EP1855007A1 - Gear pump - Google Patents

Abstract

The toothed wheel pump has a housing (9) with two toothed wheels (1). The toothed wheels engage into one another. A feed medium (M) is fed from a suction side (2) to a pressure side (3), and a return duct (4) is provided which leads feed medium which flows outward through the plain bearing back to the suction side. A valve (5) with a stationary part and a moveable part is provided. The valve has a setting characteristic which runs, as an approximation, linearly in one region, and the setting characteristic is defined by a pressure across the valve as a function of a setting path in the valve.

Description

The present invention relates to a gear pump according to the preamble of claim 1.

Gear pumps consist essentially of a housing with two intermeshing gears, which are arranged on shafts, wherein at least one of the shafts is connected to a drive. The shafts are mounted in fluid-lubricated plain bearings, which are arranged immediately adjacent to the pump interior, wherein the fluid used for lubrication of the sliding bearing passes from the pressure side via the sliding bearing gap and a return channel to the suction side of the gear pump.

In particular, in gear pumps, which are used for the promotion of low-viscosity polymers and prepolymers and having a dynamic seal - for example in the form of a labyrinth seal (threaded shaft seal) - and subsequent static seal - for example, a packing seal with or without barrier medium - must be ensured that before the dynamic shaft seal always a positive pressure against the suction side is present, otherwise - when using a barrier medium - this can get into the fluid, which is highly undesirable. The positive pressure is necessary to obtain a sufficient filling of the sealing gap of the dynamic seal. So can a penetration be prevented by blocking medium in the main flow of the pumped medium.

On the other hand, the pressure before the dynamic shaft seal should not be too large, otherwise pumped medium can pass through the dynamic shaft seal to the outside or - if a static seal is present - the fluid enters into contact with this seal, which with destruction of the static seal must be expected.

It must also be ensured that the return duct can be closed during maintenance work on the static seal. For this reason, a valve was provided in the return channel, with the ingress of air can be suppressed to the suction side of the gear pump.

However, the known valve is not suitable to meet the above conditions for adjusting the delivery medium pressure before the dynamic shaft seal. Thus, it is extremely difficult due to the adjustment characteristic of the known valve to be able to set a delivery medium pressure before the dynamic seal in compliance with the above-described pressure conditions, since the area in which an adjustment must be made is very small.

The present invention is therefore based on the object to provide a gear pump, which does not have the disadvantages mentioned above.

This object is achieved by the measures specified in the characterizing part of claim 1. Further embodiments of the invention are specified in the dependent claims.

The invention relates to a gear pump, comprising a housing with at least two intermeshing gears, each having a shaft which are mounted in fluid-lubricated slide bearings, wherein a fluid is conveyed from a suction side to a pressure side and a return passage is provided by the sliding bearing outwardly flowing fluid returns to the suction side, and wherein a valve is provided with a stationary and a movable part. According to the invention, the valve has an adjustment characteristic which extends linearly in a first approximation in at least one region, the adjustment characteristic being defined by a pressure above the valve as a function of a setting path in the valve.

This results in a substantial improvement in the setting possibility of the pressure in the transitional region between the slide bearing and a dynamic seal of an outwardly guided drive shaft.

By making the valve usable both for opening and closing the return passage and for adjusting a pressure, the functions of opening / closing and pressure adjustment in the valve being realized substantially separately, the adjustment of the pressure in front of the valve, and thus in the transitional region between the plain bearing and a dynamic seal, much easier.

In one embodiment of the present invention, the valve is contained in the return passage.

As an alternative to the above embodiment of the invention, the valve is contained in a supply channel, which leads from the pressure side in a region arranged by the gears from the slide bearing area.

In one embodiment of the present invention, the valve has a pressure adjustment section which is primarily for pressure adjustment. Furthermore, the valve has a closing section with which the channel containing the valve can be opened or closed.

In a further embodiment of the present invention, the movable part is insertable into the stationary part.

In yet another embodiment, the movable and stationary parts contact each other in the closing section when the channel containing the valve is closed.

In another embodiment of the present invention, the valve has a pressure adjusting portion mainly for pressure adjustment and a closing portion in which the passage containing the valve can be opened and closed, and in the pressure adjusting portion, the adjusting characteristic is linearly approximated in the first approximation.

In a further embodiment of the present invention, the stationary part is an exchangeable sleeve.

Yet another embodiment of the present invention, the valve has the following dimensions: x: 0.5 * D ... 5 * D, in particular 3 * D; S1: 0.008 * D ... 0.08 * D; di: di <D, di = D / 1.5 ... D / 1.2; where x is the displacement, D is the diameter of the movable part, that is the passage opening in the shooting section and S1 is the gap width between the stationary and the movable part.

In a further embodiment of the present invention, the movable part is only translationally displaceable.

In a further embodiment of the present invention, a screw jack is provided to translate the movable member.

In yet another embodiment of the present invention, the movable part at the suction-side end is conical, spherical or flat.

• Polygon, insbesondere ein Dreieck, Viereck oder Sechseck;
• oval;
• rund.

A further embodiment of the present invention is characterized in that the movable part has one of the following cross sections:

• Polygon, in particular a triangle, quadrangle or hexagon;
• oval;
• round.

Finally, another embodiment of the present invention is that the closing section is provided in the flow direction of the conveyed medium after the pressure setting section.

Fig. 1

einen Schnitt entlang einer Drehachse einer nach Aussen geführten Antriebswelle einer Zahnradpumpe in schematischer Darstellung,

Fig. 2 bis 4

verschiedene Ausführungsvarianten für ein erfindungsgemässes Ventil,

Fig. 5A und 5B

mögliche Verstellcharakteristiken für die verschiedenen Ausführungsvarianten gemäss den Fig. 2 bis 4,

Fig. 6

eine weitere Ausführungsvariante für ein erfindungsgemässes Ventil,

Fig. 7

einen Schnitt entlang einer Drehachse einer nach Aussen geführten Antriebswelle einer weiteren Ausführungsform einer Zahnradpumpe in schematischer Darstellung und

Fig. 8

ein erfindungsgemässes Ventil mit einem translatorisch verschiebbaren beweglichen Teil.

The present invention will be further explained by means of embodiments shown in figures. Showing:

Fig. 1

a section along a rotation axis of an outwardly guided drive shaft of a gear pump in a schematic representation,

Fig. 2 to 4

various embodiments for a valve according to the invention,

Figs. 5A and 5B

possible Verstellcharakteristiken for the various embodiments according to FIGS. 2 to 4,

Fig. 6

a further embodiment variant for a valve according to the invention,

Fig. 7

a section along an axis of rotation of an outwardly guided drive shaft of another embodiment of a gear pump in a schematic representation and

Fig. 8

a valve according to the invention with a translationally movable part.

In Fig. 1 is a section through a gear pump is shown, wherein the sectional plane on the one hand along the axis of rotation 13 of a shaft 8 and on the other hand perpendicular to a plane which is spanned by the two shafts of the gear pump extends. The second, not visible in Fig. 1 shaft is therefore behind or in front of the illustrated shaft 8. A medium M, which is for example a polymer or a so-called prepolymer is supplied from a suction side 2 and with a gear 1, ie in the Tooth gaps, transported on a pressure side 3. On the pressure side 3, the pumped medium M is pressed by the intermeshing of the teeth of the two gears from the tooth gaps. The gear 1 is on one Shaft 8 mounted or it forms together with the shaft 8 a workpiece.

Fig. 1 shows that shaft portion which is guided to drive the gear pump to the outside. Starting from the gear 1 follows first a slide bearing section I, in which the shaft 8 is supported or mounted in the housing 9. Subsequent to the plain bearing section I follows a dynamic seal (sealing section II), which is realized here as a so-called labyrinth seal in the form of a return thread, and a static seal (seal section III), which is here realized with stuffing box packings with a barrier medium.

The sliding bearings are lubricated with the pumped medium M in the illustrated gear pump. Thus, conveying medium M penetrates from the pressure side 3, preferably via a bearing lubrication groove 14, into the bearing gap of the slide bearing section I and effects lubrication of the shaft 8. The dynamic seal adjoining the slide bearing and the static seal adjoining this prevent the conveying medium M from moving Outside can kick. It is important to ensure that due to a high negative pressure in the transition region between the sliding bearing section I and the sealing section II (dynamic seal) no barrier liquid enters the return channel 4, since then mix the barrier liquid with the pumped medium M and this would be contaminated. At the same time, the pressure in said transition region must not be too high, otherwise the fluid is pressed into the stuffing box packing and degraded there, which can lead to destruction of the static seal.

As has already been explained, the use of a throttle screw in the return channel 4 is already known. This throttle screw was used primarily to completely close the return duct 4, as must be done, for example, in a temporary shutdown of the gear pump each. In addition, it has always been attempted to satisfy the above-described conditions with respect to the pressure conditions after the sliding bearing section I during the operation of the gear pump. This is very difficult to accomplish with a simple throttle screw, as has been used in a known manner.

FIGS. 2 to 4 show valves 5 according to the invention, which are used in the return duct 4 (FIG. 1). The valves are all characterized by a comparison with the known throttle screw improved adjustment.

Based on the embodiment according to FIG. 2, in which a valve 5 is shown in a section, the inventive principle is explained. A movable part 20, also referred to as a journal, is displaceable in a stationary part 21, also referred to as a sleeve, according to arrow 24. In this case, the sleeve 21 may be configured so that it is a separate part in the Return channel 4 can be inserted or inserted, or the return channel 4 has a corresponding shape in the region of the valve 5 to be realized. The advantage of a replaceable sleeve 21 is a rapid adaptability of the valve 5 to changed circumstances, for example, when an optimization to a specific fluid must be made. Corresponding adjustments can also be made on the side of the pin 20.

• Bei einem vollständig geöffneten Ventil 5 sind die Druckverhältnisse in Flussrichtung vor und nach dem Ventil 5 im Wesentlichen identisch. Durch das Einführen des Zapfens 20 in die Hülse 21 wird die Querschnittfläche für das Fördermedium M zunächst verringert. Damit erfolgt eine erste Zunahme der Druckdifferenz über das Ventil 5. In vielen Anwendungen ist dies die Ausgangslage, d.h. die Position mit der kleinstmöglichen Druckdifferenz.

The valve 5 according to the invention is characterized in particular by the fact that the two functions to be fulfilled by the valve, namely the opening / closing of the return channel 4 and the pressure setting in the transition region from the sliding bearing section I to the dynamic sealing section II (FIG. 1), are essentially separated are realized. This does not mean that no overlaps between the functions are possible, but that there is a high degree of independence between the functions. In the following, the relationships and the operation of the valve are explained:

• In a fully open valve 5, the pressure ratios in the flow direction before and after the valve 5 are substantially identical. By inserting the pin 20 into the sleeve 21, the cross-sectional area for the pumped medium M is initially reduced. This results in a first increase in the pressure difference across the valve 5. In This is the starting position for many applications, ie the position with the smallest possible pressure difference.

With the further penetration of the pin 20 in the sleeve 21, the cross-sectional area is no longer changed - i. a gap width S1, which is present between the pin 20 and the sleeve 21, remains substantially unchanged - but it is now alone the penetration depth (hereinafter also called effective length or adjustment) of the pin 20 in the sleeve 21, which to a pressure difference change over the valve 5 leads. This was the first time a at least partially, in a first approximation linear adjustment obtained, which significantly simplifies setting an optimal pressure in the transition region between plain bearing section I and dynamic seal section II and facilitates precise adjustment.

wobei

Δp

resultierende Druckdifferenz über dem Ventil

Q

Durchsatz

η

Viskosität

x

wirksame Länge oder Einstellweg

D

Zapfendurchmesser

S1

Spaltbreite

To further illustrate the invention, calculations have been made, the result of which can be summarized in the following formula, which for simplicity is based on some model assumptions: $$\mathrm{\Delta }p=\frac{Q\cdot 12\cdot \eta \cdot x}{\pi \cdot D\cdot {S1}^3}$$

in which

Ap

resulting pressure difference across the valve

Q

throughput

η

viscosity

x

effective length or adjustment path

D

Journal diameter

S1

gap width

In the known throttle screw, for which the above calculations are also valid, primarily the short annular gap, which can be characterized by the gap height S1, is reduced at the short end. This reduction is included in the calculations in the third power, which leads to a very large change in pressure with little change in the gap width S1.

In contrast, in the inventive device with the further advancement of the pin 20 in the sleeve 21 an almost linearly increasing pressure difference is achieved because - as can be explained with the above formula - the gap width S1 is only slightly changed and essentially only the adjustment path x is changed , The first approximation linear relationship of setting path and pressure difference remains valid under the above conditions. A change occurs in the position shown in FIG. In this position, the effective length x (adjustment) is quasi extended without the pin 20 is pushed further into the sleeve 21. The conical pin 20 and the cone-shaped sleeve 21 have in this position at a distance from each other, which corresponds to the gap width S1 in the cylindrical portion of the pin 20 and the sleeve 21. This is the effective length (adjustment x), which of medium M flows through the same gap width S1 in the valve, extended by the corresponding dimensions in the conical portion of the pin. As a result, the pressure difference increases in proportion to this new effective length, resulting in a first disproportionate increase in the pressure differential.

If now the pin pushed further into the sleeve, the distance in the conical portion of the pin 20 is smaller than the gap width S1 in the cylindrical portion. Thus, the pressure difference across the valve increases disproportionately (i.e., the importance of the effective length decreases in determining the pressure difference), and the distance (i.e., the gap width S1) now determines the pressure difference across the valve at the third power. In other words, now the function "open / close" becomes active, which follows a strongly nonlinear legislation and the pressure difference correspond strongly increases.

From the foregoing, the realization of the two functions "open / close" and "pressure adjustment" can be located within the valve 5: Thus, the function "pressure adjustment" is locally assigned to a pressure adjustment section 22 and the function "open / close" to a closure section 23, whereby the function "open / close" and the function "pressure adjustment" are realized essentially separately from each other. The meaning of the phrase "essentially" indicates the fact that there is a certain overlap in that area is, in which it comes to a quasi extension of the effective length. This is indicated by a dashed extension of the pressure adjustment section 22. In proportion to the total length of the pressure adjustment section 22, the overlap is small. The overlapping area is, for example, at most 20% of the pressure setting section 22, in particular not more than 10% of the pressure setting section 22.

Based on the above rather general embodiments, a large variety of configurations of the outer shape of the pin 20 and / or the inner shape of the sleeve 21 can now be obtained. As examples, the embodiments shown in Figs. 3 and 4 are shown. While in the embodiment according to FIG. 3 the gap width S1 is rather constant in the pressure adjustment section 22, the gap width S1 varies in the embodiments according to FIGS. 2 and 4, wherein the variation in the gap width S1 in one case is determined by the outer shape of the journal 20 (FIG. as in Fig. 2) is generated and in the other case by the inner shape of the sleeve 21 (as in Fig. 4). The variation of the gap width S1 by the design of the pin and / or the sleeve can thus be used to obtain targeted adjustment characteristics.

It has been shown that the size ratios are to be set as follows: x 0.5 * D ... 5 * D, in particular 3 * D; S1 0.008 * D ... 0.08 * D; di di <D, di = D / 1.5 ... D / 1.2;

It should be noted that, in particular with a variation of the gap width S1 via the adjustment section 22, the adjustment characteristic can be adjusted.

Fig. 5A shows the adjustment characteristics of a known throttle screw (reference numeral 50) and various valves according to the invention (reference numerals 51, 52, 53 and 54), wherein the abscissa of the adjustment path x of the pin 20 relative to the sleeve 21 is indicated. Here, the origin is the fully closed valve. The ordinate shows the pressure difference p.

In Fig. 5A, the extremely steep curve 50 of the adjustment characteristic for gear pumps with the known throttle screw is clearly visible. In contrast, the courses 51 to 54 are significantly flatter, so that a simpler and more precise pressure setting is already apparent from this. As a first approximation, the curves 51 to 54 are linear within a setting range. The linear range corresponds to the pressure adjusting portion 22 (Fig. 2). The differences between the progressions 51 to 54 can be achieved, for example, by different gap widths S1 (ie, the gap width S1 is not constant over the effective length x) in the pressure setting section 22 (FIG. 2), as indicated for example in FIGS are. In particular, the course 54 shows a pronounced linearity, which is a consequence of a constant gap width S1, as is the case, for example, in the embodiment according to FIG.

Fig. 5B shows two further courses 55 and 56, wherein the course 55 were determined for a low-viscosity and the course 56 for a highly viscous pumped medium using the same valve. Since the same valve was used in the determination of the curves 55 and 56, the pressure to be set p is also in the same operating range B. The adjustment path x or the adjustment ranges E55 and E56 resulting from the operating range and the progressions 55 and 56 are due to Different viscosities of the media differently. As can be clearly seen from the graphs 55 and 56, in the adjustment ranges E55 and E56, in a first approximation, there is a linear relationship between the adjustment path x and the pressure difference p. While the curve 56 in the adjustment range E56 even has a linear relationship between the adjustment path x and the pressure difference p, due to the slight curvature in the adjustment range, the profile 56 has a linear relationship only to a first approximation. To clarify this situation, the two end points in the adjustment range E55 were connected by a dash-lined line in Fig. 5B.

FIG. 6 shows a further embodiment according to the invention. The pumped medium M which has flowed through the bearing gap is directed onto the suction side via a return channel 4 extending at right angles (FIG. 1). the gear pump is returned, wherein the return channel 4 on the one hand as a bore in a housing part 9a and a groove in a housing part 9b is executed. In the vertex of the rectangular course of the return channel 4, a feed unit 60 is provided, by means of which a pin 20 is inserted into the formed as a bore return channel 4. In contrast to the embodiments according to FIGS. 2 to 5, in the case of that according to FIG. 6, the arrangement of the two functions "opening / closing" and "pressure setting" is reversed: the pressure adjustment takes place on the side of the end of the journal 20 and the function " Opening / closing "on the side of the feed unit 60. This also existing gear pump can be equipped in a simple manner with a novel valve without the pump housing must be changed.

It should be noted that in Fig. 6, the pin 20 is located in the fully open and in the fully closed position. Overall, the pin 20 can be moved over a maximum length L (maximum displacement x).

• Polygon, insbesondere ein Dreieck, Viereck oder Sechseck;
• oval;
• rund.

In all embodiments of the pin as well as the sleeve is conceivable to provide a deviating from a rotational symmetry cross-section. For example, it is conceivable that the pin and / or the sleeve has one of the following cross sections:

• Polygon, in particular a triangle, quadrangle or hexagon;
• oval;
• round.

Furthermore, the pointing in the direction of the suction end of the pin can be designed differently. In particular, the end may be conical - pointed or blunt -, spherical or flat.

Finally, it is also conceivable that the pressure setting section 23 (Fig. 2) is divided into subsections so as to be able to obtain a further variation in the setting characteristics. Each subsection can be customized to meet specific needs.

Fig. 7 shows, based on the representation according to FIG. 1, a further embodiment variant for a gear pump. In contrast to that according to FIG. 1, the gear pump has a supply channel 15, which connects the pressure side 3 with the region between the sliding bearing and the dynamic seal. Furthermore, the valve 5 is not arranged in the return channel 4 but in the feed channel 15. Incidentally, the gear pumps are constructed identically, which is why reference is made to the description of FIG. 1 for further explanation.

The valve 5 according to FIG. 7 is in turn used for pressure adjustment or for opening / closing the supply channel 15, the above explanations regarding the valve 5 and the corresponding adjustment characteristics also being valid here.

Finally, a special feed unit 60 is shown in FIG. 8, which is particularly suitable in connection with the previously described embodiments for setting the adjustment path x in the valves according to the invention.

The well-known throttle screws described above perform during the displacement of the pin 20 a rotation about its own axis. Thus, the seals, which ensure that no fluid flows M in the direction of feed unit, not only claimed by the actual feed motion, but also by the rotation about its own axis. During the pressure setting and in particular also when the return channel is closed or opened, these seals are stressed so heavily that their life expectancy is severely restricted.

Another aspect of the invention leads to a substantial improvement of this problem. Thus, the use of a Spindelhubgetriebes 61 it allows that a translational movement can be obtained. Thus, the seals 63 are no longer by a Self-rotation of the pin 20 claimed, but only by the actual translational movement, which is necessary to adjust the pressure or to open / close the valve. The sliding path of the seal is thus reduced.

Further, the feed unit 60 of the present invention allows a much larger stroke (maximum length L or maximum displacement x), so that pressure adjustment characteristics enabling extremely fine adjustment can be realized.

Finally, the use of the Spindelhubgetriebes 61 allows easier handling during the adjustment process. While in the known throttle screw settings had to be made very close to the rotating drive shaft, the setting in the inventive variant with a Spindelhubgetriebe 61 can be made at right angles to the rotating drive shaft. Thus, the access to the adjustment device is significantly improved and reduces the risk of injury to operating personnel by the rotating drive shaft.

Although the feed unit 60 according to the invention is particularly suitable in combination with the valve according to the invention or the various embodiments shown, a combination of the feed unit according to the invention with known valves also leads to those mentioned in connection with the screw jack Benefits. For this reason, the feed unit according to the invention is considered to be independent of the valve according to the invention and therefore deserves protection independent of the valve.

Claims (15)

Gear pump, comprising a housing (9) with at least two intermeshing gears (1) each having a shaft (8), which are mounted in medium-lubricated slide bearings (I), wherein a fluid (M) from a suction side (2) a pressure side (3) is conveyed and a return channel (4) is provided which leads back to the suction side (2) through the slide bearing (1) to the outside flowing fluid (M), and wherein a valve (5) with a stationary and a movable Part (21, 20) is provided, characterized in that the valve (5) has a Einstellcharakteristik which extends linearly in at least a first region, wherein the adjustment characteristic by a pressure above the valve (5) in function of a Einstellweges ( x) is defined in the valve (5). Gear pump according to the preamble of claim 1, characterized in that the valve (5) can be used both for opening and closing the return duct (4) and for setting a pressure, the functions opening / closing and pressure setting in the valve (5) essentially realized separately. Gear pump according to claim 1 or 2, characterized in that the valve (5) in the return passage (4) is included. Gear pump according to claim 1 or 2, characterized in that the valve (5) in a supply channel (15) is included, from the pressure side (3) in one of the gears (1) from the slide bearing (I) arranged area leads. Gear pump according to one of claims 1 to 4, characterized in that the valve (5) has a pressure adjustment section (22) which serves mainly for pressure adjustment, and in that the valve (5) has a closing section (23) with which the valve (5) containing channel (4, 15) can be opened or closed. Gear pump according to one of claims 1 to 5, characterized in that the movable part (20) in the stationary part (21) can be inserted. Gear pump according to one of claims 1 to 6, characterized in that the movable (20) and the stationary part (21) in the closing section (23) touch when the valve (5) containing the channel (4, 15) is closed. Gear pump according to claim 2, characterized in that the valve (5) has a pressure adjustment section (22) mainly for pressure adjustment, and in that the valve (5) has a closing section (23) in which the valve (5) containing Channel (4, 15) can be opened or closed, wherein in Druckeinstellungsabschnitt (22) the adjustment characteristic is linear in first approximation. Gear pump according to one of claims 1 to 8, characterized in that the stationary part (21) is an exchangeable sleeve. Gear pump according to one of claims 1 to 9, characterized in that the valve (5) has the following dimensions: x: 0.5 * D ... 5 * D, in particular 3 * D; S1: 0.008 * D ... 0.08 * D; di: di <D, di = D / 1.5 ... D / 1.2; where x is the displacement, D is the diameter of the movable part (20), di the passage opening in the shooting section (23) and S1, the gap width between the stationary (21) and the movable part (20). Gear pump according to one of claims 1 to 10, characterized in that the movable part (20) is only translationally displaceable. Gear pump according to claim 11, characterized in that a Spindelhubgetriebe (61) is provided to translate the movable part (20) translationally. Gear pump according to one of claims 1 to 12, characterized in that the movable part (20) on the suction side end facing conical, spherical or flat. Gear pump according to one of claims 1 to 13, characterized in that the movable part (20) has one of the following cross sections: - Polygon, in particular a triangle, quadrangle or hexagon; - oval; - round. Gear pump according to one of claims 1 to 14, characterized in that the closing section (23) in the flow direction of the conveying medium (M) is provided after the Druckeinstellabschnitt (22).

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