Types and uses of gears

Types and uses of gears

1. The development history of gears

According to historical records, gears have been used in ancient China as far back as 400-200 BC. The bronze gears unearthed in Shanxi, my country are the oldest gears discovered so far. As a guide car reflecting the achievements of ancient science and technology, the gear mechanism is used. The core mechanism. In the West, more than 300 years BC, the ancient Greek philosopher Aristotle expounded the problem of transmitting rotational motion with bronze or cast iron gears in "Mechanical Problems". However, the ancient gears were made of wood or cast metal, which could only transmit the rotary motion between the shafts, and could not guarantee the smoothness of the transmission, and the gears had a small bearing capacity.

With the development of production, the stability of gear operation has been paid attention to. In 1674, the Danish astronomer Romer first proposed to use the epicycloid as the tooth profile curve to obtain a smooth running gear. During the industrial revolution in the 18th century, gear technology developed rapidly, and a lot of research on gears was carried out. In 1733, the French mathematician Cammy published the basic law of tooth profile meshing; in 1765, the Swiss mathematician Euler suggested the use of involutes as tooth profile curves. The hobbing and shaping machines that appeared in the 19th century solved the problem of mass production of high-precision gears.

In 1900, Purford installed a differential device on the hobbing machine, which could process helical gears on the hobbing machine. Since then, the hobbing and cutting gears of the hobbing machine have become popular. .

In 1899, Lasher first implemented the scheme of shifting gears. The displacement gear can not only avoid the undercut of the gear teeth, but also match the center distance and improve the bearing capacity of the gear. In 1923, Wilder Haber of the United States first proposed gears with arc tooth profiles. In 1955, Sunovykov conducted in-depth research on arc gears, and arc gears were then used in production. This gear has high load-carrying capacity and efficiency, but is not as easy to manufacture as involute gears and needs further improvement.

Second, the use of gears, Gears are used for nothing more than:

slow down

increase torque

transfer of force from point to point

change the direction of force

split transmission

All these functions are embodied in the gearbox.

Third, the classification of gears

Gears are generally divided into involute gears, splines, bevel gears, worm gears, rotors, special-shaped gears (cycloidal gears, ratchet gears, herringbone gears, etc.).

3.1 Involute gear/Cylindical gear

Involute gears include involute straight teeth and involute helical teeth.

3.1.1 Involute spur gear/Spur Gear

The gear is used in low-speed matching occasions, and the matching noise is low. The advantage is that it is easy to produce and low cost, and the disadvantage is that it must be used in pairs, and the installation axes must be parallel.

3.1.2 Involute helical gear/Helical gear

The gear is generally inclined at an angle of between 10° and 45°. The advantage is that the meshing is smooth and quiet; more meshing tooth surfaces can transmit greater torque; the disadvantage is that it is expensive to process and will generate additional axial extrusion force.

3.2 Spline/Spline

Splines are divided into involute splines, triangular splines and rectangular splines, which are mostly used in the connection of couplings. It is characterized by multi-tooth operation, high bearing capacity, good neutrality, good guidance, shallow tooth root, small stress concentration, small weakening of shaft and hub strength, and convenient processing.

3.3 Bevel gear

Bevel gears are divided into straight bevel rulers and spiral bevel rulers.

3.3.1 Umbrella gear

The axis is a conical axis, the advantage is right-angle drive, the disadvantage is that due to the special transmission structure, the bearing and support are difficult to process.

3.3.2 Spiral Bevel gear

The teeth of the gear have a helical angle, which can be applied to the occasion of transmitting large torque, and is generally used in reverse gear.

3.4 Worm gear

Generally, they mesh with each other at 90 degrees. The advantage is that the transmission is quiet and smooth; it can be driven at a right angle; it will not rotate; it is suitable for positioning structures. The disadvantage is that the transmission friction leads to low transmission efficiency; it needs regular maintenance and is used in low-speed occasions.

3.5 Rotor

Rotors are generally divided into female and male rotors. Generally used in screw compressors after meshing with each other. In the process of fitting and rotating the yin and yang rotors, a process of suction-compression-exhaust is completed.

The distinction method is: generally, the tooth surface of the male rotor is relatively full, while the tooth surface of the female rotor is relatively thin and concave.

Note: Generally, the male rotor is the main rotor, and the male rotor rotates first, thereby driving the female rotor to rotate, so as to perform suction and exhaust operations.

3.6 Special-shaped gear

Special-shaped gears are more complicated, cycloidal gears, ratchets, etc. will be explained separately in the future.