EP2634430A1

EP2634430A1 - Gear pump assembly

Info

Publication number: EP2634430A1
Application number: EP12157371.1A
Authority: EP
Inventors: Jörg Giesler
Original assignee: Maag Pump Systems AG
Current assignee: Maag Pump Systems AG
Priority date: 2012-02-28
Filing date: 2012-02-28
Publication date: 2013-09-04
Anticipated expiration: 2032-02-28
Also published as: EP2634430B1

Abstract

Gear pump assembly (1) comprising at least two independently-driven gear pumps (8a,b) in a single housing (2) arranged collaterally with respect to the rotational axes of their respective drive gears (5a,b), either in the same plane or at an angle to each other. This is significantly more compact than existing solutions of multiple single gear pumps or coaxial gear pumps in a single housing, and gives great flexibility in design and of pumping parameters.

Description

The present invention relates to a gear pump assembly.
Gear pumps are positive displacement pumps, i.e. they pump a constant amount of fluid for each rotation, and they are particularly suited for pumping high viscosity fluids such as bitumen, pitch, diesel oil, crude oil, paints, inks, resins, adhesives, chocolate, molasses, and molten thermoplastics. They typically comprise a housing comprising a cavity in which is arranged a pair of gears, one of which is known as the "drive" gear, which is driven by a driveshaft attached to an external driver such as a motor, and an "idler" gear, which meshes with the "drive" gear. Both gears may be externally toothed, as in the case of an "external" gear pump, in which case the fluid is passed between the gear teeth and the wall of the cavity in the housing from the inlet to the outlet. External gear pumps typically use spur, helical, or herringbone gears, depending on intended application. Alternatively, one gear is externally-toothed, and the other gear is internally-toothed; it does not matter whether the internally or externally toothed gear is the drive or the idler gear. The axes of rotation of the gears are offset, and the externally-toothed gear is of smaller diameter than the internally-toothed gear. This type of gear pump is known as an "internal" gear pump, and the fluid is passed between the toothings of the two gears. A crescent-shaped partition may or may not be provided in the gap between the two gears, depending on application.
Although the present invention is applicable to all of the above-mentioned types of gear pumps, it is particularly applicable to external gear pumps.
It is often desirable in certain applications to have two or more gear pumps situated in close proximity, e.g. for pumping two different flows of liquid from a single source, such as a single extruder, to two or more different destinations, such as two or more different extrusion dies. Typically, this is achieved by arranging two or more separate gear pump arrangements to pump two or more flows of material. This takes up significant amounts of space due to the two separate housings of the two or more separate gear pump arrangements, and often results in longer flow channels from the extruder to the pumps than is desirable. It is advantageous in thermoplastics processing, as well as in other fields, to keep the flow channels short. The shorter the channels, the lower the pressure drop, the easier it is to maintain the temperature of the fluid, and there is less loss of material when the system is cleaned. Exactly the same problem exists in the opposite caseof multiple thermoplastic flows originating from separate extruders that are pumped together for a coextrusion process.
Various solutions have been presented in the prior art for reducing the space requirement for multiple gear pumps.
EP 0 091 347 describes a double gear pump for a hydraulic system with two coaxial gear pumps in a single housing, pumping fluid from a single inlet to two different outlets at different flow rates and pressures. The drive shafts of the drive gears are rotationally coupled and are driven in common by a single driver. This system presents the disadvantages of having a fixed flow rate and/or pressure difference between the two gear pumps due to the common drive and thus common rotational velocity of both pumps. The fluid pathways through the housing have a complicated shape which significantly complicates cleaning the pump, and even if one were to arrange the fluid pathways individually straight through the housing, due to the coaxial pump arrangement the distance between each inlet and outlet would still be quite significant, and would therefore not enable a significant reduction in the length of fluid channels required or the overall space requirement.
US 5,842,848 describes a compact high-volume gear pump consisting of three pumping sections each with its own idler gear for pumping fluid. All of the idler gears are driven by a single, common drive gear. This arrangement presents the disadvantages of fixed flow rate and/or pressure differences between each individual pump section, and again the fluid pathways follow a very complicated shape thereby presenting cleaning difficulties and indeed rendering a pump of this type entirely unsuitable for molten thermoplastics applications. Furthermore, cross contamination of fluid between the individual pumping sections is unavoidable.
It is also known to attach individual single gear pumps together coaxially by mounting the gear pump housings to one another and attaching the drive shafts together so as to drive all the pumps from a common drive means. This presents similar disadvantages to EP 0 091 347 with regard to flow ratios, pressure ratios, and angular drive velocity ratios. In addition, it is a particularly bulky solution.
It is thus an object of the present invention to overcome the above-mentioned disadvantages, and thereby to provide for the possibility of pumping multiple independent fluid flows while saving space and reducing the length of the fluid channels required.
This is achieved by a gear pump assembly with a single, unitary housing which has a plurality of external faces. Contained within this housing is a first cavity containing a first gear pump, and a second cavity containing a second gear pump. Each gear pump comprises a drive gear with a driveshaft and at least one idler gear, also known as a driven gear, meshing with the drive gear. Each gear pump is arranged such that rotation of its driveshaft causes fluid to be pumped through the housing from an inlet situated in a face of the housing to an outlet, also situated in a face of the housing. The exact shape of the gears, the proportions of the sizes of the gears, and the shape of the cavities is well-known to the skilled person and need not be discussed further. According to the invention, the two gear pumps are disposed collaterally in the housing, that is to say side-by-side, with respect to the axis of rotation of each drive gear, as opposed to coaxially (i.e. end-to-end) as is the case in EP 0 091 347 as discussed above. This presents the advantage of being able to bring the gear pumps significantly closer together than is possible with a coaxial arrangement, thereby reducing the amount of space required for the pumps, and the length of fluid conduit required between a fluid source (such as an extruder or a fluid tank) and the pumps. Reducing this length reduces the pressure drop along the conduit, and thus the arrangement permits rheological optimisation of the pumping arrangement. Additionally, each driveshaft is arranged to be driven independently, enabling each individual pump to have its rotational velocity independently determined according to the requirements of the user, which increases flexibility in design of the overall pumping system. It should be noted that the claim does not exclude the possibility of one or more of the gear pumps comprising multiple idler gears, such as in the case of three-gear or planetary pumps, such as described in GB 1,214,723 , EP 1 267 077 , and JP 64-77778 .
In an embodiment, at least one further gear pump is provided in its own cavity in the housing, which enables many gear pumps (i.e. three or more) to be situated close together as the user demands.
In an embodiment, the first gear pump and the at least one second gear pump are substantially identical, which reduces the number of different parts required for the gear pump assembly.
In an embodiment, the first gear pump and the at least one second gear pump differ by the width of the gears, and/or by the number of teeth on the drive and/or idler gears, and/or the diameter of the drive and/or diameter of the idler gears and/or by clearances in the pumps and/or by differing cooling arrangements of the gears. This enables the two or more pumps to be tailored to a specific application which requires different pumping geometry and/or parameters, for instance one pump be optimised for pressure and the other for flow velocity or flow rate, or in the case of cooling arrangements of the gears, when one pump requires cooling and the other not.
In an embodiment, each driveshaft is arranged to be driven independently with the same or different rotational velocities, enabling the pumping rate and/or pumping pressure in each pump to be tailored to the user's requirements.
In an embodiment, the drive shafts are arranged on the same or different faces of the housing. This enables a large degree of design flexibility and space optimisation for the entire pumping system, since the driving means (such as electrical or hydraulic motors) can be situated as is convenient for the user, either on the same side or on different sides.
In an embodiment, at least one inlet and at least one outlet are provided in the housing according to one of the following arrangements:

a single inlet common to at least two gear pumps and a separate outlet associated with each individual gear pump. This is useful in the case that a single source of fluid, such as an extruder, is required to feed at least two separate processes.
a separate inlet associated with each individual gear pump and a common outlet associated with at least two gear pumps. This is useful in the case that multiple sources of fluid, such as two or more extruders, are required to feed a single process such as a coextrusion process.
In the case of three or more gear pumps, one dedicated inlet and dedicated outlet for at least one gear pump, in combination with one of the above-mentioned combinations. This gives flexibility in design according to the needs of the user.
One inlet and one outlet associated with each gear pump. This provides a universal solution that can be supplemented by additional flow-controlling pieces to merge flows or to split flows where required.

In short, the following broad pump configurations are foreseen:

parallel flow (| |);
convergent flow from a plurality of inlets to one or more outlets (\/, V or Y configuration);
divergent flow from one or more inlets to a plurality of outlets (/\, inverted-V or inverted-Y configuration).

In an embodiment, the gear pump housing is provided with at least one heating zone. This heating zone is constituted in well-known fashion, e.g. by integration of channels for heating fluid or integration of electrical heating elements, and has the purpose of maintaining the temperature of the gear pump assembly for the desired application, e.g. sufficiently warm to maintain the temperature of a thermoplastic melt. This at least one heating zone may be arranged variously according to one of the following arrangements:

a single heating zone associated with one or more gear pumps, which may serve to heat a single gear pump or the entire assembly as required; or
a plurality of separate heating zones each associated with a single gear pump, enabling differing temperatures to be maintained for instance due to differing requirements e.g. for different thermoplastics in the case of a coextrusion application; or
in the case of three or more gear pumps, at least two separate heating zones each associated with at least one gear pump, again enabling differing temperatures to be maintained for instance due to differing requirements e.g. for different thermoplastics in the case of a coextrusion application.

In an embodiment, the housing comprises a heat insulating zone between two adjacent gear pumps so as to thermally isolate two adjacent gear pumps from each other, which is desirable in the case when the two pumping fluids have significantly different temperature requirements.
In an embodiment, a first plane defined by the longitudinal axes of the drive gear and idler gear of the first gear pump intersects with a second plane defined by the axes of the drive gear and idly gear of the second gear pump at an angle of less than or equal to 180°, i.e. the two gear pumps are arranged either in the same plane, with the liquid flows parallel to each other, or are arranged angled toward/away from each other. In a further embodiment, this angle is between 90° and 150°, giving angles of fluid flow of between 90° and 30° to each other, which enables positioning of the pumps for optimal use of the available space in the application in question. Essentially, this enables two (or more) gear pumps to be situated closer together than would be possible with single gear pumps each with their own housing, since it is naturally not possible for the housings to "overlap". This theoretical "overlap" can thus be eliminated by building multiple gear pumps into a single housing.
In an embodiment, the gear pump assembly is adapted to be connected to a single-screw or double-screw extruder, enabling use of the gear pump assembly as part of the manufacturing process for extruded thermoplastics, and in the case of the double-screw extruder, being able to arrange the complete system such that one screw feeds one pump, and the other screw feeds the other pump.
In an embodiment, the housing is provided with at least one cover plate, with the driveshaft of each gear pump penetrating the same cover plate, and in an alternative embodiment, a first cover plate and the second cover plate are provided on opposite faces of the housing with at least one driveshaft passing through the first cover plate and at least one other driveshaft passing through the second cover plate. This gives flexibility in design of the gear pump assembly and also of the overall system built around it by enabling driving means such as motors to be placed where convenient.
Specific embodiments are described with reference to the attached figures, which show:

Figure 1 - a first perspective view of a gear pump assembly according to the invention;
Figure 2 - a second perspective view of the gear pump of figure 1 viewed from the reverse angle;
Figure 3 - a top view of the gear pump assembly of figures 1 and 2;
Figure 4 - a cross-sectional view through the gear pump of the previous figures in the plane of the gear pump assembly;
Figure 5 - a possible application of the gear pump assembly illustrated schematically.

The figures illustrate a gear pump assembly 1 comprising a single housing 2 provided with a drive-side cover 3 and a non-drive-side cover 4. It is conceivable that one of these covers could be omitted, the omitted cover then being constructed integral with housing 2.
As best seen on figure 4, within the housing 2 are provided two gear pumps 8a, 8b, although more could be present, each consisting of a drive gear 5a, 5b, and an idler gear 6a, 6b, situated in respective cavities 7a, 7b. Each gear 5a, 5b, 6a, 6b is provided with a shaft 9a, 9b, 10a, 10b, which penetrates at least the drive-side cover 3, and is held in a bearing therein, as is conventional. Shafts 9a, 9b are driveshafts, and are adapted to be coupled with a source of rotation such as a motor (not illustrated). In the present illustration, the driveshafts 9a, 9b are provided with splines, however any other convenient geometric shape such as a square or hexagonal cross-section is also conceivable. The driveshafts and the shafts of the idler gears may be provided with cooling means (not illustrated) such as a water-based cooling system, as is known to the skilled person. It is possible that neither pump is provided with such a cooling system, only one of the pumps is provided with such a cooling system, or both pumps are provided with such a cooling system.
Openings 11a, 11b, 12a, 12b are provided in the housing 2 for the passage of fluid through wider inlet channels 13a, 13b leading to the gear pumps 8a, 8b, and narrower outlet channels 14a, 14b leading from the gear pumps 8a, 8b respectively. Each individual gear pump is of completely conventional design and need not be described further. It is of course self-evident to the skilled person that the direction of flow can be reversed through one or both of the gear pumps, and the modifications to permit this are well within the scope of normal design modifications - for instance, to permit gear pump 8a to pump in the opposite direction, channel 13a would be made narrower and channel 14a would be made wider, and the shape of the cavity 7a would be mirrored. It is entirely conceivable that each pump could be arranged to allow flow in either direction, in which case the cavity 7 would be made symmetric and the channels 13 and 14 would be made of equal cross-sectional area.
Although openings 11a, 11b are illustrated here as being separate, a further design option is that channels 14a, 14b merge on the inside of housing 2 thus resulting in a single opening 11. However, the illustrated arrangement is particularly advantageous since it has great flexibility in that it can be used with a variety of different types of flow guiding means so that an essentially standard gear pump assembly can be modified for various applications by means of external, bolt-on flow-guiding attachments.
The inlet channels 13a, 13b are coaxial with the outlet channels 14a, 14b, although this does not have to be the case: the channels may be at an angle, curved, or bent as desired by the user, however coaxial inlet and outlet channels present a significant advantage during cleaning, since solidified matter such as plastic or rubber can be withdrawn as a single piece, and/or a cleaning device can be passed easily through the straight channels.
In the illustrated example, the two gear pumps 8a, 8b are situated at an angle to each other. Defining a first plane by the axis of rotation of drive gear 5a and idler gear 6a, and defining a second plane by the axis of rotation of the other drive gear 5b and the other idler gear 6b, these planes intersect at an angle in the illustration of 140°, that is to say that in the illustrated case the angle between the channel 14a and the channel 14b is 40°. It should be noted that the channels 13a, 14a are perpendicular to the above-mentioned first plane, and the channels 13b, 14b are perpendicular to the above-mentioned second plane, although this does not necessarily have to be the case.
As is illustrated in figure 4, the housing 2 comprises channels 15 for heating fluid so as to create a heated zone, in this case encompassing the whole gear pump assembly. Of course, the arrangement could be made more complex, dividing the gear pump into separate heated zones, each associated with at least one gear pump 8a, 8b.
Figure 5 shows schematically a possible use of the gear pump according to the invention. Extruder 16 supplies a flow of molten plastic to a flow divider 17, attached to the inlets of double gear pump assembly 1. Gear pump 1 in this example is in the opposite configuration to that of figures 1-4, i.e. the inlets are closer together than the outlets. If a single inlet is present in the housing of the gear pump assembly 1, flow divider 17 may be dispensed with. Motors 18a, 18b drive the driveshafts of each respective gear pump via universal driveshafts 19a, 19b, pumping molten plastic out of the outlets 20. Pressure sensors 21 monitor the pressure at the inlets and outlet of the gear pumps, and temperature sensors 22 monitor the melt temperature at the outlets 20. Using the gear pump assembly of the invention in this application saves a significant amount of space compared to using two separate, individual gear pumps, thereby reducing the distance that molten plastic has to travel from the extruder to the gear pumps.
Although the invention has been described in terms of the above-mentioned specific embodiments, these are not to be construed as limiting the invention: many modifications are possible without departing from the scope of the invention as defined by the appended claims, and any of the embodiments described in the claims and/or the description can be combined so long as they are not mutually exclusive.
In addition, the application to extruder thermoplastics is not to be construed as limiting: many uses are foreseeable including, but not limited to, food products, pharmaceutical products, chemical products, lubricants, greases, oils, inks, and so on.

Claims

Gear pump assembly (1) comprising a single housing (2) having a plurality of faces, a first gear pump (8a) situated within a first cavity (7a) in the housing (2), and at least a second gear pump (8b) situated within a second cavity (7b) in the housing (2), each gear pump (8a, 8b) comprising a drive gear (5a, 5b) provided with a driveshaft (9a, 9b) and at least one idler gear (6a, 6b) meshing with the respective drive gear (5a, 5b), each gear pump (8a, 8b) being arranged such that rotation of its respective driveshaft (9a, 9b) causes fluid to be displaced through the housing (2) from at least one inlet (11a, 11b, 12a, 12b) situated in a face of the housing (2) to at least one outlet (12a, 12b, 11a, 11b) situated in a face of the housing (2), characterised in that the first gear pump (8a) and the second gear pump (8b) are disposed collaterally in the housing (2) with respect to the axis of rotation of each drive gear (5a, 5b), and in that each driveshaft (9a, 9b) is arranged to be driven independently by a respective source of rotation (18a, 18b) external to the housing (2).
Gear pump assembly (1) according to the previous claim, wherein at least one further gear pump is comprised within a corresponding cavity in the housing (2), the/each further gear pump comprising a further drive gear provided with a further driveshaft and at least one further idler gear meshing with the further drive gear, each further gear pump being arranged such that rotation of the further driveshaft causes fluid to be displaced through the housing (2) from at least one inlet situated in a face of the housing (2) to at least one outlet situated in a face of the housing (2).
Gear pump assembly (1) according to any previous claim, wherein the first gear pump (8a) and the at least a second gear pump (8b) are substantially identical.
Gear pump assembly (1) according to claim 1 or 2, wherein the first gear pump (8a) and the at least second gear pump (8b) differ from each other by the width of the gears (5a, 6a, 5b, 6b), and/or by the number of teeth on the drive and/or idler gears (5a, 6a, 5b, 6b), and/or by the diameter of the drive gears (5a, 5b) and/or by the diameter of the idler gears (6a, 6b) and/or by clearances in the pumps and/or by differing cooling arrangements of the gears (5a, 6a, 5b, 6b).
Gear pump assembly (1) according to any previous claim, wherein each driveshaft (9a, 9b) is arranged to be driven independently with the same or different rotational velocities.
Gear pump assembly (1) according to any previous claim, wherein the driveshafts (9a, 9b) are arranged on the same or on different faces of the housing.
Gear pump assembly (1) according to any previous claim, wherein at least one inlet (11a, 11b, 12a, 12b) and at least one outlet (12a, 12b, 11a, 11b) are provided in the housing (2) and according to one or more of the following arrangements:
- a single inlet common to at least two gear pumps (8a, 8b) and a separate outlet associated with each individual gear pump (8a, 8b); or

- a separate inlet associated with each individual gear pump (8a, 8b) and a common outlet associated with at least two gear pumps (8a, 8b); or

- in the case of three or more gear pumps, at least one gear pump associated with a dedicated inlet and a dedicated outlet, in combination with one of the above-mentioned combinations for two or more further gear pumps; or

- one inlet (11a, 11b, 12a, 12b) and one outlet (12a, 12b, 11a, 11b) associated with each gear pump (8a, 8b), each gear pump (8a, 8b) being arranged to pump in the same direction or in a different direction to at least one other gear pump (8b, 8a).
Gear pump assembly (1) according to any preceding claim, comprising at least one heating zone arranged arranged according to one of the following arrangements:
- the housing comprises a single heating zone associated with one or more gear pumps (8a, 8b); or

- the housing comprises a plurality of separate heating zones each associated with a single gear pump (8a, 8b); or

- in the case of three or more gear pumps, the housing comprises at least two separate heating zones each associated with at least one gear pump.
Gear pump assembly (1) according to any preceding claim, wherein the housing (2) comprises a heat insulating zone between two adjacent gear pumps (8a, 8b).
Gear pump assembly (1) according to any preceding claim, wherein a first plane defined by the longitudinal axis of the drive gear (5a) and the longitudinal axis of the idler gear (6a) of the first gear pump (8a), and a second plane defined by the longitudinal axis of the drive gear (5b) and the longitudinal axis of the idler gear (6b) of the second gear pump (8b) intersect at an angle of less than or equal to 180°.
Gear pump assembly (1) according to the previous claim, wherein the said angle is between 90° and 150°.
Gear pump assembly (1) according to any preceding claim, wherein the gear pump assembly pump (1) is adapted to be connected to a single-screw or double-screw extruder (16).
Gear pump assembly (1) according to any previous claim, wherein the housing (2) is provided with at least one cover plate (3, 4), the driveshaft (9a, 9b) of each gear pump passing through the same at least one cover plate (3, 4).
Gear pump assembly (1) according to any of claims 1-12, wherein the housing is provided with a first cover plate (3) and a second cover plate (4) arranged on opposite faces of the housing (2), at least one driveshaft (9a, 9b) passing through the first cover plate (3) and at least one other driveshaft passing through the second cover plate (4).
Gear pump assembly (1) according to any preceding claim, wherein the flow direction of fluid through each gear pump (8a, 8b) is arranged to be in a direction perpendicular to a plane defined by the longitudinal axis of the drive gear (5a, 5b) and the longitudinal axis of the idler gear (6a, 6b) of the respective gear pump (8a, 8b).