JP2013202964A - Insert fitting and method for insert molding of plastic using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insert fitting capable of preventing occurrence of cracks only by slight change, and a method for insert molding of plastic using the same.SOLUTION: An insert fitting 3 includes an embedded part 4 having a knurl part 4a on an outer periphery, and an exposed part 5 having an end surface exposed from plastic. The exposed part 5 has a diameter smaller than that of the embedded part 4, and has a chamfer part 5a on an outer periphery of the end surface. Even in the insert fitting having the knurl on which cracks easily occur, the occurrence of the cracks can be prevented without deteriorating fixing strength. In a method for insert molding, insert molding is performed after the insert fitting 3 is completely degreased, and thereby, occurrence of the cracks can be completely prevented.

Description

  The present invention relates to an insert fitting to be inserted at the time of plastic injection molding and an insert molding method using the fitting, and more particularly to one that prevents the occurrence of cracks around the insert fitting.

  Conventionally, for the purpose of increasing the strength of plastic parts, insert molding in which insert metal fittings are inserted during plastic injection molding has been performed. In this insert molding, there is a problem that cracks occur in the plastic around the insert fitting due to the difference in expansion coefficient between metal and plastic, and various measures have been taken to prevent the occurrence of cracks.

The countermeasures were as follows.
(1) In order to enhance the adhesion between the plastic and the insert fitting, the cutting oil adhering when the insert fitting is cut is removed.
(2) In order to remove the residual stress at the time of plastic molding, annealing is performed until just before the molding temperature.
(3) In order to reduce the temperature difference between the plastic that reaches a temperature of about 250 ° C. during molding and the insert fitting at room temperature, the insert fitting is warmed to reduce the influence of expansion and contraction.
(4) Modify the metal fittings and adjust the thickness of the plastic part around the insert metal fittings.
(5) By adjusting the mold and changing the molding conditions, the flow of plastic is adjusted to prevent the occurrence of weld lines.
(6) Eliminate the sharp edge of the outer shape of the insert bracket.

  Further, in order to prevent the occurrence of cracks, the composition of the composite material for injection molding has been changed, and the ferrite to be inserted is surface-treated with a phosphoric acid compound depending on the material (for example, Patent Document 1). And 2).

JP 2004-10830 A JP 2007-281181 A

  Any of the above countermeasures against cracks must be set by changing the conditions according to the molding material used and the shape of the insert metal fittings. Specifically, it is ambiguous how to prevent the occurrence of cracks. However, there was a problem that it was only possible to cope with repeated prototypes.

  In particular, changes in molds, molding materials, or significant changes in the shape of the insert fittings are very costly and cannot be done easily and must be handled with limited measures. It was.

  The problem to be solved by the present invention is to solve the above-mentioned problems of the prior art, and to provide an insert metal fitting that prevents the occurrence of cracks with only a slight change, and a plastic insert molding method using the same.

  The insert fitting of the present invention is a cylindrical insert fitting inserted at the time of injection molding of plastic, and is buried in the plastic and has a buried portion in which a knurled portion is formed on the outer periphery, and an end face on the surface of the plastic And a chamfering process is performed on the outer periphery of the end surface, and an exposed portion having a diameter smaller than that of the buried portion is provided. The exposed portion of the insert metal fitting is provided in a range of 1/5 to 1/2 of the entire length. Moreover, the said exposed part becomes 1-2 mm in diameter smaller than the said buried part.

  Moreover, the plastic insert molding method using the above-mentioned insert metal fitting of the present invention is a product in which the plastic insert molding is performed after the insert metal fitting is completely degreased. In the plastic insert molding method, the insert fitting is made of stainless steel, and the complete degreasing is made of a pasipate treatment.

  In the insert metal fitting according to the present invention, a knurled portion is provided on the outer periphery of the buried portion buried in the plastic, and an exposed portion whose end surface is exposed from the plastic is provided to make the diameter smaller than the buried portion and the outer periphery of the end surface is chamfered. This prevents the generation of cracks. For this reason, even with an insert fitting provided with a knurling that is likely to generate cracks, the occurrence of cracks can be prevented with only slight changes without reducing the fixing strength thereof.

  Moreover, in the insert molding method of this invention, after using the said insert metal fitting and degreasing it completely, generation | occurrence | production of a crack is prevented reliably by insert molding. For this reason, the occurrence of cracks can be almost completely prevented by a slight change.

It is principal part sectional drawing which shows the insert molding part formed using the insert metal fitting and insert molding method which concern on one Example of this invention. It is a top view which shows the example of a case which has an insert molding part shown in FIG. It is a center longitudinal cross-sectional view of the case shown in FIG. It is a side view of the insert metal fitting shown in FIG. It is a side view which shows the insert metal fitting used conventionally.

  First, the insert molding part formed using the insert metal fitting and the insert molding method in the present invention will be described. 2 and 3 are a plan view and a central longitudinal sectional view showing an upper case of a surveillance camera or the like formed by plastic injection molding. The upper case 1 is hermetically sealed by screwing it to a lower case (not shown) and accommodates a camera or the like inside. In the case of such an upper case 1, it is most suitable to form it with a plastic (for example, polycarbonate, etc.) that is excellent in weather resistance, lightweight and easy to mold. However, the boss 2 to which the screw is screwed is required to have a strength capable of firmly screwing the screw or repeatedly attaching and detaching the screw. For this reason, in order to form a metal screw hole in the boss 2, the boss 2 is formed as an insert molding portion by injection molding the upper case 1 by an insert molding method in which a cylindrical insert fitting is embedded.

  As shown in FIG. 1, the insert molding portion in this embodiment is formed by insert-molding an insert fitting 3 made of stainless steel or the like inside a cylindrical boss 2 molded of plastic such as polycarbonate. . The insert fitting 3 has a cylindrical shape, and in the present embodiment, the inside is a screw hole. Further, as shown in FIGS. 1 and 4, the insert metal fitting 3 includes an embedded portion 4 that is entirely embedded in a plastic boss 2, and an exposed portion 5 whose end surface 5 a is exposed on the surface of the boss 2. Is provided.

  The buried portion 4 of the insert fitting 3 is provided with a knurled portion 4a made of fine irregularities formed by a mesh-like groove or the like on the outer periphery thereof. Further, a chamfered portion 4 b that is chamfered so as to drop the corner is provided on the outer periphery of the end surface (lower end in the drawing) of the buried portion 4, and the corner is dropped at the boundary with the exposed portion 5. A chamfered portion 4c is provided by chamfering.

  Further, the exposed portion 5 of the insert metal fitting 3 is formed so as to be smaller in diameter than the buried portion 4. The outer peripheral surface of the exposed portion 5 is a smooth surface without unevenness formed by cutting. On the outer periphery of the end face (upper end in the figure) of the exposed portion 5, a chamfered portion 5a that is chamfered so as to drop the corner is provided.

  By using the insert fitting 3 having the above-described configuration, the buried portion 4 and its knurled portion 4a bite into the boss 2 at the time of molding, and the insert fitting 3 rotates in the boss 2 or from the boss 2 to the insert fitting. 3 prevents the withdrawal. Further, a small-diameter exposed portion 5 not provided with a knurled portion is located in the vicinity of the end portion 2a of the boss 2 where cracks are easily generated, and is further exposed by the chamfered portion 5a of the exposed end surface. The stress at the end of the portion 5 can be prevented from concentrating in the radial direction of the end 2a of the boss 2, and the occurrence of cracks can be prevented.

  With respect to the length of the buried portion 4 or the exposed portion 5 with respect to the entire length of the insert metal fitting 3 and the numerical value for making the exposed portion 5 smaller in diameter than the buried portion 4, the insert metal fitting 6 shown in FIG. Appropriate values were obtained by adding. This insert metal fitting 6 has a cylindrical shape, a knurled portion 6a is formed on the entire outer periphery, and the end face is not chamfered. An experiment was conducted to see how much cracking could be suppressed when using a modified insert fitting compared to when insert molding was performed using the insert fitting 6.

  First, paying attention to the fact that cracks are generated by the knurled portion 6a, experiments were performed with various changes in the presence or absence of the knurled portion 6a. When the knurled portion 6a was not formed at all, not only the structure related to the rotation of the insert fitting 6 and prevention of removal was weakened, but also cracks were observed. Moreover, the chamfered part was formed in the outer periphery of an end surface, without touching the knurled part 6a. Also in this case, since the occurrence of cracks is recognized, when the region for forming the knurled portion 6a is gradually reduced, for example, when the total length is 8 mm, the knurled portion 6a is removed from the end surface by 1.5 mm or more. The occurrence was greatly reduced. In consideration of this, the knurled portion 6a was left about half of the entire length in consideration of the reliable prevention of rotation and removal of the insert fitting. As a result, a portion where the knurled portion 6a is not formed is provided in the range of 1/5 to 1/2 of the entire length, and the occurrence of cracks can be almost prevented by chamfering the outer periphery of the end surface.

  At this time, the knurled part 6a was removed and the outer diameter of the part was made smaller and thinner, but about 1-2 mm necessary for removing the groove of the knurled part with respect to the diameter of 5 mm. It was judged that a sufficient effect was recognized only by the reduction, and that further reduction would only lead to a decrease in the strength of the entire insert fitting. As a result, it has been found that the part where the knurled part is not formed only needs to be 1 to 2 mm smaller than the part where the knurled part is formed.

  In view of the above results, the shape of the insert fitting 3 is set as shown in FIG. 4, and chamfered portions 4b and 4c are provided to remove all corners.

  On the other hand, the insert molding method was also improved, and after the formation of the insert fitting 3, oil removal was performed mainly for the purpose of removing chips, but this was changed to complete degreasing. . In this example, since the insert fitting 3 is made of stainless steel, complete degreasing was performed by applying a pasipate treatment. When complete degreasing by this pasipate treatment was performed, even when the insert fitting 6 having the shape shown in FIG. 5 was used, the occurrence of cracks was reduced to 1/2 to 1/3, which was greatly improved. . For this reason, in this invention, generation | occurrence | production of a crack was able to be suppressed completely by performing insert molding combining the insert molding method which performs this complete degreasing, and the insert metal fitting 3 which makes the shape mentioned above.

  In this embodiment, insert molding is performed with a combination of polycarbonate and stainless steel. However, the present invention can also be applied to a combination of polycarbonate and brass, ABS resin and stainless steel, or the like.

DESCRIPTION OF SYMBOLS 1 Upper case 2 Boss 2a End part 3 Insert metal fitting 4 Buried part 4a Knurled part 4b, 4c Chamfer part 5 Exposed part 5a Chamfer part 6 Insert metal fitting 6a Knurl part

Claims (5)

A cylindrical insert fitting that is inserted during plastic injection molding,
Buried in the plastic, buried part in which a knurled part is formed on the outer periphery, and
An end face is exposed on the surface of the plastic, and the outer periphery of the end face is chamfered, and an exposed portion having a diameter smaller than the buried portion,
Insert metal fittings characterized by comprising. The insert fitting according to claim 1, wherein the exposed portion is provided in a range of 1/5 to 1/2 of the entire length. The insert fitting according to claim 2, wherein the exposed portion is smaller by 1 to 2 mm in diameter than the buried portion. A plastic insert molding method, wherein the insert metal fitting according to claim 1 is used, the plastic insert molding is performed after the insert metal fitting is completely degreased. 5. The plastic insert molding method according to claim 4, wherein the insert fitting is made of stainless steel, and the complete degreasing is made of a pasipate treatment.

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