JPS60235663A - Electrostatic coating apparatus - Google Patents

Abstract

PURPOSE:To inhibit generation of spark securely with a simple apparatus by inserting a non-linear impedance into a high voltage feeder circuit and connecting a main electrode of a gap switch with a trigger electrode. CONSTITUTION:A non-linear impedance element 11 is connected to a high voltage feeder circuit 2 between a high voltage source 1 and a charging electrode 5 of an electrostatic coating apparatus, a main electrode 9'a at one side of a gap switch 9' is connected to the high voltage feeder circuit 2, another main electrode 9'b to a low voltage terminal at almost an earth voltage, further, a trigger electrode 9'c to the high voltage feeder circuit 2 interposing the non-linear impedance element 11 between the main electrode 9'a and the trigger electrode 9'c. By this constitution, abnormal increase of coating current is prevented in the case of abnormal access of an object to be coated, and the gap switch is held at a dischaged condition due to the drop of electric voltage. Thus, generation of spark is inhibited securely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Applicability] The present invention relates to an improvement in a static coating device with a functional material that can prevent the generation of sparks during static painting.

[Conventional technology]

Recent electrostatic coating devices are often equipped with a function to prevent the generation of sparks that can cause fires, and a typical one is shown in FIG. In FIG. 1, a high voltage power supply device 1 consisting of a high frequency inverter, a step-up transformer, a multi-stage voltage doubler rectifier, etc.
Variable high voltage output in the range of about V to about 120 KV full high voltage power supply line 2 and a current limiting resistor inserted in the middle 6.
4 to the charging electrodes 5 of the paint sprayer. The current detection resistor 6 is mainly grounded from the positive terminal of the high voltage power supply 1.
The entire current flowing to the negative terminal of the object to be coated 7, the charged electrodes 5 of the coating machine, the high-voltage power supply line 2, and the current-limiting resistor 4.5 is detected and a detection signal is given to the spark occurrence prediction circuit 8. Various methods for predicting spark occurrence have already been proposed.
For example, a method of making a judgment by comparing the level of the detection signal with a reference value, a method of making a judgment by comparing the differential signal obtained by differentiating the detection signal with the reference level, or a method of making a judgment by comparing the differential signal obtained by differentiating the detection signal with the reference level, or a method in which the differential signal of the detection signal is differentiated into a tuning fork. There are methods for making a determination by comparing the signal with a reference level, and methods that combine these methods. Therefore, when spark generation is predicted as a result of predetermined processing of all the detection signals from the spark generation prediction circuit 8Fi resistor 6, a spark generation prediction signal is applied to the high voltage grounding switch 9, and this grounding Switch 9't-closed. When the grounding switch 9 is closed, the high-voltage power supply path 2 is connected to the grounding point via the retention resistor 10 and the grounding switch 9. Therefore, the potential of the high voltage power supply line 2 is determined by the capacitance such as the ground capacitance formed between the high voltage power supply line and the ground, and the resistance 1.
It decreases according to a discharge time constant determined from 0, etc., and prevents sparks from occurring at all.

[Problem that the invention seeks to solve]

However, in conventional electrostatic coating equipment, it is necessary to select all the resistance values of the current limiting resistor 6.4 to the extent that the coating voltage does not drop too much.

When an abnormal current flows, the high voltage grounding switch 9 must be fully closed while a large voltage is applied between the charged electrode 5 of the sprayer and the object 7 to be coated.

In addition, it is very difficult to set the reference level in the spark generation prediction circuit 8, and therefore there are drawbacks such as the high voltage grounding switch 9 malfunctioning due to noise, or conversely sparking occurring before the high voltage grounding switch 9 closes. Ta.

[Means for solving problems]

In order to eliminate the drawbacks of the conventional device, the present invention uses a nonlinear impedance element that operates with a small impedance in the normal painting current range, but whose impedance increases rapidly when the normal painting current range is exceeded. An abnormal current flows by inserting the nonlinear impedance element into the power supply path, connecting one of the main electrodes and the trigger electrode of the gap switch to the high voltage power supply path, and connecting the other main electrode to the low voltage terminal. 11. As the impedance of the nonlinear impedance element increases rapidly, its voltage drop increases rapidly. It is characterized in that the total voltage of the charged electrodes of the paint sprayer is suddenly lowered, and at the same time, the gap switch is brought into a discharging state.

〔Example〕

A preferred embodiment of the present invention according to FIGS. 2 and 3
i52 As shown in Fig. 3, a high-voltage power supply line 2 between a high-voltage power supply device 1 consisting of a high-frequency inverter, a step-up transformer 1B, a multi-stage voltage doubler circuit 1c, etc. and the charged electrodes 5 of the electrostatic atomizer is connected as shown in Fig. 3. A nonlinear impedance element 11 having a current-voltage characteristic is connected to the gap switch 9', which is used as a high voltage grounding switch.One main electrode 9°a of the gap switch 9' is connected to the high voltage power supply path 2, and the other main electrode 9' b t ? '! is connected to the low voltage terminal at ground potential, and the trigger electrode 9 is connected to the main electrode 9'a with the linear impedance element 11 in between.
'c is connected to the high voltage power supply line 2.

As shown in FIG. 3, the nonlinear impedance element 11 responds to changes in voltage drop (Δl) with respect to changes in flowing current (Δl).
ΔV) is very small and the impedance is substantially small in the first region 2 region Y, and the second refraction point (b)
It has a very small region 21 of 'v/j11 exceeding 't-'.

In this embodiment, the current value H corresponding to the current at the first bending point (a) is set to be the upper limit of the range of the normal coating position i, or a value larger than this. The voltage value VH corresponding to the voltage at the inflection point (b) of No. 2 is set to approximately the maximum voltage applied to the charging electrodes 5 of the coating machine, that is, the maximum charging voltage.

Therefore, according to this embodiment, when normal painting is being performed, the impedance of the nonlinear impedance element 11 is very small, and since it is operating in the first region X, the voltage drop is small. Now, when the coating current starts to increase abnormally due to the object 7 approaching abnormally and exceeds IHt, the nonlinear impedance element 11 starts to operate in the second region Y, and its impedance, that is, the voltage drop suddenly increases. increase The cause of the abnormal increase in paint current cannot be removed,
Just before the object to be coated 7 comes into contact with the charged electrode 5, the voltage drop across the nonlinear impedance element 11 reaches approximately the voltage VH at the second bending point (b), and as a result, the potential of the charged electrode 5 of the atomizer increases. It goes to almost zero. Therefore, unless the object 7 to be coated collides with the charged electrodes 5 of the sprayer, there is almost no risk of sparks occurring.

On the other hand, when the nonlinear impedance element 11 operates in the first region X, that is, when it operates with a normal coating current, the gap switch 9'
Since the voltage drop is small, the voltage between the main type fM9'a of the gap switch 9' and the trigger electrode 9'c is small and no trigger is generated, but the nonlinear impedance element 11 operates in the second region Y. As the voltage drop increases rapidly, the potential difference between the main electrode 9''a and the trigger electrode 9'c of the gap switch 9' also increases rapidly, and a small spark is generated between these electrodes. By the main electrode 9''a.

Ionization of nearby gas occurs and a main discharge occurs between the main electrodes 91a and 9''b. When the gap switch 9' reaches the discharge state, the capacitance C81 formed between the high voltage power supply line 2 and the ground The electric charge is discharged through the gap switch 9', and the electrostatic capacitance c formed between the nonlinear impedance element 11 and the coating machine, the high-voltage power supply line between the coating machine and the ground, etc.
As shown in FIG. 6, the charge 82 is discharged through the nonlinear impedance element 11, which has a small impedance in the reverse direction, and the gap switch 9'. If necessary, such as when the impedance in the opposite direction of the nonlinear impedance element 11 is large, the coating current Ip may be changed as shown by the chain line in FIG.
The nonlinear impedance element 1 is opposite to the flow direction of
By connecting the high voltage diode 12 in parallel with the capacitance Cs2, the electric charge of the capacitance Cs2 can be discharged in a very short time.

〔Effect of the invention〕

As described above, according to the present invention, the nonlinear impedance element greatly suppresses an abnormal increase in the paint flow rate that occurs when an object to be painted approaches an electrostatic sprayer, and Since the electrical charge of the machine is significantly reduced and the rapidly increasing voltage drop causes the gap switch to enter a discharge state, the generation of sparks can be suppressed much more reliably with a simpler device than in the past.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a conventional electrostatic coating device, Fig. 2 is a diagram showing an embodiment of the electrostatic coating device according to the present invention, and Fig. 6 is a diagram for explaining an embodiment of the present invention. This is a diagram. 1... High voltage power supply device, 2... High voltage power supply line, 5゛. Charged electrodes of the JflL coating machine, 7...Object to be painted, 9
'... Gap switch, 9゛°° high voltage grounding switch, 11... Nonlinear impedance element% Applicant
Origin Electric Co., Ltd. Figure 1

Claims (1)

[Claims] An electrostatic coating device comprising: a high-voltage power supply device that supplies high voltage to an electrostatic spraying machine via a high-voltage power supply line; and a high-voltage grounding switch connected between the high-voltage power supply line and a low-voltage terminal. , a nonlinear impedance element that operates with a small impedance in the range of a normal coating current and operates in a region where the impedance increases rapidly when the range of the normal coating current is exceeded is inserted in the high voltage power supply path; A gap switch having two or more main electrodes and one or more trigger electrodes is used as a high voltage grounding switch, and the sudden increase in voltage drop of the nonlinear impedance element is fully utilized to bring the gap switch into a fully discharged state. A coating device that is characterized by particularly suppressing the occurrence of sysparks.