Method for Adjusting Mesh Size with the Raymond Mill Analyzer （3 big steps）

This is a very specific operational question. In the Raymond mill (pendulum grinding mill) system, the analyzer (also known as the classifier or separator) is the core component controlling the fineness of the finished product. Adjusting the speed of the analyzer is the primary and most precise method for changing the product "mesh size" (particle size).

The following details the steps, principles, and precautions for adjusting the analyzer to achieve the target mesh size.

I. Core Principle

The analyzer is a rotor composed of blades. Its working principle is:

1. Centrifugal Force vs. Aerodynamic Drag: When the analyzer rotates at high speed, the blades generate centrifugal force. Coarser particles experience greater centrifugal force than aerodynamic drag (from the fan suction), are thrown against the casing wall, fall back down, and return to the grinding chamber for re-grinding.

2. Fine Powder Passage: Particles meeting the fineness requirement experience greater aerodynamic drag than centrifugal force. They can pass through the gaps between the blades and are carried into the cyclone collector to become the finished product.

3. Speed Controls Particle Size: The higher the speed, the greater the centrifugal force generated, allowing only finer particles to pass, resulting in a finer product (higher mesh number). Conversely, lowering the speed results in a coarser product (lower mesh number).

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II. Standard Method for Mesh Size Adjustment (Using a Common Raymond Mill as Example)

1. Step One: Preparation

• Define the Target: Determine the specific mesh size to be produced (e.g., 200 mesh, 325 mesh).

• Equipment Status: Ensure the mill is under no load or has been shut down. Safety first; manual adjustment during operation is strictly prohibited.

• Tool Preparation: Prepare necessary tools such as wrenches, a tachometer (or rely on the VFD display).

• Consult Reference Data: Review the equipment manual or the plant's empirical data sheet to find the recommended analyzer speed range corresponding to the target mesh size. This is the most important reference baseline.

2. Step Two: Mechanical Speed Adjustment (Traditional Method - Via Pulley Change)

• Shutdown and Power Off: Completely stop the main unit and fan. Implement lockout/tagout to ensure safety.

• Remove the Belt Guard: Locate the pulley connecting the analyzer motor to the analyzer main shaft.

• Change the Pulley:

  • For Finer Mesh (Increase Speed): Replace the drive pulley on the motor shaft with a larger diameter one, OR replace the driven pulley on the analyzer shaft with a smaller diameter one. This increases the drive ratio and the speed of the analyzer.

  • For Coarser Mesh (Decrease Speed): Do the opposite. Decrease the drive pulley diameter or increase the driven pulley diameter.

• Install and Check: After changing, reinstall the belt, adjust the belt tension, and reinstall the guard.

• Start and Test: Start under no load. Measure the actual speed with a tachometer to see if it falls within the expected range. Then conduct a test run with material feed and sample the product to check fineness.

3. Step Three: VFD Speed Adjustment (Modern, Recommended Method)

• Parameter Adjustment: No need to shut down (but it's recommended under low load). Directly adjust the set frequency (Hz) on the VFD operation panel for the analyzer motor.

  • Increase Frequency (e.g., from 35 Hz to 40 Hz) → Motor and analyzer speed increase → Product becomes finer.

  • Decrease Frequency (e.g., from 40 Hz to 35 Hz) → Motor and analyzer speed decrease → Product becomes coarser.

• Fine-tuning and Verification: The system responds immediately after adjustment. Take a sample of the finished product for sieve analysis or laser particle size analysis. Perform fine adjustments to the frequency (e.g., 0.5-1 Hz per adjustment) based on the results until the target mesh size is achieved.

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III. Key Points for System-wide Coordinated Adjustment (Ensuring Stability and Output)

Simply adjusting the analyzer speed is sometimes insufficient. The entire system must work in coordination to achieve optimal output and stable fineness.

1. Main Unit (Grinding Roll) Pressure:

   • When a finer mesh is required, appropriately increase the pressure of the grinding rolls against the grinding ring to provide sufficient crushing force to generate more fine powder.

   • When a coarser mesh is acceptable, pressure can be appropriately reduced to increase output and reduce energy consumption.

2. Fan Airflow:

   • The fan provides the airflow that transports the powder upwards to the analyzer.

   • Excessive Airflow: Can carry overly coarse particles into the analyzer. Even with high analyzer speed, this may cause coarse particles to mix into the final product, widening the particle size distribution.

   • Insufficient Airflow: Qualified fine powder cannot be carried away promptly, leading to reduced output and recirculation within the grinding chamber, increasing energy consumption.

   • Recommendation: After adjusting the analyzer speed, also fine-tune the fan damper or the fan VFD to match the airflow to the current analyzer operating condition, ensuring smooth material transport and clear classification.

3. Feed Rate (Uniformity and Stability):

• A uniform and continuous feed must be maintained. Excessive or sudden feeding can overwhelm the classifier's capacity, leading to "coarse particle breakthrough" (product becomes coarser).

• After adjusting the target mesh size, a suitable, stable feed speed should be re-set according to the new operating condition (output typically decreases when grinding finer).

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IV. Operational Summary Mnemonic

• To make it finer: Increase speed, Add pressure, Stabilize feed, Adjust airflow.

• To make it coarser: Decrease speed, Reduce pressure, Check for wear, Prevent air leaks.

Safety is always paramount when using a Raymond mill. Any mechanical adjustments must be performed with the equipment completely shut down, powered off, and proper safety isolation in place. For modern mills equipped with VFDs, prioritize using the VFD for online, stepless speed adjustment. This is the safest and most efficient method for adjusting mesh size.