JPS6366919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrodeposition coating apparatus. More specifically, the present invention relates to an electrodeposition coating apparatus that prevents coating defects from occurring.

[Prior Art] Electrodeposition coating apparatuses have been widely used for coating automobile bodies and the like.

In such an electrodeposition coating device, objects to be coated, such as automobile bodies, mounted on movable hangers are sequentially placed in an electrodeposition bath, and the electrodeposition is carried out while the objects are moved from the entry section to the exit section of the bath. It is to be painted. However, such an electrodeposition coating apparatus is equipped with a large number of diaphragm electrodes in the tank along the moving direction of the body, and a DC voltage is applied between the diaphragm electrodes and the automobile body. Generally, the applied voltage is the same throughout the period from the start of operation to the end of operation of the electrodeposition coating apparatus.

When painting automobile bodies using conventional electrocoating equipment, the car body Z that is first placed in the electrocoating bath at the start of the operation of the coating line has a fifth
As shown in the figure, when the paint film is immersed in the paint liquid, uneven streaks M (hereinafter referred to as a stepped pattern) appear in the paint film, which resemble a wave pattern.

The reason for this is that at the start of operation, when no other car bodies are in the electrocoating bath, the current density for the car body that entered the bath first becomes high, resulting in a partially thick coating film. This is thought to be due to the fact that it is easily precipitated. This tendency is particularly strong in the case of cationic electrodeposition paints because the clone yield is high and a coating film is easily formed with a small electric current.

Also, during the operation of the painting line, one of the car bodies sent sequentially may fall off due to circumstances in the previous process, and the same cause as above will occur for the car body that enters the tank after it falls off. A stepped pattern may occur.

In order to solve this problem, a coating method described in Japanese Unexamined Patent Publication No. 156798/1983 has been proposed. This coating method is used when an object to be coated enters the electrocoating bath without any other objects to be coated, until the object to be coated is immersed in the paint to some extent (for example, the front fender of a car is submerged in the paint). This is a coating method in which the applied voltage is set to a low voltage, and then the applied voltage is switched to a normal high voltage.

[Problems to be Solved by the Invention] The present invention provides an electrodeposition coating apparatus that implements such a coating method and is capable of reliably performing control operations for lowering and restoring the applied voltage. The purpose is to

[Means for Solving the Problems] The electrodeposition coating apparatus of the present invention has a movable hanger that sequentially feeds the objects to be coated into the electrodeposition bath, and a position in which the objects to be coated are placed in the electrodeposition bath. An electrodeposition coating device whose steady operating state is when the objects to be coated are mounted on all movable hangers in the electrocoating bath. First thing to do
and (b) a second limit switch that operates in the initial state when the object to be coated is completely immersed in the electrodeposition bath, and (c) when the first limit switch is operated and the second limit switch is not operated. The configuration is characterized in that it includes means for lowering the voltage to the diaphragm electrode, and (e) means for restoring the voltage to a steady voltage value after a predetermined period of time after the voltage has dropped.

[Function] When using the electrocoating apparatus of the present invention, the number of objects to be coated placed in the electrocoating bath can be reduced, such as when a dropout occurs in the objects to be coated placed in the bath at the start of operation or during operation. The second limit switch is inactive when the voltage is not less than the steady operating state, while the first limit switch is activated when the object to be coated advances to just before entering the tank, so the voltage applied to the diaphragm electrode is is lowered. When the applied voltage decreases, the number of objects to be coated in the bath is smaller than in the steady state, so the current density per object to be coated becomes approximately the same. For this reason, even if the number of objects to be coated is smaller than in a steady state, a stepped pattern will not occur.

In the present invention, if the first limit switch detects that the object to be coated is just before entering the tank, and the second limit switch is not operating at that time,
It is possible to reliably detect that the object to be coated, which would have been completely immersed in the electrodeposition bath immediately before the object to be coated, is not present in a steady state [Example] Next, the present invention will be described. Examples will be described based on the drawings.

FIG. 1 is an explanatory diagram of the configuration of an electrodeposition coating apparatus which is an embodiment of the present invention, FIG. 2 is an explanatory diagram of the state of the electrodeposition coating apparatus shown in FIG. 1 at the start of operation, and FIG. FIG. 1 is an explanatory diagram of a state in which the electrodeposition coating apparatus shown in FIG.

The electro-deposition coating apparatus A shown in FIG. 1 is an electro-deposition coating apparatus for applying coating to an automobile body Z, which is an object to be coated. The interior of the electrodeposition bath 1 is of a known type, and a cationic electrodeposition paint is placed in the bath, and a diaphragm electrode 2 is provided. On the other hand, automobile bodies Z are placed on a movable hanger 4 that is moved in the direction of arrow X by a conveyor 3, and are immersed in the electrodeposition bath 1 in order. The diaphragm electrode 2 is connected to the anode of a DC power source, and the automobile body Z is connected to the cathode of the power source via a conductive cable that is in sliding contact with the movable hanger 4. In addition, when an anionic electrodeposition paint is used, a cathode is connected to the diaphragm electrode 2, and an anode is connected to the automobile body Z. In this electrodeposition coating apparatus A, the number of automobile bodies Z sequentially placed in the electrodeposition bath 1 is about three in a steady state of operation, and the voltage of the DC power supply has a steady voltage value, for example.
It is set to 300V.

In addition to the above-mentioned configuration, the electrodeposition coating apparatus A of the present invention is additionally provided with limit switches 5 and 6, and these limit switches 5 and 6 are installed immediately before a certain automobile body Z, so that the limit switches 5 and 6 This constitutes a detection means for detecting that the water is not entering the tank. The limit switches 5 and 6 are turned ON when, for example, the movable hanger 4 with the car body Z on it moves and comes into contact with it.
When the automobile body Z and the movable hanger 4 are not moving, they are attached so that they do not come into contact with each other and are turned OFF. Further, the limit switch 5 is placed in a position where it can be activated slightly before the car body Z enters the electrocoating bath 1, and the limit switch 6 is placed in a position where it can be activated in the initial state when the car body Z is completely immersed in the electrocoating bath 1. located at the location. The limit switch 5 corresponds to a first limit switch, and the limit switch 6 corresponds to a second limit switch.

With the above configuration, the limit switches 5, 6
If both are ON, it is detected that the car body Z immediately before the car body Z that is about to enter the tank is entering the tank, and limit switch 5 is turned on.
If the limit switch 6 is turned ON and the limit switch 6 is turned OFF, it is detected that no car body Z is entering the tank immediately before the car body Z that is about to enter the tank.

For example, as shown in FIG. 2, when the first car body Z carried by the conveyor 3 is about to enter the electrocoating bath 1 at the start of operation of the electrocoating apparatus A, the car Since there is no movable hanger 4 and the automobile body Z in front of the body Z1, in this case, the limit switch 6 is turned OFF, and it is detected that the automobile body Z is not placed in the electroplating bath 1. As shown in FIG. 3, during the operation of the electrocoating apparatus, a movable hanger 4 and a car body Z are placed in front of the car body carried by the conveyor 3.
If there is no 0, when the car body Z4 is about to enter the bath, the limit switch 5 is turned on, the limit switch 6 is turned off, and the inside of the electroplating bath 1 is 2
It is detected that only two car bodies Z1 and Z2 are in the tank.

Furthermore, the electrodeposition coating apparatus A of the present invention is provided with voltage adjustment means for lowering the applied voltage or returning it to a steady value. The voltage adjustment means does not need to be a special device, and can be configured using, for example, a variable resistor. Adjustment of the applied voltage using such a voltage adjustment means will be explained with reference to the time chart of FIG. 4.
is the point in time when the limit switches 5 and 6 detect that the number of automobile bodies Z immersed in the electrodeposition bath 1 is smaller than the steady state. At this point, the voltage regulating means is operated and the applied voltage is
Dropped to 100V. Then, for example, 30 seconds
When the voltage is maintained at 100V and reaches the point in time, the voltage adjustment means is operated again to increase the applied voltage.
The voltage rises slowly and returns to the steady voltage value of 300V after about 30 seconds.

In the above, the set time between and is set according to the speed at which the car bodies Z are conveyed by the conveyor 3, and at the time point, a constant number of three car bodies Z are in the electrodeposition bath 1. It is best to keep it in a tank. Further, the time can be controlled using an appropriate timer.

In the above embodiment, it is preferable to use a self-holding timer as the timer because the timing for returning the applied voltage does not change even if the conveyor 3 stops. Further, it is preferable to provide two limit switches 5 and 6 each, because even if one of them fails, normal detection can be performed with the other one.

As described above, when operating the electrodeposition coating apparatus A of this embodiment, the applied voltage may be changed to 1/1/2 of the steady voltage at the start of operation or if a car is out of stock during operation.
The applied voltage can be lowered in the range of 2.5 to 1/3.5, and when operating in a steady state, the applied voltage can be set to a steady voltage. Therefore, the current density when the first car body Z1 and the car body Z4 after the car is out of stock can be made to be approximately the same level as the current density in a steady state, and thereby the car bodies Z1 and Z4 It is possible to effectively prevent the occurrence of a stepped pattern.

Note that even if the applied voltage is temporarily lowered as described above, the quality of the finished coating film is not adversely affected, so that a good painted surface can be obtained.

[Effects of the Invention] The electrodeposition coating apparatus of the present invention can change the voltage applied to the diaphragm electrode 2 according to the number of automobile bodies Z placed in the electrodeposition bath 1. Therefore, the current density can be made substantially uniform during the operation from the start of operation to the end of operation, so that the generation of stepped patterns can be effectively prevented.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of an electrodeposition coating apparatus which is an embodiment of the present invention, FIG. 2 is an explanatory diagram of the state of the electrodeposition coating apparatus shown in FIG. 1 at the start of operation, and FIG. Fig. 1 is an explanatory diagram of a state in which the electrodeposition coating equipment is out of service while it is in operation, Fig. 4 is a time chart showing the fluctuation state of the voltage applied to the diaphragm electrode shown in Fig. 1, and Fig. 5 FIG. 2 is an explanatory diagram showing problems with the conventional device. (Main symbols in the drawings), 1: electrodeposition bath, 2: diaphragm electrode, 3: conveyor, 4: movable hanger, 5: limit switch, 6: limit switch.

Claims (1)

[Scope of Claims] 1. The objects to be coated are sequentially fed into the electrodeposition bath using movable hangers, and the objects to be coated are loaded on all the movable hangers at the position where the objects to be coated are placed in the electrodeposition bath. An electro-deposition coating device that operates normally when suspended, and includes (a) a first limit switch that operates just before the object to be coated enters the electro-deposition bath; and (b) the object to be coated is (c) means for reducing the voltage applied to the diaphragm electrode when the first limit switch is activated and the second limit switch is inactive; and (e) means for returning the voltage to a steady state after a predetermined period of time after the voltage drops.