Calculating the load
- To find the load at any working length, when
free length and rate are given, use the formula:
P = R x F
where P is the load in lbs; R is the rate in lbs per inch; F is the deflection from free length.
Given a free length of .750" and a rate of 22 pounds per inch, find the load at .500" working length.
P = 22 x (.750-.500) = 22 x .250 = 5.5lbs
- To find the load at any working length, when the
free length, rate and initial tension are given, use the formula:
P = (R x F) + I.T.
where P is the load in lbs; R is the rate in lbs per inch; F is the deflection from free length; I.T. is the initial tension.
Given a free length of 1", a rate of 6.9 pounds per inch, and .7 pounds initial tension, find the load at 1.500".
P = [6.9 x (1.500-1.000)] + .7 = (6.9 x .500) + .7 = 3.45 + .7 = 4.15 lbs
How to determine rate
- Rate, which is the change in load per unit
deflection, may be tested by the following procedure:
1. Deflect spring to approximately 20 percent of total available deflection (free
length, minus solid height) and measure load (P1) and spring length (L1).
2. Deflect spring not more than 80 percent of total available deflection and
measure load (P2) and spring length (L2). Be certain that no coils (other
than closed ends) are touching at L2.
3. Calculate rate (R) lb. per in.
R = (P2 - P1) / (L1 - L2)