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2021.6.17
The most commonly used materials in machinery manufacturing are steel and cast iron, followed by non-ferrous metal alloys, non-metallic materials such as plastics, rubber, etc., which are also widely used in machinery manufacturing.
1.Metallic Materials
Metal materials mainly refer to cast iron and steel, they are iron carbon alloy. The difference between them mainly lies in the difference of carbon content. The iron carbon alloy with carbon content less than 2% is called steel, and the iron with carbon content more than 2% is called cast iron.
Cast Iron
Commonly used cast iron are gray iron, ductile iron, malleable iron, alloy cast iron, etc. Gray cast iron and nodular cast iron are brittle materials, which can not be rolled and forged, and are not easy to weld, but they have proper fusibility and good liquid fluidity, so they can be cast into complex parts. Gray cast iron has high compressive strength, good wear resistance and vibration reduction, low sensitivity to stress concentration and low price, but its tensile strength is worse than steel. Gray iron is often used as frame or shell seat. Ductile iron has higher strength and definite plasticity than gray iron. It can be used to make crankshaft, camshaft, oil pump gear and valve body instead of cast steel and forged steel.
Steel
Steel has high strength and good plasticity. It can process various mechanical parts by rolling, forging, stamping, welding and casting, and can improve mechanical properties by heat treatment and surface treatment. Therefore, it is widely used. There are many types of steel, which can be divided into structural steel, tool steel and special purpose steel. Structural steel can be used for machining. Mechanical parts and various engineering structures. Tool steel can be used to manufacture various cutting tools and moulds. Special purpose steels (stainless steel, heat-resistant steel, corrosion-resistant steel) are mainly used in special working conditions. According to chemical composition, steel can be divided into carbon steel and alloy steel. The properties of carbon steel mainly depend on the carbon content. The more the carbon content is, the higher the strength is, but the lower the plasticity is. Carbon steel includes ordinary carbon structural steel and high quality carbon structural steel.
Ordinary carbon structural steels (such as Q215 and 0235) only guarantee mechanical strength but not chemical composition, so they are not suitable for heat treatment. They are usually used in less important parts and mechanical structures. The properties of carbon steel mainly depend on its carbon content. The carbon content of low carbon steel is less than 0.25%, its strength limit and yield limit are low, its plasticity is high, and its weldability is good. It is usually used to make screws, nuts, washers and weldments. Low carbon steel parts with carbon content of 0.1% – 0.2% can be carburized and quenched to make the surface hard and the center tough. It is generally used to manufacture gears, sprockets and other parts requiring surface wear resistance and impact resistance.
The carbon content of medium carbon steel is between 0.3% – 0.5%, and its comprehensive mechanical properties are good, so it can be used to manufacture bolts, nut keys, gears, shafts and other parts with greater stress. High carbon steel with carbon content of 0.55% – 0.7% has high strength and rigidity, which is usually used to make ordinary leaf spring, coil spring and wire rope. Alloy structural steel is made by adding some alloy elements into carbon steel. Each kind of alloy element less than 2% or the total alloy element less than 5% is called low alloy steel. Medium alloy steel with 2% ~ 5% of each alloy element or 5% ~ 10% of the total alloy element is called medium alloy steel.
Each kind of alloy element content is higher than 5% or the total alloy element content is higher than 10% is called high alloy steel. The addition of different alloying elements can change the mechanical properties of steel and have various special properties. For example, chromium can improve the hardness of steel and prevent rust and acid at high temperature; Nickel makes the steel have good hardenability and wear resistance. But alloy steel parts generally need heat treatment to improve their mechanical properties. In addition, alloy steel is more expensive than carbon steel and more sensitive to stress concentration, so it is only considered when carbon steel is not competent.
The casting made of carbon steel and alloy steel is called cast steel, which is usually used to manufacture parts with complex structure and large volume. However, the liquid fluidity of cast steel is worse than that of cast iron, and its shrinkage rate is also higher than that of cast iron. Therefore, the wall thickness of cast steel is usually greater than 10 mm, and its fillet and transition parts with different wall thickness should be larger than that of cast iron.
The metal materials commonly used in non-standard mechanical design mainly include:
Low carbon steel: the carbon content of steel is less than 0.25%, because of its low carbon content, it has low strength and low hardness, but has high plasticity and toughness, and good malleability and weldability. Generally, heat treatment is not used to manufacture small and medium-sized mechanical parts and mold with low requirements. For example, Q235 (A3) steel and steel profile commonly used in automation equipment.
Medium carbon steel: the carbon content of steel is 0.3% – 0.6%, the strength and hardness are high, the cutting performance is better but the weldability is poor, and it is mainly used for the mechanical parts with large load. Because of the high carbon content, it can be heat treated. The equipment shaft parts are usually 40.
Stainless steel: stainless steel is resistant to corrosion of acid and alkaline medium, which is not easy to rust. The commonly used grades of automatic equipment are sus303 and SUS304 (chromium nickel austenitic stainless steel). 303 has good cutting property and can be used as part material. 304 is poor in cutting property, and is often used as sheet metal parts.
6061: aluminum alloy, with copper as the main alloy element, has 470mpa strength, heat resistance, and is the most commonly used hard aluminum alloy for equipment. Surface treatment: sand blasting natural color + anodizing
6063: aluminum alloy, magnesium and silicon are the main alloy elements, with strength less than 200MPa. It is a common material for industrial aluminum profiles.
2. Nonferrous Metal Alloy
Nonferrous metal alloys have good friction reduction, running in, corrosion resistance, diamagnetism, conductivity and other special properties. Copper alloys, bearing alloys and light alloys are the most widely used in industry, but nonferrous metal alloys are more expensive than ferrous metals. Copper alloy can be divided into bronze and brass. Brass is an alloy of copper and tin. It has good plasticity and fluidity, and can roll and cast various mechanical parts. There are two kinds of bronze: tin bronze and Wuxi bronze. They have good friction reducing and corrosion resistance.
Bearing alloy
Bearing alloy (abbreviated as Babbitt alloy) is an alloy of copper, tin, lead and antimony. It has good antifriction, thermal conductivity and scuffing resistance, but its strength is low and expensive. It is mainly used to make the bearing lining of sliding bearing. The non-ferrous metal materials commonly used in non-standard mechanical design mainly include:
Cupronickel
Copper alloy with nickel as the main additive. Industrial Cupronickel is divided into structural Cupronickel and electrical Cupronickel. The structural white copper has good mechanical properties and can be used to manufacture precision machinery.
Brass
A copper alloy with zinc as the main additive. It has high strength, high hardness and strong wear resistance. It is often used as a friction guide material.
3. Non Metallic Materials
Metal materials are indispensable and important materials in modern industry and high-tech field. Nonmetallic materials include almost all materials except metal materials. There are many kinds of non-metallic materials used in mechanical manufacturing, such as plastics and rubber.
Rubber
Rubber is full of elasticity and has good properties of buffering, damping, heat resistance and insulation. It is commonly used in rubber coating and shock absorber: elastic device, rubber belt and insulating material
Plastic
Plastics are the earliest, fastest developing and most widely used materials in the synthetic polymer industry. Because of its small specific gravity, plastics are easy to be made into parts with complex shapes, and different plastics have different characteristics, such as corrosion resistance, friction and wear resistance, thermal insulation and vibration resistance. Commonly used plastics include polyvinyl chloride, polyolefin polystyrene, phenol and amino plastics. Engineering plastics include POM, Teflon, polyamine, polycarbonate, ABS, nylon, NC nylon, hydrogenated polyether, etc. Recently, the cages of some gears, wheels and rolling bearings and the bearing liners of sliding bearings are made of plastics. The general engineering plastics have poor heat resistance and are easy to aging, which makes the parts gradually worse.
Composite Materials
Composite materials are two or more kinds of materials with different properties synthesized by different process methods, which can not only ensure the original best properties of the composite materials, but also have the new properties after the combination. There is also a kind of functional composite materials, such as conductive materials, foot guide fiber insulation materials, by adding a variety of short red dimension. In recent years, for the purpose of functional composite materials, new composite materials used in light, heat, electricity, damping, lubrication, cattle, etc. have been emerging, and the application scope of composite materials is expanding.
Ceramics
Ceramic materials have high melting point and good chemical stability at high temperature, so they are suitable for high temperature materials. Generally, the temperature limit of super heat-resistant alloy is 950 ~ 11007, and the temperature limit of ceramic material is 1200-1600 ℃. Therefore, the use of ceramic materials in modern mechanical devices, especially in high-temperature mechanical parts, will be an important research direction. In addition, the high-performance materials have the characteristics of low friction coefficient, resistance to corrosion, chemical corrosion, small specific gravity and small coefficient of linear expansion. Therefore, they can be used in the fields of high temperature, medium temperature and low temperature, machining precision mechanical parts, and also can be used as motor parts. The ceramic materials represented by mechanical plate device are called engineering ceramics.