JP2008275062A - High-hardness screw made of aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-hardness screw made of an aluminum alloy which is made easily of a comparatively soft material, and enhances recyclability of the aluminum alloy. <P>SOLUTION: The high-hardness screw made of an aluminum alloy includes a head 2 and an integral shank 3. The screw is made up of a screw blank made of the aluminum alloy, and an external thread 10 is formed on the shank 3. The crest of the external thread forming the ridge of the external thread 10 is formed throughout the length of the shank 3 to have a circular-arc shape in the cross section. A root 16 and flanks 12, 13 in the external thread 10 are connected by a circular-arc face 17. The screw blank in the shape is subjected to a treatment of hard anodic oxide coating. Thus, while forming an internal thread, the high-hardness screw made of aluminum alloy can be driven into a workpiece made of a mild material such as a casting made of aluminum alloy, plate and the like. No cracks occur in the oxide film, because the flank of the external thread is connected all over by the circular-arc face, and a smooth internal-thread can be formed to improve resistance to corrosion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a screw for attaching a part to a workpiece made of a soft material such as an aluminum alloy or a magnesium alloy, and is screwed while forming a female screw in a pilot hole formed in such a workpiece made of a soft material, The present invention relates to a screw made of high-hardness aluminum alloy that is screwed while forming a pilot hole in a workpiece and forming a female screw.

  Aluminum products and magnesium alloys are widely used in electrical products and automobile parts such as mobile phones, personal computers and portable music players that have been widely used in recent years due to their light weight, small size, and good workability. Many screws are used to attach parts to such soft workpieces. This screw has been developed in various ways because it is necessary to maintain the fastening strength to the work made of the soft material. All of these screws have a female screw hole as a screw-in pilot hole in which a female screw is formed in the work in advance. There is still not enough progress in commercialization of high-strength screw parts that can be screwed stably while forming female threads with the same kind of material as these soft materials or making pilot holes in the workpiece.

As such an aluminum alloy screw, one shown in Japanese Patent Publication No. 7-92101 has been developed. This relates to a method of manufacturing an aluminum alloy bolt, and after cold forming a 7000 series aluminum alloy wire rod into a bolt shape, any one selected from galvanizing, chromic acid oxidation, and anodizing This is a method of manufacturing a bolt by performing such surface treatment. As a screw thread of a bolt in such a manufacturing method, a shape as shown in FIG. 8 is generally used, and in particular, a female screw is formed in a pilot hole of a workpiece by a conventionally used bolt made of steel material. However, when screwing in, the screw thread top angle (α) of the thread 110 is formed at 60 °, thereby facilitating the formation of the female thread. And the weight of the whole product is enabled by using the bolt made from the aluminum alloy cold-formed by such a shape for a workpiece | work. In addition, as shown in FIG. 9, there is an improved thread shape in which the valley portion 216 of the thread 210 and the flank surfaces 212 and 213 are connected in a substantially circular arc shape. This is disclosed in Japanese Patent Application Laid-Open No. 2003-4016, and is mainly a thread shape of a high-strength bolt for a structure, and stress concentration generated between the structure and the structure when screwed. It was developed for the purpose of reducing the above.
Japanese Patent Publication No. 7-92101 JP 2003-4016 A

  However, when the bolt or screw material having the above-described thread shape that is generally used is an aluminum alloy material, the strength is increased even if the product is manufactured by subjecting it to a hard anodized film treatment. The oxide film is cracked and corroded from here and lacks corrosion resistance. In addition, when cold forging using aluminum as a raw material, especially when the thread is formed by rolling, the thread is almost formed, but the surface of the thread valley is roughened by rolling. Thus, even if the hard anodized film treatment is performed on the surface where the rough surface is generated in this manner, the rough surface becomes an obstacle and a film having sufficient corrosion resistance cannot be maintained. Further, when the screw is relatively small, this rough surface affects the screwing operation, the screwing torque is not stable, and the torque management during screwing by the automatic screw tightening machine is adversely affected. Moreover, as shown in FIG. 8, the screw thread apex angle (α) is normally set to 60 °, and the apex part and the entering corner part (the intersection of the screw thread valley face and the flank face) have an angle. Therefore, even if a hard anodized film treatment is applied to such a screw, a film is not formed at the top of the screw thread or at the corner of the entering corner, and a streak-like crack occurs or the film is formed extremely thin. If the screw is screwed into the workpiece, the thread is likely to be crushed from this part. For this reason, an adhesion state occurs between the screw and the pilot hole of the workpiece, the screw is not completely screwed in, and a state in which the seat surface of the screw floats from the workpiece, a so-called screw floating phenomenon occurs. Further, even in a so-called drilling screw having a drill portion at the tip of the leg portion, there is a problem that the screw thread has a similar problem and cannot be screwed.

  An object of the present invention is to solve such problems and to easily manufacture a material similar to a workpiece made of a relatively soft material and to improve the recyclability of the aluminum alloy, and to improve the recyclability of the aluminum alloy. It is to obtain screws.

  The object of the present invention is from a screw material made of an aluminum alloy having a screw portion formed of a head portion 2 having a drive hole 4 and a leg portion 3 integral with the head portion 2 and having a screw thread 10 formed on the leg portion 3. A thread apex that forms a ridge line of the thread 10 of the thread is formed in a cross-sectional arc shape over the entire length of the leg 3, while a valley of the thread 10 is formed. High-hardness aluminum alloy screw in which the trough surface 16 and the flank surfaces 12 and 13 of the screw thread 10 are connected by an arcuate surface 17 having a circular arc cross section, and a screw material having these shapes is subjected to a hard anodized film treatment Is achieved by providing

  Another object of the present invention is to set the angle (α) formed by the flank surfaces 12 and 13 forming the thread 10 in the cross section perpendicular to the lead wire in the above-described configuration to a range of 60 ° to 70 °. By using the high hardness aluminum alloy screw, the balance between the strength of the thread and the formation of the anodized film at the corners of the thread is optimized.

  In addition to the above-described structure, the present invention has an object in which the screw portion is on the head side, the normal screw thread portion 11 on which the complete screw thread portion is formed, and the tip end side of the leg portion 3 and the screw thread height. The guide screw thread part 14 which is a low incomplete thread part, and the top of the screw thread over the circumference of the leg 3 between the normal screw thread part 11 and the guide screw thread part 14. This can also be achieved as a high-hardness aluminum alloy screw in which the internal thread forming part 18 having an arc-shaped cross section of the part is formed with an arc larger than the cross-section of the thread top part of the normal thread part 11 and the guide thread part 14, The screw portion is on the head side, and the normal screw thread portion 11 on which the complete screw thread portion is formed and the guide screw thread on the tip end side of the leg portion 3 and the incomplete screw thread portion having a low screw thread height. And the guide screw thread portion 14 and the following portion. The substantially one round of the regular thread portion 11 constitutes the female thread forming portion 18, and the top portion of the thread portion of the female thread forming portion 18 is generally formed by an arc larger than the cross section of the top portion of the thread portion of the thread portion 11. It can also be achieved as a hard aluminum alloy screw, it is possible to suppress the screwing resistance at the normal thread part, the thickness of the guide thread part becomes thicker, and the thread is crushed at the start of female thread formation in the pilot hole Therefore, stable female thread forming is possible.

  In addition, the female thread forming portion in the above-described configuration has a radius (Rb) constituting the top surface 15 of the arcuate cross section of the apex portion of the arc-shaped top surface formed at the apex portion of the normal thread portion ( Since it is set so that Rb ≦ 1.8 × Ra with respect to Ra), the effect of preventing loosening due to the springback action of the work after screwing also occurs. In addition, in all of these configurations, the screw material is Al-Zn-Mg, and the aluminum alloy of JIS standard material symbols A7050 and A7075 is subjected to forging and rolling, and then subjected to T73 treatment. Therefore, the internal thread can be formed smoothly without crushing the thread.

  According to the present invention, it is possible to screw in a pilot hole made of a soft material such as an aluminum alloy casting or a plate material while forming a female screw with an aluminum alloy screw. In addition, since all the flanks of adjacent threads are connected by arc-shaped surfaces, this thread is formed smoothly without cracking or cracking in the oxide film formed in the hard anodic oxide film treatment. The cause of corrosion is eliminated and the corrosion resistance is improved. Moreover, even if the thread formed on the aluminum material is rolled, there is no corner in the threaded part as in the past, so the occurrence of rough skin at the threaded valley is eliminated and the thread surface is smooth. Thus, sufficient corrosion resistance can be maintained by applying the coating treatment to the surface of the film. Further, even if the screw is relatively small, this rough surface does not occur, so that the screwing operation is not affected, the screwing torque is stabilized, and torque management during screwing by an automatic screw tightener is easy. Moreover, since the top angle of the screw thread is normally set to 60 ° to 70 °, and the cross section of the apex portion and the cross section of the entering corner portion are both arc-shaped, the coating is uniformly formed on them. In addition, there are no streak-like cracks or thin coatings, no sticking occurs when screwed into the workpiece, and the screw is securely screwed so that the seating surface can always be seated on the workpiece. Stable screwing operation can be obtained. In addition, the screw material is Al-Zn-Mg based aluminum alloy material of JIS standard material symbols A7050 and A7075, and this material was subjected to forging and rolling, followed by heat treatment by T73 treatment. Later, by using a screw that has been subjected to a hard anodized film treatment on this screw material, for example, even if the workpiece is an aluminum alloy die-cast (JIS standard ADC12), the surface hardness of this screw is Hv 350 or more, Since the core has a hardness of Hv 170 to 200, it can be used as a so-called tapping screw that is screwed in while forming a female screw in the pilot hole, and can be used as a drilling screw having a drill portion at the tip. Will not collapse. Furthermore, even when used for aluminum sashes, there is no occurrence of electrolytic corrosion due to differences in screw materials, especially when aluminum alloy screws are screwed into a magnesium alloy workpiece. Does not occur and magnesium does not melt. In addition, the difference in material between the screw and the workpiece, for example, the occurrence of condensation due to the difference in thermal conductivity when using an aluminum alloy screw compared to when an aluminum sash is assembled using stainless steel screws. Also decreases. Moreover, aluminum alloy screws have similar properties to resin materials in terms of specific gravity and tensile strength, which contributes to weight reduction and makes it difficult for the screws to be loaded at the fastening points. Further, since the workpiece and the screw screwed into the workpiece are both aluminum alloys, there is a specific effect such that separation processing in reuse is unnecessary and the recycling rate is improved.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2, reference numeral 1 denotes a tapping as an example of a screw made of an aluminum alloy having a head 2 and a leg 3 formed integrally therewith and having a female screw forming function. The head 2 is formed with a drive hole 4 in which a screw driving force is transmitted to the screw 1 from a driver bit (not shown). A single thread 10 is formed on the leg 3 integral with the head 2 from the vicinity of the seating surface 5 of the head 2 to the tip of the leg 3, and from the middle of the leg 3 to the head side. In the meantime, a normal thread portion 11 having a height similar to that of a general tapping screw and a complete thread portion having the same height is formed. Further, a guide screw thread portion 14 which is an incomplete screw thread portion whose height decreases as the screw thread 10 reaches the distal end is formed at the tip of the leg portion 3 continuously from the normal screw thread portion 11. The apex portion of the screw thread forming the ridge line of the screw thread 10 of the normal screw thread portion 11 and the guide screw thread portion 14 is formed in a cross-sectional arc shape over the entire length thereof.

  As shown in FIG. 4, the screw thread 10 has an angle (α) composed of a follower-side flank surface 12 and a lead-side flank surface 13 forming the screw thread 10 in a cross section perpendicular to the lead wire. The range is set to 70 °. Further, the thread apex portion composed of these flank surfaces 12 and 13 is configured by smoothly connecting the top surface 15 having an arcuate cross section and the flank surfaces 12 and 13 so that the hard anodized film is evenly distributed. Allowing to be formed. On the other hand, the valley surface 16 forming the valley portion of the screw thread 10 and the flank surfaces 12 and 13 of the screw thread 10 are also connected by the arc-shaped arc surface 17, and thus the axis of the screw 1 is connected. The thread cross-sections that follow have shapes that are connected by arcs without forming corners, so that even if this thread material is treated with hard anodized film, streaks and cracks occur in the film It comes to be formed without.

  Further, as shown in FIG. 3, the leg 3 has a substantially triangular cross section so that the resistance at the time of female screw formation during screwing can be reduced even slightly. Moreover, the diameter of the locus circle formed by the thread ridge line at the tip of the guide thread 14 is the same as or slightly larger than the diameter of a pilot hole (not shown) formed in the workpiece 20. Usually, the thread diameter is set smaller than the thread section 11. For this reason, the streak-like female thread by the thread ridgeline is slightly formed in the prepared hole at the start of screwing.

  Further, as shown in FIG. 5, between the guide screw thread portion 14 and the normal screw thread portion 11, an arc shape of the screw thread ridge line of the normal screw thread portion 11 extends over approximately one turn of the leg portion 3. A female thread forming portion 18 having a cross-section arc-shaped top surface 15 having a screw thread apex portion having a radius (Rb) larger than the radius (Ra) forming the top surface 15 is formed. The flank surfaces 12 and 13 of the female thread forming portion 18 are usually parallel to the flank surfaces 12 and 13 of the screw thread portion 11 and slightly thicker than the thickness therebetween. The radius (Rb) constituting the top surface 15 having a circular arc shape in section is generally Rb ≦ 1.8 × Ra with respect to the radius (Ra) of the circular arc-shaped top surface 15 formed at the top of the screw thread portion 11. It is set to become. As a result, resistance at the time of screwing is generated in the guide screw thread portion 14, but resistance at the time of screwing is not normally generated in the screw thread portion 11, and the workpiece 20 after screwing is loosened by the springback action at this portion. A stop effect is produced. .

  Further, in this embodiment, the female thread forming portion 18 is formed approximately one round between the normal thread portion 11 and the guide thread portion 14, but this is not limited to this and is not shown. The guide screw thread portion 14 and the subsequent normal screw thread portion 11 are substantially rounded as a female screw forming portion 18, and all the screw thread apex portions of the female screw forming portion 18 are larger than the screw thread apex portion of the normal screw thread portion 11. It may be formed by the arc-shaped top surface 15 having a radius (Rb). By doing so, the phenomenon that the screwing torque at the time of screwing increases rapidly can be solved. Further, in the above-described embodiment, the cross section of the leg portion 3 of the screw 1 has been described by showing a tapping screw having a substantially triangular shape. The shape may be the same as that of the embodiment. In this case, the torque at the time of screwing tends to be slightly increased.

  FIG. 6 is a manufacturing process diagram for machining such an aluminum alloy tapping screw, and 30 is a forging process for forming the head 2 on an aluminum alloy material (not shown) of a predetermined length. is there. The material on which the head 2 is formed in this step moves to the next rolling process step 31 where the thread 10 is rolled on the outer periphery of the leg 3. The screw material thus obtained is subjected to a heat treatment by T73 treatment in the next heat treatment step 32, and then proceeds to a hard anodic oxide film treatment step 33, where the aluminum alloy screw 1 has a hard surface on its surface. An anodized film is applied. This hard anodic oxide film treatment is commonly called a hard alumite treatment, and this treatment is a treatment for making the surface hardness of the aluminum alloy higher than the material state.

  This process is generally used for screws 1 manufactured using aluminum alloy material symbols 1000, 2000, 5000, 6000, 7000 series and others shown in JIS standards. Al-Zn-Mg based aluminum alloy of JIS standard material symbols A7050 and A7075, forming the screw blank by subjecting the head 2 to the forging and the leg 3 to the thread rolling process, and T73 The screw obtained by applying the heat treatment by the treatment and then carrying out the hard anodic oxide film treatment has a surface hardness of Hv 350 or more and a core hardness of Hv 170 to 200, which is most suitable for the tapping screw 1. It is. This T73 treatment is a treatment required for alloys of JIS standard material symbols A7050 and A7075. Of course, if the type of aluminum alloy changes, there are things that do not need this treatment and other treatments that are different. It should be understood.

  Even if the tapping screw 1 obtained by such treatment is sufficiently usable, if the screw is further transferred to the lubrication treatment step 34 arranged subsequent to this treatment, the surface of the tapping screw 1 is not changed. Lubricant adheres to the surface, thereby obtaining a lubricating effect. On the other hand, since innumerable fine holes (not shown), i.e., porous, are formed on the surface of the screw 1 in the hard anodic oxide film treatment step 33, the porous hole diameter and the lubricant particle diameter can be changed. Thus, the lubricant can permeate into the hole, and the screw impregnated with the lubricant in this way has a screwing resistance during the screwing operation as compared with the product 35 of the tapping screw in which the lubricant is adhered to the screw surface. The occurrence of seizure with the workpiece 20 is reliably eliminated.

  In these embodiments, the tapping screw that is screwed while forming the female screw 21 mainly in the pilot hole of the workpiece 20 has been described. However, for example, although not shown, a pilot hole is directly drilled in the workpiece 20 and then, It can also be used for a so-called drilling screw in which a drill portion is integrally formed and screwed while forming a female screw.

  When screwing of the aluminum alloy tapping screw 1 obtained in this way into a pilot hole formed in the workpiece 20 in advance is started, at the start of screwing, the leg 3 of the screw 1 shown in FIGS. The guide screw thread portion 14 is pushed into the prepared hole. In this state, since the tapping screw 1 is rotating, the tapping screw 1 continues to be screwed in without being idled while forming a female screw 21 by biting into the prepared hole. At this time, even if the tapping screw 1 is slightly tilted with respect to the pilot hole of the work 20, it is possible for the operator to correct it along the pilot hole at the start of screwing. The screw 1 is smoothly screwed.

  By this screwing operation, the female screw 21 is formed in the female screw forming portion 18 as shown in FIG. 7, and the screw thread 10 of the normal screw thread portion 11 is screwed in a state where the contact with the female screw 21 is relaxed. It is. When the seating surface 5 of the tapping screw 1 is seated on the workpiece 20 in this way, the screwing operation is completed, an axial force is generated on the leg 3 of the screw 1, and the follower flank surface of the screw thread 10 is generated on the female screw 21. 12 comes into contact with each other and a strong fastening force is obtained.

  In such a screwing operation, since a lubricant (not shown) adheres to the tapping screw 1, the lubricant is interposed between the work 20 and the tapping screw 1 and the work 20. A large contact resistance does not occur between the two, and a smooth screwing action is obtained. The lubricant may be encapsulated in a microcapsule having a particle size of 100 to 300 μm, and the leg 3 of the screw 1 may be covered with a coating material (not shown) containing the microcapsule. Thus, even during reuse, this lubricating action can be sufficiently exerted, and the life of the lubricant can be extended.

It is a principal part front view which shows embodiment of this invention. 1 is an overall front view of a tapping screw according to the present invention. FIG. 3 is a bottom view of FIG. 2. It is an enlarged principal part front view of the normal thread part in FIG. It is a principal part enlarged front view which shows a female screw formation part. It is a schematic process drawing which shows the manufacturing process in this invention. It is a principal part expanded sectional view which shows the screwed state of this invention. It is a front view of the screw thread which shows the prior art example of this invention. It is principal part sectional drawing which shows another prior art example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tapping screw 2 Head part 3 Leg part 4 Drive hole 5 Seat surface 10 Screw thread 11 Normal thread part 12 Follow side flank face 13 Advance side flank face 14 Guide thread part 15 Top face 16 Valley face 17 Arc-shaped face 18 Female thread molding 20 Workpiece 21 Female thread 30 Forging process 31 Rolling process 32 Heat treatment process 33 Hard anodized film treatment process 34 Lubrication process 35 Product

Claims (6)

  A screw material made of an aluminum alloy having a screw portion which is composed of a head portion (2) having a drive hole (4) and a leg portion (3) integral with the head portion, and a thread (10) formed on the leg portion. A thread apex that forms the ridgeline of the thread of this threaded portion is formed in a cross-sectional arc shape over the entire length of the leg, while a trough that forms a trough of this threaded thread (16) and the thread flank surface (12, 13) are connected by an arcuate surface (17) having a circular arc cross section, and further, a hard anodized film treatment is applied to a screw material having these shapes. High hardness aluminum alloy screws.   The high-hardness aluminum alloy according to claim 1, wherein an angle (α) constituted by a flank surface forming the screw thread in a cross section perpendicular to the lead wire is set in a range of 60 ° to 70 °. Screw making.   The screw portion is on the head side, and is a normal screw portion (11) in which a complete screw thread portion is formed, and a guide screw that is on the tip side of the leg portion and is an incomplete screw thread portion having a low screw thread height. And a female thread forming section (18) having a circular arc cross-section at the top of the thread over the circumference of the leg between the normal thread section and the guide thread section. The high-hardness aluminum alloy screw according to claim 1 or 2, wherein the high-hardness aluminum alloy screw is formed with a larger arc than the cross section of the thread and the thread apex of the guide thread.   The screw part is on the head side, and the normal screw thread part where the complete screw thread part is formed and the guide screw thread part on the tip side of the leg part that is an incomplete screw thread part with a low thread height In addition, the guide screw thread portion and the subsequent substantially one round of the normal screw thread portion constitute a female screw forming portion, and the screw thread apex portion of the female screw forming portion is the screw apex portion of the normal screw thread portion. The high-hardness aluminum alloy screw according to claim 1 or 2, wherein the high-hardness aluminum alloy screw is formed by an arc larger than the cross section of the above.   The female thread forming portion has a radius (Rb) that constitutes the top surface (15) of the arcuate cross section of the apex portion thereof with respect to the radius (Ra) of the arcuate top surface formed at the top of the thread of the normal thread portion. The high-hardness aluminum alloy screw according to claim 3, wherein Rb ≦ 1.8 × Ra is set.   The screw material is Al-Zn-Mg, and is formed by subjecting aluminum alloys of JIS standard material symbols A7050 and A7075 to forging and rolling, and then heat treatment by T73 treatment. The high-hardness aluminum alloy screw according to claim 1, 2, 3, 4, or 5.

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