FILTER CLOTH SELECTION
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?
- 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 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.
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.
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.
- 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.
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.