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Captive Fasteners
Captive fasteners are used to meld with the material into which they are joined
through a process known as cold forming. Captive fasteners are available in
three basic categories: self-clinching fasteners (used for ductile materials),
broaching fasteners (used for non-ducticle materials), and weld nuts (used for
sheet metal). Each type of captive fastener becomes a permanent part of the
panel or item to which it is installed. This permanent installation eliminates
loose hardware problems. Both a self-clinching fastener or a broaching fastener
will withstand high push-out and torque-out forces. Weld nuts self pilot into
pre-drilled holes and are round, thus eliminating need for indexing. A weld nut
is best suited for applications needing high strength.
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Regardless of type, a captive
fastener is installed by pressing the fastener into a pre-drilled or punched
hole. Next, a squeezing force is applied to embed the fastener in the panel. The
squeezing process causes displaced panel material to flow into the shank of the
fastener (through a cold flow process) locking the fastener to the panel. The
amount of time that force is applied to captive fasteners is important; enough
time must be allowed for the material to flow. Because of this, hammers cannot
be used to apply force to the captive fastener as the force does not last long
enough for the cold flow process to take place.
Captive fasteners are valuable as they add speed during initial assembly and
field servicing, thus keeping costs low. Generally captive fasteners use less
space and require fewer assembly operations than caged or anchor nuts. Captive
fasteners can be used whenever a component must be easily replaced or where
hardware cannot be accessible. It is important to keep in mind that the fastener
must be compatible with the panel or sheet material being used. In addition, the
hardness of the fastener must be greater than the hardness of the panel
material.
Related keywords: clinch nut
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and Loop Fasteners Industrial
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