1. Scope and Purpose
This practical maintenance guide was developed for technicians and field engineers responsible for the maintenance and optimization of linear motion systems that employ ball screws in industrial machines. Covers critical procedures for measuring and adjusting preload, properly replenishing lubrication and compensating axial clearances (backlash). Strict application of these guidelines ensures positioning accuracy, extends component and equipment life, and maintains operational reliability, essential elements for productivity in the manufacturing sector.
Perform this maintenance preventively, according to the established schedule, or correctively, when identifying signs such as loss of precision, abnormal noises, excessive vibrations, localized heating or unstable movements in the axis.
2. Safety Precautions
⚠ CRITICAL SAFETY WARNING ⚠
Before beginning any maintenance procedure, ensure that the machine is completely de-energized and locked. Perform the Locking and Tagging (LOTO) procedure in accordance with ABNT NBR 16499 and NR-10/NR-12. Confirm that all electrical, hydraulic, pneumatic and mechanical power sources have been turned off. Depressurize hydraulic and pneumatic systems. Be careful with residual energies such as pre-charged springs or capacitors. Failure to follow these instructions could result in serious accidents, equipment damage or fatality.
2.1. Mandatory Personal Protective Equipment (PPE):
- Safety Gloves: Resistance to cuts and chemicals (nitrile) for handling lubricants and sharp components.
- Safety Glasses: Protection against lubricant splashes and particles during cleaning.
- Safety Shoes: With steel toe cap to protect against falling heavy objects.
- Hearing Protection: If the work environment requires it or during machine testing.
3. Tools and Materials Required
Adequate preparation is essential for an efficient and safe intervention. Make sure you have all listed items on hand.
| Tool/Material | Typical Specification | Quantity |
|---|---|---|
| Snap Torque Meter | Range from 5 Nm to 50 Nm (1/4" drive) Range from 20 Nm to 200 Nm (3/8" or 1/2" drive) |
2 |
| Comparator Clock | Resolution 0.001mm to 0.01mm, 10mm travel | 1 |
| Hinged Magnetic Base | For fixing the dial indicator | 1 |
| Feeler Gauge (Feel Gauge) | Set of blades from 0.02 mm to 1.00 mm | 1 |
| Manual/Pneumatic Grease Gun | With standard nozzle and assorted adapters | 1 |
| Ball Screw Grease | Lithium-complex, grade NLGI 1 or 2, with EP additives, according to OEM (e.g. Klüber NBU 15, Mobilux EP2). | As needed |
| Ball Screw Oil | ISO VG 32, 46 or 68, with anti-wear additives, according to OEM. | As needed |
| Degreasing Solvent | Non-residual, non-flammable, compatible with seals (e.g. Isopropyl Alcohol, non-chlorinated brake cleaner). | 1 Liter |
| Clean, Lint-Free Cloths | Cotton or microfiber | Package |
| Soft Bristle Brushes | For delicate cleaning | Varied |
| Allen/Torx wrenches | Complete set | 1 |
| Open/Combination Wrenches | Complete set | 1 |
| Pin/Pulley Extractor | If necessary for decoupling | 1 |
| Laser Alignment Tool | For alignment of couplings (optional, but recommended) | 1 |
| Infrared Thermometer | For temperature monitoring | 1 |
| Digital Caliper | Accuracy 0.02mm, range 150mm | 1 |
4. Pre-Maintenance Inspection Checklist
Before starting maintenance procedures, perform a thorough visual and functional inspection. Record all observations.
| Item | Verification | Accept/Reject Criteria | Notes |
|---|---|---|---|
| Abnormal Noises | Listen carefully during operation (if safe and permitted) or move manually. | Absence of squeaks, pops, creaks or metallic noises. Noises present = REJECT. | |
| Excessive Vibration | Touch the spindle housing and support bearings; watch the table move. | Minimal or no vibration. Noticeable vibration = REJECT. | |
| Seal Integrity/Dust Scraper | Visually inspect the nut and bearing seals. | Absence of tears, hardening, cracks or deformations. Visible damage = REJECT. | |
| Lubricant Leak | Check for grease or oil leaking through seals or around bearings. | Dry or lightly greased surfaces. Visible leak = REJECT. | |
| Smoothness of Movement | Move the shaft manually (if possible) or observe the machine cycle. | Free movement, without blocking points or roughness. Roughness/stuckness = REJECT. | |
| Operating Temperature | Measure the temperature of the spindle nut and bearings with an infrared thermometer (if there is a history). | Stable temperature within the range specified by the OEM (e.g. < 50°C). Excessive heating = REJECT. | |
| Fixing Components | Check the tightness of the bearing fixing screws, nut and coupling. | Screws firmly tightened, without looseness. Loose screws = REJECT. | |
| Lubrication Color | If visible, note the color and consistency of the grease/oil. | Color and consistency typical of new/good condition lubricant. Darkening/contamination = REJECT. |
5. Step by Step Procedure
Follow each step carefully to ensure maintenance is performed correctly. Record the measured values.
5.1. De-energization and Access
- De-energize the Machine: Strictly follow the LOTO (Lockout and Tagout) procedure. Verify “zero power” status using suitable test equipment.
- Remove Protections: Carefully dismantle covers, bellows and other protections that prevent access to the ball screw. Arrange the removed components to facilitate reassembly.
- Uncouple the Spindle (if necessary): If the nut or spindle needs to be removed for deep cleaning or replacement, uncouple the coupling from the motor. Caution: When removing the coupling, mark its position to ensure original alignment upon reassembly.
5.2. Deep Cleaning
- Remove Old Lubricant: Using clean cloths and degreasing solvent, remove all old lubricant and contaminants from the spindle thread and nut surface. Use soft-bristled brushes for the grooves if necessary. Avoid: Using aggressive solvents that could damage the seals or paint of the machine.
- Visually Inspect: Examine the spindle thread and ball nut (if accessible) for signs of wear, pitting (minor corrosion), corrosion, dents, or overheating (discoloration). Minor damage may indicate the need for replacement.
5.3. Preload Measurement and Adjustment (if applicable)
Preload is essential to eliminate internal play and increase system rigidity.
- Prepare for Measurement: With the spindle clean and uncoupled, mount it on its support bearings. Rotate the spindle manually to ensure free movement.
- Measure the Rotation Torque: Attach the torque meter to the spindle shaft. Rotate the spindle slowly through its entire length (if possible) or a representative section, recording the torque required to turn it without the nut connected to any external load. Reference value: For a precision spindle with light preload, the rotation torque can vary from 0.1 Nm to 0.3 Nm, but should always be confirmed with the manufacturer's manual.
- Compare with OEM Specification: Check the value obtained with the manufacturer's preload specification. Deviations indicate incorrect fit or wear.
- Adjust Preload (if adjustable): If the spindle has a preload adjusting ring or spacers, carefully adjust them to achieve the specified rotational torque. Generally, this adjustment is made by compressing or expanding the nut or double nut assembly.
- Check Again: After adjustment, recheck the rotation torque to confirm that it is within the acceptable range.
- Common Error: Exaggerating the preload results in excessive friction, overheating, increased energy consumption and premature wear of the balls and bearing races. Insufficient preload causes excessive play and loss of stiffness.
5.4. Proper Lubrication
Lubrication is vital to reduce friction, dissipate heat and protect against corrosion.
- Choice of Lubricant: Use only the grease or oil specified by the ball screw manufacturer. Compatibility is critical. For greases, observe the NLGI grade and type of thickener (e.g. lithium-complex); for oils, ISO VG viscosity.
- Grease Application: If it is grease, use the grease gun. Clean the grease fitting nozzle. Connect to nut or bearing lubrication nipple. Inject the grease slowly, making a few movements with the nut to distribute the lubricant. Continue until a small excess of new, clean grease begins to emerge from the seals. Reference volume: For a typical spindle nut, 5 to 10 cm³ of grease may be enough for one cycle, but consult the manual for exact volume and frequency.
- Oil Application: If it is oil, check the level in centralized lubrication systems or add the specified volume. In oil bath systems, ensure the level is correct.
- Distribution Cycles: After lubrication, move the ball screw manually (if possible) or via machine control through its entire stroke several times to ensure even distribution of the lubricant.
- Common Mistake: Using inappropriate lubricant or mixing different types of grease can lead to lubricant degradation and premature failure. Excessive lubrication can cause overheating; Insufficient lubrication causes friction and wear.
5.5. Axial Clearance Compensation (Backlash)
Axial play is the dead movement between the spindle and nut. In precision systems, it must be minimized or eliminated.
- Position the Dial Dial: Fix the magnetic base on a stable part of the machine, adjacent to the spindle nut. Position the measuring tip of the dial indicator so that it touches the spindle nut parallel to the spindle axis, measuring the axial movement.
- Measure the Backlash: Move the spindle nut slowly in one direction (e.g. forward) until the movement stops. Zero the dial indicator. Then move the spindle nut slowly in the opposite direction (e.g. backwards) until the movement stops. The value read on the dial indicator is the axial clearance (backlash).
- Compare to OEM Specification: The allowable axial clearance is typically very small for precision screws (e.g. 0.005 mm to 0.015 mm). Values above indicate wear or misadjustment.
- Adjust Clearance (if adjustable): On preloaded double nuts, adjustment is made by turning an adjusting ring between the two nuts, or through spacer shims. On single nuts, excessive play often indicates the need for replacement. Follow the manufacturer's manual for the exact procedure.
- Check at Multiple Points: Measure end play at at least three different points along the spindle travel (start, middle, and end) to ensure consistency of adjustment.
- Common Error: Not checking the play in different stroke positions can hide uneven wear. Adjusting the clearance without knowing the OEM reference value can lead to incorrect adjustment, impacting accuracy or causing binding.
5.6. Assembly and Alignment
- Reassemble Components: Replace the spindle nut (if removed), support bearings and motor coupling, ensuring all parts are clean and positioned correctly.
- Align the Coupling: Accurate alignment between the spindle and motor is crucial. Use a feeler gauge or, ideally, a laser alignment tool. Check and correct angular and parallel misalignments. Typical tolerance: Maximum angular misalignment 0.05 mm/100 mm and maximum parallel misalignment 0.02 mm.
- Final Tightening: Tighten all bearing fixing screws, nut and coupling with the torque wrench, according to the values recommended by the manufacturer. Torque Examples: M8 Screw (class 8.8) with 25 Nm; M10 screw (class 8.8) with 49 Nm. Always check the equipment manual for exact values.
- Replace Protections: Assemble all protective covers and bellows, ensuring that they do not interfere with the movement of the spindle.
- Common Error: Improper alignment of couplings generates excessive stresses on the spindle and motor bearings, causing vibration, noise and premature failure. Failure to tighten screws to the correct torque can lead to loose or deformed components.
6. Post-Maintenance Verification Checklist
After the procedures are completed, perform these checks to confirm the effectiveness of the maintenance.
| Test | Expected Result | Actual Result | Pass/Fail |
|---|---|---|---|
| Absence of Abnormal Noises | Smooth and silent movement. | ||
| Stable Operating Temperature | Nut and bearing temperatures within the normal range (e.g. < 50°C), without peaks. | ||
| Positioning Accuracy (Repeatability) | Positioning measurement within the tolerance specified by the OEM (ex: ±0.005 mm). | ||
| Smooth Movement Throughout | Shaft moves freely, without roughness, locking or torque variations. | ||
| Seal tightness | No lubricant leakage through the seals. | ||
| Rotation Torque (Preload) | Within the range specified by the OEM (ex: 0.1 Nm - 0.3 Nm). | ||
| Axial Clearance (Backlash) | Within the range specified by the OEM (ex: 0.005 mm - 0.015 mm). |
7. Troubleshooting Guide
This guide provides guidance for diagnosing and correcting common ball screw problems.
| Symptom | Probable Cause | Corrective Action |
|---|---|---|
| Excessive noise (squeaking, squeaking) | Insufficient or degraded lubrication. Excessive preload. Wear on balls/races. Lubricant contamination. Misalignment. |
Refill/replace lubricant. Adjust preload. Replace spindle/nut. Clean and relubricate. Check and correct alignment. |
| Abnormal Heating of the Nut/Bearings | Excessive preload. Inadequate lubrication (type, quantity). Contamination. High speed/continuous load. Misalignment. |
Adjust preload. Check/replace lubricant. Clean system. Reevaluate operating conditions. Check and correct alignment. |
| Loss of Precision / Inaccurate Movement | Excessive axial play (backlash). Wear on the spindle/nut. Problems in the control system (CNC). Instable bearing fixation. Contamination. |
Adjust clearance. Replace spindle/nut. Check CNC parameters. Retighten fastenings. Clean system. |
| Excessive Vibration | Spindle/coupling misalignment. Wear or damage to spindle/nut. Inadequate preload. Problems in support bearings. |
Correct alignment. Inspect/replace spindle/nut. Adjust preload. Inspect/replace bearings. |
| Difficulty in movement/locking | Excessive preload. Absent lubrication. Foreign body. Severe misalignment. Mechanical damage (seized balls). |
Adjust preload. Lubricate. Disassemble and inspect/clean. Correct alignment. Replace spindle/nut. |
| Lubricant Leak | Damaged or aged seals. Excessive lubricant. Excessive internal pressure. |
Replace seals. Reduce amount of lubricant. Check pressure relief system (if applicable). |
8. Recommended Maintenance Schedule
Ranges can vary significantly depending on application, load, speed, environment and manufacturer specifications. Use these guidelines as a starting point and adjust based on experience and operating conditions.
| Task | Recommended Frequency | Estimated Duration | Skill Level |
|---|---|---|---|
| Visual and Auditory Inspection | Daily/Weekly | 10-15 minutes | Junior Operator/Technician |
| Lubricant Level/Condition Check | Monthly/Every 250 hours | 15-30 minutes | Junior/Full Technician |
| Refilling/Replacing Lubricant | Every 500-2000 hours of operation or Annually | 30-90 minutes | Full Technician |
| Preload Measurement and Adjustment | Every 2000-4000 hours of operation or biannual | 1-3 hours | Senior Technician/Specialist |
| Measurement and Adjustment of Axial Clearance (Backlash) | Every 2000-4000 hours of operation or biannual | 1-3 hours | Senior Technician/Specialist |
| Alignment Check (Spindle/Motor) | Every 4000-8000 hours of operation or Annually | 1-2 hours | Full/Senior Technician |
| Detailed Wear Inspection (Partial Disassembly) | Every 8000 hours of operation or biannual | 2-4 hours | Senior Technician/Specialist |
9. Spare Parts Reference
Always maintain a strategic inventory of critical spare parts to minimize downtime. Consult the OEM catalog and UNITEC-D e-catalog for exact identification.
| Part Description | Typical Specification | UNITEC category |
|---|---|---|
| Complete Ball Screw | Diameter, pitch, length, type of nut, precision (e.g. Ø32mm, pitch 10mm, Class C3) | Linear Transmission |
| Ball Nut (individual) | Type (single, double preloaded), diameter, pitch, material, precision | Linear Transmission |
| Ball Nut Repair Kit | Contains balls, spacers, seals (model specific) | Maintenance Kits |
| Spindle Support Bearings | Type (fixed/support), shaft diameter, bearing type (e.g. contact angle) | Bearings and Bearings |
| Flexible/Rigid Coupling | Shaft diameter, material, nominal torque (ex: Ø25xØ32, Aluminum) | Couplings |
| Nut Seals/Dust Scraper | Material (NBR, FKM), inner/outer diameter (model specific) | Seals |
| Lubricant (Grease or Oil) | According to OEM specification (e.g. NLGI 2 lithium-complex grease, ISO VG 68 oil) | Lubricants |
For consultation and purchase of original and compatible spare parts, visit our e-catalog: www.unitecd.com/e-catalog/
10. References
- Equipment Manufacturer (OEM) Operation and Maintenance Manual.
- ABNT NBR ISO 3408-1 to 3408-5: Ball screws - Parts 1 to 5 (If applicable for the specific technical characteristics of the screw).
- ABNT NBR 14039: Medium voltage electrical installations from 1.0 kV to 36.2 kV. (For electrical safety and LOTO procedures).
- Regulatory Standard NR-10: Safety in Electrical Installations and Services.
- Regulatory Standard NR-12: Workplace Safety in Machines and Equipment.
