Phosphate Rock Filter Cloth for Horizontal Vacuum Belt Filters

Recommended material direction

The distinguishing variable here is mechanical rather than chemical. The siliceous gangue is hard and angular and it works on the cloth surface, at the edges and at the discharge roller. The liquor is recycled process water carrying flotation reagent residue rather than acid from a reactor — but what its pH actually is depends on your reagent scheme and is not something this page knows. So abrasion resistance moves to the front of the polymer decision on the evidence available, and the chemistry has to come back and confirm it.

This narrows the field; it does not pick. Which polymer goes on your machine is settled against your measured numbers and not on a web page — the same position the selection section above takes. What follows is the reasoning behind that position, not a departure from it.

• Polyester (PET) PET

  Continuous reference up to ~150 °C — a published property of the polymer, not a value of ours

  • Acid Good
  • Alkali Limited
  • Hydrolysis Limited
  • Abrasion Excellent

  Excellent abrasion resistance and dimensional stability under tension, and nothing in a non-acidic reagent-bearing process water attacks it. This is the duty where the abrasion column of the polymer table earns its place.

• Polyamide (Nylon 6 / 6.6) PA

  Continuous reference up to ~110 °C — a published property of the polymer, not a value of ours

  • Acid Poor
  • Alkali Good
  • Hydrolysis Moderate
  • Abrasion Excellent

  The other polymer with excellent abrasion resistance — and here the usual objection to it, acid attack, does not apply. The remaining objection does: it absorbs moisture and changes dimension with it, which complicates a tensioned belt.

• Polypropylene PP

  Continuous reference up to ~90 °C — a published property of the polymer, not a value of ours

  • Acid Excellent
  • Alkali Excellent
  • Hydrolysis Excellent
  • Abrasion Good

  Chemically untroubled by this liquor, but its abrasion resistance is good rather than excellent, and that is the wrong column to compromise on a hard angular gangue.

What actually decides it The measured pH of the recycled water — including after a reagent change, because the scheme is what sets it — and then a mineralogical breakdown or assay if the plant has one. Photographs of where the last belt actually wore settle the rest: edge wear and discharge-zone wear tell a different story from general surface wear, and they lead to different answers.

Everything in this block is reasoning from published polymer behaviour applied to the chemistry described further up this page. It is a direction, not a selection — and the selection is made against your measured numbers during the engineering review, then written into the quotation. The full polymer envelope is on the materials page.

Weave options

On an abrasive duty the structural back is doing mechanical work, not just carrying the filtering face.

• Double layer / multi-layer Two or more interlaced fabric layers woven as one. A fine filtering face carried on a coarse structural back — high strength with fine retention, and drainage channels inside the fabric. Watch: Thicker and heavier; more expensive to weave. The usual answer on heavy belt duties.
• Plain One over, one under. The most stable and the most rigid. Tight, uniform pores; lower permeability for a given yarn. Watch: Least forgiving of dimensional movement; can blind faster on fine solids.
• Twill The crossing point steps sideways each pick, giving a diagonal rib. More flexible and more permeable than plain at the same yarn count, with better cake release. Watch: Slightly less dimensionally stable than plain.

Strength and retention are chosen together as one requirement. A fabric specified only for its rating will meet the rating and lose the belt.

Yarn form. Monofilament gives the surface that releases and washes back; where the feed carries a wide particle distribution a mono-and-multi combination is the usual compromise between release and retention.

Yarn form, weave and surface finish are settled as one decision. The four yarn forms available are monofilament, multifilament, mono + multi combination and staple / spun.

Permeability considerations

Air permeability is the figure everyone compares and the easiest one to quote meaninglessly. It is measured per ISO 9237 at a stated pressure drop — often 200 Pa — or per ASTM D737 (Frazier). A value with no stated pressure and no stated unit is not comparable to anything, including ours. The same applies to a pore or retention rating: on a woven cloth that is a nominal figure and not an absolute cut-off, because woven media do not have a single pore size and the cake quickly becomes the real filter.

Permeability on this duty has to be read alongside the abrasion question: a very open structure discharges and washes well and offers the gangue less material to work on per unit of surface. Ask for the figure with its method and pressure; a number on its own settles nothing.

How each property is measured, and what to ask any supplier for alongside the number, is set out on the testing and inspection page. Naming the method is a fact about a public standard, not a claim about our laboratory.

Joint options

• Clipper (metal hook) Interlocking metal hooks crimped onto both cloth ends, joined by a pintle wire. Fitted and replaced on the machine without dismantling it. The fastest change-out. Watch: The joint is a discontinuity: it leaks vacuum as it passes the box, and it is where most belt failures start. Hook material has to suit the liquor.
• PAD / welded overlap The two ends are overlapped and thermally fused. A smoother, quieter joint that seals better than a clipper and carries load more evenly. Watch: Made off the machine or with a portable press; a change-out takes longer.
• Spiral Spiral coils on each end interlaced and pinned. Flexible, drains through the joint, distributes load along the full width. Watch: Adds an open line across the belt — not appropriate where the joint must seal.

The joint is where the belt carries its load and where it loses its vacuum seal. Match it to what the machine is already set up for, from a close-up photograph of both faces.

The four constructions drawn in cross-section: how joints fail and what each one costs you.

Edge treatment

• Cut and sealed The cut edge is thermally sealed against fraying. The baseline. Adequate where the machine edge seal is in good condition.
• Folded / hemmed The selvedge is folded back and secured. Adds thickness and stiffness at the edge where the seal rubs.
• Reinforced edge band A separate band is bonded along the selvedge. For machines that chew edges — the usual answer when a belt keeps failing at the edge while its body is sound.
• Coated / sealed band A polymer band is applied to the edge. Seals the edge against vacuum bypass as well as protecting it mechanically.
• Guide strip / tracking profile A profile bonded to the underside to run in the machine guide. Only where the machine is built for it. Fitting one to a machine that is not is a common and expensive mistake.

A reinforced edge band is the usual answer when a belt keeps failing at the edge while its body is still sound, and on a hard angular gangue the edge is exactly where the wear concentrates. A guide or tracking profile is a different matter: it goes on only where your machine is built to take one, because fitting one to a machine that is not causes the fault it was meant to prevent.

Relevant equipment

A filter belt is decided at the loom before it is decided anywhere else: what a weaving platform can hold — pick density, tension, width — sets what the finished cloth can be asked to do. Our weaving runs on DORNIER (Germany) and Sulzer (Switzerland) platforms, machines built for technical textiles rather than for apparel.

A mine-duty belt is wide, heavy and stiff, and holding a consistent pick density right across the web is a property of the weaving platform rather than of the finishing line. What width we can hold it across is the one number we have not confirmed in writing yet — send your measured width and we will answer it rather than assume it.

Model designations, working widths and installed quantities are being confirmed against the machine nameplates and are not published until they are. A weaving platform is easy to name and hard to fake, and we would rather you were able to check.

The full platform description, the eleven process stations from yarn to crate, and the nine laboratory checks: manufacturing.

Factory capability for this duty

The rows below are the part of our capability envelope that this duty touches. The last group is the one that makes the rest of it worth reading — a supplier who can do everything has told you nothing.

The full envelope, including the machine families and services we decline: what we build to order and what we will not take on. Fifteen pages on how a specification like this is built and read: the filter cloth specification guide.