During centerless cylindrical grinding, the workpiece is placed between the guide wheel and the grinding wheel; one is used for grinding, and the other is used for transmission, called the guide wheel. A support plate supports the lower part of the workpiece. The guide wheel is made of a rubber bonding agent, and its axis forms an angle θ with the grinding wheel in the vertical direction, driving the workpiece to rotate and feed.
Common grinding defects of centerless grinders and their elimination methods are summarized as follows:
Causes
(1) The guide wheel is not rounded.
(2) The number of grinding times is small, or the ovality of the previous process is too large.
(3) The grinding wheel is blunt.
(4) The grinding amount is too large, or the cutting amount is too large.
Elimination methods
(1) Rebuild the guide wheel and wait until the guide wheel is rounded (generally, it stops when there is no intermittent sound).
(2) Increase the number of grinding times appropriately.
(3) Rebuild the grinding wheel.
(4) Reduce the grinding amount and re-cutting speed.
Causes
(1) The center height of the part is not high enough.
(2) The axial thrust of the part is too large so that the part is pressed tightly against the stop pin and cannot rotate evenly.
(3) The grinding wheel is unbalanced.
(4) The center of the part is too high.
Eliminate the problem
(1) Accurately advance the center of the part.
(2) Reduce the inclination of the grinder guide wheel to 0.5° or 0.25°. If the stop cannot solve the problem, check the balance of the fulcrum.
(3) Balance the grinding wheel.
(4) Properly reduce the center height of the part.
Causes
(1) Machine tool vibration caused by the unbalanced surface of the grinding wheel.
(2) The center of the part moves forward and causes the part to jump.
(3) The grinding wheel is blunt, or the surface of the grinding wheel is too smooth.
(4) The guide wheel rotates too fast.
Eliminate methods
(1) Carefully balance the grinding wheel.
(2) Properly reduce the center of the part.
(3) Grinding wheel or properly increase the grinding wheel dressing speed.
(4) Properly reduce the guide speed.
Causes
(1) The front guide plate is too low in the guide wheel generatrix, or the front guide plate is tilted toward the guide wheel, causing the front part of the part to be smaller.
(2) The rear guide plate surface is lower than the guide wheel generatrix, or the rear guide plate is tilted toward the guide wheel, causing the rear part of the part to be smaller.
(3) The front or rear part of the part has taper due to the following reasons.
① The grinding wheel has taper due to improper dressing.
② The grinding wheel and the guide wheel surface are worn.
Eliminate method
(1) Move the front guide plate appropriately and adjust the front guide plate to be parallel to the guide wheel generatrix.
(2) Adjust the guide surface of the rear guide plate to be parallel to the guide wheel generatrix and on the same line.
① According to the direction of the part taper, adjust the angle of the grinding wheel in the grinding wheel modification.
② The grinding wheel and the guide wheel.
Cause
(1) The front and rear guide plates are evenly tilted toward the grinding wheel.
(2) The grinding wheel is trimmed into a waist drum shape.
Elimination method
(1) Adjust the front and rear guide plates.
(2) Modify the grinding wheel. The allowance for each modification should not be too large.
Cause
(1) The front and rear guide plates protrude from the surface of the guide wheel, causing the part to be scraped by the edge of the guide wheel at the exit or entrance.
(2) The support is too soft, and the cuttings are embedded in the support surface to form protruding burrs, which are engraved into threads on the surface of the part.
(3) The coolant is not clean and contains chips or sand.
(4) Due to the large amount of grinding at the exit, it is scraped by the edge of the grinding wheel.
(5) The center of the part is lower than the vertical pressure of the grinding wheel center Large so that the sand and chips stick to the bristles.
(6) The grinding wheel is blunt.
(7) Too much excess is ground at one time, or the grinding wheel is too coarse, resulting in beautiful threads on the surface of the other part.
Elimination method
(1) Adjust the front and rear guide plates.
(2) Replace the bristles with lubricated surfaces and higher hardness.
(3) Replace the coolant.
(4) Round the edge of the grinding wheel, and finally, make sure that the 20mm area at the exit of the part is not ground.
(5) Properly advance the center height of the part.
(6) Grinding wheel.
(7) Properly reduce the grinding amount and slow down the modification speed.
Cause
(1) The front guide plate protrudes from the surface of the guide wheel.
(2) The front end of the grinding wheel and the guide wheel are very different and not in a straight line.
(3) Too much grinding at the entrance.
Eliminate method
(1) Move the front guide plate back a little.
(2) Replace or modify the longest one of the two.
(3) Reduce the grinding amount at the entrance.
Cause
(1) The rear guide plate is out of the guide wheel surface, preventing the part from rotating and the grinding of the tread surface from continuing.
(2) The rear support pad extends too long, and the ground part does not fall off, preventing the ground part from rotating and moving forward.
Eliminate method
(1) Move the rear guide plate back appropriately.
(2) Reinstall the support pad.
Cause
(1) The rear guide plate lags behind the guide wheel surface.
(2) The center of the part moves too high, causing the part to jump at the exit.
Eliminate the problem
(1) Move the rear guide plate slightly forward.
(2) Appropriately lower the center height of the part.
Cause
(1) The guide wheel inclination is too large, causing the part to move too fast.
(2) The grinding wheel is modified too fast, and the surface of the grinding wheel is not bright.
(3) The guide wheel is modified too roughly.
Eliminate the problem
(1) Reduce the inclination.
(2) Reduce the modification speed and modify the grinding wheel from the beginning.
(3) Rebuild the guide wheel.
Note: When the grinding wheel is not running, it is forbidden to open the coolant. If the coolant is opened first, to prevent the occurrence of faults, intermittent start-up (i.e., open, close, open, close) should be adopted to wait for the coolant to be dispersed from all sides before starting work.
