JPS6312159B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to polishing of metal surfaces,
The frequency at which a metal material and an insoluble electrode as a counter electrode are immersed in an electrolytic polishing solution, and positive and negative voltages are applied alternately between the metal material and the counter electrode, and the ratio of negative voltage application to positive voltage application. This paper relates to a method for efficiently polishing the surfaces of many types of metals by changing the . (Prior art) After machining, metal products are generally subjected to surface treatments such as plating and alumite, but since metal materials can have unevenness and get scratches from machining, a satisfactory finish cannot be obtained with this method. Because of this, the surface is usually smoothed and polished. For this purpose, polishing is performed using various polishing methods, but there are problems such as the polishing requires a lot of labor, the mirror gloss cannot be obtained, and the cost is high. The main polishing methods currently used include buff polishing, barrel polishing, electrolytic polishing, and chemical polishing.The most widely used polishing method is buffing, which is laborious and expensive to achieve a mirror-like finish. There are problems such as it is difficult to finish materials such as stainless steel and aluminum to a mirror shine, it is difficult to polish small items, special shapes, wires, foils, etc., and mass production is difficult and requires skill. In order to compensate for these drawbacks, electrolytic polishing and chemical polishing, which polish electrochemically or chemically, are used. Chemical polishing does not require electricity because it dissolves chemically, but because it uses chemicals to dissolve, the chemicals are consumed rapidly and the life of the bath is short, resulting in high costs. Furthermore, the bath composition changes drastically, making bath management difficult, and the materials that can be polished are limited to aluminum, copper alloys, etc. In electrolytic polishing, a smooth mirror surface can be easily obtained by electrolyzing the material in a polishing solution using a direct current as an anode for several tens of seconds to several minutes. Moreover, it can easily polish complex shapes, easily deformed thin plates, foils, etc. that are difficult to polish by mechanical polishing, and it has the advantage of being mass-produced. However, with this electrolytic polishing, there are only a limited number of materials that can be easily polished, and a highly concentrated electrolytic solution must be used, resulting in high costs and a heavy burden on wastewater treatment. Furthermore, since a highly concentrated electrolytic solution is used, gas generated during polishing adheres to the surface of the polished object and is difficult to remove, resulting in gas pits or streaks being likely to occur. Furthermore, there are drawbacks such as the need to polish at a high temperature of 70°C or higher. In the present invention, in place of conventional DC electrolysis for polishing metal surfaces, by applying current reversal in which positive and negative voltages are applied alternately and by changing the reversal ratio, low concentration polishing liquid and low bath temperature can be used. It was discovered that a smooth mirror surface without gas pits can be obtained. (Objective of the Invention) That is, the object of the present invention is to polish the surface of a metal material that cannot be obtained with the direct current method by alternately applying positive and negative voltages instead of conventional DC electrolysis and changing the reversal ratio. The present invention provides a method. (Structure of the Invention) The present invention includes aluminum, stainless steel, steel,
The metal to be treated, such as copper alloy, and an insoluble electrode are immersed in an acidic or alkaline electrolyte as a counter electrode, and the metal to be treated is heated by current reversal electrolysis, in which positive and negative voltages are alternately applied between the metal to be treated and the counter electrode. By selecting an appropriate frequency and inversion ratio for polishing, the metal to be treated is electrochemically dissolved to obtain a glossy, smooth mirror surface. FIG. 1 shows a voltage application method using the conventional anodic direct current electrolysis method, and FIG. 2 shows a voltage application method according to the present invention. In the figure, during time T ₁ , a positive voltage is applied to the metal to be treated to melt the metal surface, and during time T ₂ , a negative voltage is applied to the metal to be treated to intermittently inject a large amount of hydrogen gas. Electrolytic polishing is performed while removing the gas that is generated and adhered to the metal surface. Furthermore, since the polishing effect differs depending on the reversal period and the ratio of the positive applied voltage time _T1 to the negative applied voltage time _T2 , that is, the reversal ratio, a smooth mirror surface is obtained by changing these. A major feature of the present invention is that the polarity is changed in one period and a large amount of hydrogen gas is generated intermittently by the negative current, thereby eliminating gas pits generated by DC electrolysis. Passivation is prevented and dissolution is promoted by the negative current flowing intermittently, so that a smooth mirror surface can be obtained even with a low concentration polishing liquid and a low bath temperature, and polishing costs can be significantly reduced. Since there is a wide allowable range of electrolytic conditions such as three-liquid composition, bath temperature, and current density, products can be finished uniformly and can be easily managed. 4. Since the concentration of the polishing solution may be low, the amount of electrolyte pumped out is reduced, and the load on wastewater treatment is reduced. Also, depending on the type of metal to be treated, it is possible to polish with an inexpensive bath such as sodium carbonate or sodium hydroxide, and it has the effect of solving the problem of phosphorus and nitrogen, which are difficult measures to prevent pollution. This is a revolutionary invention. Next, the present invention will be explained in more detail with reference to Examples. (Example 1) Electrolyte Phosphoric acid 700ml Sulfuric acid 200ml Water 100ml Bath temperature 50℃ Current density 20A/dm ² Reversal ratio 5% Processing time 5 minutes Material 1080Al Under the above conditions, a carbon plate was used as the counter electrode, and the reversal ratio was set to negative Time for current to flow (T ₁ )/time for one cycle (T ₁ + T ₂
) x 100 = reversal ratio (%) This reversal ratio was set as 5%, and the glossiness when changing the frequency was as shown in Table 1.

[Table] In Table 1, frequency 0 indicates the brightness of DC anodic electrolysis without polarity change, but compared to current reversal electrolysis in which polarity is changed periodically and negative current is passed intermittently. The gloss was poor, and many pits were formed due to adhesion of gases generated during electrolysis. On the other hand, electrolytic polishing using reverse electrolysis has a higher gloss level than polishing using direct current electrolysis in all frequency ranges. Furthermore, since a large amount of hydrogen gas is generated by passing a negative current intermittently, gas pits, which are a major problem in electrolytic polishing, are completely eliminated, and polishing can be performed at a lower voltage than in direct current electrolysis. (Example 2) Electrolyte phosphoric acid 500ml Water 500ml Current density 20A/dm ² Reversal ratio 5% Processing time 5 minutes Material 5052Al Under the above conditions, using a carbon plate as a counter electrode, 30℃ and 50℃
Table 2 shows the glossiness when changing the frequency at a bath temperature of . As is clear from Table 2, in polishing by current reversal electrolysis, the gloss is higher at a relatively lower temperature, and a better polished surface can be obtained. This tendency is common to almost all metals to be processed; for example, 5052Al

In the case of [Table], polishing is possible at 30℃, which is close to room temperature.
In conventionally used DC electrolysis, the lower the bath temperature, the more gas pits there are, and the lower the melting power, making it impossible to obtain a glossy surface, and generally requires a high bath temperature of 70°C or higher. As described above, according to the method of the present invention, polishing can be performed at a significantly lower bath temperature, thereby reducing costs due to energy savings. (Example 3) Electrolyte Phosphoric acid 700ml Sulfuric acid 200ml Water 100ml Chromic acid 50g/l Bath temperature 50℃ Frequency 13.3Hz Current density 20A/dm ² (Steel) 30A/dm ² (Stainless steel) Processing time 5 minutes Material Steel, Stainless steel Table 3 shows the glossiness when the reversal ratio was changed using a stainless steel plate as a counter electrode under the above conditions.

[Table] From this result, for steel, the greater the inversion ratio, that is, the greater the negative current, the greater the luster. On the other hand, stainless steel has excellent gloss when the reversal ratio is as low as 5%, and becomes inferior as the reversal ratio increases. In this way, just as the frequency of current reversal electrolysis, the reversal ratio at which a negative current flows is also greatly involved in the polishing effect, and the frequency and reversal ratio naturally vary depending on the type of metal to be treated and the type of polishing liquid. . (Example 4) Electrolyte No.1 Phosphoric acid 900ml Water 100ml No.2 Phosphoric acid 500ml Water 500ml Bath temperature 50℃ Frequency 13.3Hz Reversal ratio 5% Processing time 5 minutes Material Stainless steel Under the above conditions, a stainless steel plate was used as the counter electrode. Table 4 shows the glossiness when the polishing solution concentration and current density were changed. Table 4 also shows the results of DC anodic electrolysis for comparison. In direct current electrolysis, high-concentration phosphoric acid baths produce better gloss, while lower concentrations are inferior. However, in high concentration baths, gas pits are likely to occur due to the high viscosity of the liquid. On the other hand, in reverse electrolysis, a low concentration bath

[Table] has higher gloss and provides a mirror surface without streaks. As can be seen in this example, polishing using current reversal electrolysis allows polishing using a bath with a lower concentration than direct current electrolysis, reducing polishing costs and reducing the burden on wastewater treatment. (Example 5) Electrolyte Sodium phosphate 100g/l Sodium hydroxide 5g/l Bath temperature 50°C Frequency 13.3Hz Reversal ratio 5% Processing time 5 minutes Material 1080Al Polished in an alkaline bath with a stainless steel plate as the counter electrode under the above conditions The glossiness at that time was as shown in Table 5. Table 5 also shows the results of DC anodic electrolysis for comparison. Direct current electrolysis does not give a glossy surface at all, and it is matte and has pits. In contrast, reverse electrolysis does not produce pits and provides extremely good specular gloss over a wide current density range.

[Table] Can be done. In addition to this example, a polishing solution of sodium carbonate and sodium hydroxide can also be used to obtain a specular gloss, which is not only an inexpensive polishing bath, but also solves the problems of phosphorus and nitrogen, which are difficult to prevent pollution, and is not found in conventional polishing methods. There are major advantages that could not be avoided. (Effects of the Invention) As stated above, the present invention (1) periodically changes polarity and generates a large amount of hydrogen gas intermittently due to negative current, thereby eliminating gas pits generated by DC electrolysis. (2) Intermittently flowing negative current prevents passivation and promotes dissolution, making it possible to obtain a smooth mirror surface even with low concentration polishing liquid and low bath temperature, significantly reducing polishing costs. can. (3) Since there is a wide allowable range of electrolytic conditions such as liquid composition, bath temperature, and current density, the product can be finished uniformly and is easy to manage. (4) Since the concentration of the polishing solution may be low, the amount of electrolyte pumped out is reduced and the load on wastewater treatment is reduced. Depending on the type of metal to be treated, it is possible to polish with an inexpensive bath such as sodium carbonate or sodium hydroxide, and the problem of phosphorus and nitrogen, which are difficult to prevent pollution, can be solved. It has the following effects.

[Brief explanation of the drawing]

FIG. 1 shows the voltage waveform of the conventional anodic electrolysis method, and FIG. 2 shows the voltage waveform of the current reversal electrolysis method.

Claims (1)

[Claims] 1. The metal to be polished and the insoluble counter electrode are each immersed in an electrolytic polishing solution, and positive and negative voltages are alternately applied between the metal to be polished and the counter electrode, and the frequency thereof is varied. An electrolytic polishing method using current reversal electrolysis, which is characterized by polishing the surface of metal. 2. In current reversal electrolysis in which voltage is applied alternately, the surface of any metal is polished by changing the reversal ratio in which a negative voltage is applied to the metal to be polished to which a positive voltage is applied. An electrolytic polishing method using current reversal electrolysis according to claim 1, characterized in that: