Q
What is the material classification of mechanical parts?
A
As a mechanical designer must understand the industrial development trend when selecting materials. According to national standards, combined with China's resources and production conditions, comprehensive consideration of materials and their choice. The most commonly used materials in mechanical manufacturing are steel and cast iron, followed by non-ferrous metals. alloy. Non-metallic materials such as plastics, rubber, etc., also have unique use value in mechanical manufacturing.

The metal material:
1. Cast iron
Both cast iron and steel are iron-carbon alloys, and the difference is mainly due to the difference in carbon content. An iron-carbon alloy containing less than 2% carbon is called steel, and a carbon content of more than 2% is called cast iron.

2. Steel
Compared with cast iron, steel has high strength, toughness and plasticity, and can be heat treated to improve its mechanical properties and processability. The blanks of steel parts can be obtained by forging, stamping, welding or casting, so they are widely used. Steel can be divided into structural steel, tool steel and special steel according to the application.

1) Carbon structural steel The carbon content of such steels generally does not exceed 0.7%. Low carbon steel with carbon content less than 0.25%, its strength limit and yield limit are low, plasticity is high, and it has good weldability. It is suitable for stamping and welding. It is commonly used to make screws, nuts, washers, shafts, Valve guides and welded components.
2) Alloy structural steel
The addition of alloying elements in steel serves to improve the properties of the steel.
3) Cast steel

The liquid fluidity of cast steel is inferior to that of cast iron, so when casting with ordinary sand type, the wall thickness is often not less than 10 mm. The shrinkage rate of steel castings is larger than that of cast iron parts, so the rounded corners of steel castings and the transition parts of different wall thicknesses should be larger than cast iron parts.

3. Copper alloy
Copper alloys are 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.

Non-metallic materials:
1. Rubber
The rubber is elastic and absorbs a lot of impact energy. It is often used as a spring element for couplings or shock absorbers, tape with belt drive, etc. Hard rubber can be used to make water-lubricated bearing linings.

2. Plastic
Plastics have a small specific gravity and are easy to form parts with complex shapes, and various plastics have different characteristics, such as corrosion resistance, heat insulation, insulation, friction reduction, and friction coefficient, so in recent years in mechanical manufacturing. Its application is increasingly widespread.

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