JP5333380B2 - Drilling tapping screw - Google Patents

Description

  The present invention relates to a drilling tapping screw formed by integrating a drill portion for making a pilot hole of a screw with respect to an object to be fastened such as a steel material at the tip of the tapping screw.

  As a method for fastening a steel material or the like, a method using a drilling tapping screw (hereinafter abbreviated as a drill screw) is known. A drill screw is a tapping screw that can be used without making a pilot hole in a steel material when, for example, a steel material is fastened, and a drill portion is integrally formed at a tip portion thereof. The tip of the screw has a sharp point and a cutting edge, and when the object to be fastened is hard like steel, it is common to use a drill screw with a cutting edge that has the same shape as the drill blade. It is.

  The tip of the drill screw has a drill shape in order to ensure piercing properties, and the surface hardness of the steel serving as a base material is increased by carburizing and tempering treatment. However, when a hard material such as a steel material is fastened, the fastening work using this drill screw is not always easy. In particular, the fastness of a plated screw is often difficult, and the cause is the edge of the screw. A drill screw whose base material is steel is galvanized for rust prevention. For example, JIS B1125 (drill screw) stipulates that a steel drill screw should be electrogalvanized in principle. If the thickness of the plating is thin, there is almost no effect on the fastening operation. However, if the steel is thick-plated for long-term corrosion protection, the screws must also have the same corrosion resistance as the steel to be fastened. Will do. Due to this thick plating, the shape of the cutting edge becomes dull and the biting into the steel material becomes worse, which is a cause of deterioration in fastening performance.

  For example, in Patent Document 1, in order to improve drill performance, after zinc or tin electroplating is performed on the entire surface of a drill screw, a zinc-iron alloy layer or a tin-iron alloy layer is formed by heat treatment. A forming technique is disclosed.

  In Patent Document 2, a cold-forged drill screw is subjected to carburizing and tempering treatment, and further immersed in a molten bath of 40% -60% zinc alloy at 380 to 400 ° C. for about 1 minute, and then immediately lifted and centrifuged. It is disclosed that a machine is used to shake off excess molten alloy on the surface of a drill screw. Patent Document 3 also discloses a method in which a drill screw is subjected to centrifugal treatment while being heated at a temperature equal to or higher than the melting point of zinc or zinc alloy after being hot-plated with molten zinc or molten zinc alloy.

  In Patent Document 4, after forming a corrosion-resistant film such as electrogalvanizing on the entire surface of the drill screw, the corrosion-resistant film is removed only at the drill part, or the drill part is previously coated so that the corrosion-resistant film is not formed. Thus, a technique for shortening the operation time while maintaining the drilling performance is disclosed. Patent Document 5 discloses a technique in which a chemical resistant resin masking film is formed on the surface of a drill part, and then a corrosion resistant film is formed on the surface other than the drill part.

JP-A-3-149407 JP-A-4-312207 JP 2000-266023 A JP 2000-170730 A JP 2002-330221 A

  In the invention described in Patent Document 1, after a zinc film is formed on the surface of the drill screw, a step of performing heat treatment and further removing the oxide is required. Moreover, since iron is contained as a plating component, there may be a problem that the bare corrosion resistance (red rust resistance) is poor.

  In the inventions described in Patent Documents 2 and 3, after the drill screw is pulled up from the plating bath, a rotating centrifugal force is applied before the plating melt is solidified, or the centrifugal treatment is performed while heating at a high temperature. A process is required.

  Further, in the invention described in Patent Document 4, since the corrosion resistant film is not formed on the drill portion and the base iron is exposed, the corrosion resistance of the drill portion is inferior, and the drilling workability may be reduced due to generation of rust or the like. Furthermore, in the invention described in Patent Document 5, the type and thickness of the resin are finely defined for the method of masking the drill part surface of the drill screw with the resin, but only the drill part of the enormous number of drill screws. It is envisaged that the pickling process or the masking process is very troublesome. However, the specific method is not described in Patent Document 5, and therefore it is expected that it is difficult to actually carry out these methods on a commercial basis.

  Accordingly, in view of the above problems, the present invention improves the drilling tapping efficiency of improving the screwing work efficiency by improving the drilling ability and workability of the drill screw with respect to a fastened object such as a thin metal plate while maintaining the corrosion resistance of the entire drill screw. The purpose is to provide a screw.

The present invention is as follows.
(1) A drilling tapping having a shank having a thread on the outer periphery and a drill part integrally formed at one end of the shank in the axial direction, and at least the surface of the drill part is subjected to zinc plating. In the screw, the plating thickness of the drill portion at the screw tip is 30 μm or less, and between the screw tip portion and the screw thread forming portion, an auxiliary cathode for controlling the screw tip portion plating adhesion amount, A drilling tapping screw, wherein the auxiliary cathode is detached during screw joining.
(2) The drilling taping according to (1), wherein the distance between the corner closest to the drill tip of the auxiliary cathode and the center line of the drill is not more than a value obtained by adding 3 mm to the radius of the drill part. screw.
(3) The auxiliary cathode has a pull-in distance from a screw front end to a corner closest to the auxiliary cathode drill front end of 2 mm or less, according to (1) or (2), Drilling tapping screw.
(4) The drilling tapping screw according to any one of claims (1) to (3), wherein the drilling tapping screw has two or more auxiliary cathodes.

  ADVANTAGE OF THE INVENTION According to this invention, without reducing the corrosion resistance of a drill screw, the plating thickness of the front-end | tip part of a drill screw can be reduced and workability | operativity, such as steel materials joining, can be improved.

It is a figure which shows the thread part of the drilling tapping screw with a reamer which concerns on a prior art. It is a figure which shows the thread part of the drilling tapping screw which concerns on the 1st Embodiment of this invention. It is a figure which shows the thread part of the drilling tapping screw which concerns on the 2nd Embodiment of this invention. It is a figure which shows the thread part of the drilling tapping screw which concerns on the 3rd Embodiment of this invention.

  The present inventors examined the cause of poor piercing performance of electrogalvanized screws. The inventors are concerned with workability in a drill screw when the plating thickness of the screw head is set to 20 μm or more, which is the plating thickness of a galvanized steel sheet with a large thickness. Corrosion resistance is a problem mainly at the head of the screw that contacts the steel. Naturally, this part needs to have corrosion resistance equivalent to or better than that of steel. However, in barrel-type electroplating, the plating thickness varies greatly, and in particular, the plating thickness at the tip of the drill part and the cutting edge part is thicker than the head of the screw. It was found that when the plating thickness of the screw head portion was 20 μm, the maximum thickness of the drill tip and the cutting edge portion plating was 40 μm or more, which was twice or more the plating thickness of the head. In addition, pure zinc plating applied by electrogalvanization has a Vickers hardness of the plating layer of around 50 and is very soft. For these two reasons (the tip of the drill part and the cutting edge part are thickly covered with soft galvanizing), it has been found that the workability of the drill screw is greatly reduced.

  In addition, it was found that the workability is hardly deteriorated with a commercially available drill screw having a screw head plating thickness of 10 μm or less as compared with the case where there is no plating. As a result of investigating the plating thickness of the tip of this commercially available screw, it was found that the maximum thickness was 20 to 30 μm, and if this thickness, the workability of screw fastening was not affected.

  Therefore, the inventors determined the upper limit of the plating thickness at the screw tip necessary for ensuring the piercing property, and studied to control the plating thickness at the screw tip to be thinner than this upper limit. First, the inventors investigate the relationship between the plating thickness of the drill tip and the cutting edge and the piercing property, and by setting the plating thickness of the drill tip to 30 μm or less, a piercing property having no practical problem can be obtained. It was confirmed. This finding is consistent with the commercial screw survey results. Since the plating thickness of the drill cutting edge is equal to or thinner than the plating thickness of the drill tip, the plating thickness of the drill cutting edge can be controlled by using the plating thickness of the drill tip as a management index. It was found that upper limit management is possible.

Next, the inventors examined a method for controlling the plating thickness at the tip of the drill screw to 30 μm or less while ensuring the corrosion resistance required for the drill screw. Here, the reason why the plating at the tip of the drill screw becomes thick in the barrel plating is as follows.
(1) First, in barrel plating, since a large number of screws are plated together while stirring, in the assembly of screws in a spherical or rectangular lump, the screw at the center is difficult to be plated. The plating tends to adhere to the screws distributed on the surface. In addition, when plating an elongated object such as a screw, both ends of the screw are likely to jump out of the assembly of screws. Becomes thicker.
(2) Since the tip of the screw is long and narrow with respect to the head having a large shape and a large surface area, if the same amount of current is applied to the plating, the tip of the screw with the smaller surface area is plated. Thickness increases.
(3) Furthermore, since the tip portion of the screw and the cutting blade portion are sharply sharp in function, the plating current tends to be concentrated. Therefore, the plating becomes thicker at the tip and cutting edge of the screw, which should be sharp.

  From the above, in order to reduce the plating thickness at the tip of the screw, the above (1) to (3) may be considered. However, on the other hand, it cannot be functionally changed that the screw has an elongated shape and that the tip portion and the cutting blade portion are sharp. Therefore, as a result of investigating reducing the plating thickness by increasing the current-carrying area at the screw tip in the plating process, the inventors added an auxiliary cathode between the screw tip and the thread formation portion, It has been found that the plating thickness at the tip of the screw can be reduced by letting a part to the auxiliary cathode (hereinafter referred to as “relief”). However, this “relief” is necessary only in the plating process, and is not necessary at the time of screw joining. For this reason, it is necessary to quickly and easily disengage this when screwing.

Here, regarding the drill screw, the “reamer” is known as a structure that is provided at the shaft portion of the screw and is detached when the screw is joined, in the same manner as the escape of the present invention. For example, FIG. 1 shows a conventional drill screw with a reamer, and a reamer 3 is provided on a side portion of a drill portion 1 having a cutting edge 2 at the tip. A reamer is a blade-like protrusion that is attached to expand the diameter of the hole that is drilled at the tip of the screw, depending on the application of the drill screw. After opening, it is structured to eventually fall off in the process of drilling in hard materials such as steel.
In the present invention, by applying this reamer screw manufacturing technology, it is possible to install a “relief” between the screw tip and the thread forming portion, and the “relief” obtained in this way is an assist. The present invention has been completed by finding that it can function as an electrode and that it can be removed at the time of screw joining to solve the above problems.

  The “relief” that is a constituent element of the present invention needs to have a shape in which the electrolysis current easily flows at the same time as increasing the current-carrying area of the screw tip. In addition, the “relief” is required to be surely detached in the step of joining the steel materials without falling off in the plating step. Furthermore, since the detachment is performed by “relief” coming into contact with the surface of the steel material, there is a possibility that the surface of the steel material may be wrinkled. In addition, it is preferable that the “relief” can be manufactured by applying the current technology for manufacturing a screw with a reamer.

  The plating thickness required for the screw is not uniformly determined and varies depending on the required anticorrosion ability. Also, the workability of the screw varies depending on the structure of the screw head. For example, hexagon head screws have good holdability and excellent workability during joining work, so it is necessary to extremely reduce the plating thickness at the screw tip. Absent. Conversely, countersunk head screws have poor holdability and poor workability, so it is preferable to reduce the plating thickness at the tip of the drill screw as much as possible.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. 2 to 4 each show a relief drill screw according to the present invention, which is integrally formed with a shank 10 having a thread on the outer periphery and one end of the shank 10 in the axial direction. Drill part 1 and a head (not shown) formed integrally with the other end of shank 10, and zinc-based plating is applied to at least the surface (usually the entire part) of drill part 1. Yes. At least one (two in the illustrated example) relief 4 is provided on the side portion of the drill portion 1 provided with the cutting edge 2 at the tip, and the relief 4 is configured to be detached at the time of screw joining. . In the present invention, in order to ensure the drillability of the drill screw, the drill tip plating thickness is set to 30 μm or less. In addition, when applied to a screw having a low holdability by a bit at the screw head, such as a flat head screw, and having poor workability, it is preferably 20 μm or less. Although there is no lower limit to the plating thickness at the tip of the drill from the viewpoint of drillability and workability, it is preferable to ensure 5 μm or more from the viewpoint of ensuring corrosion resistance. However, as described above, the plating thickness required for the tip of the drill screw differs depending on the type of screw as well as the usage environment. For this reason, the escape condition is not uniquely determined. For this reason, the conditions under which the escape works effectively will be described below.

  The factors affecting the effect of the relief 4 include the thickness a of the relief 4 shown in FIGS. 2 to 4 (not shown for the thickness direction of the paper surface), the relief width b, the angle c of the relief tip 5, screw Pull-in distance from the tip 6 (axial distance between the relief tip 5 and the screw tip 6) d, the axial length e of the relief, and the corner closest to the drill tip 6 of the auxiliary cathode (relief) 5 and the radial distance f between the drill center line g and the like. Further, depending on the shape of the relief, as shown in FIGS. 3 and 4, instead of the relief width b, the radial distance width b1 between the side surface of the drill portion 1 and the tip 5 of the relief, and the drill portion 1 Alternatively, the radial distance b2 between the side surface and the radial outermost portion 7 of the relief may be used. The above a to f, b1, and b2 are defined as parameters.

  The most important of the above parameters is the radial distance f between the corner closest to the drill tip of the auxiliary cathode (relief) and the drill center line, and the shorter the distance f, the greater the effect as the auxiliary cathode. . The value of f is preferably (the radius of the drill part 1 + 3 mm) or less, and more preferably (the radius of the drill part 1 + 2 mm) or less.

  The next most important parameter is the pull-in distance d. If this distance exceeds 2 mm, the escape effect becomes extremely small, so that it is within 2 mm. Further, the smaller d is in the range of 0 or more, the larger the effect is. However, in consideration of positioning during the joining operation, it is preferably 0.5 mm or more.

  It is also possible to make d negative, that is, a shape protruding from the tip of the screw. Moreover, it may not be necessary to consider the conditions such as the shape as described below. However, since the relief protrudes from the tip of the screw, there is a possibility that another problem may occur in workability such as an obstacle to accurate positioning of the screw at the time of construction.

  Next, it goes without saying that the greater the number of escapes, the greater the effect. Moreover, it is necessary to install a plurality of reliefs in contrast to the balance when rotating the screw. For this reason, it is preferable that the number of escapes is two or more. However, in actual mass production of the screw of the present invention, it is practical to use two, because the current manufacturing technology of the screw with reamer is applied, and the effect of escape is not the number, but the shape and area. -It is preferable to control at the installation position.

  The relief thickness a is preferably thicker from the viewpoint of securing an area as an auxiliary cathode, and is preferably 0.4 mm or more. On the other hand, from the viewpoint of a sharp shape for concentrating current, ease of escaping and falling off at the time of screw joining, and difficulty in catching the steel material due to escaping, it is preferable that the thickness a of escaping is thin. It is preferable to be 2 mm or less. The thickness a is preferably set in accordance with the effect required within the above range and the size of the screw. In order to facilitate the release of the relief in the screw fastening process, it is preferable that the thickness of the joint portion between the drill screw and the relief is 0.1 to 0.5 mm thinner than the relief thickness a.

  The escape width b is preferably 1.5 mm or more. This is because if it is less than 1.5 mm, the relief effect is not clear regardless of the size and type of the drill screw.

  In the case of the screw having the shape shown in FIG. 2, b is limited to 3 mm or less from the above condition f. In order to increase the relief area by increasing the relief area, for example, the shapes shown in FIGS. 3 and 4 may be selected. In this case, it is necessary to consider the full width b2 of the relief and the distance b1 from the screw to the tip portion separately as parameters. The total escape width b2 is set to a size that provides the necessary auxiliary cathode effect. In addition, for the relief 4 having the shape shown in FIGS. 3 and 4, since “b1 + screw radius” corresponds to “the distance f between the corner of the auxiliary cathode and the tip of the drill”, b1 is 3 mm or less, preferably 2 mm. Less than. In addition, it is preferable that both b1 and f have such a size as to be hidden by the screw seating surface even when a flaw is attached to the steel material or the like at the time of joining. In addition, although there is no restriction | limiting in the upper limit of b2 from the function as an auxiliary electrode, From an effect and the point on manufacture at the time of integral molding, it is preferable to set it as 3 times or less of the diameter of the drill part of a screw.

  The axial length e of relief is preferably 5 mm or more and 15 mm or less. The effect as the auxiliary cathode is influenced by the shape and width (b, b1, b2) of the escape, but is sufficiently manifested by setting e to 5 mm or more. Increasing the length e does not change the effect. On the contrary, if the length e is too long, the possibility that it will not drop off during construction increases. Is preferably 15 mm or less.

  By providing a relief between the screw tip and the thread forming portion so as to satisfy the above conditions, the plating thickness of the screw tip and the cutting edge can be made 30 μm or less, and the workability of the screw is Greatly improved.

  Hereinafter, the present invention will be described in detail using examples.

  The relief of various dimensions as shown in Table 1 is joined to the tip of the pan head drill screw having a thread diameter of 4 mm by soldering, and this relief screw is 1 and the normal drill screw is 5 They were mixed and galvanized by barrel plating. The plating bath was a chloride bath using commercially available additives. The electrolysis current and electrolysis time were adjusted so that the screw head plating thickness was 20 μm.

  In the plating thickness measurement part, the screw head was the top of the side of the pan-like head, directly above the part in contact with the steel plate, and the most advanced part of the drill screw. The plating thickness was measured by embedding a screw after completion of plating in a resin and polishing it to prepare a sample for observing the cross section of the measurement target portion, and measuring the plating thickness of the screw head and the most advanced portion with a microscope. Measurement was performed on three screws for each condition, and the average value was used as evaluation data.

  For corrosion resistance, the screw is joined to a hot-dip galvanized steel sheet with a plating thickness of about 20 μm with an electric screwdriver, and the salt spray test (JIS Z 2371) is performed with the screw head protruding as the test surface. Compared to a commercially available drill screw (pure galvanized 20 μm, no. 1), it was confirmed that there was no difference in corrosion resistance.

  Workability is in accordance with JIS B 1059, using an electric screwdriver with no load at 2500 rpm and a maximum torque of 140 N · m, joining 10 screws to a rolled steel plate with a plate thickness of 1.0 mm and Vickers hardness of 120 to 130 The required time was measured and compared with a commercially available drill screw (pure galvanized 20 μm, no. 1). As an evaluation method, when the time required for joining was shortened, it was improved, and when it was prolonged, it was indicated as deteriorated, and the difference in required time was indicated in%.

  A relief of the shape of FIG. 4 having various dimensions as shown in Table 2 is joined to the tip of a flanged hexagonal head drill screw having a thread diameter of 4 mm by soldering. Drill screws were mixed at a ratio of 5 and galvanized by barrel plating. The plating bath was a chloride bath using commercially available additives.

  In the plating thickness measurement part, the screw head was measured by microscopic observation of a cross-section sample prepared by embedding polishing in the same manner as in Example 1 and the plating thickness of the top end part of the screw head flange and the drill tip part. Plating was performed under various electrolysis conditions, and corrosion resistance and workability (perforation) were investigated.

  For corrosion resistance, the screw was joined to a galbarium-plated steel plate having a plate thickness of 1.0 mm and a plating thickness of 20 μm, a salt spray test was performed, and the red rust occurrence time of the screw head was examined.

  Workability was evaluated by the same method as in Example 1.

DESCRIPTION OF SYMBOLS 1 Drill part 2 Cutting blade 3 Reamer 4 Relief 10 Shank b Relief width c Relief tip angle d Relief pull-in depth e Relief length b1 Screw-relief tip distance b2 Relief width f Screw tip-relief angle part Distance g Drill screw center line

Claims (4)

In a drilling tapping screw having a shank having a thread on the outer periphery and a drill portion integrally formed at one end of the shank in the axial direction, and at least a surface of the drill portion is zinc-based plated,
The plating thickness of the drill portion at the screw tip is 30 μm or less, and has an auxiliary cathode for controlling the screw tip portion plating adhesion amount between the screw tip portion and the screw thread forming portion. A drilling tapping screw characterized in that detaches when screwing.   2. The drilling tapping screw according to claim 1, wherein a distance between a corner portion closest to a drill tip of the auxiliary cathode and a center line of the drill is equal to or less than a value obtained by adding 3 mm to a radius of the drill portion.   3. The drilling tapping screw according to claim 1, wherein a pull-in distance from the tip of the auxiliary cathode to the corner closest to the tip of the drill of the auxiliary cathode is 2 mm or less.   The drilling tapping screw according to any one of claims 1 to 3, wherein the drilling tapping screw has two or more auxiliary cathodes.

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