Expansion bolts are used to anchor into materials like concrete and brick. They come in different configurations, all using a lead sleeve to expand. They are rated by tonnage and can be coated with cadmium for moisture resistance. ANSI mandates standard sizes and drive types.
An expansion bolt is a bolt, nut, and lead sleeve assembly that expands when tightened. These bolts anchor into materials that don’t allow for reliable thread formation, such as concrete, brick, and the like. While similar in concept to nail anchors with expandable nylon sleeves, expansion bolts are used in heavy-duty applications such as fastening benches and stadium seating. There are several configurations.
In the bolt-lead sleeve-tapered nut configuration, a tapered nut rests in a lead sleeve. The entire component is inserted into a pre-drilled hole. The bolt is then driven in and, once secured, the tapered nut is pulled towards the head of the bolt, causing the lead sleeve to expand.
Another configuration is the bolt-lead bushing-cone-nut. In this type, a metal cone and sleeve rest on the bolt assembly. As the bolt is tightened, pressure forces the metal cone into the lead sleeve and this expansion secures the bolt in place. The cone bolt-lead sleeve-cone-metal nut configuration, while similar to the previous group, relies on a conical bolt head, not a nut, to expand the lead sleeve.
The lead sleeve is the common factor connecting the different types of expansion bolt configurations. Lead is malleable, so it easily fills the drilled space in which it is set. Also, due to the lead sleeve, the expansion bolts allow for minimal risk of cracking or shattering of the anchor material because the expansion bolts do not rely on individual fixing points. The risk of pulling or stripping is also reduced by lead sleeves.
Depending on the bolt diameter and the materials the bolts are tested in, expansion bolts smaller than 5 inches (12.7 mm) may be rated in tonnage. Specifications can be found on the expansion bolt packaging and the correct tolerances should be chosen based on usage and risk of corrosion. If there is a high likelihood of continued exposure to water, cadmium, a group 12 transition metal with similar anticorrosive properties to zinc, may be added to help the expansion bolt resist moisture.
In the United States, the American National Standards Institute (ANSI) mandates, among other things, standard and metric sizes and drive types – spline, hex, double hex, etc. – of the machined parts. You can find various sizes and types of expansion bolt units to fit any need. Expansion bolts and their lead-free components are made of steel and are plated according to the standards and specifications of the American Society for Testing and Materials (ASTM).
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