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Crane Overload Safety Switch

A manufacturer approached SPIROL for assistance on designing a stack of Disc Springs that would reliably activate an overload mechanism for a warehouse crane. The manufacturer’s design allowed the crane to function within a range 800 - 2400kg (7.85 - 23.54kN), and the Disc Springs were to activate the overload mechanism preventing the use of the crane at loads over 2700kg (26.48kN). The manufacturer’s design parameters limited the maximum Disc Spring diameter to 94mm and a stack height of 150mm.

Although the stop mechanism is only used on the rare occasion when the crane is overloaded, this is considered a dynamic application as the Disc Springs will be cycling each time the crane is used.

SPIROL’s Application Engineering Team determined that (20) alloy steel (51CrV4) Disc Springs (DSC 90 x 46 x 5mm WR) stacked in series would provide the nominal force/deflection requirements within the physical constraints of the design. To ensure the Disc Spring Stack would perform as desired at the minimum and maximum material conditions, SPIROL Engineering’s evaluation included calculating the performance of the Disc Spring Stack at the extreme limits of the tolerance range. This included the spring force tolerance of the Disc Spring (+10 / -5% @s = 0.75ho) coupled with ± 2-3% applied to the final force value to account for the minimal effect of friction between the Disc Springs since there were no Discs stacked in parallel.

In the end, the recommended Disc Spring Stack met all performance requirements within the physical constraints of the design.

For more information, read our White Paper How to Determine the Proper Disc Spring Stack Configuration

Complimentary Applications Engineering Support: Although this article offers general guidelines, it is recommended that Application Engineers who specialise in Disc Springs are consulted to ensure a properly configured Disc Spring Stack for each application.