JP2012112476A - High-hardness aluminum tapping screw, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-hardness aluminum tapping screw which promotes recycling of an aluminum product and allows mass production of the high-hardness aluminum tapping screw, and a method of manufacturing the same.SOLUTION: In a tapping screw 1 formed by performing a surface treatment to a screw material comprising a head part 2 and a leg part 3 having a thread 10, since this high-hardness aluminum tapping screw includes a coating film of a laminated structure to which an electrodeless nickel plating treatment followed by a zinc plating treatment is performed after the screw material is made of an aluminum alloy, the thread 10 is formed on the leg part 3 of the screw material by form rolling, and a solution heat treatment is performed to the screw material formed with the thread 10, the tapping screw can be screwed in a prepared hole of a workpiece made of an aluminum alloy while directly forming a female screw by a screw component of the same material. A plated coating film is smoothly formed, the cause of occurrence of corrosion is eliminated and corrosion resistance is improved. Since both the workpiece and the screw are formed of the aluminum alloy, the need of sorting treatment is obviated and the rate of recycling is improved.

Description

  The present invention relates to a screw for attaching a part to a workpiece made of a soft material such as an aluminum alloy or a magnesium alloy and a method for manufacturing the screw, and forming a female screw in a pilot hole formed in such a workpiece made of a soft material. The present invention relates to a high-hardness aluminum tapping screw to be screwed in and a method for manufacturing the same.

  In recent years, electrical appliances such as mobile phones, personal computers and portable music players, automobile parts, and aluminum fittings are often used with aluminum alloys and magnesium alloys because of their light weight, small size, and good workability. Many screws are used to attach and assemble parts to such soft workpieces. Various types of such screws have been developed in recent years because it is necessary to maintain the fastening strength to the workpiece made of the soft material, but these are pre-formed with a female screw hole as a screw-in pilot hole in which a female screw is formed on the workpiece, Parts are attached or assembled by screwing aluminum screws into these female screw holes. In addition, recently, a tapping screw that is screwed in while forming a female screw into the pilot hole is also being used. As a manufacturing method thereof, as shown in FIG. The mainstream is a product made by heat-treating an aluminum alloy screw material in a heat treatment step 122 and subsequently subjecting the screw material to a hard anodizing treatment (alumite treatment) step 123 to improve the surface hardness. It has become. However, mass production of an aluminum tapping screw having a stable and high strength that can be stably screwed into a workpiece while forming a female screw with the same kind of material as the workpiece made of the soft material has not yet progressed sufficiently.

  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 into a bolt shape, rapid cooling from a temperature exceeding 480 ° C. and a range of 150 to 220 ° C. In this method, a bolt is manufactured by applying a heat treatment including an aging treatment therein, and then performing any surface treatment selected from galvanizing, chromic acid oxidation, and anodic oxidation. Bolts are manufactured by such a process in order to relieve the distortion of the crystal structure inside the material disturbed by forging and strengthen the grain boundaries, and is necessary to prevent the occurrence of stress corrosion. Yes. As the screw thread of the bolt in such a manufacturing method, the screw thread apex angle (α) is formed at an angle set according to the JIS standard, that is, 60 °, thereby making it easy to form the female screw with the bolt. I have to. And the weight of the whole product is enabled by using the bolt made from the aluminum alloy cold-formed by the same shape as this for a work.

Japanese Patent Publication No. 7-92101

  However, when the material of the bolt or tapping screw having the above-mentioned generally threaded shape is made of an aluminum alloy, even if it is commercialized by applying a hard anodizing treatment, so-called hard alumite treatment, the strength is However, when cold forging is performed using aluminum as a raw material, especially when a thread is formed by rolling, the thread is almost formed, but the flow of the material by rolling becomes complicated, and FIG. As shown in FIG. 3, the surface of the valley portion of the thread 210 is rough, and even if the rough anodized surface is subjected to the hard anodizing treatment, the rough surface becomes an obstacle and has a coating having sufficient corrosion resistance. It cannot be maintained. Furthermore, when the screw is relatively small, this rough surface acts as a screwing resistance and affects the screwing work, which increases the screwing torque and tends to cause seizure during screwing with an automatic screw tightening machine, which adversely affects torque management. Has occurred. In addition, the screw thread apex angle (α) is normally set to 60 °, and the apex part 213 and the entering corner part 214 (the intersection of the screw thread valley face and the flank face) have an angle. Even if a hard anodizing treatment is applied to the screw, a thin streak-like crack or a gap 217 is generated at the corner of the screw thread top portion 213 or the entering corner portion 214, while this is extremely thin even if a film is formed. When this is screwed into the workpiece, the thread is liable to be crushed from this portion. This is because the film covering the surface is as thin as 30 to 40 μm, and if there are many irregularities such as threads, a sufficient thickness cannot be obtained at this boundary and the surface hardness is also low as Hv 300 to 350 is doing. Then, an adhesion state occurs between the screw and the pilot hole of the workpiece, the screw is not completely screwed in, and a state where the seat surface of the screw is lifted from the workpiece, that is, a so-called screw floating phenomenon also occurs. Moreover, if the workpiece is made of an aluminum alloy or a magnesium alloy having similar properties, and the screw used for this is made of iron or stainless steel, the screw and the workpiece are compared with the case of using an aluminum alloy screw. When the potential difference between the two becomes high and moisture intervenes between them, contact corrosion occurs between the screw and the workpiece. In addition, when iron or stainless steel screws are used for aluminum sashes such as window frames that have a large heat dissipation effect, such as aluminum alloys and magnesium alloys with high heat conduction efficiency, these screws have low heat conduction efficiency. For this reason, water droplets adhere to the screws because they cannot respond to changes in room temperature in a short time. On the other hand, soft materials such as aluminum and magnesium alloys and iron and stainless steel materials have different expansion coefficients, that is, soft materials have a larger expansion coefficient than iron and stainless steel materials. A gap is formed in the film, and the water droplets repeatedly enter the gap, and corrosion is likely to proceed. In addition, the anodizing treatment used in the production thereof requires that one current be conducted to an aluminum screw in the treatment plating tank, which increases the cost for this. In addition, the cost of the screw increases in this way, so that the unit price of the screw increases, and the screw manufactured by this method has various problems such as limited use.

  The object of the present invention is to solve such problems and to promote the recycling of products using aluminum alloy workpieces, and to enable mass production of high hardness aluminum tapping screws. It is to obtain a tapping screw made and a manufacturing method thereof.

  A high-hardness aluminum tapping screw for achieving the object of the present invention includes a head 2 having a drive hole 4 and a leg 3 integrally formed with the head 2 and having a screw thread 10 around it. In the tapping screw in which the screw material is subjected to surface treatment, the screw material is made of an aluminum alloy, and the screw thread 10 is rolled on the leg portion 3 of the screw material, and the screw thread 10 is formed. It is characterized by a structure having a surface treatment film of a laminated structure in which a screw material is subjected to solution heat treatment, followed by electroless nickel plating and subsequently zinc plating.

Moreover, the said structure WHEREIN: As for the leg part of a screw raw material, it is characterized by the corner | angular part being circular arc shape, and, thereby, a surface treatment film is hard to peel off.
Further, in the above-described configuration, a heat treatment step 26 for heat treatment for a predetermined time at a constant high temperature lower than the solution heat treatment temperature is disposed on the screw material between the electroless nickel plating treatment and the zinc plating treatment, so that the electroless nickel plating treatment is performed. Therefore, a tapping screw having a stable and high surface hardness can be obtained.
Moreover, in the said structure, the chromate treatment process 25 is arrange | positioned following a zinc plating process, and a corrosion resistant and glossy aluminum tapping screw is obtained by performing a chromate process on the zinc raw material.

  Furthermore, the manufacturing method of the high hardness aluminum tapping screw of the present invention includes a forging step 20 for forming the head 2 having the drive hole 4 and a screw thread around the leg 3 formed integrally with the head 2. In the manufacturing method of a tapping screw for forming a screw material from a rolling process step 21 for rolling and forming 10, the screw material is made of an aluminum alloy, and the thread 10 is formed by rolling after the rolling process step 21. A solution heat treatment step 22 for performing a solution heat treatment on the aluminum alloy screw material is arranged, and following this treatment step, the surface hardness is further increased with respect to the material whose internal strength is increased thereby, and the screw material and Electroless nickel plating treatment step 23 for improving adhesion with zinc plating in zinc plating treatment step 24 as a nickel plating and post-treatment step is disposed, and a surface treatment film having a laminated structure It is characterized in configuration to produce an aluminum tapping screw having.

Further, in the manufacturing method, between the electroless nickel plating treatment step 23 and the zinc plating treatment step 24, a heat treatment for heat treating the screw material subjected to the electroless nickel plating treatment at a constant high temperature lower than the solution heat treatment temperature for a predetermined time. The step 26 is arranged.
Further, the manufacturing method is characterized in that a chromate treatment step 25 for chromate treatment for improving the corrosion resistance is arranged on the zinc-plated screw material following the zinc plating treatment step 24.

  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 directly with a screw component made of aluminum alloy. In addition, since all the flanks of adjacent threads are connected by arc-shaped surfaces, the plating film formed by the plating film treatment is smoothly formed along the curved surface, eliminating the cause of corrosion. Corrosion resistance is improved. Moreover, since the thread formed by rolling on the aluminum material has no corners in the thread part as in the past, the occurrence of rough skin at the thread valley is eliminated, and the thread surface becomes smooth, Corrosion resistance can be maintained for a long time by applying the coating treatment on the surface thereof. 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 facilitated. In addition, the thread crest angle is usually set to 70 ° centered around 70 °, and the allowable range is set to ± 5 °, and the cross section of the apex portion and the cross section of the entering corner portion are both arc-shaped. Therefore, a streak-like crack is not generated and the film is not formed thin, and a film having a stable thickness can be obtained. For this reason, gloss and aesthetics are maintained in the screw, and the screw is reliably screwed in, thereby obtaining a stable screwing operation.

  In addition, the screw material is Al-Zn-Mg, and is made of aluminum alloy material of JIS standard material symbols A7050 and A7075. After the material is pressed and rolled, and heated to a predetermined temperature, Use a screw that has been subjected to electroless nickel plating treatment for this screw material after quenching and adjusting the mechanical properties, followed by solution heat treatment that again performs heat treatment (age hardening T73 treatment). For example, even if the workpiece is an aluminum alloy die-cast (JIS standard ADC12), the surface hardness of the screw is Hv 350 or more, and the core hardness thereof is Hv 170 to 200, and the surface hardness is more than this. Since it is high, it can sufficiently be used as a so-called tapping screw that is screwed in while forming a female screw in the prepared hole. Furthermore, the difference in material between the screw and the workpiece, for example, when using an aluminum alloy screw compared to the case where an aluminum sash is assembled using a stainless steel screw, the thermal conductivity is almost the same. Since there is no difference in effect, the occurrence of condensation is also reduced. Moreover, since the expansion coefficient of the work and the screw part is the same, there is almost no gap between the screwed screw part and the work, and water droplets caused by condensation do not repeatedly enter this gap. This also reduces the progression of corrosion. In addition, since both the work and the screw screwed into the work are aluminum alloys, there is a specific effect such that separation processing in reuse is unnecessary and the recycling rate is improved. Further, the chromate treatment is applied to the leg parts of the threaded parts to which the plating film is applied, and thus there are specific effects such as an improvement in aesthetics and a lubrication effect.

It is an expansion principal part partial front view which shows embodiment of this invention. It is a whole front view of the tapping screw which is an embodiment of the invention. FIG. 3 is a bottom view of FIG. 2. It is a schematic process drawing which shows the manufacturing process of the aluminum tapping screw which concerns on this invention. It is a principal part schematic process drawing which shows another Example of this invention. It is a schematic process drawing which shows the process process of the prior art example of this invention. It is an expanded principal part sectional drawing of the prior art example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 2 and 3, reference numeral 1 denotes a tapping screw as an example of a high hardness aluminum alloy screw part made of an aluminum alloy having a head 2 and a leg 3 formed integrally therewith and having a female screw forming function. It is. The head 2 is formed with a drive hole 4 through which a screw driving force is transmitted from a driver bit (not shown) to the tapping screw 1. 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 12 which is an incomplete screw thread portion whose height decreases as the screw thread 10 reaches the tip end is formed at the tip end 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 screw part made up of the normal screw thread part 11 and the guide screw thread part 12 is formed in a circular arc shape over the entire length. A ridge line of the thread is formed across the normal thread part 11 and the guide thread part 12.

  As shown in FIG. 1, the screw thread 10 is composed of a follower flank surface 13 and a leading flank surface 14 that form the screw thread 10 in a cross section perpendicular to the lead wire. The angle (α) is set in a range of 70 ° ± 5 °. The apex portion of the thread formed from the flank surfaces 13 and 14 is formed by smoothly connecting the top surface 15 having an arcuate cross section and the flank surfaces 13 and 14, so that the electroless nickel plating shown in FIG. The hard nickel plating film in the processing step 23 can be uniformly formed on the surface. On the other hand, the valley surface 16 forming the valley portion of the screw thread 10 and the flank surfaces 13 and 14 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. Since the thread cross-section along the surface has curved surfaces that are connected by arcs without forming corners, even if electroless nickel plating treatment is applied to this thread material, streaky cracks and cracks are formed on the coating. It will not occur.

  Further, as shown in FIG. 3, the leg portion 3 has a substantially triangular shape in the bottom view and the cross section perpendicular to the axis, so that the resistance at the time of forming the female screw during screwing can be reduced even slightly. Moreover, the locus circle diameter formed by the three apexes of the substantially triangular shape located near the tip of the guide screw thread portion 12 is the diameter of a pilot hole (not shown) formed in the work (not shown). The thread diameter is set to be the same diameter or slightly larger than this and smaller than the normal thread section 11. For this reason, a streak-like female screw (not shown) with a slightly threaded ridge line is formed in the prepared hole at the start of screwing.

  Moreover, since the thread 10 becomes higher as the guide thread 12 reaches the normal thread 11, a female thread is formed in the pilot hole as the tapping screw 1 is screwed. . In the above-described embodiment, the tapping screw 1 having the substantially perpendicular triangular section of the leg 3 is described. However, a tapping screw having the leg 3 in a circular shape may be used. Since the number of contact points between the screw thread 10 and the female screw is larger than that of the tapping screw 1 having the shape, the torque at the time of screwing tends to be slightly increased.

  FIG. 4 is a manufacturing process diagram for processing such an aluminum alloy tapping screw 1, and 20 is a forging process for forming the head 2 on an aluminum alloy material (not shown) of a predetermined length. It is. In this process, the material in which the head 2 is integrally formed moves to the next rolling process 21 where the thread 10 is formed around the leg 3 by rolling. The screw material thus obtained is transferred to a solution heat treatment step 22 where a solution heat treatment is performed on the aluminum alloy screw material arranged as the next step, and this screw material is specifically heated to a predetermined temperature. After that, it is rapidly cooled to adjust the mechanical properties such as the hardness and stickiness of the core of the material, and then the solution heat treatment is performed to perform the heat treatment again (T73 treatment defined in JIS which is age hardening). It has become. This treatment hardens the material. Following this treatment step, the surface hardness of the material with increased internal strength is further increased, and the adhesion between the screw material, nickel plating and zinc plating in post-treatment zinc plating step 24 is improved. The electroless nickel plating process 23 to be performed is arranged. In this step, the surface of the aluminum alloy screw 1 is provided with a hard nickel plating film. Thereby, the hardness of the surface of an aluminum alloy is still higher than a raw material state.

  The T73 treatment is generally used for screws 1 manufactured using aluminum alloy material symbols 1000, 2000, 5000, 6000, 7000 series and others shown in JIS standards, and among them, , Al-Zn-Mg based aluminum alloy of JIS standard material symbols A7050 and A7075, forming the screw material by forging the head 2 and thread rolling the leg 3, A screw obtained by applying a solution heat treatment with T73 treatment and then applying an electroless nickel plating film has a surface hardness of Hv 350 or higher and a core hardness of Hv 170 to 200, which is a tapping screw. 1 is most suitable. 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.

  In addition, a zinc plating treatment step 24 is arranged after the electroless nickel plating treatment step 23, thereby improving chromate adhesion in the chromate treatment step 25 as a subsequent step. Furthermore, by performing this zinc plating treatment, a high rust prevention effect can be obtained and excellent corrosion resistance can be exhibited. Moreover, after the zinc plating process 24, a chromate treatment process 25 for performing a chromate treatment for improving the corrosion resistance of the zinc-plated screw material is arranged, and the aesthetic appearance of the aluminum tapping screw 1 is improved. Thus, the aluminum alloy tapping screw 1 has a surface treatment film having a laminated structure of three layers, and has excellent durability and aesthetics.

  Even the tapping screw 1 obtained by such a treatment can be sufficiently used, but as shown in FIG. 5, there is no need to place a gap between the electroless nickel plating treatment step 23 and the zinc plating treatment step 24. A heat treatment step 26 for heat treating the screw material subjected to electrolytic nickel plating at a constant high temperature (about 200 ° C. in this embodiment) lower than the solution heat treatment temperature for a predetermined time (about 1 hour) may be arranged. By doing so, the surface of the screw material can be further cured, and finally a hardness close to Hv500 can be obtained. Needless to say, the heat treatment temperature at this time is a temperature at which the aluminum alloy material is not dissolved or a temperature and time at which the electroless nickel plating is not peeled off from the screw material. Is.

  In these embodiments, the tapping screw 1 that is mainly screwed in while forming a female thread in the prepared hole of the workpiece has been described. However, other than this, for example, although not shown, the same process as described above is applied to a small screw made of an aluminum alloy. A high hardness aluminum machine screw can be obtained by applying a plating film.

  When the screwing of the aluminum alloy tapping screw 1 obtained in this way is started with respect to the prepared hole formed in the workpiece in advance, the legs of the tapping screw 1 shown in FIGS. 3 guide screw threads 12 are pushed into the pilot holes. In this state, since the tapping screw 1 is rotating, the tapping screw 1 is screwed in without being idled while being bitten into the pilot hole to form a female screw.

  By this screwing operation, a female screw is formed, and the screw thread 10 of the normal screw thread portion 11 is screwed in a state where contact with the female screw is relaxed. Thus, when the seating surface 5 of the tapping screw 1 is seated on the work, the screwing operation is completed. In such a screwing operation, since the zinc adheres to the tapping screw 1, a slight lubricating effect is obtained between the screw and the workpiece at the time of screwing. Burning in between is prevented, and a smooth screwing action is obtained.

  Five samples of the aluminum tapping screw of the present invention and the conventional aluminum tapping screw with a hard anodized coating were prepared, and the respective breaking torques were measured. The results are compared as shown in Table 1. became. The name of the screw in this measurement was M4, the workpiece into which this was screwed was an aluminum alloy die casting (ADC12), the thickness t = 5 mm, the pilot hole diameters were 3.6 mm and 3.7 mm, and the breaking torque of each screw was measured.

  As a result, in the case of the pilot hole diameter of 3.6 mm, the breaking torque of the conventional example was slightly larger than the breaking torque of the present invention in two of the five samples, but on average, this is the tapping screw of the present invention. The breaking torque of 1 is large. On the other hand, in the case of the workpiece prepared hole diameter of 3.7 mm, the breaking torques of all five samples of the aluminum tapping screw 1 of the present invention are larger than those of the conventional example. It is confirmed that the strength of the tapping screw 1 is large. In addition to this, when electroless nickel plating treatment was performed and then changed to zinc plating treatment, other surface treatments, that is, screws subjected to electroless fluorine resin-dispersed nickel plating were tested under the same conditions. In the case of a screw plated with dispersed nickel, there are problems such as skipping of the head and occurrence of rust in the salt spray test, as well as high costs in this treatment. .

  The aluminum tapping screw and the manufacturing method of the screw of the present invention can be applied to bolts, rivets, nuts and the like which are fastening parts other than the screws, and are widely used for mass production of aluminum fastening parts.

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 Guide thread part 13 Follow-up side flank surface 14 Advance side flank surface 15 Top surface 16 Valley surface 17 Arc-shaped surface 20 Forging processing Process 21 Rolling process 22 Solution heat treatment process 23 Electroless nickel plating process 24 Zinc plating process 25 Chromate treatment process 26 Heat treatment process

Claims (7)

  In a tapping screw in which a screw material made of a head portion (2) formed with a drive hole and a leg portion (3) formed integrally with the head portion and having a screw thread (10) around the surface is subjected to surface treatment. The screw material is made of an aluminum alloy, a thread is rolled on a leg portion of the screw material, a solution heat treatment is performed on the screw material made of an aluminum alloy on which the screw thread is formed, and then an electroless nickel plating treatment is performed. A high-hardness aluminum tapping screw characterized by having a surface treatment film having a laminated structure subjected to zinc plating treatment.   2. A high hardness aluminum tapping screw according to claim 1, wherein the leg portion of the screw material has an arc shape at the corner.   Between the electroless nickel plating treatment and the zinc plating treatment, a heat treatment process is performed on the screw material for a predetermined time at a constant high temperature lower than the solution heat treatment temperature, and the screw material treated with electroless nickel plating is heat treated. The high-hardness aluminum tapping screw according to claim 1, wherein:   2. A high-hardness aluminum tapping screw according to claim 1, wherein a chromate treatment step is arranged subsequent to the zinc plating treatment, and the zinc-plated screw material is subjected to chromate treatment.   A screw material is formed from a forging process (20) for forming a head having a drive hole and a rolling process (21) for rolling a thread around a leg integrally formed with the head. In the manufacturing method of the tapping screw, the solution material is made of an aluminum alloy, and a solution heat treatment step is performed in which a solution heat treatment is performed on the screw material made of an aluminum alloy in which the thread is rolled after the rolling process step ( 22) is arranged, and after this treatment step, the surface hardness is further increased with respect to the material whose internal strength is enhanced thereby, and the zinc in the zinc plating treatment step (24) as a screw material, nickel plating and post-treatment step. High-hardness characterized in that an electroless nickel plating treatment step (23) for improving the adhesion with the plating is arranged, and an aluminum tapping screw having a laminated surface film is manufactured. Method of manufacturing the aluminum-tapping screws.   In the manufacturing method, a heat treatment step (26) of heat-treating the screw material subjected to the electroless nickel plating treatment at a constant high temperature lower than the solution heat treatment temperature for a predetermined time between the electroless nickel plating treatment step and the zinc plating treatment step. The manufacturing method of the high hardness aluminum tapping screw of Claim 5 characterized by the above-mentioned.   6. The high hardness aluminum tappin according to claim 5, wherein a chromate treatment step (25) for chromate treatment for improving corrosion resistance is disposed on the zinc-plated screw material subsequent to the zinc plating treatment step. Screw manufacturing method.

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