Finding the right screening media for your operation involves balancing out a lot of objectives, constraints, and variables. The variety of options on the market should make it easier to find the ideal solution, but it can be difficult to understand exactly what’s available. To help you get a picture of the full range of screening media today, we’ve broken it down into four categories – modular systems, self-supporting, tensioned and pre-tensioned.
The key characteristic of a modular screening system is that the screening media is made of a series of smaller panels, that can be individually replaced when worn out or otherwise damaged. There’s obviously an economic benefit in not having to replace an entire screen when only one area is worn out, but they also give users a lot of flexibility through the availability of panels of various materials and apertures. Some operations even use screens with different apertures in different parts of the deck, allowing for fine tuning of the grading.
WN4000, WN5000, WN6000, WN7000H and WN8000
The panels are normally flat, which helps the material spread evenly over the full width off the deck. They are made from rubber or polyurethane, which allows for an almost limitless variety of aperture shapes and sizes. A benefit that is often overlooked is that screens that use rubber or polyurethane are significantly quieter than those with screening media made from steel. That might seem like an insignificant matter, but loud screening operations restrict the amount of time that personnel can work in the area without damaging their hearing.
There are a number of industry standards for the dimensions of modules – the modules in Sandvik’s WN range, for example, are available in 1’ x 1’ or 1’ x 2’. There’s also a range of different fastening methods to keep the modules in place – most screens use some type of snap-on or pin-and-sleeve mechanism to connect to either the longitudinal or transversal beams underneath.
Self-supporting screening media is designed for demanding applications, like primary scalping or screening coarse material. The screens are robust and fairly rigid, and are often clamped or bolted into place with side and center hold-down bars.
Some self-supporting panels, like Sandvik’s WS6000H, have integrated skid bars. These are a set of raised bars that run along the panel, preventing larger stones from entering the panel surface and guiding fines towards the apertures.
Despite the increased popularity of modular systems, tensioned screens remain the most widely used screening setup.
The most straightforward, and probably the most common type of tensioned screen involves using a mesh of woven wire as the screening media.The mesh, or cloth, is attached to side rails. Support bars underneath the mesh give the deck its familiar convex shape (its camber or crown), with the center higher than the sides.
Sandvik’s WX6500 combines the advantages of hard-wearing rubber with the large open area of a woven wire mesh.
A central hold-down bar could be used to help keep the screening media firmly in place, in which case the deck will have a double-crown, with the bar running along the valley between the two crowns. The bolts on the side rails are tightened to provide tension across the screening media.
That describes the most basic setup, but a massive amount of variations can be made on this model. For example, the material can be length tensioned rather than side tensioned. This means rails at the entry and exit of the screen are used to tighten it. Then there is an ever-expanding range of materials that can be used, including various alloys of steel, polyurethanes and rubber.
One of the main advantages of using a simple wire mesh is that, because of the thinness of the wires, it has a large number of holes. On the other hand, wire mesh is prone to pegging (when material lodges in the apertures of the screen), so any efficiency gains may be short-lived. Similarly, wire meshes may be the cheapest screening material available, but they are likely to wear out quicker than a rubber or polyurethane alternative, so it may be a more expensive option in the long run.
Pre-tensioned screening media fills a gap between traditional tensioned screens and self-supporting systems. They are screening panels made from rubber or polyurethane, and strengthened with a flat bar steel frame. This provides the necessary rigidity for them to be used on a crowned screen deck – and unlike wire meshes, they do not have to be tightened across the entire deck. This eliminates the need to periodically check and adjust the tension of screening material.
Sandvik’s pre-tensioned media panels have the additional benefit of being flexible enough to use in trommel screens as well as in vibrating screens.