Hydrostatic bearing failure 1: Pure liquid lubrication cannot be established

Failure phenomenon: After the automatic oil pump, if pure liquid lubrication has been established, it should generally be able to rotate easily by hand; if it cannot be rotated or it is more difficult to rotate than when no oil is supplied, it means that pure liquid lubrication has not been established.

Cause of failure: The pressure of an oil chamber of the bearing cannot be established, or the assembly quality of the bearing is too poor, such as:

(1) There is oil leakage in an oil cavity, causing the shaft to be squeezed on one side of the bearing;
(2) There is no lubricating oil in an oil cavity of the bearing, and each oil inlet hole is dislocated during processing and assembly, or the restrictor is blocked;
(3) The difference in liquid resistance of each restrictor is too large, causing a certain oil cavity to have no bearing capacity;
(4) The stiffness of the elastic element of the feedback throttle is too low, causing the oil outlet hole at one end to be blocked;
(5) The coaxiality of the radial bearing is too large, or the verticality of the thrust bearing is too small, so that the lifting clearance of the main shaft is too small.

Elimination method:
(1) Check whether the pressure of each oil chamber has been established. For oil leakage or no pressure oil cavity, find out the specific cause and take corresponding measures to overcome it;
(2) Adjust the throttle ratio of each oil cavity to make it within a reasonable range;
(3) Reasonable design of the throttle;
(4) Keep the lubricating oil clean;
(5) Ensure the manufacturing accuracy and assembly quality of the parts.

Hydrostatic bearing failure 2. Unstable pressure
Fault phenomenon:
(1) When the main shaft does not rotate, after starting the oil pump, the pressure of each oil chamber gradually drops or the pressure of some oil chambers drops;
(2) After the spindle rotates, the pressure of each oil chamber changes periodically (if the change is greater than 0.05~0.1MPa, the cause must be checked);
(3) When the main shaft does not rotate, each oil chamber vibrates due to the pressure (it should be checked when it exceeds 0.05~0.1MPa);
(4) When the spindle speed is high, the pressure of the oil chamber fluctuates irregularly.

cause of issue:
(1) The throttling ratio β value is too poor;
(2) Oil supply pressure p. too low;
(3) The bearing clearance is too large;
(4) The design of the restrictor is unreasonable.

Elimination method:
(1) Replace the oil, clean the oil filter and throttle;
(2) Check whether there is a large centrifugal force on the shaft and the parts on the shaft. If so, check whether the unloading belt has interference force to eliminate the dynamic balance. Reduce the coaxiality error between the unloading pulley and the main shaft;
(3) Check the oil pump and pressure valve;
(4) Improve the type of oil cavity.

Hydrostatic bearing 3. Insufficient oil film stiffness
Fault phenomenon: The oil film stiffness of the spindle bearing does not meet the design requirements.

cause of issue:
(1) The oil is not clean and the filtration clarity is not enough;
(2) Impurities stored in bearings and oil pipes are not removed;
(3) The throttle is blocked;
(4) The stiffness of the journal is insufficient, resulting in metal contact.
(5) The safety protection device fails.

Elimination method: according to the adjustment of oil film stiffness.

Four, the main shaft is brushed or the shaft is held
Fault phenomenon: After the shaft rotates for a period of time, the main shaft may be found to have a hair-pulling phenomenon or the shaft-holding phenomenon occurs during operation.

Cause of issue:
(1) The oil is not clean and the filtration clarity is not enough;
(2) Impurities stored in bearings and oil pipes are not removed;
(3) The throttle is blocked;
(4) The stiffness of the journal is insufficient, resulting in metal contact;
(5) The safety protection device fails.

Elimination method:
(1) Overhaul the oil filter;
(2) Cleaning parts;
(3) Calculate journal stiffness;
(4) Maintenance of safety protection devices.

Hydrostatic bearing failure five: insufficient increase in oil chamber pressure
Fault phenomenon: Although the oil in the restrictor is smooth, the pressure in the oil chamber is insufficient.

Cause of issue:
(1) The bearing clearance is too large;
(2) There is oil leakage in the oil circuit;
(3) The oil pump is unqualified;
(4) The viscosity of lubricating oil is too low.

Elimination method:
(1) Measure the fit clearance, if it is too large, the spindle needs to be reconfigured;
(2) Eliminate oil leakage;
(3) Replace the oil pump;
(4) Select the appropriate lubricating oil.

Hydrostatic bearing failure six: bearing temperature rise is too high
Fault phenomenon: When the spindle runs for about 2 hours, the temperature of the oil pool or the outer wall of the spindle box is out of tolerance.

cause of issue:
(1) The bearing clearance is too small;
(2) The pressure of the shaft pump is too high;
(3) The viscosity of lubricating oil is too high;
(4) The friction area of ​​the oil chamber is too large.

Elimination method:
(1) Increase the bearing clearance;
(2) Reduce the pressure of the oil pump when the bearing capacity and stiffness allow;
(3) Reduce the viscosity of lubricating oil;
(4) Reduce the width of the oil sealing surface, but the widths a and b of the oil sealing surface should be greater than 40 times of the gap and ensure that Re>2000.