KEVOS® MAKEOS · Maintenance
Thermal Growth for Hot Shaft Alignment
How much will each machine’s shaft rise when hot, and what cold offset should be set?
Vertical thermal growth of the driver and driven shafts from foot-to-centreline height, expansion coefficient and temperature rise, and the cold alignment offset that gives true alignment at operating temperature.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Stationary machine (e.g. driver) | ||
| Foot to shaft centreline height | mm | Height from the stationary machine’s feet (or baseplate) to its shaft centreline. |
| Expansion coefficient | µm/(m·K) | Expansion coefficient of the stationary machine’s casing or supports (cast iron about 10.5, steel about 11–12 µm/m·K). |
| Temperature rise of supports | K | Average temperature rise of those supports from cold to running. |
| Movable machine (e.g. pump) | ||
| Foot to shaft centreline height | mm | Height from the movable machine’s feet to its shaft centreline. |
| Expansion coefficient | µm/(m·K) | Expansion coefficient of the movable machine’s supports. |
| Temperature rise of supports | K | Average temperature rise of the movable machine’s supports. |
Method and formulas
- Growth = α × H × ΔT for each machine.
- Relative growth = movable growth − stationary growth.
- Set the movable machine this much lower (positive) or higher (negative) than the stationary one when cold.
- Example: the movable machine grows 165 µm and the stationary one 66 µm, so set the movable machine 99 µm low when cold.
Limitations
- Uniform temperature rise of the supports; piping loads and uneven heating also move machines.
- Vertical growth only; horizontal growth is usually small but not always.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set cold alignment targets for hot pumps, compressors and turbines
- Explain why hot machines need offset alignment
- Check alignment targets supplied by a maker
Who it is for
- Maintenance engineers
- Reliability engineers
- Maintenance technicians
What you get
- Thermal growth of each shaft
- Relative growth
- Cold vertical offset to set
Interpreting the result
- Confirm with hot alignment checks (laser or proximity probes) where accuracy matters.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2645–2650, 375–376. Topic reference; no source tables or recommended settings are reproduced.
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