Quick Answer: How Do You Calculate a Shrink Fit Heating Temperature?
A shrink fit assembles an interference fit by heating the hub so its bore expands enough to slip over the shaft, then letting it cool so it grips. The required temperature rise is ΔT = (interference + assembly clearance) / (bore diameter × CTE). For a 1.000″ aluminum hub with 0.0010″ interference and 0.0020″ clearance, that is about a 234°F rise, or roughly 304°F from a 70°F start.
This calculator uses the thermal expansion equation ΔL = L × α × ΔT to compute: required hub temperature, temperature rise needed, bore expansion at temperature, interference at ambient and estimated cool-down time. Inputs include shaft OD, hub bore ID, hub OD, hub material CTE, target interference, desired assembly clearance and ambient temperature.
Material CTE (×10⁻⁶ /°F): Steel 6.5 | Stainless 8.9 | Cast Iron 5.9 | Bronze 10.0 | Aluminum 12.8 | Titanium 4.8. Typical shrink fit interference 0.001–0.003″ per inch of diameter | steel heating range 300–600°F | aluminum below 400°F to avoid temper loss.
How Shrink Fits Work
A shrink fit uses thermal expansion to assemble interference fit parts without pressing. You heat the hub (or cool the shaft) until the bore expands enough to slip over the shaft. When the hub cools back to ambient temperature, it contracts and grips the shaft with tremendous force.
Thermal Expansion
All metals expand when heated. The amount of expansion depends on three factors: the original dimension, the coefficient of thermal expansion (CTE), and the temperature change. The formula is simple: ΔL = L × α × ΔT.
Assembly Clearance
You need more than just enough expansion to overcome the interference. Add assembly clearance (typically 0.002″ to 0.005″) so you have time to position the hub before it cools and seizes. More clearance means more time to work, but requires higher temperature.
Pro tip: Use an oven for uniform heating. Torches create hot spots that cause uneven expansion and can damage the material. For aluminum, keep below 400°F to avoid temper changes.
Material Considerations
Aluminum expands nearly twice as much as steel per degree. This means aluminum hubs need lower temperatures for the same interference. But it also means aluminum hubs lose their grip faster in high-temperature environments.