Pit & Quarry, September 2012

MAINTENANCE TIPS FROM EQUIPMENT MANUFACTURERS AND OUR READERS Hardfacing effectiveness Use these 26 tips to increase uptime and reduce costs T he process of hardfacing has evolved from the oxyacetylene applied rods of 90 years ago to a complex material science and application driven solution In the simplest sense hardfacing helps aggregates operations increase profitability This is accomplished in a number of ways By reducing downtime through increased time between scheduled maintenance procedures By using lower cost base metals that are then overlaid with a specialized alloy of superior durability By rebuilding worn components rather than replacing them With a focus on cost reductions and productivity enhancements the selection of the correct alloy and proper application is critical What follow are 26 of Stoodys top tips to maximize hardfacing effectiveness broken down to five basic steps base metal identification wear factor identification alloy selection weld process selection and bead pattern Base metal identification 1 Know your base metal before welding Base metal type and its carbon and total alloy content is an important factor in the hardfacing process Some metals tolerate extremes in heat or cold well others do not Common base metals include low medium and high carbon steels wear resistant and abrasion resistant AR steels manganese steels Mn steels stainless steels 300 and 400 series tool die and mold steels and cast irons 2 Preheating is often required This is especially true when welding onto higher carbon and alloy steels wear resistant or AR steels all tool steels cast irons and 400 series stainless steels Preheating minimizes distortion shrinkage cracking and spalling lifting of the weld deposit and it greatly reduces thermal shock to the part Carbon and alloy content of the base metal influence the recommended preheat temperature 3 Preheat slows the cooling rate of the base metal Rapid air quenching the abrupt air cooling from welding temperature embrittles the part in the heat affected zone For higher carbon and alloy steels preheating greatly reduces this tendency 4 Austenitic Mn steel is non magnetic and tough and it work hardens under high impact loads For this reason Mn steel parts are often found in machinery that uses high impact loads to render and crush Example applications include rock crushers roll and impact crushers swing hammers and car shredders Mn steel parts are often used without hardfacing Prior to work hardening Mn steel has low abrasion resistance Applying a suitable hardfacing will increase the part life significantly 5 The toughness of Mn steel can be lost if the base metal temperature exceeds 500 F Avoid applying prolonged and concentrated heat to any single area on the part overheating causes embrittlement 6 Weld Mn steel base metals only with manganese alloy consumables Avoid using carbon steel materials These will cause brittle weld deposits that will spall By DaviD Hami lton Hardfacing can save producers money by helping them get long wear life from their equipment 92 PIT QUARRY September 2012 www pitandquarry com