Engineering tool
Thermal Expansion Joint Calculator
Size the expansion allowance for a refractory lining from the material, the cold length and the temperature rise — the joint that stops a lining pushing itself apart.
Recommended joint — mm
Free expansion ΔL — mm
Strain — %
Coefficients are typical published values; use the figure from your supplier datasheet where you have one.
Formulas used
- ΔL = α × L₀ × ΔT
- Recommended joint = ΔL × 1.1
- Strain % = ΔL ÷ L₀ × 100
Practical notes
- The recommended joint carries a 10% margin over free expansion, for installation tolerance. It is an allowance, not a specification — the lining designer decides the final figure.
- A lining with no room to grow does not simply expand: it loads itself in compression until something spalls. Joints are cheaper than that.
Frequently asked questions
Why add 10% to the calculated expansion?
Because installed dimensions vary, temperature is not uniform along a lining, and mortar joints close up unevenly. The margin absorbs that without leaving a gap so wide it fills with slag.
Can I use one coefficient for the whole lining?
Only if it is one material. A working lining and its backup expand at different rates, which is exactly why the interface between them needs thinking about.