Shrink-fit hub
Check a Ø50 H7/s6 hub on a shaft: interference, contact pressure, transmissible torque and shrink temperature, then make it carry more torque and run faster.
- ISO 286-1:2010
- ISO 286-2:2010
- DIN 7190-1:2017
A coupling hub of C45 is shrunk onto a 42CrMo4 shaft of Ø50 mm with the fit H7/s6. It must carry 250 N·m by friction alone. This tutorial rebuilds the Shrink-fit hub example, then raises the torque, fixes the joint and spins it up.
The numbers are those of this version of Axomek. To compare: open the Shrink-fit hub example. It starts a new project from the example in place of yours, so save yours first (the app asks) and come back to it with Switch project (Ctrl+P).
Step 1: add the fit
- Start a Blank project and open Fits in the navigation.
- Choose Add a fit. Fit F1 appears.
- Set Name to
Coupling hub.
The starting values are those of the example:
| Group | Input | Value |
|---|---|---|
| Fit | Nominal diameter | 50 mm |
| Hole, Shaft | H7, s6 | |
| Press fit | Hub outside diameter | 100 mm |
| Joint length | 50 mm | |
| Hollow shaft bore | 0 (solid) | |
| Friction μ | 0.12 | |
| Hub bore roughness Rz, Shaft roughness Rz | 4 µm, 4 µm | |
| Torque to carry | 250 N·m | |
| Assembly temperature | 20 °C | |
| Materials | Hub material | C45 +QT, Re 490 MPa |
| Shaft material | 42CrMo4 +QT, Re 900 MPa | |
| Requirements | Min slip safety, Min yield safety | 1.5, 1.1 |
The press fit is analysed because a Hub outside diameter is given. Without one, the module only reports the ISO 286 limits and the fit type.
Step 2: read the results
The centre shows the Tolerance zones of hole and shaft about the nominal size, the Stresses through the joint (radial and hoop stress over the radius) and the press fit's details. The results column shows:
| Result | Value |
|---|---|
| Hole H7 | 0 to +25 µm |
| Shaft s6 | +43 to +59 µm |
| Interference | 18 to 59 µm (fit type: interference) |
| Lost to smoothing of the surfaces | 6.4 µm |
| Effective interference | 11.6 to 52.6 µm |
| Contact pressure | 18.3 to 82.8 MPa |
| Transmissible torque | 430.5 N·m (at the smallest interference) |
| Axial force it could carry instead | 17.2 kN |
| Hub stress at the bore (DIN 7190) | 191.3 MPa |
| Shrink temperature of the hub | 218.2 °C |
| Speed at which it comes loose | 16 565 rpm |
| Check | Value / minimum |
|---|---|
| Slipping | 1.72 / 1.5 |
| Hub yield | 2.56 / 1.1 |
| Shaft yield | 10.9 / 1.1 |
How to read it:
- The slip check uses the smallest interference: the loosest pair of parts the tolerances allow must still carry the torque. 430.5 / 250 = 1.72.
- The yield checks use the largest interference: the tightest pair must not yield the hub.
- Turned surfaces are flattened when pressed together. The app takes this smoothing off the interference before computing the pressure, from the two Rz values.
- The shrink temperature is how hot the hub must be for it to slide on freely, with some assembly clearance.
Step 3: carry more torque
Set Torque to carry to 400 N·m.
Slipping fails at 1.08 (400 N·m against the 430.5 N·m the joint can transmit).
There are three levers: more interference, more length, more friction. The shaft class s6 is already the tightest one the app offers. A longer hub is often the easiest change:
Set Joint length to 70 mm.
The transmissible torque rises in proportion to the length, to 602.7 N·m. Slipping passes at 1.51, barely above its minimum of 1.5, so the row shows the warning mark. The pressures and the yield safeties do not change, because the pressure does not depend on the length.
Step 4: spin it up
Set Speed to 6000 rpm.
A turning hub grows more than the shaft inside it, because the hub's hoop stress from its own centrifugal force is larger. Part of the interference is lost:
| Result at 6000 rpm | Value |
|---|---|
| Interference lost | 1.5 µm |
| Contact pressure | 15.9 to 80.4 MPa |
| Centrifugal hoop stress at the hub bore | 6.7 MPa |
| Transmissible torque | 523.6 N·m |
The slip check now reads Slipping at speed and fails at 1.31: the joint that held at standstill no longer carries 400 N·m with the required margin at 6000 rpm. At 16 565 rpm it would come loose altogether.
To pass at speed, make the hub longer again: at a Joint length of 85 mm the joint transmits 731.8 N·m at standstill and passes Slipping at speed at 1.59. A lower minimum safety is an option only if the torque is known well.
What you learned
- Slip is checked at the smallest interference, yield at the largest.
- Surface roughness costs interference before any pressure builds up.
- Length scales the torque capacity without changing the stresses.
- Speed loosens a hub; the app reports the loosening speed and checks slip at speed.