Expansion bolts are multi-component fasteners that expand upon installation to provide secure fastening in materials that do not permit reliable thread formation as is needed for other types of bolts. Materials such as concrete and brick are easily damaged by threaded screws and bolts as the treads strip the material rather than biting into it.
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Expansion Bolt Applications
Instead of creating cracks and crevices as other bolts do, expansion bolts fill these deformities, which improves aesthetics as well as strengthening the connection. This allows the use of these bolts even in vibratory environments. This reliable anchor bolt can therefore be used in a wide variety of industries. Masonry walls, construction, turbines, motor couplings, gears, mining, seating and sign installation all use expansion bolts to avoid material damage while creating a firm bond. This bond offers an extreme carrying weight. A relatively small bolt, ¼" for example, can have a pullout weight of up to 2,700 pounds. These carrying weights, measured in tonnage, provide the rating system for expansion bolt manufacturers and suppliers. Bolt length, diameter, materials and configuration should all be carefully considered with regards to the materials to be fastened. These materials should also be considered as poor quality concrete will crumble under such extreme weights no matter the type or class of bolt.
Design of Expansion Bolts
Each bolt system has three basic parts, the bolt, nut and sleeve, which may be assembled in a number of configurations. In the bolt-lead sleeve-tapered nut set up the entire mechanism is inserted into a pre-drilled hole and the tapered nut is drawn back towards the head to compress and expand the lead sleeve. The bolt-lead sleeve-metal cone-nut functions in the same manner though the metal cone is driven into the sleeve causing expansion rather than the nut. The tapered bolt-lead sleeve-metal cone-nut configuration is similar in assembly although the tapered bolt is responsible for expansion rather than the nut or the metal cone. In any assemblage the bolt, nut and cone, if present, are made of steel alloys which offer strength and corrosion resistance. Cadmium and zinc plating are common finishes for bolts that may face continual exposure to water and other environmental elements. While each of these components is integral to the bolt design, the lead sleeve is the crucial element of the expansion bolt. Lead is a malleable substance. When compressed it easily fills the drilled spaces as well as any surrounding cracks or pores. This creates multiple points of attachment while minimizing the risk of cracking or shattering the anchoring material.