Release Source:NAIGOO
|Release Time:2019/08/13
|Number of Views:0
Gears rely on their structural dimensions and material strength to withstand external loads, which requires the material to possess high strength, toughness, and wear resistance. Due to the complex shape of gears and the high precision requirements, it also demands good processability of the material. Common materials used are forged steel, cast steel, and cast iron.
1. Forged steel
Based on the hardness of the tooth surface, it can be divided into two major categories
When HB is less than 350, it is referred to as a soft tooth surface
When HB is greater than 350, it is referred to as a hardened tooth surface
l. Tooth surface hardness HB＜ 350
Process: forging blank → normalizing → rough turning → tempering and finishing
Common materials: 45#, 35SiMn, 40Cr, 40CrNi, 40MnB
Features:
It possesses excellent comprehensive performance, with the tooth surface exhibiting high strength and hardness, and the tooth core demonstrating good toughness. After heat treatment, the gear cutting accuracy can reach Grade 8. It is simple to manufacture, economical, and has high productivity, with low precision requirements
2. Tooth surface hardness HB > 350
When using medium carbon steel:
Process: Forging blank → Normalizing → Rough cutting → Tempering → Fine cutting → High and medium frequency quenching → Low temperature tempering → Honing or abrasive running-in, electric spark running-in.
Common materials: 45, 40Cr, 40CrNi
Features:
The tooth surface has high hardness (HRC=48-55), high contact strength, and good wear resistance. The tooth core maintains toughness after quenching and tempering, with good impact resistance and high load-bearing capacity. The accuracy is reduced by half, reaching Level 7 accuracy. It is suitable for mass production, such as gears for medium-speed and medium-load gearboxes in automobiles, machine tools, and other applications.
When using low-carbon steel:
Forging blank → Normalizing → Rough cutting → Tempering → Fine cutting → Carburizing and quenching → Low-temperature tempering → Gear grinding. Reaching Level 6 and Level 7.
Common materials: 20Cr, 20CrMnTi, 20MnB, 20CrMnTo
Features:
The tooth surface exhibits high hardness and strong load-bearing capacity. The core possesses excellent toughness and impact resistance, making it suitable for high-speed, heavy-load, overload transmission or applications requiring compact structures, such as main transmission gears in locomotives and aviation gears.
II. Steel casting
Common materials for gears (essential knowledge excerpts for gears, Christmas dry goods sharing by mechanical friends)
When the gear diameter d is greater than 400mm, and the structure is complex, making forging difficult, cast steel materials ZG45 and ZG55 can be used, with normalizing treatment, normalization, and tempering.
III. Cast iron
It has strong resistance to adhesive and pitting corrosion, but poor impact resistance and wear resistance. It is suitable for applications with stable operation, low power, low speed, or large size and complex shape. It can operate under oil-deficient conditions and is suitable for open transmission.
IV. Non-metallic materials
Cloth, wood, plastic, nylon, suitable for high-speed light loads. When selecting materials, consideration should be given to the different working conditions of gears and the different failure modes of gear teeth, which serve as the basis for determining gear strength calculation criteria and selecting materials and heat treatment.
1. For gear teeth prone to fracture under impact loading, materials with good toughness should be selected, such as low-carbon steel that has undergone carburizing and quenching.
2. For high-speed enclosed transmissions, the tooth surface is prone to pitting corrosion, so materials with better tooth surface hardness should be selected. Medium carbon steel with surface hardening can be chosen.
3. For low-speed and medium-load conditions where tooth fracture, pitting, and wear may occur, materials with good comprehensive mechanical properties such as mechanical strength and tooth surface hardness should be selected. Medium carbon steel can be chosen for quenching and tempering followed by fine cutting.
4. Strive to reduce the variety of materials for ease of management, taking into account resources and supply conditions.
5. When compact structure size and high wear resistance are required, alloy steel should be used.
6. Equipment and technical conditions of the manufacturing unit.
