JP2005350733A - Structure and its electrolytic-corrosion prevention method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structe and its electrolytic-corrosion prevention method capable of effectively preventing the electrolytic-corrosion between different kinds of metal members. <P>SOLUTION: This structural body is composed of: a first member 1 having a first outside edge part 10 consisting mainly of a first metal element: a second member 2 mainly consisting of a second metal element different from the first metal element and having a second outside edge part 20, which is arranged in contact with the first outside edge part 10; and a coating member 3 consisting of a film made of fluorinated high polymer material at least on the outside surface part and coating at least a part of the both members so as to cover the contact part 50 between the first outside edge part 10 and the second outside edge part 20. In this electrolytic-corrosion prevention method, the electric conduction between the first outside edge part 10 and the second outside edge part 20 in the structure is prevented with the coating member 3, thereby inhibiting the progressing of the electrolytic-corrosion caused so as to stradle over the contact part 50 between the first outside edge part 10 and the second outside edge part 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a structure that can effectively prevent electrolytic corrosion that occurs between different metals and a method for preventing electrolytic corrosion.

  In general, any device is constituted by a combination of members made of metal. And the kind of metal used is also various according to the performance requested | required of each site | part. Therefore, it is not uncommon for the dissimilar metal members to be disposed close to each other in the apparatus.

  When dissimilar metal members are arranged close to each other, it is known that electric corrosion (electric corrosion) occurs between the two using water as a medium. This electrolytic corrosion occurs when various metals have a specific corrosion potential (reference potential) and a potential difference occurs between them. That is, electrolytic corrosion proceeds by forming local batteries using both metals as electrodes and water or salt water interposed between the two as an electrolyte. Therefore, galvanic corrosion between dissimilar metal members is not only caused by the intrusion of water between the contact surfaces of both, but if water adheres to the outer periphery of adjacent dissimilar metal members, the water will be electrolyzed. A local battery is formed to play the role of liquid and straddle both contact portions, and electrolytic corrosion proceeds.

  In other words, in order to effectively suppress and prevent electrolytic corrosion, not only water (electrolyte) that penetrates between contact surfaces of different metal members, but also water that adheres across the contact portions of different metal members is used for local batteries. Need to be formed.

  And depending on the use environment and use conditions of an apparatus, it is inevitable that rainwater, seawater, condensation, etc. adhere to a dissimilar metal member. As a result, electrolytic corrosion proceeds using the attached water or the like as the electrolyte, resulting in a decrease in the function of the member, and it becomes impossible to ensure the durability and reliability of the device. Therefore, many electric corrosion prevention measures have been proposed conventionally.

Patent Documents 1 to 3 disclose a method for suppressing electrolytic corrosion by interposing an insulating material between different metal members so that the different metal members are not in direct contact with each other. Patent Document 4 discloses a method of suppressing electrolytic corrosion by painting a conductive coating material that covers a boundary portion between dissimilar metal members arranged adjacent to each other and electrically shorting the dissimilar metal members to each other. doing.
JP-A-6-136295 JP 2003-64492 A JP 2003-253481 A JP-A-6-287778

  However, when an insulating material is interposed between different metal members as disclosed in Patent Documents 1 to 3, there is a risk that the insulating material may be damaged by a bolt or the like due to vibration during use, etc. There is. When a defect occurs, water or the like enters from the defective part, and electrolytic corrosion progresses. In addition, in an apparatus such as a compressor that requires airtightness, pressure leakage may occur from the defective part. I don't want it.

  Further, in the method disclosed in Patent Document 4, it may be possible to short-circuit the dissimilar metal members, but water or the like is prevented from penetrating the coating material and entering the boundary between the dissimilar metal members. Because there is no idea, it is hard to say that it is a reliable means of preventing electric corrosion.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a structure that can effectively prevent electrolytic corrosion between dissimilar metal members and a method for preventing the electrolytic corrosion.

  The structure of the present invention includes a first member having a first outer end mainly composed of a first metal element, and a first outer end mainly composed of a second metal element different from the first metal element. A second member having a second outer end portion disposed in contact with the first outer end portion, and a first outer end portion and a second outer end portion formed of a coating film having at least an outer surface portion made of a fluoropolymer. And a covering member that covers at least a part of both so as to cover the contact portion.

  In addition, the method for preventing galvanic corrosion of a structure according to the present invention includes a first member having a first outer end mainly composed of a first metal element and a second metal element different from the first metal element as a main component. A second member having a second outer end portion disposed in contact with the first outer end portion, and a first outer end portion comprising at least an outer surface portion of a coating film made of a fluorine-based polymer substance. And a covering member that covers at least a part of the contact portion between the first outer end portion and the second outer end portion so as to cover the contact portion between the first outer end portion and the second outer end portion. The electrical continuity between the first outer end portion and the second outer end portion is hindered, and the progress of electrolytic corrosion that can occur across the contact portion between the first outer end portion and the second outer end portion is prevented.

  Here, the designations “first” and “second” are merely designations for convenience for distinguishing members and the like. For example, either the first metal element or the second metal element may be an electrically base metal (a metal having a low reference potential) or a noble metal (a metal having a high reference potential). For the sake of convenience, the first metal element may be a base metal (eg, Mg) and the second metal element may be a noble metal (eg, Fe).

  According to the structure of the present invention and the method for preventing galvanic corrosion, the covering member having the above-described configuration prevents intrusion or adhesion of water or the like that electrically connects the first outer end and the second outer end. It is possible to prevent electric corrosion that occurs across the contact portion.

  Furthermore, since the said covering member should just coat | cover at least one part of both so that the contact part of a 1st outer side edge part and a 2nd outer side edge part may be covered, a 1st outer side edge part and a 2nd outer side edge part, There is no need to interpose an insulator or the like between them.

  Moreover, since the said covering member consists of a coating film, even if a dissimilar metal member has a complicated shape, it is possible to coat | cover a covering member easily with a normal coating method.

  Hereinafter, the best mode for carrying out the structure of the present invention and the method for preventing electrolytic corrosion will be described with reference to FIG.

  The first member has a first outer end portion mainly composed of the first metal element, and the second member has a second outer end portion mainly composed of a second metal element different from the first metal element. The first outer end and the second outer end are not limited in shape and material as long as they are made of different metals. This is because as long as the metal is different, galvanic corrosion can occur between the two. In particular, if the first metal element (or the second metal element) is Mg, that is, if the first outer end portion is magnesium or a magnesium alloy, the electrolytic corrosion is more likely to proceed. In this case, the present invention is effective. is there. At this time, the second metal element is not particularly limited and may be any of Al, Zn, Fe, Cu, etc. Among them, it is Fe that is often used in a normal apparatus and a local battery is easily formed.

  That is, it is sufficient that the first member and the second member have the outer end portions as described above. That is, the whole need not be made of a metal material. For example, a portion other than the outer end portion may be a composite member made of resin or the like. Moreover, the form, function, etc. are not ask | required of both members.

  The second outer end portion is disposed in contact with the first outer end portion, but may be in any contact state of point contact, line contact, or surface contact. Furthermore, even if the first member and the second member are not in direct contact with each other, the first member and the second member may be electrically coupled with a fastener such as a bolt. Moreover, as shown in FIG. 4, both end surfaces (11, 21) may not protrude on the same surface and may protrude.

  In addition, the specific area | region is not specified for the outer side edge part said by this invention. This is because the range in which electrolytic corrosion can occur varies depending on the form of the member and the use environment. If it dares to say, it will be the area | region containing the contact part which both contacted at least.

  Examples of the structure of the present invention include a compressor, an engine block, and a hydraulic pump. In particular, in a compressor consisting of a front housing, a cylinder, and a rear housing, with a gasket interposed between the cylinder and the rear housing, a rear housing mainly composed of Mg and a gasket mainly composed of Fe are used. In this case, if water droplets such as rain water or dew condensation adhere to the outer peripheral surface and the electrolytic corrosion proceeds, the rear housing (Mg) may be corroded to cause pressure leakage, which greatly affects the performance of the compressor.

Here, the partial expanded sectional view at the time of arrange | positioning the 1st outer side edge part 10 of the 1st member 1 and the 2nd outer side edge part 20 of the 2nd member in contact is shown in FIG. In FIG. 4, the metal which comprises the 1st member 1 is made into magnesium, and the metal which comprises the 2nd member 2 is made into iron for description. Depending on the environment in which this structure is used, water droplets 4 such as rain water and condensation adhere to the outer peripheral sides (11, 21) of the first member 1 and the second member 2 in a state of straddling the contact portions 50 of both. Sometimes. In this way, a local battery is formed using the dissimilar metal member as the electrode (1, 2) and the water droplet 4 as the electrolyte. Then, Mg having a very low corrosion potential starts to elute into the water droplet 4 from the end surface 11 of the first outer end portion 10 as Mg ²⁺ . That is, the electrolytic corrosion of the first member 1 made of magnesium proceeds. Of course, when the water droplet 4 enters between the contact surfaces of the contact portion 50, the same electrolytic corrosion proceeds.

  The covering member of the present invention may occur so as to straddle the contact portion between the first outer end portion and the second outer end portion by inhibiting electrical conduction between the first outer end portion and the second outer end portion. It prevents the progress of electric corrosion. In other words, the coating member eliminates a series of electrolytes such as water that electrically connect the first outer end and the second outer end.

  Therefore, the covering member needs to be made of a coating film having at least an outer surface portion made of a fluorine-based polymer material. The “outer surface portion” refers to the surface portion of the covering member to which water or the like can adhere. That is, for example, when the coating film has a strip shape, it includes not only the surface portion composed of the width direction and the length direction but also the side surface in the thickness direction. Furthermore, the covering member needs to cover at least a part of both so as to cover the contact portion between the first outer end and the second outer end.

  At least the outer surface portion of the coating film made of a fluorine-based polymer substance is a high-density coating film with at least the outer surface portion having low moisture permeability and water permeability. As a result, a series of electrolytes that electrically connect both members is prevented. That is, electric corrosion can be prevented satisfactorily. In the case of a coating film containing a silicon-based polymer such as silicon rubber or silicon resin, depending on the silicon content, water may penetrate the coating film and electrically connect both members in the contact area or coating film. Therefore, electrolytic corrosion cannot be effectively suppressed.

  Furthermore, the covering member is also required to have adhesion with a dissimilar metal member. If it is a covering member with high adhesion, it is possible to prevent intrusion of water or the like from the interface between the dissimilar metal member and the covering member. For this reason, if the coating film made of a fluorine-based polymer material alone is poor in adhesion, a multilayer structure member in which an underlayer capable of enhancing both adhesion and preventing peeling can be used. In addition, although adhesiveness becomes so high that the surface roughness of a dissimilar metal member is roughened, if the surface roughness is rough, it will be easy to be subjected to electrolytic corrosion.

  And it is preferable that a coating | coated member contains the sealing layer which apply | coated and hardened | cured the fluorine-type sealing agent. This seal layer may be a single layer structure or a multilayer structure. However, a seal layer made of a fluorine-based sealant has a low moisture permeability and water permeability, a high-density coating film, and a single layer. It has excellent adhesion to dissimilar metal members and does not peel off due to vibration. Moreover, heat resistance is also favorable. Therefore, the covering member including the seal layer is suitable for a dissimilar metal member used in a device such as a compressor that is used under a high temperature condition or generates vibration during use of the device. In addition, examples of the fluorine-based sealant suitable for the sealing layer of the covering member include fluorosilicone rubber and the like, and liquid fluororubber is particularly preferable.

  The covering member depends on the type of fluorine-based polymer and the structure of the covering member (single layer / multi-layer), but if a fluorine-based sealant is used, the thickness of the seal layer is preferably 100 μm or more. . If the thickness of the seal layer is 100 μm or more, it is sufficient to prevent intrusion of water and the like, and the effect of suppressing electrolytic corrosion can be obtained satisfactorily.

  There is no particular limitation on the shape and dimensions of the covering member as long as at least a portion to which water or the like can adhere is covered in the contact portion between the first outer end portion and the second outer end portion. However, regarding the width of the covering member, although it depends on the shape of the dissimilar metal member and the size of the attached water droplet, the width across the contact portion is preferably 10 mm or more. If the width of the covering member is 10 mm or more, even if water or the like adheres, it is possible to effectively connect the electrolyte solution such as water that electrically connects the first outer end and the second outer end. It can be eliminated, and formation of a local battery using a different metal member as an electrode can be sufficiently blocked or suppressed.

  In addition, since a covering member is a coating film, even if the object part which forms a covering member among a dissimilar metal member is a part which has a complicated shape (for example, as shown in FIG. 4, a contact part has a level | step difference), It is possible to easily coat the covering member. As a method for forming a coating film, it is obtained by applying a paint to a target portion by a usual coating method such as a coating method, a flow coating method, a spray coating method, a spin coating method, a roll coating method, and drying and curing. At this time, the drying conditions and the like may be appropriately selected according to the type of paint.

  Note that the structure of the present invention is not limited to the above-described embodiment, and other structures may be added, for example, a protective layer that further protects the covering member.

  Moreover, this invention can be grasped | ascertained not only as said structure but as the electrolytic corrosion prevention method.

  Below, the structure of this invention and the Example of the electrolytic corrosion prevention method are described using FIGS. 1-2. 1 and 2 are diagrams schematically showing a test piece made of a dissimilar metal member. FIG. 1 is a side view of the test piece seen from the outer side, and FIG. 2 is a test piece of FIG. It is the partial expanded sectional view which cut | disconnected in the axial direction.

[Example 1]
A specimen having a dissimilar metal member was prepared. This test piece is composed of an Mg alloy member 1 and an Fe alloy member 2. The Mg alloy member 1 is a 16 mm × 16 mm × 35 mm AZ91 (JIS) Mg alloy block, and a screw hole 16 extends in the longitudinal direction at the center thereof. The surface of the Mg alloy member 1 was subjected to surface treatment (electrodeposition coating), and the surface roughness was Ra = 0.11 [μm]. The Fe alloy member 2 is an Fe alloy block of cold rolled steel plate SPCC (JIS) of 16 mm × 16 mm × 16 mm, and a screw hole 26 having the same diameter as that of the screw hole 16 extends in the center thereof.

  Then, the bolt 6 was screwed into the screw holes 16 and 26 of the Mg alloy member 1 and the Fe alloy member 2 and was fastened coaxially so as to contact each other. As a result, the outer end portion 10 of the Mg alloy member 1 and the outer end portion 20 of the Fe alloy member 2 are in contact with each other, and the end surfaces 11 and 21 of the outer end portions 10 and 20 are positioned on the same plane. The test piece which consists of a dissimilar metal member was obtained.

  And the coating | coated member 3 was formed in the outer peripheral surface of a test piece so that the contact part 50 of the outer side edge part 10 of the Mg alloy member 1 and the outer side edge part 20 of the Fe alloy member 2 might be covered. Specifically, the covering member 3 includes a contact end portion 51 that exists linearly on the outer peripheral surface side of the test piece in the contact portion 50 with the outer end portions 10, 20, and the end surface 11 of the outer end portion 10. The contact part 50 was covered by covering a part and a part of the end surface 21 of the outer end part 20.

  The covering member 3 is made of a coating film of liquid fluoro rubber (SIFEL600 series manufactured by Shin-Etsu Chemical Co., Ltd.). The liquid fluororubber is made of a fluorine-based polymer material obtained by applying it to the outer peripheral surface of the test piece so as to have a width of 10 mm (centering on the contact end 51), and drying and curing at 150 ° C. for 1 hour. It was set as the coating film which becomes. Moreover, the film thickness of the coating | coated member 3 was 100-200 micrometers.

  The member obtained by the above procedure was designated as sample A.

[Comparative Example 1]
The test piece of Example 1 was coated with a commercially available silicon-based sealant as the covering member 3, dried at room temperature for 5 days, and cured to form a coating film similar to that of Example 1. The obtained member was designated as Sample B.

[Comparative Example 2]
The test piece of Example 1 was coated with a fluorine-containing silicon resin-based coating material as the covering member 3, dried at room temperature for 24 hours, and cured to form a coating film similar to that of Example 1. The obtained member was designated as Sample C.

[Evaluation]
In order to evaluate the electrolytic corrosion prevention effect, a salt spray test was conducted. The salt spray test was conducted under constant conditions of salt water concentration: 5%, spray amount: 1 to 2 ml / hr, spray pressure: 0.098 ± 0.002 MPa, test temperature: 35 ° C., air saturator: 47 ° C. Went for hours.

  After the test, except for fastening of the Mg alloy member 1 and the Fe alloy member 2, the appearance of the Mg alloy member 1 was visually observed from the axial direction side with the contact portion 50 as the front surface. The results are shown in Table 1. In addition, FIG. 3 is a photograph which substitutes for the sample A and the sample C, which is a photograph taken from the axial direction side with the surface corresponding to the contact portion 50 of the Mg alloy member 1 as the front, and shows the state of corrosion.

  As shown in FIGS. 1 and 2, the samples A to B are sufficiently covered with the covering member 3 having a certain width over the entire circumference of the contact end portion 51. Therefore, even if water droplets adhere to the surface of the test piece, no electrical continuity is formed between the end face 11 and the end face 21 and no electric corrosion should occur.

  However, only the sample A had a good appearance after the test, and the sample B and the sample C were corroded. The covering member 3 of the sample A is made of a coating film made of a fluorine-based polymer material, and salt water can enter from the interface between the sample pieces (1, 2) and the covering member 3 and from the surface of the covering member 3. As a result, the electrolytic corrosion of the Mg alloy member 1 could be prevented. On the other hand, in the covering member 3 using the silicon-based sealant as in the sample B, the intrusion of salt water could not be prevented. Furthermore, in sample C, a fluorine-containing silicon resin paint is used, and a fluorine-based polymer substance is present in a part of the covering member 3, but salt water has partially infiltrated from the portion where the silicon resin is present. , Locally large corrosion formed.

  In addition, since the said dissimilar metal member uses the combination of the same kind of alloy metal as the compressor which has the rear housing which has Mg as a main component, and the gasket which has Fe as a main component, for example, in an Example and a comparative example Needless to say, the same results can be obtained even when the above-described covering member is used in the above compressor.

It is the figure which showed typically the test piece which consists of a dissimilar metal member of an Example, Comprising: It is the side view which looked at the test piece from the outer surface. It is the figure which showed typically the test piece which consists of a dissimilar metal member of an Example, Comprising: It is the elements on larger scale which cut | disconnected FIG. 1 in the axial direction. It is a photograph taken from the axial direction side with the surface corresponding to the contact portion of the Mg alloy member as the front surface, and is a drawing substitute photograph showing the state of corrosion. It is a schematic diagram explaining the progress of the electrolytic corrosion in a dissimilar metal member.

Explanation of symbols

1: First member (Mg alloy member)
10: (first) outer end portion 2: second member (Fe alloy member)
20: (second) outer end portion 3: covering member 50: contact portion

Claims (9)

A first member having a first outer end mainly composed of a first metal element;
A second member comprising a second metal element different from the first metal element as a main component and having a second outer end disposed in contact with the first outer end;
A covering member that at least an outer surface portion is made of a coating film made of a fluorine-based polymer substance and covers at least a part of both so as to cover a contact portion between the first outer end portion and the second outer end portion;
A structure characterized by comprising   The structure according to claim 1, wherein the covering member includes a seal layer that is cured by applying a fluorine-based sealant.   The structure according to claim 2, wherein the sealant is liquid fluororubber.   The structure according to claim 2, wherein the seal layer has a thickness of 100 μm or more.   The structure according to claim 1, wherein the covering member has a width of 10 mm or more across the contact portion.   The structure according to claim 1, wherein the first metal element or the second metal element is Mg.   The structure according to claim 1, wherein the first metal element is Mg and the second metal element is Fe.   The structure according to claim 7, wherein the first member is a rear housing of the compressor, and the second member is a gasket. A first member having a first outer end mainly composed of a first metal element and a second metal element different from the first metal element as a main component are disposed in contact with the first outer end. A second member having a second outer end and at least an outer surface comprising a coating film made of a fluorine-based polymer substance so as to cover a contact portion between the first outer end and the second outer end. And a covering member covering at least a part of both,
The covering member prevents the electrical continuity between the first outer end portion and the second outer end portion so as to straddle the contact portion between the first outer end portion and the second outer end portion. A method for preventing galvanic corrosion of a structure, which obstructs the progress of galvanic corrosion obtained.

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