By Mark Albert , Editor-in-Chief
From: Modern Machine Shop
Posted on: 10/23/2013
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Strong bonds formed by advanced adhesives enhance machine tool construction, improve part assembly and make structural fabrications lighter and stronger. These and other applications have given machine shops and other manufacturers attractive alternatives to using welds, rivets, bolts, gaskets and other bonding techniques or materials. Henkel AG & Co. KGaA, the German manufacturer of Loctite, Bonderite and Teroson brands for adhesives, sealants and surface treatments, describes a number of uses for adhesives and sealants in machine design and part production that can yield superior performance, lower cost and greater versatility.
Examples likely to be found in a machine shop, factory or production plant include flexible adhesives and sealants capable of joining and sealing dissimilar substrates in machine design. These bonding agents can absorb assembly stress and deformation resulting from effects like load transfer, impact, vibration or differential thermal expansion. Such constructions retain their structural integrity even with fragile elements, such as windows, contributing to overall strength. These solutions have proven to be resistant to most industrial fluids, including cutting oils and emulsions.
Another area in which adhesives are finding important applications is in bed and frame construction. Materials such as composites or polymer concrete (mineral castings) are preferred for these machine structures because they have low expansion coefficients. However, they often need adhesives for certain assembly operations.
These structural bonding technologies reduce weight and increase stiffness, therefore enhancing equipment accuracy. This is because they evenly distribute stresses when joining dissimilar metals or joining composites and plastics. Material selection is not restricted to a limited number of materials, and customers can base material selection on purely functional criteria, enabling them to choose the most appropriate substrates. Using adhesives, manufacturers can readily incorporate new materials, thus combining their characteristics in the most advantageous way. For example, fast-cure flexible sealants bond materials such as painted and bare steel, stainless steel, castings and glass. This versatility makes innovative designs possible, enabling producers to create or repair new generations of readily marketable machines.
Plastics, composites and other lightweight materials can be incorporated and joined with conventional materials using structural adhesives. Even cast and carbon steel can be bonded together. Flanged joints in cast components can be sealed and reinforced using anaerobic liquid gaskets, thus improving their load transmission capability. In addition, the company’s sealants enable manufacturers to build machines for highly clean environments, or to prevent chemical ingress and mechanical damage in machines operating in harsh working environments. In addition, thread sealants and liquid gaskets can solve many common fluid sealing problems: from low-pressure fluid drainage or air recirculation systems that can be sealed with high-performance yarns, to high-pressure hydraulic, lubricant and pneumatic supply connections with screw threads that require high-performance anaerobic sealants. Thread sealants, such as Loctite 55 yarn, enable threaded connections to be sealed instantly, yet allow part repositioning if required.
One of the earliest uses of anaerobic adhesives, which cure without exposure to air, is thread locking to secure bolts. As economical as washers, threadlockers are more efficient because they resist vibration as well as temperature changes, pressure, component settlement and other phenomena that can loosen a bolt. This commonplace but essential application is not to be overlooked.
Machinery builders have used cyanoacrylates, or superglues, to bond materials like plastics, rubbers and other materials present in parts such as guards, door wipers or tags. These applications have benefited from increased resistance to weakening at high temperatures. Henkel’s cyanoacrylates, for example, have increased their temperature resistance by 50 percent to 120ºC (248ºF), and their setting time to a few seconds under most working conditions.
Gap-filling cyanoacrylates are another recent innovation, based on two-component systems able to bond and fill dissimilar substrates at the same speed as standard instant glue. Other hybrid adhesives are closing the gap between instant adhesives and structural adhesives, creating highly durable grades with a universal bonding capability and enhanced thermal resistance.
Finally, use of advanced adhesives promotes an emerging priority for machine designers—aesthetics. For example, pressure molded composites and formed plastic panels help machinery builders create appealing, lighter designs with rounded shapes and eye-catching contours for machine guarding or exterior features. These components can be assembled readily with sturdy, long-lasting bonds, and then attached to machine structures of traditional materials. Stiffeners bonded to the underside of these panels provide strength and rigidity where needed, without compromising stylistic appearance.