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Checking for the hidden crank

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Only a comprehensive analytical approach of a kiln’s state can help in identifying the hidden causes of its failures. We can detect such hidden cranks through meticulous measurements and analysis.

Akiln’s shell state is usually used to evaluate its mechanical condition. This is done by measuring the shell run-out in individual shell planes located along the kiln`s length at adequate density. These measurements are used to understand a kiln’s shell`s eccentricity and local deformation distribution. Vector eccentricity in the kiln’s shell can be observed from the visual distribution of the map. Generally, the eccentricity adjacent to the support positions is minimum. Does the eccentricty of a shell’s axis arises only between supports?. The answer is no.

With a relatively flexible shell and with the significant weight of the tyre and stiffness, the shell remains constrained. Only in extreme cases does the bend in the shell lead to a tyre lift creating a gap between the tyre and the rollers.

The tyre lift phenomenon occurs very rarely and does so when the vector of eccentricity is larger than the static deflection of the shell at the support point. For example, moving the support roller out by a couple of millimeters creates this situation. An inability to view the tyre lift may give a wrong impression that the kiln’s shell is healthy, while the problem remains hidden. This hidden crank goes unnoticed. A hidden crank leads to cyclical changes in loads on the support rollers creating cyclical deflections on the rollers’ shafts. These deflections are different from the static deflections coming from the roller and are due to the kiln’s nominal weight. They are called dynamic deflections. Such excessive deflections lead to metal fa-tigue and the cracking of the support roller shafts. When this happens, it is a nightmare for engineers.

The hidden crank remains invisible in geometric measurements and if not fixed it can lead to:

  • Increased stress and shell deformation (ovalisation), can impacts the shell’s strength and fatigue state and radically reduce the durability of the kiln’s lining;
  • Increased pressures between the raceways of rollers and rings, leading to the accelerated wear and tear of raceways;
  • Increased load on the support roller bearings, which significantly raises the bearing temperature and causes seizing;
  • Foundation deflection causing excessive stresses to the base frame`s foundation bolts, through cracks and damages continuously;
  • Breakdowns such as a sudden stoppage of the kiln due to cracks in the shafts or destruction of drive sys-tem, destruction of outlet and inlet seal elements, etc.

Only a comprehensive analytical approach of the kiln’s state can help in identifying the hidden causes of failure. The insight gained helps in increasing the life of the kiln and its components (bearing / roller shaft / raceway wear/ refractory brick damage, etc). ASE is measuring and considering the hidden crank vector as a standard element of its shell state measurements.

Allan Smith Engineering Pvt. Ltd. 9-C, Linden, Eden Woods, Off. Pokhran Road #2, Thane (West), Mumbai, India. Tel-Fax: +91 22 2589 3469,

(Communication by the management of the company)

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