1. Preparation for disassembly:
Clean the outside of the screw and the surrounding area thoroughly to prevent contaminants from entering during disassembly.
Record the original state: mark the position and direction of the nut and support bearing; measure and record the original preload (if possible) and axial clearance (usually measured with a dial indicator).
Disconnect the coupling. Carefully disassemble the motor, sensor and other accessories.
Remove the connection of the nut mounting seat (workbench/slider).
2. Disassemble the screw assembly:
Loosen and remove the support bearing seat fixing bolts at both ends of the screw in sequence. Note that the bearing may have a preload structure (such as a locking nut, spacer), and pay attention to the sequence and direction when disassembling.
Carefully extract the screw: It is usually necessary to extract the screw together with the nut from the equipment horizontally or vertically. Extremely important: During the entire extraction process, it is necessary to ensure that the nut always moves within the effective travel range of the screw! It is absolutely forbidden to screw the nut out of the threaded end of the screw! Once the nut is screwed out of the end, the balls inside will scatter and it is almost impossible to put it back in place, which usually causes the nut to be scrapped.
For long screws, multiple people are required to cooperate or use auxiliary supports when pulling them out to prevent the screw from bending due to its own weight.
3. Removing the nut (if necessary):
Only when necessary and with special tools and skills! The internal structure of the nut is delicate and complex, and improper removal can easily cause permanent damage.
Use the nut removal tools or methods specified by the manufacturer (common methods include using removal holes, special clamps, etc.).
Pay attention to the arrangement of the balls and the return path when removing, and it is best to do it in a very clean environment. It is recommended to take photos to record the internal structure.
4. Thorough cleaning:
Use special solvents (such as precision instrument cleaning agents, sulfur-free kerosene) to thoroughly clean all parts such as the screw shaft, nut housing, balls (if removed), returners, seals, etc. It is strictly forbidden to use strong acids, alkalis or corrosive cleaning agents!
Wipe clean with a dust-free cloth and blow dry with compressed air (the air needs to be filtered, dry and oil-free). Make sure all parts are absolutely clean and free of residue.
5. Detailed inspection:
Screw shaft:
Visually inspect the thread raceway: Are there any scratches, indentations, pitting, peeling, cracks, rust? Use a magnifying glass or microscope for better results.
Measure the critical diameter (usually measured at multiple locations with a micrometer).
Check straightness: Place the screw on a V-block and measure the full-length runout with a dial indicator. If it is out of tolerance, it needs to be straightened (specialized equipment and technology required) or replaced.
Check the amount of thread wear (specialized measuring tools or compare with a new screw).
Nut (internal raceway): Also carefully inspect the raceway surface condition (scratches, pitting, peeling, etc.). Check thread wear.
Ball: Check each ball for chipping, indentation, deformation, and severe wear. Even if only one is damaged, it is recommended to replace the entire set. Mixing old and new balls will accelerate wear.
Returner/Ball Stopper: Check for breakage, deformation, and wear.
Seals: Check whether the lip is aged, cracked, deformed, or worn. It is usually recommended to replace new seals.
Support bearings: Check whether the bearings rotate smoothly, whether there is any abnormal noise, whether the clearance is too large, and whether the raceways and rolling elements are damaged. It is usually recommended to replace the support bearings when repairing the screw.
Bearing seat/nut seat: Check whether the mounting surface is flat, whether there is any damage from bumps, and whether the threaded holes are intact.
6. Repair or replacement decision:
Minor damage (such as very minor scratches, minor pitting): Sometimes you can try to repair it through fine polishing (professional techniques are required), but the risk is high and the effect is uncertain. It is generally not recommended.
Moderate to severe damage (obvious peeling, cracks, deep scratches, severe wear): The damaged parts must be replaced! Forced use will rapidly deteriorate, damage other parts, and even cause equipment accidents.
Bending deformation is out of tolerance: Professional straightening or replacement is required.
Key advice: For high-precision, high-load or core equipment, and when there is any visible damage to the screw or nut raceway, the most reliable and economical long-term solution is to replace the parts with new ones. Repairing old parts often makes it difficult to restore the original accuracy and life.
7. Assembly (critical step!):
Environment: Perform in a clean and dust-free environment as possible.
Lubrication: Apply the specified brand and sufficient amount of high-performance ball screw special grease evenly to all friction surface such as raceway, balls, return channel. The cleanliness of the grease is critical.
Inserting the balls (if the nut has been disassembled): This is the most delicate step. The balls must be installed back into the circulation channel one by one using the special auxiliary tools provided by the manufacturer (guide tube, cage, etc.) or extremely carefully according to the path and number of balls recorded during disassembly. Make sure that all balls roll smoothly without sticking. It is strongly recommended to operate by experienced personnel or directly replace the pre-assembled nut assembly.
Installing the seal: Install the new seal correctly, paying attention to the direction and lip orientation.
Close the nut (if disassembled): Carefully assemble the internal components of the nut in the reverse order of disassembly and close the shell, tighten the fixing screws/clamps using special tools or according to specifications.
Pre-installation of nuts: For nuts that require preload adjustment (such as double nut gasket type, double nut threaded type), it may be necessary to perform preliminary preload setting or gasket selection according to manufacturer requirements before installation on the equipment.
8. Install the screw assembly:
Carefully insert the assembled screw nut assembly into the base hole of the equipment. Also ensure that the nut does not escape the effective stroke of the screw.
Install the support bearing seat. Critical: Ensure the coaxiality of the support bearing seats at both ends! Use a precision level, laser calibrator or dial indicator to carefully adjust so that the screw axis is parallel to the guide rail and the support seat hole is concentric. Improper installation is one of the main causes of early failure.
Install and preload the support bearing according to specifications and requirements (angular contact ball bearings usually need to be preloaded in pairs). Tighten the locking nut.
Install the coupling to ensure good alignment with the motor shaft (radial and angular deviations must be within the allowable range).
Install the nut seat (workbench/slider) to ensure reliable connection and no torsional stress is applied to the nut.
9. Adjustment and testing:
Adjust the preload: For nuts with adjustable preload, use special tools (such as torque wrench, preload measuring instrument) or measure the axial displacement to accurately adjust the preload according to the value specified by the manufacturer. Too large or too small is harmful.
Measure the axial clearance: Use a dial indicator to measure the displacement of the workbench under the action of small forces in the positive and negative directions to confirm that the clearance meets the requirements (usually very small, a few microns to more than ten microns).
Manual operation: Manually move the workbench at low speed throughout the entire process to feel whether it is smooth, whether there are any stuck points or abnormal resistance.
10. Power-on test:
Run at low speed without load and listen for abnormal noise.
Gradually increase the speed and observe the vibration.
After running for a period of time, check whether the temperature rise is normal.
Perform positioning accuracy and repeat positioning accuracy detection. This is the gold standard for testing the effectiveness of maintenance.