Wear bars in mining truck bodies block material and prevent the aggregate from sliding directly onto the floor.

Transverse or along the flow

When an excavator pushes and slides its bucket against a rock bed, the force is high. To protect the underside of the bucket, wear bars are typically installed. These wear bars disrupt the scratching motion of the rocks, causing them to rotate. This mechanism helps shield the bucket shell from excessive wear. Wear bars are also installed along the digging direction, typically at the edges and sometimes in the midsection of the bucket. These longitudinal wear bars are always thicker than the transversely installed ones. Additionally, heel shrouds are often mounted on top of the wear bars for extra protection, though they can increase friction.

Transversal wear bars create rotation on the abrasives to reduce wear. Slightly thicker wear bars are often installed along the digging direction to reduce friction, enabling the excavator to better leverage its power. The wear bars installed along the digging direction are exposed to higher wear.

Designing wear bars

Thicker wear bars reduce wear by lasting longer before the abrasive material reaches the welds. However, they also increase friction and trap more material. If the bars are too tall, they can create additional friction and instability, particularly in applications like mining trucks, where the body must reach a higher tipping angle to unload. This results in slower unloading times. Additionally, wear bars can generally increase the risk of clogging and carryback, especially when transporting sticky materials. A notable advantage of Hardox^® 450 is its ability to accommodate 25 mm wear strips that can be welded without the need for preheating. 
There is also a rough relationship between thickness and width. For a given thickness, excessively wide wear bars do not provide extra service life because most of the wear occurs on the leading edge. Once this edge wears down, the weld becomes exposed and starts to wear away, as illustrated in the figure below.

It appears that a wear bar does not provide additional benefit if its width exceeds three times its thickness.

As guidance, the bar’s width (W) should be less than three times its thickness (T). For example, a wear bar for a mining truck body can be 25 mm thick and 75 mm wide. 

The recommended gap (G) between wear bars varies depending on the material flow direction. For instance, in mining truck bodies, the material flows over the wear bars, while in excavators, the abrasives flow on the underside. Excavator buckets must be installed with a smaller gap (G), since their primary function is to rotate the rocks, preventing them from wearing down the bottom and the shell. 

SSAB’s field studies on mining trucks indicate that a gap (G) of three times the width (W) provides effective protection for the tail in dump trucks. Additionally, installing new wear bars between the old ones after several thousand hours of use can help extend the service life.

The gap (G) between the wear bars has different requirements depending on whether the abrasive material flows along the top of the bars or slides over them, as in the bottom of an excavator bucket.

The pros and cons of wear bars

+ Wear is reduced without substantially increasing the weight.
+ Wear bars can be added in between existing ones to achieve efficient maintenance.
- Unloading is slightly slower in mining trucks.
- A higher center of gravity in the trucks can cause instability during unloading.
- Risk of carryback exists.