The other loads that fasteners see are tension- and, to a lesser extent, compression-loads. In the case of a connecting rod bolt, for example, the bolts are continually being stretched (once for every cycle the bolt material is put in tension), then the material is relaxed. Combine this severe tension loading with hundreds of thousands of cycles, and you can begin to appreciate the physical requirements of fasteners operating in these extreme circumstances.
Because of the different loading requirements on a fastener, many different grades of materials are used. In fact, four grades are generally recognized in fastener manufacturing: commercial, aircraft, CHQ (cold head quality), and SDF (seam- and defect-free). SDF is typically the highest-grade steel available and is what ARP uses. The use of different materials will provide bolts with strengths ranging from 120,000 psi (tensile strength) all the way up to 300,000 psi. With that type of variance in strength of fasteners, understanding use and load requirements is essential.
Quality ProductionPrevents Fastener Failure Incorrect application and/or installation is the result of 80- to 90-percent of fastener failures, says Florine. That's a high figure, but after a tour of the operations of ARP, you begin to realize why manufacturing or material defects are essentially nonexistent. Except for the purchase of specialty premium-grade wire from the best mills in the country, ARP completes 100 percent of the manufacturing in-house (actually, ARP has four different plants for production). That's everything from cold and hot forgings to heat-treating, to machining, and finally, plating. There is a good reason why ARP chooses to have complete production control.
"There are many steps to making superior-quality fasteners, which start from proprietary steels with extremely high tensile strengths and proceeds with up to 20 or 30 separate operations," says Florine. "Each step has to be closely monitored to ensure exact tolerances. For example, heat-treating is critical to bolt strength. We found that we could not get the consistency we required from outside sourcing, so we brought complete heat-treating equipment in-house. That's not an easy thing to do, but it is part of our dedication to making the finest quality fasteners available."
Testing is an integral part of fastener development and production consistency. Whether it's an initial design or just sampling a production run, ARP pushes the limits on fastener strength. It's one of the things that separates race car fasteners from aircraft fasteners. Most aerospace industry standards set test standards at 120,000 cycles. ARP will test bolts until they break. That can mean running bolts through millions of cycles.
Great emphasis is put on discovering why a fastener fails in use, and often a broken fastener can lead to the discovery of another problem.
"When we see a failed connecting rod bolt, for example, we must look at everything to discover what caused the bolt to break. Most often that broken bolt will lead to what caused it to break, such as a lack of oil for lubricating the piston. Obtaining the real cause of a broken fastener requires that we look at all the related components. Essentially, we must solve the puzzle to find the real reason for a problem."
ARP is not the only company making quality fasteners, but its diversified product line allows them to be uniquely specialized in all areas of race car fastener production. This has led to some unique answers when faced with real racing problems.
Troubleshooting fastener problems are what every fastener manufacturer must face. Making engines and race car parts lighter, faster, stronger, and more reliable requires constantly upgrading performance. For fastener manufacturers, that means solving problems posed by the racing industry.