SU1585399A1 - Apparatus for automatic control of mean current density in electroplating bath - Google Patents

Abstract

The invention relates to electroplating and can be applied in electroplating baths to control and automatically control the average current density. The purpose of the invention is to improve the accuracy of controlling the average current density when processing parts of complex shape. The device contains two groups of sensors 1, 2 and 3, 4 of average current density, with one group located equipotentially at the cathode, another at the anode, three differential amplifiers 5, 6, 7, the inputs of the first of which are connected to one group of sensors 1, 2 , the inputs of the second amplifier are to another group, the first input of the third amplifier 7 is connected to the output of the first amplifier 5, and the second to the output of the second amplifier 6, an adjustable current source 12, a control unit 11 a current source, a setpoint 10 current density and a comparison unit 9, one input is connected to the output th third amplifier 7, the other input - with the current density setter 10, and the output - to the input of the control unit 11 a power source. The device can operate in baths powered by a cut-off sinusoid current or a constant coherent current. In the process of electrolysis, a change in the polarization potential is taken into account. 1 il.

Description

The invention relates to electroplating and can be used in automated galvanic lines in the process of coating.

The purpose of the invention - an increase accuracy ⁵ NOSTA regulating the average current density in the processing of complex shape by taking into account changes in polarization potential electrolysis process ed 3 <1 ·

The drawing shows a structural diagram of a device for automatic control of current density in a plating bath. fifteen

The device contains current density sensors 1, 2 and 3, 4 (titanium, titanium, platinum coated ^, or graphite) installed, equidistant (equipotentially) - respectively, for jq of the grounded cathode K and anode A, differential amplifiers 5-7, indicator 8 average current density, comparison unit 9, software. current density sensor 10, including a timer, overdrive / 25 current density switch and a managed switch (not shown), control unit 11 and current source 12.

The device operates as follows. fifty

Current density sensors have a polarization potential relative to the electrolyte and EMF between the sensors and the cathode Up, which changes during electrolysis. The potential between sensors 1 and 2 is U = 0, since they are installed equipotentially to the cathode K. The potential of the grounded cathode U _k = 0 _o Changing the polarization potential by ZlUp affects both inputs of differential amplifier 6 equally, but the change in potential ZlUp affects the output of this amplifier does not affect. The signal at the output of this amplifier is tuned to a minimum value, experimentally selecting the locations of sensors 1 and 2 close to the cathode, taking into account possible changes in the dimensions and configuration of the cathode. Sensors 3 and 4, similarly to sensors 1 and 2, are located equipotentially and close to the anode, (with a rectangular arrangement of the anode and cathode, sensors 3 and 4 are also equipotential to the cathode). Sensors 3 and 4 are a-like sensors 1 and 2 are connected to the first and second inputs of the second differential amplifier 6. The voltage between these sensors is also zero (Ζΐυ _5Λ - 0). The location of these sensors is determined experimentally under the condition of a minimum voltage at the output of the second differential amplifier 6. The bath electric current flowing between the anode and. cathode, creates a voltage drop on the resistance of the electrolyte and in its sections. A voltage drop (U _3i ~ U _{f / 2} ) is created in the electrolyte section between two pairs of sensors 3, 4 and 1.2, which is proportional to the current density of the bath D. Voltage drop U _i4 ^U f, z ^{= It is} fixed and amplified by the third differential amplifier 7, the first input of which is supplied with a potential U ^ ₂ close to the cathode U _K (i.e., О), and to the second input U _3i close to the anode. The voltage drop between two pairs of sensors can be approximately expressed where is the current flowing through the electrolyte section between two pairs of sensors;

^R 34_ ₁₂ ^{- const} ° F ^TIV Leniye this electrolyte portion;

and _IR -voltage between the anode and the cathode.

The current is Ι _{5Λ 1 l} and the resistance is difficult to calculate, but it is possible to experimentally establish the dependence = = f (I s, 4_ t, v.). The magnitude of the current 1 ^ _4. , ₂ depends in turn on the total anode current T o ( _K , since the average current density is D = where S / is the active area of the cathode.

The voltage drop between two pairs of sensors C ^ is proportional to the bath current 1 _{0 (k} , and the density in turn is proportional to Ι _ακ . Therefore

U о! = F (¼) = f (D).

The measurement indicator must first be calibrated by the cathode with known geometric areas S _n , which can be considered equal to active as a first approximation. During calibration of the dependence of D = f (Uj) (bath voltage and _yak) and the anode area is kept constant, and changes only the cathode area.

Sensors of current density to differential amplifiers are connected through resistors of several kOhm, small current flows through them (a few '1585399 mA), so they are not coated with metal. I

In a bathtub with a flat anode, sensors 3 and 4 can be connected and connected to the second input of the third differential amplifier, bypassing the second differential amplifier.

The comparison unit 9 compares the voltage proportional to the current density U ^ i on the indicator 8, with the voltage set by the programmer 10 current density U ^. Using a software adjuster, you can set the required current density at each time t. The output of the comparison unit 9 produces a voltage equal to the voltage difference U _r = U y - U. ^. The voltage through unit 11 changes the output voltage of the regulated current source 12. Thus, the required current density D is automatically set in the galvanic bath at each time t is applied.

The device can also be used in the mode for measuring and monitoring the average anode current density in a van — not at a constant cathode density; accordingly calibrating the area of the anodes in a similar way.

The proposed installation allows to increase the accuracy of the average current density, which is especially important when coating parts with precious metals.

Claims (1)

SUMMARY OF THE INVENTION A device for automatically controlling the average current density in a plating bath, comprising an adjustable current source connected to the cathode and anode, a current source control unit and medium current density sensors combined in two groups, characterized in that, in order to increase the accuracy of the average control current density at 15 processing parts of complex shape by taking into account changes in the polarization potential in the electrolysis process, it is equipped with three differential amplifiers, software a current density sensor and a comparison unit, each group of sensors being installed equidistant respectively to the anode and cathode and connected to the inputs of the first and second differential amplifiers, the outputs of which are connected to the inputs of the third amplifier, the output of which is connected through the comparison unit and the control unit to an adjustable current source, software a density adjuster of 30 ka is connected to the second input of the comparison unit, and the bath cathode is grounded and connected to one of the inputs of the second differential amplifier.