System for the circulatory conveyance of media

Abstract

The invention relates to a system for the circulatory conveyance of media, with a drive and with two conveying chambers, the first conveying chamber constituting a feed chamber and the second conveying chamber a return chamber.

Description

[0001] The invention relates to a system for the circulatory conveyance of media, in particular of coating masses, such as, for example, glues and inks in the printing and packaging industry, between a first and a second container and claims the priority of German patent application 100 44 868.2-15 to the contents of which reference is made.

[0002] When a firmly adhering layer of originally formless material is coated, that is to say applied to a workpiece, the homogeneity of the coating mass is particularly important. The coating masses are therefore often circulated continuously between the stock or supply vessel and what is known as the doctor blade chamber. The doctor blade chamber constitutes the laterally delimited space in which the inking or printing rollers are provided with the coating medium. The doctor blade chamber advantageously has as constant a filling height as possible.

[0003] In order to make it possible for the coating mass to be applied evenly to the rollers, it is advantageous, furthermore, to feed the coating mass from the stock container into the doctor blade chamber without any pulsation, so that the formation of foam or of waves in the doctor blade chamber is avoided.

[0004] For this purpose, it is known to convey the coating mass out of the stock container into the doctor blade chamber with the aid of a centrifugal pump. The disadvantage of these pumps, however, is that they have only a restricted regulating range which is determined by the throttle curve of the pump. If the centrifugal pumps are not regenerative, they are often used as what are known as submerged pumps, that is to say the medium flows into the pump under gravity. The result of this is that, during emptying, for example in the event of a product change, a large residual quantity often remains in the stock container.

[0005] Centrifugal pumps have an electric drive. This electric drive constitutes a considerable risk during coating, particularly with solvent-containing media, for example solvent-based inks. To be precise, in order to counteract the risk of fire and explosion resulting from the use of combustible materials, comprehensive safety measures are necessary.

[0006] Moreover, centrifugal pumps, particularly in the form of submerged pumps, are unwieldy when the coating baths are being changed, that is to say in the event of a product change.

[0007] Insofar as a centrifugal pump is used for feeding the coating medium into the doctor blade chamber, the discharge of the medium from the doctor blade chamber back into the stock container takes place by gravity. This means that the doctor blade chamber has to be arranged at a particular height in relation to the stock container, in order to make outflow possible. Furthermore, the discharge lines must have a wide diameter, in order to ensure a sufficient return speed. Otherwise, precisely in the case of changing viscosities of different media, it would not be possible to ensure a return which is sufficient for homogenizing the medium.

[0008] This results directly in the disadvantage that the media within the discharge lines are exposed over a large area to the ambient air, so that precisely solvent-containing coating masses give off gas. The tendency of the medium to hardening and encrustation consequently increases. The consequences of this are a lowering of the coating quality and additional cleaning measures.

[0009] Moreover, there is the risk that the doctor blade chamber will run empty in the event of a failure of the feed pump.

[0010] In order to counteract these disadvantages, it is known to equip the coating systems with a separate recirculating pump.

[0011] In this case, however, there is a considerable difficulty in coordinating the performance values of the feed pump and recirculating pump. Thus, to avoid any overfilling of the doctor blade chamber, it is necessary for the performance of the recirculating pump always to be kept somewhat above that of the feed pump. This coordination is difficult, however, particularly because a decrease of coating media occurs in the doctor blade chamber due to the rollers, that is to say a reduction in the coating medium must be taken into account. If the performance of the recirculating pump is too high, however, the rollers and the doctor blade chamber may run dry.

[0012] The use of two different pumps for feeding the medium and for discharging it from the doctor blade chamber therefore fundamentally entails the risk of overfilling or running dry of the doctor blade chamber in the event of failure or of unintentional underconveyance or overconveyance by one of the two pumps.

[0013] Proceeding from these disadvantages, the object on which the invention is based is to provide a pump assembly which reliably and safely ensures the feed of a medium from a first vessel into a second vessel, with a medium being at the same time returned from the second vessel into the first vessel.

[0014] This object is achieved by means of a pump assembly as claimed in claim 1. Advantageous further developments are in each case the subject matter of the subclaims. T

[0015] he invention is based on the notion of using a pump system with two conveying chambers which have a common drive. In this case, one of the conveying chambers serves as a feed chamber, while the other chamber serves as a return chamber. This makes it possible to coordinate the two chambers automatically. In their function as a feed chamber or a return chamber, the conveying chambers in each case have the necessary connections, lines and, if appropriate, valves, in order to convey the medium from a first container into a second container (feed chamber) and from this second container back into the first container (return chamber).

[0016] In a particular embodiment, this pump assembly is a double-diaphragm pump, the two conveying chambers of which are separated from one another.

[0017] The particular advantage of using a common drive is that interlocking between the conveying chambers is largely superfluous, since, even if the drive fails, there is no fear either of dry running or of overfilling of the vessel to be charged or to be emptied, that is to say of the doctor blade chamber where coating is concerned. Complicated valves or regulations for the purposes of coordinating the chambers with one another can also largely be dispensed with.

[0018] In order to prevent an overfilling of the doctor blade chamber reliably at any time, the conveying capacity of the return chamber should be slightly higher than that of the feed chamber. This is achieved in an advantageous embodiment, according to the invention, in that the medium is first conducted into an integrated pulsation damper via suction and delivery valves of the feed chamber. This pulsation damper is preferably formed by an actively operating selfregulating pulsation damper with its own air control, the supply of which is derived internally from the supply of the pump. Consequently, the pulsation damper can be adapted to the changing operating states of the pump, and the maximum possible pulsation damping is ensured at all times.

[0019] The following pulsation damper necessarily results in some loss of performance and therefore in a slight reduction in the feed quantity, while the return into the stock container can take place in an undamped manner. This produces a ratio between return and feed to the benefit of the return, so that overfilling of the doctor blade chamber can be reliably avoided.

[0020] Furthermore, the advantage of the pulsation damper is that the feed into the doctor blade chamber takes place in as pulsation-free a manner as possible and therefore a high quality of, for example, the coatings becomes possible.

[0021] After leaving the pulsation damper, the medium advantageously passes through an integrated needle valve. The necessary conveying quantity into the doctor blade chamber can thus be regulated continuously and sensitively.

[0022] In a further embodiment, the return of the medium out of the doctor blade chamber into the stock container can take place via a reservoir, the volume of which corresponds to that of the displacement volume of the diaphragms. This makes it possible largely to prevent the situation where influences, for example turbulences, during the suction stroke of the undamped return side disturb the liquid level in the doctor blade chamber and have an adverse effect on the coating process. Moreover, the undamped return can assist the desired effect of the intermixing of the medium.

[0023] Since the pump assembly is also used for returning the medium into the stock container, the discharge line can be small and also flexible. This avoids one disadvantage of the prior art, in which the outflowing medium is exposed over a large area to the ambient air due to large diameters of the discharge lines.

[0024] In an advantageous embodiment, the pump assembly according to the invention may have a four-way valve which may be arranged on the delivery side of the conveying chamber downstream of the pulsation chamber and of the needle valve. The conveying direction of the feed chamber is therefore reversed simply by a lever being changed over. Whereas, in normal conveying operation, the medium is sucked in and conveyed into the doctor blade chamber via a pulsation damper, by this valve being changed over the doctor blade chamber and the lines, including the pump chamber, can be sucked empty and the medium conveyed back into the stock container. The necessarily corotating return chamber simultaneously empties the line and the pump chamber. The entire emptying process can thus be achieved independently of gravity and merely as a function of the suction capacity of the pumps. This makes it possible to shorten the emptying times considerably, reduces the residual volume remaining in the system and consequently allows a smaller amount of solvents to be used.

[0025] Advantageously, the four-way valve is designed as a disk valve, so as to avoid any dead spaces in which the medium could otherwise harden in the event of lengthy nonactuation. Irrespective of this, feed and discharge to the pump assembly may also take place from below.

[0026] Advantageously, the housing parts are formed from conductive polyethylene which has good chemical resistance to a multiplicity of media and, in particular, meets the requirements demanded of materials for the use of solvent-containing substances. Furthermore, having a specific gravity of 0.95, it is light, thus making it easier to handle the pump assembly.

[0027] The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the drawings in which:

[0028] FIG. 1 shows a top view of the delivery side of the pump assembly of the system according to the invention;

[0029] FIG. 2 shows a top view of the suction side of the pump assembly of the system according to the invention;

[0030] FIG. 3 shows a cross section through the feed chamber, including the integrated pulsation damper;

[0031] FIG. 4a shows a cross section through the feed chamber along the line A-A of FIG. 3;

[0032] FIG. 4b shows a cross section through the plane B-B of FIG. 4a;

[0033] FIG. 5 shows a cross section through the return chamber of the pump assembly of the system according to the invention;

[0034] FIG. 6 shows a cross section through the return chamber along the line C-C of FIG. 5;

[0035] FIG. 7 shows a diagrammatic illustration of the conveying path during the regular operation of the system according to the invention;

[0036] FIG. 8 shows a diagrammatic illustration of the conveying path for emptying the coating system, including the pump assembly, and

[0037] FIG. 9 shows a cross section through the doctor blade chamber.

[0038] The system according to the invention has a drive 1 with a central compressed-air connection 2 and a return chamber 3 and with a feed chamber 4 which is equipped with an integrated pulsation damper 5.

[0039] The coating medium is conducted via a vertical connection 6 into an integrated pulsation damper 5 via suction and delivery valves of the feed chamber which are not illustrated in any more detail. This pulsation damper has its own control 8.

[0040] After leaving the pulsation damper, the coating medium passes through the needle valve 10 via the duct 9 and is conducted into the doctor blade chamber 14 via the feed line 11.

[0041] A four-way valve 12 on the delivery side of the feed chamber 4 makes it possible, by being actuated, for coating media to be sucked in from the doctor blade chamber 14.

[0042] The return of the coating medium takes place in the doctor blade chamber 14 via a small reservoir 13, the volume of which corresponds to that of the displacement volume of the diaphragm 15. The coating medium is administered to the return chamber 3 through the return conveyance line 17 via the connection 16. The coating medium is subsequently conveyed out of the return chamber back into the stock container 7 directly via the vertical outlet 18.

[0043] When the system is emptied in the event of a product change, after the changeover of the four-way valve 12 the medium is sucked via the line 19 into the feed chamber and from there into the stock container. The necessarily corotating return chamber empties the line and the pump chamber.

Claims

1. A system for the circulatory conveyance of media, with two conveying chambers and with a common drive (1), wherein the first conveying chamber constitutes a feed chamber (4) and the second conveying chamber a return chamber (3).

2. The system as claimed in claim 1, defined by a double-diaphragm pump.

3. The system as claimed in claim 1 or 2, defined by a pulsation damper

4. The system as claimed in claim 3, wherein the pulsation damper (5) is integrated into the feed chamber (4).

5. The system as claimed in one of claims 1 to 4, defined by a needle valve (10).

6. The system as claimed in one of claims 1 to 5, wherein at least one line connection is arranged perpendicularly to the feed chamber (4) and/or return chamber (3).

7. The system as claimed in one of claims 1 to 6, defined by polyethylene housing parts of the drive (1) and/or of the conveying chambers (3,4).

8. The system as claimed in one of claims 1 to 7, defined by a reservoir (13).

9. The system as claimed in one of claims 1 to 8, defined by a four-way valve (12).

10. The system as claimed in claim 9, wherein the four-way valve (12) is designed as a disk valve.

11. A use of a system as claimed in one of claims 1 to 10 for the conveyance of media along a circulatory path between a first and a second container.

12. A use of a system as claimed in one of claims 1 to 10 for regulating the filling-level height in a doctor blade chamber.

13. A use of a system as claimed in claim 9 or 10 for emptying a first and a second container.

14. A method for conveying a medium from a first container into a second container, with the following steps:

operating a pump assembly with a feed chamber and with a discharge chamber by means of a common drive;

sucking the medium out of the first container into a feed chamber;

discharging the medium from the feed chamber into the second container;

sucking the medium out of the second container into a return chamber, and

discharging the medium from the return chamber into the first container.

15. The method as claimed in claim 14, defined by a pulsation damping of the medium.