Explosion-proof special inserts

When a company using moulded-in inserts trialled a plastic enclosure that was required to withstand an internal explosion, the existing insert came close to meeting the requirements during the various test cycles: but ultimately one insert had failed. Thread forming screws had also been trialled with some success in the project, but industry standards for the application meant that they could not be used, so Tappex Thread Inserts was asked to develop a solution.

Restricted space meant that a simple increase in insert length as a means of increasing the resistance to pull out was not possible. After discussions with the customer, two variants of the existing insert used in the project were tested with larger diameters and undercut forms, but still without success.

In an attempt to give some direction to the project, a range of inserts of different types were then moulded in and tested. As a means of comparing the inserts, a simple jack out test was devised where torque was applied to the unsupported insert and value at which the insert failed was then recorded.

Results showed that the oversize self tapping style insert with no cutting features offered the greatest performance gain in pull-out. To maximise the benefit of this enhanced pull-out performance whilst retaining an acceptable level of rotational performance, a combination of the features of both a self tapping insert and a moulded-in insert were designed by Tappex, and samples were manufactured for testing by the customer.

The result was the special bespoke design of this thread insert from the Tappex team exceeded the customer’s required performance. Despite this, prior to production the design was further enhanced to increase the bolt engagement length by 1mm to ensure that the bolt could be tightened without any risk of bottoming in the insert.

Tappex says that over the years it has often been tasked with developing variations of its standard products (as well as bespoke special inserts), and that this latest example is further evidence of its ability to respond swiftly and positively to customer needs.