If the spring diameter and length are known go directly to dimension tables to select spring with desired total load.
Case II
If the spring diameter and length are not known follow the following seven steps in order that they appear and refer to the rate column of the dimension tables for spring selection.
In determining the length of a spring it should be remembered that the maximum delivered spring load is obtained by selecting longer springs. For best economy and saving of space choose light and medium load springs or the heavy load spring having a free length equal to six times the travel or an extra heavy load spring having a free length equal to eight times the travel. If the ratio lower than these are used because of height limitations, the no. of springs required will be substantially increased.
Combined Formula Diagram for Steps 1 to 6
Step 1
Estimate the level of production required of the die - short run, constant production etc.
Step 2
Determine Compressed Spring length "H" and Operating Travel "T" from Die Layout.
Step 3
Determine Free Length "C" as follows. Decide the load classification the spring should be selected from - Light, Medium, Heavy, Extra Heavy Load. Then choose the figure nearest the compressed length "H' required by the die design from the charts. Read the corresponding Free Length "C".
Step 4
Determine initial compression "X" by using the formula.
X = C - H - T
Step 5
Estimate total initial spring load "L" required for all springs when springs are compressed "X" mm.
Step 6
Determine Total Rate for all springs in Newton/mm "R" by using the formula
R = L/X
Step 7
Select spring as follows:
1. The free length must comply with the length determined in step 3.
2. Divide R (calculated in Step 6) by the no. of springs to be used if known in order to get the rate per spring. Then refer to the following pages for the catalogue nos. of springs having the desired rate.
3. If the no. of springs is not known divide "R" by the rate of the spring you select to get the desired no. of springs.
Chart that converts Compressed Lengths To Free Lengths
