JP2008214725A - Surface treatment method for stainless steel, and fluid apparatus such as electromagnetic pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the elution of sulfur contained when the surface of the stainless steel is worked, though stainless steel, particularly, sulfur based free-cutting stainless steel such as SUS303 and SUS430 having a high sulfur content for securing free-cutting properties is used. <P>SOLUTION: For surface treatment for stainless steel, the surface of the stainless steel is subjected to shot blast treatment. Then, the surface of the stainless steel is subjected to passivation treatment. In this way, the content of sulfur in the surface is made low, and also, a protective film is formed, thus the elution of sulfur in a liquid can be suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface treatment method for preventing elution of ions from stainless steel, particularly sulfur-based free-cutting stainless steel having SUS303 and SUS430F as representative steel types, and to a fluid device such as an electromagnetic pump manufactured using the method.

  Since stainless steel is a rust-resistant steel, it is widely used for household goods such as tableware and sinks, storage tanks for liquor, beer, and industrial liquid tanks. When Cr is added to iron, a dense passive film of Cr hydroxide is formed on the surface, which acts to protect the steel from the environment, and therefore has high corrosion resistance. Generally, steel containing about 11% or more of Cr is called stainless steel.

  There are two types of stainless steel, Cr-based, which contains only Cr as an important alloy element, and Cr-Ni-based, which contains a large amount of both Cr and Ni. And in each, sulfur free-cutting stainless steel exists, The representative steel types are SUS303 and SUS430F. In addition, electromagnetic stainless steel and steel types with further improved free-cutting properties are commercially available.

  The stainless steel SUS303 contains 17.00 to 19.00 (wt%) of Cr, 8.00 to 10.00 (wt%) of Ni, and about 0.15 (wt%) of S. . In SUS304, Cr contains 18.00 to 20.00, Ni 8.00 to 10.50 (wt%), and S is 0.030 (wt%) or less.

  SUS303 is easier to cut than SUS304 and can be applied to an automatic lathe. Recently, the use of lead-containing materials for such automatic lathe materials has become difficult due to environmental regulations, and the main focus has been shifted to sulfur-based free-cutting materials. Compared to this, SUS304 is a difficult-to-cut material with a low S content, has poor cutting waste discharge performance, is slow in processing speed, and is expensive in material cost, so the material cost is markedly high. To rise.

  Naturally, when a wetted part is manufactured using SUS303, ions such as sulfur are eluted in the liquid. For example, there is no problem in oil burner equipment, but there is ion elution when used in a household fuel cell system. Inconveniently damages the catalyst.

Currently, Patent Literature 1 and Patent Literature 2 can be cited as surface treatments for stainless steel. Patent Document 1 provides a stainless steel material for food production and food storage and transportation in which a stainless steel member is washed with an organic acid, thereby forming a passive film mainly composed of Cr and suppressing the elution of Fe. ing.
Japanese Patent Application No. 2003-131050 Japanese Patent Application No. 2005-182259

  In Patent Document 2, there is a polymer electrolyte fuel cell separator member used for automobiles, small-scale power generation systems, etc. that use electric power as a direct drive source, and the flatness of the member is improved, and the surface thereof The surface treatment for lowering the electrical contact resistance is performed. The specific manufacturing method uses a particle coated with super hard particles with a conductive compound with minimal ion elution, and collides against the surface of stainless steel at a low projection pressure, so that the surface is electrically conductive with minimal ion elution. The active compound is embedded and the shape is flat.

  In the electromagnetic pump, sulfur-based free-cutting stainless steel such as SUS303 is adopted from the viewpoint of ease of cutting and price, but there is a disadvantage that ions such as sulfur contained are eluted as described in paragraph 0006 above. If this is not solved, it cannot be adopted for a household fuel cell system.

  Therefore, this invention uses stainless steel, particularly sulfur-based free-cutting stainless steel such as SUS303, which has a high sulfur (S) component, to secure free-cutting properties, but the surface is processed into a liquid such as sulfur. The purpose is to reduce elution.

  The stainless steel surface treatment method according to the present invention includes subjecting the surface of the stainless steel to shot blasting and passive treatment (claim 1). Thereby, a plastic fluidized bed is generated on the surface of the stainless steel, and sulfur on the surface can be removed and reduced. Further, since the surface is further passivated, elution of fine sulfur is removed and formation of a protective film can surely suppress elution of sulfur, such as metals contained therein, and provide corrosion resistance.

  The stainless steel is a sulfur-based free-cutting stainless steel having SUS303 and SUS430F as representative steel types (Claim 2). It is a material with a relatively large amount of sulfur (S) and good free-cutting properties.

  Zirconia is preferably used as the type of particles sprayed by the shot blasting (Claim 3), and the diameter of the particles is preferably about 0.3 mm or less (Claim 4).

  In addition, the fluid device such as an electromagnetic pump according to the present invention is that the surface treatment method according to claim 1 is used to manufacture a portion where the liquid flows using the surface-treated stainless steel (claim). Item 5). In particular, the surface treatment method is applied to a liquid contact portion such as a piston, a plunger, or a joint of an electromagnetic pump. Thus, elution of sulfur ions can be suppressed particularly when the electromagnetic pump is used to transfer the liquid and when the liquid is retained. In addition, as a fluid apparatus, not only an electromagnetic pump but an electromagnetic valve, piping, etc. may be sufficient.

  As described above, according to the present invention, the surface plastic fluidized bed is generated by shot blasting, and metal, particularly sulfur, can be reduced. In addition, since a protective film is formed on the surface, it is possible to reliably prevent metals, particularly sulfur, from eluting as ions (claim 1).

  Furthermore, SUS303, SUS430F, etc. can be adopted as the stainless steel, and an advantage that the machinability can be maintained, and an increase in the material unit price can be suppressed.

  Furthermore, since the fluid flow device such as an electromagnetic pump is made of stainless steel subjected to the surface treatment method according to claim 1 and the liquid flowing portion is manufactured, it is possible to suppress elution of ions such as contained metal. It can be used as an equipment part of a household fuel cell system. In particular, it is extremely effective to perform the surface treatment on the wetted parts of the electromagnetic pump. Elution of ions of metals and the like is suppressed, and an excellent effect as a liquid transfer means in a household fuel cell system can be exhibited (claims 5 and 6).

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

  1 and 2, an electron micrograph of stainless steel using the surface treatment method of the present invention and an electron micrograph of untreated stainless steel are disclosed. The stainless steel used here is SUS303, which is first shot blasted under the following conditions.

  The particles to be sprayed are zirconia, the diameter is about 0.3 mm or less, and the spraying time is about 5 seconds. As a result, as shown in FIG. 1, there are no sulfur element particles (indicated by black dots) near the surface.

  This is probably because the sulfur element S was struck out by the surface being struck by particles. A plastic fluidized bed can be seen on the outermost surface.

  When the shot blasting is finished, the passivation process is performed. For example, a method of immersing in concentrated nitric acid is used. Thus, since the passive treatment is performed after the shot blasting process, the elution of sulfur in the liquid is suppressed.

  FIG. 3 is a characteristic diagram obtained by EDS mapping analysis of the surface-treated stainless steel. Si and S are minutely present, but S is hardly detected and no distribution is observed.

4 and 5 are tables of the results of the dissolution test, which are performed by two analysis methods. The first method is based on an inductively coupled high-frequency plasma emission spectrometer (ICP), and the second method is based on an ion chromatograph analyzer (IP). The result of ICP analysis is shown in FIG. 4, where A1 is only slightly eluted. The results of IP analysis are shown in FIG. 5, and NH and SO _{4 are} only slightly eluted. From this result, it can employ | adopt as a liquid transfer means in a household fuel cell system.

  FIG. 6 shows an example in which the stainless steel (SUS303, SUS430F) according to the surface treatment method of the present invention (Example 1) is used for the piston 37 and the plunger 51 of the electromagnetic pump 11. From the liquid contact parts such as the piston 37 and the plunger 51, the elution of sulfur was suppressed when the liquid was transferred. The electromagnetic pump 11 will be briefly described below.

  The electromagnetic pump 11 is a constant displacement electromagnetic pump, and includes a coil 13 to which a pulse current is applied in a case 12 made of a magnetic material such as iron. The coil 13 has a wire wound around a resin bobbin 14. A guide pipe 16 made of a nonmagnetic material is fitted into a through hole formed through the center of the bobbin 14.

  A lower magnetic pole cylinder 18 made of a magnetic material is connected to the lower side of the guide pipe 16 in FIG. 6 and an upper magnetic pole cylinder 19 made of a magnetic material is connected to the upper side of the guide pipe 16, respectively. . A suction passage 23 is connected to the lower opening of the lower magnetic pole cylinder 18.

  The lower magnetic pole cylinder 18 includes a large-diameter hole 26 formed in the axial direction at the center thereof and a small-diameter hole 27 connected thereto, and the small-diameter hole 27 serves as a valve seat 32 of an intake valve 30 described below.

  The suction valve 30 is a conical valve made of stainless steel (SUS303), which is subjected to shot blasting and passivation as described above, and is provided by a spring 34 interposed between the spring receiver 31 and the valve seat 32. , Is seated on the valve seat 32.

  The cylinder 36 is a cylindrical member and is fitted into a large-diameter hole 26 formed in the lower pole cylinder 18 of polyetheretherketone (PEEK), and the tip thereof reaches the intake valve 30.

  The piston 37 is manufactured from SUS303, and is subjected to shot blasting and passivation as described above. The piston 37 is a cylindrical body having a through hole 38 in the axial direction at the center, and is slidably inserted into the cylinder 36. It is driven by the reciprocating motion of the plunger 51. A discharge valve 39 is attached to the tip which is the lower end of the piston 37. The discharge valve 39 is made of PEEK and is seated on the valve seat 41 by a spring 43.

  A retainer and a cushion 49 are attached to the upper end of the cylinder 36 in the drawing, restricting the downward movement of the plunger 51 described below, and preventing noise and vibration. The cushion 49 is made of an elastic fluororubber so that ions are not eluted into the fluid to be transferred.

  The plunger 51 is made of a magnetic material such as SUS430F, and is subjected to shot blasting and passivating as described above. The return spring is provided between the lower end of the cylinder 36 in the drive space 20 of the plunger. It is arranged so as to be pressed to the opposite cylinder side by 52. The plunger 51 has a through hole 53 formed therein, and the piston 37 is fitted using the through hole 53. Therefore, the reciprocating motion of the plunger 51 is transmitted to the piston 37, and the fluid from the pump chamber 45 is caused to flow through the through hole 38 and the through hole 53 of the piston 37 and reach the plunger drive space 20.

  Further, a shutoff valve 54 is disposed at the upper end (downstream end) of the plunger 51, and the shutoff valve 54 is seated on the valve seat 56 when the coil 13 is not energized, thereby closing the valve hole 55. The stop valve 54 and the valve seat 56 restrict the movement of the plunger 51 toward the non-piston side, and also prevent the fluid from flowing out from the driving space 20 of the plunger and conversely when the pump is stopped.

  When the coil 51 is energized and energized, the plunger 51 is displaced toward the cylinder against the return spring 52, and the lower end (upstream end) thereof reaches the cushion 49. When the coil 13 is de-energized, it is returned by the force of the return spring 52 and the closing valve 54 at the upper end thereof is seated on the valve seat 56.

  As described above, the plunger drive space 20 includes the guide pipe 16, the upper magnetic pole cylinder 19, the lower magnetic pole cylinder 18, and the cylinder 36, is located downstream from the discharge valve 39, and is located in the plunger drive space 20. Discharged fluid flows into the plunger 51 through a through-hole 53 formed. The plunger drive space 20 communicates with a discharge passage 59 described below via a valve seat 56 having a seat hole 55 formed at the upper end of the upper magnetic pole cylinder 19.

  The discharge passage 59 is provided with a backflow prevention valve 61 biased by a spring 65 so as to face the fluid flow direction and is seated on the valve seat 56. The backflow prevention valve 61 prevents the backflow of the plunger into the drive space 20 when the closing valve 54 is opened. The backflow prevention valve 61 allows fluid flow in the forward direction and opens and closes due to a pressure difference with the plunger drive space 20.

  In the above configuration, when a pulse current of 5 Hz, for example, is passed through the coil 13, when the coil 13 is excited when it is turned on, the lower magnetic pole cylinder 18, the upper magnetic pole cylinder 19, and the plunger 51 are magnetized, and the plunger 51 is moved to the return spring 52. The lower end moves against the cushion 49, and a lower end of the lower end abuts against a cushion 49 provided on the cylinder 36 to stop the downward movement. The movement of the plunger 51 is transmitted to the piston 37, the piston 37 is driven downward, and the pump chamber 45 is reduced from the state shown in the figure to a dead space. As a result, the pressure in the pump chamber 45 rises, and the discharge valve 39 is opened from the pressure difference to discharge the fluid into the plunger drive space 20.

  When the pulse current is turned off, the lower magnetic pole cylinder 18, the upper magnetic pole cylinder 19, and the plunger 51 are demagnetized, and the plunger 51 is moved upward by the return spring 52, and the pressure inside the plunger driving space 20 is compressed. The fluid in the plunger drive space 20 opens the backflow prevention valve 61 due to the pressure difference from the discharge passage 59 side and flows out into the discharge passage 59. Then, the stop valve 54 contacts the valve seat 56, and the compression stroke in the plunger drive space 20 is stopped. At that time, the volume in the pump chamber 45 increases. As a result, the pressure in the pump chamber 45 decreases, and the suction valve 30 is opened from the pressure difference to suck the fluid.

  When the pulse current is turned on again, the plunger 51 and the piston 37 move downward, and the pressurizing action in the pump chamber 45 is started. Such an action is repeated and a pump action is performed.

  The intake valve 30 as well as the piston 37 and plunger 51 described above are made of stainless steel (SUS303), and the shot blasting and passive processing are performed as described above. Is also made of stainless steel (SUS303) and has the surface treatment described above. Further, the spring 52 and the guide pipe 16 other than the machined product are also made of SUS340 or SUS304, and are subjected to a passive treatment of immersion in concentrated nitric acid. As described above, the surface treatment of the present invention is performed on the liquid contact portion with the liquid, and in particular, elution of sulfur is suppressed.

It is an electron micrograph of the section in the state where surface treatment was given to stainless steel concerning this invention. It is an electron micrograph of a section of untreated stainless steel. It is a characteristic diagram of an EDS mapping analysis result. It is a table | surface of an ICP analysis result. It is a table | surface of an IC analysis result. It is sectional drawing of the electromagnetic pump using the piston and plunger which gave surface treatment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Electromagnetic pump 12 Case 13 Coil 16 Guide pipe 20 Plunger drive space 23 Suction passage 24 Suction joint 30 Suction valve 32 Valve seat 36 Cylinder 37 Piston 39 Discharge valve 41 Valve seat
45 Pump chamber 49 Cushion 51 Plunger 52 Return spring 54 Stop valve 56 Valve seat 59 Discharge passage 61 Backflow prevention valve

Claims (6)

  A surface treatment method for stainless steel, characterized in that the surface of stainless steel is subjected to shot blasting and passive treatment.   2. The surface treatment method for stainless steel according to claim 1, wherein the stainless steel is sulfur-based free-cutting stainless steel having SUS303, SUS430F or the like as a representative steel type.   The surface treatment method for stainless steel according to claim 1, wherein the kind of particles sprayed by shot blasting is zirconia.   4. The surface treatment method for stainless steel according to claim 3, wherein the diameter of the particles sprayed by the shot blasting is 0.3 mm or less.   A fluid device such as an electromagnetic pump, wherein the surface treatment method according to claim 1 is used to produce a portion through which a liquid flows using a surface-treated stainless steel.   6. A fluid device such as an electromagnetic pump according to claim 5, wherein the surface treatment method according to claim 1 is applied to the liquid contact portion of the electromagnetic pump which is a fluid device.