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Wear types

Wear commonly occurs when abrasive particles, rocks or objects strike or scratch the surface of steel. These particles can slide, rotate or impact against the steel, resulting in different types of damage. Wear types are categorized based on the specific nature of the damage inflicted on the steel.

Steel hardness and toughness

The increased wear resistance provided by Hardox® wear plate is well-known, with hardness being the primary factor. However, the material’s toughness also plays a significant role in enhancing wear resistance. When rocks slide across the steel, they exert a force on the plate and transfer energy into it. This energy causes scratching, but the hardness of the steel minimizes penetration and requires more energy to create scratches on the surface.

Hardox® grades

Hardox® wear plates are available in a range of hardness grades.

Properties of abrasives

The hardness of abrasives plays a major role in causing wear. Hardness testing originally began with the Mohs scale, which ranks minerals on a scale from 1 to 10 based on their ability to resist scratching. For example, limestone and coal are rated as 1 while diamond is rated as 10.

How to analyze mineral composition and hardness

The mineral composition of abrasives is commonly analyzed using two methods: XRF (X-ray fluorescence) and XRD (X-ray diffraction). The XRF method provides the proportion of oxides, while XRD determines the specific chemical formula of the minerals present.

Surface damage

Hardox® steel is manufactured through a controlled industrial process, ensuring consistent quality and minimal variation in hardness. Abrasives, on the other hand, originate from solidified magma or metamorphosed sedimentary rock, resulting in significant variability in their mineral composition, volume and density, among other factors.

Relative wear

The SSAB wear model provides a relative measure of wear performance. By keeping all variables –such as abrasive particle type, density and volume – constant, and varying only the hardness of the steel, the model estimates how much an increase in steel hardness extends the service life.

Absolute wear

When designing new equipment or planning investments, it is essential to accurately determine how many millimeters of material are worn away per unit of time. This is referred to as absolute wear.

Measuring wear

Most mining operations have structured monitoring for mining trucks and larger buckets. Regular inspections using an ultrasonic thickness gauges are highly effective for assessing wear rates and for planning maintenance schedules.

Wear testing

Wear testing plays an important role in evaluating the performance of wear-resistant steel before its installation in real-world applications.

Wear bars

A common method for reducing wear is the use of wear bars. These bars are designed to encourage abrasives to roll rather than slide. Another function of wear bars is to trap aggregates between the bars, causing the abrasive material to slide against itself.

Transversal welds

The front weld of a liner, which runs transverse to the flow of abrasive material, is susceptible to wear, increasing the risk of the entire plate breaking off quickly. When a weld becomes cracked or worn, small particles and dirt begin to accumulate between the liner plate and the floor structure. These particles act as a strong wedge, exerting pressure that gradually separates the liner plate from the floor, causing further cracking of the weld until the plate eventually falls off. To prevent this, it is crucial to regularly inspect and maintain the welds.

Welds in sliding direction

Welds also experience wear in the sliding direction, especially from fine abrasive particles that wear down the welds in the gap between the two liner plates.

Material selection

The service life of liner plates is mainly affected by two factors, hardness and thickness.

Standardized liner sizes

The mining industry does not have regulations regarding standard sizes and patterns for drilled holes. However, certain regions may have rules that dictate the sizes and hole patterns. A typical size in the US is shown in the figure below on the left.

Liner plate size

For workplace health and safety reasons, liner plates should not be too heavy. When plates need to be handled manually, there is a weight limitation of approximately 25 kg (55 lbs.), which corresponds to dimensions of 400x400x20 mm.

Bolting liners

Bolted joints, whether standard or stud-welded, should be designed and installed following the VDI 2230 guidelines to ensure proper functionality. Using the correct tools and expertise is essential for achieving the desired performance and durability.

Pre-loading bolted joints

Bolting is the most effective method for quickly replacing Hardox® liners and minimizing maintenance downtime. However, achieving a properly secured bolted joint requires taking some precautions.

Stud welding

Stud welding is an increasingly popular method for attaching threaded bolts to liner plates due to its speed and relatively low cost.

Special solution bolts

In industrial shotblast chambers, bolts are subjected to direct erosion.

Ore or overburden

The service life of liners in mining trucks varies depending on the abrasiveness of the hauled materials. The minerals present in the ore determine the aggressiveness of the wear. However, there are exceptions to this rule. For instance, in cases where quartz content is high, the service life may still be relatively long. This can be attributed to the low toughness of the rocks, which, despite containing hard minerals, are more likely to collapse or pulverize under pressure rather than cause aggressive wear.

Wear and impact

When an excavator dumps its first load onto the floor of a mining truck, the body must withstand the heavy impact from large boulders striking the floor’s midsection. This initial damage is typically caused by plastic deformation or cracking, with wear being a secondary factor. After the first load, the floor becomes covered, and subsequent bucket loads no longer hit the floor directly. As more material is added, a heap forms, and the boulders might roll or slide into the sides or front plate, causing denting.

Strategy for designing liners

In many cases, building a thicker structure and foregoing the use of a liner can be the most cost-effective solution. In coal or limestone mining, the structure can often be used without liners, allowing the extra capacity to boost production.

Attaching liner packages

Before selecting the appropriate lining material and solutions, the condition of the backing structure must be carefully assessed.

Maintenance

An installed liner package requires regular inspection, with particular attention to the welds.

Lining at the tail

The tail is the area most exposed to wear, and there are various strategies to address this challenge. However, any solution that deviates from a flat plate design is likely to cause material sticking, which can result in increased carryback.

Carryback

Ore or overburden can become very sticky after rainfall or when materials are at risk of freezing. Sharp corners tend to accumulate this sticky material, and the relatively low flow in these corners makes it difficult for the material to wear off. To address this issue, the corners can be redesigned with a larger radius to improve flow and reduce material buildup.