Vibratory sieves and separators, commonly referred to as gyratory separators or screening machines, are a normal feature of processing dry bulk powders. They classify materials by separating them by particle size through a screen mesh. Using a combination of horizontal and vertical movements, they spread the powder over a screen in controlled flow patterns and stratify the product.
No matter what brand or style of vibratory sieve you use, proper installation, operation, and maintenance is crucial. Premature screen failure can often cause unscheduled down time, inferior product quality, and can shrink your company’s profit margin. There are many factors that can decrease the mesh life of a vibratory sieve, but here are just a few suggestions to help avoid this potentially costly problem.
1. Use Good Quality Mesh
Using top of the range stainless steel mesh for your vibratory sieve, will give you maximum wire strength. Mesh made from the very best wire drawing techniques will mean you can rely on your screens lasting considerably longer than screen frames made from inferior quality mesh. There are a wide variety of meshing/screening techniques available and it is important you choose the correct one that best suits your application.
2. Correct Method of Cleaning
Every powder has different characteristics and so the correct method of cleaning mesh screens will differ from application to application. There are many different ways to clean a screen, from manual cleaning to ultrasonic deblinding systems. However, when looking at manual cleaning, the most widely used technique involves a three-step process. First, wash the mesh, then lightly clean it with a suitable cleaning agent. Follow up with a gentle blow dry using compressed air. It is important to remember that whatever cleaning procedure you use, you must prevent the loss of tension in the screen. If the mesh loses tension and becomes slack, separation efficiency will significantly drop.
3. Handling and Storage
Have a dedicated storage area for your mesh screens. Encourage machine operators to handle all screens with care and avoid touching the mesh. If possible, operators should hold the screen frame when handling. Some vibratory sieve suppliers offer protective casing for mesh screens, which act as a “second skin” to help protect them from accidental puncture or damage.
4. Ensure the Correct Weight Setting
Having the correct weight setting for your sieve will ensure the powder product is on the mesh for the appropriate amount of time (also known as the dwell time). If the weight setting is incorrect, the product will stay on the screen longer, resulting in product build up and increased weight on the mesh. Over time this will cause excessive stress to the screen mesh, leading to premature failure. Instructions about how to adjust your machine will be in your operator manual. Alternatively you should contact your supplier for more information.
5. Keep Mesh Clear During Operation
If powder product starts to build up on a sieve screen during operation, the mesh will block and powder will no longer pass through the screen. If left to accumulate, the increased weight on the screen will reduce the mesh tension resulting in inefficient sieving and a considerable decrease in the life of your mesh. To prevent mesh blocking or blinding, try using an ultrasonic deblinding system or a mechanical mesh un-blocking system such as balls or discs.
6. Accurate Wire Diameter
Choosing the correct wire diameter for your application is very important. As a rule, the thinner the wire diameter, the bigger the open area. A thin wire diameter and large open area is most desirable, because a higher throughput can be achieved. However, a thin wire diameter is also prone to frequent screen breakages, due to the mesh being unable to cope with the product weight (dependent on the powder product and feed method). A mesh screen made with larger diameter wire is likely to last longer, but the drawback will be a reduction in screening throughput.
Rob O’Connell is president of U.S operations at Russell Finex Inc. He can be reached at 704-588-9808, [email protected], or www.russellfinex.com. He holds a B.Eng in Mechanical Engineering from Nottingham University in England. He has more than 18 years experience with screening, sifting, and separation equipment.
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