Controlling in-situ Microstructure of S. G Iron Castings

摘要

With modern Foundries using Chemically bonded sand moulds for producing SG Iron Castings such as Windmill castings, Phenolic-Acid, Furan-Acid no-bake systems are very much attractive due to the bigger size of the moulds. These resin-sand systems add to the graphite degeneration on the surface of the spheroidal graphite cast iron, as a flake graphite. Sulphur in the Para Toluene Sulphonic Acid which is used as the hardener in the resin system is one of the contributory factors resulting in non-nodular gTaphite, micro-porosity and other surface defects, reducing all properties and affecting fatigue properties. Various measures taken to reduce these defects for having low sulphur level in the moulding sand, include optimum nodulizer addition, lower PTSA addition ideally less than 50% of resin, lower reclaimed sand addition, and using High density Mold coating. In Windmill castings the surface microstructure is normally observed at a depth of 1.5-2.0 mm and the Foundry needs to grind the total surface of the casting, increasing the post casting operations which is very expensive. This paper deals in controlling and achieving the Surface Microstructure of S G Iron Castings in particular, Windmill Castings to a depth of about 0.5 mm as per EN-GJS-400-18U LT specifications and reducing the surface grinding of about 1 mm to 1.50 mm of windmill castings and reducing the post casting operations to a great extent.