Casting process design and production practice of 360m2 sintering trolley intermediate
Fourth, the choice of iron smelting and spheroidizing treatment process
Smelting equipment
The smelting of molten iron by a 5t power frequency furnace has the following effects:
(1) Facilitate the adjustment and control of chemical composition.
(2) Conducive to controlling the melting, tapping and pouring temperatures.
(3) Avoid the smelting of molten iron from the cupola to bring in harmful elements.
(4) Easy to purify molten iron.
2. Selection of metal raw materials
(1) Metal materials are made of high quality scrap steel and low phosphorus pig iron. The chemical composition is shown in Table 5.
(2) The spheroidizing agent adopts a ruthenium-based heavy rare earth composite spheroidizing inoculant, which can effectively prevent spheroidization and inhibit the generation of carbides.
(3) Inoculant is selected from 75SiFe and compound inoculant.
3. Chemical composition control
The chemical composition control is shown in Table 6, and the selection is based on the following.
。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 In actual production, carbon is generally taken as an upper limit, mainly for improving casting properties, and utilizing graphitization expansion to compensate shrinkage and increase the compactness of the casting.
(2) The wSi of the Si iron solution is controlled in the range of 1.0% to 1.5%, mainly considering the increase of silicon during the spheroidization process. In a certain range, the amount of silicon in the ductile iron can increase the ferrite content, refine the graphite, and improve the roundness of the graphite ball, but because silicon can improve the ductile-brittle transition temperature and reduce the impact toughness, it is in iron. The upper limit of silicon in the elemental matrix ductile iron is generally taken, and the lower limit of the pearlitic base ductile iron is taken. 8%。 The selected material of the casting material QT500-7 is a ferritic-pearlite type, so we choose the final wsi control range of 2.3% ~ 2.8%.
(3) Mn Because the spheroidizing agent can neutralize a part of sulfur, the harmful elemental sulfur in the molten iron is reduced to a lower value. At this time, manganese basically no longer acts as a neutralizing sulfur, but mainly distributed and concentrated in the eutectic. On the grain boundary, pearlite is formed, so it has the function of stabilizing carbide and pearlite, but the high manganese will reduce the plasticity and toughness of ductile iron.
(4) S and P Sulfur and phosphorus can be regarded as harmful elements in ductile iron. During spheroidization, sulfur will consume spheroidizing agent, reduce spheroidization rate, accelerate spheroidization, cause microscopic slag, and reduce or unstable the mechanical properties of spheroidal graphite cast iron. Therefore, it should be strictly smelted and spheroidized. Reduce the sulfur content of the original iron liquid, if necessary, use desulfurization means to reduce sulfur. Phosphorus mainly exists in cast iron in the form of Fe-Fe3P, Fe-FeP-Fe3P and composite phosphorus eutectic. Phosphorus eutectic has high hardness and brittleness, and is distributed on the boundary of crystal grains, and the continuity between grains is divided. The strength and plasticity of the cast iron are lowered, and the hardness is improved. The increase in phosphorus also increases the tendency of shrinkage, porosity and cracking of cast iron parts. However, it is difficult to dephosphorize during the smelting process, so the phosphorus content in the raw materials should be strictly controlled.
4. Spheroidization and birth treatment
(1) Spheroidizing treatment bottom punching method, the dam height is 150mm, and the spheroidizing agent is placed at the bottom of the bag, and the amount of addition is 1.4% to 1.8%, and the slab is sturdy and the particle size is 20-30mm. Then add 0.3% of the inoculant, the particle size is 20 ~ 30mm, and the iron plate is covered on it. The molten iron was flushed in two times, accounting for 2/3 and 1/3 of the total, respectively, and the slag was sampled before pouring.
(2) Inoculation treatment, the second inoculation is carried out with a flow of 0.5% inoculant, with a particle size of 5 to 10 mm. 2% Special inoculant for intensive gestation treatment.
5. Casting process
The pouring temperature is controlled at 1300 ~ 1330 °C, and the control is completed within 15 minutes after the molten iron is processed. When pouring, keep the pouring cup in a full state (fast pouring), and then pour the riser after pouring to prevent casting defects such as cold separation and shrinkage.
V. Other process measures and operational points
(1) The main points of the molding and boxing process are due to the good fluidity of the resin sand, mainly by hand-tightening, and the local hard-to-tight parts are tamped with metal rods; the time of mold-cutting is controlled at 30 to 40 minutes, which is convenient for production organization; Brush paint, especially the position of the ribs, must not be leaked to avoid sticking sand. The finished mold needs to be fastened with clips to avoid lifting the box.
(2) The cooling time of the falling sand cleaning and heat treatment castings in the mold is ≥48h; the castings are cleaned and polished, and there is no floating sand or burrs. The castings with casting defects are treated in time, and the welded parts are welded after welding. It must be re-annealed to ensure its processing properties; all castings are subjected to low temperature annealing before delivery to eliminate internal stress. The annealing process is shown in Figure 2.
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