Advanced materials and functional coatings can be a good way to improve fastener performance, but finding the right coatings and materials isn't easy. Steve Buzolits, manager of product engineering for high-tech fastener maker SPS Technologies, notes that advanced alloys developed for non-fastening applications don't always make good fasteners. Bolt threads and the cross-section change from head to shaft add "lots of stress concentration sites" that sometimes rule out otherwise promising alloys, he says. Implementing new functional coatings, meanwhile, can require expensive research and manufacturing investments. What's more, fastener coatings and surface treatments may raise red flags from an environmental standpoint. These difficulties, however, have not stopped fastener makers from trying new materials and coatings. Here's a look at a couple of recent product developments and a cool new on-line calculator that helps identify fastener-related RoHS issues:
Light and Strong
Titanium fasteners can weigh 40 percent less than their steel counterparts, but these lightweight fasteners have had strength and size limitations that kept them out of heavy-duty structural fastening applications. Now SPS Technologies has come out with a proprietary titanium alloy that ups the ante on strength and size. Steve Buzolits., manager of product engineering, notes that titanium fasteners have traditionally been made from an alloy (Ti-6Al-4Va) that could achieve strengths of 160 ksi tensile and 95 ksi shear. And bolts made from this alloy could be heat treated effectively only up to diameters of 3/4-inch. SPS's Titan 761 alloy, Ti-3Al-8V-6Cr-4Zr-4Mo, run through a proprietary process to transform it into bar stock, does much better on both the strength and size scores. It offers guaranteed minimum strengths of 180 ksi tensile and 108 ksi shear. It can also be effectively used in bolts up to 1-1/8-inch diameter. These strong titanium bolts have been used in racecars for a few years now. Over the past year, military and commercial aerospace companies have shown interest too because these bolts can serve as drop-in replacements for steel (CRES) bolts. "For a technical report on Titan 761, go tohttp://rbi.ims.ca/4397-647.
Environmentally Friendly Fastening
The European Union's RoHS regulations target all kinds of components used in electronic products. And amidst all the circuit boards, capacitors, and wires, it's all too easy to forget that mechanical fasteners have potential compliance issues. The reason why comes down to the myriad of platings and surface treatments used on today's fasteners. Only a small portion of these have environmental implications that run afoul of RoHS, which bans lead and other heavy metals, among other substances. One manufacturer has recently taken steps to clear up any confusion related to the compliance of its fasteners. PennEngineering Fastening Technologies has launched an on-line lookup tool that returns compliance information on specific fastener-and-plating combinations with just two clicks. To access the RoHS Lookup Tool, go to http://rbi.ims.ca/4397-645.
Stopping the corrosion that can occur between dissimilar metals in contact has been a long-standing fastening problem solved by various plating and coating techniques. Nylok Corp., already known for its thread coating technologies, has developed a line of powder coated fasteners designed to prevent this galvanic corrosion. According to Gregory Alaimo, engineering manger, the company powder coats the head surfaces and un-threaded portion of the shank with nylon-11. "The coating forms a dielectric barrier that prevents metal-to-metal contact," he explains. Nylok launched this process a couple of years ago for a single high-volume application—an M8 × 42 mm fastener used in an transmission housing made from an aluminum-magnesium alloy. More recently, the company has expanded the technology to other corrosion-sensitive fastening applications. It has applied the same coating to different sizes and types of fasteners, including studs with welded-on, coated washers. For more information, visit:http://rbi.ims.ca/4397-646.
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