Thrust bearing assembly

The statistical rated life of a bearing is generally predicted using the following formula  

It is important to notice that increased load, i.e., increased diehead pressure, reduces the bearing life by a power of three or more Also, the life L will be reached more quickly when the extruder runs at high speed. The predicted life, Ly, expressed in years, is obtained from the following expression  

The predicted B-10 life at any diehead pressure and/or screw can be found by the following relationship  

The thrust bearing assembly consists of four or five roller bearings in tandem arrangement with a special pressure balancing system. Advantages and disadvantages of certain types of thrust bearings are listed in Table 3.3. 

Fluid film thrust bearings have been applied to extruders on a few occasions. Their load carrying capability at low speed is generally poor and a loss of fluid film would have disastrous results. If a hydraulic drive is used to turn the screw, application of hydraulic thrust bearings may deserve some consideration. Reference 28 describes an extruder with hydraulic drive that incorporates a patented thrust bearing assembly with hydraulic axial screw adjustment. By measuring the pressure of the hydrostatic chamber of the thrust bearing, the pressure in the polymer melt at the end of the screw can be determined. 

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Figure 3.9 Thrust bearing assembly for single screw extruder...

Figure 3.10 shows an example of a thrust bearing assembly of a counter-rotating twin screw extruder. 

Thrust disc Thrust disc fits between the thrust bearing assemblies. Thrust disc and bearing arc desisted to absorb the rest 25% of the rotor thrust. 

FIG. 12-61 Rotary-dryer components, a) Alternative rotary gas seals, (h) Alternative trunnion roll bearings, (c) Thrust roll assembly. (ABB Raymond/Battlett-Snow TM.)... 

Usually, a journal bearing and a thrust bearing are combined in one assembly, and oil is injected so as to feed both of them. The rate of flow usually is adjusted so as to carry the heat away with a temperature rise of the order of II to 17° C (20 to 30° F). 

Loose assembly of bearing liner, bearing casing, or casing and support Loose rotor shrink fits Friction-induced whirl Thrust bearing damage... 

INTEGRAL CHECK VALVES INSTALLED IN EACH OF THE THRUST BEARING PRO ASSEMBLIES... 

If the vibrational frequency can be assumed the degrees of freedom can be reduced by the pad assembly technique commonly used for tilting pad journal bearings. First, pad data are calculated for a fixed pad and then the pad are assembled to form a complete thrust bearing. The degrees freedom of each pad are eliminated in terms of the degrees of freedom of the runner. The stiffness and damping matrix order may be reduced to (3x3). 

Because of the extremely close clearances that must exist within the blower, the potential for serious mechanical damage or catastrophic failure is higher than with other rotating machinery. The primary failure points include thrust bearing, timing gears, and rotor assemblies. 

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