Mechanical Technology July 2016

⎪ Power transmission, bearings, bushes and seals ⎪

Effective tools and fasteners enhance reliability

BMG’s extensive range of fasteners, tools and related equipment is used to enhance reliability of equipment in diverse sectors, including light, medium and heavy industries, pulp and paper, construction, original equipment manufacturing and agriculture.

“ B MG’s portfolio of over 15 000 locally manu- factured and imported fastener stock items are available in a variety of grades, materials and strengths that meet stringent quality and safety specifications,” says Andrew Johns, manager, BMG’s fasteners, tools & equipment. “These fasteners are enhanced by products that prevent the loss of joint clamp. Equally important are installation and disassembly tools that ensure each fastener can be correctly installed and efficiently removed. “For a fastener to be effective, key factors that require attention are the type of bolted joint design required and whether the joint should be serviceable or permanent. There are two types of joint for consideration – tension joints or shear joints.

“Tension joints are simply explained by the tension created on the bolt and clamped components of the joint, by stretching the fastener when torque is applied during tightening. This torque needs to be accurately calculated to ensure that the fastener’s limits are not exceeded. Conversely, the application of insufficient torque and thus an ineffective clamp of components, could mean the joint will self-loosen prematurely. “The second type of bolted joint uses the shear strength of the bolt to transmit the load and often relies on a locking mechanism to retain the joint integrity as opposed to a high clamp force.” If a serviceable joint is required, a number of factors need to be considered to ensure that bolt-securing elements are effective and that the joint tension is maintained over the life of the joint. These factors include thread size, clamp length ratio, preload, amplitude, lubrica- tion and surface quality. The selection of appropriate assem- bly and loosening tools, coupled with accessibility to the joints, is critical to overcome factors that cause the loss of clamp and to ensure ease of assembly and disassembly. Some of these products include Nord-Lock wedge locking washers, which when tested according to DIN 25201-4:2010-01, have a remaining joint clamp load of more than 80%

BMG’s Superbolt multi-jackbolt tensioners, which form part of the Nord-Lock range, are designed to reduce downtime and eliminate unsafe and laborious bolting methods for equipment, particularly in harsh operating conditions. They are shown here being used to secure the guides of a forging press. after 2 000 cycles. Nord-Lock washers are available in standard, over-size and X-Series for softer materials or flexible joints, as well as stainless steel to combat corrosion. BMG’s Nord-Lock bolt securing sys- tem uses tension instead of friction to ensure that joints holding sub-assemblies together remain secure. Bolts need to be easily removable during maintenance procedures, but must resist the loosening effects of vibrations and dynamic loads. Bolts that are locked conventionally by friction between components tend to lose most of their preload through vibration, while those locked by the tension of this system present only minor preload loss, which is caused mainly by settlement between contact surfaces. Even after moderate tightening, the bolt is safely locked when using Nord-Lock’s wedge- locking method. Nord-Lock washers, which are in- stalled in pairs, cam face to cam face, have cams between them with a greater rise than the pitch of the bolt thread. When the bolt and/or nut is tightened, the radial teeth on the opposite side grip and seat the mating surfaces. The teeth also lock the washers in place, allowing movement only across the face of the cams. If the bolt or nut starts to rotate loose in relation to the other, the resulting tension caused by a rise over the cams

Nord-Lock X-series washers.

BMG’s Nord-Lock multifunctional wedge-locking solution combines a wedge-effect to prevent spontaneous bolt loosening with a spring effect to compensate for loss of preload due to slackening.

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Mechanical Technology — July 2016