High Temperature Joint Fastening Considerations and Solutions

High Temperature Joint Fastening Considerations and Solutions

In automotive and industrial engine applications, high temperature joints are those joints in the exhaust system which include the exhaust manifold, turbocharger, heat shield, EGR (Exhaust Gas Recirculation), SCR (Selective Catalytic Reduction), and catalytic convertor attachment points.

In applications where the temperatures exceed the capability for that of carbon steel or carbon alloy fasteners, the use of a high temperature-stable material will be required. The majority of fasteners used in automotive and industrial vehicle manufacturing are carbon alloy varieties which are typically property class 8.8 or 10.9 heat treated materials (grade 5 or 8 for inch size). These materials are heat treated with a quench and temper process which fall into the 370-425°C (700-800°F) tempering range. The mechanical capability of these materials begins to diminish in operating temperatures above this range. The fasteners may begin to anneal or soften which will result in clamp load loss or failure.

Most solid joints designed for ambient temperatures are typically very predictable based on mathematical formulations for torque versus load, mechanical strength of the fastener, and external forces exerted on the joint; but high temperature applications do not behave similarly. Designing fasteners for high temperature joints can be a difficult task due to the vast number of variables involved. The effects of carbon monoxide, hydrocarbons, nitrogen oxides, water vapor, cyclic vibration and high temperature all contribute to the complexity of designing a system that provides long-term durability and performance in an economical way.

Because these temperatures wreak so much havoc on joints, causing bolts to loosen and clamp loads to be lost, the experts at MacLean Maynard, a division of MacLean Fogg Component Solutions, have designed products that hold up in these extreme environments.  These products include fasteners manufactured from A286, Nimonic (TM) 80A, Inconel (TM) 718 and other exotic materials.  For those high temperature and high vibration applications like engine exhausts and turbo chargers, the top OEMs turn to our High Temperature Bolts and Studs.

The team at MacLean-Fogg Component Solutions are ready to help with your fastener engineering needs.  Have comments, questions or feedback regarding this paper, please feel free to contact us by clicking here.

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