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Sep 10, 2021

How to improve your screening process with media

Claes Larsson
Claes Larsson
Product Manager, Screening Consumables
Your choice of screening media has a great impact on your screening process. Making the wrong choice may not only lead to broken cloth and a damaged screen structure, it can also limit the performance and thus reduce output. Pegging, blinding and maintenance are three areas that greatly impact the screening process.
Uneven distribution on screening media

Pegging

Pegging occurs when rocks get trapped in the openings of the screen surface. It can vary from minor pegging to the most challenging situation in which the entire cloth is clogged with rocks. Pegging limits screening capacity, and it can be difficult to know what the best solution for the problem is. However, there are some things to know that can help with the issue.

The size of the apertures can contribute to the different reasons for pegging to occur. In the case of smaller openings (<30 x 30 mm), factors like screen settings and conditions, level of flexibility and cloth design should be taken into account. With larger openings (>30 x 30 mm), crossbeams, ledge angles and other mechanical parts are factors to consider.

Moreover, the thickness and stiffness of a traditional, or woven, wire cloth can cause rocks to peg in the cloth. The wires in a self-cleaning wire cloth are not interlocked, so they are able to flex between each other – and that leads to less pegging. Therefore, choosing the right mesh for a screen, changing the screen cloth design, using smaller apertures, having blank areas and using more flexible media options can all help to prevent pegging.

Pegging on screening media

Blinding

Blinding is another performance limiting factor that can highly influence your screening process. Humidity causes blinding, a buildup of fines and dirt materials that stick to the screen surface. It gradually covers the openings, and it can eventually cover your entire screen area. The level of blinding depends on how sticky the material is.  

Reducing blinding requires the right balance for the particular application. For example, there is no blinding with a panel that is too soft, but a high screen load can cause the membrane to deflect and thus increase the wear on the panel. When there is high support and no flexibility, fines tend to blind up in that area. The key is to find the right combination between the load of the screen in relation to the softness of the materials and media flexibility.  

Blinding on screening media

Maintenance

Maintenance and simple measures are often overlooked as factors that affect the performance of the screening media as much as pegging or blinding.

The wrong level of tension can lead to a lot of damage. For example, the cloth can be torn if the panel is not properly tensioned: during screening, the rubber panel will move against the supports in the screen deck. This can be resolved by rebuilding the screen frame to the original height of the supports, reinstalling the rubber on top of the supports and setting the tension so that there is no vibration between the supports and underneath the rubber cloth. An improperly tensioned cloth can also lead to cracks in the broken wires.

Another maintenance task that is typically overlooked relates to feed and the uneven feed chute distribution and/or wrong location of the feed area. Feeding in the wrong location shortens the lifetime of the installation because the screen panel will not last as long as the feed box. This is another factor to take into account for a more efficient screening process.

 

Lack of maintenance on screening media

Want to hear more and see some real-life examples? Check out our webinar for more details about these issues.

You can also learn more about Metso Outotec’s different screening media systems by visiting our webpage.

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