Imperforate bowl: centrifugal separators – Rotatable bowl – Including driven material-moving means therein
Patent
1992-06-23
1995-02-07
Scherbel, David A.
Imperforate bowl: centrifugal separators
Rotatable bowl
Including driven material-moving means therein
494 64, 494 83, B04B 120, B04B 900
Patent
active
053871758
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a decanter centrifuge comprising a frame in which a drum is rotatably journalled in a bearing at either side of the drum and a conveyor rotatably journalled in the drum and extending throughout the separating compartment of the drum, said separating compartment being delimited in the axial direction of the drum by an end wall at either end of the drum, and in which the ratio between the length and the diameter of the separating compartment is larger than four.
In decanter centrifuges of this type an improvement of the separation effect and an increase of the capacity of the centrifuge may be obtained by increasing the number of revolutions (RPM) of the drum. The highest RPM as used depends on various factors, such as the strength of the drum material and the first critical RPM of the drum with contents. In decanter centrifuges in which the ratio .lambda. between the length and the diameter of the separating compartment is greater than four, the drum is comparatively slender and has a comparatively low critical RPM determining the highest allowable service RPM, generally set to about two thirds of the critical RPM.
It is the object of the invention to provide a decanter centrifuge with a drum having a critical RPM that is higher than in corresponding prior decanter centrifuges of the above mentioned type.
The decanter centrifuge according to the invention differs from the known centrifuge in that at least one of the bearings of the conveyor is supported at the free end of a trunnion extending axially into the conveyor from an end wall and that the trunnion has a length in the range from 0.5 to 3 times the largest diameter of the separating compartment.
Experiments and calculations have shown that the critical RPM of the drum to a high degree depends on the structure of the conveyor journalled in the drum. It has in particular been found that the tendency of the conveyor to deflect while rotating is of essential importance to the critical RPM of the drum and by journalling the conveyor at least at one of its ends on a trunnion projecting into the conveyor the distance between its bearings decreases and a considerably more rigid conveyor is obtained. It has been found advantageous that the trunnion has a length ranging from 0.5 to 3 times the diameter of the separating compartment. If the trunnion is shorter than 0.5 times the diameter of the separating compartment, the resulting increase of rigidity of the conveyor is not sufficiently high to exert a substantial influence on the critical RPM. If the trunnion is longer than three times the diameter of the separating compartment the conveyor becomes, on one hand, substantially more rigid but, on the other hand, the trunnion gets softer and the total result is that no substantial improvement of the critical RPM is obtained.
A preferred embodiment of the decanter centrifuge is characterized in that the portion of the conveyor surrounding the trunnion projecting into the conveyor is comparatively lighter and more fragile than the portion of the conveyor located between the conveyor bearings. The portion of the conveyor located between the bearings is dimensioned so as to have the required rigidity and to be capable of transferring the forces occurring in operation to the bearings. On the other hand, only small forces are transferred in the portion of the conveyor surrounding the inward projecting trunnion and it may therefore have a comparatively smaller mass and be more fragile than the remaining part of the conveyor. This reduces the mass of the conveyor further, thereby contributing to increasing the critical RPM and at the same time it is possible to decrease material costs as well as processing costs in manufacturing the conveyor.
The comparatively lighter and more fragile portion of the conveyor may be detachably secured to the portion of the conveyor located between the conveyor bearings and it may for instance be secured by means of a threaded joint. It is hereby obtained that upon cleansing and repairing the decanter centrifuge t
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Alfa Laval Separation A/S
Cooley Charles
Scherbel David A.
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