Patent Application
20130319878
The present invention relates to electropolishing, and in particular, electrolytic solution, electrolysis case, electropolishing system to be used to the electropolishing, and the electropolishing method.
It is the electropolishing that is frequently used as a method for removing rust and stain of metals.
That is to say, the electropolishing, wherein metal (work-piece) and a cathode are immersed in an electrolytic solution keeping a specific distance from each other, and a specific current flow by applying a positive charge on the metal and a negative charge on the cathode, and then metal elements on a surface of the work-piece are dissolved, has a purpose to improve the durability of the work-piece by a modification of the metal surface. However, it is general that the work-piece before the electropolishing needs to be mechanically polished by the buffing.
When the metal work is a stainless work-piece, phosphoric acid or a mixed solution of phosphoric acid and sulfuric acid is always used as an electrolytic solution. The distance between the electrodes is about 10 cm, and the current flows at 10 A to 20 A.
There is a case where a large-size tank is used for storage of food and drink or storage of chemical agent and medical agent. Due to the aging deterioration, stain and rust would adhere to an inner surface of the tank. When the tank is in this condition, the equipment is required to be renewed. Since the renewal of equipment is very expensive, there is a method of prolonging the life of the tank by a temporary repair, that is, a mechanical polishing like the buffing.
For the buffing operation, workers come into the tank in hot and humid condition, and must do a heavy physical work therein. It is an extremely hard operation. In addition, a simple buffing treatment breaks the surface texture and causes the rusts and deterioration. Therefore, there is a trial to perform the electropolishing after the buffing.
When the electropolishing is performed on the inner surface of the large-size tank, an extraordinary volume of electrolytic solution is required. The electropolishing is not a realistic method in view of the cost. The applicant of the present invention has suggested a method of electropolishing the inner surface of the tank using a small volume of the electrolytic solution after assembling a frame body and electrodes along the inner surface of the tank, in Japanese Unexamined Patent Application Publication No. 2010-209423.
Moreover, there is a conventional method for applying voltage on a felt cloth impregnated with the electrolytic solution when the electropolishing or the electroplating is performed in a space that is hard to hold the electrolytic solution.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2010-209423
Even in the method disclosed in Japanese Unexamined Patent Application Publication No. 2010-209423, the workers have to work in the tank till assembling the frame body and the electrodes. It is hard to say that such work is comfortable, though it is not hard as the buffing operation. In the method of holding the electrolytic solution in the felt, the resistance between the electrodes becomes large, and it is not possible to flow the large current. Accordingly, the working time gets longer. It is hard to apply this method to a large-scale electropolishing, in particular, the electropolishing of the inner surface of the tank that is an object of the present invention, in view of the working environment.
The present invention is suggested in view of the above problems in the conventional methods, and has an object to provide with the electropolishing method without assembly operation of the frame body and the electrodes, facilitate the work of the workers inside the tank, and provide with the electrolytic solution, the electrolysis case, and the electropolishing system to be used thereto.
To begin with, the electrolytic solution to be used in the present invention is the one for the conventional electropolishing, but is given a specific viscosity by reacting inorganic acid with gelling agent.
The inorganic acid used as the electrolytic solution of the electropolishing is generally a phosphoric acid solution or a mixed solution of the phosphoric acid and a sulfuric acid, and this is same as the conventional method. A silicon dioxide is used as the gelling agent. The silicon dioxide reacted with the inorganic acid is dissolved to gel, and the electrolytic solution has viscosity. The viscosity can be adjusted by changing an additional amount of the silicon dioxide.
The electrolytic solution is desirable to be added with a very small amount of a surface active agent in order to ensure the wettability to the work-piece.
The electropolishing is progressed, while the electrolytic solution is introduced to a following electrolysis case, and the first introduced electrolytic solution is discharged by introducing the new electrolytic solution continuously.
The electrolysis case has a cathode placed at a specific height from a lower open end of a case frame in a specific size and specific depth; an introduction port on the cathode for introducing the electrolytic solution with a specific viscosity; a discharge port for discharging the electrolytic solution introduced in the case frame from the case frame of the electrolysis case.
When a net is used as the cathode, the introduction port has a pipe arranged along the net and having a plurality of small holes facing to meshes of the net, and the electrolytic solution is introduced to the pipe. The mesh of the net is available as the discharge port. Moreover, the space between the lower open end of the case frame and the cathode may be filled with a holding member for holding the electrolytic solution with the specific viscosity.
An electropolishing system may be configured by the above-mentioned electrolysis case, an electrolytic solution tank for holding the electrolytic solution, a pump for pumping out the electrolytic solution from the electrolytic solution tank at a specific discharge rate, a flow control valve for controlling the flow rate of the pumped-out electrolytic solution at a specific flow rate per unit volume of the electrolysis case, and then feeding the electrolytic solution to the introduction port, and a direct current source for applying negative voltage on the cathode of the electrolysis case and positive voltage on the work. Accordingly, the electrolytic solution is always transported to the electrolysis case at the specific flow rate per unit volume of the electrolysis case, so that the fresh electrolytic solution can be supplied between the cathode and the work-piece of the electrolysis case. It is possible to perform the electropolishing for the work-piece W with high quality and few faults.
Moreover, the electrolysis case is placed so that the lower open end of the case frame faces to the surface of the work-piece, and the specific viscous electrolytic solution is introduced from the small holes to a space between the work-piece of the case frame and the cathode. And then, the specific voltages are applied on plus to the work-piece side and minus to the cathode side, so that the electropolishing for the work-piece is proceeded. At this time, since oxygen is generated at the work-piece side, the first introduced electrolytic solution is discharged from the discharge port while the electrolytic solution is continuously introduced from the introduction port. Accordingly, the generated oxygen is forced out, and the electropolishing is not disturbed.
In the above mentioned system, by moving the electrolysis case on the work-piece, it is possible to perform the electropolishing for an object area on the work-piece.
Moreover, the electrolytic solution is introduced to the space between the work-piece and the cathode at a specific flow rate per unit volume of the space between the work-piece and the cathode, so that the high quality electropolishing can be performed.
When the above mentioned electrolysis case is used, it is possible to hold the viscous electrolytic solution in ease, and the distance between the cathode of the electrolysis case and the lower open end corresponding to the work-piece surface can be shortened (5 to 20 mm, for example). In result, since the resistant of the electrolytic solution can be reduced to small value, it is possible to pass the large current (30 to 100 A/dm2) and to shorten the operation time.
Since the electrolytic solution has the viscosity, bubbles (oxygen generated at an anode (work-piece)) are accumulated in the electrolytic solution when the current flows, but the bubbles can be forced out by introducing the electrolytic solution from the introduction port to the case frame and concurrently discharging the solution from the discharge port. Therefore, the operation of the workers in the tank is only moving the electrolysis case, and the workload can be reduced extremely. In addition, the electrolysis case is configured so as to be moved along with the work-piece by automatic control while keeping the electrolysis case contact with the work-piece surface, so that the electropolishing inside the tank can be performed without workers.
Moreover, the electropolishing is configured so that the specific amount of electrolytic solution in continuously supplied to the electrolysis case, in result with that the high quality electropolishing can be performed for the work-piece.
The electrolytic solution to be used in the present invention is the one for the conventional electropolishing, but is given a specific viscosity by reacting inorganic acid with gelling agent.
The inorganic acid generally uses a phosphoric acid solution or a mixed solution of the phosphoric acid and a sulfuric acid. A silicon dioxide is used as the gelling agent. The silicon dioxide reacted with the inorganic acid is dissolved to gel, and the electrolytic solution has viscosity. The viscosity can be adjusted by changing an additional amount of the silicon dioxide.
When 500 mL/L to 1000 mL/L of 85% phosphoric acid is used, 0 mL/L to 500 mL/L of water is added to the phosphoric acid, which reacts with 100 g to 200 g/L of silicon dioxide. As result, it is possible to produce the electrolytic solution having the viscosity corresponding to the amount of the silicon dioxide.
When the phosphoric acid is not more than 500 mL/L, the polishing function does not work fully. When the total amount of the electrolytic solution is the phosphoric acid, the object of the present invention can be achieved. But there is no room to add the sulfuric acid, and it is not possible to gloss a finishing surface.
Moreover, it is general that 0 mL/L to 500 mL/L of the sulfuric acid (e.g., 98% concentration) is added to the phosphoric acid. Since the sulfuric acid has a function to gloss the finishing surface, it is added when the gloss is necessary. However, when the sulfuric acid is not less than 500 mL/L, the amount of the phosphoric acid reduces and the polishing function does not work fully.
The electrolytic solution is desirable to be added with a surface active agent in the amount of 0.001% to 0.01% (in the outer percentage). The surface active agent is added in order to ensure the wettability to the work-piece in the viscous electrolytic solution. When the surface active agent is not more than 0.001%, it is not possible to obtain the satisfactory wettability. Even if it is not less than 0.01%, the wettability decreases.
It is configured so as to carry out the electropolishing by passing the current in the electrolytic solution held in following electrolysis case. The electrolysis case is configured as shown in
The electrolysis case is provided with a cathode 12 placed at specific height from a lower open end 11o of a case frame 11 surrounding the case. On the cathode 12, an introduction port 13 for introducing the specific viscous electrolytic solution into the case frame 11 and a discharge port 14 for discharging from the case frame 11 the introduced electrolytic solution in the case frame 11 are arranged.
The cathode 12 consists of a net, and an introduction pipe 13p having a plurality of small holes 13h facing to meshes of the net is arranged along the net. On the introduction pipe 13p, a guide pipe 13g is built for guiding the viscous electrolytic solution. Hereby, the introduction port 13 can be configured, and the mesh of the net 12 is available as the discharge port 14e.
It is nevertheless to say that the cathode 12 is provided with leads 16. The shape and size of the case frame are not limited in particular. In the following embodiments, however, the case frame is formed and sized enough to freely move on the surface of the work-piece by hands. This size and shape are modifiable according to its applied situation. Since the comparatively small-size and strong case frame 11 becomes a support of the cathode, the distance between the lower open end 11o (the surface of the work-piece) of the case frame 11 and the cathode can be reduced remarkably, 5 mm to 20 mm, for example. Hereby, it is possible to obtain large current (30 to 100 A/dm2, for example). The time for the electropolishing can be shortened remarkably.
Besides, in order to hold the electrolytic solution in the electrolysis case with ease, the electrolysis case may be filled with a holding member 15 like an artificial turf. In
Thus configured electrolysis case is placed so that the lower open end 11o of the case frame 11 faces to the surface of the work-piece (see
Besides, when oxygen bubbles are generated from the work-piece side, the volume of the generated bubbles increases as the current increases, and the bubbles are accumulated in the viscous electrolytic solution and increases the electric resistance. Accordingly, the electrolytic solution is continuously introduced into the case frame 11, whereby the electrolytic solution first introduced to the electrolysis case 11 is forced out from the discharge port 14e by the electrolytic solution next introduced (a dotted arrow,
As proceeding with the electropolishing of a work-piece portion corresponding to the electrolytic case, the whole of the work-piece or a specific portion of the work-piece W can be electropolished by moving a place on the work-piece of the electrolytic case in order.
<Electrolytic Solution>
The following electrolytic solutions are prepared.
85% phosphoric acid: 750 mL/L
98% sulfuric acid: 250 mL/L
85% phosphoric acid: 750 mL/L
98% sulfuric acid: 250 mL/L
SiO2.XH2O: 200 g/L
<Electropolishing>
Test pieces, SUS 316L, (30×30×3) mm, are subjected to the following electropolishing treatment. The coating electropolishing in under-mentioned (b) and (c) is done so as to impregnate the felt or medical-resistant cloth with the electrolytic solution and pass the current between the work-piece and the cathode sandwiching the felt (cloth) between them. The treatments applying the present invention using the electrolytic case (having the distance between the work-piece and the cathode is 10 mm) are done for the under-mentioned (d) and (e).
(a) The buffing only.
(b) The coating electropolishing (1 minute) using the normal solution (electrolytic solution (1)), 11V of voltage, 0.1 A/dm2 of current.
(c) The coating electropolishing (2 minutes) using the normal solution (electrolytic solution (1)), 11V of voltage, 0.1 A/dm2 of current.
(d) The coating electropolishing (1 minute) using the high-viscous solution (electrolytic solution (2)), 11V of voltage, 35 A/dm2 of current.
(e) The coating electropolishing (2 minute) using the high-viscous solution (electrolytic solution (2)), 11V of voltage, 35 A/dm2 of current.
(f) The dipping electropolishing (5 minutes) using the normal solution, 11V of voltage, 10 A/dm2 of current.
The liquid circulation is performed in the above (b) to (e).
<Performance Evaluation Method>
(1) Surface roughness measurement:
Five point height of roughness measurement by means of SJ-301 made of Mitutoyo Corporation
Roughness parameters are,
Ra: Mean value of roughness within a sampling length,
Ry: Sum of the largest peak height and the largest valley depth within a sampling length, and
Rz: Sum of mean value of the largest peak to the fifth largest peak and mean value of the largest valley to the fifth largest valley with in a sampling length.
(2) Surface observation:
The observation is done by a scanning electron microscope JCM-5700 made of Nihon Denshi Kabushiki Kaisha.
<Result>
(1) The result of the surface roughness measurement is shown in Table 1.
(2) The result of surface observation by the electron microscope is shown by micrographs (a) to (f) in
<Evaluation>
In the micrographs (b) and (c) in
In case of the test pieces (d) and (e), the austenite is produced on the surfaces of the test pieces like the test piece (f) and the surface modification is done. Therefore, it is understood that the electropolishing with the high-durability can be carried out in the present invention.
<Electrolytic Solution>
The normal solution and the high-viscous solution are the same as the electrolytic solutions (1) and (2) in the above Embodiment 1.
<Electropolishing>
The treatments are almost same as Embodiment 1, but the voltage is set for large value in the under-mentioned (c) and (d) that correspond to the present invention. Accordingly the current increases, too. In addition, the processing time in (c) and (e) is set for three minutes.
(a) The buffing only.
(b) The coating electropolishing (1 minute) using the normal solution (the electrolytic solution (1)), 11V of voltage, 0.1 A/dm2 of current.
(c) The coating electropolishing (3 minutes) using the normal solution (the electrolytic solution (1)), 11V of voltage, 0.1 A/dm2 of current.
(d) The coating electropolishing (1 minute) using the high-viscous solution (the electrolytic solution (2)), 20V of voltage, 50 to 70 A/dm2 of current.
(e) The coating electropolishing (3 minute) using the high-viscous solution (the electrolytic solution (2)), 20V of voltage, 50 to 70 A/dm2 of current.
(f) The dipping electropolishing (5 minutes) using the normal solution, 11V of voltage, 10 A/dm2 of current.
The liquid circulation is performed in the above (b) to (e).
<Performance Evaluation Method>
The same as Embodiment 1, but the surface observation is done by visual check.
<Results>
The result of the surface observation is shown in Table 2, and the result of the surface observation by visual check is shown in Table 3.
<Evaluation>
Compared with Embodiment 1, the voltage is set for a large value in the test pieces (d) and (e) of the present invention. As a result, the current also increases, but, on the contrary, it can be evaluated that it is possible to pass the current to such extent. In the test pieces (d) and (e), the current is within the large range of 50 to 70 A/dm2. This is fluctuation current when the electrolytic case is moved.
Regarding the surface roughness of the test pieces (d) and (e) of the present invention, in particular, the surface roughness of (e) (processing time: 3 minutes), has been improved dramatically rather than the result of (e) (processing time: 2 minutes) in Embodiment 1. And it stands comparison with the comparative tests (b), (c) and (f). Additionally, it has an excellent glossiness of external appearance, and shows the superiority of the present invention. Like Embodiment 1, the austenite is produced on the surface of the test pieces (d) and (e) as well as the test piece (f), and the surface modification is generated. Hereupon, it is possible to expect the electropolishing with high-durability.
<Electropolishing System>
The electropolishing system is configured so that an electrolytic solution L held in an electrolytic solution tank 3 is pumped to the introduction port 13 of an electrolysis case 2 via a flow control valve 5 by a pump 4. The cathode 12 of the electrolysis case 2 is applied with a negative voltage, and a work-piece W is applied with a positive voltage, from a direct current source 6 via leads 16.
The electrolytic solution tank 3 holds the electrolytic solution L having the specific viscosity. The pump 4 pumps out the electrolytic solution L from the electrolytic solution tank 3 at a specific discharge rate.
Since the electrolytic solution is high acidic and high viscosity, the pump 4 employs a synthetic resin diaphragm pump that is high chemical resistance and high discharge rate (high lifting range) for the electrolytic solution.
It is desirable that the pump 4 has higher discharge rate or higher lifting range, for example, a maximum discharge rate is 50 L/min and more, and a maximum self-suction lifting range is 2.0 m and more. The diaphragm pump wherein the maximum discharge rate is 54.5 L/min and the maximum self-suction lifting range is 2.4 m is applied to the pump 4 in
The flow control valve 5 is provided between the pump 4 and the electrolysis case 2, and controls the flow rate of the electrolytic solution L pumped out from the pump 4 to a specific flow rate per volume (1000 cm3) of the electrolysis case 2, namely, a specific flow rate per unit volume (1 cm3) of the electrolysis case 2, and then introduces the electrolytic solution L to the introduction port 13.
Accordingly, the electrolytic solution L is always transported to the electrolysis case 2 at the specific flow rate per unit volume of the electrolysis case 2, so that the fresh electrolytic solution L can be supplied between the cathode 12 and the work-piece W of the electrolysis case 2. It is possible to perform the electropolishing for the work-piece W with high quality and few faults. Besides, the specific flow rate per unit volume of the electrolysis case 2, namely, corresponds to the specific flow rate per unit volume of a space between the work-piece W and the cathode 12.
Since the specific flow rate of the electrolytic solution L controlled by the flow control valve 5 is the specific flow rate per unit volume of the electrolysis case 2, where the size of the electrolysis case 2 is 20 cm in length, 10 cm in width, and 5 cm in height, the volume of the electrolysis case 2 is 1000 cm3, and the ideal flow rate is in a range of 20 to 100 mL/min per volume (1000 cm3) of the electrolysis case 2, namely, a range of 0.020 to 0.100 mL/min per unit volume (1 cm3) of the electrolysis case 2.
The direct current source 6 is to apply the negative voltage on the cathode 12 and the positive voltage on the work-piece W in the electrolysis case 2 via the leads 16. The voltage to be applied by the direct current source 6 gets a very large value, for example, in a range of 11V to 20V, as described above. When the distance between the cathode 12 and the work-piece W in the electrolysis case is 5 mm to 20 mm, the current passing between them can be set to 30 to 100 A/dm2 as described above.
As described above, in the electropolishing system 1 of the present invention after assembling the electrolysis case 2, the electrolytic solution tank 3, the pump 4, the flow control valve 5 and the direct current source 6, the electrolytic solution L is always supplied at the specific flow rate per unit volume of the electrolysis case 2, so that the fresh electrolytic solution L always flows between the cathode 12 and the work-piece W in the electrolysis case 2, and it is possible to perform the high quality electropolishing for the work-piece W.
Besides, in the electropolishing system 1 of the present invention, the workers carry the electrolysis case 2 by hand, and freely move (scan) the cathode 12 (bottom surface) of the electrolysis case 2 on the surface of the work-piece W, thereby the work-piece W is subjected to the electropolishing.
At this time, the electrolysis case 2 is placed on the surface of the work-piece W, and allowed to remain at specific processing time, and then the electropolishing can be performed. For example, the inverse of the processing time corresponds to the scanning speed of moving (scanning) the electrolysis case 2 on the work-piece W.
The processing time is not limited in particular, but it is desirable to be in a range of 5 min/m2 to 15 min/m2. Specifically, in case of 10 min/m2, it is possible to give the work-piece W gloss like the dipping electropolishing.
Besides, the processing time can be modified freely according to a shape of the work-piece W, the current density of the current by the direct current source 6, and a purpose of the electropolishing. When the purpose of the electropolishing is the surface degreasing and the small dissolution of the work-piece W (dissolution for a few μm thickness of the surface of the work-piece W), the processing time is set to smaller than the above range. When the purpose of the electropolishing is a large scaled dissolution as well as the dipping electropolishing (dissolving the surface of the work-piece W in a few tens of μm thickness), the processing time is set to within or over the above range.
As described above, the present invention is allowed to perform the electropolishing using large current, so that the working time can be shorten. Since the processing is facilitated by holding the small amount of the electrolytic solution, it is possible to simplify the electropolishing process. The present invention can carry out the high quality electropolishing, so that there is a strong industrial applicability.
11 Case frame
12 Cathode
13 Introduction port
14 Discharge port
15 Holding member
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-268643 | Dec 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/006691 | 11/30/2011 | WO | 00 | 8/7/2013 |
