A speed reducer is a commonly used transmission device for reducing speed between a driving component and a working machine, mainly composed of gear transmission and other mechanisms. To enhance everyone's understanding of speed reducers, this article will introduce the causes of speed reducer oil leakage and countermeasures for fixing it. If you are interested in speed reducers, please continue reading.
I. Analysis of the causes of oil leakage in the speed reducer
1. Pressure difference between inside and outside the reducer: During the operation of the reducer, the friction of the moving parts generates heat and is affected by the ambient temperature, causing the reducer temperature to rise. If there is no vent or the vent is blocked, the internal pressure will gradually increase. The higher the internal temperature, the greater the pressure difference with the outside. Under the action of the pressure difference, the lubricating oil will leak out from the gaps.
2. The reducer's structural design is unreasonable.
1) If the inspection hole cover plate is too thin, it is prone to deformation after tightening the bolts, resulting in uneven mating surfaces and oil leakage from the contact gaps;
2) If the castings are not annealed or aged during the manufacturing process of the speed reducer, and internal stress is not relieved, deformation will inevitably occur, resulting in gaps and leakage;
3) The housing lacks an oil return groove, causing lubricating oil to accumulate at the shaft seal, end cover, and mating surfaces. Under pressure differential, this oil leaks outwards from the gaps.
4) Inadequate shaft seal design. Early reducers often used oil groove and felt ring shaft seal structures. During assembly, the felt was compressed and deformed to seal the gaps at the mating surfaces. If the contact between the journal and the seal was not ideal, the seal would fail quickly due to the poor compensation performance of the felt. Although there were oil return holes in the oil groove, they were easily clogged, making it difficult for the oil return function to be effective.
3. Excessive oil filling: During the operation of the reducer, the oil sump is agitated and the lubricating oil splashes everywhere inside the machine. If too much oil is added, a large amount of lubricating oil will accumulate in the shaft seal, mating surfaces, etc., leading to leakage.
4. Improper maintenance process: During equipment maintenance, oil leakage may also occur due to incomplete cleaning of dirt on the mating surfaces, improper selection of sealant, reversed installation of sealant, or failure to replace sealant in a timely manner.
II. Countermeasures for Controlling Oil Leaks in Gearboxes
1. Improved Vent Cap and Inspection Hole Cover: One of the main causes of oil leakage is that the internal pressure of the reducer is greater than the external atmospheric pressure. If the internal and external pressures are balanced, oil leakage can be prevented. Although reducers have vent caps, the vent holes are too small and easily clogged by coal dust and oil. Furthermore, each time oil is added, the inspection hole cover must be opened, increasing the possibility of leakage and causing leaks in previously leak-free areas. Therefore, an oil cup-type vent cap was manufactured, and the original thin inspection hole cover was changed to 6 mm thick. The oil cup-type vent cap is welded to the cover plate, with a 6 mm diameter vent hole for easy ventilation and pressure equalization. Moreover, oil is added through the oil cup, eliminating the need to open the inspection hole cover and reducing the chance of leakage.
2. Smooth Flow: To prevent excess lubricating oil thrown onto the bearing by the gears from accumulating at the shaft seal, the excess lubricating oil must flow back to the oil sump in a certain direction, i.e., smooth flow. The specific method is to open an oil return groove inclined inward in the center of the lower bearing shell of the bearing housing, and at the same time, open a notch at the straight opening of the end cover, with the notch facing the oil return groove. In this way, excess lubricating oil flows back to the oil sump through the notch and the oil return groove.
3. Improve shaft seal structure
1) Improvement of shaft seal for reducers with a half-shaft output shaft: The output shaft of reducers in most equipment such as belt conveyors, screw unloaders, and impeller feeders is a half-shaft, making modification relatively convenient. Disassemble the reducer, remove the coupling, and take out the reducer shaft seal end cover. Machine a groove on the outside of the original end cover according to the dimensions of the matching skeleton oil seal, and install the skeleton oil seal with the spring side facing inwards. During reassembly, if the end cover is more than 35 mm from the inner end face of the coupling, a spare oil seal can be installed on the shaft outside the end cover. If the oil seal fails, the damaged oil seal can be removed, and the spare oil seal can be pushed into the end cover, thus saving the time-consuming and laborious process of disassembling the reducer and removing the coupling.
2) Improvement of shaft seal for reducers with a single-shaft output shaft: Reducers with a single-shaft drive lack a coupling on the output shaft. Modifying it according to the 2.3.1 scheme would be too labor-intensive and impractical. To reduce workload and simplify the installation procedure, a split-type end cover was designed, and an open-type oil seal was tested. A groove is machined on the outer side of the split-type end cover. When installing the oil seal, first remove the spring, then saw the oil seal into an open shape. Place the oil seal onto the shaft through the opening, use adhesive to align the openings, with the opening facing upwards, then install the spring and push in the end cover.
4. Use new sealing materials: For leaks at the static sealing points of the reducer, new polymer repair materials can be used for sealing. If oil leaks at the static sealing points during reducer operation, surface engineering technology oil surface emergency repair agent-polymer 25551 and 90T composite repair material can be used to seal the leak, thereby eliminating the oil leakage.
5. Strictly follow the maintenance procedures: When overhauling the reducer, strictly follow the procedure specifications. The oil seal must not be installed backwards, the lip must not be damaged, the outer edge must not be deformed, the spring must not fall off, the mating surfaces must be cleaned, the sealant must be applied evenly, and the amount of oil added must not exceed the mark on the dipstick.
6. Wiping: The static sealing points of the reducer can generally be made leak-free through treatment. However, due to reasons such as aging of the seals, poor quality, improper assembly, and high surface roughness of the shaft, some dynamic sealing points may still have slight leakage. Due to the poor working environment, coal dust sticks to the shaft, making it look oily. Therefore, it is necessary to wipe the oil stains on the shaft after the equipment stops running.
