Flexible Metallic Media

Flexible metallic media are especially suitable for handling corrosive liquors and for high-temperature filtration. They have good durability and are inert to physical changes. Metallic media are fabricated in the form of screens, wire windings, or woven fabrics of steel, copper, bronze, nickel and different alloys. Perforated sheets and screens are used for coarse separation, as supports for filter cloths or as filter aids. Metallic cloths are characterized by the method of wire weaves as well as by the size and form of holes and by the wire thickness. Metallic cloths may be manufactured with more than 50,000 holes/cm2 and with hole sizes less than 20

Table 2. Properties of woven filter cloth fibers

Fiber

Temperature

Tensile

Limit

Fibers

Acids

Alkalies

Solvents

Strength

(°F)

Acrilan

Good

Good

Good

High

275

Asbestos

Poor

Poor

Poor

Low

750

Cotton

Poor

Fair

Good

High

300

Dacron

Fair

Fair

Fair

High

350

Dynel

Good

Good

Good

Fair

200

Glass

High

Fair

Fair

High

600

Nylon

Fair

Good

Good

High

300

Orion

Good

Fair

Good

High

275

Saran

Good

Good

Good

High

240

Teflon

High

High

High

Fair

180

Wool

Fair

Poor

Fair

Low

300

METALLIC/NONMETALLIC CLOTH

Combination metallic and nonmetallic cloths consist of metallic wires and weak cloth or asbestos threads. There are some difficulties in weaving when attempting to maintain uniformity between wires and the cloth, and considerable dissatisfaction has been experienced with such construction. While cotton weaves well with the asbestos, the cotton fibers destroy the fabric's resistance to heat and corrosion. Its use is, therefore, quite limited, despite its resistance to high temperatures, acids and mildew.

Cotton cloths are sometimes treated with metallic salts (copper sulfate) to improve their corrosion-resistant qualities. Such cloths are in the usual cotton filter cloth grades, and while they are not equivalent to metallic cloths, the treatment does materially prolong the life of the cotton fiber. When dealing with metallic cloths, the following terms are important:

Mesh - Number of openings per lineal inch. Measured from the center of wires. The number of openings precedes the word "mesh".

Wire - The diameter of wire used in weaving cloth measured by gauge or decimal inch.

Opening - The size of clear opening between parallel wires. For a given mesh, the space is determined by the diameter of wire used.

Woven wire cloth is available in a broad range of alloys with mesh counts as coarse as 1" in most alloys and as fine as 635 in some alloys. The following is a list of alloys normally used:

Stainless Steel Type 304 Aluminum

Galvanized Steel Plain Steel Brass Copper

Galvanized Steel Monel 400 Plain Steel

Stainless Steel Type 304 Stainless Steel Type 321 Stainless Steel Type 347 Stainless Steel Type 430

Bronze

Exotic Alloys

High Temperature Alloys

Nickel

Precious Metals Stainless Steel Type 316 Stainless Steel Type 330 Stainless Steel Type 410

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