JP3773168B2 - Cylindrical injection mold, molding method and molded product - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cylindrical injection molded product, a molding die, and a molding method, in which weld strength is improved by providing a weld line in a spiral shape in an oblique direction with respect to a central axis.
[0002]
[Prior art]
Cylindrical resin injection-molded products are widely used for automobile parts, optical lens barrels, etc., but usually on the opposite side of the gate during molding, a weld line that is linear in the length direction of the cylinder (ie, in the thrust direction) (See FIG. 1), the dimensional accuracy and the strength in the radial direction are likely to decrease. In particular, in the case of a cylindrical molded product provided with a metal insert on the inner side, cracking occurs when the metal and resin have different thermal expansion coefficients when subjected to a cold cycle such as -20 to 100 ° C. for a long time during use. There is an easy problem (see FIG. 2).
Therefore, a method is used in which a film gate is provided on one end face and resin is filled from the circumference on one end face of the cylinder. However, the mold structure is complicated and post-processing is often difficult. . Even if the gate is provided obliquely with respect to the molded product, the weld line is formed almost linearly in the thrust direction, and no improvement is observed. Although there is a method using a rotating core, there is a problem that the mold structure becomes extremely complicated.
[0003]
Japanese Patent Application Laid-Open No. 61-110522 discloses an upper gate portion and a lower gate portion formed at different radial positions on both upper and lower end faces of a cylinder, and the radial wall positions of the both end faces from the different radial directions. A hollow cylindrical forming frame having a thrust weld line partially formed in the thrust direction along the end and an endless weld line formed in an endless manner in a direction crossing the wall surface of the frame body. It is disclosed. However, in this hollow cylindrical frame, a weld line that intersects the Y-shape is formed, so that when the external force is applied or subjected to a cooling cycle for a long time, the intersection point shows the effect of a wedge. Prone to strength problems.
[0004]
[Problems to be solved by the invention]
An object of the present invention, or have a complex structure such as a rotating part, without this causing the Y-weld line of the molded article and the molding an improved tubular injection molded article of the weld strength it mold capable of, it is to provide a no cylindrical injection-molded article of the Y-shaped weld line using molding method using the mold, and the method.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object , the present inventor has provided Y or more to a molded product by providing two or more gates at different positions and filling a resin at a specific distance from the mold parting line. It has been found that the occurrence of a mold weld line can be prevented, thereby achieving the above object , and the present invention has been completed.
[0006]
That is, the present invention is a mold for molding a cylindrical injection molded product in which one or more shallow gates 11 and deep gates 12 are provided on a cylindrical surface of a mold cavity and does not produce a Y-shaped weld line, shallow gate 11 and the depth gate 12, a distance from the tubular mold cavity of one end surface mold parting line 18 provided at a position of 16 to the shallow gate 11 (d '), the cylindrical mold When the distance from the other end surface 17 of the one end surface 16 of the cavity to the deep gate 12 is (d ″) and the cylinder height is (h), d ′ / h and d ″ / h are both less than 0.5. The present invention provides a mold for molding a cylindrical injection-molded product, a method for molding a cylindrical injection-molded product using the mold, and a cylindrical injection-molded product using the method. . The d ′ / h and d ″ / h are preferably in the range of 0 to 0.4, and the positional relationship between the shallow gate 11 and the deep gate 12 as viewed from the upper part of the cylinder end face is alternated. Is preferred.
By using the cylindrical injection molded product molding die of the present invention, the weld line extends from one end surface side to the other end surface side, and has at least a portion formed obliquely with respect to the length direction of the cylinder, A cylindrical injection-molded product having no Y-shaped weld line can be obtained.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
An example of the mold of the present invention is shown in FIGS. 3 and 4, reference numeral 10 denotes a mold cavity for obtaining the tubular molded product 1, 11 is a shallow gate, 12 is a deep gate, 13 is a runner, and 18 is a parting line of the mold. The molten resin from the injection molding machine is filled into the mold cavity from the runner 13 through the gates 11 and 12. Both the shallow gate 11 and the deep gate 12 are provided on the cylindrical surface 15 of the cavity, and their gate positions are represented by positions from the parting line 18 (or one end surface 16 of the cylindrical mold cavity), and the shallow gate is formed. 11 is provided at a position where the distance from the parting line is short, and the deep gate 12 is provided at a position where the distance from the parting line is long. As a result of the resin filled from the shallow gate 11 and the deep gate 12 substantially simultaneously, a weld line 3 oblique to the thrust direction is generated in the molded product as shown in FIG. However, the shallow gate 11 and the deep gate 12 are not on the same thrust line. In the example of FIG. 3, the shallow gate 11 ′ is opposite to the deep gate 12, with the cylindrical central axis as the rotational symmetry axis. Is provided with a deep gate 12 '.
[0008]
The shallow gate 11 may be a side gate that is substantially the same height as the parting line 18, but is provided near the upper part of the cylinder below the parting line 18, and resin is supplied to the gate through a tunnel from the runner. You may make it do. The ratio of the distance (d ′) from the parting line 18 to the shallow gate 11 to the cylinder height (h) (ie, d ′ / h) is less than 0.5, preferably 0 to 0.4. It is done. When it exceeds 0.5, the inclination of the weld line 3 decreases.
Similarly, the distance (d ″) of the deep gate 12 from the other end surface 17 of the one end surface 16 of the cylindrical mold cavity is the ratio of the distance (d ″) to the cylinder height (h) (ie, d ″). / H) is less than 0.5, preferably 0 to 0.4.
Although the distance (d ′) and the distance (d ″) depend on the distance (d) between the shallow gate 11 and the deep gate 12, the weld line 3 is slanted from the one end surface 6 to the other end surface 7 of the molded product 1. May be the same as or different from each other as long as the Y-shaped weld line is not generated.
[0009]
In the present invention, the entire gate including the shallow gate 11 and the deep gate 12 is referred to as a stepped gate. The stepped gate may be provided with an intermediate gate having a depth between the shallow gate 11 and the deep gate 12 depending on the molded product. The number of shallow gates 11 and deep gates 12 provided in the stepped gate may be plural, and the number of shallow gates 11 and deep gates 12 may be the same or different. 11 and deep gate 12 are provided alternately, preferably in point symmetry or line symmetry (see FIG. 6). When it is desired to improve the weld strength over the entire circumference, the shallow gates 11 and the deep gates 12 are provided in the same number, preferably an even number of two or more points, and it is not necessary to improve the weld strength over the entire circumference. For example, the number of shallow gates 11 may be one or less than the number of deep gates 12 in order to improve the weld strength only locally, such as in a thin portion, or may be an odd number.
[0010]
The number of the shallow gates 11 and the deep gates 12 is not particularly limited, but the actual distance (d) along the cylindrical surface of the shallow gates 11 and the deep gates 12 and the cylinder height (h) of the molded product 1 The ratio (ie h / d) is selected to be less than 1. If the distance (d) is too larger than the above range, a Y-shaped weld line is formed. The smaller the distance (d), the less the inclination of the weld line 3 and the weaker the effect of the present invention.
The number of shallow gates 11 and deep gates 12 is usually 1 or more and 20 or less, respectively, and in many cases 2 or more and 10 or less. The larger the number of gates, the more the stress is dispersed and the more difficult it is to break. However, when the number is too large, there arises a problem that the manufacturing cost of the mold increases.
[0011]
The stepped gate may be provided at any position inside or outside the cylindrical molded product 1. When the molded product 1 is cylindrical and the inner diameter is φ5.0 mm or less, there are restrictions such as difficulty in providing a gate on the inside, and inability to provide a gate on the side with a metal insert. Are not restricted by the size, length, thickness, etc. of the cylindrical molded product. Further, the relationship between the height (h) and the radius (r) of the cylindrical molded product is not particularly limited.
The amount of resin filled from each gate is not particularly limited, but is preferably substantially the same amount.
[0012]
FIG. 7 is a developed view of the cylindrical surface 5 of the cylindrical molded product of an example of the present invention obtained by a cylindrical mold provided so that the shallow gate 11 and the deep gate 12 are provided at two equal intervals. It is. Assuming that the angle formed with the end surface 6 of the weld line 3 generated in the molded product 1 is θ, when the tensile force F acts in the circumferential direction, the force F ′ acting perpendicular to the weld line 3 is expressed by the following formula (1). expressed.
F ′ = F × sin θ (1)
It is better that θ is smaller as long as the Y shape does not occur in the weld line. The effect is less likely to appear as the angle approaches 90 degrees.
In the above range, the force applied perpendicular to the weld line is reduced by about 10 to 30% so that F ′ = 0.71 F when θ is 45 degrees and F ′ = 0.87 F when θ is 60 degrees. .
On the other hand, the length (L) of the weld line becomes longer with respect to the weld length (that is, the cylinder height h) when θ is 90 degrees, so that the weakened portion increases, but the weld line length per unit length of the weld line increases. Since the tearing force becomes small, it becomes difficult to break.
[0013]
The cylindrical molded article 1 may be a cylinder, a polygonal cylinder, or a kamaboko type. The diameter does not have to be constant in the height direction, and may be, for example, a truncated cone other than a cylinder, or a stepped cylinder or a truncated cone. The height may not be constant over the entire circumference of the diameter, and may be a shape obtained by obliquely cutting a cylindrical portion or the like.
[0014]
The metal insert used in the present invention may be of any material and surface shape (knurling or the like).
The resin may wrap around the back surface of the metal insert by insert molding. That is, resin may be present on both the inside and outside of the metal insert. However, the outer resin is effective in preventing cracking.
When the metal insert is provided in the intermediate layer of the molded product, the resin may be filled from the outside of the molded product or from the inside.
[0015]
The type of molding resin is not particularly limited as long as it is a resin that can be injection-molded. General-purpose resins such as polyolefins such as polyethylene and polypropylene, polystyrene and polyvinyl chloride; aromatic or aliphatic polyesters, polyamides, polycarbonates, and polyacetals , Liquid crystalline polymers, engineering plastics such as polyphenylene ether and polyphenylene sulfide, and other celluloses. These can also be used as a mixture. These resins may be new or recycled. These resins may contain various resin additives, fillers, reinforcing materials such as glass fibers. In the case of a resin composition having a strong tendency to reduce the weld strength in which the reinforcing material is blended, the effect of the present invention is more exhibited.
[0016]
【Example】
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
[0017]
Example 1
FIG. 8 is a diagram showing a result of analyzing the formation state of a weld line of a molded product molded using a four-point gate by CAE (resin flow analysis). Two shallow gates are provided on the opposite side of the upper surface of the cylinder at a position 5 mm from the upper end surface. Two deep gates are provided on the opposite side of the upper surface of the cylinder at a position 5 mm from the lower end surface. The shallow gate and the deep gate are shifted by 90 degrees when viewed from the upper end surface side. The height of the molded product is 30 mm, and the diameter is 44 mm.
Resin: Reinforced polybutylene terephthalate resin containing 30% by weight of glass fiber Temperature: 260 ° C.
Mold temperature: 60 ℃
Injection flow rate: 4.9 cm ³ / s
Analysis model: Shell element (960 mesh)
As a result, as shown in FIG. 8, an oblique weld line is generated with respect to the length direction of the cylinder, and cracks are less likely to occur even in the case of a molded article having a metal insert.
[0018]
(Example 2)
FIG. 9 is a diagram showing a result of analyzing the formation state of a weld line of a molded product molded using a 6-point gate by CAE (resin flow analysis). Three shallow gates are provided at a position of 5 mm from the upper end surface and shifted by 120 degrees on the upper surface of the cylinder. In addition, three deep gates are provided at a position 5 mm from the lower end surface, shifted by 120 degrees on the upper surface of the cylinder. The shallow gate and the deep gate are shifted by 60 degrees when viewed from the upper end surface side. The height of the molded product is 30 mm, and the diameter is 44 mm.
As a result, as shown in FIG. 9, an oblique weld line is generated with respect to the length direction of the cylinder, and cracks are less likely to occur even in the case of a molded product having a metal insert.
[0019]
【The invention's effect】
According to the present invention, when a cylindrical molded product is injection-molded, the circumferential strength is improved by making the gates arranged differently and providing an angle between the direction in which the stress is generated and the weld line.
[Brief description of the drawings]
FIG. 1 is a view showing a weld line of a conventional cylindrical injection molded product.
FIG. 2 is a diagram showing the occurrence of cracks in a conventional cylindrical injection molded product.
[Figure 3] cylindrical injection molding products mold of an example of a cavity of the present invention, the gate is a perspective view showing a runner.
[4] tubular injection molding products mold of an example of a cavity of the present invention, the gate is a cross-sectional diagram showing an example of a runner.
FIG. 5 is a view showing a weld line as an example of a cylindrical injection molded product of the present invention.
6 is a top view of an example of a cylindrical injection molding products mold of the present invention.
FIG. 7 is a development view of a cylindrical surface of an example of a cylindrical injection molded product of the present invention.
FIG. 8 is a diagram showing an example of resin flow analysis of a cylindrical injection molded product by the molding method of the present invention.
FIG. 9 is a diagram of another example of resin flow analysis of a cylindrical injection molded product by the molding method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cylindrical injection molded product 2 Metal insert 3 Diagonal weld line 4 Weld line formed in the thrust direction 5 Molded product cylindrical surface 6 Molded product one end surface 7 Molded product other end surface 10 Mold 11 Shallow gate 11 'Shallow gate 12 Deep gate 12 'Deep gate 13 Runner 14 Cylindrical surface 16 of gate 15 cavity One end surface 17 Other end surface
18 Parting line

Claims (6)

A mold for molding a cylindrical injection-molded product in which one or more shallow gates 11 and deep gates 12 are provided on a cylindrical surface of a mold cavity and does not generate a Y-shaped weld line. The deep gate 12 has a distance (d ′) from the mold parting line 18 provided at the position of the one end face 16 of the cylindrical mold cavity to the shallow gate 11, and the one end face 16 of the cylindrical mold cavity. When the distance from the other end surface 17 to the deep gate 12 is (d ″) and the cylinder height is (h), d ′ / h and d ″ / h are both set to be less than 0.5. A mold for forming a cylindrical injection molded product.   The cylindrical injection-molded product molding die according to claim 1, wherein both d '/ h and d "/ h are in the range of 0 to 0.4.   The mold for molding a cylindrical injection molded product according to claim 1 or 2, wherein the positional relationship between the shallow gate 11 and the deep gate 12 as viewed from the upper part of the cylinder end surface is alternate. Metal insert, provided on the inside of the molded product resin portion of the pre-pre-Symbol mold cavity, cylindrical injection-molded article mold according to any of claims 1 to 3. Using a mold according to any of claims 1 to 4, characterized in that filling the shallow gate 11 and the depth gate 12 or we simultaneously resins, molding method of the cylindrical injection-molded article.   A cylindrical injection formed by the molding method according to claim 5, wherein a weld line extends from one end surface side to the other end surface side of the cylinder and has at least a portion formed obliquely with respect to the length direction of the cylinder. Molding.

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