DE10129247A1 - Arrangement for wide area application of liquid coating to workpiece surface produces air flow about liquid coating leaving liquid outlet gap that carries liquid to workpiece surface - Google Patents

Abstract

The arrangement has a liquid output nozzle with a liquid output gap (28) to which the liquid to be applied is delivered. An air flow (64,66) is generated about the liquid coating leaving the gap that carries the liquid along with it and feeds it to the workpiece (70) surface. The air flow has two sub-flows on both sides of the liquid coating and is heated to above the temperature of the coating. Independent claims are also included for the following: a liquid output nozzle.

Description

The invention relates to a method for wide area Applying a layer of liquid to a workpiece top area according to the preamble of claim 1 and a Liquid dispensing nozzle for performing such according to the preamble of claim 7.

It is known that surfaces of workpieces can electrostatically coat, the coating material can be powdery or liquid. The night Part of the electrostatic coating is in particular the other is that the flow rate of the coating liquid when applied is so low that cannot achieve sufficiently short switching times.

Then when you electro the underside of a workpiece want to statically coat with a liquid there are also irregularities in the liquid application.

The present invention is intended to provide a method according to the preamble of claim 1 are further formed that it also works to coat the undersides pieces with liquid is suitable, and it should be a suitable for carrying out such a process Liquid dispensing nozzle can be created.

According to the invention, these objects are achieved by a  Method with the features listed in claim 1 or a liquid discharge nozzle with the in claim 7 specified features.

In the method according to the invention, the thin river liquid layer from the end of the dispensing gap under the influence of the air stream detached in the form of a drop and towards accelerates the workpiece surface.

Even when applying layers of liquid on top Workpiece surfaces are those proposed according to the invention Generation of liquid drops by an air stream advantageous in terms of good uniformity of the Coating and fast switch-on and switch-off times.

Advantageous developments of the invention are in Unteran sayings.

In the method specified in claim 2, the Liquid particularly well at the end of the gap in uniform Droplets are torn off and are the liquid droplets on both sides on the way to the workpiece surface flowing air, so that you have a particularly good Stabilization of the droplet flow in a desired one Curtain geometry obtained.

With the development of the invention according to claim 3 it is guaranteed that the coldest point in the way of the Liquid layer to the workpiece surface at the factory piece surface lies. This gives a high level of effectiveness the liquid absorption through the workpiece surface.

The further development of the invention according to claim 4 is advantageous in terms of appending the Favor liquid on the workpiece surface.  

With the development of the invention according to claim 5 ensures that the relaxation energy of the air is balanced and not to cool the liquid keitsschicht leads, so that the workpiece surface of the coldest point in the liquid's conveyance path remains through reversed the airflow but not the workpiece surface is heated up appreciably and the liquid layer, whose temperature also with regard to the liquid Flow control through a dispensing nozzle to a higher one Temperature (up to 80 to 90 ° C) is set, somewhat cooled on the way to the workpiece surface becomes.

In the method according to claim 6, one additionally obtains an electrical contribution to movement and stabilization of the droplet curtain and also an even better job effectiveness because all liquid droplets along the electrical field lines to the workpiece and there due to the electrostatic attraction stick better.

A liquid discharge nozzle according to claim 7 enables it, the liquid that comes out of its housing, to be divided into drops immediately at the point of exit and to guide and accelerate through the air flow.

A dispensing nozzle according to claim 8 enables a close Delivery of the partial air streams directly next to the liquid keits-discharge gap.

A liquid discharge nozzle according to claim 9 is symme cally.

With the development of the invention according to claim 10  is achieved that the partial air streams, which the flat Liquid needle-like or drop-shaped to both of them Sides, with a perpendicular to the liquid Conveying level directed movement component to the sides the liquid layer. This will Detachment of the liquid is affected by the nozzle tip.

With the development of the invention according to claim 11 becomes a slight fanning out of the liquid jets receive. This gives you an overlapping spray pattern on the workpiece when you go through a wide workpiece a plurality of liquid displaced in the transverse direction dispensing nozzles coated.

Has in a liquid dispensing nozzle according to claim 12 compressed air uniform in the longitudinal direction of the gap loading of the air discharge gaps. This results in good droplet size and uniformity Droplet distribution in the droplet led to the workpiece curtain.

Choosing the pressurization of the air discharge gaps according to claim 13, can be considered here drawn thicknesses of the air discharge gaps ensure that the liquid as a droplet curtain and not as a mist is led to the workpiece. This is with regard to one good deposition efficiency and avoidance of Air pollution in the environment is an advantage.

Select the pressurization of the liquid exhaust bespaltes according to claim 14, one can in here Ensure the considered thicknesses of this gap, that the amount of liquid applied is adjustable and the liquid as a uniform droplet curtain is led to the workpiece.  

The developments of the invention according to the claims 15 to 17 are with respect to a in the longitudinal direction of the gap uniform application of liquid to the liquid feed gap starting from a liquid feed channel advantageous.

Gap thicknesses as specified in claims 18 and 19 are good for applying liquids that are have a viscosity similar to that of light oils, especially drawing oils, such as those used for the pretreatment of Sheets can be used before pressing and deep drawing.

The invention will now be further elucidated with reference to the following play explained with reference to the drawing.

In this show:

Figure 1 is a transverse section through a strip-shaped liquid discharge nozzle of an electrostatic liquid coating system.

Fig. 2 is a side view of the liquid dispensing nozzle of Figure 1, seen from the right there.

Fig. 3 is a block diagram of a liquid coating line for sheet metal, the two liquid dispensing nozzles according to Figures 1 and 2.

Fig. 4 is an end view of a modified liquid dispensing nozzle;

Fig. 5 is a side view of the liquid dispensing nozzle of Figure 4 seen from the right there.

Fig. 6 is a plan view of the inwardly facing boundary surface of a left housing portion of the liquid discharge nozzle Fig. 4;

Fig. 7 is a plan view of a liquid discharge gap of a modified liquid discharge nozzle; and

Fig. 8 shows a longitudinal section through the part shown in Fig. 7 liquid discharge gap along the section line VIII-VIII of Fig. 7.

1 and 2, a liquid dispensing nozzle is designated by 10 in total. It comprises a total of 12 designated stretched housing, which is composed of two housing parts 14 , 16 which are clamped by means of screws 18 which pass through the housing part 16 and run in threaded holes in the housing part 14 . Between the two housing parts 14 , 16 , a sealing part 20 is arranged, which is shown in the drawing for explanatory purposes with a greatly excessive thickness.

In practice, the sealing part 20 has a thickness of a few 10 μm. It is cut out of a plastic or aluminum foil or from an elastomeric material. The sealing member 20 has a substantially U-shaped contour with a lower base portion 22 and side legs 24th

As can be seen from the drawing, the housing parts 14 and 16 each have an essentially rectangular cross section, bevels 26 being provided at the upper outer corners. The top of the liquid dispensing nozzle 10 thus has essentially the shape of a saddle roof with a broken tip.

By the two housing parts 14 and 16 and through the U-shaped sealing member 20, a liquid discharge gap 28 is limited, which is about inner channels 30 of the housing parts 14, 16 connected to a liquid feed valve 32nd The latter is an electromagnetic valve capable of high switching frequencies, as it is known for. B. is used for fuel injection in internal combustion engines. An electromagnet 34 of the liquid feed valve 32 is connected to a control line 36 , and via a valve body 38 of the liquid feed valve 32 , the channels 30 and thus the liquid discharge gap 28 can be connected to a liquid feed line 40 .

Flat depressions 42 are provided in the bevels 26 , which in practice can have a depth of fractions of a mm to one mm. The recesses 42 can in practice have a depth of 20 microns to 200 microns and run freely into the upper boundary surface of the housing parts 14 , 16 . About the recesses 42 baffles 44 are attached, for. B. screwed by screws 46 . The guide surfaces 44 extend completely over the depressions 42 up to their upper end.

The depressions 42 are connected via internal channels 48 of the housing parts 14 , 16 to an air feed opening 50 of the housing part 14 .

Inside the housing parts 14 , 16 , two bores 52 , 54 extending in the longitudinal direction are provided. From this, the upper bore receives a resistor chain 56 , which together forms a protective resistor in the order of magnitude of 100 MOhm, via which the housing parts 14 , 16 are connected to the one terminal of a high-voltage source. The lower bore 54 receives a heating resistor 58 , which is coupled via a thermal coupling mass 60 to the housing part 14 or 16 under consideration.

In the housing parts 14 , 16 temperature sensors 62 are also embedded in order to continuously determine the actual temperature of the housing 12 and to regulate the housing temperature to a predetermined value via the current loading of the heating resistors 58 .

The liquid dispensing nozzle 10 described above operates as follows:
For the coating, the voltage difference mentioned above between the workpiece surface and the liquid discharge nozzle 10 is applied to the liquid discharge nozzle 10 . Then, the air supply port 50 with air of 0.2 to 1.5 bar is and the discharge gap with the liquid of 0.1 to 0.8 bar applied. Then the liquid speed feed valve 32 is turned on.

The sharp air curtains that emerge from the air discharge gaps tear off individual droplets at the liquid pushed out of the liquid discharge gap and at the end of the gap forming a meniscus. As it is removed from the nozzle, the air relaxes and becomes slower and forms a droplet layer 68 together with the droplets.

The droplets layer 68 is thus both under the influence of the electrostatic field and in particular with the help of fine air curtains 64, 66 against the lower side of the workpiece 70 moves and lays down on the bottom of the workpiece 70 from which shown in FIG. 3 as plate is and is moved past the liquid dispensing nozzle 10 to the right.

If one wishes on the workpiece 70 coated and uncoated subareas which are sharply separated from one another, the channels 30 can additionally be connected via a liquid relief valve 72 to a pressurized liquid return line 74 . The liquid relief valve 72 is preferably constructed the same as the liquid feed valve 32 and also includes an actuating electromagnet 76 which is activated via a control line 77 .

Where sharp transitions between coated and uncoated areas of a workpiece are less important, the liquid relief valve 72 can also be omitted.

Fig. 3 shows a system with which both the top and the bottom schematically shows a workpiece 70 can be coated. To move the workpiece 70 , a conveyor tongs 78 is provided which is moved by a drive (not shown in more detail) and which engages at one end of the workpiece 70 and at the same time serves to place the workpiece at ground potential.

Above and below the conveying plane of the workpiece 70 , two identical liquid dispensing nozzles 10 are seen before, each of which has the structure shown in FIGS . 1 and 2 with respect to the fluid guide mirror image structure.

The liquid feed lines 40 of the two liquid discharge nozzles are connected via a pressure regulator 80 to the outlet of a liquid feed pump 82 which draws in from a reservoir 84 . This contains a volume of liquid 86 to be applied. The liquid can in particular be a drawing oil, as it is applied in whole or in part to metal sheets before they are deformed in a press.

The liquid return lines 74 are connected to the inlet of a suction pump 88 , the feed inlet of which feeds back into the reservoir 84 .

The air feed openings 50 of the two liquid discharge nozzles 10 are connected to the outlet of a blower 92 via a pressure regulator 90 . To control the air flow to the liquid discharge nozzles 10 is an Luft-Speiseven valve 94 , which is also designed as a solenoid valve.

To control the various solenoid valves, to control the heating housing 12 by means of the heating resistors 58 and to apply high voltage to the housing 12 , a control unit, designated overall by 96, is provided, which provides for the control of the dispensing quantities of the liquid and the liquid pattern on the workpiece surfaces.

If a liquid dispensing nozzle 10 is used alone, the corners of the ridge line are rounded, as shown at 98 , to avoid high field peaks that could affect the uniformity of the liquid layer 68 . Where liquid nozzles are juxtaposed to form a longer nozzle unit, the ridges remain, as indicated at 100 .

In a modification of the exemplary embodiment described above, a plurality of liquid discharge nozzles 10 can be provided successively above and below the workpiece in a liquid coating system for metal sheets perpendicular to the drawing plane, whereby the liquid discharge through these different nozzles can be selected differently in order to different parts of the To coat or leave the workpiece surface free.

The housing 12 consisted of metal in the exemplary embodiment described above. It goes without saying that it is also possible to manufacture only the section of the housing 12 which is directly adjacent to the liquid discharge gap 28 , while the outer housing regions are made of an insulating plastic material. In any case, the housing of the valves 32 and 74 are preferably also produced from such a valve, so that their actuating magnets 34 and 76 are only at a low potential.

With nozzles working without electrical field support the housing can also be made of a non-conductive material be made, e.g. B. plastic materials with wear fixed inserts at the higher flow velocities exposed areas, which e.g. B. made of ceramic material can be made.

It also goes without saying that the liquid discharge gap 28 can also be sealed by a sealing part 20 which is designed differently in detail, insofar as only the peripheral seal of the discharge gap in FIG. 1 downwards and to the sides of the liquid discharge nozzle 10 is ensured.

The sealing part 20 also does not need to perform the function of a spacer at the same time. Instead, you can work into the mutually facing inner boundary surfaces of the two housing parts 14 , 16 very shallow depressions and accomplish the circumferential sealing of the discharge gap by a round cord seal, which are inserted in semicircular sealing grooves with a U-shaped shape, which the just mentioned surrounded very shallow depressions.

In the above described embodiment of a liquid discharge nozzle 10 of the liquid discharge gap 28 air curtains were provided on both sides. It goes without saying that for some applications it is also possible to use a single air curtain.

In the coating system described above, the amount of liquid dispensed and thus the thickness of the droplet layer applied to the workpiece surfaces can be controlled via the following parameters: size of the pressure set by the pressure regulator 80 , level of the temperature set in the liquid dispensing nozzle 10 by the heating resistors 58 , Strength of the electrostatic field, size of the relative speed between workpiece 70 and liquid dispensing nozzles 10 . The droplet size can be specified via the setting of the pressure regulator 90 . When designing the nozzle, the thickness of the liquid discharge gap and the thickness of the air discharge gap can be specified with regard to the intended use.

The liquid dispensing nozzle described above can also can be used as a purely fluid nozzle without Use of an electrostatic field.

The pressure of the air provided by the pressure regulator 90 is then chosen to be higher, so that the air alone can sufficiently accelerate the liquid emerging from the air discharge gaps. In practice, the air pressure under these conditions is between 0.5 and 1.5 bar.

The pressure of the liquid supplied to the discharge gap 28 is again set to 0.2 to 8 bar by the pressure regulator 80 .

Under these conditions, the liquid is dispensed at the dispensing gap 28 such that individual droplets detach from the gap in essentially the same density in the longitudinal direction of the gap. This droplet curtain is accelerated by the air flow and moves onto the surface of the workpiece 70 , where a large part of the droplets is deposited and grows tightly into a coherent liquid.

The speed at which the liquid droplets in the droplet curtain 68 run from the liquid discharge nozzle 10 to the workpiece 70 can be specified via the pressure of the air set on the pressure regulator 90 . The amount of liquid that is deposited per unit area on the workpiece surface can be adjusted by adjusting the pressure regulator 80 .

In the modified liquid discharge nozzle of FIGS. 4 to 6 are components which have above been described with reference to FIGS. 1 and 2, are again provided with the same reference numerals, if these components have the same function, even if they differ in their geometry.

Instead of the thin guide plates 44 , thicker guide plates 44 are screwed onto the chamfered surfaces of the housing parts 14 , 16 over the shallow depressions 42 .

The application of air to the shallow depressions 42 takes place via a plurality of feed channels 102 , which are connected to the air line coming from the pressure regulator 94 via pressure lines not shown in the drawing. The feed channels 102 in turn split into two delivery channels 104 , which open into the associated shallow recess 44 . As can be seen from FIGS. 5 and 6, pressurized air is thus applied to the depressions 42 at points which follow one another regularly in the longitudinal direction of the housing part.

In FIGS. 5 and 6 is also denoted by 106 is a threaded bore into which a liquid feed valve is screwed 32nd The latter acts on a feed channel 108 , which opens into the discharge gap 28 .

As can be seen from the drawing, the discharge gap 28 has a first gap region 110 which is adjacent to the discharge opening and has the edge contour of a narrow rectangle.

A second gap region 112 is placed on the gap region 110 , the edge contour of which corresponds to an obtuse-angled triangle. The first gap region 110 has a first thickness which is selected with regard to the size of the droplets dispensed at the gap opening and in practice is in the range between 10 μm and 100 μm, preferably around 50 μm.

The second gap region 112 has a greater thickness, e.g. B. 200 microns.

In this way it is ensured that the delivery end of the Dispensing gap in the longitudinal direction of the gap homogeneous with liquid is applied.  

In a further modified embodiment, which is shown in FIGS. 7 and 8 (only the contours of the discharge gap are shown), the second gap region 112 has the same thickness as the first gap region 111 . A third gap region 114 adjoins the second gap region 112 , the edge contour of which corresponds to an acute-angled triangle. The third gap area has a significantly increased thickness compared to the first of the second gap area. In practice, this thickness can be approximately 400 µm.

It is understood that the gap thickness in general and the thickness of the different gap areas under consideration considering the viscosity of the liquid, choose which one to be applied to the workpiece.

Claims (19)

1. A method for applying a liquid film to a workpiece surface, in which a liquid discharge nozzle, which has a liquid discharge gap, the liquid to be applied is supplied, characterized in that one generates an air stream around the liquid layer leaving the liquid discharge gap, which the Takes liquid and leads to the workpiece surface. 2. The method according to claim 1, characterized in that that the airflow two to either side of the liquid partial layers. 3. The method according to claim 1 or 2, characterized net that the airflow to a above the workpiece temperature lying temperature is heated. 4. The method according to any one of claims 1 to 3, characterized characterized in that the liquid layer on a temperature above the workpiece temperature is heated. 5. The method according to claim 4 in conjunction with claim 3, characterized in that the air flow to a between the workpiece temperature and the liquid temperature temperature is heated. 6. The method according to any one of claims 1 to 5, characterized characterized in that between the liquid dispensing nozzle and a voltage is applied to the workpiece. 7. liquid discharge nozzle for performing the method according to any one of claims 1 to 6, with a housing ( 10 ) in which a liquid discharge gap ( 28 ) is formed, which opens freely into a boundary surface of the housing ( 10 ) and with a liquid Feed channel ( 30 ) is connected, characterized in that the housing ( 10 ) in the vicinity of the liquid discharge gap ( 28 ) is provided with at least one air discharge gap ( 42 , 44 ) which cut at least in its end section in the liquid conveying direction seen to the liquid discharge gap ( 28 ) is parallel and seen perpendicular to the liquid conveying direction has an extension component parallel to the liquid discharge gap ( 28 ). 8. A liquid discharge nozzle according to claim 7, characterized in that the housing ( 10 ) has two air discharge gaps ( 42 , 44 ) lying on both sides of the liquid discharge gap ( 28 ). 9. A liquid discharge nozzle according to claim 8, characterized in that the air discharge gaps ( 42 , 44 ) to the central plane of the liquid discharge gap ( 28 ) are symmetrical. 10. Liquid dispensing nozzle according to one of claims 7 to 9, characterized in that the liquid-dispensing gap ( 28 ) containing the boundary surface of the housing ( 20 ) is substantially roof-shaped ( 26 ) and the air-dispensing gap ( 42 , 44 ) depressions ( 42 ) in the roof surfaces ( 26 ) and the latter covering guide elements, in particular guide plates ( 44 ). 11. A liquid dispensing nozzle according to one of claims 7 to 10, characterized in that the boundary surface of the housing containing the liquid dispensing gap ( 28 ) is rounded at its ends ( 98 ). 12. Liquid discharge nozzle according to one of claims 7 to 11, characterized in that the air discharge gap ( 42 , 44 ) at a plurality of points spaced apart in the nozzle longitudinal direction ( 104 ) pressurized air is supplied. 13. Liquid discharge nozzle according to one of claims 7 to 12, characterized in that they are with air is applied, the pressure between 0.5 and 1.5 bar lies. 14. Liquid discharge nozzle according to one of claims 7 to 13, characterized in that they are mixed with liquid speed is applied under a pressure of 0.1 up to 0.8 bar. 15. Liquid discharge nozzle according to one of claims 7 to 13, characterized in that the liquid discharge gap ( 28 ) has increasing thickness with increasing distance from its free end. 16. A liquid discharge nozzle according to claim 15, characterized in that the liquid discharge gap ( 28 ) in a rectangular edge contour having a first region ( 110 ) which adjoins the free end of the discharge gap and has a first thickness, and in a direction towards it a second region ( 112 ) adjoining a liquid feed channel ( 108 ) with the edge contour of an obtuse-angled triangle and preferably a second thickness that is larger than the first. 17. A liquid dispensing nozzle according to claim 16, characterized in that the second region ( 112 ), which preferably has an increased thickness, is followed by a third region ( 114 ) of the dispensing gap ( 28 ), which has the edge contour of a triangle of greater height, and that the depth of this third region ( 114 ) of the discharge gap ( 28 ) is greater than the depth of the second region ( 112 ) of the discharge gap. 18. Liquid discharge nozzle according to one of claims 7 to 17, characterized in that the thickness of the air discharge gaps ( 42 , 44 ) is between approximately 20 µm and approximately 200 µm. 19. A liquid discharge nozzle according to one of claims 7 to 18, characterized in that the thickness of the liquid discharge gap ( 28 ) is between approximately 10 µm and approximately 100 µm.