GEAR PUMP AND ITS USE

Gear pump with intermeshing gearwheels enclosed by a housing with bearing journals on shaft axes projecting laterally from the gear wheels mounted in the housing by slide bearings each having a slide bearing length, each having a lubrication pocket with radial expansion. The lubrication pocket is spaced from a gear-side end face of the respective slide bearing by a first distance, having a first bar with a first bar width with axial expansion corresponding to a slide bearing surface. The lubrication pocket is spaced apart by a second distance from the bearing end face opposite the gear end face. A second bar with a second bar width with axial extension corresponds to a slide bearing surface, a bore leads through the slide bearing and communicates with the lubrication pocket at an injection point. The bore is operatively connected to a conveying device for conveying lubricating medium into the lubrication pocket.

TECHNICAL FIELD

The present invention relates to a gear pump according to the pre-characterizing part of claim1and to a use of the gear pump according to claim15.

STATE OF THE ART

Gear pumps essentially consist of a pair of intermeshing gear wheels, which are enclosed in a housing and from which bearing journals arranged laterally around the longitudinal axis protrude, which are in slide bearings lubricated with the pumped medium.

As gear pumps have a rigid characteristic curve, they are particularly suitable for transporting pumped media from a suction side to a pressure side. A pressure gradient is created between the two latter sides due to the pumped volume flow in the downstream units, which is particularly large with highly viscous media and leads to a transmission of force to each gear wheel.

A known gear pump is described, for example, in EP-1 790 854 A1, which is a gear pump in which a bearing journal diameter is almost or equal to a root diameter of the toothing.

The known gear pumps have slide bearings that are lubricated with the pumped medium. There is high pressure on one side of the slide bearings on the gear pump outlet side, whereas the pressure behind the slide bearing is approximately equal to the one on the suction side of the gear pump, which is significantly lower than the pressure on the pump outlet side. Due to this pressure difference, pumped medium, which is required to build up the lubricating film in the slide bearing, flows from the pump outlet into the slide bearing. A pressure lubrication groove in the face of the slide bearing forms a direct connection from the outlet side to the slide bearing in order to supply the lubrication groove in the slide bearing as well as possible with pumped medium.

If a polymer melt is used as the conveying medium, which also contains a high proportion of solids or solids above a critical size (generally referred to as foreign particles), this poses a problem for sufficient lubrication in the slide bearing. For the slide bearings to function properly, it is important to build up a lubricating film of pumped medium. If too many or too large foreign particles get into the narrow lubrication gap between the shaft and the slide bearing, there is a risk of damage to the slide bearing or the shaft, which can lead to failure of the gear pump. This is particularly the case if the particle size is larger than the height of the minimum lubricant film, as this leads to an interruption of the lubricant flow due to blockage in the slide bearing and thus to a failure of the gear pump. If too little melt enters the slide bearing, there is a risk of insufficient lubrication. An increased flow of melt (pumped medium) comprising particles can also lead to increased abrasive wear of the slide bearing surfaces.

Furthermore, if a polymer is used as the pumped medium, unmelted polymer particles (small lumps) that enter the slide bearing via the lubrication groove can block the lubrication flow and cause the gear pump to fail.

The problem of foreign particles can be tackled within certain limits by using a slide bearing with filling pockets, as described, for example, in EP 4 083 428 A1. The filling pocket incorporated into the slide bearing is characterized by a bar between the end face of the slide bearing on the gear wheel side and the filling pocket, whereby the bar prevents large foreign particles in the pumped medium from entering the lubrication gap between the gear wheel shaft and the slide bearing. For many applications, this approach already offers a good solution for “filtering out” solids from the main flow before the filtered medium enters the slide bearing to build up the lubricating film.

However, with polymer melts as the pumped medium with low viscosity, which can only form a thin lubricating film in the slide bearing, this known method of filtering the pumped medium is not sufficient. Too many foreign substances still get into the lubrication gap and the risk of damage (so-called seizure) increases.

SUMMARY OF THE INVENTION

It is therefore a task of the present invention to provide an improved gear pump which is considerably more robust in operation than known solutions.

This task is solved by the features specified in the characterizing part of claim1. Further embodiments of the present invention and a use are defined in further claims.

A gear pump according to the invention comprises intermeshing gear wheels enclosed by a housing with bearing journals arranged on shaft axes and each projecting laterally from the gear wheels, which are mounted in the housing by means of slide bearings each having a slide bearing length, which each have a lubrication pocket with radial extension, the lubrication pocket being spaced from a gear-side end face of the respective slide bearing by a first distance, so that a first bar with a first bar width with axial extension corresponding to a slide bearing surface is present. The invention is characterized inthat the lubrication pocket is also spaced apart by a second distance from the bearing end face opposite the gear end face, so that a second bar with a second bar width with axial expansion corresponding to a slide bearing surface is present,that a bore leads through the slide bearing and communicates with the lubrication pocket at an injection point andthat the bore is operatively connected to a conveying device for conveying lubricant into the lubrication pocket.

The gear pump according to the invention is therefore considerably more robust compared to known gear pumps, as neither unmelted polymer particles (small lumps) nor foreign particles can get into the lubrication groove in the slide bearing when a polymer is used as the pumping medium. This significantly reduces the risk of blockage of the lubricant flow. The lubrication flow is therefore blocked much less, which significantly reduces the probability of failure of the gear pump according to the invention.

One embodiment of the gear pump according to the invention consists in that the first bar width is at least 5% to 20%, preferably 15%, of the slide bearing length.

Further embodiments of the gear pump according to the invention consist in that the second bar width is at least 5% to 15%, preferably 10%, of the slide bearing length.

Still further embodiments of the gear pump according to the invention consist in that the lubrication pocket begins in relation to a plane spanned by the two shaft axes and in the direction of rotation of the gear wheels in an angular range of 210° to 315°, preferably at 270°.

Still further embodiments of the gear pump according to the invention consist in that the lubrication pocket ends at an angle of 300° to 30°, preferably at 355°, in relation to a plane spanned by the two shaft axes and in the direction of rotation of the gear wheels.

Still further embodiments of the gear pump according to the invention consist in that the injection point is being arranged in the center of the lubrication pocket in the axial extension of the lubrication pocket.

Still further embodiments of the gear pump according to the invention consist in that the injection point is arranged in relation to a plane spanned by the two shaft axes and in the direction of rotation of the gear wheels in an angular range of 225° to 315°, preferably in an angular range of 240° to 300°, preferably at 270°.

Still further embodiments of the gear pump according to the invention consist in that the lubrication pocket is deepest in the area of the injection point.

Still further embodiments of the gear pump according to the invention consist in that the injection point, viewed in the direction of rotation of the gears, is arranged at the beginning of the lubrication pocket.

Still further embodiments of the gear pump according to the invention consist in that the lubrication pocket, starting from the injection point and viewed in the direction of rotation of the gear wheels, is wider.

Still further embodiments of the gear pump according to the invention consist in that cross-sectional areas of the lubrication pocket, starting from the injection point and viewed in the direction of rotation of the gear wheels, are the same size over ⅔ of their unwound length and that cross-sectional areas of the lubrication pocket are designed to decrease steadily over the remaining unwound length to the end of the lubrication pocket.

Still further embodiments of the gear pump according to the invention consist in that a cross-sectional area of the bore is the same size as the cross-sectional areas of the lubrication pocket in the first ⅔ of the unwound length of the lubrication pocket.

Still further embodiments of the gear pump according to the invention consist in that the bore is being arranged radially to an outer diameter of the respective slide bearing.

Still further embodiments of the gear pump according to the invention consist in that at least one of the bearing journals has, at least over part of its axial extent, a bearing journal diameter which lies in the range from 90% to 100% of a root circle diameter of the toothing of the associated gearwheel.

Finally, the present invention comprises a use of the gear pump according to one or more of the above-mentioned embodiments for conveying highly viscous conveying media, such as polymer, with a mass percentage of fillers (e.g. titanium dioxide TiO2, calcium carbonate, wood flour, stone, chalk, tallow, talc, silicates, carbons, in particular in the form of carbon black) of more than 60% of the total mass of the conveying medium.

The present invention also includes a use of the gear pump according to one or more of the above-mentioned embodiments for conveying media with low viscosity (greater than or equal to one Pascal second), as well as polymer melts loaded with foreign particles, in which the foreign particles have a size which is equal to or greater than the minimum lubricating film in the slide bearing.

The aforementioned embodiments of the present invention can be combined in any order. Only those combinations of embodiments are excluded which would lead to a contradiction due to the combination.

DETAILED DESCRIPTION OF THE INVENTION

FIG.1shows a perspective view of a gear wheel1known per se with bearing journals5and6for a gear pump according to the invention. Over part of their axial extension, the bearing journals5and6have a bearing journal diameter DLwhich is approximately as large as a root diameter DFof the toothing. The bearing journal diameter DLis at least in the range of 90% to 100% of the root circle diameter DF. Of course, this also applies to the bearing journals of the second gear wheel not shown inFIG.1. However, it is expressly pointed out that the aforementioned design variant with the bearing journal diameter and root circle diameter defined above does not necessarily have to be realized in this way. A conventional design variant in which the bearing journal diameter is smaller than 90% of the root diameter is also conceivable.

In contrast to the proven principle of bearing lubrication by means of a pumped medium, which is fed into the slide bearings through grooves (see for example EP 833 068 B1), a clean, contaminant-free lubricating medium for lubricating film build-up is now provided by a separate external pumping device and pressed into a lubricating pocket2(FIG.2) in the slide bearing3(FIG.2) via a bore4(FIG.2). In this way, the lubricating film build-up between the slide bearing3and the bearing journal5,6is largely independent of the lubricating film-building properties of the pumped medium, as this task is performed by a suitable, clean and largely foreign substance-free lubricating medium. Reference is expressly made to the advantage that this external lubricating medium for lubricating film build-up can be different from the pumped medium to be recycled. It is expressly emphasized that the external lubricant can differ significantly from the pumped medium. Depending on the application data, a suitable external pumped medium (lubricating medium) with specific properties can be selected, in particular due to the fact that only a negligibly small amount is required for the lubrication of the slide bearings.

For example, a lubricant is used that has a viscosity of 1 Pas in the pumpable state.

FIG.2shows a cross-section through a slide bearing3according to the invention with a slide bearing length L. The cut plane runs parallel to the shaft axis9and is positioned so that the lubrication pocket2incorporated in the slide bearing3is visible.

As can already be seen fromFIG.2, the lubrication pocket2is spaced from a gear-side end face7(also referred to as the inner side of the bearing) of the slide bearing3by a first distance d1, so that a first bar11with radial expansion corresponding to the sliding surface of the slide bearing3is present. The first bar11has a first bar width D1, whereby this is smaller than the first distance d1, because a transition from the sliding surface to the end face of the slide bearing3is not part of the first bar11. It has been shown that the bar width D1should be 5 to 20%, preferably 15%, of the slide bearing length L. It should be noted that the bar width D1is a minimum specification, i.e. a gear-side edge of the lubrication pocket2does not have to run parallel to the gear-side end face. Furthermore, it is not absolutely necessary for the lubrication pocket2to have the minimum bar width D1.

Furthermore, the lubrication pocket2on the other bearing side is spaced apart from a second end face8(also referred to as the outer bearing side), which is located opposite the gear-side end face7of the slide bearing3, by a second distance do, so that a second bar12is present, which has a second bar width D2, whereby this in turn is smaller than the second distance do because a transition from the sliding surface of the slide bearing3to the second end face8of the slide bearing3is again not counted as part of the second bar12. It has been shown that the bar width D2should be 5 to 15%, preferably 10%, of the slide bearing length L. It should also be noted here that the bar width D2is a minimum specification, i.e. a bearing outer-side edge of the lubrication pocket2does not have to run parallel to the bearing outer side. In addition, it is not absolutely necessary for the lubrication pocket2to have the minimum bar width D2.

This means that a maximum axial expansion (in relation to the shaft axis) of the lubrication pocket2is determined by the above definitions of the first and second bars11and12. A maximum expansion of the lubrication pocket2along the sliding surface of the slide bearing3will be explained below with reference toFIGS.3and4.

FIG.3shows a partial cross-section through the slide bearing3according to the invention in the region of the bore4and the associated lubrication pocket2, the lubrication pocket2shown being only one of many possible embodiments of the present invention. The position of the lubrication pocket2is represented by an angle to a plane spanned by the two shaft axes9, the so-called angular reference plane10, and the angle is indicated in the direction of rotation R of the shaft in the slide bearing3. The angular reference plane10is thus perpendicular to a chordal surface14of the slide bearing3. The lubrication pocket2begins at an entry edge16into the lubrication pocket2. Viewed in the direction of rotation R and in relation to the angular reference plane10, the lubrication pocket2begins with the entry edge16after a start angle α and ends with the exit edge15after an end angle β. In the embodiment of the lubrication pocket2according to the invention as shown inFIG.3, the start angle is α=265° and the end angle is β=355°. The bore4, through which the lubricant is fed into the lubrication pocket2, has an injection point13that coincides at least partially with the leading edge16. After the injection point13, the lubricant is distributed both in the axial direction and in the direction of rotation R within the lubrication pocket2until the lubricant enters a lubrication gap at the outlet edge15, which is formed on the one hand by the shaft or the bearing journal5,6and on the other hand by the slide bearing3and forms a lubricant film.

FIG.4, which shows a section through the entire slide bearing3according toFIG.3, defines the angular ranges according to the invention, within which both the start angle α and the end angle β as well as the injection point13of the bore4into the lubrication pocket2lie. It has been shown that the lubrication pocket2has a minimum start angle α of 210° and a maximum end angle β of 30°, meaning that such a lubrication pocket2covers the maximum angle range of 210° to 30°. The injection point13and thus one end of the bore4in the lubrication pocket2lies in an angular range of 225° to 315°, whereby, restrictively, the injection point13must always end in the lubrication pocket2: In other words, the injection point13must necessarily be arranged after the start angle α and before the end angle β of the selected lubrication pocket2, but at the same time must also lie within the angular range of 225° to 315°. The injection point13is preferably located within an angular range of 240° to 300°. It has also been shown that the injection point13is located in particular at an injection point angle δ of 270°. For its part, the lubrication pocket2preferably extends over an angular range of 265° to 355°.

It follows from the above angle specifications that the injection point13does not necessarily have to be located directly after the start angle α, even if this is preferably intended. Rather, it is conceivable that the injection point13—taking into account the aforementioned conditions for the angle range for the injection point13and the expansion of the lubrication pocket13—can be at any point, in particular also in the area of the end angle β.

While the position of the injection point13is sufficiently defined, the associated bore4is designed, for example, as a radial bore4through the slide bearing3. However, any drilling direction through the slide bearing3to the injection point13is conceivable.

This defines a maximum frame20—now again with a view toFIG.2—within which the lubrication pocket2is located or which the lubrication pocket2fills to the maximum. This maximum frame20is shown inFIG.2by a dashed line.

As already briefly pointed out in connection with explanations ofFIG.2, the lubrication pocket2incorporated in the slide bearing3is supplied with a lubricating medium which is pressed into the lubrication pocket2through the bore4via the injection point13. Viewed in the direction of rotation R of the bearing journal5,6, the lubrication pocket2can start at or in front of the injection point13at a minimum lubrication pocket start and end at a maximum lubrication pocket end. So while the maximum width of the lubrication pocket2is defined by the bar widths D1and D2as a proportion of the slide bearing length L, the maximum length of the lubrication pocket2—viewed in the direction of rotation R of the bearing journals5,6—is defined by the lubrication pocket start16and the lubrication pocket end15by means of angles, which have been explained with reference toFIG.4.

As already mentioned, the injection point13can be located anywhere within the maximum frame20(FIG.2). Preferably, the injection point13is located in the center of the frame20and becomes steadily larger as the angle increases, as shown in the specific embodiment example for the lubrication pocket2inFIG.2.

In contrast to the proven principle of bearing lubrication by means of a conveying medium, which is fed through grooves into the slide bearings according to the state of the art, a clean, low-impurity lubricating medium for lubricating film build-up is now provided by a separate external conveying device, which can be an extruder or a gear pump, for example, and pressed into the slide bearing3. In this way, the lubricating film build-up is largely independent of the lubricating film-building properties of the conveying medium, as this task is performed by a suitable, clean and, above all, low-impurity lubricating medium. Express reference is made to the advantage that this external lubricating medium can be different from the conveying medium to build up the lubricating film. However, the lubricant must be selected in such a way that it is compatible with the lubricant, as the lubricant subsequently mixes with the pumped medium, i.e. after exiting the slide bearing gap.

According to the invention, the geometry of the slide bearing3and the design of the lubrication pocket2in the slide bearing3are designed in such a way that the smallest possible quantity of lubricating medium is required for the hydrodynamic slide bearings3. At the same time, the design of the slide bearing3and the geometry of the lubrication pocket2must ensure that as little contaminated pumped medium as possible enters the slide bearing3from the main flow, as otherwise the good lubricating properties of the clean, externally supplied lubricant cannot be utilized. A suitable choice of geometry for the slide bearing3and the design of the lubrication pocket2ensures that the contaminated pumped medium is largely kept out of the lubrication gap of the slide bearing3without additional components in the gear pump itself (such as a shaft seal, etc.).

In further development of the above explanations, it is expressly pointed out that the present invention can also be used excellently for critical applications in which no foreign particles are contained in the pumped medium, but a very thin lubricating film is nevertheless desired in the slide bearing, i.e. if the pumped medium does not permit such a thin lubricating film.

FIG.5shows a curve of the cross-sectional area Q as a function of an increasing angle of rotation r, starting from the starting edge16(FIG.2) of the lubrication pocket2, which widens continuously as the angle of rotation r increases. This is an embodiment variant for a lubrication pocket2that has a constant cross-sectional area Q over a significant extension in the direction of rotation R. Preferably, the cross-sectional area of the bore4—and consequently also the cross-sectional area of the injection point13—is constant over a large area of its expansion (for example, over ⅔ of the entire expansion of the lubrication pocket2in the direction of rotation R up to a boundary line21). In the last third of the lubrication pocket2(again viewed in the direction of rotation R), the cross-sectional area Q decreases steadily, for example, up to the outlet edge15. Due to the lubrication pocket2widening steadily in the direction of rotation R (seeFIG.2), a depth of the lubrication pocket2decreases in the first ⅔ of the expansion of the lubrication pocket2in the direction of rotation R in such a way that the cross-sectional area Q is constant. This achieves optimum distribution of the lubricant within the lubrication pocket2before the lubricant reaches or is pressed into the slide bearing gap between the shaft and slide bearing3.

REFERENCE LIST

1gear wheel2lubrication pocket3sliding bearing4bore5,6bearing journals7bearing inner side; gear-side end face; gear end face;8bearing outer side; end face opposite the end face on the gear side; bearing end face;9shaft axis10angle reference plane11first bar12second bar13injection point14chordal surface15exit edge16starting edge20maximum frame21boundary lineR rotation direction of the shaftr rotation angleα starting angleβ end angleδ injection point angleDLbearing journal diameterDFbase circle diameterLG slide bearing lengthQ cross-sectional aread1first distance of the lubrication pocket from the face of the slide bearing on the gear sided2second distance of the lubrication pocket from the opposite side to the face of the slide bearing on the gear sideD1first bar widthD2second bar width