Common Faults Of Hydrostatic Bearings, Their Causes And Elimination Methods

1: Pure liquid lubrication cannot be established

Fault 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 rotate or 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 in an oil chamber of the bearing failed to build up, or the assembly quality of the bearing was too poor, such as:

(1) There is oil leakage in a certain oil chamber, causing the shaft to be squeezed to one side of the bearing;

(2) There is no lubricating oil in a certain oil chamber of the bearing, and the oil inlet holes are misaligned during processing and assembly, or the throttle is blocked;

(3) The difference in liquid resistance of each throttle is too large, causing a certain oil chamber to have no load-bearing capacity;

(4) The stiffness of the elastic component 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, making the lifting clearance of the spindle too small.

Elimination method:

(1) Check whether the pressure in each oil chamber has been established. For oil leakage or no pressure oil chamber, find out the specific reasons and take corresponding measures to overcome them;

(2) Adjust the throttling ratio of each oil chamber to a reasonable range;

(3) Reasonably design the throttle;

(4) Keep the lubricating oil clean;

(5) Ensure the manufacturing accuracy and assembly quality of parts.

Static pressure bearing failure 2. Pressure instability

Fault phenomenon:

(1) When the main shaft is not rotating, after starting the oil pump, the pressure in each oil chamber gradually decreases or the pressure in some oil chambers decreases;

(2) After the spindle rotates, the pressure in each oil chamber changes periodically (if the change is greater than 0.05~0.1MPa, the reason must be checked);

(3) When the spindle is not rotating, each oil chamber will vibrate due to pressure (should be checked if it exceeds 0.05~0.1MPa);

(4) When the spindle speed is high, the oil chamber pressure fluctuates irregularly.

cause of issue:

(1) The throttling ratio β value is out of tolerance;

(2) Oil supply pressure p. too low;

(3) The bearing clearance is too large;

(4) The design of the throttle is unreasonable.

Elimination method:

(1) Replace the oil and 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, perform dynamic balancing to eliminate it. Check whether the unloading belt has any interference force and 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 chamber.

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 purity is not enough;

(2) The impurities stored in the bearings and oil pipes have not been removed;

(3) The throttle is clogged;

(4) The journal stiffness is insufficient, resulting in metal contact.

(5) The safety protection device fails.

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

Hydrostatic bearing 4. Spindle roughening or holding the shaft

Fault phenomenon: After the shaft rotates for a period of time, the main shaft may be found to have lint or the shaft may be held during operation.

cause of issue:

(1) The oil is not clean and the filtration purity is not enough;

(2) The impurities stored in the bearings and oil pipes have not been removed;

(3) The throttle is blocked;

(4) The journal stiffness is insufficient, resulting in metal contact;

(5) The safety protection device fails.

Elimination method:

(1) Repair the oil filter;

(2) Clean parts;

(3) Calculate the journal stiffness;

(4) Repair safety protection devices.

Static pressure bearing failure five: insufficient increase in oil chamber pressure

Fault phenomenon: Although the throttle oil is smooth, the pressure in the oil chamber does not rise enough.

cause of issue:

(1) The bearing clearance is too large;

(2) There is oil leakage in the oil line;

(3) The oil pump is unqualified;

(4) The viscosity of the lubricating oil is too low.

Elimination method:

(1) Measure the fit gap. If it is too large, the spindle needs to be re-aligned;

(2) Eliminate oil leakage;

(3) Replace the oil pump;

(4) Select appropriate lubricating oil.

Static pressure bearing failure 6: Bearing temperature rise is too high

Fault phenomenon: After the spindle has been running for about 2 hours, the temperature of the oil pool or the outer wall of the spindle box exceeds the tolerance.

cause of issue:

(1) The bearing clearance is too small;

(2) The shaft pump pressure is too high;

(3) The viscosity of the lubricating oil is too high;

(4) The friction area of the oil chamber is too large.

Elimination method:

(1) Increase bearing clearance;

(2) Reduce the oil pump pressure under the conditions allowed by the load-bearing capacity and stiffness;

(3) Reduce lubricating oil viscosity;

(4) Reduce the width of the sealing surface, but make the width a and b of the sealing surface greater than 40 times the gap and ensure Re>2000.