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Engineering plastics make rust a thing of the past

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HIGH performance engineering plastics that don't corrode and never need lubrication are making inroads into mining and minerals processing applications once exclusively the preserve of metals, according to Aldo Mostacci of Dotmar EEP Pty Ltd .

Their many advantages - including good wear characteristics, light weight, low friction, low inertia and long operational life- are why the super plastics are replacing phosphor bronze, stainless steel and other metals in applications where metals have ruled for decades.

From conveyor impact beds to sheaves and wear blocks on draglines; from flow promotion liners on dump trucks to safety guards on machinery; from cranes and earthmoving equipment to chutes, bins and hoppers; the change is happening in a myriad of applications where long-life products such as the Ertalon, Nylatron and Polystone families of plastics are displacing costlier counterparts in grimy environments where reliability is at a premium, a smooth flow of material is essential, and downtime is an enormous liability.

An example is custom engineered plastic sheaves, which can weigh as little as one-seventh steel equivalents yet offer longer wear life- and, importantly, give two to six times the rope life.

Then there is safety equipment fabricated from polycarbonate Safeguard PC, which is among the strongest and safest rigid see-through material available to safety conscious managers, machine builders and OH&S safety teams. This rugged material has:

* 250 times the impact strength of glass of equal thickness

* has 30-40 times higher impact strength than clear acrylic sheet

* maintains its high impact strength even after long outdoor periods

* and is easily fashioned for applications ranging from guards on machinery to see-through doors and hatches

So superior is the performance of engineering plastics in many areas of mining and resources that the only reason they are not used almost universally is habit and resistance to change.

Ertalon's scope is one of the broadest in the mining industry because each application's requirement can almost always be facilitated by subtle variations in physical properties afforded by different additives in each grade of the product.

The range of Ertalon (commonly recognised as nylon) stock shapes can be engineered to suit applications requiring high mechanical strength, stiffness hardness and toughness, fatigue resistance, high mechanical damping ability, good sliding properties, noise damping, electrical insulating, dielectric properties and excellent wear resistance.

The complementary family of Nylatron thermoplastics can be similarly formulated for outstanding performance characteristics suiting different applications, such as wear resistance and fine motion control in production and processing.

Nylatron703 XL, for example, features 'Zero Slip-Stick' performance for precise and efficient motion control of machinery components including wear pads, bearing blocks, wear guides and linear bearings.

Machinery equipped with Nylatron 703XL can accurately produce the smaller movements made possible by today's sophisticated control devices. Telescoping or sliding parts - such as those in cranes and materials handling equipment - move smoothly over pads made from Nylatron 703XL, without sticking or jumping. Such precision is made possible by the material's "Zero Slip-Stick Performance" in which static and dynamic coefficients of friction approximate each other at virtually every point over the product's useful range.

Members of the Ertalon and Nylatron families have been successfully employed as:

* Wear pads on side guides, rollers, conveyors, presses and telescopic booms

* Gears on winders, lifts and escalators, and in drives for processing equipment

* Bearings or bushes, where the materials have found extensive uses in draglines, cranes, rolling stock, earthmoving equipment and processing machinery

* Pulleys and sheaves for overhead cables, or as rollers for electric hoists, conveyor components, boring and bolting equipment, and heavy duty sections on draglines.

Draglines themselves are host to a myriad of uses for Ertalon and Nylatron, which are virtually maintenance-free and hardly ever suffer from high wear, corrosion, lubrication breakdowns, dirt or dust effects, splitting or abrasion.

Uses on draglines have expanded to encompass slap blocks for drag ropes, drag rope sheaves, deflection rollers, tower sheaves, fair lead sheaves, drag tunnel wear blocks, shoe alignment sheaves, walking shoe wear blocks and wear pads for pedestal and brake arrangements.

Even in the harsh environs of foundries and open cast mines, Ertalon has been used to engineer replacements for existing steel bearings because of its impregnated lubricant. Whereas traditional roller bearings carry a wet lubricant that traps the abundant dirt and dust, Ertalon obviates this problem. The same result is achieved on conveyor systems and entry guides, which in many industries are subjected to similar working environments.

The ultra high molecular weight (UHMW) family of Polystone plastics is especially formulated for optimum sliding characteristics and resistance to wear, abrasion and environmental stress cracking. This means it is ideally suited to mechanical transmission support products and to flow promotion.

It displays some of its greatest benefits when employed as conveyor components such as mechanical chain guides and mechanical wear strips - or, in another form, as liners for hoppers, bins and truck trays.

Key features and benefits of the material include:

* Impact strength combined with light weight. It is easy to handle without special equipment (having a specific gravity of 0.93).

* Weatherproof - it doesn't absorb water

* Chemically resistant - it resists corrosive material (such as sulphuric acid, caustic soda)

* Abrasion resistant - rated better than carbon steel for sliding abrasion applications

Common uses of Polystone include conveyor systems, for example, where chain guides and support profiles made from metals such as steel cause heavy wear on the link plates and rollers of the roller chains, and on the links of round link chains.

Another important area in which UHMW plastics are increasingly important is in dump trucks, trailers, hoppers and bins for flow promotion where common problems include product sticking, rat-holing and generally clogging processes that require a smooth flow of material.

The smooth paraffin-like surface of Polystone prevents the adherence of bulk solids to the walls of transporting and storage equipment. It allows regular mass flow patterns and consistent release of product. The surface friction properties of Polystone provide an economical way of ensuring maximum discharge.

Dump truck liners made from such materials have evolved considerably with the availability of new sheet sizes, special grades and improved fastening systems. From independent owners and operators to large fleet managers, Polystone Matrox liners provide a quick return on investment.

Dotmar EPP has a team of highly trained engineer machinist who work exclusively with these plastics on state-of-the-art CNC and CAD CAM systems fabricating mining components to individual applications.

Engineers should consult appropriate technical guidance for which engineering plastics suits particular applications (one such resource being www.dotmar.com.au)

Aldo Mostacci, BE (MECH), is Engineering Manager for leading plastics engineering specialist Dotmar EPP, which operates throughout Australia

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