All rotary kilns have many rotation surfaces working together that has to be set with high geometrical precision. Any damage of working components will accelerate very fast if the geometry is not maintained properly. The alignment inspections of all components are a very good solution to find the problems before it starts. The maintenance routine should be performed regularly daily, weekly, monthly and yearly.
We can divide the kiln design to: 2-pier units and multiple pier units. The 2-pier is geometrically simpler solutions. It is composed with four big support rollers with shafts and bearing. All components are design to be as mechanically frictionless as possible. Also the load is evenly distributed to supports. The multiple pier design means three or more supports. The design is quite the same but more components making more difficulties to maintenance work. Identification of mechanical problems is a very wide subject in this area. To provide continuous operation and costs effectiveness the alignment inspections are recommended.
The rotary kiln mechanical condition largely depends on supports. Geometrical deviation, movement, settlement of supports has direct influence on the general operation of the working equipment and components. Kiln’s supports are normally design and made of concrete and all component are attached by special anchors. Its condition can be the subject of destruction by: mechanical damage, climatic changes, poor maintenance, age, improper lubrication procedure or vibration. Damaged supports process transfers to higher wear of other rotating components.
Identifying the problems the user should look for cracks, erosion, fractures, damaged anchor bolts. Any gap appeared allows water and other substances to weaken all construction. Also unstable ground condition may cause the settlement or pier movement. The inspection should take place every week. The user should control the housekeeping, look for cracks or any other irregularities compared to previous inspection.
Problems with concrete and roller base creates another problem. This time with rollers, shafts and bearings making operation life shorter (accelerate wear). Mechanical wear, during inspections missing or damaged bolts should be checked. If some is missing immediately should be repaired. Besides the user have to control any gap, cracks, spend lubrication, accumulation of material and overall cleanliness. This conditions can change the axial thrust balance of the unit. Also the “foreign” object can go to the running surfaces creating more damages.
Due to axial thrust can be changed the thrust roller base should be inspected as well. The components like mounting bolts, tension bolts and roller running surface are crucial. This is especially important when flat spot occurs on the roller surface, where constant changing of pressure can create components failure.
Similarly drive base condition should be inspected carefully. Poor condition of this part of kiln support can lead to girth gear and pinion failure. Troubleshooting: look for cracks, location shifts, broken welds, vibration, loose parts of drive system, lubrication condition. When the drive base is linked to pier base the inspection is easier, otherwise the control procedure has to be more precise. Correct alignment is crucial. At this point general housekeeping is especially important factor that should be included to maintenance program schedule.
Thrust roller problem identification.
The main function of thrust roller is to keep kiln and tires centered on the support rollers. Also the girth gear is placed above the pinion thanks to this device. They are also take care of kiln “floating”. There are two different kind of thrust roller components: fixed or hydraulic.
As thrust roller controls the axial movement of whole kiln its working condition should be in good shape. Excessive range of working (and same too high value of axial movement) affect on many components. Fixed type of thrust roller work 75% of the time with the tire side surface. Floating appears from time to time. With hydraulic thrust roller contact between running surfaces will be all the time. The unit is pushed up and down (pressure cycle). Recommended cycle is from 2 to 8 hours. The problem can appear when this cycle is too short or too long. The rotary kiln is not mechanically stable. Points that should be checked during inspection: wear patterns, damaged bolts, position change, flat spots, surface condition, pressure value, time of pressure cycle, unusual noise etc.
The running surface of thrust roller is design that way to allow maximum contact with tire side surface. Working plane is designed in such a way to reflect the correct angle and linear speed. The speed of each part of running surfaces are matched to prevent too high wear and scuffing. Thrust roller should be inspected every day. The points that have to be checked: general condition, axial position, surface contact, wear, lubrication.
The geometrical position of thrust roller is also very important to failure-free operation. For most of rotary kiln producers the tolerance is from 5mm to 10mm on attacking side. In most cases this position extends bearing life.