Mining and construction equipment wear is caused by a number of mechanisms. In addition, wear in chutes, feeders, hoppers or other transfer components is not usually uniform at entry and exit. At entry, impact wear predominates; at exit, sliding wear is greatest. A uniform lining cannot perform best in all areas.

Trellsquares, developed by Svedala, can reduce wear in different applications and in different locations in the same application. The system uses square modules of different materials, each suited to resisting a particular type of wear. In a chute application, rubber modules can be fitted at the entry to absorb impact and ceramic modules used at the discharge where sliding wear is at a peak.

Modular wear plates Several material options exist for modular wear plates, each with unique characteristics.

Rubber modules for high-impact applications reduce wear, increase service life and provide noise reduction. They are available in two thicknesses: 50 mm and 40 mm.

Polyurethane is available in two types: polyurethane 80, which is slightly harder than the other option, polyurethane 70. These materials are used in sliding-wear situations, especially with particles smaller than 100 mm (about 4 in.) and with wet material.

Ceramic, which is harder than steel, is suited for abrasive sliding applications. Brittleness, however, can be a problem with ceramics. Trellsquares are built from ceramic cylinders, 20 mm in diameter and 20 mm long, embedded in polyurethane so that adjacent cylinders do not touch. There is also a 10-mm layer of polyurethane underneath the ceramic cylinders. The polyurethane acts as a shock absorber and provides flexibility to counter the brittleness of the ceramic. In some applications, ceramic wear modules provide a service life 10 to 20 times longer than steel.

The modular wear plate concept can be adapted to any piece of equipment. The 300- Yen 300-mm (about 12- Yen 12-in.) wear plate modules are so lightweight they can be transported, stacked and manipulated manually by a single person and fitted on site by operators without special tools or training.

The modules are fitted on the floor-tiling principle. The area to be covered is first fitted with whole tiles. Tiles are cut to size to fill to the edges. There is no steel or fabric in the squares so they are easy to cut with a knife or jigsaw. The ceramic squares are not cut. Edge fitting, where the wear tends to be less, is done with polyurethane modules arranged in a zigzag design to give maximum coverage by the ceramics.

System benefits Applying wear modules on site and fitting them to any component shape saves operators about 20% compared with the cost of fitted linings, said Peter Skoog, Trellsquare product manager. Savings accrue from fewer delays caused by custom-fabricated linings and smaller inventory requirements.

The modular wear plate pick-and-mix approach to materials selection can work by using different materials in combinations and then changing square composition according to performance. Another method is to fit modular wear plates of a single material, observe the wear patterns and replace worn modules with others of a more appropriate material.

Fastening the modules The wear plate fastening system uses an anchor point on two sides of each square with a cruciform spider bracket that clamps each two adjacent squares. These spiders fit into slots in the top of each module and lock the modules together. They are sprung so when they are tightened in place, pressure at the tip of each arm ensures a good fit and keeps the module corners firmly in place.

An overlapping lip underneath each module also locks it down and prevents particle penetration through the sheet to the metal underneath. The metal spiders are protected from wear by shaped plugs which fit tightly into the slots.

The rubber and polyurethane modules are easy to recycle because they are homogeneous without fabric or steel reinforcement. Noise also is reduced with typical attenuations of 40% to 75% compared to a traditional steel lining. A 10-dB (decibel) attenuation is approximately equal to reducing audible noise by 50%.

Two case studies Infrastructure Recycling Plant in Holland-Theo Pouw bv operates an infrastructure materials recycling plant in Utrecht. About 80% of the material the plant produces is artificial sand made by reducing rubble from demolition sites. About 5% of the sand used in Holland is recycled and the product from Theo Pouw's plant is about 30% cheaper than natural sand, said Plant Manager Frank Prins.

The plant began operation in 1994 and has a capacity of about 90 metric tons per hour (mtph). A chute now fitted with modular wear plates was originally lined with old conveyor-belt sections 12 to 15 mm thick. That liner did not have to be purchased, but it had to be changed about once a month. When the plant began running 24 hours a day, the monthly change period became costly.

Trellsquare lining was fitted to the chute in June 1998. Installing the 50-mm-thick rubber wear plates took about four hours and wear plate replacement has not been necessary despite continuous running. The rubble drop height onto the lining is about 1.5 to 2 m.

Aggregate quarry in Belgium-Carrihres Unies de Porphyre operates a porphyry quarry and plant in Lessines, about 50 km west of Brussels. It produces about 2 million mtpy of crushed porphyry rock for two main applications; bigger sizes are used as rail ballast, 4- to 14-mm particles are sold for road surfacing.

A new processing plant was built at the quarry in the 1970s; new hoppers and new screens were added in early 1999. Modular wear plate linings were fitted in the two new hoppers during the construction phase.

The material goes through primary and secondary crushing before arriving at the hoppers less than 10-mm in size. It is highly abrasive, being both hard (second to granite) and sharp. The two hoppers have a throughput of 100 mtph each.

Plant Manager Jhrtme Flament said the original hoppers were lined with 10-mm-thick steel plates that often wore through within a week. These were repaired by welding steel plates directly over the holes. Another problem was material buildup on the sides of the hoppers; it had to bemanually cleaned every two days.

"Porphyry is a moist and compressible material when it goes into the hoppers and is therefore liable to stick to surfaces and cause a buildup," said Flament. "This is worse in the winter because of the wet weather.

"When we looked at constructing the two new hoppers, our goals were to get a very long-life lining material and to avoid the material buildup on the sides of the hopper," said Flament. "We also wanted to use light materials so we would not need to have a heavy and expensive structure for the hoppers. We looked at three possibilities, rubber, 20- to 25-mm-thick Nihard automotive steel and polyurethane. In the end we decided on rubber modular wear plates."

Heavy section steel would have required strengthening the hoppers' structure. It also would have been difficult to install, and had a lifespan of only a month to one year. Complete lining with polyurethane was too expensive.

One reason for choosing modular wear plates was that it would be possible to fit polyurethane plates at the top of the hoppers where material buildup is most likely.

Historically, wear parts were made from rubber. This was followed in the 1970s by polyurethane and ceramics in the 1990s.

"We've moved from supplying rubber parts to supplying wear resistant solutions," said Peter Skoog, Trellsquare product manager. "The big competitor in terms of wear material is steel. Polymers-including rubber-plastics and ceramics together, represent only 15% to 20% of the total world market in wear-protection parts."

Skoog said that potentially 80% of the market could be appropriate for polymers, plastics and ceramics. The use of steel is traditional, he said, and stems from the mining and quarrying practice of cutting out the worn area and welding in a new piece of steel without really regarding it as an opportunity for using a new type of wear product.

"There are certain exceptions where some of these materials may not be appropriate," he said. "Mainly where the components operate at temperatures above 70degreesC. Where material flow is faster than 7 meters per second, plastics and polymers may be undesirable, but ceramics are still excellent."