Two ways to install a gas spring badly
Gas springs deliver far more force in a far smaller envelope than mechanical die springs, which is exactly why installation errors are expensive. Two mistakes account for most premature failures: mounting through the wrong threads, and modeling the force as a constant.
Mount through the base, never the rod
Kaller gas springs are mounted using the threaded holes in the base of the cylinder — never the threaded hole in the top of the piston rod. The rod-end thread exists for the press interface, not for load transfer into the tool. Load carried through the rod thread puts bending and tension into the rod seal, which is the fastest route to a leak.
Thread engagement rules are published and worth following exactly:
- Engagement of 2 to 4 times the thread diameter.
- Thread depth at least 1.5 times the diameter in steel and at least 2 times in cast iron.
Force is not a single number
A gas spring's force rises through the stroke. Kaller publishes two models for this: an isothermal model that assumes constant temperature, and a polytropic model that accounts for stroke and used stroke, gas volume, press velocity, strokes per minute, operating temperature, and internal friction. The polytropic model is the realistic one for a running press.
Sizing from the initial force alone, and ignoring how force climbs across the stroke, is how tools end up over- or under-powered at the bottom of the stroke.
The series to match to the job
Kaller's range covers the force envelope from light ejector work to heavy forming: the EP3 16 / EPS3 16 series at 420 N (95 lbf) initial force for compact, color-coded ejector-pin duty; the R12 / R15 / R19 series at 500 / 700 / 900 N in fully adjustable rod-sealed bodies; the EP2 24 / EPS2 24 at 1,700 N (382 lbf); and the repairable M2 / MM2 series at 2,000 N (450 lbf). Available strokes run from 7 to 125 mm depending on series.
Related catalog item: Kaller gas springs — EP3/EPS3, R12/R15/R19, EP2/EPS2, and M2/MM2 series with published isothermal and polytropic force models.
Contact Tooling Components for gas spring sizing and installation review.
Check the stroke budget before the spring
Gas springs are chosen for force in a small envelope, but they are installed for stroke. Before specifying a series, confirm the available mounting depth, the stroke the tool needs, and the temperature the cylinder will see in service. A spring that is right on force and wrong on stroke will either bottom out or deliver its force at the wrong point in the press cycle. The published stroke range per series — 7 to 125 mm depending on the model — is the first filter; the polytropic model is the second.