Characteristics of commonly used casting structures
1. Gray cast iron parts
Performance: good fluidity, small body shrinkage and linear shrinkage. The comprehensive mechanical properties are low, and the compressive strength is about 3 to 4 times higher than the tensile strength . Good vibration absorption. The elastic modulus is low.
Structural features: The shape can be complex and the structure allows for asymmetry. There are box type, cylinder type, etc., for example, used in engine cylinder blocks, cylinder sleeves, various machine tool beds, bases, flat plates, platforms and other castings.
2. Ductile iron castings
Performance: The fluidity is similar to that of gray cast iron; the volume shrinkage is greater than that of gray cast iron, while the linear shrinkage is smaller, and shrinkage holes and looseness are easily formed. It has higher comprehensive mechanical properties, higher elastic modulus than gray cast iron; good wear resistance; good impact toughness and fatigue strength. The vibration absorption capacity is lower than that of gray cast iron.
Structural features: Generally designed with uniform wall thickness; for thick and large-section parts, a hollow structure can be used, such as the ductile iron crankshaft journal part.
3. Malleable iron castings
Performance: The fluidity is worse than gray cast iron; the body shrinkage is large, and after annealing, the final linear shrinkage is very small. Before annealing, it is very brittle and the blank is easily damaged. The comprehensive mechanical properties are slightly inferior to ductile iron, and the impact toughness is 3 to 4 times greater than gray cast iron .
Structural characteristics: Since the cast state requires a white mouth, it is generally a thin-walled uniform piece, with a common thickness of 5 to 16mm . In order to increase its rigidity, the cross-sectional shape is mostly I-shaped, T-shaped or box-shaped to avoid cross-shaped sections; the protruding parts of the parts should be reinforced with ribs.
4.Steel castings
Performance: Poor fluidity, large volume shrinkage, linear shrinkage and crack sensitivity. High comprehensive mechanical properties; compressive strength and tensile strength are almost equal. Poor vibration absorption.
Structural features: The structure should have a minimum number of hot nodes and create conditions for sequential solidification. The connection and transition of adjacent walls should be smoother; the casting cross-section should adopt a box-shaped and trough-shaped and other approximately closed structures; some horizontal walls should be changed into inclined walls or wavy shapes; the overall wall should be changed into a wall with a window, and the window shape It is best to be oval or round, and the edge of the window must be made with bosses to reduce the possibility of cracks.
5. Tin bronze and phosphor bronze parts
Performance: Casting properties are similar to gray cast iron. However, it has a large crystallization range and is prone to shrinkage cavities; has poor fluidity; has poor high-temperature performance and is easily brittle. The strength decreases significantly as the cross-section increases. Good wear resistance.
Structural features: The wall thickness should not be too large; the protruding parts of the parts should be reinforced with thin reinforcing ribs to avoid thermal cracking; the shape should not be too complex.
6. Wuxi bronze and brass parts
Performance: Large shrinkage, small crystallization range, easy to produce concentrated shrinkage cavities; good fluidity. Good wear resistance and corrosion resistance.
Structural features: similar to steel castings.
7.Aluminum alloy parts
Performance: The casting performance is similar to that of cast steel, but the strength decreases more significantly as the wall thickness increases.
Structural features: The wall thickness cannot be too large; the rest is similar to steel castings.
Categories, characteristics and application scope of special casting methods
1. Pressure casting
Main features: It uses metal casting molds, fills the mold under high pressure and high speed, and solidifies quickly under pressure. It is a metal forming method with high efficiency and high precision, but the manufacturing cost of die-casting machines and die-casting molds is high.
Scope of application: Mass production of small and medium-sized thin-walled castings mainly made of zinc alloy, aluminum alloy, magnesium alloy and copper alloy, and also used for steel castings.
2.Investment casting
Main features: Using a wax mold, an integral refractory thin-shell casting is made outside the wax mold. After the wax mold is melted away by heating, it is poured by gravity. Castings have high precision and good surface quality, but the molding manufacturing cost is high and the processes are numerous. Working conditions are poor when operated manually.
Scope of application: Various production batches, various alloys mainly carbon steel, alloy steel and complex parts of high melting point alloys that are difficult to process are suitable. The quality of castings is generally < 10kg .
3.Metal mold casting
Main features: Using metal molds and casting under gravity, it has the effect of refining the structure of non-ferrous alloy castings. Gray iron castings are prone to white spots, high productivity, no dust, high equipment costs, and labor conditions during manual operation. Difference.
Scope of application: Batch, mass production, mainly non-ferrous alloys. It can also be used for thick-walled, simple or moderately complex small and medium-sized castings of cast steel and cast iron.
4. Low pressure casting
Main features: using metal mold, graphite mold, sand mold, filling and crystallization solidification under gas pressure, the casting is dense, the metal yield is high, and the equipment is simple.
Application scope: single piece, small batch or mass production, medium and large thin-walled castings mainly made of non-ferrous alloys.
5. Ceramic mold casting
Main features: Using high-precision molding, self-hardening refractory slurry injection molding, gravity pouring, high casting precision and fine surface roughness, but the ceramic slurry is expensive.
Scope of application: Single piece, small batch production of medium and small, thick-walled and medium complex castings, especially suitable for metal molds, templates, hot core boxes and various hot forging dies.
6. Centrifugal casting
Main features: It is cast with metal sand or sand mold under the action of centrifugal force. The casting structure is dense, the equipment is simple, the cost is low, and the productivity is high, but the amount of mechanical processing is large.
Scope of application: Single piece, mass production of rotating castings such as iron pipes, copper sleeves, rollers, metal bearing bushes, cylinder liners, etc.
7.Full mold casting
Main features: Use foamed polystyrene plastic molds to partially or completely replace wooden molds or metal molds, which will burn out during pouring. It can save wood and simplify the process, but smoke and harmful gases are relatively large.
Scope of application: medium and large castings produced in single pieces and small batches, especially 1 to 2 pieces, or parts of castings where it is difficult to take molds.
8.Magnetic casting
Main features: Use magnetic materials (iron shots, steel shots) instead of molding sand as molding materials. The magnetic materials can be reused and simplify the sand treatment equipment. However, the surface of the steel castings is carburized, the coating takes a long time to dry, and the productivity is low.
Scope of application: Mass production of small and medium-sized and moderately complex steel parts, such as anchor chains, valve bodies, etc.
9. Continuous casting
Main features: The casting mold is a water-cooled crystallizer. After the molten metal is continuously injected, the solidified casting is continuously pulled out from the other end of the crystallizer. Productivity is high, but equipment costs are high.
Scope of application: Mass production of cast pipes, ingots, strips, rods, etc. of various alloys.
10. Vacuum suction casting
Main features: Evacuate the crystallizer to create negative pressure and suck in liquid metal for molding. The casting has no pores and blisters, has a dense structure, high productivity and simple equipment.
Scope of application: Mass production of copper alloy and aluminum alloy cylindrical and rod castings.
11. Squeeze casting
Main features: First pour a certain amount of liquid metal into the lower mold of the casting mold, quickly close the mold, and solidify under pressure. The casting has a dense structure and no pores, but the equipment is complicated. Die life is shorter when extruding steel alloys.
Scope of application: Mass production of thin-walled castings mainly made of non-ferrous alloys with simple shapes, high internal quality requirements or large outline dimensions.
12.Graphite mold casting
Main features: Made of graphite material and gravity cast. The casting structure is dense, the dimensions are precise, and the productivity is high. However, the casting mold is brittle and fragile, and the labor conditions are poor during manual operation.
Scope of application: Batch production of small and medium-sized parts with less complex shapes such as copper alloy propellers. It can also be used for titanium alloy castings.
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