Temperature affects a rotating ball nut system by changing the length of the screw shaft, lubricant viscosity, ball-contact preload, support-bearing condition and final positioning accuracy. The important value is not only the ambient temperature but also the temperature rise generated inside the rotating nut assembly during operation.
A rotating ball nut contains more heat-sensitive elements than an ordinary non-rotating nut. In addition to the balls and raceways, the complete assembly may include support bearings, seals, a housing, pulley, belt or coupling. All these components can influence the operating temperature and running torque.
A rotating ball nut system combines the rolling ball nut with a driven rotary structure and external support components.
Ambient Temperature and Operating Temperature Are Different
Ambient temperature is the temperature of the air or surrounding machine environment. Operating temperature is the actual temperature of the nut, bearings, screw shaft and housing after the axis has been running.
The operating temperature may be higher than the surrounding air because heat can be generated by:
- Preload between the balls and raceways
- Support-bearing preload and friction
- Ball recirculation at high rotational speed
- Seal contact resistance
- Excessive or unsuitable lubricant
- Misalignment between the screw shaft and rotating nut
- An eccentric pulley, coupling or drive belt
- Heat transferred from the motor or nearby machine components
For this reason, measuring room temperature alone cannot show whether the rotating nut is operating under a stable thermal condition.
1. Thermal Expansion Changes Screw Length
The steel screw shaft expands as its temperature rises. A useful approximate relationship is:
The linear thermal expansion coefficient of steel is approximately 11–12 × 10−6/°C. Therefore, a 1,000 mm steel screw that becomes 10°C warmer may lengthen by approximately 0.11–0.12 mm.
This value is much larger than the positioning tolerance of many precision axes. Even when the screw itself has good lead accuracy, thermal elongation can change the actual position reached by the moving table.
2. Temperature Can Change Preload and Running Torque
The screw shaft, nut body, balls, bearings and housing do not necessarily heat at the same rate. A temperature difference between these components can temporarily change their dimensional relationship.
Possible effects include:
- Increased internal preload and running torque
- Reduced preload or increased axial clearance
- Uneven torque during machine warm-up
- Changes in support-bearing preload
- Local stress caused by restricted thermal expansion
A rising temperature does not always make the nut bind, and cooling does not automatically create excessive clearance. The result depends on the materials, component geometry, preload method, bearing arrangement and temperature distribution through the assembly.
If the rotating torque increases continuously as the machine warms, inspect preload, lubrication, alignment and support bearings rather than assuming that expansion of the nut body is the only cause.
3. Lubricant Viscosity Changes with Temperature
Lubricant becomes less viscous as temperature rises and more viscous as temperature falls. Both conditions can affect a rotating ball nut.
| Temperature Condition | Possible Lubrication Effect | Possible Operating Symptom |
|---|---|---|
| Low temperature | Grease becomes more resistant to movement | Higher starting torque and slow initial movement |
| Normal operating range | Lubricant forms a stable film and circulates normally | Stable torque and smooth movement |
| Excessive temperature | Viscosity drops and oxidation may accelerate | Reduced lubricant life, leakage or increasing wear |
The lubricant should be selected according to the actual speed, load, temperature range, relubrication method and operating environment. Do not assume that adding more grease will solve a temperature problem. Excessive grease can increase churning resistance and generate additional heat.
4. The Support Bearings May Generate More Heat Than the Nut
In a rotating nut structure, the nut is normally supported by bearings so that it can rotate while transmitting axial force to the housing. Bearing preload, lubrication and installation accuracy can therefore have a major influence on temperature.
Check the bearing system when:
- The housing becomes hot near the bearing position.
- Temperature rises even when the axial load is low.
- Rotational torque increases after the bearing locknut is tightened.
- Noise changes with rotating speed.
- The assembly temperature is much higher than the screw shaft temperature.
Possible causes include excessive bearing preload, incorrect bearing installation, too much grease, contamination or an eccentric drive pulley. Replacing the ball nut alone will not correct these problems.
5. High Rotational Speed Increases Heat Generation
One reason for using a rotating nut is to keep a long screw shaft stationary and reduce screw-whipping risk. However, the nut, bearings and drive components still rotate at the speed required by the selected lead and linear velocity.
The relationship is:
For the same linear speed, a smaller screw lead requires a higher nut rotational speed. This can increase bearing, seal and ball-circulation heat. Lead selection should therefore consider both positioning resolution and the rotational speed of the nut assembly.
DLY's ball screw rotating nut solutions can be checked according to the screw diameter, lead, stroke, load, speed, housing structure and drive arrangement.
6. Installation Alignment Affects Temperature
The rotating nut axis must be aligned with the fixed screw shaft and the machine guideways. Misalignment applies additional radial force to the nut and support bearings, increasing friction and temperature.
During installation:
- Clean the screw shaft, nut housing and carriage mounting surfaces.
- Install the screw shaft without forcing it into an offset position.
- Mount the rotating nut housing with the bolts initially loose.
- Move the carriage slowly through the available stroke.
- Check that the nut rotates smoothly at several positions.
- Tighten the housing bolts gradually and recheck the torque.
- Confirm that the pulley or coupling is concentric with the nut axis.
If the housing temperature rises after final tightening, loosen the housing and compare the running condition. A clear reduction in torque or temperature indicates that installation alignment should be corrected.
7. Thermal Expansion Must Be Allowed in the Machine Design
A long screw shaft should not be constrained in a way that prevents normal thermal growth. If both ends and the surrounding structure lock the shaft without an appropriate design, temperature rise can introduce additional axial stress.
The correct solution depends on the rotating nut structure and machine layout. Possible engineering approaches include:
- Defining a fixed thermal reference point
- Allowing controlled axial expansion at the opposite end
- Using a designed tension or pretension arrangement
- Monitoring screw temperature for compensation
- Applying position compensation in the control system
- Reducing heat transfer from the motor and surrounding equipment
Do not add uncontrolled clearance to the nut as a general solution. Excessive clearance reduces reversal stability and does not compensate consistently for screw elongation.
Rotating Nut Views and Inspection Areas
Check temperature near the nut body, seals, support bearings and drive connection.
Bearing preload, housing alignment and pulley concentricity can affect operating temperature.
How to Monitor Temperature Correctly
Measure temperature under repeatable operating conditions rather than checking one random point after the machine stops.
A useful test record includes:
- Ambient temperature before startup
- Nut-housing temperature
- Support-bearing temperature
- Screw-shaft temperature at several positions
- Nut rotational speed
- Axial load and duty cycle
- Running torque or motor current
- Time required to reach a stable temperature
Use the same measurement locations each time. A temperature trend is more useful than one isolated reading because it shows whether the assembly is stabilizing or continuing to heat.
Temperature Troubleshooting Guide
| Observed Condition | Possible Cause | Check First |
|---|---|---|
| High torque immediately after cold startup | Lubricant viscosity is too high at low temperature | Lubricant temperature range and grease quantity |
| Torque and temperature rise together | Excessive preload, poor alignment or bearing friction | Housing alignment, bearing preload and lubrication |
| Bearing area is hotter than the nut body | Bearing preload, contamination or installation error | Support-bearing condition and locknut setting |
| Position changes as the machine warms | Screw elongation or machine-frame thermal drift | Screw temperature and position-error trend |
| Temperature rises only at high speed | Bearing, seal, ball-circulation or lubricant loss | Rotational speed, lead and lubricant specification |
| Temperature increases after mounting bolts are tightened | Housing is pulling the nut off-axis | Housing height and lateral alignment |
Information Needed for a Temperature-Sensitive Application
Before selecting a nut rotary ball screw set, provide:
- Minimum and maximum ambient temperature
- Required linear speed and screw lead
- Nut rotational speed
- Axial load and duty cycle
- Screw diameter, total length and stroke
- Required positioning accuracy
- Preload or axial-clearance requirement
- Lubrication method and maintenance interval
- Pulley, belt, coupling and housing structure
- Available cooling, protection and temperature monitoring
DLY can check the ball screw and rotating nut configuration according to the model, machine conditions and installation drawing. The permitted operating temperature should be confirmed for the complete assembly, including lubricant, seals, bearings and drive components-not only the steel nut body.
Need a rotating ball nut for a temperature-sensitive application?
Send DLY the temperature range, load, speed, lead, stroke and rotating nut installation drawing.
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