How to reduce pegging and blinding

Two ways to reduce pegging - aperture size matters!

1. Smaller aperture size (typically less than 30 x 30 mm).

In the case of smaller openings, factors such as screen settings and conditions, level of flexibility and cloth design should be taken into consideration. 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, which results in 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 may all be options which can prevent pegging. A blank area is a part of a screening media without apertures.

Image 2 below showcases wire cloth to the left compared to rubber tension mat to the right. It is evident that pegging occurs more in the wire cloth. The main reason for this is that wire cloth is a less flexible screening media compared to rubber cloth. The rubber cloth also has the advantage of blank areas above the supports which prevents pegging between the hole and support on the rubber cloth.

2. Larger aperture size (typically bigger than 30 x 30 mm).

With larger openings, crossbeams, ledge angles and other mechanical parts are factors to consider to prevent pegging. Making sure that the cloth opening is not interfering with the screen cross beams or similar is important.

One way of addressing this is to introduce blank areas in the screening media on top of the cross beams and also to modify the aperture patterns to avoid exposing parts of the screen.

Three ways to reduce blinding

Reducing the effects of blinding is about finding the right balance in a specific application between the lifetime of the screen cloth and how much blinding is actually acceptable. With the right combination of reinforcement and material hardness both cloth life and blinding issues can be solved. 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, resulting in increased service time as panels fail too early. When there is high support and no flexibility, fines tend to blind up excessively 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.

1. Minimize the blank area on the screen

Blank area is the part of the screening media panel which has no apertures/holes. Depending on media type and aperture size, this area varies in size. When reducing the blank area, there will be less surface for moist particles to stick to and begin gradual blinding buildup. It is important to keep in mind that blank areas in some cases are important parts of the screen deck. In the article How to reduce pegging it is mentioned that blank areas can be used to protect the screen structure.

2. Reduce thickness of media if possible.

A thinner media is more flexible, thereby continuously getting rid of the particles which potentially could stick to the deck and gradually cause blinding. A heavy material load can however cause higher wear on thinner screen media, so it is important to weigh the pros and cons of choosing a thinner media option.

3. Try softer synthetic materials.

Due to its larger flexibility, rubber screening media usually results in less clogging. Read more about the benefits that can come from using a synthetic screening media in aggregate production in Synthetic media in the aggregate production - Metso.

The final screening media set-up is dependent on your specific application, and processing conditions. Consult the screening media team at Metso to find the most suitable solution for you!