Gears and meshing

Problems of drive system components troubleshooting is very important to any kind of rotary equipment. That is why knowledge about different type of designs, advantages and disadvantages, correct operation condition is crucial. The experienced user or diagnostician can find the causes of potential problems or eliminate existing problems based on symptoms observation. So the drive components like pinions, girth gear, reductors, coupling components should be inspected very carefully. The correct alignment of whole drive system is the base of kiln maintenance.

There are two different types of design of rotary kiln gear:

Fixed gears – consist of two to six parts of gear fived to flange  (welded directly to the kiln shell). This kind of components we can find a older kilns where the operation temperature is lower. When some problem with gear teeth appears it is easy to reverse to prolong component service life. Disadvantage of that kind of solution is – shell deformation. If shell become deformed due to  for example temperature difference of brick damage will cause the problems with meshing. The run-out parameters can increase and the wear of components become higher. The repositioning can be difficult in this case as well. Often re-welding of flange is necessary, sometimes if it is possible making oval fixing holes are enough.

Spring-fixed gears – currently used  in most rotary kilns. This kind of design is independent to shell thermal expansion. The whole gear is fixed on springs attached to shell.  The advantage of this solution is also easy reversing procedure. The run-out parameter can be compensate by spring fixing adjustment. Generally consist of two to four equal parts.  During renovation work or adjustment  of gear fixing it is important to keep in mind that springs are vulnerable to damage (material memory).

So what should be inspected to extend the life of the drive?

  • Meshing – correct alignment of working teeth of pinion (or pinions) and girth gear. The root clearance and backlash parameter should be measured and recorded.
  • Teeth contact – can be observed by analyzing the contact pattern
  • Teeth line separation – checking whether overlapping exist.
  • Axial run-out measurement – should not exceed design tolerance
  • Radial run-out measurement – can be observed by root clearance changes observation.
  • Drive support condition
  • Lubrication efficiency
  • General condition of surrounding space
  • Vibration (especially at reductor component)
  • Non-standard noises
  • Welds condition
  • Loosen bolts, cracks.
  • Rotary kiln axial position
  • The mechanical wear of gear an pinion (and type of wear)

Very useful for gear inspection is pitch line separation parameter. On each teeth we can observe some lines manufactured. This line should match each other for gear and pinion lot sides of drive (upper and down).  The perfect situation is when there is no pitch line separation. It is also acceptable separation lines outside but overlapping (inside separation) is very dangerous for mesh operation. In this case adjustment is neccesery.