Why Glove Batches Fail AQL When the Sample Was Fine

A distributor approves a sample carton of nitrile examination gloves. Feel is right, thickness is right, the printing on the box is right. Four weeks later a container arrives and the incoming inspection finds a pinhole rate that fails the standard.

Nothing was faked. The sample was genuinely good. The bulk was genuinely bad. The variable is the part of the process nobody photographs.

Pinholes are a process problem, not a material problem

A dipped glove is formed on a ceramic former that goes through a coagulant bath, a polymer bath, a leach bath, an oven and a stripping station. A pinhole is almost always one of four things:

• A bubble in the compound — air entrained during mixing, invisible until the film cures thin over it
• A contaminated former — residue from the previous cycle that repels the film at one point
• A former with a surface defect — a scratch or a chip that produces a thin spot on every glove that former makes
• A cure that ran hot — film cured too fast, pinholed at the fingertip where thickness is lowest

None of these show up in a hand-feel check. All of them show up in a water test, which is why EN 455-1 specifies one.

What the standards actually require

For examination gloves the two numbers that matter:

AQL 1.5 means roughly 1.5 percent of the batch may be defective and still pass. On a 100,000 piece order that is 1,500 gloves. Nobody is going to inspect 1,500 gloves by hand — which is the point of sampling, and also where it goes wrong.

The two sampling failures

Failure one: the sample size is too small. A carton of 100 pulled from a 2,000 carton lot tells you almost nothing, because defects cluster. If one former on the line is producing pinholes, the gloves from that former are not randomly distributed across the lot — they are concentrated in the boxes filled during that run.

Failure two: the sample is pulled from the top of the pallet. The boxes at the bottom took the compression and the humidity. If the plant knows an inspection is coming, the top layer is the good layer.

The fix for both is the same: sample from cartons that were selected at random by number before anyone knew they would be sampled, and pull boxes from at least three different pallet positions including the bottom layer.

What to ask for beyond the AQL report

A pinhole count is a snapshot. Three other numbers predict whether the next batch will hold:

1. Former count and age. Ask how many formers are on the line and when the set was last replaced. A plant running 8,000-cycle formers is producing a slow drift in pinhole rate that no single inspection catches.
2. Water test failure position. Fingertips failing is a cure problem. Palm failing is a compound or former problem. The position tells you which to fix.
3. Compound lot traceability. Nitrile compound is bought in lots. If the batch that failed traces to a compound lot that arrived in a rainy week, the moisture content of the raw material is a candidate.

A factory that can answer these three is a factory that measures its own process. Most cannot, and that is itself the finding.

The commercial side

Gloves are a commodity with a very thin margin, and the market has a habit of selling to the price. When a quotation comes in ten percent under everyone else, the difference is usually one of: thinner film (lower gram weight), shorter leach (residual chemicals), fewer formers run faster (higher pinhole rate), or a compound with more filler.

None of these are visible in a photograph of a carton. All of them are visible in a water test and a gram-weight check — which is what we run before the balance moves, on the pallet that will actually ship.

Related reading

• medical consumables we buy
• what a CE certificate does not prove
• how to verify a Chinese supplier
• inspection and testing, in detail

Importing disposable gloves and want a pinhole and gram-weight check before shipment? Send us the specification — we will tell you what the batch needs testing for.