In the deep processing of manganese products, particularly in the chemical combination (leaching) process of electrolytic manganese dioxide, we frequently employ ordinary worm gear reducers to stir the mineral slurry or solution. These reducers are well-suited for harsh conditions such as heavy dust, strong acid-base corrosion, and high ambient temperatures. They are simple to manufacture, low in cost, and easy to maintain and replace compared to other types of reducers, which is why many factories favor them.
Taking the agitator in the combination workshop of an electrolytic manganese dioxide plant as an example, the WHC360-37KW worm gear reducer is horizontally mounted. It delivers high output torque, excellent stirring effect, and high leaching efficiency, all at a low price. However, after a period of use, oil leakage occurs at the oil seals on both ends of the worm shaft. This not only wastes lubricating oil and deteriorates workplace hygiene but also leads to inadequate bearing lubrication due to the leakage, causing the reducer to fail and the agitator to stop, thereby disrupting the normal progress of the leaching process. Therefore, improving the oil seal structure is essential.
1. Operating Environment and Leakage Status of the Reducer
In the production of electrolytic manganese dioxide using the carbonate manganese ore method, the leaching process involves a vigorous chemical reaction in the leaching tank (or vat) among manganese carbonate powder, concentrated sulfuric acid, and electrolytic return waste liquor (at about 70°C). The main technical conditions are: leaching temperature ≥ 90°C, leaching time 4–6 h, neutralizer calcium oxide, neutralization time 0.5 h, and final pH 6–7.
The agitator reducer is typically installed at the center of the support frame above the leaching tank, running at approximately 40 r/min. It is exposed to manganese carbonate dust, lime dust, sulfuric acid mist, steam, and high temperatures—a very harsh environment. The high temperature and medium-speed rotation of the worm accelerate the wear and melting of the skeleton oil seal, leading to increasingly severe oil leakage over time.
The leakage point of the WHC360-37KW reducer is at the worm shaft seal on the gearbox housing. Under prolonged harsh conditions, the sealing performance deteriorates. Lubricating oil seeps from the gland cover on the worm input shaft and accumulates on the tank cover plate near the pulley.
2. Analysis of the Original Seal Structure at the Worm Shaft End
Upon disassembling a damaged reducer, we found that the original sealing mechanism at the worm shaft end employed a single ordinary skeleton oil seal. Both the bearing and the worm wheel were lubricated with liquid oil. On the worm shaft’s right side (pulley side), the fit was a transition fit with a linear speed of 5.5 m/s; on the left side was a cooling fan. Both ends used ordinary skeleton oil seals. During operation, the oil temperature inside the reducer housing was about 75°C, while the stirred slurry temperature was above 85°C, and the housing surface temperature was around 70°C.
In the original design, the gland cover had a recessed area serving as an oil collection groove. When the worm rotated, the bearing balls (rollers) flung oil into this groove. A single ordinary skeleton oil seal was installed at the center of the gland cover. However, ordinary skeleton oil seals cannot withstand the combination of high temperature, medium-speed rotation, and the corrosive environment in the leaching process. They easily wear out and melt, causing oil leakage. The lubricating oil inside the worm gear housing would flow through the bearing and the oil collection groove, leaking directly from the melted oil seal, depriving the bearing and worm wheel of proper lubrication, and eventually damaging them. Moreover, replacing the oil seal required disassembling the pulley (or cooling fan). Because of the tight fit and the large, heavy reducer, maintenance and replacement were labor-intensive and inconvenient.
3. Improved Seal Structure at the Worm Shaft End
Under high-temperature, medium-speed conditions, oil leakage from worm gear reducers can be categorized into two situations: dynamic leakage (during operation) and static leakage (when the reducer is stopped). The improved seal structure combines non-contact and contact seals to address both situations.
The improvement consists of three sealing stages:
- First seal (dynamic): A spiral seal (thread) machined on the gland cover. This non-contact seal uses the rotation of the worm shaft to drive the leaked hot oil back into the oil collection groove, simultaneously providing good lubrication to the bearing.
- Second seal (static): After shutdown, oil may still pass through the spiral seal section. A packing felt ring (made of PTFE fiber) provides a contact seal for static condition. This packing operates at temperatures 65–260°C, speeds 100–1750 r/min, and pressures 0–3 MPa.
- Third seal (static): A newly added oil seal end cover with a gasket, and a bidirectional dynamic oil seal (nitrile rubber, suitable for medium speed, temperature <150°C). The oil seal lip has symmetrical shallow patterns (e.g., triangular bumps) that create a dynamic pumping action in both rotational directions, returning any oil about to drip back into the groove.
The following table summarizes the three sealing stages and their characteristics:
| Seal Stage | Type | Component | Material | Operating Condition | Function |
|---|---|---|---|---|---|
| 1st | Non-contact (spiral) | Thread on gland cover | Steel (cover) + oil | Dynamic (rotation) | Pump oil back into groove |
| 2nd | Contact (packing) | Packing felt ring | PTFE fiber | Static (stop) & low speed | Block oil leakage |
| 3rd | Contact (oil seal) | Bidirectional dynamic oil seal | Nitrile rubber (NBR) | Static & low speed; temp. <150°C | Return oil via pumping action |
In the improved design, the thread on the gland cover (first seal) acts as a viscous pump. For a rotating shaft, the pumping effect can be described by the relationship between the thread geometry and the fluid viscosity. The axial leakage flow rate due to pressure difference is opposed by the thread’s pumping action. The net flow rate can be approximated by:
$$ Q_{\text{net}} = Q_{\text{leak}} – Q_{\text{pump}} $$
where \( Q_{\text{leak}} = \frac{\pi d h^3 \Delta p}{12 \mu L} \) (assuming laminar flow through a concentric annulus) and \( Q_{\text{pump}} = \frac{\pi d h v \tan \alpha}{2} \) for a single-start thread. Here \( d \) is the shaft diameter, \( h \) is the thread depth, \( \Delta p \) is the pressure difference, \( \mu \) is dynamic viscosity, \( L \) is the seal length, \( v \) is the linear speed of the worm, and \( \alpha \) is the thread helix angle. By designing the thread pitch and depth appropriately, the pumping action can prevent oil from escaping during rotation.
The second seal (PTFE felt ring) provides a backup when the shaft is stationary. The PTFE material resists high temperatures and chemical attack, which are common in the manganese leaching environment.
The third seal (bidirectional dynamic oil seal) further enhances static sealing. The nitrile rubber lip with symmetrical patterns generates a reverse pumping effect in both clockwise and counterclockwise directions. The pumping rate of such a seal can be expressed empirically as:
$$ Q_{\text{seal}} = K \cdot \frac{d^2 \omega \cdot \delta^3}{\mu} $$
where \( K \) is a factor depending on lip geometry, \( d \) is the shaft diameter, \( \omega \) is angular speed, \( \delta \) is the film thickness under the lip, and \( \mu \) is viscosity. At standstill (\(\omega=0\)), the seal prevents leakage by static contact.
The following table compares the original and improved designs:
| Parameter | Original Design | Improved Design |
|---|---|---|
| Number of seals | 1 (ordinary skeleton oil seal) | 3 (spiral + felt + bidirectional oil seal) |
| Dynamic sealing | Poor, seal melts/wears | Excellent, spiral returns oil |
| Static sealing | None (only dynamic seal) | Two contact seals |
| Maintenance | Must remove pulley/fan | Easy access to packing and oil seal without removing pulley |
| Oil consumption | ~0.5 kg/day | ~0.5 kg every 2 months |
| Service life of seal components | Short (weeks to months) | Long (months to years) |
4. Results and Discussion
After implementing the improved sealing scheme on the worm gear reducers in our plant, we observed significant benefits. The oil replenishment interval extended from daily (0.5 kg/day) to once every two months. The frequency of replacing skeleton oil seals and other parts dropped dramatically, along with repair man-hours. Because the new oil seal end cover is bolted to the gland cover (removable without disturbing the pulley), field replacement of the felt packing or the oil seal can be done quickly without heavy disassembly.
The combination of a non-contact spiral seal (dynamic) and two contact seals (static) effectively solves the oil leakage problem at the worm shaft ends of worm gears operating under high-temperature, medium-speed conditions. The spiral seal not only prevents oil escape but also provides continuous lubrication to the bearing, extending the bearing life. The PTFE felt ring withstands the corrosive environment and high temperature. The bidirectional oil seal provides a final barrier and self-pumping action that returns any leaked oil.
We also measured the temperature at the seal area before and after improvement. The improved design reduced local temperature by about 5–10°C due to better oil circulation and reduced friction. The following table summarizes the thermal data:
| Measurement Point | Original (°C) | Improved (°C) |
|---|---|---|
| Gearbox housing surface | 72 | 68 |
| Oil sump inside gearbox | 75 | 72 |
| Gland cover near seal | 78 | 70 |
Furthermore, the reliability of the agitator improved, reducing unplanned downtime. The overall production efficiency of the leaching process increased. The maintenance cost per reducer per year decreased by approximately 60%.
5. Conclusion
The oil leakage problem at the worm shaft ends of worm gear reducers used in manganese product processing has been effectively mitigated by adopting a three-stage sealing approach. The non-contact spiral seal addresses dynamic leakage during rotation, while the contact PTFE felt ring and bidirectional oil seal provide robust static sealing when the reducer is stopped. This combined sealing method is particularly suitable for the harsh conditions of high temperature, medium speed, and corrosive atmosphere that are typical in the manganese industry. The improved design not only reduces oil consumption and environmental contamination but also extends the service life of the worm gears and associated bearings. Implementing this simple yet effective modification on similar worm gear reducers can yield significant economic and operational benefits.
As we continue to optimize our equipment, we plan to further investigate the long-term wear behavior of the PTFE packing and the nitrile rubber oil seal under the actual plant environment. The success of this project demonstrates that thoughtful attention to sealing details can greatly improve the reliability of worm gears in demanding applications.