There are various methods by which to evaluate zipper strength. The basic strength can be determined based on the results of the following inspection methods, from which all around strength appropriate for respective uses can be judged.
Crosswise Strength of chain (per 2.5cm)
To determine ordinary zipper strength: a zipper chain is interlocked, pulled at a fixed speed at a right angle to the chain interlocked direction, and the resistance is measured.
Vertical tensile strength of the top stop
The lower part of an interlocked zipper is fixed and the slider is pulled up to the top stop.
Holding strength is measured by pulling the slider top stop firmly.
Bottom stop tearing strength
A slider is pulled down to the bottom stop and single chains are opened to the right and left sides.
Bottom stop holding strength and resistance of the elements inside the slider are measured.
Horizontal tensile strength of the box
The open part is fixed to the tensile tester
(Only the open part as shown in the figure) so that the end of the last element falls into line with the clamp edge and the tensile strength can be measured.
Slider lock strength
A slider is locked at the middle of a zipper chain and single chains are opened to the right and left sides. Locking strength and resistance of the elements inside the slider are measured.
Overall strength of the slider (90 degrees)
For a completed slider, resistance of the slider is measured when power is put on the pull tab and the lower part of the body. In addition to the 90 degree method of measuring shown in the figure at left, there is one of 45 degrees.