Enlarged pit furnace accommodates larger components

Keighley Labs increase furnace size to meet increasing demand for heat treatment of large components

Developments in mining, quarrying and other engineering applications have led to significant increases in the size of power transmission components such as gears, shafts, pinions and bearings, to handle greater productivity demands. As these large components are exposed to severe duty cycles, there is renewed emphasis on the heat-treating methods needed to enhance their wear resistance and strength properties.

Estimated by industry sources to represent around 10% of component manufacturing costs, heat treatment modifies the microstructure of metallic materials, increasing the service life and technical performance of metallic parts, which is critical for the new generation of larger components that are crucial to mechanical function and usually difficult to replace.

Anticipating growing customer demand for processing larger gears, shafts and other components, sub-contract heat-treatment specialists Keighley Laboratories of West Yorkshire have increased the size of one of their largest pit furnaces to 1,110mm working diameter x almost 1,800mm maximum length, in the process gaining 30% in overall capacity.

At the same time, the company has upgraded the lifting capacity of its overhead crane (which services all seven pit furnaces, a salt bath and tempering equipment) to 3.0 tonnes maximum lift, and is already considering upgrading other in-house pit furnaces and its programmable process controllers.

‘This has opened up a new market for us among engineering companies and OEMs who are looking to heat treat larger components,’ explained divisional commercial director Michael Emmott (pictured). ‘This involves physical issues regarding accommodating the size of these parts, then lifting them out of the furnace and into the quench tank, as well as demanding special skills for treating very large workpieces without damage or distortion.’

Keighley Labs employ their pit furnaces for carburising, carbonitriding, hardening and tempering, stress relieving, homogenising and carbon restoration, working at temperatures up to 980°C and handling steel, iron, high-chrome iron, cast iron, ADI (austempered ductile iron) and alloy steel materials.

Pit furnaces are vertically oriented batch furnaces that are particularly suitable for treating long parts such as shafts, tubes and rods, although a wide variety of shapes and sizes can be accommodated, either singly or in batches.

Apart from offering significant savings in floor space, this type of furnace offers very high repeatability, extremely precise thermochemical treatment, economic effectiveness, proven flexibility and the capacity to treat both long components and large rounded parts, such as gear wheels.

Depending upon the required case depth, component geometry and specific customer requirements, heat-treatment cycles can take anything from two or three hours to two or three days.

Pit furnaces are also renowned for producing minimal distortion, which 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.

‘With our new heat-treatment department, modern furnaces and advanced low-temperature, low-distortion thermochemical processes coming on stream later this year, we wanted to renew the focus on our pit furnace capability, where we rank among the leaders in the contract heat-treatment industry,’ added Mr Emmott.

‘When it comes to minimizing distortion in heat-treated components, pit furnaces still have a lot to offer, and with gears, shafts and other parts increasing in size, the distortion challenge is becoming even greater. It’s an area where we can usefully contribute, drawing upon our many years’ experience.’