Since the early 1950's Vincent screw presses have used dewatering screens made of perforated stainless steel sheetmetal. It has been only since 1994 with the advent of the Series CP presses that the use of profile bar construction has become common.

The fractional and millimeter dimensions are nominal.

In general, the maximum thickness a sheet of stainless steel in which a hole is punched is limited to one gauge thickness less than the diameter of the hole. Thus the small perforation material is very thin, typically 24 to 28 gauge steel. In contrast, 14 and 16 gauge sheets are used for the 3/32 perf.

The 3/32 perforation is the standard used in orange peel presses and most other applications. It is preferred because its thickness makes it resistant both to tramp metal damage and to wear when screw-to-screen interference occurs. The solids that get through the 3/32 holes are screened from the press liquor, to be added back to the flow entering the press.

The small perforation sizes are used where the material being pressed tends to extrude through the holes. This typically occurs with producers of fruit juices (apples, grapes, pineapple, cranberries, pear, tropicals, etc). To improve the bursting strength of the 1/32" and half millimeter materials, a 1/8" thick back-up reinforcing screen is employed. Back-up screens are made of 3/8" or 1/2" perforated sheet.

Perforated screens have the advantage of being an inexpensive material that can be changed out with a minimum of labor.

Perforated screens generally have 20% to 25% open area. Surprisingly, in most applications the smaller holes have significantly more press capacity than larger holes. Of course, the smaller hole screens are thinner and more susceptible to damage.

Profile bar and wedgewire screens are made by resistance welding wedge shaped bars of stainless steel parallel to each other. These bars have a truncated triangle cross-section. The wires are generally 0.219" and 0.247" high, and bars are either 3/8" or 1/2" in height.

Bar screens are produced in flat panels that are subsequently rolled to the diameter specified by the OEM. With bar screens the wide base of the triangle faces the material being filtered, thus providing relief on the discharge side.

Typically, Vincent presses use nominal slot widths of 0.010" and 0.018". These have a tolerance of plus or minus 0.005". Manure presses use 0.020", 0.030" and 0.040" slots. For cooking oil, slots of 0.008" to 0.010" are specified.

An important advantage of profile bar is that it can be self-cleaning. In some applications there is less chance of a profile bar screen blinding than there is with perforated metal.

Another advantage lies in the greater thickness of the bars as compared to perforated sheet. It means that the useful life is extended when pressing abrasive materials (paper, plastic, sand, glass) or materials containing tramp metal. This thickness also results in greater burst strength.

Profile bar and wedgewire screens typically have 12% open area. Surprisingly, they generally have the same screw press capacity as perforated screens with double the open area.