How to Improve and Enhance the Cooling and Lubrication Effect of Bearings?

Preface

The lubrication system of the vertical grinding roller is also crucial for the operation of the vertical grinding mill. It can continuously cool and lubricate the grinding roller bearings, thereby ensuring the service life of the grinding roller bearings and the continuity and stability of the vertical mill operation; However, the current technology principles introduced from abroad also have their own shortcomings and shortcomings: for example, poor oil return and shortened service life of the oil return pump, high pressure inside the grinding roller caused by poor oil return, leakage of the sealing of the grinding roller shaft, poor oil return causing poor cooling effect and higher bearing temperature. How to continue to enhance its advantages and address shortcomings or weaknesses has become the topic of today's discussion. Explore some new technologies and methods to improve and enhance the cooling and lubrication effects of bearings.

1.The classification, differences, and advantages of current grinding roller lubrication stations

There are currently two widely used grinding roller lubrication stations. One type is self priming, also known as vacuum negative pressure pump type oil return. Another type is the return oil from the oil suction pump. The former uses a composite casing, where the high-pressure and high-speed oil from the feed pump flows through the inside of the casing, causing the air in the return pipe to be gradually swept into the oil tank by the oil, gradually reaching a vacuum inside the pipeline. At this time, the external atmospheric pressure passes through the air filter, which is the oil in the grinding roller oil pool, and returns to the lower oil tank through the return pipe. It belongs to a type of vacuum self weight return oil. This technology originated in Germany and was subsequently optimized and widely utilized by companies such as Ube in Japan. As shown in the following figure:

Another method is to use an oil pump to actively retract. Each grinding roller corresponds to a return oil pump. Gradually draining the air inside the valve through a tooth cooling pump or screw pump is also a form of vacuum oil return under atmospheric pressure and pump force. As shown in the following figure:

The difference between the two:

1.1 In terms of pressure, the pressure of vacuum negative pressure pumps is generally slightly lower than -0.02MPa, while the pump suction oil pressure is better, generally around -0.02-0.03MPa;

1.2 Requirements for oil viscosity: Vacuum negative pressure pumps have high requirements for oil viscosity, and are generally suitable for composite or synthetic gear oils with viscosity below 320; Direct suction return oil form, as the pump has power, can use gear oil with a viscosity between 320 and 640.

The advantages and disadvantages of both: the vacuum negative pressure pump returns oil without a power source, has the characteristic of infinite maintenance cycle, almost zero failure rate, and zero energy consumption. Shortcomings: Under low temperature conditions, the compatibility with high viscosity oil return oil is relatively poor. The pump directly sucks back oil, which is compatible with high viscosity oil and has the characteristic of faster oil return. However, there is a situation where the pump replacement cycle is short. The common situation is that the oil leakage from the shaft seal of the pump is relatively common; At the same time, there is a certain amount of energy consumption.

2.Disadvantages and Improvement Direction and Methods of Vertical Mill Lubrication Station

2.1 The disadvantage of vacuum negative pressure pumps is poor compatibility with oil viscosity. A heater can be installed in the fuel tank and a thermal insulation sleeve can be installed on the return oil pipe. Before starting, manually turn on the heater in advance. Introduce hot air in advance to increase the temperature inside the mill. After the starting oil temperature meets the requirements, restart the oil station. Try to use composite gear oil with a viscosity of 220 or less as much as possible.

2.2 Adopting a pump suction type to ensure that the oil suction pump is lower than the oil tank, and selecting a pump with a lubricating oil port and a lubricating oil return port. Try to choose pumps with excellent quality, and the pump shaft seal should be made of fluororubber material (heat-resistant temperature can reach up to ≤ 120 ℃), which is better. Similarly, it is best to turn on the heater and grinding roller as early as possible to increase the temperature first.

3. Suggestions for the use of grinding roller lubrication stations and exploration of new technologies

3.1 Working conditions of the grinding roller lubrication station

Based on my long-term observation and maintenance experience, combined with analysis, the grinding roller bearing is a low-speed running bearing. But the working environment temperature is high. Therefore, the heating capacity of the bearing itself is low, but the ambient temperature is high and the temperature rises quickly. Therefore, the demand for cooling is greater than for moisturizing. Therefore, the return oil speed and flow rate of the grinding roller lubrication station are crucial. Secondly, the natural loss of grinding roller bearings is mainly caused by iron powder. Therefore, it is crucial to periodically clean the iron powder in the magnetic filter on the pipeline (such as within the agreed weekly or two weeks) and the iron powder on the magnetizing rod set inside the oil station. You can write the last maintenance time on the maintenance card to remind maintenance personnel to clean it online in a timely manner next time.

3.2 Usage suggestions

Use low viscosity composite gear oil. High viscosity oil does indeed have a better lubrication effect on bearings, but the actual requirement for bearings is cooling. Because it is not recommended to use hydraulic oil with high viscosity, whether it is in the form of self suction or vacuum negative pressure pump return oil. Especially in the north (areas with temperatures above zero in winter), it is not recommended to use high viscosity composite gear oil (recommended: 320 # and 220 # gear oil in summer; 220 # and 150 # viscosity composite gear oil in winter). High viscosity gear oil, once encountering low temperature and poor oil return, can easily cause overheating and burning of the shaft seal of the self priming oil return pump, resulting in oil leakage and increased maintenance costs. At the same time, the air filter can also leak oil, polluting the environment. Vacuum negative pressure oil return can easily cause oil to escape from the air filter and pollute the environment.

Once the oil inlet speed is greater than the oil return speed, the air filter position will be higher, which will gradually increase the pressure in the grinding roller oil pool and easily cause the sealing leakage of the grinding roller shaft. In fact, many times, the leakage of shaft seals is not due to the poor quality of the shaft seal (Stuart seal+precision machined wear-resistant shaft sleeve), but rather to the leakage caused by the overpressure of the shaft seal. Once the oil return is good and the liquid level in the oil pool drops to a suitable position, the pressure drops and the sealing effect comes out. Therefore, high viscosity gear oil is more likely to cause shaft seal leakage and short service life.

3.3 Exploration of New Technologies

Based on the above discussion, it can be seen that if the liquid level in the grinding roller oil pool can be tracked, then a variable frequency servo system can be used? Lubrication (1 feed pump and 1 return pump mode for each roller).

A. Equip the grinding roller with corresponding two position liquid level gauges. When the oil level in the grinding roller is higher than the maximum required height, the feed pump slows down and the return pump accelerates. However, when the liquid level is lower than the normal safety value, the return pump slows down and runs at the normal speed. Increase the speed of the oil pump for operation. Ensure that the liquid level is within a safe range.

B. When the temperature exceeds the conventional required temperature, such as 55 ℃, the self circulation pump starts, and the radial or plate water cooler forcibly cools. When the temperature drops below 45 ℃, the self circulation pump stops working.

C. A bottom oil level alarm switch is installed inside the oil station. When the oil level is lower than the normal value and greater than the minimum oil level, a yellow alarm can be prompted. Remind maintenance personnel to check for any oil leakage from the grinding roller seal. After falling below the conventional safety value scale, a red alarm is triggered and a shutdown is required. Remind maintenance personnel to stop and repair the oil leakage. After recovery, restart after the signal disappears. The internal structure diagram of the grinding roller is shown below:

Another method is to track the level of the fuel tank to its height.

A. If the oil level in the fuel tank is at the normal high level, the oil supply can be increased. Until the oil level reaches normal value;

B. If the oil level in the fuel tank is below the average value, the return oil volume can be increased. Until the oil level reaches normal value;

C. If the entire process is not balanced after 15-20 minutes, a yellow alarm needs to be given. Prompt to check if there is a possibility of leakage in the seal of the grinding roller shaft or bearing end cover.

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