Abstract: Gear transmission is an important transmission method in agricultural machinery, and there are many factors that affect gears. From the overall composition, it mainly includes parts such as gearboxes, bearings, and shafts. From the perspective of manufacturing and assembly accuracy of parts, the design of parts is related to material selection and heat treatment, and the use is related to gear maintenance and lubrication. 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 malfunction. The article analyzes the failure judgment and maintenance methods of agricultural machinery gears for reference.

Keywords: Agricultural machinery; Gear; Failure determination; maintenance

Gear transmission is an important transmission method in agricultural machinery, and there are many factors that affect gears. From the overall composition, it mainly includes parts such as gearboxes, bearings, and shafts. From the perspective of manufacturing and assembly accuracy of parts, the design of parts is related to material selection and heat treatment, and the use is related to gear maintenance and lubrication. 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 malfunction. The article analyzes the failure judgment and maintenance methods of agricultural machinery gears for reference.

1. The causes of gear failure

1.1 Tooth fracture

1) Overload breaking. Mechanical gears may experience short-term overloading, overload, or severe concentration of contact line load, which can lead to gear overload and fracture. Overloading can lead to gear breakage in the following situations: gear overload caused by bearing damage; Sudden occurrence of impact overload; Foreign objects between two paired gears causing overload load; The bending of the shaft itself causes overload. When overload causes the gear to break, the cross-section becomes coarse-grained, which usually occurs in high hardness steel gears or cast iron gears, ultimately leading to gear fracture.

2) Fatigue fracture. Once the material's alternating ability at the tooth root reaches the fatigue limit, fatigue cracks will appear in the tooth root fillet, and the cracks will rapidly expand, ultimately leading to gear bending and fracture. The contact line between the helical cylindrical gear and the herringbone gear is inclined, and the root cracks of both gears usually propagate in the inclined direction. The surface where the fracture occurs is relatively smooth, and a shell like pattern can be seen around the crack.

1.2 Tooth surface bonding

In the case of low-speed gear transmission, poor contact of the gear itself or irregular shape of the tooth surface results 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 oil film. This leads to direct contact between the metal surfaces of the teeth, local high temperature and fusion welding, and tearing along the sliding direction to produce grooves, which is called cold bonding. Tooth surface adhesion 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. The metal on the two contact surfaces will undergo fusion welding, while tearing in the direction of sliding and producing grooves, 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 in the meshing area, the tooth surface will also be damaged at sliding speed, and such wear is called abrasive wear. Excessive tooth thickness wear can lead to fracture. According to the wear mechanism, wear can be divided into abrasive wear, scratch, corrosion 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 burns

Tooth surface burns are mainly caused by excessive friction due to overload, overspeed, or improper selection of lubricating oil, which in turn leads to local temperature rise. Excessive local temperature can cause discoloration, over tempering, or re quenching of quenched steel, and the rate of fatigue failure at burn prone locations will also accelerate.

1.5 Plastic deformation of tooth surface

Under the influence of heavy loads, the yield of surface metal will cause plastic deformation on the surface. Short term overload or an increase in tooth friction coefficient can cause the surface metal of soft tooth surfaces to flow in the sliding direction, resulting in plastic deformation. After plastic deformation occurs on the gear working face, the main external characteristics 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.

2. Correct maintenance methods for transmission gears

2.1 Choose the correct lubricating oil

In the transmission of gears, lubricating oil is an indispensable lubricating medium that can protect the teeth and avoid damage. Transmission gears have special requirements for the viscosity of lubricating oil. If the viscosity is too low, it will not be able to form a protective film and will not provide protection for the meshing surface of the gear teeth; If the viscosity is too high, it will 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. Under high temperature conditions, gear oil has good antioxidant stability, and standard specifications of lubricating oil must be used to ensure the oxidation resistance of the gear.

2.2 Ensure the cleanliness of the gear surface

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

2.3 When replacing accessories, original factory parts should be selected

Due to different processing methods, production standards, and selected materials, non original parts cannot meet the requirements of the factory parts, and even after maintenance, they cannot meet the requirements? The effect is likely to cause malfunctions during use. When selecting gears, it is important to pay attention to the surface roughness of the gears. 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 initial surface roughness of the parts. The higher the probability of wear and tear, it is important to choose gears with smooth surfaces.

3. Conclusion

After replacing and maintaining the failed gears of agricultural machinery, it is necessary to do a good job of running in before use to ensure that there is 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.

2024 January 2nd Week VAFEM Product Recommendation:

Agricultural Wheel Hub Unit:

This type of product provides a complete maintenance-free sealed bearing unit with important advantages for farm applications. These quick-mount bearing units use long-life grease and seals.

Features and advantages of agricultural machinery hub unit:

Extended length, field-tested performance, stronger sealing performance, life-long grease lubrication, basic maintenance-free, simple installation and replacement procedures, special application design, low grease consumption, reduced maintenance and ownership costs, and ease of environmental Influence, improve production efficiency.

https://www.vafem.com/products/Agricultural-Wheel-Hub-Unit/898.html