Preheat Unit Eliminates Bottleneck

James Walker & Co. Ltd have installed a purpose built, low voltage electric heating unit, which has eliminated a production bottleneck and increased output from their Cockermouth plant.

The new facility has been specially designed to preheat moulding tools used in the manufacture of high performance rubber seals. To achieve the quality required it is essential that the tool is heated uniformly to the correct temperature. This ensures that the rubber will 'flow' to take on the shape of the mould when it is transferred to the press.

Walker seals are the UK's largest gasket and seal manufacturers. Their range starts at simple tap washers and extends to special seals of up to 2.5 metres in diameter used in the petrochemical steel, power and shipping industries. Tony Magorrian of James Walker & Co. Ltd said "the new preheat unit has made a vast improvement since the tools are now warm enough to form within minutes and the in-built flexibility allows production to be varied as required".

The preheat unit was manufactured by Mannings Thermal & Environmental Engineers of Southport. They had to come up with a design which would not only allow several metal tools of various sizes to be heated simultaneously to a controlled temperature of 170 degrees centigrade but also maintain temperature uniformity within very tight limits. The new unit can hold up to 10 tonnes of moulds and these are placed on a refractory base, which has a top layer of load bearing firebrick. A motorised, insulated cover is then moved over the base to form a sealed heating chamber.

The thermal performance of the process lies in the design of the heating system, which has been incorporated into the base construction. Low voltage ceramic heating elements are laid in slots in the base brickwork so that the whole hearth area is uniformly heated. The elements were selected from the standard range manufactured by Mannings and use multi-strand nickel chrome wire electrically insulated by means of interlocking sintered alumina beads. These elements have a high mechanical strength and are easily removable for maintenance purposes. Les Oliver, who is Manager of Industrial Heating at Mannings said, "this is a perfect example of how the use of modern electric heating can produce cost savings and increased production".

The preheat unit mobile cover is manufactured from sheet steel, fixed to a steel superstructure. This is internally lined with low thermal mass insulation secured to the roof and walls by inconel studs and quick release washers. The cover is motorised by an electrically powered haulage unit, which enables it to be moved away from the hearth to permit access. A re-circulation fan has also been incorporated into the cover design as well as internal air distribution ducting. This helps to produce uniform heat distribution throughout the chamber. The cover is open at one end since one of the chamber end walls is fixed to the hearth base. Special seals on the cover, end wall and hearth ensure performance and energy efficiency. Control of the unit is from a panel, which incorporates automatic temperature control, temperature indicators as well as all the necessary safety interlocks, and alarms.

Before installing the new electric preheat furnace, James Walker & Co. Ltd used steam as the source of heat but this was inefficient and caused production delays. An urgent solution to the problem was sought and Mannings carried out a study of the requirements before recommending the custom built design.