Measuring Tyre Migration with MMD
A field-proven method to detect tyre creep on rotary kilns using the Multi Measurement Device — circumferential measurement of kiln tyres, support rollers, and tyre runout, girth gear axial runout and radial deflection, support roller deflection. No additional hardware required.
What is Tyre Migration?
In a rotary kiln, the riding ring — commonly called the tyre — sits loosely over the kiln shell, separated by filler bars or pad plates. Because the tyre and shell have slightly different effective diameters and stiffnesses, they do not rotate at exactly the same angular velocity. This relative slip between the tyre's inner bore and the shell beneath it is called tyre migration or tyre creep.
A small amount of creep is not only normal — it is desirable. The relative movement allows the shell to thermally expand and contract freely beneath the tyre. Problems arise when creep becomes excessive or when it disappears entirely.
Too tight — risk of shell deformation and hot spots under tyre
Healthy operating range for most rotary kilns
Excessive wear on filler bars and tyre bore — investigate immediately
The MMD Circumferential Approach
The MMD already carries a precision measurement wheel with an encoder and a rotation trigger. This existing hardware is all that is needed to measure tyre creep accurately — the method simply requires two sequential passes at the same tyre station, with the trigger attachment point changed between them.
Trigger on the Tyre
Attach the MMD rotation trigger to a fixed reference point on the tyre. Place the measurement wheel on the tyre surface. Allow one complete tyre revolution and record the total distance travelled. This is your tyre circumference.
Trigger on the Shell
Without moving the measurement wheel, relocate the trigger to a reference mark on the kiln shell adjacent to the tyre. Allow one complete shell revolution and record the distance. This is your shell circumference.
Because the measurement wheel remains in the same position and on the same surface throughout both passes, there is no positional error introduced between measurements. Only the trigger definition of "one full revolution" changes — which is precisely the variable of interest.
The Formula
Once both distances are recorded, the creep calculation is a simple subtraction and ratio:
Since the tyre sits on top of filler bars, its effective rolling circumference is always slightly larger than the shell's. A positive result (tyre distance greater than shell distance) is normal and expected. The percentage value is the most universally comparable metric across different kiln diameters and operating speeds.
Reading the Results
| Creep Value | Condition | Likely Cause | Recommended Action |
|---|---|---|---|
| 0% (zero) | Critical | Tyre seized on shell | Immediate inspection — high risk of shell damage |
| < 0.5% | Too Tight | Filler bars worn, tyre migrated inward | Inspect filler bar thickness, plan replacement |
| 0.5% – 1.5% | Normal | Correct tyre fit | Continue monitoring at next planned survey |
| 1.5% – 3% | Elevated | Filler bars worn, excessive clearance | Schedule filler bar inspection at next stop |
| > 3% | Excessive | Severely worn filler bars or tyre bore | Prioritize repair — risk of impact loading on shell |
Improving Accuracy
While the two-pass method is inherently robust — same wheel, same surface, same position — a few field practices further improve the quality of results:
Average multiple revolutions. Rather than capturing a single revolution per pass, record two or three and average the results. This smooths out any minor surface irregularity or encoder jitter.
Measure at stable operating temperature. Tyre fit changes with kiln temperature. For comparable data over time, always record measurements under similar operating conditions — ideally at normal process temperature after the kiln has stabilized.
Record kiln RPM alongside creep. Expressing creep in mm/hour rather than mm/rev gives a more operationally meaningful figure and allows direct comparison between kilns running at different speeds.
Repeat at each tyre station. Creep can vary significantly between tyre positions on the same kiln due to differences in filler bar wear, local shell temperature, or tyre bore condition. Measuring all stations in a single survey gives a complete picture.
A Complete Kiln Survey, One Device
Tyre migration measurement has traditionally required dedicated standalone tools. With this method, the MMD adds creep monitoring to an already comprehensive measurement workflow — circumferential measurement of kiln tyres and support rollers, tyre runout, girth gear axial runout and radial deflection, and support roller deflection — all from a single device, without any hardware changes.
The two-pass circumferential method is elegant in its simplicity: no assumptions about nominal diameters, no contact with hot surfaces, no additional sensors. Just two trigger placements and the encoder data the MMD is already capturing.
For more information about the MMD and its measurement capabilities, contact Alpha Teknoloji.
Ready to Measure?
The MMD delivers tyre migration measurement as part of a complete kiln geometry survey. Contact us or see the full MMD system.