JPS6047349B2 - Equipment for painting enamel onto metal objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for applying enamel to a metal object.

Currently, there is a slight distance between the objects to be enameled,
Enameling in dry powder form is typically applied by projecting a cloud of dry glaze powder from a distance of about 20 yrwt.

Note that this object usually consists of a steel sheet.
To improve deposition on the object, an electrostatic field is created within the spray group, whereby the powder particles carry an electrostatic charge. Generally, the powder particles receive a negative electrostatic charge while the electrically conductive object to be enameled is grounded, and thus come to have a relative positive potential. This results in a traction of the negatively charged enamel particles by the electrically conductive material to be enameled which has an electrostatic potential. As for the projection itself, in the current state of the art various means are used to aerate the powder, generally with the projection secured by one or several compressed air sprays, guns.

The electrostatic field is generated by a continuous current generator.

Note that this generator charges the electrode negatively and creates an electrostatic field. Typically 60,000 volts and 100
It is possible to adjust the electrostatic field between 000 volts and when a projection occurs, i.e. from J object to 2
An electrode is placed at the location O0wun. More particularly, when the powder is projected from a compressed air spray gun, the electrode is placed in the center of the nozzle of the spray gun. Enamel coating according to the technology commonly used at present, as described above, has an average thickness of 0.20Tn and after baking 0.1477W! A dry enamel layer is deposited giving a baked enamel layer with an average thickness of .

Despite the application of an electrostatic field that directs the particles of powdered enamel to the electrically conductive object to be enameled, it is possible that only a part of the spray of particles effectively reaches the object. will be observed.

Enamel deposition efficiency ranges from 30 to 40% (
This is the ratio between the amount of enamel deposited on the object and the amount of enamel projected. ) The undeposited portion of the enamel (70-60%) is recovered by various devices consisting mainly of cyclone separators and filters, and the recovered powder is recycled towards the spray gun for reuse. I am made to do so. Although this circulation considerably limits the loss of enamel powder, the efficiency of collection devices such as cyclones and filters is not 100%, and furthermore, the collected powder becomes somewhat contaminated during collection and circulation. That is a fact. It would thus be advantageous to increase the efficiency of projection, and this is currently being done by various means. These measures are, inter alia, - improvements in the device for projecting the enamel powder, in the arrangement and structure of the electrodes for electrostatically charging the enamel particles, and in the enamel powder to increase its ability to receive an electrostatic charge. . Despite all these measures, the efficiency achieved is only 40%
It is almost impossible to exceed. Another drawback to the methods and equipment currently used for applying enamel in powder form is the phenomenon of counter-emission, which results from the electrical resistance of the enamel particles. This phenomenon is due to the electrical resistance of enamel particles. After enamel particles are deposited on a conductive object to be coated due to an electrostatic field, the electric charge of these enamel particles is difficult to be released immediately due to the electrical resistance of the particles. It is preserved for some time in a coating layer made of enamel particles. This preservation of charge increases the adhesion of the particles to the object, but this adhesion is lost when the charge is completely released. While the charge is stored in the covering layer, the deposition of enamel particles on the surface of the object, i.e. the increase in the thickness of the covering layer, causes the outer surface of the layer to become negatively charged and the object due to the deposition of charge. , that is, between the outer surface of the layer, which functions as a capacitor, and the object. When the electrostatic field within the covering layer between the outer surface of the layer and the object, which functions similarly to a capacitor, reaches a certain value, distortion occurs throughout the layer. Such an electrostatic field that causes distortion throughout the layer generally occurs at a thickness of 0.15 to 0.25 mm, depending on the electrical resistance of the powder.

These distortions appear as pinholes that occur in the surface of the coating layer on the surface of the conductive object. Electric lines of force directed from the electrode toward the object are concentrated in these pinholes, and the pinholes where these lines of electric force are concentrated cause the release of ions with the opposite polarity to the charged enamel particles emitted from the electrode. Become the center.

This is called counter emission. Irregular deposits of powder then result, and the main loss of coverage at the location of these pinholes appears as a loss in the enamel surface after baking. Similarly, counter-emission fields that occur around these pinholes affect the distribution of the enamel, leading to localized irregularities in the film thickness.

Note that the thickness of this film appears as a defect after printing, resulting in a counter-emission defect (Cun
ter-EmissjOndefect),
This procedure gives rise to enamel defect characteristics. Besides localized defects, the appearance of counter-emissions weakens the electrostatic field, resulting in the newly projected powder receiving a weaker charge and its adhesion being insufficient. Become.

The deposition becomes discontinuous, with a maximum of 0.15 to 0.25?
thickness.

The technology currently in use has at least three drawbacks:
namely, relatively low projection efficiency (in the range of 30-40%), maximum thickness of the layer insufficient to ensure good protection (b). 15 to 0.25 wun) and an irregular enamelled surface with defects.

The present invention aims to reduce the disadvantages mentioned above.

According to the invention, the object is to provide support means for supporting a metal object, projection means for projecting glaze in powder form onto the metal object, and charging the powder to a higher potential than the support means. The above pitch should be made. voltage generating means connected to the radiation means; at least one insulating member disposed between the metal object and the support means to ensure insulation of the metal object; This is achieved by means of an apparatus for coating a metal object with an enamel comprising at least one electrostatic field emitter coupled to said projection means for emitting a strong supplementary directional electrostatic field directed towards the metal object.

The invention consists in electrically insulating the object to be enameled from earth using an insulating element placed between the object and electrical earth.

This is fundamentally and in practice contrary to currently accepted principles for explaining the deposition of enamel on electrically conductive objects. This is because all equipment intended for coating enamel in dry powder form by electrostatic methods directly applies the above-mentioned accepted principles, and There are some that deposit negatively charged enamel onto objects. Implementation of the device of the invention provides the following benefits: (1) The phenomenon of counter-emissions is eliminated with all that results from it, i.e. surface defects and thickness reductions due to counter-emissions. ．． Completely suppressed with limitations.

At this time, due to the traction force of the powder layer with respect to the weight of the layer,
A new maximum layer appears.

However, the thickness of this new maximum layer is greater than the layer to be deposited and does not cause any problems. In other words, the device of the present invention has the advantage of being able to arbitrarily set the electric field that will provide a maximum layer thickness sufficient for the desired layer thickness. (2) The powder layer deposited is at least adhesive before baking, similar to that resulting from conventional methods.

When insulated, objects acquire an electrostatic charge. actual,
Experience has shown that these insulated objects act as self-charging capacitors, but this is not the case if the objects are anode grounded and if it is certain that the charge is permanently dissipated. I couldn't see it. This acquired charge is discharged in large quantities when the object passes from the insulating support on the grounded metal support to the conveyor of the baking oven to the next stage. Only the charges on the particles remain, and these charges are retained for as long as the electrical resistance of the powder acts. The layer of powder that has already been deposited does not undergo this discharge phenomenon and remains unchanged. Burning of the enamel takes place, as before, if the object is grounded during the projection of the enamel.

This results in a homogeneous enamel adhesion layer after baking. (3) The powder deposition efficiency with respect to the projected powder is the same as that of a parabolic electrostatic emitter when the object to be enameled is grounded and the same powder is
) is not placed,
To increase. (4) In the device of the present invention, since the counter-emission phenomenon is suppressed, the choice of powder morphology and the resistance of the powder are more free, and therefore there is a further possibility of improving the efficiency. exist.

The device of the invention consists in electrically insulating the object to be enameled from the earth by means of an insulating element placed between the object to be enameled and a grounded support.

The device of the present invention is similar to the “Method and Apparatus for Electrostatically Depositing Powder on a Grounded Metal Substrate” filed on the same day.
Occess and Apparatus of Or The El
ectrOstaticDepOsitiOnOfPO
wdErtOaGrOundedMetallcSu
It would be advantageous to combine it with the device of the US patent ``bstrate''. Additionally, the device of the invention can be placed in a location where it comes into direct contact with the powder during its projection by means of a strong directional electrostatic field capable of guiding the enamel suspended particles in the air towards the object. This consists of reinforcing the electrostatic field produced by the electrodes. This strong directional electrostatic field is generated by a field emitter (Field), each in the form of a television set antenna, placed at the focal point of a parabolic reflector.
eldemitter). Note that this field emitter emits a strong electrostatic field. These emitters are given the same potential as the electrodes. In this way, Wrap-ArOun
A very strong implementation of the development called d) is achieved.

This phenomenon causes enamel particles that do not reach the front surface of the object directly to be pulled and deposited on the sides or upper or lower surfaces, completely distributing them around the object and, in some cases, at a distance. Also deposit on the sides. This wrap-around phenomenon is very important in order to deposit the enamel powder on all sides of the metal object and not only on the part facing the enamel projection device.

The invention of a simple self-operating device for enameling objects with edges is an application of this phenomenon.

This is because in the past, in order to project the enamel directly on the front side of the edges, a device capable of complex maneuvers was required, otherwise automatic operation for these parts had to be abandoned. , the enamel must be projected with the aid of a hand-operated projection device.
A suitably positioned field emitter ensures that the spray swarm profile is projected in the direction of the object, so that
The efficiency of particle deposition on the object is greater and the edge coverage is better. That is, these effects are due to improvement of the wrap-around phenomenon. Furthermore, the fact that these are at the same potential as the electrodes eliminates interference and disturbance phenomena regarding the glaze spray group.

The present invention will be readily understood from the following description and accompanying drawings. FIG. 1 depicts in side view a device for applying enamel to metal objects, comprising a device having the arrangement described above.

FIG. 2 is a top view of the same device.

In order to understand the device for applying enamel to metal objects according to the invention in more detail, an example will be described as follows, according to a preferred embodiment.

First, according to an essential feature of the invention, a metal object 1, such as a steel sheet, is electrically insulated from ground 2.

The object 1 is supported from the upper rail 3 by a cable 4 with an intervention of an insulating element 5 between the part of the cable 4 that is electrically grounded and the object 1, for example. There is. The metal object 1 not only consists of a plate, but can also be an object of any shape and size, and has an electrostatic feed emitter, so that it has folded edges. Even those having 1a are included.

It can be made not only of steel, but also of cast iron and other metals, especially aluminum and copper. The enamel powder is projected onto the object 1 after being exposed to air by means of a compressed air spray gun 6 having an electrode 7 in the center. The electrode 7 is provided with a high potential between 60,000 and 100,000 volts, continuous current, negative polarity by a high tension generator 8. Spray guns of this type are well known in the art. As for the enamel powder, it may consist of any suitable aerated enamel powder. For example, "Electrostatic Deposition of Dry Ceramic Powders 2'"
pOsitiOnOfDryCeramjc″POwd
Powders of the type described in U.S. Pat. No. 3,928,668 entitled 1, 3,9,2, and 3,928,668, ie, ceramic powders coated in the solid state with organopolysiloxanes, can be used. Enamels having the following composition (parts by weight) can also be used.

The present invention is in no way limited to these two forms of enamel.

The means for displacing the spray gun 6 with respect to the plate 1 are, of course, conceivable in a known manner.

Thus, in FIG. 1 the two extreme positions (with respect to height) of the spray gun 6, namely the positions 6a and 6b, are illustrated by dashed and solid lines, respectively.
In FIG. 2, 6c represents a spray group of enamel powder suspended in air and projected by spray gun 6. In FIG. The system described above differs from conventional devices due to the presence of the insulating element 5, which also affects the electrical insulation between the object 1 to be enameled and the earth.

This arrangement can be advantageously combined with another one, namely that described in the said patent application filed on the same day, and also with two electrostatic fields on either side of the projection spray gun 6. - Consists of 10 emitters.

These two emitters are parabolic and directed towards the object. Advantageously, each emitter 10 consists of a television set antenna 11 which is placed at the focal point of a parabolic reflector 12 and emits a strong electrostatic field.

A conductive wire 13 is arranged on a support 14 by means of each emitter 10 (an insulating bar 15 supported by a rod 16).
) is brought to the same potential as the electrode 7 of the spray gun 6.
As a result, the emitter 10 has 600
A potential between 00 and 100,000 volts, continuous current, negative polarity is provided. Optionally, other field emitters can be placed below or above the object 1, depending on the direction in which it is desired to force the spray group 6c, especially if the object 1 has edges higher and/or lower. It's coming.

According to the method and apparatus of the present invention, enameled household items such as cans and pots can be manufactured.

The method and device of the invention also make it possible to coat enamelled iron sheet plates for microwave ovens or gas stoves, washing machines, and refrigerators. The method and apparatus of the invention can also be used to produce enamelled panels for building exteriors.
The particular embodiments, types of objects to be enamelled, and possible applications of the enamel powder explained in FIGS. 1 and 2 are for illustration purposes only and do not depart from the essence of the invention. Variations may be made over a wide range without exception. Furthermore, if the object 1 is insulated, the electrode 7 and the emitter 10 can be provided with a high positive potential instead of a high negative potential. If part of the television antenna provides a convenient means of achieving an auxiliary field emitter element 11, the design and dimensions of the element 11 can be varied widely to accommodate various processing requirements. It is clear that variations may be made and that any kind of branched or straight bar elements would serve equally well.

Although the preferred embodiment illustrated above discloses a parabolic reflector, it should be understood that this particular configuration is illustrative and dependent on certain coating operation parameters. .

As long as the reflector is generally concave and capable of reflecting and directing the field emitted by the element 11,
It may take any of a variety of forms. Thus, in the apparatus for coating metal objects with enamel of the present invention, at least one at least one electric field connected to the projection means is used to emit a strongly auxiliary directional electrostatic field that guides the charged powder onto the metal object. Since it has an electrostatic field emitter, it is possible to keep the electric field set in the insulated metal object at a constant strength, and it also prevents the powder from flowing only along the lines of electric force emitted from the electrode. The coating of objects of complex shape, which otherwise could not be achieved satisfactorily, can be supplemented and ensured by the auxiliary directional electrostatic field emitted from the electrostatic feed emitter. Further, in the apparatus of the present invention, the projection means is connected to the voltage generating means in order to charge the enamel powder to a higher potential than the support means on which the metal object is supported, and the projection means is connected to the voltage generation means, and the metal object is Since the metal object is kept completely insulated by at least one insulating means disposed between the metal object and the metal object, the metal object has a potential corresponding to the strength of the electric field set. An amount of charged powder corresponding to the potential is obtained.

In other words, the apparatus of the present invention is configured so that the potential of the metal object can be set according to the strength of the electric field so that the required thickness of the coating layer is formed on the object to be painted. - With such a configuration, it is possible to achieve highly efficient coating by eliminating waste of coating material, and it is also possible to accurately and easily form a coating layer of a desired thickness. Only with this device can the disadvantages of conventional devices be overcome, and unique effects that cannot be obtained with conventional devices can be achieved. Below, embodiments included in the present invention are listed.

(1) A method for coating a metal object with enamel, which comprises electrically insulating the object from the ground when enamel charged to a high electrostatic potential is projected onto the metal object in powder form.

(2) means for supporting a metal object, means for projecting a glaze in powder form, and means for electrostatically charging said powder to a high potential, comprising at least one insulating An apparatus for coating a metal object with enamel, characterized in that an element is placed between the object and the ground.

(3) When projecting enamel charged to a high electrostatic potential in the form of powder onto a metal object, the object to be enameled is electrically insulated from the ground, and the charged powder is applied to the object. 1. A method for coating metal objects with enamel, characterized in that it involves a combination with a simultaneously occurring strong auxiliary directional electrostatic field, which tends to guide. (4) Enamel comprising means for supporting the metal object, means for projecting the enamel in powder form, and means for electrostatically charging the powder to a high potential. 5, in which at least one insulating element is arranged between the object and the ground to ensure insulation of the object, and a strong auxiliary element is provided to guide the charged powder to the object. Device for painting metal objects with enamel, characterized in that it is equipped with at least one electrostatic field emitter for emitting a directional electrostatic field.

(5) means for supporting a metal object; means for projecting enamel in powder form toward the metal object; and means for electrostatically charging said powder to a high potential; at least one insulating element disposed between the object and the earth for insulating the object with respect to earth, and a strong directional electrostatic field for directing the charged powder towards the object. coating a metal object with enamel, comprising at least one auxiliary electrostatic field emitter with Device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an apparatus according to the invention for applying enamel to metal objects, and FIG. 2 is a top view of said apparatus.

In Figure 1, 1 - metal object, 2 - ground, 3 - rail, 4
~ Cable, 5 ~ Insulating element.

Claims (1)

[Scope of Claims] 1. Support means for supporting a metal object, projection means for projecting glaze in powder form onto the metal object, and charging means for charging the powder to a higher potential than the support means. at least one insulating member disposed between the metal object and the support means to ensure insulation of the metal object; and the charged powder. at least one electrostatic field emitter coupled to said projection means for emitting a strong auxiliary directional electrostatic field that directs an electrostatic field to said metal object. 2. The apparatus for coating a metal object with enamel according to claim 1, wherein the high potential is negative. 3. An apparatus for coating a metal object with enamel according to claim 1, wherein the high potential is positive.