It is difficult to imagine a fluid-handling system that does not use wire cloth, mesh or screen for an industrial process. Proper selection of wire cloth makes a major difference in cost and efficiency when separating solids from liquids. Important factors must be considered when applying wire cloth in fluid handling systems.
Wire cloth has been applied to sizing and screening for many years to separate the desirable from the undesirable. Today, its capabilities are applied more rigorously and more extensively. It can filter micron-sized particulate matter as well as materials inches in diameter. It is also applied frequently as a structural member in systems to provide strength, rigidity and size integrity. By virtue of its design, a solution will retain impurities or treatment materials without impeding process flow.
A process engineer who decides to use wire cloth in a liquid system must coordinate pressure-drop requirements with liquid temperature, viscosity and specific gravity. The engineer must also integrate information on particulate matter size and flow rates, and consider the nature of the contaminants or corrosive environment to be encountered.
Once the parameters are set, hundreds of standard cloths are available in the common metals. In most cases, the engineer will not need to custom design a cloth, and manufacturers are helpful with application and metallurgical assistance for specific problems.
Wire cloth varieties
Like ordinary fabrics, wire cloth is woven on looms and produced in a wide variety of weave types. It uses a range of wire gauges with diameters ranging from slimmer than a hair strand with a diameter of 0.0008 inch to a 1-inch diameter, and it is produced in innumerable combinations of diameters and mesh counts.
Shute wires are the cross wires, also called fill or weft wires. In weaving, warp wires, which run lengthwise, are set first at the desired spacing in a procedure called warping the loom.
Common weave types are as follows:
- "Pre-crimped" weave has both the warp and shute wires crimped prior to weaving. Typically used for wire mesh specifications with large openings, pre-crimped wires nest into each other at their point of intersection, minimizing wire movement and variation of opening size.
- Plain, or double crimp, weave is the most common type of wire cloth. The crimp that is set in both the warp wire and the shute wire is a result of the weaving process. The wires are not pre-crimped or crimped prior to weaving. A plain weave pattern has each warp wire pass over and under each successive shute wire, and vice-versa.
- Twill weave is similar to plain weave. Again, the wires are not pre-crimped. Instead, the pattern has every two warp wires passing over and under every two shute wires. This weave pattern permits incorporation of heavier wires into various mesh counts as compared to some plain weave specifications.
Plain Dutch weave filter cloth is woven using two different diameter wires. The larger diameter warp wire is for strength, and the smaller diameter shute wire is for filtration. The shute wires are driven up close to one another, forming a dense surface with irregular shaped openings well suited to trap particles larger than the filter cloth’s micron rating. Plain Dutch weave allows for high flow rates with relatively low pressure drops. Filter cloth is also available in a twill Dutch weave and a reverse Dutch weave.
Corrosion resistance versus cost
In applying wire cloth, engineers select the alloys least susceptible to environmental hazards. Stainless steels are most commonly used for working with water because they provide the greatest range of corrosion resistance at a practical cost. Of course, certain concentrations of contaminants in liquids may require use of more exotic materials.
Wire cloth is frequently selected for its strength and corrosion resistance. Titanium and other exotic alloys can be applied as a strengthening backing cloth or as the actual filter medium, where free sulfides are a particular problem.
In reviewing corrosion resistance requirements, it is important to remember that by nature wire cloth is susceptible to corrosion. A corrosion rate that might be considered negligible for metal plate could be excessive for wire cloth, so choose material of the highest corrosion resistance available and that is also consistent with the economics of the application.
Major value is derived from wire cloth based on its physical strength and relatively light weight. Actual weight is based on the specific metal, wire diameter and cloth mesh chosen. Used as a structural member, wire cloth provides support without impeding flow or excessive weight. Used as a screen, it resists abrasion and can be cleaned with high-velocity water or chemical cleaners, mechanically scraped or rapped. In some cases ice can also be pounded off with a hammer with little chance of damage.
Equally important for applications such as spark arresters and petrochemical pressure filtration applications, wire cloth can be produced in higher temperature, more corrosion-resistant alloys such as Nichrome, Inconel, Hastelloy and Alloy 20. These materials often suit the application better than the more common stainless steels.
Final points
In applications involving the throughput of liquid or gas, the pressure differential of the wire cloth selected is a critical consideration. Cloths that appear similar actually produce different pressure differential. Direct orifice calculations, charts and graphs specify pressure differentials.
Many filter cloths, such as the Dutch weaves, do not have an easily measurable opening. The opening sizes are classified as either "nominal" or "absolute" micron retention ratings. The absolute micron retention rating of filter cloth can be measured by using a bubble point test. As suggested, a forward bubble point integrity test measures the pressure needed to be applied to the upstream side of a filter to cause bulk or open pore flow through the largest pores of a wetted filter.
Strong, flexible, uniform and workable, wire cloth works well for many rigorous processing services, even with temperature and pressure extremes or mechanical and thermal shock. Many case studies conducted by the wire cloth industry document its effectiveness when it is selected right, supported properly and used within its limits.
Richard Campbell is president of Newark Wire Cloth Company. The company, based in Clifton, New Jersey, has been providing wire cloth products and solutions since 1911, including the fabrication of wire cloth parts and assemblies.
