Simple Solutions That Work! Issue 12

P roducing large steel castings can test any foundry’s materials, systems, and equipment to their limits. The effects of pouring temperature, pouring time and turbulence have a huge effect on as cast quality. When this is coupled with aspiration, undesirable oxygen activities within the melt and large changes in section thicknesses can produce both slag, inclusions and tearing defects. changes in section thickness between the body and the flange. CASE STUDY Our customer was producing a 15 ton finished weight turbine casing, which with feeders padding and ingating system took the liquid cast weight to approximately 33 tons. Initially they were using a fibre board feeder lining and tapper padding, the wall of the casing up to the flange to achieve the required soundness. This method created a number of problems: JOE HOWDEN EILDON REFRACTORIES Ltd. ARTICLE TAKEAWAYS: • Challenges in producing a 30 ton casting • Solving burn on / sand frit problems below the feeders • Preventing erosion associated with running metal through sleeves TURBINE 30 TON STEEL CASE STUDY 4 Our philosophy therefore is, that in a perfect world the ideal situation for casting is: solidification time zero, pouring time zero, ingate velocity zero. This is obviously impossible, but it does create a very firm direction, i.e., that everything in the process that increases these values is undesirable. Turbine cases often present the ultimate challenge, not only are they pressure vessels, which have to meet high integrity quality requirements and often have a huge surface area to weight ratio while exhibiting very significant 1. Their largest furnace could only produce 30 tons and their largest ladle had a capacity of 30 tons. This meant they needed to use two furnaces and two ladles, which not only added to costs but complicated the metal handling and pouring enormously. 2. They had a burn on / sand frit problem below the feeders caused by overheating of the fibre board feeder lining , which in turn gave them a cutting problem, in that if they tried to cut the feeders too close to the flange, the flame was deflected by the burnt on sand and cut into the flange. 3. The padding on the inner wall of the body virtually doubled the wall thickness as it approached the flange which resulted in a lot of extra machining, but it also meant that they were machining into the centre line of the cast wall section exposing centre line type defects. 4. The ingating system and their experience with severe erosion associated with running metal through sleeves meant that they were unwilling to fill the mold through the thin section at the bottom. Unfortunately this led to some dead spots / slag traps in this area.