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Designs to enhance wear performance

There are three ways in which one can increase the service life of wear applications without extensive changes. Jonas Gozzi and Dr Patric Waara explain.
In all wear applications, a long service life is desired because of reduced maintenance costs and better production flow. The service life can be extended in several ways, eg by using more wear resistant materials, but there are other good options.

This article will give three examples, related to dump truck bodies and transfer chutes, of how it is possible to increase the service life with small design changes.

DUMP TRUCK BODIES
In general, a dump truck body is subjected to both wear and dents from impact. The wear can be divided into impact wear and sliding wear of which the latter represents the major part.


There is a difference between dents from impact and impact wear. For locations on the body where there are significant possibilities for dents, it is important to have a ductile and crack resistant material, eg Hardox 400 to 450, with hardness of 400 HB and 450 HB respectively.

In areas with impact and sliding wear, a harder material will increase the service life and common alternatives are Hardox 450 up to Hardox 550.

In Figure 1, typical damages are marked. The grey round mark in the middle shows where the impact dents, from the loading of the body, will usually appear. The orange part of the bottom and the sides will be subjected to medium wear while the red part in the back of the body will experience heavy wear.

The front part of the body is normally subjected to low wear but will be exposed to some impact wear when the body is almost full and rocks start to roll and hit the front plate and sides.

Impact wear is the surface damage that gives the highest wear rate per volume of abrasive material. Fortunately, the first material loaded will create a protective layer on top of the bottom plate and the rest of the load will fall on this layer. This is the reason why the plates can survive the impact wear for a reasonably long time.

 At unloading, the material will slide on the bottom and the back part of the bottom will be exposed to most sliding wear since this is the region where most material will pass.

The idea of a protective layer of material, ie from the quarry or mine, can be utilised in different ways for a dump truck body but also in other applications and will be further discussed in this article.

Wear strips
One quite common way to improve the wear life of the back part of the dump truck body is to apply wear strips transversally to the sliding direction (see Figure 2).


The idea of the wear strips is to get material to stick in between and to build up a “pillow” of material to protect the bottom plate and get a more favourable material flow. This is a very effective solution to reduce the wear rate in the back part of the dump truck body.

Dead bed liner
The “Dead bed liner” is based on the same idea as the wear strips and is a very good alternative to solid liner plates for dump truck bodies.

It gives a very good wear life, the same or better compared with solid liner plates, and a significant reduced weight. The concept has been tested and the result shows that the wear life is around 16 per cent longer for the dead bed concept, compared to a solid liner plate. Figure 3 shows one example to the left of a dump truck body with a dead bed liner.

To the right in Figure 3, a close up is shown when in use and it is clear that the pockets have been filled with material protecting the bottom plate.

The main benefit with the “Dead bed liner” is of course the weight and the fact that the performance is actually better compared to a solid liner. Examples show that it is possible to reduce the weight of the liner package with 30 to 40 per cent which can be used to increase the payload.

The “Dead bed liner” plates are normally used in the back part and sides of the body while solid liner plates are used in the impact zone and in the front part.

The disadvantage is the extra production cost for the cutting but that is considered as small compared to the gain from the extra payload. A good material choice for the “Dead bed liner” is Hardox 500 and for the solid liner plates Hardox 400 or 450 due to its high toughness.




TRANSFER CHUTES

When material from a feeder hits the wall in a transfer chute there will be a high level of impact wear on the wall. One solution, if the support is rigid, is to use a wear plate like Hardox 500 or 550 but we can also use a similar concept as for dump truck bodies, ie let a layer or material/dirt protect the liner plates. In Figure 4, different examples for this are shown.

The first case is to rely on the sticky effect and hope that some dirt will stick and create a protective layer. The next example is to attach a wear bar on the wall which will help the material to stick and create the wanted dirt pocket.

The last example is to build a dirt box which really will create a protective layer and the wear part, pointed out in the figure, will be easy to replace, especially if compared to the liner plates.

There is a lot to gain from a design perspective when it comes to wear applications. Of course, the type of abrasive material is important and these solutions might not work for all conditions but they are very effective in the right environment.

Jonas Gozzi is the R&D manager for SSAB APAC. Dr Patric Waara is a specialist in wear technology for SSAB EMEA.









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Monday, 16 September, 2019 8:46am
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