Vertical Mill

Grinding Disc: A large cast steel (ZG35CrMo) disc with a diameter of 1.5–5 m, featuring a groove or step structure on the surface to drive materials to the edge. It is mounted on the main shaft and rotated by the motor.

Grinding Rollers: 2–4 rollers (depending on the model) made of high-chromium cast iron (Cr20–25) or alloy steel, with a diameter of 0.5–2 m. They are installed above the grinding disc, pressing materials under hydraulic pressure (10–30 MPa) to realize grinding.

Main Shaft: A forged alloy steel (42CrMo) shaft connecting the grinding disc and the motor, with a diameter of 200–600 mm. It transmits torque and bears the weight of the grinding disc and materials.

Frame: A welded or cast steel structure supporting all components, including the upper frame (housing the classifier) and lower frame (supporting the main shaft and motor).

Feeding Device: A screw feeder or belt conveyor that feeds materials into the grinding disc at a stable rate. It is equipped with a material level sensor to control the feeding amount.

Hot Air System: Includes a hot air furnace or waste gas pipeline, which introduces hot air (150–350°C) into the mill. The hot air dries materials (moisture content ≤15%) and carries powder to the classifier.

Classifier: A dynamic rotor classifier installed at the top of the mill, consisting of a rotating impeller and a stationary guide vane. It separates fine and coarse particles by centrifugal force: fine particles pass through the impeller gap, while coarse particles are thrown back. The classifier speed (1000–3000 rpm) is adjustable to control product fineness.

Hydraulic Cylinders: 2–4 cylinders that provide pressure to the grinding rollers, adjusting the grinding force according to material hardness. The system is equipped with a pressure relief valve for overload protection.

Lifting Device: Hydraulic cylinders for lifting the grinding rollers during maintenance, allowing easy access to the grinding disc.

Motor: A high-power asynchronous motor (160–1000 kW) connected to the main shaft via a reducer (planetary or bevel gear reducer) to reduce speed and increase torque. The grinding disc speed is 30–100 rpm.

Cyclone Separator: Collects most of the fine powder from the air flow, with a collection efficiency of ≥95%.

Bag Filter: Further captures fine dust in the exhaust gas to meet environmental standards (emission concentration ≤30 mg/m³).

Pattern Making: A full-scale wooden or metal pattern is made with a shrinkage allowance of 1.2–1.5%, including groove details.

Molding: Resin-bonded sand molds are used, with the cavity coated with a zirconium-based refractory coating to improve surface quality.

Melting and Pouring: Cast steel is melted in an arc furnace at 1520–1560°C, then poured into the mold at 1480–1520°C. The pouring process is controlled to avoid porosity and cold shut defects.

Heat Treatment: Normalization at 880–920°C (air-cooled) followed by tempering at 550–600°C to relieve internal stress and achieve hardness HB 200–240.

Casting: Foam patterns are used for sand casting. Molten iron (1450–1500°C) with chromium and molybdenum additives is poured into the mold.

Heat Treatment: Solution annealing at 980–1020°C (air-cooled) and tempering at 280–320°C to achieve hardness HRC 60–65 and wear resistance.

Forging: Steel billets are heated to 1150–1200°C, then forged into a stepped shaft shape through upsetting and drawing to align grain flow.

Heat Treatment: Quenching at 840–860°C (oil-cooled) and tempering at 560–600°C to reach HRC 28–32, with tensile strength ≥900 MPa.

Rough Machining: CNC milling shapes the disc surface and grooves, leaving a 2–3 mm allowance. Boring machines process the central hole for the main shaft.

Precision Machining: Grinding the disc surface to flatness ≤0.1 mm/m and surface roughness Ra1.6 μm. Groove dimensions are finished to ensure uniform material movement.

Turning: CNC lathe processes the outer circle and roller shaft, leaving 0.5–1 mm grinding allowance.

Grinding: The roller surface is ground to a cylindrical shape with IT6 tolerance and Ra0.8 μm roughness, ensuring even contact with the grinding disc.

Turning: CNC lathe processes steps, keyways, and threads, leaving 0.3–0.5 mm grinding allowance.

Grinding: Journal surfaces are ground to IT5 tolerance and Ra0.4 μm roughness, ensuring coaxiality ≤0.01 mm for stable rotation.

Welding and Stress Relief: Welded frames are annealed at 600–650°C to eliminate stress.

Milling: CNC milling machines process mounting surfaces for the main shaft, grinding rollers, and classifier, ensuring flatness ≤0.15 mm/m.

Material Testing:

Spectrometric analysis verifies chemical composition (e.g., Cr content in grinding rollers).

Tensile and impact tests confirm mechanical properties (e.g., main shaft impact energy ≥60 J/cm²).

Dimensional Inspection:

CMM checks critical dimensions: grinding disc flatness, roller roundness, and main shaft coaxiality.

Laser scanning validates the classifier impeller profile to ensure accurate classification.

Non-Destructive Testing (NDT):

UT detects internal defects in the grinding disc and main shaft (defects >φ3 mm rejected).

MPT inspects grinding rollers and shafts for surface cracks.

Performance Testing:

Dynamic Balancing: The grinding disc and classifier rotor are balanced to G2.5 grade (vibration ≤2.5 mm/s).

Test Run: Empty run for 4 hours to check bearing temperature (≤70°C) and noise (≤85 dB). Load test with limestone for 12 hours to verify output (50–500 t/h), product fineness, and energy consumption.

Foundation Preparation: Reinforced concrete foundation (C30 grade) with embedded bolts, cured for 28 days. Levelness tolerance is ≤0.1 mm/m.

Lower Frame Installation: Hoisted to the foundation, leveled with shims, and anchor bolts tightened to 70% torque.

Main Shaft and Grinding Disc Assembly: Main shaft is installed in the lower frame’s bearing seats, grinding disc mounted on the shaft, and aligned to ensure runout ≤0.05 mm.

Grinding Rollers Installation: Rollers are lifted into position, hydraulic cylinders connected, and initial pressure (5–10 MPa) applied for alignment.

Classifier and Feeding Device Mounting: Classifier is bolted to the upper frame, with impeller clearance adjusted to 1–3 mm. Feeding device is installed and aligned with the grinding disc center.

Hydraulic and Electrical System Connection: Pipes are flushed (NAS 8 cleanliness), and wiring is checked for correct phase sequence. The PLC control system is programmed with grinding parameters.

Commissioning:

Hot air system is tested to ensure temperature and flow stability.

Empty run for 2 hours, then gradual feeding to 100% load. Classifier speed is adjusted to achieve target fineness.

All systems are monitored for 24 hours to confirm stable operation, with no leaks or abnormal vibrations.