Production of castings and forgings
Release time:
2023-01-13 11:24
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Production of castings and forgings
Casting and forging. Casting and forging to use electric furnace melting, mainly electric arc furnace and induction furnace. According to the different lining materials and slag system, can be divided into acidic furnace and alkaline furnace. Carbon steel and low alloy steel can be smelted in any furnace, but high alloy steel can only be smelted in alkaline furnaces. Casting process. The forging melting point is high, the fluidity is poor, and the forging liquid is easy to oxidize and inhale. At the same time, its volume shrinkage is 2 to 3 times that of gray cast iron. Therefore, the casting performance of cast steel is poor, and defects such as insufficient pouring, porosity, shrinkage cavity, hot cracking, sand sticking and deformation are easy to appear. In order to prevent the above defects, corresponding measures should be taken in the process of processing. The sand used in the production of castings and forgings should have high fire resistance and sand resistance, as well as high strength, air permeability and surrender. The original sand is usually made of silica sand with large and uniform particles; in order to prevent sand sticking, the cavity surface should be coated with a higher refractory coating; when producing large parts, the use of sand or water glass sand is faster than the use of casting molds. In order to improve the strength and flexibility of the mold, various additives are often added to the sand. In the design of the gating system and the riser. Since the cast carbon steel tends to solidify in layers and the shrinkage is large, the rigid sequential solidification principle is used to set the gating system and riser to prevent shrinkage cavity and shrinkage porosity. Generally speaking, steel castings should have risers. Cold iron is also widely used. In addition, the bottom injection system with simple shape and large cross-sectional area should be used as much as possible to make the molten steel fill the mold quickly and smoothly. Heat treatment. The heat treatment of cast steel is usually annealing or normalizing. Annealing is mainly used for steel castings with W(C)≥ 0.35% or with particularly complex structures. Such castings have poor plasticity, high casting stress and are prone to cracking. The normalizing is mainly used for castings and forgings with W(C)≤ 0.35%, with low carbon content, good plasticity, and not easy to crack during cooling.
For China's small and medium-sized castings and forgings, its small size, light weight, processing capacity is also small, can be in the fixed magnetic particle inspection machine at least in two aspects roughly divided into vertical direction of magnetization. A good method uses a DC or pulsating DC working current, with a wet continuous method of inspection. We can use it directly through the energization method, the rod wearing method, the magnetic flux method and the different coil methods.
For larger, heavier castings, the position or diaphragm is magnetized in at least two roughly perpendicular directions. It is better to use DC or half-wave rectifier portable or mobile magnetic particle detector, contact method or yoke method, dry continuous method or wet continuous method, local or split casting detection. The detection should normally take place in two mutually perpendicular directions.
In order to prevent the casting in contact with the electrode from burning out, it is recommended to take the following measures: When the contact is not in full contact with the surface of the casting, do not turn on the current, and when the current is cut off, remove the contact. and have sufficient cleanliness and proper contact. The yoke method is preferred for machining smooth surfaces. Due to the influence of the stress of the casting and forging, some cracks (cold cracks) will delay cracking, so it should not be detected immediately after casting, but should be detected after 1-2 days. If the casting and forging defects exceed the acceptance criteria and are rejected, but digging (shovel) welding repair welding is allowed, and the repair welding area should also pay attention to control the generation of delayed cracks.
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