RU2352692C1 - Low-pressure plating process - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: low-pressure component plating process in electrolysis with electrolyte circulation involves plating process ensured in a bath or out-bath plating cell with continuous, unidirectional and rate-regulated electrolyte circulation enabled by connecting the bath or the cell to two equivalent tanks. Electrolyte from the tanks is supplied in turn to the bath or the cell under atmospheric pressure in one tank and low pressure in the other one, while synchronous changeover of the tanks as well as the pressure are regulated with distributing valves automatically.

EFFECT: higher metallic power yield, considerably improved plating uniformity, better adhesion, stabilised temperature conditions in the working bath with complete cleaning of sucked gases from electrolyte vapour and complete elimination electrolyte discharge into the atmosphere.

5 dwg

Description

The invention relates to the field of applying electrolytic coatings under reduced pressure and can be used to obtain coatings during hardening and restoration of machine parts both with immersion in an electrolytic bath and without immersion, i.e. by supplying electrolyte to the coating site outside the bath (implementation of implanted deposition of metal in the cell).

A known method of producing chromium coatings under reduced pressure [1]. If the pumping device is connected directly to the working electrolytic bath, then there is no electrolyte circulation in this bath, since it only pumps out the gases released during the electrolysis and maintains pressure above the electrolyte, while the electrolyte itself remains stationary. If the working bath is connected to the pumping device through intermediate containers, then the electrolyte in the working bath will not circulate continuously, but only the time it will take to fill the intermediate tanks, after which the circulation process must be stopped to prevent the electrolyte from entering the pumping device, and to release intermediate tanks from the electrolyte (drain the electrolyte into a reserve tank).

After that, by opening the suction and discharge valves, the process of circulation of the electrolyte in the working bath will resume and continue until the intermediate containers are filled with electrolyte. Next, the drain cycle of the electrolyte is repeated.

Thus, the circulation of the electrolyte in the working bath is cyclical (intermittent) in nature, while the duration of the circulation of the electrolyte in the working bath is much shorter than the stagnation time in the bath when the intermediate tanks are released. The deposition conditions of the coatings and their properties are not constant, since the deposition conditions change (the termination of the circulation of the electrolyte in the working bath leads to an increase in its temperature and an increase in pressure above it due to the release of electrolytic gases). Therefore, this device cannot be used for non-applied (local) deposition of electrolytic coatings, for example on the necks of crankshafts and other parts.

The problem to which the invention is directed, is to provide continuous and controlled circulation of the electrolyte at reduced pressure in the working electrolytic bath or in the cell with implanted deposition of metal on machine parts to improve the output parameters of the galvanic process: increase the current yield of the metal, improve the physicomechanical and physico-chemical properties of coatings, a significant increase in adhesion and uniformity of their deposition, stabilization of the temperature regime in the working bath, complete cleaning ue gases aspirated from the liquid phase of the electrolyte and the complete cessation of electrolyte emissions, improving the environmental parameters on the galvanic production station.

This is achieved by the fact that with the method of applying electrolytic coatings at a reduced pressure in the electrolysis zone, in contrast to the prototype, a continuous unidirectional and intensity-controlled electrolyte circulation is maintained in the working galvanic bath or cell under continuous reduced atmospheric pressure, which is created by connecting to the bath or cell of two equal capacity containers, the electrolyte of which is continuously and alternately fed into the bath or cell under atmospheric pressure in one and the pony ennogo pressure gas in another vessel, a synchronous switching process tanks and pneumatic modes are adjusted automatically in distribution taps.

The assembled cell is an autonomous closed-loop technical device mounted on that part of the machine part that undergoes electrochemical processing (electrodeposition of coatings). This autonomous device is equipped with one electrode (anode), while the other electrode is the workpiece. The electrode is positioned in such a way that a space is formed between it and the part, which in the process of coating deposition is filled with continuously circulating electrolyte. For supply and removal of electrolyte in the device corresponding channels are made.

As a result, this technical device operates autonomously, locally (in a certain area of the part), outside the plating bath, in which, unlike the cell, the parts to be processed are immersed entirely in the electrolyte.

The invention is illustrated by drawings:

figure 1 presents a diagram of the device in the position of the taps 4, 5, 6 for pumping the electrolyte from the tank 1 to the tank 2 through the working bath or cell 3;

figure 2 presents the cross section of the valve 4 in the pumping position of the electrolyte from the tank 2 into the tank 1 through the working bath or cell 3;

figure 3 presents the cross section of the tap 5 in the pumping position of the electrolyte from the tank 2 into the tank 1 through the working bath or cell 3;

figure 4 presents the cross section of the valve 6 in the pumping position of the electrolyte from the tank 2 to the tank 1;

figure 5 presents a cross section aa (figure 1) of the connecting groove 23 (figure 1).

The method is as follows: when the cover is removed, the electrolyte is poured into the container 1 to a level not reaching the edge of the pipes 12 and 13 by 100 ... 150 mm, and the electrolyte is poured into the container 2 to a level above the pipe edge 11 by 50 ... 100 mm. The pumping device through the pipes 19 and 16 pumps air from the tank 20, and through the pipe 15, which is connected through the distribution valve 6 to the pipe 14, the vacuum is transferred to the tank 2. The reduced air pressure through the pipe 10, the distribution valve 5, the working electrolytic bath or cell 3, pipe 8, distribution valve 4, pipe 7 is transferred to the tank 1. At the same time, through the window 22 and the groove 23 of the valve 6 and through the pipe 13, atmospheric pressure is transmitted to the tank 1, i.e. In this container, the electrolyte is at atmospheric pressure. The pipe 12 is closed by a faucet 5. Under atmospheric pressure, the electrolyte from the tank 1 through the pipe 7 rises and through the faucet 4 and the pipe 8 enters the working electrolytic bath or cell 3 and then through the pipe 9 through the faucet 5 and the pipe 10 enters the tank 2, where continuously discharged state of gases.

Thus, a cycle of pumping the electrolyte from the tank 1 to the tank 2 is carried out, maintaining a continuous circulation of the electrolyte in the working bath or cell 3 under reduced pressure. The position of the distribution valves 4, 5, 6 during the implementation of this cycle of operation of the device shown in figure 1. Upon reaching the electrolyte level of capacity 2 to a height below the cutoffs of pipes 10 and 14 by 100 ... 150 mm, the control equipment using actuators synchronously changes the position of the plugs of valves 4 and 5, turning them clockwise by an angle of 90 °, and the valve plug 6 counterclockwise at a 90 ° angle. In this case, the vacuum pump runs continuously and the next cycle of equipment starts. The reduced air pressure through the pipe 15 through the valve 6 is transmitted through the pipe 13 to the empty container 1. At the same time, one end of the pipe 7 is continuously immersed in the electrolyte of the container 1, and the other is closed by a plug 4. At the same time, the valve plug 6 connects the pipe 14, and therefore the container 2 with the atmosphere through the groove 23 and the window 22. Under the influence of atmospheric pressure in the tank 2, the electrolyte through the pipe 11 through the valve plug 4 and the pipe 8 enters the working electrolytic bath or cell, maintaining its circulation in the same direction. Further along the pipe 9, the valve 5 and the pipe 12, the electrolyte enters the tank 1.

Thus, the electrolyte flow in the working electrolytic bath or cell 3 is not interrupted, the pressure is kept low, and the electrolyte circulation has a continuous character and direction.

When the capacity 1 is filled with electrolyte to a predetermined level, the control equipment provides the appropriate signals to the actuators of the distribution valves, and the previous cycle is repeated. The specified vacuum value is maintained by the vacuum regulator 17 (Fig. 1) and is controlled by vacuum gauges 21 in the working galvanic bath 3 and in the compensation tank 20. If necessary, the valve 18 can disconnect the system from the vacuum pump. Due to the tightness of the joints, there are no harmful emissions at the installation workplace, and the gases released during the electrodeposition process, mixed with a large portion of air from containers 1 and 2, are released into the atmosphere, becoming explosion-proof. In addition, the reduced pressure in the plating bath 3 and tanks 1 and 2 completely free the gas bubbles from the electrolyte shell, the electrolyte remains in the tanks 1, 2 and 3, without posing any threat to the environment, and the suction gases do not require any cleaning.

The analysis of gas samples emitted by the vacuum pump into the atmosphere showed a complete absence of traces of electrolyte in them.

Providing continuous circulation of the electrolyte in the electrolytic bath or cell for local coating at a residual reduced pressure of 0.04 ... 0.06 MPa allows you to stabilize the temperature in the electrolysis zone, to conduct the electrolysis process at cathodic current densities of up to 400 A / dm ² , the chromium output current up to 43% ... 45% and chromium deposition rate 0.75 mm / h, to obtain non-porous and harder coatings of considerable thickness (up to 1 mm), more evenly deposited over the entire cathode surface in cold self-regulating electrolyte second configuration compared with the conventional method of chromizing.

Since the chrome coatings obtained under reduced pressure are crackless, there is no “flow over chrome” on the chrome parts of hydraulic equipment and the precision parts of diesel fuel equipment, which ensures more efficient and economical operation of interfaces and assemblies. At the same time, the adhesion strength of chromium to the substrate increases, which prevents the formation of chipped chrome on the sharp edges of parts (for example, on plungers of fuel pumps), and the contact strength and endurance of chrome parts increase.

The proposed method can be applied electrolytic precipitation of iron, nickel, cobalt, zinc, tin, lead, gold, silver, copper, etc., alloys based on iron, chromium and other metals, composite electrochemical coatings based on iron, chromium, etc.

In addition to the process of deposition of chromium, a reduced pressure over the electrolyte must be maintained within 0.055 ... 0.065 MPa, given the reduced specific gravity of electrolytes.

As an example, we give a possible list of parts and the purpose of the coatings obtained under reduced pressure. In this way, it is possible to deposit iron coatings on such parts as pivots of the front axle of cars, seats for connecting rods of the connecting rods, rollers of liquid pumps of internal combustion engines, etc. to increase the wear resistance of the parts.

Copper electrolytic coatings can be applied by the bath at reduced pressure as a sublayer in the preparation of anticorrosive and decorative three-layer deposits: copper-nickel-chromium. They can also find application in electrical engineering, electronics to increase the electrical conductivity of products.

Injected deposition of iron, copper and other metals is impractical due to the solubility of the anodes and their frequent change.

This method allows under reduced pressure in the electrolysis zone to maintain an intensity-controlled electrolyte circulation created by connecting to the bath or cell two containers of equal volume, the electrolyte of which constantly and alternately serves a working bath or cell under the influence of atmospheric pressure in one and reduced pressure gases in another tank, and the process of synchronous switching of tanks and pneumatic modes in them is regulated automatically by distribution valves.

Sources of information taken into account

1. Tunturi P.J. Hard-chrome plating method under reduced pressure / "Metals australasia", v.13, 1981. p.20.

Claims (1)

A method of applying an electrolytic coating to a part under reduced pressure in the electrolysis zone during electrolyte circulation, characterized in that the coating is applied in a bath or cell for implanted application with continuous, unidirectional and intensity-controlled electrolyte circulation, which is created by connecting two or two cells to the bath or cell equal in volume of containers, moreover, the electrolyte from the tanks is alternately fed into the bath or cell under the influence of atmospheric pressure in one container and reduced pressure in another , and the synchronous switching of containers and the pressure in them are automatically regulated by distribution valves.

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