FastenersASIA May 2021

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Longer lasting bolts The performance of threaded fasteners – screws, nuts, and bolts – is critical in commercial engineering. The Fastener Quality Act of 1990 was enacted by Congress in the USA after several high- profile fastener failures, such as the San Francisco bridge collapse, according to the National Institutes of Standards and Technology.

metal components using a custom- designed hydrostatic burnishing tool. The pressure is delivered with enough force to generate plastic deformation, compressing a layer of the metal so that it resists damage from foreign objects, corrosion fatigue, fretting, stress corrosion cracking and other common damage mechanisms. “The LPB process provides a means of introducing an optimal compressive residual stress in the thread root where failures occur,” explained Doug Hornbach, CEO of Lambda Research, Inc, the research and materials testing laboratory that is part of Lambda Technologies Group. “Manufacturing processes used to form threads do not produce the compression that can be generated with LPB. Shot peening, which is a widely used surface enhancement method, will dimple and distort the thread face while not adequately treating the thread root. LPB works because we can design custom-

shaped tooling that fits into the root of the thread.” Lambda conducted the experiment on steel, but LPB can be performed on almost any alloy. “The speed at which we can treat the screws and bolts is another major benefit of the process,” commented Paul Prevéy, CEO of Surface Enhancement Technologies (SET), thedivisionof Lambda Technologies Group that develops surface treatment solutions for commercial engi- neering applications. “LPB is performed on conventional CNC machines. With customised tooling installed on a high- speed lathe application, LPB is applied in a second or less.” The complete case study on improving threaded fastener fatigue performance is available on Lambda’s website at www. lambdatechs.com/diffraction-notes Lambda Technologies Group www.lambdatechs.com

Lambda Technologies Group has released a study showing how threaded fastener fatigue life can be improved by using compressive residual stress. In an experiment conductedon a threaded rod manufactured from B7 steel (AISI 4140, ASTM A193), Lambda Technologies used low plasticity burnishing (LPB) to introduce high compressive residual stress into a threaded fillet. Fatigue testing showed the LPB samples had a fatigue life 15 times greater than the untreated specimens. LPB® is a patented mechanical process that applies pressure to the surface of

Clipped washers for limited space applications Boker’s, Inc produces a range of clipped washers that provide solutions for design engineers who have limited space and need to control axial motion within their applications.

Boker’s clipped washers are custom produced in short, medium and long runs with fast delivery, minimal tool cost and with 3D prototypes available. The company also maintains more than 32,000 stock tools for flat round washers, spacers and shims without tool charges. With outside diameters of 0.08" to 5.14" and a wide variety of inside diameters, the company states that there are millions of flat and speciality washer possibilities. Boker’s, Inc www.bokers.com

Clipped washers have a flat edge on either the outside diameter (OD), inside diameter (ID) or both. This flat edge helps prevent the washer from rotating in applications, especially when space is limited and component performance is critical. Applications that use clipped washers occur in industries such as automotive, marine, aerospace and medical. “Clipped washers, also referred to as D-washers, are generally used in applications where space limitations do not allow the use of a flat round washer, as well as when keeping an assembly stationary is required,” said Chuck Kersey, assistant sales manager. “Clipped washers can be used with shafts, rods or mating parts that are shaped like a ‘D’.” The functionality of the clipped washers comes from providing a flat bearing surface within assemblies. They are generally used under the head of a bolt and/or a nut to disperse loads as well as to prevent the washer from turning in the application. They are mounted with the flat edge of the washer facing a flat surface or recessed hole to prevent rotation. Clipped washers are available in steel, stainless steel and aluminium, as well as over 2,000 other stock metallic and non- metallic materials to meet specific applications needs. Design engineers can choose from a wide variety of sizes, thicknesses and materials.

❍ Clipped washers from Boker’s

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May 2021