Thermal spray used for mining equipment? You bet! But before
you choose a thermal spray coating (also known as 'hardfacing'), you must first
understand the type of wear. The answers may surprise you.
Abrasive wear can include lower impact, lower stressed
conditions. Here, there will be no fracture, no sudden loss of parent material.
Rather, material removal is the result of scratching, filing, a consistent loss
in metal at some micro-level. Of course, wear rates will be more dramatic when
the mined abrasives are sharp, angular in nature. Proper material hardness,
such as an abrasion-resistant steel or ceramic, is key.
Adhesive wear is more of a tearing or material separation
between interacting surfaces. It begins with rubbing, and ends with phenomena
known as scoring, galling, or seizure. Their occurrence is typically associated
with like materials and structure, under an applied load, without lubrication.
Here, material choices should consider attributes like ductility, for impact
strength. These "softer" alloys available can actually work harden
with impact or deformation. The result is increased strength and resistance to
abrasion.
Have you already identified the wear mechanism? Made the
proper material selection? Well, now it is time to consider thermal spraying.
Hardness is the normal measurement for material choice. Again, keep in mind
that, under abrasive conditions, harder material choices, like tungsten carbide
or ceramic coatings are ideal. But for adhesive wear, where impact strength can
be crucial to success, softer, more ductile choices are the answer.
Did you know that how (or where) the thermal spray coatings
are applied can also slow down rates of wear? Depending on mined material type
and shape, the success of a hardface deposit will be in how it is aligned on
the surface. Parallel, perpendicular, even coating spacing and overlap can mean
the difference between success and failure. Dissimilarity in thermal expansion
characteristics between the coating and parent metal is also something to
consider.
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