A ball screw does not have a fixed lifespan such as three, five or ten years. Its service life is normally estimated in revolutions, total travel distance or operating hours according to the basic dynamic load rating, applied axial load, screw speed and machine duty cycle.
Under correct selection, installation, lubrication and protection, a ball screw may operate for many millions of revolutions. However, contamination, misalignment, inadequate lubrication, shock loads or an incorrect preload can cause failure much earlier than the calculated fatigue life.
How Long Does a Ball Screw Last?
The most accurate answer depends on how the ball screw is selected and used. A lightly loaded ball screw operating in a clean, well-lubricated and correctly aligned system may continue working long after the machine has completed millions of cycles. The same model can fail much earlier when exposed to excessive axial load, metal chips, coolant, poor lubrication or installation error.
Ball screw life is therefore normally described in three ways:
| Life Expression | Unit | What It Describes |
|---|---|---|
| Nominal life | Revolutions | Calculated rolling-fatigue life based on dynamic load rating and axial load |
| Travel life | Kilometres | Total linear distance travelled by the nut |
| Operating life | Hours | Estimated running time at a specified average rotational speed |
| Machine service period | Months or years | Calendar time determined by daily operating hours, cycles and downtime |
For example, two machines may use the same ball screw and complete the same total number of revolutions, but the machine operating 16 hours per day will reach that total much sooner than one operating only two hours per day.
How to Calculate L10 Ball Screw Life
L10 nominal life is the calculated rolling-fatigue life that 90% of a group of identical ball screws are expected to reach or exceed under the same operating conditions without fatigue flaking.
It is calculated from the ball screw's basic dynamic axial load rating and the applied axial load:
Ca = basic dynamic axial load rating in N
Fa = equivalent applied axial load in N
The basic dynamic load rating is not the maximum load that the ball screw can survive. It is a reference value used for rolling-fatigue life calculation. Static load capacity, shock load, shaft buckling and critical speed must be checked separately.
Because the load ratio is raised to the third power, applied load has a major influence on calculated life. If the equivalent axial load increases while the selected ball screw remains unchanged, the calculated L10 life falls rapidly.
Converting Revolutions to Travel Distance
Once nominal life in revolutions is known, it can be converted into total linear travel using the ball screw lead:
A larger lead produces more linear travel per revolution. It therefore changes the calculated travel distance, even when the nominal life in revolutions remains the same.
Converting Revolutions to Operating Hours
When the average rotational speed is known, nominal life can also be converted into operating hours:
Average rpm should reflect the actual duty cycle. Using only the maximum motor speed may produce an unrealistic operating-life estimate when the axis frequently accelerates, decelerates, stops or runs at several different speeds.
Ball Screw Life Calculation Example
The following example is for explaining the calculation method. It is not a load rating for a specific DLY ball screw model.
- Basic dynamic axial load rating: 12,000 N
- Equivalent applied axial load: 3,000 N
- Ball screw lead: 10 mm
- Average operating speed: 500 rpm
Step 1: Calculate Nominal Life
L10 = (12,000 ÷ 3,000)3 × 106
L10 = 43 × 106 = 64,000,000 revolutions
Step 2: Convert to Travel Distance
Travel life = 64,000,000 × 10 ÷ 1,000,000
Travel life = 640 km
Step 3: Convert to Operating Hours
Operating life = 64,000,000 ÷ (60 × 500)
Operating life ≈ 2,133 hours
If the machine operates eight actual running hours per day, the calculated value corresponds to approximately 267 operating days. This is still a nominal fatigue-life calculation rather than a guaranteed replacement date.
Calculated Life vs. Actual Service Life
L10 predicts rolling-contact fatigue under defined load conditions. It does not include every failure mode that can occur in a real machine. A ball screw may reach the end of its usable service life because of contamination, corrosion, collision damage, poor alignment or loss of positioning performance before fatigue flaking occurs.
| Condition | Possible Effect | Included in Basic L10 Formula? |
|---|---|---|
| Normal axial operating load | Rolling-contact fatigue over time | Yes |
| Fluctuating duty-cycle load | Changes the equivalent load and calculated life | Only when correctly converted to an equivalent load |
| Shock or collision | Raceway dents, ball damage or permanent deformation | No |
| Misalignment | Uneven load, heat and accelerated wear | No |
| Dust, chips or coolant entry | Abrasive wear, corrosion and return-system damage | No |
| Incorrect or insufficient lubrication | Higher friction, temperature and wear | No |
For a detailed explanation of these premature-failure conditions, see What Causes Premature Ball Screw Failure?
When Should a Ball Screw Be Replaced?
A ball screw should not be replaced only because a calculated number of hours has been reached. Its actual condition and the accuracy required by the machine must also be considered.
Inspection or replacement should be considered when one or more of the following changes appear:
- Axial clearance or backlash has increased beyond the machine's allowable limit.
- Positioning accuracy or repeatability can no longer be restored through normal adjustment.
- Running torque has increased or become irregular.
- The nut feels rough, tight or uneven when moved along the screw.
- Abnormal noise or vibration continues after lubrication and alignment have been checked.
- Raceways show pitting, flaking, corrosion, dents or severe wear.
- The return system, seals or nut body has been damaged.
- The screw shaft is bent or its runout affects installation and rotation.
- Lubricant repeatedly contains visible metallic particles.
Before deciding that the ball screw itself has failed, also inspect the support bearings, coupling, nut housing, motor alignment and linear guide system. Noise, vibration and positioning errors can come from surrounding components rather than the screw and nut alone.
How to Extend Ball Screw Life
Long service life begins with correct selection. The screw diameter, lead, dynamic load rating, static load rating, critical speed, buckling resistance, accuracy grade and support arrangement should match the machine conditions.
During installation and operation, the following measures help reduce avoidable damage:
- Align the screw, nut housing, support units and guide system before full-speed operation.
- Use a lubricant suitable for the load, speed, temperature and operating environment.
- Set a maintenance interval according to actual operating hours and contamination level.
- Use bellows, telescopic covers or other protection where chips and dust are present.
- Avoid impact at the end of travel by setting suitable limits, buffers and deceleration.
- Do not remove the nut from the screw without a suitable transfer sleeve.
- Monitor changes in backlash, torque, noise, vibration and temperature.
Zhejiang DLY Automation Manufacturing Co., Ltd. supplies cold-rolled and ground ball screws for CNC machines, automation equipment, linear modules and industrial motion systems. Available services include customized length, shaft-end machining according to drawings, nut matching and related support-unit supply.
To evaluate a ball screw for a new machine, provide the model, diameter, lead, total length, axial load, speed, stroke, duty cycle, installation direction and required accuracy. For a replacement project, provide the original drawing, model number and clear photographs of the complete assembly.
View the DLY ball screw product range .
Need Help Checking Ball Screw Life?
Send DLY your ball screw model, load, speed, stroke, operating cycle, drawing and required quantity. We can help check the main selection and machining information before quotation.
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