JPS6124469B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of coating a first metal with a second metal of the same or different type.

Conventionally, it has been common practice to coat a metal surface with the same or different metals for the purpose of preventing corrosion or changing or improving the electrical, mechanical, or physical properties of a part or all of the surface. It's being done. Among such metal coating methods, the so-called electroplating method, in which metal ions are moved in an electrolytic solution to form a deposited layer on the surface of another metal body, has been used for the longest time. On the other hand, in recent years, methods such as ion plating and vapor deposition, in which ions are created in the vapor of one metal and the ion stream is projected onto the surface of the other metal to form a metal layer, have also been developed, as well as the movement of metal ions by arc discharge. A metal coating method using

However, the electroplating method using electrolytic deposition must be carried out through a complicated mechanism of chemical changes during electrolysis and deposition, which generally imposes large restrictions on the selection of metal materials, and in order to carry out this process industrially, it is difficult to control the electrolyte. Maintenance often requires many steps. In addition, electric discharge machining methods using arc discharge include:
There are two methods: a method in which both metals are used as both discharge electrodes, and a method in which the metal ions of one metal generated by arc discharge are solid-phase metallized on the surface of the other metal. Except for a few metals that do not oxidize, they will oxidize in the air or in an atmosphere containing oxygen due to the high heat generated by the arc, and will be coated with metal oxides. Furthermore, even if the atmosphere is not an oxidizing atmosphere, it is impossible to coat pure metal in an atmosphere that reacts with the metal to be coated at high temperatures, which inevitably complicates the equipment. Furthermore, in the latter method, when the temperature of the metal surface to be coated is low, it becomes difficult for both metals to diffuse on the metal surface to be coated, resulting in a decrease in adhesion. On the other hand, in the former method, a large area near the arc spot of the metal coated by the arc becomes high temperature, so generally the two metals diffuse to each other to a remarkable extent, and when the coating layer is thin, a large amount of the metal coated is coated. May remain on subsequent surfaces.

An object of the present invention is to provide a metal coating method that is generally applicable to a wide variety of metals and can easily form a high-purity metal coating with high adhesion even in the atmosphere.

The metal coating method of the present invention provides a first
and forming a molten metal bridge by gradually separating the two metals while passing electricity between the second metals, and the voltage between the two metals is at least a voltage at which at least one of the metals melts and at least a minimum arc voltage. The method further comprises the step of cutting the bridge and transferring one of the first and second metals to the other metal for coating.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram showing an embodiment of the metal coating method according to the present invention. Moreover, FIG. 2 is a waveform diagram showing the relationship between the temporal change in the current applied between the first and second metals shown in FIG. 1 and the voltage drop occurring between the two metals, and the voltages a to d are Process I in Figure 1
Each corresponds to d. In addition, in Figure 2,
Vm indicates the melting voltage and Vc indicates the minimum arc voltage.

Referring to both figures, step A in FIG. 1 shows an initial state in which the first metal 1 and the second metal 2 are in contact.

In this state, current begins to flow in the direction of arrow A, that is, from the second metal 2 to the first metal 1, and the relative position between the two metals is gradually moved in steps B and C. When the contact area becomes sufficiently small in the process of increasing the gap between the two metals, the electrical resistance of the contact surface increases and current is concentrated in that narrow area, resulting in Joule heat. As a result, both metals begin to melt and a bridge 4 is formed by the molten metal as shown in step B. If the current does not decrease in this state, the joule heat in the cylindrical molten metal bridge 4 between the two metals will increase, and the melting of both will further increase, creating a larger bridge 4 between the two metals, as shown in step C. . Next, using FIG. 3, which shows an enlarged view of the structure of the bridge 4, we will explain the transition to step 2 in FIG. metal 1
The mechanism of movement (transfer) to the surface of The heat generated in the right cylindrical bridge 1-5-6-2 between the second and first metal surfaces, indicated by straight lines 3-4 and 5-6 in FIG. 3, is conducted to both metals. Hemispherical melted parts 3-11-4 and 5-12-6 are formed. The size of this melted portion differs in both metals due to the thermoelectric effect.
Generally, the amount of heat transferred to the second metal serving as the anode is greater than the amount of heat conducted to the first metal serving as the cathode, so the thermal conductivity and temperature near the end of the second metal bridge are lower than those of the first metal. If the volume of the second metal molten part 3-11-4 is equal to or larger than that of the first metal molten part 5-12-6, the molten metal supplied to the bridge is approximately The boundary surface 9- of molten metal flowing into the bridge from both metals is considered to be proportional to the volume of both molten parts.
10 occurs on a surface closer to the first metal than the center of the bridge perpendicular to the bridge axis 11-12.

On the other hand, the temperature distribution within the bridge is quadratic, with the highest temperature occurring at the surface 7-8 closer to the second metal than the center of the bridge. As the bridge becomes longer, the temperature of the bridge increases, and when the bridge reaches a critical temperature at which the surface tension of the bridge approaches zero, the bridge will break at the highest temperature surface 7-8. Here, the metal in the bridge portion separated by the bridge maximum temperature, plane 7-8 and molten metal interface 9-10 is supplied from the second metal, and when the bridge is cut at plane 7-8, this metal is The second metal of the portion will be transferred onto the first surface. Normally, bridge transfer is caused by this bridge cutting, and the amount thereof is proportional to the third power of the applied current.

Now, after the molten metal bridge breaks, an arc will occur between the first and second metals if the voltage drop between the first and second metals increases and the minimum arcing voltage of the second metal is exceeded. When an arc occurs, a melting transition occurs between the two metals, and the amount thereof is proportional to the arc energy, which is proportional to the arc time. The direction of transition due to the arc is determined by the length of the arc, ie, the gap between the two metals. The arc temperature at the ends on both metal surfaces is more than twice the temperature at the bridge end.

As explained above, according to the present invention, even when the bridge is cut, the voltage drop is less than a few volts, and as the current increases, the current density decreases, and the temperature rise around the bridge end is also comparable to arc discharge. Because of its small size, oxidation of both metal surfaces can be suppressed, and even metals that are easily oxidized can be easily coated in the atmosphere without the need for an inert gas atmosphere. In addition, since the amount of transfer at one time per gap between both metals is proportional to the cube of the current, if the current value when the bridge is cut is increased, for example, if the current is doubled, the amount of transfer will be eight times, and the current efficiency will be You can get a large amount of Furthermore, the amount of metal transfer increases in proportion to the difference in volume between the molten parts of both metals, so even if the electric circuit is kept constant, heating one metal can further increase or decrease the amount of transfer. It is also possible to do so.

In the above-mentioned embodiments, one separation of the first and second metals was considered, but when covering a large area of one metal, the position of the contact point of both metals may be changed. This can be done by sequentially moving to the entire required surface. Furthermore, locally thick metal coatings can be applied by accumulating a large number of transfers, such as when creating a hemispherical contact on a portion of one metal.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an embodiment of the metal coating method according to the present invention, and FIG. 2 is a diagram showing temporal changes in the current applied to the first and second metals shown in FIG. 1 and the current generated between the two metals. A waveform diagram showing the relationship with voltage drop, and FIG. 3 is a configuration diagram of a molten metal bridge. 1...first metal, 2...second metal, 3...
Contact point, 4... Molten metal bridge.

Claims (1)

[Claims] 1. Step of forming a molten metal bridge by gradually separating the first and second metals while passing current between the first and second metals in contact, and the voltage between the two metals being a voltage at which at least one of the metals melts. A metal coating method characterized by comprising the step of cutting the bridge at the above and below the minimum arc voltage and transferring one of the first and second metals to the other metal for coating. .