U.K. Heat Treatment Specialist Keighley Expands Furnace Capacity
Estimated by industry sources to represent around 10% of component manufacturing costs, heat treatment modifies the microstructure of metallic materials, influencing mechanical characteristics like strength, ductility, toughness, hardness and wear resistance.
Keighley said it enlarged the size of one of its largest pit furnaces, increasing dimensions to 1,110-mm working diameter and almost 1,800-mm maximum length, in the process gaining 30% in overall capacity. At the same time, it has upgraded the lifting capacity of the overhead crane that services all seven pit furnaces, a salt bath and tempering equipment, to 3-metric tons maximum lift.
The company said enlarging the pit furnace involved fabricating a custommade inner shell or retort, made from exotic duplex stainless steel, but the considerable investment has already been offset by new orders. The company is already considering upgrading other inhouse pit furnaces and its programmable process controllers.
Keighley employs its pit furnaces for carburizing, carbonitriding, hardening and tempering, stress relieving, homogenizing and carbon restoration, working at temperatures up to 980°C. It handles steel, iron, high-chrome iron, cast iron, ADI (austempered ductile iron) and alloy steel materials.
Pit furnaces are vertically oriented batch furnaces, with the furnace section buried in a pit and extending up to floor level and a hydraulically operated sealed cover extending above the surface. Workpieces are held in a jig or charge basket in the furnace, the inner retort protecting them from the direct radiation of heat; this configuration is particularly suitable for treating long parts such as shafts, tubes and rods, although a wide variety of shapes and sizes can be accommodated, singly or in batches.
According to the company, pit furnaces produce minimal distortion, and this is particularly critical for larger components, where the same percentage of deformation equates to a much greater absolute distortion, possibly leading to the scrapping of parts. Defined as irreversible and usually unpredictable dimensional changes during the process, distortion occurs when heating the work piece above the transformation temperature results in it losing the inherent strength it possesses at room temperature, often causing it to distort under its own weight. Thus, long parts are preferably heated in a vertical pit furnace, to ensure they are properly suspended during heating, while other parts must be carefully supported to suit their geometry, employing welldesigned jigs and fixtures.