1. Introduction
In industrial applications, the dry ball mill remains a critical equipment for superfine grinding, particularly in processing materials like fly ash and slag into high-functional cement additives. However, operational challenges such as excessive bush temperature (瓦温) often lead to unplanned downtime, increased maintenance costs, and even equipment failure. This article explores structural optimizations applied to a Φ3.5 m × 17.5 m dry ball mill to address bush overheating, enhance operational efficiency, and extend equipment lifespan.
Key focus areas include:
- Feed device redesign
- Cylinder structure modification
- Bearing lubrication system upgrades
- Bush geometry improvements
- Enhanced sealing mechanisms
By systematically addressing heat generation and dissipation, these optimizations aim to reduce bush temperatures by 10–15°C, significantly improving the ball mill’s reliability.
2. Working Principle of the Dry Superfine Ball Mill
The dry ball mill operates via a dual sliding bearing support system with central drive transmission. Key components include:
- Feed device: Directs material into the rotating cylinder.
- Rotary section: Contains grinding media (balls) that pulverize material through cascading motion.
- Sliding bearings: Support the cylinder at both ends, utilizing hydrodynamic lubrication.
- Discharge system: Filters and ejects processed material.
During operation, friction between grinding media, materials, and liners generates significant heat. This heat transfers to the sliding bearings, elevating bush temperatures. Excessive temperatures (>70°C) compromise lubrication efficiency, accelerate wear, and risk thermal deformation.
3. Structural Optimization Strategies
3.1 Feed Device Optimization
Problem: Uncontrolled material entry caused localized friction and heat accumulation near the feed end.
Solution: A return plate was installed at the feed chute’s tail (Fig. 3 in PDF). This modification:
- Redirects material flow vertically, minimizing impact forces.
- Ensures uniform material distribution across the grinding chamber.
- Reduces direct grinding media-to-liner contact, lowering frictional heat.
Impact:
| Parameter | Before Optimization | After Optimization |
|---|---|---|
| Effective Grinding Length | 16.5 m | 17.2 m |
| Liner Wear Rate | 12 mm/month | 8 mm/month |
| Bush Temperature | 70°C | 65°C |
3.2 Cylinder Structure Optimization
Problem: Heat from discharged material accumulated near sliding bearings due to a conical discharge chute.
Solution: Replaced the conical chute with a straight cylindrical chute (Fig. 5 in PDF). Key advantages:
- Reduced heat retention at the discharge end.
- Improved material flow dynamics.
- Enhanced thermal isolation between the cylinder and bearings.
Thermal Analysis:
The heat flux (QQ) through the cylinder wall is governed by:Q=2πLk(Tin−Tout)ln(rout/rin)Q=ln(rout/rin)2πLk(Tin−Tout)
Where kk = thermal conductivity, LL = cylinder length, rr = radii.
Optimizing rout/rinrout/rin reduced heat transfer to bearings by 18%.
3.3 Bearing Lubrication System Optimization
Problem: Insufficient oil flow led to inadequate cooling and unstable hydrodynamic films.
Solution: Upgraded lubrication parameters:
| Parameter | Original | Optimized |
|---|---|---|
| Low-pressure Flow | 80 L/min | 125 L/min |
| High-pressure Flow | 2 × 2.5 L/min | 2 × 5 L/min |
| Oil Film Thickness | 0.2 mm | 0.26 mm |
Mechanism:
- Increased low-pressure flow enhances convective cooling.
- High-pressure flow sustains thicker oil films during operation, isolating heat.
Result: Bush temperature dropped from 70°C to 60°C under ambient temperatures >38°C.
3.4 Bush Structure Optimization
Problem: Traditional oil grooves relied on self-priming, causing inconsistent lubrication.
Solution: Redesigned bush with direct oil supply channels (Fig. 6 in PDF):
- Added axial oil grooves and inlet ports.
- Ensured continuous oil coverage on the bearing surface.
Performance Metrics:
| Metric | Before | After |
|---|---|---|
| Lubrication Coverage | 70% | 95% |
| Friction Coefficient | 0.008 | 0.005 |
| Heat Generation | 12 kW | 8 kW |
3.5 Sealing Structure Optimization
Problem: Single-layer rubber seals allowed oil leakage and dust ingress.
Solution: Implemented a dual-seal system (Fig. 7 in PDF):
- Rotating oil-retaining ring: Prevents splashing.
- Combined rubber-felt seal: Blocks contaminants.
Outcomes:
| Parameter | Improvement |
|---|---|
| Oil Leakage Rate | Reduced by 90% |
| Dust Ingress | Eliminated |
| Maintenance Intervals | Extended by 40% |
4. Application and Results
The optimized Φ3.5 m × 17.5 m dry ball mill demonstrated exceptional performance in a cement plant:
- Bush Temperature: Consistently maintained at 60–65°C (previously 70–75°C).
- Operational Uptime: Increased from 82% to 94%.
- Maintenance Costs: Reduced by 30% annually.
Case Study Data:
| Metric | 12-Month Average |
|---|---|
| Grinding Efficiency | 18.5 t/h |
| Energy Consumption | 32 kWh/t |
| Bush Replacement | 0 instances |
5. Conclusion
Through targeted structural optimizations, the dry ball mill achieves:
- Heat Reduction: Minimized frictional heat generation and improved thermal isolation.
- Enhanced Lubrication: Stable oil films and direct cooling mechanisms.
- Reliability: Robust sealing and reduced maintenance demands.
These advancements position the ball mill as a sustainable solution for superfine grinding, aligning with industrial demands for efficiency and cost-effectiveness.