Q: How do QB/T 2173 metal zipper requirements differ from nylon?
QB/T 2173 covers metal zippers, and its differences from the nylon standard follow from the material. Metal zippers add corrosion testing, plating adhesion and finish appearance to the common strength and life tests, because the failure modes are rust, flaking and discolouration rather than coil deformation. Strength values are also set separately, since a brass chain and a coil chain do not fail at the same load.
Corrosion is usually assessed by a salt spray exposure of a stated duration, with the acceptable area of white or red rust defined in the standard's table. Plating adhesion is checked by a bend or tape test on the teeth and the slider. Reciprocating life and pull strength are run with the same logic as for nylon, but with metal-specific acceptance values and attention to slider wear. Refer to the standard text for durations and limits.
In practice, specify the standard, the size and the finish on the purchase order, and test the finish that will actually ship. A metal zipper that passes strength but fails salt spray is a finish problem, and the corrective action belongs with the plating line, not with the assembly.