BIZOMAT 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. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Stationary machine (e.g. driver)
What this means: Foot to shaft centreline height
- What it is
- The vertical distance from the stationary machine’s mounting feet (or baseplate top) to the centreline of its shaft. This height grows as the supports warm up.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Growth rises in direct proportion to this height.
- Get it right
- Measure from the underside of the feet that sit on the base, not from the floor.
What this means: Expansion coefficient
- What it is
- How much the stationary machine’s casing or supports lengthen per metre for each degree of temperature rise, from material data for the casing material.
- Units and format
- Enter a number in µm/(m·K): micrometres per metre per kelvin. The form accepts 0.000001 µm/(m·K) to 100 µm/(m·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11 µm/(m·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter micrometres per metre per kelvin, which is the usual table unit (×10⁻⁶ per K).
What this means: Temperature rise of supports
- What it is
- The average rise in temperature of the stationary machine’s supports from cold (when aligning) to normal running.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts -200 K to 1000 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Growth rises in direct proportion to the temperature rise.
- Get it right
- Measure the support or casing temperatures in service with a contact thermometer or infrared gun; it is not the process fluid temperature.
Movable machine (e.g. pump)
What this means: Foot to shaft centreline height
- What it is
- The vertical distance from the movable machine’s mounting feet to the centreline of its shaft, which grows as its supports heat up.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Growth rises in direct proportion to this height.
- Get it right
- Measure from the underside of the feet, at the same reference as the stationary machine.
What this means: Expansion coefficient
- What it is
- How much the movable machine’s casing or supports lengthen per metre for each degree of temperature rise, from material data for that machine.
- Units and format
- Enter a number in µm/(m·K): micrometres per metre per kelvin. The form accepts 0.000001 µm/(m·K) to 100 µm/(m·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11 µm/(m·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter micrometres per metre per kelvin (×10⁻⁶ per K).
What this means: Temperature rise of supports
- What it is
- The average rise in temperature of the movable machine’s supports from cold to normal running.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts -200 K to 1000 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Growth rises in direct proportion to the temperature rise.
- Get it right
- A hot pump casing can run much warmer than its motor; measure each machine separately.
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.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Thermal growth and cold targets
In Shaft Alignment by the Numbers
What it covers: How machines grow as they warm, how to estimate each machine's vertical growth from its centreline height and support temperature, and how to set a cold target that is true hot.
Method explained here · BIZOMAT original book
Designing machines for movement
In Thermal Expansion by the Numbers
What it covers: Design machines that stay accurate and free as they warm: fixed and floating bearings, hot alignment of pumps and motors, warm-up drift, mixed materials and slotted fixings, each with its numbers.
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