JPH0849094A - Local anodization method and device therefor - Google Patents

Abstract

PURPOSE:To always keep the inner surface of the parts to be treated close to the temp. of an electrolyte. CONSTITUTION:Temp. sensors 7, 8, 9 and 10 set respectively at the feed and discharge parts of an electrolyte 19 and the feed and discharge parts of a liq. coolant 18, a flow rate sensor 11 and a control computer 3 for inputting the detected temp. and flow rate from the temp. sensors 7, 8, 9 and 10 and flow rate sensor 11 and the voltage value and current value from an electrolyzing power source 4 to calculate the target temp. of the coolant feed part after the time tx are provided to the device. Since the coolant temp. after the time tx is controlled to the target temp. by a coolant refrigerator 6, the temp. of the surface of a hollow part 15 is rapidly approached to the electrolyte temp., and the surface is controlled to an appropriate temp. as the heat released due to the thickening of an anodic oxide film is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a local anodic oxidation method and apparatus applied to the surface treatment of aluminum and aluminum alloy products.

[0002]

When it is desired to form an anodic oxide film only on a part of the surface of a part, a method of applying a masking agent to the part other than the surface to be processed is usually used, but the surface to be processed corresponds to the inner surface of the hollow part. In this case, in order to save the trouble of masking and to prevent problems due to the rise of the liquid temperature and the formation of air pockets in the internal space of the parts, the electrolytic solution is circulated by the pump and supplied only to the surface to be processed inside the parts. However, a method of electrolyzing was sometimes used.

In the method of electrolyzing while circulating the electrolytic solution with a pump, especially in the case of hard anodizing treatment in which electrolysis is performed at a high current density, Joule heat generated in the anodic oxide film having high electric resistance is not sufficiently removed. However, the temperature of the surface to be treated may be considerably higher than the temperature of the electrolytic solution, and in this case, a good film cannot be formed.

Therefore, a method has been proposed in which the outer surface of the untreated part is brought into contact with a cooling liquid to remove the Joule heat from the back side of the surface to be processed (the invention of the applicant's application "local anodizing method"). (Japanese Patent Application No. 03-18097
1)). In this method, there is no particular standard for setting the temperature of the cooling liquid, and the temperature is often set to almost the same as that of the electrolytic solution.

However, in this case, the temperature of the surface to be treated may be significantly higher than the temperature of the electrolytic solution.
After the heat transfer coefficient h [W / m ² K] is obtained in advance, the coolant temperature is T _A −IV / Ah [K] (where T
_A [K]: Electrolyte temperature, A [m ² ]: Area to be treated, I
[A]: current, V [V]: voltage) has been proposed as a control method (the invention of the applicant of the present invention "local anodizing method and apparatus" (Japanese Patent Application No. 05-9927).
7)).

The structure of the above-mentioned "local anodizing apparatus" of the invention is as shown in FIG. 3, in which the cathode / liquid supply port 16 and the liquid discharge port 17 are set in the hollow part 15 and the electrolytic solution 19 is placed inside.
And the outside is cooled by the cooling liquid 18, and the temperature of the cooling liquid 18 is a set value T _A -IV obtained based on the input T _A from the temperature sensor 8 and the inputs I and V of the current and voltage 12.
The refrigerator 6 was controlled so as to be / Ah [K].

[0007]

Electrolyte solution (anodizing solution)
The temperature is set to an appropriate value determined so that a high quality anodic oxide film can be obtained, and it is desirable that the surface temperature to be treated is originally maintained at substantially the same temperature as the liquid temperature.

The contact of the cooling liquid with the back side of the surface to be treated (outside of the component when the inner surface of the hollow component is treated) is an effective method for suppressing the temperature rise of the surface to be treated.
For example, if the temperature of the cooling liquid is controlled to be equal to the temperature of the electrolytic solution, the temperature of the surface to be treated cannot be made equal to the temperature of the electrolytic solution. In particular, if the amount of heat generated is large, as in the case of hard anodization, the temperature of the surface to be treated may rise considerably.

The conventional coolant temperature is T _A -IV / Ah.
The method of controlling the temperature to be [K] is effective in bringing the temperature of the surface to be treated close to the temperature of the electrolytic solution, but when the capacity of the refrigerator is not sufficient, the cooling liquid reaches the control temperature. There was a problem that it took time.

In the case of constant current electrolysis, the voltage increases as the thickness of the anodic oxide film, which is an insulator, increases, and the amount of heat generated increases with time. There was a problem that I could not do it enough. The present invention is intended to solve the above problems.

[0011]

[Means for Solving the Problems]

(1) In the local anodizing treatment method of the present invention, a hollow component having a surface to be treated on its inner surface is used as a component to be treated, an electrolytic solution is circulated and supplied to the surface to be treated, and a cooling jacket is provided on the outside to cool the component. In the local anodizing treatment method in which a liquid is circulated and supplied, and a voltage is applied from the power source for electrolysis between the cathode and the cathode inserted thereinto to anodize the inner surface of the component to be treated, prior to the anodizing treatment. Circulate and supply the electrolytic solution to the surface to be treated, and circulate and supply the cooling solution to the cooling jacket.
Temperature TAin [K] of electrolyte supplied to the surface to be treated, temperature TAout [K] of electrolyte discharged from the surface to be treated, temperature TCin [K] of coolant supplied to the cooling jacket, from cooling jacket The temperature TCout [K] of the discharged cooling liquid and the circulating flow rate F [m ³ / s] of the cooling liquid were measured, and the specific heat C _P [J / kgK] and the density ρ [kg / m ³ ] of the cooling liquid were measured. Processed area A [m ² ] and the measured temperatures TAout, TCin, TCout
And the flow rate F are used to obtain the heat transfer coefficient h (W / m ² K) from the surface to be treated to the cooling liquid by the following equation: h = (ρC _P F / A) · (TCout−TCin) / (TAout
-TCout) The temperature TAin [K] of the electrolytic solution supplied to the surface to be treated is kept constant, and while measuring the voltage value V [V] and the current value I [A], the electrolysis power source supplies the treated portion and the cathode. Voltage is applied to start electrolysis, and the voltage value V, the current value I, and the voltage value Vt _- Δt [V] and the current value It _- Δ before Δt time.
Using t [A], the predicted heat generation amount Q _x [W] after the time t _x [s] has elapsed is calculated by the following equation, and Q _x = I · V + [(I · V−It ₋ Δt · Vt ₋ Δt)
/ Delta] t] · t _X t _X [s] target temperature of the cooling liquid supplied after a time lapse of determined by the following equation, the temperature TCin of _{TAin -Q X / Ah-Q X} / ρC P F [K] coolant It is characterized in that the refrigerator for cooling liquid is controlled so as to be equal to or lower than the target temperature.

(2) The local anodizing apparatus of the present invention comprises:
A hollow part having a surface to be processed on its inner surface is used as a part to be processed, an electrolytic solution is circulated and supplied to the surface to be processed, and a cooling jacket is provided on the outer side to circulate and supply the cooling liquid, and a cathode inserted inside the part. In the local anodizing device for applying an electric voltage from the power source for electrolysis to the inner surface of the part to be processed, the temperature sensor provided at the inflow part of the electrolytic solution on the surface to be processed, the surface to be processed Temperature sensor provided in the discharge part of the electrolyte solution, a temperature sensor provided in the cooling solution inflow part of the cooling jacket, a temperature sensor provided in the cooling solution discharge part of the cooling jacket, provided in the cooling liquid circulation pipe Flow rate sensor, the detected temperature is input from each of the temperature sensors, the detected flow rate is input from the flow rate sensor, the voltage value and the current value are input from the electrolysis power source, and the calculation described in the above invention (1) is performed. _X time A control computer that outputs the target temperature of the cooling liquid in the inflow portion after the excess, and the above target temperature is input from the computer to control the refrigerator for the cooling liquid so that the cooling liquid in the inflow portion becomes the target temperature or less. It is characterized by having a refrigerator controller.

[0013]

In the above invention (1), when the electrolytic solution is circulated and supplied to the surface to be treated and the cooling liquid is circulated and supplied to the cooling jacket, the heat of the electrolytic solution is transferred to the cooling solution, but the cooling solution is electrolyzed. The amount of heat received from the liquid is expressed by the following equation.

ΡC _P F (TCout−TCin) [W] where TCout [K] is the temperature of the cooling liquid discharged from the cooling jacket, TCin [K] is the temperature of the cooling liquid supplied to the cooling jacket, and ρ [ kg / m ³ ]: Density of cooling liquid, C _P [J
/ KgK]: specific heat of the cooling fluid, F [m ³ / s]: flow rate of the cooling fluid.

On the other hand, the amount of heat transferred to the cooling liquid is expressed by the following equation.

Ah (TAout-TCout) [W] where TAout [K] is the temperature of the electrolytic solution discharged after being supplied to the surface to be treated, A [m ² ]: Area of the surface to be treated, h
[W / m ² K]: Apparent heat transfer coefficient from the surface to be treated to the cooling liquid.

Since both are the same, the apparent heat transfer coefficient h is calculated by the following equation (1).

[0018] _{h = (ρC P F / A} ) · (TCout-TCin) / (TAout-TCout) ... (1) above during anodization of the treated parts, anodized film formed is a resistor to be treated Joule heat is generated on the surface, and the amount of heat generated is expressed by the following equation, where the electrolytic voltage is V [V] and the current is I [A].

I · V [W] Approximate time until the coolant reaches a new set temperature is defined as t _X [s], and the calorific value Q _X [W] after t _X hours is predicted. _X is shown by the following equation.

Q _X = I · V + [(I · V−It ₋ Δt ·
Vt _- Δt) / Δt] · t _X here, Δt [s] minute time is set appropriately, It _-
Δt and Vt ₋ Δt are current value and voltage value before time Δt [s].

Under the condition that the surface temperature T _W [K] to be treated is almost equal to the temperature of the electrolytic solution, the following relationship is established.

T _W ≈TAout ≈TAin Here, TAin is the temperature of the electrolytic solution supplied to the surface to be treated.

Assuming that the heat quantity Q _X is almost transmitted to the cooling liquid side, the heat quantity Q _X is represented by the following equation.

Q _X ≈Ah (TAin−TCout) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… collapse.

[0025] TCout = _{[Ah / (ρC P F + Ah} ) ] -
TAout + [ρC _P F / (ρC _P F + Ah)] · TCin Substituting this into Eq. (2) and setting TAout = TAin, t
The following equation for obtaining the target temperature of the cooling liquid supplied after the lapse of _X hours is obtained.

[0026] _{TCin = TAin -Q X / Ah-} Q X / ρC P F [K] .................. (3) Therefore, in order to properly set the time t _X, coolant supplied to the cooling jacket By controlling the temperature obtained by the equation (3) to be equal to or lower than the target temperature, the surface temperature to be treated can be made close to the electrolytic solution temperature.

In the above invention (2), the control computer inputs the detected temperature from the temperature sensors provided at the inflow part of the electrolytic solution, the exhaust part thereof, the inflow part of the cooling liquid, and the exhaust part, and the cooling liquid is supplied. Coolant supplied after t _X time has elapsed by inputting the detected flow rate from the flow rate sensor provided in the circulation pipe, inputting the voltage value and current value from the electrolysis power source, and performing the calculation described in the above invention (1). Since the target temperature is calculated and output, the temperature of the surface to be treated can be set to a value close to the temperature of the electrolytic solution, as in the above-mentioned invention (1).

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus according to an embodiment of the present invention will be described with reference to FIG. The apparatus according to this embodiment shown in FIG. 1 includes a cathode / liquid inlet 16 inserted from above into a hollow component 15 having a liquid discharge port 17 at the top, and a cooling liquid provided outside the hollow component 15. A cooling jacket 24 in which a supply line 25 and a cooling liquid discharge line 26 are connected, an electrolytic solution tank 27 in which a cathode / inflow port 16 and a liquid discharge port 17 provided in the hollow component 15 are connected through a pipe, and the same electrolysis. The refrigerator 21 connected to the liquid tank 27 and provided with the refrigerator controller 20, and the refrigerator 6 provided with the refrigerator controller 5 connected to the cooling jacket 24 through the cooling liquid supply line 25 and the discharge line 26. A local anodizing process comprising a control computer 3 connected to the refrigerator control device 5, and an electrolysis power source 4 connected to the computer 3 to which the hollow component 15 and the cathode / liquid inlet 16 are connected. It is for the apparatus.

The cathode / liquid inlet 16, the electrolytic solution tank 27, the refrigerator control device 20, the refrigerator 21, and the cooling jacket 24 form the electrolysis device 2, and the control computer 3, the electrolysis power source 4, The refrigerator controller 5 and the refrigerator 6 form a controller 1.

In the present embodiment, in addition to the above-mentioned device, the temperature sensors 7, 8 provided on the cathode / liquid inlet 16, the liquid outlet 17, the cooling liquid supply line 25, and the cooling liquid discharge line 26, respectively. 9, 10 and a flow rate sensor 11 provided in the cooling liquid discharge line 26, the temperature sensors 7, 8 and the flow rate sensor 11 are connected to the control computer 3, and the temperature sensors 9, 10 are a refrigerator controller. 5
It is connected to the.

Next, the procedure of anodizing the inner surface of the hollow component 15 using the apparatus according to this embodiment will be described.
The contents will be described below based on the operation flow chart shown in FIG.

First, the hollow part 1 is placed in the cooling jacket 24.
5 is set, the cathode / liquid inlet 16 is inserted into the hollow component 15, and after connecting various pipes, etc., the electrolytic solution 19 is circulated and supplied into the hollow component 15, and the cooling liquid is fed into the cooling jacket 24. 18 is circulated.

The circulating supply of the electrolytic solution 19 and the cooling solution 18 is performed.
At this time, the control computer 3 causes the temperature sensors 8, 9,
The temperature TAout of the discharge side of the electrolytic solution 19 from 10
[K], temperature TCin [K] of supply side of coolant 18 and discharge
Input the side temperature TCout [K] and cool from the flow sensor 11.
Liquid circulation flow rate F [m³/ s] and enter the ratio of the coolant 18
Heat C _P[J / kgK] and density ρ [kg / m³] And treated area
A [m²] To the cooling liquid 18 from the surface to be treated by the following equation
Heat transfer coefficient h [W / m²K].

[0034] _{h = (ρC P F / A} ) · (TCout-TCin
) / (TAout−TCout) Next, the supply side temperature TCin of the cooling liquid 18 is reset to the same supply side temperature TAin of the electrolytic solution 19, and the hollow component 15 and the cathode / liquid inlet 16 are supplied from the electrolysis power source 4. A voltage is applied between them to start electrolysis.

At this time, the control computer 3 constantly monitors the current value I and voltage value V of the electrolysis power source 4, and Δ
While memorizing the current value I and the voltage value V before t time, the target value 14 of the cooling fluid supply side temperature TCin after the time t _{X has} elapsed is calculated by the following equation.

T <Δt TCin = TAin −IV / Ah-IV / ρC _P F t> Δt TCin = TAin −Q _X / Ah-Q _X / ρC _P F Here, Q _X = I · V + [(I・ V-It _- Δt ・ Vt
_{- Δt)} / _Δt] · t _X.

The target value 14 of the supply side temperature TCin of the cooling liquid 18 obtained as described above is input to the refrigerator controller 5.
The control device 5 controls the refrigerator 6 so that the supply side temperature TCin of the cooling liquid 18 becomes the target value 14 described above.

As described above, the temperature of the surface to be treated, which was difficult in the case of the conventional device, is quickly brought close to the temperature of the electrolytic solution, and the amount of heat generated by the increase in the amount of heat generated by the increase in the thickness of the anodic oxide film is increased. It is possible to appropriately control the temperature of the surface to be processed corresponding to the increase.

In this embodiment, the hollow component 15 made of 7075 aluminum alloy is actually subjected to anodizing treatment with the inner surface thereof being the surface to be treated. The contents and results thereof will be described below.

The hollow part 15 is hermetically sealed with the cathode / liquid inlet 16 and the liquid outlet 17 attached, and the hollow part 1
A cooling jacket 24 was provided on the outer side of 5. Coolant 18
Is used, and its density ρ = 1.0 × 10 ³
[Kg / m ³ ] and specific heat C _P = 4.2 × 10 ³ [J / kgK].

In the control computer 3, the processed area A =
Input 0.020 [m ² ] and then Δt = 60 [s],
t _x = 180 [s] was input. As a result, the current I [A] and the voltage V [V] before Δt time are stored, and the I and V after t _X time are predicted.

The electrolytic solution 19 is the temperature TAi detected by the temperature sensor 7.
The cooling liquid 18 was circulated with n maintained at 7.5 ° C., and the coolant 18 was initially circulated with the detected temperature TCin of the temperature sensor 10 maintained at 4.0 ° C.

At this time, the temperature TAout detected by the temperature sensor 8
Is 7.2 ° C, and the temperature TCout detected by the temperature sensor 9 is 4.4.
C, and the flow rate F detected by the flow rate sensor 11 is 0.0002.
[M ³ / s], and the heat transfer coefficient h is h≈6000 [W / m
² K] was calculated.

Thereafter, the cooling water temperature was reset so that TCin = TAin (7.5 ° C.), and electrolysis was started. The electrolyte solution 19 is sulfuric acid (135 kg / m ³ ) and oxalic acid (15 kg / m ³ ).
^The electrolysis conditions are as follows. The electrolysis condition is to increase the current density from 0 to 280 [A / m ² ] over 20 minutes after the start of electrolysis, and then at 280 [A / m ² ] for a constant current for 50 minutes. Electrolysis was performed to form a hard anodic oxide film.

Between t <Δt (t: time after the start of electrolysis)
Is the coolant temperature is TAin-IV / Ah-IV / ρC_PF
[K] (I [A]: current, V [V]: voltage)
However, if t ≧ Δt, t_XHeat value Q after hours_XQ_X=
I ・ V + [(I ・ V-It_-Δt ・ Vt_-Δt) / Δ
t)] ・ t_X(However, It_-Δt, Vt_-Δt is Δt
Predicted by the previous current and voltage) and set the coolant temperature as
TAin-Q_X/ Ah-Q _X/ ΡC_PAim for F [K]
Controlled.

After electrolysis for a total of 70 minutes in this way, the energization and circulation of the electrolytic solution are stopped, and washing water is introduced through the pipe 22,
It was washed with water by being discharged into the pipe 23 through the hollow component 15.

After washing with water, the hollow part 15 was removed, cut and the inner surface was examined. As a result, the appearance was black gray and was uniform and smooth, and the film thickness was 51 to 53 μm. A film equivalent to that with hard anodization was obtained.

The hollow component 15 is anodized by changing the temperature TAin of the electrolytic solution and the circulating flow rate F of the cooling liquid. The contents and results will be described below. apparatus,
The electrolytic solution and the electrolytic conditions are the same, the electrolytic solution temperature TAin is 10.6 [° C.], and the coolant circulating flow rate F is 0.0001.
[[M ³ / s]]. Further, Δt = 60 [s], t _X = 3
00 [s].

When the cooling liquid temperature TCin was circulated while keeping it at 7.0 (° C.), TAin was 10.4 [° C.], TCout was 7.3 [° C.], and the heat transfer coefficient h was h≈2030 [. W /
m ² K] was calculated.

The cooling liquid temperature during electrolysis was controlled in the same manner as in the first embodiment. After electrolysis and washing with water, the parts were taken out, cut and the inner surface was examined.As a result, the appearance was black gray, uniform and smooth,
The film thickness was 52 to 54 μm, and a film equivalent to that obtained by the ordinary hard anodization performed by immersing the flat plate in the electrolytic solution was obtained.

[0051]

The method and apparatus for local anodizing treatment of the present invention are provided in the temperature sensor and the cooling liquid circulation pipe respectively provided in the inflow portion of the electrolytic solution, the exhaust portion thereof, the inflow portion of the cooling liquid and the exhaust portion thereof. Target temperature of the coolant inflow section after t _X time has elapsed by inputting the detected temperature and detected flow rate from the respective flow rate sensors and the temperature sensors and flow rate sensors above, and the voltage value and current value from the electrolysis power source. By including a control computer for calculating, the refrigerator for cooling liquid controls the temperature of the cooling liquid after the lapse of t _X time to the target temperature,
The temperature of the surface to be processed of the hollow part can be quickly brought close to the temperature of the electrolytic solution, and the temperature of the surface to be processed can be controlled appropriately in response to the increase in the amount of heat generated as the thickness of the anodic oxide film increases. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation procedure according to the above-mentioned embodiment.

FIG. 3 is an explanatory diagram of a conventional device.

[Explanation of symbols]

 1 Control Device 2 Electrolysis Device 3 Control Computer 4 Power Supply for Electrolysis 5 Refrigerator Control Device 6 Refrigerator 7, 8, 9, 10 Temperature Sensor 11 Flow Sensor 12 Electrolysis Voltage and Current 13 Cooling Liquid Temperature 14 Cooling Liquid Inlet Side Target Temperature 15 Hollow Parts 16 Cathode and Liquid Inlet 17 Liquid Discharge Port 18 Coolant 19 Electrolyte 20 Refrigerator Controller 21 Refrigerator 22 Rinsing Water Introducing Pipe 23 Rinsing Water Discharging Pipe 24 Cooling Jacket 25 Cooling Liquid Supply Line 26 Coolant Discharging Line 27 Electrolyte tank

Claims (2)

[Claims] 1. A hollow part having a surface to be processed on its inner surface is used as a part to be processed, and an electrolytic solution is circulated and supplied to the surface to be processed,
A cooling jacket is provided on the outside to circulate and supply the cooling liquid, and a voltage is applied between the cathode and the cathode inserted from the electrolysis power supply to anodize the inner surface of the part to be treated. In the method, the electrolytic solution is circulated and supplied to the surface to be treated and the cooling liquid is circulated and supplied to the surface to be treated prior to the anodizing treatment so that the temperature TAin [K] of the electrolytic solution supplied to the surface to be treated, The temperature TAout [K] of the discharged electrolyte, the temperature TCin [K] of the cooling liquid supplied to the cooling jacket, the temperature TCout [K] of the cooling liquid discharged from the cooling jacket, and the circulation flow rate F [m of the cooling liquid. ³
/ s], the specific heat of the cooling liquid C _P [J / kgK], the density ρ [kg / m ³ ], the treated area A [m ² ] and the measured temperatures TAout, TCin, TCout and the flow rate. after using the F obtained by the following equation heat transfer coefficients h (W / m ² K] of the cooling liquid from the treated _{surface, h = (ρC P F /} a) · (TCout-TCin) / (TAout
-TCout) The temperature TAin [K] of the electrolytic solution supplied to the surface to be processed is kept constant, and while measuring the voltage value V [V] and the current value I [A], the electrolysis power source supplies the above-mentioned processed parts and cathode. A voltage is applied between the two to start electrolysis, and the above voltage value V and current value I
A Delta] t time before the voltage value Vt _- Delta] t [V] and current value It _-
Using Δt [A], the predicted heat generation amount Q _X [W] after elapse of t _X [s] time is obtained by the following equation, and Q _X = I · V + [(I · V−It ₋ Δt · Vt ₋ Δt)
/ Delta] t] · t _X t _X [s] target temperature of the cooling liquid supplied after a time lapse of determined by the following equation, the temperature TCin of _{TAin -Q X / Ah-Q X} / ρC P F [K] coolant A method for local anodization treatment, characterized in that a refrigerator for a cooling liquid is controlled to be equal to or lower than the target temperature. 2. A hollow component having a surface to be treated on its inner surface is a component to be treated, and an electrolytic solution is circulated and supplied to the surface to be treated,
A cooling jacket is provided on the outside to circulate and supply the cooling liquid, and a voltage is applied between the cathode and the cathode inserted from the electrolysis power supply to anodize the inner surface of the part to be treated. In the apparatus, a temperature sensor provided at the inflow portion of the electrolytic solution on the surface to be processed, a temperature sensor provided at the exhaust portion of the electrolytic solution on the surface to be processed, a temperature sensor provided at the inflow portion of the cooling liquid of the cooling jacket, The temperature sensor provided in the cooling liquid discharge part of the cooling jacket, the flow rate sensor provided in the coolant circulation pipe, the detected temperature from each of the above temperature sensors, the detected flow rate from the above flow rate sensor, and the electrolysis power supply described above. Inputting a voltage value and a current value more than Claim 1.
The control computer that outputs the target temperature of the inflow cooling liquid after the time t _{X has} elapsed by performing the calculation described in (4), and the above target temperature is input from the computer so that the inflow cooling liquid becomes equal to or lower than the target temperature. A local anodizing apparatus comprising a refrigerator controller for controlling a refrigerator for cooling liquid.