Causes And Control Of Distortion Graphite Defect Of Ductile Iron Cast Surface

The graphite distortion defects in ductile cast iron surface are the main object of this paper. By pouring test, obtaining as-cast structure, preparing metallographic specimen, observing the surface of graphite morphology, the best casting solution was applied to practical production. First of all, the effects of some factors such as casting wall thickness, coating thickness, cooling rate, molding materials, cauterant decrease of resin sand, the amount of curing agent, pouring temperature and curing agent type, etc on the distortion of the graphite of surface of ductile iron castings were investigated. Through research and analysis of the test,all the factors are at the best level of casting solution, and the scheme was applied to comprehensive experiments and production practice.Experiment shows that with the increase of wall thickness of nodular cast iron, the graphite distortion depth on casting surface increases, and the shape of the graphite is also changed from ball to thin sheets. Compared with the ordinary bauxite coating, ductile iron coating can effectively reduce the graphite distortion layer of casting. The thicker the coating, the thinner the thickness of distortion of graphite layer on ductile iron surface. The thickness of distortion of graphite layer reduced from 1490 μm with a layer of coating to 453 μm with three layers of coating. When the coating thickness increased to more than 2 mm, anti-sulfuring effect of coating tends to be the same. The less amount of resin and curing agent is added, the thinner thickness of graphite distortion layer on ductile cast iron surface is. The depth of the biggest distortion layer of graphite reduced from 1551 μm to 455 μm when the amount of curing agent also reduced from 0.7% to 0.4%. Among molding sand, the higher proportion of the addition of new sand, the lower the cauterant decrease of molding sand and sulfur content, the thinner the thickness of graphite distortion on ductile cast iron surface. Among them, when 100% of new sand specimens are used, the minimum depth of graphite distortion on surface in 100 mm wall thickness is 397 μm, however, when 100% of the reclaimed sand sample is used, the maximum depth of graphite distortion is 2512 μm. The more the cold iron is added in the mold, the thinner the thickness of graphite distortion layer on the casting surface is, and among the samples the largest wall thickness of graphite distortion layer decreases from 1490 μm without cold iron to 596 μm with double-side cold iron.The lower the pouring temperature of ductile iron casting, the thinner the thickness of distortion of graphite layer on ductile cast iron surface with the wall thickness of100 mm, and the depth of graphite distortion layer sample changed from 1822 μm to 694 μm when the temperature change from 1406 to 1327 ℃ ℃.In the 7 kinds of new type of anti-sulfuring coating, the effect of reaction-sintering, a compound new seepage coating 5 is the best. The coating eliminates the distortion layer of graphite under the wall thickness of 50 mm, and makes the distortion layer of the graphite reduce to less than 100 μm. Using new type of low sulfur curing agent in molding sand, the thickness of graphite distortion layer on ductile cast iron surface becomes thin. Among them, the thickness of graphite distortion layer on the 100 mm wall thickness reduced from 1490 μm greatly to 259 μm, and at the same time, the shape of graphite distortion also tend to tadpole and vermicular.Through comprehensive investigation on some factors, such as the amount of curing agent, new type of low sulfur curing agent, cold iron, the reduced amount of sand mould, pouring temperature, new seepage coating and coating thickness, etc applied on the stepped sample, the deformity graphite on surface of specimen can completely be eliminated, and the shape of graphite is round, the distribution of the graphite is uniform. Using measures that easy to operate and control in the production, namely, low sulfur curing agent and cold iron is added in the moulding sand in casting surface, two layers of sulfur anti-sulfuring coating 5 is brushed, wind power torque arms were produced and the defects of graphite distortion in the surface of nodular cast iron were completely eliminated.