Disclosure to Promote the Right To Information

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1 इ टरन ट म नक Disclosure to Promote the Right To nformation Whereas the Parliament of ndia 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 ndian 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. ज न1 क अ+धक र, ज 1 क अ+धक र Mazdoor Kisan Shakti Sangathan The Right to nformation, The Right to Live प0र 1 क छ ड न' 5 तरफ Jawaharlal Nehru Step Out From the Old to the New S (1978): Helical Compression Springs, Part V: Design and Calculations for Springs Made from Rectangular Section Bar-Steel [TED 21: Spring]! न $ एक न' भ रत क +नम-ण Satyanarayan Gangaram Pitroda nvent a New ndia Using Knowledge! न एक ऐस खज न > ज कभ च0र य नहB ज सकत ह ह Bhartṛhari Nītiśatakam Knowledge is such a treasure which cannot be stolen

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4 UDC : : 666*76 ( Second Reprint SEPTEMBER 1993 ) [ Reaffirmed1990) -1 /ndian Standard HELCAL COMPRESSON SPRNGS PART V DESGN AND CALCULATONS FOR SPRNGS MADE FROM RECTANGULAR SECTON BAR-STEEL. Scope- Lays down calculations for design of helical compression springs made from rectanguar or square section wire or bar. 1.1 This standard applies to springs of special designs where it becomes imperative to use them fue to space limitations. Springs made from rectangular section bar should be avoided as far as )ossible as the springs made from circular section bar can be stressed to the same values for a ower weight of material used and for shorter overall length. The design of such springs is based )n the final rectangular section. Suitable trapezoidal section may have to be selected to arrive at inal rectangular section.!. Terminology - Following symbols shall apply ( see also figure )., A fl b = Side of cross-section perpendicular to axis of the spring, mm! i i : t c fl, f2 = Sp.ring deflections corresponding to axial loads F, f2, mm fb = Lo - LB - Spring deflectlon in mm, related to axial load FE, mm h = Side of cross-section parallel to axis of the spring, mm if = Number of working coils 10 = Total number of coils & w = - = Coil ratio ( w ) 4 ) b Do = External coil diameter, mm 0, = nternal coil diameter, mm & = Mean coil diameter, mm Fl, F2, etc = Axial load, related to load lengths, L, LP, etc, N Adopted 26 December June 1979, BS Gr3. BUREAU OF NDAN STANDARDS MANAK BHAVAN. 9 BAHADUR SHAH ZAFAR MARG NEW DELH

5 S : 7906 ( Part V ) Fe = Axial load related to length of compressed spring Ls, N G - Modulus of rigidity, N/mm? LO = Length of unloaded spring, mm L, LZ = Load lengths of spring, mm fs = Length of compressed spring (all coils closed ), mm R, = Shear stress under load F, N/mm2 R,B = Shear stress under load FB, N/mm* Spring rate, N/mm E = Elasticity ( resilience) coefficient, dependent on ratio of cross-section side lengths b/h or h/b. $ = Stress coefficient, dependent on ratio of cross-section side lengths b/h or h/b and on coil ratio w. 3. Type of Coiling -Springs made from rectangular section bar are used with advantage tor the types of coiling given in 3.1 and Coiled on Edge - n this case longer side of the cross-section is perpendicular to the axis of the spring. This type of coiling enables large deflections, short block lengths and a high ratio of internal to external coil diameters. 3.2 Flat Coiled -n this case the longer side of the cross-section is parallel to the axis of the sphng. This type of coiling enables large free lengths and low ratios of external to internal diameters. 4. Loading - Spring made from rectangular section bars are usually used to obtain the maximum load capacity for a given space. Consequently such springs are often highly stressed. Long service cannot be expected under such conditions, especially if the range of stress is high as well as the stress at maximum load. 5. Design Formulae 5.1 Shear Stress, R, J x Dm R *= bxhxbxh 5.2 Spring Deflection, f f- E x D,,,3 x if. 6 x h* x3 F 5.3 Number of Turns b x h* x G 1, = --- E X SC X D,,,3 ig - if

6 S : 7906 ( Part V ) Values of dr and E are given in figure below. 2 VALUES FOR W 5 h Values for E: b h - or - h b l l E ' b - h or $ E la Examples of design of compression springs made from square and rectangular section material are as follows: Example A A-. Design of cold coiled compression spring made from square section material, subjected to a static or infrequently varying load. A compression spring is required to meet a load F = 250 N at L = 50 mm and F2 = 400 N at f2 = 40 mm. The space available permits a maximum outside coil diameter Do = D,,, + b = 30 mm. A-Y.1 Spring rate SC from F, F2 and L, Lp is obtained as under: -~= F2 - fl 150 N Ll - LP O mm = 15 N/mm 3

7 S : 7906 ( Part V) Moreover, from load/deflection line we can obtain the free length as under: f+,( kz;,)=250n x -$= mm The free length of the spring is therefore LJ = mm = mm t-1.2haytr;i a mean Dia Dm = 26 mm, so that the side length of the section is restricted to - From formula 5.3 7c-- h2 6 E x Sc x Dm3 f G 5 59 x 15 x 263 = ----X h2b2 -.- = -_ h4 = f f. h4.. jf since h = b ;;.3 Assuming a minimum space S, between individual coils as 0 1 x h since the specified length = 40 mm, we have the following: (if +2) h+if x S, -40 ( if h -- 2h ) + (if x 0 1 h ) = 40 jf=+!l($--2) :.-;y (T - 2)= &- The result of the graphic solution is b = h = 3 5 if = and fb = mm Coil ratio W -+- = 7 65 A-l.4 Checking the maximum shear stress from formula 5.1 R 8 4~ x Dm x Flax h3 = 2 4 x 26 x = 745 N/mm* The above stress is safe and plain carbon spring steel wire can be chosen for the manufacture of the springs. 4

8 S : 7906 ( Part V ) Example B Design of a cold coiled helical spring made from rectangular section wire subjected to a static or infrequently varying load. B-l. A compression spring is required to meet a load F1 = 530 N at L - 55 mm and F2 = N at Ls = 45 mm. The space available permits a maximum outside dia Do = Dm -- b of 25 5 mm and a rod of 14 mm should pass freely inside the spring in fitment. B-l.1 Spring rate SC from F, FP and L, fp is obtained as under: F2 - F 4 - L2 530 N = - = 53 N/mm 10 mm From load/deflection line we can obtain the free length as under: x 530=10mm The free length of the spring is therefore Lo = 65 mm B-1.2 Assuming a mean dia of Dm = 20 and b - 5 and h = 3 5 we shall calculate the number of coffs from formula 5 3 if = b x h* x G c x S, x Dm3 ~ 52 x 3 52 x x 53 x 203 = 10 coils 0 * =10+2=12 Solid height fs - 12 x 3 5 = 42 0 mm Assuming minimum space S, between individual COifS as 0 1 X h, the required total clearance is 0 1 x 3 5 x 10 = 3 5 mm whereas clearance available between $ and fs is only 3 mm, f-fence try alternative thickness of wire. Choose a thickness say 3 45 mm and recalculate the number of coils it = 52 x x x 53 x 203 = LBL = 40 mm 8-l.3 Check for maximum shear stress Rs~ from formula 5-l R do x & bxhxbxh sb = ~- X FB 3 15 x 20 x = _ x 3 45 x 5 x = N/mm2 n view of the above high stress, material chosen should be alloyed spring steel wire such as chrome silicon or chrome vanadium spring steel wire. 6. Shot Peening of Springs -Springs made from rectangular section bars may be shot peened to increase their life. Lower stress range shall be used for the purposes of calculations even when the springs are shot peened. 5

9 S : 7906 ( Part V ) EXPLANATORY NOTE This standard is one of a series of ndian Standards on the design, calculation and specifications of helically coiled springs. Other standards in this series are: S : 7906 ( Part )-1976 Helical compression springs: Part Design and calculation for springs made from circular section wire and bar S : 7906 ( Part )-1975 Helical compression springs: Part Specification for cold coiled springs made from circular section wire and bar S: 7906 (Part ll )-1975 Helical compression sprinns: Part Data sheet for specifications _- for springs made from circular section wire and bar S : 7906 (Part V)-1975 Helical compression springs: springs made from circular section bar S : 7907 ( Part )-1976 Helical extension springs: Part made from circular section wire and bar S : 7907 ( Part )-1976 Helical extension springs: Part made from circular section wire and bar Part V Specification for hot coiled Design and calculation for springs Specification for cold coiled springs S : 7907 (Part )-1975 Helical extension springs: Part Data sheet for specification for springs made from circuiar section wire and bar n the preparation of this standard, considerable assistance has been derived from DN Helical compression springs made of rectangular steel, calculation, issued by Deutsches lnstitut fur Normung. Reprography Unit, BS, New Delhi, ndia