CAPITULO III. ANALISIS
ANEXO 3. Códigos que emergen de la 2ª etapa de codificación
13.1 OBJECTIVE AND SCOPE
The objective of this procedure is to develop a control of sets to have in the kiln tires (support rollers) bearings, in order to prevent premature damages.
13.2 METHOD BASIS OR FOUNDATION
The rotary kiln kiln tires bearings, are of self-adjustable type (spherical base), or without adjustment (straight base).
The lubrication principle normally, is of a hydrodynamic type, i.e. that during the rotation a support oil layer is formed between the bearing and the trunnion shaft.
That is the reason why it is very important - due to the kiln low rotation speed - that the difference between the diameter of the trunnion shaft and bearing is exactly of the same size making possible the wedge effect, necessary to form the support oil layer under the trunnion shaft.
Consequently, the oil viscosity has decisive influence on the bearing running and, therefore, it is very important to note down carefully the lubrication directions.
If the correct oil is used at the correct bearing temperature, the perfect liquid friction can be obtained between the trunnion shafts and the bearings, this prevents wear of bearings. There are examples of kilns, which have been running during fifteen years, without any possible detection of a remarkable bearings wear.
Nevertheless, in case a bearing must be replaced, certain actions must be observed.
By general rule, the bearings are provided with a machining application corresponding to the original diameter of kiln tire trunnion shaft (or support roller), and with an appropriate sized clearance between the trunnion shaft and the bearing.
The nominal clearance between the kiln tires shaft and the bearing is obtained from Table 13.1 and it is conformed according to the hydrodynamic lubrication principle of bearing.
The trunnion shaft (or trunnion) of the kiln tire rests, theoretically, in a generatrix at the back of the bearing. At a sufficient shaft rotation speed, the oil will be introduced in the space between the shaft and bearing, with wedge effect, so that a thin film will support the shaft. Depending on the speed and temperature, the thickness of such oil film can be approximately 0.01- 0.02 mm.
The evolution (or course) of pressure in the oil film is illustrated in Figure 13.l
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Figure 13.1 13.2.1 Self adjustment bearings
In the self adjustable bearings, the spherical seat of the bearings guarantees that there is always a perfect support for the trunnion shaft (or trunnion), despite one of the bearings is displaced regarding the other, whether in vertical or horizontal sense.
13.2.2 Straight bearings
The straight bearings, do not allow alignment deviations, therefore the kiln must be checked in its alignment with higher frequency. These bearings allow only longitudinal displacements, and in the modern kilns or recently manufactured this type of bearings are not manufactured anymore, but only self adjustable or spherical.
13.2.3 Bearing cooling
The bearing cooling is made through a constant current of cooling water. Cooling is necessary to prevent the lubricant oil from turning too hot by reducing its lubrication capacity. The cooling water is supplied to the kiln tire bearings (or support rollers) through a common admission conduit. The cooling water at the entrance must not be higher than 10°C, in order to assure a low oil temperature. A failure in the bearing cooling process will damage it, its replacement will be necessary.
13.3.4 Kiln startup
Whenever a kiln is started again after a long duration shutdown, the trunnion shafts (trunnions) of the kiln tire (or support), can be so dry that it becomes necessary to supply oil to prevent rubbing during the first rotation until the moment when the bearing lubrication device procures the necessary oil film. In case the bearing does not receive the oil application, it will suffer premature wear, and its replacement will be necessary through the time.
13.3 METHOD DEVELOPMENT
13.3.1 Equipment and tools to be used- Shimming gauge
- Tools such as wrenches, etc. in order to remove and put the bearing cap.
This measuring is made with the kiln shutdown, therefore every kiln shutdown advantage must be utilized, but at least this measuring must be made monthly.
13.3.3 Procedure, calculation methods and results
For measuring, first the bearings are removed, then the measuring for clearance between the kiln tire shaft and bearing writing such data in Form number 13.1. The data obtained is compared with the Table 13.1, and if there is an out of tolerance condition, its replacement must be programmed.
13.3.4 Interpretation of results
The results that are made under this procedure must be positive, because when having a new bearing installed, the kiln will be running correctly.
13.3.5 Safety aspects
It is always dangerous to work close to a rotary kiln. If it is required to work close to it, appropriate clothing, safety goggles, safety shoes, gloves and safety shield must be utilized.
Table 13.1 13.3.6 Condemning or permissible limits
Whenever exceeding 10 % of the tolerance shown in Table 13.1, the bearing replacement must be scheduled.
13.4 COMMENTS AND OBSERVATIONS
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Kiln Tires (Support Rollers) / bearings : Diverse tolerance (in millimeters)
Nominal
The bearings adjustment measuring, is an activity which must be periodically performed, the good running of the kiln depends on it.
13.5 ATTACHMENTS AND FORMS UTILIZED
- Form number 13.1 Measuring of bearing set for kiln tires.
13.6 REFERENCES
- Support type 1958, Manual F.L.Smidth 19024-04 - Bearings for kiln tires, Manual F.L. Smidth 18064-13