1. Structure principle of HVM type vertical mill
The motor drives the gear box which, in turn, drives the mill table to rotate. Material is fed into the center of the mill table from the rotary feeder. Under centrifugal force, the material moves towards the edge of the mill table and gets into the grinding roller table where it is crushed by extrusion, grinding and shearing under roller pressure. Hot air ejects evenly from the wind ring around the mill table at high speed and the ground material is blown up by the high-speed air flow at the wind ring. On the one hand, coarse material is blown back to the mill table to be ground again, on the other hand, suspended material is dried and the fine powder is brought by hot air into the separator to be graded. The qualified fine material goes out of the mill with the air flow, and is collected by a dust collector as product. The unqualified coarse powder falls back to the mill table under the action of the separator blade, and is ground again with the newly-fed material, and so on, until the whole grinding process is completed.
The driving system of HVM type vertical mill adopts the structure of direct connection between motor and gear box through coupling, with high driving efficiency and low failure rate. The gear box is a mature and reliable product manufactured by specialized manufacturer, which does not need to be disassembled and repaired within at least five years if it is normally used. Well sealed, without oil leakage, it only needs daily maintenance, and spare parts can be easily replaced.
The drive system of Raymond Mill adopts the structure of motor and gear box driven by belt, with low driving efficiency and high failure rate. Designed and manufactured independently by Raymond Mill manufacturers (in order to reduce costs), the gear box is poorly sealed, with frequent oil leakage and failure maintenance, and inconveniently maintained since it is generally arranged in pits. In addition, spare parts heavily depend on the original equipment manufacturers.
Comparison between HVM type vertical mill and Raymond Mill in grinding principle and structure of grinding parts
The grinding principle of HVM type vertical mill is to grind material through material bed. With a stable material layer between roller and mill table, material is crushed as the mill table rotates and the roller rolls (through the supporting independent hydraulic loading system). As there is no direct contact between mill table and roller, the grinding method is efficient, no open fire, low grinding wear, and effectively secure for flammable and explosive materials. As main grinding parts, roll sleeve and grinding disc liner are made of high chromium multi-element alloy materials, with service life of more than 8000 hours. Due to modular design, roll sleeve and grinding disc liner can be easily replaced and maintained.
The grinding pressure of roller is pressurized by liquid + gas. Roller pressure and lifting can be adjusted by remote control or manual operation on site. Mill hydraulic system includes hydraulic system, cylinder, accumulator and pipeline. Hydraulic pressure can be realized by cylinder and accumulator plays a cushioning role.
Roller sleeves are reversible; rollers can be turned out of the grinding chamber simultaneously or respectively with the hydraulic system, convenient for repair and maintenance;
The grinding principle of Raymond Mill is that the roller is tightly rolled on the grinding ring under the action of centrifugal force, and the material is shoveled and sent by the spade to the middle of the roller and the grinding ring and crushed into powder under the action of grinding pressure. It can be seen that there is no independent hydraulic system and the material is crushed by the disorderly collision between the roller and the grinding ring under the action of centrifugal force, resulting in low grinding efficiency. The inevitably direct collision between the roller and the grinding ring not only produces a lot of useless work, but also causes unnecessary wear and tear of grinding parts, so that grinding parts need to be replaced and maintained in 2-3 months. In addition, the direct collision between metal grinding parts can easily produce open fire, and explosion accidents are likely to occur when flammable and explosive materials are ground, with great potential safety hazards. The grinding parts of Raymond Mill are rollers and rings, made of manganese steel, which are frequently replaced (at least twice a year) due to poor wear resistance and difficult to be maintained.
HVM type vertical mill adopts short-circuit-proof dynamic-static separator. Designed as a squirrel cage, the separator rotor is added with static blade and recycling cone, which is not only convenient to control the fineness of the product, but also can make the unqualified material fall into the center of the mill table to be ground again through the cone. When the moving blade rotates, the upper part produces some certain positive pressure, which forces the dust-bearing gas to move through the separator blade, thus making the mill product finer and the fine adjustment range wider. The emphasis should be to select the powder area and control particle movement so as to limit the irregular movement in the mill. Through adjustment of the spacing between the dynamic rotor and the guide blade, the rotational speed of the dynamic rotor, the number and geometric size of the guide blade and arrangement of air seal on the rotor, large particles can be effectively prevented from entering the finished product, thus reducing the cycle load and improving the grinding efficiency. For flammable and explosive materials, the separator is installed with explosion-proof valves to release explosion in time.
The powder separation analyzer of Raymond Mill adopts simple dynamic powder separation structure, which has low powder separation efficiency, high resistance and small fine adjustment range.
Comparison between HVM type vertical mill and Raymond Mill in frame and mill body
The frame of HVM type vertical mill is welded with 18-20mm steel plate, which is durable and can be repaired. The frame of Raymond Mill is mostly cast with low-cost nodular cast iron, which is not durable. Once damaged, it cannot be repaired due to poor welding performance.
Conclusion
Through a large number of practical engineering cases, it is proved that vertical mill has the following advantages:
(1) High output and low power consumption. Vertical mill adopts extrusion and grinding, with the lowest grinding energy consumption and the highest grinding efficiency. The ground material has good fineness, uniform particle size and large output.
(2) Small medium wear, high product purity and long service life of vulnerable parts. This is because the roller sleeve does not contact directly the grinding disc liner, and high chromium multi-alloy wear-resisting material is adopted as wear-resisting material, and the service life of vulnerable parts is more than 3-4 times that of Raymond Mill.
(3) Low noise, no dust pollution. The system works at normal pressure without direct metal collision, and the recovery rate of finished products is almost 100%, which saves environmental protection costs.
(4) The fineness of the product is well adjusted. The vertical mill system can adjust the fineness of the product between 80 and 400 by means of dynamic-static powder separator, with slight over-grinding and high efficiency.
(5) There is no need to manually operate and maintain the equipment and production can be automatically and remotely controlled, with large output, low power consumption, good energy-saving effect, thus greatly reducing subsequent production costs.
(6) Due to limited capacity of Raymond Mill, large-scale production requires operation of several Raymond Mills at the same time. In this way, it requires a large amount of land and increase in investment in civil engineering and labor cost as production personnel are required for management. Even though the cost per Raymond Mill is lower than that per vertical mill, the accompanying investment cost and subsequent production and maintenance cost for Raymond Mill are much higher than that for vertical mill.
Ultra-fine powder processing industry belongs to labor-intensive, low value-added and scale-effective industry. Therefore, the key is to select reliable equipment, which is advanced and applicable, environmentally friendly, stable and durable, low in failure rate and easy to maintain, reduce consumption and save costs. Because of novel and unique grinding principle, reasonable and reliable structure and high wear-resistance alloy material, efficient, energy saving and environmentally friendly vertical mill is superior to other grinding equipment, such as Raymond Mill and ball grinding mill.
