Metlab Heat Treating, Niagara Falls, N.Y., announces completion of a successful project with a major crane manufacturer to flame harden the bridge crane wheels for a large overhead multiple bridge crane system. Installed at an aircraft manufacturer, the crane lifts airplanes as they are being assembled. Over 1,500 wheels made of 1045 steel, approximately 6.5 in. O.D. by 2.5 in. wide, were hardened to a hard and uniform outside rim of 425 BHN (HRC 45) and a case depth of 0.125 in. minimum.
Flame hardening is a surface hardening treatment where the outside of the component is uniformly heated by direct application of a flame. Special burners combining a fuel gas (typically acetylene or) and oxygen are used to generate the flame, and temperature is monitored by optically comparing the color of the heated steel to a color/temperature chart as well as using infra-red temperature sensors.
When the surface of the part has been hardened to a sufficient depth, the surface is rapidly cooled by either oil or water quenching. The advantage of flame hardening for a part like a crane wheel is that the process hardens the outside surface only providing a deep case, resulting in a highly wear resistant surface, as well as increased bending fatigue strength, while leaving a tough core which can absorb shock, and loading with little or no distortion. Metlab has the ability to flame harden many sizes and types of parts up to 14 inches in diameter.
