One of the index test pull head lock function on the chain belt is self-locking pull head strength index which is a minimum.
Asked to pull the head is installed on the chain belt, exerting certain pulling force on the chain belt, pull head remain locked in a chain, no slippage. A numerical force applied on the chain belt is standard. Pull head self-locking force is the pull heads in clothing should have an important function, in order to improve the zipper using the reliability, in the new standard of the metal zipper ", on the part of the type pull head improves the self-locking pull head strength index.
In the standard, the load pull times also made some modifications to test the overall performance of the zipper or the service life of the indicator, is the load pull. This requires exerts a force on the zipper, and reciprocating pull head, within the provisions of reciprocating pull count, zippers keep good condition, does not appear broken belly phenomenon, taking into account the reliability of the use of zipper, in the process of production and can reach the level and load of zipper pull index for improving, especially improve the zipper 3 greatly: previous 3 standard is 200 double and other 500 double, and now are 600 double.