What are the commonly used materials and selection requirements of mechanical parts?

Mechanical parts refer to the undetachable basic units that make up a machine, such as bolts, screws, keys, belts, gears, shafts, springs, pins, etc. Mechanical parts are divided into general parts and special parts. General purpose parts refer to parts that can be widely used in a variety of machines, and special purpose parts refer to parts that can only be used in a particular class of machines.

First, mechanical parts commonly used materials

The materials of machine parts are metal materials, non-metallic materials and composite materials.

Metal materials are divided into black metal materials and non-ferrous metal materials. Ferrous metal materials, including a variety of steel, cast steel and cast iron, have good mechanical properties (such as strength, plasticity, toughness, etc.), are relatively cheap and readily available, and can meet the requirements of a variety of properties and applications. Alloy-steel is often used to make important parts among ferrous metals because of its excellent properties. Non-ferrous metal materials include copper alloy, aluminum alloy, bearing alloy, etc., with low density, good thermal and conductive properties, etc., usually can also be used for anti-friction, wear and corrosion requirements of the occasion.

Non-metallic materials refer to plastics, rubber, synthetic fibers and other polymer materials and ceramics. Polymer materials have many advantages, such as rich raw materials, low density, good elasticity in the appropriate temperature range, good corrosion resistance. Its main disadvantage is easy to aging, many of them poor flame retardant materials, generally speaking, heat resistance is not good. The main characteristics of ceramic materials are high hardness, wear resistance, corrosion resistance, high melting point, high stiffness and density than iron and steel. At present, ceramic materials have been used in seals, rolling bearings and cutting tools and other structures. Its main disadvantages are relatively brittle, low fracture toughness, high price, poor processing technology, etc.

Composite material refers to a new type of material with two or more kinds of materials with obviously different physical and mechanical properties through composite processing. For example, glass, graphite (carbon), boron, plastic and other non-metallic materials can be composite into a variety of fiber reinforced composites. In the surface of ordinary carbon steel plate attached plastic, can obtain high strength and corrosion resistance of plastic composite steel plate, the main advantages are high strength and elastic modulus, and the quality is particularly small, but also has the disadvantage of poor heat resistance, poor thermal and electrical conductivity. In addition, composite materials are more expensive. So at present, composite materials are mainly used in aviation, aerospace and other high-tech fields. In civil products, composite materials also have some applications.

Two, mechanical parts material selection principle

Selecting suitable materials from a variety of materials is a job restricted by many factors. The commonly used materials for mechanical parts include steel, cast iron, non-ferrous metals and non-metallic metals, etc. For the brand, performance and heat treatment knowledge of commonly used materials, please refer to the mechanical design manual. Selecting materials is an important step in mechanical design. With the continuous development of material science, the requirement of parts in machinery manufacturing industry is increasing. Therefore, when choosing materials, designers should fully understand the properties and applicable conditions of materials, and consider the use of parts, technology and economic requirements. The following is a brief introduction to the general selection principles of metal materials (mainly steel).