Filter Cloth FAQ
The questions a quotation cannot start without, answered the way an engineer would answer them on the phone.
Product and application pages carry their own questions in context. This page is the hub — the answers that apply whatever machine you run. Where we do not have a confirmed answer, the question still appears and says so.
How do I choose a filter cloth for my duty?
Selection runs backwards from the slurry, not forwards from a catalogue. The chemistry, temperature and particle size of your stream narrow the polymer and the finish; the weave sets the balance between filtrate clarity, cake release and resistance to blinding; the machine fixes width, length, seam type and edge treatment. Polymers commonly used on these machine families include PET monofilament, PET monofilament and multifilament combinations, polypropylene, and alkali- and hydrolysis-resistant specials — that is the industry-level range, not a statement about our own looms. Our mill’s confirmed weavable polymer list is being confirmed in writing and is not published yet. There is no single cloth for an industry — two plants in the same industry can need different cloth, because they are running different slurries through different machines.
Phosphogypsum vs FGD gypsum — a worked example → HVBF cloth product family →
Why do you ask for photos of the old cloth and the seam?
Because the cloth on your machine is a more reliable record of that machine than any drawing. The photograph tells us which seam type is fitted, how the edge is finished, and — most usefully — where the cloth actually failed. Machine drawings are often the as-supplied version rather than the as-running version, and a belt rebuilt from an out-of-date drawing is a belt that does not fit. A close-up of the seam takes thirty seconds and removes most of the guesswork from the quotation.
What is the difference between a replacement cloth and an OEM spare part?
Independent replacement cloth — not an OEM spare part. Dimensions and construction are confirmed per enquiry. In plain terms: we do not supply the original equipment manufacturer’s branded part, and we never present our cloth as any brand’s own catalogue item. That distinction matters for your warranty position and for your procurement paperwork, so we state it on every page that names a machine brand.
How should I measure my old belt?
Measure the cloth, not the machine. Take the width across the cloth itself rather than the roller or the frame, take the total length of the endless belt, and photograph the seam close up with something in frame for scale. Note the edge treatment and whether the failure started at the edge, at the seam, or in the body of the cloth. If the belt is already off the machine and cut, say so — a cut belt can still be measured, but we need to know it was cut.
Is phosphogypsum the same as FGD gypsum?
No. Phosphogypsum is the calcium sulphate by-product of wet-process phosphoric acid production and comes out of a fertilizer plant. FGD gypsum, as this site uses the term, is the calcium sulphate by-product of wet-lime flue-gas desulphurisation at a power station. Sinter-plant flue-gas desulphurisation produces a third by-product again; we treat it as its own duty and ask which one you are running rather than assuming one belt covers both. Different origin, different process chemistry — the phosphate side is described in the literature as fluoride-bearing and the scrubber side as chloride-bearing. Cloth manufacturers that publish their ranges split the two into separate belt classes rather than offering one gypsum belt, so treating them as interchangeable is a real risk, not a pedantic distinction.
What information do you need before you can quote a filter cloth?
Six things get a quotation moving: your company and country; the machine brand and model, or the word unknown if the nameplate is unreadable; the cloth width and length, or the plate area for a pressure filter; a photograph of the old cloth and its seam; which slurry the machine is running; and what went wrong last time — short life, blinding, tracking, a seam leak or poor cake release. Slurry pH, temperature and particle size distribution are optional but genuinely useful if your process sheet has them.
How long will the cloth last?
That depends on your duty, and we do not publish a service-life promise. Third-party case material shows cloth life varying widely between installations running comparable machines, which is the clearest evidence available that life is a property of the installation and the slurry rather than a property of the cloth. What we can usefully do is work on the failure mode you are actually seeing — a cloth failing at the seam, at the edge, or by blinding are three different problems with three different fixes.
Do you supply cloth for FGD wastewater treatment?
FGD wastewater treatment is a different duty from FGD gypsum dewatering, and it is frequently handled with filter bags rather than with a vacuum belt filter cloth. We do not publish a page for it, because pointing a wastewater enquiry at a belt page would be misleading. If that is what you are working on, describe the machine and we will tell you plainly whether it is something we make.
How can replacement belt seams withstand heavy operating tension?
Seam durability depends on the interaction between base fabric weave and fastener geometry. Heavy-duty double-layer monofilament constructions distribute tensile pull evenly across warp yarns. Fasteners in AISI 316L, 904L, or Hastelloy C-22, along with PEEK or synthetic pintle options, are evaluated against machine roller diameters and slurry chloride/acid concentrations rather than assumed as a single blanket standard.
How are filter cloth polymers selected for extreme acid or alkali slurry conditions?
Polymer selection is dictated by process thermodynamics and ionic species rather than catalogue convenience. For acidic fluorinated duties like wet-process phosphogypsum (pH 1–2), hydrolysis-stabilized Polyester (PET) or Polypropylene (PP) is specified, while Polyamide (PA) is barred because mineral acids rapidly hydrolyze amide bonds. Conversely, for caustic duties like Bayer red mud or lithium hydroxide (pH 12–14 at 80°C), Polyester is barred due to alkaline ester saponification, and high-crystallinity PP or PVDF/PPS is deployed.
How do asymmetric weave and thermal calendering prevent cloth blinding in fine mineral slurry?
Asymmetric double-layer cloth pairs a high-density fine monofilament satin weave on the slurry face with an open coarse drainage weave on the underside. The fine top layer acts as a surface-filtration barrier that halts sub-20 micron fines before they can lodge in the yarn core. Controlled thermal calendering creates a smooth face that prevents mechanical keying of crystalline scale, enabling cake release by gravity and allowing oscillating water spray bars to displace residual particles.
Can a replacement filter cloth be specified without the original OEM machine drawings?
Yes. Machine drawings often reflect as-supplied configurations rather than the as-running physical reality of a modified machine. Direct measurements of the running cloth, taken with the 6-Photo Protocol, are a usable starting point for the specification. Tolerances are agreed on the order drawing against your machine’s take-up carriage travel; no blanket tolerance is published.
What is the procedure for laboratory coupon testing before ordering a full-size filter belt?
Coupon or seam samples may be discussed during technical pre-screening for unfamiliar slurries; availability, candidate permeability samples, freight and review timing are confirmed per inquiry rather than issued as an unverified blanket catalog policy.
What are your lead times, and how does a sample work?
Not confirmed yetWe are not publishing a lead time or a sample policy here, because we do not yet have a confirmed one to publish and a made-up figure would be worse than silence. Ask in your enquiry and you will get a specific answer for your item and your destination rather than a generic number.
Ask the question against your own machine
A general answer can only take you so far. Send the machine, the slurry and the failure and you get an answer about your installation instead of about the category.