Abstract: Gear transmission is an important transmission method in agricultural machinery, and there are many factors that affect gears. From the overall composition, there are mainly parts such as gearboxes, bearings, and shafts. From the perspective of manufacturing accuracy and assembly accuracy of parts, the design and selection of materials, heat treatment of parts are related, and the use is related to the maintenance and lubrication of gears. The gear transmission rate of agricultural machinery is relatively high, often operating under high loads and low speeds, with harsh working conditions and inadequate maintenance, which can easily lead to gear transmission failure and malfunctions. The article analyzes the failure determination and maintenance methods of agricultural machinery gears for reference.

Keywords: agricultural machinery; Gear; Failure determination; maintain

Gear transmission is an important transmission method in agricultural machinery, and there are many factors that affect gears. From the overall composition, there are mainly parts such as gearboxes, bearings, and shafts. From the perspective of manufacturing accuracy and assembly accuracy of parts, the design, material selection, and heat treatment of parts are related, and the use is related to the maintenance and lubrication of gears. The gear transmission rate of agricultural machinery is relatively high, often operating under high loads and low speeds, with harsh working conditions and inadequate maintenance, which can easily lead to gear transmission failure and malfunctions. The article analyzes the failure determination and maintenance methods of agricultural machinery gears for reference.

01 Reasons for gear failure

1.1 Tooth fracture

1) Overload breakage. Short term overload, overloading, or severe concentration of contact line load on mechanical gears may lead to gear breakage due to overload. Overloading can cause gear breakage in the following situations: gear overload due to bearing damage; Sudden occurrence of impact overload; Foreign objects between two paired gears cause overload load; The bending of the shaft itself causes overload. When overload causes gear breakage, the cross-section appears as coarse grain, which usually occurs in high hardness steel gears or cast iron gears, ultimately leading to gear fracture.

2) Fatigue induced fracture. Once the alternating ability of the material at the tooth root reaches the fatigue limit, fatigue cracks will appear at the fillet of the tooth root, and the cracks will rapidly expand, ultimately causing the gear to bend and break. The contact line between helical cylindrical gears and herringbone gears is inclined, and the root cracks of both gears usually propagate along the inclined direction. The surface that breaks is relatively smooth, and shell like patterns can be seen around the cracks.

1.2 Tooth surface bonding

In the case of low-speed gear transmission, the poor contact of the gear itself or the irregular shape of the tooth surface result in excessive local pressure on the normal tooth surface, making it impossible to form a lubricating oil film on the gear surface, or the viscosity of the lubrication itself is too low, resulting in insufficient thickness of the formed oil film. This leads to direct contact between the metal teeth, causing local high temperature and welding, while tearing along the sliding direction to produce grooves, which is called cold bonding. The bonding of tooth surfaces usually occurs during the transmission process of quenched and tempered gears. Under high-speed and heavy load conditions of gears, it may cause an instantaneous increase in local temperature, leading to the rupture of the oil film, fusion welding of the metal on the two contact surfaces, and tearing along the sliding direction, resulting in groove marks, which is called hot bonding.

1.3 Tooth surface wear

Tooth surface wear can be defined as the loss of material on the contact surface of the gear teeth. If dust or dirt is mixed into the meshing area, the tooth surface will also be damaged at the sliding speed, and this type of wear is called abrasive wear. Excessive tooth thickness wear can lead to breakage. According to the wear mechanism, wear can be divided into abrasive wear, scratching, corrosive wear, and wear caused by insufficient lubricating oil. Among them, destructive wear is usually caused by problems with the use of lubricating oil or improper selection of materials between the designed gears and the gears themselves.

1.4 Tooth surface burn

Tooth surface burns are mainly caused by overload, overspeed, or improper use of lubricating oil, resulting in excessive friction and causing local temperature rise. Excessive local temperature can cause discoloration, over tempering, or re quenching of quenched steel, and accelerate the rate of fatigue failure at the location where burns occur.

1.5 Plastic deformation of tooth surface

Under the influence of heavy loads, the yielding of surface metal will cause plastic deformation on the surface. Short term overloading or an increase in the friction coefficient of the tooth surface will cause the surface metal of the soft tooth surface to flow in the sliding direction, resulting in plastic deformation. After plastic deformation occurs on the gear working surface, the main external features formed are wrinkling deformation, ripple deformation, as well as collapse and flash deformation. The main reasons for plastic deformation on the gear tooth surface are improper heat treatment, overload, and improper lubrication.

02 The correct maintenance method for transmission gears

2.1 Selecting the correct lubricating oil

In gear transmission, lubricating oil is an indispensable lubricating medium that can protect the gear teeth and prevent damage. Transmission gears have special requirements for the viscosity of lubricating oil. If the viscosity is too low, a protective film cannot be formed and the meshing surface of the gear teeth cannot be protected; Excessive viscosity can cause the transmission gear to lose friction and cannot start even in low temperatures. In addition, under high load and high-speed operation, the high oil temperature on the surface of the gear can easily lead to oxidation and deterioration. At high temperatures, gear oil has good anti-oxidation stability, and standard specifications of lubricating oil must be used to ensure the anti-oxidation performance of the gear.

2.2 Ensure the cleanliness of the gear surface

When using agricultural machinery and large agricultural equipment, it is important to avoid overloading and ensure the sealing of the gear transmission system to prevent hard objects and dust from entering the gearbox.

2.3 When replacing accessories, choose original parts

Due to differences in processing methods, production standards, and selected materials, non original parts cannot meet the requirements of the factory's accessories, and even after repair, they cannot meet the standards? The effect is likely to cause malfunctions during use. When choosing gears, it is important to pay attention to the roughness of the gear surface. Related studies have found that the surface roughness of low-speed heavy-duty gears can cause significant wear on the gear surface, and the higher the roughness of the initial part surface. The probability of wear and tear is also higher, so it is necessary to choose gears with smooth surfaces.

03 Conclusion

After replacing and maintaining the faulty gears of agricultural machinery, it is necessary to do a good job of running in before use to ensure that there will be no wear during use. In addition, it is necessary to continuously improve the surface quality of new gears, enhance their load-bearing capacity and wear resistance, and thereby extend the service life of agricultural machinery.

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