Question 1

How do I calculate thermal expansion?

Accepted Answer

Linear thermal expansion is ΔL = α × L0 × ΔT, where α is the coefficient of linear expansion (per °C), L0 is the original length and ΔT is the temperature change. For aluminium (α ≈ 23 × 10⁻⁶/°C), L0 = 1000 mm heated by 100 °C, ΔL = 23e-6 × 1000 × 100 = 2.3 mm, so the final length is 1002.3 mm.

Question 2

What is the difference between linear, area and volume expansion?

Accepted Answer

For an isotropic solid the area expansion coefficient is about 2α and the volume (cubical) expansion coefficient is about 3α. So a hole or surface grows roughly twice as fast as a length, and a volume about three times as fast, for the same temperature change.

Question 3

How does thermal expansion help with shrink fits?

Accepted Answer

Heating the outer part makes its bore grow by ΔL = α·L0·ΔT, opening enough clearance to drop it over the shaft. On cooling it shrinks back and grips. Use this tool to find the bore growth for a given temperature, then size the actual interference with a press-fit calculator.

Question 4

Why is the calculated expansion only an estimate?

Accepted Answer

The coefficient α is a representative value that changes with temperature range and alloy, and the formula assumes linear behaviour. Phase transformations, anisotropy and constraint stresses are not modelled, so treat the result as a design starting point rather than an exact figure.

Question 5

Can the temperature change be negative?

Accepted Answer

Yes. A negative ΔT (cooling) gives a negative ΔL, so the part contracts and the final dimension is smaller than L0. This is exactly the basis of cooling a shaft in liquid nitrogen for an interference fit.

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