Drawbar springs are assemblies in which the spring will compress as the drawbar arms extend under an applied load. They are often capable of withstanding loads far in excess of the compression spring closing force and should be considered in applications where a positive stop or overload protection is required.
Compression springs can be used as an extension spring when it is fitted with a drawbar. This is often done when a regular extension spring might be deflected excessively and results in failure.
The compression spring should be designed with a safe stress at the solid height so that it will not take a permanent set. The drawbar can be made from any grade of hard-drawn wire, as they are quite strong if made with the same diameter of wire as used in the spring.
The drawbar ends should be closed, but not ground. Many sizes of springs have been made in this manner. One of the features is that such springs have a fixed stop when the spring goes solid, thereby eliminating overstretching. Another good feature of the drawbar is the elimination of buckling. The drawbar should be lubricated during operation to reduce friction.
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Graphic layout of Specificiations for Drawbar Springs