Screen Separating Guidelines

The ability to separate parts from media must be taken into consideration early in the development of the finishing process. Keep in mind that media wears down and should be periodically screened to remove undersized media pieces that can jamb holes.

If one piece of equipment is intended to be used for many jobs, a rotary screen separator would be the closest to a universal machine.
If height space is limited due to low clearance, a flat bed screen separator can be made to fit in a space as small as ten inches high, whereas a rotary screen separator requires a minimum of thirty to forty inches in height.
If limited length space is available, a rotary screen separator can be used since, due to its greater efficiency, it is half the length of a flat bed screen.
If long, thin parts need to be separated, a slotted screen material works best.
If a very small screen opening is required, but a durable material is needed, choose a wire mesh.
If an accurate opening size is needed, perforated metal would be the best choice.
If a crevasse or pocket must be reached, but a large media is necessary to provide the pressure to abrade, use a machine with screens stacked end-to-end or one screen on top of another, allowing multiple items to be separated in one pass.

Screen Separating Basics - Part 2

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.

Screen Separating Basics

There are a couple of ways to separate parts from media. Basically, a screen is used to separate out smaller items from larger items. The best separation is achieved when the media and parts (or whatever is being separated) are different enough in size and shape to make separation simple.

A tubular rotary screen separator will tumble the items to be separated while the load passes through the screen tube and the smaller items are separated. This type of process can be used for separating almost anything and works great for parts that 'hold' the media and need to be over-turned to be emptied. A tubular rotary screen separator can also process high volume loads (hundreds of pounds per minute if necessary). Multiple tubes in sequence can be used for multiple separations.

A flat vibrating screen is a good general purpose method to separate parts and media. Loads are simply emptied onto the vibrating screen and the smaller pieces fall through the screen. This is more of a batch process and ideal for small load sizes. A flat vibrating screen can be incorporated into vibratory tumbling systems for automated separation of media and parts in process.

The biggest challenge with screen separating is identifying a screen opening (size and shape) that will quickly and efficiently separate the load. If parts and media (or whatever is being separated) are very close in size and shape the optimal results will be much more difficult to achieve.