JPH09249994A - Electrocoating equipment - Google Patents

Abstract

(57) [Abstract] [Problem] Even if there is a dissimilar metal joint on the object to be coated,
It eliminates appearance defects caused by current concentration when entering the tank, and
Provided is an electrodeposition coating device capable of reducing the difference in coating film thickness. SOLUTION: A sensor 8 for detecting entry of an object to be coated 5 into an electrodeposition vessel 3, an auxiliary electrode 7 arranged in the vicinity of an entry portion in the electrodeposition vessel 3, and a pulse to the auxiliary electrode 7. A pulse power supply 6 for applying a voltage and a pulse power supply for applying a pulse voltage to the auxiliary electrode 7 when a dissimilar metal bonding portion on the article 5 is bathed by a signal from the sensor 8. 6. A control device 9 for controlling 6 and an electrodeposition coating device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrodeposition coating apparatus, and more particularly to an electrodeposition coating apparatus capable of obtaining a good coating appearance even when a dissimilar metal joint is present on an object to be coated.

[0002]

2. Description of the Related Art Conventionally, in electrodeposition coating of automobile bodies and parts, as shown in FIGS. 5 and 6, a plurality of electrodes 2 connected to a power supply device 1 are filled with electrodeposition coating. An article to be coated 5 arranged in the electrodeposition tank 3 and connected to the power supply device 1 and electrically connected to a collector bar 4 provided outside the tank.
Is immersed in the electrodeposition tank 3 to control the potential difference between the object 5 to be coated and the electrode 2 to coat the object 5 to be coated with an appropriate coating thickness. 5 is a plan view, FIG. 6a is a side view of the electrodeposition tank shown in FIG. 5, and FIG. 6b is a view of the electrodeposition tank shown in FIG. It is a figure.

In such electrodeposition coating, the potential difference generated between the electrode and the object to be coated when the object to be coated enters the tank is such that the object to be coated is completely immersed in the tank and the coating material aggregates and adheres. Unlike the potential difference at this time, current concentration occurs on the object to be coated when entering the tank, resulting in uneven coating film or appearance defects such as pinholes and hash marks.

In order to prevent such defective appearance due to current concentration at the time of entering the bath, various methods have been proposed in the past (for example, JP-A-58-93894 and JP-A-2-22497). Gazette, JP-A-5-70997, etc.).

In these conventional methods, the current concentration generated on the object to be coated at the time of entering the tank can be suppressed by various means such as energizing the tank, totally submerged energizing, and changing the energizing stepwise. The appearance defect resulting from this is prevented.

[0006]

In any of the conventional methods for suppressing current concentration at the time of entering a bath, the voltage applied to the article to be coated at the time of entering the bath is lowered in any of the methods described above, so that the electrodeposition in the initial stage of electrodeposition can be reduced. This is to prevent current concentration.

However, when the applied voltage is lowered at the initial stage of electrodeposition, there is a dissimilar metal joint portion on the surface of the object to be coated, for example, dissimilar metal joint by MIG welding to a steel plate or buildup of dissimilar metal. However, there is a problem that a difference in coating film thickness occurs between different metals, resulting in poor appearance. It is known that, in electrodeposition coating, generally, when the voltage applied to an object to be coated is lowered, throwing power to the object to be coated is deteriorated. It is considered that there is a difference in the amount of current flowing between the two and the throwing powers of those metals are different, which causes a difference in coating film thickness.

In order to avoid such a problem due to the application of a low voltage, if a high voltage is applied to improve the throwing power of the entire article to be coated, even if there is dissimilar metal bonding, the coating film between the metals is high. Although there is almost no difference in thickness, however, if a high voltage is continuously applied at the initial stage of electrodeposition, the appearance defects such as pinholes and hash marks will occur due to the current concentration at the time of bathing as described above.

Therefore, an object of the present invention is to prevent appearance defects such as pinholes and hash marks due to current concentration when entering a tank, and even when there is a dissimilar metal joint on the object to be coated, An object of the present invention is to provide an electrodeposition coating apparatus capable of reducing the difference in coating film thickness.

[0010]

According to the present invention for achieving the above object, a plurality of electrodes connected to a power supply device are arranged in an electrodeposition tank filled with an electrodeposition paint. ,
The article to be coated, which is electrically connected to the power supply device via a current collecting bar, is immersed in the electrodeposition tank, and the potential difference between the article to be coated and the electrode is controlled to apply the article to be coated. In an electrodeposition coating apparatus for coating an object, an object position detecting means for detecting that the object has reached a position where it enters the electrodeposition tank,
An auxiliary electrode arranged in the vicinity of a portion where the object to be coated in the electrodeposition tank enters, a pulse power source for applying a pulse voltage to the auxiliary electrode, and a signal from the object position detecting means, When the dissimilar metal joint on the object to be coated enters the tank,
Control means for controlling the pulse power source so as to apply a pulse voltage to the auxiliary electrode, and an electrodeposition coating apparatus.

According to a second aspect of the present invention, in the structure according to the first aspect, the pulse power source gradually increases the pulse frequency of the pulse voltage generated by the pulse power source as the object to be coated moves. It is an electrodeposition coating device characterized by having.

According to a third aspect of the present invention, in the structure according to the first aspect, the pulse power source gradually changes the pulse width of the pulse voltage generated from sparse to dense with the movement of the object to be coated. An electrodeposition coating apparatus having a pulse width modulation means.

According to a fourth aspect of the present invention for achieving the above object, a plurality of electrodes connected to a power supply device are arranged in an electrodeposition tank filled with an electrodeposition coating material, The article to be coated electrically connected via a current collecting bar is dipped in the electrodeposition tank to control the potential difference between the article to be coated and the electrode to coat the article to be coated. In the electrodeposition coating apparatus to perform, the auxiliary electrode is arranged in the vicinity of the portion where the object to be coated enters the electrodeposition tank, and it is detected that the object to be coated enters the electrodeposition tank, The electrodeposition coating apparatus is characterized in that a coating voltage is made uniform at a dissimilar metal joint portion on the object to be coated by applying a pulse voltage to the auxiliary electrode.

[0014]

First, the effects of the present invention will be described for each claim.

According to the first aspect of the present invention having the above-mentioned structure, the position of the object to be coated is detected by the object position detecting means, and the object position detecting means is detected. The signal from the control means, when the dissimilar metal joint on the coated object enters the bath, controls the pulse power source to apply the pulse voltage to the auxiliary electrode arranged in the vicinity of the bath in the electrodeposition bath. Since it is decided to apply the voltage, it is possible to avoid the low voltage application state in the dissimilar metal joint, and also avoid the concentration of current at the time of bathing to reduce the difference in the coating film thickness in the dissimilar metal joint, High-quality electrodeposition coating can be performed without causing appearance defects such as pinholes and hash marks.
Further, the configuration of the present invention requires only minor improvements such as providing an auxiliary electrode in the electrodeposition tank of the conventional electrodeposition coating apparatus, so that the facility investment is small and the economy is high.

According to a second aspect of the present invention, in the configuration according to the first aspect, the pulse power source has a pulse frequency modulating means, and the pulse frequency of the pulse voltage applied to the auxiliary electrode is gradually increased. Therefore, since it is possible to compensate for the current value that decreases as the coating film is formed on the object to be coated so that a substantially constant amount of electricity can be added, in addition to the effect of the configuration of claim 1, efficient electrodeposition can be achieved. The effect is that painting can be performed.

According to a third aspect of the present invention, in the structure according to the first aspect, the pulse power source has a pulse width modulation means, and the pulse width of the pulse voltage applied to the auxiliary electrode is gradually and densely varied. Since it is possible to compensate for the current value that decreases as the coating film is formed on the object to be coated, and to add a substantially constant amount of electricity, in addition to the effect of the configuration of claim 1, The effect is that good electrodeposition coating can be performed.

Further, according to the invention of claim 4,
When the dissimilar metal joint on the object to be coated enters the tank,
Since the pulse voltage is applied to the auxiliary electrode located near the bath in the electrodeposition bath, it is possible to avoid the low voltage application state at the dissimilar metal joint and to concentrate the current during bath. By avoiding the above, it is possible to reduce the difference in coating film thickness between the dissimilar metal joints and perform high-quality electrodeposition coating without causing defective appearance such as pinholes and hash marks.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described. The members having the same function are designated by the same reference numerals.

FIG. 1 is a plan view of an electrodeposition coating apparatus to which the present invention is applied, FIG. 2a is a side view of the same, and FIG. 2b is a view seen from the downstream side in the moving direction of an object to be coated. In addition, in FIG.
The electrical connection is shown by a dotted line, and in FIG. 2a, the auxiliary electrode 7, the article 5 to be coated, and the carrier 51 for carrying the article 5 are those existing inside the electrodeposition tank 3. All are shown by solid lines for the sake of clarity.

As shown in the figure, this electrodeposition coating apparatus is connected to the power source apparatus 1 which receives power from a main power source 20 and supplies each electrode with a voltage suitable for electrodeposition coating.
A plurality of electrodes 2 arranged in an electrodeposition tank 3 filled with electrodeposition paint, a collector bar 4 which is connected to a power supply device 1 and supplies power to an object to be coated 5, and further an object to be coated 5 An auxiliary electrode 7 is provided in the electrodeposition tank 3 so as to be positioned in the vicinity of the dissimilar metal joint on the object to be coated 5 when the tank is formed.
It is connected to a pulse power supply 6 connected in parallel to the power supply device 1, and the pulse power supply 6 is controlled by a control device 9 which is a control means. Further, near the entrance of the electrodeposition tank 3, there is provided a position sensor 8 which is an object position detecting means for detecting that the object 5 has reached the entrance position, and a signal from the position sensor 8 is provided. The control device 9 controls the pulse power supply 6 in accordance therewith.

The article to be coated 5 is conveyed inside and outside the electrodeposition tank by a carrier 51 which is suspended and moved by a carrier line 52, and the carrier 51 has a sliding contact terminal 41 and a current collecting bar 4
And the object 5 to be coated are electrically connected.

The control device 9 controls the position sensor 8 to the object 5 to be coated.
When it receives a signal that detects that the metal has arrived at the bathing position, the pulse power source 6 is instructed to apply the pulse voltage to the auxiliary electrode 7 at the time when the dissimilar metal joint portion on the object 5 is bathed. . Here, the control device 9 determines the position sensor 8 based on the moving speed of the carrier and the position of the dissimilar metal joint on the article 5.
A simple configuration is possible in which the time for which the dissimilar metal joint portion enters from the time of receiving the signal from is received is set in advance, the time is measured by the timer, and then the pulse power supply 6 is instructed. Further, in such a coating process, when a system that centrally manages the whole is used, the movement state of the article to be coated 5 is grasped from the computer in the system and the dissimilar metal joint is inserted. The pulse power supply 6 may be operated at the time of tanking.

The pulse power supply 6 is instructed by the controller 9
The pulse voltage applied to the auxiliary electrode 7 by the frequency modulation as shown in FIG.
The frequency of the pulse applied gradually is controlled to increase with the movement of the object to be coated, or, as shown in FIG. 3b, the pulse width gradually changes from sparse to dense with the movement of the object to be coated. Control to do. By changing the pulse frequency or the pulse width in this way, the current value that decreases as the coating film is formed on the article 5 is compensated for, and a substantially constant amount of electricity is added, making electrodeposition coating efficient. , Can be done uniformly.

Such pulse frequency modulation or pulse width modulation is performed by a thyristor having a chopper function which operates as pulse frequency modulation means or pulse width modulation means.

The pulse voltage is turned off immediately before the next object 5 to be coated enters the tank, for example, when the position sensor 8 detects that the next object 5 has reached the tank position. The pulse voltage may be turned off, or the pulse voltage may be turned off by previously measuring the time until the next object enters the tank according to the moving speed of the object to be coated.

The pulse voltage applied to the auxiliary electrode 7 is substantially the same as that of the electrode 2 because the circuit system of the pulse power supply 6 and the auxiliary electrode 7 is connected in parallel with the circuit system of the power supply device 1 and the electrode 2. The voltage is a constant voltage of, for example, about 200 to 350V. This is a voltage that is high enough to suppress the difference in coating film thickness between dissimilar metals, and considers the balance with the voltage applied to the electrode 2 to prevent equipment and quality problems due to stray currents. It is the value.

In this way, when the dissimilar metal joint portion on the article 5 enters the tank, a relatively high constant voltage pulse voltage is applied to the vicinity of the dissimilar metal joint portion by the auxiliary electrode 7.
In particular, by gradually increasing the pulse density and width, it is possible to avoid the low voltage application state at the dissimilar metal joint and to avoid current concentration at the time of bathing. The difference in coating thickness at the joint is reduced, and appearance defects such as pinholes and hash marks do not occur.

The power supply to the pulse power supply 6 may be taken from the main power supply 20 as shown in FIG. 1, but as shown in FIG. 4, for example, from the power supply line from the power supply device 1 to the electrode 2. A branched line 10 may be provided to supply power. Further, in the practice of the present invention, a conventional power supply device may be used as it is, one power supply device may be provided for one electrodeposition tank, or a plurality of power supply devices may be used. Furthermore, as in the conventional case, the voltage control when the coating object is placed in or out of the tank may be performed in combination with the present invention.

[Brief description of drawings]

FIG. 1 is a plan view for explaining the configuration of an electrodeposition coating apparatus to which the present invention has been applied.

FIG. 2a is a side view of the electrodeposition tank shown in FIG.
2b is a view of the electrodeposition tank shown in FIG. 1 as viewed from the downstream side in the direction in which the article to be coated is conveyed.

FIG. 3 is a drawing showing an example of a pulse voltage used in the above electrodeposition coating apparatus.

FIG. 4 is a view showing another example of the connection form of the pulse power source used in the above electrodeposition coating apparatus.

FIG. 5 is a plan view for explaining the configuration of a conventional electrodeposition coating apparatus.

FIG. 6a is a side view of the electrodeposition tank shown in FIG.
FIG. 6b is a view of the electrodeposition tank shown in FIG. 5 as seen from the downstream side in the direction in which the article to be coated is conveyed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrodeposition power supply, 2 ... Electrode, 3 ... Electrodeposition tank, 4 ... Current collecting bar, 5 ... Coating object, 6 ... Pulse power supply, 7 ... Auxiliary electrode, 8 ... Position sensor, 9 ... Control device.

Claims (4)

[Claims] 1. An article to be coated in which a plurality of electrodes connected to a power supply device are arranged in an electrodeposition tank filled with an electrodeposition paint, and which are electrically connected to the power supply device via a collector bar. Is immersed in the electrodeposition tank to control the potential difference between the object to be coated and the electrode to coat the object to be coated, wherein the object to be coated is the electrodeposition An object position detecting means for detecting that the object has reached a position where the object enters the tank; an auxiliary electrode disposed in the vicinity of a portion of the electrodeposition tank where the object enters the tank; A pulse power source for applying a pulse voltage to the object, and a signal from the object position detecting means, so that when the dissimilar metal joint on the object enters the tank, the pulse voltage is applied to the auxiliary electrode. A control means for controlling the pulsed power source, and an electrodeposition coating apparatus. 2. The electrodeposition coating apparatus according to claim 1, wherein the pulse power source has a pulse frequency modulation means for gradually increasing the pulse frequency of the pulse voltage generated as the object to be coated moves. . 3. The pulse power supply has pulse width modulation means for gradually changing the pulse width of the pulse voltage to be generated from sparse to dense as the object to be coated moves. Electro-deposition coating equipment. 4. An article to be coated in which a plurality of electrodes connected to a power supply device are arranged in an electrodeposition tank filled with an electrodeposition paint, and which are electrically connected to the power supply device via a collector bar. Is immersed in the electrodeposition tank to control the potential difference between the object to be coated and the electrode to coat the object to be coated, wherein the object to be coated is the electrodeposition The auxiliary electrode is arranged in the vicinity of the portion to be entered into the bath, the entry of the article to be coated into the electrodeposition bath is detected, and a pulse voltage is applied to the auxiliary electrode to form the article to be coated. An electrodeposition coating apparatus characterized in that the coating film thickness at the above dissimilar metal joint is made uniform.