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Insight - How Expandable Screw Works

Written By: 

Bijal Parikh

Expandable Screw

This structure is known as expander cone. The cone is a very important part of the Expander screw and known as end nut. The design of the expander cone is very interesting. There are threads inside the cone. The threads on the expander cone are present in opposite direction to the threads on the screw. Apart from threads, another interesting part from designing perspective is teeth cut on the bottom part of expander cone. There are three teeth that are cut on the expander cone. These teeth lock the expander cone to the metal sleeves and restrict their movement before rotation. Expander cone is placed at the front of the sleeves and as we tighten the screw cone climbs up on the threads and moves in between the metal sleeves. It forces the sleeves to move outward or expand increasing the size.

The shape of the screw after expansion can be seen in the image below.

Expandable Screw

The strong  grip in the expander screw is because of two reasons.

{C}{C}{C}{C}{C}{C}      1.The expansion of sleeves increases the size of the screw in the hole and hence making it difficult to move. This locks the screw inside the hole.

{C}{C}{C}{C}{C}{C}     2. The metal sleeves expand into the concrete with local crushing. Local crushing increases the concrete in the hole and when the sleeves expand they push the concrete against the interior wall of the hole which creates friction.


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