TWI457467B - A production method in which a molded product made of a magnesium alloy is a - Google Patents

Description

Production method for chemically forming a molded article made of a magnesium alloy while performing barrel polishing

The present invention relates to a method of chemically forming a molded article made of a magnesium alloy while performing barrel polishing.

The inventor of the case operated a company that mainly engaged in the surface grinding of metal parts related to conveyors. Recently, the work of grinding a molded article made of a magnesium alloy as a workpiece (hereinafter referred to as a workpiece) has been increasing. The magnesium alloy refers to an alloy containing magnesium as a main component, and the molded article formed of the following magnesium alloy is also referred to as a magnesium alloy. Magnesium is the lightest among the metals used in reality, has high thermal conductivity and good heat release, and is more excellent in recycling than resin. Therefore, it is widely used in automotive parts and the like, and because it has electromagnetic wave shielding properties, Most of them are also used as a frame for mobile phones and notebook PCs. However, in the grinding of magnesium, especially polishing, the dust of magnesium scatters in the air and also has the risk of dust explosion, and a method of barrel grinding by a wet method is expected as much as possible. With the wet cylinder, there is no possibility that the dust of the magnesium is scattered in the air, but it is absorbed by the water.

By barrel polishing, a workpiece is placed, and a particulate abrasive or a medium (hereinafter referred to as a compound) is placed in a drum (bucket) together with water, and the cylinder is rotated/up and down to thereby grind the workpiece. However, it is also included in a method in which a workpiece having a particle-shaped abrasive, a mixture, and water is placed, and the workpiece is rotated/up and down to be polished. Generally, water is placed in the cylinder, and because of the use of water, it is also called a wet cylinder.

Fig. 1 is a schematic view showing a barrel mill for rotating and moving a workpiece in a cylindrical groove in which a particle-shaped abrasive, a mixture, and water are placed and polished.

The elevator 22 is mounted on the support column 21 on the base 2, and the moving plate arm 24 and the elevator moving plate 23 to which the pendulum moving cylinder 5 is fixed are slid up and down along the support column 21. The moving plate arm 24 is attached with an inclined plate 3 and an upper and lower sliding plate 31. The sloping plate 3 is provided with an up-and-down sliding plate 31 and an up-and-down moving cylinder 4 that moves the vertical sliding plate 31 up and down. The vertical sliding plate 31 is attached with a rotating shaft 32 that holds the workpiece 7 and rotates it; The rotation shaft that rotates the rotation shaft 32 drives the motor 33. The pendulum movement cylinder 5 is coupled to the inclined plate 3, and by the expansion and contraction of the pendulum movement cylinder 5, the inclined plate 3 generates front and rear pendulum movements, and the rotation shaft 32 also generates front and rear pendulum movements.

The dotted line shows the state in which the workpiece descends and enters the slot. In Fig. 1, the pendulum motion is limited to the forward and backward movement. However, although not shown, the left and right pendulum movements can be performed by attaching a cylinder that generates a right and left motion to the moving plate arm. Here, in this case, the cylinder is particularly set as a cylinder groove.

The grinding process is roughly divided into rough grinding and final grinding. The particle size and material of the abrasive are divided into rough grinding and final grinding. In terms of the material of the abrasive, there are sand, plastic, ceramics, and the like. The mixture is in the form of a liquid, and includes a fatty acid salt, nitrite, IPA, and the like in addition to the surfactant. The mixture is added in a ratio of 0.1 to 0.5% with respect to water, and also has a function of emitting gloss on the surface of the workpiece.

The surface treatment of the magnesium alloy is generally carried out by polishing as shown in Fig. 2 after performing polishing or barrel polishing. The ground workpiece is partially removed from the grease in the degreasing process. The surface chemistry of the workpiece is formed to be uniform by the subsequent etching process. In the case of an etchant, phosphoric acid, hydrochloric acid, or the like is used. Then, a chemical conversion process is performed. One of the surface treatments of the chemical conversion treatment is a treatment in which a treatment agent such as phosphoric acid acts on the surface of the metal to cause a chemical reaction, and the metal surface is imparted with a property different from the original material, such as corrosion resistance or adhesion to a coating material. There is anodization, or formation of a film by phosphate, and the like.

As described above, the surface treatment of the magnesium alloy as the workpiece requires a large amount of engineering, which is a factor of cost increase. There are also requests for cost reduction from trading companies, etc., and the inventors of this case have considered the surface treatment methods of magnesium alloys. Magnesium ionization tends to be second highest and metallic corrosive. In other words, magnesium reacts even if it is weakly acidic. The present inventors who focused on this point focused on an oxalic acid or citric acid solution which is relatively easy to treat with an inorganic acid as compared with a mineral acid, and when a magnesium test piece is put into the test piece, a bubble reaction occurs on the surface of the test piece. This reaction is presumed as shown in Fig. 3. The presumed citric acid is also used as a chelating agent, and the reaction with cations is also unclear. The citric acid of Figure 3 The reaction formulas (1) and (2) are not in the estimated range.

When a magnesium test piece immersed in an oxalic acid or citric acid solution was observed, it was observed that a film which is considered to be a film was formed on the surface thereof. The metal salts of oxalic acid and citric acid and magnesium are considered to have low solubility and produce a film. In addition, the treatment of the wastewater after the dissolution of oxalic acid or citric acid has the advantage of being less labor-intensive than the wastewater after the dissolution of hydrofluoric acid or phosphoric acid.

Therefore, the applicant of the present application puts the particulate abrasive, mixture, and water used in the company into the cylinder, and adds oxalic acid and citric acid to the cylinder to form a pH of about 4, and is subjected to experimental barrel grinding. As a result, it was found that the chemical conversion treatment can be carried out simultaneously with the polishing. Therefore, when investigating the prior art of the method of chemical conversion processing simultaneously with barrel polishing, the following cited documents were found.

In the method of forming a chemical conversion treatment film which is excellent in corrosion resistance and resin coating film adhesion on the surface of a molded article made of magnesium or a magnesium alloy by a simplified process, it is useful to use a polishing method. In the chemical conversion treatment of the particles, the surface of the molded article made of magnesium or a magnesium alloy is subjected to a chemical conversion treatment, and a chemical conversion treatment film is formed on the surface of the molded article (Patent Document 1); For the surface treatment method of removing the foreign matter such as oil, grease, rust, and unnecessary substances on the surface of the metal or non-metal, and removing the phosphate treatment, the pretreatment process is omitted, and the metal or non-metal is used. The surface is treated with a phosphate, a surface by a physical means, and the surface is treated with the phosphate to form a metal or non-metal surface treatment method (Patent Document 2); From aluminum alloy In the method of chemically forming the surface of the molded body of at least one alloy of the magnesium alloy, the following process is included: (a) in the barrel polishing apparatus, the etching liquid and the polishing agent which are not at pH 7 are introduced together with the molded body, and the a barrel polishing process for polishing the formed body at least 15 seconds after the pH of the etching solution is neutralized; (b) a process of washing the molded body with water; (c) a process of forming a film on the molded body; A chemical conversion treatment method (Patent Document 3) in which the molded body is dried. Further, in the case of the magnesium low-resistance film treatment and the surface treatment method thereof, there is a treatment method characterized by comprising etching the magnesium-containing metal material by an acid and/or a weak alkali solution, and then performing the inclusion A process for chemical conversion treatment of a calcium ion, a manganese ion, a phosphate ion, or a chemical conversion treatment agent containing an oxidation treatment agent (Patent Document 4).

[Previous Technical Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-169580

[Patent Document 2] Japanese Patent Laid-Open No. Hei 10-315137

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2004-10998

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2000-96255

In each of the above-mentioned patent documents, Patent Document 1 and Patent Document 2 are subjected to surface polishing while being subjected to surface polishing. However, in any of the inventions, phosphoric acid is used as a chemical conversion treatment agent. Patent Document 3 also performs a chemical conversion process while performing barrel polishing, but uses phosphoric acid, nitric acid, hydrofluoric acid, hydrochloric acid or the like as an etching liquid. In any patent document, it is not Oxalic acid and citric acid are used as a chemical treatment agent. Further, Patent Document 4 relates to an invention for a chemical conversion treatment agent for a magnesium alloy, which is different from the problem of the present invention.

The problem to be solved in this case is a surface treatment of a magnesium alloy molded article while performing barrel polishing, which greatly shortens the surface treatment work and contributes to cost reduction.

According to the invention of the present invention, when the workpiece of the magnesium alloy is subjected to barrel polishing, a particulate abrasive, a mixture and water are placed in the cylinder, and oxalic acid or citric acid or oxalic acid and citric acid are added to polish the workpiece. The chemical conversion process is performed.

In the first aspect of the invention, the molded article made of the magnesium alloy as the workpiece is simultaneously subjected to barrel polishing and chemical conversion treatment. Therefore, a particulate abrasive, a mixture, and water are placed in the cylindrical tank, and oxalic acid or citric acid is additionally added. In the case of oxalic acid and citric acid, the pH of the aqueous solution in the cylinder is set to 3 or more and 6 or less, and the chemical conversion treatment is performed while performing barrel polishing for a predetermined period of time.

The barrel polishing, the particulate abrasive, and the mixture are as described above. The barrel polishing is roughly divided into rough grinding and final grinding, but is subjected to barrel polishing and chemical conversion processing at the same time, and therefore belongs to the final polishing. Set The cylindrical groove is based on a cylinder only, but it is expressed as a container for storing water.

The structural formula of oxalic acid is HOOC-COOH, which is strongly conjugated to calcium ions in the blood in the body. Therefore, it is toxic. Since it is designated as a non-medical harmful substance according to the toxic and harmful substance ban, it must be taken care of. It is a colorless crystal at normal temperature and has a solubility in water of about 10 g/100 cc. Since it has a carboxyl group, it is ionized in an aqueous solution to form a divalent acid to exhibit an effect. Most are classified as weak acids, but the acid dissociation constant is higher than that of phosphoric acid or the like.

The chemical formula of citric acid is C ₆ H ₈ O ₇ , and the structural formula is shown in Fig. 3. In the case of a weak acid having three carboxyl groups, the aqueous solution is weakly acidic. It is a colorless or white solid at normal temperature, and has an crystallization of an anhydrate and a monohydrate. It is known to make metal ions and chelate complexes. The solubility in water is 73 g/100 cc. Since the metal ion and the chelate complex are produced, the reaction formula of citric acid and magnesium in Fig. 3 is repeated, which is a range of speculation.

The barrel grinding time varies depending on the material, shape, or desired surface smoothness of the workpiece. There are enough workpieces in 10 minutes, and there must be 30 minutes of workpieces. If the barrel polishing time is long, if the pH is low, the workpiece is etched to a desired level or more, and the pH is determined in accordance with the polishing time to have a pH of 3 or more and 6 or less.

The reason why oxalic acid or citric acid, or oxalic acid and citric acid are selected based on the properties of the coating applied to the coating on the surface, such as corrosion resistance and adhesion, may be selected. It is easier to compare these wastewater treatments with other chemical treatment agents. The reason. The reason why the aqueous solution in the cylinder is based on the dissolution of the mixture with oxalic acid or citric acid or a mixture with oxalic acid and citric acid.

According to the first invention, as shown in Fig. 4, the engineering can be greatly shortened as compared with the general construction shown in Fig. 2.

According to the second aspect of the invention, the aqueous solution in the cylinder is maintained at a constant pH range, and the oxalic acid solution or the citric acid solution prepared in advance or the mixed solution in which oxalic acid and citric acid are dissolved at a predetermined ratio is used by the pH maintaining device. When the aqueous solution of the cylindrical tank is added, the method of chemical conversion processing is performed while performing barrel polishing for a predetermined period of time in the first invention.

In the barrel grinding, a predetermined amount is thrown into the cylinder to perform barrel polishing, but there are not many examples of updating the aqueous solution in the cylinder each time, and the workpiece whose barrel polishing has been completed is taken out from the cylinder groove, and a new workpiece is put into the cylinder. The barrel is used for barrel grinding. Therefore, the oxalic acid and the citric acid react with the magnesium alloy, and the pH of the aqueous solution in the cylinder rises. Therefore, the oxalic acid solution or the citric acid solution or the mixed solution in which oxalic acid and citric acid are dissolved at a predetermined ratio is added to the tank by the pH maintaining device, and the pH of the aqueous solution in the cylinder is maintained within a certain range. The oxalic acid and the citric acid are water-soluble as described above, and it is easy to handle in the case where the aqueous solution is added while being kept in a solid state in the cylindrical tank.

An example of a pH maintaining device is shown in FIG. The pH of the aqueous solution in the tank 6 is sent to the personal computer 8 by the pH meter 81. When it is judged that oxalic acid or citric acid must be supplied from the value, the personal computer 8 transmits the instruction to the controller 82, and the controller 82 is Open oxalic acid aqueous solution storage tank The solenoid valve 63 of the 61 or aqueous citric acid storage tank 62, the oxalic acid solution or the citric acid solution is sent to the tank. The pH of the aqueous solution in the tank is always measured by a pH meter, and when the pH is lowered to a predetermined pH value, the solenoid valve 63 is closed and supply of oxalic acid or citric acid is stopped. This process is performed by a program that is previously incorporated. The pH maintenance device refers to a series of devices for automatically feeding oxalic acid or citric acid or oxalic acid and citric acid into the tank in order to maintain the aqueous solution in the cylinder at a certain pH range. In Fig. 5, the oxalic acid solution storage tank 61 and the citric acid solution storage tank 62 are described, but there is also a case where any one of the storage tanks is sufficient, and in addition, a mixed solution of oxalic acid and citric acid is prepared and stored in one storage. The case of the slot. The reason why it is set to a certain pH range is based on the management range of pH.

In the case where the pH electrode is glass, there is a possibility that the glass is broken due to the polishing material or the workpiece, and it is necessary to have a place where the glass solution enters into the cylinder. For example, a method of attaching a stainless steel pipe member whose upper and lower sides are released to the inner wall surface of the cylindrical groove, and placing a glass electrode there, and the like are considered.

Next, the third invention is a molded article made of a magnesium alloy which is chemically treated by the method of the first invention or the second invention and additionally coated by a surface coating.

A molded article made of a magnesium alloy which is chemically treated by the methods of the first invention and the second invention is used.

In the first invention, since magnesium is to be processed Since the molded product of the alloy is simultaneously subjected to barrel polishing and chemical conversion treatment, the engineering can be greatly shortened, and oxalic acid or citric acid can be used as a chemical conversion treatment agent, so that the wastewater treatment becomes easy. In the second aspect of the invention, the pH of the aqueous solution in the cylinder can be maintained constant, and the chemical conversion treatment can be performed. According to a third aspect of the invention, a molded article made of a magnesium alloy which has been chemically treated by the method of the first invention or the second invention and additionally coated by a surface coating is used as a protection target.

1‧‧‧ barrel grinding device

2‧‧‧Abutment

3‧‧‧ sloping plate

4‧‧‧Up and down motion cylinders

5‧‧‧ pendulum movement cylinder

6‧‧‧Cylinder

7‧‧‧Workpiece

8‧‧‧PC

21‧‧‧Support column

22‧‧‧ Lifts

23‧‧‧ Lift mobile board

24‧‧‧Mobile arm

31‧‧‧Up and down sliding plate

32‧‧‧Rotary axis

33‧‧‧Rotary shaft drive motor

34‧‧‧Workpiece grip

61‧‧‧ oxalic acid aqueous solution storage tank

62‧‧‧Aqueous citric acid storage tank

63‧‧‧ solenoid valve

81‧‧‧pH meter

82‧‧‧ Controller

Figure 1 is a schematic view of a barrel grinder.

Figure 2 is a general engineering drawing of the surface treatment.

Figure 3 shows the reaction formula of magnesium with oxalic acid and citric acid.

Fig. 4 is a view showing a process of chemical conversion processing while performing barrel polishing.

Fig. 5 is a schematic view of a pH maintaining device.

Fig. 6 is a table showing the results of the adhesion test.

The embodiment is shown below.

[Example 1]

A preliminary test as shown below was performed.

(1) If 5 g of oxalic acid is dissolved in water of 1 Liter (hereinafter referred to as L) (Set to liquid A), and when a magnesium test piece was put in, it was found that a bubble of hydrogen was generated on the surface to cause a chemical reaction. When the test piece is taken out and the surface is observed, a film is formed. The pH of solution A was about 2.5.

(2) When 5 g of citric acid is dissolved in 1 L of water (as liquid B) and a magnesium test piece is put into it, it is found that a bubble of hydrogen is generated on the surface to cause a chemical reaction. Similarly, when the test piece is taken out and the surface is observed, a chemical conversion film is produced. The pH of solution B was about 3.

(3) The pH of the liquid C in which 10 CC of the mixture used in daily use was dissolved in 10 L of water (as liquid C) was about 8. Prepare 3 liquids C.

(4) As a result of adding 0.5 L of the solution A to the solution C, the liquid C was slightly cloudy. The pH of the liquid C at this time was about 3.5. A test piece of the abrasive and the magnesium alloy was placed in the liquid C to which the liquid A was added, and stirred for about 10 minutes.

(5) Similarly, when 0.5 L of the solution B was added to the solution C, the liquid C was slightly cloudy. The pH of the liquid C at this time was about 4. A test piece of the abrasive and the magnesium alloy was placed in the liquid C to which the liquid B was added, and stirred for about 10 minutes.

(6) Similarly, 0.25 L of the A liquid and 0.25 L of the B liquid were added to the liquid C, and the liquid C was slightly cloudy. The pH of the liquid C at this time was about 3.5. A test piece of the abrasive and the magnesium alloy was placed in the liquid C in which the liquid A and the liquid B were added, and the mixture was stirred for about 10 minutes.

In the case where the liquid A, the liquid B, and the mixture of the liquid A and the liquid B are added to the liquid C, the liquid C is cloudy, but when it is stirred for 1 to 2 minutes, the white turbidity disappears.

(7) The test piece which was chemically processed by the above (4), (5), and (6) was dried by a dryer and spray-coated.

[Example 2]

The adhesion test was performed on the test piece which carried out the above-mentioned spray coating. The adhesion test refers to the use of a cutting knife on the test surface to form 11 checkerboards by forming 11 cuts of the texture at right angles to each other. The interval between the cuts was set to 1 mm. After the cellulose tape is strongly crimped to the checkerboard portion, the number of peeled off the inner coating film of 100 checkers is counted, and is also called a checkerboard test. The results of the checkerboard test are shown in Figure 6. Fig. 6 A liquid + C liquid, B liquid + C liquid, A liquid / B liquid + C liquid is a test piece which was tested by the methods (4), (5), and (6) described above, and three test pieces were separately prepared. sheet. As can be seen from Fig. 6, the test piece which was subjected to the chemical conversion treatment while being subjected to barrel polishing on one side was superior in adhesion to the test piece which was subjected to top coat after degreasing.

[Industrial Applicability]

This case is a process in which the barrel is polished and processed, and the work up to this point can be greatly shortened. In addition, the chemicals used in the chemical conversion treatment are also oxalic acid and citric acid, and the wastewater treatment is also easy. Significant cost reductions are expected to be needed.

Claims (3)

A method of performing a chemical conversion treatment while performing barrel polishing for a predetermined period of time, in which a molded article made of a magnesium alloy as a workpiece is simultaneously subjected to barrel polishing and chemical conversion treatment, and a particulate polishing is placed in the cylindrical groove. In addition, citric acid is added to the material, the mixture, and the water, and the pH of the aqueous solution in the cylinder is set to 3 or more and 6 or less, and the method of chemical conversion is performed while performing barrel polishing for a predetermined period of time. A method for performing a chemical conversion treatment while performing barrel polishing for a predetermined period of time, in order to maintain an aqueous solution in the cylinder at a constant pH range, and to add a previously prepared citric acid solution to the aqueous solution in the tank by a pH maintaining device. A method of performing a chemical conversion treatment while performing one-shot polishing on a surface of the first item of the patent application. A molded article obtained by a method of chemical conversion treatment according to the method of claim 1 or 2 and additionally coated by a magnesium alloy.