KR0127775B1 - Method and device for powder-coating - Google Patents

Abstract

Proposed is a method of powder-coating electrically conducting workpieces (1) with a coating powder, in particular a paint coating powder. The method comprises the following steps: first, the optionally cleaned and/or surface-treated workpiece (1) is heated inductively by means of an inductor (2) to the processing temperature or melting or softening point of the coating powder. The coating powder is then sprayed on to the inductively heated workpiece (1) by means of a spraying device (3, 8) so that the coating powder is at least fused on to the inductively heated workpiece (1) by the heat of the workpiece (1).

Description

Powder Coating Method and Apparatus

The present invention relates to a method and apparatus for powder coating electrically conductive workpieces by coating powder, in particular powdered paint.

In the art, powder coating methods and devices thereof have long been known. Essentially, powder coating is used in the field of surface treatment, which is the process of creating a coating on the surface by thermal action so that the workpiece surface can be protected from the outside. Unlike conventional methods of spraying paint containing solvents, in the present invention a coating powder or powdered paint is sprayed onto the surface to be treated, the coating powder having a uniform coating on the workpiece surface. It is melted by thermal action until it is produced.

However, the basic problem of powder coating is that the adhesion of the coating powder to the surface to be treated is absolutely necessary. The need for such adhesion prior to the heat treatment to form the coating has been addressed by an electrostatic powder coating process, which is also known in the prior art level and has particles of opposite charge. They are based on the fact that they attract each other. As a result, only conductive solids or thermally stable solids are suitable for powder coating. To date, it has been customary to coat appliance workpieces, garden ornaments, automotive ornaments, fixtures, wire workpieces, cross sections, building exterior elements, and the like in this manner.

Known methods to date have been carried out in which a dry coating powder has been filled into a supply container, fluidized or agitated, and then fed into a spray gun by compressed air. In the spray gun, a low voltage of about 10 V is converted to high pressure by the cascade principle, and one or several electrodes charge the powder to a voltage of 60-100 kV during spraying. An electric field is created between the gun and the grounded workpiece. Even though the powder particles follow a force line, the residual charge causes them to adhere to the workpiece to be coated. The workpieces treated as above are transferred either manually or automatically to subsequent dryers, where the coating powder, which is mainly composed of plastic, is melted and cured at a temperature of 200 ° C. to form a smooth film. When enamel powder is used as coating powder, the curing temperature will be about 800 ° C. Basically, however, when trying to produce a kind of colored coating, the coating powder mainly comprises thermoplastic and thermosetting plastics. However, it is basically possible to coat with a powder whose melting point is below the melting point of the workpiece to be treated. In the past, not only epoxy powders but especially polyester resin powders and polyurethane powders have proven useful.

However, a problem common to all methods of powder coating is that the coating powder used for the coating must be attached in some way to the workpiece to be treated. Most of the methods for achieving this purpose require expensive equipment or so-called adhesives, which interfere with the coating itself or are environmentally toxic.

Moreover, known powder coating methods and apparatuses have the problem that it is always necessary to heat the workpiece to be coated in a furnace or the like so that the coating powder attached to the surface can be melted and become a cracked coating.

Thus, the temperature affects the workpiece from the outside, which shows the temperature change inwards with heating time. As a result, when the known powder coating method is applied to the coating of large products, for example the coating of long pipes, a special large scale industrial furnace is required, which is very uneconomical as it requires high energy.

Finally, with the known method, it is very difficult to effectively coat the inner surface of the pipe because the effective heat coming from outside penetrates the inner wall unevenly. At best, a very long warm-up time to heat the entire workpiece may be helpful in this case, but this also requires a lot of money. Accordingly, it is an object of the present invention to apply a coating powder used for coating to a workpiece to be treated by a simple method, and furthermore to provide a uniform coating on the inner surface of a hollow body such as a pipe. It is to provide a coating method and an apparatus thereof.

The method of the invention, which coats an electrically conductive workpiece with a coating powder, in particular powder paint, and solves the problems of the prior art as described above, is characterized in that it consists of the steps described in claim 1. Thus, the method according to the invention first inductively heats a workpiece to be coated, which is cleaned and / or surface treated, if necessary, to the processing temperature or melting point or softening temperature of the coating powder. And spraying the coating powder onto the inductively heated workpiece using a spraying device continuously, ie immediately after the end of heating. Since the workpiece is already heated, it melts as soon as the coating powder impinges on the workpiece surface and adheres to the workpiece, so no adhesive is required. The temperature obtained on the workpiece surface by induction heating is adjusted not only to melt the coating powder but also to produce a smooth and uniform surface by increasing surface tension.

Thus, the method according to the invention has the problem of attaching the coating powder to the workpiece to be coated and the workpiece to be coated by inductively heating and spraying the coating powder immediately in the heated state prior to actually coating the workpiece. It is possible to solve the problem of heating the battery from the outside in one operation.

According to the method of the present invention, no expensive method or apparatus for attaching the coating powder to the workpiece is required, and no industrial furnace for continuously melting the coating powder is required.

Instead, as described above, independent steps of deposition and melting occur in one operation. In other words, by the induction heating and the coating which takes place continuously, the time interval between the heating operation and the coating operation becomes meaningless. The apparently fused work takes place in one place, eliminating wasted time and the cost of moving from one work station to another.

As for the practical coating process, there is a particular advantage that once the spraying of the coating powder begins after the preceding heating step by the inductor, heating and powdering continue. To complete the coating process, stop the inductor and spray the remaining area completely.

If the workpiece to be coated is an elongated accessory, such as a shaft or pipe, it is preferably clamped on the basis of the rotational symmetry of the workpiece during inductive heating and spraying operations. It is possible by means of the device to rotate the workpiece around the longitudinal axis. As a result, in this case, the inductor and the sprayer can be placed in a fixed state so that the workpieces can be rotated within the effective range of the inductor and the sprayer to uniformly coat the long part or the entire tube. have.

Moreover, during inductive heating and spraying operations, there is an advantage that the workpiece can move relative to the induction and spray device or the inducer and spray device can move relative to the workpiece. This relative movement occurs in the axial direction of the workpiece, such that the rotational movement of the workpiece by the clamping device and the axial movement of the workpiece or inductor so that workpieces such as pipes can be efficiently coated throughout its length May be promoted by a spray device.

In particular, if the workpiece to be coated is a pipe, inductive heating of the pipe wall, in particular heating through the frequency control of the induced current, is such that the inner wall, i. It is advantageous to arrange the pipe so that it can be sprayed or coated from the inside. According to the method of the present invention, the tube is heated in a strip shape from the outside by induction, which heating can be extended directly into the inside of the pipe, which is very advantageous. When the nozzles are arranged both outside and inside the pipe, the spraying device following the inductor applies the coating powder inside and outside, and the coating powders are attached as soon as they hit each surface.

Moreover, the inside and outside of the pipe can be heated by independent inductors on each side, preferably simultaneously and can be sprayed or coated by the corresponding spraying device. The inductor entering the tube must be designed in the form of a probe, preferably a bar, the two inductors being in position to operate completely independently and in different places. It is also readily possible to partially coat the pipe from the outside and from the inside.

It is particularly advantageous that the thickness of the coating can be controlled by the speed of movement of the inductor and the spray device. Furthermore, the thickness of the coating can be adjusted in consideration of the rotational speed of the induction heating device and the workpiece.

The surface to which the coating powder has already been sprayed is again heated by an inductor so that at least the partially molten coating powder can be applied smoothly onto the surface according to the specific surface tension in the molten or softened state. Is a special advantage. Such reheating may be understood as an aftertreatment if the deposition of the coating powder takes place only in the first route. In any case, the heat can control the flatness of the coating surface.

When spraying the coating powder onto an inductively heated workpiece, it is directed to the workpiece in the form of a spraying mist, i.e., having a desired dispersion, rather than in the form of a jet or a point. It is advantageous. Doing so causes more powder particles to be distributed towards the workpiece than the workpiece can accommodate.

Therefore, in order to prevent contamination and external side effects of the coating powder and to reduce the cost due to the loss of the powder, the unsmelted powder particles sprayed on the workpiece are removed by a special suction device. can do. The aspirated powder particles are fed back to the sprayer for respraying, first returned to the collection container or feed container by the sprayer and then back to the sprayer.

Another object of the present invention is to provide an apparatus having the features as claimed in claim 12. Thus, an apparatus for powder coating an electrically conductive workpiece with a coating powder, in particular powder paint, preferably the apparatus used in the above-described method of the invention, has at least one inductor for induction heating the workpiece, and And at least one spraying device for spraying the coating powder onto the finished workpiece. It has also been found that in the device according to the invention, the integrated use of the inductor and the spray device can solve all the problems encountered in known powder coating devices and methods.

Preferably, the inductor is connected to an inverter and biased by varying the current at various frequencies. Preferably, the frequency of the inductor is infinitely convertible so that it can affect the penetration depth of the eddy current induced by the inductor in the workpiece. In addition, each step of adjusting the various frequencies can be easily determined.

When the workpiece to be coated is of elongated shape, such as a pipe, the inductor surrounds the workpiece, at least a portion of which is preferably at an adjustable distance, and in such arrangements, no relative movement between the workpiece and the inductor occurs. Instead, the inductor should be designed to bias a relatively large area of the workpiece. It is more advantageous to make the inductor semicircular. When the workpiece to be coated is at least tubular, one can think of a semicircular structure, which allows the inductor to move from the free side above the pipe. Finally, the inductor is designed in the form of a forceps so that both ends can be moved independently, and can be used in half around the workpiece to be coated, and can close the half to generate a circular inductor.

To secure the workpiece to be coated, it is more advantageous to have a clamping device, preferably with two fastening devices. Fixtures or carriers for mounting the workpieces are well suited as they can support the workpieces on both sides, for example the front end thereof.

A further advantage is that the clamping device or the clamping devices of the clamping device can be driven in rotation so that the fixed workpieces can be rotated. Even when the inductor is designed to be semicircular, the rotational movement of the workpiece to be coated is very advantageous as it allows the entire workpiece site to be heated.

For a uniform coating of the entire workpiece surface, as a supplement to the rotational movement of the workpiece, it is possible to move the clamping device in the axial direction of the workpiece so that it can be coated after being heated both around the workpiece and onto the ground. do. The fixation of the workpiece due to the arrangement of the clamping device is such that the workpiece is fixed in the horizontal direction. In addition, it is also possible to fix the workpiece so that it extends vertically. In that case, it is necessary to adjust the arrangement and the moving direction of the inductor each time according to each direction or the fixing direction of the workpiece.

It is also possible to move the inductor linearly along the workpiece such that the clamping device rotates only for rotation of the workpiece. It is also possible for both the inductor and the workpiece to move in the axial direction, such that the inductor and the clamping device are laterally moved by only about half of the gap. Thus, the maximum traverse of the inductor and the clamping device can be reduced efficiently.

The movement of the inductor and the linear speed of movement of the clamping device are variable, which affects the efficient processing of the coating.

If the workpiece to be coated is a pipe, the pipe inner wall is preferably provided with one further secondary spraying device which can be adjusted to enter the pipe by crossbeam and lance or cable. It is possible to spray or coat it. In such a case, however, it is necessary to inductively heat the pipe from the outside so that the heat-generating overcurrent can penetrate into the pipe to an appropriate depth and the pipe inner surface can be properly heated. Corresponding to the primary spraying device operating outside the pipe, the secondary spraying device coats the inside of the pipe, the two office devices operating at the same height and advancing at the same speed along the pipe. At the same time, the pipes rotate simultaneously to allow coating throughout the pipe circumference.

In addition to the possibility of such a design, it is possible to heat the pipe inner wall, preferably by installing a secondary inductor which enters the pipe by crossbeam and lance or cable. The secondary inductor assists in the heating operation of the inductor working externally to enable uniform heating of the entire workpiece wall.

When following the sprayer or inductor, it is possible to spray the coating powder onto the inductively heated area of the workpiece above the inductor, as seen in the direction of travel of the inductor, resulting in the heating of the workpiece and the coating powder onto the workpiece It is advantageous to install a nebulizer so that it can be attached, melted and evenly sprayed. In this case, the spraying device can be combined with a sieve fixed to the inductance. That is, for example, the spray device can be mounted on a frame with the inductor. In addition, this arrangement allows the coating powder to always be sprayed onto the inductively heated region, which is in the rear of the inducer in the direction of induction of the inducer and the inducer always moves the same as the spray device. As such, because it is adjustable, the predetermined spacing between the inductor and the spray device does not change at least during the coating operation.

In view of the prevention of contamination or annular protection, as well as minimal waste of the coating powder, it is advantageous to combine the spray device with the suction device which is used to suck and remove the unmelted powder particles from the workpiece surface. The suction device may have a funnel-shaped hood, at least a portion of which spans around the spray device. That is, the hood may be at least partially formed or curved around the workpiece. Suction hoods are also possible that are adapted to each type of workpiece to be coated to efficiently suck or catch ink coated powder particles.

The suction device transports the removed powder to a collection bin. In addition, the suction device is operated by a sieve connected to the supply container of the spray device to directly supply the suctioned and removed coating powder back to the spray device.

Finally, in view of the removal of the bulk coating powder by the appearance and suction of the workpiece, the sprayer nozzle can be adjusted each time to the workpiece to be coated.

For this purpose, the spray device nozzles need to be replaceable, and it is possible to re-adjust the thickness of the coating formed by the different nozzle shapes and the speed of movement of the literary device or inductor.

There are many possibilities for completing and further developing the lessons of the present invention. For this purpose, reference has been made to the following embodiments of the invention based on the claims and claims dependent on claims 1 and 12. Regarding the detailed description of the preferred embodiment of the present invention based on the drawings, general preferred embodiments and progressive embodiments of the present invention are described.

In the drawings, FIG. 1 is a block diagram in which a portion of an embodiment of the device according to the invention for powder coating an electrically conductive workpiece with a coating powder is cut out, the embodiment consisting of one inductor and two spraying devices .

1 shows an embodiment of an apparatus according to the invention for powder coating an electrically conductive workpiece, which is pipe 1. The powder paint used as coating powder in this embodiment is not shown in the figure but is used to coat the surface of pipe 1.

According to the invention, inductance 2 is used for inductively heated pipe 1. Sprayer 3 is a device for spraying coating powder onto a heated workpiece, ie pipe 1.

As noted in detail in FIG. 1, inductor 2 is connected to inverter 4, which biases inductor 2 by varying the current at various frequencies. The frequency regulation of inductor 2 affects the penetration depth of the overcurrent induced on the tube 1 by inductor 2, preferably the frequency is infinitely variable.

FIG. 1 shows that part of the inductor 2 surrounds pipe 1. FIG. Furthermore, inductor 2 can be designed in the form of a semi-circular, circular, as well as in the form of tongs with two inductor parts.

In order to support pipe 1, a clamping device 5 is provided for securing pipe 1 between the fixing devices 6, 7. The clamping device 5 or the clamping devices 6, 7 of the clamping device 5 are rotationally driveable so that the pipe 1 mounted thereon can also be rotated by the clamping device 5. The clamping device 5 and the inductor 2 can be adjusted to move in the axial direction of the pipe 1 so that it can be efficiently coated over the entire length of the pipe 1.

In this embodiment, the clamping device 5 is provided so that the workpiece, that is, pipe 1, can extend vertically in a fixed state. Inductor 2 is movable linearly along the workpiece, ie pipe 1. Inductor 2 travels at various or adjustable speeds.

Furthermore, in addition to the primary spraying device 3, a secondary spraying device 8 is provided, which makes it possible to spray or coat the inner wall of the pipe 1. The spraying device 8 is adapted to allow the support part 6 to enter pipe 1 by means of the crossbeam 9 and lance 10.

Viewed in the advancing direction of the inductor 2, the spraying devices 3 and 8 move along the inductor 2, allowing application of the coating powder to the inductively heated region of the pipe 1, the inductively heated region of the inductor. Followed by inductor 2 in the direction of travel. Moreover, spraying device 3 is fixedly coupled to inductor 2 on a common frame or support 11 such that spraying device 3 is forced to follow inductor 2.

Spray devices 3 and 8 are connected to suction devices 12 and 13, respectively, which can remove undissolved powder particles on the workpiece, ie the surface of pipe 1. Each of the suction devices 12, 13 is provided with funnel suction hoods 14,15, respectively. The suction hoods 14 and 15 face the tube 1 and completely surround the nozzles of the sprayers 3 and 8 on the opposite side of the sprayer.

The secondary suction device 20 is arranged at the lower end of the tube 1, which is operated entirely over the opening of the tube 1. The suction device is connected to or becomes an integral part of the lower fixture 7.

Finally, the suction devices 12, 13, 20 are operated with a sieve connected to the supply container 18 of the spray device 3, 8 via the compressed air hoses 10, 17, 21 so that the removed coating powder can be fed back to the spray device 3, 8. It can be seen from the figure. Compressed air from the pressure tank 19 feeds the coating powder back to the spraying device 3, 8 via the secondary compressed air hoses 22, 23.

The above examples are intended to better understand the teachings of the present invention and do not limit the present invention.

Claims (34)

Inductively heating the optionally cleaned and / or surface treated workpiece 1 to the processing temperature or melting point or softening point of the coating powder and inductively by the sprayer 3 ) Spraying the heated workpiece (1), wherein during induction heating, the workpiece (1) moves relative to the inductor (2) and the atomizer (3) and the inductor (2) and In the method of powder coating the electrically conductive workpiece 1 with a coating powder, in particular powdered paint, in which the spraying device 3 moves relative to the workpiece 1. The method, in the direction of the induction of the inductor, causes the coating powder to be sprayed onto the inductively heated region of the workpiece 1 which extends behind the inductor 2 so that the coating starts after induction heating of the outer region. Characterized by Way. The method according to claim 1, characterized in that the spraying of the coating powder begins after the preceding heating step by the inductor (2) and subsequently coincidentally with heating. 3. The workpiece 1 according to claim 1, wherein the workpiece 1 is preferably a clamping device during inductive heating and spraying operations when the workpiece 1 to be coated is an elongated part, preferably a pipe. And 5) rotated about its longitudinal axis. Method according to claim 1 or 2, characterized in that the relative movement occurs in the axial direction of the workpiece (1). 3. The pipe (1) according to claim 1 or 2, wherein when the workpiece is a pipe (1), induction heating of the pipe wall, in particular heating by the induced current above frequency, is designed to occur all over the right side of the inner wall. Is also sprayed or coated from the inside by a secondary spray device (8). The pipe (1) according to claim 1, wherein the pipe (1) is heated by both inductors (2) and sprayed by a spray device (3, 8), both from the outside and from the inside, preferably simultaneously. Characterized in that it is coated. 3. The coating thickness according to claim 1, wherein the resulting coating thickness is controlled by the speed of movement of the inductor 2 and the spraying devices 3, 8 and / or the speed of rotation of the workpiece 1 and / or the heating rate. How to feature. 3. The surface of the workpiece 1 to which the coating powder has already been sprayed is heated again by an inductor 2, so that at least partially molten coating powder is melted or softened. And surface spraying by surface tension to smoothly spray onto the surface. 3. Method according to claim 1 or 2, characterized in that the unattached sprayed powder particles of the workpiece (1) are sucked through the inhalation device (12, 13) and removed. 10. Method according to claim 9, characterized in that the powder particles removed by suction are fed back to the spraying device (3,8) for secondary spraying. Has at least one inductor 2 for inductively heating the workpiece 1 and at least one sprayer 3 for spraying the coating powder onto the heated workpiece 1, During the dispensing operation, the workpiece 1 moves relative to the inductor 2 and the sprayer 3 and the inductor 2 and sprayer 3 move relative to the workpiece 1, In an apparatus for powder coating an electrically conductive workpiece 1 by coating powder, in particular powdered paint, the apparatus, in the direction of travel of the inductor, Followed by the inductor 2, characterized in that the coating powder is sprayed onto the inductively heated region of the workpiece 1 extending behind the inductor so that the coating starts after induction heating of the outer region. Device. Device according to claim 11, characterized in that the inductor (2) is connected to the transducer (4) and biased with currents of different frequencies. 13. Device according to claim 12, characterized in that the frequency of the inductor (2) which affects the penetration depth of the overcurrent induced by the inductor (2) to the workpiece (1) is preferably variable indefinitely. 14. Workpiece according to any one of claims 11 to 13, wherein at least part of the inductor 2 is preferably at adjustable intervals when the workpiece 1 is in the form of an elongate shape, preferably in the form of a pipe. Device characterized in that it surrounds the piece (1). 15. The device according to claim 14, wherein the inductance (2) is made similar to a semicircular shape. 15. The device according to claim 14, characterized in that the inductor (2) is circularly enclosed around the pipe (2) and, if necessary, is designed to bifurcate. Device according to claim 15, characterized in that the inductance (2) is designed in the form of tongs. Apparatus according to claim 11, characterized in that the clamping device (5), preferably having two fasteners (6, 7), is provided on the workpiece (1). 19. Device according to claim 18, characterized in that the clamping device (5) or the holding device (5,7) of the clamping device (5) is rotationally driven so that the fixed workpiece (1) can be rotated. 19. The device according to claim 18, wherein the clamping device (5) is moved in the axial direction of the workpiece (1). Device according to claim 18, characterized in that the clamping device (5) is arranged to be fixed in the horizontal direction of the workpiece (1). Device according to claim 18, characterized in that the clamping device (5) is arranged such that the workpiece (1) can be fixed in the horizontal direction. Apparatus according to claim 11, characterized in that the inductor (2) is moved linearly along the workpiece (1). 23. The device according to claim 22, wherein the inductance (2) moves at various speeds. The method according to any one of claims 11 to 13, wherein when the workpiece 1 is a pipe, it is preferably by means of a crossbeam 9 and a lance 10 or a cable. A secondary spray device (8) is provided which can enter the pipe (1) so that it can spray or coat the inner wall of the pipe (1). The method according to any one of claims 11 to 13, wherein when the workpiece is a pipe (1), it can enter the pipe (1) by means of a crossbeam (9) and a lance (10) or a cable. The device is characterized in that a secondary inductor is provided to heat the inner wall of the pipe (1). 14. A spray according to any one of claims 11 to 13, wherein the spraying devices (3, 8) are connected to suction devices (12, 13), which are not melted on the surface of the workpiece (1). Device for inhaling and removing particles. Apparatus according to any one of claims 11 to 13, characterized in that the suction device (12, 13) has a funnel shaped suction hood (14, 15). 28. The device according to claim 27, characterized in that the suction hood (14,15) is at least partly around the atomizer (3,8). 25. A device according to claim 24, characterized in that at the lower end of the pipe, a secondary suction device (20) is provided, said secondary suction device (20) operating entirely over the hole of the pipe (1). 30. Device according to claim 29, characterized in that the suction device (20) is connected to the lower fixing device (7). 30. The device according to claim 29, characterized in that the suction device (20) forms an entire part of the lower fixing device (7). 28. The apparatus according to claim 27, wherein the suction devices (12, 13, 20) are operated while being connected to the supply containers (18) of the spray devices (3, 8) to supply the removed coating powder back to the spray devices (3, 8). Device characterized in that. 14. The nozzle of any one of claims 11 to 13, wherein the nozzles of the spraying apparatuses 3 and 8 are interchangeable, and the thickness of the coating obtained is in the form of the nozzles and of the spraying apparatuses 3 and 8 or the inductor 2. A device characterized in that it is adjustable via a moving speed.