Patent Application
20140048015
The invention relates to a screen insert according to the preamble of independent patent claim 1.
Accordingly, the invention relates in particular to a screen insert for a powder container of a powder supplying device, the screen insert having a screen unit for screening coating powder and an ultrasonic transducer for generating ultrasonic vibrations, the screen unit being connected to the ultrasonic transducer in such a way that the ultrasonic vibrations generated by the ultrasonic transducer can be transferred to the screen unit.
With the increasing quality requirements in powder coating, the screening technique is playing an increasingly important role. It is known in this connection from powder coating technology to use ultrasonic screening systems, which are particularly distinguished by their high screening performance in comparison with classical vibration screens. The screening of the coating powder is intended to separate out contaminants from the coating powder and break up or keep back agglomerations of powder that may occur in particular as a result of mechanical action during the conveying of coating powder. It is intended in this way to ensure that, in the powder coating mode, the coating powder is always fed to the powder spraying device with a consistent high quality.
The screen insert according to the invention is suitable in particular for supplying power to a powder coating installation which is used for the electrostatic spray coating of objects with powder and in which fresh coating powder (hereafter also referred to as “fresh powder”) and possibly recovered coating powder (hereafter also referred to as “recovery powder”) are located in the powder container and are fed to a spraying device by a powder discharge device, for example in the form of an injector. The spraying device may be, for example, a handheld gun or an automatic gun.
As and when required, fresh powder is fed from a supplier's container, in which the powder supplier supplies the fresh powder to the powder user, to the powder container by way of a fresh powder line.
In the supplier's container, the powder forms a compact mass. By contrast, the coating powder in the powder container should be in a fluidized state, in order for example that it can be sucked out by the suction effect of an injector and fed to the spraying device in a stream of compressed air. A powder supplying device consequently includes in particular a powder container which serves as a powder chamber for keeping coating powder, the coating powder usually being fluidized in the powder container in order that it can be pneumatically conveyed easily, either to another powder container or to a powder spraying device. As already stated, the powder spraying device may be a manual or automatic powder spraying device, which may have a spray nozzle or a rotary atomizer.
The invention is based on the object of making the powder feed to a powder spraying device more effective, with the intention in particular that the powder that is fed is of a consistent high quality.
This object is achieved according to the invention by the features of independent patent claim 1.
Accordingly, the invention relates to a screen insert for a powder container of a powder supplying device, the screen insert having a screen unit for screening coating powder and an ultrasonic transducer for generating ultrasonic vibrations, the screen unit being connected to the ultrasonic transducer in such a way that the ultrasonic vibrations generated by the ultrasonic transducer can be transferred to the screen unit. The invention is particularly distinguished by the compact construction of the ultrasonic screen insert. For this purpose, according to the invention a screen carrier which can be placed onto the powder container is provided, serving and designed for holding the ultrasonic transducer, with the screen unit connected thereto, in such a way that the screen unit is arranged below the screen carrier, so that the screen unit is inside a powder chamber, formed by the powder container, when the screen carrier has been placed onto the powder container.
The object according to the invention is also achieved by a powder supplying device for a powder coating installation, the powder supplying device having at least one powder container with a powder chamber for coating powder, and the at least one powder container being assigned a screen insert of the aforementioned type, the screen carrier of the screen insert being configured as a cover 23, matching the powder container, and being placed or able to be placed onto the powder container in such a way that the screen unit of the screen insert is inside the powder chamber defined by the powder container.
The advantages that can be achieved with the solution according to the invention are obvious: in particular, an ultrasonic screen insert that can be integrated as an operational unit in a powder container is provided. The powder container is preferably a fluidized powder container, i.e. a powder container which has a fluidizing device for introducing fludizing compressed air into the powder chamber. In this case, it is of advantage if the powder container has at least one outlet, leading out of the powder chamber, in order to be able to discharge the fludizing compressed air introduced into the powder chamber and thereby automatically create a pressure equalization. Of course, the screen insert according to the invention is suitable not only in connection with a fluidized powder container. Rather, it is equally conceivable to integrate the screen insert according to the invention in a non-fluidized powder container.
Since, in the case of the screen insert according to the invention, the screen unit that serves for screening the coating powder is arranged below the screen carrier and is connected to this screen carrier in such a way that the screen unit is inside the powder chamber of the powder container when the screen carrier has been placed onto the powder container, this provides a compactly configured screen unit which can be placed as a subassembly onto the powder container, in order to integrate the screen unit that can be excited by ultrasonic vibrations in the powder chamber of the powder container.
In a preferred implementation of the solution according to the invention, it is provided that the screen unit is connected to the ultrasonic transducer by way of an angle connection, in particular an L-shaped angle connection, the ultrasonic transducer being fastened to the screen carrier. The screen carrier is preferably formed as a container cover 23, matching the powder container, so that the screen carrier can be used instead of a conventional standard container cover 23s for covering the powder container. As already stated, the screen unit of the screen insert is then inside the powder chamber.
In this connection, it is of advantage if a fastening device, in particular a quick-action clamping means, such as for instance a vertical clamping means, is also provided, in order to fix the screen carrier, formed as a container cover 23, in relation to the powder container in the state in which it has been placed onto the powder container. Of course, however, other embodiments come into consideration for releasably fixing the screen carrier.
In a preferred configuration of the screen unit it is provided that it has a screen frame, surrounding a screen area, and a screen, held by the screen frame, the ultrasonic transducer being connected to the screen frame. It is conceivable here that the screen comprises a screen mesh with a previously specifiable or specified mesh width, the screen mesh preferably being releasably fastened to the screen frame (clamped on).
It should be noted here that the screen mesh width of the screen can be kept very small in comparison with the screen mesh width of conventional vibration screens, since according to the invention the screen is excited by ultrasonic vibrations. In this way, particularly fine screening of the coating powder can be carried out. In particular, possible contaminants and/or agglomerations of powder that may occur as a result of mechanical action during the conveying of coating powder can be effectively kept back or broken up by the screen of the screen insert.
The fact that, according to the invention, the screen insert is configured as a compact subassembly, with the screen carrier of the screen insert being used instead of a conventional container cover 23s and in this way allowing the screen unit to be integrated in the powder chamber, makes it possible that the coating powder is screened directly upstream of the powder injectors, so that there is no need for other screening devices, such as for instance screening devices in the lower powder run-out region of a cyclone separator. In other words, the screen insert according to the invention makes it possible that the screening of the coating powder can be performed in the fluidized powder container, that is to say directly before the fluidized powder is fed to the powder spraying devices by way of a powder supply line.
Exemplary embodiments of the solution according to the invention are described below with reference to the accompanying drawings, in which:
a shows a plan view of a powder container with a screen insert according to the invention for the screening of fresh powder and recovery powder;
b shows a plan view of a powder container with a screen insert according to the invention for the screening of fresh powder only;
c shows a plan view of a powder container with a screen insert according to the invention for the screening of recovery powder only; and
d shows a plan view of a conventional powder container without a screen insert.
Powder pumps 4 are provided for pneumatically conveying the coating powder. These pumps may be injectors into which coating powder is sucked out of a powder container by means of compressed air serving as conveying air, after which the mixture of conveying air and coating powder together flows into a container or to a spraying device.
Suitable injectors are known, for example, from the document EP 0 412 289 B1.
It is possible also to use as the powder pump 4 those types of pump which convey small portions of powder one after the other by means of compressed air, a small portion of powder (amount of powder) being respectively stored in a powder chamber and then forced out of the powder chamber by means of compressed air. The compressed air remains behind the portion of powder and pushes the portion of powder in front of it. These types of pump are sometimes referred to as compressed-air feed pumps or plug-conveying pumps, since the compressed air pushes the stored portion of powder in front of it through a pump outlet line like a plug.
Various types of such powder pumps for conveying dense coating powder are known, for example, from the following documents: DE 103 53 968 A1, U.S. Pat. No. 6,508,610 B2, US 2006/0193704 A1, DE 101 45 448 A1 or WO 2005/051549 A1.
To generate the compressed air for the pneumatic conveyance of the coating powder and to fluidize the coating powder, a compressed air source 6 is provided, connected to the various devices by way of corresponding pressure setting elements 8, for example pressure controllers and/or valves.
Fresh powder from a powder supplier is fed from a supplier's container, which may be for example a small container 12, for example in the form of a dimensionally stable container or a sack with an amount of powder of for example between 10 and 50 kg, for example 35 kg, or for example a large container 14, for example likewise a dimensionally stable container or a sack, with an amount of powder between for example 100 kg and 1000 kg, by means of a powder pump 4 in a fresh powder line 16 or 18 to a screening device 10. The screening device 10 may be provided with a vibrator 11.
In the following description, the expressions “small container” and “large container” each mean both a “dimensionally stable container” and a “not dimensionally stable, flexible sack”, unless reference is expressly made to one or the other type of container.
The coating powder screened by the screening device 10 is conveyed by gravitational force, or preferably in each case by a powder pump 4, by way of one or more powder supply lines 20, 20′ through powder-inlet openings 26, 26′ into a powder chamber 22 of a dimensionally stable powder container 24. The volume of the powder chamber 22 is preferably much smaller than the volume of the small fresh-powder container 12.
However, the provision of a screening device 10 in the fresh powder line 16 or 18 is not absolutely necessary, but only optional. The use of a screen insert 70, which is not explicitly represented in
Embodiments of the screen insert 70 that are not explicitly represented in
It is conceivable that the powder pump 4 of the at least one powder supply line 20, 20′ to the powder container 24 is formed as a compressed-air feed pump.
Here, the initial portion of the powder supply line 20 may serve as a pump chamber into which powder screened by the screening device 10 optionally falls through a valve, for example a pinch valve. Once this pump chamber contains a certain portion of powder, the powder supply line 20 is isolated in terms of flow by closing the valve of the screening device 10. After that, the portion of powder is pushed into the powder chamber 22 by means of compressed air through the powder supply line 20, 20′.
Powder pumps 4, for example injectors, for conveying coating powder through powder lines 38 to spraying devices 40 are connected to one or preferably a number of powder outlet opening(s) 36 of the powder container 24. The spraying devices 40 may be spray nozzles or rotary atomizers for spraying the coating powder 42 onto the object 2 to be coated, which is preferably located in a coating cubicle 43.
The powder outlet openings 36 may be located—as represented in FIG. 1—in a wall of the powder container 24 that lies opposite the wall in which the powder inlet openings 26, 26′ are located. In the case of the embodiments of the powder container 24 represented in
The powder outlet openings 36 are preferably arranged near the bottom of the powder chamber 22.
The powder chamber 22 is preferably of a size that lies in the range of a coating powder capacity of between 1.0 kg and 12.0 kg, preferably between 2.0 kg and 8.0 kg. According to other aspects, the size of the powder chamber 22 is preferably between 500 cm3 and 30 000 cm3, preferably between 2000 cm3 and 20 000 cm3. The size of the powder chamber 22 is chosen in dependence on the number of powder outlet openings 36 and the powder lines 38 connected thereto, in such a way that continuous spray coating operation is possible, but the powder chamber 22 can be quickly cleaned, preferably automatically, during coating breaks for changing the powder.
The powder chamber 22 may be provided with a fluidizing device 30 for fluidizing the coating powder received in the powder container 24. The fluidizing device 30 contains at least one fluidizing wall of a material with open pores or provided with narrow bores, which is permeable to compressed air but not to coating powder. Although not shown in
Coating powder 42 that does not adhere to the object 2 to be coated is sucked into a cyclone separator 48 as excess powder by means of a stream of suction air of a blower 46 by way of an excess powder line 44. In the cyclone separator 48, the excess powder is separated as far as possible from the stream of suction air. The separated powder fraction is then conducted as recovery powder from the cyclone separator 48 by way of a powder recovery line 50 to the optionally provided screening device 10, where it passes through the screening device 10, either alone or mixed with fresh powder, by way of the powder supply lines 20, 20′ back into the powder chamber 22.
As already indicated, it is possible to dispense with the screening device 10 if, according to the invention, the powder container 24 is provided with a screen insert 70, so that the fresh powder and/or recovery powder fed to the powder chamber 22 is screened by the screen insert 71 integrated in the powder chamber 22. The screening of the coating powder (fresh powder and/or recovery powder) fed to the powder container 24 inside the powder chamber 22, and consequently directly before the coating powder is conveyed by way of powder pumps 4, in particular injectors, through powder lines 38 to the spraying devices 40, guarantees a consistent high quality of the coating powder that is fed to the spraying devices 40.
Depending on the kind of powder and/or the degree of powder contamination, the possibility of isolating the powder recovery line 50 from the optionally provided screening device 10 and conducting the recovery powder into a waste container may also be provided, as schematically represented in
The powder container 24 may have one or more, for example two, sensors S1 and/or S2, in order to control the supply of coating powder into the powder chamber 22 by means of the control device 3 and the powder pumps 4 in the powder supply lines 20, 20′. For example, the lower sensor S1 detects a lower powder level limit and the upper sensor S2 detects an upper powder level limit.
The lower end portion 48-2 of the cyclone separator 48 may be formed and used as a storage container for recovery powder and provided for this purpose with one or more, for example two, sensors S3 and/or S4, which are functionally connected to the control device 3. This allows, for example, the feeding of fresh powder through the fresh powder supply lines 16 and 18 to be automatically stopped as long as there is sufficient recovery powder in the cyclone separator 48 to feed recovery powder to the powder chamber 22 in a sufficient amount required for the spray coating operation by means of the spraying devices 40. If there is no longer sufficient recovery powder in the cyclone separator 48, it is possible to switch over automatically to the feeding of fresh powder through the fresh powder supply lines 16 or 18. Furthermore, there is also the possibility of feeding fresh powder and recovery powder to the optionally provided screening device 10 or the pump chamber 22 at the same time, so that they are mixed with each other.
The exhaust air of the cyclone separator 48 passes by way of an exhaust-air line 54 into an after-filtering device 56 and through one or more filter elements 58 therein to the blower 46 and after that into the outside atmosphere. The filter elements 58 may be filter bags or filter cartridges or filter plates or similar filter elements. The powder separated from the stream of air by means of the filter elements 58 is normally waste powder and falls by gravitational force into a waste container or, as shown in
Depending on the kind of powder and the powder coating conditions, the waste powder may also be recovered again, to re-enter the coating cycle. This is schematically represented in
In the case of multi-color operation, in which different colors are respectively sprayed only for a short time, the cyclone separator 48 and the after-filtering device 56 are usually used and the waste powder of the after-filtering device 56 passes into the waste container 62. Although the powder separating efficiency of the cyclone separator 48 is usually less than that of the after-filtering device 56, it can be cleaned more quickly than the after-filtering device 56. In the case of single-color operation, in which the same powder is used for a long time, it is possible to dispense with the cyclone separator 48 and to connect the excess powder line 44 to the after-filtering device 56 instead of the exhaust-air line 54, and to connect the waste lines 60, which in this case contain powder to be recovered, as recovery powder lines by way of the optionally provided screening device 10 or directly to the powder container 24.
In the case of single-color operation, the cyclone separator 48 is usually only used in combination with the after-filtering device 56 when a problematic coating powder is involved. In this case, only the recovery powder of the cyclone separator 48 is fed by way of the powder recovery line 50 and optionally by way of the screening device 10 or directly to the screen unit 71 integrated in the powder chamber 22 (cf.
The lower end of the cyclone separator 48 may have an outlet valve 64, for example a pinch valve. Furthermore, a fluidizing device 66 for fluidizing the coating powder may be provided above this outlet valve 64, in or at the lower end of the lower end portion 48-2, formed as a storage container, of the cyclone separator 48. The fluidizing device 66 contains at least one fluidizing wall 80 of a material which has open pores or is provided with narrow bores and is permeable to compressed air but not to coating powder. The fluidizing wall 80 is arranged between the powder path and a fluidizing compressed-air chamber 81. The fluidizing compressed-air chamber 81 can be connected to the compressed air source 6 by way of a pressure setting element 8.
The fresh powder line 16 and/or 18 may be connected in terms of flow at its upstream end, either directly or through the powder pump 4, to a powder conveying tube 99, which can be immersed in the supplier's container or 14 for sucking out fresh coating powder. The powder pump 4 may be arranged at the beginning, at the end or in between in the fresh powder line 16 or 18 or at the upper or lower end of the powder conveying tube 99.
Two or more small containers 12 each in a sack receiving hopper 94 and/or two or more large containers 14, which can be alternatively used, may be provided. As a result, a quick change from one to another small container 12 or large container 14 is possible.
Although not shown in
In the case of the embodiments represented in
An exemplary embodiment of a powder container 24 of a powder supplying device for a powder coating installation 1 is described in detail below with reference to the representations in
As represented in
The powder containers 24 represented in
In the case of the exemplary embodiment represented in
In this connection, reference should be made to the representation in
Of course, however, it is also conceivable that, in the powder coating mode of the powder coating installation 1, both recovery powder and fresh powder can be fed, as and when required, by way of the inlet opening from one and the same powder inlet 20-2, 20-1.
In the case of both embodiments represented in
In order that, during the operation of the fluidizing device 30, the pressure within the powder chamber 22 does not exceed a previously specified maximum pressure, the powder chamber 22 has at least one fluidizing compressed-air outlet 31 with an outlet opening for removing the fluidizing compressed air introduced into the powder chamber 22 and for bringing about a pressure equalization. In particular, the outlet opening of the at least one fluidizing compressed-air outlet 31 should be dimensioned in such a way that, during the operation of the fluidizing device 30, there is in the powder chamber 22 a positive pressure of at most 0.5 bar with respect to atmospheric pressure.
In the case of the embodiments represented in
As revealed particularly by the representation in
For removing the fluidizing compressed air introduced into the powder chamber 22, it is also conceivable to provide a venting line which preferably protrudes into the upper region of the powder chamber 22. The protruding end of the venting line may protrude into an intake funnel of an extraction installation. This extraction installation may be configured for example as a booster (air mover). A booster, which is also known as an “air mover”, operates on the basis of the Coanda effect and requires for its drive customary compressed air, which must be supplied in a small amount. This amount of air has a higher pressure than the ambient pressure. The booster produces in the intake funnel an air flow of high velocity, with great volume and low pressure. Therefore, a booster is particularly well suited in connection with the venting line or the fluidizing compressed-air outlet 31.
In the case of the exemplary embodiment represented in
Preferably, the level sensor S1, S2 for detecting the powder level in the powder chamber 22 is a contactlessly operating level sensor and is arranged outside the powder chamber 22, separate from it. As a result, soiling of the level sensor S1, S2 is prevented. The level sensor S1, S2 generates a signal when the powder level has reached a certain height. It is also possible for a number of such powder level sensors S1, S2 to be arranged at different heights, for example for detecting predetermined maximum levels and for detecting a predetermined minimum level.
The signals of the at least one level sensor S1, S2 are preferably used for controlling an automatic powder supply of coating powder through the powder inlets 20-1, 20-2 into the powder chamber 22, in order to maintain a predetermined level or a predetermined level range therein even during the time period while the injectors 111 are sucking coating powder out of the powder chamber 22 and pneumatically conveying it to spraying devices 40 (or into other containers).
During such a powder spray coating mode, cleaning compressed air is not conducted into the powder chamber 22, or is conducted only with reduced pressure.
As revealed by the representation in
The powder container 24 shown in
As represented in
The powder discharge openings 36 are arranged as deeply as possible in the powder chamber 22, in order to be able as far as possible to suck out all of the coating powder from the powder chamber 22 by means of the injectors 111. The injectors 111 are preferably located at a point higher than the highest powder level and are respectively connected to one of the powder discharge openings 36 by a powder discharge or powder intake channel 100. The powder discharge openings 36 correspond here to the powder intake openings of the powder intake channels 100. The fact that the injectors 111 are arranged higher than the maximum powder level avoids the coating powder rising up out of the powder chamber 22 into the injectors 111 when the injectors 111 are not switched on.
As represented in
In the case of the embodiments represented in
Possible embodiments of the solution according to the invention are described below with reference to the representations in
As shown, the screen insert 70 has a screen unit 71, which has a screen frame 76, surrounding a screen area S, and a screen 77, held by the screen frame 76. In the case of the embodiment represented, the screen 77 is a screen mesh with a previously specifiable or specified mesh width, the screen mesh preferably being releasably fastened to the screen frame 76.
The screen insert 70 according to the invention also has a screen carrier 73. In the case of the embodiment represented, the screen carrier is configured as a container cover 23, matching the powder container 24 and inserted in the container cover opening 91 of the powder container 24. In the inserted state, the screen carrier 73, configured as a container cover 23, is releasably fixed in the container cover opening 91 of the powder container 24 with the aid of a vertical clamping means 75.
The screen insert 70 according to the invention also has an ultrasonic transducer 72, which can be connected to an ultrasonic generator (not represented). The ultrasonic transducer 72 is connected accessibly from the outside to the screen carrier 73 configured as a container cover 23. In the embodiment represented, the lower end portion of the ultrasonic transducer 72 is inserted in a bore provided in the screen carrier 73 and is fixed there, for example by adhesive bonding. Of course, however, it is also conceivable to connect the ultrasonic transducer 72 releasably to the screen carrier 73. For example, the ultrasonic transducer 72 may have a threaded portion and be able to be screwed into a corresponding counter-thread provided in the screen carrier 73.
As revealed particularly by the representation in
The invention is distinguished by the fact that the screen insert 70 is configured in the form of a compact component which can be inserted into any desired powder container 24 without the powder container 24 having to be structurally modified for this. It is merely required to remove the standard cover 23 or the upper top wall 90 of the powder container 24 and insert the screen carrier 73, configured as a container cover 23, into the cover opening 91 of the powder container 24. In the inserted state (cf.
In the case of the embodiment represented in
In the case of the embodiment represented in
In
It is of course also optionally conceivable in this respect, however, that both the recovery powder and the fresh powder are screened by the screen unit 71. In this case, the fresh-powder feed opening 20-1 should be arranged in the top wall of the powder chamber 22 in such a way that the fresh powder fed by way of the fresh-powder feed opening 20-1 also falls onto the screen area S of the screen unit 71 (cf.
On the other hand, it is also conceivable—as represented in
In
On the other hand, however, it is also possible that the screen carrier 73 of the screen unit 70 is made compatible with the upper top wall 90 of the powder container 24. In such a case, a conventional powder container 24, such as that shown for example in
To make it possible for the screen unit 70 or the screen carrier 73 to be inserted as easily as possible in the container cover opening 91, corresponding handles 79 are preferably provided on the screen carrier 73.
To sum up, the invention proposes an ultrasonic screen or ultrasonic screen insert which can be integrated as an operational unit in a container—preferably a fluidized powder container. In the case of the exemplary embodiment, the ultrasonic screen insert 70 is installed in the powder container 24 of a powder coating installation 1. However, the ultrasonic screen insert 70 according to the invention is suitable for any desired fluidized or non-fluidized powder container.
A fundamental idea of the invention is that a compact ultrasonic screen unit 71 can be accommodated in a fluidized powder container 24. The open construction of the ultrasonic screen unit 71 has the effect of creating an automatic pressure equalization in the vented powder container 24. Trouble-free and consistent powder application is thereby ensured.
The feeding of fresh powder and recovery powder can take place in different variants.
The present invention achieves high-quality screening of the coating powder even in the case of quick color-changing systems with a cyclone separator. All of the screening devices 10 that were previously accommodated in the lower powder run-out region of the cyclone separator or in the powder supply line to the powder container 24 can be eliminated by the provision of the screen unit 70 according to the invention. Relocating the screen unit 71 from the run-out region of the cyclone separator or from the powder supply line into the fluidized powder container 24 achieves the effect of increasing the quality of the powder. In this way, the screening of the powder takes place directly upstream of the injectors 111. As a result, possible contaminants or, for example, platelets or agglomerations of powder that may occur as a result of mechanical action during the conveying of coating powder can be kept back before the injectors 111 in the screen 77.
In addition to this, when ultrasonic screens 77 are used, the screen mesh widths of the screens can be kept very small in comparison with conventional vibration screens. The consequence is a significant increase in the quality of the powder.
This invention also provides the latter in the case of quick color-changing systems with a cyclone separator. The compact construction of this ultrasonic screen insert allows very little expenditure of time to be required for cleaning in the event of a change of color.
The invention is not restricted to the embodiments represented in the drawings, but is made up of all the features disclosed herein considered together.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102011004595.3 | Feb 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2012/026245 | 2/23/2012 | WO | 00 | 10/29/2013 |
