Heat Treatment

CP&A have specified heat treatments for many different types of components including; hoist drums, rail runners, sheaves, gears, and wheels.

A hard surface is sometimes necessary to prevent wear on certain items such as cable drums, sheaves, running surfaces and gears. It may not always be necessary to make the entire piece out of 200 ksi steel, so only hardening the surface makes sense. Sometimes the part needs a hardness value that starts creating manufacturing problems. Generally, it is possible to machine up to 70 HRC with ceramic bits. Beyond 70 HRC it gets very difficult/expensive. Using standard cutting tools, it is possible to machine steel up to the mid 40’s Rockwell C.

A common mistake we see is to use a quench and tempered billet with the specified hardness desired for the part and machine it down. Depending on the size of the billet and material grade, the hardness is not uniform. So it is possible that the hardened material was removed from the billet and the remaining material doesn't meet the specified hardness. As a billet is quenched, the cooling rate is an important factor in determining hardness. The core of the billet will cool much slower than the material near the surface. This is what creates an difference in hardness between the core and case.

Testing is an important consideration. Gas and Ion nitride create a very hard and thin layer. In fact, nitride layers can be so thin that Rockwell C and Brinell measure too deep. Vickers and Rockwell Superficial 15n are more appropriate test methods for thin layers. Hardness can then be converted to HRC or Brinell.