Antiquated manufacturing methods and the use of inferior materials can lead to screen media that simply doesn’t last – but more importantly, it produces out-of-spec material.
Producing aggregates that conform to today’s tight concrete and asphalt specifications can be difficult enough without the unnecessary added challenge of screen cloths with inconsistent aperture size and shape. Supplying out-of-spec product to your customer can result in stiff penalties and fines, plus associated delayed project costs while the non-conforming stone is being replaced.
Furthermore, inconsistent gradings can cause concrete and asphalt mix complications, sometimes requiring complete jobs or portions of jobs to be replaced – another significant and potentially crippling cost in itself.
Good quality self-cleaning screens are made to strict manufacturing tolerances. For accurate sizing, all apertures should be square, not diamond or irregular shaped. A tolerance of ≤3 per cent is achievable and should be the minimum you expect from your screen media supplier.
Loose weaves
Loose weave commonly found in cheap woven mesh cloths will also have a significant impact on screen cloth performance. Any movement within the crimp causes additional wear and shortens the life of the screen. Fortunately, a loose weave is fairly easy to spot due to distortion of the wires when the cloth is fitted and tensioned.
If your mesh looks like the ones in Figure 1, you can be certain the weave is loose and wear life will be compromised.
Good quality woven mesh has zero tolerance to any movement within the crimp or weave. Tight weave improves wear life in the field.
All wire is not equal
Wire with greater hardness provides better resistance to abrasion. Ductility, hardness and tensile strength is determined by the metallurgical content – or what the wire is made of – and wire processing.
Quality woven wire mesh is manufactured with a higher carbon and manganese content than traditional high tensile woven wire mesh, providing more resistance to abrasion, longer wear life and better overall performance.
Its high ductility, hardness and tensile strength make it less susceptible to breaking in high impact conditions, and its extended wear life reduces downtime and replacement costs.
Some manufacturers have less carbon and manganese content, which are two critical ingredients for strength, hardness and abrasion resistance. They also use a cheaper method to process the wire. As a result, these manufacturers are offering woven wire at considerably lower prices. But what you get is a brittle woven wire that breaks easier and wears faster, eventually screens out-of-spec product and costs you significantly more in labour, maintenance and lost production.The best screens will have the right combination of all three critical factors – ductility, tensile strength and hardness.
Return on investment
When choosing which brand of wire screen media to use in your operation, look at the entire picture. Cheaper pricing up front often leads to higher costs incurred by the end of each screen cloth’s life.
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| CASE STUDY |
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A 600 tonne per hour (tph) Queensland quarry operator suffered an 18 per cent variance in grading when changing from a tried brand of self-cleaning screen to another. In a bid to save a few hundred dollars for a deck of cheaper brand screens, the producer lost several days of production, incurred the additional cost of rescreening the out-of-spec material, and had to replace the screens to bring the product back into spec. He calculated the cost as follows: Estimate lost production @ 50 tph x 20 hours(2 days) = 1000 tonnes 1000 tonnes x $10 = $10,000 lost production + rescreening and maintenance costs Another operator of a 250 tph basalt quarry in the ACT realised the benefits of using quality product over cheap alternatives. He experienced first-hand how quality screens consistently pass the same size material each and every time. As an added bonus, the superior metallurgy of the wire plus the advanced manufacturing process ensures much longer wear life for fewer screen cloth changeouts and reduced screen cloth consumption, making his job of running a screening plant so much easier. Reduced maintenance along with consistent predictable gradings made investing in quality an easy choice for this aggregate producer. |
Source: Nepean Rubber & Plastics