JPS5835600B2 - Black chrome plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a black chrome plating method used for small parts such as screws.

In black chrome plating, in order to obtain good black chrome plating, not only a relatively large current density is required, but also it is necessary to maintain the bath temperature at a low temperature.

Because of the high current density, conventionally the objects to be plated were held one by one by clips provided on a rack, and the elasticity of the clips increased the contact pressure with the objects to be plated.

Black chrome plating was then carried out by suspending this rack in a plating tank maintained at a constant low temperature and using this rack as a cathode.

However, manually holding small parts such as screws into clips one by one is extremely troublesome and inefficient, which increases the price of black chrome-plated screws. There was this inconvenience.

This invention was made in view of these circumstances,
The object of the present invention is to provide a black chrome plating method that can efficiently apply black chrome plating to small parts such as screws and can greatly contribute to cost reduction.

In order to achieve such an object, the present invention disposes a substantially cylindrical cathode, which has a slightly enlarged diameter at the top and rotates on its own axis, in a revolving plating tank, and uses the centrifugal force caused by the revolution to
pressing an object to be plated against the inner surface of the cathode, and filling a space between the anode and the cathode facing the cathode with a plating solution;
The plating solution in the plating tank is circulated between an auxiliary tank and a cooling device provided outside the plating tank, and the plating solution is mixed with 300 to 400 g/l of chromic acid anhydride and 5 to 9 g/l of chromic anhydride.
g/l oxalic acid, 0.5-0.8, 9/1 barium carbonate, 0.1-0. : 1/1 of hydrosilicic acid, and black chromium plating is carried out by keeping the plating solution at a temperature of minus 0 to 10°C.

The present invention will be described in detail below based on the drawings.

FIG. 1 is a partial cross-sectional overall configuration diagram of an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of the main parts in the stationary state, and FIG. 3 is a cross-sectional view in the operating state.

In these figures, reference numeral 1 denotes a circular plating solution tank, which is open at the top and has a bearing portion 1a integrally formed in its center.

Reference numeral 2 denotes a revolving frame, which is formed in the shape of a cylindrical drum.

This frame 2 includes a base plate 3, an outer wall plate 4, and an upper cover plate 5, and a shaft 6 projecting downward is integrally formed in the center of the base plate 3.

This shaft 6 is inserted into the bearing portion 1a of the tank 1, and 2
It is rotatably supported by two bearings 7a and 7b.

8 is a large cylinder fixed to the center of the upper cover plate 5, and 9 is this large cylinder 8.
The lower end of the narrow tube 9 is enlarged in diameter and welded to the inner surface of the large tube 8.

Between the large tube 8 and the narrow tube 9 is a plating liquid pool 10.
It becomes.

Reference numeral 11 denotes a revolution gear, which is fitted and fixed to the upper end edge of the large cylinder 8.

This revolution gear 11 is rotated by a drive mechanism (not shown), and rotates the entire drum 2 at a substantially constant speed (for example, 130 to 1
70 R, P, M,).

Reference numerals 15 and 16 denote slip rings attached to the outer circumferential surface of the large cylinder 8 via an insulating material 17, and these slip rings 15 and 16 each receive a negative voltage from a DC power source (not shown) via brushes 18 and 19. and a positive voltage is applied.

25 is a shaft located on the center line of the revolution frame 2, and this shaft 25 is pivotally supported by the base plate 3 and the upper cover plate 5,
Its upper end protrudes above the narrow tube 9, and here the rotation gear 2
6 is fixed.

The rotation gear 26 is for rotating the plating tanks 30 and 31 described later at a low speed (for example, about 1 to 5 R, P, M), and is rotated by a drive mechanism (not shown).

Denoted at 30 and 31 are plating tanks, which, as shown in FIG. 1, are arranged at symmetrical positions with respect to the axis 25.

As shown in Fig. 2.3, the plating baths 30 and 31 have a substantially cylindrical cathode 32 whose diameter is slightly enlarged at the top, and a cathode 3
2, and an auxiliary anode 34 surrounding the outside of the cathode 32.

Note that this auxiliary anode 34 also serves as a case for the plating tanks 30 and 31.

The anode 33 is formed to hang downward from a lid member 35 that is covered with a circular opening formed in the upper lid plate 5,
Further, the auxiliary anode 34 is attached to the lower surface of the upper cover plate 5 so as to hang down.

Insulating members 36 and 37 are interposed between the anode 33 and the auxiliary anode 35 and the upper cover plate 5, and are further electrically connected by a conductive material 38 that does not come into contact with the upper cover plate 5.

This conductive material 38 is connected to the slip ring 16 on the positive voltage side.

An opening 39 is formed in the center of the cover plate 35, and this opening 39
is covered with a lid 40.

This lid 40 is formed with an inlet 41 for inserting a screw (an iron material coated with nickel plating) as an object to be plated.

The lower part of the cathode 32 is a small-diameter cylindrical part 45, and the vicinity of the upper end of this cylindrical part 45 is pivotally supported by a member 46.

That is, the member 46 connects to the auxiliary anode 3 via the insulating material 47.
A cylindrical portion 45 extends downwardly through the center of this member 46, and is supported by a seal member 48 and a bearing 49 in a watertight manner.

A gear 51 is fixed to the lower end of the cylindrical portion 45 via an insulating material 50, and this gear 51 is pivotally supported by the substrate 3.

A passage 52 communicating from the inside of the cathode 32 to the inside of the plating solution tank 1 is formed in the gear 51 and the cylindrical part 45.
The opening of this passage 52 on the cathode 32 side is closed by a lid 53.

The upper end of a push rod 54 passing through the passage 52 is rotatably locked on the lid 53, and the lower end of the push rod 54 is connected to a lever 55.
is connected to one end of the

The lever 55 is pivotally supported near the center by a bracket 56 fixed to the lower surface of the base plate 3, and is biased by a tension spring 57 so that the lid 53 closes the passage 52.

Therefore, when the drive end (right side in the figure) of the lever 55 is pushed downward, the push rod 54 moves upward and the lid 53 is opened.

Therefore, the screws housed in the cathode 32 fall into the tank 1.

Note that if a plate or the like is placed in the receiver having a small hole below the passage 52, only the plated screws can be easily collected.

58 is a cathode brush, which is connected to the slip ring 15.
It is connected to the.

59 is a gear fixed to the shaft 25;
9 meshes with the gear 51 to rotate the cathode 32.

Next, the circulation path of the plating solution will be explained.

The tank 1 is provided with an outflow path 60 for the plating solution.

An auxiliary tank 61 is provided below this tank 1 (underground in this embodiment), and the plating solution flowing out from the tank 1 flows down into this auxiliary tank 61.

A cooling section 63 of a cooling device 62 is disposed inside this auxiliary tank 61, and the plating solution accumulated here is cooled down to -10°C.
Maintain the specified temperature within the range of .

64 is a pump, and this pump 64 is an auxiliary tank 61
The plating solution inside is supplied to the plating solution reservoir 10.

65 is the plating tank 30 from this plating liquid reservoir 10.
This is a pipe that guides the plating solution into the inside of the Vibro 5.
The downstream side thereof passes through the lid 40 and faces into the opening 39.

That is, the downstream opening of this vibro 5 is the plating tank 30.
．． It serves as an inlet 66 for the plating solution into 31.

The cathode 32 is provided with some small holes, and the plating bath 30
．． Due to the centrifugal force caused by the revolution of the revolving frame 2, the plating solution in the anode 31 passes through the small holes of the cathode in the outer circumferential direction and rises along the inner surface of the auxiliary anode 34.

A plurality of outlets 67 are provided near the upper edge of the auxiliary anode 34, and the plating solution flows from these outlets 67 to the plating tanks 30, 3.
1 and flows down along the inner surface of the outer wall plate 4 of the revolving frame 2.

A plurality of through holes 68 are provided in the substrate 3, and the plating liquid flowing down along the outer wall plate 4 passes through the through holes 68 and flows into the tank 1.
flow down inside.

Note that a protection plate 69 is installed between the tank 1 and the revolving frame 2 to prevent the plating solution from scattering.

The plating solution used in this example was prepared with the following composition.

Chromic anhydride 300-400g//1 Chromic acid 5-9 fl/13 Barium carbonate 0
．． 5-0.8 g/l hydrofluoric acid o, i-0
．． 3 g71 Next, the plating process using this device will be explained.

First, when screws are introduced through the input port 41 of the lid 40 and the pump 64 is activated, the screws and the plating solution are collected in the plating tank 30, 31.

When the revolving frame 2 is revolved in this state, the screws are pressed toward the outer circumference of the revolving frame 2 together with the plating liquid (see FIG. 3).

Then, the screw gradually moves upward along the inner surface of the cathode 32.

Between the cathode 32 and the anode 33, and between the cathode 32 and the auxiliary anode 34
If a constant voltage is applied between them, black chrome plating will be applied to the screws.

Then, if the cathode 32 is further rotated, the screws will be attached to the cathode 32.
Since the screws roll on the inner surface of the screw, the entire surface of the screw is uniformly plated with black chrome.

During this time, the plating solution continues to be circulated by the pump 64, so the plating solution cooled in the auxiliary tank 61 is constantly supplied to the plating bath, and plating proceeds at a substantially constant bath temperature, resulting in beautiful plating. It becomes possible to apply black plating.

After plating is completed, the circulation of the plating solution is stopped and the drive end of the lever 57 is further pushed downward to open the lid 53 and the screws fall down from the passage 52.

By continuing the above operations, it is possible to efficiently plate a large number of screws with black chrome.

While general metallic-colored bright chromium plating deposits only metallic chromium, black chromium plating is obtained by eutectoiding this metallic chromium and chromium oxide.

It is believed that trivalent chromium ions greatly contribute to the precipitation of metallic chromium.

The precipitation mechanism of the metallic-colored chromium plating layer is thought to be as follows.

Chromic acid solution consists of hexavalent chromium ions, and when oxalic acid is added as a reducing agent, the hexavalent chromium ions are reduced to 3
It becomes a valent chromium ion.

These trivalent ions become metallic chromium and are reduced and precipitated on the surface of the object to be plated.

Therefore, when obtaining a metallic luster plating layer, reducing agent (oxalic acid)
It is desirable to add a large amount of.

However, in the case of black chromium plating, it is necessary to reduce trivalent chromium ions and leave a large amount of hexavalent ions in order to promote the precipitation of chromium oxide.

In the present invention, 300 to 400,971 chromic anhydride,
A small amount of oxalic acid (5-9, 9/1) is added to prevent trivalent chromium ions from becoming excessive.

Barium carbonate is removed by precipitating sulfuric acid, which is normally mixed into chromic acid as an impurity, as barium sulfate.

Barium carbonate is added in an amount of 0.5 to 0.8 F/1, but if the amount is outside this range, the sulfuric acid content in the plating solution will be too high or too low, making it impossible to achieve homogeneous electrodeposition.

Hydrosilicofluoric acid acts as a catalyst plate and has the effect of enabling plating at low temperatures and improving the coverage of plating, but if the amount added is less than 0.1 g/l, it has no effect.

If the amount is more than 0:l/1, the plating will not be black but will be grayish white, and the plating layer will be brittle and have poor mechanical properties.

Although the temperature of the plating solution rises due to heat generated during the plating reaction, it is constantly cooled to 0 to -10°C by a cooling device as it is circulated between the plating tank and the auxiliary tank.

This increases the amount of plating solution used, reduces changes in the solution composition during plating, and makes it possible to maintain a uniform plating temperature, making it possible to apply uniform and good plating to a large number of parts using a rotating plating bath. It becomes like this.

In particular, setting the liquid temperature to a low temperature of 0 to -10°C has a great influence on the color of the plating layer and the quality of electrodeposition.

Moreover, if it is above 0°C, a large current density is required, and if it is below -10°C, the plating speed is slow and good plating cannot be obtained.

That is, a good homogeneous black chromium plating layer can be obtained at low current density only by setting the liquid temperature to 0 to -10°C.

In addition, the revolution speed of the revolution frame 2 is increased, and the cathode 32
If the rate of expansion of the upper end is reduced (closer to the shape of an inner cylinder), the centrifugal force will also increase, so that the object to be plated and the cathode 32
This also increases the contact pressure with the metal, making it possible to further increase the current density and providing even better black chrome plating.

As described above, this invention is configured so that the object to be plated is pressed against the cathode by centrifugal force, and the plating solution is circulated between the plating tank and the cooling device located outside the plating tank. There is no need to hold the objects one by one between clips on a rack or the like, and the plating solution is always kept at a constant temperature or below, so it is possible to efficiently apply black chrome plating to a large number of objects to be plated.

In addition, the plating solution for black chrome plating that has been used in the past has been used for plating that is manually hooked onto clips, etc., so when using such a conventional plating solution in a rotating plating tank, However, there were problems in terms of plating quality, plating speed, etc.

The present invention uses a plating solution for black chrome plating having a specific component ratio as described above, and since black chrome plating is performed while cooling to a predetermined temperature within the range of -10°C, the quality of black chrome plating can be improved. , the speed is also significantly improved,
It also becomes possible to significantly reduce plating costs.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional overall configuration diagram of an embodiment of the present invention, FIG. 2 is a partially enlarged cross-sectional view, and FIG. 3 is a cross-sectional view of the same during operation. 30.31...Plating bath, 32...Cathode, 33...Anode, 62...Cooling device, 64...Pump, 66・・・・・・Inlet,
67... Outlet.

Claims (1)

[Claims] 1 A substantially cylindrical cathode with a slightly enlarged diameter at the top and rotating on its own axis is disposed in a revolving plating tank, and the object to be plated is pressed against the inner surface of the cathode by the centrifugal force caused by the revolution, and an anode is placed opposite the cathode. A plating solution is filled between the plating tank and the cathode, and the plating solution in the plating tank is circulated between an auxiliary tank and a cooling device provided outside the plating tank, and the plating solution is heated to an anhydrous concentration of 300 to 400 g/l. Chromic acid and 5-9
A bath is prepared with 9/1 oxalic acid, 0.5 to 0.8 g/l barium carbonate, and 0.1 to 0.39/1 hydrofluorosilicic acid, and the plating solution is heated to minus O to 10 A black chrome plating method characterized by performing black chrome plating while maintaining the temperature at ℃.