Feed pump for powder and its method of operation

p0001The invention relates to an operating method for a powder-feed pump and a correspondingly formed powder conveying pump for carrying out the operating method according to the invention.

p0002In powder coating systems, the so-called thin-current method was used for the promotion of serving as a coating material powder before, wherein the powder in a fluidized state was conveyed in a stream of air through tubular feed lines to the application device (for example, spray gun or rotary atomizer). The term thin-stream method is because the powder fraction in the produced powder-air mixture is relatively low, so that the tubular conveying lines had to have a correspondingly large cross section in order to promote the desired amount of powder.

p0003For this reason, the so-called dense phase powder promotion (PDF) has been proposed, which has a larger amount of powder in the powder-air mixture conveyed. The actual powder feed can be effected by a designated as a PDF-pump powder feed pump having a pumping chamber having an inlet and an outlet, is drawn through the inlet powder into the feed chamber and then discharged through the outlet to a delivery device (eg, to reach the spray gun or rotary atomizer). To fill the feed chamber of the outlet of the feed chamber is first closed while the inlet of the feed chamber is opened to suck powder from a powder container can. a vacuum is then subsequently in the conveying chamber created by air is sucked off via a filter element from the feed chamber, wherein the filter element is permeable to air, but pulverundurchlässig so that the powder located in the feed chamber is not sucked. After a sufficient filling of the pumping chamber, the suction is terminated and the inlet valve is closed. For ejection of the present in the feed chamber powder then the outlet is opened and blown through the filter element compressed air into the feed chamber, whereby the powder is discharged from the feed chamber. By a cyclic operation of the intake and discharge phases described above, powder is conveyed from the powder container to the applicator. The delivery chamber can in this case consist of a hose or tube section, the hollow cylindrical wall is gas permeable, but pulverundurchlässig, thus forming the filter element, wherein the inlet to the feed chamber is closable by an inlet valve, while the outlet can be closed off from the delivery chamber through an outlet valve ,

p0004A disadvantage of this known powder conveying pump for dense phase powder promotion (PDF) is the unsatisfactory dosing.

p0005Out <patcit id="pcit0001" dnum="WO03029762A1"><text>WO 03/029762 A1</text></patcit> is known a generic powder conveying pump. A disadvantage of this known powder conveying pump is the fact that powder particles can get into the suction line.

p0006Further, on the prior art <patcit id="pcit0002" dnum="CH676112A5"><text>CH 676 112 A5</text></patcit> and <patcit id="pcit0003" dnum="WO8200349A1"><text>WO 82/00349 A1</text></patcit> noted.

p0007The invention is therefore based on the object to improve the accuracy of dosing in the powder conveying pump described above.

p0008This object is achieved by an operating method according to claim 1 and an apparatus suitable for execution of the operating method of the invention powder feed pump according to claim 10th

p0009The invention is based on the insight that the unsatisfactory dosing of the known powder conveying pump comes from the fact that the vacuum structure in the feed chamber is subject to fluctuations, which lead to corresponding fluctuations of sucked in and then ejected amount of powder.

p0010The invention therefore relates to the general technical teaching, at least partially establish the vacuum in the feed chamber before the inlet of the feed chamber is opened. The inlet into the feed chamber is thus only opened when the feed chamber already has built a vacuum. This offers the advantage that fluctuations in the pressure build-up in the feed chamber have less influence on the metering accuracy. Therefore, the powder conveying pump according to the invention comprises an intake valve and an exhaust valve, which are controllable independently of one another, to before opening the inlet valve initially open the purge valve can, therefore, a negative pressure in the transfer chamber is constructed.

p0011Here, the generation of negative pressure is terminated even in the feed chamber before the inlet of the feed chamber is opened. The phase of vacuum generation and Einsaugphase therefore preferably have no overlap in time. This offers the advantage that during suctioning of air from the pumping chamber due to the then closed inlet no powder can be filtered off, which would be undesirable. For this reason, it is even possible to dispense with a filter element for air extraction from the feed chamber, resulting in a higher vacuum can be generated in the feed chamber with a given equipment expenses. Preferably, however, also within the scope of the invention, the extraction from the feed chamber through a filter element to prevent the extraction of residual powder, which may still be located in the feed chamber.

p0012The inlet of the feed chamber is preferably not open when in the feed chamber, a predetermined negative pressure has built up. This offers the advantage that at the beginning of the reign Einsaugphase defined pressure conditions, so that the sucked amount of powder can be easily calculated and controlled or regulated.

p0013For this purpose, the negative pressure in the transfer chamber can be measured by a pressure sensor, a control unit closes the exhaust valve and at the same time or with a delay time opens the inlet valve when the measured negative pressure has reached a predetermined limit value in the feed chamber.

p0014However, it is alternatively also possible that in the feed chamber before opening of the intake valve, a predetermined negative pressure is built up by the purge valve is opened corresponding to the desired negative pressure for a predetermined period of time, wherein the functional relationship between the opening period of the suction valve and the resulting underpressure can be determined by tests.

p0015The delivery of the present in the feed chamber powder through the outlet is preferably carried out by the powder is discharged from the feed chamber. These preferably opens a pressure connection into the feed chamber through which a fluid to the discharge of the powder can be introduced into the feed chamber, wherein the pressure connection can be closed by a discharge valve. Preferably the discharge valve is independent of the intake valve, the exhaust valve and / or the suction valve controllable. This offers the advantage that the vacuum generating phase, the Einsaugphase, the exhaust phase and the ejection phase are independently controlled in order to achieve an optimal promotion behavior.

p0016Unlike the known PDF-pump described above, the fluid (eg compressed air) for discharging the powder from the feed chamber preferably bypassing the filter element is introduced directly into the feed chamber. This offers the advantage that the pressure build-up in the pumping chamber during the ejection of the powder is not hindered by the filter element, whereby the delivery chamber can be emptied faster.

p0017In addition can be carried out a cleaning of the feed chamber in connection with the invention by providing a cleaning fluid (eg compressed air) is introduced into the feed chamber. Unlike the known PDF-pump described above, the cleaning fluid is in this case preferably not introduced through the filter element and directly into the feed chamber. This offers the advantage of a slower pressure build-up in the pumping chamber during the cleaning operation, whereby the risk of bursting of the delivery hose is reduced. However, it is within the scope of the invention also the alternative possibility that the cleaning fluid is introduced directly, bypassing the filter element in the feed chamber.

p0018Preferably, the duration of a complete work cycle including vacuum generating phase, Einsaugphase and ejection phase in the range of 200 ms to 1 s, wherein any intermediate values ​​are also possible and a value of the clock period of 500 ms is particularly advantageous.

p0019The vacuum generating phase Einsaugphase and the ejection phase can have different lengths or be of equal length, with values ​​between 50 ms and 200 ms, or any intermediate values ​​within this interval are possible. Here, a time period of 150 ms for the negative pressure generating phase Einsaugphase and / or the ejection phase has been found to be advantageous. The invention is not limited to the above-mentioned values ​​for the duration of the vacuum generating phase, the Einsaugphase and the ejection phase, but in principle can also be realized with other values.

p0020Furthermore, it should be mentioned that between the vacuum generating phase, the Einsaugphase and / or the ejection phase preferably delay times which can for example be in the range of 20 ms to 200 ms. These delay times to ensure that the respective valves have reached the desired valve position for a corresponding control. However, the invention is in terms of the duration of the delay times is not limited to the values ​​described above, but in principle with other values ​​for the delay time realized.

p0021Finally, it should be mentioned that the invention is not limited to a powder feed pump as a single part, but also includes a powder coating plant with such a powder conveying pump.

p0022Other advantageous developments of the invention are characterized in the dependent claims or are explained in detail together with the description of the preferred embodiment of the invention using the figures. Show it:<dl id="dl0001" compact="compact"><dt>figure 1</dt><dd>a Fluidikdiagramm a preferred embodiment of a powder coating system with a powder feed pump according to the invention and </dd><dt>figure 2</dt><dd>several time diagrams to illustrate the opening and closing behavior of the individual valves of the powder conveying pump according to the invention from FIG. 1</dd></dl>

p0023The Fluidikdiagramm in Figure 1 shows a powder coating system according to the invention with a powder feed pump 1 to the powder supply of a rotary atomizer 2, wherein the rotary atomizer 2 may be of conventional design and will therefore not be further described in the following. Instead of the rotary atomizer 2 but also another powder application device can be used, such as a spray gun.

p0024For receiving a serving as a coating agent powder 3, the powder conveying pump 1 whose input side is connected to a powder container 4, wherein the powder container 4 may be of conventional construction also, and will therefore be described hereinafter in more detail.

p0025In addition, the powder conveying pump 1 whose input side is connected to a compressed air tank 5, which is fed by a compressed air pump. 6

p0026For powder delivery, the powder conveying pump 1 two parallel conveyor branches, each with a feed chamber 7, 8.

p0027The two pumping chambers 7, 8 each have an inlet, the inlets of the two feed chambers 7, 8 are connected via a respective inlet valve 9, 10 with the powder container 4th When the intake valve 9, 10 is open, so the powder can 3 from the powder container 4 into the pumping chambers 7, 8 are sucked, as will be described in detail.

p0028Further, the pumping chambers 7, 8 are each an outlet, wherein the two outlets of the pumping chambers 7, 8 are connected via a respective outlet valve 11, 12 with the rotary atomizer second For open exhaust valve 11, 12, ie the powder contained in the pumping chambers 7, 8 3 can be ejected from the pumping chambers 7, 8, as will also be described in detail.

p0029The inlet valves 9, 10 and the exhaust valves 11, 12 can in this case be designed as a pinch valves, which can be pneumatic, hydraulic or electrically driven.

p0030For sucking the powder 3 on the inlet valves 9, 10 in the pumping chambers 7, 8, the powder conveying pump 1 is a vacuum generator 13 which is of conventional design per se. The vacuum generator 13 has an injector nozzle, which is fed by the compressed air tank 5 with compressed air and produces a vacuum at a vacuum port on the venturi principle.

p0031The vacuum connection of the vacuum generator 13 is connected via a suction valve 14 and a filter element 15 with the feed chamber 7 and a suction valve 16 and a filter element 17 connected to the conveying chamber eighth When the purge valve 14 is opened, the vacuum generator 13 draws through the filter element 15, air from the feed chamber 7 from where it generates a negative pressure for sucking the powder 3 from the powder container 4. Accordingly, the vacuum generator 13 generates a negative pressure in the feed chamber 8 when the is purge 16 is opened.

p0032The two filter elements 15, 17 are in this case no separate components, but rather consist of the wall of the feed chambers hollow cylindrical 7, 8, which is permeable to air but pulverundurchlässig.

p0033The compressed air tank 5, however, is not only connected to the vacuum generator 13 to generate a negative pressure in the pumping chambers 7, 8, but also serves for ejecting the powder 3 of the pumping chambers 7, 8. For this purpose, the compressed air container 5 via a discharge valve 18 with the feed chamber 7 and is connected via a further discharge valve 19 with the feed chamber. 8 In the open state of the exhaust valves 18, 19 so pressurized air is injected from the compressed air container 5 in the pumping chambers 7, 8, whereby the powder located in the pumping chambers 7, 8 3 is ejected from the pumping chambers 7, 8, if the exhaust valves 11, 12 open are. Of importance here is that the exhaust valves 18, 19 bypassing the filter elements 15, 17 open directly into the pumping chambers 7. 8 This offers the advantage that the pressure build-up in the pumping chambers 7, 8 at the discharge of the powder from the three pumping chambers 7, 8 not by the flow resistance of the filter elements 15 is slowed down 17th The direct supply of the pressurized air into the pumping chambers 7, 8 therefore makes it possible advantageously a faster pressure build-up and thereby a rapid emptying of the pumping chambers 7, the eighth

p0034The energy stored in the compressed air tank 5 Compressed air not only serves to eject the contained in the feed chambers 7, 8 powder 3, but also for cleaning the pumping chambers 7, 8. For this purpose, the compressed air container 5 via a purge valve 20 and a filter element 21 with the delivery chamber 7 and in a corresponding manner via a purge valve 22 and a filter element 23 is connected to the feed chamber eighth The compressed air tank 5 so blows compressed air for cleaning purposes in the feed chamber 7 a, if the purge valve 20 is opened. Accordingly, compressed air is blown for cleaning purposes in the feed chamber 8, when the purge valve 22 is opened.

p0035The two filter elements 21, 23 are in this case also no separate components, but consist of the wall of the hollow cylindrical conveying chambers 7, 8, which is permeable to air but pulverundurchlässig.

p0036The supply of the cleaning air over the filter elements 21, 23 provides the advantage that the pressure build-up in the cleaning operation is slower, so that the risk of bursting of a conveying tube is reduced in the cleaning operation.

p0037Below the operating process of the invention the powder conveying pump 1 will now be described with reference to FIG. 2 The four upper timing charts in Figure 2 show this from the top down, the time opening behavior of the purge valve 14, the intake valve 9, the exhaust valve 11 and the discharge valve 18. The bottom four timing diagrams in Figure 2 on the other hand show from top to bottom, the time opening behavior of the suction valve 17, the intake valve 10, outlet valve 12 and the discharge valve 19th

p0038At the beginning of a working cycle, the exhaust valve 14 is first opened while the intake valve 9, the exhaust valve 11 and the discharge valve 18 are closed. The opening of the purge valve 14 is carried out in this case for a period T_SAUG, Which may be in the range of 50 ms and 200 ms. During this vacuum generating phase, a defined negative pressure is generated in the feed chamber 7, which is used later for sucking the powder 3 into the feed chamber 7, as will be described in detail.

p0039After expiration of the negative pressure producing phase the purge valve 14 is closed, wherein the inlet valve 9, the exhaust valve 11 and the discharge valve 18 during a predetermined delay time T_PAUSE remain closed. The delay time T_PAUSE here comes within the range of 10 ms to 200 ms and ensures that no time overlaps between the individual phases of a working cycle occur.

p0040After the delay time T_PAUSE is then the inlet valve 9 open, so that the negative pressure previously built up in the pumping chamber 7, the powder 3 sucks from the powder container 4, whereby the discharge chamber 7 is filled with powder. The inlet valve 9 is in this case for a period T_ON open that may range between 50 ms and 200 ms. After this intake phase, the inlet valve 9 is closed, the outlet valve 11, the discharge valve 18 and the purge valve 14 initially remain closed also during a further delay time.

p0041After expiration of this delay time, the outlet valve 11 and the discharge valve 18 are then opened simultaneously, so that compressed air is blown from the compressed air container 5 in the feed chamber 7, so that the powder located in the feed chamber 7 3 is discharged via the outlet valve eleventh The opening phase of the exhaust valve 11 may in this case a period T_OUT have, ranging from 50 ms to 200 ms. Also, the opening phase of the exhaust valve 18 may have a duration T_PUSH have, ranging from 50 ms to 200 ms.

p0042After the expiration of the outlet and discharge phase, the discharge valve 11 and the discharge valve 18 are closed, the inlet valve 9 and the suction valve 14 also remain closed for a delay time. After this delay time of the above described operating cycle is repeated cyclically, a clock, a period T_PERIOD having that is eg 500 ms.

p0043The inlet valve 10, exhaust valve 12, the discharge valve 19 and the purge valve 16 are controlled in the same way, but with a phase shift T_PHASE is provided, which can be in the range of 250 ms.

p0044An advantage of the lack of temporal overlap of the vacuum generating phase and Einsaugphase is the fact that at the beginning of Einsaugphase already defined vacuum in the feed chamber 7 or 8 was prepared, so that the flow rate can be determined with accuracy.

p0045The direct connection of the exhaust valves 18, 19 with the pumping chambers 7, 8, bypassing the filter elements 15, 17, 21, 23 offers the advantage that the pressure build-up is not hindered by the filter elements 15, 17, 21, 23, which allows faster emptying the pumping chambers 7, 8 allows.

p0046The invention is not limited to the preferred embodiment described above. Rather, a plurality of variants and modifications are possible, which also make use of the inventive concept and therefore fall within the scope.