JP2016070364A - Metal bolt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal bolt used for mutual fastening of electrodeposited dissimilar metallic members not producing any potential difference corrosion and poor chemical conversion treatment accompanied by formation of a local cell with a further convenient configuration.SOLUTION: This invention relates to a metallic bolt 10 used for mutual fastening of electrodeposited dissimilar metallic members (a fender 42 and an upper frame 44). This bolt has: protrusions 18b formed by the same metallic material as that of the upper frame 44 and protruded out of a seat surface 18 of a head part 12; and a covering film part 20 covering the seat surface 18 under an insulated state. The protrusions 18b are directly contacted with the fender 42 under a state in which they are engaged with a nut insert 40 to connect the dissimilar metallic members to each other, the covering film part 20 covering an area A of the seat surface 18 ranging from the protrusions 18b to an outer end part 18a is closely contacted with the fender 42, and a form of a flange part 14 is set in such a way that a range showing occurrence of poor chemical conversion treatment caused by a direct contact between each of the protrusions 18b and the fender 42 is kept in the area A of the seat surface 18. With this arrangement, some problems of potential difference corrosion and poor chemical conversion treatment can be eliminated with a further convenient configuration.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a metal bolt used for fastening metal members, and more particularly to a metal bolt used for fastening different metal members to be electrodeposited.

  In recent years, in order to reduce the weight of a vehicle body in a vehicle such as an automobile, there is an increasing need to employ an aluminum member for a vehicle body constituent member mainly made of an iron-based material such as a steel material. However, if the aluminum member is simply joined to the vehicle body component made of an iron-based material, the contact portion of both the members to be joined (the iron-based member such as a bolt used for joining the two members and the aluminum-made member) In other words, there is a problem that potential corrosion due to local battery formation occurs. In addition, when electrodeposition coating is applied to the surface of an aluminum member, chemical conversion treatment is performed on the surface of the aluminum member in advance in order to increase the adhesion of the electrodeposition paint to the surface of the aluminum member. In the vicinity of the contact portion between the vehicle body constituting member and the aluminum member, the formation of the chemical conversion film on the surface of the aluminum member is inhibited. Therefore, the adhesion of the electrodeposition paint in the vicinity of the contact portion between both members is lowered.

  Such problems of potential difference corrosion and inhibition of chemical conversion film formation (hereinafter referred to as chemical conversion treatment failure) can be solved by applying an insulating film to the joint portion between both members. Is cut off, and electrodeposition coating on the surface of the aluminum member cannot be performed.

  Therefore, a measure has been taken in which a separate conductive contact is provided between the members to be joined and the conductive contact is eliminated after electrodeposition coating.

  Patent Document 1 discloses a technique for preventing infiltration of water into a contact portion while ensuring conduction at a contact portion between different members. Specifically, as shown in FIG. 7, the bearing surface 101 a of the head 101 of the earth bolt 100 is provided with a protruding portion 101 b arranged in an annular shape capable of stripping the insulating coating 103 on the surface of the metal plate 102. It has been. According to this, in a state in which the ground bolt 100 is attached to the metal plate 102, the protruding portion 101 b and the metal plate 102 are in contact with each other, and conduction between the ground bolt 100 and the metal plate 102 is ensured. At the same time, the insulating coating 103 on the surface of the metal plate 102 is cut by the protruding portions 101b, and both end surfaces of the protruding portions 101b are covered with the end portions of the insulating coating 103 generated by the cutting, so that the ground bolt 100 and the metal plate 102 are covered. The water-tightness of the contact portion is ensured.

JP 2012-219854 A

  However, an insulating film is applied to the joint part of the body component made of aluminum and iron-based material, and a separate contact is provided before electrodeposition coating. It causes a decline in sex.

  In addition, according to the ground bolt of Patent Document 1, the projecting portion is formed by an annular projecting portion while ensuring conduction between the ground bolt and the metal plate by a simple operation of fastening the ground bolt to the insulating-coated metal plate. Therefore, even if a dissimilar metal member is used, potential difference corrosion between the ground bolt and the metal plate can be prevented. However, since Patent Document 1 is a technique for grounding a metal plate that is a casing of an automobile or the like from an electric device, the surface of the metal plate is already provided with an insulating coating to insulate the charged metal plate surface. Therefore, neither chemical conversion nor electrodeposition coating can be applied to the surface.

  The present invention has been made in view of the above-mentioned problems, and its object is to fasten different metal members to be electrodeposited without causing potential difference corrosion and chemical conversion treatment failure due to local battery formation with a simpler configuration. It is providing the metal volt | bolt used for.

  In order to achieve the above object, the invention according to claim 1 is the metal bolt used for fastening the different metal members to be electrodeposited, and among the different metal members, the metal member on the lower side in the screwing direction. The dissimilar metal member formed of the same kind of metal material, having a projection protruding from the seating surface of the head, and a coating film part for insulatingly covering at least the seating surface, and engaging with a corresponding nut In a state where they are joined to each other, the protrusion directly contacts the metal member on the upper side in the screwing direction among the dissimilar metal members, and covers the region from the protrusion on the seat surface to the outer end of the seat surface. The coating film portion to be in close contact with the metal member on the upper side in the screwing direction, and the form of the lower part of the head is formed by direct conversion between the protrusion and the metal member on the upper side in the screwing direction. The area where the defect occurs remains in the area of the seat Characterized in that the sea urchin set.

  According to this configuration, the form of the lower part of the head is changed from the protrusion on the seat surface to the outer edge of the seat surface, where the chemical conversion treatment failure due to the direct contact between the protrusion and the metal member on the upper side in the screwing direction occurs. Because it is set so that it stays in the area up to, the dissimilar metal members with metal bolts and nuts are joined to each other, and there is no lower part of the head of the metal bolt in the surface of the metal member on the upper side of the screwing direction. A region (that is, a region touched by the chemical conversion treatment solution) is subjected to a chemical conversion treatment to form a good film and can be subjected to a good electrodeposition coating.

  Furthermore, in the state of joining the dissimilar metal members by metal bolts and nuts, the coating film portion covering the region from the protrusion on the seat surface to the outer end of the seat surface is against the metal member on the upper side in the screwing direction. Since they are in close contact with each other, conduction between the metal bolt and the metal member on the upper side in the screwing direction and water tightness of the contact portion of both members are ensured, and potential difference corrosion does not occur even in a wet environment.

  In addition, the fastening of the different metal members is not different from the conventional operation of engaging the bolt and the nut, and the productivity is not lowered.

  The invention according to claim 2 is the metal bolt according to claim 1, characterized in that the distance of the region from the protrusion on the seat surface to the outer end of the seat surface is 3 mm or more. To do.

  According to this configuration, a range of less than 3 mm in radius from the contact portion between different kinds of metal members under the conditions of a general chemical conversion treatment performed prior to the electrodeposition coating of the vehicle body in the vehicle is a range where the chemical conversion treatment failure occurs. However, by setting the distance from the protrusion on the seating surface to the outer end of the seating surface to be 3 mm or more, the region not covered with the metal bolt seating surface of the surface of the metal member on the upper side in the screwing direction is subjected to chemical conversion treatment. As a result, a good film can be formed and good electrodeposition coating can be achieved.

  According to a third aspect of the present invention, in the metal bolt according to the first or second aspect, the lower portion of the head is a flange portion having a substantially circular shape in plan view, and a radially outer edge of the flange portion is It is characterized in that it has a curved end portion with no corners in a longitudinal sectional view.

  According to this configuration, since the radially outer edge of the flange portion is a curved end portion having no corners in a longitudinal sectional view, the metal member on the upper side in the screwing direction and the seating surface are acute angles except for the protrusions. There is no possibility of peeling off the insulating coating on the seating surface. That is, it is possible to ensure the covering of the region from the protrusion on the seating surface to the outer end of the seating surface by the coating film portion, and to securely retain the range where the chemical conversion treatment failure occurs in the covering region.

  According to the present invention, since the covering region under the head covers the range where the chemical conversion treatment failure occurs while having watertightness, potential difference corrosion and chemical conversion treatment failure caused by the joining of dissimilar metal members occur. Absent. Therefore, the surface of the metal member on the upper side in the screwing direction after the electrodeposition coating is satisfactorily electrodeposited, and the problem of corrosion due to contact with water is solved. At the same time, since the bolt and nut tightening is simple, productivity of the vehicle body such as a vehicle is not reduced.

1A is a partially broken side view of a metal bolt 10 according to an embodiment of the present invention, and FIG. It is a principal part enlarged view of the vehicle width direction cross section of the front part of a vehicle for demonstrating the use condition of the metal volt | bolt 10 which concerns on this Embodiment. (A) It is explanatory drawing of the sample used for the examination test of the range which the chemical conversion treatment defect resulting from the contact of a dissimilar metal member arises, and (B) The III _B- III _B sectional view taken on the line of the same figure (A). It is the figure which showed the examination test result as a vertical axis | shaft and the distance from a contact point with the horizontal axis | shaft as the score of a chemical crystal. It is an electron micrograph which shows a favorable chemical conversion treatment state (score 5). It is an electron micrograph which shows the state (score 3) of a chemical conversion treatment defect. It is a longitudinal cross-sectional view which shows the joining state of the conventional earth bolt and this earth bolt and a metal plate.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. A metal bolt 10 according to the present embodiment used for fastening different metal members to be electrodeposited will be described with reference to FIGS. 1 and 2.

  FIG. 1 (A) is a partially broken side view of a metal bolt 10 according to an embodiment of the present invention, and FIG. 1 (B) is a bottom view.

  As shown in FIG. 2A, the metal bolt 10 according to the present embodiment is a flanged hexagon bolt (so-called flange bolt) in which the lower portion of the head 12 becomes the flange portion 14. The head portion 12 has a substantially hexagonal shape in plan view, and the lower portion is a flange portion 14 having a substantially circular shape in plan view. The shaft portion 16 of the metal bolt 10 is provided with a male screw portion (thread) 16 a that is screwed with a female screw portion of a corresponding nutsert (nut) 40. The lower surface of the flange portion 14 becomes the seat surface 18 of the head portion 12 that comes into contact with the surface of the metal member (fender 42) on the upper side in the screwing direction of the metal bolt 10.

  The seat surface 18 is not a horizontal plane but has a taper shape that is slightly downwardly inclined toward the radially outer outer end portion 18a with the axial center position of the shaft portion 16 as an apex, and is gently in the vicinity of the outer end portion 18a. To the upper surface portion 14a of the flange portion 14. That is, the radially outer end portion 14b of the flange portion 14 is a curved end portion having no substantially U-shaped corner in a vertical view. The inclination of the seating surface 18 is a slight inclination not noticeable to the eye.

  Further, as shown in FIG. 1B, on the shaft portion 16 side of the seating surface 18, six conical projections 18 b projecting downward are circular in the bottom view centering on the shaft portion 16. Each is arranged at equal intervals.

  The metal bolt 10 is made of a ferrous metal material of the same kind as a metal member (upper frame 44) on the lower side in the screwing direction of the metal bolt 10 to be described later, and has conductivity, but the entire surface is made of a resin-free colorless material. It is covered with a transparent insulating film (coating film part 20).

  The form of the lower portion of the head 12, that is, the flange portion 14, is such that the range in which a chemical conversion treatment failure due to direct contact between the protrusion 18b and a metal member (fender 42) on the upper side in the screwing direction described later occurs on the seating surface 18 It is set so as to remain within the range of the region A from the portion 18b to the outer end portion 18a of the seating surface 18. Preferably, the distance D of the region A from the protrusion 18b on the seat surface 18 to the outer end 18a of the seat surface 18 is 3 mm or more. In the present embodiment, this distance D is 3 mm.

  The dimensions of each part of the metal bolt 10 are such that the distance from the radially inner end of the seat surface 18 to the radially outer outer end 18a is 5 mm or more, the width of the protrusion 18b is 2 mm or less, The height of the portion 18 is 0.3 mm or more, and the height between the radially inner end of the seating surface 18 and the radially outer outer end 18a is less than 0.2 mm.

  Next, a state where dissimilar metal members are fastened to each other, which should be referred to as a use state of the metal bolt 10 according to the embodiment of the present invention, will be described with reference to FIG.

  FIG. 2 is an enlarged view of a main part of a vehicle width direction cross-section of the front part of the vehicle for explaining a use state of the metal bolt 10 according to the present embodiment. In the present embodiment, the metal bolt 10 fastens the fender 42 and the upper frame 44, and the upper part of the joint portion between both members is covered by the end side of the bonnet 46.

  The fender 42 is made of aluminum, and the upper frame 44 is formed of an iron-based metal member. That is, both are in the relationship of different metal members. As shown in the figure, the fender 42 is a metal member on the upper side in the screwing direction of the metal bolt 10, and the upper frame 44 is a metal on the lower side in the screwing direction of the metal bolt 10. It is a member.

  As shown in the figure, an annular plate member 48 having an insulating coating on the upper surface of the upper frame 44 and a fender 42 are sequentially stacked, and the bolt insertion holes are aligned to align the shaft portion 16 of the metal bolt 10. Is inserted into the bolt insertion hole, and the corresponding nutsert 40 is screwed onto the shaft portion 16 and is strongly tightened. By this tightening, the flange portion 14 of the metal bolt 10 is elastically deformed, and the region of the seating surface 18 excluding the protruding portion 18 b comes into close contact with the surface of the fender 42 through the coating film portion 20. At the same time, the insulating film portion 20 covering the tip of the protrusion 18b is pressed against the surface of the fender 42 and is broken, and the tip of the protrusion 18b directly contacts the surface of the fender 42 and bites.

  In the state in which the fender 42 and the upper frame 44 are fastened by the metal bolt 10, the fender 42 and the upper frame 44 do not have a direct electrical contact because the insulating coated annular plate member 48 is interposed. However, when the nutsert 40 is screwed to the shaft part 16, the coating film part 20 of the male screw part 16a is broken, and the shaft part 16a and the nutsert 40 are in direct contact. Further, since the nutsert 40 is an iron-based material and is not covered with insulation, the nutsert 40 and the upper frame 44 are in direct contact with each other.

  Therefore, as shown by the arrow 200 in FIG. 2, the upper frame 44 is electrically connected to the fender 42 via the nutsert 40 and the metal bolt 10. That is, electrodeposition coating can be applied to the entire vehicle body with the entire vehicle body including the fender 42 and the upper frame 44 as one cathode (in the case of cationic electrodeposition coating) without providing a separate conductive contact. Note that the direction of the arrow 200 indicates the direction of current flow when performing cationic electrodeposition coating.

  According to the present embodiment, the form of the flange portion 14, which is the lower portion of the head portion 12, is a range in which a chemical conversion treatment failure occurs due to direct contact between the protrusion 18 b and the fender 42 (the upper metal member in the screwing direction). Is set so as to remain in the region from the protrusion 18b to the outer end 18a of the seating surface 18 in the seating surface 18, so that the dissimilar metal members are joined to each other by the metal bolt 10 and the nutsert 40 (nut). The region of the surface of the fender 42 that is not covered by the lower part of the head of the metal bolt 1012 (that is, the region that is touched by the chemical conversion solution) is formed with a good film by chemical conversion treatment, and is subjected to good electrodeposition coating. It becomes possible.

  Furthermore, the covering film portion 20 that covers the region from the protrusion 18b of the seating surface 18 to the outer end portion 18a of the seating surface 18 in a joined state between the different metal members by the metal bolt 10 and the nutsert 40 (nut). Since it is in close contact with the fender 42 (the metal member on the upper side in the screwing direction), the electrical connection between the metal bolt 10 and the fender 42 and the water-tightness of the contact portion between the two members are ensured, and the potential difference even in a wet environment Corrosion does not occur.

  In addition, the fastening of the different metal members is not different from the conventional operation of engaging the bolt and the nut, and the productivity is not lowered.

  Also, under the conditions of general chemical conversion treatment performed prior to the electrodeposition coating of the vehicle body in the vehicle, the range where the radius of less than 3 mm from the contact portion between the dissimilar metal members is the range where the chemical conversion treatment failure occurs. 18 is covered with the seating surface 18 of the metal bolt 10 out of the surface of the fender 42 (the metal member on the upper side in the screwing direction) by setting the distance from the projection 18b to the outer end 18a of the seating surface 18 to 3 mm or more. In the unexposed region, a good film is formed by chemical conversion treatment, and good electrodeposition coating becomes possible.

  Further, since the radially outer end edge 14b of the flange portion 14 is a substantially U-shaped curved end portion having no corners in a longitudinal sectional view, the fender 42 (the metal on the upper side in the screwing direction) is excluded except for the protrusion 18b. There is no acute contact between the member) and the seating surface 18, and there is no possibility that the insulating coating 20 on the seating surface 18 is peeled off by this contact. That is, the covering of the region A from the protrusion 18b on the seating surface 18 to the outer end 18a of the seating surface 18 by the coating film portion 20 is ensured, and the range where the chemical conversion treatment failure occurs is more reliably retained in this coating region. Is possible.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples.

[Sample preparation]
As shown in FIG. 3, an aluminum plate 52 having a width of 70 mm and a length of 150 mm suspended by a string 50 was sandwiched between iron flange bolts 54 and nuts 58 and tightened to prepare a sample. The entire surface of the nut 58 is insulated (not shown), and there is no influence on the chemical conversion treatment of the aluminum plate 52 by the nut 58.

  The aluminum plate member 52 corresponds to the metal member on the upper side in the screwing direction of the present invention, and the flange bolt 54 is an iron-based metal member formed of the same metal material as the metal member on the lower side in the screwing direction. It corresponds to.

[Chemical conversion treatment]
The sample was subjected to chemical conversion treatment according to the steps shown in Table 1 below. The chemical conversion treatment process in Table 1 is a general chemical conversion treatment process for a vehicle body.

[Evaluation of chemical conversion treatment results]
With respect to the sample after the chemical conversion treatment, the contact between the outer end portion 56a of the seat surface 56 of the flange bolt 54 and the aluminum plate member 52 is set to 0 mm, and 0.5 mm, 1 mm, 2 mm in the direction away from the seat surface 56 of the flange bolt 54. The formation state of chemical conversion crystals on the surface of the aluminum plate 52 at positions of 3 mm, 4 mm and 5 mm was observed with an electron microscope. FIG. 4 is a diagram showing the relationship between the distance from the contact point and the score of the chemical crystal.

  As shown in FIG. 4, the conversion crystal score is converted to 0 to 100% based on an electron micrograph, distributed to 0 to 5 scores, and 0 to 3 scores are poorly converted. As a result, a score of 4 to 5 was judged as a good chemical conversion treatment state. The formula for calculating the crystal formation rate is shown below.

  Crystal formation rate (%) = area of a portion where crystals are formed in a predetermined region of an electron micrograph / area of a predetermined region of an electron micrograph × 100

  FIG. 5 is an electron micrograph showing a good chemical conversion treatment state (score 5), and FIG. 6 is an electron micrograph showing a chemical conversion treatment failure state (score 3). As shown in the figure, a good chemical conversion treatment state refers to a state in which formation of a chemical conversion crystal is seen in almost the entire electron micrograph, and a chemical conversion treatment failure state refers to a chemical conversion crystal in a predetermined region of the electron micrograph. The state where the generation of is seen is less than 75%.

  According to FIG. 4, in the site | part on the aluminum plate 52 whose distance from the contact point of the outer side edge part 56a of the bearing surface 56 of the flange bolt 54 and the aluminum plate 52 is 3-5 mm, a favorable chemical conversion treatment state It was. On the other hand, in the site | part on the aluminum board | plate material 52 whose distance from the said contact is 3 mm or less (0.5 mm, 1 mm, and 2 mm), it was in the state of a chemical conversion treatment defect.

  Therefore, it has been found that a good chemical conversion coating cannot be applied to the surface of the aluminum plate 52 unless it is 3 mm or more away from the contact portion between the flange bolt 54 and the aluminum plate 52.

  That is, with reference to FIG. 2, the seating surface 18 is covered at a position 3 mm or more radially outward from the contact point between the metal bolt 10 and the fender 42 (that is, the contact portion between the protrusion 18b and the fender 42). The case where there is an unfinished surface of the fender 42 is an embodiment of the present invention, and the surface of the fender 42 that is not covered by the seating surface 18 is present at a position less than 3 mm from the contact portion between the protrusion 18b and the fender 42. Is a comparative example.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of invention. For example, in the present embodiment, an aluminum fender 42 is used as a metal member on the upper side in the screwing direction fastened by the metal bolt 10, and an upper frame 44 made of an iron-based metal material is used as the lower metal member in the screwing direction. However, this combination is not restrictive. Any combination is possible as long as they are dissimilar metal members that are joined to each other and electrodeposited.

  In addition, the metal bolt 10 according to the present embodiment is entirely covered with the insulating film 20, but at least the region from the protruding portion 18 b to the outer end portion 18 a of the seat surface 18 is covered with the seat surface 18. Just do it.

10 Metal bolt 12 Head 14 Flange (lower part of head)
14b Radial direction outer end 18 Seat surface 18a Outer end 18b Protrusion 20 Covering film 40 Nutsert (nut)
42 Fender (metal member on the upper side in the screwing direction)
44 Upper frame (metal member below the screwing direction)
A Area from the projection on the seating surface to the outer edge of the seating surface D Distance of the region from the projection on the seating surface to the outer edge of the seating surface

Claims (3)

In metal bolts used for fastening different metal parts to be electrodeposited,
Of the dissimilar metal member, formed of the same metal material as the metal member on the lower side in the screwing direction,
A protrusion projecting from the seating surface of the head, and a coating film part for insulatingly covering at least the seating surface,
In a state where the dissimilar metal members are joined to each other by engaging with corresponding nuts, the protrusion directly contacts the metal member on the upper side in the screwing direction of the dissimilar metal member, and from the protrusion on the seat surface A coating film covering the region up to the outer edge of the seating surface is in close contact with the metal member on the upper side of the screwing direction;
The shape of the lower part of the head is set such that a range in which a chemical conversion treatment defect due to direct contact between the protrusion and the metal member on the upper side in the screwing direction remains within the region of the seating surface. Features metal bolts.   2. The metal bolt according to claim 1, wherein a distance of a region from the protruding portion on the seat surface to an outer end portion of the seat surface is 3 mm or more. The lower portion of the head is a flange portion having a substantially circular shape in plan view,
3. The metal bolt according to claim 1, wherein a radially outer end edge portion of the flange portion is a curved end portion having no corner in a longitudinal sectional view.

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