Textile Structure
how cloth is put together
Concept

Retention — where it appears

Holding soil back while still passing water, specified as an opening size against a stated fraction of the soil's own grain size. It is one of two requirements that pull opposite ways, since the hole that passes water is the hole that passes soil.

Named by 3 essays across one field — each of them below, with the objects they name alongside it.

The hole between four threads. Three millimetres of a woven filter cloth in plan, with one clear opening dimensioned and a grain of the soil it must retain drawn at the same scale. Every hole in the repeat is this size — a woven cloth's pore distribution is a single value, which is why it is specified by an opening size while a nonwoven needs a curve.

The hole between four threads

A woven cloth's holes are all the same size. That is not an approximation — it is what a repeat means — and it is the whole reason a woven filter is specified by one number while a nonwoven needs a curve. The number is the spacing less the diameter, which this site has been computing since its first questions about setting.

applied · Cover A filter cloth has two jobs. Opening size against sett for a woven filter cloth, with the two limits that specify one: the soil is retained below the retention line, and the water passes above the open-area floor. They pull opposite ways, so the answer is an interval in the sett — and for a fine enough soil there is no interval at all.

A filter cloth has two jobs

Hold the soil back and pass the water. The first wants a close sett and the second wants an open one, so a filter cloth is not a fabric but an interval — one that is sometimes a single sett wide, and for a fine enough soil is empty. The empty case is the useful one, because it says the answer is not a woven cloth at all.

applied · Openings A woven filter catches what its rating says it cannot. What fraction of a particle stream is intercepted by the hair layer of a filter cloth, against particle size, at three levels of raising. The cloth's own largest opening is 290 µm, so by geometry it stops nothing smaller than that at all — and the hairs catch a few per cent of particles ten and a hundred times finer, because a particle whose path passes within its own radius of a hair touches it. On a bare cloth the numbers are small; the point is that they are not zero, because a cake grows from the particles that stop, and once a cake exists the cloth is no longer doing the filtering. Raising the same cloth 32-fold takes a ten-micrometre capture from 0.8% to 23%, which is why a napped filter cloth exists. Interception is taken as the bare geometric ratio of the two diameters with no flow model behind it, so every number here is a lower bound.

A woven filter beats its own rating

A filter cloth's rating comes from the largest channel through it, and by geometry it stops nothing smaller. It stops a few per cent of particles ten times smaller anyway, on the fibre ends standing in its holes — and a few per cent is not filtration. It is exactly enough to start a cake, and after that the cloth is not filtering.

applied · Filtration

Named alongside it

The objects these essays reach for when they reach for this one.

CoverNonwovenOpening sizeSettSpecificationApparent opening sizeCanopy criterionClear openingCover factorHair coverageHair layerInterception

All concepts