Lesson 4 - Hardox

Lesson 4 - The service life

The service life

The service life of a bucket is very much the same as the service life of its wear parts. For a heavy duty bucket, the cutting edge and the teeth will be changed many times. In some cases, a bucket’s wear parts are worn down fast, in other cases they last a lot longer. Why the difference? Wear depends mainly on three conditions:

The abrasive materials
Steel type
General conditions

These factors decisively influence the bucket’s service life. It is essential to choose the right equipment for the actual conditions. Variations of 15 to 20 times can be noted.

The abrasive material

Rocks or other materials vary in hardness and shape. Rocks consist of mineral grains. A single rock often contains different mineral grains of varying hardness and shape. Hardness is measured in Hardness Vickers (HV) or Hardness Brinell (HBW). Granite consists of quartz, feldspars and biotite. Quartz is predominantly the most abrasive material in all ore and rock handling. The higher the content of quartz or other hard minerals, the greater the wear. A cutting edge of 500 HBW hardness lasts almost three times longer in rock material with 15% quartz than in rock with 90% quartz. There may be significant variations. Coarse shot-rock does not necessary mean greater wear. Finer crushed rock may lead to increased wear (higher wear frictional heat due to more contact points).

Steel grade

The steel type is of decisive importance for service life. Hard steel types withstand hard minerals. There are two types of wear. Heavy and fast wear as well as a milder and slower wear.

Tests have shown that if the mineral is at least 1.8 times harder than the steel, the steel wears fast.
If you choose a sufficiently hard steel (the mineral is less than 1.5 times harder than the steel), you get slower wear.
Every rock type wears in its own unique way.

With a hard steel grade, the wear rate will be considerable slower (typical example for a medium-hard mineral).

General conditions

Wear is also affected by some other factors. The most important are: Bucket equipment:

Bolt-on edge (good)
Teeth (better)
Teeth and segments (even better)

Operating technique:

Bucket’s angle of approach (not to steep angle)
Unmotivated ground contact (as little as possible)

Production conditions:

Cycle frequency gives different wear intensity per production hour
Warm materials, i.e. slag (decreases the wear resistance of the steel plates)
Wet or dry materials (humidity decreases the wear resistance of the steel plates)