EP2269741B1 - Piston metering apparatus for fluids and system for coating objects - Google Patents

Description

1. a) einen Zylinder mit wenigstens einer Öffnung für fluides Medium;
2. b) eine in dem Zylinder mittels einer Antriebseinrichtung verfahrbare Kolbenanordnung, welche von einer Kolbenstange getragen und einen mit der Öffnung des Zylinders kommunizierenden Arbeitsraum des Zylinders begrenzt;
   wobei
3. c) einem Aufnahmeraum der Kolbenanordnung Spülfluid zuführbar ist, welcher fluidisch mit dem Arbeitsraum des Zylinders verbunden ist;
4. d) die Kolbenanordnung ein dem Arbeitsraum des Zylinders zugewandtes erstes Kolbenelement und ein vom Arbeitsraum des Zylinders abliegendes zweites Kolbenelement umfasst, welche relativ zueinander in dem Zylinder verschiebbar sind, so dass zwischen den Kolbenelementen der Aufnahmeraum ausbildbar ist.

The invention relates to a piston dispenser for fluid media, in particular for supplying an application device in a system for coating objects, which comprises:

1. a) a cylinder with at least one opening for fluid medium;
2. b) a movable in the cylinder by means of a drive means piston assembly which is supported by a piston rod and defining a communicating with the opening of the cylinder working space of the cylinder;
   in which
3. c) flushing fluid can be fed to a receiving space of the piston arrangement, which is fluidically connected to the working space of the cylinder;
4. d) the piston assembly comprises a working chamber of the cylinder facing the first piston member and a second piston from the working space of the cylinder second piston element, which are displaceable relative to each other in the cylinder, so that between the piston elements of the receiving space can be formed.

Moreover, the invention relates to a system for coating objects with an application device, which is connected to a supply and purging device.

In coating systems, especially in paint shops, Often application devices are used which ionize the spray material to be sprayed from them by means of a high voltage electrode. This ionized material is then drawn by electrostatic forces to generally ground potential objects to be coated.

In paint shops, it often happens that for the coating of an object, a different paint is to be used as the paint with which a previous object has been coated. Before a paint change, the lines leading to the application device and the supply system for the paint must be rinsed and freed from paint residues of the first paint. This leads to paint losses. In order to keep these as low as possible, for example, the so-called pigging technique has been developed in which paint and detergent can be kept separated by pigs. However, this technique is relatively expensive.

In order to be able to supply the application device with a well-dosed coating, piston dispensers have established themselves on the market, among other things. A piston dispenser operating according to the double piston principle is known, for example, from US Pat DE 10 2004 058 053 B4 known. There, the working space of the cylinder is filled with paint and this then fed to the application device. Rinsing of the piston dispenser and the lines leading to the application device, which is necessary before a color change, takes place by means of a rinsing agent supplied from another source. However, this can lead to relatively large paint losses, which can be counteracted again, for example, by the above-mentioned pigging technique.

A piston dispenser of the type mentioned is from the CA 2 674 912 known.

There, first, the receiving space of the piston assembly filled with a particular liquid detergent and the working space of the cylinder can be charged with paint. If the paint has then been released from the working space of the cylinder completely to the application device and the line between piston dispenser and application device must be flushed, the detergent is discharged from the receiving space of the piston assembly, which is still in the line befindlicher paint pushed to the application device and there can be discharged for coating until the phase boundary between the paint and detergent reaches the application device.

A potential separation between an electrostatically operating application device and a lying at ground color reservoir or color changer can also be done simply by the construction of an insulating air layer in the connecting line to the piston dispenser, the piston dispenser itself is at the potential of the application device.

Because the piston arrangement comprises a first piston element facing the working space of the cylinder and a second piston element remote from the working space of the cylinder, which are displaceable relative to one another in the cylinder, so that the receiving space can be formed between the piston elements, the volume of the receiving space and thus the usable volume of the detergent so depending on the position of the piston elements are set to each other. In addition, rinsing agent can be pushed out of the receiving space by a movement of the second piston element in the direction of the first piston element. The volume of detergent required depends on the length of the rinse Lines off. In the dimensions of systems used in practice, for example, a detergent volume of about 16 ml has proven to be favorable.

In the from the CA 2 674 912 However, known piston dispenser is a flushing at a color change with the recording and delivery of the detergent in or out of the receiving space but relatively expensive.

It is therefore an object of the invention to provide a piston dispenser and a system of the type mentioned by which the paint loss can be reduced in a color change, without complex additional measures must be taken, and the absorption and release of the detergent in or out of the Recording room is facilitated.

• e) das erste Kolbenelement mit der Kolbenstange gekoppelt und das zweite Kolbenelement gegenüber der Kolbenstange verfahrbar gelagert ist, wobei das zweite Kolbenelement mittels einer Druckfeder von der Kolbenstange weg in axialer Richtung auf das erste Kolbenelement gedrückt wird;
  oder
• f) das zweite Kolbenelement mit der Kolbenstange gekoppelt und das erste Kolbenelement gegenüber der Kolbenstange verfahrbar gelagert ist, wobei das erste Kolbenelement mittels einer Druckfeder von der Kolbenstange und dem zweiten Kolbenelement in axialer Richtung weg gedrückt wird.

This object is achieved with a piston dispenser of the type mentioned by the fact that

• e) the first piston element is coupled to the piston rod and the second piston element is movably mounted relative to the piston rod, the second piston element being pressed away from the piston rod in the axial direction onto the first piston element by means of a compression spring;
  or
• f) the second piston element is coupled to the piston rod and the first piston element is movably mounted relative to the piston rod, wherein the first piston element is pressed away by means of a compression spring from the piston rod and the second piston element in the axial direction.

In the first case, the dispensing of detergent from the receiving space with an open flow path can be done automatically; in the second case, the filling of the receiving space and the dispensing of the rinsing agent can be controlled from this by moving the piston rod.

In the case of the piston dispenser according to the invention, it is possible to reduce possible lacquer losses to a low value of 1 ml per color change operation.

It is structurally advantageous if a flow channel for medium leads through the first piston element, which connects the receiving space with the working space.

In order to be able to control the dispensing of rinsing agent safely, it is particularly advantageous if the flow channel can be optionally closed or released. This can preferably be done by means of a valve.

Manufacturing technology, it is advantageous if the first piston member is a piston ring, which is supported by an axial connecting member, in which the flow channel extends at least partially. The flow channel can be made relatively simple.

It is advantageous if the cylinder comprises a valve block, which defines the opening for fluid medium as the only such opening of the cylinder. The valve block can then be manufactured as a separate component and include all the necessary connections for the cylinder and leading away from the lines.

The above object is solved in a system for coating objects of the type mentioned above alternatively characterized in that the supply and purging at least one piston dispenser according to one of claims 1 to 6. The advantages correspond to the above explained to Kolbendosierer advantages.

The system may preferably comprise an electrostatically operating application device. The necessary isolation distances for potential separation of individual components can be well formed and maintained in the piston dispenser.

Here it is favorable if coating medium is conveyed within a fluid line of the system by means of a flushing fluid, which is introduced into the fluid line under a pressure which is increased in relation to normal pressure.

Figur 1

eine perspektivische Ansicht eines ersten Ausführungsbeispiels eines Kolbendosierers;

Figur 2

eine perspektivische Ansicht des Ventilblocks des Kolbendosierers von Figur 1 in größerem Maßstab aus einer anderen Blickrichtung;

Figur 3

einen Schnitt durch den Dosierzylinder des Kolbendosierers von Figur 1, wobei eine Kolbenanordnung mit zwei Kolbenelementen zu erkennen ist;

Figur 4

einen Schnitt durch die Kolbenanordnung von Figur 3 in größerem Maßstab;

Figur 5

einen der Figur 3 entsprechenden Schnitt durch den Dosierzylinder, wobei die zwei Kolbenelemente der Kolbenanordnung eine voneinander beabstandete Stellung einnehmen, wodurch ein Aufnahmeraum gebildet ist;

Figur 6

einen Schnitt durch die Kolbenanordnung in der Stellung von Figur 5 in größerem Maßstab;

Figur 7

einen Schnitt durch den Dosierzylinder eines zweiten Ausführungsbeispiel eines Kolbendosierers mit einer abgewandelten Kolbenanordnung mit zwei Kolbenelementen;

Figur 8

einen Schnitt durch die abgewandelte Kolbenanordnung von Figur 7 in größerem Maßstab;

Figur 9

einen der Figur 7 entsprechenden Schnitt durch den Dosierzylinder, wobei die zwei Kolbenelemente der abgewandelten Kolbenanordnung eine voneinander beabstandete Stellung einnehmen, wodurch auch hier der Aufnahmeraum gebildet ist;

Figur 10

einen Schnitt durch die abgewandelte Kolbenanordnung von Figur 9 in größerem Maßstab;

Figuren 11 bis 16

verschiedene Betriebsphasen eines Systems zur Beschichtung von Gegenständen, welches zwei Kolbendosierer verwendet.

Embodiments of the invention will be explained in more detail with reference to the drawings. In these show:

FIG. 1

a perspective view of a first embodiment of a piston dispenser;

FIG. 2

a perspective view of the valve block of the piston dispenser of FIG. 1 on a larger scale from a different perspective;

FIG. 3

a section through the metering cylinder of the piston dispenser of FIG. 1 wherein a piston assembly with two piston elements can be seen;

FIG. 4

a section through the piston assembly of FIG. 3 on a larger scale;

FIG. 5

one of the FIG. 3 corresponding section through the metering cylinder, wherein the two piston elements of the piston assembly has a spaced-apart position occupy, whereby a receiving space is formed;

FIG. 6

a section through the piston assembly in the position of FIG. 5 on a larger scale;

FIG. 7

a section through the metering cylinder of a second embodiment of a piston dispenser with a modified piston assembly with two piston elements;

FIG. 8

a section through the modified piston assembly of FIG. 7 on a larger scale;

FIG. 9

one of the FIG. 7 corresponding section through the metering cylinder, wherein the two piston elements of the modified piston assembly occupy a spaced-apart position, whereby also here the receiving space is formed;

FIG. 10

a section through the modified piston assembly of FIG. 9 on a larger scale;

FIGS. 11 to 16

various operating phases of an article coating system using two piston dispensers.

In FIG. 1 is generally designated 10 a piston dispenser, which comprises a hollow cylinder 12 which is made of glass in the present embodiment and whose one end face is closed with a plate 14. The cylinder 12 has in close proximity to the plate 14 on a not specifically illustrated vent hole, as it is known per se. As in FIG. 3 can be seen, the plate 14 has a coaxial passage 16 in which a piston rod 18 is held by means of a sliding bearing 20 movable.

The piston rod 18 extends outside of the glass cylinder 12 in a housing 22 which is flanged at one end to the plate 14 and at the opposite end in a belt housing 24 opens. The piston rod 18 is formed in the present embodiment at its end facing the belt housing 24 as a threaded spindle of a ball screw not specifically shown, the spindle nut is mounted in the belt housing 24. The spindle nut can be rotated by means of a drive belt running in the belt housing 24 and also not specifically shown, which is coupled to a drive motor 26 mounted on the belt housing. Depending on the direction of rotation of the spindle nut, the piston rod 18 moves into or out of the glass cylinder 12. By the drive belt a potential separation between the piston rod 18 and the drive motor 26 is ensured.

At the remote from the plate 14 end face of the glass cylinder 12, this is closed with a valve block 28 made of an electrically non-conductive plastic, which is in particular graphite-free. Like in FIG. 3 can be seen, the valve block 28 has a main channel 30 which extends between an externally accessible connection thread 32 and a connection opening 34, through which the main channel 30 opens into the glass cylinder 12. In the region of the connection opening 34 of the main channel 30 to the glass cylinder 12, a contact lug 35 is provided coaxially with the glass cylinder 12, which will be discussed again below.

Close to the connection opening 34 of the main channel 30, the latter communicates in the valve block 28 via a first valve seat-like opening 36 with a first pre-chamber 38, which in turn widens to form a first externally accessible valve receiving bore 40. The opening 36 can be closed by the closing element 42 of a seated in the valve receiving bore 40 compressed air-actuated first valve 44.

The first pre-chamber 38 communicates via a secondary passage 46 and a second valve seat-like opening 48 with a second prechamber 50, which in turn widens to a second externally accessible valve receiving bore 52. The second opening 48 can be closed by the closing element 54 of a pressure-actuated second valve 56 seated in the valve receiving bore 52.

Between the first valve seat-like opening 36 and the connecting thread 32 of the valve block 28, the passage of the main channel 30 can be closed by means of the closing element 58 of a pneumatically operated third valve 60. The third valve 60 is seated in an externally accessible third valve receiving bore 62.

Of the three valve receiving bores 40, 52 and 62, a compressed air duct, not shown here, leads to a compressed air connection piece 64 for a compressed air hose on the outside of the valve block 28. By means of a valve control system which is known per se and not specifically shown here, the valves 44, 56 and 60 are pressurized air, whereby the first and second valves 44 and 56 associated openings 36 and 48 and the passage of the main channel 30 can be selectively released or closed.

In the connecting thread 32 of the main channel 30, a discharge connection piece 66 can be screwed, which can be connected to a supply hose, which leads to an electrostatically operating application device.

The first pre-chamber 38 of the valve block 28 is connected via a not visible here side channel with an externally accessible inlet connection piece 68, which only in FIG. 2 can be seen.

The second pre-chamber 50 of the valve block 28 is connected in a corresponding manner via a likewise not visible here side channel with an externally accessible return connection piece 70.

As in FIG. 3 can be seen, carries the piston rod 18 at its arranged in the interior of the glass cylinder 12 end 18a a piston assembly 72, which is now based on FIG. 4 is explained in more detail. For clarity, some components of the piston assembly 72 in the Figures 3 and 5 not provided with reference numerals.

The piston assembly 72 comprises a in FIG. 4 On the right of the first end face 74a, the through hole 76 has a threaded portion 76a, a radially inwardly projecting circumferential rib 76b and an adjoining thereto smooth wall portion 76c.

Further, the piston assembly 72 includes a tubular connector 78 having a first end surface 78a. Its outer circumferential surface 80 has an external thread 80a complementary to the threaded portion 76a of the through-bore 76 of the first piston element 74. This merges into a circumferential groove 80b, which in turn is followed by a smooth wall section 80c. The connecting member 78 is screwed into the first piston element 74 such that its end face 78a is aligned with the end face 74a of the first piston element 74. Between the groove 80b and the wall portion 80c and the projection 76b and the wall portion 76c of the through hole 76 of the first piston member 74 remains in this arrangement, an angled annular space 82 which extends to the second end face 74b of the first piston member 74.

The wall section 80c of the connecting member 78 is adjoined by a wall end section 80d which is offset radially inwards and whose end region carries an external thread 84. On this external thread 84, a coupling sleeve 86 is screwed with complementary internal thread 88 which extends between the first end face 86a and the second end face 86b.

The piston arrangement 72 also comprises a second annular piston element 90 with a stepped coaxial through-bore 92. Starting from a first end face 90a of the piston element 90, this has a first bearing section 92a whose inner diameter is complementary to the outer diameter of the wall section 80d of the connecting member 78. The first bearing portion 92 a of the through hole 92 widens to a second bearing portion 92 b, whose inner diameter is complementary to the outer diameter of the coupling sleeve 86.

The second piston element 90 is arranged so that it slides with its first bearing portion 92a on the wall portion 80d of the connecting member 78 and with its second bearing portion 92b on the coupling sleeve 86, with its first end face 90a in the direction of the second end face 74b of the first piston member 74th has.

The second piston member 90 further includes an annular space 94 which extends from the second bearing portion 92b of the through-bore 92 toward the first end face 90a of the second piston member 90 coaxially therewith and has an annular bottom surface 94a which extends in from the End face 90a of the second piston member 90 pioneering direction shows.

In the annular space 94, a helical compression spring 96 is arranged, which rests with its one end on the bottom surface 94a of the annular space 94 and with its opposite end on the first end face 86a of the coupling sleeve 86. In this way, the second piston member 90 relative to the coupling sleeve 86 and thus always pressed against the piston rod 18 in the direction of the first piston member 74.

On its first end face 78a, the connecting member 78 has a valve seat-like opening 98, which leads to an antechamber 100 in the interior of the connecting member 78, which in turn widens to an externally accessible valve receiving bore 102. The opening 98 is closed by the closing element 104 of a seated in the valve receiving bore 102 spring-loaded valve 106, the spring 106 a only in FIG. 4 is indicated. The closing element 104 of the valve 106 is designed to be in the in FIG. 4 shown closed position of the valve 106 projects beyond the end face 78a of the connecting member 78.

The pre-chamber 100 of the connecting member 78 communicates via a plurality of channels 108, of which in FIG. 4 two are visible and only one is provided with a reference numeral, with the annular space 82 between the connecting member 78 and the first piston member 74th

The first piston member 74 and the second piston member 90 carry radially outward circumferential piston seals 110 and 112. Further, the first bearing portion 92a of the through hole 92 of the second piston member 90 is provided with two circumferentially arranged in the axial direction circumferential ring seals 114a and 114b.

As based on the Figures 5 and 6 can be seen, the second piston member 90 on the connecting member 78 and the coupling sleeve 86 slidably displaced away from the first piston member 74. Thus, a receiving space 116 can be formed between the second end face 74b of the first piston element 74 and the end face 90a of the second piston element 90, the volume of which depends on the distance between the two piston elements 74 and 90 and which is bounded radially by the inner lateral surface of the glass cylinder 12. The latter is in the FIGS. 4 and 6 indicated by dashed lines. The maximum volume of the receiving space 116 may be several 10 ml. In practice, the amount of detergent received by the piston assembly 116 is about 17 ml.

The piston assembly 72 is connected via the coupling sleeve 86 with the end 18 a of the piston rod 18. Between the piston assembly 72 and the valve block 28 is a working space 12 a (see. Figures 3 and 7 ) of the glass cylinder 12, the volume of which depends on the position of the piston arrangement 72 in the gas cylinder 12 and which is also bounded radially by the inner circumferential surface of the glass cylinder 12.

In the FIGS. 7 to 9 is shown as a second embodiment, a piston dispenser 10 '. Components of the piston dispenser 10 ', which correspond to those of the piston dispenser 10, bear the same reference numerals.

The piston dispenser 10 'differs from the piston dispenser 10 after the FIGS. 1 to 6 by a modified piston assembly 72 'which includes an altered second piston member 90'. In this case, a coaxial annular space 118 for the helical compression spring 96 is embedded in the end face 90'a, which does not communicate with the through-bore 92 or its second bearing section 92b and which one has in the direction of the end face 90'a of the second piston member 90 'facing bottom surface 118a.

In addition, the second piston member 90 'immovably connected to the coupling sleeve 86, for example via corresponding thread. Alternatively, the coupling sleeve 86 can also be integrally integrated into the second piston element 90 '. Also, the connecting member 78 is not fixedly connected to the coupling sleeve 86 in the piston dispenser 10 ', but can slide in this. Thus, the coupling sleeve 86 and the second piston member 90 'can be moved together relative to the connecting member 78.

The arranged in the annular space 118 helical compression spring 96 abuts with its one end to the bottom surface 118a of the annular space 118 and with its opposite end to the second end face 74b of the first piston member 74, to which the helical compression spring 96 thus always exerts a force.

The valve 106 in the connecting member 78 can be brought in the piston dispenser 10 'by means of compressed air in its open position, for which leads through the piston rod 18, a not specifically shown compressed air line to the valve 106. The closing element 104 of the valve 106 does not protrude beyond the end face 78a of the connecting member 78 at the piston dispenser 10 ', but aligns with the latter.

In the FIGS. 11 to 16 For example, a system 120 is shown that includes a first piston feeder 10a and a second piston feeder 10b. Their respective inlet connection pieces 68 are fluidically connected via respective lines 122a, 122b to outputs 124a, 124b of a mixing block 126, which can optionally be released or closed in a manner known per se. The mixing block 126 is over a detergent inlet 128 connected to a not specifically shown Spülmittelreservoir. In addition, the mixing block 126 via a compressed air inlet 130 compressed air from a compressed air source also not specifically shown can be supplied.

A further input 132 of the mixing block 126 is also connected via a line 134 to a color changing device 136, as it is known per se. This has a plurality of paint inputs 138a to 138i, which are each connected to a paint reservoir, not shown here. The color changing device 136 also has a flushing agent inlet 140 (not shown) connected to a flushing agent reservoir, an inlet 142 for compressed air and an outlet 144. The inputs 138, 140 and 142 and the output 144 can be selectively opened or closed by means not separately shown valves.

The discharge ports 66 of the piston dispensers 10a, 10b are each connected via a line 146a or 146b to an electrostatic application device 148, as it is known per se.

Apart from the application device 148 itself, the components of the system 120 form a supply and purging device 150 for the application device 148.

The operation of the system 120 will now be explained, from which also the operation of the piston dispenser 10 can be seen:

Starting from the in FIG. 11 shown operating state in which both piston dispensers 10a, 10b are unfilled, first, the receiving space 116 in the piston assembly 72 of the first piston dispenser 10a with a liquid Rinsing agent charged. For this purpose, the piston assembly 72 of the first piston meter 10a is moved so far in its direction when the valve 60 of the valve block 28 is open until the first end face 74a of the first piston member 74 rests against the valve block 28. In this case, the closing element 104 of the valve 106 is pushed in the connecting member 78 by the contact lug 35 of the valve block 28 to the inside and are the connecting member valve seat opening 98 free.

Then, the valves 44 and 56 of the valve block 28 are opened and the valve 60 is closed and the valve block 28 of the piston dispenser 10a is supplied with detergent from the color changer 136 via the line 134, the mixing block 126 and the line 122a. Since the valve 56 releases the flow path to the return connection piece 70, air is first forced out of the valve block 28 via this.

Then, the valve 56 is closed, whereby rinsing agent flows through the connection opening 34 through the valve seat opening 98 of the connecting member 78 in the antechamber 100 and further through the channels 108 and the annular space 82 to the second piston member 90 of the piston assembly 72.

By the rinsing agent, the second piston member 90 is moved against the force of the helical compression spring 96 relative to the connecting member 78 and the coupling sleeve 86, whereby the receiving space 116 is formed, which fills up with detergent. This is in FIG. 12 to recognize. For this purpose, the pressure with which the rinsing agent is supplied, must be greater than the force of the helical compression spring 96th

When the receiving space 116 is filled with the intended amount of detergent, the valve 44 is closed and the valve 56 is opened. Thereafter, the desired color is supplied to the valve block 28 from the color changer 136, which initially still in the lines 134 and 122a located rinsing agent pushes in front of it, which is discharged via the return port 70 of the valve block 28. A sensor system known per se is detected when the ink is applied to the valve 44 of the valve block 28, whereupon it is opened and the valve 56 is closed. Now, the color is thus directed in the direction of the glass cylinder 12.

The piston assembly 72 is left in the position in which its valve 106 is opened until the defined volume of flushing agent, which is still between the valve seat opening 98 and the closing element 42 of the valve 44, of the color in the piston assembly 72nd was pressed into it. Then, the piston assembly 72 is moved away from the communication port 34 of the valve block 28, whereby the valve 106 of the piston assembly 72 again assumes its closed position and the ink can flow into the working chamber 12a of the glass cylinder 12, which results from the movement of the piston assembly 72.

When the volume of the working space 12a of the glass cylinder 12 and the volume in the conduits between the valve block 28 and the color changer 136 give the desired total volume of paint, the color changer 136 is again driven to emit detergent. This pushes now still in the lines 134 and 122a located color in the working space 12a of the glass cylinder. If the above-mentioned sensor detects that the flushing agent is in the antechamber 38 of the valve block 28, the valve 44 is closed. This operating state is in FIG. 13 shown.

Now, the valve 60 of the valve block 28 is opened and color is pressed via the discharge connector 66 in the direction of the application device 148 by the piston assembly 72 is moved to the valve block 28 to. Then, the valve 56 of the valve block 28 is opened and this is acted upon via the mixing block 126 with compressed air, whereby all medium from the prechamber 38, the secondary channel 46 and the prechamber 50 is pushed out via the return connection piece 70.

In the line 122a between the valve block 28 and the mixing block 126 then an insulating air gap is constructed, which leads to a potential separation between piston meter 10a and mixing block 126. The compressed air in the line 122a is at about 10 bar to the antechamber 38 of the valve block 28 at.

Now, the color metered from the working chamber 12a of the piston dispenser 10a delivered to the application device 148 by the piston assembly is moved accordingly in the direction of the valve block 28.

During the painting process, in which the application device 148 is fed by the first piston dispenser 10a, the receiving space 116 of the second piston dispenser 10b is filled with rinsing agent in the manner described above for the first piston dispenser 10a. This operating state of the system 120 is in FIG. 14 shown.

In the further course of the painting process, the working space 12a of the second piston dispenser 10b is filled with a paint in the manner described above for the first piston dispenser 10a. This operating state of the system 120 is in FIG. 15 to recognize.

When all paint has been discharged from the working space 12a of the first piston dispenser 10a, its piston assembly 72 again assumes a position in which the closing element 104 of the Valve 106 in the connecting member 78 by the contact lug 35 of the valve block 28, the valve seat opening 98 releases. By the spring force of the helical compression spring 96, the rinsing agent is then pushed out of the receiving space 116 in the main channel 30 of the valve block 28 to the application device 148, whereby these and the conduit 146 a are flushed (see. FIG. 16 ).

The dispensing of the rinsing agent may e.g. be metered by the valve 106 is opened or closed as needed, which can be done by a corresponding method of the piston assembly 72 to the contact lug 35 of the valve block 28 on or away.

When the rinsing process is completed, the application device 148 can now be supplied with ink by means of the second piston dispenser 10b. During the painting with paint from the second piston dispenser 10b, in turn, the first piston dispenser 10a is charged with rinsing agent and paint in the manner explained above, after it has previously been rinsed in a conventional manner, and the cycle begins again.

If instead of two piston dispenser 10 with a piston assembly 72, as shown in the FIGS. 3 to 6 is shown, two piston dispenser 10 'with a piston assembly 72' according to the FIGS. 7 to 10 is used, the operation of the system 120 is basically in the manner explained above.

In contrast to the piston dispenser 10, however, the second piston element 90 'must be actively moved in the modified piston dispenser 10' by the piston rod 18 being moved accordingly when the receiving space 116 is filled with detergent or when flushing agent is to be dispensed from the receiving space 116.

To fill the receiving space 116 with rinsing agent, the piston assembly 72 'in the corresponding operating step is initially approached completely to the valve block 28, so that it rests against this. Then the valve 106 of the connecting member 78 is brought by compressed air in its open position.

In order to fill the receiving space 116 with detergent, the piston rod 18 is then moved away in the direction of the valve block 28. With the piston rod 18 then move the coupling sleeve 86 and the second piston member 90 'of the valve block 28 away. By the helical compression spring 96, the first piston member 74 is always pushed away from the second piston member 90 and thus of the piston rod 18 in the direction of the valve block 28 at Kolbendosierers 10 'according to the second embodiment and thus initially remains in its position on the valve block 28. After the desired amount of detergent is introduced into the receiving space 116 of the piston assembly 72 of the piston dispenser 10 ', the valve 106 is transferred to its closed position.

The filling process of the piston dispenser 10 'with paint takes place in the manner described above for the piston dispenser 10 according to FIGS FIGS. 1 to 6 was explained. Although the first piston member 74 and the second piston member 90 'are not coupled to each other at the piston dispenser 10', the first piston member 74 follows the movement of the piston rod 18 and the associated second piston member 90 'due to the rinsing agent present between the piston members 74 and 90' and the resulting negative pressure.

When the flushing agent is to be discharged from the receiving space 116 of the piston assembly 72, the valve 106 is first opened again. The piston rod 18 is moved in the direction of the valve block 28, whereby the second piston element 90 is pressed against the force of the helical compression spring 96 in the direction of the first piston member 74. In this case, detergent is pressed from the receiving space 106 through the valve seat opening 98 into the main channel 30 of the valve block 28.

In principle, only a single piston dispenser 10 or 10 'can be used to operate the application device 148, but this leads to delays in a color change.

In the present system 120 with the piston dispensers 10a and 10b, the rinsing agent is used as a pushing medium for the paints used. This works especially with waterborne paints and paint systems. Depending on the paint used, a rinsing agent can be used in which the transition region between the paint and the rinsing agent, in which the two media mix, is as small as possible.

In the present exemplary embodiments, the rinsing agent is always introduced into the fluid lines of the system 120 at a pressure which is higher than standard pressure, which pressure is approximately 6 bar in practice.

With the piston dispensers 10 and 10 'can also easily determine whether there is a leak or air pockets. For this purpose, the receiving space 116 of the piston assembly 72 or 72 'is first filled with a predetermined amount of flushing fluid and the working chamber 12a of the cylinder 12 is charged with the desired amount of paint. Then, the three valves 44, 56 and 60 of the valve block 28 are closed and the motor 26 driven with increasing torques until the torque is reached, which is normally used to move the piston assembly 72 and 72 'towards the valve block 28.

In a properly working piston dispenser 10 or 10 'is a method of the piston assembly 72 and 72', however, not possible because only incompressible fluids are in the system. If, on the other hand, a movement of the piston arrangement 72 or 72 'takes place, this indicates either a leakage or air pockets, which can then be investigated in detail.

Claims (9)

1. Piston metering apparatus (10, 10') for fluid media, in particular for supplying an application device (148) in a plant for coating objects, which apparatus comprises:

   a) a cylinder (12) with at least one opening (34) for fluid medium;

   b) a piston arrangement (72; 72') which is displaceable in the cylinder (12) by means of a drive device (26) and which is carried by a piston rod (18) and delimits a working space (12a) of the cylinder (12) communicating with the opening (34) of the cylinder (12),
   wherein

   c) a receiving space (116) of the piston arrangement (72, 72') can be supplied with flushing fluid and is fluidically connected to the working space (12a) of the cylinder (12);

   d) the piston arrangement (72; 72') comprises a first piston element (74) facing the working space (12a) of the cylinder (12) and a second piston element (90; 90') facing away from the working space (12a) of the cylinder (12), which are displaceable relative to one another in the cylinder (12), so that the receiving space (116) can be formed between the piston elements (74, 90; 74, 90'),
   characterised in that

   e) the first piston element (74) is coupled to the piston rod (18) and the second piston element (90) is mounted displaceably with respect to the piston rod (18), the second piston element (90) being pressed by means of a compression spring (96) away from the piston rod (18) in the axial direction towards the first piston element (74);
   or

   f) the second piston element (90') is coupled to the piston rod (18) and the first piston element (74) is mounted displaceably with respect to the piston rod (18), the first piston element (74) being pressed by means of a compression spring (96) away from the piston rod (18) and the second piston element (90') in the axial direction.
2. Piston metering apparatus according to Claim 1, characterised in that a flow duct (82, 108, 100) for medium passes through the first piston element (74) and connects the receiving space (116) to the working space (12a).
3. Piston metering apparatus according to Claim 2, characterised in that the flow duct (82, 108, 100) can be selectively closed or opened.
4. Piston metering apparatus according to Claim 3, characterised in that the flow duct (82, 108, 100) can be closed by means of a valve (106).
5. Piston metering apparatus according to Claim 3 or 4, characterised in that the first piston element (74) is a piston ring which is carried by an axial connecting member (78), in which the flow duct (82, 108, 100) extends at least partially.
6. Piston metering apparatus according to one of Claims 1 to 5, characterised in that the cylinder (12) comprises a valve block (28) which predetermines the opening (34) for fluid medium as a single such opening of the cylinder (12).
7. System for coating objects having an application device (148) which is connected to a supplying and flushing device (150), characterised in that the supplying and flushing device (150) comprises at least one piston metering apparatus (10, 10') according to one of Claims 1 to 6.
8. System according to Claim 7, characterised in that the application device (148) operates electrostatically.
9. System according to Claim 7 or 8, characterised in that coating medium is conveyed within a fluid line (134, 122a, 122b, 146a, 146b) of the system (120) by means of a flushing fluid which is introduced into the fluid line (134, 122a, 122b, 146a, 146b) under a pressure increased with respect to normal pressure.

Images