Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
1999-09-17
2001-04-03
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
C418S206400
Reexamination Certificate
active
06210139
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus for conveying highly viscous fluids and, more particularly, to gear pumps.
BACKGROUND OF THE INVENTION
Gear pumps are used for conveyance of highly viscous fluid, such as polymer melts. For example, gear pumps are typically used for conveying a viscous polymer melt from a vessel, such as a devolatilizer, to another unit operation, such as a pelletizer. In most cases, the highly viscous polymer melt enters the pump inlet under the influence of gravity with essentially no positive pressure. Known gear pumps are susceptible to a number of difficulties in their operation. In particular, for any given pump geometry, known gear pumps are extremely limited with respect to the range of viscosity of fluids that they can handle. Generally, as fluid viscosity increases, the throughput rate of the gear pump decreases, often resulting in a production bottleneck. Also, in general, as gear pump speed (RPM) increases, pump throughput initially increases, but eventually reaches a plateau level, wherein further increases in pump speed do not result in any significant increase in throughput and can lead to a production bottleneck. Heretofore it has generally not been possible to effectively overcome a production bottleneck of this type once the plateau level of the pump speed verses pump throughput has been reached without replacing the existing pump with a larger pump. However, the devolatilizer is typically specially configured to be coupled to a gear pump of a particular size, and it is not generally possible to switch to a larger capacity gear pump of conventional design without also replacing or significantly modifying the devolatilizer. Accordingly, it would be highly desirable to provide a gear pump which operates more efficiently to eliminate such production bottlenecks without requiring replacement or significant modification of the devolatilizer.
Various attempts have been made to design gear pumps which are capable of operating efficiently over a wider range of fluid viscosity and over a wider range of pump speeds. These efforts have focused primarily on pump geometry, particularly at the inlet side of the pump. However, the known pump designs have not been entirely satisfactory and further improvements are desirable.
SUMMARY OF THE INVENTION
The invention provides a gear pump having an improved geometry which attenuates the limitations relating to the viscosity of the fluid being pumped and the pump speed. More specifically, the gear chamber has been designed to provide compression zones which enable more fluid to be compressed over a longer path length into the teeth of the pump gears, and, therefore, provide higher production rates and higher fill efficiency. The improved geometry allows the gear pumps of this invention to operate more efficiently over a relatively broader range of pump speed and with a relatively broader range of fluid viscosity.
The gear pumps of this invention include a compression zone defined between each of a pair of pump gears and internal walls of a gear chamber, in which the compression zones have a non-uniform thickness, that is, the spacing between the teeth of the pump gears and the internal walls of the gear chamber in the vicinity of the compression zones varies along the length of the gears.
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Hyun Kun S.
Parsons Thomas J.
Ramanathan Ravi
Wrisley Robert E.
The Dow Chemical Company
Vrablik John J.
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