spring rating

7/31/2019 Spring Rating

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S P R I N G C A L C U L A T I O N S

To Calculate Coil Spring Rate-

RATE= (9909 x material dia. x material dia. x material dia. x material dia.)

divided by

(no. of active coils x mean dia. x mean dia. x mean dia.)

Mean dia. = I.D. + material dia. All measurements are in millimetres Result is in N/mm To convert answer to Kg/mm = N/mm x 0.10192

To Calculate Coil Spring Stress-

STRESS= (2.545 x rate(N/mm) x required travel x mean dia. x Wahl factor)

divided by

(material dia. x material dia. x material dia.)

Mean dia. = I.D. + material dia. C: (spring index) = mean dia. / material dia. Wahl factor = (C+0.2) / (C-1) All measurements are in millimetres Results is in N/mm / MPa Stress not to exceed 827 N/mm / MPa

Please note these formulas are provided as a guide only. Industrial Engineers & Spring Makers (Sales)

Pty. Ltd provides no guarantee to their accuracy.


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Testing a spring

For a constant rate spring, that is exactly how you test the rate.

You must check the rate between 20 and 80 % of the total possible deflection range. Thedeflection range is the range from the free length to the solid length.

Example:Free Height: 10 inchesSolid Height: 5 inchesDeflection range would be from 10-5 = 5 inches.Rate must therefore be checked at heights between 9 inches and 6 inches.

Load at 8.5 inch height: 15 LbsLoad at 7.5 inch height: 25 Lbs

Rate = Difference in Load / Difference in Length= (25 15) / (8.5 7.5)

= 10 / 1= 10 Lbs / Inch

Hope this explains it to you. Any further questions, just mail them to us.

Kind Regard s,

Daniel Shepard .Managing Director.W H Rooke & Co.


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Techn i ca l I n fo rm a t i on

Techn ica l I n fo r m a t ion

The num ber o f co i l s

The number of coils in tensionsprings varies with commercialproduction as follows:

Number of Coils Tolerance

3 to 5 20

6 to 8 30

9 to 12 40

For each additional coil, add 1 per coil. Springs can be built to closer tolerances by trimming aftercoiling, with additional cost.

Exam ple Load To lerances :

The load tolerances for tension springs are listed in the above table. For example of how to use these,let us take a spring of the following dimensions: Free Length 4.050"; Mean Dia. .390"; Wire Dia. .048"to give a load of 3.5lb when extended .900".

First we calculate the index orD

d

=.390"

.048"

= 8

Secondly we calculate thath

f

=4.050"

.900"

= 4.5

FindD

d

= 8 on the table, take the adjacenth

f

= 4.5.

Where the line 4.5 intersects with the column of wire dia. of .048" we get a figure of 10.1%.

This is the load tolerance of the above example.

Convert 10.1% to 3.5 lb. which gives a tolerance of 5.6 oz. at .900" deflection.


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A-DActive coils (na):Coils that are free to deflect under load.

Angular relationship of ends:

Relative position (in degrees) of the plane of the hooks or loops of extension springs to each other.

Baking:

Heating of electroplated springs to relieve hydrogen embrittlement.

Closed ends:Ends of compression springs where the pitch of the end coils is reduced so that the end coils touch.

Closed and ground ends:

Same as closed ends except the end coils are ground to provide a flat surface.

Close-wound:

Coiled so that adjacent coils are touching.

Deflection (F):Motion of spring ends or arms under external load (P).

E-L

Free angle:

Angle between the arms of a torsion spring when no load is applied.

Free length (L):

Overall length of a spring when no load is applied.

Helix:

The spiral shape of compression, extension and torsion springs.

Hooks:Open loops at the end of extension springs.

Hydrogen embrittlement:

Hydrogen absorbed in electroplating of carbon steels causing the spring material to become brittle, leading

to cracking and spring failure.

Initial tension (Pi):The force that causes the coils of extension springs to stay together and which must be overcome before the

coils begin to open.

Load (P):The force applied to a spring that causes deflection.

Loops:

Closed hooks at the end of extension springs.

M-P

Mean coil diameter (D):Outside diameter (O.D.) of a spring minus one wire diameter (d).


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Open ends, not ground:

End coils of a compression spring having the same pitch as the body of the spring.

Open ends ground:

Same as open ends except the end coils are ground to provide a flat surface.

Passivating:The treatment of stainless steel springs with acid to remove contaminants and improve resistance to

corrosion.

Permanent set:

A condition that comes from deflecting a spring beyond the elastic limits of the material; the spring does not

return to its original condition when the load is released.

Pitch (p):

The distance between two adjacent active coils measured from the center of the wire of each coil.

Preset:To remove permanent set prior to application installation.

R-T

Rate (R):

Change in load per unit of deflection, usually in pounds per inch.

Remove set:The process of deflecting to solid height a spring which has been coiled longer than the requested finished

length, so as to increase the apparent elastic limit.

Solid height:

Length of a compression spring when it has been deflected enough to allow each adjacent coil to touch each

other.

Spring index:

Ratio of the mean coil diameter (D) of a spring to its wire diameter (d).

Squared and ground ends:See Closed and ground ends.

Squared ends:See Closed ends.

Stress relieve:

The heat treating of springs at a temperature so as to relieve stresses.

Torque (M):A twisting action in torsion springs equal to the load multiplied by the distance (or moment arm) from the

load to the axis of the spring body.

Total coils (Nt):The active coils (Na) plus the number of coils forming the ends.

spring rating

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