STEEL AND WEAR IN QUARRIES

TEJ PANESAR, TSP Group of Companies reports on the usage of steel materials in quarries.

STEEL is the predominant material used in various pieces of equipment in Quarries and by the very nature of the operation it is subject to wear. Various types of steel are used for various applications based on the environment, impact, under foot conditions, Wear scenario and the frequency of actions. Some examples of equipment are: Truck Bodies, Dozer Blades, Grader Blades, Cutting Edges, Tracks and Rollers, Feeders and Hoppers, Screens and Crusher Parts.

There are a few important elements of steel to understand when it comes to durability, appearance, protection, performance and wear resistance. Surface Coatings, alloying elements, hardness, heat treatment, and Wear Resistance are the major factors that we will discuss here.

HARDNESS

Hardness is resistance to deformation and Carbon is the cheapest and most popular hardening element. The higher the Carbon greater the hardness (see graph above). Brinell Hardness is generally represented for Steel Plates and the Rockwell Hardness for Drilling bits. Here is a general equivalent chart for comparison:

WEAR RESISTANCE

Wear is the erosion of material from a solid surface by the action of another surface Unlike Hardness, Wear has no general unit of measurement – It’s relative. Generally, the Harder the Steel, the more Wear Resistant it is. Higher hardness makes Steel brittle and more difficult to weld. However, wear resistances can be increased for the same hardness of steel. Th is is done through alloying elements added at the time of manufacture of steel and the heat treatment process.

IMPACT OF ALLOYING ELEMENTS ON STEEL

• Silicon: Increases hardness and strength but reduces wear resistance
• Chromium: Increases hardness, strength and corrosion resistance
• Nickel: Increases hardness and strength but reduces wear resistance
• Manganese: Increases hardness wear resistance and impact strength
• Tungsten: Increases hardness, strength and yield strength and vastly increases wear resistance
• Cobalt: Increases hardness, strength and yield strength and vastly increases wear resistance
• Molybdenum: Increases hardness, strength and yield strength and increases wear resistance
• Vanadium: Increases hardness, strength and yield strength and increases wear resistance
• Boron: Increases hardenability of steel. Used with low carbon steel

Depending on the application, smart combination of the various alloying elements can create the right quality of steel. However, sometimes due to paucity of demand for a particular combination, the closest compromise is used. Different types of wear in quarries include.

• Sliding/Rolling: Dump truck bodies, Cutting Edges, GET
• Impact: Feeders and Hoppers, Screens, Dump truck bodies
• Squeezing/Compression: Crushers, Cutting Edges, GET
• Rusting and Corrosion of various structures
• Oxidation of various exposed materials.

HEAT TREATMENT

Various heat treatments are done to manufactured steel to improve and stabilise its properties. The popular ones are:

• Annealing: Heating then slow cooling process to induce ductility, soften material, relieve internal stresses
• Case Hardening: Infuse elements into the material’s surface, forming a thin layer of a harder alloy
• Tempering: “Toughen” the brittle metal by controlled reheating of the work piece to a temperature below its lower critical temperature and holding it there for a while in inert conditions.
• Quenching: Rapid cooling of a work piece to obtain certain properties e.g. reduce crystallinity and thereby increase toughness

PROTECTION & COATINGS

Steel is protected via various surface coatings. Popular ones include:

• Blackening: A finishing operation that chemically coats the surface to enhance its appearance and hold the sealant (usually oil) into the oxide coating.
• Blue Finish: A thin layer of iron oxide produced by a carefully controlled steam tempering process which acts as a lubricant and resistance to corrosion.
• Bronze Finish: A thin oxide layer formed generally on tool surfaces.
• Hard Chromium Plating: Improves wear resistance and reduces sliding wear.
• Nitriding: Increase hardness and wear resistance of the steel surface.

The hardness is easier to generate on the surface of a metal and is more challenging to harden all the way through. Thus the popular terms Case Hardened (just the top case to a small depth of a few millimetres) and Through Hardened (hardened all the way through the thickness of Steel). Th is can vastly change the way steel wears initially and when it reaches deeper into the care. The through hardened steel will wear better than the Case Hardened Steel through its life.

MANUFACTURING STEEL COMPONENTS

Various methods have been used over the years and there is continuous development in the processes to produce better purpose based properties:

• Casting: Pouring or injecting molten metal into a mould containing a cavity with the desired shape of the casting. Porosity and shrinkage control is important.
• Forging: Metal is shaped by plastic deformation under great pressure. The only metal forming process that orients the grain of metal to the shape of the part. Control Die Costs
• Fabrication: Rolling, Bending, Cutting, Drilling, Counter sinking, Turning, Milling, Welding, Grinding using Off the shelf Steel. Properties can be further enhanced by wear material deposit.

There are various factors that define the life we get from steel components in the quarries and a healthy discussion to improve its life will always add value to the operations, directly or indirectly.

Please contact Tej Panesar (0421 380 700) of TSP Group of Companies for any discussions on wear components or email tej@tspgroup.com.au

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