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Wear Protection Products and Systems

Greenbank offers a comprehensive range of lining materials designed to combat erosion and have more than 60 years of expertise on their applications.

Since 1957, Greenbank Terotech’s core business has specialised in the design, manufacture and application of abrasive and corrosive resistant products.

Ceramic-based products such as basalt, Zalcon® and alumina are the most well-known lining materials. Other lining materials include nickel and chrome alloys, silicon nitride bonded silicon carbide, epoxy and polyester coatings, Ultra High Molecular Weight Polyethylene (UHMWPE) and an array of performance steels.

These products extend the life of pipework, chutes, hoppers and plant items which are used in many areas of heavy industry.

Cast Basalt

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Cast basalt is a material formed from neo-volcanic basaltic rock combined with crystallising agents. When cast it has two exceptional qualities. Firstly, a high resistance to abrasion, which is the most important factor, becoming multiple times higher than that of iron or performance steel. Secondly, it has a very high degree of chemical resistance.

For lining of pipework, chutes, bunkers, cyclones and hoppers, cast basalt is an all-round cost-effective and adaptable lining material that extends the life of equipment where affected by erosion or corrosion.

Its coefficient of friction is similar to steel but improves with wear, which improves the flow of the material being handled, leading to lower pressure drop and improved efficiencies.

Zalcon™ [Zirconium Alumina Ceramic]

/media/terotech/library/zalcon-pf-pipework.jpgZalcon™ is an advanced fusion-cast ceramic, developed specifically to resist impact and sliding abrasion in extreme and arduous conditions.

Zalcon™ is cast at approximately 1800˚ C into virtually any required lining shape, eliminating many joints which cause premature failure in other ceramic linings, especially tiled.

Its resistance to impact and thermal shock makes it the perfect liner in areas where aggressive materials are handled at velocity or temperature. Its interlocking crystalline structure of Zalcon gives the material superior physical characteristics.

Alumina Ceramics

/media/terotech/library/alumina-southwestern-rugeley-burner-elbows-on-wagon-close-up.jpgThe term Alumina is usually applied to ceramics based predominantly on aluminium oxide and products containing more than 85% are often referred to as high density alumina.

Alumina ceramic has been developed and optimised for maximum wear resistance and corrosion resistance. The high density diamond-like hardness, fine grain structure and superior mechanical strength are the unique properties that make it a material of choice for a wide range of demanding applications. For uses similar to Cast Basalt but where greater resistance to wear especially in high velocity lean and dense phase systems is required.

Alumina is produced in tile form by die pressing, extrusion or slip casting. The method of manufacture influences the shape and dimensional tolerances of the tiles but does not generally affect the wear resistant qualities.

Die pressed tiles are usually a flat, square-edged shape and, in the smaller tiles particularly, have good dimensional tolerance. Other shapes are available such as tongue and groove and bookend, both in flat and curved shapes which are useful for interlocking and avoiding direct gaps between adjacent tiles in the direction of flow.

Some tiles forms are produced by the extrusion process and they are generally of the flat, square-edged type. The dimensional tolerance and density is not as good as a die pressed tile.

Slip cast tiles can be produced in a variety of shapes and sizes, the process being particularly versatile for producing irregular shaped components. Slip cast components can have a dimensional tolerance of up to +/-4% after firing and therefore not always suited for pipe linings in the form of medium to large diameter cylinders due to mismatch and the potential for steps at joints.

Nickel and Chrome Alloys

The frequently used materials are wear resistant cast iron to BS 4844 grade 2A or 28 (nickel chromium) and BS 4844 grade 30 or 3E (high chromium grades). They can be cast into complex shapes and are therefore suitable for all components where weight is not a limitation. When used in pipework the construction normally consists of a single casting or a number of ring sections.

Silicon Nitride Bonded Silicon Carbide

This is a low density pre-cast material, consisting of silicon carbide grains bonded together with a matrix of silicon nitride. The material can be manufactured by a number of methods and large complex shapes can be produced.

Unlike Alumina’s, the production method appears to have a significant effect on the product's erosion resistance. Only those products which have been proved sufficiently resistant in the particle erosion rig are recommended.

Some of the products have been shown to have excellent erosion resistance at normal pulverised fuel (PF) flow rates and are not impingement angle sensitive like Alumina’s.

However, experience has shown that at high PF impingement velocities, such as those experienced by exhauster casings, the wear rate increases rapidly. Generally, it is a high cost material which generally precludes it from use in pipework applicAbrasion & Corrosion Resistant Lining Systems ation, but its ability to be cast into complex and large shapes offsets the economic considerations in some applications like burners. It is a very brittle material and needs to be well supported within the component.

Castings can be manufactured with securing holes but care should be taken when fitting to avoid fracture. The use of self supporting designs is recommended.

Epoxy Based Coatings.

Epoxy coatings with aluminium oxide, bauxite or PTFE fillers can be built up on the surface to be protected by trowel, brush or by airless spray. The material has moderate abrasion resistance and protects well against corrosion.

It has excellent adhesion to both steel and concrete. Epoxy based coatings are essentially low temperature materials, having a continuous service temperature range of -20°C to 90°C with short exertion allowable up to 110°C .

In areas where the upper range is likely to be exceeded over a period of time, other lining materials should be considered. Where increased mass flow is likely to result, checks should be made to ensure the structure can withstand the potentially higher stresses.

Ultra High Molecular Weight Polyethylene (UHMWPE).

This is often used in bunkers, hoppers and chutes. It gives a superior performance to glass with a much longer life. It can also accommodate flexing. The main drawbacks are high cost and the care needed during installation to ensure adequate preparation and mechanical fixing of the large sheets.

Its low coefficient of friction may alter the coal flow pattern at the bunker throat, which may lead to a requirement for structural strengthening. UHMWPE is basically a low temperature material.

 It will progressively weaken up to its melting point of around 130°C and has a high coefficient of thermal expansion, so will buckle if overheated. With main coal bunkers there is the potential, if the coal level drops sufficiently, for hot primary air to enter the bunker, leading to heating of the bunker outlet.   If this situation exists, it is recommended that an ultrasonic low level warning system is installed. In any case the bottom of the bunker should be fabricated from, or lined with, stainless steel.

Performance Steels

Many areas of chutes and bunkers are lined with carbon, low alloy or austenitic stainless steel plate. This allows for easy fabrication. There are also several types of proprietary brands of wear plate available. The use of a lining can add rigidity to a structure, whereas weight limitations may preclude the use of some other wear resistant materials.

Stainless steels remain the best choice in some chute areas and in the lower areas of bunkers where temperatures may be excessive for other linings or their adhesives. The grades used have traditionally been either 304 or 316 austenitic, but ferritic stainless steels, with their lower cost and easier fabrication have often been found to be more cost effective.

Although stainless steel may show low initial hardness and relatively poor wear properties in dry conditions, it improves in service due to work hardening and surface polishing. Its advantages are most pronounced under wet and corrosive conditions.