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Second generation Trib technology for making precision press-fit assemblies  

Press-fits are frequently used attractive for making built-up composite assemblies because they are potentially cheap and easy to make, but are difficult to control in series production due to tolerance and surface finish variations that cause variations in grip. Thermal shrink-fits provide a stronger and potentially more accurate method of assembly, but also have practical and safety limitations. This process is less conveinent due to the need to handle the heated or cooled parts. Also the heating or cooling leads to the formation of excess oxidation or moisture condensation, both of which potentially  intereferes with the chemical action of the friction enhancing agent.

We have applied for patents directed to an improved method of making high strength precision co-axial assemblies that overcome these problems by cleaning the surfaces and applying a thin film of friction enhancing agent to one of the surfaces. Then precisely pre-positioning free fitting ambient temperature parts one with respect to the other, then radially deforming one part into high pressure contact with another, leaving the critical axial and radial positioning undisturbed. This provides a coupling with similar fatigue characteristics to a shrink fit but stronger. A further advantage is this assembly can be released and re-made cold and it provides instant full strength (no cooling or warming time).

The above mentioned deformation may be provided by for example, a hydro-mechanical expander or cam action expander or parallel or tapered slide-in/over lubricated sleeves or bungs. Thus the assembly can be made by inserting an interfering lubricated locking sleeve with a coefficient of friction of the order of 0.1 or less for hard steel parts to secure the high grip load bearing interface with a static coefficient of friction of 0.4 or more.

Potential applications for this technology include improving the load carrying properties over press-fit assemblies and making new light-weight crankshafts, drive shafts, shaft couplings, flow pipe couplings etc.

We further envisage using the technology to make high strength light-weight shaft couplings and dowels by employing mono fibre Metal Matrix Composites in which the load carrying coupling element employs mono fibres running parallel to the coupled axis and a sliding interference fit deforming element with radially wound mono fibres. The cold-welding agent is effective between steel and aluminium; hence the MMC matrix material can be aluminium.

For more information go to App Note 23


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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: 29th Sept 2016 copyright 1999/2016. 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. Be aware this site uses cookies, your continued use implies you accept these.