It mainly includes appearance quality, intrinsic quality and quality of use. Appearance quality refers to the surface roughness, surface defects, dimensional deviation, shape deviation and weight deviation of the casting; the intrinsic quality mainly refers to the chemical composition, physical properties, mechanical properties, metallographic structure of the casting, and the holes, cracks, inclusions existing in the casting. Segregation and other conditions; the use of quality refers to the working durability of the casting under different conditions, including wear resistance, corrosion resistance, chilling heat, fatigue, shock absorption and other properties as well as machinability, weldability and other process properties.
Casting quality has a major impact on the performance of mechanical products. For example, the wear resistance and dimensional stability of machine tool castings directly affect the accuracy of the machine tool to maintain the life; the size of the impeller, the housing and the internal cavity of the hydraulic pump, the accuracy of the profile and the surface roughness directly affect the pump. And the hydraulic system's working efficiency, energy consumption and cavitation development; the strength of the internal combustion engine cylinder block, cylinder head, cylinder liner, piston ring, exhaust pipe and other castings and the resistance to chilling heat, directly affect the working life of the engine.
There are many factors affecting the quality of castings. The first is the design and craftability of castings. When designing, in addition to determining the geometry and size of the casting according to working conditions and metal material properties, the rationality of the design must be considered from the perspective of casting alloy and casting process characteristics, namely obvious dimensional effect and solidification and shrinkage. Problems such as stress, to avoid or reduce the occurrence of defects such as segregation, deformation, cracking of the casting. The second is to have a reasonable casting process. That is, according to the structure, weight and size of the casting, casting alloy characteristics and production conditions, select the appropriate parting surface and shape, core making method, reasonable setting of casting ribs, cold iron, riser and casting system. To ensure the quality of castings. The third is the quality of raw materials for casting. Metal furnace materials, refractory materials, fuels, fluxes, modifiers, and materials such as foundry sand, sand binders, coatings, etc., are substandard, which may cause defects such as pores, pinholes, slag inclusions, and sanding of castings, affecting the appearance quality of castings. And internal quality, serious castings will be scrapped. The fourth is the process operation, it is necessary to formulate reasonable process operation procedures, improve the technical level of workers, and make the process procedures correctly implemented.
In casting production, the quality of castings is controlled and tested. First, we must formulate the technical rules and technical conditions for the control and inspection of raw materials and auxiliary materials to each specific product. Each process is strictly controlled and tested according to the technical code and technical conditions. Finally, the quality of the finished castings is checked. Be equipped with reasonable testing methods and appropriate inspectors. Generally, for the appearance quality of the casting, the comparative sample can be used to judge the surface roughness of the casting; the fine crack of the surface can be inspected by the coloring method and the magnetic powder method. The internal quality of the casting can be checked and judged by means of audio, ultrasound, eddy current, X-ray and gamma ray.
Sand casting casting defects include: cold insulation, insufficient pouring, pores, sand, sand, sand, and sand.
1. The cold metallization and pouring of liquid metal is insufficient, or the filling condition is poor. Before the cavity is filled, the molten metal stops flowing, which will cause the casting to have insufficient or cold insulation defects. When the pouring is insufficient, the casting cannot obtain a complete shape; while the cold insulation, the casting can obtain a complete shape, but the mechanical properties of the casting are seriously impaired due to the existence of the joint which is not completely fused.
Prevent under- and cold-separation: increase the pouring temperature and casting speed.
2. The pore gas does not escape in time before the molten metal shells, and the pores generated in the casting are defective. The inner walls of the pores are smooth, bright or have a slight oxidized color. When the air holes are formed in the casting, the effective bearing area is reduced, and stress concentration is caused around the air holes to reduce the impact resistance and fatigue resistance of the casting. The vents also reduce the compactness of the casting, causing some castings that are subject to the hydrostatic test to be scrapped. In addition, the pores have an adverse effect on the corrosion resistance and heat resistance of the casting.
Prevent the generation of pores: reduce the gas content in the molten metal, increase the gas permeability of the sand type, and add a gas riser at the highest point of the cavity.
3. A layer of sand that is difficult to remove adhered to the surface of the bonded sand casting is called sticky sand. Sticking sand affects the appearance of the casting, increases the workload of casting cleaning and cutting, and even affects the life of the machine. For example, when the surface of the casting tooth is sanded, it is easily damaged. If there is sticky sand in the machine parts such as a pump or an engine, it will affect the flow of fluid such as fuel oil, gas, lubricating oil and cooling water, and will stain and wear the entire machine.
Prevent sticking sand: Add coal powder to the molding sand, and apply anti-stick sand coating on the surface of the mold.
4. Grooves and scar defects formed on the surface of the casting sand are easily produced when wet-casting thick flat castings.
Most of the parts in the casting that are sanded are in contact with the upper surface of the sand. The upper surface of the cavity is affected by the radiant heat of the molten metal, which is easy to be arched and warped. When the raised sand layer is continuously washed by the molten metal flow It may break and break, stay in place or be taken to other parts. The larger the upper surface of the casting, the larger the volume expansion of the molding sand, and the greater the tendency to form sand.
5. The blisters are filled with voids in the sand or in the surface of the casting.
6. Under the pressure of the molten metal under the pressure of the molten metal, the mold-shaped wall moves and the casting is partially expanded to form defects. In order to prevent sand expansion, the sand strength, the rigidity of the sand box, the pressure box force or the fastening force when the box is combined should be increased, and the pouring temperature should be appropriately lowered to make the surface of the molten metal prematurely crust, so as to reduce the metal liquid to the mold. pressure.
Butt Weld Reducer,Pipe Reducer,Carbon Steel Reducer
Group Steel Pipe Engineering Co., Ltd. , http://www.hbsteelpipes.com