Force Plus: Causes of Gearbox Oil Leaks and Solutions

        Gear reducer This equipment is widely used in industrial enterprises. Once oil leakage occurs, it not only causes economic losses but, in severe cases, can also lead to insufficient or complete absence of lubrication in the gearbox, accelerating wear on the gear meshing surfaces and eventually resulting in tooth damage or spalling, which may trigger equipment failures. Gearbox oil leaks severely pollute the surrounding environment and corrode the underlying foundations, thereby disrupting civilized production practices and wasting a significant amount of lubricating oil that could otherwise be recycled and reused.

Gearbox oil leakage is a common failure phenomenon in the operation of gear reducers. Correctly analyzing and diagnosing the causes of oil leakage in gear reducers, and adopting effective solutions tailored to these causes, are crucial for ensuring the normal operation of gear reducers and extending their service life.

Analysis of the Causes of Gearbox Oil Leakage

Generally speaking, the main causes of gearbox oil leakage are: 5 Various reasons:

1. The pressure difference generated inside and outside the reducer

In a closed gearbox, each pair of meshing gears generates friction and, consequently, heat. According to Boyle’s Law and Mariotte’s Law, as operating time increases, the temperature inside the gearbox gradually rises. Since the volume of the gearbox remains constant, the pressure inside the housing also increases accordingly. As a result, the lubricating oil within the housing is flung around and splashes onto the inner walls of the gearbox. Under the influence of the pressure differential, the lubricating oil leaks out through any available gaps or cracks.

2. The reducer’s structural design is unreasonable or there are problems with its manufacturing process.

The designed reducer lacks a ventilation cover or has no vent plug on the inspection port cover.

The shaft seal structure is improperly designed; it employs an oil-groove and felt-ring type shaft seal. Due to the extremely poor compensating performance of the felt, the seal quickly fails within a short period of time.

Although there are oil return holes on the oil groove, they tend to clog easily, making it difficult for the oil-return function to work effectively.

During the manufacturing process, the casting was not subjected to annealing or aging treatment, and the internal stresses within the casting were not relieved, leading to deformation, gaps, and subsequently, oil leakage.

There are defects such as sand holes, slag inclusions, porosity, and cracks;

Oil leakage caused by poor machining accuracy can occur in gear reducers due to factors such as insufficient machining accuracy of the mating surfaces on the reducer housing, improper tolerances, and inadequate assembly practices, all of which may lead to oil leaks.

3. Excessive fuel quantity

During operation, the gearbox’s oil sump is vigorously agitated, causing the lubricating oil to splash around inside the machine. If the oil level is too high, a large amount of lubricant can accumulate at areas such as shaft seals and joint surfaces, leading to leaks.

4. Improper installation and maintenance procedures

Oil leakage caused by insufficient installation accuracy. When a gearbox is started, it experiences significant dynamic loads. Once the installation accuracy of the gearbox fails to meet the standard requirements, the base bolts will loosen, thereby intensifying the gearbox’s vibration. This, in turn, accelerates the wear of the sealing rings at the high- and low-speed shaft holes, leading to lubricant leakage. Additionally, during equipment maintenance, oil leakage can also occur if contaminants on the mating surfaces are not thoroughly removed, if inappropriate sealants are selected, if sealing components are installed in the wrong direction, or if sealing components are not replaced in a timely manner.

5. Improper oil selection

Generally, gear reducers commonly use HJ-40 and HJ-50 mechanical lubricating oils. Alternatively, HL-30, HL-20 gear oils, and HJ3-28 rolling mill oils can also be used as lubricants. In short, the lubricant for a gear reducer should be selected based on factors such as load, rotational speed, and temperature. It is incorrect to simply assume that the higher the viscosity of the lubricant, the better.

Countermeasures for Gearbox Oil Leaks

1. To address the issue of oil leakage from the reducer caused by pressure differences, the problem can be resolved by improving the breather cap and inspecting the inspection port cover plate.

Although all gear reducers are equipped with breather caps, the vent holes are often too small and tend to become clogged with dust and oil contamination. Moreover, each time oil is added, the inspection hole cover must be opened; every time the cover is opened, there’s an increased risk of oil leakage—even in areas that were originally leak-free. To address this issue, we can design a cup-shaped breather cap and replace the original thin inspection hole cover with one that’s 6 mm thick. The cup-shaped breather cap will then be welded onto the cover plate, with a vent hole diameter of 6 mm, ensuring smooth ventilation and balancing the pressure inside and outside the gearbox. In the future, when adding oil, we’ll simply pour it directly into the oil cup without having to open the inspection hole cover again, thereby significantly reducing the likelihood of oil leaks.

2. Clear the return passage for the lubricating oil.

To prevent excess lubricating oil thrown onto the bearing by the gears from accumulating at the shaft seal, it is essential to ensure that the excess oil flows back into the oil sump in a specific direction. Specifically, a groove inclined inward toward the machine interior should be machined at the center of the lower bearing shell.

The oil return groove is provided, and a notch is also cut at the straight opening of the end cover, with the notch aligned directly with the oil return groove. This allows excess lubricating oil to flow back into the oil sump via the notch and the oil return groove.

3. Adopt new sealing materials.

For leaks at static seals of gear reducers, a new type of sealing material can be used for bonding and plugging. During major overhauls of gear reducers, applying polymer sealant to mating surfaces and end covers—replacing earlier products—generally prevents leakage. If oil leakage occurs at static seals during operation of the gear reducer, an emergency repair compound based on surface engineering technology can be used for bonding and plugging, thereby effectively eliminating the oil leak.

4. Strictly follow the maintenance procedures.

During the maintenance of gear reducers, it is essential to strictly follow the process specifications. The oil seal must not be installed backward; the lip must not be damaged; the outer edge must remain undeformed; the spring must not fall out; the mating surfaces must be thoroughly cleaned; the sealing compound must be applied evenly; and the oil level must not exceed the mark on the oil dipstick.

5. Wipe and clean oil stains.

Generally, static sealing points on gear reducers can achieve zero leakage after proper treatment. However, dynamic sealing points may exhibit slight leaks due to factors such as aging of sealing elements, poor sealing quality, improper assembly, and roughness of the shaft surface. Given the harsh working environment in cement plants—where dust adheres to the shafts, leaving them slick and oily—it is necessary to wipe off the oil and grease from the shafts after the equipment has been shut down.

Oil leakage in gear reducers is a relatively common issue and can be difficult to eliminate completely. By implementing the preventive and control measures outlined above, oil leakage in gear reducers can be largely contained, extending the service life of the gear reducers and ensuring the smooth and stable operation of production equipment.