The design guide and whitepaper for hinges comes from Spirol International Corp. and describes two primary hinges. One, a free fit hinge, has little to no friction or drag when the latch or handle rotates. Hinge components are “free” to rotate independent of one another. The second, a friction fit hinge, requires interference to prevent the free rotation of components relative to one another. Depending on design intent, resistance can vary from a slight drag to a value sufficient to maintain the fixed position of components anywhere in their full range of rotation. Although many pin styles are available, Coiled Spring Pins are well suited for use in both friction and free-fit hinges. For best long-term hinge performance, designers should observe a few simple design guidelines. Regardless which pin type is used, the gap, indicated in the accompanying illustration, between hinged components should be minimized to reduce clearance and avoid bending the pin.
When a free-fit hinge is needed, the Coiled Pin’s pre-installed diameter is of negligible importance because pin diameter is determined by the retaining or smallest hole(s). Coiled Pins are functional springs, so consider recovery and retention in free fit locations. The amount of recovery and retention depends on the diameter of the tight (retaining) hole(s) and the ‘free span’ of the pin. Free span would be defined as the distance a pin passes through a free-fit component. As free span increases, the pin diameter also increase as it “recovers” a portion of its pre-installed diameter. The illustration A few dimensions and terms, shows them. For better load distribution and closer tolerance hinges, it is recommended that the tight fit of the Coiled Pin be in the outer members of the hinge. The minimum thickness of the outer members should be 1 to 1½ times the diameter of the pin. If the thickness of the outer members are less than the diameter of the pin, then the tight fit should be in the inside hole.
In a friction-fit hinge, all holes should be identically sized within the assigned tolerances. If the manufacturer is unable to maintain the same hole size within each component, the tolerance should be split between the components. It is most common to assign the smaller half of the tolerance to the outside holes and larger half to the inside hole.
The Coiled Pin simplifies design because there is no need to incorporate misalignment between holes to achieve friction, as is the case with rigid solid pins. Also, Coiled Pins perform best when installed in straight, properly aligned holes. Although the complete this article offers general design guidelines, it is recommended that Application Engineers who specialize in fastening and joining be consulted to ensure the optimum hinge design is employed for each application. Here is the link to the complete White Paper: http://www.spirol.com/library/whitepapers/How_to_Design_the_Optimum_Hinge.pdf
Spirol International Spirol.com
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