JPS59198127A - Injection molding - Google Patents

Abstract

PURPOSE:To obtain a high accuracy product free of flaws such as surface sink by a method wherein a small amount of melt molding material is jetted into a cavity to be attached to the entire wall surface and then, a pressure air is injected into hollows therein to solidify it under pressure. CONSTITUTION:A smaller amount of melt molding material than the internal capacity of a cavity is jetted into the cavity in a mold 60 held at the temperature below the solidifying point of the molding material from a small-diameter jet hole so as to be attached to the entire wall surface of the cavity. A pressure air is injected from the jet hole before the molding material is solidified as a whole to solidify the all molding material with the hollow within the molding material pressurized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for injection molding a disappearing model used in investment casting such as lost wax casting or a thermoplastic molded article.

(Prior Art) It is widely practiced to make disappearing models (hereinafter referred to as wax models) used in investment casting and thermoplastic plastic molded products by injection molding.

In this case, the wax model etc. shrinks due to cooling after injection molding, so it is made slightly larger than the final product. However, when a wax model or the like has a relatively wide flat area, the shrinkage of the thermoplastic molding material causes the horizontal shape and surface of the molded product to become depressed, resulting in so-called surface deviation. This causes a problem that the dimensional accuracy of the final product deteriorates.

Conventionally, in order to prevent this surface deviation, a layer of other thermoplastic material was embedded in advance in the thick part of the wax barrel, etc., or a core was incorporated into the mold cavity. It was practiced to store meat in wax barrel shapes. However, all of these methods have low productivity and are not suitable for mass production.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an injection molding method that does not cause surface deviation and is suitable for mass production of high-precision wax models and plastic molded products. With the goal.

(Structure of the Invention) In order to achieve this object, the present invention injects hot molten molding material into the mold cavity from a small-diameter nozzle to generate a turbulent flow of the molding material in the cavity, and cools the molding material. While solidifying this molding side slope into a shell shape on the inner surface of the mold cavity, pressurized air is sent into the cavity formed inside the mold cavity.
The molded product, such as a model, was pressurized from the inside to solidify and cool the entire product. That is, a small-diameter nozzle is formed that opens into the mold cavity of a mold that has been cooled to a temperature below the solidification humidity of the thermoplastic molding material, and a pressurized molten molding material with a volume smaller than that of the mold cavity is injected from this UnD. A part of the molding material is deposited and solidified on the inner surface of the gold burr cavity to form a cavity surrounded by an oblique molding side in the mold cavity. Pressurized air was supplied from the nozzle to the cavity, and the entire molding material was solidified by pressurizing the mold from the cavity side. The present invention will be described in detail below based on the illustrated embodiments.

(Example) Fig. 1 is a sectional view showing one embodiment of the nozzle device according to the present invention, Fig. 2 is an explanatory view of its operation when injecting molten wax, and Fig. 3 is an operation explanatory diagram showing when pressurized air is fed. It is.

In No. 11, reference numeral 1o indicates a body of an injection nozzle device, and this body 10 includes a casing 12, a bearing 14, a housing 16, a bush 18, and a nozzle cover 20. A cylinder portion 22 is formed in the bearing 14 and the casing 12 and penetrates in the vertical direction.
It is connected to 24. This injection port 24 is located at the cylinder section 22.
It has a smaller diameter. The housing 16 has an L fitting 2.
A wax channel 28 is formed in the L fitting 26 as a molding material channel that passes through the housing 16 and the bearing 14 and opens to the inner circumferential wall of the cylinder portion 22. Reference numeral 30 denotes an air passage through which pressurized air passes, and opens in the inner circumferential wall of the cylinder portion 22.

A heated water channel 32 is provided between the fitting surfaces of the housing 16 and the bearing 14.
However, a warm water channel 34 is also formed between the joint between the bushing 18 and the nozzle cover 20. The hot water pumped from the plurality of hot water channels 36 surrounding the wax channel 28 of the L fitting 26 passes through the hot water channels 32 and 34 and is discharged to the outside from the wet water outlet 38, and this discharged hot water flows through a pipe (not shown). The wax is heated by a heating device and circulated through each of the water drain channels 36, 32, and 34. As a result, the area through which the molten wax passes is heated to a temperature below its coagulation humidity.

A cylinder tube 42 is held between the lower surface of the casing 12 and the base 40 and is concentric with the cylinder portion 12 .

A plunger 44 is slidably fitted into the cylinder portion 22, and a piston 46 that slides within the cylinder tube 42 is fixed to the lower end of the plunger. A passage 50 opens into the upper air chamber 48 in the cylinder tube 42 defined by the piston 46, and a passage 54 opens into the upper air chamber 52, respectively. Therefore, if pressurized air is supplied to the passage 50, the piston 46 and the plunger 44 will descend and move to the lowered position shown in FIG. Move to the raised position shown in Figure 2.

A second wax passage 56 as a second molding material passage and a second air passage 58 are formed in the plunger 44 . The second wax flow path 56 communicates the wax flow path 28 and the injection port 24 when the flancia 44 is in the raised position. At this time, the second air flow path 58 is connected to the cylinder portion 22.
, that is, the inner surface of the nozzle cover 20, and is blocked from the air flow path 30 on the body 10 side. In the lowered position of the plunger 44, the second wax channel 5
6 is cut off from the wax flow path 28 on the body 10 side, and a second air flow path 58 communicates with the air flow path 30 on the body 10 side. In FIG. 1, reference numeral 59 denotes a guide pin, which engages a long groove 59a formed in the plunger 44 to restrict rotation of the plunger 44.

60 is a bottom-split mold, and this mold 60 has a mold cavity 62 (62a, 62h) and an injection path 64 formed therein.
2 has a small-diameter nozzle 66 (66a, 6
6b) is formed. This mold 60 is pressed and held by the body 10 so that the injection passage 64 communicates with the injection port 24 on the body 10 side. A cooling water passage (not shown) is formed in the mold 60, and the cooling water circulating through the cooling water passage keeps the mold 60 at a temperature below the solidification temperature of wax as a molding material.

Next, the operation of the device of this embodiment will be explained. If pressurized air is sent to the passage 54 and the plunger 44 is raised as shown in FIG.
Closed by an inner wall. If molten wax is forwarded to the wax flow path 28 in this state, this wax will flow through the second wax flow path 56 of the plunger 44, the injection port 24, and the injection path 6.
4 and is vigorously injected into the mold cavity 62 from the small-diameter nozzle 66. Since the mold r60 is cooled below the wax solidification temperature, the molten wax injected into the cavity 62 adheres to the inner wall of the cavity 62 and solidifies, but since this wax has poor thermal conductivity, a turbulent flow occurs. The molten wax solidifies in an overlapping manner starting from the lower temperature parts, that is, the thinner parts of the solidified wax. For this reason, the thickness of the solidified wax is averaged, and the solidification of the wax progresses in a shell-like manner, and there are cavities 68 (68a, 68a,
68b) is formed. In this process, the cavity 62
The wax in the center is still in a molten or semi-molten state.

When the amount of wax flowing into the cavity 62 reaches a fraction of the volume of the cavity 62, for example, about 8 to 4 tablespoons, the supply of pressurized air to the passage 54 is cut off, and pressurized air is supplied to the passage 50. Switching is performed using a solenoid valve (not shown) or the like. The plunger 44 then begins to descend. During the downward movement of the plunger 44, the second wax flow path 56 is first cut off from the wax flow path 28, and the pressure feeding of wax to the cavity 62 is stopped. As the plunger 44 further descends, the two channels 56 of the plunger 44
, 58 remain closed by the inner wall of the cylinder portion 22, the internal pressure of the injection passage 64 and the cavity 68 is reduced. When the plunger 44 descends to the position shown in FIG.
The air passage 58 communicates with the air passage 30 on the bow=”-10 side, and the pressurized air previously supplied to the air passage 30 passes through the injection passage 64 and the nozzle 66 to the cavity 68 in the cavity 62.
to flow into.

The wax passing through the injection path 64 in the mold 60 is
Solidification progresses from the portion that contacts the inner wall 64, and the actual cross-sectional area of the passage through which the molten wax actually passes becomes smaller, so generally it is difficult for pressurized air to pass through the injection passage 64. However, in this device, since the pressure inside the cavity 68 is once increased to ρ, the air j
The differential pressure between the air pressure in m-path 30.58 and the air pressure in cavity 68 increases. Therefore, at the moment when the air 1 passages 30 and 58 communicate with each other, a large amount of air flows into the cavity 68 into the heather 5, and this initial air flow ensures that a narrow air passage is formed in the injection passage 64 and the nozzle 66. It is formed. Therefore, the air pressure of the air passage 30.58 is then fully applied within the cavity 68.

With the cavity 68 pressurized in this way, the cavity 62
Let the wax inside completely solidify. Therefore, no surface deviation occurs in the wax model inside the cavity 62, making it possible to efficiently make a highly accurate model. money type 6
0 and take out the model, the cavity 68 will communicate with the atmosphere through the passage through which pressurized air passed, so even if the model cools down, the inside of the cavity 68 will not have angular pressure, and the model It won't break or break.

In the above embodiments, a wax model for lost wax casting was made, but the method of the present invention is also applicable to the production of polyethylene resin, urea resin, and other thermoplastic plastic molded products. In addition, in this embodiment, the molding machine is of a vertical type, and the nozzle 66 is provided at the bottom of the cavity 68, so that the molten wax that accumulates at the bottom of the cavity 68 is efficiently blown upward by the molten wax that is spouted from the nozzle 66, and the model is Convenient for equalizing wall thickness. However, the present invention is 1
Of course, the intended purpose can be achieved even if the IC 50 is placed in another position.

Furthermore, in this embodiment, the pressure inside the cavity 68 is reduced once before the pressurized air is fed into the cavity 68, so that the pressurized air enters the cavity 68 more smoothly and the pressure of the pressurized air is reduced. The effect is that the desired purpose can be sufficiently achieved without increasing the amount excessively.

(Effects of the Invention) As described above, the present invention injects a volume of molten molding material smaller than the mold cavity from a small-diameter nozzle into the mold cavity to adhere and solidify the molding material to the inner wall surface of the cavity. It was constructed so that the entire structure was solidified while pressurized air was sent into the cavity at the center. Therefore, since the molding material is solidified into a shell shape while being pressurized from the inside, there is no occurrence of surface deviation and it is possible to manufacture highly accurate products. Furthermore, since inlays and cores are not required at all, productivity is high and it is suitable for mass production. Furthermore, since the usage of molding material is reduced by the amount of air 1i1i4, there is also the effect that molding material can be saved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of a nozzle device used in the present invention, and FIGS. 2 and 3 are explanatory views of its operation during injection and pressurized air supply. 60... Mold, 62... Mold cavity, 66 - Spout, 68... Cavity. Patent applicant MCL Co., Ltd. Agent Patent attorney Yama 1) Yu Fumi (1 idiot) (11) Figure 1 (12) Figure 2 Teitosari amendment (self-motivated) December 20, 1982 Kazuo Wakasugi, Commissioner of the Japan Patent Office, 1. Indication of the case, Patent Application No. 72975, filed in 1982. 2. Name of the invention, injection molding method 3. Relationship with the supplementary person case. Name of patent applicant: Kogyo Co., Ltd. 1. EL representative: Nobuyoshi Sasaki 4, agent address: Daiwa Bank Toranomon Building, 1-6-21 Nishi-Shinbashi, Minato-ku, Tokyo 105 (telephone: 591-7556) 6, number of inventions increased by amendment: 07, amendment Column 8 of Detailed Description of the Invention in the Subject Specification, Contents of Amendment (1) The phrase "dimensional accuracy" in line 11 of page 2 of the specification is amended to read "dimensional accuracy." (2) The text "vertical type" in lines 16-17 of page 10 of the same book is corrected to "wax model." (below)

Claims (1)

[Claims] When the mold is cooled below the solidification temperature of the thermoplastic molding material, the mold gear is opened to form a small-diameter nozzle, and from this nozzle, pressurized molten metal molding with a volume smaller than the mold cavity is carried out. A part of the molding material is injected and solidified on the inner surface of the mold cavity, forming a cavity surrounded by the molding material inside the mold cavity. An injection molding method characterized in that pressurized air is supplied from the nozzle while the molded material t1 is in a molten state, and the entire molded material t1 is solidified while being pressurized from the cavity side.