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Metal Materials

1. Cast iron

Cast iron and steel are both iron-carbon alloys, and their difference is mainly in the carbon content. Iron-carbon alloys with a carbon content of less than 2% are called steels, and those with a carbon content of more than 2% are called cast irons. Cast iron has appropriate fusibility and good liquid fluidity, so it can be cast into parts with complex shapes. In addition, its shock absorption, wear resistance, machinability (referring to gray cast iron) are good and the cost is low, so it is widely used in machinery manufacturing. Commonly used cast irons are: gray cast iron, ductile iron, malleable cast iron, alloy cast iron, etc. Among them, gray cast iron and ductile iron are brittle materials and cannot be rolled and forged. Among the above cast irons, gray cast iron is the most widely used, followed by ductile iron.

2. Steel

Compared with cast iron, steel has high strength, toughness and plasticity, and its mechanical properties and processing properties can be improved by heat treatment. The blanks of steel parts can be obtained by forging, stamping, welding or casting, so they are widely used. According to the application, 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, molds and measuring tools; special steel (such as stainless steel, heat-resistant steel, acid-resistant steel, etc.) is used to manufacture in special environments working parts. 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 strength of the steel, but the lower the plasticity. In order to improve the properties of steel, steels with some alloying elements are specially added are called alloy steels. 1) The carbon content of carbon structural steel is generally not more than 0.7%. Low carbon steel with a carbon content of less than 0.25% has low strength limit and yield limit, high plasticity, and good weldability. It is suitable for stamping and welding. It is often used to make screws, nuts, washers, shafts, Valve guides and welded components, etc. Low carbon steel with carbon content of 0.1% to 0.2% is also used to make carburized parts, such as gears, piston pins, sprockets, etc. Through carburizing and quenching, the surface of the part can be hard and wear-resistant, and the core is tough and impact-resistant. If higher strength and impact resistance are required, low carbon gold bearing steels can be used. carbon content in 0.3%~0.5% medium carbon steel, it has good comprehensive mechanical properties, not only high strength, but also certain plasticity and toughness. It is often used as bolts, nuts, keys, gears and shafts with high stress Components. High carbon steel with a carbon content of 0.55% to 0.7% has high strength and elasticity, and is mostly used to make ordinary leaf springs, coil springs or wire ropes.

2) Alloy structural steel

The effect of adding alloying elements to steel is to improve the properties of steel. For example: nickel can increase the strength without reducing the toughness of steel; chromium can improve hardness, high temperature strength, corrosion resistance and wear resistance of high carbon steel; manganese can improve the wear resistance, strength and toughness of steel; the role of aluminum Similar to manganese, its effect is greater; vanadium increases toughness and strength; silicon increases elastic limit and wear resistance, but reduces toughness. The effect of alloying elements on steel is very complex, especially when several alloying elements need to be added simultaneously in order to improve the properties of the steel. It should be noted that the good properties of alloy steels depend not only on chemical composition but also to a greater extent on proper heat treatment.

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