In most applications where fasteners are required, ensuring that the fastener offers the right strength and fastening performance to avoid failure in its intended application. However, many suppliers only evaluate the dimensional size of fasteners without properly exploring the strength of the given fasteners. Many screw specifications will specify the torsional strength test as a measure of a screw’s ability to perform its intended function in its final application. With the torsional strength test, a screw is evaluated to measure its ability to resist twisting into two pieces.
To test the torsional strength, a torsional strength apparatus is typically used. This equipment generally has an adjustable upper arm that can accommodate various screw lengths and a rotating shaft that applies the torsional testing force while the base has a groove to clamp the split collets that holds the screw’s threads. The collets serve to protect the screw’s threads from being crushed or cut by the clamping action that’s needed to prevent the screw from rotating during the test. Without the collet, the torsional values may be lower if the threads are damaged.
At the top of the apparatus, a calibrated torque wrench is installed into the rotating shaft. This component measures the torque that’s required to twist the screw into two pieces. The wrench can be either analog or digital, however, it’s important for it to have a needle that displays the highest value measured during the test. Generally, this component is calibrated to be accurate in the upper 80% of its torque range.
The testing procedure is generally as follows:
- A collet is chosen that matches the screw size and thread pitch. The screw is threaded into the collet so that at least two threads remain above the top surface.
- The collet is placed into its holder and inserted into the base of the testing apparatus. The collet is then clamped tightly enough to prevent the screw from rotating when force is applied.
- A driver bit or socket matching the screw is inserted into the rotating shaft and engaged with the head of the screw.
- A smooth force is applied to the screw until it twists into two separate pieces. The highest observed value is the torsional strength.
This test ensures that screws meet the required standards and specifications for use. If screws exceed their minimum torsional strength, that is an even better indication that it will perform in its intended applications. For over 60 years, One Monroe EFI has specialized in sophisticated and specialized fasteners. Our experienced team can help you find the right screws and other fasteners strong enough for any application. Contact us today to learn more or get a quote for your next project.