The hydraulic tensioning system is one of the most important equipment systems in the vertical mill. It plays a key role in the stable operation of the vertical mill and is also a link that is prone to failure. The huge grinding pressure exerted by the grinding rollers on the material is transmitted through the hydraulic system. which provides.
1. Accumulator nitrogen bladder failure
The accumulator plays the role of energy storage, pressure maintenance, shock absorption and shock absorption in the hydraulic system. However, if the mill runs erratically, the stretching rod moves frequently or the movement range is too large, and the nitrogen bag shrinks frequently, the nitrogen bag will burst.
The nitrogen gas in the accumulator airbag works like a gas spring, and the transmission of pressure is accomplished by the transmission of hydraulic oil, so slight changes in pressure will affect the flow of oil, resulting in elastic buffering. If the nitrogen gas bag is damaged or the pressure is too low, the influence of the change in the thickness of the grinding machine material layer on the hydraulic system cannot be absorbed, and the vibration of the grinding machine increases, which is likely to cause frequent breakage of tie rods and tie rod bolts.
Therefore, it is necessary to find the cause of the damage to the nitrogen bag in time, and replace and supplement it.
How to judge the status of the nitrogen bag
It is very important to quickly and accurately judge the quality of nitrogen bags in the production process of vertical mills. The simplest diagnosis method is to rely on the experience accumulated by the operator, with the help of simple instruments, to analyze and diagnose through the three methods of “touch”, “quantity” and “look” to determine the cause and location. mistake.
“Touch” is to judge the quality of the nitrogen bladder by touching the temperature of the accumulator shell. If the temperature of the accumulator shell is close to the oil temperature, the accumulator is working normally; if the temperature is obviously too high or too low, and there is a knocking sound at the bottom of the battery, the battery is damaged. After the nitrogen bag is damaged, the accumulator will not play the role of buffering and shock absorption. Therefore, the damaged energy must be stored in time. Repair equipment, replace bladder or check valve.
“Test” is to install a pressure gauge on the valve nozzle of the accumulator to check and judge after the hydraulic station is unloaded when the vertical mill is stopped. If the pressure gauge shows low or no pressure, the accumulator is damaged; if the pressure is close to the normal pressure of the nitrogen bladder, the accumulator is in good condition.
“Look” is to observe whether the lifting or pressing time of the grinding roller is normal. If the grinding roller is elevated or the pressurization time is significantly prolonged, the accumulator nitrogen bladder is damaged.
How to Prevent and Resolve Nitrogen Bag Damage
Solving the problem of nitrogen bladder damage cannot be limited to the accumulator itself. The most fundamental measure is to stabilize the operating conditions of the mill and avoid the severe vibration of the mill. In addition, a reasonable nitrogen filling method is also a factor to avoid the bursting of the nitrogen bag.
The accumulator must be filled with nitrogen, and it is strictly forbidden to replace it with other gases. Before filling with nitrogen, the air remaining in the nitrogen bag must be exhausted, otherwise the mixture of air and nitrogen will easily cause the nitrogen bag to burst. According to relevant standards, the general inflation pressure is controlled at 60%-70% of the system working pressure.
During normal production, it is stipulated that the nitrogen gas of the accumulator should be checked once a week. When the nitrogen bag is inflated, the nitrogen bag first expands at the upper part, with a large diameter and a thin wall, and then gradually expands to the lower part, pushing the nitrogen bag outward to the side wall of the shell, and at the same time, the nitrogen bag fills the entire container, the outer wall and the outer shell of the nitrogen bag. . The inner wall has high friction.
Therefore, during installation, apply hydraulic oil to the outer wall of the nitrogen bag and the inner wall of the casing to reduce the friction between the nitrogen bag and the inner wall of the casing and protect the nitrogen bag. Before disassembling the accumulator, the pressure oil in the accumulator must be discharged first, and then the nitrogen gas in the air bag must be released with an inflation tool, and then other parts must be removed.
2. The high-pressure oil pump of the hydraulic station frequently starts to fail
During the operation of the vertical mill, the pressure of the hydraulic system often cannot be maintained. The high-pressure oil pump starts frequently, and the temperature of the hydraulic oil rises. This phenomenon can easily cause damage to the oil pump and increase energy consumption.
There are two main reasons for the frequent start of the high-pressure pump:
1. The tie rod seal of the hydraulic cylinder is damaged, which is caused by the oil leakage of the cylinder;
Second, the oil return valve (or pressure relief valve) leaks or is damaged, causing the high-pressure oil pump to run frequently.
In production, measures can be taken for inspection and processing from the following aspects:
The first is to check the hydraulic cylinder for internal leakage. The most direct method is to cut off the oil pump of the tensioning hydraulic station after grinding, and observe whether the oil pressure of the hydraulic station gradually decreases in a static state. If the drop indicates that the hydraulic cylinder has internal leakage, the sealing ring should be replaced in time.
The second is to reasonably determine the setting range of the tension force. If the setting range of the grinding pressure is narrow, it will not only weaken the buffer capacity of the nitrogen bladder of the hydraulic system, but also make the high-pressure oil pump of the hydraulic station frequently start and stop in a very short period of time. time. In severe cases, the high-voltage motor will be burned out. Generally, reasonable grinding pressure parameters should be determined according to the grindability of materials.
The third is to check and clean the hydraulic valve (and pressure relief valve). Hydraulic valves are precision parts. Once there is debris blocking the valve port, it will cause pressure relief. How the Raymond Mill works
3. The hydraulic cylinder body is pulled or oil leakage failure
The reasons for hydraulic cylinder block strain or oil leakage are as follows:
First, there are impurities in the hydraulic oil, which will cause the cylinder body to be pulled, the seal to be damaged, and oil to leak;
2. Due to the top punching, the fine particles are sandwiched between the hydraulic cylinder and the piston rod, and the chrome-plated layer on the surface of the piston rod produces longitudinal stretch marks due to wear, and the oil seal is damaged, resulting in oil leakage;
The third is that due to the rupture of the valve handle of the accumulator check valve, the bolts and washers enter the hydraulic cylinder, resulting in longitudinal pull marks, pulling the piston ring, causing the hydraulic cylinder body to be pulled or oil leakage;
4. The hydraulic cylinder sealing ring leaks oil due to long-term use and aging;
5. The setting range of grinding pressure is unreasonable, and the setting tension is too high, which makes the oil pressure in the hydraulic cylinder continue to be high. Such high oil pressure puts high pressure on the seal ring. When it is stable, the mill vibrates violently, which will cause large fluctuations in the tensile force, and the instantaneous high pressure impacts the sealing ring, and the sealing ring is also easily damaged.
In order to ensure the normal operation of the hydraulic system, the following points should be done in production:
First of all, the hydraulic oil in the hydraulic system is required to have a high degree of cleanliness. In order to keep the hydraulic oil clean, the surrounding environment must be kept clean during the inspection of the cylinder block, the cleaning of the pipeline, the replacement of the nitrogen gas bag and the hydraulic conveying process to prevent the introduction of small particles into the hydraulic oil and cause scratches on the cylinder block and the nitrogen gas bag. damaged;
Secondly, in order to prevent fine particle materials from entering the cylinder, a soft connection sheath can be made on the outside to protect it;
Third, during the use of hydraulic oil, the oil quality should be regularly tested and checked every six months. If the oil is emulsified and deteriorated, the hydraulic oil should be replaced in time;
The fourth is to set a reasonable grinding pressure according to the material characteristics. Under normal production conditions, the actual working pressure should generally be set between 70% and 90% of the maximum pressure limit.
In a word, the correct use and maintenance of the hydraulic system and the good operation of the hydraulic system are one of the main ways to reduce system failures and improve the grinding efficiency of the mill.