Feed pump for powder and its method of operation

0001The invention relates to an operating method for a powder conveying pump and a correspondingly shaped powder feed pump the implementation of the operating method of the invention.

0002In powder coating systems has been promoting as a coating material serving powder before the so-called Dilute phase method is used, in which the powder in the fluidized State in a flow of air through tubular conveying lines to the application device (eg spray gun or Rotary atomizer) was promoted. The term thin-flow process is because the powder content in the produced Powder-air mixture is relatively low, so that the tubular conveyor lines a correspondingly large had to have cross-section to the desired amount of powder to promote.

0003For this reason, the so-called dense phase powder promotion has already been (PDF) proposed that a larger amount of powder has in the produced powder-air mixture. The actual powder feed may in this case by a well PDF pump Marked done powder conveying pump, a Feed chamber having an inlet and an outlet, said sucked in via the inlet in the powder delivery chamber and is subsequently ejected through the outlet to a Application equipment (eg spray gun or rotary atomizer) to get. To fill the feed chamber is first the outlet of the feed chamber is closed while the opens inlet of the feed chamber to powder of a to suck powder container. Subsequently, then in the delivery chamber a vacuum is produced by blowing air through a Filter element is sucked from the delivery chamber, the Filter element permeable to air but pulverundurchlässig is, so that the powder contained in the feed chamber is not sucked becomes. After a sufficient filling of the pumping chamber the extraction is then ended and the intake valve closed. For ejection of contained in the feed chamber Powder of the outlet is then opened and the filter element Compressed air is blown into the feed chamber, thereby the powder is discharged from the feed chamber. Through a cyclic operation of Einsaug- described above and will discharge phases powder from the powder container to the applicator promoted. The delivery chamber can be made of this a hose or pipe section made whose hollow cylindrical Wall permeable to gas, but pulverundurchlässig is, thus forming the filter element, wherein the inlet to the feed chamber is closable by an inlet valve, while the outlet from the pumping chamber through an outlet valve can be closed.

0004A disadvantage of this known powder conveying pump for powder dense phase conveying (PDF) is the unsatisfactory dosing.

0005The invention is therefore based on the object, the metering in the powder conveying pump described above to improve.

0006This object is achieved by an operating method according to claim 1 and the implementation of the operating method of the invention suitable powder feed pump solved according to claim 11th

0007The invention is based on the insight that the unsatisfactory Dosing of the known powder conveying pump therefore stirred, that the vacuum structure in the feed chamber fluctuations subject to the fluctuations of the corresponding aspirated and then ejected powder quantity lead.

0008The invention therefore relates to the general technical teaching the vacuum in the feed chamber at least partially build before the inlet of the feed chamber is opened. The inlet into the feed chamber is thus open only when already built up in the feed chamber, a vacuum Has. This offers the advantage that fluctuations in the pressure build-up in the feed chamber less influence have on the metering accuracy. The powder conveying pump according to the invention Therefore, a intake valve and an exhaust valve which are independently controllable from each other in order before first open the intake valve opening the purge valve to be able to allow a negative pressure built up in the feed chamber becomes.

0009Preferably, the generating of the negative pressure in the feed chamber is even terminates before the inlet of the delivery chamber opens. The phase of vacuum generation and So Einsaugphase preferably have no overlap in time on. This offers the advantage that during suctioning of Air from the pumping chamber due to the then closed Inlet no powder can be sucked what undesirable would. For this reason, even on a filter element for Air extraction are omitted from the feed chamber, thereby with a given equipment expenses, a higher vacuum can be produced in the feed chamber. preferably takes place but also in the context of the invention the extraction of the feed chamber through a filter element, to the suction to prevent residual powder that may still be in the feed chamber.

0010The inlet of the feed chamber is preferably only opened when in the feed chamber, a predetermined vacuum has built. This offers the advantage that at the beginning the Einsaugphase rule defined pressure conditions, so that calculate the amount of powder sucked easily and control or regulate leaves.

0011For this purpose, the negative pressure in the conveying chamber through a Pressure sensor to be measured, wherein a control unit the purge closes and simultaneously or with a delay time the inlet valve opens when the measured vacuum reaches a predetermined limit value in the feed chamber Has.

0012However, it is alternatively also possible that in the feed chamber before opening of the intake valve, a predetermined vacuum is constructed by the purge valve in accordance with the open desired vacuum for a predetermined period is to give the functional relationship between the opening period of the suction valve and the resulting can be determined by vacuum tests.

0013The delivery of the present in the feed chamber through powder the outlet is preferably carried out by the powder from the Feed chamber is ejected. These preferably opens a Via pressure port in the delivery chamber through which a fluid initiated at the discharge of the powder into the feed chamber can be wherein the positive pressure port by a discharge valve is closable. Preferably, the discharge valve regardless of the intake valve, the exhaust valve and / or the purge controllable. This offers the advantage that the Vacuum generating phase Einsaugphase, the exhaust phase and the ejection phase are controllable independently of one another, In order to achieve an optimal promotion behavior.

0014In contrast to the known pump described above PDF the fluid (eg compressed air) for discharging the powder from the pumping chamber preferably bypassing the Filter element directly introduced into the feed chamber. This offers the advantage that the pressure build-up in the feed chamber not hindered by the filter element during the ejection of the powder will, whereby the feed chamber emptied faster can be.

0015Moreover, in the context of the invention a cleaning the delivery chamber carried by a cleaning fluid (for example, Compressed air) is introduced into the feed chamber. In contrast to the known PDF-pump described above is the Cleaning fluid in this case preferably over the filter element and not directly introduced into the feed chamber. This provides the advantage of a slower pressure build-up in the feed chamber during the cleaning operation, whereby the risk of an Bursting of the delivery hose is reduced. However, there is in the context of the invention also the alternative possibility, that the cleaning fluid directly, bypassing the filter element is introduced into the feed chamber.

0016Preferably, the duration of a complete working cycle is 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 is 500 ms particularly advantageous.

0017The vacuum generating phase Einsaugphase and the ejection phase may have different lengths or be of equal length, with values ​​between 50 ms and 200 ms or any intermediate values ​​within this interval possible are. Here, has a time duration of 150 ms for the negative pressure generating phase, the Einsaugphase and / or the ejection phase has proved advantageous. The invention is, however, not limited to the above-mentioned values ​​for the duration of the Vacuum generating phase, the Einsaugphase and the ejection phase limited, but in principle with other values realizable.

0018Furthermore, it should be mentioned that between the vacuum generating phase, the Einsaugphase and / or the ejection phase preferably Delay times are, for example, in can be range from 20 ms to 200 ms. These delay times to ensure that the respective valves after a corresponding triggering the desired valve position achieved. However, the invention is with respect to the duration of the delay times not limited to the above- Values ​​described limited, but in principle with other values ​​for the delay time realized.

0019Finally it should be mentioned that the invention is not limited to a Powder conveying pump is limited as a single part, but Rather, a powder coating plant with such a comprising powder feed pump.

0020Other advantageous developments of the invention are in the are in dependent claims or together hereinafter with the description of the preferred embodiment the invention based on the figures explained. Show it:<dl tsize="7" compact="compact"><dt>figure 1</dt><dd>a Fluidikdiagramm a preferred embodiment a powder coating plant 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 the powder feed pump of Figure 1 according to the invention.</dd></dl>

0021The Fluidikdiagramm in Figure 1 shows a powder coating plant a powder conveying pump 1 according to the invention powder supplying a rotary atomizer 2, wherein the Rotary atomizer 2 may be of conventional and will therefore not be further described in the following. instead However, the rotary atomizer 2 can also another powder application device be used, such as a spray gun.

0022To pick up a serving as a coating agent powder 3, the powder conveying pump 1 on the input side with a powder container 4, wherein the powder container 4 also may be conventionally constructed and therefore hereinafter is not described in detail.

0023In addition, the powder feed pump 1 is the input side to a compressed air container 5 is connected, which from a compressed air pump 6 is fed.

0024For powder delivery, the powder conveying pump 1 two parallel connected conveyor branches, each with a feed chamber 7, 8.

0025The two pumping chambers 7, 8 each have an inlet , wherein the two inlets of the pumping chambers 7, 8 via in each case an inlet valve 9, 10 is connected to the powder container 4 are. When intake valve 9, 10 open so can the 3 powder from the powder container 4 into the pumping chambers 7, 8 be sucked in, as will be described in detail.

0026Furthermore, the pumping chambers 7, 8 each have an outlet on, whereby the two outlets of the pumping chambers 7, 8 via each exhaust valve 11, 12 with the rotary atomizer 2 are connected. When can open exhaust valve 11, 12 So the left in the conveying chambers 7, 8 powder 3 from the pumping chambers 7, 8 ejected, as also still is described in detail.

0027The inlet valves 9, 10 and the exhaust valves 11, 12 can be designed here as pinch valves, the pneumatic, can be hydraulically or electrically powered.

0028For sucking the powder 3 via the inlet valves 9, 10 in the pumping chambers 7, 8, the powder conveying pump 1 a Vacuum generator 13, which conventionally constructed se is. The vacuum generator 13 has an injector nozzle, which is fed from the compressed air tank 5 with compressed air and according to the Venturi principle a vacuum at a vacuum port generated.

0029The vacuum connection of the vacuum generator 13 is connected via a suction valve 14 and a filter element 15 with the delivery chamber 7 and connected via a suction valve 16 and a filter element 17 connected to the feed chamber. 8 If that Purge 14 is opened, the vacuum generator sucks 13 via the filter element 15 from the air feed chamber 7 from where it generates a vacuum to suck the powder 3 from the powder container 4. Accordingly, the generated negative pressure generator 13 is a negative pressure in the feed chamber 8 when the purge valve 16 is opened.

0030The two filter elements 15, 17 are in this case no separate Components, but rather consist of the wall of the hollow cylinder running conveying chambers 7, 8, the air-permeable, but is pulverundurchlässig.

0031The compressed air tank 5 is, however, not only with the vacuum generator 13 connected to a vacuum in the pumping chambers 7, 8 to produce, but also serves for ejecting the powder 3 from the pumping chambers 7, 8. To this end, the Compressed air tank 5 via a discharge valve 18 with the feed chamber 7 and another discharge valve 19 with the feed chamber 8. In the open state of the exhaust valves 18, 19 so pressurized air from the compressed air container 5 blown into the conveying chambers 7, 8, whereby in the Conveying chambers 7, 8 located powder 3 from feed chambers 7, 8 is discharged, if the exhaust valves 11, 12 open are. Of importance here is that the exhaust valves 18, 19 bypassing the filter elements 15, 17 directly open into the conveying chambers 7. 8 This offers the advantage that the pressure build-up during ejection in the pumping chambers 7, 8 the powder 3 from the pumping chambers 7, 8 not by the slow flow resistance of the filter elements 15, 17 becomes. The direct supply of the compressed air in the delivery chambers 7, 8 thus advantageously allows a faster Pressure build-up and thereby a rapid emptying of the delivery chambers 7, the eighth

0032The energy stored in the compressed air tank 5 of compressed air is used However, not only for the ejection of the pumping chambers 7, 8 powder contained 3, but also for cleaning the feed chambers 7, 8. To this end, the compressed air tank 5 through 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 blows so for cleaning compressed air into the feed chamber 7 a when the purge valve 20 is opened. Accordingly, compressed air is to Cleaning purposes blown into the feed chamber 8, when the is cleaning valve 22 is opened.

0033The two filter elements 21, 23 are in this case also no independent components, but consist of the wall of the hollow cylindrical conveying chambers 7, 8, the air-permeable, but is pulverundurchlässig.

0034The supply of the cleaning air over the filter elements 21, 23 provides the advantage that the pressure build-up in the cleaning operation slower, thereby reducing the risk of a burst a conveyor tube is reduced in the cleaning operation.

0035It will now be based on figure 2 of the invention Operating procedures of the powder conveying pump 1 described. The four upper timing charts in Figure 2 show this from the top Down the temporal behavior of the suction opening 14, the intake valve 9, the exhaust valve 11 and the exhaust valve 18. The bottom four timing diagrams in Figure 2 show contrast from top to bottom, the temporal behavior of opening of the suction valve 17, the intake valve 10, outlet valve 12 and the discharge valve 19th

0036At the beginning of a work cycle, first the purge 14 is opened while the intake valve 9, the exhaust valve 11 and the discharge valve 18 are closed. The opening of the Purge valve 14 takes place here for a period T_SAUGThat in may be the range of 50 ms and 200 ms. During this vacuum generating phase is in the feed chamber 7 a defined generated vacuum, the later for sucking the powder 3 is used in the feed chamber 7, as in more detail will be described.

0037After the vacuum generating phase the purge is 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 the individual phases of a working cycle occur.

0038After the delay time T_PAUSE is then the inlet valve 9 is opened, so that the in the feed chamber 7 before Under pressure built up, the powder from the powder container 3 4 sucks, whereby the feed chamber 7 is filled with powder. The inlet valve 9 is in this case for a period T_ON open, which may range between 50 ms and 200 ms. After Expiry of the intake phase, the inlet valve 9 is closed, wherein the exhaust valve 11, the discharge valve 18 and the Purge valve 14 during a further delay time, first also remain closed.

0039After this delay time are then simultaneously the exhaust valve 11 and the discharge valve 18 is opened, so that compressed air from the compressed air container 5 in the feed chamber 7 is blown, whereby the present in the feed chamber 7 Powder 3 discharged through the exhaust valve 11 becomes. The opening phase of the exhaust valve 11 may in this case a duration T_OUT have, in the range of 50 ms to 200 ms lies. Also, the opening phase of the exhaust valve 18 may include a Take_PUSH have, ranging from 50 ms to 200 ms.

0040After the expiry of the discharge outlet and then the phase Exhaust valve 11 and the discharge valve 18 is closed, whereby the inlet valve 9 and the suction valve 14 for a delay time also remain closed. After this Delay time is the work cycle described above repeated cyclically, a clock, a period T_PERIODhaving that is eg 500 ms.

0041The inlet valve 10, exhaust valve 12, the discharge valve 19 and the purge valve 16 are controlled in the same way, but a phase shift T_PHASE scheduled which may be in the range of 250 ms.

0042An 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 was created in the feed chamber 7 or 8, so that the flow rate can be determined with accuracy.

0043The direct connection of the exhaust valves 18, 19 with the delivery chambers 7, 8, bypassing the filter elements 15, 17, 21, 23 provides the advantage that the pressure buildup through the filter elements 15, 17, 21, 23 is not hindered, which is a allows faster emptying of conveying chambers 7. 8

0044The invention is not limited to the above-described preferred Embodiment limited. Rather, it is a Plurality of variants and modifications are possible which likewise make use of the inventive idea and therefore fall within the scope.