XPC FASTENER
THE STEALTH FIXING FOR TUBULAR STRUCTURES
JUST PUT IT IN AND TIGHTEN IT UP
XPC USES PURE FRICTION TO CREATE A ROBUST, LOAD BEARING END-JOINT IN METAL TUBE


EXPANDING COLLAR FASTENER (XPC) PATENT FILING APPLICATION NO. PCT/GB2005/002788 www.xpcfastener.com


email xpcfastener@aol.com


SOME PICTURES MAY SHOW XPC SAMPLES MADE FROM CAPSCREWS
XPC consists of a tapered stud -which may be threaded in order to generate preload, and a tapered collar with an annular face at the outer end. XPC is available in several materials and current threaded generations are M8 thru M16 with a wide variety of collars and stud lengths available.

At right - prototype M16 with steel and Nylatron collars, and production M8 versions with titanium nitrided steel collar, Nitrotec coated stud, and (far right) mild steel.

The mating angles are carefully disposed in order to give a component of axial force between the collar outer face and counterface to prevent the fastener from spinning during tightening. The outer circumference of the collar is smooth to avoid stress concentrations. XPC grips by generating linearly dispersed frictional force between the outer diameter of the collar and the tube.

The more preload - the more grip up to the ultimate strength of the tube
The collar is chamfered to facilitate fitting, and has a slot along its length to permit it to expand freely and engage with an anti-rotation lug if used.
At centre - close up of TiN-Nitrotec version M8

The materials and sizes of stud and collar are selected to give strength and properties to suit the environment and applied loads.
A nut or other means of applying preload is attached to the outboard section of the XPC stud and after a small amount of preload has been applied to bring the collar into light contact with the counterface and tube bore, XPC is tightened up. The adjoined part or ‘counterface’ must be restrained, and in the initial tightening phase a modest amount of restraint is required to prevent the tube from turning, just until the XPC collar makes close contact with the tube bore.
At right lower - M16 variant showing tapered sections and anti-rotation pin. High volume applications have an anti-rotation lug forged into the head.

An XPC ‘thrust nut’ - in effect an artificial counterface - can be used to fix a thread rigidly in the end of the tube - with a very high degree of concentricity.
Simply fit the thrust nut onto the fastener and tighten the nut by hand - till all the mating faces are in contact - insert in the tube, secure the thrust nut in the vice or with a spanner, and tighten the outboard nut to the XPC recommended preload. A modest amount of restraint is required to prevent the tube from turning until the XPC Collar comes into close contact with the tube bore. The fixed thread can typically be used to fix the tube to a node joint or clevis for the creation of tubular structures and sway braces.


A reinforcing collar can be fitted to augment the holding strength of the tube. Shown is a ductile copper alloy band simply slipped onto the aluminium alloy tube. Because XPC does not expand in a perfectly circular form, the ductile collar conforms to the expanding shape of the tube under hoop strength and massively enhances its strength.
See XPC Tests



XPC Plastic collars require no notch due to the inherent property of the material to recover its shape and relax radial load when preload is removed.
Plastic collars give medium holding strength and are ideal in applications where bimetallic corrosion must be avoided.


Metal XPC collars can be notched along the full length to deliberately weaken them to aid disassembly. It is quite normal for fracture along the notch line to occur during tightening and dismantling.

Intimate surface contact takes place between the collar and tube bore - on a microscopic scale. It is quite usual for the collar to be tight in the tube even after release of preload. Retraction holes can be incorporated in the outer end face of the collar to facilitate removal.


UNDOING XPC IS AS EASY AS 1-2-3
1. RELEASE (remove nut)
2. STRIKE (the end of the stud to release tapers)
3. RETRACT (the collar if it’s not free already using the retraction hole s and circlip pliers)

Using an XPC Fastener to secure tube to plate is simplicity itself. L-R - fit the XPC stud thru the plate and attach washer and nut. Tighten XPC by hand until the collar is in close contact with the plate, offer up the tube ............

...tighten XPC lightly once in the tube to bring the collar into close contact with the tube bore, either by hand as shown if the collar is a snug fit already, or by using a spanner, hold the plate in a vice, restrain the tube by hand initially, and torque up.