Composite crankshafts made with Trib-joins

Application Note 4.

The diagram shows a small composite crankshaft assembled by push together cold pressure welds made by treating surfaces with Trib-Tools™. This method provides savings in time, materials and weight. The webs and counter-balance weights are either fine-blanked or sintered steel.

A section view is shown on the left. The parts are assembled as follows:

1).    The main shaft is over pushed into web to position BB. This is done dry and is jigged to ensure near perfect alignment.

2).    The exposed shaft (over pushed region) projecting beyond web is treated with a Trib-Tool and the shaft is pushed back flush with the face of web  that is supported  at AA. As a quality monitor it is advisable to monitor the push back forces. 

3).     The three "semi-piercings" at CC on the web are also treated with a Trib- Tool and the counterbalance weights are forced into position, the interference of the semi-piercing being typically the elastic limit of bore in the web.

4).    The two reduced diameters of the big-end cross shaft are separately rubbed with a Trib-Tool which incorporates the cold welding agent into the surface dry - to eliminate any risk of contamination the bottom con-rod bearing.

5).    Finally the two halves are jigged to establish alignment for final assembly. The big-end cross member is suspended in the con-rod (not shown) on the DD axis and the two halves are finally forced together (not shown).   

The background to this is that dry press fit assemblies are commonly used for crankshafts in small engines and compressors but they struggle to achieve acceptable strength joins without heat-treating the webs, which is more expensive than Trib-Joining!. The introduction of the Trib joins permit the use of soft cheaper materials and thinner sections for the webs. Trib-joins increase strength by typically by a factor of four over best dry press fits. The Trib-joins are unaffected by heat,  lubricating oils or fuel vapours.

The nominal pre-sizing on all the joins is ISO H7/p6 (class 7 in USA). The fine-blanked bores are used as stamped  and the bores in sintered parts are ballized before assembly.

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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. Registered Office 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 based on aspects of  tribology, the science of surfaces. All rights reserved by Ball Burnishing Machine Tools Ltd. Last modified:  31-Oct-2011 copyright © 1999/2011. 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.