Part I: Filter Cloth 101
In the first part of our Filter Cloth 101 series, we’re going to give you the basics: terminology and materials. Please feel free to ask questions in the comments section or give us a call (616.399.8850).
It can be easy to look past the filter cloth’s true role in a process, believing that the cloth does the filtering, when in reality most of the filtering gets done by the cake itself forming in the recessed chamber.
Understanding this, it becomes easier to improve the press operation and to adjust to problems and changes.
In this post we’ll cover the basics – filter cloth terminology and different filter cloth materials. If you haven’t already, don’t forget to subscribe to our blog for the next post in the filter cloth series: Part II – Troubleshooting and Frequently Asked Questions.
Filter Cloth 101: Terminology
CGR vs. NG
“CGR” is an acronym for “Caulked, Gasketed, Recessed chamber.” CGR filter plates and cloths should provide a virtually leak-proof filter press. Cloths for these plates are octagon shaped, with a caulking rope or cord sewn into the edge of the cloth.
“NG” means “Non-Gasketed.” The NG filter cloth is faster and simpler to install, though the trade off is that occasionally some dripping can happen when using NG cloths.
When a cloth’s porosity is hindered, and the cloth no longer allows the filtrate to flow.
These fibers are single, smooth extrusions and have high strength. “Mono” cloths have excellent cake release characteristics and resistance to blinding. This style has low particle retention. This material is very similar to fishing line, and has higher tensile strength.
Multi-filament or “Spun” Fibers
Compared to the “Mono” fiber above being similar to fishing line, “Multi-filament” threads, think “yarn”. The fibers vary in size, but are grouped together in a single strand. The main benefit of multi-filament fibers is better particle retention.
This blend of both types of fibers is extremely popular, as it encompasses benefits from both types of thread, in particular, strength from the mono- fiber, and particle capture from the multi-fiber.
A coating added to the edges of a filter cloth to prevent leaks. This coated edging reduces NG leakage.
“Cubic Feet per Minute” is the measure of flow or air permeability of the cloth media.
The most common are plain, twill, and satin:
- Twill Weave adds a diagonal rib or line to the weave, adding strength at the expense of a little stability. Cake release is average
- Satin Weave is popular for its excellent cake release and excellent resistance to blinding
- Plain Weave is average in strength, cake release, and stability
Filter cloths come in many different materials including polypropylene, polyester, cotton, nylon, felt, and many other materials. The most common filter material:
- Polypropylene: Polypropylene is the most common material. It has strong resistance to acid and alkali alike. A satin finish added to the fiber can allow for easy cake release. “PP” is a top choice for a wide range of applications, and is by far the most popular material. 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.
Coming up next in our Filter Cloth 101 series: Troubleshooting and Frequently Asked Questions.