Common failure and prevention of cement grinding system equipment

Mill mill is divided into two kinds of tube mill and vertical mill, mainly introduced in this tubular mill. Tubular grinding is divided into double sliding shoe grinding and hollow shaft grinding according to the support mode, bearing alloy bearing. Double bearing for sliding shoe grinding, single bearing for hollow shaft grinding. The transmission mode has edge transmission, and now the large mill basically uses the center transmission mode of double shunt reducer. Cause analysis and preventive measures of mill failure
(1) a: hollow shaft mill, the structure of the hollow shaft mill is installed at both ends of the mill cylinder, the support is made of spherical sliding alloy bearings, the material enters the mill through the hollow shaft into the grinding cone, and the inlet cone is equipped with thermal insulation material. Since the cylinder and the hollow shaft of the mill are connected by bolts, and the mill is running under off-load load, when the mill is running, the steel ball and the material in the mill rotate, and form a certain Angle with the rotation of the mill, when the mill revolution is 15.3 revolutions, the ball’s departure Angle is about 50°.
The large ball on the surface does the dropping movement, and the small ball does the sliding movement, so as to crush and grind the material. Compared with the equipment, it is doing the uneven rotating movement. The end plate, lining plate, grate plate and other parts of the mill grind with the material, and the impact will cause different degrees of wear or fracture, and it will fall off after wearing to a certain degree. It causes a series of problems, such as the wear of silos or cylinders, the damage of compartments and so on, leading to equipment or quality accidents. At the same time, this movement has an impact on the hollow shaft reducer, etc. because the output force of the mill to the reducer is a variable, and not in the center, and the formation of torsional vibration, which also causes serious damage to the long-term operation of the hollow shaft, resulting in the fracture or crack of the hollow shaft, generally the fracture surface caused by torsional vibration into 45 ° Angle, fatigue caused by straight section, according to our years of observation, General hollow shaft mill hollow shaft crack at the earliest time more than 2 years, so the problem of spare parts should be paid attention to;
b: How to find and judge this problem? According to experience, there will be many manifestations before the problem of the middle empty axis, mainly include: The flange bolt breaks and breaks soon after replacement, the reasons for the fracture in addition to the above reasons, the foundation is not uniform settlement, the mill bearing shell and the mill rotation direction into the direction of wear, the reducer and the mill center line changes will cause this situation, so comprehensive inspection, judgment and timely adoption of measures; Example: A 3.8*13m mill in a factory used many hollow shafts and barrel bolts constantly broke, and broke again shortly after replacement. Later, the two flange end faces were welded to strengthen the reinforcement. After use, bolt breakage was reduced. Targeted to solve the problem, the above problems can be solved by measuring methods and adjusting the bearing seat. The fracture can be treated by welding. Replace if necessary.
c: The oil level of the thin oil station continues to decrease, and the oil level of the thin oil station is relatively small in daily consumption. The oil level of the cement grinding head oil tank of a factory has irregular consumption, decline, and oil replenishment, sometimes 200kg a week, sometimes a little half a month, repeatedly searching and finding no oil leakage point, no trace of oil in the tank, oil sump, etc., and no leakage after the cooler of the thin oil station is pressed down. Carefully check the hollow shaft, found that there are two cracks, when the high pressure pump is opened, the mill hollow shaft crack position in the high pressure oil tank, the oil will directly into the hollow shaft, resulting in oil running.
In the same way, the oil level of the thin oil station in a factory continues to decrease and replenish the oil, the phenomenon is the same as above. After inspection, no cracks in the hollow shaft are found. After the pressure on the bearing seat, leakage is found and the pressure cannot be maintained. Must be seriously and carefully analyzed, treated, and solved.
d: There are many reasons for the heating of the bearing, mainly
(1) When the scraping assembly is not qualified during installation, it can occur in the early stage of trial production;
(2) The bearing side of the positioning end of the mill heats up. Inside or outside, the expansion amount reserved for installation is not qualified;
(3) Poor ventilation in the mill, the occurrence of over-grinding phenomenon, or the high temperature of the raw material into the mill, resulting in an increase in the temperature of the mill barrel, and the conduction to the sliding shoe is an increase in the bearing temperature. The over-grinding phenomenon can be reformed by adjusting the air parameters, changing the orientation and shape of the grate.
Cement production is a system project, all kinds of problems need to be considered comprehensively, a factory 4.2*13 mill put into operation (with roller press) often occur full wear phenomenon, by the mill head feeding, output decline, bearing temperature rise and other problems, the formation of production capacity, especially hot days can not run, stop grinding cooling, open and stop, after inspection found that, The coarse silo compartment board is a sieve plate, the sieve plate is behind the sieve plate, the small ball and large particle material will almost all block the sieve plate and screen after operation, resulting in poor material flow, the coarse silo to the fine silo in the grinding, the ventilation is seriously insufficient, resulting in full grinding and grinding phenomenon, the original sieve plate and screen can be removed, replaced by a new type of grate, and the grate grate has been reformed. The problem of grinding the grate easily stuck ball and blocking was solved, the production capacity has broken through the original design capacity, and the patent won the first prize of Tianjin Quality Research project.
e: Grate support Two Φ3.8*13m hollow shaft mills in a factory have been running for more than two years, and the grate support has broken off, the grinding body has entered the middle of the support, broken the reinforcement plate, and made the support broken and deformed, and the grinding phenomenon has occurred, and the production capacity has been seriously reduced. Replacement of the grate bracket due to the need to enter the empty shaft workload is too large, can only be entered by the grinding door, the original bracket has 9 pieces, limited by the size of the grinding door, need to be divided into 27 pieces into the grinding welding, due to the large amount of welding construction period is longer, welding stress is too large, use less than a year, and continuous fracture, warehouse, according to this situation, We designed a complete set of 8 pieces, which can be directly welded into the grinding assembly by the grinding door, so that its strength is greatly improved, the welding workload is reduced, and the construction period is shortened by 2 times. Since 2003, it is still in use, and this project has won the national practical patent.
(2) There are problems and treatment methods in the double slide mill
(a) The overheating problem of the main shaft tile, especially the high temperature of the tail tile, which causes the temperature overheating of the main bearing shell of the mill, is mainly related to the structure of the mill.
First of all, the bearing ring of the mill slide shoe is welded into the cylinder body, and the high temperature of the mill body is transmitted to the slide shoe, resulting in the temperature of the mill bearing bush rising. Second, poor ventilation in the mill. The separator plate in the original mill is in the form of sieve plate, and the small balls and material particles often block the sieve hole, resulting in poor material flow. The lack of material flow and air flow from coarse bin to fine bin in the mill leads to the phenomenon of full grinding and over-grinding, and also causes the decrease of output and the increase of the temperature of the mill body.
Third, the temperature of raw materials is high.
Fourth, some mills have thin slip-on thickness, no heat insulation material between the grinding lining plate and the grinding body, no heat insulation layer in the grinding cone, or a thin heat insulation layer.
(a) Transform the compartment grate plate and the grinding grate plate: remove the original sieve plate and screen all and replace it with a redesigned grate plate. The form and arrangement of the original grate were changed. By running comparison, the problems of insufficient feed, over grinding and full grinding in the mill are basically solved. When the temperature of the grinding body decreases by 2-3 degrees, the yield increases significantly. This renovation project won the first prize of quality research of Tianjin Quality Supervision Bureau.
(b) The treatment of high grinding tile temperature: the cement material enters the discharge bin after grinding in the coarse and fine silo. The position of the sliding shoe bearing is in the combined section of the two silo, and the material is discharged after grinding, and the temperature is the highest at this time, and the corresponding grinding body temperature is also the highest here. After field measurement, the highest temperature here is about 90-110 degrees, which is transmitted to the sliding shoe bearing, thereby raising the tile temperature and causing the grinding to stop and cool down. Install 20m thick insulating rubber asbestos pads between the cylinder and the liner after removing 5 to 10 turns of the liner on the side near the outlet grate plate to ensure that the liner installation is not affected. Reduce the heat conduction from the temperature inside the mill to the barrel, and fill more than 100mm thick thermal insulation rock wool between the lining plate of the discharge cone and the barrel to isolate the influence of reducing the temperature of the material inside the mill on the sliding shoe.
(c) The transformation of the thin oil cooling system: due to the high temperature of the sliding shoe bearing, the temperature of the thin oil station oil rises and the viscosity decreases, and the problem of too high oil temperature is solved. It can be adopted to increase the area of the cooler, change the row type cooler to the radiator type cooler, increase the circulation cooling of the cooling water jacket in the oil return pipe, etc., to control the temperature of the circulating oil below 40 degrees, which can significantly reduce the temperature of the sliding shoe bearing. After the above comprehensive improvement, the grinding stop caused by high temperature will be completely changed. The temperature of the sliding shoe can be basically maintained at about 70 degrees, and it can be maintained at about 60 degrees in winter, which ensures the normal operation of the grinding body.
(d) To minimize the temperature of the raw material, mainly the clinker temperature.
(e) Other problems to note: the main problem of the mill is that when the grinding body is used for a period, the ball is blocked out of the grate joint; Improper operation of feed port return; Lubricating oil polluted by dust from oil station; The shoe cover is not tightly sealed, dust enters the shoe, and the bearing bush accelerates the wear problem;
Therefore, (1) it is necessary to strictly adjust the process requirements and operating requirements of the wind and material in a timely and reasonable manner to prevent the occurrence of full grinding. (2) Filter and replace the oil regularly. The management department shall inspect the oil products regularly. According to the test results, the lubrication scheme is reasonably formulated. The oil pan of the sliding shoe bearing is cleaned once every six months, and the number of times is increased if necessary to reduce dust accumulation and ensure lubrication. The function of the thin oil station is cooling and lubrication.
Main reducer easy to occur problems and measures
(1) Reducer structure and principle: the structure of the reducer adopts double shunt reducer. Double shunt reducer, the input shaft gear to the left and right sides of the gear at the same time transfer torque and change the output speed, the processing and installation requirements are higher, the left and right two gear input and output force and contact must be consistent. Problems can occur if the two gears are stressed differently. Such as partial load, pitting, uneven force, bearing temperature rise, vibration, noise and other problems.
(2) Prone to problems: A. After the mill is used for a period, due to the wear of the mill bearing shell, the settlement of the foundation, the force transmitted to the reducer during the mill operation is a variable, which affects the gear of the reducer, the common left or right shunt gear pitting, serious tooth surface peeling, broken teeth. b. Burning tile caused by oil pipe blockage, pressure drop of oil pressure, and failure of thin oil station. Pitting corrosion due to poor gear lubrication.
(3) Treatment methods, measures: (a), lubrication and cooling are the key to ensure the normal operation of the equipment. Maintenance and inspection are fundamental to ensure the safe operation of equipment, so it is required to do a good job. (b) The operator should pay close attention to the temperature change of each bearing and the change of momentum in the operation of the equipment, which is displayed on the instrument panel. According to the different seasons, the daily temperature of each point is different, and the change is mastered, especially when the bearing temperature spikes, the temperature rises linearly within a few minutes, and parking measures must be taken immediately. According to experience, when the equipment encounters a sudden rise in temperature within a short period of time, the equipment has already failed, and timely stopping can reduce the loss. (c) The daily inspection must be checked regularly according to the standard and the number of times, timely discovery of problems and timely reflection treatment, while focusing on the filter cleaning of the thin oil station in time, when the oil pressure difference is found to be greater than 0.1MP, timely replacement and cleaning, at least once a month to clean the oil filter, in the cleaning process to pay attention to whether there is metal debris in the filter, in order to find the problem in time. (d) Regularly check the gear condition, the oil intake of each bearing point, the meshing condition of each gear, whether there is pitting, whether there is crack denudation on the tooth surface, and clean and check the reducer at least once a year. (e) Maintenance checks and requirements for the main motor are basically the same as above. (f) Pay attention to the internal gear coupling of the reducer and the main motor, and disassemble and clean the oil every six months. The problems in this device are mostly caused by the lack of oil, such as the tooth surface bonding and broken teeth. (g) When gear pitting occurs, it is necessary to measure the coaxiality between the mill and the reducer in time, change the center line of the mill and the reducer, and adjust it in time to prevent further damage to the gear. The pitting corrosion or tooth surface damage that has been produced can be treated by grinding method. The tooth surface crack that has been cracked should be repaired into an arc shape, and the through crack tooth must be removed to prevent the broken tooth from falling into other gears and causing more damage.
ball mill
Use and maintenance of thin oil station
Thin oil station is the auxiliary equipment for cement enterprises to ensure the operation of the main engine, and it is the key to ensure the safe, efficient and stable operation of the equipment. To do a good job of maintenance and maintenance of thin oil station is an important link to ensure production. The main mill reducer, the main motor, the bearing of the mill, the main reducer of the powder separator, the main reducer of the roller press, the pressure device and other main equipment are all lubricated by the thin oil station. The function of the thin oil station is cooling and lubrication.
Failure causes and analysis: First, the reasons for the failure of the oil station are roughly divided into the following points:
(1) No oil pressure: (2) Low oil pressure for other reasons, such as electrical instrument reasons, pressure sensors or line reasons.
Two: fault check and judgment
(1) Pump fault judgment: open the oil return valve open the low pressure pump, close the low pressure oil outlet door slowly close the oil return valve, check the pressure gauge reading, when the pump pressure ≥ 0.4Mpa, the pump should be normal, according to the above parts of the operation is still not up pressure, disassemble the motor is normal, whether the internal gear coupling is damaged, such as normal can determine the pump damage.
(2) Open the high-pressure pump after the low-pressure pump is normal, and slowly close the valve at the outlet pipe of the high-pressure pump. If the pressure gauge value of the high-pressure pump reaches more than 25Mpa, it can be determined that the oil pump is normal and the system pressure does not go up. A, check the relief valve, according to the above method, the pump can not reach the pressure value, whether the relief valve is damaged or overflow. The relief valve of high pressure pump can be treated by blocking the oil return port. Because the pump rises to a certain pressure of about 10-12mpa, that is, pressure relief, the maximum working pressure of the pump is 32Mpa, so it will not cause damage to the pump. B, if the pump and relief valve are normal, check whether the pipeline behind the oil outlet door is leaking, and whether the high pressure oil pipe joint under the tile is leaking. C, adjust the high pressure piston pump, adjust the bolt, reverse adjustment to increase the pressure, positive adjustment to reduce the pressure. This method is used for 10SCY14-1B high pressure pump.
(3) When the temperature of the fuel tank in the oil station suddenly rises, check whether the electric heater is on (the power is generally off in summer). Three. System pressure adjustment and attention problems Thin oil station using quantitative pump, the liquid flow per minute output is relatively constant, the pressure increases, the flow rate increases, the pressure is small, the flow rate slows down. The safe operation signal of the oil station is transmitted by the pressure sensor, and when the pressure value of the filter outlet is lower than the set value, the standby pump will be activated and the stop will be stopped. Therefore, it is necessary to control the opening of the interceptor door behind the pressure sensor, and the opening of the outlet interceptor door can be properly adjusted to ensure the stability of the signal under the condition that the pressure value before the filter is not less than 0.4MPA. Whether the pump is normal or not and the inspection method have been explained before. Therefore, it is very important to check the pump regularly. If the pressure value of the pump is lower than 0.4MPA, it indicates that the pump has been worn, the efficiency is reduced, and it cannot meet the needs of the equipment. It is necessary to replace the new pump immediately to ensure the operation of the equipment. During operation, pay special attention to whether there is a sudden drop in the oil tank level (if there is an indication of oil leakage at the oil supply point) and maintain the oil tank level and replenish oil in time. The oil management department should regularly test the oil station and the oil quality, and have continuous records of the oil indicators. When the oil is used for a period of time, the indicators tend to decline, especially when there are more oil manufacturers and the quality is not the same, it will cause great harm to the operation of the equipment. A factory uses a brand of oil for many years, but the oil in the same year, after 2 months of use, the viscosity index of the oil has doubled. Fortunately, the discovery was timely and there was no major accident. Therefore, the quality of oil products should be paid special attention.
Common faults and prevention of roller press The working principle of roller press:
Under the action of the hydraulic cylinder pressure, the two press rollers rotating opposite will squeeze the material through them into a dense flat sheet, and the material between the two rollers will be squeezed by about 150MPA pressure, so that the granular material is squeezed and crushed, thereby improving the particle size of the material and increasing the grindability.
First, the common failure analysis and maintenance of the roller press: the parts and reasons for the failure of the roller press are roughly as follows:
(1) Main reducer failure and maintenance reducer failure, the reason is the output shaft oil seal damage, oil leakage, dust into the output shaft end, resulting in seal damage, wear and serious injury to the bearing. The input and output shafts of the reducer are equipped with butter nozzles for dust prevention and lubrication. The oil seal is fixed with a small bolt to prevent the oil seal from escaping. When the bolt is loose, the dust cover and shaft will rotate together, thus making the dust enter the oil seal, causing damage to the equipment, and the direct result is oil leakage. Therefore, special attention should be paid to daily maintenance inspection to check whether the end cover of the reducer rotates with the shaft. If synchronous rotation is found, it should be handled immediately and the bolts should be tightened. At the same time, the butter nozzle should be refueled regularly according to the regulations. The purpose of refueling is to prevent dust and to lubricate and reduce wear.
(2) roll surface damage: roll surface damage is the biggest problem affecting the output of the roll press, one is natural wear, the other is hard object damage. The cause of natural wear is caused by the extrusion wear of the material and the roll surface under high pressure, which is normal. Generally, the life of the roller surface is about 5000 ~ 5500 hours, and with the increase of wear, the diameter of the stick becomes smaller, and the output will gradually decrease. The main cause of hard object damage is foreign body entry. The main reason is that the damage caused by the entry of metal objects is relatively large, because the two rollers rotate opposite to each other under 150MPA pressure, and the gap between the two rollers is between 25-30mm. When the metal objects enter more than this distance, the roll surface will be strongly damaged and damaged, and the roll surface will be spalling or crack, resulting in convex and uneven roll surface, which gradually makes the roll out of round and out of balance. It causes a series of problems such as vibration of roller press, heating of reducer and fluctuation of motor power. In particular, the entry of large steel objects will cause accidents to the operation of the entire roller press, and some units have a hammer head into the accident, resulting in the entire equipment to stop production for more than half a year, the frame cracking, the reducer shell cracking, gear damage, almost scrapped. Therefore, preventing foreign bodies from entering is the key to ensure the safe operation of the roller press. For example, a grate can be installed in the clinker outlet plate feeding machine, a grid bar can be installed on the outlet shell lead wheel, and an iron remover can be installed on the warehouse belt, but only large foreign bodies or clinker surface iron can be controlled, but small devices can not be completely removed. In particular, the roller press system, including the ink, small warehouse, static powder separator has not yet eradicated-out method, can only be strengthened in the daily work, inspection and exclusion, one is the inspection of all equipment in the system, especially in the small warehouse, V separator, cyclone dust collector, found lining plate, deflector, wear-resistant parts in the rink, Angle iron is not welding, falling off. Roller press lower sluice without iron parts, and even processing. The second is the control of maintenance quality, especially the internal welding of the above equipment, the installation of the liner must be firm, and the liner wear must be replaced in time to prevent falling off into the roller press. Third, the roller press under the skid regularly, bucket lift bottom regularly clean, check the iron.
(3) Roller surface repair According to the operating life, the roller surface of the roller press shall be repaired, surfacing and restored to the original state no less than once a year. The repair process involves a series of professional technologies such as welding materials, technology, temperature, and technical level, which are divided into two good ways: online repair and offline repair. It is suggested that the new roll can be repaired online in the first year of use, and it is more advantageous to repair the roll offline in the second year.
(4) The support device of the roller press is the main part of the normal operation of the roller. The supporting device is equipped with bearings, shaft seals, oil passages, cooling water channels, etc., and a lot of heat energy will be generated by the extrusion friction between the roller and the material during operation, and its cooling is carried away by the circulating water. Bearing cooling also depends on circulating water cooling, bearing lubrication is provided by the centralized intelligent lubrication system, timed quantitative oil supply to different parts of the four bearing seats, oil supply time and oil supply interval time can be set and adjusted by itself. Each support device has 6 oil supply pipes, two of which supply oil to the bearing end cap respectively, which is used to dust and exhaust dust. Since the bearings used in the structure and maintenance of the roller press support device are large imported bearings, the price is high, and the order cycle is long, once the problem occurs, the simple replacement of the bearing time will not be less than one week, so the lubrication of the roller press is an important part of the maintenance. The failure of dry oil station is mostly caused by the failure of oil pump, and mostly caused by the wear of components. The other is the distributor, the solenoid valve is damaged. The dry oil station adopts electric dry oil pump or pneumatic dry oil pump, which requires higher oil quality during operation. In order to eliminate secondary pollution, the on-site oil cylinder can be canceled, effectively reducing the secondary pollution of oil products. In view of the high oil viscosity, especially in winter, the dry pump can not work normally, can be installed in the outer cylinder of the mixing tropical heating device and insulation layer, effectively solve the problem of vacuum absorption. At present, the failure of dry oil pump is mostly caused by internal leakage caused by component wear. The oil pressure does not go up, usually by changing the pump, the second is the air entry, the reason for the air entry is mostly during the use of the middle oil level of the cylinder to withdraw, and the surrounding oil does not come down. Therefore, pay attention to check the cylinder oil level and ensure that it is about 2/3 of the cylinder body. When air pumping occurs, oil should be replenished in time, and the oil surface can be smoothed. Third, the distributor or solenoid valve is blocked and damaged, and the fault determination method; When the dry oil pump is working, the pressure gauge of the oil pump is above 6MPA and accompanied by regular exhaust sound. When there is only exhaust sound and the pressure gauge does not move, it indicates that the pump is faulty, the oil pump should be cleaned or checked the oil cylinder oil level, or replace the oil pump (2) the dry oil pump is running normally, check whether the oil is filled at each fuel point, you can check through the main instrument panel, the upper row single indicator is on, the lower row indicator is on at an interval of 5 seconds, and the corresponding control cabinet next to the bearing seat is on. When the distributor is blocked, whether a supply point is supplied with oil, the above method can not be found, so it is necessary to check regularly, the method is to open the joint of each oil supply point, open the pump to check the oil flow of each oil pipe, and find that the problem is dealt with, this way is the most reliable. To sum up, the inspection and maintenance should pay attention to two problems, one is to prevent oil pollution, and the other is to regularly check the oil supply status of each refueling point. This is the basic guarantee to ensure the safe operation of the roller press.
4, rotary joint: the role of the rotary joint is used for the cooling of the roller, the cooling of the bearing. The circulating water supplies the circulating water to the roller through the rotary joint, taking away the heat. If the pipe is blocked, the bearing temperature will rise, and the heat source is generated by the extrusion friction between the two rollers and the material. Bearing setting alarm temperature 70 degrees. Most of the faults occur in the return water pipe of the rotary joint, or the bearing and seal damage and water leakage. Treatment methods, one is to backwash the circulating water. The second is to remove the rotary joint and clean the inner casing. The third is to remove the joint and replace the seal and bearing. When disassembling and replacing, pay attention to the rotation of the joint, which is divided into left and right rotation, opposite to the running direction of the roller. There are a lot of scale and impurities in the circulating water, and regular backwashing can effectively solve the problem of pipeline blockage, thus ensuring the service temperature of the roller bearing and extending the service life of the roller, which is another basic guarantee for the safe operation of the roller press. I hope you have enough understanding of this.
5, other faults: (1) uneven current fluctuation, mainly the roller is out of round, imbalance caused by current fluctuation and caused by vibration (2) hydraulic cylinder leakage, the main reason is seal damage (3) wear: including the upper and lower sluice, small bin, side plate, shell, etc. Wear parts, such as small warehouse with wear-resistant lining, gate valve to increase the use of wear-resistant lining, wear-resistant materials. Summary: The roller press system has two key problems, one is lubrication and cooling, the second is to prevent foreign bodies from entering, which is to ensure the safe and efficient operation of the roller press, if the reducer or bearing problems, roll surface problems, the production time will be very long, the cost is quite large. Therefore, the task and responsibility of cement mill inspection is larger. Only early detection of problems, treatment of problems, to ensure lubrication and cooling. The wear resistance of the impeller of the circulating fan of the raw material grinding system and the circulating fan of the cement grinding system with a roller press is an important issue that baffles the production of cement enterprises. Due to the different working conditions of various enterprises, the raw materials, temperature, dust concentration, and duct direction of the circulating fan are different, and the wear parts are formed. The degree is not the same. Even if the same enterprise, the same equipment, the same raw materials of the same arrangement of the production line, the impeller wear is not the same. Ordinary impeller is used for cement grinding system circulator service life of up to 3 months, less than 1 month, it needs to be repaired, when the blade and wall board root wear to a certain extent, the blade will be separated from the wall board resulting in equipment accidents. Such accidents are not uncommon in cement companies. Therefore, it is necessary to carry out anti-wear transformation of the impeller according to various aspects to solve the wear problem of the circulating fan and reduce the occurrence of accidents.


Post time: Nov-13-2024