As a mechanical designer, we must understand the trend of industrial development when selecting materials. According to the national standards and combining with the resources and production conditions of our country, we should give comprehensive consideration to materials and selection from the actual materials, which are steel and cast iron, followed by non-ferrous metal alloy. Non-metallic materials, such as plastic and rubber, also have unique use value in machinery manufacturing.
Metal material
1, cast iron
Cast iron and steel are iron - carbon alloys, which differ mainly in their carbon content. Iron-carbon alloys with less than 2% carbon are called steel, and those with more than 2% carbon are called cast iron. Cast iron has proper fusibility and good liquid fluidity, so it can be cast into parts with complex shapes. In addition, its shock absorption, wear resistance, cutting property (referring to gray cast iron) are good and low cost, so it is widely used in mechanical manufacturing. Commonly used cast iron is: gray cast iron, ductile cast iron, malleable cast iron, alloy cast iron and so on. Gray cast iron and nodular cast iron are brittle materials, which cannot be rolled and forged. Among the above cast iron, gray cast iron is widely used, followed by ductile cast iron.
2, steel
Compared with cast iron, steel has high strength, toughness and plasticity, and its mechanical and machining properties can be improved by heat treatment. The blank of steel parts can be obtained by forging, stamping, welding or casting, so it is widely used. According to the use, steel can be divided into structural steel, tool steel and special steel. Structural steel is used to manufacture various mechanical parts and components of engineering structures; Tool steel is mainly used to manufacture various cutting tools, dies and measuring tools; Special steels (such as stainless steel, heat resistant steel, acid resistant steel, etc.) are used to make parts that work in special conditions. According to the chemical composition, steel can be divided into carbon steel and alloy steel. The properties of carbon steel mainly depend on the carbon content, the higher the carbon content, the higher the steel strength, but the lower the plasticity. In order to improve the performance of steel, deliberately added some alloying elements of steel called alloy steel. 1) Carbon structural steel the carbon content of this type of steel is generally not more than 0.7%. Carbon content is less than 0.25% of low carbon steel, its strength limit and yield limit is low, high plasticity, and has good weldability, suitable for stamping, welding, commonly used to make screws, nuts, washers, shafts, valve guide rod and welding components. Carbon content in 0. L % ~ 0.2% of low carbon steel is also used to make carburizing parts, such as gear, piston pin, sprocket, etc. Through carburizing and quenching can make the surface of the parts hard and wear-resistant, the heart tough and impact resistant. If higher strength and impact resistance are required, low carbon gold-containing steel can be used. Carbon steel with a carbon content of 0.3% ~ 0.5%, its comprehensive mechanical properties are better, both high strength, and a certain degree of plasticity and toughness, commonly used for larger stress bolts, nuts, keys, gears and shafts and other parts. Carbon content in 0.55% to 0.7% of high carbon steel, with high strength and elasticity, is used to make ordinary plate spring, coil spring or wire rope.
2) Alloy structural steel
The effect of alloying elements in steel is to improve the properties of steel. Nickel, for example, increases strength without reducing toughness; Chromium can improve the hardness, high temperature strength, corrosion resistance and improve the wear resistance of high carbon steel; Manganese can improve the wear resistance, strength and toughness of steel. The effect of aluminum is similar to that of manganese, which has a greater effect; Vanadium can improve toughness and strength; Silicon increases elastic limits and wear resistance, but decreases toughness. The influence of alloying elements on steel is complex, especially when several alloying elements are added simultaneously to improve the properties of steel. It should be noted that the excellent properties of alloy steels depend not only on their chemical composition but also, to a greater extent, on proper heat treatment.
3) cast steel
The liquid fluidity of cast steel is worse than that of cast iron, so when casting with ordinary sand, the wall thickness is often not less than 10mm. The shrinkage of cast steel is larger than that of cast iron, so the rounded corners of cast steel and the transition parts of different wall thicknesses should be larger than that of cast iron. When CHOOSING steel, carbon steel with low price and sufficient supply should be used as far as possible under the condition of meeting the use requirements. Silicon, manganese, boron and vanadium alloy steel should be preferred when alloy steel must be used.
3. Copper alloy
Copper alloys can be divided into bronze and brass. Brass is an alloy of copper and zinc, and contains a small amount of manganese, aluminum, nickel, etc., it has good plasticity and fluidity, so it can be rolled and cast. Bronze can be divided into tin-containing bronze and tin-free bronze, which have good antifriction and corrosion resistance, and can also be rolled and cast. In addition, there are bearing alloys (or Babbitt alloys), which are mainly used to make bearing liners for sliding bearings.
Non-metallic material
1, rubber
Rubber is elastic and can absorb more impact energy. It is commonly used as elastic element of coupling or shock absorber and belt for transmission. Hard rubber can be used to make water-lubricated bearing linings.
2, plastic
The proportion of plastic is small, easy to make the shape of complex parts, and a variety of different plastic has different characteristics, such as corrosion resistance, thermal insulation, insulation, friction, friction coefficient, so in recent years in machinery manufacturing its application is increasingly widely. The plastic made of wood chips, asbestos fibers, etc., and pressed with thermosetting resin is called binding plastic, which can be used to make instrument support, handle and other parts with little force. With cloth, asbestos, thin board and other lamellar filler as the matrix, with thermosetting resin pressed into plastic known as lamination plastic, can be used to make silent gear, bearing village and friction sheet. When designing mechanical parts, selecting suitable materials is a complex technical and economic problem. The designer should consider comprehensively according to the use of parts, working conditions and physical, chemical, mechanical and process properties of materials, as well as economic factors. This requires designers to have extensive knowledge and practical experience in materials and technology. What has been said before is only a general description. The chemical composition and mechanical properties of various materials can be found in relevant national standards, industry standards and mechanical design manuals.
Metal material
1, cast iron
Cast iron and steel are iron - carbon alloys, which differ mainly in their carbon content. Iron-carbon alloys with less than 2% carbon are called steel, and those with more than 2% carbon are called cast iron. Cast iron has proper fusibility and good liquid fluidity, so it can be cast into parts with complex shapes. In addition, its shock absorption, wear resistance, cutting property (referring to gray cast iron) are good and low cost, so it is widely used in mechanical manufacturing. Commonly used cast iron is: gray cast iron, ductile cast iron, malleable cast iron, alloy cast iron and so on. Gray cast iron and nodular cast iron are brittle materials, which cannot be rolled and forged. Among the above cast iron, gray cast iron is widely used, followed by ductile cast iron.
2, steel
Compared with cast iron, steel has high strength, toughness and plasticity, and its mechanical and machining properties can be improved by heat treatment. The blank of steel parts can be obtained by forging, stamping, welding or casting, so it is widely used. According to the use, steel can be divided into structural steel, tool steel and special steel. Structural steel is used to manufacture various mechanical parts and components of engineering structures; Tool steel is mainly used to manufacture various cutting tools, dies and measuring tools; Special steels (such as stainless steel, heat resistant steel, acid resistant steel, etc.) are used to make parts that work in special conditions. According to the chemical composition, steel can be divided into carbon steel and alloy steel. The properties of carbon steel mainly depend on the carbon content, the higher the carbon content, the higher the steel strength, but the lower the plasticity. In order to improve the performance of steel, deliberately added some alloying elements of steel called alloy steel. 1) Carbon structural steel the carbon content of this type of steel is generally not more than 0.7%. Carbon content is less than 0.25% of low carbon steel, its strength limit and yield limit is low, high plasticity, and has good weldability, suitable for stamping, welding, commonly used to make screws, nuts, washers, shafts, valve guide rod and welding components. Carbon content in 0. L % ~ 0.2% of low carbon steel is also used to make carburizing parts, such as gear, piston pin, sprocket, etc. Through carburizing and quenching can make the surface of the parts hard and wear-resistant, the heart tough and impact resistant. If higher strength and impact resistance are required, low carbon gold-containing steel can be used. Carbon steel with a carbon content of 0.3% ~ 0.5%, its comprehensive mechanical properties are better, both high strength, and a certain degree of plasticity and toughness, commonly used for larger stress bolts, nuts, keys, gears and shafts and other parts. Carbon content in 0.55% to 0.7% of high carbon steel, with high strength and elasticity, is used to make ordinary plate spring, coil spring or wire rope.
2) Alloy structural steel
The effect of alloying elements in steel is to improve the properties of steel. Nickel, for example, increases strength without reducing toughness; Chromium can improve the hardness, high temperature strength, corrosion resistance and improve the wear resistance of high carbon steel; Manganese can improve the wear resistance, strength and toughness of steel. The effect of aluminum is similar to that of manganese, which has a greater effect; Vanadium can improve toughness and strength; Silicon increases elastic limits and wear resistance, but decreases toughness. The influence of alloying elements on steel is complex, especially when several alloying elements are added simultaneously to improve the properties of steel. It should be noted that the excellent properties of alloy steels depend not only on their chemical composition but also, to a greater extent, on proper heat treatment.
3) cast steel
The liquid fluidity of cast steel is worse than that of cast iron, so when casting with ordinary sand, the wall thickness is often not less than 10mm. The shrinkage of cast steel is larger than that of cast iron, so the rounded corners of cast steel and the transition parts of different wall thicknesses should be larger than that of cast iron. When CHOOSING steel, carbon steel with low price and sufficient supply should be used as far as possible under the condition of meeting the use requirements. Silicon, manganese, boron and vanadium alloy steel should be preferred when alloy steel must be used.
3. Copper alloy
Copper alloys can be divided into bronze and brass. Brass is an alloy of copper and zinc, and contains a small amount of manganese, aluminum, nickel, etc., it has good plasticity and fluidity, so it can be rolled and cast. Bronze can be divided into tin-containing bronze and tin-free bronze, which have good antifriction and corrosion resistance, and can also be rolled and cast. In addition, there are bearing alloys (or Babbitt alloys), which are mainly used to make bearing liners for sliding bearings.
Non-metallic material
1, rubber
Rubber is elastic and can absorb more impact energy. It is commonly used as elastic element of coupling or shock absorber and belt for transmission. Hard rubber can be used to make water-lubricated bearing linings.
2, plastic
The proportion of plastic is small, easy to make the shape of complex parts, and a variety of different plastic has different characteristics, such as corrosion resistance, thermal insulation, insulation, friction, friction coefficient, so in recent years in machinery manufacturing its application is increasingly widely. The plastic made of wood chips, asbestos fibers, etc., and pressed with thermosetting resin is called binding plastic, which can be used to make instrument support, handle and other parts with little force. With cloth, asbestos, thin board and other lamellar filler as the matrix, with thermosetting resin pressed into plastic known as lamination plastic, can be used to make silent gear, bearing village and friction sheet. When designing mechanical parts, selecting suitable materials is a complex technical and economic problem. The designer should consider comprehensively according to the use of parts, working conditions and physical, chemical, mechanical and process properties of materials, as well as economic factors. This requires designers to have extensive knowledge and practical experience in materials and technology. What has been said before is only a general description. The chemical composition and mechanical properties of various materials can be found in relevant national standards, industry standards and mechanical design manuals.
