Hardfacing, or hardsurfacing, is wear insurance for your heavy equipment. Chris Monroe at Hobart Brothers says hardfacing old equipment can restore worn components to almost-new condition for up to 75 percent less than what it could cost to purchase a replacement part. Hardfacing stress areas on new equipment before it is put in service can extend the life of those surfaced parts up to 300 percent, he says.
There are two hardfacing methods: build up and over lay. Build up welds layers of filler material to a worn surface to restore the area to its original dimensions. Overlays weld protective “buffers” on wear points to guard surfaces from abrasion and impact. Used separately or in combination, both bond a metal alloy to the equipment’s base metal using either stick or flux-cored welding processes.
The type of wear equipment displays will determine which filler to use. The causes and cures for the three most common types of equipment wear and tear are:
• Abrasion: Surface wear such as scratches, grooves and gouges caused by repeated contact with hard materials, usually found on blades, buckets, and attachments. Carbide or chrome carbide filler metal protects against low-stress abrasion. The best filler metals for high-stress grinding abrasion contain austenitic manganese, martensitic irons or titanium carbides.
• Adhesive (metal on metal) wear: Found on steel track components and exposed gears that experience nonlubricated friction as they roll or slide against each other. Hard surfacing alloys such as austenitic manganese or cobalt-based filler metal will reduce wear for these applications.
• Impact: Caused by a compressive load such as repeated pounding, or by random contact with rocks or other hard objects, which places high mechanical stress on equipment. Often found on attachments such as hydraulic hammers and buckets. Austenitic manganese steel filler metal offers the best protection for impact wear.
Most welding wires contain chromium to improve wear resistance, but when chromium is heated it produces hexavalent chromium fumes, which OSHA says causes lung cancer. New chromium-free hardfacing wires eliminate fumes and provide a layer of wear resistance and hardness said to be equal to or better than conventional chromium carbide.
Also new to the hardfacing industry are gas-shielded, all-position flux-cored wires for general hardfacing applications. The deposit is a specially formulated, wear-resistant alloy that produces a uniform distribution of small primary carbides in a martensitic matrix. The small carbides provide greatly improved wear resistance over martensitic steel, many tool steels, and some conventional chromium carbide alloys.