JP6898633B2 - Lightweight alloy bolts - Google Patents

Description

The present invention relates to lightweight alloy bolts.

For example, bolts used as automobile parts are required to be lighter in order to improve fuel efficiency and non-magnetic for electronic devices, and the need for lightweight alloy bolts such as magnesium alloys and aluminum alloys is increasing. The need for such bolts tends to expand widely and industrially, not limited to automobile parts.

Japanese Unexamined Patent Publication No. 2011-190493 Japanese Unexamined Patent Publication No. 2013-160298

As is well known, when assembling a part on a production line, a bolt is driven and rotated by a driver bit of a power tool, screwed into a female screw of the member to be fastened, and then a predetermined tightening torque is applied to the member to be fastened. To conclude.

The bolt receives a driving force from the driver bit engaged with the recess of the head, screwes the male screw of the screw shaft part to the female screw of the fastened member, and then fastens the fastened member, so that the bolt can be fastened. As soon as it starts, a strong tightening torque is generated between the head and the screw shaft.

Steel bolts such as stainless steel have high strength and high toughness. Therefore, the maximum value of the tightening torque reaching the plastic region of the bolt is high, and the screw shaft portion breaks after the plastic deformation progresses from the maximum value. Therefore, the operator can easily find the tightening limit of the bolt during the fastening operation, and can easily stop the driver bit by operating the power tool before the screw shaft portion breaks.

However, according to the findings of the present inventor, in the case of lightweight alloy bolts, the strength and toughness are low, and the plastic region is small. Therefore, unlike steel bolts, there is no maximum value, and the screw shaft portion breaks while the tightening torque increases. For this reason, it is difficult for the operator to determine whether or not the tightening has been completed, and if the driver bit is stopped early due to fear of breakage, there is a risk of improper tightening, and the driver bit is driven in an attempt to completely tighten. There is a problem of unexpected breakage when continuing. Further, if it breaks, it is difficult to remove the bolt from the female screw.

The present invention provides a lightweight alloy bolt that solves the above-mentioned serious problems with a simple technical configuration, and transmits a driving force from a driver bit to the head of the bolt when a predetermined tightening torque is generated. Made of lightweight alloy configured to prevent the screw shaft from breaking and to allow the head to rotate with another tool when the driver bit becomes unusable. Bolt is an issue.

Therefore, what is configured by the present invention as a means is provided with a head having a recess into which a driver bit of an electric tool is fitted in an engaged state, and a screw shaft portion having a male screw extending from the head. A bolt for screwing and fastening the male screw into the female screw of the member to be fastened, and the recess has a cross section in which a general-purpose hexarobuler type bit is fitted and engaged with the inner circumference of a concave groove having a maximum diameter T. An engaging portion in which a star-shaped hex lobe protrusion is provided parallel to the axial direction of the concave groove is formed over a depth D , and a change in tightening torque occurs between the head of the bolt to be driven and rotated and the screw shaft portion. With respect to F1 <F2, in a configuration in which a male screw is screwed and fastened to a female screw at a torque F1 or higher and the screw shaft is broken at a torque F2 or higher, the metal material of the bolt is a recess in which the driver bit is engaged. With respect to the depth D1 <D2 of the engaging portion under the same condition as the maximum diameter T of, the engaging portion is destroyed by the screwdriver bit when the depth D1 is less than the torque F1, and when the depth D2 is the torque F2 or more. The head of the bolt is formed of an alloy in which the engaging portion is not broken by the driver bit, and the depth DX of the engaging portion of the recess is formed at D1 <DX <D2, and the outer circumference of the head surrounding the recess is formed. The point is that the portion is provided with an engaging means that can be freely engaged with a rotating tool consisting of a wrench or a spanner.

In a preferred embodiment of the present invention, the bolt of the metallic material is an alloy composed mainly of magnesium.

At this time, the depth Dx of the recess engaging portion is M / T × 1.3 or more and M / T × 1.7 with respect to the ratio M / T of the screw outer diameter M of the bolt and the maximum diameter T of the recess. It is preferably formed as follows.

According to the present invention, in a lightweight alloy bolt having low strength and toughness and a small plastic region, it is necessary and sufficient to secure the tightening torque generated between the head of the bolt driven and rotated by the driver bit and the screw shaft portion. When the tightening torque exceeds a predetermined torque, the driver bit is idled by appropriately breaking the engaging portion of the recess, whereby the screw shaft portion of the screw shaft portion can be fastened. It has the effect of preventing breakage.

Then, when it is necessary to remove the bolt from the fastened portion after the engaging portion of the recess is broken, a rotating tool made of a wrench or a spanner is engaged with the engaging means provided on the outer peripheral portion of the head. This has the advantage that the bolt can be rotated.

Regarding one embodiment of the present invention, (A) is a perspective view showing a bolt and a driver bit, (B) is a front view of the bolt, and (C) is a cross-sectional view of the bolt. It is explanatory drawing which shows the breaking property of a steel bolt, the breaking characteristic of a magnesium alloy bolt, and the problem solving means of this invention with respect to the breaking property of a bolt corresponding to a tightening torque. Regarding the problem-solving means of the present invention, (A) is a table showing an experiment conducted to confirm the magnitude of the tightening torque that causes recess fracture or thread fracture in a test product of a bolt having a different recess depth. (B) is a table showing the chemical composition of the bolt material used in the experiment, and (C) is a table comparing the experimental results with a graph. The action of the bolt of the present invention with the recess depth as Dx is shown, (A) is a cross-sectional view showing a state in which the bolt is being screwed into the member to be fastened, and (B) is a cross-sectional view showing the fastened state of the bolt. FIG. 6C is a cross-sectional view showing a state in which the recess is broken, and FIG. 3D is a cross-sectional view showing a method of pulling out a bolt in which the recess is broken with a wrench or a spanner. Regarding the comparative example for the present invention, (A) and (B) show the first comparative example in which the recess depth is D2, (A) is a cross-sectional view showing a fastened state, and (B) is a screw shaft portion. (C) and (D) show a second comparative example in which the recess depth is D1, and (C) is a cross-sectional view showing the state of being screwed, (D). ) Is a cross-sectional view showing a state in which the recess is broken before the completion of fastening.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a bolt 1 made of a lightweight alloy as an example of the present invention. The bolt is formed of a magnesium alloy, an aluminum alloy, or another lightweight alloy as a material. It is formed of an alloy containing magnesium as a main component as shown in [Table 2].

The bolt 1 includes a head portion 2 and a screw shaft portion 3, and the screw shaft portion 3 is provided with a male screw 3a indicated by an outer diameter M. The head portion 2 raises a trapezoidal portion 2b having a conical outer peripheral surface upward from the center of the flange portion 2a to open a recess 4 that opens in the center of the top surface of the trapezoidal portion 2b, and also provides an outer peripheral surface of the trapezoidal portion 2b. Is provided with an engaging means 5 having a hexagonal shape in a plan view.

The recess 4 is composed of a concave groove into which a driver bit 6 of a power tool (not shown) is fitted in an engaged state, and as shown in the figure, a commercially available general-purpose hexarobula type bit 6a is fitted in the recess 4. The engaging portion 4a is provided by providing a hex lobe protrusion having a star-shaped cross section on the inner peripheral surface in parallel with the axial direction of the concave groove so as to be engaged with the above. Therefore, the recess 4 is recessed from the trapezoidal portion 2b toward the center of the screw shaft portion 3 in a state where the engaging portion 4a is projected inward from the concave groove having the maximum diameter T, and the engaging portion 4 is formed. It is formed so that the depth of 4a is the depth Dx described later.

The engaging means 5 provided on the trapezoidal portion 2b engages an externally fitted rotary tool 7 (see FIG. 4D) such as a wrench or a spanner different from the driver bit 6 to engage the bolt 1. It is not limited to a hexagon as long as it is rotatable.

As described above with respect to the prior art, generally, a bolt receives a driving force from a driver bit engaged with a recess of the head, and after screwing a male screw of a screw shaft portion into a female screw of a member to be fastened. , Start fastening the members to be fastened. At this time, a strong tightening torque is generated between the head and the screw shaft portion.

The one-point chain wire in FIG. 2 shows the experimental results of a test product (screw diameter M6) of a steel bolt, and since it has high strength and high toughness, the maximum value of the tightening torque reaching the plastic region of the bolt. The screw shaft portion breaks at the PA point where the Max is high and the tightening torque is reduced while being accompanied by plastic deformation from the maximum value Max.

On the other hand, the solid line in FIG. 2 shows the experimental result of the test product (screw diameter M6) of the magnesium alloy bolt, which has low strength and toughness and a small plastic region, so that it has a maximum like a steel bolt. There is no value, and there is a characteristic that the screw shaft portion breaks at the PB point while the tightening torque is increasing.

Therefore, in the present invention, as shown by the alternate long and short dash line in FIG. 2, the transmission of the driving force between the recess of the bolt head and the driver bit is cut off before the magnesium alloy bolt reaches the PB point. This is characterized in that the screw shaft portion is prevented from breaking. Then, as a result of knowing based on experiments that such disconnection of the transmission of the driving force is possible by setting the depth condition of the recess engaging portion, the conditions that can be satisfactorily implemented are investigated and confirmed. It is characterized by the fact that it was done.

Therefore, to summarize the findings of the present invention, the present invention is characterized in that a lightweight alloy bolt is constructed based on the following conditions (1), (2) and (3).
(1) With respect to the change in tightening torque F1 <F2 that occurs between the head of the rotating bolt driven by the driver bit 6 and the screw shaft, the male screw is screwed into the female screw and fastened at a torque F1 or higher. Then, the screw shaft portion 3 breaks when the torque is F2 or more.
(2) The metal material of the bolt is such that when the depth of the engaging portion 4a of the recess 4 to which the driver bit is engaged is D1 <D2, the torque is less than F1 when the depth is D1 and the engaging portion is formed by the driver bit. It is formed of an alloy having a condition that the engaging portion 4a is not destroyed by the driver bit even when the torque F2 or more is obtained when the depth 4a is destroyed and the depth is D2.
(3) The depth Dx of the engaging portion 4a of the recess 4 is formed so that D1 <Dx <D2.

(Example)
In order to verify the above, the test product No. 1 formed from the magnesium alloy shown in [Table 2] of FIG. 3 (B). 1-No. The relationship between the recess depth and the fracture torque was tested for No. 9. The experimental results are shown in [Table 1] of FIG. 3 (A) and [Table 3] of FIG. 3 (C).

Test product No. 1 to test product No. No. 9 differs only in the depth of the engaging portion 4a of the recess 4 based on the bolts having the same shape as illustrated in FIG. 1, and all have the same conditions except for this depth. The screw diameter is M6 (outer diameter 6 mm), and the maximum recess diameter is T20 (3.8 mm). The experimental conditions were that all the test products were screwed to the same member to be fastened, and the screwing conditions were a rotation speed of 6 rpm and a load of 100 N.

As shown in FIG. 3 (A), the test product No. 1 to No. Each test product up to 9 is formed so that the depth of the recess engaging portion is gradually increased in units of 0.1 mm, and as a result of the experiment, the test product No. In No. 1 (depth of engaging portion 2.0 mm), the recess was destroyed when the torque was 4.79 Nm (the driving force of the driver bit was not transmitted to the recess and slipped), and the test product No. In No. 9 (depth of engaging portion 2.8 mm), when the torque was 6.53 Nm, the recess was not broken and the screw shaft portion was broken.

According to the experimental results, the test product No. 1 (depth of engaging part 2.0 mm) or test product No. It was confirmed that the object of the present invention can be achieved in 8 (depth of the engaging portion of 2.7 mm) because the engaging portion of the recess is broken before the screw shaft portion of the bolt is broken.

However, in order to secure a sufficient fastening force without causing insufficient tightening of bolts, it is desirable that the recess can withstand a torque of 5.0 Nm or more without breaking. Test product No. 1 (depth of engaging part 2.0 mm, recess fracture torque 4.79 Nm). 2 (depth of engaging portion 2.1 mm, recess breaking torque 5.12 Nm) is preferable.

In addition, the test product No. No. 8 (depth of engaging part 2.7 mm, recess breaking torque 6.50 Nm) breaks the recess engaged part before breaking the screw shaft part of the bolt. Assuming from the fact that the screw shaft portion of No. 9 is broken at a torque of 6.53 Nm, the test product No. Even if the screw shaft portion of No. 8 is not broken, there is a possibility that cracks or the like may occur. Therefore, in order to dispel the anxiety of this point, the test product No. Test product No. 8 (depth of engaging part 2.7 mm, recess fracture torque 6.50 Nm). 7 (depth of engaging portion 2.6 mm, recess fracture torque 6.12 Nm) is preferable.

As a result of the above, among the above test products, the preferred example adopted as the present invention is Test Product No. 2 (depth of engaging part 2.1 mm, recess fracture torque 5.12 Nm) or test product No. 7 (depth of engaging portion 2.6 mm, recess breaking torque 6.12 Nm), and it can be determined that the depth Dx of the recess engaged portion should be set within that range.

By the way, when tightening a bolt, the magnitude of the tightening torque generated between the head and the screw shaft is determined by the outer diameter M of the screw shaft that is screwed to the member to be fastened and the driving force of the driver bit. Since the maximum diameter T of the recess to be received is considered to be an important condition, all of the above-mentioned test products have M = 6 mm and T = 3.8 mm, so that the depth of the engagement portion between the M / T and the recess is deep. From the above relationship, the depth Dx of the recess engaging portion that can be implemented in the present invention can be determined.

As shown in FIG. 3 (A), with respect to the examples adopted as the present invention, the test product No. No. 2 has a recess engaging portion depth of 2.1 mm = M / T × 1.330, and the test product No. 2 is used. No. 7 has a recess engaging portion depth of 2.6 mm = M / T × 1.646, and the test product No. 3 or test product No. The depth of the recess engaging portion of 6 exists in the middle.

Therefore, in a bolt made of a magnesium-based alloy provided as a test product and the recess engaging portion is composed of hex lobe protrusions, the depth Dx of the recess engaging portion is M / T × 1. If the thickness is 3 or more and M / T × 1.7 or less, the engagement part of the recess is appropriately broken before the screw shaft part is broken to allow the driver bit to idle, and the necessary and sufficient tightening torque is applied. It can be confirmed that the bolts can be fastened.

(Operation of the present invention)
FIG. 4 shows the usage and operation of the present invention. The bolt 1 is fastened by screwing the male screw 3a of the screw shaft portion 3 into the female screw 8a of the nut or other member to be fastened. The mounting member 9 is sandwiched between the fastening member 8 and the head 2.

The bolt 1 is fitted with the driver bit 6 in the recess 4 of the head portion 2 in an engaged state, and at this time, the depth Dx of the engaging portion 4a of the recess 4 is the M / T × 1 described with respect to the above embodiment. It is formed to be .3 or more and M / T × 1.7 or less.

FIG. 4A shows a state in which a bolt 1 that rotates under the driving force of a driver bit 6 is screwed into a screw shaft portion 3 into a member 8 to be fastened and is being screwed. At this time, Fa acts between the head portion 2 and the screw shaft portion 3 to apply a tightening torque required for screwing the male screw 3a to the female screw 8a.

Therefore, as shown in FIG. 4B, when the screw shaft portion 3 finishes screwing into the member to be fastened 8 and starts fastening, the torque Fa is larger than the torque Fa between the head portion 2 and the screw shaft portion 3. The increased tightening torque Fa + α (referred to as torque F1) acts, and the male screw 3a of the screw shaft portion 3 is fastened to the female screw 8 of the member to be fastened 8 by this tightening torque F1.

When the male screw 3a is completely fastened to the female screw 8, as shown in FIG. 4C, the tightening torque F1 + β, which is further higher than the torque F1, is between the head portion 2 and the screw shaft portion 3. (However, it is smaller than the torque F2 that breaks the screw shaft portion 3) acts, and this tightening torque breaks the engaging portion 4a of the recess 4, and the driver bit 6 idles. Therefore, the screw shaft portion 3 is fastened to the fastened member 8 without being broken.

When it is necessary to remove the bolt 1 from the fastened portion 8 after the engaging portion 4a of the recess 4 is broken in this way, as shown in FIG. 4 (D), the engaging means 5 of the head 3 is used. Since the rotating tool 7 can be engaged, the head 3 can be reversed by the rotating tool 7 and the male screw 3a can be screwed back from the female screw 8a.

(Comparison example)
FIG. 5 shows a first comparative example having a recess with a depth D2 deeper than the recess depth Dx of the present invention and a second comparison having a recess with a shallow depth D1 with respect to the recess depth. It shows the action of the example.

The bolt 1a of the first comparative example has the engaging portion 4a of the recess 4 having a depth D2 (D2> Dx), and as shown in FIG. 5A, while rotating under the driving force of the driver bit 6. After the screw shaft portion 3 is screwed into the fastened member 8, the male screw 3a of the screw shaft portion 3 is fastened to the female screw 8 of the fastened member 8 as shown in FIG. 5 (B). The engaging portion 4a of the recess 4 is not destroyed even if a tightening torque F2 is generated between the head portion 2 and the screw shaft portion 3. That is, the driver bit 6 does not slip. Therefore, as shown in FIG. 5B, the tightening torque F2 breaks the screw shaft portion 3.

The bolt 1b of the second comparative example has a recess engaging portion 4a having a depth D1 (Dx> D1), and as shown in FIG. 5C, while rotating under the driving force of the driver bit 6. After the screw shaft portion 3 is screwed into the fastened member 8, the screw shaft portion 3 starts fastening to the fastened member 8 as shown in FIG. 5 (D), and between the head portion 2 and the screw shaft portion 3. When the tightening torque Fa + α is generated in the screwdriver bit 6, the engaging portion 4a of the recess 4 is broken and the driver bit 6 idles. Therefore, the screw shaft portion 3 cannot be fastened to the fastened portion 8 with a sufficient tightening force.

In contrast to such a comparative example, in the present invention, since the depth Dx of the engaging portion 4a of the recess 4 is formed in D1 <Dx <D2, the engaging portion 4a is broken even if the tightening torque F1 + α is generated. However, the screw shaft portion 3 can be fastened to the member to be fastened 8 with a necessary and sufficient fastening force, and when the tightening torque further increases from that state, the engaging portion 4a is engaged before the tightening torque increases to F2. By breaking and idling the driver bit 6, it is possible to suitably prevent the screw shaft portion 3 from breaking.

1 Bolt 2 Head 2a Flange part 2b Trapezoidal part 3 Screw shaft part 3a Male screw 4 Recess 4a Engaging part 5 Engaging means 6 Driver bit 6a Hexalobular type bit 7 Rotating tool 8 Fastened member 8a Female screw 9 Mounting member

Claims (3)

A head having a recess into which a driver bit of a power tool is fitted in an engaged state and a screw shaft portion having a male screw extending from the head are provided, and the male screw is screwed into a female screw of a member to be fastened. It is a bolt that is inserted and fastened.
The recess is an engaging portion in which a star-shaped hex lobe protrusion having a cross section for engaging a general-purpose hexarobula type bit in a fitted state is provided parallel to the axial direction of the concave groove having a maximum diameter T. (4a) is formed over the depth D ,
With respect to the change in tightening torque F1 <F2 that occurs between the head (2) and the screw shaft (3) of the bolt that is driven and rotated, the male screw is screwed into the female screw and fastened at torque F1 or higher, and the torque. In the configuration where the screw shaft (3) breaks at F2 or higher,
The metal material of the bolt has a torque F1 or less when the depth D1 is the depth D1 <D2 of the engaging portion (4a) under the same condition as the maximum diameter T of the recess (4) with which the driver bit is engaged. The engaging portion (4a) is destroyed by the driver bit, and when the depth is D2, the engaging portion (4a) is not destroyed by the driver bit even if the torque is F2 or more.
The head (2) of the bolt has a depth Dx of the engaging portion (4a) of the recess formed at D1 <Dx <D2, and a rotating tool made of a wrench or a spanner is formed on the outer peripheral portion of the head surrounding the recess. A bolt characterized by being provided with an engaging means (5) that can be freely engaged with the bolt. The bolt according to claim 1, wherein the metal material of the bolt is made of an alloy containing magnesium as a main component. The depth Dx of the recess engaging part is formed to be M / T x 1.7 or less at M / T x 1.3 or more with respect to the ratio M / T of the bolt screw outer diameter M and the maximum recess diameter T. The bolt according to claim 2, wherein the bolt is made.

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