Like any fastener, spring pins are designed to join two or more parts of an assembly together. Sometimes called tension pins or roll pins, these fasteners are hollow, tube-like components made from spring steel or materials. Unlike solid pins, which are typically held tight within a hole by displacing the surrounding material, the right spring pins do not damage the hole and can be serviced without reworking the hole. Since spring pins are flexible, they can take larger hole tolerances than solid pins, making them less expensive and requiring less tedious hole preparation. These fasteners typically come in two varieties; slotted and coiled spring pins.
As their name suggests, slotted spring pins have a slot that runs parallel to the axis. When looking at the cross-section, the fastener appears in a “C” shape. The history of this fastener is not well understood; however, they have been a common feature in modern mechanical devices.
Coiled spring pins are fasteners that were first introduced in the late 1940s. These components were developed to be used in applications that experience harsh vibrations and dynamic loads, specifically that of a jet engine’s rotor. Fasteners like nuts and bolts loosen when exposed to these conditions while solid pins transmit loads to the hole that can compromise the joint. As its name suggests, the cross-section displays a coil with two and one-quarter rotations. This design makes it strong, yet flexible.
The cross-section is the most notable difference between the two types of spring pins. Slotted pins are generally made of a thicker material that can only flex so much before the slot closes. Coiled pins are made from a thinner material to accommodate the coils and have almost unlimited flexibility, enabling them to indefinitely absorb vibrations and shock. Another key difference is that coiled pins have a smooth outer surface for rotation, while also avoiding interlocking. And since coiled pins have a more uniform cross-section, their strength is not dependent on orientation.
Because of its ability to ensure shock and vibrations coiled spring pins are great for use in dynamic applications. When a slotted pin is used, once the slot closes, the fastener essentially functions like a solid pin and becomes stiff and inflexible. Because of its unique features, generally, coiled springs are better for use in automatic assemblies.
To learn more about fasteners like the spring pins, contact the experts at OneMonroe EFI. Our experienced team will help you understand which type of pin is best suited for your intended application.