In the first post about screen separators, the different types of separators were noted. In addition to determining the type of separator, it is important to choose a screen type based on the application requirements. Screens can be made of wire mesh, perforated metal or even expanded metal.
Wire mesh is preferred because it has the greatest percentage of open area and an irregular surface to which flat parts will not cling. The wire mesh can have a square opening or a slot mesh. A slot mesh is made with one or more parallel wires eliminated in one direction, yielding a rectangular versus a square slot opening. This creates a greater ease of separation when parts are long and narrow. Wire mesh is available in a broad range of wire thicknesses and openings. Very small openings can be obtained using a heavy, durable wire.
Perforated metal has the advantage over wire mesh of being more precise. If uniform openings are needed to separate parts and media that are very close in size, perforated metal screens are the best choice. Perforated metal screens are available with round, square or oblong openings. Due to the nature of the stamping process, the smaller the opening, the thinner the selected metal has to be; this is needed in order to have a reasonable punch life. If a material with the proper opening and thickness cannot be found, specially sized or configured openings can be achieved through the use of a numerically controlled laser or plasma cutting machine.
For applications that have a significant difference between media and part sizes, expanded metal screens are an economical and durable option. Openings on an expanded metal screen are diamond shaped, allowing for quick separation of both round and cube parts, as well as longer, narrow parts. Expanded metal screens may exhibit limitations with parts that have “arms” or other areas that could get caught in the openings and carried around the tube or damaged during vibration on a flat bed screen.