JPS629386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic coating method that prevents over-activation of a high voltage interrupting device.

Electrostatic painting is a method in which charged paint discharged from a paint sprayer is adsorbed onto the object to be coated, which has a potential difference with respect to the charged paint, but since the painting is performed in a high voltage atmosphere, it is difficult to prevent danger. Therefore, a safety device built into the high voltage generator, that is, a high voltage cutoff device in case of an emergency, is provided.

This high-voltage cutoff device is designed to prevent people from entering a high-voltage atmosphere.
It is designed to be activated when a change that occurs when an object or the like enters is detected, and is normally activated depending on the magnitude of the current change.

That is, the cutoff operating point of this high voltage cutoff device is set to about three times the normal current that flows during painting, and the high voltage is cut off when the current reaches the set value. However, if the current setting value for high-voltage cutoff is set to the above value, that is, about three times the normal current, it will not work even if there is a slight change, and the sensitivity will be very poor, making it difficult to improve sensitivity. It was hoped that improvements would be made in this respect. Therefore, in order to improve sensitivity and accuracy, a device was invented that grasps the rate of increase in current in relation to time and detects abnormal events that cause an increase in current at an early stage. (See Publication No. 102638 and Japanese Unexamined Patent Publication No. 102639).

By the way, when electrostatically painting a fairly large object such as a car body, the total area to be coated is large, so the object to be coated must be moved relative to the coating machine while the object is being painted. The surface is painted in small sections one by one. When painting in this way, there are small parts of the object that do not require painting at all (for example, wheel housing parts of a car body). Conventionally, when such a small part that does not require painting is located within the painting range of the paint sprayer, the discharge of charged paint from the paint sprayer is temporarily stopped (paint off), and the part that requires painting is moved according to the relative movement. When the paint was located within the painting range, the paint was again sprayed with charged paint from the paint sprayer.

However, according to the conventional method as described above, when the discharge of charged paint from a paint sprayer is temporarily stopped, a large current change occurs similar to the case in an emergency as described above, and this is Due to this, the high voltage cut-off device that sensitively detects over-operates, that is, cuts off the high voltage at high speed,
A situation where the subsequent painting process had to be temporarily interrupted was likely to occur. This over-actuation, or large current change, was particularly likely to occur when metallic paints were used.

The present invention solves the above-mentioned problems, and when a part that does not require painting is located within the coating range of the paint sprayer, the paint sprayer discharges a very small amount of charged paint without temporarily stopping the discharge. At the same time, it is characterized by reducing the potential difference between the charged paint and the object to be coated. As a result, large current changes do not occur during normal painting environments, making it possible to completely prevent over-operation of the high-voltage cut-off device.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes an automobile body as an object to be coated, and the body 1 is conveyed and moved in the direction of the arrow in the figure by a conveyance device (not shown). On the sides of this conveyance device, a pair of left and right electrostatic coating machines 2 are arranged either fixedly or movably reciprocating a certain amount in the vertical direction (vertical direction in Figure 2) in order to electrostatically coat the left and right side surfaces of the body 1. has been done.
Although not shown, an electrostatic coating machine for coating the upper surface of the body 1 is also arranged.

As shown in FIG. 3, the electrostatic atomizer 2 is equipped with a so-called bell-shaped rotary atomizing head 2a, which has an electrostatic paint reservoir connected to it via an electrostatic paint supply hose 3. Tank 4 is connected. Further, a power source 6 is connected to the rotating atomizing head 2a via a high voltage generator 5 having a built-in high voltage cutoff device (safety device) 5a for cutting off high voltage at high speed.
During electrostatic painting, for example, the electrostatic paint is negatively charged and the body 1 is grounded, so that a high potential difference is applied between the two.

In the above configuration, the atomizing head 2a is rotationally driven.
When the paint is supplied from the pump 7, the charged electrostatic paint is atomized and applied to the body 1 by suction. Therefore, while the body 1 is being moved, it is electrostatically coated sequentially from the left side to the right side in FIGS. 1 and 2.

As is clear from FIG. 2, in the side surface portion of the body 1, the front wheel housing portion 1a and the rear wheel housing portion 1b are essentially unnecessary parts that do not require painting, and the remaining portion 1c is the unpainted portion. This is a part that requires painting. The action of the coating machine 2 on the parts requiring painting 1c and the parts not needing painting 1a, 1b are different as shown in FIG.
In other words, when the area to be painted 1c is located in front of the coating machine 2 (painting range), an extremely high potential difference of, for example, 90 kV is applied between the electrostatic paint and the body 1, and at the same time, the voltage from the coating machine 2 is The discharge amount of the charged paint is large, and the areas 1c that require painting are subjected to normal electrostatic painting.

When the unnecessary parts 1a and 1b are located in front of the coating machine 2, for example, there is a gap between the electrostatic paint and the body 1.
At the same time that a relatively small potential difference of 60 kV is applied, the amount of charged paint discharged from the sprayer 2 is reduced. The amount of paint to be discharged at this time is set to an extremely low amount that does not interfere with painting, that is, a level that does not cause dripping of paint on the edge portions of the wheel housing portions 1a and 1b. The actual value of this low discharge amount varies depending on the coating distance between the coating machine 2 and the body 1. For example, if the coating distance is
In the case of 300mm, it is assumed to be 100c.c./min or less (of course, it is not considered zero). By the way, the discharge amount when painting the area 1c that requires painting is, for example, the above painting distance 300
In mm, it is 400c.c./min.

When electrostatic painting was carried out as described above, a large current change occurred during the painting from the left end to the right end of the body 1 in Figure 1, unless a foreign object such as a human body entered the high voltage atmosphere. Therefore, it is possible to completely prevent malfunction of the high voltage interrupting device 5a. Of course, if a foreign object such as a human body enters the high voltage atmosphere, the high voltage cutoff device 5a will operate normally.
High voltage application is cut off.

By the way, it has been confirmed that when electrostatic painting is performed using a paint other than metallic paint, over-operation of the high voltage interrupting device 5a can be prevented by simply lowering the applied potential difference. However, when metallic paint is used, it is not enough to simply lower the applied potential difference, and by simultaneously lowering this potential difference and simultaneously discharging a small amount of paint from the sprayer 2, the high voltage interrupting device 5a must be activated. It was possible to completely prevent the operation. In this way, the reason why the conditions for overactivation of the high voltage interrupting device 5a are different between metallic paints and other paints is thought to be due to the difference in the change in resistance between the paint sprayer 2 and the body 1. In other words, both types of paint share the same aspect of resistance change based on the change in vapor concentration in the space due to discharge and stop of discharge of charged paint, but in metallic paint, in addition to this change in vapor concentration, there is also a change in resistance value. It is thought that this is because metal powder such as Al contained in the metal powder has a large influence on the resistance value.

In addition, in the example, the case where one object to be coated has a part that requires painting and a part that does not need to be painted is explained.
All the objects to be coated require painting, and if the next object to be coated follows after a short interval, the space between the objects to be coated should be treated as an unnecessary part and painted as described above. Good too.

As is clear from the above description, the present invention has the advantage of completely preventing over-operation even if the high-voltage interrupting device is highly sensitive and can detect an increase in current at an early stage in relation to time. play.

[Brief explanation of the drawing]

FIG. 1 is a top view showing an example of electrostatic painting of an automobile body, FIG. 2 is a side view of FIG. 1, and a diagram showing a time chart of electrostatic painting.
FIG. 3 is a diagram showing an example in which a high voltage interrupting device is connected to an electrostatic coating machine. 1... Automobile body, 2... Electrostatic coating machine, 5a
...High voltage cutoff device.

Claims (1)

[Claims] 1. An electrostatic coating machine equipped with a high-voltage cutoff device that detects and responds to changes in current is used to paint the object to be coated, which has a potential difference with respect to charged paint particles, while moving it relative to the electrostatic coating machine. In the electrostatic coating method, when the atomizer is relatively displaced to a position corresponding to an area that does not need to be painted, a very small amount of paint is ejected from the atomizer without stopping the paint ejection, and the potential difference is An electrostatic coating method characterized by reducing the size of