In certain industries and/or applications, separating one material from a second material is often desired and/or required. Further, the separation of solids based upon the relative size of the solids is generally known in a variety of industries and/or applications. Typically, separation by size is performed for various reasons. For example, separation of a like material by size may be desired to categorize the material into different sizes. Certain sizes may be more valuable or desirable. Thus, separating and/or categorizing the material by size may optimize the value of the material for a subsequent sale of the separated material. Further, certain food products are separated by size for grading purposes. Certain sizes of a particular food product may be more valuable or desirable.
To this end, separators may be used to separate different materials and/or to separate like materials by size. Typically, separators may use screens having different mesh sizes. The screens may be arranged relative to one another to allow the smaller material that may pass through a top screen to flow onto the screen below so that the materials may be separated. A series of stacked screens may be used in the separator. Also, the separator may use vibration and/or other motion to aid in the separation process.
Conventional vibratory separators generally utilize screens of either hook strip or pretensioned design. The screens may be tensioned after the screens have been mounted in the basket of the vibratory screen apparatus. Two opposed ends of the screen are fitted with a turn back element to form a hook strip. The hook strip may be hooked around a tension rail which may be attached to the side wall of the basket. Typically, a tension bolt may be used. However, other loading means to apply tensioning and securing forces may be employed. Tightening the tension bolt may move the tension rail outwardly towards the walls of the basket to apply tension to the screen.
Hook strip screens may be pretensioned prior to mounting in the basket by attachment of the screen mesh element to an apertured support plate, typically by means of an adhesive. A screen having a plurality of mesh layers may be pretensioned. In some designs, layers of fused mesh may be corrugated prior to mounting to an apertured support plate and the hooks applied thereafter to the mesh-plate combination.
Hook strip screens have a number of disadvantages including the complex and time consuming mounting of the screen members in the basket which results in significant downtime of the vibratory screen apparatus and requires the use of multiple parts. Attaining the correct screen tension for the sieved material also involves intricate fine tuning. The screens may be easily damaged if too much force is applied when tightening the bolts or loading means to tension the screens.
A further disadvantage is the relatively poor sealing between the screen and the basket. The metal-on-metal seal often results in leakage. Unscreened material may pass through gaps between the screen and the basket and may mix with already screened material below the mesh screen. Attempts to overcome the poor seal by placing rubber strips and/or gaskets at the metal/metal interfaces are time-consuming. The strips and/or gaskets frequently loosen during vibration and become lost or lodged in the vibratory machine which obstructs and/or damages the machinery. In addition, applying tension to the screen when tightening the tension bolt adds undesirable stresses to the machine frame.
Pretensioned screens generally have one or more layers of mesh permanently bonded under tension onto a generally rigid steel and/or plastics material apertured plate support frame. The screen and frame are inserted into the basket and are normally secured in the machine by clamps.
Conventional pretensioned screen units with integral support frames have significant disadvantages. For example, conventional pretensioned screens may be bulky, heavy and difficult to handle, transport and store. Typically, the design may be complex, and the frames may be expensive to construct.
Further, the material and/or the product may build up and may be trapped between the spacing frame and other parts of the separator as the material and/or the product may be separated. Therefore, the machine must be taken apart for cleaning which may create a non-productive, labor-intensive step.