FEATURE FASTENINGS & ADHESIVES
What are coiled spring pins? What applications can they be used for? And how do you go about specifying them? Spirol explains
an assembly, and can dampen shock/impact loads and vibration, preventing damage to the hole. Coiled spring pins are also well suited to automated assembly systems. To enable the engineer to select the
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oiled spring pins can be used for numerous applications. An example
is hinge applications – here, the pin can be used as a hinge in door handles, glove box latches, trigger assemblies in medical instruments, and in plastic latches and locks, to name just a few. In alignment applications, the pins can be used, for instance, to align the oil pump housing to the engine block in a car, or to align a crankshaft cover to the engine block in a lawn mower assembly. Coiled pins can also be used to fix a gear to a shaft, or to fasten one component to another. In this case, this can be whenever a pin is used to fix one component to one or more other components – such as a retaining pin in a differential assembly or when the pin is used to retain a check ball from falling out of a valve, etc. But what exactly are coiled spring pins? According to Spirol, it invented the coiled
spring pin in 1948 to address deficiencies associated with conventional methods of fastening, such as threaded fasteners, rivets and other types of pins subject to lateral forces. The pins, the company explains, can be recognised by their 21
/4
coil cross section and are retained by radial tension when installed into the host component. After insertion, they provide uniform strength and flexibility. Not only does the pin distribute static and dynamic loads equally throughout its cross section without specific point of stress concentration, but the flexibility and strength are unaffected by the direction of the applied load, so the pin does not require orientation in the hole during assembly to maximise performance. Of additional benefit, the pins are an active component within
32 DEC/JAN 2016 | DESIGN SOLUTIONS
To enable the engineer to select the optimum combination of strength, flexibility and diameter to suit different host materials and application demands, coiled spring pins are available in three ‘duties’ – standard, heavy duty, or light
optimum combination of strength, flexibility and diameter to suit different host materials and application demands, coiled spring pins are available in three ‘duties’. There are a number of reasons for this. The flexibility, strength and diameter need to be in the right relationship to each other and to the host material to maximise the features of the pin. After all, a pin that is too stiff for the applied load would not flex, damaging the hole; and a pin that is too flexible would be subject to premature fatigue. According to Spirol, essentially, balanced strength and flexibility must be combined with a large enough pin diameter to withstand the applied loads without damaging the hole.
MAKING THE SELECTION When specifying coiled spring pins for an
application, start with the load to which the pin will be subjected. Following this, evaluate the material of the host to determine the duty of the pin. The pin diameter to transmit this load in the proper duty can then be determined from shear strength tables (available in the product catalogue), taking into account these further guidelines: • Wherever space permits, use standard duty pins. These have the optimum combination of strength and flexibility for use in nonferrous and mild steel components; and are also recommended for hardened components because of their greater shock absorbing qualities. • Heavy duty pins should be used in hardened
materials where space or design limitations rule out a
large diameter standard duty pin.
• Light duty pins are recommended for soft, brittle or thin materials and
where holes are close to the edge. In situations not subject to significant loads, light duty pins are often used because of easy installation resulting from lower insertion force.
Spirol T: 01536 444800
www.spirol.com
SELF-CLINCHING FLUSH-HEAD STUD RANGE
PennEngineering’s PEM self-clinching flush-head studs with X-Press threads enable quick mating with push-on plastic nuts, wire tie products, or other plastic fasteners in thin metal assemblies. These, the company explains, have a coarse thread design which reduces assembly time by
allowing for easy mating of plastic parts and promotes especially high retention force of the stud upon installation. The thread design also accommodates paints and coatings without compromising fastener performance in service. The X-Press studs (Type FHX) press easily into place in metal sheets as thin as 1mm. On installation,
the head of the stud mounts flush in the metal sheet. The studs are manufactured from hardened carbon steel and finished with zinc plus clear chromate as standard, or a rust-preventive oil finish as an option. They are available with 5mm and 6mm metric threads and in lengths from 10mm to 25mm. The studs perform reliably in metal sheets with hardness of HRB 80 or less on the Rockwell ‘B’ scale and HB 150 or less on the Brinell scale.
Penn Engineering
www.pemnet.com
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