Concrete Overlay

Machine screw anchors are a female type anchor into which a threaded item is placed. Machine screw anchors are made up of two parts, the internally threaded cone and the sleeve. The sleeve is place over the threaded cone and inserted into a hole drilled in to the base material of concrete, brick or block, threaded cone first. The machine screw anchor is set by the sleeve being pushed over the expander sleeve wedging the sleeve between the expander sleeve and the inside wall of the concrete. The anchor is properly set when the lip of the setting tool meets the lip of the anchor. Each diameter machine screw anchor has a specific setting tool that is designated by the diameter of anchor being used. The machine screw anchor size is designated by the inside diameter of the bolt to be used with the anchor, the hole size required is larger than the anchor size being used.

Strike Anchor

Strike anchors are for use in solid concrete and are considered an impact expansion type of anchor. The strike anchor is made up of four parts: the body that is made from carbon steel with an interior hole the entire length of the anchor, a drive pin that is hardened, and a nut and washer plated in a yellow zinc. The body of the anchor is threaded on one end with the other end having four slots cut a portion of the length – the surface of this part of the body has ribs around the circumference. The length of the drive pin that is hardened must equal the length of the anchor and is placed inside the interior hole of the anchor body. The anchor is set by placing anchor into a predrilled hole in concrete with the nut and washer attached. The anchor must be tapped lightly until the nut and washer are against the base material or fixture being fastened down. The hardened pin is then driven into the anchor until the head of the pin meets the end of the anchor body, which will provide for the proper setting. As the pin is pushed into the anchor, the anchor is expanded. The hole that is needed to be drilled for the strike anchor is the same diameter as the diameter of the anchor being used.

Hammer Drive Anchor

Hammer drive anchors are made from a Zamac material that is strong and malleable. Hammer drive anchors are a light duty concrete anchor, made up of two parts the body and the zinc plated steel pin. The body of the hammer drive anchor is split from the bottom up for most of its length, with a mushroom head. The anchor body is hollowed out that runs through the head thickness and down into the shank for the entire length. The steel pin is what expands the anchor; it is made of high carbon steel, with a small head on one end and with the other end pointed. The anchor is set by hammering the steel pin into the anchor body. As the nail pushes through the anchor body, the split part expands to push against the interior wall of the hole in the base material. The hole diameter to be drilled for the hammer drive anchor is equal to the diameter of the anchor being used.

Split Drive Anchor
Split drive anchors are made from carbon steel that is heat-treated concrete stamping tampa through, hardened and zinc plated. Split drive anchors are one piece with either a flat countersunk head or a round head. At the base of the anchor, opposite sides of the head the shank is sheared into two pre-expanded parts. These two halves are compressed when the anchor is driven into a predrilled hole in concrete. These two halves continually try to get back to their original shape, pushing against the inside wall of the hole. The split drive anchor requires a hole size that is equal to the diameter of the anchor being used.

Lag Shield

Lag shields are made up of two parts that are assembled into one piece. The lag shield is made from a Zamac material, which is a zinc alloy that is rust-resistant. The inside of the lag shield has internal threads designed to accept lag screw threads and its threads are tapered and run the length of the anchor. The outside body of the anchor has ribs that run the majority of the length of the anchor. The lag shield is set by inserting a lag screw into the anchor. Turning the lag screw into the tapered threads expands the two halves of the anchor and pushes against the base material. Lag shield anchors are designated by the diameter of the bolt that goes into the anchor. It is important that the hole size to be drilled is larger than the designated anchor size.

For years creating a nice consistent diameter hole in concrete was painstakingly difficult, until the invention of the electric hammer drill. Before the electric hammer drill holes where made by using what was called a star drill. The star drill was a steel bar with one end shaped like a large X (the drilling end) the other end a stud (the striking end). The drilling end was place on to the concrete, the striking end was hit with a heavy hammer, and after each blow with the hammer the operator would turn the stud slightly, over time a hole could be drilled into the concrete. Before the star drill, other methods where used to create holes in concrete, using chisels and punches.


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