Metering pump for varnish or lacquer

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metering pump for varnish or laquer. The pump includes a housing in which are arranged a first gear wheel and a second gear wheel which is in engagement with the first gear wheel. At least the first gear wheel is mounted with a shaft in the housing. The pump further has a sealing device provided for the first gear wheel, wherein each gear wheel has a conveying area formed by a toothing, and wherein the sealing device is arranged between the conveying area and an end face area of the gear wheel.

2. Description of the Related Art

A gear pump having the features described above is known from DE 19 56 528 A. In order to seal the area of the pump which does not come into contact with the material to be conveyed, for example, the shaft, relative to the conveying area, an elastic or resilient sealing device is arranged at the end faces of the gear wheels directly underneath the toothing. For accommodating the sealing device, recesses are provided either in the housing walls or in the end faces of the gear wheels.

Metering pumps for varnish or lacquer have been found useful in the lacquering technology. They are important means for achieving a varnish application which is of a high quality and uniform.

When carrying out many lacquering tasks, for example, lacquering of motor vehicle bodies, a color change is relatively frequently required. It is essential in this connection that the color metered by the metering pump is not contaminated by the previously used color. For example, if a white lacquer is applied to a vehicle body, even the smallest residues of the lacquer are extremely detrimental to a previously applied red color.

Consequently, the metering pump is cleaned between the application of two colors. For this purpose, a rinsing liquid is conducted through the pump in the same manner essentially as the previously conducted lacquer or color liquid. The pump is operated, so that the rinsing liquid can flush out the color residues which are still in the pump. However, this procedure requires a relatively long time and also a relatively large quantity of rinsing liquid.

The prior art discloses measures for minimizing the area which comes into contact with the lacquer or colored liquids in order to be able to effectively rinse out the color residues.

WO 01/86150 A1 discloses a metering pump in which the first gear wheel is unilaterally connected to a shaft in the housing. The second gear wheel is freely arranged in the housing and is guided by a wall which surrounds the second gear wheel. The shaft of the first gear wheel is guided by a sleeve which is radially sealed relative to the housing by means of an O-ring.

DE 198 49 200 A1 discloses a gear pump with sealing devices, wherein the sealing devices are arranged between the end face of the gear wheels and the housing wall. Chambers which can be pressurized are arranged underneath the sealing devices. This pressure then acts from the other side of the sealing device against the pressure of the liquid to be conveyed and thereby, in addition to the sealing devices, prevents the penetration of the liquid into protected areas.

WO 98/25029 A1 discloses a motor pump unit in which the pump is constructed as a gear pump. in order to protect the drive shaft of the gear wheel from the conveyed liquid, an annular groove is provided at the end face of the gear wheel, wherein the annular groove receives a sealing means which seals the end face of the gear wheel relative to the housing wall. The sealing means is composed of an O-ring and an additional ring which is stationary relative to the O-ring and protects the O-ring against wear due to friction.

EP 1 164 293 A2 describes a rinsable gear pump. Additional ducts ensure that the rinsing agent flows through the bearing gap of the drive shaft over the entire width of the bearing. This ensures an effective cleaning of the gear pump, so that no sealing device is required between the end faces of the gear wheels and the housing wall.

DE 26 06 172 C2 discloses a rotary piston machine for liquids. The machine has an externally meshing gear wheel which is in engagement with an internally meshing gear wheel which has one tooth more than the externally meshing gear wheel. The sealing device between the externally meshing gear wheel and the housing wall is accommodated in an annular groove and consists of an elastic sealing ring and a metal sealing ring. The metal sealing ring remains stationary relative to the elastic sealing ring, however, the metal sealing ring produces a slight friction with respect to the side wall.

SUMMARY OF THE INVENTION

Therefore, it is the primary object of the present invention to provide a metering pump which operates economically.

In accordance with the present invention, in a metering pump of the above-described type, the above object is met by sealing the sealing device in the housing by means of a radial sealing device.

As a result of the configuration according to the present invention, it is ensured that no varnish or lacquer liquid can flow past the sealing device so that a contamination of the components which should be kept clean will not occur. This radial sealing device may be constructed simply as an O-ring, because it must only seal between two static components, i.e., the housing and the sliding ring seal. The areas into which the lacquer liquid can penetrate remain small because they are defined by the sealing device. The farther out the sealing device is arranged, the greater is an end face area at the end face of the gear wheel to which the lacquer liquid can no longer be admitted. Consequently, the sealing device automatically also holds back lacquer liquid from the shaft, so that sealing the shaft relative to the outside is essentially less complicated. Of course, there still remain in the area of the toothing surfaces of the gear wheel on the side of the end face, namely, the end faces of the individual teeth. Lacquer liquid can penetrate into these areas. However, this is not critical because rinsing liquid can also penetrate into these areas in a manner which is comparable to the penetration of the lacquer liquid. Consequently, it is relatively simple to ensure that the rinsing liquid has sufficiently removed the previous color since the area to be rinsed is smaller, less rinsing agent is required. This saves cost. The rinsing time is shortened. This also increases the useful life of the pump. The pump also usually has a longer service life because it is reliably ensured that the lacquer liquid does not penetrate into the bearing areas by means of which the shaft is supported in the housing. All of these factors make the operation of the pump constructed in this manner extremely economical.

Preferably, the toothing has a base circle, and a radial distance between the sealing device and the base circle is smaller than a radial distance between the sealing device and the shaft. Independently of the diameter of the gear wheels being used, it is ensured that the lacquer liquid which can be admitted into the area between the gear wheel and the housing can be kept small.

The radial distance between the base circle and the sealing device is preferably ≦1 mm. The sealing device should not be arranged directly at the base circle, so that the risk of damage due to passing tooth gaps is kept small. However, if a spacing is provided which is 1 mm or less, it is ensured, on the one hand, that the risk of damage to the sealing device is small. On the other hand, it is ensured that the area which can be contaminated does not become too large.

The sealing device is arranged preferably in the housing so as to be nonrotatable relative to the housing. Accordingly, the sealing device remains stationary. The sealing device is not taken along by the rotating gear wheel. This keeps the wear down.

The gear wheel preferably has at least in the area of the sealing device a wear-resistant surface. This wear-resistant surface can be deposited on the gear wheel. This wear-resistant surface can also be formed by an insert which interacts with the sealing device. A wear-resistant surface increases the service life.

In accordance with a particularly preferred feature, the wear-resistant surface has a DLC-coating. “DLC” means “diamond-like carbon,” i.e., a carbon coating similar to diamonds. The material especially has excellent sliding properties. The coating is particularly suitable for interacting with low friction with the sealing device. It is also possible to provide the entire gear wheel with a DLC-coating.

Preferably, the sealing device is a sliding ring seal. Such seals can be manufactured of materials which are wear and corrosion resistant and have good frictional properties.

It is particularly preferred in this connection that the sliding ring seal has at least at its sealing surface a metal, particularly a hard metal, a ceramic material or a fluorocarbon material. Such materials have a sufficient wear resistance and additionally ensure a sufficient sealing effect. Preferably, silicon carbide SiC is used.

The radial sealing device is preferably arranged with little dead space in the housing. In other words, the radial sealing device is arranged in such a way that only a small space remains between the conveying area and the radial sealing device which could be contaminated by lacquer liquid. In the same manner, cleaning of this small dead space is equally simple.

It is equally advantageous if a mounting gap remains between the radial sealing device and the conveying area, wherein a rinsing agent which flows through the conveying area can flow through the mounting gap. In the same manner in which lacquer liquid can penetrate to the radial sealing device, it is ensured that the rinsing liquid, which must be introduced anyway for cleaning the conveying area and the remaining areas of the metering pump, can penetrate up to the radial sealing device in order to rinse out the lacquer liquid.

The sealing device preferably provides a sealing effect axially at the gear wheel and radially in the housing toward the conveying area. The most important aspect is the axial sealing effect relative to the gear wheel. This ensures that the end face of the gear wheel can for the most part be kept free of lacquer liquid. The radial sealing device merely prevents a circumvention of the axial sealing device.

It is also advantageous if the sealing device is axially and radially pretensioned by means of a tensioning device. The tensioning device makes it possible to adjust the sealing forces, so that the penetration of lacquer liquid in areas in which the lacquer liquid is not desired, can be reliably avoided.

A supply connection of a protective medium preferably ends radially within the sealing device. Such a protective medium may be a liquid, for example, a protective oil. The protective medium can be used for building up a pressure within the sealing device, wherein the pressure corresponds to the pressure of the lacquer liquid outside of the sealing device. This reliably prevents lacquer liquid from penetrating past the sealing device.

Preferably, both gear wheels are mounted with a shaft each in the housing. This keeps the wear of the second gear wheel low. This does result in an additional area, i.e., the bearing area of the shaft of the second gear wheel, which theoretically could be contaminated. However, if a corresponding seal is also provided at the gear wheel, this risk again is eliminated.

The gear wheels are preferably supported axially on both sides in the housing. In other words, a shaft extends through each gear wheel or the gear wheels have shaft stubs on both sides. This has the advantage that practically no bending forces act on the bearing of the gear wheels. The shafts on both sides can also be reliably sealed by means of the sealing device described above.

The housing preferably has an assembly surface where a lacquer supply connection and a lacquer discharge connection are located, wherein a drive train for the first gear wheel extends through the assembly surface, wherein a supply block is mounted at the assembly surface. Even when the metering pumps operate reliably, it is occasionally necessary to carry out maintenance or an exchange. If the connections are provided practically only in the assembly surface, the connections at supply and discharge and the connection in the drive train are simultaneously disconnected when the housing is separated from the supply block. Additional measures for providing lines or other connections are practically not required. Accordingly, the metering pump is divided into two modules, i.e., the supply block on the one hand, and the housing with the two gear wheels, which form the actual pump, on the other hand. This significantly facilitates maintenance.

The shaft of the first gear wheel preferably ends in the area of the assembly surface and is provided there with a coupling profile. When the housing is to be exchanged, then the shaft does practically not project beyond the assembly surface or projects only to a slight extent. This means that the housing remains very compact which, in turn, facilitates transport and reduces the danger of injury.

Preferably, the supply block has a projection which surrounds the drive train, wherein the projection engages in a recess of the assembly surface. This projection facilitates the assembly of the housing at the supply block. Moreover, the area of the connection between the supply block and the housing which is subjected to the greatest mechanical load, is constructed in such a way that this load can be absorbed without problems.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a longitudinal sectional view of a metering pump for varnish or lacquer, shown in a partially disassembled state;

FIG. 2 is a sectional view taken along sectional line II-II of FIG. 1; and

FIG. 3 is a detail of FIG. 1 on a larger scale.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 of the drawing shows a metering pump 1 for varnish or lacquer in a cross-sectional view and divided into two structural groups.

The metering pump 1 has a housing 2 which is formed by an upper plate 3, a lower plate 4, and an intermediate plate 5. As can be seen in FIG. 2, the intermediate plate 5 has two approximately circular recesses 6, 7 which partially overlap. A first gear wheel 8 is arranged in the first recess 6 and an second gear wheel 9 which meshes with the first gear wheel 8 is arranged in the second recess 7.

A gear pump of this type operates as follows. The first gear wheel 8 is driven by a shaft 10 in a direction 11 and drives the second gear wheel 9 which rotates in a direction 12 having an opposite direction of rotation. The teeth of the two gear wheels 8, 9 engage in each other in an engagement area 13. When leaving the engagement area 13, a volume existing between the teeth is enlarged, so that a lacquer liquid can flow from a supply connection 14 into the intermediate spaces between the teeth. A lacquer liquid present in the intermediate spaces between the teeth is then taken along by the teeth of the two gear wheels 6, 7 in the direction of movement. The intermediate spaces between the teeth are closed after a short duration of rotation by the intermediate plate 5. The liquid present in the intermediate spaces between the teeth is then displaced in the engagement area from the intermediate spaces and can be discharged through the discharge connection 15. The operation of such a gear pump is known in the art.

Instead of a gear pump having two gear wheels with external gear engagement, it is also possible in a corresponding manner to use a gear pump having an externally engaging gear wheel and an internally engaging gear wheel, wherein the externally engaging gear wheel has a smaller diameter than the internally engaging gear wheel and both gear wheel are arranged eccentrically relative to each other. In that case, a sickle-shaped disc is arranged in a gap area between the two gear wheels. This type of sickle pump is also known in the art and can be used in a similar manner in the present case.

Each gear wheel 8, 9 has teeth with tooth tips and intermediate spaces between the teeth, and tooth bases. The tooth tips are situated in each gear wheel 8, 9 on a tip circle 16. The tooth bases are located in each gear wheel on a base circle 17. A conveying area 18, 19 seen in FIG. 1 is defined between the tip circle 16 and the base circle 17.

As can be seen in FIG. 1, the two gear wheels 8, 9 and the intermediate plate 5 have practically the same thickness. Accordingly, the two gear wheels 8, 9 rest against the plate 3 and the lower plate 4; of course, a small play exists in order to facilitate the rotary movement of the two gear wheels 8, 9 in the housing 2.

In order to prevent the lacquer liquid from penetrating into the area between the two gear wheels 8, 9 and the upper plate 3 or the lower plate 4, each gear wheel 8, 9 has a sealing device 20-23 at its upper side as well as at its lower side. All sealing devices 20-23 are principally of the same construction. These seals 20-23 will therefore be explained in connection with the sealing device 21 seen in FIG. 1 or the sealing device 20 seen in FIG. 3.

The sealing device 21 has an axial projection 24 which does not extend over the entire circumference of the sealing device 21. This projection 24 engages in a corresponding recess in the lower plate 4 and, thus, ensures that the sealing device 21 does not rotate.

A spring element 25 biases the sealing device 21 with a small force in the direction of the gear wheel 8. Consequently, an O-ring 26 surrounds the sealing device 21 and ensures that lacquer liquid does not flow from the conveying area 18 past the side of the sealing device 21 facing away from the gear wheel 8.

The sealing device 21 interacts with an insert 27 which is arranged in the end face of the gear wheel 8. This insert 27 has an increased resistance to wear. It may be made, for example, of ceramic or a metal, particularly a hard metal. It is also possible to provide this insert 27 with a DLC-coating, i.e., a diamond-like coating. A DLC-coating may also be applied directly on the end face of the gear wheel 8.

As can be seen in FIG. 3, the radial sealing device 26 which seals the sealing device 20 relative to the housing 2 is mounted with little dead space in the housing 2. The dead space is practically only determined by the fact that the web which holds the radial sealing device 26 may not be too thin, so that it will not break. Remaining between the conveying area 18 and the radial sealing device 26 is a mounting gap 47 which is dimensioned in such a way that a rinsing liquid which flows through the conveying area 18 can also flow through the mounting gap 47, so that any lacquer liquid which has penetrated up to this point can be conveyed away by the rinsing liquid.

As can be seen in FIG. 3, the tensioning means 25 is constructed as a set of springs. The tensioning means tensions the sealing device 20 axially relative to the end face of the gear wheel 8. Simultaneously, the tensioning means 25 can be constructed in such a way that it radially outwardly tensions the sealing device relative to the housing 2. This can be realized in a simple manner by providing the set of springs 25 with an external diameter which is slightly greater than the internal diameter of the sealing device 20.

The sealing device 21 is constructed as a sliding ring seal. The sealing device 21 may also be of a material which is resistant to wear, particularly metal, for example, hard metal, a ceramic material or a fluoroplastic material, preferably silicon carbide.

As mentioned above, the first gear wheel 8 is mounted with a shaft 10 in the housing 2. The second gear wheel 9 is also mounted with a shaft 28 in the housing. The two shafts 10, 28 are rotatable, wherein the shaft 10 is connected through a wedge 29 so as to rotate with the first gear wheel 8.

As can be seen in FIG. 1, the radial distance of the sealing devices 20-23 from the conveying area 18, 19 is significantly smaller than the radial distance between the sealing devices 20-23 and the shafts 10, 28. More precisely, the distance refers to the side of the sealing devices 20-23 which faces the lacquer liquid, i.e., the point up to which the lacquer liquid can penetrate. Accordingly, it is clearly visible that the areas at the end faces of the gear wheels 8, 9, which could be contaminated by the lacquer liquid, are relatively small. Similarly, only a small quantity of rinsing liquid is required if the metering pump 1 must be cleaned between two colors.

The radial distance between the sealing devices 20-23 and the conveying areas 18, 19 should in all cases be at most 1 mm. On the one hand, this maintains the area at the end faces of the gear wheels 8, 9 which can be contaminated by lacquer liquid. On the other hand, there is little danger that the sealing devices 20-23 will be located alternatingly opposite a tooth and a tooth gap and will wear.

For cleaning the metering pump, a cleaning liquid or rinsing liquid is supplied in a similar manner as the lacquer liquid through the supply connection 14 and is discharged through the discharge connection 15. This rinsing liquid penetrates into the same areas as previously the lacquer liquid and takes with it the color residues in these areas.

In addition, a sealing oil supply 30 is provided which ends radially within the sealing devices 20-23. For this purpose, a sealing oil supply has a main duct 31 from which extend two branch ducts 32, 33 which, in turn, have branches 34 to 37 which extend radially in the shafts 10, 28 and end approximately in the areas of the axial ends of the gear wheels 8, 9 in an area between the shaft 10 or 28 and the gear wheel 8 or 9.

The shaft 10 additionally has a shaft sealing device 38 whose primary purpose is to prevent the sealing oil from emerging from the housing 2. Lacquer liquid is already prevented by the sealing devices 20-23 to a sufficient extent from being able to escape from the housing 2.

The housing 2 has an assembly surface 39 in which the supply connection 14 ends. The supply connection 14, as seen in FIG. 2, is not arranged in the same plane as the axes of the shafts 10, 28. The discharge connection 15 also ends in the assembly surface, however, it is perpendicularly offset relative to the drawing plane of FIG. 1. The shaft 10 ends approximately in the assembly line 39. It has a coupling profile 40 at this end.

The purpose of the assembly surface 39 is to be able to mount a supply block 41 on the housing 2. The supply block 41 is fastened to the housing 2 by means which are not illustrated in detail, such as bolts. Lines 42 to the supply connection 14 or the discharge connection 15 are arranged in the supply block 41, wherein the lines can be closed or opened by a valve 43. Moreover, a drive shaft 44 is arranged in the supply block 41, wherein the drive shaft 44 is connected to a drive motor which is not illustrated in detail. When the supply block 41 is mounted on the housing 2, the drive shaft 44 is in engagement with the shaft 10, so that the gear well 8 can be driven.

The supply block 41 has a projection 45 which surrounds the drive shaft 44, wherein the projection 45 protrudes into a corresponding recess 46 in the upper plate 3 when the supply block 41 is mounted on the housing 2. On the one hand, this makes it possible to achieve an alignment of the drive shaft 44 relative to the shaft 10. On the other hand, the mechanical strength of the connection between the housing 2 and the supply block 41 is increased.

Accordingly, if the metering pump 1 is to be disassembled by removing the housing 2 from the supply block 41 it is only necessary to separate the mechanical connection between the supply block 41 and the housing 2 and it is then possible to pull the housing 2 from the supply block 41, which usually is mounted so as to be stationary, perpendicularly relative to the assembly surface 39. This separates the mechanical drive connection to the drive shaft 44 as well as the liquid connection to the ducts 42.

Of course, it is also possible that the sealing oil supply 30 extends through the supply block 41, however, this feature is not illustrated.

While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.