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Foundry casting technology

6/5/2019 - What is casting?Methods for casting

What is casting? Casting refers to a process in which a solid metal is melted into a liquid form and poured into a mold of a specific shape to be solidified and formed. The metal to be cast includes: copper, iron, aluminum, tin, lead, etc. The materials of the ordinary mold are raw sand, clay, water glass, resin and other auxiliary materials. Special casting molds include: investment casting, lost foam casting, metal casting, ceramic casting, etc. (Original sand includes: quartz sand, magnesia sand, zircon sand, chromite sand, forsterite sand, lanite sand, graphite sand, iron sand, etc.) Early castings are mostly tools for agricultural production, religion, life, etc. Or utensils, artistic color is strong.

After the industrial revolution of the 18th century, industries such as steam engines, textile machines and railways rose, castings entered a new era of service for large industries, and casting technology began to develop. In the 20th century, castings developed rapidly. One of the important factors is that advances in product technology require better mechanical and physical properties of castings, while still having good machining performance. Another reason is the machinery industry itself and other industries. The development of such industries as chemicals and meters has created favorable material conditions for the foundry industry. For example, the development of testing methods ensures the improvement and stability of casting quality and provides conditions for the development of casting theory. Inventions such as electron microscopy have helped people penetrate into the microscopic world of metals, explore the mysteries of metal crystallization, study the theory of metal solidification, and guide casting production. During this period, a large number of new cast metal materials with excellent performance and rich variety, such as ductile iron, weldable malleable cast iron, ultra-low carbon stainless steel, aluminum-copper, aluminum-silicon, aluminum-magnesium alloy, titanium-based, nickel-based alloy, etc.

And invented a new process for the inoculation of gray cast iron, making the casting more adaptable. After the 1950s, there were new technologies such as wet sand high pressure molding, chemical hardening sand molding and core making, negative pressure molding (see negative pressure casting) and other special casting and shot blasting (see casting cleaning), which made the castings very high. The shape, dimensional accuracy and good surface finish are also greatly improved in the foundry's working conditions and environmental hygiene. In the major progress of the foundry industry since the 20th century, the two new processes of gray cast iron gestation treatment and chemical hardening sand styling have special significance. These two inventions have broken through the traditional methods that have lasted for thousands of years, opening up new fields for the casting process and having a major impact on improving the competitiveness of castings. Many structural parts and main components of copper castings are made of castings, and they are closely related to the quality and precision of copper. The quality of copper castings has a vital impact on the quality, life and precision of machine tools. Copper castings can be used in valves, speakers, injection molding machines, water pipes, etc. .

There are many classification methods for castings: according to the metal materials used, they are divided into steel castings, cast iron parts, cast copper parts, cast aluminum parts, and copper castings. Each type of casting can be further divided into different varieties according to its chemical composition or metallographic structure. For example, cast iron parts can be divided into gray cast iron parts, malleable cast iron parts, alloy cast iron parts, etc.; according to the different molding methods, the castings can be divided into ordinary sand castings, metal castings, die castings, ceramic castings, electroslag remelting castings. Parts, bimetal castings, etc. Among them, ordinary sand castings are the most widely used, accounting for about 80% of all castings. Non-ferrous metal castings such as aluminum, magnesium and zinc are mostly die-casting parts.

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16/4/2019 - About high-performance precision casting

High-performance precision casting should create conditions that use technologically advanced modeling and core making methods. The productivity of the old-fashioned shock-type or shock-pressure molding machine production line is not high enough. The labor intensity of the workers is large, the noise is large, and it is not suitable for the requirements of mass production. It should be gradually modified. For small precision castings, it is possible to use a horizontal or vertical type of boxless high-pressure molding machine production line, real modeling and high production efficiency, and a small footprint; for the middle parts, various high-pressure molding machine production lines with boxes can be selected. The air-punching molding line is suitable for the requirements of fast and high-precision modeling production lines. The core-making method can be used: high-efficiency core making methods such as cold core box, hot core box and shell core.

What are the 5 advantages of using precision castings?

1. Precision casting parts forging precision, high finish, and can cast complex parts

2. Can forge various alloys (shell is advanced refractory)

3. Single piece, small batch, large batch production

4. Less, no cutting (Ra3.2~1.6um) slightly grinding

5. The precision casting material is expensive, the process is complicated, and the production cycle is long.

How to carry out the shell mold burning work of precision casting parts

When the shell mold is formally sintered for precision casting, the shell of the wax shell is removed from the shell mold to the side of the sintering furnace, and the shell mold is taken out to check whether there is any break or crack, and the cup is cleaned. Next, place it neatly on the shell mold cart. Start the main power of the sintering furnace, open the furnace door, and clean the furnace with a broom and air gun. Use the shell mold fork to carefully fork the shell mold and slowly put it into the furnace. Note that during the insertion process, the shell mold should not be touched to the bottom of the furnace or the furnace wall to prevent it from breaking. Set the sintering temperature according to the product type and technical requirements, generally 1000~1200 °C. Start the sintering oil pump, the oil pressure is about 105~2.0kg/m2. Use the torch to ignite in the combustion nozzle. After the ignition is successful, the flame is burned stably and the furnace is preheated. When the first furnace is heated to 600 °C or above, the shell is heated, the furnace door is closed, and the oil quantity and wind pressure are adjusted again to make it completely combustible.

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