Filter Press Cloths

A Filter Press Cloth is a specialized fabric used in filter presses to separate solids from liquids. It is installed over the filter plates, acting as a filtration medium that allows liquid to pass through while trapping solid particles.

The choice of material depends on the chemical compatibility with the slurry being filtered, temperature resistance, and the required filtration efficiency. Matching the material to specific applications is crucial for optimal performance.
Filter Press Cloths are typically made from synthetic fibers such as polypropylene, polyester, or nylon:

Polypropylene: Known for its excellent resistance across the full pH range (0-14), making it suitable for various chemical environments. It has a maximum operating temperature of 90°C but is affected by many common oxidizing agents.

Polyester: Offers excellent resistance to most mineral acids and solutions in the pH range of 1-8. It has a higher maximum operating temperature of 140°C, making it suitable for more demanding applications requiring increased tensile strength, higher temperature resistance, and the ability to withstand higher oxidation levels.

Nylon: Exhibits good resistance to alkalis but is vulnerable to strong acids and solutions within the pH range of 1-6. It has a maximum operating temperature of 105°C and possesses very good abrasive resistance, making it ideal for applications involving rough or sharp particles.

When a slurry (a mixture of solids and liquids) is pumped into the filter press, the cloth traps the solid particles on its surface, forming a filter cake. The liquid passes through the cloth and exits as filtrate. The process continues until the filter cake reaches the desired thickness.

Filter Press Cloths can vary based on yarn constructions, weave types, and porosity:

Yarn Constructions:

Monofilament Yarns: Made from single, continuous fibers; ideal for easy cake release and good filtration with minimal blinding.

Multifilament Yarns: Made from twisted strands of fibers; provide a tighter weave, better for filtering fine particles.

Spun (Staple) Yarns: Created from filaments cut into short lengths and then twisted or “spun” together. Staple fibers offer good gasketing and particle retention characteristics, but the hairiness of the yarn can make cake release more challenging.

Needle-felt Cloths: Made from random fiber arrangements, needle-felt cloths are designed for specific applications where excellent filtration is needed without the need for weaving.

Weave Types:

Plain Weave: The simplest and most common weave, produced by passing the weft thread over and under each successive warp thread. It offers low permeability and excellent particle retention but is susceptible to blinding.

Satin Weave: A weave in which warp yarns are carried uninterruptedly over many weft yarns, producing a smooth-faced fabric. This weave offers superior cake release and excellent resistance to blinding.

Twill Weave: A weave where the weft threads pass over one and under two or more warp threads, creating an appearance of diagonal lines. It offers medium retention and blinding properties, high abrasion resistance, and good flow rates.

Porosity, or permeability, refers to the rate of flow of air through a filter cloth under differential pressure. It is generally measured in liters per minute per square decimeter (L/min/dm²) at 200 Pascal.

Lower air permeability: Indicates greater retention ability, meaning the cloth can trap smaller particles but may result in a slower filtration process. This is often prioritized in industries where fine filtration is critical, such as chemical processing.

Higher air permeability: Indicates faster filtration with larger particles passing through, which might be suitable for applications where quick processing is required but fine particle retention is less critical, such as in mining.

Choosing the right cloth depends on several factors:

Chemical compatibility: The cloth material must withstand the chemical properties of the slurry.

Particle size: The size of the particles being filtered will determine the yarn construction, weave type, and required porosity.

Temperature: High-temperature applications require materials that can endure heat, like polyester for its higher temperature and oxidation resistance.

Filtration rate: The desired filtration speed and clarity will influence the cloth selection.

For excellent cake release, choose monofilament cloths or cloths with a satin weave. Monofilament fibers are smooth and allow the filter cake to release easily, while a satin weave provides a smooth surface that minimizes cake adherence and facilitates easy removal.

To minimize blinding, select a monofilament cloth or a Mono/Multifilament blend. These types of cloths have smoother surfaces that prevent fine particles from clogging the fabric, reducing the likelihood of blinding and maintaining consistent filtration performance.

For filtering very fine particles, multifilament cloths or a tightly woven plain weave are recommended. These cloths offer a tighter weave that can capture smaller particles more effectively, ensuring better retention and filtration efficiency.

A support or backing cloth is needed to reduce cloth edge leaking and primarily to protect the filter cloth from premature failure due to the plates during high filtration velocities. It also helps with creating better drainage during the filtration process and can extend the life of the main filter cloth by absorbing some of the wear and tear.

Filter press cloths with latex edge treatment are used to seal and help reduce or eliminate wicking of the effluent between the filaments. Wicking occurs when liquid moves along the threads of the fabric, potentially leading to leaks at the cloth edges. Latex treatment substantially reduces press dripping and leaking.

Cake moisture increases when the cloths are blinding. To reduce cake moisture, select a media that reduces blinding. Monofilament or Mono/Multifilament cloths are effective in preventing blinding and, therefore, help in reducing cake moisture.

The filter cake will begin to become wet, slimy, and less dry, indicating that the cloths need to be cleaned. If the cloths have already been cleaned, and the process has not changed, but the cake remains slimy, it may be time to replace the cloths. Cloth life varies based on factors like the frequency of cycles, proper cleaning and maintenance, and the type of sludge generated. Generally, cloths can last up to 6 months in most installations.

Installing a Filter Press Cloth involves the following steps:

Remove the old cloth and clean the filter plate.

Align the new cloth with the filter plate, ensuring it covers all openings.

Secure the cloth by tying, clamping, or using hook-and-loop fasteners, depending on the filter press design.

The frequency of replacement depends on several factors, including the type of slurry, filtration frequency, and the cloth material. Generally, a cloth should be replaced when it shows signs of wear, such as tears, holes, or reduced filtration efficiency.

Regular cleaning: Rinse the cloths with water after each use to remove residual solids.

Deep cleaning: Periodically soak the cloths in a chemical solution compatible with the cloth material to remove deeply embedded particles.

Inspection: Regularly check for damage or clogging. Replace or repair as necessary. For large-scale operations, automated cleaning systems can ensure consistency and thoroughness in maintenance.

Wear and tear on Filter Press Cloths can be caused by:

Abrasive slurries: Constant exposure to sharp or coarse particles.

Chemical degradation: Exposure to harsh chemicals that weaken the fibers.

Mechanical stress: Over-tightening or improper handling during installation and removal.

Yes, Filter Press Cloths can be reused multiple times as long as they are properly cleaned and maintained. However, over time, they may lose efficiency and need replacement.

Choose the right material, yarn construction, weave type, and porosity for your application.

Follow proper cleaning and maintenance routines.

Avoid using excessive force during installation and removal.

Store cloths in a clean, dry place when not in use.

Common issues include:

Clogging: When particles block the cloth’s pores, reducing filtration efficiency.

Tears or holes: Damage due to wear, leading to slurry leakage.

Blinding: When the cloth becomes impermeable, usually due to the buildup of fine particles or improper cleaning.

Yes, Septek Filters offers custom Filter Press Cloths tailored to specific applications. Customizations can include size, shape, material, yarn construction, weave type, and even specific coatings to enhance performance. For example, specific coatings can enhance chemical resistance, or custom sizes can be created for non-standard filter presses.