The sector of Earth Moving Machines, which are internationally known as YELLOW GOODS, includes dozens of different machines that operate in various fields of application: excavation, movement, transport, crushing, processing of aggregates, demolition, land drilling and consolidation, compaction, land reclamation, road works and many more.
The structure which represents the main part of the earth moving machines does not usually require particularly sophisticated steels, as structural solidity is achieved by adopting greater thickness or higher performance steels. The tools however, both large and small ones, and some parts of the machine are subject to wear.
WEAR can be of different types: impact, abrasive, adhesive, slightly corrosive or deriving from fatigue (and rarely also from cavitation).
Wear depends on the materials that the machines work with, depending on the difference between the hardness of the tool and that of the material to be processed, removed, transported, drilled, crushed, etc. (Mohs scale).
Wear can cause many problems including machine standstill for days, with consequent production losses, stop of the work on the production line, replacement of a part instead of maintenance or repair, breakdown of a machine or part of it with serious consequences for people and property.
Wear-resistant steels have been invented to counteract this physical phenomenon that is intrinsic in all objects, and all the more so in machines that work with materials of different degrees of hardness in harsh environments, in arid or humid conditions, in extremely high or low temperatures.
HARDNESS is, in fact, used to identify the differential between the tool and the material and in steels this is normally determined through mechanical tests which establish the degree of hardness:
Brinell, Vickers, Rockwell, Shore and other measurement scales for materials other than steel. Hardness is closely related to the mechanical characteristics of the steel to be used (directly proportional), and in the case of earth moving equipment, Brinell hardness (HBW) is the most commonly used scale.
Earth moving machines and similar machines are built using wear resistant steels and often if one specific part is appropriately built with suitable wear resistant steel it guarantees the success of the entire structure.
In the recent past, very thick steels were used to minimise wear mechanisms, as well as heavy armours, complex external structures coupled with casings made of cast iron or other high alloy steels that inhibited the weldability and burdened the structure. Nowadays there are wear resistant steels that are weldable and cold-formable, with degrees of hardness that can be used for structural purposes; these steels not only guarantee wear resistance but also the production of light machines or parts, with all the consequent advantages.
The lower the tare weight, the greater the weight carried; less weight equals less fuel consumption; thin and cold formable steels mean less welds, which cause localised weaknesses; there are also many other important advantages such as environmental sustainability.
Wear can also be aggravated by impact and consequent elastic or plastic deformation, which can create additional localised wear. Modern steels create the conditions to avoid, as much as possible, plastic deformation (permanent) caused by an accidental yet unavoidable mechanical impact or blow caused for example by rocks falling from an excavator into a dumper’s skip during loading operations on a work site.
VENTURI ACCIAI stocks a wide range of wear resistant steels of varying degrees of hardness and has the know-how and expertise to determine what degree to use, how to cut the steel, in which situation to use it to fully exploit its characteristics; the steel plates are certified and are supplied by top European steel companies, such as the world leading Swedish company SSAB which, with its HARDOX brand founded in 1974, has permanently changed the design of certain machines thanks to the appropriate use of the steel’s characteristics. If we consider for example the evolution of load body of trucks, they have gone from having thick beds, heavily welded sides, useless reinforcements and kilometres of weld seams to being curved (bath like shape), with light sides, a few metres of welds, a 30% reduction in tare weight, as well as being safer and environmentally sustainable.
The wear resistant steels of reference are: SSAB’s HARDOX 400,450,500 and 600 and other steels such as QUARD and DILLIDUR, just to mention some of the most well-known ones with the same degrees of hardness, which are identified by the numbers after the brand.
Obviously there would be much more to say about wear, wear resistance, applications and processing.
Earth moving machines have parts which are subject to stress due to extensive use and constantly wearing work, such as excavator buckets, dumper and truck skips, crushers, demolition claws, auger screw blades, the blades of levelling machines or snow ploughs. Wear causes the breakdown of a part and only a careful choice of the steel coupled with manufacturing expertise can normalise the cost of the original equipment, maintenance and repair.