Making The Grade

Don’t let screen media inefficiencies ruin your profits

Screen media inefficiencies can have just as much of an effect on product quality, production and profit as a poorly performing screenbox. But screen media modifications cost less than screenbox upgrades, so it is always a good idea to check screen media first, before spending money unnecessarily. In this article, Major Wire Industries Ltd, one of the leading global manufacturers of screen media, identify some of the most common screening problems, determine their causes and offer some solutions.

Problem 1: Material is coming off the end of the deck instead of passing through the screen cloth

Cause: The wire diameter is too large for the application, resulting in a loss of open area.
Solution: Consider reducing wire diameter size to increase the open area, while expecting to see some possible reduction in wear life.

Cause: The bed depth is too heavy for the screen deck due to too much feed material, eg running 400 tonnes/h on a plant designed for 250–300 tonnes/h.
Solution: Make sure you do not run more material than the screen deck was designed to handle.


Cause: Material is being dropped or fed too far down the screen, wasting potential open area.
Solution: Reposition the conveyor or drop box feeding the screen so that the material lands on the feed plate of the screen, or as close as possible to the back of the feed end. Make sure that the material spreads evenly across the screen.

Cause: The screen cloth is blinded by wet, sticky material, or is pegged with near-size material, resulting in a loss of screen cloth open area.
Solution: Consider changing woven-wire screen cloth to a self-cleaning screen cloth design. Self-cleaning screen media, such as Major Wire’s Flex-Mat 3, is one of easiest ways to eliminate this problem. Polyurethane strips bond the individual wires and allow them to vibrate independently at different frequencies. This creates more screening action so properly sized material falls through instead of falling off the end of the deck. Flex-Mat-type screens also produce up to 30% more screen capacity, providing even more potential for material to fall through.

Problem 2: The screen cloth is breaking or failing before it wears out

Cause: The screen cloth is too wide or too narrow for the screen deck.
Solution: Check to make sure that the screen cloth hooks are not hitting the side of the screen or that the cloth is not too narrow to allow proper tensioning by the clamp rails.

Cause: The crown bar rubber is either missing from the crown rails or is worn out.
Solution: Replace the crown bar rubber and be sure to completely cover the crown rails.

Cause: There are gaps between the screen cloth and the crown bar rubber, the screen deck may be damaged, or the crown rails might be bent or excessively worn.
Solution: Check for damage or wear and make sure all crown bars support the screen cloth with no gaps between the screen cloth and crown bar rubber.

Cause: The feed material is being dropped from too great a height on to the screen deck.
Solution: Consider repositioning the feed conveyor or chute, or adding a feed lip or feed box.

Cause: The screen cloth is loose.
Solution: Check the screen cloth for proper tension and tighten the clamps or add ‘j-bolts’ to cross members, if necessary. If the hardware is loose, retighten or replace as necessary, and check frequently.

Cause: Material feed size may be too large.
Solution: Reduce material feed size or replace the screen with cloth that has larger diameter wires or a double-wire screen cloth designed for applications with heavier feed.

Cause: The screen may not be level, causing uneven wear and/or breakage.
Solution: Check to make sure the screen is level. If not, check for broken or sagging springs or settling in the foundation and replace springs or crib to re-level the screen.

Note, a stronger woven wire is often the best way to eliminate premature screen cloth breakage. A woven wire with a high carbon and manganese content, such as Major Wire’s OptimumWire, is designed to withstand high-impact conditions and abrasive materials. A wire with these characteristics can last up to 40% longer, reducing the number of screen cloth changes and increasing productivity.

Problem 3: Materials are bouncing across and over the side of the screen

Cause: The screen is under-loaded, so there is not enough material weight on the screen, causing the materials to bounce.
Solution: Increase the feed.

Cause: The stroke angle is too high, making the material bounce, rather than vibrate on and through the screen.
Solution: Flatten the stroke angle and/or decrease the stroke amplitude.

Cause: The screen is running too fast and not allowing the material time to fall through the screen openings.
Solution: Decrease the screen revs/min.

Problem 4: The screen deck is overflowing

Cause: The screen is overloaded and the bed depth is not allowing the material to pass through the screen openings.
Solution: Decrease the feed.

Cause: The screen is missing a weight plug or the plugs have been installed improperly.
Solution: Check to make sure that all of the weight plugs are properly inserted.

Cause: The stroke timing is too slow.
Solution: Increase the revs/min.

Prevention, prevention, prevention

Simple maintenance checks can help keep an operation running efficiently and often prevent unnecessary wear and equipment failure. Operators should observe the clamp bar rails to make sure they are never bent or damaged. Either situation can cause the screen cloth to become loose or damage the cloth due to the volume and flow of large material. Clamp rails can also fall off into the crusher or stockpile. Bolts and wedges should be kept tight at all times. If they become loose, they will cause the screen cloth to lose tension and cause damage. Loose bolts can even ‘back out’ and fall on staff working below.

To protect against screening problems that could decrease operational efficiency and possibly cause injuries to workers, daily inspections should be conducted before start-up and after shut-down. If any of the above situations is recognized, it should be fixed before it can cause even greater problems.

For further information visit: www.majorwire.cc