Vertical mill application:
Vertical grinding mills are energy-saving, versatile new equipment for powder grinding, suitable for industries such as cement, power, chemicals, and non-metallic minerals. They are particularly used in cement plants for grinding black raw materials and in the preparation of white cement raw materials. Known for their high efficiency, low electricity consumption, large drying capacity, easily adjustable product fineness, uniform particle size, easy-to-control chemical composition, low noise, minimal metal wear, dust-free operation, simple system process flow, small land occupation, and cost-effectiveness, they are widely applied in the cement and non-metallic mineral industries both domestically and internationally.
Primary Structure and Functions:
The vertical grinding mills of RHM and PRM models are mainly composed of separator, grinding roller, grinding disc, pressure device, reducer, motor, and housing, etc.
The separator is a critical component determining the fineness of the product, consisting of a variable-speed transmission, wheels, air guide vanes, housing, coarse powder discharge cone, and outlet, similar in working principle to the classifier.
The grinding roller is the main component for material crushing and grinding, with two pairs of grinding rollers installed inside. Each pair is mounted on the same shaft and rotates at different speeds.
The millstone is mounted on the output shaft of the reducer, with the upper part serving as a material bed, featuring annular grooves.
The pressure unit is a component that provides crushing pressure, consisting of a high-pressure oil station, hydraulic cylinder rod, accumulator, etc., and can apply sufficient pressure to the grinding roller to crush the material.
The reducer, in addition to transmitting power, also bears the weight and grinding force of the millstone.
Operating Principle:
The motor drives the grinding wheel through a reducer, while hot air enters the mill from the intake. Material falls onto the center of the grinding wheel through the feed opening, and due to centrifugal force, it moves towards the edge of the wheel. As it passes through the ring grooves on the wheel, it is crushed by the roller, then continues to move towards the edge until it's picked up by the air flow at the wind ring, with larger particles falling back onto the wheel for regrinding. As the material passes through the separator, under the action of guide vanes and the rotor, coarse material falls onto the wheel, while fine powder is carried out with the air flow and collected in the system's dust collection device, which is the final product. The material is dried during contact with the gas to reach the required moisture content of the product. By adjusting the angle of the guide vanes and the speed of the separator rotor, products of different fineness can be obtained.
Compared to ball mills, vertical mills have the following characteristics:
High powder grinding efficiency; vertical mills use the powder bed grinding principle to grind materials, with low energy consumption. The electrical consumption of the powder grinding system is 20-30% lower than that of the ball mill system, and the energy-saving effect becomes more pronounced with the increase of raw material moisture.
2. Large drying capacity; vertical mills use gas to convey materials. When grinding materials with high moisture content, the inlet air temperature can be controlled to achieve the required moisture in the product. The vertical mill can dry materials with up to 12-15% moisture content, whereas ball mills can only dry materials with -4% moisture content.
3. The product's chemical composition is stable with uniform particle grading. Since the material stays in the vertical mill for only 2-3 minutes, compared to 15-20 minutes in a ball mill, the chemical composition of the product produced by the vertical mill can be quickly measured and corrected. The fluctuation in product chemical composition is minimal, which is beneficial for homogenization. Additionally, qualified products in the vertical mill can be separated out in a timely manner, avoiding over-grinding. The fineness of the product can be rapidly adjusted by changing the speed of the separation rotor, ensuring uniform particle size, which is advantageous for calcination.
4. The process is simple with a small building area and minimal space requirement. The vertical mill includes a separator, eliminating the need for a classifier and elevator. The dusty gas from the mill can be directly fed into a dust collector or a baghouse, where it is collected as the final product. Thus, the process is straightforward, the layout is compact, and the building area is only 50-60% of the ball mill system.
5. Low noise, minimal dust, and a clean operating environment. The vertical mill operates with the grinding roller and grinding disc not directly contacting each other, eliminating the metallic impact sounds of steel balls colliding in a ball mill or hitting the lining plates. Due to the reduced noise, it is approximately 20-25 decibels quieter than a ball mill. Additionally, the vertical mill features a complete seal, and the system operates under negative pressure, resulting in less dust and a cleaner environment.
6. Low metal loss and high utilization rate; due to no direct metal contact during the vertical mill's operation, wear is minimal. The average wear per ton of product is typically 5-10 grams. For grinding cement raw materials, the lifespan of the roller sleeve and liner is over 8,000 hours, with an operational rate of up to 95%.
7. Economical in use.
