DE1402625A1 - Method and device for the electrostatic coating of objects with an atomized liquid - Google Patents

Description

"Method and device for electrostatic Coating objects with an atomized liquid

Additional application to patent (Az. Χ R 20 698 Ib / 75a)

Priority of the American application No. 598 168 of July 16, 1956

The invention relates to an electrostatic method Coating "of grounded objects with a liquid produced by an annular spray pattern Atomizer is atomized, according to patent ...... (Az.ι R 20698 Ib / 75a ^ and to a device for performing this method.

In the aforementioned main patent is a hand-operated electrostatic spray gun that works without compressed air for atomizing electrically charged color particles described in the form of a ring-shaped pattern. ' This ring-shaped pattern has an inner part which is free of color parts »

The invention is now based on the object of improving the method and the device of the main patent so that one of Inner part free of paint particles in the spray pattern is completely avoided or at least significantly reduced · To solve this Task is proposed according to the invention in the area of the inner part of the annular spray pattern, which at least initially remains free of atomized liquid to apply such an electrostatic potential field that the spray particles also be forced into the inner part and sick

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also deposit on this otherwise free part. Preferably the zone into which the color particles are to be forced is kept at a potential that is in the middle between the potential of the atomizer (usually at high potential) and the object to be coated (usually This can be achieved by connecting the atomizer to high voltage and providing an electrode which is at a potential between that of the nebulizer and earth. The electrode can have a high resistance earthed or connected to a high voltage source will.

Further features of the invention, in particular those of the devices for carrying out the method according to the invention, can be taken from the drawing and the associated description.

In the drawing, several embodiments of the invention are shown, namely shows ι

1 shows a side view of an electrostatic manual spray gun, partly in section (after 1-1 in Pig. 3),

Fig. 2 is a partial view of the hand spray gun according to Fig. 1 (Sonitt 2-2 in Fig. 3),

3 shows a rear view of the hand spray gun in section (according to 3-3 in FIG. Z) ₉

4 shows a front view of the rotatable atomizer head of the hand-held spray gun,

Fig. 5 is a schematic representation of the spray apparatus using those shown in Figs. 1-4 Pistol,

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6 shows a schematic representation of the electrical connections for actuating the spray gun,

7 shows a spray pattern of the gun shown in FIGS. 1-5 sprayed onto a flat surface without using the means provided by the invention,

Fig. 8 shows an improved spray pattern of the gun Figs. 1-5 using the means according to the invention,

9 shows a further embodiment of an electrostatic manual spray gun according to the invention,

Fig.10 is a perspective view of the front Part of the atomizer according to Fig. 9 and

11 shows the circuit according to a further arrangement the invention,

In Figs. 1 to 4 the handgun is designated 10. It consists of a housing 11 made of insulating material and a handle 12 made of metal, which is attached to the housing 11. A cover cap 13, also made of metal, is attached to the rear end of the housing 11 and connected to the handle. A flexible drive shaft, a high-voltage supply cable and a line carrying the liquid spray material run in a grounded flexible protective sleeve 15.

The flexible drive shaft 18 extends from a drive motor, not shown, into the tube 19 made of insulating material. At the end of the flexible shaft there is a projection 18a which engages in a longitudinal groove 20a of a metal bushing 20. the Bushing 20 is connected by hinge 21 to a shaft 22 made of insulating material. The shaft 22 is rotatable in a sleeve 23 stored, which in the housing 11 duroh a locking screw 24-held is.

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A rotatable atomizer support 26 is attached to the front end of the shaft 22 by means of a screw 27. A ring-shaped one Atomizer 28, which has a forwardly directed atomizing edge 28 of preferably knife-like sharpness rotatably mounted on the shaft 22 and connected to the atomizer support 26 by means of pins 29, whereby an annular Opening 30 between the outer edge 26a of the carrier and the inner surface 28b of the atomizer that receives the spray agent arises. The carrier 26, screw 27, atomizer 28 and pins 29 are all made of insulating material . The rotational movement of the flexible shaft 18 is imparted to the atomizer by the sleeve 20, the shaft 22 and the carrier 26 28 transferred.

A metal electrode 32, which has a free-standing hemispherical tip, protrudes beyond the front end of the shaft 22 and is located about 7> 5 cm in front of the edge 28a. To the rear At the end of the electrode 32 is a high resistance 34 of a certain value, for example of the order of 1500

Megohm, connected. The resistor 34 is with the electrode wire connected by a peder 35, which is also an electric Connection between the rear end of the resistor 34 and the socket 20 creates. The socket is at ground potential, since it is connected to the flexible shaft 18 which is grounded.

The high-voltage line consists of a metal wire 38 which is embedded in an insulating tube 39. The insulating tube 39 is protected by an insulating tube 40. A high voltage source is supplied through the wire 38, at the front thereof At the end there is a high resistance 42 of a certain value, for example in the order of magnitude of 1000 megohms, the gun with high voltage. The front end of the resistor 42 is electrically connected to a small metal spring 44

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bound, which is a kind of brush contact, and on one Resistance layer 28o on the outer surface of the atomizer 28 rests. The total resistance of resistive layer 28c measured from spring 44 to a conductive one Metal plate placed over atomizer edge 28a should be at least 20 megohms; preferably lies it is in the 3 order of 100 megohms.

The spray liquid is pressed with overpressure through a line which is connected by suitable connecting pieces 48 (see Fig. 2) is inserted into the rear part of the handle 12. The handle 12 is designed to be comfortable to hold leaves, and has a pusher 50 which acts on a needle valve, the needle by a spring 52 against the front End of the connector 48 is pressed. When the pusher 50 is operated, the needle of the needle valve follows forward against the spring force and opens the connecting piece 48, so that the spray liquid in a chamber 53 in the handle can occur. The spray liquid then runs out of this chamber into a passage 54 'the rear end of which has a stopper 54a, through the gun body to a mouthpiece at the front end of the gun. The spray material that comes from the Mouthpiece 55 emerges on the inner surface of the rotating atomizer 28, flows through the opening 30 and covers the surface 28b of the atomizer in a thin film.

In FIG. 5, the spray gun 10 is held by a worker whose hand is indicated at 60. The spray gun is located compared to a workpiece 61, which is normally at ground potential, that is to say has exactly the same potential like the worker · The high-voltage line 38 is on a high voltage source 63 is connected, which supplies a voltage in the Q-röse order of 100 kV. The rotating parts

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of the gun 10 have a speed of 900 revolutions per minute and are driven by the grounded motor 65 via the flexible shaft 18 · The spray liquid is the Gun at a rate of about 100 cc / min · through the line 46 supplied by a pump 66.

The high voltage comes from a voltage source of 100 kV and flows through line 38, resistor 42, spring, and resistor layer 28c to atomizer edge 28a. Under Taking into account the voltage drop across the resistor and layer 28o, the voltage is at the atomizer edge 28a almost 85 kY with paint on the edge and the gun 30 cm from the grounded workpiece is. If one assumes, as is normally also the case, that the workpiece 61 to be sprayed is a closed one Surface and 30 cm from the gun, then an / electrostatic field is generated by a Average potential G radius of nearly 7000 Y per 2.5 cm generated between the edge, which is at high voltage potential, and the earthed workpiece. When the trigger is pressed 50 the liquid flows from the pump 66 through the conduit 6 pounds and duroh the system shown in Fig. 2 in order to be thinner Film to emerge at the atomizer edge 28a. In the vicinity of the edge 28a the liquid is almost at the potential of the edge 28a charged, atomized and introduced as spray particles into the electric field.

The solid column of liquid between the chamber 53 in the handle 12 and the Zerstäuberkant · 28a may optionally form an electrical conduction path between the socket located on Hoohspannungspotential "28a and the grounded handle.

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While the ingredients (containing the solvent and the thinner) that are used in the composition of the spray liquid The vast majority of the commercially available ones can vary in their conductivity as far as possible Spray liquids are considered to be relatively poor conductors showing considerable resistance, especially in in the form of thin films and columns of small diameter. Accordingly, in most spray liquids, the liquid column forms there is no conductor to earth between the chamber 53 and the edge 28a, even if the liquid is in the Kanmer is at zero potential or naleau at zero potential.

Between the highly charged atomized spray liquid particles and there is an electrical attraction to the grounded workpiece, causing the atomized particles to move into To move the direction of the workpiece and to form a coating on this. If a sheet metal is used as the workpiece, the parallel to the atomizer edge, and if there is no electrode 32 on the gun, then they will point to the workpiece settling spray particles form an annular pattern, which has a central inner part, which is free from spray particles is (see. Fig. 7).

Although the workpiece 61 is the grounded object closest to the edge 28a, the electrode 32 is connected to a high resistance 34, the rear end of which is grounded through the flexible shaft 18. The free end of the electrode 32 lies at a point within the electrostatic field between the edge 28a and the Y / piece 61, which in the absence of the electrode 32 has a potential of almost 70 kV. If the electrode 32 were connected directly to earth and not through the high resistance 34, it would depress the voltage at the edge 28a, so that the spray particles atomized at the edge are attracted and settle along the electrode 32.
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However, if the electrode 32 has a high resistance 34 grounded on the order of 1500 megohms, then the Tip of the electrode 32 held at a potential which is in. of the order of magnitude of 30 kV, so that the sprayed particles are attracted by the electrode 32, but the attraction force is not sufficient to generate a greater number of To deposit spray particles on the electrode or its insulating sleeve 22. In this way it becomes a substantial number deflected by injection particles from their normal trajectory within the annular pattern, and the particles can also move into penetrate the otherwise empty inner part of the pattern in order to fill this part more or less. Continue to be the outer borders of the pattern moved back and the spray jet denser, so that a significantly better spray pattern arises on the grounded workpiece than was previously the Pall.

V / ird in the device described above is an atomizer of 10 cm diameter was chosen and the front end of the pistol was held at a distance of about 30 cm from a metal sheet, this essentially creates a spray pattern as shown in FIG. The two patterns shown in Fig. 7 and 8 arise, when the spray gun has sprayed 100 ecm per minute ·! red synthetic enamel diluted with xylene <

and supplied from a certain viscosity. By changing the resistor 34, the position of the electrode 32 With regard to the edge 28a and other variables in the system, other patterns can also be more or less in their inner part are made less filled with color.

In addition to reducing the empty inner part of the annular Spray pattern is another advantage of the invention is

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that a fine atomization takes place at lower operating voltages and in some even the uniformity the distribution of the spray particles is relatively sharp protruding edges and in depressions of the Yferkstückes increases.

With electrostatic paint sprayers there are both an upper as well as a lower voltage limit, within which the greatest fineness of atomization is achieved when all other conditions remain constant. This optimum voltage increases more than the distance between the atomizer and the workpiece to be coated. When spraying on the assembly line, this requires a close relationship between the voltage optimum and nebulizer depletion of close monitoring this distance.

When using a conventional diffuser bell with a diameter of 10 cm and synthetic enamel results in an optimal atomization of the color liquid at a distance of 15 cm from the workpiece, if the G-locke has a potential of 70 kV j at a distance of 30 cm the potential for optimal atomization is 100 kV and at a distance of 45 cm it is 125 kV. In contrast, with the same atomizer bell, which has a central eye with an intermediate potential - as described above, at a distance of 15 om a voltage of 65 kV is required for optimal atomization, at 30 cm 75 kV and at 45 om only 95 kV. All of the above-mentioned tensions on the edge of the bell are determined by direct measurement.

Since the subject of the invention allows the use of a lower voltage under otherwise identical conditions, can the dimensions of the voltage generating system kept smaller

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· Changes in the distance between the atomizer and the workpiece also have only a minor influence on the quality atomization than is the pail in older arrangements. The invention is in no way limited to hand-operated atomizers, Rather, it can also be used in stationary, automatically operating atomizers, in particular what the Reduction of the empty inner part is concerned with the annular spray pattern.

FIG. 6 shows a further exemplary embodiment according to the invention. The gun 70 has the same shape and dimensions as the gun 10 described above. The gun 70 has a rotatable bell-shaped atomizer 71 with the atomizing edge 71a to which paint is applied via the same paint delivery arrangement as the gun 10. The high voltage for the edge 71a is supplied by a high voltage source 75 via the line 74, the high resistance 75 (e.g. 500 megohms), the spring 76 and the resistance section 71o of the outer surface of the atomizer 71

An electrode 78, which is inserted into a shaft 79 made of insulating material except for its front tip, lies in the Axis of the atomizer 71 'is preferably about 7.5 cm with its free end in front of the edge 71a. At the point where the electrode is connected to the high voltage source, it is advantageously provided with a punctiform and not with a hemispherical tip. The shaft 79 rotates, similarly, like the shaft or shaft 22, the atomizer 71 and is driven by a motor 82 by a flexible shaft 81. Through the electrical line 83 from the resistor 75 to the front one At the end of the shaft 81, both the shaft 81 and the motor 82 are connected to high voltage. The electrode 78 is also located via line 83 and another high resistance

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85 (e.g. 5000 megohms) of high voltage and can be achieved through this circuit with a suitable choice of the values for the resistors 75 and 85 at any desired potential between that the high voltage source 73 and earth are held, which is more advantageous than if the electrode has a potential due to its proximity to the atomizer edge and the value of the resistance, which is connected between earth and electrode, assumes, as the circuit in Pig. 5 shows.

In Pig. 9 to 11 show a further exemplary embodiment according to the invention, specifically using the spray gun 110. This pistol is composed of an insulating housing 111 and a metal handle 112. A high voltage flexible line 115 and a fluid line 116 are inserted into the rear of the gun 110. The three lines mentioned are located in a protective cap 118.

The high voltage line 114 is made of an insulating material covered metal wire, which is protected by a piece of insulating tube 119. A voltage source 120 supplies the Pistol via line 114, the front end of which is connected to a high resistance 122 in the order of magnitude of 1000 megohms is, with high voltage. A thin wire 124 is attached to the front end of the resistor 122, which acts as a spring contact on a resistive layer 125a on the outer surface of the atomizer 125 is seated. The resistive layer 125 is preferably a glyptal alkyd resin layer finished with a specific Amount of finely divided coal is interspersed. This mixture is cured in heat and shows up after being on the base area is applied and dried, high chemical and physical resistance to the components the commonly used spray liquids

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and also has relatively constant electrical characteristics, so that it does not emit any stored electrical energy and a sudden discharge is impossible

The torque for the atomizer 125 is provided by a small electric motor 126 built into the housing 111. The current for the motor flows through the low voltage line 115. The motor is grounded by the handle 112 and is operated by an on / off switch. Its shaft drives the shaft 130, at the front end one Hub 131 is attached. The atomizer 125 sits over the hub 131 and is secured in one by a number of pins 133 Maintained some distance from it, around an annular opening 135 between the outer edge of the hub and the inner liquid ^ guiding surface 125b of the atomizer. The surface 125b runs in a forwardly extending direction annular edge 125 ο off. Atomizer 125, shaft 130, Nahe 131 and pins 133 are made of nylon or the like. When the motor 126 is running, the atomizer 125 is driven by the shaft 130 and preferably rotates with it 600 revolutions per minute

The color liquid runs through the line 116. A pusher 136 regulates the flow from the line 116 into a channel of the pistol 110. A mouthpiece (not shown), which is located at the front end of the Q-ehtuse 111, emits a jet of liquid to the inner surface 125b of the atomizer 125 so that the liquid can form a thin film, which occurs through the ring-shaped opening 135 on the atomizing edge 125 ο.

The electrical probe consists of a concave disk 138 made of nylon or the like and is on the front side of the hub 131

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assembled. In two ways, the disk 138 has a closed cylindrical band 138a with relatively sharp Edge that lies approximately behind the atomizing aunt 125c. the The entire pane 138, both front and back, is coated with a layer 138 of semiconductor material, which has the same composition as the resistive layer 125a · The disc is high resistance 14-0 of about 10,000 megohms by a spring 142 and a conductor 143 electrically connected. The rear end of the resistor 140 is via the motor 126 and the handle grounded·

When spraying, the gun is at a certain distance from the grounded workpiece 145 · High voltage of about 120 kV is applied via resistors with the above values of the voltage source 120 is supplied.

A spatially distributed stream flows from the atomizer edge 125o to the base 138 and through the resistor 140 to Earth, and as a result of the voltage drop across the resistor, the disk is at a potential between dtr Ztrstäuberkante and dtr earth. The resistance of the transfer resistance 138b is so low ^ In comparison with the resistance resistance 140, that in most cases the presence does not need to be taken into account · Dtm according to the presence dtr Disk 138 tint im located on tintm intermediate potential essential inwardly directed radial component dts tltktrisohtn field created, gives way to dtr Ztrstäuberkantt attacks. The Spritzttilohtn wtrdtn so in the center dt Spritxmustre pushed, in the weeentliohtn sohon with her · » Flying away from dtr with Ilüssigktit transferred to Fläoht. Duron dlt probe effect is dit utsamtgrustt dts fuel sample trs rtdusitrt, dlt admittedly Ytrttilung dts fuel «good ·· vtrbee-

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sert and the empty inner part of the spray pattern is significantly reduced. The spray particles are pushed inwards with little force and can therefore only move to a negligible extent Deposit the amount on the disc 138. Furthermore, the concave shape and the recess of the disc 138 oppose the atomization edge 125c helps to ensure that it remains free of deposited molded parts.

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Claims (11)

Claims 1. Process for the electrostatic coating of earthed objects with a liquid that is released from a an atomizer producing a ring-shaped spray pattern is atomized, naoh patent ... ·. · .. (Az.t R 20698 Ib / 75a) characterized in that in the area of the inner part of the annular spray pattern, the at least initially remains free of atomized liquid, such an electrostatic potential field is applied is that injection molded particles are also forced into the inner part and otherwise remain free on this Also deposit part (Fig. 7 and 8). 2. The method according to claim 1, characterized in that the atomizer is connected to high voltage and the potential field generated by an electrode to force the spray particles into the empty inner part of the spray pattern which is at a potential between that of the atomizer and earth (Figs. 5 and 6). 3. The method according to claim 2, characterized in that the electrode has a high resistance of certain Value is grounded (Fig. 5) 4. The method according to claim 2 or 3, characterized in that the electrode mi, t a high voltage source connected via a high Y / resistance of a certain value becomes (Fig. 6). Ha 6981 / July 15, 1957 9 0 9812/0009 5. The method according to claim 1, characterized in that that to achieve ptes desired potential gradient in the sputtering zone with a lower voltage, an electrode is used which is different from the The atomization zone is separated only by a small gap and which is subject to a voltage between that of the atomization zone and earth (Figs. 9 to 11). 6. Device for performing the method according to a of claims 1 to 5 »characterized by an atomizer for generating an annular spray pattern, whose interior is initially free of spray particles, a high voltage source for the atomizer, an electrode and an electrode carrier To hold the electrode in the area of the empty inner part of the spray pattern as well as means to keep the electrode at such a potential that the sprayed particles be pushed into the otherwise empty part of the spray pattern * ' 7. Device according to claim 6, characterized! that the carrier for the electrode is placed on the atomizer. 8. Apparatus according to claim 6 or 7, characterized in that a high resistance in the atomizer of a certain value is installed, one end of which is connected to the electrode and the other end of which is connected to the electrode is grounded. Ea 6981 / July 15, 1957 909812/0009 Λ * U02625 9 · Device according to claim 6 or 7, characterized by that a resistor of a certain value is built into the atomizer, one end of which with the electrode and its other end to the high voltage source connected is. 10 · Yorriohtulig according to one of claims 6 to 91 daduroh marked that the electrode ils he the front The end of the atomizer protrudes (Fig · I to 6). 11. Device according to one of claims 6 to 9 »daduroh marked ι that the electrode closes with the front end of the atomizer (Mg. 9 to 11) · 12 · Device according to one of claims 6 to 9, daduroh characterized in that the atomizer has an annular atomizer rim and the electrode has the shape a disc which is arranged concentrically to the atomizer »edge and with the hand a narrow space forms. la 6981 / 7/15/1957A. 909812/0009