It is not possible to stop the effect of steal thermal expansion. All kiln components like shell, tires under-tire shims, even rollers are susceptible to temperature influence. From maintenance point of view the difference in thermal expansion of different components are important. The type of tire and chair pads installation is a large part in solving the problem of unequal expansion. Each alignment inspection of rotary kiln should take a closer look to these components. All measurement and data should be collected carefully with high precision because even small irregularities in this field can create larger problems in a very short time.
Tires guarantee significant strength to shell keeping it round. Shell integrity is linked to the width, thickness, material and installation type of tire. The tires construction can be divided into:
- Fixed tires – it can be found on equipment where operating temperature do not exceed 100 degree Celsius.
- Floating tires – this kind of installation is normally required for “hot kilns” where the thermal expansion (differential) between the components (tire and shell) must be accommodated on those shells whose surface temperature is very high.
To fix the tire to the shell there are couple of method required. The most common way is simply welding the tire to the shell segment. Other possibilities are mechanical solutions like block, splined, pinned, keyed etc. When this kind of tire getting loose it is a serious symptom of failure and should be repaired with one of the method of tire fixing.
The most important difference between floating and fixed type is migration parameter. Because of that loose tires are much more difficult to maintain. The tires creep, even if kiln is aligned correctly, creating higher wear of components like stop-blocks, chair pads, rollers, shell. The problem appear especially when migration is both too high and too low.
Tire migration creates especially mechanical wear of tire-shell contact surfaces and side walls. This symptom can be identified visually. Rollers edges, cracks and undercutting is a first sign of excessive distress. Besides the problem increases with the combination of other deviations like misalignment, not correct skewing or inclination of rollers, differential shell slope, warped shell etc. But even of many disadvantage of this solution it is the best compromise between thermal expansion of components and mechanical wear.
Main problems of floating type of tires:
- Wear occurs on outer diameter of chair pads (shims)
- Some wear on tires inner diameter
- Foreign objects can wear or groove
- Wear on both sides of tire and stop block.