Plastic materials generally have lower physical properties than metals and hence it is important when joining them to spread the shear loads over as wide a surface area as possible.  To do this, the essential role of the fastener is to clamp the materials tightly together to develop frictional grip between the mating surfaces.

 Ariel has developed a Pierce-&-Full-Roll rivet which can be driven through plastic materials and when the tubular end of the rivet comes into contact with a setting die can roll outwardly to form a full-roll set beneath the lower sheet.  With this arrangement the plastic components can be held tightly together over a wide range of material thicknesses and environmental conditions.

 The Pierce-&-Full-Roll rivet is made from stainless steel and was originally developed for use in the aerospace industry.  It is a semi-tubular rivet which has a hard stainless steel core within a soft stainless steel skin.  The hard core provides the rivet with the strength required to self-pierce the plastic materials and then to generate a roll-set on the underside of the assembly.    The soft skin prevents the build-up of stress concentrations.  The combination of the hard core and the soft skin enables the rivet tube to roll through an angle in excess of 270º  without splitting or collapsing.

 The performance of a rivet changes dramatically once the roll passes through 270º.  Normally rivets are roll-set to a maximum of 180º, and consequently when the setting forces are removed the roll-set tends to unwind and spring away from the components being assembled.  However when the roll is carried through an angle in excess of 270º the natural spring-back of the rolled tube when the setting forces are removed is towards the components being assembled.  With this arrangement the rivet acts as a spring and thereby provides a number of advantages : 

1.                  The spring action clamps the plastic components tightly together thereby  generating surface friction between the components and this enables them to withstand shear forces significantly greater than they could withstand if free to move relative to each other.  

2.                  The spring action enables the rivet to continue clamping the components even if the materials involved are subject to “creep”.

A significant further advantage is that  the piercing action of the rivet is such that the plastic material grips the shank of the rivet tightly.  The combination of radial shank grip and axial clamping of the components prevents any relative movement of the components and hence gives a rattle-free assembly.

 In operation the Pierce-&-Full-Roll rivets are fed into a specially designed rivet applicator which brings the rivets into contact with the upper surface of two or more plastic components mounted over a setting die.

The rivets are forced into piercing engagement with the plastic components by means of a plunger.  During the initial stage of penetration the displaced material enters the tube of the rivet.  As the plunger force increases, the displaced material is progressively forced through a cavity in the setting die.  When the tubular end of the rivet comes into contact with the die it rolls outwardly to form a full roll set beneath the lower surface of the components being fastened.