KEVOS® MAKEOS · Strength
Interference Fit at Operating Temperature (Different Materials)
If the hub and shaft are different materials, how much interference is left at the operating temperature, does the fit still hold the torque hot, and is the hub overstressed at its tightest?
Check of an interference fit between a hub and shaft of different materials (aluminium on steel, bronze on steel): the interference at the operating temperature from the difference in expansion, contact pressure, holding torque and hub stress at assembly and at operating temperature (as the press and shrink fit tool), the torque against the required torque times the slip factor at the weaker condition, and the hub safety factor at the tighter one.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Interface diameter | mm | Nominal diameter of the fit. |
| Hub outside diameter | mm | Outside diameter of the hub. |
| Shaft bore (0 = solid) | mm | Bore of a hollow shaft. |
| Diametral interference at assembly temperature | mm | Diametral interference at the assembly temperature. |
| Engagement length | mm | Length of the fit. |
| Coefficient of friction at interface | Friction coefficient at the interface. | |
| Materials | ||
| Hub elastic modulus | GPa | Elastic modulus of the hub. |
| Hub Poisson’s ratio | Poisson’s ratio of the hub. | |
| Hub expansion coefficient | µm/(m·K) | Expansion coefficient of the hub. |
| Hub yield strength | MPa | Yield strength of the hub. |
| Shaft elastic modulus | GPa | Elastic modulus of the shaft. |
| Shaft Poisson’s ratio | Poisson’s ratio of the shaft. | |
| Shaft expansion coefficient | µm/(m·K) | Expansion coefficient of the shaft. |
| Duty | ||
| Assembly temperature | °C | Temperature at which the interference is measured. |
| Operating temperature | °C | Temperature of the joint in service (both parts at the same temperature). |
| Torque to transmit | N·m | Torque the fit must transmit. |
| Safety factor on slip | Safety factor against slipping. | |
| Required safety factor on hub | Safety factor you need on hub yield. | |
Method and formulas
- Interference hot = δ₀ + d (α_shaft − α_hub)(T_op − T_a).
- At each interference: p = δ ÷ {d [(k_h + ν_h) ÷ E_h + (k_s − ν_s) ÷ E_s]}; torque = μ p π d² L ÷ 2; hub von Mises stress (as the press and shrink fit tool).
- Grip checked at the smaller interference; hub stress at the larger.
- Example: the interference drops from 80 to 34 µm at 100 °C, so the fit holds 750.48 N·m hot.
Limitations
- Both parts at the same uniform temperature; transient heating of the hub alone loosens the fit further.
- Thick-cylinder theory; stress concentrations at the hub ends are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check an aluminium pulley or hub pressed on a steel shaft
- Check a bronze bush in a steel housing hot
- Choose interference for a fit that runs hot or cold
Who it is for
- Design engineers
- Machine designers
- Maintenance engineers
What you get
- Interference at operating temperature
- Pressure, torque and hub stress cold and hot
- Checks at the weaker and tighter conditions
Interpreting the result
- An aluminium hub on a steel shaft loosens as it warms: choose the interference for the hottest running condition.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 631–634, 375–376. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Interference Fit at Operating Temperature (Different Materials) calculator
