# Calculation of spring extension

A spring is a tool that can stretch freely, so how is its stretch value calculated? Let’s take a look at this formula.
1. Automatic reset (ie return pin spring)

L free = (S + preload) / compression ratio

Among them (1) S: ejection stroke S> finished product height + <15~20>

(2) The amount of preload is 5~10mm, which is determined according to the resistance when returning. If the resistance is small, the preload is small.

(3) The free length of L must be taken up to the specification length.

Remarks: (1) The spring in the assembly drawing is in a preloaded state. L=L free length preload

(2) Strength to be checked: h≧1.5d (see Figure 1)

2. Positioning: (slider spring)

L free = (S + preload) / compression ratio

Among them: (1) S: Slider core pulling distance

(2) Preloading amount: Determined by calculation. Slider preloading amount = pressure/fixed number. Coefficient. The slider pressure is the weight of the slider.

(3) The free length of L must be taken from the specification length

Remarks (1) The spring is assembled in the slider in a compressed (working) state. L=L free length-preload-core pulling distance.