how to select the proper filter cloth for your application

FILTER CLOTH SELECTION

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Determining the proper cloth construction requires knowledge of the slurry characteristics and the filtration requirements. Below are some of the factors we consider in the filter cloth selection process.

Contact M.W. Watermark to learn more about how to identify or measure these variables.

• Is the cake or the filtrate a product?
• pH?
• Slurry temperature?
• Slurry particle size?
• Is the slurry preconditioned (Polymer, DE, Ferric, Lime, etc.)?
• Abrasive, coarse particles?
• Existence of solvents, oils or greases?
• Number of filtration cycles per day?

The above data helps in determining the following:

• Fabric raw materials / compatibilities
• Type of yarn (fibers)
• Fabric weave
• The type of fabric finishing needed to produce the best filter cloth for the application

Common filter cloth materials

Polypropylene

Polypropylene is the standard for filter cloths and performs ideally in most applications. This material can withstand higher temperatures, does not easily succumb to blinding (clogging of the weave) and has a smooth surface which aids in cake removal. However, it&#;s important to know the make-up of the slurry before assuming that polypropylene is the material of choice.  For example, if the slurry is bleach, polypropylene will not be compatible, and polyester filter cloth materials must be used.  Latex borders can be applied to a non-gasketed cloth to provide a better seal under pressure.

Nylon

This durable fiber is often chosen for its long life in the face of abrasives. Though higher in cost, nylon blends offer such durability that the higher cost can be justified by longer service life.

Polyester

Often chosen when sustained operating temperatures are over 180 degrees, or when oxidizing agents are present. 

FILTER CLOTH FIBER TYPES

Filter cloths are manufactured using synthetic fibers.

• Monofilament: Single, smooth, continuous extrusion. Highest flow rates, good resistance to blinding, good abrasion and scaling resistance. Fibers are typically between 4 mil and 10 mil (.004&#; to .01&#;) in diameter. Best cake release.

• Multifilament: Multiple continuous fibers twisted together to form one yarn. Excellent retention for smaller particles. Good cake release.

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• Staple (Spun): Short lengths of fibers (similar in appearance to cotton) spun into a yarn. Tends to have a &#;hairy&#; appearance. Best solids retention. Poorest cake release.

FILTER CLOTH FABRIC WEAVES

• Satin: Satin Weave (or Sateen Weave) has a smooth surface caused by carrying the warp yarn on the fabric surface over many weft yarns. Intersections between warp and weft are kept to a minimum. Very flexible, easily conforms to most curved surfaces. Satin weave is popular for its excellent cake release and resistance to blinding. Particle retention is average.

• Twill:  Twill Weave adds a diagonal rib or &#;twill&#; line into the weave, adding strength at the expense of some stability. These diagonals are caused by moving the yarn intersection one weft thread higher on successive warp yarns. Cake release is average. Average resistance to blinding.

• Plain: Plain Weave (or Checkerboard Weave) is the most basic weave, with a weft thread alternately going over one warp thread and then under one warp thread. Average in strength, cake release, and stability. High particle retention and low resistance to blinding.

ADDITIONAL WEAVE PATTERNS

• Leno Weave: The leno weave involves two or more warp threads crossing over each other and interlacing with one or more filling threads. This is known as a &#;locking&#; weave, as it is mainly used to prevent the shifting of fibers in open weave fabrics. This type of weave is usually only found in backing cloths.

• Basket Weave: Basket weave is a variation of the plain weave. Two or more warp yarns alternately cross with two or more filling yarns. Stronger than a plain weave, at the expense of stability. Typically used for backing cloth or basic applications requiring additional strength.

FABRIC FINISHING

Finishing of the fabric enhances the cake release, filtration quality and stability.

• Singeing: Removal of fibers on the surface of staple and felt fabrics to enhance cake release.
• Calendaring: With use of heated compression rolls, the fabric is &#;melted&#; to adjust the permeability and provide a smoother surface for cake release.
• Heat Setting: Through a wet or dry process to create a dimensional stable fabric that will not shrink, stretch, etc.

Contact M.W. Watermark to discuss your particular application.

Micronics supplies filter cloths to you based on detailed process criteria that you and your team provide to us. Often, our recommendations will be based on filtration testing. Should your process change, we do recommend that your filter cloth type is evaluated specifically for your new process & operating conditions. Time and time again, customers will find that a process change necessitates a change in cloth to ensure that the filter press operation is fully optimized.

For instance, did you know that a change in polymer or other chemical or physical treatments may alter the performance of your filter press?

Filter cloths come in many different materials including polypropylene, polyester, cotton, and various synthetic materials. The cloths are made from monofilament fibers, multifilament fibers, or spun fibers. Learn more about filter cloth terminology in our recent blog post.

Did you know that the smooth surface characteristic of monofilament fibers can help to improve cake release properties? The uniform circumference of monofilaments also enables fabrics to be produced with consistent pore sizes.

Multifilament and spun fibers are produced are produced by twisting several smaller diameter monofilament fibers together into a single strand. They are used to produce filter cloth fabrics that require a very tight weave and fabrics where high flow rates are not critical.

Pore size is an important consideration when selecting the proper filter cloth for a particular application. Pore size is determined by the number of fibers, fiber size, and the type of weave. These influence flow rates, particle retention, and the tensile strength of the fabric.

Filter cloth is the key foundational ingredient for any filter press operation. Filter cloth is the initial barrier that separates the solids from the liquid. The filter press cloth must remain porous in order to provide high filtration rates!

Contact us for filter cloth recommendations, to discuss recent process changes in your press operation, or to re-order filter cloth. Micronics&#; sales, engineering, and filter cloth manufacturing team &#; are all eager to put our know-how to work for your filter cloth needs.

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