JPS59182998A - Method for removing coated carbide layer - Google Patents

Abstract

PURPOSE:To remove efficiently a coated carbide layer from a metallic material without damaging the base metal by carrying out electrolysis in an alkali soln. using the metallic material as an anode. CONSTITUTION:When a mandrel for cold rolling having a coated V carbide layer is scratched and required to be exchanged, it is regenerated by recoating. Ten such mandrels are vertically suspended in an electrolytic cell at proper intervals, and electrolysis is carried out at about 5V voltage and about 0.4A/ cm<2> current density for about 10min using the mandrels as an anode and an about 10% aqueous soln. of Na2CO3 as an electrolytic soln. The carbide layers of about 8mum thickness are thoroughly removed by electrolysis without causing surface roughening. The time required by this method is not changed as compared with the conventional time, yet many members are electrolyzed at once, so the efficiency can be increased several times.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily removing a carbide coating layer stuck to the surface of metal parts, metal parts, etc.

In recent years, various carbide coating methods have been proposed and used as surface treatment methods for imparting wear resistance to metal materials. Some of these carbide-coated parts can be reused after they have reached the end of their service life by being coated again. In this case, all of the original coating layer must be removed.

Furthermore, depending on the part, the coating layer may have to be partially removed.

In other words, in this type of coating treatment, it is difficult to prevent the coating layer from sticking to some parts, so if it is necessary to do so, the entire area is coated and then only that part is removed. .

Conventionally, the coating layer has been removed in such cases by mechanical grinding using a diamond grindstone, silicon carbide shot, or the like. However, such mechanical treatment is difficult because the carbide coating layer itself is extremely hard with Hv2000-3500.
Grinding took a long time and uniform removal was difficult.

In view of the above, the present invention is a removal method that has been developed from a completely different perspective from conventional mechanical removal methods, and its gist is to remove metal materials having a carbide coating layer in an alkaline solution. This is a method for removing a carbide coating layer, which is characterized by electrolyzing the carbide coating layer by using the carbide as an anode.

Conventionally, there has been no technical idea to remove the carbide coating layer by electrolysis. That is, the carbide layer has not generally been considered as a target for electrochemical treatments such as electroplating and electropolishing. The inventors focused on this point and conducted experiments using various electrolytic solutions. As a result, they obtained very satisfactory results for electrolysis in an alkaline aqueous solution and completed the present invention. . That is, in a 6-alkaline aqueous solution, the carbide coating layer is electrolyzed faster than the base metal, and only the carbide layer is removed while the base metal is hardly attacked, and the subsequent surface is smooth. On the other hand, although the carbide layer is removed in an acidic aqueous solution, the base metal is also dissolved and the process does not go well1.
%Na.

This figure shows the anodic polarization potential curves of vanadium carbide and iron in COI, 5% NaOH, and 10% NaOH aqueous solutions. As you can see in the figure,
In an alkaline solution, all carbides have a lower polarization potential than iron, indicating that they start electrolysis earlier, and if electrolysis is performed with a voltage and current between the two, only carbides will be electrolyzed.
This shows that the scalp is not affected at all. Industrial electrolytes use higher voltages and have observed a favorable phenomenon in which the carbide layer is preferentially electrolyzed, although both should be decomposed simultaneously. On the other hand, Fe is much lower in hydrochloric acid, which indicates that it is not suitable for the purpose Q of the present invention.

Electrolytes that can be used in the present invention 1 are NaC/', Na, C
o, , Na.

A 1 to 20% aqueous solution of SiO, etc. alone or in a mixture is practical, but aqueous solutions of various alkali salts of the oil can also be used. Also, its concentration voltage,
Electrolytic conditions such as current density may be appropriately selected depending on the case.

Next, embodiment Q of the present invention will be described.

(Example 1) In order to recoat and regenerate a cold rolling mandrel coated with vanadium dihydride that has reached the end of its service life due to scratches due to use, the original coating layer was replaced with the coating layer of the present invention. removed by method.

The electrolysis conditions were as follows.

Applicable material: Mandrel for cold drawing of seamless steel pipe, root diameter 3
2 cm, tip diameter 2.1 (7), length 75 (7), carbide layer thickness 8 μm Electrolyte: Anhydrous soda carbonate (Nu, Co,) 10% aqueous solution Voltage/current: 5 ■, 0 .4 A/d Pond Ten mandrels were hung vertically in an electrolytic cell at appropriate intervals and electrolyzed for about 10 minutes. As a result, the carbide coating on all mandrels was completely removed and the skin was not roughened at all. FIG. 2 and FIG. 3 (showing micrographs of surface cross sections before and after treatment by the method of the present invention).

In these photographs, A is the carbide layer and B is the base iron. As seen in the photograph e in FIG. 3, the surface after the treatment of the present invention is extremely smooth.

In addition, in the case of conventional mechanical grinding, it took about 30 minutes for each piece. In the case of this example, it takes about 30 minutes including preparation time, but since a large amount of processing can be done at once, efficiency is improved several times, and running costs are low, so in the end, processing costs are reduced to a fraction of that. Ta.

(Example 2) The shaft hole of a roll of a steel straightening machine coated with titanium carbide with a thickness of approximately 10P [in order to shrink fit the roll shaft, it was necessary to correct and finish the 1lQ11 hole. The carbide coating on the shaft hole was removed by the method of the present invention. Vinyl tape was wrapped around the parts other than the shaft hole, and electrolysis was carried out under the following conditions.

Applicable material: straightening machine roll, diameter 150 MM, shaft hole 45
．． 15 mm Electrolyte: Caustic soda (NaOH) 7% aqueous solution Voltage
Current: 6V, 0.5A/Cj Others The roll was placed vertically in an electrolytic solution, a rod-shaped cathode was inserted into the shaft hole, and electrolysis was performed for about 20 minutes.

As a result, the carbide layer on the shaft hole surface was completely removed, making correction and finishing easier.

As described above, the removal of carbide layers such as V, Ti, Nl), Cr, etc. was done by expensive and inefficient grinding using a diamond grinding wheel, etc., but the present invention makes it extremely easy to remove. It can now be done cheaply, and the benefits of carbide coating treatment are even greater.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the positive (T polarization curves) of the present invention and a comparative example, Figure 2 is a micrograph of the surface 1tTi of an article coated with carbide, and Figure 3 is a diagram showing the positive (T) polarization curves of the present invention and a comparative example. This is a microscopic photograph showing a cross section of the surface. Fig. 2 (3) Formerly dated August 24, 1982 Issued on August 25, 1980 Kazuo Wakasugi, Commissioner of the Patent Office 1 Indication of the case Patent Application No. 57131 of 1983 2
, Title of the invention Method for removing immediate layer of carbide coating 3, Relationship to the case of the person making the amendment Applicant address 3007-4, Nakajima-ji, Shikama-ku, Himeji City Date of amendment order July 26, 1982 ( Date of dispatch) □ 5 Subject of amendment 6, Contents of amendment 0 The matters in the "Brief explanation of drawings" preference list in the specification will be amended. Note 1, page 7, line 5, the phrase ``micrograph of a cross section'' is corrected to ``micrograph showing the metallographic structure of a cross section.'' 2. On page 7, line 6, the phrase "This is a microscopic photograph showing a surface cross section." is corrected to "This is a microscopic photograph showing the metal structure of a surface cross section."

Claims (1)

[Claims] A method for removing a carbide coating layer, which comprises electrolyzing a metal material having a carbide coating layer in an alkaline solution as an anode.