Filter Press Cloth 6L: the 20 micron hybrid between fine filtrate and workable cycles

The cloth for the gap between 10 and 25 micron

This grade exists for a situation that comes up more often than a product list suggests: the 3L creates too much resistance, and the 7L lets too much fine material through.

The 6L is the answer to that. A 20 micron filter press cloth covers a band that would otherwise have nothing in it, and the hybrid construction is the reason it can. At 400 g/m² it weighs well below the 3L at 620 and above the 15L at 320. Where filtrate quality has to be good and the cycle still has to fit the shift, this is the grade to look at first.

The tightest thread grid in the range, and still the more open cloth

If fabric construction interests you at all, the 6L is the one worth reading about.

It carries 120 warp threads and 28 weft threads per centimetre. The 3L runs 60 and 12, the 15L 44 and 14. So the 6L has by a clear margin the tightest grid in the family, roughly twice as many threads as the 3L, and it is still the more open of the two.

The yarn explains it. In the warp the 6L uses monofilaments, smooth single strands that weave into a close, defined structure. The weft carries multifilament yarn, which consists of many fine filaments and closes the surface further. The 3L works throughout with multifilament and staple fibre yarn, whose fibres fill the gaps and produce a denser but less regular structure.

Two routes to fineness, then: the 3L through the fibre, the 6L through the grid. In service that matters. A defined structure of monofilaments tends to trap less solid material permanently between individual filaments and is usually easier to clean down.

Satin weave, heat set and calendered

The fabric is woven in a satin construction. In a satin the weft thread passes over several warp threads before it dips under again, so one thread system dominates the surface and the face comes out smoother than a plain weave.

Two finishing steps follow. Heat setting stabilises the fabric under heat so that it holds its dimensions better in service. Calendering smooths it under pressure between rollers.

Together they give a closed, smooth face, and that can help the cake come away. Whether your cake actually releases more easily also depends on what it is made of, how compressible it is and how much moisture is left in it.

A permeability of 6 with the test pressure stated

The datasheet gives 6 l·dm⁻²·min⁻¹ at 200 Pa, which means the test pressure is on record. That is twice the permeability of the 3L and well under half that of the 15L.

Stating the test pressure is more than a formality. It makes this value directly comparable with the 67L, which is tested at 2 mbar, and 2 mbar is the same pressure as 200 Pa. For the 3L and the 15L no test pressure is documented in the papers we hold.

The usual caveat applies here too. The figure describes dry fabric. It is a yardstick between grades, not a promise about the liquid throughput of your press.

The only grade with a documented temperature limit

For the 6L the datasheet states a maximum working temperature of 90 °C. That figure is on record, and in this range it is the only one of its kind: for the other four grades no corresponding release exists.

If your process runs warm, that is a solid reason to choose this grade. It does not replace a check of the actual medium. Chemical resistance depends on the medium, the concentration, the temperature and the contact time together, and polypropylene is not universally resistant.

Technical data for the 6L filter press cloth

Where the 6L sits between the other grades

Common questions about the 6L filter cloth

The questions here are usually about the boundaries in both directions and about the hybrid weave.

When is a 20 micron filter cloth the sensible choice?

When the 3L creates too much resistance and the 7L lets too much fine material through. The 6L is deliberately positioned as an intermediate step and is not a replacement for either.

What do monofilament and multifilament mean in one fabric?

Monofilaments are smooth single strands that weave into a defined structure. Multifilament yarn is made of many fine filaments and closes the surface more. In the 6L the warp is monofilament and the weft is multifilament. The selection guide goes into this in more detail.

Is 20 micron a guaranteed separation limit?

No, it is a nominal range classification. Real retention comes out of the interplay between fabric, filter cake and operating conditions.

What temperature is documented for the 6L?

The datasheet states a maximum working temperature of 90 °C. No equivalent figure exists for the other grades, so we do not transfer this one to them.

Why does the 6L have more threads per centimetre than the 3L and still run more open?

Because fineness does not come from the grid alone. The 3L uses multifilament and staple fibre yarn whose fibres fill the spaces between threads. The 6L builds its structure from fine monofilaments in a close grid. Two construction principles, two different behaviours in service.

Is polypropylene resistant to my process medium?

Polypropylene handles many aqueous and industrial media, but not all of them, and concentration, temperature, pH and any solvents present all count. Send us the medium and the operating data and we will look at it for your case.

Can head and end cloths be made in the 6L fabric?

Yes, as in all five grades. For a quotation we need the plate size, the position in the pack, the inlet geometry, the edge finish and the fixing method.