Gear transmission is a widely used form of mechanical transmission. It offers precise transmission, high efficiency, a compact structure, reliable operation, and a long service life.

Gear Classification

1. Based on the relative positions of the two shafts and the direction of the gear teeth, they can be classified into the following types:

Straight-toothed cylindrical gear transmission

Helical cylindrical gear transmission

Rack and Pinion Gear Transmission

Bevel Gear Transmission

Intersecting-Axis Helical Gear Transmission

2. Based on the operating conditions of the gear, they can be classified as:

Open gear drives expose the gears directly, making it difficult to ensure proper lubrication.

Partially enclosed gear drive, with gears immersed in an oil bath and protected by a guard, though not fully sealed.

Closed gear drives enclose gears, shafts, and bearings within a sealed housing, ensuring excellent lubrication conditions while preventing dust and debris from entering. With precise installation, these gear drives operate under optimal conditions and are the most widely used type of gear transmission.

How to Handle Gear Transmission Failures

[Failures Caused by Manufacturing Errors]

When manufacturing gears, several typical errors commonly arise, such as eccentricity, pitch errors, base circle errors, and tooth profile errors. These errors can result from various sources, including inaccuracies in machine tool motion, imperfections in cutting tools, improper installation or misalignment of the tool, workpiece, and machine system, as well as deformations caused by thermal stresses during heat treatment. When these gear errors become significant, they can lead to subtle, intermittent fluctuations in gear rotation—causing micro-inertia disturbances—and may trigger abrupt impacts and vibrations during gear meshing, ultimately resulting in excessive noise.

[Failures Caused by Assembly Errors]

Due to factors such as assembly techniques and methods, gear assembly often results in an alignment error where one end makes contact while the other remains unsupported. This includes linear deviations in the gear shaft (such as coaxiality or misalignment errors) as well as gear imbalance. When one end is in contact or when there are linear deviations in the gear shaft, it leads to uneven load distribution across the gears, causing some individual teeth to bear excessive stress and experience premature localized wear—in severe cases, this can even result in tooth fracture. Additionally, gear imbalance triggers impact vibrations and noise.

[Failures Caused by Operation]

1. Tooth Fracture

When gears are in operation, the force exerted by the driving gear and the reaction force from the driven gear both act on each other’s teeth through the point of contact. The most critical scenario occurs when, at a particular instant, the contact point happens to be located at the tip of the tooth. At this moment, the tooth behaves like a cantilever beam: once loaded, the bending stress generated at the tooth root reaches its maximum. If the gear experiences a sudden overload or impact load under these conditions, failure—specifically, fracture at the tooth root due to overloading—is highly likely to occur.

2. Tooth surface wear or scratches

During the meshing and transmission process, relative sliding occurs between the gear teeth. Combined with poor lubrication, unclean or degraded lubricants, low-speed heavy loads, or inadequate heat treatment quality, these factors can lead to adhesive wear, abrasive wear, corrosive wear, and even scratching on the tooth surfaces.

3. Tooth Surface Fatigue

So-called gear surface fatigue primarily includes pitting and spalling. The primary cause of pitting is the formation of microscopic fatigue cracks on the working surfaces of gear teeth, triggered by pulsating contact stresses during operation. When lubricating oil enters these surface cracks—first sealing the entry points and then being squeezed under load—the oil within the micro-crack zones exerts high pressure, causing the cracks to propagate further into the tooth surface. This process ultimately leads to the detachment of tiny metal particles from the tooth surface, leaving behind small pits that characterize gear surface pitting. If the fatigue cracks continue to expand deeper and wider across the tooth surface, they may eventually result in large-scale or extensive flaking, thereby giving rise to gear surface spalling.

4. Plastic Deformation of Tooth Surfaces

When the gear material is relatively soft but subjected to high loads, plastic deformation of the tooth surfaces is likely to occur. Under the influence of excessive friction between the tooth surfaces, the contact stress exceeds the material's compressive yield strength, causing the tooth surface material to enter a plastic state and triggering plastic flow of the metal. This results in concave grooves forming on the active gear’s tooth surface near the pitch line, while convex ridges develop on the driven gear’s tooth surface in the same region—ultimately leading to severe tooth profile damage.