JP4085182B2 - Extrusion pin in injection molding - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an extrusion pin in injection molding in which various products are manufactured by filling a molten raw material into a mold.
[0002]
[Prior art]
In the injection molding operation to obtain a product by pressurizing and filling a molten material into a mold, it is necessary to quickly and surely spread the filled material throughout the interior space of the mold, which is the point of the mold design and filling machine Improvements are accumulated and technical progress is recognized. The general procedure of such work is as shown in FIG. 8 to FIG. 10, and the raw material supplied from the hopper H to the superheated cylinder M by the injection plunger I is melted, and the nozzle N and the cavity as shown in FIG. The movable plate B supporting the core C and the protruding pin E is united with the fixed plate A supporting the tee K, and injection from the nozzle N is performed. When the filling is finished, the movable platen B is separated from the fixed platen A, and at the same time, the protruding pin E protrudes from the core C, and the molded product engaged with the core C is separated from the core C to obtain a finished product. By repeating the above steps continuously, a large number of injection molded articles having the same shape are produced.
[0003]
Injection molding is the same idea as traditional metal casting with metal molds, so when material is poured into the mold, it is necessary to discharge the air inside the mold to the outside. Has been devised. At present, it is common to adopt a method of venting gas from the space installed around the protruding pin E to the movable platen B side. However, with good degassing effect, it is inevitable that the material flows into the space and a large amount of burrs are generated in the resulting product, which is different from the metal mold casting that has obtained the product by its own weight. Is needed. In addition to the problem of burrs, in the case of injection molding using synthetic resin, high-precision molds that can eliminate secondary processing after molding are now available. Surface finishing by molding, production of transparent products It has been discovered that this degassing is of great importance in terms of, etc.
[0004]
Various proposals have been made so far to solve these problems of degassing, but the point is to achieve how quickly and properly degass depending on the structure of the parts or the material of the parts. For example, the structure of the protruding pin disclosed in Japanese Patent Application Laid-Open Nos. 61-235108 and 8-197592 has been disclosed in the past.
[0005]
[Problems to be solved by the invention]
The problem to be solved is how to quickly and smoothly discharge the gas generated from the superheated material at the time of filling from the inside of the cavity, how to devise so that the material does not flow into the means for discharging, These two points are exhausted. When degassing is not performed quickly and smoothly, the effect of residual gas occurs at unspecified parts inside the mold, and the detailed pattern that should appear on the surface of the product disappears, resulting in a simple glossy surface. The surface of the mold before and after the work to remove the rough surface due to the corrosion and contamination of the mold surface, and the silver wire pattern (silver) appears radially around the vent hole There is a problem that the injection pressure needs to be set high in order to repeatedly perform cleaning and to perform degassing more quickly and reliably. Conventionally, all of these problems are unavoidable in the operation of injection molding, and it has been considered that these problems should be solved by materials, heating temperature, injection pressure, equipment maintenance, and the like.
[0006]
[Means for Solving the Problems]
The present invention follows the conventional idea of using a protruding pin for degassing as it is, speeds up degassing by improving its structure, and prevents the flow of material into the degassing hole as much as possible. The problem was solved by utilizing the difference in density between the gas to be removed and the material to be filled. The structure for that purpose is not a desk plan calculated from fluid theory, but a simple one that has been repeatedly accumulated through actual use, and this has not been proposed in various disclosure examples in the past. It is not.
[0007]
In general, various fluids including gas flow while maintaining the initially applied pressure and flow velocity if the inner diameter of the flow path is constant. For example, when the fluid flows horizontally from left to right, as shown in FIG. When the diameter-reduced portion W exists in the flow direction, the pressure increases on the left side X of the diameter-reduced portion and the pressure decreases on the right side Y. At the same time, the flow velocity is decelerated on the left side of the reduced-diameter portion and accelerated on the right side. It has been known. Such a phenomenon has been widely used for various operations.
[0008]
In the present invention, the fact that the pressure on the upstream side of the reduced diameter portion W is increased is used to prevent the filled resin from flowing into the degassing gap, and at the same time, the flow velocity on the downstream side of the reduced diameter portion W is increased. The main point of the present invention is to take measures for degassing by utilizing the above. For this purpose, the ejector pin is processed, but in that case, the tip of the ejector pin is slightly cut off and a gas vent passage is continuously formed in the cut portion instead of performing special processing. All problems are solved by drilling.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, an embodiment of the present invention will be described. In FIG. 1, reference numeral 1 denotes a projecting pin slidably inserted into a pin hole 3 on a movable platen side 2, 4 is a fixed platen side having a cavity 5, and 6 is movable. A core 7 installed on the panel side 2 is a product filled in a mold space formed by the cavity 5 and the core 6.
[0010]
The main part of the projecting pin 1 is as shown in FIGS. 2, 3 and 4, and the distal end portion 1a facing the cavity 5 of the projecting pin 1 having a circular cross section that is slidably inserted into the pin hole 3. Is formed so as to be narrowed toward the rear end 1b on the opposite side, and the peripheral edge of the protruding pin 1 is obliquely cut out at one or more positions to form a cutout portion 1c, and the narrowed portion W of the cutout portion 1c protrudes. The pin 1 opens in a gas vent groove 1d formed in the rear end 1b.
[0011]
When the protruding pin 1 according to the present invention is inserted into the pin hole 3 and the fixed platen side 4 and the movable platen side 2 are combined as shown in FIG. 1 in preparation for filling, the inner wall of the pin hole 3 and the cutout portion of the protruding pin 1 A structure similar to that of FIG. 11 is created by 1c, the narrowed portion W and the gas vent groove 1d. As a result, when filling is started, the gas flows into the cutout portion 1c and is compressed by the narrowed portion W, and then rapidly flows into the degassing groove 1d, and from the degassing groove 1d quickly due to the decompression effect. Although it is discharged, it is compressed in the notch 1c and the pressure increases, so that the pressure prevents the molten resin from flowing into the notch 1c as necessary. As a result, the two purposes of quickly venting and preventing the resin from flowing into the notch 1c are reliably achieved.
[0012]
A further feature of the present invention is that the manufacturing accuracy of the cutout portion 1c, the narrowed portion W, and the gas vent groove 1d is not a problem. For example, a protruding pin in a round bar state may be manually machined with a glider or the like. , Can fully achieve its purpose. However, exemplifying the dimensions of the specific example, in the protruding pin in accordance with the international standard of circular cross section, the cross-sectional diameter (diameter of the tip portion 1a in FIG. 3) is 6 mm, the notch portion 1c is 2 mm wide, and the narrowed portion It is desirable to manufacture an actual protruding pin with a width of 0.1 to 0.2 mm of W and a width of 2 mm of the gas vent groove 1d. The size of each of the perforated portions is preferably finely adjusted depending on whether the material to be filled has good fluidity.
[0013]
FIG. 5 is a cross-sectional view of the second embodiment of the present invention. Instead of providing a notch 1c, a narrowed portion W and a gas vent groove 1d on the surface of the projecting pin 1, the projecting pin 1 ′ is shown. The cutout portion 1c is provided with portions equivalent to those, and by devising the planar shape of the notch portion 1c, it is possible to obtain a protruding pin 1 'that can withstand practical use.
[0014]
6 and 7 show a third embodiment, which is a protruding pin having a rectangular cross section. Also in this case, the same effects as those of the first and second embodiments having a circular cross section can be achieved by forming the notch 1c, the narrowed portion W, and the gas vent groove 1d on the side surface. Further, the one illustrated in FIGS. 1 to 7 is provided with two notches 1c for one protruding pin 1, but the number of notches 1c is arbitrary and necessary. Accordingly, the peripheral edge of the tip 1a may be cut over the entire circumference in the previous week. The number of the gas vent grooves 1d is also arbitrary, but the narrowed portion W is the same as the number of the gas vent grooves 1d.
[0015]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a protruding pin that can quickly degas and eliminate the occurrence of burrs only by performing extremely simple processing on the protruding pin, and as a result, in an unspecified portion inside the mold. Eliminates the situation where detailed patterns that should appear on the surface of the product due to the effects of residual gas disappear, resulting in a simple glossy surface, and a silver line pattern (silver) appears radially around the vent hole. This eliminates the inconvenience of fouling the product, prevents corrosion and fouling of the mold surface with gas, and eliminates all the conventional problems such as setting the injection pressure high.
[Brief description of the drawings]
FIG. 1 is an overall cross-sectional view of an embodiment of the present invention.
2 is a cross-sectional view of the main part of what is shown in FIG. 1. FIG.
FIG. 3 is a plan view of the ejection pin of the example shown in FIG. 1;
4 is a side view of the ejection pin shown in FIG. 1. FIG.
FIG. 5 is a cross-sectional view of a second embodiment.
FIG. 6 is a plan view of a third embodiment.
FIG. 7 is a front view of a third embodiment.
FIG. 8 is a conceptual diagram of a conventional injection molding apparatus and shows a state where the apparatus is not instructed before filling.
9 shows the operation injection state of FIG. 8. FIG.
FIG. 10 shows the operation state of the ejecting pin after the injection in FIG. 8;
FIG. 11 is a schematic diagram showing the principle of degassing used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Extrusion pin 1a Front end part 1b Rear end part 1c Notch part 1d Gas vent groove W Narrow part 2 Movable board side 3 Pin hole 4 Fixed board side 5 Cavity 6 Core 7 Product

Claims (3)

In the projecting pin in which the projecting pin that is slidably inserted into the pin hole drilled in the mold on the core side is installed so as to project into the cavity,
The cross-sectional area other than the projecting pin with respect to the cross-sectional area of the pin hole becomes wider toward the tip part facing the cavity of the projecting pin, and the cross-sectional area of the pin hole toward the rear end part of the projecting pin At least one edge of the projecting pin is diagonally cut out to form a notch so that the cross-sectional area other than the projecting pin becomes narrower, and the projecting to the cross-sectional area of the pin hole toward the rear end of the notched portion A projecting pin characterized in that a portion other than the pin having the narrowest cross-sectional area opens in a gas vent groove formed toward the rear end of the projecting pin. The extrusion pin according to claim 1, wherein the cross section is circular. 2. The ejection pin according to claim 1, wherein the cross section is polygonal.

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