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New enlarged pit furnace accommodates today's larger components

article image The pit furnace

There has been a significant increase in the size of power transmission components such as gears, shafts, pinions and bearings to handle greater productivity demands in renewable energy, mining and quarrying, oil exploration and marine applications. 

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 per cent of component manufacturing costs, heat treatment modifies the microstructure of metallic materials, influencing mechanical characteristics such as strength, ductility, toughness, hardness and wear resistance, which in turn, increase the service life and technical performance of metallic parts. This is even more critical for the new generation of larger components that are crucial to mechanical function and usually difficult to replace. 

Anticipating this growing customer demand for processing larger gears, shafts and other components, sub-contract heat treatment specialist Keighley Laboratories of West Yorkshire has enlarged the size of one of its largest pit furnaces, increasing dimensions to 1110mm working diameter and almost 1800mm maximum length, thereby gaining 30 per cent in overall capacity. It has also 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. 

Enlarging the No 1 pit furnace involved fabricating a custom-made inner shell or retort, made from exotic duplex stainless steel, but this considerable investment has already been offset by orders for heat treating 1108mm diameter gear wheels for an offshore application and 1755mm long, 1 tonne shafts for a renewable energy project. Keighley Labs is already considering upgrading other in-house pit furnaces and its programmable process controllers. 

Divisional Commercial Director, Michael Emmott explains that this has opened up a new market for Keighley Labs amongst engineering companies and OEMs, who seek to heat-treat larger components. 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 employs its pit furnaces for carburising, carbonitriding, hardening and tempering, stress relieving, homogenising 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 for aviation, marine, defence, rail, mobile plant, energy and general engineering companies. 

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. Apart from offering significant savings in floorspace, with one sealed quench occupying the same floor area as four pit furnaces, this furnace type 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. 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. 

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 well-designed jigs and fixtures. 

According to Michael Emmott, with their new heat treatment department, modern furnaces and advanced low temperature, low distortion, thermochemical processes coming on stream later this year, Keighley Labs wanted to renew the focus on their pit furnace capability, where the company is ranked amongst the leaders in the contract heat treatment industry. 

He adds that many customers have highly technical resources and can specify unambiguously the heat treatment processes required; this motivates the company to continually invest in their heat treatment resources to keep abreast of their clients’ exacting requirements and offer alternative solutions across the whole spectrum of surface engineering. 

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