Knowledge

Classification by gear shape

1. Cylindrical gears

Spur cylindrical gears:

§ Features: Spur cylindrical gears are one of the most basic and common types of gears in reducers. Their structure is simple, and the manufacturing process is relatively easy to understand and operate, which makes their manufacturing cost relatively low. During the manufacturing process, as the teeth are parallel to the axis, no complex processes or special equipment are required, and ordinary machine tools can complete the processing tasks. During transmission, the teeth enter and exit mesh simultaneously along the entire tooth width. Although this meshing method ensures direct transmission to a certain extent, it also brings some disadvantages. Because the teeth enter and exit simultaneously, the instantaneous impact force is relatively large, which can cause shock and noise. Therefore, it is suitable for low-speed and low-load transmission applications. For example, in some small manual mechanical equipment, such as small manual juicers, the internal reducer using spur cylindrical gears can meet the simple transmission requirements, and since the speed and load are not large, the impact and noise problems of spur cylindrical gears will not have a significant impact on the normal use of the equipment.

o Helical cylindrical gears:

§ Features: Helical cylindrical gears are developed based on spur cylindrical gears. Due to the angle between the teeth and the axis, they do not enter and exit mesh simultaneously along the entire tooth width like spur cylindrical gears, but gradually. This gradual meshing method results in a larger overlap, meaning more teeth are engaged at the same time. This characteristic makes helical cylindrical gears more stable in transmission and have a higher load-carrying capacity than spur cylindrical gears. They can withstand greater loads without easy damage and can adapt to higher speeds. However, helical cylindrical gears generate axial forces during transmission because the inclination angle of the teeth creates a component force along the axis direction when transmitting power. To support this axial force, corresponding bearings are required, which increases the complexity of the structure. Helical cylindrical gears are commonly used in high-speed and high-load applications, such as automotive transmissions and industrial reducers. In automotive transmissions, they can stably transmit power during high-speed operation and frequent gear changes, ensuring the normal operation of the vehicle.

Herringbone cylindrical gears:

§ Features: Herringbone cylindrical gears are equivalent to two helical cylindrical gears with opposite helical directions combined. This special structure design ingeniously eliminates axial forces. Because the axial forces generated by the two helical parts are in opposite directions, they cancel each other out. They have a very high load-carrying capacity and can withstand huge loads, performing well in heavy-duty transmission applications. They are often used in large mining machinery, large ships' power transmission, etc. In large mining machinery, such as rock crushers, they need powerful forces to crush hard rocks. Herringbone cylindrical gears can stably transmit power under high loads, ensuring the normal operation of the equipment. However, the manufacturing process of herringbone cylindrical gears is relatively complex. Due to their special shape and structure, high-precision equipment and complex processes are required during processing, which leads to higher manufacturing costs.

 

2. Bevel gears

Straight bevel gears:

§ Features: Straight bevel gears are mainly used for transmission between intersecting shafts, with their teeth distributed on a conical surface. This unique structure enables them to transmit power between shafts in different directions. Their structure is relatively simple, and manufacturing and installation are relatively easy. Although their shape is more complex than cylindrical gears during manufacturing, compared to other types of bevel gears, their processing technology is still relatively easy to master. During installation, no overly complex adjustments or positioning are required. However, the transmission smoothness of straight bevel gears is relatively poor because their teeth also have significant impact during meshing, similar to straight cylindrical gears. Their load-carrying capacity is limited and they are generally suitable for low-speed, light-load, and low-precision transmission applications. For instance, in some simple agricultural machinery transmissions, such as parts of small walk-behind tractors, straight bevel gears can meet the basic transmission requirements. Due to the relatively low demands of their working environment and conditions, the shortcomings of straight bevel gears do not have a significant impact on the equipment.

 

Spiral Bevel Gears:

§ Features: Spiral bevel gears have significantly improved transmission performance compared to straight bevel gears. Their transmission is smoother because the inclined design of their teeth makes the meshing process more gradual, reducing shock and vibration. Their load-carrying capacity is also enhanced, allowing them to handle greater loads. They are suitable for high-speed, heavy-load, and intersecting shaft transmission applications. However, the design and manufacturing of spiral bevel gears are more challenging than those of straight bevel gears. Due to the inclination angle of their teeth and the conical surface, precise calculations and optimizations are needed during design to ensure their transmission performance. Advanced equipment and processes are also required during manufacturing to guarantee processing accuracy.

 

Curved Tooth Bevel Gears:

§ Features: Curved tooth bevel gears, also known as spiral bevel gears, have curved tooth profiles. This unique tooth design offers several advantages. They have a high contact ratio, meaning more teeth are engaged simultaneously at any given moment, and the number of teeth in contact is greater. This results in smoother transmission, higher load-carrying capacity, and lower noise. During operation, they can transfer power more smoothly, reducing vibration and noise generation. They are commonly used in high-speed, heavy-load applications, such as the rear axle transmission of automobiles. In automotive rear axle transmissions, curved tooth bevel gears can stably transfer engine power to the wheels during high-speed driving and under heavy torque, ensuring the vehicle's performance. However, their manufacturing requires specialized equipment and complex processes because of the complex shape of the curved teeth, which demands high-precision processing equipment and advanced processing techniques to ensure their accuracy and quality, resulting in higher costs.

 

Classification of gears based on tooth surface hardness

1. Soft Tooth Surface Gears

Features: The tooth surface hardness of soft tooth surface gears is generally less than 350HBS. These gears have relatively simple manufacturing processes and do not require complex heat treatment processes. Ordinary processing and treatment methods can meet the requirements, making their manufacturing costs lower. Due to the soft tooth surface, they are prone to wear during operation. As the gears rotate, the friction between the tooth surfaces gradually wears down the material. However, if the load is not too large, the speed is not too high, and the precision requirements are not particularly strict, soft tooth surface gears can meet the usage requirements. For example, in some small light industrial machinery, such as the reduction gears inside small sewing machines, since the working load is small, the operating speed is not high, and the transmission precision requirements are not very strict, soft tooth surface gears can handle the job, and their low-cost advantage also reduces the manufacturing cost of the equipment.

 

2. Hard Tooth Surface Gears

Features: The tooth surface hardness of hard tooth surface gears is greater than 350HBS. After heat treatment processes such as quenching and carburizing, the tooth surface hardness is significantly increased. This high hardness enhances their wear resistance and anti-scuffing ability, allowing them to resist wear and scuffing during long-term operation. Their load-carrying capacity is greatly improved, enabling them to operate under high-speed and heavy-load conditions. They are commonly used in the reducers of large-scale mechanical equipment in industries such as metallurgy, mining, and cement. In large rolling mills in the metallurgical industry, hard tooth surface gears can withstand huge loads and high-speed operation requirements, ensuring the stable operation of the equipment. However, the processing of hard-toothed gears is highly challenging due to the need for precise control of heat treatment processes to ensure the quality of tooth surface hardness and internal structure. It demands advanced processing equipment and professional technicians for operation, which leads to relatively high costs.

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