Rotary expansible chamber devices – Heat exchange or non-working fluid lubricating or sealing – With coolant air impelling means or finned cylinder surface
Reexamination Certificate
2000-07-18
2001-11-13
Vrablik, John J. (Department: 3748)
Rotary expansible chamber devices
Heat exchange or non-working fluid lubricating or sealing
With coolant air impelling means or finned cylinder surface
C418S102000, C418S196000, C418S087000, C418S087000
Reexamination Certificate
active
06315537
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a spin pump for conveying a liquid polymer melt.
In the spinning of synthetic yarns, a polymer melt is supplied by a spin pump to a spinneret and extruded. Such a spin pump is known, for example, from EP 0636190 and corresponding U.S. Pat. No. 5,637,331. In this spin pump, individual pumps advance the polymer melt from an inlet channel to one or more outlet channels. The individual pumps are driven by a common drive shaft which extends outside of the pump housing. For the power transmission, the drive shaft is supported in a bearing bore of the pump housing and possesses an external end for coupling to the drive. This arrangement makes it necessary to seal the gap that is formed between the drive shaft and the pump housing, while taking into account that the polymer melt has a temperature of more than 200° C. To ensure a uniform temperature as well as viscosity of the melt, the pump housing may be heated. However, such high demands cannot be met by conventional seals.
In the case of the pump known from EP 0189670, it is proposed to form a seal by means of a conveying screw thread. In particular, a section of the drive shaft is provided with a spiral flute. The threaded section of the drive shaft extends through a bushing that is joined to the pump housing by flanges. In the case of this seal, the rotation of the drive shaft generates a conveying effect in the sealing gap, which returns the polymer melt to the interior of the pump. Due to the low drive speeds in the range of at most 100 rpm, the spin pumps reach only a very low peripheral speed on the drive shaft. This generates a small conveying effect, and the sealing of the gap remains inadequate.
EP 0602357 discloses a pump, wherein the conveying screw thread is provided in a bushing, through which the drive shaft extends. The bushing is inserted into a housing cover. Likewise in this arrangement, the sealing effect is dependent on the peripheral speed of the drive shaft. To this extent, this seal is unsuited for low rotational speeds. For tempering the bushing, the housing cover accommodates a channel system, through which a cooling medium flows. However, this arrangement has the disadvantage of an additional tempering device inside the pump housing as well as a high coolant consumption that is thereby necessitated.
It is therefore an object of the invention to provide a spin pump for conveying a liquid polymer melt of the initially described type with a shaft seal, which operates uniformly and is in particular independent of the drive speed.
A further object of the invention is to provide a sealing system, which does not require a cooling by a separately supplied coolant.
SUMMARY OF THE INVENTION
The above and other objects and advantages are achieved by the provision of a pump which comprises a housing having a melt inlet and a melt outlet, and conveying means such as intermeshing gears for conveying a liquid polymer melt from the melt inlet to the melt outlet. The conveying means includes a drive shaft which extends through a bearing bore in the housing and which includes an external end for connection to a drive. A cooling sleeve is tightly mounted to the housing so as to coaxially surround the portion of the external end of the drive shaft which is adjacent the housing so as to form a narrow annular gap therebetween which communicates with the bearing bore.
The invention as described above is characterized by a selfsealing effect. In this connection, the conveyed polymer melt serves as a sealing material which enters into the sealing gap. The invention is based on the knowledge that the polymer melt becomes more viscose as its temperature drops, and even solidifies at a certain temperature. Thus, it is possible to influence by a tempering of the polymer melt in the sealing gap the flow properties of the polymer in the sealing gap and to adapt it to the sealing requirements. For tempering the polymer melt in the sealing gap, the drive shaft extends through the cooling sleeve of a cooling body. To this end, the cooling body connects in a pressure tight fashion to the pump housing. Between the drive shaft and the cooling sleeve the narrow annular gap is formed. For tempering the polymer melt, the outer surface of the cooling sleeve is cooled by a coolant, preferably a cooling air. This causes the polymer to solidify or thicken, at least in a subsection of the gap, and leads to a sealing effect. A further advantage of the invention lies in that the tempering of the polymer melt occurs outside of the pump housing, which is usually heated. To this extent, there exists no significant influence of the tempering of the melt inside the pump housing. In addition, the solidified or highly viscose polymer results in no significant frictional losses of the drive shaft.
It has been shown that in proportion to the diameter of the drive shaft, a length of the cooling sleeve of at least 1.0 times the diameter of the drive shaft permits realizing an adequate solidification for sealing the gap. Preferably, the cooling sleeve is made with a minimum length of 1.5 times the diameter of the drive shaft.
A cooling rib, or a plurality of cooling ribs, are preferably mounted to the exterior of the cooling sleeve. By this construction, the cooling effect of the cooling sleeve increases substantially. In this connection, it is possible to arrange the cooling ribs so as to be oriented in the axial direction, or in the radial direction of the cooling sleeve, for the transfer of heat.
In the case of vertically arranged drive shafts, an annular cooling rib may be configured to include a circumferential collar. This renders it possible to collect polymer particles that may exit from the end of the cooling sleeve, in the event of a vertical arrangement of the drive shaft.
To influence the amount of heat that is removed from the cooling sleeve, a particularly preferred embodiment of the invention provides that the cooling ribs are designed and constructed for adjustment on the circumference of the cooling sleeve. Thus, it is possible to cool subsections in the axial direction of the cooling sleeve differently.
To intensify the cooling, at least one cooling rib may be arranged on the circumference of the drive shaft, outside of the cooling sleeve. The rib thus rotates at the speed of the drive shaft, so as to generate an air turbulence. This air turbulence leads to an intensive heat exchange on the surface of the cooling sleeve, so that the heat can rapidly dissipate in the sealing gap between the drive shaft and the cooling sleeve.
To support the sealing effect, a further development of the invention provides a conveying screw thread, which returns the polymer melt to the interior of the pump during the rotation of the drive shaft.
The conveying screw thread is arranged at least in one subsection in the cooling sleeve or in the drive shaft. Preferably, the subsection is located in the region in which the polymer has not yet undergone a substantial solidification, so that it is possible to return to the pump interior only liquid polymer. However, it is also possible to arrange a conveying screw thread over the entire length of the cooling sleeve.
To achieve a reduced pressure in the sealing gap between the drive shaft and the cooling sleeve, the sealing gap may be connected upstream of or at the beginning of the cooling sleeve to the inlet channel by means of a connection, for example, a bypass channel.
The conveying means of the spin pump may be in the form of pistons, blades, vanes, or similar parts. Especially advantageous is the construction of conveying means in the form of intermeshing gears. Such gear pumps are characterized in particular by an even volume flow.
To distribute, besides the conveying, the polymer melt evenly to a plurality of outlet channels, the pump may take the form of a multiple gear pump composed of a sun gear and multiple planetary gears, with the sun gear forming an individual pump with each planetary gear.
REFERENCES:
patent: 2699122 (1955-01-01), Erickson
patent: 40603
Gathmann Egon
Hasenburg Jürgen
Helbing Ulrich
Kramer Thomas
Alston & Bird LLP
Barmag AG
Vrablik John J.
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