|grey cast iron||GB/T9439-1988||HT150||A48||No20A||G5501||FC150||1452||150||1691||GG-15||0.6020|
|Weldable high temperature carbon steel||GB/T12229-1989||WCA||A216||WCA||G5151||SCPH1||1504||161Grade 430F||17245||GS-C25||1.0619|
|High temperature and high pressure alloy steel cast steel||-||A217||WC4||G5151||SCPH-21||1504||621||17245||GS-14CrMo55||1.7357|
|Heat-resistant Fe-Cr and Fe-Cr-Ni alloy steel cast steel||GB/T2100-1980||ZG1Cr13||A217||CA15||G5121||SCS1-T2||1504||420C29||-||-|
|Austenitic cast steel for high temperature||-||-||A297||HU||G5122||SCH20||3100||331C40||VDEhSPW471||G-X40CrNiSi3818||1.4365|
|Austenitic cast steel||GB/T12230-1989||ZG00CrNi10||A351||CF3||G5121||SCS19A||1504||304C12||-||-||-|
Ferritic cast steel for low temperature and high pressure
Techniques and methods for producing castings using casting theory and system knowledge. Including casting process, casting system, feeding system, vent, chill system, special casting process and so on.
The casting process design includes: the design of the casting process drawing, the design of the casting drawing, the design of the casting assembly drawing and the production of the craft card .
Casting is an ancient manufacturing method that dates back to 6,000 years in China. With the development of industrial technology, the quality of casting large castings directly affects the quality of the products. Therefore, casting plays an important role in the machinery manufacturing industry. The development of casting technology is also very rapid, especially in the late 19th century and the first half of the 20th century, many new casting methods, such as low pressure casting, ceramic casting, continuous casting, etc., were perfected and put into practical use in the second half of the 20th century. .
Method of operation
Casting is a process in which a molten metal liquid is poured into a mold and cooled to solidify to obtain a desired shape and performance. Casting is a common manufacturing method, with low manufacturing cost and high process flexibility. It can obtain complex shapes and large castings, and it occupies a large proportion in mechanical manufacturing, such as machine tools account for 60-80%, cars account for 25%, and tractors account for 50 to 60%.
Due to the improvement of casting quality, casting precision, casting cost and casting automation, casting technology is developing in the direction of precision, large-scale, high-quality, automation and cleanliness. For example, in China, precision casting technology and continuous Casting technology, special casting technology, casting automation and casting molding simulation technology have developed rapidly.
The main processes of casting include: metal melting, model making, casting solidification and demoulding cleaning. The main materials used for casting are cast steel, cast iron, cast non-ferrous alloys (copper, aluminum, zinc, lead, etc.).
The casting process can be divided into a sand casting process and a special casting process.
Special casting process
Special casting processes include centrifugal casting, low pressure casting, differential pressure casting, supercharged casting, gypsum casting, ceramic casting, etc. 
Pressure casting refers to the process in which molten metal is injected into a mold under the action of other external forces (excluding gravity). Generalized pressure casting includes pressure casting and vacuum casting of die casting machines, low pressure casting, centrifugal casting, etc.; narrowly defined pressure casting refers to metal type pressure casting of die casting machine, referred to as die casting. These casting processes are currently the most commonly used and least expensive in the casting of non-ferrous metals.
Metal casting is a modern process for casting hollow molds made of metal (heat resistant alloy steel, ductile iron, heat resistant cast iron, etc.).
The metal type can be either gravity casting or pressure casting. The metal mold can be used repeatedly and repeatedly. Once the molten metal is poured once, the casting is obtained once, and the life is long and the production efficiency is high. The metal castings not only have good dimensional accuracy, but also have a smooth surface, and the casting strength is higher than that of the sand type when casting the same molten metal, and it is less likely to be damaged. Therefore, in the case of mass production of medium and small castings of non-ferrous metals, as long as the melting point of the casting material is not too high, metal casting is generally preferred. However, metal casting also has some shortcomings: because the heat-resistant alloy steel and the hollow cavity on which it is processed are relatively expensive, the metal mold is expensive, but the overall cost is cheaper than that of the die-casting mold. too much. For small batch production, the cost of the mold allocated to each product is obviously too high, which is generally not easy to accept. Moreover, because the metal mold is limited by the size of the mold material, the ability of the cavity processing equipment, and the casting equipment, it is also ineffective for particularly large castings. Therefore, metal casting is rarely used in small batches and large parts. In addition, although the metal mold uses heat-resistant alloy steel, its heat resistance is still limited. It is generally used for the casting of aluminum alloy, zinc alloy and magnesium alloy. It has been used less in copper alloy casting and used for ferrous metal casting. It's even less.
Die-casting is a metal-type pressure casting on a die-casting machine, which is currently the most productive casting process.
Die casting machines are divided into two types: hot chamber die casting machine and cold chamber die casting machine. The hot chamber die casting machine has high degree of automation, less material loss, and higher production efficiency than the cold chamber die casting machine. However, due to the heat resistance of the machine parts, it can only be used for the production of castings of low melting point materials such as zinc alloy and magnesium alloy. . Aluminum alloy die castings, which are widely used today, can only be produced on cold chamber die casting machines due to their high melting point. The main feature of die casting is that the molten metal fills the cavity under high pressure and high speed, and is formed and solidified under high pressure. The insufficiency of the die casting is: because the molten metal is in the process of filling the cavity under high pressure and high speed, it is inevitable The air in the cavity is wrapped inside the casting to form the subcutaneous pores, so the aluminum alloy die-casting parts are not suitable for heat treatment, and the zinc alloy die-casting parts are not suitable for surface spraying (but can be painted). Otherwise, the internal pores of the casting will expand with heat when the heating is performed as described above, causing the casting to deform or bubble. In addition, the mechanical cutting allowance of die-casting parts should also be smaller, generally about 0.5mm, which can reduce the weight of castings, reduce the amount of cutting processing to reduce the cost, and avoid the penetration of the dense layer on the surface, revealing the subcutaneous pores, resulting in The workpiece is scrapped.
Lost wax casting, now known as investment casting, is a casting process with little or no cutting. It is an excellent process technology in the foundry industry and its application is very extensive. It is not only suitable for the casting of various types and various alloys, but also produces castings with higher dimensional accuracy and surface quality than other casting methods, and even castings that are difficult to cast by other casting methods, which are difficult to cast, are not easy to process. Can be cast by investment casting.
Investment casting is based on the ancient wax mold casting. As an ancient civilization, China is one of the countries that used this technology earlier. In the hundreds of years before BC, the ancient Chinese working people created this lost wax casting technique, which was used to cast a variety of fine patterns and texts. The products of Zhong Ding and utensils, such as the tomb of Zeng Houyi at the Spring and Autumn Period. The base of Zenghouyi's tomb is a pair of intertwined dragons. They are connected end to end and are staggered up and down to form a multi-layered cloud pattern in the middle. These patterns are difficult to manufacture by ordinary casting techniques and are cast by lost wax method. The process can take advantage of the fact that paraffin has no strength and is easy to engrave. With ordinary tools, it can engrave the paraffin-like handicrafts like the Zenghouyi tomb of the tomb, and then add the pouring system, paint, dewaxing and pouring. You can get the exquisite Zenghou Yi tomb.
The practical application of modern investment casting methods in industrial production was in the 1940s. At that time, the development of aviation jet engines required the manufacture of heat-resistant alloy parts such as blades, impellers, nozzles, and the like, which were complex in shape, accurate in size, and smooth in surface. Since the heat-resistant alloy material is difficult to machine, the shape of the part is so complicated that it cannot be or is difficult to manufacture by other methods. Therefore, it is necessary to find a new and precise molding process, so that the lost wax casting which has been handed down from ancient times is passed through the materials and processes. Improvements, modern investment casting methods have gained important development on the basis of ancient techniques. Therefore, the development of the aviation industry has promoted the application of investment casting, and the continuous improvement and improvement of investment casting has also created favorable conditions for the aviation industry to further improve its performance.
In the 1950s and 1960s, China began to apply investment casting to industrial production. Since then, this advanced casting process has been greatly developed and has been widely used in the manufacturing industries of aviation, automobiles, machine tools, ships, internal combustion engines, gas turbines, telecommunications equipment, weapons, medical equipment and cutting tools, as well as in the process. The manufacture of art.
The so-called investment casting process, simply by using a fusible material (such as wax or plastic) to make a fusible model (referred to as investment or model), coated with several layers of special refractory coating, dried and hardened After forming a monolithic shell, the model is melted from the shell by steam or hot water, and then the shell is placed in a flask, filled with dry sand molding around it, and finally the mold is placed in a roaster at a high temperature. Calcination (for example, when a high-strength type shell is used, the demolded shell can be directly fired without styling), and the mold or shell is fired, and molten metal is poured therein to obtain a cast piece.
Investment castings have high dimensional accuracy, generally up to CT4-6 (sand casting is CT10~13, die casting is CT5~7). Of course, due to the complicated process of investment casting, there are many factors affecting the dimensional accuracy of castings, such as mold. The shrinkage of the material, the deformation of the investment mold, the change in the amount of the shell during heating and cooling, the shrinkage of the alloy, and the deformation of the casting during solidification, etc., so the dimensional accuracy of the ordinary investment casting is high, but Consistency still needs to be improved (the dimensional uniformity of castings using medium and high temperature waxes is much higher).
When the investment mold is pressed, the molding having a high surface finish of the cavity is used, and therefore, the surface finish of the investment mold is also relatively high. In addition, the shell is made of a refractory coating made of a special binder and a refractory material which is resistant to high temperature, and is coated on the investment mold, and the inner surface of the cavity which is in direct contact with the molten metal has a high surface finish. Therefore, the surface finish of investment castings is higher than that of general castings, generally up to Ra.1.6~3.2μm.
The biggest advantage of investment casting is that because of the high dimensional accuracy and surface finish of the investment casting, it can reduce the machining work, but only a small amount of machining allowance is required on the parts, even some castings only Leave the grinding and polishing allowance and use it without machining. It can be seen that the investment casting method can save a lot of machine tool equipment and processing man-hours, and greatly save metal raw materials.
Another advantage of the investment casting process is that it can cast complex castings of various alloys, particularly casting high temperature alloy castings. For example, the blade of a jet engine, its streamlined profile and cooling cavity, can hardly be formed by machining. The production by the investment casting process can not only achieve mass production, but also ensure the consistency of the castings, and avoid the stress concentration of the residual knives after machining.
Lost foam casting
Lost Foam Casting Technology (EPC or LFC) is a solid mold made of foamed plastic with the same structure and dimensions as the part. It is dipped with refractory bonded paint, dried and then dried, shaped, vibrated and then poured. The molten metal causes the pattern to be vaporized by heat, and a casting method of the metal part conforming to the shape of the pattern is obtained. Lost Foam Casting is a new technology with no margin and precise forming. It does not need to take the mold and use the binderless dry sand to reduce the pollution. It is considered to be the most likely process to achieve green casting in the 21st century. technology.
The lost foam casting technology mainly has the following types:
1. Pressure lost foam casting technology
The pressure lost foam casting technology is a new casting technology combining the lost foam casting technology and the pressure solidification crystallization technology. It is in the pressure irrigation with a sand box. After pouring the molten metal to vaporize the foam, the pressure irrigation is quickly sealed. A casting method in which a certain pressure of gas is introduced to solidify and crystallize the molten metal under pressure. This casting technology is characterized by significantly reducing casting defects such as shrinkage, shrinkage, and porosity in the casting, increasing the density of the casting and improving the mechanical properties of the casting.
2. Vacuum low pressure lost foam casting technology
Vacuum low pressure lost foam casting technology is a new casting technology developed by combining negative pressure lost foam casting method and low pressure anti-gravity casting method. The characteristics of vacuum low pressure lost foam casting technology are: combining the technical advantages of low pressure casting and vacuum lost foam casting, the filling process is completed under controlled pressure, which greatly improves the casting filling ability of the alloy; compared with die casting, the equipment The investment is small, the casting cost is low, and the casting can be heat-treated and strengthened. Compared with the sand casting, the casting has high precision, small surface roughness, high productivity and good performance; under the action of anti-gravity, the sprue becomes the supplementary shortening channel and the pouring temperature. The loss is small, the liquid alloy is filled and solidified under the controllable pressure, the casting system of the alloy casting is simple and effective, the yield is high, and the structure is compact; the vacuum low pressure lost foam casting has a low pouring temperature and is suitable for various colored alloys.
3. Vibration lost foam casting technology
The vibration lost foam casting technology applies vibration of a certain frequency and amplitude during the lost foam casting process, so that the casting solidifies under the action of the vibration field. Since the solidification process of the lost foam casting is applied to the metal solution for a certain period of time, the vibration force makes the liquid The relative motion between the phase and the solid phase causes the dendrites to break, and the crystal core in the liquid phase is increased, so that the final solidification structure of the casting is refined, the feeding is improved, and the mechanical properties are improved. The technology utilizes the ready-made compact vibrating table in lost foam casting, and the mechanical vibration generated by the vibrating motor causes the molten metal to nucleate under dynamic excitation to achieve the purpose of refining the structure, and is an easy operation, low cost and no environment. The method of pollution.
4, semi-solid lost foam casting technology
Semi-solid lost foam casting technology is a new casting technology that combines lost foam casting technology with semi-solid technology. Because the process is characterized by controlling the relative proportion of liquid-solid phase, it is also called transformation control semi-solid forming. This technology can increase the density of castings, reduce segregation, improve dimensional accuracy and casting performance.
5. Lost shell casting technology
The lost shell casting technology is a new casting method combining investment casting technology and lost foam casting. The method is to apply a plurality of layers of refractory material to the surface of the foam molding which is made of a foaming mold and has the same shape as the part, and after hardening and drying, the foamed plastic pattern is burned and disappeared to form a shell, and is fired. And then casting, to obtain a new precision casting method for higher dimensional precision castings. It has the characteristics of large size and high precision in the lost foam casting, and has the advantages of crust precision and strength in investment casting. Compared with ordinary investment casting, it is characterized by low cost of foam plastic molding, convenient combination of pattern bonding, easy disappearance of gasification, overcoming the problem of melt deformation caused by easy softening of investment casting mold, and can be produced. Large size alloy complex castings
6. Lost foam suspension casting technology.
The lost foam suspension casting technology is a new practical casting technology that combines the lost foam casting process with suspension casting. The technical process is that after the molten metal is poured into the mold, the foam plastic pattern is vaporized, and the suspending agent is mixed in the riser model (or the suspending agent is placed at a specific position of the pattern, or the suspending agent is foamed together with the EPS. Physicochemical reaction with molten metal to improve the overall (or partial) structural properties of the casting.
Due to the low cost, high precision, flexible design, clean and environmental protection, and suitable for complex castings, the lost foam casting technology meets the general trend of casting technology development in the new century and has broad development prospects.
Fine grain casting
The principle of fine-grain casting technology or process (FGCP) is to strengthen the nucleation mechanism of the alloy by controlling the common investment casting process, forming a large number of crystal cores in the casting process, and preventing the grain from growing, thereby obtaining the average grain size. Uniform, fine, isotropic equiaxed crystal castings less than 1.6 mm in size, and the typical fine-grained castings have a grain size of US Standard ASTM 0~2. Fine-grain casting reduces the size of the primary carbide and strengthening phase γ' in the superalloy while improving the grain size of the casting. Therefore, the outstanding advantages of fine-grain casting are to greatly improve the low-cycle fatigue life of castings under medium-low temperature (≤760 °C) conditions, and significantly reduce the dispersion of mechanical properties of castings, thereby improving the design tolerance of cast parts. . At the same time, the technology also improves the tensile properties and long-lasting properties of the castings to a certain extent, and the castings have good heat treatment properties.
Fine-grain casting technology can also improve the machinability of high-temperature alloy castings and reduce the potential for machining cracks in screw holes and sharp edges. Therefore, this technology can extend the application range of investment castings to the fields of forgings, thick machined parts and forging assemblies. In the precision casting of aero-engine parts, it is common to use fine-grain castings instead of certain forgings or to use fine-grained ingots for forging.
The “short-flow” casting process uses the blast furnace molten iron directly into the electric furnace to heat up and adjust the composition. After the metamorphic treatment, the casting is cast, eliminating the process of re-melting the molten iron into a molten iron, which is energy-saving and efficient. The cost reduction casting production method is one of the optimization technologies promoted by the foundry association.
The “short process” process has been well applied in Shandong and other provinces. Among the 72 national high-quality foundry pig iron base pilot enterprises announced recently, the number of Shandong enterprises using “short process” has reached 12. It has played a great role in promoting the construction of foundry pig iron bases and optimizing the development of foundry industry clusters, which will promote the casting industry to a higher level.
Sand casting process
Sand casting is a traditional casting process that uses sand as the main molding material to make a mold.
Sand casting mainly uses gravity casting process:
Gravity casting refers to the process of injecting molten metal into a mold under the action of gravity of the earth, also called casting. Generalized
Foundry craft books
Gravity casting includes sand casting, metal casting, investment casting, mud casting, etc.; narrow gravity casting refers to metal casting.
Sand type is generally cast by gravity, and when it has special requirements, it can also be used in low pressure casting and centrifugal casting. Sand casting has a wide adaptability, and small pieces, large pieces, simple pieces, complicated parts, single pieces and large quantities can be used. The mold used for sand casting was previously made of wood and is commonly known as wood mold. The disadvantage of the wood mold is that it is easily deformed and easily damaged; in addition to the sand casting produced by a single piece, an aluminum alloy mold or a resin mold having a high dimensional accuracy and a long service life can be used. Although the price has increased, it is still much cheaper than the mold for metal casting, and the price advantage is particularly prominent in small batches and large parts. In addition, the sand type has a higher degree of refractoriness than the metal type, and thus a material having a higher melting point such as a copper alloy or a ferrous metal is also used in this process. However, sand casting also has some shortcomings: because each sand casting can only be poured once, the casting is damaged after obtaining the casting, and must be reshaped, so the production efficiency of sand casting is low; and because the overall nature of sand is soft Porous, so sand casting castings have lower dimensional accuracy and rougher surfaces.
Casting process design
The casting process design involves the process design of the part itself, the design of the gating system, the design of the feeding system, the design of the venting hole, the design of the chilling system, and the design of the special casting process. 
The process design of the part itself involves the machining allowance of the part, the selection of the casting position, the parting surface, the selection of the casting process parameters, the dimensional tolerance, the shrinkage rate, the drafting angle, the correction amount, the negative type of the design, etc.  .
The pouring system is the channel for guiding the molten metal into the mold cavity. The design of the pouring system is reasonable or not, which has a great influence on the quality of the casting. It is easy to cause various types of casting defects, such as insufficient pouring, cold separation, sand washing, Casting defects such as slag inclusions, inclusions, sand inclusions, etc. The design of the gating system includes the selection of the type of gating system, the selection of the location of the gating gate, and the determination of the cross-sectional dimensions of the components of the gating system. In addition, the choice of the gating system is also very important, so how can we choose the right gating system?
For mechanized assembly line, mass production, in order to facilitate production and to ensure the quality of the casting, the runner is generally placed at the parting surface of the mold, and the in-line is selected according to the casting position of the casting blank and the selection of the parting surface. The road opening at the parting surface of the mold belongs to the "intermediate injection type" casting system. Liquid metal will inevitably contain a certain amount of "slag" during the casting process. In order to improve the slag blocking capacity of the casting system, it is suitable to adopt a "closed" casting system.
In the casting process, the design of the casting process has a great influence on the quality of the cast product, but the choice of the casting system can not be ignored.
The design of the feeding system is a reasonable design of the riser and subsidies to compensate for the liquid and solidified body shrinkage of the casting during solidification to obtain an engineering technique for sound castings .
The vent hole is used to discharge the gas in the cavity, improve the filling ability of the molten metal, and eliminate the supercooled metal liquid and scum which are first filled into the cavity, and can also be used as a sign to observe whether the cavity is filled or not.
Introduction to ductile iron
Ductile iron is iron containing carbon. We know that iron or steel contains a certain amount of carbon. Why is it called ductile iron? This is because they contain different forms of carbon. Ductile iron It contains spherical carbon, so it will have this more stable nature. The manufacture of ductile iron is generally obtained by melting molten iron or scrap iron at a high temperature and then casting it in a mold. After the casting is cooled and formed, the surface will appear in the shape of carbon, which may appear in the form of a sheet depending on the process. Four types of worm-like, globular, floc-like, each with its own name, of which spherical is what we call spherical cast iron.
What are the characteristics of ductile iron?
Feature 1: Ductile iron has very good impact resistance and ductility. This is because the graphite flakes in the ductile iron become a very fine carbon element through a special treatment, and these tiny carbon elements enter the gap of the iron element, which greatly enhances the ductile iron. Physical properties and thus very good impact resistance. We also know that graphite is not ductile, but iron has good ductility. The combination of the two is a perfect inheritance of their respective advantages, making ductile iron both impact resistant and ductile.
Characteristic 2: Ductile iron can effectively prevent cracks. In the industry, our image is called the crack terminator. Through the microscope, the experts can clearly see that the crack generated by the iron stops after cracking into the graphite ball. This is because the graphite ball has a very high stability and the probability of cracking is very small.
Characteristic three: anti-corrosion. As we said above, ductile iron is a graphite element that enters the gap of iron. As a result, corrosive objects cannot corrode iron.
Compared with cast iron, ductile iron has an absolute advantage in strength. The tensile strength of ductile iron is 60k, while the tensile strength of cast iron is only 31k. The yield strength of ductile iron is 40k, while cast iron does not show yield strength and eventually breaks. The strength-cost ratio of ductile iron is much better than that of cast iron. Ductile iron is the same as cast iron in terms of corrosion resistance. Ductile iron has high strength, and gray cast iron has good wear resistance and good vibration damping. This is the reason why imported vehicles use a lot of high-strength gray cast iron as gears.
Compared with grey cast iron and malleable cast iron, why is the mechanical properties of ductile iron higher?
The key is that the carbon exists in the form of cast iron. The carbon in the gray cast iron exists in the free flake graphite, which has a great influence on the weakening of the matrix. The malleable cast iron phase is relatively better. The carbon exists in the form of graphite in the flocculation state, while in the spheroidal graphite. In cast iron, carbon exists as spheroidal graphite, which has less influence on the weakening of the matrix and higher mechanical properties.
Due to the extremely low fracture sensitivity of ductile iron, high mechanical properties are directly formed. Common sense problem
Why is the mechanical properties of ductile iron higher than that of gray cast iron and malleable cast iron?
Organizational differences lead to huge differences in their performance:
Gray cast iron is a flake graphite splitting matrix, which is easy to cause stress concentration, brittleness and good vibration damping performance. It is mainly used to produce a variety of cabinets/bases that are not required for high strength and are mainly subjected to compressive stress.
Ductile iron is a spherical graphite matrix. The splitting between the crystal grains is minimized and the stress concentration is the smallest. Therefore, the strength is high, which is comparable to that of medium carbon steel. It can fully exert the performance of the matrix and has certain plasticity. Good toughness. It is often used to make parts with high toughness and complex shapes, such as internal combustion engine crankshafts/links. Ductile iron can also generally be heat treated for reinforcement, while gray cast iron is generally not heat treated to increase strength (the effect of flake graphite).
Malleable cast iron is a ferrite (F) + clustered graphite (G) matrix that can be used to make impact or vibration and torsional loads. It is commonly used in the manufacture of automotive rear axles, spring brackets, low pressure valves, pipe joints, tool wrenches. Wait.