Its large size means we can fit fabrications or plates up to 6.2 metres long by 2.6 metres wide & 1.8 metre high with a maximum weight of 20 tonnes. Being a 3 zone electrically fired thermal stress relieving oven allows us much greater temperature control over the post weld heat treatment process than gas fired or other furnace types, especially in the climb and cool down phases of the process. The electric type of thermal stress relieving oven also produces less scale on the fabrications due to there being significantly less oxygen present during the firing. Our standard soak temperature is 600°C but can be adjusted for individual customer specifications as well as the climb and cool down ramps.
We normally fire 5 nights a week & most weekends, which can accommodate longer soak time items or be set to customer specific temperatures. Our oven is fully calibrated in all 3 zones & for each 'furnace batch' we can supply a calibrated heat cycle chart to ensure soak times and temperatures have been achieved & to ensure that steel and welds have been adequately stress relieved.
Thermal stress relief is normally carried out as a post weld heat treatment to release any build of stresses caused by the welding process. As the rapid input of heat and subsequent rapid cooling can cause tension to form in the material as well as hardening and changes to the crystalline structure while most of the changes metallurgical changes take place in the weld fusion zone and the heat affected zone (HAZ) the subsequent tension in the base material can affect the whole of the fabrication. This will often become apparent during machining, where a fabrication loss of the surface and reduction in material thickness can cause the item to “spring” or distort and result in a loss of tolerance.
Welding isn’t the only process to cause a buildup of stresses, the manufacture of steels leaves behind residual stresses as well as any cutting, burning, bending and other plastic deformation processes. Sometimes minor stresses are enough to effect high precision machined parts and may require multiple stress relieving operations throughout the machining process.