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 of carbon steel or carbon alloy fasteners, the use of a high temperature-stable materials is 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 using a quench and temper process which falls into the 370-425°C (700-800°F) tempering range. The mechanical capability of these materials begins to diminish in operating temperatures above that range. The fasteners may begin to anneal or soften, which will result in loss of clamp load or failure.
Most joints designed for ambient temperatures are typically determined using standard calculations for torque versus tension, mechanical strength of the fastener, and external forces exerted on the joint; however, high temperature applications do not behave similarly. Designing fasteners for high temperature joints can be a difficult task due to the greater number of variables involved. The effects of high temperature, cyclic vibration, creep, and thermal expansion, all contribute to the complexity of designing a system that provides long-term durability and performance.
The experts at MacLean Maynard, a division of MacLean-Fogg Component Solutions, have designed products that perform extremely well in these harsh environments and have become the industry standard. These products include fasteners manufactured from A286, Nimonic (TM) 80A, Inconel (TM) 718, and other specialty alloys. For high temperature and high vibration applications like engine exhausts and turbo chargers, the top OEMs turn to our High Temperature Bolts and Studs.
Questions to Resolve During Joint Design
Which temperature matters when selecting a fastener?
The fastener's temperature is a key input. Its exposure depends on the joint materials, proximity to the heat source, airflow and operating cycle. A temperature reading from another part of the assembly may not describe the fastener's conditions.
Why does thermal cycling matter?
Joint components can expand at different rates as an assembly heats and cools. The design needs to account for that movement along with vibration and the fastener's ability to maintain the required joint load.
Where should the review start?
Start with the application and the complete joint. Review temperature exposure, mating materials, geometry and loading before selecting the fastener material and thread design.
Continue with thermal analysis of high temperature joints or explore Maynard 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.
Related Products