JP7704619B2 - Fastening structure - Google Patents

Description

The present invention relates to a fastening structure.

When fastening multiple components made of metal, such as vehicle body parts and aircraft parts, a fastening structure is used in which the male thread of a bolt passes through a through hole in the component and is screwed into the female thread of a nut. Since the bolts and nuts are made of metals such as stainless steel, nickel, and nickel alloys, friction between the bolt and nut makes them prone to seizure. Therefore, to prevent seizure between the bolt and nut, the surfaces of the bolt and nut are treated to reduce frictional resistance.

As an example of a fastening structure that has been treated to reduce frictional resistance, a fastening member has been disclosed in which the surface of the fastening portion is coated with a friction coefficient stabilizer made of an aqueous liquid containing a polyolefin wax emulsion and a urethane-modified polyolefin emulsion or an olefin-unsaturated carboxylic acid copolymer emulsion (see, for example, Patent Document 1).

JP 2006-206683 A

However, in the fastening member of Patent Document 1, the friction coefficient stabilizer is composed of a resin component, so the heat resistance temperature of the friction coefficient stabilizer is not high. Therefore, when the fastening member is exposed to high temperatures (for example, 100°C to 150°C), the properties of the friction coefficient stabilizer change, causing the friction coefficient to decrease and preventing the fastening member from exhibiting an appropriate friction coefficient.

One aspect of the present invention aims to provide a fastening structure that can suppress changes in the friction coefficient and maintain a stable low friction coefficient.

One aspect of the fastening structure according to the present invention is a fastening structure that fastens a plurality of components together by screwing the bolt and the nut or the component together, and at least a part of the bolt or the nut in the contact area between the bolt and the nut or the component and the contact area between the nut and the component is coated with an alumina thin film formed by atomic layer deposition.

One aspect of the fastening structure of the present invention is able to suppress changes in the friction coefficient and maintain a stable low friction coefficient.

1 is a side view showing a schematic diagram of a fastening structure according to an embodiment of the present invention; FIG. 2 is an exploded side view of the fastening structure of FIG. 1 . FIG. 2 is a cross-sectional view showing the fastening structure of FIG. 1 in an exploded state. FIG. 13 is a diagram showing the relationship between the sliding distance and the friction coefficient when a sliding test of a fastening structure is carried out while changing the film thickness of an alumina thin film.

The following is a detailed description of an embodiment of the present invention. To facilitate understanding of the description, the same components in each drawing are given the same reference numerals, and duplicate descriptions are omitted. The scale of each member in the drawings may differ from the actual scale. In this specification, unless otherwise specified, "~" indicating a range of values means that the values before and after it are included as the lower and upper limits.

A fastening structure according to an embodiment of the present invention will be described. The fastening structure according to this embodiment is a fastening structure that fastens multiple components together by screwing together a bolt (screw) as one fastening member and a nut or one or more components as the other fastening member, and at least a portion of the contact area between the bolt and the nut or component and the contact area between the nut and the component are coated with an alumina thin film formed by atomic layer deposition (ALD).

Figure 1 is a side view showing a schematic diagram of a fastening structure according to an embodiment of the present invention, Figure 2 is a side view showing the fastening structure of Figure 1 in an exploded state, and Figure 3 is a cross-sectional view showing the fastening structure of Figure 1 in an exploded state. Figures 1 to 3 explain the form in which a bolt and a nut constituting the fastening structure according to this embodiment are screwed together to fasten two components.

As shown in Figures 1 and 2, the fastening structure 1 according to this embodiment has a bolt 10, a nut 20, and an alumina thin film 30, and two components 2 and 3 may be fastened together by screwing the bolt 10 and the nut 20 together.

The dashed and dotted lines in Figures 1 to 3 indicate the central axis J of the fastening structure 1. The central axis J is the axis that is the center of the fastening structure 1 when the bolt 10 and the nut 20 are screwed together.

As shown in Figures 1 and 2, the bolt 10 is a flanged hexagonal bolt that is inserted into the bolt holes 2A and 3A of the components 2 and 3, and has a head 11 and a shaft 12.

The head 11 has a base 111 and a flange portion 112.

The base 111 is a columnar member and is formed into a substantially hexagonal shape in a planar view. The shape of the base 111 in a planar view is not particularly limited, and may be a polygon such as a substantially triangular or substantially rectangular shape, or a circle, etc.

The flange portion 112 is a disk-shaped member and is provided on one end face of the base body 111 (the lower end face in Figs. 1 to 3). The flange portion 112 is formed with a larger diameter than the base body 111.

The shaft 12 extends from the head 11 at a substantially right angle to the back surface of the head 11. The shaft 12 is formed in a cylindrical shape, and has a male thread (external thread) 121 formed midway from the tip 12a so that it can be screwed into the female thread (internal thread) 20a of the nut 20.

The base 111, flange portion 112, and shaft portion 12 may be formed integrally, or may be joined by welding, adhesive, etc.

As shown in Figures 1 and 2, the nut 20 is a flanged hexagonal nut that is fastened to the male threads 121 of the bolt 10 by sandwiching the components 2 and 3 between them, and has a nut base 21 and a flange portion 22.

The nut base 21, like the base 111 of the head 11, is a columnar member and is formed into a substantially hexagonal shape in a plan view. The shape of the nut base 21 in a plan view is not particularly limited, and may be a polygon such as a substantially triangular or substantially rectangular shape, or a circle, etc.

The flange portion 22 is formed on one end face of the nut base 21 (the upper end face in Figures 1 to 3) and is formed with a larger diameter than the nut base 21.

As shown in FIG. 3, the nut 20 has a female thread 20a on the wall surface of its through hole, which is screwed into the male thread 121 of the bolt 10. The female thread 20a has a female thread 21a provided on the wall surface of the through hole of the nut base 21 and a female thread 22a provided on the wall surface of the through hole of the flange portion 22.

The bolt 10 and nut 20 can be made from metals such as steel, stainless steel, titanium, nickel, nickel alloys, aluminum, aluminum alloys, and brass.

The bolt 10 and the nut 20 may be surface-treated in part or in whole. Examples of surface treatments that can be used include plating, phosphate treatment, blackening treatment, metal impregnation treatment, zinc-chromium treatment, and trivalent chromium conversion coating treatment (trivalent chromate treatment).

The alumina thin film 30 may be provided so as to cover at least a portion of the bolt 10 or nut 20, including the contact area where the bolt 10 and nut 20 contact each other, the contact area where the bolt 10 and component 2 contact each other, and the contact area where the nut 20 and component 3 contact each other.

In this embodiment, the contact areas are four areas: one end face (the lower end face in Figs. 1 to 3) 112a of the flange portion 112, the male thread 121 of the shaft portion 12, the female thread 20a of the nut 20, and one end face (the upper end face in Figs. 1 to 3) 22b of the flange portion 22. As shown in Fig. 3, the alumina thin film 30 may be provided in these four areas. Note that the alumina thin film 30 only needs to be provided in any of these four areas, and may be provided in one to three of these four areas.

The alumina thin film 30 is formed by the ALD method. The ALD method is a vacuum film formation technique that utilizes the self-controlling nature of atoms to expose a vapor phase source to at least a portion of the contact area of the bolt 10 or nut 20 to be deposited, and form a thin film one atomic layer at a time. The ALD method can form a film with a higher coverage rate than other general film formation methods such as chemical vapor deposition (CVD). Therefore, the alumina thin film 30 can cover at least a portion of the contact area of the bolt 10 or nut 20 with a substantially uniform film thickness so as to conform to the shape of the bolt 10 or nut 20.

In addition, because the ALD method can form a film one atomic layer at a time, the alumina thin film 30 formed by the ALD method is less likely to have cracks or defects, or particles such as those adhering to the inside or surface of the alumina thin film 30, so the alumina thin film 30 can have fewer film defects than films formed by other general film formation methods.

Furthermore, because the ALD method is a film formation method that uses a surface reaction, the film thickness can be controlled to, for example, several nm to several tens of nm. Therefore, even if the alumina thin film 30 is, for example, a 3.5 nm thick film, the alumina thin film 30 can reliably cover at least a portion of the above-mentioned contact area of the bolt 10 or nut 20 with a substantially uniform film thickness.

The alumina thin film 30 is formed by the ALD method, and can coat the above-mentioned contact area of the bolt 10 or nut 20 with a substantially uniform film thickness, thereby preventing the intrusion of moisture and oxygen from the outside and suppressing deterioration of the components 2 and 3.

The thickness of the alumina thin film 30 is preferably 100 nm or less, more preferably 1 nm to 35 nm, and even more preferably 3.5 nm to 30 nm. If the thickness of the alumina thin film 30 is 100 nm or less, the alumina thin film 30 can reduce the coefficient of friction of its surface. If the thickness of the alumina thin film 30 is 1 nm to 35 nm, the coefficient of friction of the surface can be reduced and peeling from the bolt 10 and nut 20 can be suppressed.

In this specification, the film thickness of the alumina thin film 30 refers to the length in the direction perpendicular to the main surface of the alumina thin film 30. The film thickness of the alumina thin film 30 is, for example, the thickness measured at any location on the cross section of the alumina thin film 30. When measurements are taken at several locations on the cross section of the alumina thin film 30, the average value of the thicknesses at these measurement locations may be used.

Figure 4 shows the relationship between the sliding distance and the coefficient of friction when a sliding test of a fastening structure was carried out with the thickness of the alumina thin film changed. The substrate on which the alumina thin film was formed was SUS304, and the coefficient of friction was measured by moving a sphere (ball) back and forth in one direction on the substrate on which the alumina thin film was formed using a reciprocating sliding tester. The load of the sphere was 8.6 N, the surface pressure was 934 MPa, the moving speed of the sphere was 33 mm/sec, the maximum sliding distance when the sphere was moved back and forth in one direction was 500 mm, the measurement time for the sliding distance of the sphere was 15 seconds, and the state on the substrate on which the alumina thin film was formed was dry. The sliding distance in Figure 4 indicates the sum of the lengths when the sphere was moved back and forth on the plate using the reciprocating sliding tester. In FIG. 4, in Example 1, the alumina thin film formed on the substrate had a thickness of 3.5 nm, in Example 2, the alumina thin film formed on the substrate had a thickness of 35 nm, in Example 3, the alumina thin film formed on the substrate had a thickness of 180 nm, and in Example 4, no alumina thin film was formed on the substrate.

As shown in Figure 4, it was confirmed that when the thickness of the alumina thin film was between 3.5 nm and 35 nm, the friction coefficient was stably kept low at approximately 0.15 or less.

The variation in thickness of the alumina thin film 30 is preferably ±30% or less, more preferably ±25% or less, and even more preferably ±20% or less. If the variation in thickness of the alumina thin film 30 is within the above preferred range, the uniformity of the surface of the alumina thin film 30 is improved, and the alumina thin film 30 can better exert the effect of reducing the friction coefficient of its surface.

In this specification, the variation in the thickness of the alumina thin film 30 may be calculated by dividing the difference between the maximum and minimum thicknesses at the measurement points by the average thickness of the alumina thin film 30 at the measurement points, and multiplying the result by 100 (the variation in the thickness of the alumina thin film 30 (%) = (the maximum thickness of the alumina thin film 30 - the minimum thickness of the alumina thin film 30) / the average thickness of the alumina thin film 30 x 100). The variation in the thickness of the alumina thin film 30 may also be calculated by dividing the deviation from the average thickness of the alumina thin film 30 at the measurement points by the average thickness of the alumina thin film 30, and multiplying the result by 100 (the variation in the thickness of the alumina thin film 30 (%) = (the deviation from the average thickness of the alumina thin film 30) / the average thickness of the alumina thin film 30 x 100).

The manufacturing method of the fastening structure 1 will now be described. As shown in FIG. 2, first, an alumina thin film 30 is formed on the contact area of the bolt 10 or the nut 20 using the ALD method (alumina thin film formation process).

As described above, the contact areas are four areas: one end surface 112a of the flange portion 112, the male thread 121 of the shaft portion 12, the female thread 20a of the nut 20, and one end surface 22b of the flange portion 22.

The film formation conditions for the ALD method are explained.

When forming the alumina thin film 30 using the ALD method, only at least a portion of the above-mentioned contact area of the bolt 10 or nut 20 is exposed, and the other portions are covered and placed in a reaction apparatus. Then, a material for forming the alumina thin film 30 is supplied as a precursor into the reaction apparatus and adhered to at least a portion of the above-mentioned contact area of the bolt 10 or nut 20.

It is preferable to use an aluminum compound as the material for forming the alumina thin film 30. The aluminum compound may be any gas component that contains aluminum and can be vaporized, and examples of the aluminum compound that can be used include trimethylaluminum (TMA), triethylaluminum (TEA), trichloroaluminum, and dimethylaluminum hydride (DMAH).

After the material forming the alumina thin film 30 is applied to at least a portion of the contact area of the bolt 10 or nut 20, the remaining material forming the alumina thin film 30 is exhausted from within the reactor. An oxidizing agent is then supplied into the reactor to react with the material forming the alumina thin film 30 applied to at least a portion of the contact area of the bolt 10 or nut 20 to form alumina.

The oxidizing agent may be any material capable of oxidizing aluminum compounds, such as water vapor, ozone, and oxygen radicals excited by plasma.

The reaction time in the reactor is not particularly limited and can be designed as appropriate.

The reaction temperature in the reactor can be designed as appropriate, and is preferably 400°C or less.

By forming the alumina thin film 30 under the deposition conditions of the ALD method, the variation in the thickness of the alumina thin film 30 can be suppressed to ±30% or less, even if the alumina thin film 30 is formed on uneven parts such as threads of the male thread 121 of the shaft portion 12 and the female thread 20a of the nut 20.

Next, the shaft 12 of the bolt 10 is inserted into the bolt holes 2A and 3A of the components 2 and 3, and the male thread 121 formed from the tip 12a of the shaft 12 to its middle is screwed into the female thread 20a of the nut 20, thereby fastening the bolt 10 and the nut 20 (fastening process).

This results in a fastening structure 1 in which components 2 and 3 are fastened with bolts 10 and nuts 20.

In this way, the fastening structure 1 covers at least a part of the contact area of the bolt 10 or nut 20 with the alumina thin film 30 formed by the ALD method. Since the alumina thin film 30 is formed by the ALD method, the surface of the alumina thin film 30 is smooth and the unevenness can be reduced, so that the coefficient of friction can be kept small. In addition, even if the fastening structure 1 is placed in a high temperature environment (e.g., 100°C to 150°C), the change in the characteristics of the alumina thin film 30 can be suppressed, so that the desired coefficient of friction can be stably maintained. Therefore, the fastening structure 1 can suppress the change in the coefficient of friction of at least a part of the contact area of the bolt 10 or nut 20, and can stably maintain a small coefficient of friction. The coefficient of friction can be, for example, 0.2 or less, more preferably 0.15 or less.

The fastening structure 1 makes it easier to tighten the bolt 10 and nut 20, so that the axial force required for tightening can be obtained with a smaller force (torque). In actual fastening work, the axial force is generally controlled by the magnitude of the torque. In order to obtain a constant axial force with a smaller torque, the coefficient of friction needs to be kept stable and small. The fastening structure 1 allows the bolt 10 and nut 20 to be stably screwed together with a smaller torque when fastening the components 2 and 3 together, so that the components 2 and 3 can be reliably fastened together even with a small torque.

The friction coefficient refers to the overall friction coefficient μ when the bolt 10 and the nut 20 slide due to tightening. The friction coefficient is a value obtained by combining the various friction coefficients that occur in the above-mentioned contact area of the bolt 10 and the nut 20. The value obtained by combining the various friction coefficients may be a value that represents the various friction coefficients, or may be a value that integrates the various friction coefficients. The above-mentioned combined value, representative value, and integrated value may all be a value that averages the various friction coefficients that occur in the contact area, rather than a value that combines the various friction coefficients that occur in the contact area.

In general, when bolts and nuts are made of stainless steel, stainless steel has a lower thermal conductivity and a larger coefficient of friction than carbon steel and the like, making the bolt and nut particularly susceptible to seizure when fastened. Even when the bolt 10 and nut 20 are made of stainless steel, the fastening structure 1 can stably reduce the coefficient of friction in the contact area between them, thereby suppressing heat generation in the contact area between the bolt 10 and nut 20 when fastened. This makes it possible to make the bolt 10 and nut 20 less susceptible to seizure.

The surfaces of the bolt 10 and nut 20 may be subjected to trivalent chromate treatment as an anti-rust treatment to form an anti-rust coating containing trivalent chromium chromate (chromate salt). Even if the bolt 10 and nut 20 have an anti-rust coating on their surfaces, the fastening structure 1 has an alumina thin film 30 in the contact area of the bolt 10 and nut 20, so that the coefficient of friction in the contact area can be kept stable and small, and the required axial force can be obtained with a smaller torque when fastening the bolt 10 and nut 20.

In the fastening structure 1, the thickness of the alumina thin film 30 can be set to 100 nm or less. If the thickness of the alumina thin film 30 is 100 nm or less, the friction coefficient of the alumina thin film 30 can be kept sufficiently small. Therefore, the fastening structure 1 can sufficiently suppress the change in the friction coefficient of at least a part of the above-mentioned contact area of the bolt 10 or the nut 20, and can more stably maintain a small friction coefficient.

The fastening structure 1 can reduce the variation in the thickness of the alumina thin film 30 to ±30% or less. This makes the surface of the alumina thin film 30 smoother and reduces the variation in unevenness, thereby further reducing the friction coefficient of the alumina thin film 30. Therefore, the fastening structure 1 can further reduce the change in the friction coefficient of at least a portion of the above-mentioned contact area of the bolt 10 or nut 20, and can therefore maintain a small and stable friction coefficient.

As described above, the fastening structure 1 can suppress changes in the friction coefficient of at least a portion of the contact area of the bolt 10 or nut 20 even when exposed to high temperature conditions, and can maintain a stable low friction coefficient. Therefore, the fastening structure 1 can be suitably used for fixing vehicle body parts, aviation parts, space parts, etc. that are used under high temperature conditions, such as space-related structures such as vehicles, aircraft, and artificial satellites.

In this embodiment, the bolt 10 is described as passing through the bolt holes 2A and 3A of the components 2 and 3 and screwed into the nut 20, but it is also possible to form a female thread in the bolt holes 2A and 3A of the components 2 and 3 and screw the bolt 10 into the bolt holes 2A and 3A.

In this embodiment, one of the fastening members may be a threaded bolt, an embedded bolt, a tapped screw, or the like, instead of the bolt 10. In this case, the bolt holes 2A and 3A of the components 2 and 3 may be female threaded. As a result, the fastening structure 1 according to this embodiment can be constructed by screwing a threaded bolt, an embedded bolt, a tapped screw, or the like into the bolt holes 2A and 3A.

In this embodiment, the fastening structure 1 fastens two components 2 and 3, but the number of components may be one or three or more.

Although the embodiments have been described above, they are presented as examples, and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their variations are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

REFERENCE SIGNS LIST 1 Fastening structure 2, 3 Component 10 Bolt 11 Head 111 Base 112, 22 Flange 112a, 22b End surface 12 Shaft 121 Male thread (external thread)
20 Nut 20a, 21a, 22a Female thread (inner thread)
21 Nut base 30 Alumina thin film

Claims (1)

A fastening structure for fastening a plurality of components together by screwing a bolt and a nut or a component,
At least a part of the bolt or the nut in the contact area between the bolt and the nut or the component and at least a part of the contact area between the nut and the component are coated with an alumina thin film formed by atomic layer deposition;
The alumina thin film has a thickness of 1.0 nm to 3.5 nm;
The variation in thickness of the alumina thin film is ±25% or less;
A fastening structure, wherein the alumina thin film has a friction coefficient of 0.15 or less.

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