Fusion Roller assembly for copying machine made with Trib-Joint. 

Application Note 18

Some Fusion Roll designs suffer reliability problems due to thermal fatigue. Typically the roll comprises an aluminium tube with a hard stainless steel stub-shaft welded onto each end. A heating element is positioned inside the role to heat the assembly to almost 200°C for normal operation. Upon heating the aluminium expands at twice the rate of stainless steel and the weld's eventually fail in fatigue. Complex weld joint shapes are used but they still fail eventually.

The Trib-Joint assembly shown in the cut-away picture below overcomes the differential expansion problem by splitting the skirt of the stainless shaft to allow it to move with the aluminium. The split skirt is trapped between an inner aluminium expansion ring and the aluminium roll. When heated the diameter of the inner ring expands at the same rate as the roll to hold the stainless fingers in firm frictional contact with the roll. The stainless skirt fingers are coupled to the aluminium roll by asperity cold pressure weld junctions formed after the surfaces are treated with a Trib-Tool, which releases trace amounts of cold welding agent as the surface is rubbed with the tool. Providing the individual segments of the skirt are not too long, then the cold pressure welds at the centres of each segment can withstand the local differential expansion -hence the joint is unaffected by thermal fatigue.

Experimental joints proved exceedingly rugged and easily exceeded the required assembly strength. The final turning operation on the hardened stub shafts was performed after assembly of the shafts into the roll, by gripping the roll and plunge turning without a centre support. There was no movement of the stub shafts during machining despite being subjected to a high side load and a severe rise in temperature due to cutting. Torsional strength exceeded 2kNM  on a 54mm diameter joint. The pre-fit was H7/p6.

for more information email: info8@tribtech.com

The TribTech name derives from "tribos" - Greek for 'rubbing'. 'TribTech' is a trade name used by Ball Burnishing Machine Tools Ltd. of 12 Brookmans Av. Hatfield, Herts. AL9 7QJ. United Kingdom;  Company Reg. No. 1408807, VAT Reg. No. 421 6210 04; a knowledge based company that develops, patents and licenses technology. All rights reserved by Ball Burnishing Machine Tools Ltd. Last modified: May 01, 2008 copyright © 1999/2008. The information and data provided herein should be considered generally representative for the tools and technologies described. In all cases users should carefully evaluate the tools and technologies to determine their suitability for a particular purpose.