Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

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“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 7907-1 (2004): Helical Extension Springs, Part 1: Designand Calculation for Springs Made from Circular Section Wireand Bar [TED 21: Spring]

,

1

IS 7907 (Part 1): 2004

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Indian Standard

HELICAL EXTENSION SPRINGS

October 2004

PART 1 DESIGN AND CALCULATION FOR SPRINGS MADE FROMCIRCULAR SECTION WIRE AND BAR

(First Revision)

ICS 21.160

0 BIS 2004

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Price Group 9

*

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.

.

●

Automotive Springs and Suspension Systems Sectional Committee, TED 21

FOREWORD

This Indian Standard (Part 1) (First Revision) was adopted by the Bureau of Indian Standards, afier the draftfinalized by the Automotive Springs and Suspension Systems Sectional Commitle~ had been approved by theTransport Engineering Division Council.

This standard was originally published in 1976. This revision incorporates a number of changes which were feltnecessary as a result of further experience gained in the manufacture, use of compression spring, revision of basestandard and due to other developments in this field.

The following technical changes have been incorporated:

a) Values of various spring parameters for cold formed and hot formed extension springs (see Table 1).

b) Design stresses/mQdes df loqding is elaborated. i,

c) Information provided on the modulus of elasticity and rigidity as a function of operating temperaturefor mat&ial; s~ecified.

,. ,!,. ., , .,

‘This standard is one of the series of st&~ards on design, calculation &d specifications of helical coiled springs.Other standards in this series are: .,

I IS No.

~7906

(Part 1): 1997(Part 2): 1975(Part 3): 1975(Part 4): 1987(Part 5): 1989

7907(Part 2): 1976(Part 3): 1975(Part 4): 1987

Title

Helical compression springs:Design and calculations for springs made from circular section wire and barSpecification for cold coiled springs made from circular section wire and barData sheet for specifications for springs made from circular section wire and barGuide for selection of standard cold coiled springs made from circular section wire and barSpecification for hot coiled springs made from circular section bars (second revision)

Helical extension springs:Specification for cold coiled springs made from circular section wire and barData sheet for specification for springs made from circular section wire and barGuide for selection of standard cold coiled springs made from circular section wire and bar

The object of the present standard is to provide an accurate and rapid method of determining the dimensions ofhelical extension springs made fkom circular section wire and bar. It can be used both for calculating thespecification from available data and also for checking purposes. Worked examples have been included to promoteunderstanding of the calculation methods.

The main requirements to be satisfied in the design of helical springs are maximum possible dependability andlife combined with lowest possible weight and cost. At the same time the expenditure of time and effort involvedin the calculation procedure needs to be reduced as much as possible. Two nomograms have been incorporatedin the standard which can be used as a rapid method of arriving at provisional figures.

In spring calculations a distinction is made between springs subjected to a static or infrequently varying load andsprings subjected to alternating load.

The cross-section of the wire or bar of which a helical spring is made is stressed mainly in torsion. In thecalculations, therefore, the shear stresses likely to occur under load are compared with the permissible shearstresses. The stressing imposed on the spring, consisting in fact of an overwhelmingly torsional element and anegligibly small bending element, is more severe on the inside of the coil than on the outside. This stress maximumis taken into account in the calculation by introducing stress correction factor, k. Tests have shown, however, thatstress correction factor k can be omitted in calculations concerned with springs subjected to a static or infrequentlyvarying load.

(Continued on third cover)

r., J.. —_

IS 7907 (Part 1) :2004

Indian Standard

HELICAL EXTENSION SPRINGS

PART 1 DESIGN AND CALCULATION FOR SPRINGS MADE FROMCIRCULAR SECTION WIRE AND BAR

(First Revision)

1 SCOPE

This standard (Part 1) lays down calculations for designof helical extension springs made from circular sectionwire and bar.

1.1 Itapplies to cold and hot coiled springs loaded inthe direction of the spring axis and operated at normalroom temperature. For operations at considerablyhigher or lower temperatures, spring manufacturershould be consulted.

The values specified in Table 1 shall also apply.

Table 1 Quality Requirements of Hot and ColdFormed Extension Springs

(Foreword and Clause 1.1)

SI Spring Cold Formed Hot Formed

No. Parameter Extension Extension

Springs Springs

(1) (2) (3) (4)

i) Diameter of wire Not exceeding From 10 to 35 mmor rod, d 17mm

ii) Mean coil Not exceeding Not exceeding

diameter, D 160 mm 300 mm

iii) Number of active Not less than 3 Not less than 3

coils, niv) Spring index, w From 4 to 20 From 4 to 12

2 REFERENCES

The following standards contain provisions whichthrough reference in this text, constitute provisions ofthis standard. At the time of publication, the editionsindicated were valid. All standards are subject torevision, and parties to agreements based on thisstandard are encouraged to investigate the possibilityof applying the most recent editions of the standardsindicated below:

IS No. Title

3195:1992 Steel for the manufacture of voluteand helical springs (for railwayrolling stock) (third revision)

3431:1982 Steel for the manufacture of volute,helical and laminated springs forautomotive suspension (secondrevision)

IS No.

4076:1983

4454

(Part 1): 2001

(Part 2): 2001

(Part 4): 2001

7608:1987

7811:1985

7814:1985

7907(Part 2): 1976

(Part 3): 1975

3 SYMBOLS

Title

Hard brass wires for springsand other special purposes (firstrevision)

Specification for steel wires for coldformed springs:Patented and cold drawn steel wires— Unalloyed (third revision)

Oil hardened and tempered springsteel wire and valve spring wire —Unalloyed (second revision)

Stainless spring steel wire fornormal corrosion resistance (second

revision)

Phosphor bronze wire for generalengineering purposes @rst revision)

Phosphor bronze rods and bars (/lrst

revision)

Phosphor bronze sheet and strip@-st revision)

Helical extension springs:Specification for cold coiled springsmade from circular section wire andbarData sheet for specification forsprings made from circular sectionwire and bar

Following symbols and units shall apply (see Fig. 1).

A=

DO =

Di =

Dm =

G=

LO =

1

work done by spring, mJ;

outside diameter of coil, mm;

inside diameter of coil, mm;

D.+ D,mean diameter of coil, mm;

2modulus of rigidity of spring material,N/mmz;

unloaded length of spring (in the case ofsprings provided with loops or tapered-inhooks, this distance is measured from inneredge to inner edge of the loops or hooksunder loop length), mm;

,- - *.-.

IS7907

(Part

1):2004

I

0

‘i--=+-F

A——

—

2,-

L1 toLm =

LH –—

L~ -—

Lm =

FO =

F, to Fm =

Fm =

s, =

d- —

~ tofm =

h=

k ——

m——

n ——

t ——

w ——

Rm =

R, =

R,O =

R,l to R,m =

R=

R; =

R~l to R~m=

load lengths, measured from inner edgeto inner edge corresponding to the axialloads F, to Fm, mm;

distance of inside edge of the hook fromthe body of spring, mm;

body length when not loaded but subjectto initial tension, mm;

maximum allowable test length of spring,mm;

initial tension, N;

axial loads including initial tension FO,corresponding to the load lengths L1 toLm, N;

maximum permissible axial load corres-ponding to load length Lm, N;

~ = Spring rate, N/mm;

wire or bar diameter, mm;

deflections corresponding to the axialloads F, to Fm, mm;

stroke (differenceyieldedby two deflectionsor two load lengths, mm;

number of working coils;

total number of coils;it + Number of coils made non-workingby tapered-in or screwed-in end fittings;

stress correction factor, depending on thecoil ratio w. In springs subjected toalternating load the stress correction factork takes account of the non-uniform shearstress distribution over the wire cross-section resulting from the curvature of thewire (see 5);

hook opening width, mm;

load cycle frequency, Hz;

maximum working temperature, ‘C;

DQ = coil ratio;

d

ultimate tensile strength of the material,N/mmz;

uncorrected shear stress, N/mmz;

initial shear stress, N/mmz;

shear stress corresponding to the axialloads F1 to Fm for springs; subjected to astatic or infrequently varying load,N/mmz;

permissible shear stress, N/mm2;

corrected shear stress taking account ofthe influence of coil; curvature by meansof stress correction factor k, N/mmz;

corrected shear stress values corresponding

IS 7907 (Part 1): 2004

to axial loads F, to Fm; for springssubjected to alternating load, N/mm*; and

Rkh

= stress range corresponding to stroke h

(amplitude of stress), N/mm2.

4 DESIGN STRESSES

Prior to designing springs, it shall be specified whetherthey will be subjected to static loading, moderatefatigue conditions or fatigue loading.

4.1 Static Loading and Moderate Fatigue Conditions

a)

b)

Springs shall be deemed to be subject to staticloading where such loading does not changeover time.

Springs shall be deemed to be subject tomoderate fatigue conditions where the loadingchanges over time but the magnitude of meanfatigue stress is negligible (that is, it does notexceed a value of 0.1 times the torsional elasticlimit), or where the loading changes overtimeand the magnitude of mean fatigue stress ishigher than above, but the number of cycles towhich they are exposed does not exceed 104.

4.2 Fatigue Loading

a)

b)

c)

3

Springs shall be deemed to be subject tofatigue loading where the loading changesover time and the number of cycles to whichthey are exposed exceeds 104,at constant orfluctuating mean fatigue stresses exceeding0.1 times the torsional elastic limit.

Depending on the specified number of cyclesto failure, N, a distinction shall be madebetween:

1)

2)

springs with a high endurance life, thatis those which are able to withstand atleast 107cycles, where the mean fatiguestress is lower than the torsional elasticlimit; and

springs with a limited endurance life, thatis those which are able to withstand lessthan 107cycles, where the mean fatiguestress exceeds the torsional elastic limitbut is lower than the short-term fatiguestrength.

In the case of springs subjected to fluctuatingmean fatigue stresses or moderate stresseswhose maximum values are higher than thetorsional elastic limit, their endurance life canonly be’: ‘imated with the aid of the damageaccumulation hypothesis and shall beestablished more accurately by means offatigue testing in service.

IS 7907 (Part 1): 2004

5 SPRING DESIGN FORMULAE

5.1 Shear Stresses

8x Dmx FR, =

nd’...(1)

~ =kx8x Dmx Fk ..

nd’

~ =kx Gxdxfk

zi, x (D~ )2

5.2 Wire or Bar Diameter, d

.(2)

,(3)

...(4)

‘=PT=PT ...(5)

5.3 Deflection, f

f.8x( D~)3xi, xF

Gxd4...(6)

In the case of extension springs with initial tension thedifference (F – FO) shall be substituted for F.

5.4 Number of Working Coils, it

Gxd’xfi, =

8X(D. )3 XF.,,.(7)

In the case of extension springs with initial tension,the difference (F–FO) shall be substituted for F.

The following expression gives an approximate figurefor the total number of coils in an extension springwith initial tensions:

L~ig= —-l

d...(8)

For extension springs with open loops as given inFig. 2 to Fig. 9 and Fig. 14 of IS 7907 (Part 2), it= i .

“kFor extension springs with tapered in hooks or wltthreaded plugs, as shown in Fig. 10 to Fig. 13 of1S 7907 (Part 2), ig = it+ number of coils renderedineffective.

5.5 Load, F

~= Gxd’xf

8x(D~)3 xi,...(9)

In the case of extension springs with initial tension,the difference (F–FO) must be substituted for F.

5.5.1 A4axirrtum Permissible Load, F.

xd’F=— x Rp

8xDm

5.6 Spring Rate, SC

For extension springs without initial tension:

SC=A~=~=Gxd4

Af f 8x( D~)’ xi,

For extension springs with initial tension:

...(10)

...(11)

S .AF F–FO Gxd4—=— =

CAff 8x( D~)3xi,...(12)

5.7 Initial Tension, F.

Gxd4xfFO=F-fx SC= F-

8x(D~)’ xi,...(13)

5.8 Work Done by Spring, A

A=~x(F+FO)xf ...(14)

5.9 Modulus of Rigidity, G

The modulus of rigidity for wires for design of springis as given in Table 2. These values are given at ambientworking temperature:

Table 2 Values of Modulus of Rigidity ofSpring Wire Materials

(Clause 5.9)

s]No.

O

ii)

iii)

iv)

v)

vi)

Material Modulus of

Rigidity, G N/mmz

Patented and cold drawn spring steel 81370

wires-unalloyed, Grades 1, 2, 3 and

4 to Is 4454 (Part 1)

Oil hardened and tempered spring 81370

steel wire and valve spring wire-unalloyed, Grades SW and VW toIs 4454 (Part 2)

Alloyed, oil hardened and tempered 81370

value spring wire and spring steelwire for use under moderately

elevated temperature, Grades 1S, 2S,ID and 2D to IS 4454 (Part 2)

Hot rolled steel for hot formed 80000

springs, Grades 1, 2 and 3 to1s 3431.

Hot rolled steel for hot formed 80 Ooi-r

springs, Grades 98C6, 113C6,

55Si7, 60Si7, 50Cr4V2 and

60Cr4V2toIS3195

Stainless spring steel wire, Grade I 73530 (tempcxed)

to Is 4454 (Part 4) 69610 (untempered)

Table 2 (Concluded)

SINo.

vii)

viii)

ix)

x)

xi)

Material Modulus ofRigidity, G N/mmz

Stainless spring steel wire Grade 2 78430 (tempered)to 1S 4454 (Part 4) 73530 (untempered)

Hard drawn brass wires to 1S 4076 35000

Phosphor bronze wire for general 42000

engineering purposes to IS 7608

Phosphor bronze rods and bars to 42000

1S7811

Phosphor bronze sheet and stri~ to 42000

1s 7814

NOTE — If the springs are made from wires to IS 4076 and

IS 7608/78 11/7814 wire diameters not covered in Jhese

standards may conform to IS 4454 (Part l).

5.9.1 For materials other than those specified in 5.9,the values of G shall be obtained from the manu-facturer.

I =Od

FIG.

1S 7907 (Part 1): 2004

6 STRESS CORRECTION FACTOR, k

The curvature of the wire or bar axis brings about anunsymmetric distribution of shear stress over the wireor bar cross-section when an extension spring isextended. The shear stress is higher on the inside ofthe coil than on the outside (see Fig. 2). This leads to astress maximum in the inside fibres which may giverise to cracks followed by fatigue failure in the case ofalternating load,

6.1 The stress correction factor, k in the designformulae (3) and (4) makes allowance for the stressmaximum developed. The design calculations ofextension springs subjected to alternating load should,therefore, contain factor, k.

6.2 Correction factor, k depends on the coil ratio, wand increases rapidly as the coil ratio becomes smaller(see Fig. 3). The formula corresponds to that given byBergstraessar.

mz MAXIMUM MINIMUM6 ‘ SHEAR SHEARg STRESS STRESS

En

“}-+-42 DISTRIBUTIONOF SHEARSTRESSESOVER CIRCUMFERENCEOF WIRE

ORBAR CROSS-SECTIONOFA HELICALSPRING

11.55

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1S 7907 (Part 1) :2004

6.3 In the case of extension springs subjected to a 600 N/mm2 for the maximum permissible load F~

static or infrequently varying load, the local stress should not be exceeded.maximum is not harmful owing to the supporting effect

8.2.1 Hot coiled extension springs may only beof less strained regions of the cross-sections. The designcalculations of these springs can be carried out without

used in bar diameters up to 25 mm maximum. For

using the stress correction factor, k,manufacturing reasons it is recommended that the typewithout loops and with threaded end plugs to

7 INITIAL TENSION, F’O IS 7907 (Part 2) should be used.

Initial tension is the load needed to overcome theforce which presses coils against one another. Initialtension is introduced by coiling the springs so thatthe coils exert a certain pressure against each other.The initial tension obtainable in this way is governedprimarily by the quality of the wire, the diameter d

of the wire, the coil ratio w and the manufacturingmethod used. In addition, the initial tension dependson the maximum shear stress R,~ (see 8.3). Theintroduction of initial tension FOis only practicablefor cold coiled extension springs which are notfinally hardened.

7.1 Extension springs with initial tension have theircoils pressed tightly together. It may be specified foran extension spring that its coils shall lie loosely incontact with each other without any initial tension. Insuch cases, however, a small amount of initial tensionshall be accepted, since it is not possible to achieveuniformly tensionless coiling

7.2 Hot coiled extension springs cannot be made withinitial tension. The heat treatment applied causes airgaps to occur between the coils, the size of the gapsbeing dependent on the coil ratio w and the degree ofstressing. For hot coiled extension springs up to 25 mmbar diameter the following approximate figures apply:

Space between coils = 0.5 to 5 mm correspondingto a permissible shear stress, R,ps 400 to 600 N/mm2(at maximum load FJ.

8.3 Initial Shear Stress, (RJ

The stress experienced by cold coiled extension springsas result of the initial tension FOis called the initialshear stress, R~O.

8.3.1 The attainable initial tension, FOdepends on thelevel of the permissible initial shear stress, R,O. Thelatter can be found from Fig. 7 to Fig. 14 for variousconditions.

8.3.2 Assuming otherwise similar conditions, the levelof the initial shear stress, R,O is in turn influenced bythe manufacturing method (coiling on hand coilingmachines or on automatic toilers).

8.3.3 In the design of extension springs with initialtension, therefore, it shall be borne in mind thatautomatic toilers can produce more economically, butthe initial tension obtained is not high.

8.3.4 Under certain working conditions, for example,when high initial tension and small deflection aredesired, it is possible that at the maximum load F~ thepermissible value of shear stress, R,p will not be fullyexploited (Fig. 4 to Fig. 6). In this case the indicatedvalues of initial shear stress R,p for hand coilingpurposes (see Fig. 7, Fig. 9, Fig. 11 and Fig. 13) canbe exceeded. The spring manufacturer’s advice shouldbe sought where necessary.

8.3.5 Examples of spring design calculations are givenin Annex A.

8 CALCULATION AND DESIGN OF EXTENSION 9 CALCULATION AND DESIGN OF EXTENSION

SPRINGS SUBJECTED TO A STATIC OR SPRINGS SUBJECTED TO ALTERNATING

INFREQUENTLY VARYING LOAD LOAD

Apart from the space available, the principal data for The calculation and design of cold coiled extension

the design of an extension spring are the work done by springs subjected to alternating load is difficult, owing

the spring and the maximum permissible load F~. to the characteristic form of extension springs. Whenan extension spring is extended the cross-section of

8.1 Permissible Shear Stresses, R,p for Cold Coiled the wire, comprising the working coils, experiencesExtension Springs stress differences through the curvature of the wire axis

For cold coiled extension springs the values of R,pin just the same way as compression springs (see

shown in Fig. 4, Fig. 5 and Fig. 6 may be taken as the Fig. 2). The stress maximum arising in this way should

basis for the load F~, but these values may not be be taken into account by calculating with stress

exceeded. correction factor, k (see 6).

8.2 Permissible Shear Stress, R,p for Hot Coiled9.1 Calculation with k is only effective for the working

Extension Springscoils. The criterion for these, apart from the availablespace, is the stress range R,k, that is, the difference of

For hot coiled extension springs the value R =5P

the shear stresses at F] and”’~2.

6

.. -—

n-i.u 1 1 1 I 1 I 1 1 i I I 1 I r

Li-R ~p= 0.45 Rm 1111 {11Rm =

IS 4454 (Part 1) ! I I I I I I1

1 1

MINIMUM VALUE OF TENSILESTRENGTH ACCORDING TO

11111111!s= I I I 1 1 I I I 1 , ,

I I I I I

1 –I I 1 I I 1 I 1 I 1 1 I

9 10 11 12 13 14 15 16

WIRE DIAMETER d, mm ~

FIG. 4 PERMISSIBLESHEARSTRESSR,, FORCOLD COILEDEXTENSIONSPRINGSMADE OF COLDDRAWNANDPATENTEDSPRINGSTEELWIRES GRADES1,2, 3 AND4 TO IS 4454 (Part 1)

.s

2

17

-dm

A

Y!

cc

Lo

‘* 750CKa

HARDENED AND TEMPERED SPRING STEEL WIRE

IHARDENE13 AND TEMPERED VALVE SPRING WIRE

I I I I I I I I 1 1

I I IRp =0.5Rm IIrKmlutiRm = MINIMUM VALUE OF ULTIMATE TENSILE

7STRENGTH ACCORDING TO IS 4454(PART 2)

-+— — —

-WA!

1 I I [ Ill I1 I I I ! 1 I 1 1 I I I I I I

i 2 3 4 5 6 7 8 9 10 ~1 12 13 1~ 15 16 17

WIRE DIAMETER d, mm ~

1-W..

N00a

FIG.5 PERMISSIBLESHEARSTRESSR,, FORCOLD COILEDEXTENSIONSPRtNGSMADEOF OrLHARDENEDANDTEMPEREDSPRINGSTEELWIRESANDVALVESPRINGWIRES— UNALLOYEDGRADESSW ANDVW TOIS 4454 (Part 2)

IS7907

(Part1)

:2004

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d

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300

280

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100

80

60

I 1 I 1 1 1 I

IW=4 t I I I I

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W=12

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FIG. 7 HAND COILING— APPROXIMATEVALUESOFPERMISSIBLEINXTIALSHEARSTRESSESRWFORCOLDCOILEDEXTENSIONSPRINGSMADE FROMCOLDDRAWNANDPATENTEDSPRINGSTEELWIRES

OFGRADES3 AND4 TO IS 4454 (Part 1)

10

IS 7907 (Part 1) :2004

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260

240

220m

180

160

140

120

100

80

60

40

20

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WIRE DIAMETER d, mm

FIG. 8 AUTOMATKCOILING— APPROXIMATEVALUESOF PERMLWBLEINITIALSHEARSTRESSESR~ FOR

COLD COILEDEXTENSIONSPRINGSMADE FROMPATENTEDANDCOLDDRAWNSPRINGSTEELWIRES

OF GRADES3 AND4 TO IS 4454 (Part 1)

11

,-k.. -.

240

220

200

180

60

40

201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

WIRE DIAMETER d, mm

FIG. 9 HANDCOILING— APPROXIMATEVALUESOF PERMISSIBLEINITIALSmwt Smwss RW FORCOLDCOILEDEXTENSIONSPRINGSMADE FROMPATENTEDANDCOLDDrum SPRINGSTEELWnws OFGRADE2 TOIS 4454 (Part 1)

\

. ..’

w

240

220

200

180

60

40

20

FIG. 10 AUTOMATICCOILING— APPROXIMATEVALUESOF PERMISSIBLEINITIALSHEARSTRESSRW FORCOLDCOILEDEXTENSIONSPRINGSMADEFROMPATENTEDANDCOLDDRAWNSPRINGSTEELWIRESOFGRADE2 TOIS 4454 (Part 1)

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FIG. 12 AUTOMATICCOILING— APPROXIMATEVALUESOF PERMISSIBLEINITIALSHEARSTRESSR,O

yFORCOLD COILEDEXTENSIONSPRINGS

MADE FROMPATENTEDANDCOLD DRAWN SPRINGSTEELWIRESOFGRADE 1 TO IS 4454 (Part 1)

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180

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FIG. 13 HAND COILING— APPROXIMATEVALUESOF PERMISSIBLEINITIALSHEARSTRESSRW FORCOLD COILEDEXTENSIONSPRINGSMADE FROMOIL HARDENEDANDTEMPEREDSPRINGSTEELWnws — UNALLOYEDGRADESW TOIS 4454 (Part 2)

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17WIRE DIAMETER d, mm

;

FIG. 14 AUTOMATICCOILING— APPROXIMATEVALUESOF PERMISSIBLEINITIALSHEARSTRESSR~ FORCOLDCOILEDEXTENSIONSPRINGS

MADE FROMOIL HARDENEDAND TEMPEREDSPRINGSTEELWIRES— UNALLOYEDGRADESW TOIS 4454 (Part 2)

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IS 7907 (Part 1) :2004

9.2 The life of extension springs is also affected inparticular by the form of the loops or end fittings. Atthe transition between the spring body and the loops, aloaded spring undergoes extra stressing which may goconsiderably above the permitted values of stress. Thatis why no universally valid fatigue strength figures canbe given. When possible, therefore, it is desirable toavoid using extension springs under conditions ofalternating load, particularly since cold work hardeningby shot peening, which is an important method ofincreasing the fatigue strength of compression springs,is impracticable owing to the fact that the coils are inclose contact with each other.

9.2.1 When the use of an extension spring underalternating load is unavoidable, the spring specifiedmay be of the cold coiled type with tapered-in orscrewed-in end fittings to Fig. 10 to Fig. 13 ofIS 7907 (Part 2). If imperative design reasons makethe use of loops or hooks necessary, however, the radiusof curvature at the transition point should be at least1.5 d. It is advisable to polish or shot-peen extensionsprings with a view to reducing stress concentrationpoints. If Fz is equal to F~ for an extension springsubjected to alternating load and if this result in thelimit R,P being reached, then it must be considered thatafter a certain operating period the load F2 will becomesmaller owing to a decline in the initial tension FO.

Even failure through excessive fatigue of the materialis not ruled out.

9.3 Hot coiled extension springs are not recommendedfor alternating loads.

9.4 Where special applications are involved, it isadvisable to consult the spring manufacturer regardingthe form of loops or end fittings.

10 NOMOGIWWS FOR PRELIMINARY DESIGNCALCULATION

10.1 Nomograms as shown in Fig. 15 and Fig. 16 forhelical springs embody the wire or bar diameter d theshear stress R%the load F and the mean coil diameterD~ in the relationship given by equation (l).

10.2 The two nomograms are an aid to be used inpreliminary design calculations (see example below).It is not possible to make an exact calculation of datawith their aid. Nomogram as shown in Fig. 15 isintended for the preliminary calculation of the smallersizes of springs and nomogram as shown in Fig. 16 forthe preliminary calculation of the larger sizes. The twoinner scales for F and Dm and the two outer scales forR, and dare always used together in pairs. Each pair ofscales is joined by a straight line. The straight linethrough F and Dm and the straight line through R, andd must intersect the pivot line in the same point.

Example (see Fig. 15):

Given: loadF= 550 N, mean coil diameterD. = 32 mm

Find: wire diameterd and shear stressR,

Join the point for F= 550 N with the point for D~ =

32 mm by a straight line. Pivot a second straight lineon the point of intersection of the first line with thepivot line. The second line gives the shear stress R, forvarious values of d. The result obtained for d = 4.5mm is R** 480 N/mm*.

18

- . .&. -.

IS 7907 1) : 2004

Rs FN/mmz N

& 2000

1500

Dm d

1000mm mm

900L 20

800 181500 — -

700 16

600 14

900 12

800700 10

600 - ~ 300 9

500 8

400 300 — _ 7

200

300 —

200 100908070

3060

20100 ~ — 5090 – -80 – — 40 1070 — - w60 — – 30 z

55

50 — - 1-g 4— .

40 – — 20 K 3- -1.5

2T -

30 — -

1- -

20 – — 101

0.9

0.8

0.7

10 – — 5 0.6

0.5

[

0.4

2v 0.3

FIG. 15 NOMOGRAMFORPRELIMINARYDESIGN CALCULATIONSOF SMALL SIZE SPRINGS

19

,...

IS 7907 (Part 1): 2004

R.N/mma

1500 + -

1000900800‘loo

600

500

Loo

300-

200- -

100

FN

100000900000000070000

60000

50000

40000

30000

20000

10000900000007000

6000

5000

4000

3000

2000

1000900800700

600

500

400

300

200

\oo

FIG. 16 NOMOGRAMFORPRELIMINARYDESIGNCALCULATIONSOF

Dm dmm mm

50

45

40

35

30

25

20

15

1000900600 10

500 9400

300e

200 7

6

10089 5

6050 y40 -

30-

20-

LARGESIZE SPRINGS

20

“ —

IS 7907 (Part 1) :2004

ANNEX A

(Clause 8.3.5)

EXAMPLES OF SPRING DESIGN CALCULATIONS

A-1 CALCULATION OF A COLD COILEDEXTENSION SPRING SUBJECT TO A STATICOR IN FREQUENTLY VARYING LOAD ANDWITH INITIAL TENSION

An extension spring is required with Form B loops toFig. 3 of IS 7907 (Part 2), for a load F, = 250 N at adeflection ~1 = 30 mm and a spring length L, s180 mm. The spring shall permit a further stroke ofapproximately 65 mm without the load Fz = F~

exceeding 550 N. The space available admits anoutside diameter of coil DOof not more than 40 mm.It is thus necessary to determine the requisite springdata, that is d, LO,L~, ie FO,R,O,R,l, R,l and the springmaterial.

A-1.l Wire Diameter, d

From Equation (5):

In Equation (5) R, has to be replaced by the permissibleshear stress R, the values of which can be taken fromFig. 4 to Fig. {. It can be found by trial and error fromthe nomogram (see 10) as follows:

On

Using the nomogram as shown in Fig. 15 drawa straight line joining the maximum load; F~ =

F2 = 550 N and the diameter D~= 32 mm, beingthe value assumed on the basis of the availablespace. This line cuts the pivot line at a pointwhich serves as a pivot for a second straight line.By rotating this second line coordinate valuesof the shear stress R~ and the diameter d can befound. Diameter d= 4.5 mm, for example, yieldsR,= 480 N/mm*. According to Fig. 4 spring steelwire of Grade 2 to IS 4454 (Part 1) having R,P =

660 N/mm* is suitable for this purpose.

using this value in the calculation, the followingresult is obtained:

‘=R2F=41mmThe next larger wire diameter to IS 4454 (Part 1)namely, d = 4.25 mm, is selected.

A-1.2 Length of the Unloaded Spring, LO

LO= L1–fi = 180-30 = 150 mm

A-1.3 Body Length of the Unloaded Spring Subjectto Initial Tension, L~

From IS 7907 (Part 2) Fig. 3, it is seen that.

L~=LO–2LH= L0–2X0.8XDi

D, = D. – d= 32 – 4.25 = 27.75 mm

L~= 150–2 x 0.8 x 27.75= 105.6mm

A-1.4 Number of Working Coils, it

According to 5.4, if = it for extention springs with openloops. Using Equation (8):

L~i~=i, =—–l

d

i _ 105.6t -—-1=24

4.25

A-1.5 Initial Tension, FO

From Equation (13):

F _F Gxd4xfo-

‘8x(D~)3 xi,

Since F, and~ are given, these values are inserted forF and$

Fo=fl -Gxd4x&

8x( D~)3xi,

Putting G = 81370 N/mm* (according to 5.9) gives:

F. = 250-81370X(4.25)4X30 =128 8N

8 X(32)3X 24

A-1.6 Deflection,J2

From Fig. 1 the following relationship is derived:

f2 =550-128.8

x30 = 100.4 mm250-128.8

21

.-

IS 7907 (Part 1) :2004

A-1.7 Length, L2

= 100.4 + 150 = 250.4 mm

The stroke between LI and Lz is Lz – L] = 250.4 – 180= 70.4 mm

A-1.8 Coil Ratio, W

32w=% .— = 7.53d 4.25

A-1.9 Checking the Initial Shear Stress, R,O

From Equation (l):

RW =8x32

x128.8 = 134.5 N/mm2Z(4.25)3

For spring steel wire of Grade 2 to IS 4454 (Part 1),Fig. 9 gives a value of approximately 135 N/mm* aspermissible for R,O(obtained by interpolating between

the curves for w= 4 and w= 12) assuming hand coilingwith w = 7.5 and d= 4.25 mm.

A-1. 10 Checking the Shear Stresses R,l and R$2

8xD XF4= ~;,

8x32XF =1.06F

= n (4.25)3

R,l = 1.06 x F,

= 1.06 x 250= 265 N/mm2

R,2 = 1.06 XF,

= 1.06 x 550= 583 N/mm2

The above values are permitted by Fig. 4 (R,P =

670 N/mm*).

The first calculation performed does not always yieldthe desired and permitted results. In such cases thecalculation must be repeated by starting from differentassumptions.

A-1.11 Summary of Spring Data

The data comprising the spring specifications shall beentered in the form according to IS 7907 (Part 3).

22

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IS 7907 (Part 1) :2004

ANNEX B

(~oreww~

COMMITTEE COMPOSITION

Automotive Springs and Suspension Sectional Committee, TED 21

Organization

Tata Motors Ltd, Jamshedpur

Akal Springs Pvt Ltd, Ludhiana

All India Springs Manufacturers Association, Mumbai

Ashok Leyland Ltd, Chennai

Association of State Road Transport Undertakings, New Delhi

Central Institute of Road Transpo~ Pune

Central Mechanical Engineering Research Institute, Drrrgapur

Conventry Springs & Engineering Co Pvt Ltd, Kolkata

CQA (OFV) Vehicle Factory, Jabal Pur

Gabriel India Ltd, Mumbai

Jai Parabolic Springs Ltd, Chandigarh

Jamna Auto Industries Ltd, Yamrrna Nagar

Kemen Springs Pvt Ltd, Mumbai

Mack Springs Pvt Ltd, Tharre

Mahindra & Mahindra Ltd, Nashik

Maruti Udyog Ltd, Gurgaon

Ministry of Heavy Industry & Public Enterprises, New Delhi

Research Designs & Standards Organization, Lucknow

Stumpp, Schuele & Somappa Pvt Ltd, Bangalore

The Automotive Research Association of India, Pune

Upper India Steel Manufacturing & Engineering Co Ltd,

Ludhiana

Vehicle Factory, Jabaipur

BIS Directorate General

Representative(s)

SUUI A. G. PRADHAN (Chairman)

SHRI K. GOPALAKRJSHNA(Alternate)

GENERAL MANAGSR

SHRI A. A. MIRCHANDANI

SNRI APPALARAJU

SHRI U. JAIKRISHNA(Alternate)

SIIRI A. S. LAKRA

Sum P. M. PHATS (Alfernale)

Stuu N. R. KACNARE

StIRI P. S. MUNOU (A/fernate)

DR J. BASU

DR T. K. PAUL (A1/erna/e)

SHRI A. BAPNA

SHru A. S. KotlLl (Ahernafe)

GENERALMANAGER

SHRI K. SUNOARARAMAN

SMRI S. K. BHAUMICK (Alfernate)

SHRI SUNIL HAROLIYA

SHRI D. S. GILL

SHRI B. K. KHANDELWAL(Alferna/e)

SHRI P. K. MIRCNANOANI

SHiU D. V. SHARMA

SHRI RAVINDRA DSSNMUKH

SHRI KAILASN JAT (AOerrrate)

SHRI D. N. DAVE

SHJUG. VIJAYAN (Alternate)

SHW S. K. BNAKJJ

SHRI R. K. TRJPATHI(Ahernale)

JoIrw DIKSCTOR (STANDARDS)

ASSISTANTDSSIGN ENGINEER

SHJUB. S. MOOKHSRJSE

SHiU N. C. SRJNIVASAN(Alternate)

!$HRJS. RAJU

SHRJ R. P. ENGIRA

SHJU M. K. MISHRA

Sms R. LODWAL (Af/errrate)

SHRJK. K. VASHISTHA, Dkcctor & Head (TED)

[Representing Director General (Ex-o@cio)]

Member &cretarySHRI P. K. SHARMA

Dhector (TED), BIS

23

,- +,..

(Continuedfiom second cover)

If the shear stresses occurring in the spring remain below the permissible range of stress or below the fatiguestrength values in the case of springs subjected to alternating’ load, the spring will not fail due to fatigue withinthe envisaged life.

The permissible shear stresses and initial shear stress figures for cold coiled springs have been included forspring materials meeting general requirements.

In the preparation of this standard considerable assistance has been derived from DIN 2089 (Part 2) : 1992‘Design of cold or hot formed helical extension springs’ issued by Deutsches Institut tltr Normung (DIN).

The composition of the Committee responsible for the formulation of this standard is given at Annex B.

In this standard the unit of force used is Newton (N) and that for stress is N/mm2:

1 kgf = 9.80665 N (exactly)

or 1 kgf x 9.81 N (approximately)

s 10 N (within 2 percent error)

1 N/mm2 = 1 MN/m2

= 1 MPa [1 pascal (Pa)= lN/m2]

s 0.1 kgf /mm2 (within 2 percent error).

For the purpose of deciding whether a particular requirement of this standard is complied with, the finalvalue, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance withIS 2:1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retained in therounded off value should be the same as that of the specified value in this standard.

Jib

Bureau of Indian Standards

BIS is a statutory institution established under the Bureau oflrrdian Standard Act, 1986 to promote harmoniousdevelopment of the activities of standardization, marking and quality certification of goods and attending toconnected matters in the country.

Copyright

BIS has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course of implementingthe standard, of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating tocopyright be addressed to the Director (Publication), BIS.

Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, h is taken up for revision. Users of Indian Standards

SI1OUId ascertain that they are in possession of the latest amendments or edhion by referring to the latest issue of‘B 1S Catalogue’ and ‘Standards: Monthly Additions’.

This Indian Standard has been developed from Dot: No. TED 21 (341).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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*

....—,–. _.

k-