Maintenance method for static bearing of imported grinding machine in imported bearing

pressure imported bearings with high rotation precision, good steel, high bearing capacity, no wear and high durability. The following are some of the experiences that static pressure imported bearings have explored and tried during the maintenance process.
The static pressure imported bearing has high rotation precision, good steel property, high bearing capacity, no wear and high durability. The following are some of the experiences of static pressure imported bearings in the process of repair and try to obtain, for your reference only.

    1. Small hole throttle:
    (1). Change the internal throttling to external throttling, and add a pressure gauge to instantly display the upper and lower chamber pressure. It is easy to maintain, especially it can be cleaned regularly, which is unmatched by the internal throttle.

    (2). Throttling ratio. The theoretical value of the throttle ratio β is between 1.2 and 1.5, and 1.25 is preferred based on years of experience. In this way, the geometric accuracy of the main shaft, the geometrical accuracy of the front and rear bearing pads, the concentricity, the roundness and the taper need to be strictly controlled in order to ensure the β value. The e value (the eccentricity of the main axis and the geometric center of the bearing bush) is determined according to the load carrying capacity of the machine tool to optimize the β value.

    (3). When the oil chamber is not equipped with the main shaft, the oil column of each oil outlet must be consistent (observation method). If it is inconsistent, the flow rate should be changed by changing the orifice diameter of the restrictor. Taking 4 chambers as an example, the oil column of the lower, left and right chambers is generally between 20 and 25 mm, and the diameter of the small holes is 0.25 to 0.4 mm.

    2. Thin film feedback throttle:

    The film feedback throttling bearing stiffness is very large, but the machine tool often appears to hold the tile, pull the hair, reduce the pressure and so on. The most critical of the film feedback is the film. In practice, the main reasons for the bearing lock and pulling are: 1 plastic deformation of the film; 2 slow feedback. When the external load is abrupt, the shaft and the tile have already rubbed when the film has not reacted; 3 the film is fatigued. The film is used for a long time and fatigue deformation, which is equivalent to changing the feedback parameters.

    Increased film thickness and the use of some fatigue-resistant materials can achieve good results. Generally, a rigid film, a preload, and a gap are reserved. The specific method is: change the 1.4mm thick film to a 4mm thick rigid film, and place a 0.05mm thick tin foil in the lower cavity to adjust the spindle to a position 0.05mm higher than the ideal position. The purpose is to return to the ideal center just after the spindle is stressed (grinding weight, cutting force).

    3. Improvement of the oil supply system:

    In the static pressure inlet bearing oil supply system, in addition to the coarse filter and the fine filter, the other components have a protective effect on the hydrostatic bearing. The oil supply system is improved on the basis of the original system.
    (1). Connect the pressure relay and pressure gauge (originally in front of the accumulator) at the oil outlet behind the throttle plate so that the operator can see the pressure of the chamber and the inlet pressure. When the pressure difference is greater than a certain value, in order to stop immediately, so as to avoid the axle lock. Such as: the inlet pressure 2MPa, the oral pressure 1.2 ~ 1.6MPa, less than 1.2MPa will stop.

    (2). Add digital detection device:

    There is a gap of 0.04~0.05mm between the main shaft of the static pressure imported bearing and the bearing bush. The oil in the process has a certain resistance value. When the change of the resistance value is detected, the gap of the period can be known. Take the main shaft as one pole and the bearing bush as the other pole, and measure its resistance change. This signal is processed and sent to the photoelectric alarm and control system amplifier to control the start and stop of the spindle motor to avoid the friction between the shaft and the tile.

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Analysis of the Causes of Overheated Bearing Temperature in Cryogenic Low Pressure Expander

Core Tip: The expander used in the cryogenic device is a speed turboexpander that transfers energy in response to changes in the velocity of natural gas. High-pressure natural gas is close to isentropic expansion in the expander.
The expander used in the cryogenic device belongs to a velocity turboexpander, which transfers energy in response to changes in the velocity of natural gas. The high-pressure natural gas is close to isentropic expansion in the expander, causing a drop. At the same time, the output work, consume energy, increase the enthalpy drop, reduce the natural gas outlet temperature, and achieve the purpose of refrigeration. The expansion impeller belongs to the radial axial flow reverse radial impeller, the impeller of the coaxial brake centrifugal turbocharger is semi-open, and the expander and supercharger are single. The expander is the main equipment of the cryogenic station refrigeration system, which plays an important role in cooling and recovering energy. The design flow rates of the high and low pressure expanders are 18623/17388 Nm3/h, the rotational speed is 39000/47000r/min, the inlet temperature of the high and low pressure expanders is -69.15/21.55 °C, and the outlet temperature is -105.32/-39.55 °C. Through analysis, the main factors affecting the bearing temperature of the expander are lubricating oil, water cooler, sealing gas, accessory quality, maintenance quality, etc. The oil film thickness of the lubricating oil is the main reason for restricting the bearing temperature, and the bearing temperature is the influence. The key to long cycle and efficient operation of the expander.

    1 Problems with the expansion unit

    In May 2005, the expansion unit showed high bearing temperature and chain shutdown phenomenon for a week (data shown in Table 1), which caused the unit to be in a lower load operation state. The refrigeration negative temperature was around -50 °C, which was far from the designed cooling temperature.

    2 Expander bearing lubrication mechanism

    The lubrication and cooling of the shaft and bearing of the expander are mainly based on lubricating oil. The main function of the lubricating oil is to provide lubrication and cooling for the shaft, bearing and seal. A dynamic pressure oil film of a certain thickness is formed between the journal and the bearing to form an oil film contact, the oil film holds the shaft, the bearing and the shaft are not in direct contact, and the shaft and the bearing are in fluid friction, and the friction factor is small. At the same time, the metal chips and impurities falling off between the friction pairs are taken away by the lubricating oil, which reduces the abrasive wear, removes the heat generated by the friction, and prevents the shaft and the bearing from being too hot to burn the tile.

    3 Low-pressure expander structure and lubricant flow

    The structure of the low-pressure expander is mainly composed of an expander casing, a rotor shaft, an impeller, a bearing, a key, a back bolt, a heat insulation plate, a back pressure seal, a sealing rubber ring, a temperature probe, a vibration probe and the like. The auxiliary system includes a supercharger, a sealed gas system, a cold blowing system, an accumulator, a balancing valve, and the like.

    Lubrication of bearings and shafts of low pressure expanders

    Lubricating oil of L-TSA68 is lubricated. The viscosity index of lubricating oil is 55.08~82.28mm2/s, and the flash point (opening) index is ≥185°C. The lubricating oil process is lubrication of the oil tank-rough filter-oil pump-lubricating water cooler-double filter-line valve-pre-machine filter-shaft and bearing of the expander.

    4 Troubleshooting and analysis

    4.1 Checking the instrumentation system

    Look at the low expansion machine bearing return oil temperature field data and the main control room computer display bearing temperature data comparison, and then with the infrared thermometer to measure the data comparison, the measured data is basically the same, the error is about 2 ° C; check the low expansion machine Temperature probe installation, if the probe is loosely installed or the probe is not linear, it will also affect the data change, re-calibrate the temperature of the field, re-confirm the sensitivity of the instrument probe, and check that no abnormalities are found.

    4.2 Check the oil tank's test indicators, temperature and pressure

    The main factors affecting the bearing temperature in the lubricating oil test index are kinematic viscosity and lightning. When the kinematic viscosity is higher than the standard value, the movement resistance of the oil film between the journal and the bearing is large, and the heat generated by the movement cannot be taken away in time, which is easy to cause the bearing temperature of the low-pressure expander to be high; when the kinematic viscosity is less than the standard value, the journal and the bearing are The thickness of the oil film is thin, and dynamic lubrication cannot be formed. The boundary between the shaft and the bearing is friction. At this time, the friction factor is several times that of liquid lubrication, and the heat generated between the shaft and the bearing is large, which tends to cause high temperature of the low-pressure expander bearing; lubrication The oil lightning is low, the oil film cannot be formed between the journal and the bearing, or the oil film formed is thinned, and the boundary friction between the shaft and the bearing is easy to cause the bearing temperature of the low-pressure expander to be high. The influence of the temperature of the lubricating oil on the bearing in the fuel tank, the temperature of the oil tank is too high (the normal tank temperature is 58 ° C), and the heat exchange area of ​​the lubricating oil water cooler is constant, and the temperature of the lubricating oil is correspondingly high, resulting in the bearing of the low pressure expander. When the temperature rises, the pressure of the tank on the bearing temperature, the pressure of the tank is too high, which directly affects the speed of the lubricating oil returning to the tank, which also easily causes the bearing temperature of the low-pressure expander to rise. Therefore, to ensure that the low-pressure expander bearing temperature is not high, it is necessary to control the lubricating oil test indicators, tank temperature and pressure.

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