1. Scope and purpose
This manual covers critical maintenance procedures for precision ball screws used in industrial equipment, including CNC machine tools, robotic systems, manufacturing automation equipment, and other mechanisms where precise linear motion is required. The purpose of the manual is to provide competent technicians with detailed instructions for ensuring reliable operation, extending the life, and restoring specified parameters of ball screws by measuring preload, relubrication, and backlash compensation. Following these procedures is essential to maintain positioning accuracy, minimize wear, and prevent unexpected failures.
2. Precautions
CAUTION: Before starting any maintenance work, be sure to carry out lockout/tagout (LOTO) procedures in accordance with DSTU EN 1037:2001 "Safety of Machinery. Prevention of Unexpected Start". Failure to do so could result in serious injury or death.
CAUTION: Always use appropriate personal protective equipment (PPE), including safety glasses (DSTU EN 166), protective gloves (DSTU EN 388) and, if necessary, safety shoes (DSTU EN ISO 20345).
CAUTION: Lubricants can be harmful in contact with the skin or if inhaled. Work in well-ventilated areas. Use recommended PPE and dispose of used materials in accordance with local environmental regulations.
CAUTION: When working with heavy components or in awkward positions, use appropriate lifting equipment and follow safety rules when working at heights or in confined spaces.
3. Necessary tools and materials
Before starting work, prepare the following tools and materials:
| Name of tool/material | Specification | Quantity |
|---|---|---|
| Torque wrench | Range 10-100 Nm, accuracy ±4% (according to DSTU ISO 6789-1:2019) | 1 |
| A clock-type indicator with a magnetic base | Range 0-10 mm, accuracy 0.001 mm | 1 |
| A set of probes | The range is 0.02 - 1.00 mm, with a step of 0.01 mm | 1 set |
| A set of hex keys (Allen keys) | Metric, from 2 mm to 14 mm | 1 set |
| A set of socket wrenches | Metric, from 8 mm to 24 mm | 1 set |
| Brake cleaner/solvent | No residue, quick drying | 1 bottle (500 ml) |
| Lint-free napkins | Industrial, for cleaning | Package (50 pcs.) |
| Lubrication syringe/Centralized lubrication system | The appropriate type for the selected lubricant | 1 |
| Lubricant for ball screws | High quality lithium soap, NLGI class 1-2, (eg ISO L-XBCIA 2 or OEM equivalent) | 500 g |
| Micrometer | Range 0-25 mm, accuracy 0.001 mm (DSTU ISO 3611) | 1 |
| Vernier caliper | Range 0-150 mm, accuracy 0.02 mm (DSTU ISO 13385-1) | 1 |
4. Checklist before maintenance
Perform the following checks before disassembly or adjustment:
| Item | Verification | Acceptance/rejection criteria | Notes |
|---|---|---|---|
| 1. Visual inspection | Check the screw and nut for visible damage, cracks, deformation or corrosion. | No damage. Minor surface corrosion is acceptable provided there are no deep pits. | Pay attention to the areas of seals and support bearings. |
| 2. Inspection of seals | Inspect the ball nut seal for cracks, hardening, or displacement. | Seals must be intact, flexible, without visible signs of wear. | Damaged seals can lead to oil leakage and contamination. |
| 3. Presence of lubricant | Assess the condition and quantity of lubricant in the contact area of the screw and nut (if visually available). | Lubricant must be clean, without impurities, in sufficient quantity. | Signs of dryness, dirt, or discolored oil indicate the need for refilling. |
| 4. Backlash | Move the nut along the screw manually or with the system. Assess for noticeable backlash. | Minimal or no noticeable backlash. | Excessive backlash is an indication for compensation. |
| 5. Temperature | Record the operating temperature of the ball nut housing and thrust bearings after long-term operation. | The temperature should be within the limits specified by the manufacturer (usually up to +60°C). | Elevated temperature may indicate insufficient lubrication or excessive preload. |
| 6. Noises and vibrations | Listen to the ball screw as it moves. | Smooth, quiet operation. Absence of extraneous noises (creaking, crackling). | Any unusual noises or vibrations require immediate investigation. |
5. Step-by-step procedure
5.1. Equipment preparation
- De-energize and lockout: Turn off equipment power, perform full lockout/tagout (LOTO) procedure according to internal instructions and DSTU EN 1037:2001. Make sure all moving parts are locked.
- Access: Remove protective covers, covers or other elements that prevent access to the ball screw and its supports. Ensure that disassembly will not displace precision components.
- Cleaning: Using lint-free wipes and brake cleaner, thoroughly clean the outer surface of the screw and ball nut of old grease, dirt and dust. Do not allow cleaner to get inside the ball nut or support bearings.
5.2. Measurement of pretension (preload)
Preload is a critical parameter that ensures the stiffness and accuracy of a ball screw. Its measurement is mandatory for systems with a double nut or those where the manufacturer provides regulation.
- Installing the indicator: Install the clock-type indicator with a magnetic base on the stationary part of the equipment bed. The measuring tip of the indicator must rest against the end of the ball nut or a special measuring surface, perpendicular to the axis of the screw.
- Determining the zero point: Move the ball nut to the position where the measurement will be most stable and set the indicator dial to "0".
- Applying an axial load: Carefully, using a dynamometer or special device, apply an axial load to the ball nut in the direction opposite to the indicator measurement. The load must be sufficient to overcome the friction and select the possible backlash. A load equivalent to 5-10% of the dynamic load capacity of the nut is usually applied.
- Value reading: Record the indicator reading. This value represents the deformation caused by the preload, or the total axial play if there is no preload.
- Comparison: Compare the obtained value with the data provided by the manufacturer (OEM). For most precision ball screws, the preload is 0.005 – 0.015 mm. Deviation from the norm indicates the need for adjustment or replacement.
5.3. Replenishment of lubricant
Proper lubrication is key to minimizing friction, wear, and preventing overheating. Follow the manufacturer's recommendations for type and quantity of lubricant.
- Removing old grease: If the ball nut can be disassembled or has service holes, try to remove as much of the old, contaminated grease as possible. This can be done by slowly moving the nut along the screw while removing the protruding grease with lint-free wipes. Never use compressed air to remove grease, as this can drive dirt inside.
- Applying new grease:
- Through the oil pan: If the nut has an oil pan, connect the grease syringe and slowly feed the grease until fresh grease starts to come out of the seals. Usually it is 1-5 grams for small nuts, up to 10-20 grams for large ones.
- Manual application (for open systems): For open ball screws or after thorough cleaning, apply a thin, even coat of lubricant along the entire length of the screw and to the outer surface of the ball nut.
- Centralized lubrication systems: Activate the centralized lubrication system and ensure that the lubrication is supplied to the ball screw.
- Grease Distribution: After applying the grease, slowly move the ball nut along the entire length of the screw several times to ensure even distribution of the grease throughout all the ball tracks.
- Excess Removal: Remove any excess lubricant that protrudes with lint-free wipes to prevent dirt and dust from accumulating.
5.4. Backlash compensation
Backlash (backlash) in the ball screw leads to a decrease in positioning accuracy. Backlash compensation is critical to maintaining equipment performance.
- Nut Type Identification: Determine if the ball nut is single, double preloaded, or uses spacers. The compensation method depends on the design.
- For single nuts (without pretension): If the play is excessive and the design does not allow for adjustment, the only effective solution is to replace the ball nut or the entire screw-nut assembly. Unauthorized adjustment attempts can lead to rapid wear.
- For double pre-tensioned nuts (double nut):
- To loosen the locknuts: Loosen the locknuts that fix the position of the two parts of the ball nut relative to each other.
- Preload Adjustment: Carefully tighten the adjusting nut (or the nut connecting the two halves) to the slight torque specified by the manufacturer (usually 5-15Nm). Over-tightening will result in excessive preload, overheating and rapid wear.
- To check the resistance to rotation: Turn the screw by hand. It should rotate smoothly, without jamming, but with appreciable resistance.
- Tightening the locknuts: Tighten the locknuts to the recommended torque (usually 30-50Nm) while holding the adjusting nut to prevent it from turning.
- Retest backlash/preload: Repeat the preload measurement procedure (paragraph 5.2) to ensure that the value is within the manufacturer's tolerance.
- For nuts with spacer rings:
- Disassembly: Remove the ball nut from the screw (if it is provided by the design).
- Replacing spacer rings: Measure the thickness of the existing spacer rings (spacers) with a micrometer. Replace them with thinner rings to reduce backlash. Reducing the thickness by 0.01-0.02 mm usually leads to a significant reduction of the backlash.
- Assembly and inspection: Assemble the nut and install it on the screw. Repeat the backlash/preload measurement procedure (section 5.2). Use only original or high precision spacer rings.
5.5. Final assembly and inspection
- Installing protective elements: Replace all protective covers and covers that were removed. Make sure all fasteners are tightened to recommended torques (see OEM manual).
- Unblock: Perform the Unblock/Tag (LOTO) procedure and restore power to the equipment.
- Functional test: Run the equipment in test mode. Move the ball screw-driven axis through its entire stroke several times at different speeds. Check for smooth operation, absence of unusual noises and vibrations.
- Temperature monitoring: During the first hours of operation after maintenance, regularly check the temperature of the ball nut and support bearings. It should not exceed the norm.
6. Checklist after maintenance
Perform the following checks after completing the work and starting the equipment:
| Test | Expected result | Actual result | Result (Pass/Fail) |
|---|---|---|---|
| 1. Smoothness of movement | The axis moves smoothly, without jerks and jams along the entire length of the stroke. | ||
| 2. Absence of unusual noises | There is no grinding, crackling, howling or other extraneous noises during operation. | ||
| 3. Temperature of components | Ball nut and thrust bearing temperatures are within normal range (see OEM specification, typically < 60°C). | ||
| 4. Positioning accuracy | After several positioning cycles, test measurements confirm the claimed accuracy of the equipment. | ||
| 5. Absence of lubricant leaks | The seals are clean, there are no signs of leakage or excessive lubrication. | ||
| 6. Fastening reliability | All fasteners are tight, there is no vibration or backlash at the ball screw and support mounting points. |
7. Troubleshooting guide
The table shows typical faults, their probable causes and corrective actions.
| Symptom | Probable cause | Corrective action |
|---|---|---|
| Excessive axle backlash | Wear of the ball nut or balls; insufficient pretension; deformation of bearing supports. | Measure pre-tension, adjust or replace spacer rings. In case of significant wear, replace the screw-nut set. Check the rigidity of the supports. |
| Increased noise during operation | Insufficient or contaminated lubricant; excessive pretension; damaged balls/tracks; uneven lubrication. | Top up or replace the oil. Check the pre-tension. Inspect the ball nut for damage. |
| Overheating of the ball nut/support | Excessive pretension; insufficient lubrication; excessive axial load; pollution. | Check and adjust the pre-tension. Top up the oil. Check the operating conditions and clean the system. |
| Low positioning accuracy | Excessive backlash; component wear; problems with the control system. | Perform backlash compensation. Inspect the mechanical components. Check the parameters of the CPC system. |
| Stuck or uneven movement | Insufficient lubrication; contamination in the ball nut; damage to raceways; twisting of the screw. | Clean and refill the oil. Inspect the screw and nut. Check the straightness of the screw. |
| Lubricant leakage from seals | Damage or wear of seals; excessive oil pressure during filling; wrong type of lubricant. | Replace damaged seals. Control the amount of lubricant when refilling. Use the recommended type of lubricant. |
8. Recommended maintenance schedule
The following schedule is a general guideline. Follow the equipment manufacturer's specific instructions.
| Task | Frequency | Estimated duration | Qualification level |
|---|---|---|---|
| Visual inspection, seal check, oil level control (if available) | Monthly / Every 500 hours of operation | 15-30 min | Operator/Technician |
| Lubricant replenishment (for systems without centralized lubrication) | Quarterly / Every 2000 hours of operation | 30-60 min | Technician |
| Complete cleaning and replenishment of lubricant, backlash check | Annually / Every 8000 hours of operation | 1-2 hours | Service technician |
| Preload measurement, backlash compensation (if necessary) | Every 2 years / Every 16,000 operating hours | 2-4 hours | Senior Technician/Engineer |
| Full inspection and overhaul (replacement of components) | Every 5 years / 40,000 hours of operation or according to the results of diagnostics | From 1 day | Specialized staff |
9. Directory of spare parts
UNITEC-D GmbH offers a wide range of components for ball screws and lubrication systems. Consult our electronic catalog to select the necessary spare parts.
| Part description | Typical specification | Category UNITEC |
|---|---|---|
| Ball nuts | Various types (flange, cylindrical), diameter, pitch, accuracy class (according to ISO 3408) | Elements of linear movement |
| Seals for ball nuts | Material (NBR, FKM), inner/outer diameter | Sealing |
| Lubricants for ball screws | Lithium, synthetic, NLGI grade, temperature range | Lubricating materials |
| Maslyanka (Tavotnitsy) | Thread (M6, M8, 1/8" BSP), material | Lubrication systems |
| Spacer rings (spacers) | Thickness, diameter, accuracy class | Elements of linear movement / Precision elements |
| Support bearings (support assemblies) | Type (radial-thrust), shaft diameter, accuracy class | Bearings |
Visit our unitec-D e-catalogue for detailed selection and ordering.
10. Links
- DSTU EN 1037:2001. Machine safety. Prevention of unexpected start.
- DSTU EN 166:2017. Means of individual eye protection. General technical requirements.
- DSTU EN 388:2017. The gloves are protective against mechanical damage.
- DSTU EN ISO 20345:2019. Personal protective equipment. Protective shoes.
- DSTU ISO 3611:2015. Micrometers for external measurements. Technical conditions.
- DSTU ISO 13385-1:2019. Geometric characteristics of products (GPS). Devices for measuring linear dimensions. Part 1. Vernier calipers.
- DSTU ISO 6789-1:2019. Wrenches with controlled tightening torque. Part 1. Requirements and test methods for structural control of tightening torque.
- ISO 3408. Ball screws.
- OEM and ball screw manufacturer recommendations.
- ISO L-XBCIA. Classification of lubricants.
