Hobson Engineering, a leading Australian-based supplier of quality fasteners for the mining, oil, construction and manufacturing industries, is leading the evolution of the fastener market – addressing the growing needs of updated safety standards, general performance, as well as time and cost savings, with its wide range of washers for numerous applications.
Hobson’s extensive product offering includes standard flat washers, which are a thin plate, typically round or square, with a hole that is normally in the centre. They are used for two main reasons; the first to minimise scouring or scratch damage to mating material as a result of nut rotation; the second to increase the effective bearing surface of the bolt and or nut. That is, to distribute the load of a threaded fastener over a larger area and prevent deformation of the bearing surfaces.
Also offered by the company are squirter washers, known as DTIs (Direction Tension Indicating). DTI washers are used to ensure the required pre-load tension in a joint is achieved. They are hardened washers with protruding lugs or bumps on the bearing face. When the bolt assembly is tightened, these lugs are deformed to a prescribed level and hence indicate the required tension in the assembly has been achieved. During the lug deformation process, silicone is squeezed out – giving visible sign of correct tension in the bolt assembly. Hobson also offers load indicating washers (LIWs) which work much the same as DTIs, but don’t require the silicone process.
Spring washers, also called Split-lock washers, can help to resist counter-clockwise rotation caused by external forces, such as vibration, thanks to the protruding corner edges that, when the threaded fastener is tightened, bite into both compressing surfaces. Also available from Hobson, these washers should be used under the head of the bolt with the assembly being tensioned by rotating the nut. If the washer needs to be used on the nut side, another hardened flat round washer should be used between the nut and the split washer. Hobson develops its split lock washers from hardened spring steel that strongly resists compression.
Other washers that are specially designed to prevent loosening of bolted assemblies include spring washers. A Belleville washer, also known as a coned-disc spring or conical washer and cupped spring washer, is a type of spring shaped like a washer. It has a frusto-conical shape that gives the washer a spring characteristic. In the initial tightening, the effect on the joint is similar to a split type spring washer. However, as the tightening continues and the washer is flattened, it actually reduces the applied load in the bolt assembly. In this way, if the joint is loosened, the load will increase and hence counteract the loosening of the joint. Multiple Belleville washers can be stacked to modify the spring constant or amount of deflection.
Lock washers, also known as a star washer, with teeth or prongs that extend radially inward and/or outward, are also available. These washers are designed to retain fasteners by achieving an increased friction between the fastener and the mating material – through mechanical interlocking or interference. Lock washers include two main types, teeth twisted out of plane (Type A) and edges of the teeth folded in opposite directions (Type B). Hobson offers two piece type lock washers from Nord-Lock, designed to prevent bolt assemblies loosening through vibration.
Nord-Lock washers comprise of two parts with serrated edges that grip the mating material. Its internal cam system boasts an angle exceeding the bolt thread pitch, requiring any force attempting to loosen the bolt to overcome resistance from the cams. Once a Nord-Lock washer is installed, the bolt is not going to come loose on its own.
Finally, nylon and isolating washers, which prevent increased speed of corrosion due to the galvanic reaction of dissimilar metals coming into contact with each other, are also available, as well as hardened washers used in high-tensile applications to resist washer deformation under high loads.
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