Gear refers to a mechanical element with gears on the wheel edge that continuously meshes to transmit motion and power. The application of gears in transmission has appeared very early. At the end of the 19th century, the principle of the tooth cutting method and the special machine tools and tools using this principle for tooth cutting appeared one after another, and with the development of production, the stability of gear operation was valued.

Gear transmission is one of the most widely used forms of transmission. It can transmit motion and power between any two shafts, the transmission is smooth and reliable, high efficiency, long life, compact structure, transmission speed and power range. However, special equipment is required for manufacturing, with high processing accuracy and installation accuracy, and is not suitable for long-distance transmission.

Gears are widely used and are important parts in various mechanical equipment, such as machine tools, aircraft, steamboats and fans.

Gears can be classified by tooth shape, gear shape, tooth line shape, surface on which the tooth is located, and manufacturing method.

1) Gears can be classified according to tooth shape, tooth profile curve, pressure angle, tooth height and displacement.

2) Gears are divided into cylindrical gears, bevel gears, non-circular gears, racks, worm-worm gears according to their shape.

3) According to the shape of the tooth line, gears are divided into spur gears, helical gears, herringbone gears, and curved gears.

4) According to the surface gear where the gear teeth are located, it is divided into external gear and internal gear. The top circle of the external gear tooth is larger than the circle of the tooth root; The top circle of the internal gear tooth is smaller than the circle of the tooth root.

5) According to the manufacturing method, gears are divided into casting gears, cutting gears, rolling gears, sintered gears, etc.

Selection guide
1. Select the gear that meets the speed or module requirements according to the speed and module calculation results,

2. Determine the diameter and number of teeth of the gear according to the speed calculation result or gear bite distance.

3. Choose whether to use spur gear, cam gear, helical gear, etc. according to practical functions such as speed, friction, transmission conversion angle and direction.

4. Choose wood, steel, plastic, steel-plastic gears according to the material.

5. Choose your own standard gear in the national standard.

Maintenance
To inject lubricating oil into the motor equipped with gears, when the motor is running, the rated current should not exceed the motor, the nameplate indicates the current value, always pay attention to the surrounding temperature, humidity, pH and other problems, according to the product label prompt temperature to maintain the environment as much as possible within the adapted temperature and humidity, in order to ensure the normal operation of the machine. If there is a problem or failure of the machine, it is necessary to carry out timely maintenance treatment, and confirm that the external power supply is completely detached from the reducer during maintenance and disassembly. If the geared motor rotates at low speed with the inverter, an independent auxiliary cooling fan needs to be installed.
Notes
Gear transmission structure design considerations:
      
1. The gear arrangement should be considered to facilitate the shaft and bearing forces

2. The joint point of the two-direction tooth of the herringbone gear should enter the meshing first

3. When the gear diameter is small, it should be made into a gear shaft

4 . The diameter of the gear root circle can be smaller than the shaft diameter

5. The pinion width should be greater than the large gear width

6. The gear block should consider the distance cut out of the tool when machining the gear

7. The connection between gear and shaft should reduce the machining during assembly

8. Pay attention to ensure that the stiffness of the gear along the tooth width is consistent

9. Use the uneven deformation of the gear to compensate for the deformation of the shaft

10. Split large gears should be separated without spokes

11. The hardened layer of the tooth surface should not be interrupted

12. Bevel gear shafts must be fixed in both directions

13. Both large and small bevel gear shafts should be able to be adjusted axially

14 . In the combined bevel gear structure, the bolt is not subject to tensile forces

Troubleshooting
Due to different factors such as structural type, material and heat treatment, operating environment and conditions, the form of failure is also different, and common gear faults have the following forms.

(1) Tooth surface wear

Insufficient lubricating oil or unclean oil quality will cause abrasive wear on the tooth surface, change the tooth profile, increase the backlash, and even break the tooth due to excessive gear thinning. Under normal circumstances, only when the lubricating oil is mixed with abrasive particles, it will cause tooth surface abrasive wear during operation.

(2) Tooth surface gluing and abrasion

For the transmission of heavy-duty and high-speed gears, the working area temperature of the tooth surface is very high, and once the lubrication conditions are poor, the oil film between the tooth surfaces will disappear, and the metal of one tooth surface will be fused and welded on the other tooth surface meshed with it, forming a scratch-like glue perpendicular to the joint line on the tooth surface. When the new gear is put into use without running-in, this phenomenon often occurs in a certain part, causing the gear to be scratched.

(3) Contact fatigue of the tooth surface

In the actual meshing process, the gear has both relative rolling and relative slipping, and the friction of relative sliding is opposite in the direction on both sides of the node, resulting in pulsating load. When this shear stress exceeds the fatigue limit of the gear material, the contact surface will produce fatigue cracks, and with the expansion of the crack, the tooth surface will eventually peel off a small piece of metal, forming a small pit on the tooth surface, which is called pitting corrosion. When the "pitting corrosion" expands into continuous sheets, the metal block on the tooth surface is formed to peel off. In addition, uneven material or local abrasions are also prone to contact fatigue and peeling on a certain tooth first.

(4) Bending fatigue and broken teeth

The gear teeth that bear the load during operation, like the cantilever beam, the root of which is subjected to the bending stress of the pulse cycle has the greatest effect, when this periodic stress exceeds the fatigue limit of the gear material, cracks will be generated at the root, and gradually expand, and when the remaining part can not withstand the transmission load, the phenomenon of broken teeth will occur. Gear breakage may also occur due to severe impact, eccentricity and uneven material during operation. Broken teeth and pitting corrosion are the main forms of gear failure.

Gear faults can also be divided into local faults and distributed faults. Local faults are concentrated on one or a few teeth, while distributed faults are reflected in each tooth of the gear.