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Applications



Coiled Spring Pins
Application: Heavy Duty Storage Case

A plastic storage case had been designed with a latch/hinge assembly requiring two pins.  One pin was used to connect the entire latch assembly to the case lid, and the other pin was used as a hinge pin within the latch assembly.

The original pins that were used were solid pins that had a barb on one end.  Due to its asymmetrical design these pins could not be easily oriented for use in automated feed equipment.  In addition, the solid pin could not provide a reliable friction fit hinge so a feature had to be designed into the case to create interference.  The manufacturer decided to replace the current pins with one that was better suited for use in automated equipment and capable of providing a quality friction fit hinge without the need of additional features built into the case.

Coiled Spring Pins are commonly used in hinged plastic assemblies.  Because the Coiled Pin has a pre-installed diameter larger than the hole in which it is used, once installed the radial force exerted by the pin in its attempt to open back up to its original diameter results in excellent retention.  With simple adjustments to the hole size the same pin could be used to create either free or friction fit hinges.  Coiled Pins are symmetrical and therefore do not require end-to-end orientation for use in automated installation equipment.  Coiled Pins also have a seam rather than gap so they cannot nest or interlock.

SPIROL Engineering recommended a light duty Coiled Pin for use in this assembly.  Light duty pins offer superior flexibility, which eases installation and protects hole integrity in plastic components.  This results in reliable retention and a consistent “feel” of the hinge throughout the life of the product.  A single pin could be used in both locations, and SPIROL Engineering provided the hole sizes necessary to achieve the desired “fits.”  A 300 series austenitic stainless steel pin was selected as it provided excellent corrosion resistance in the environments in which the case would be used.  This cost effective solution satisfied all of the application requirements and could quickly be manufactured to meet demand.

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