Aluminum castings refer to equipment and components made of pure aluminum or aluminum alloys obtained by casting. Generally, sand molds or metal molds are used to pour heated liquid aluminum or aluminum alloy into the mold cavity, and the obtained aluminum parts or aluminum alloy parts of various shapes and sizes are usually called aluminum die castings.
Aluminum Casting Modern Molding Technology
Complex aluminum casting casting is a new technology with electromagnetic pump low-pressure casting technology as the core, aluminum smelting and molding composite purification technology and manufacturing core, and a modern technology for producing high-quality aluminum castings. The electromagnetic pump low-pressure casting molten metal transmission system has a stable flow, convenient flow control, ease of suction of molten alumina in the process and easy realization. The advantage is the automation of the use process, which not only improves the casting quality of aluminum castings, but also It can also improve the working environment. Reduce labor intensity and realize automation and modern casting production.
Purification of molten enamel alloy castings is an important part of aluminum smelting and composite purification facilities in addition to gas injection and spin foam ceramic filters with high degassing properties except for metal inclusions. In addition, it uses a new long-life lining material, and has an independent insulation/heating system that can be used for a large number of continuous production, but also for intermittent production. This technology of molten aluminum purification has high efficiency, long life, low cost effective, easy to install, use and flexible. Casting experience tells us that to solve complex problems of quality aluminum castings in three main aspects:
(1) molten aluminum smelting and melting,
(2) Smooth transition of molten aluminum metal halide lamps
(3) The size and stability of the mold and sand core process.
Modeling the core manufacturing process can see a direct impact on casting quality and yield. The relationship between casting porosity, sand sticking, scarring, thermal cracking and surface quality, dimensional accuracy, and the performance of the sand used is very good. The new technology in modeling and manufacturing is the PEPSET core resin binder used in raw zirconia sand. The resin from hard sand, the difficult kind of no-bake sand mechanism, is an independent, non-hardening chemical reaction. Initially, it is time to start hardening and curing. The reaction is fast once started. So the coach bags, because in a tough, high-strength, small fat gas collapse, have good performance is the complexity of the casting surface, ensuring quality and stability of dimensional accuracy.
Performance and application
Cast aluminum alloy has some advantages that other castings cannot match, such as beautiful appearance, light weight, corrosion resistance and other advantages, making it widely favored by users, especially since the lightweight of automobiles, cast aluminum alloy castings have been widely used in the automotive industry Applications.
The density of cast aluminum alloy is lower than that of cast iron and cast steel, but its specific strength is higher. Therefore, the use of aluminum alloy castings under the same load conditions can reduce the weight of the structure, so aluminum alloy castings are widely used in the aviation industry, power machinery and transportation machinery manufacturing. Aluminum alloy has good surface gloss and good corrosion resistance in the atmosphere and fresh water, so it is widely used in the manufacture of civil utensils. Pure aluminum has good corrosion resistance in oxidizing acid media such as nitric acid and acetic acid, so aluminum castings also have certain uses in the chemical industry. Pure aluminum and aluminum alloys have good thermal conductivity. They are also suitable for heat exchange devices used in chemical production and parts that require good thermal conductivity on power machinery, such as cylinder heads and pistons of internal combustion engines. manufacture.
Aluminum alloys have good castability. Due to the low melting point (the melting point of pure aluminum is 660.230C, the pouring temperature of aluminum alloy is generally about 730-750oC), so casting methods such as metal mold and die casting can be widely used to improve the internal quality, dimensional accuracy and surface of castings. cleanliness and productivity. Due to the large solidification latent heat of aluminum alloy, under the same weight conditions, the solidification process of aluminum liquid lasts much longer than cast steel and cast iron, and has good fluidity, which is beneficial to casting thin-walled and complex-structured castings.
Cast aluminum alloy castings have many advantages, making it one of the most popular casting products for the development direction of the foundry industry and purchasing customers. In the future, with the advancement of aluminum alloy casting technology, it will show itself on a larger stage style.
Analysis of urgent problems to be solved in the future development of domestic aluminum alloy casting industry
Reducing energy consumption, reducing environmental pollution and saving limited resources is a very important and urgent task facing all countries today. Driven by the general trend of lightweighting of automobiles and other products, it can be expected that my country’s light metal casting market will develop substantially in the next 10 years. The proportion of aluminum and magnesium alloy castings in each major casting production country is between 13% and 19%, and some countries (such as Italy) are as high as 30% to 40%, while the proportion of aluminum and magnesium alloy castings in my country is not high. to 10%. More than 90% of aluminum castings in developed countries are used in the automobile parts manufacturing industry. In my country, there are still many problems to be solved in order to form large-scale production of aluminum alloy castings and meet the requirements of lightweight automobiles:
First, the requirements of automobiles for aluminum castings are developing in the direction of thin wall, complex shape, high strength and high quality. In order to meet this requirement, the casting process should be further optimized and the development of new alloy materials should be carried out.
Second, the production cost should be reduced from the perspective of design and process, such as using one-mold multi-piece technology and automation technology to increase productivity, prolong the service life of the mold, and adopt an integrated design to reduce the number of parts.
Third, use computer simulation technology to shorten the development cycle of process solutions.
Fourth, increase the recycling of aluminum.
Recycled aluminum is the main raw material for aluminum casting. While developing the foundry industry in my country, we should pay attention to the utilization of recycled aluminum resources, develop technologies for effectively separating aluminum from composite materials and waste materials combined with dissimilar materials, and establish a wide range of waste recycling systems.
Defect characteristics: Oxidized slag inclusions are mostly distributed on the upper surface of the casting, in the corners of the mold that are not ventilated. The fracture is mostly off-white or yellow, which can be found by X-ray perspective or during mechanical processing, and can also be found during alkali cleaning, pickling or anodizing
1. Furnace charge is not clean, too much recycle charge is used
2. Poor gating system design
3. The slag in the alloy liquid is not cleaned
4. Improper pouring operation, bringing in slag inclusions
5. The standing time is not enough after refining and deterioration treatment
1. Furnace charge should be sand blasted, and the amount of returned charge should be appropriately reduced
2. Improve the gating system design and improve its ability to retain slag
3. Use appropriate flux to remove slag
4. When pouring, it should be stable and pay attention to slag blocking
5. After refining, the alloy liquid should be allowed to stand for a certain period of time before pouring
Defect characteristics: The pores in the wall of the three castings are generally round or oval, with a smooth surface, usually shiny oxide skin, sometimes oily yellow. Surface pores and bubbles can be found by sandblasting, internal pores and bubbles can be found through X-ray perspective or mechanical processing. The bubbles appear black on the X-ray film
1. The pouring alloy is not stable and gas is involved
2. Organic impurities (such as coal chips, grass root horse manure, etc.) are mixed into the type (core) sand
3. Poor ventilation of mold and sand core
4. There are shrinkage holes on the surface of cold iron
5. Poor gating system design
1. Correctly grasp the pouring speed to avoid getting involved in gas.
2. The type (core) sand shall not be mixed with organic impurities to reduce the gas generation of the molding material
3. Improve (core) sand venting ability
4. Proper selection and handling of cold iron
5. Improve gating system design
Defect characteristics: Shrinkage porosity of aluminum castings generally occurs at the thick and large parts of the root of the flying riser near the inner runner, the thickness transition of the wall and the thin wall with a large plane. The fracture is gray in the cast state, light yellow after heat treatment, grayish white, light yellow or gray black, and cloudy on the X-ray film. Severe filamentous shrinkage can be found by inspection methods such as X-ray and fluorescence low-magnification fracture.
1. Riser feeding effect is poor
2. Too much gas content in the charge
3. Overheating near the inner runner
4. There is too much moisture in the sand mold, and the sand core is not dried
5. Coarse alloy grains
6. Improper position of the casting in the mold
7. The pouring temperature is too high and the pouring speed is too fast
1. Add molten metal from the riser and improve the design of the riser
2. Furnace charge should be clean and corrosion-free
3. Riser is set at the shrinkage part of the casting, and cold iron is placed or used in combination with cold iron and riser
4. Control the moisture content of molding sand and dry the sand core
5. Take measures to refine the grain
6. Improve the position of the casting in the mold to reduce the pouring temperature and pouring speed
Developing along the grain boundary, often accompanied by segregation, is a kind of crack formed at higher temperature, which is easy to appear in alloys with larger volume shrinkage and castings with more complex shapes
2. Heat treatment cracks
Transgranular cracks are often caused by overheating or overheating in heat treatment. It is often caused by excessive cooling of alloys with large stress and thermal expansion coefficient. or other metallurgical defects
1. The structural design of the casting is unreasonable, there are sharp corners, and the thickness of the wall varies greatly
2. The sand mold (core) has poor yield
3. Local overheating of the mold
4. The pouring temperature is too high
5. Taking out the casting from the mold too early
6. Overheating or overburning of heat treatment, excessive cooling speed
1. Improve the structural design of castings, avoid sharp corners, strive for uniform wall thickness, and smooth transition
2. Take measures to increase the yield of the sand mold (core)
3. Ensure simultaneous solidification or sequential solidification of all parts of the casting, and improve the design of the gating system
4. Properly reduce the pouring temperature
5. Control the mold cooling time.
6. The thermal correction method is adopted when the casting is deformed.
7. Correctly control the heat treatment temperature and reduce the quenching cooling rate
Problem Due to the loose structure and high porosity of aluminum castings, containing a variety of metal and non-metallic impurities, the anodized film is prone to white spots after dyeing, and the quality of the anodized film of aluminum castings is difficult to guarantee. In this regard, relevant experts said that the following methods can be used to avoid this problem: First, the high-voltage and high-current-density shock method is used. In the initial stage of anodic oxidation, high voltage and high current impact are adopted, so that the large and small “islands” originally divided by impurities are connected into pieces by high current impact. Second, casting surface grinding method. Grinding can make the ground aluminum powder fill the pores of the casting and act as a bridge connecting the “islands” separated by impurities. Third, the casting surface shot peening method. Before the trial of the shot peening method, the author used the method of knocking with a round-headed hammer. The original intention was to close the gaps blocking the “islands” by knocking, so as to achieve the purpose of connecting them into pieces, and the effect was remarkable. Using these methods can effectively avoid the occurrence of white spots on the anodized film of aluminum castings after dyeing, so as to ensure its quality.
Advantages of Castings
1 It can produce parts with complex shapes, especially blanks with complex inner cavities (such as heating)
2 Wide adaptability, metal materials commonly used in industry can be cast. A few grams to hundreds of tons.
3 Wide range of sources of raw materials. Inexpensive. Scrap, scrap, swarf
4 The shape and size of the casting are very close to the parts, reducing the amount of cutting, which is less and no cutting
Post time: Mar-27-2023