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Liner Materials

Using poorly designed liners or liners that are not compatible with the surfaces they contact can greatly reduce product quality and increase maintenance expense.

Though many materials are available for liner systems, the most common materials used when engineering a liner system follow:

• Solid steel
• Clad (composite) steel
• Bronze and brass
• Plastic

The most commonly used material is steel. The major factors which affect the performance of steel liners are:

• Carbon content
• Alloy content
• Heat treatment

In general, high-carbon steels are more wear resistant and low-carbon steels are more impact resistant.

Alloys are elements added to carbon steel to transform it to alloy steel, or tool steel. Specific alloy additions are selected to cause steel to become stronger, tougher, abrasion resistant, more responsive to heat treatment, and corrosion resistant. A few of the commonly used alloy additions are: nickel (Ni), manganese (Mn), chromium (Cr), vanadium (V), and molybdenum (Mo). When an application requires high wear resistance, the alloy elements chromium (Cr), vanadium (V), and molybdenum (Mo) are added. Nickel (Ni) and manganese (MN) are added for impact resistance because they add toughness to the steel.

It is possible to create a highly wear-resistant liner which sacrifices little impact resistance. The key is the correct chemistry of alloying elements and the proper heat treatment techniques. Certain tool steels meet these criteria.

When corrosion resistance is needed, the obvious material to select is stainless steel. It is preferable to use a hardenable grade of stainless in order to get the necessary degree of hardness for optimum wear resistance in a corrosive environment.

The correct chemistry and heat treatment must be selected and practiced in order to attain satisfactory uniformity of hardness throughout the liner.

Heat Treating
Heat treating improves wear resistance by changing the crystalline structure of the steel to impart hardness. This change only happens correctly when the right balance of elements receive the proper heat treatment.

Clad (Composite) Liner Systems
Clad plate is a plate made from two different materials which are metallurgically joined together by one of several available techniques. Usually, the backing material is a soft carbon steel and the face is a wear and/or corrosion resistant material. The mild carbon steel back protects the chock or housing while the hardened outer surface provides wear resistance between mating liners. As with normal through-hardened liners, the hardness must be engineered to optimize the performance of the liner system.

Bronze and Brass Liners
Bronze and brass liners are still used in some mill applications. These materials have two major benefits: corrosion resistance and softness. The corrosion resistance is needed where elevated coolant temperatures exist, such as hot strip mills. As with the softer backing materials in clad liners, the softer brass material abrades more quickly than the mill housing.

The trade off is that the softer materials in this class wear more quickly than other liner materials. The hardenable grades of bronze and brass that have better wear properties will not withstand high impact forces and will not maintain dimensional accuracy.

Plastic Liners
This is a new class of liner which is applicable in cold mills. A potential benefit of plastic is the ability to reduce design clearances to half of their original design specifications, which may assist in reducing vibration.

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