Dense phase powder pump and corresponding operating method

Abstract

The invention relates to a method and a dense phase powder pump (1) for conveying coating powder from a first powder reservoir (101) to a second downstream powder reservoir or to a downstream powder spray-coating gun (102) or the like installation for spraying coating powder. In order to reduce the number of components of the dense phase powder pump (1) that require maintenance, the dense phase powder pump (1) is designed as a single-chamber dense phase powder pump and has only a single powder conveyor chamber (4) for conveying coating powder.

Claims

1. A dense phase powder pump for conveying coating powder in a powder path from a first powder reservoir to a second downstream powder reservoir or a downstream powder spray-coating gun or similar device for spraying coating powder disposed downstream of the dense phase powder pump, wherein the dense phase powder pump is designed as a single-chamber dense phase powder pump and comprises just one single powder conveyor chamber for the conveying of coating powder, wherein: at least one auxiliary compressed air inlet device opens into at least one location in the powder path after a powder outlet valve of the dense phase powder pump to supply auxiliary compressed air as additional conveying compressed air as needed, wherein the dense phase powder pump further comprises: a powder inlet connected or connectable to the first powder reservoir; and a powder outlet connected or connectable to the second reservoir or to the powder spray-coating gun or other such mechanism for spraying coating powder, wherein the powder inlet is arranged at a first end region of the dense phase powder pump and the powder outlet at an oppositely situated second end region of the dense phase powder pump, and wherein the single powder conveyor chamber is arranged between the powder inlet and powder outlet of the dense phase powder pump, wherein the single powder conveyor chamber has a chamber powder inlet on a first end region and a chamber powder outlet on an oppositely situated second end region, wherein the dense phase powder pump further comprises: a powder inlet valve by means of which the chamber powder inlet of the single powder conveyor chamber can be fluidly connected or connectable to the powder inlet of the dense phase powder pump, and a powder outlet valve by means of which the chamber powder outlet of the single powder conveyor chamber can be fluidly connected or connectable to powder outlet of the dense phase powder pump, and wherein the powder outlet of the single powder conveyor chamber is or can be fluidly connected to the powder outlet of the dense phase powder pump by means of the powder outlet valve.

2. The dense phase powder pump according to claim 1, wherein a control unit is further provided to actuate the powder inlet valve and/or powder outlet valve as well as alternatingly apply a negative pressure and an excess pressure in the single powder conveyor chamber.

3. The dense phase powder pump according to claim 2, wherein the single powder conveyor chamber comprises at least one air exchange vent in order to alternatingly subject the single powder conveyor chamber to excess pressure or negative pressure; and wherein the control unit is designed to alternatingly connect the air exchange vent of the single powder conveyor chamber to a vacuum line or vacuum source to suction coating powder into the single powder conveyor chamber through the open powder inlet valve while the powder outlet valve is closed, and to a compressed air supply line or compressed air source to pneumatically discharge a portion of powder from within the single powder conveyor chamber through the open powder outlet valve while the powder inlet valve is closed.

4. The dense phase powder pump according to claim 3, wherein the at least one air exchange vent of the single powder conveyor chamber opens into the intermediate chamber, wherein the excess pressure and the negative pressure can be transmitted into the single powder conveyor chamber through the filter.

5. The dense phase powder pump according claim 1, wherein the powder inlet valve and the powder outlet valve can be actuated separately from each other.

6. The dense phase powder pump according to claim 1, wherein the powder inlet valve and the powder outlet valve are each designed as a pinch valve having a flexible elastic tube as a valve channel which can be squeezed by actuating compressed air in a pressure chamber surrounding the tube to close the respective valve.

7. The dense phase powder pump according to claim 6, wherein application of a negative pressure in the pressure chamber of the respective valve causes opening of the powder inlet valve and/or powder outlet valve.

8. The dense phase powder pump according to claim 1, wherein the single powder conveyor chamber comprises at least one air exchange vent in order to alternatingly subject the single powder conveyor chamber to excess pressure or negative pressure.

9. The dense phase powder pump according to claim 8, wherein the dense phase powder pump comprises a compressed air/ vacuum source, and wherein the at least one air exchange vent of the single powder conveyor chamber is or can be connected to the compressed air/vacuum source.

10. The dense phase powder pump according to claim 9, wherein the single powder conveyor chamber comprises at least one air exchange vent by means of which the single powder conveyor chamber can be intermittently subjected to conveying compressed air for discharging portions of powder out of the single powder conveyor chamber, wherein the at least one auxiliary compressed air inlet device is designed such that the pneumatic resistance which occurs when auxiliary compressed air is fed into the powder path is substantially equal to the pneumatic resistance distributed when conveying compressed air is fed into the single powder conveyor chamber, and wherein the at least one auxiliary compressed air inlet device comprises a chamber wall formed by a filter over at least part of its length which surrounds the powder path and separates the single powder conveyor chamber from an intermediate chamber surrounding the filter and formed between the filter and a housing, wherein the filter of the auxiliary compressed air inlet device is structurally identical to the filter of the single powder conveyor chamber.

11. The dense phase powder pump according to claim 1, wherein the dense phase powder pump further comprises: a powder inlet connected or connectable to the first powder reservoir; a powder outlet connected or connectable to the second reservoir or to the powder spray-coating gun or other such mechanism for spraying coating powder; a powder inlet valve by means of which the chamber powder inlet of the single powder conveyor chamber can be fluidly connected or connectable to the powder inlet of the dense phase powder pump; and a powder outlet valve by means of which the chamber powder outlet of the single powder conveyor chamber can be fluidly connected or connectable to powder outlet of the dense phase powder pump; wherein the powder inlet is arranged at a first end region of the dense phase powder pump and the powder outlet at an oppositely situated second end region of the dense phase powder pump; wherein the single powder conveyor chamber is arranged between the powder inlet and powder outlet of the dense phase powder pump, and has a chamber powder inlet on a first end region and a chamber powder outlet on an oppositely situated second end region; wherein the powder outlet of the single powder conveyor chamber is or can be fluidly connected to the powder outlet of the dense phase powder pump by means of the powder outlet valve; and wherein the single powder conveyor chamber comprises a chamber wall, wherein the chamber wall of the single powder conveyor chamber is formed at least over part of its length by a filter which surrounds the single powder conveyor chamber and separates it the single powder convey or chamber from an intermediate chamber surrounding the filter and formed between the filter and a powder conveyor chamber housing, wherein the filter is permeable to gas but not to coating powder.

12. The dense phase powder pump according to claim 1, wherein the at least one auxiliary compressed air inlet device opens into at least one location in the powder path between the powder outlet valve and a powder outlet of the dense phase powder pump.

13. The dense phase powder pump according to claim 1, wherein the auxiliary compressed air inlet device comprises a filter tube having a circumference of at least 180 and forming a channel wall inner surface over at least 180 of the powder path circumference on a partial length of the powder path between the powder outlet valve and a powder outlet of the dense phase powder pump.

14. The dense phase powder pump according to claim 13, wherein the filter tube consists of microporous material and is permeable to compressed air but not to coating powder.

15. The dense phase powder pump according to claim 14, wherein micropores in the inner circumferential surface of the filter tube lead into a filter tube channel of the filter tube in a plurality of at least four different directions, of which at least two are differently angled longitudinal tube directions, so as to conduct the auxiliary compressed air in a correspondingly plurality of various directions in the filter tube channel in the form of micro-thin streams.

16. The dense phase powder pump according to claim 13, wherein the filter tube is surrounded by a pressure chamber which can be connected to a compressed air supply line or a compressed air source.

17. The dense phase powder pump according to claim 13, wherein the filter tube and the channel wall inner surface it forms extends around 360 of the powder path circumference.

18. The dense phase powder pump according to claim 13, wherein the filter tube is a sintered body of metal or plastic or of a material mixture containing metal or plastic.

19. The dense phase powder pump according to claim 13, wherein the filter tube is a rigid body.

20. The dense phase powder pump according to claim 1, wherein the auxiliary compressed air inlet device is designed to introduce auxiliary compressed air into the powder path after the powder outlet valve in pulses.

21. The dense phase powder pump according to claim 20, wherein a mechanism for supplying auxiliary compressed air to the at least one auxiliary compressed air inlet device is provided, and wherein a pulse frequency of the auxiliary compressed air is at least equal to a frequency of the single powder conveyor chamber at which portions of powder are discharged from said powder conveyor chamber.

22. The dense phase powder pump according to claim 21, wherein the pulse frequency of the auxiliary compressed air is equal to the frequency of the single powder conveyor chamber at which portions of powder are discharged from said powder conveyor chamber, and wherein the mechanism for supplying auxiliary compressed air to the at least one auxiliary compressed air inlet device is designed to supply the auxiliary compressed air to the at least one auxiliary compressed air inlet device in phase opposition relative to the powder discharge cycle of the single powder conveyor chamber.

23. The dense phase powder pump according to claim 21, wherein the single powder conveyor chamber comprises at least one air exchange vent via which the single powder conveyor chamber can be intermittently subjected to conveying compressed air for the expelling of powder portions from the single powder conveyor chamber, and wherein the mechanism for supplying auxiliary compressed air to the at least one auxiliary compressed air inlet device comprises a control element, particularly a three/two-way valve or similar control valve, by means of which compressed air from a common compressed air source can be alternatingly supplied to the at least one air exchange vent of the single powder conveyor chamber or the at least one auxiliary compressed air inlet device.

24. The dense phase powder pump according to claim 21, wherein the single powder conveyor chamber comprises at least one air exchange vent by means of which the single powder conveyor chamber can be intermittently subjected to conveying compressed air for discharging portions of powder out of the single powder conveyor chamber, wherein the mechanism for supplying auxiliary compressed air to the at least one auxiliary compressed air inlet device is designed to set the amount of auxiliary compressed air supplied to the at least one auxiliary compressed air inlet device per pump cycle as a function of the amount of conveying compressed air supplied to the at least one air exchange vent per pump cycle.

25. The dense phase powder pump according to claim 24, wherein the mechanism for supplying auxiliary compressed air to the at least one auxiliary compressed air inlet device is designed to set the amount of auxiliary compressed air supplied to the at least one auxiliary compressed air inlet device per pump cycle such that the amount of auxiliary compressed air fed into the powder path per pump cycle via the at least one auxiliary compressed air inlet device is substantially equivalent to the amount of conveying compressed air fed into the single powder conveyor chamber via the at least one air exchange vent per pump cycle.

26. The dense phase powder pump according to claim 21, wherein a control unit is provided by means of which the auxiliary compressed air frequency can be automatically adjusted, automatically controlled or regulated, as a function of the powder discharge frequency of the single powder conveyor chamber.

27. The dense phase powder pump according to claim 1, wherein the single powder conveyor chamber comprises at least one air exchange vent by means of which the single powder conveyor chamber can be intermittently subjected to conveying compressed air for discharging portions of powder out of the single powder conveyor chamber, and wherein the at least one auxiliary compressed air inlet device is designed such that the pneumatic resistance which occurs when auxiliary compressed air is fed into the powder path is substantially equal to the pneumatic resistance distributed when conveying compressed air is fed into the single powder conveyor chamber.

28. The dense phase powder pump according to claim 1, wherein a control unit is provided by means of which the amount of auxiliary compressed air flowing through the auxiliary compressed air inlet device per unit of time can be adjusted, automatically controlled or regulated, as a function of the amount of powder conveyed.

29. The dense phase powder pump according to claim 1, wherein a control unit is provided by means of which auxiliary compressed air is always fed when the powder outlet valve is closed.

30. The dense phase powder pump according to claim 1, wherein an integrally formed material block is provided, in or on which the single powder conveyor chamber is formed or arranged, and wherein a plurality of control valves are fluidly connected to the single powder conveyor chamber for supplying conveying compressed air and vacuum, and are arranged on the material block and fluidly connected directly to the single powder conveyor chamber by means of channels formed in the material block.

31. The dense phase powder pump according to claim 30, wherein the powder inlet valve and the powder outlet valve are arranged on the material block, and wherein some of the control valves fluidly connected directly to the powder inlet valve and the powder outlet valve via channels formed in the material block for supplying and removing actuating compressed air.

32. A powder spray-coating mechanism for spraying objects with coating powder, wherein the powder spray-coating mechanism comprises the following: a dense phase powder pump in accordance with claim 1; and at least one automatic or manual spray-coating gun having a coating powder inlet, wherein the coating powder inlet of the spray-coating gun is or can be connected to the powder outlet of the dense phase powder pump via a powder line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following will reference the accompanying drawings in describing the invention in greater detail by way of example embodiments of the inventive dense phase powder pump.

(2) The figures show:

(3) FIG. 1 a longitudinal sectional representation along the powder path through a first example embodiment of the dense phase powder pump according to the invention;

(4) FIG. 2 a perspective view of the first example embodiment of the inventive dense phase powder pump according to FIG. 1;

(5) FIG. 3 a perspective view of a second example embodiment of the inventive dense phase powder pump;

(6) FIG. 4 a schematic representation of a first example embodiment of a powder spray-coating mechanism employing a dense phase powder pump according to the present invention;

(7) FIG. 5 a schematic representation of a second example embodiment of a powder spray-coating mechanism employing a dense phase powder pump according to the present invention;

(8) FIG. 6 a schematic representation of a third example embodiment of the inventive dense phase powder pump; and

(9) FIG. 7 a schematic representation of a fourth example embodiment of the inventive dense phase powder pump.

DETAILED DESCRIPTION

(10) The following will reference the representations provided in FIGS. 1-3, 6 and 7 in describing example embodiments of the dense phase powder pump 1 according to the invention.

(11) FIGS. 4 and 5 schematically depict the powder spray-coating devices 100 in which embodiments of the inventive dense phase powder pump 1 are used to convey coating powder from a first powder reservoir 101 to a powder spray-coating gun 102 arranged downstream of the dense phase powder pump 1. Another mechanism for spraying coating powder onto an object to be coated or a second powder reservoir can also be used in place of powder spray-coating gun 102.

(12) As FIG. 4 shows, the example embodiment of the inventive dense phase powder pump 1 used therein comprises a powder inlet 2 fluidly connected or connectable to the first powder reservoir 101 by means of a powder line 103, particularly by means of a suction tube or the like. A powder outlet 3 is provided on the opposite end region of the dense phase powder pump 1, which is connected or connectable to a coating powder inlet 105 of the powder spray-coating gun 102 by means of a powder line 104, particularly by means of a powder tube.

(13) Specifically, and as can be noted particularly from the FIGS. 1 to 3 representations, both the powder inlet 2 as well as the powder outlet 3 of the dense phase powder pump 1 in the first and second example embodiment are formed as respective hose connectors able to be fit onto the respective powder line 103/104 and fixed with a hose clip. However, other embodiments for the powder inlet 2 and/or powder outlet 3 are of course also conceivable.

(14) The dense phase powder pump 1 according to the invention is characterized by being designed as a single-chamber dense phase powder pump, wherein only one single powder conveyor chamber 4 is provided for conveying coating powder from the first powder reservoir 101 to the powder spray-coating gun 102 or another mechanism for spray coating objects or to another powder reservoir.

(15) In the example embodiments of the inventive dense phase powder pump 1 according to FIGS. 1 to 5, the (single) powder conveyor chamber 4 has a powder inlet 5 pointing toward the powder inlet 2 of the dense phase powder pump 1 at a first end region. The powder conveyor chamber 4 further has a powder outlet 6 pointing toward the powder outlet 3 of the dense phase powder pump 1. A powder inlet valve 7 is arranged directly adjacent the powder inlet 5 of the powder conveying chamber 4, and in a manner such that this powder inlet valve 7 is situated between the powder inlet 5 of the powder conveyor chamber 4 and the powder inlet 2 of the dense phase powder pump 1. A powder outlet valve 8 is similarly arranged directly adjacent the powder outlet 6 of the powder conveyor chamber 4.

(16) In contrast to the powder inlet region of the dense phase powder pump 1, however, the powder outlet valve 8 is not arranged directly between the powder outlet 6 of the powder conveyor chamber and the powder outlet 3 of the dense phase powder pump 1 in the powder outlet region of the dense phase powder pump 1; instead, an auxiliary compressed air inlet device 9 is arranged between the powder outlet valve 8 and the powder outlet 3 of the dense phase powder pump 1. As will be further described below, this auxiliary compressed air inlet device 9 serves to feed additional conveying compressed air into the powder path between the powder outlet valve 8 and the powder outlet 3 of the dense phase powder pump 1 when needed.

(17) It is to be noted at this point that it is not imperative for the auxiliary compressed air inlet device 9 to be arranged between the powder outlet valve 8 and the powder outlet 3 of the dense phase powder pump 1. The effects achievable with the auxiliary compressed air inlet device 9, which will be described in greater detail below, can also be realized when the auxiliary compressed air inlet device 9 is arranged behind the powder outlet 3 of the dense phase powder pump 1.

(18) Although not shown in the drawings, a further valve, particularly a pinch valve, is provided between the auxiliary compressed air inlet device 9 and the powder outlet 3 of the dense phase powder pump 1 in advantageous realizations of the inventive dense phase powder pump 1 which, as it is arranged directly at the powder outlet 3 of the dense phase powder pump 1, then assumes the function of the powder outlet valve.

(19) As can be seen particularly from the FIG. 1 representation, the powder inlet 2 of the dense phase powder pump 1, the powder inlet valve 7, the powder inlet 5 of the powder conveyor chamber 4, the powder conveyor chamber 4, the powder outlet 6 of the powder conveyor chamber 4, the auxiliary compressed air inlet device 9 as well as the powder outlet 3 of the dense phase powder pump 1 all lie along a common longitudinal axis L. In other words, the powder inlet 2 of the dense phase powder pump 1 is disposed at the opposite end from the powder outlet 3 of the dense phase powder pump 1.

(20) The following will describe in greater detail the structure and functioning of particularly the single powder conveyor chamber 4 of the example embodiment of the dense phase powder pump 1 depicted in the drawings.

(21) As can be noted from the longitudinal sectional view of FIG. 1 or the schematic depiction of FIG. 3, the powder conveyor chamber 4 is formed between its powder inlet 5 and its powder outlet 6 by the cylindrical wall of a tubular filter 10 which is permeable to air but not, however, to coating powder and can be made for example from sintered material. The filter 10 configured as a filter tube is surrounded by an intermediate chamber 11, its exterior limited by a housing 12 of the powder conveyor chamber 4.

(22) An air exchange vent 13 fluidly coupled to a control valve V1 leads through the housing 12 (see FIG. 3). The control valve V1 can alternatingly supply the powder conveyor chamber 4 with conveying compressed air from a compressed air supply line 50 or apply a vacuum or negative pressure from a vacuum source 52.

(23) In the embodiments of the inventive powder spray-coating device 100 depicted schematically in FIGS. 4 and 5, the vacuum source 52 comprises an injector 55 which is supplied with injector compressed air from a compressed air supply line 54, a compressed air source 58 respectively, for example by way of a pressure regulator 53 and a further control valve V2.

(24) In order for coating powder to be able to be suctioned from the first powder reservoir 101 into the powder conveyor chamber 4 via the powder inlet 2 of the dense phase powder pump 1 during a suction phase of the dense phase powder pump 1, the powder outlet valve 6 arranged at the powder outlet 6 of the powder conveyor chamber 4 is closed and the powder inlet valve 7 arranged between the powder inlet 2 of the dense phase powder pump 1 and the powder inlet 5 of the powder conveyor chamber 4 is open. At the same time that the powder outlet valve 8 and the powder inlet valve 7 are actuated, or immediately thereafter, the powder conveyor chamber 4 is connected to the vacuum source 52 by means of control valve V1 and the thereby connected air exchange vent 13, so that the powder conveyor chamber 4 is subjected to a negative pressure and coating powder can be suctioned out of the first powder reservoir 101.

(25) After the coating powder has been suctioned into the powder conveyor chamber 4, a change occurs from the suction phase to the phase of discharging coating powder from the conveyor chamber 4. To this end, the powder inlet valve 7 is closed and the powder outlet valve 8 opened while the control valve V1 fluidly connects the air exchange vent 13 and the compressed air supply line 50 so that the portion of coating powder previously suctioned into the powder conveyor chamber 4 during the suction phase is expelled through the open powder outlet valve 8 by means of the conveying compressed air supplied via the air exchange vent 13.

(26) The operating phase of suctioning coating powder via the powder inlet 2 of the dense phase powder pump 1 and via the open powder inlet valve 7 occurs again thereafter. This change of operating phases is repeated continuously.

(27) The term pump cycle as used herein is to be understood as one cycle consisting of a suction phase and a discharge phase.

(28) The valves disposed at the intake and discharge side of the powder conveyor chamber 4 (powder inlet valve 7, powder outlet valve 8) are preferably designed as pinch valves, whereby different types of valves are however also generally conceivable.

(29) The powder inlet and powder outlet valves 7, 8 respectively configured as pinch valves in the example embodiment depicted in the drawings each comprise a flexible elastic tube 14.1, 14.2 serving as the valve channel. Actuating compressed air in a pressure chamber 15.1, 15.2 surrounding the flexible elastic tube 14.1, 14.2 can squeeze the flexible elastic tube 14.1, 14.2 in order to close the respective valve (powder inlet valve 7, powder outlet valve 8).

(30) To this end, a respective air exchange vent 16 connected to a respective control valve V3, V4 is provided in each pressure chamber 15.1, 15.2. The control valves V3, V4 serve to alternatingly subject the pressure chambers 15.1, 15.2 of the two powder inlet/powder outlet valves 7, 8 respectively designed as pinch valves to excess pressure from a compressed air supply line 56.

(31) As depicted, the compressed air supply line 56 is connected to a pressure storage unit 57, wherein the pressure storage unit 57 is itself connected to a compressed air source 58. It is however of course also conceivable for the compressed air supply line 56 to be connected directly to the compressed air source 58 (i.e. without the interposition of a pressure storage unit 57).

(32) The flexible, elastic tube 14.1, 14.2 of the powder inlet valve 7 and/or powder outlet valve 8 designed as pinch valves preferably has such an elasticity or inherent tension that it automatically expands again after the pressure of the actuating compressed air in the pressure chamber 15.1, 15.2 ceases, with the respective valve channel thereby opening. In order to support the opening of the pinch valve and thus increase the switching frequency able to be realized with the dense phase powder pump 1, it is conceivable for a negative pressure to be applied via the corresponding air exchange vents 16.

(33) The inventive solution provides for different measures for the inventive single-chamber dense phase powder pump to achieve a homogeneous flow of powder downstream of the powder outlet 3 of the dense phase powder pump without disruptive pulsing.

(34) For example, the dense phase powder pump 1 is structurally designed and configured in such a manner that the pumping frequency which the dense phase powder pump 1 is able to achieve can be increased compared to the pump frequency achievable with conventional multi-chamber dense phase powder pumps. To this end, in advantageous realizations of the inventive dense phase powder pump 1, the inventive solution makes use of a material block 60 to which the powder inlet valve 7 required for the conveying of coating powder as well as the powder outlet valve 8 likewise required for the conveying of coating powder including the control valves V3, V4 required in actuating the valves 7, 8 can be affixed (not explicitly shown in the drawings). Both the powder inlet valve 7 as well as the powder outlet valve 8 and the control valves V3, V4 required for the actuation are preferably connected to channels formed in the material block 60 (not shown in the figures). The same also applies to control valve V1 which is fluidly coupled to the air exchange vent 13 of the powder conveyor chamber 4 by means of at least one channel formed in the one-piece material block 60.

(35) Arranging the respective control valves V1, V3 and V4 as well as the powder inlet and powder outlet valve 7, 8 as closely as possible to the components of the dense phase powder pump 1 to be operated in example embodiments of the dense phase powder pump 1 according to the invention prevents the occurrence of large volumes in the corresponding pressure lines to the pneumatically actuated valves 7, 8 or the corresponding pressure line to the air exchange vent 13 of the powder conveyor chamber 4 which would either have to be selectively evacuated or filled with compressed air in the alternating operation of the dense phase powder pump 1. This can thus prevent excessive response delay times, which ultimately would also limit the frequency at which the dense phase powder pump 1 could convey coating powder.

(36) As can in particular be noted from the FIGS. 1 and 2 representations, the inventive dense phase powder pump 1 advantageously exhibits a modular structure in which the powder inlet 2 of the dense phase powder pump 1, powder inlet valve 7, powder conveyor chamber 4, powder outlet valve 8 and auxiliary compressed air inlet device 9 components together with powder outlet 3 of the dense phase powder pump 1 are each designed as modular elements. In the drawings, the module which forms the powder inlet 2 of the dense phase powder pump 1 is identified by reference numeral 61 while module 62 arranged downstream thereof constitutes the powder inlet valve 7. Modules 63 and 64 form the powder conveyor chamber 4 and the powder outlet valve 8 while module 65 forms the combination of auxiliary compressed air inlet device 9 and powder outlet 3 of the dense phase powder pump 1. The individual modules 61, 62, 63, 64 and 65 are axially arranged relative to the common longitudinal axis L and mounted on the material block 60 one after the other.

(37) The modular structure to the dense phase powder pump 1 considerably simplifies the maintenance of the pump since the pump's individual modules 61, 62, 63, 64 and 65 can be particularly easily and particularly quickly replaced by respective other components when needed, for example in case of failure or for the purpose of servicing and/or cleaning.

(38) Using a total of only two powder valves preferably configured as pinch valves (powder inlet valve 7 and powder outlet valve 8) in the inventive dense phase powder pump 1 significantly reduces the pump's susceptibility to failures compared to conventional multi-chamber dense phase powder pumps in which at least four powder valves and a correspondingly higher number of control valves for controlling the powder valves need to be employed. In particular, the number of parts subject to wear is reduced to a minimum in the inventive dense phase powder pump 1 such that the settings of the dense phase powder pump 1 require significantly less frequent adjusting due to expendable parts and high reproducibility of the pump's settings is ensured.

(39) The single-chamber design of the inventive dense phase powder pump 1 moreover allows a particularly compact structure to the pump. For example, in the case of a dense phase powder pump 1 having a pump length of approximately 250 mm, up to 400 g coating powder can thus be conveyed per minute (pump width: 40 mm).

(40) In the example embodiments of the inventive dense phase powder pump 1 depicted in the drawings, the previously cited auxiliary compressed air inlet device 9 is however particularly provided to reduce or prevent pulsations downstream of the powder outlet 3 of the dense phase powder pump 1, same being provided at the outlet of the powder outlet valve 8, or powder outlet 3 of the dense phase powder pump 1 respectively, so as to be able to feed auxiliary conveying compressed air into the powder path at that point as needed.

(41) In the implementations of the auxiliary compressed air inlet device 9 employed in the example embodiments of the inventive dense phase powder pump 1 depicted in the drawings, same comprises a filter tube 17 having a circumference of at least 180 (in the depicted embodiments, the circumference is 360) and forming a channel wall inner surface over at least 180 (in the embodiments depicted in the drawings, the channel wall inner surface covers 360) of the circumference of the powder path at least over part of the length of the corresponding powder path.

(42) In other words, in the depicted embodiments of the dense phase powder pump 1 according to the invention, the auxiliary compressed air inlet device 9 has a filter tube 17 surrounding the corresponding powder path by 360 over at least part of its length so that the portion of powder expelled from the powder conveyor chamber 4 of the dense phase powder pump 1 during a powder discharge phase can flow homogeneously through the filter tube channel 18 formed by the filter tube 17.

(43) A compressed air chamber 19 designed as an annular compressed air chamber in the embodiment depicted in the drawings surrounds the outer circumference of the filter tube 17. The radially inner circumference of the compressed air chamber 19 configured here as an annular compressed air chamber is surrounded by the filter tube 17 and its radially outer circumference by a housing 20 at a distance from the filter tube 17. An air exchange vent 21 is provided in the housing 20 via which compressed air can flow as needed from a compressed air line 59 into the compressed air chamber 19 by way of a control valve V5 and from there through the filter tube 17 into the filter tube channel 18.

(44) Depending on the amount of auxiliary conveying compressed air to be fed into the powder path per unit of time, the compressed air chamber 19 and the filter tube channel 18 formed by the filter tube 17 are to be of correspondingly large-volume configuration.

(45) As indicated above, the filter tube 17 of the auxiliary compressed air inlet device 9 is made of a microporous material so as to be permeable to air but not to coating powder. The filter tube 17 preferably consists of a sintered body, for example of metal or plastic, or of a material mixture containing metal or plastic. It can further consist of one material and/or be formed by a filter membrane.

(46) The filter pores of the filter tube 17 are preferably designed such that compressed air is directed over a large powder path area both in the circumferential direction as well as in the longitudinal direction of the powder path. The micropores of the powder tube 17 can be radially or axially inclined toward the powder path and/or run from the filter tube 17 into the filter tube channel 18 tangentially to the powder path circumference and direct the compressed air accordingly. The large inner circumferential surface of the filter tube 17 can homogenize the axial distribution of powder in the filter tube channel 18 and thus also in the powder path downstream of the powder outlet 3 of the dense phase powder pump 1 with a small volume of compressed air. This can prevent or at least reduce pulses in the powder flow along the powder path. Homogenization of the powder density in the longitudinal direction and over the cross section of the powder path can furthermore be achieved.

(47) The amount of conveying compressed air fed into the powder path per unit of time can be kept so low that it has no or only a small influence on the flow rate of the coating powder in the flow path. There is additionally the possibility of increasing the flow volume to influence the flow rate of the coating powder by increasing the pressure of the conveying compressed air additionally supplied by the auxiliary compressed air inlet device 9.

(48) The compressed air additionally fed as needed into the powder path of the dense phase powder pump 1 by the auxiliary compressed air inlet device 9 can flow from the filter tube 17 into the filter tube channel 18 in the form of streams or in the form of small bubbles depending on the type of the filter pores and the air pressure.

(49) The filter tube 17 of the auxiliary compressed air inlet device 9 is to extend around the powder path over at least 180 of the powder path circumference, preferably the full 360 of the powder path circumference.

(50) The filter tube 17 of the auxiliary compressed air inlet device 9 is preferably a rigid body but can also be a flexible body.

(51) In accordance with one preferential embodiment of the invention, the auxiliary compressed air of the auxiliary compressed air inlet device 9 is supplied in pulses at a pulse frequency which is equal to or preferably greater than the frequency of the powder conveyor chamber 4 at which the powder conveyor chamber 4 dispenses the portions of powder. The auxiliary compressed air inlet device 9 can be provided with a pulsating source of compressed air or a compressed air pulse generator for this purpose.

(52) In accordance with a further advantageous embodiment of the invention, a control unit 90 is provided which is designed so as to be able to adjust the pulse frequency of the auxiliary compressed air supplied by the auxiliary compressed air inlet device 9 as a function of the powder output frequency of the powder conveyor chamber 4 in at least one of the following ways: for example as a manual adjustment and/or preferably automatically controllable or preferably regulatable. The auxiliary compressed air pulse frequency can thereby be advantageously increased with increasing powder output frequency and reduced with decreasing powder output frequency.

(53) In accordance with a further preferential embodiment of the invention, the control unit 90 can be advantageously designed so as to adjust the amount of auxiliary compressed air flowing through the auxiliary compressed air inlet device 9 per unit of time as a function of the amount of powder conveyed in at least one of the following ways: for example as a manual adjustment and/or preferably automatically controllable or preferably regulatable.

(54) The control unit 90 of the powder spray-coating device 100 can be designed for the cited adjusting of the auxiliary compressed air pulse frequency or the cited adjusting of the auxiliary compressed air volume or for both adjustments. The control unit 90 can contain all the control elements or two or more control units can be provided. If desired, the auxiliary compressed air pulse frequency or the auxiliary compressed air flow volume can be manually set, a respective manual adjusting element can be provided thereto.

(55) As indicated above, the powder inlet valve 7 and the powder outlet valve 8 of the inventive dense phase powder pump 1 are each preferably realized as a pinch valve since less coating powder can accumulate in pinch valves than in other types of valves and since powder deposits can be easily cleared by the air flowing through them. Pinch valves are valves able to be controlled by means of compressed air or by means of negative pressure. In principle, however, other controllable valves can also be used. There is moreover the possibility of using automatic valves, for example ball valves or check valves, instead of controllable valves which are controlled by the difference in pressure between the valve inlet side and the valve outlet side and thus automatically by the excess pressure and negative pressure prevailing in the powder conveyor chamber 4.

(56) The above cited control unit 90 which is schematically suggested in FIG. 3 is used to control the operation of the dense phase powder pump 1. The control unit 90 is designed to appropriately actuate the individual controllable components of the dense phase powder pump 1, particularly the control valves V1, V2, V3, V4 and V5 and coordinate their operation.

(57) A further control valve V6 is provided in the embodiments of the inventive powder spray-coating device depicted schematically in FIGS. 4 and 5, by means of which the powder conveyor chamber 4 is subjected to high pressure during a cleaning cycle of the dense phase powder pump 1.

(58) The control unit 90 is preferably designed so as to open the control valve V4 in preparation of the suction phase of the powder conveyor chamber 4 so that the compressed air provided in the pressure storage unit 57 or by the compressed air source 58 respectively is directed via the compressed air supply line 56 and the air exchange vent 16 into the pressure chamber 15.2 of the powder outlet valve 8 designed as a pinch valve. As a consequence, the flexible elastic tube 14.2 of the powder outlet valve 8 designed as a pinch valve is squeezed, resulting in the closing of the powder path through the powder outlet valve 8 provided by the flexible elastic tube 14.2.

(59) With the closing of the powder outlet valve 8, the control unit 90 fluidly couples the air exchange vent 13 provided in the housing 12 of the powder conveyor chamber 4 to the vacuum source 52 so as to generate a negative pressure inside the powder conveyor chamber 4 such that coating powder can be suctioned into the powder conveyor chamber 4 via powder inlet 2 of the dense phase powder pump 1 and (open) powder inlet valve 7 as well as powder inlet 5 of the powder conveyor chamber 4.

(60) In accordance with preferential embodiments of the invention, the control unit 90 produces a control signal in initiating the suction phase of the dense phase powder pump 1 to generate the negative pressure in the powder conveyor chamber 4 at the earliest simultaneously to or preferably after a predetermined delay period following a control signal for opening the powder inlet valve 7 so that the negative pressure in the powder conveyor chamber 4 begins to build at the earliest at the same time the powder inlet valve 7 opens, preferably after the cited predetermined delay period following the opening of the powder inlet valve 7. The predetermined delay period is preferably in the range of between 0 ms and 50 ms at a powder conveyor chamber 4 conveyance cycle of approximately 200 ms.

(61) Doing so thereby achieves the negative pressure in the powder conveyor chamber 4 having a weaker counteraction on an opening movement of the powder inlet valve 7, particularly if it is a pinch valve, at least at the time the powder inlet valve 7 begins its opening movement, than is the case in the prior art where the pressure usually already drops in the respective powder conveyor chamber prior to the opening of the powder inlet valve.

(62) The control valve V3 is thereafter fluidly coupled to the compressed air supply line 56, in consequence of which an excess pressure is applied in the pressure chamber 15.1 of the powder inlet valve 7 designed as a pinch valve which effects a squeezing of the flexible elastic tube 14.1 of the powder inlet valve 7 designed as a pinch valve. Doing so closes the powder inlet valve 7. Control valve V4 depressurizes the air exchange vent 17 of the pressure chamber 15.2 of the powder outlet valve 8 designed as a pinch valve or evacuates the air from the pressure chamber 15.2 respectively. Due to the elasticity of the tube 14.2 of the powder outlet valve 8 designed as a pinch valve, it then immediately changes into its open state.

(63) At this instant or immediately thereafter, the control valve 90 switches control valve V1 so as to fluidly couple the air exchange vent 13 disposed in the housing 12 of the powder conveyor chamber 4 to the compressed air source 58. The compressed air then flows via the compressed air supply line 50, the control valve V1, the intermediate chamber 11 and the filter element 10 into the powder conveyor chamber 4 and expels the portion of powder previously suctioned inside through the powder outlet 6 of the powder conveyor chamber 4.

(64) With the help of the conveying compressed air fed into the powder conveyor chamber 4 via the compressed air supply line 50, the portion of powder is then further conveyed through the open powder outlet valve 8, the filter tube channel 18 of the auxiliary compressed air inlet device 9 and the powder outlet 3 of the dense phase powder pump 1.

(65) The control unit 90 is in particular designed to pulse auxiliary conveying compressed air into the powder path between the powder outlet valve 8 and the powder outlet 3 of the dense phase powder pump 1 via auxiliary compressed air inlet device 9. It has hereby proven advantageous for the auxiliary conveying compressed air fed into the powder path via the auxiliary compressed air inlet device 9 in pulses to be continuously supplied over the entire powder conveyor chamber 4 suction phase or during a predetermined or predeterminable part of the suction phase so as to thereby effectively prevent and/or minimize pulsations in the flow of powder discharged from the dense phase powder pump 1.

(66) Specifically, the control unit 90 is to this end designed to fluidly connect the air exchange vent 21 of the compressed air chamber 19 of the auxiliary compressed air inlet device 9 to the compressed air source 58 whenever the powder outlet valve 8 is closed.

(67) In the embodiments of the inventive powder spray-coating device 100 depicted in FIGS. 4 and 5, the individual compressed air supply lines 50, 54, 56 and 59 run into a controller 91 which coordinates and controls the compressed air supply of the individual components of the powder spray-coating device 100. In particular, the controller 91 can also set the amount of auxiliary compressed air fed to the powder spray-coating gun 102 per unit of time via compressed air inlet 106 of the powder spray-coating gun 102, which serves in the atomizing, forming and/or otherwise influencing of the coating powder to be sprayed by the powder spray-coating gun 102, and/or the amount of electrode flushing air fed to the powder spray-coating gun 102 per unit of time via the compressed air inlet 107 of the powder spray-coating gun 102.

(68) As can particularly be noted from the schematic representation provided in FIG. 5, it is advantageous to employ components for the feeding of the auxiliary compressed air into the powder path which are structurally identical here to the components of the powder conveyor chamber which feed conveying compressed air into the powder conveyor chamber 4 during the discharge phase. To be understood by the term structurally identical as used herein is in particular the size and the structure of the filter tube 17 used in the auxiliary compressed air inlet device 9 and the filter 10 used in powder conveyor chamber 4. This measure ensures that the conveying compressed air introduced into the powder conveyor chamber 4 during the discharge phase undergoes the same pneumatic resistance as the auxiliary compressed air fed into the powder path downstream of the powder outlet valve 8 by way of the auxiliary compressed air inlet device 9 during the powder suction phase.

(69) The inventive solution is not limited to a dense phase powder pump 1 having a powder inlet 2 at a first end region and a powder outlet 3 at an opposite second end region as shown in the representations pursuant to FIGS. 1 to 5. In fact, the inventive solution is also suited to embodiments in whichas FIGS. 6 and 7 depict schematicallythe single powder conveyor chamber 4 of the dense phase powder pump 1 comprises a powder 30 at an end region which serves both as powder inlet as well as powder outlet for the powder conveyor chamber 4. In the embodiments depicted in FIGS. 6 and 7, the powder inlet 2 of the dense phase powder pump 1 is fluidly coupled to the powder passageway 30 of the powder conveyor chamber 4 via powder inlet valve 7 and the powder outlet 3 of the dense phase powder pump 1 fluidly coupled to the powder passageway 30 of the powder conveyor chamber 4 via powder outlet valve 8. A distributor 31 is in particular employed here, configured in the embodiments depicted in FIGS. 6 and 7 as a Y-piece. Said distributor 31 fluidly couples the powder passageway 30 of the powder conveyor chamber 4 to the powder inlet valve 7 on one side and to the powder outlet valve 8 on the other side.

(70) The embodiment of the dense phase powder pump 1 schematically depicted in FIG. 7 differs from the embodiment shown in FIG. 6 by the auxiliary compressed air inlet device 9 being of identical configuration to the conveying compressed air inlet device of the powder conveyor chamber 4 in order to equalize the pneumatic resistances occurring upon the introduction of conveying compressed air and upon the introduction of auxiliary compressed air.

(71) The structure and functioning of the remaining components of the embodiments depicted in FIGS. 7 and 8 correspond to the components of the embodiments according to FIGS. 1 to 5, whereby reference is made in this context to the previous remarks.

(72) The invention is not limited to the example embodiments of the inventive dense phase powder pump depicted in the drawings but rather yields from a synopsis of all the features disclosed herein together.