(1) rapid solidification is carried out at the thick and hot spots where the machine tool casting structure is formed, which artificially causes the basic balance of the temperature field in all parts of the machine tool casting. Internal and external chills are used, and zircon sand, chromite ore or special coatings with large heat storage capacity are used locally.
(2) reasonable process design. The inner sprue is located at the opposite wall of the machine tool casting, which is scattered for many hours. The molten metal that first enters the thick wall solidifies first, and then solidifies at the thin wall, thus basically achieving balanced solidification everywhere. For machine tool castings with uniform wall thickness, multiple inner runners and air outlets are used. There are many internal sprues, which are dispersed and evenly distributed, so that the overall heat is balanced. The air outlet holes are thin and numerous, which not only can exhaust smoothly, but also can dissipate heat.
(3) Changing the position of the inner runner
(4) Choosing a molding material with large heat storage capacity is extremely important for producing wear-resistant products by EPC! Chromite sand replaces quartz sand and other sand with low heat storage capacity, which will achieve good results, especially after pouring.
(5) Low-temperature quick firing and open gating system. Make the molten metal fill the mold quickly, steadily and evenly. This should be tailored to the piece.
(6) The machine tool mold of ductile iron has high strength, surface hardness ≧9 and sand box rigidity, which is beneficial to eliminating shrinkage porosity.
(7) When the riser is needed, move the hot riser first and leave the hot section. If the riser is placed on the hot joint, the riser size will be increased, forming "hot heating". If it is not well done, not only shrinkage porosity is difficult to remove, but also centralized shrinkage cavity will occur, which will reduce the process yield.
(8) Tilt placement and alloying of molds benefit both. Eliminating shrinkage defects of machine tool castings is a complicated process of understanding and implementation. Based on the basic principle of "heat balance", we should make scientific analysis of the holmium castings, formulate reasonable technological scheme, select suitable molding materials, tooling, correct operation and standardization. Then the shrinkage defect of any machine tool casting can be solved.
due to various factors, defects such as blowholes, pinholes, slag inclusions, cracks and pits often occur. Commonly used repair equipment is argon arc welding machine, resistance welding machine, cold welding machine, etc. For casting defects with low quality and appearance requirements, argon arc welding machine and other welding machines with high calorific value and high speed can be used to repair them. However, in the field of precision casting defect repair, due to the great influence of argon welding heat, secondary defects such as casting deformation, hardness reduction, sand holes, local annealing, cracking, pinhole, wear, scratch, undercut, or insufficient bonding force and internal stress damage will be caused during repair. Cold welding machine has just overcome the above shortcomings, and its advantages mainly lie in the small heat affected zone, no need for preheating and cold welding repair at room temperature, so there is no deformation, undercut and residual stress, no local annealing and no change in the metal structure of the casting. Therefore, cold welding machine is suitable for repairing surface defects of precision castings. The welding repair range of cold welding is the process of repeated melting and accumulation of φ 1.5-φ 1.2 mm welding repair points. In the process of repairing large-area defects, repair efficiency is the only factor that restricts its wide application. For large defects, the composite application of traditional welding repair process and casting defect repair machine is recommended.