A zipper that “feels smooth” in a showroom has not been tested. Chain lateral strength, top-stop and bottom-stop hold, slider lock, pin-and-box shift, and reciprocating life are separate measurements. Chinese light-industry standards QB/T 2171 (metal), QB/T 2172 (moulded plastic) and QB/T 2173 (nylon coil) plus GB/T 30420 methods are what domestic mills already run. Export brands add ASTM D2061 (strengths), ASTM D2062 (operating characteristics) and, in the UK, BS 3084. Put the method on the PO or the mill will send a smoothness opinion.
TrimGem University files zipper tests with button pull-off and nickel release: they are how a Guangzhou accessory programme fails or ships, and the test list only gets longer as the catalogue grows.
What the numbers mean (metal QB/T 2171 as a map)
Gauge is closed-chain width. Physical minima rise with gauge. Illustrative metal floors from the current QB/T 2171 table (always read the edition on the report):
| Gauge | Lateral strength ≥ | Opening smoothness ≤ | Top stop ≥ | Bottom stop ≥ |
|---|---|---|---|---|
| #3 | 220 N | 4.0 N | 40 N | 30 N |
| #5 | 350 N | 7.0 N | 70 N | 70 N |
| #8 | 450 N | 9.0 N | 90 N | 100 N |
Separating zippers add open-end lateral strength and box-shift strength. Slider puller attachment, puller twist, slider tensile, and auto-lock force are their own rows. Coil and moulded standards use the same ideas with different floors — do not paste a metal table onto a #5 coil.
Lateral (crosswise) pull is run on a tensile tester, typically 300 mm/min, jaws on the tape with the elements aligned to the jaw face. Failure is teeth off the tape or a burst chain. Coil often fails in the tape first; metal often deforms the tooth.
Stops, lock and the slider
Top-stop strength is the force that would yank the slider off the top of the chain. Bottom-stop is the closed-end equivalent. On open-end zippers the weak joint is usually the box walking on the tape, not the pin snapping.
Auto-lock force is measured with the slider locked, pulling along the chain until it slips. A jacket that opens in the wind failed this test, or never had a lock slider. Puller-to-body strength is the kidswear and backpack complaint: the tab comes off in the hand.
Cycling is the life test
Reciprocating (open–close) tests run the slider over the useful chain at a set stroke and rate (often 60–120 strokes per minute). Commodity floors in older QB language were a few hundred double strokes; brand and industrial programmes ask 5,000 or 10,000 cycles, then re-pull lateral strength. A common acceptance rule: remaining lateral strength ≥ 80% of the original, or still above the standard minimum. If the chain is smooth on cycle 1 and sandy on cycle 3,000, the slider cavity or the tooth hardness is wrong.
Salt spray (ISO 9227 NSS, 24–48 h) belongs on metal elements and sliders. Tape gets wash and rub fastness, not a salt cabinet.
Sampling, not theatre
Condition ≥ 30 cm specimens 24 h at 20 ± 2 °C, 65 ± 4% RH. Outgoing inspection follows GB/T 2828-style AQL: smoothness, lock, missing teeth and slider-cavity defects as majors; straightness, shade and dimensions as minors. Type tests after a material or tool change, not once per decade.
Name standard + gauge + chain type + which rows (lateral, stops, lock, cycles, fastness). “Tested zipper” is not a line a lab can run.