Suggested minimum number of teeth on a small sprocket

Smallsprocket

speed

Chain pitch

0.250 0.375 0.500 0.625 0.750 1.00 1.25 1.50 1.75 2.00 2.25 2.50 3.00

10,000 278,000 256,500 25 265,000 23 25 27

4,000 22 24 25 273,500 22 24 25 26 273,000 21 23 24 25 262,500 21 22 23 24 25 27

2,000 20 21 22 23 24 25 271,760 19 21 22 23 24 25 261,600 19 20 22 22 23 24 25 261,400 18 20 21 22 23 24 25 26 26

1,200 18 19 20 21 22 23 24 25 26 261,000 17 19 20 21 21 22 23 24 25 25 26 27900 17 18 19 20 21 22 23 24 24 25 26 26800 17 18 19 20 20 22 22 23 24 24 25 25 26

700 16 18 18 19 20 21 22 23 23 24 24 25 26600 16 17 18 19 19 20 21 22 23 23 24 24 25500 15 16 17 18 19 20 21 21 22 22 23 23 24400 15 16 17 17 18 19 20 20 21 22 22 22 23

300 14 15 16 16 17 18 19 19 20 20 21 21 22200 13 14 15 15 16 17 17 18 18 19 19 20 20100 11 12 13 13 14 15 15 16 16 17 17 17 1890 11 12 13 13 14 14 15 15 16 16 17 17 18

80 11 12 12 13 13 14 15 15 16 16 16 17 1770 11 11 12 13 13 14 14 15 15 16 16 16 1760 11 12 12 13 13 14 14 15 15 15 16 1650 11 11 12 12 13 13 14 14 15 15 15 16

40 11 11 12 12 13 13 14 14 14 15 1530 11 11 12 12 13 13 13 14 14 1420 11 11 12 12 12 13 13 1310 11 11 11 11 12



Roller Chain Drives

133

large as 10:1 with careful design and very good maintenance. A two-stage drive usually is better(Figure 5-4b) when the drive ratio is more than 7:1. Check high-ratio drives carefully to ensurethere is adequate wrap on the small sprocket.

C

HAIN

L

ENGTH

Chain length must always be an integral number of pitches. Design the drive to use an even numberof pitches whenever possible. An offset link is required in a chain with an odd number of pitches.Avoid using offset links because they reduce chain capacity 30% or more and are expensive.

C

ENTER

D

ISTANCE

Minimum Center Distance

To avoid tooth interference, the minimum center distance is one-half the sum of the outsidediameters of the two sprockets (Figure 5-5). To ensure adequate wrap on the small sprocket, theACA suggests a minimum center distance of the sum of the outside diameter of the large sprocketplus one-half the outside diameter of the small sprocket.

FIGURE 5-4

7:1 ratio drive layouts.

FIGURE 5-5

Minimum center distance.



134


Practical Center Distances

It is good practice to set the center distance at 30 to 50 times the chain pitch (Figure 5-6). Thelongest practical center distance is about 80 times the chain pitch because chain sag and catenarytension become very large. It may be desirable to set the center distance to as little as 20 times thechain pitch for a pulsating drive or a drive with fewer than 17 teeth on the small sprocket.

Adjustable Centers

Chain drive designers should provide adjustable centers, commonly a moveable motor mount,whenever possible. The range of adjustment should be equal to at least 1

∫

pitches of chain.

Fixed Center Distance

Sometimes adjustable centers or idlers cannot be provided. Then the designer must calculate andspecify an exact center distance. The designer should make a conservative selection (overchain thedrive somewhat) and specify type B or type C lubrication to minimize wear.

C

HAIN

W

EAR

AND

S

AG

As explained in chapter 3, chain elongates as it wears. Wear elongation is limited to a maximumof about 3% for standard and heavy series chain drives. However, wear elongation may be limitedto only 1% in drives where timing or smooth operation is critical. In addition, using sprockets withmore than 67 teeth gradually reduces the allowed wear percentage for all teeth more than 67.

Elongation appears as sag in the slack span, as shown in Figure 5-7. The designer must providesufficient clearance to prevent the chain from contacting the bottom of the chain case or other partsof the machine. Information on the design of chain cases can be found in chapter 13.

I

DLER

S

PROCKETS

When adjustable centers cannot be provided, an idler sprocket may be used to maintain correctstatic chain tension (Figure 5-8 and Figure 5-9). An idler sprocket should have at least as manyteeth as the small sprocket, and should engage the slack span of the chain. An idler sprocketengaging the taut strand will reduce the chain’s service life because there will be more articulationsunder load.

The chain should engage at least three teeth on the idler sprocket. Where two consecutivesprockets mesh with opposite sides of the chain, leave at least three free pitches of chain betweenthe points of engagement.

FIGURE 5-6

Preferred center distance.



Roller Chain Drives

135

FIGURE 5-7

Chain sag with wear elongation.

FIGURE 5-8

Idler sprocket application on horizontal drives.

FIGURE 5-9

Idler sprocket application on vertical drives.



136


M

ULTIPLE

-S

TRAND

C

HAIN

Where the transmitted power or speed is too high, or the space is too small, for a single-strandchain with sufficient capacity, the designer may need to select multiple-strand chain. Multiple-strand chain can transmit more power at higher speeds than larger single-strand chain with equalor greater load capacity.

D

RIVE

A

RRANGEMENTS

Drive arrangements that represent good practice are shown in Figure 5-10. Consult an ACA rollerchain manufacturer about other drive arrangements.

M

ULTIPLE

-S

PEED

D

RIVES

When a drive operates over a range of speeds and loads, the designer must ensure that the selectedchain and sprockets have adequate capacity at the most severe operating condition. Those conditionsare often, but not always, the highest and lowest operating speeds.

M

ULTIPLE

D

RIVEN

S

PROCKETS

Roller chain drives with multiple driven sprockets are fairly common (Figure 5-11). The drivedesigner should consult an ACA roller chain manufacturer for advice on drives with multiple drivensprockets. This is because each manufacturer uses different service factors for multiple drivensprockets.

FIGURE 5-10

Preferred drive arrangements.



Roller Chain Drives

137

No equations are given to calculate the required chain length on drives with multiple drivensprockets. The chain length usually is found by a large-scale layout or multiple geometric calcu-lations.

Software is available to select roller chain drives with multiple driven sprockets. That softwareis very useful and convenient, but the methods and equations are proprietary to the particulardeveloper.

R

ACK

D

RIVES

An unusual use of roller chain to drive several sprockets simultaneously is the rack drive, illustratedin Figure 5-12. In a rack drive, the pinions are arranged with their tooth contact surfaces in astraight line, and a straight run of roller chain acts as a rack. The pinions usually have a cycloidaltooth form to enable proper single-tooth engagement with the chain and a guide shoe may be usedat each sprocket to keep the chain rollers engaged with the sprockets. Consult an ACA roller chainmanufacturer for assistance with designing a rack drive.

FIGURE 5-11

Multiple sprocket drive.

FIGURE 5-12

Rack drive.



138


ROLLER CHAIN DRIVE SELECTION PROCEDURE

S

TEP

1: O

BTAIN

N

ECESSARY

I

NFORMATION

Obtain the following listed information before selecting a roller chain drive. Make every effort toobtain all of the needed information.

• Type of power source.• Type of driven equipment.• Power required, or input power.• Size and speed of the driver shaft.• Size and speed of the driven shaft.• Shaft center distance and drive arrangement.• Available center distance adjustment, if any.• Space restrictions.• Available lubrication.

In addition, the designer should determine if there are any unusual drive conditions, such as

• Adverse environment (corrosive, wet, dirty, etc.).• Frequent stops and starts.• High starting or inertial loads.• Temperatures greater than 150˚F or less than 0˚F.• Large cyclic load variations in each revolution.• Multiple driven shafts.

If any of the listed or other unusual drive conditions are found, contact an ACA roller chainmanufacturer for assistance. Many chain manufacturers offer self-lubricating, sealed joint, corro-sion-resistant, plated, coated, or other specialty chains designed to operate in particular hostileenvironments.

S

TEP

2: D

ETERMINE

THE

S

ERVICE

F

ACTOR

The nominal required power, or input power, is usually given. Peak power may be much larger,depending on the type of power source and driven equipment. Drive designers use a service factorto account for the difference between nominal and peak power. Service factors to estimate thedifference between nominal and peak loads induced by combinations of different types of powersources and driven equipment are shown in Table 5-2. The load characteristics of various types ofdriven equipment are shown in Table 5-3.

S

TEP

3: C

ALCULATE

D

ESIGN

P

OWER

Calculate the design power by multiplying the nominal required power, or input power, by the

S

TEP

4: S

ELECT

A

P

RELIMINARY

C

HAIN

S

IZE

Enter the chain selection charts, Figure 5-13 and Figure 5-14, with the design horsepower and thespeed of the small sprocket (faster shaft). The area in which the two lines intersect indicates thepitch size (chain number) of the preliminary chain selection.



service factor obtained from Table 5-2.

Roller Chain Drives

139

If the power, or speed, is more than the rating for single-strand chain, multiple-strand chainmay be needed. Multiply the rated power, or divide the design power, by the multiple-strand factorfrom Table 5-4 and select a multiple-strand chain from Figure 5-13 or Figure 5-14. This chapterhas factors for selecting multiple-strand chains only of up to four strands. However, many ACAroller chain manufacturers offer wider multiple-strand chains. Consult an ACA roller chain man-ufacturer for assistance with selecting five-strand or wider multiple-strand chains.

Note that an optimum selection is where the drive operates near the peak of the rating curve.That is where one can use the maximum capacity of the chain.

TABLE 5-2Service factors for roller chain drives

Type of Input Power

Type of DrivenLoad

Internal Combustion Engine with

Hydraulic Drive

Electric Motor or

Turbine

Internal Combustion Engine with

Mechanical Drive

Smooth 1.0 1.0 1.2Modreate Shock 1.2 1.3 1.4Heavy Shock 1.4 1.5 1.7

TABLE 5-3Load classifications

Smooth load Moderate shock load Heavy shock load

Agitators – Pure liquidBlowers – CentrifugalBucket elevators – Uniformly loaded or fed

Conveyors – Uniformly loaded or fed

Feeders – Rotary tableGeneratorsMachine tools – Drills, grinders, lathes

Pumps – CentrifugalScreens – Rotary, uniformly fed

BeatersBucket elevators – NOT uniformly loaded or fed

Clay working machinery – Pug millsCompressors – CentrifugalReciprocating, 3+ cylindersConveyors – Heavy duty, NOT uniformly loaded

Cranes and hoists – Medium duty, skip hoists (travel and trolley motion)

Dredges – Cable, reel, and conveyor drives

Feeders – Apron, screw, rotary vaneFood processing machinery – Slicers, mixers, grinders

Kilns and dryersMachine tools – Boring mills, milling machines, hobs, shapers

Mills – Ball, pebble, and tubePaper processing machinery – Pulp grinders

Pumps – Reciprocating, 3+ cylindersTextile machinery – Calendars, mangles, nappers

Woodworking machinery

Boat propellersClay working machinery – Brick pressesBriquetting machinesCompressors – Reciprocating, 1 or 2 cylinders

Conveyors – Reciprocating and shakerCranes and hoists – Heavy-duty, logging, and rotary drilling

CrushersDredges – Cutter head, jig, and screen drives

Feeders – Reciprocating, shakerMachine tools – Punch presses, shears, plate planers, cold formers

Mills – Draw benches, hammer, rolling, wire drawing

Paper processing machinery – Calendars, mixers, sheeters

Pumps – 1 or 2 cylindersPrinting pressesTextile machinery – Carding machinery



140


S

TEP

5: SELECT THE SMALL SPROCKET AND SPECIFIC CHAIN SIZE

Select the Small Sprocket

5-28) with the faster shaft speed for the selected chain. Follow that column down until the designpower is reached or exceeded. The number of teeth on the small sprocket can be read from theleftmost column of the table. Check this selection against Table 4-7 to ensure that it will accom-modate the specified shaft size. Also, check this selection against Table 5-4 to ensure that thenumber of teeth on the sprocket is appropriate for the shaft speed (within two or three teeth). Repeatthis procedure for heavy series chain of the same pitch. If the preliminary selection is multiple-strand chain, or if you want to consider multiple-strand chain, divide the design power by themultiple-strand factor from Table 5-4 before entering the rating table.

Select a Specific Chain Size

It is suggested that the drive designer select a small sprocket and chain from at least the next smallerand next larger pitch sizes. The designer may then select the chain that best meets the user’sparticular requirements.

FIGURE 5-13 Chain selection chart: standard series.

0.1

1.0

10.0

100.0

1000.0

10 100 1000 10000

Rotational speed of small (25-tooth) sprocket, r/min

Sin

gle-

Str

and

Des

ign

Hor

sepo

wer

25

35

41

40

50

60

80

100

120

140160

180200

240

10

100

1000

0.2

0.4

0.7

2

4

7

20

40

70

200

400

700

1



If the preliminary selection is single-strand chain, enter the rating table (Table 5-5 through Table

Roller Chain Drives 141

STEP 6: SELECT THE LARGE SPROCKET

Calculate the number of teeth on the large sprocket by multiplying the number of teeth on the smallsprocket by the desired drive ratio (faster shaft speed/slower shaft speed). Round the result to thenearest integral number of teeth.

Check the sprocket sizes and center distance to be sure the drive will fit within any spacerestrictions. If it does not fit, return to the previous step and consider multiple-strand chain.

If the drive ratio is critical, one can adjust the number of teeth on the small and large sprocketsto obtain an exact, or more nearly exact, drive ratio. If the drive ratio is not critical, one can adjustthe number of teeth on the small and large sprockets to permit the use of stock sprockets with anacceptable speed ratio.

FIGURE 5-14 Chain selection chart: heavy series.

TABLE 5-4Multiple-strand factors

Number of Strands Multiple-Strand Factor2 1.73 2.54 3.3



142 Standard Handbook of Chains

STEP 7: CALCULATE THE CHAIN LENGTH

Chain length is a function of the center distance and the number of teeth on each of the sprockets.Chain length must be an integral number of pitches, and preferably an even number of pitches toavoid using an offset link. Sometimes an exact chain length cannot be calculated because therequired length of the chain changes as it engages each sprocket tooth. However, a nearly exactchain length can be calculated using Equation 5.1, which is derived from the data in Figure 5-15.Note that the chain length calculated by Equation 5.1 and Equation 5.2 is in pitches. That calculatedchain length must be multiplied by the chain pitch to convert it to inches (or millimeters):

pitches, (5.1)

where

C is the desired center distance (in pitches), L is the chain length (in pitches), N is the number of teeth on the large sprocket, and n is the number of teeth on the small sprocket.

Equation 5.1 can be simplified to Equation 5.2. That gives a good approximation of the requiredchain length and is adequate when the center distance is adjustable by at least plus or minus one-half pitch:

TABLE 5-5 Center Distance Factors

L - n N - n KCD

L - n N - n KCD

L - n N - n KCD

L - n N - n KCD

13 0.24991 2.7 0.24735 1.54 0.23758 1.26 0.2252012 0.24990 2.6 0.24708 1.52 0.23705 1.25 0.2244311 0.24988 2.5 0.24678 1.50 0.23648 1.24 0.2236110 0.24986 2.4 0.24643 1.48 0.23588 1.23 0.222759 0.24983 2.3 0.24602 1.46 0.23524 1.22 0.221858 0.24978 2.2 0.24552 1.44 0.23455 1.21 0.220907 0.24970 2.1 0.24493 1.42 0.23381 1.20 0.219906 0.24958 2.0 0.24421 1.40 0.23301 1.19 0.218845 0.24937 1.95 0.24380 1.39 0.23259 1.18 0.217714.8 0.24931 1.90 0.24333 1.38 0.23215 1.17 0.216524.6 0.24925 1.85 0.24281 1.37 0.23170 1.16 0.215264.4 0.24917 1.80 0.24222 1.36 0.23123 1.15 0.213904.2 0.24907 1.75 0.24156 1.35 0.23073 1.14 0.212454.0 0.24896 1.70 0.24081 1.34 0.23022 1.13 0.210903.8 0.24883 1.68 0.24048 1.33 0.22968 1.12 0.209233.6 0.24868 1.66 0.24013 1.32 0.22912 1.11 0.207443.4 0.24849 1.64 0.23977 1.31 0.22854 1.10 0.205493.2 0.24825 1.62 0.23938 1.30 0.22793 1.09 0.203363.0 0.24795 1.60 0.23897 1.29 0.22729 1.08 0.201042.9 0.24778 1.58 0.23854 1.28 0.22662 1.07 0.198482.8 0.24758 1.56 0.23807 1.27 0.22593 1.06 0.19564

L CN n

N n= + + + −( )⎡

⎣⎢

⎤

⎦⎥2

4 360cos α α

DK4023_C005.fm 2 Wednesday, August 17, 2005 10:23 AM


Roller C

hain Drives

143

TABLE 5-6Horsepower ratings for single-strand no. 25 chain

DK4023_C005.fm Page 143 W

ednesday, August 17, 2005 10:23 A

M


144Standard H

andbook of Chains




M


Roller C

hain Drives

145




M


146Standard H

andbook of Chains




M


Roller C

hain Drives

147




M


148Standard H

andbook of Chains




M


Roller C

hain Drives

149

TABLE 5-12Horsepower ratings for single-strand no. 60H chain



M


150Standard H

andbook of Chains




M


Roller C

hain Drives

151




M


152Standard H

andbook of Chains




M


Roller C

hain Drives

153




M


154Standard H

andbook of Chains




M


Roller C

hain Drives

155




M


156Standard H

andbook of Chains




M


Roller C

hain Drives

157




M


158Standard H

andbook of Chains




M


Roller C

hain Drives

159




M


160Standard H

andbook of Chains




M


Roller C

hain Drives

161




M


162Standard H

andbook of Chains




M


Roller C

hain Drives

163




M


164Standard H

andbook of Chains




M


Roller C

hain Drives

165

TABLE 5-28Horsepower ratings for no. 240H chain



M



pitches. (5.2)

STEP 8: CALCULATE THE FINAL CENTER DISTANCE

The calculated chain length is often fractional. If so, the designer must select a whole, preferablyeven number of pitches, and determine the center distance from that. The most convenient way todetermine center distance is by the use of center distance tables, or personal computer programs,provided by some ACA roller chain manufacturers. An approximate center distance, in pitches, canbe calculated using Equation 5.3. Equation 5.3 was derived by rearranging Equation 5.2, and isacceptable when the center distance is adjustable by at least plus or minus one-half pitch. Notethat the center distance calculated by Equation 5.3 and Equation 5.4 is in pitches. That calculatedcenter distance must be multiplied by the chain pitch to convert it to inches (or millimeters):

pitches. (5.3)

A more exact center distance C can be calculated using Equation 5.4 from the data in Figure5-16:

pitches. (5.4)

The trigonometric functions in Equation 5.4 have been combined into a single factor, KCD, for

selected values of the term . Values for the factor KCD are tabulated in Table 5-5. Using the

factor KCD, a nearly exact center distance C’ can be calculated using Equation 5.4a:

pitches. (5.4a)

FIGURE 5-15 Chain length calculation.




The center distance obtained from a table, or computer program, or calculated from Equation5.4 or Equation 5.4a must be multiplied by the chain pitch to obtain the center distance in inches(or millimeters). The center distance obtained from a table, or computer program, or calculatedfrom Equation 5.4a are maximums. Any tolerance applied must be negative only. If a positivetolerance is applied, it may damage the chain or other components of the drive.

STEP 9: SELECT THE TYPE OF LUBRICATION

The designer should select the type of lubrication recommended in the power rating tables. Moredetailed information on roller chain drive lubrication can be found in chapter 13.

SAMPLE ROLLER CHAIN DRIVE SELECTION

STEP 1: OBTAIN NECESSARY INFORMATION

The power source is an electric motor. The driven equipment is a two-cylinder pump. Input poweris 40 hp. The driver shaft turns at 900 rpm and is 2.375 in. in diameter. We want to turn the drivenshaft at 300 rpm and it is 3 in. in diameter. The desired center distance is 40 in. and the shafts andcenters are both horizontal. The center distance adjustment can be 2 in. or more if needed.Lubrication will be what is recommended by the ratings. There are no space restrictions or unusualdrive conditions.

STEP 2: DETERMINE THE SERVICE FACTOR

The service factor, from Table 5-2, is 1.5.

STEP 3: CALCULATE THE DESIGN POWER

Input power is 40 hp and the service factor is 1.5. Thus the design power is 40 hp × 1.5 = 60 hp.

STEP 4: SELECT A PRELIMINARY CHAIN SIZE

Entering Figure 5-13 with a design power of 60 hp and a speed of 900 rpm yields a preliminaryselection of ANS no. 80 chain (on a 25T sprocket). Entering Figure 5-14 with a design power of60 hp and a speed of 900 rpm yields a preliminary selection of ANS no. 80H chain (on a 25Tsprocket). However, since no. 80 chain is adequate, there is no need for no. 80H. The preliminaryselection is no. 80 chain.

STEP 5A: SELECT THE SMALL SPROCKET

Entering Table 5-13, the rating table for no. 80 chain, at 900 rpm shows that no. 80 chain on a 21-tooth sprocket has adequate capacity. The no. 80, 21-tooth sprocket will accept the 2.375-in.diameter shaft (Table 4-7) and is very close to the suggested minimum of 22 teeth for no. 80 chainat 900 rpm. Examining Table 5-15 and Table 5-11, the rating tables for no. 100 and no. 60 chain,shows that a no. 100 chain on a 19-tooth sprocket or a no. 60-2 chain on a 28-tooth sprocket wouldalso be adequate. Both of these sprockets will accept a 2.375-in. diameter shaft.

STEP 5B: SELECT A SPECIFIC CHAIN SIZE

The suggested minimum number of teeth for no. 100 chain at 900 rpm is 23. The no. 100 chainon a 19-tooth sprocket might run too rough. A no. 60-2 chain on a 28-tooth sprocket would be




considerably more expensive than a no. 80 chain on a 21-tooth sprocket. The best selection appearsto be a no. 80 chain on a 21-tooth sprocket.

STEP 6: SELECT THE LARGE SPROCKET

The speed ratio is 900/300 = 3.0. Thus the large sprocket should have 3.0 ∞ 21 teeth = 63 teeth.This is a nonstock sprocket for most manufacturers. The nearest size stock sprocket is a 65-toothsprocket. The 65-tooth sprocket gives an output speed of 291 rpm, or 3% less than the desiredspeed. If maintaining the output shaft speed is critical, the added expense of a made-to-order 63-tooth sprocket might be justified. In this example we will assume that a 3% speed difference isacceptable and select the stock 65-tooth sprocket.

STEP 7: CALCULATE THE CHAIN LENGTH

Now we can calculate the chain length using Equation 5.2:

.

We round the chain length down to 124 pitches to obtain an even number of pitches and avoidusing an offset link.

STEP 8: CALCULATE THE FINAL CENTER DISTANCE

We now calculate the final center distance using Equation 5.3:

C ± 0.5 pitches.

Next, we calculate a more nearly exact center distance using Equation 5.4a:

,

and from Table 5-28, KCD = 0.24618 (interpolated between 2.3 and 2.4):

C′ = 0.24618(2(124)–65–21) = 0.24618(162) = 39.88 pitches (and inches).

STEP 9: SELECT THE TYPE OF LUBRICATION

The type of lubrication, indicated in Table 5-13, is type B, “Oil Bath or Slinger Disc TypeLubrication.” A chain case is required for type B lubrication. Information on the design of chaincases can be found in chapter 13.

EQUATIONS FOR HORSEPOWER RATINGS

GENERAL

Extensive research by ACA members has produced reliable power ratings for ANS roller chaindrives conforming to the ASME B29.1 standard. The power capacity of roller chain drives operating

L = ( ) + + +−( ) = + + =2 40

65 212

65 21

4 4080 43 1 23 1

2

2π ( ). 224 23.

= − + =124 43 78 544

39 9.

.

L nN n

−−

= 2 34.




within standard conditions is limited by link plate fatigue strength, roller and bushing impact fatigue,galling between the pin and bushing, the type of lubrication. The standard conditions are

• Chain length of 100 pitches.• Service factor of one.• A well-aligned two-sprocket drive on parallel horizontal shafts.• Use of the recommended type of lubrication.• A nonhostile environment.• An expected service life of approximately 15,000 hours.

A sample graph of the horsepower ratings for no. 60 chain is shown in Figure 5-16.

LINK PLATE FATIGUE STRENGTH

Equation 5.5 defines the power rating of ANS roller chains, limited by link plate fatigue strength:

, (5.5)

where

HPL is the horsepower rating limited by link plate fatigue strength; KL is 0.0044 for all standard series chains except no. 41, 0.0044(TH/TS)0.5

for heavy series chains, and 0.00242 for no. 41 chain; n is the number of teeth on the small sprocket; p is the chain pitch (in inches); R is the speed of the small sprocket (in rpm); TH is the link plate thickness for heavy series chains; and TS is the link plate thickness for standard series chains.

FIGURE 5-16 Sample roller chain power rating chart.

HP K nR pL Lp= −0 96 3 0 0 07. ( . . )




ROLLER AND BUSHING IMPACT

Standard Conditions

Equation 5.6 defines the power rating of ANS chains limited by roller and bushing impact fatigueat the standard conditions of 15,000 hours of life and 100 pitches of chain length:

, (5.6)

where

HPR is the horsepower rating limited by roller and bushing impact fatigue; KR is 17,000 for all standard and heavy series chains except no. 25, no. 35,

and no. 41, 29,000 for no. 25 and no. 35 chains, and 3400 for no. 41 chain.

Adjustment for Life and Chain Length

The power rating at a chain length and life other than 100 pitches and 15,000 hours may be obtainedby multiplying Equation 5.6 by the following factors:

For chain length other than 100 pitches, multiply Equation 5.6 by the factor

.

For life other than 15,000 hours, multiply Equation 5.6 by the factor

.

These factors may be combined to yield

.

Galling between Pins and Bushings

Equation 5.7 defines the power rating of ANS chains limited by galling between the pins andbushings:

, (5.7)

where

HPK n p

RR

R=1 5 0 8

1 5

. .

.

KChainLength pitches

Length = ⎛⎝⎜

⎞⎠⎟

,.

100

0 4

KDesiredLife hours

Life =⎛⎝⎜

⎞⎠⎟

150000 4

,

.

KChainLength pitches

DesiredLifCombined = 7 42.

,ee hours,

.⎛⎝⎜

⎞⎠⎟

0 4

HP K npR n p n

G G= − +⋅

⎡

⎣⎢

⎤

⎦⎥

23 3 5

12

2 0 032263 96 10( . ).




HPG is the horsepower rating limited by galling between the pins and bushings; KG is 6.452 for all standard series chains except no. 41, 5.807 for heavy series chains,

and for no. 41 chain, use the same speed limits as for no. 40 chain.

TYPE OF LUBRICATION

Equation 5.7, with a different constant KG, also defines the power rating of ANS chains limited bythe type of lubrication.

Oil Bath or Slinger Disc Lubrication

For oil bath or slinger disc lubrication,

KG equals 3.226 for all standard series chains except no. 41, 2.903 for heavy series chains, and for no. 41 chain, use the same speed limits as for no. 40 chain.

Manual or Drip Lubrication

For manual or drip lubrication,

KG equals 0.3226 for all standard series chains exceptno. 41, 0.2903 for heavy series chains, and for no. 41 chain, use the same speed limits as for no. 40 chain.

ADJUSTMENT FOR CHAIN LENGTH

The galling and lubrication limits are greater for longer chains than for shorter chains. If the selectedchain length, L, is much longer or shorter than 100 pitches, Equation 5.7 can be modified to accountfor the different chain length. The modified equation is shown in Equation 5.8:

. (5.8)

One normally needs to account for chain length only if the chain is operating at the galling (orlubrication) limit and the chain length is more than 10 pitches different from 100 pitches.

HORSEPOWER RATING TABLES FOR ANS CHAINS

The horsepower rating tables for ANS standard and heavy series roller chains at the standardconditions listed above are shown in Table 5-5 through Table 5-28.

VIBRATION

GENERAL

It is well known that a roller chain can vibrate noticeably when the frequency of an exciting sourceis close to one of the natural frequencies of the chain. Under certain conditions, the vibration maybe so severe that it can damage or destroy the chain or the drive.

Some factors of the drive are fixed, such as shaft speed, the amount of power transmitted, theload characteristics of the driven machine, and any space limitations. Other factors may be controlled

HP K np LR n p n L

G G= − +⋅

⎡23 3 5

12

2 0 032263 96 10

(( . ) / ).⎣⎣

⎢⎤

⎦⎥




by the drive designer, such as the pitch, the number of strands of chain, the number of teeth onthe sprockets, and the type of input power. When the designer knows the fixed characteristics ofthe drive and the factors that can be controlled, he or she can use the following explanations andequations to determine if a proposed drive might have a serious vibration problem. Then the designercan select a chain and sprockets that will minimize the chances of destructive vibration.

The information given here is very basic and brief. If chain vibration is suspected or found,contact an ACA roller chain manufacturer for assistance.

SOURCES OF EXCITEMENT

Large Cyclic Loads

Many roller chain drives have large cyclic loads or impulses. These cyclic loads may occur once,or a few times, per revolution and they may come from either the driven machine or input powersource. The magnitude of the impulse depends on how much the peak load exceeds the mean load,how much the peak power pulse exceeds the mean input power, the inertia of the driving and drivenmachines, and the stiffness of the drive. The frequency of the impulses is the sprocket speed, inrevolutions per second, divided by the number of impulses per revolution.

Machines that cause one impulse per revolution are punch presses, shears, one-cylinder pumpsor compressors, and one-cylinder engines. Machines that cause a few impulses per revolution areduplex and triplex pumps or compressors, two-, three-, and four-cylinder internal combustionengines, and other reciprocating or cam-actuated machines. The effects of large cyclic loads oftencan be reduced by putting a fluid coupling or some other type of cushioning device in the drive.

Chordal Action

As was shown earlier in this chapter, chordal action produces at least two possible sources ofvibration. Each time a chain roller engages a sprocket tooth, chordal action makes the chain spanboth rise and fall laterally, and increase and decrease in speed. The procedure for calculating theforce caused by chordal action is beyond the scope of this book. However, it is known that theforce increases very rapidly with speed and somewhat less rapidly with the chain pitch. Thefrequency of the impulses caused by chordal action is the tooth contact frequency, or the sprocketspeed, in revolutions per second, times the number of teeth on the sprocket.

The effects of the impulses caused by chordal action can be reduced by selecting a smallerchain pitch or a sprocket with more teeth. Multiple-strand chain may be needed when a smallerpitch chain or a sprocket with more teeth is used.

Roller-Tooth Impact

When the chain roller engages a sprocket tooth, there is an impact caused by chordal action. Themaximum force during this impact depends on the chain pitch, the sprocket speed, the effectivestiffness of the roller against the sprocket tooth, and the effective mass of the part of the chaininvolved in the impact. The effective stiffness and mass are very difficult to determine. They areaffected by sprocket and roller materials, the amount and quality of lubrication, and possibly otherfactors. However, it is known that roller-tooth impact forces increase with chain pitch and sprocketspeed. The frequency of roller-tooth impact is the tooth contact frequency and its harmonics.

Roller-tooth vibration, and the impacts that incite it, are the source of most of the noise in aroller chain drive. The amplitude of roller-tooth vibration increases approximately with the squareof sprocket speed, so it is very important in high-speed drives. This is one of the reasons why thepower capacity of a roller chain decreases so rapidly at high speeds (see Equation 5.6).

The effects of roller-tooth impact forces can be reduced by selecting a smaller chain pitch ora sprocket with more teeth. Multiple-strand chain may be needed when a smaller pitch chain is used.




TYPES OF VIBRATION AND NATURAL FREQUENCIES

Lateral Vibration

In lateral vibration, the chain vibrates up and down (in a horizontal drive) about the chain’s axislike a plucked string. It is the most visible, and may be the most common, type of chain vibration.The natural frequency of lateral vibration in a chain is given by Equation 5.9:

Hz, (5.9)

where

fL is the natural frequency of lateral vibration in the chain (in Hz), n is an integer representing the harmonic of the vibration, l is the length of the taut span of the chain (in ft), g is a gravitational constant (32.17 ft/sec2), T is the tension applied to the chain (in lb), and W is the unit weight of the chain (in lb/ft).

The natural frequency for lateral vibration is usually quite low. The excitation from chordalaction is probably too small at such slow speeds to cause noticeable vibration. However, theexcitation from a large cyclic load may be enough to cause damaging vibration at resonance. Thefrequency of the exciting force should be at least 1.4 times the natural frequency to avoid resonanceand damaging vibration.

The very low tension in the slack span normally gives a natural frequency that is too low tocause a vibration problem. A spring-loaded idler in the slack span may increase the tension andnatural frequency enough for it to cause a destructive vibration, either at the resonant frequencyor at one of the harmonics of that frequency. The drive designer should always check the resonantfrequency of the slack span when considering or using a spring-loaded idler in the slack span.

Axial, or Spring-Type, Vibration

In axial vibration, the chain acts like a spring connected between two rotors. This type of vibrationis not readily seen, but at resonance it may be identified by increased noise. The natural frequencyof axial vibration in a chain is given by Equation 5.10:

Hz, (5.10)

where

fA is the natural frequency of axial vibration in chain (in Hz), J1 is the rotating inertia related to the input sprocket (in lbm·ft2/g), J2 is the rotating inertia related to output sprocket (in lbm·ft2/g), R1 is the pitch radius of the input sprocket (in ft), R2 is the pitch radius of the output sprocket (in ft), g is the gravitational constant (32.17 ft/sec2), k is the unit stiffness of the chain (in lbf), and k is approximately 1,000,000p2 lbf for ANS chains, where p is the chain pitch (in inches).

fnl

gTW

L =2

fk

lJ JJ R J RA = +( )1

2 1 21 2

22 1

2

π




Here again, the natural frequency for axial vibration is usually quite low and the force fromchordal action at such slow speeds is probably too small to cause noticeable vibration. However,the impulse from a large cyclic load may be enough to cause damaging vibration at resonance. Thefrequency of the exciting force should be at least 1.4 times the natural frequency to avoid resonanceand damaging vibration.

Wave-Type Vibration

In wave-type vibration, the chain vibrates axially like an elastic bar that is excited at its ends. Wave-type vibration usually cannot be seen. The natural frequency of wave-type vibration in a chain isgiven by Equation 5.11:

Hz, (5.11)

where fW is the natural frequency of wave-type vibration in chain (in Hz).The natural frequency of wave-type vibration is usually much higher than that of either lateral

or axial vibration. Often it is close to the tooth contact frequency of a drive running at moderateto high speeds. When that happens, wave vibration can increase chain tension quite a lot and causeearly chain failure. Damaging wave-type vibration can also occur when the tooth contact frequencymatches the second harmonic of the natural frequency of the chain, but that is beyond the scopeof this book. The designer should contact an ACA roller chain manufacturer for assistance whenthis type of vibration is found.

Roller-Tooth Vibration

In roller-tooth vibration, the chain roller vibrates from the impact of the roller against the sprockettooth each time a roller engages a tooth. The frequency of roller-tooth vibration depends on theeffective contact stiffness of the roller on the tooth and the effective mass of the joint engaging thetooth. It is extremely difficult to estimate values for the effective stiffness and effective mass, soan equation for calculating the frequency of roller-tooth vibration is not given here. Experimentshave found that roller-tooth vibrations have a frequency in the range of 2 kHz to 10 kHz.

NOISE

As stated above, roller-tooth impact, and its resulting vibrations, are the source of most of the noisein a roller chain drive. Noise is a serious consideration in many roller chain drives. The roller chainindustry has done considerable research on roller chain drive noise and has learned a lot about themany factors that cause roller chain drive noise. Even so, they did not find a way to calculate orpredict with reasonable accuracy the noise that will be made by a given drive.

Many factors affect the noise level of a drive. Some of these factors include the amount andtype of chain loading, the amount and quality of lubrication, the number of sprocket teeth, thechain pitch, the fit between the chain and sprocket, chain wear, and sprocket wear. There may be,and probably are, additional factors that have not yet been clearly identified. Usually it is necessaryto make a series of sound tests on a prototype or the actual drive to determine the noise level ofthe drive. One or two tests are not enough to show the normal variation in noise levels betweenone set of chains and sprockets and the next.

Certain noise factors are related to the basic mechanics of a roller chain drive. Some of thebasic findings of research on roller chain drive noise include the sound level (in decibels) increaseswith chain pitch, increases with chain tension, increases with the logarithm of the sprocket speed,and peaks at a frequency of about 6 kHz.

fnl

gkW

W =2




Fortunately, industry research also found that drive designers and users could do a number ofthings to reduce the noise from a roller chain drive. Some things that can be done to quiet a noisydrive, along with a short explanation, include

• Select a chain with smaller pitch. Note that multiple-strand chain may be required.• Select a chain and sprocket combination that avoids resonant frequencies.• Use a better type of lubrication than recommended. Tests show that superior lubrication

can reduce the noise level of a drive by 6 dB or more.• Ensure that the chain has adequate slack at installation and when readjusted. Tests show

that a very tight chain is several decibels noisier than one that is correctly adjusted.• Replace a worn chain well before it reaches the accepted 3% wear elongation limit. Tests

show that noise is minimized when the chain and sprocket pitch are exactly the same.• Replace sprockets before the teeth are noticeably hook shaped. A worn, hook-shaped

tooth form is much noisier than a new tooth form.• Consider using precision grade sprockets with hardened teeth for high-speed drives. This

maintains the desired exact match of chain and sprocket pitch for a longer time.

There may be other ways to quiet or avoid a noisy drive. Contact an ACA roller chain manufacturerfor assistance with reducing drive noise.

ACKNOWLEDGMENT

Parts of S. W. Nicol and J. N. Fawcett, “Vibrational characteristics of roller chain drives,” Engi-neering, January 1977, pp. 30–32, were used in preparing the section on vibration.



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