Published: October 26, 2023

Raymond Mills, particularly those designed for processing non-metallic minerals like calcite, are robust and reliable workhorses in many industrial grinding operations. However, like any complex mechanical system, they can encounter operational issues that affect output, fineness, energy consumption, and equipment longevity. This comprehensive guide, drawing from Liming Heavy Industry's decades of engineering and manufacturing expertise, outlines common problems encountered with calcite Raymond Mills, their root causes, and practical, step-by-step solutions. By understanding these troubleshooting principles, operators can minimize downtime, maintain consistent product quality, and ensure the mill operates at its designed efficiency. The focus will be on the core grinding mechanism, air flow system, and feeding components, which are critical to the performance of any Raymond-type mill processing materials like calcite to finenesses between 44μm and 613μm.

1. Insufficient Output or Low Production Capacity

A sudden or gradual drop in mill output is a frequent concern. The root cause often lies in the feed system or grinding element wear.

• Clogged Feeder: Check the vibrating feeder or variable-frequency belt feeder for blockages. Calcite feed with high moisture content (exceeding the recommended 6% humidity) or oversized lumps can cause bridging and irregular feed. Ensure the crusher (e.g., jaw crusher) preceding the mill is correctly set to provide the specified 15-25mm input size.
• Worn Grinding Rollers and Grinding Ring: This is the most common mechanical cause. After prolonged operation, the grinding surfaces wear down, reducing the effective grinding force and efficiency. Inspect these components regularly. Liming's Raymond Mills are designed for easy replacement of these wear parts to restore original capacity.
• Incorrect Blower Airflow: The Raymond mill is a closed-circuit air system. If the air volume from the blower is too low, it cannot carry sufficient ground material to the classifier, causing recirculation and over-grinding within the grinding chamber, which hampers throughput. Verify the blower settings and check for leaks in the piping or cyclone system.

2. Excessive Vibration and Abnormal Noise

Unusual vibration and noise typically indicate mechanical imbalance, looseness, or failure.

• Unbalanced Grinding Roller: Severe or uneven wear on a grinding roller can create imbalance. Stop the mill immediately and inspect all rollers. Replace them in sets to maintain balance.
• Loose Foundation Bolts or Fasteners: Constant vibration can loosen anchor bolts and structural fasteners. Conduct regular checks and tighten all bolts according to the specified torque.
• Foreign Objects in the Grinding Chamber: Metal or other hard debris entering with the feed can cause severe impact noise and damage. Ensure the magnetic separator or other protective devices upstream are functioning correctly.
• Bearing Failure: Worn-out or damaged bearings in the main shaft or roller assemblies will produce a grinding or rumbling noise. Monitor bearing temperature and lubricate them strictly as per the maintenance schedule.

3. Poor Product Fineness or Inconsistent Particle Size

When the product fails to meet the target fineness range or shows high variability, the issue usually resides with the classifier or air system.

• Classifier Speed Malfunction: The rotating classifier (separator) is crucial for controlling particle size. If its speed is unstable or not correctly adjusted for the desired fineness, oversized particles will pass through. Check the classifier motor, variable frequency drive, and blades for damage or wear.
• Worn Classifier Blades: Like grinding parts, classifier blades wear over time, reducing their separation efficiency. Inspect and replace them as needed.
• Air Leakage in the System: Leaks in pipes, housing, or the dust collector (like the pulse dust collector) disrupt the designed air flow path. This disruption affects the material conveying velocity and classification accuracy, leading to poor cut-point. Perform a pressure decay test or use smoke to identify leaks.
• Inconsistent Feed Rate: A fluctuating feed rate causes the material-to-air ratio in the grinding chamber to vary, which directly impacts grinding efficiency and classifier loading, resulting in an inconsistent product. Calibrate and maintain the feeding device to ensure a steady, uniform flow.

4. High Energy Consumption

Rising power costs without a corresponding increase in output signal inefficiency.

• Over-grinding Due to Incorrect Settings: If the classifier speed is set too high (finer target) or the feed rate is too low, the mill grinds material repeatedly, consuming excess power. Optimize the balance between feed rate, classifier speed, and blower power.
• Increased Grinding Resistance from Worn Parts: Ironically, severely worn rollers and rings can also increase energy use. As the grinding profile changes, more power is required to achieve the same size reduction. Timely replacement is key to energy efficiency.
• High System Resistance: Blockages in the piping, a clogged bag filter in the pulse dust collector, or a dirty cyclone increase the system's back pressure. The main blower then works harder to maintain airflow, drawing more power. Regularly clean the entire air circuit.

5. Excessive Dust Emission or Material Leakage

This is both an operational and environmental issue, often related to the sealing and dust collection system.

• Pulse Dust Collector Malfunction: The pulse-jet dust collector is vital for meeting environmental standards. If its solenoid valves, timer, or compressed air supply fails, bags will not be cleaned properly, causing high pressure drop and potential bag rupture or dust emission. Check the pulsing sequence and compressed air quality.
• Poor Sealing at Access Points: Leakage around inspection doors, shaft seals, or pipe flanges allows fine calcite powder to escape. Replace worn gaskets and sealing felts regularly.
• Overloaded Dust Collector: If the mill is operated above its designed capacity or if the feed moisture is too low generating excessive fines, the dust collector may be overloaded. Ensure operation is within the mill's specified parameters.

Preventive Maintenance: The Key to Reliability

Adhering to a strict preventive maintenance schedule is the most effective way to avoid the problems listed above. This includes daily checks of lubrication, vibration, and unusual sounds; weekly inspection of key fasteners and the feeding system; and scheduled shutdowns for thorough internal inspection of wear parts, classifier blades, and the integrity of the air system. Using genuine Liming Heavy Industry spare parts ensures dimensional accuracy, material integrity, and optimal performance, preserving the mill's design efficiency and longevity.

Frequently Asked Questions (FAQs)

1. Q: How often should I replace the grinding rollers and ring in my calcite Raymond mill?
   A: There is no fixed timeline; it depends on material abrasiveness, operating hours, and desired fineness. Monitor output and power consumption. A steady decline in capacity or a rise in energy use typically indicates it's time for inspection and likely replacement.
2. Q: Can I use my Raymond mill to grind material with moisture content above 6%?
   A: It is not recommended. Moisture above this level can cause feed clogging, material adhesion inside the mill (packing), and reduced classification efficiency. For moist calcite, consider a system with integrated drying like Liming's LM Vertical Roller Mill.
3. Q: What causes the pressure in the grinding chamber to become unstable?
   A: Unstable pressure is often linked to a fluctuating feed rate, a blockage in the outlet pipe or cyclone, or an issue with the air blower's operation. Check for consistent feed and inspect the air circuit for obstructions.
4. Q: Why is there a sudden metallic screeching sound during operation?
   A: Stop the mill immediately. This usually indicates direct metal-to-metal contact, likely due to a broken part, a severely worn roller scraping the ring, or a failed bearing. Immediate inspection is required to prevent catastrophic damage.
5. Q: How can I improve the whiteness of my ground calcite product?
   A> Ensure the grinding chamber and all contact parts are clean and free from contamination from previous materials. Also, check that wear parts are made of the appropriate material to minimize iron contamination. For ultra-high whiteness, consider mills with ceramic or special alloy linings.