JPS6313806B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an injection molding nozzle device for highly accurate injection molding of lost models for investment casting such as lost wax casting and thermoplastic plastic molded products. It is.

(Prior Art) It is widely practiced to make disappearing models used in investment casting and plastic molded products by injection molding. In this case, due to thermal contraction of the molding material, a phenomenon in which a relatively wide flat portion of the disappearing model or the like becomes depressed occurs, a so-called "surface sinking" phenomenon. In order to prevent this surface deviation, conventional methods have been to embed an inlay inside the model or use a metal core, but these methods have poor productivity and are not suitable for mass production. The problem was that it was not suitable.

Therefore, the same applicant proposed a nozzle mechanism in which molten molding material is injected into the mold cavity so as to fill it, and pressurized air is sent into the void created by the shrinkage of the molding material during the cooling and solidification process ( (Special Application No. 123944, 1973). However, since this mechanism sends air into the mold cavity filled with molding material under high pressure, the amount of air flowing in is small, and the molding material cools and hardens in the injection path inside the mold through which the air passes. There was a problem that it was easy to get blocked. There was also the problem that a sufficient amount of air could not be fed unless the air pressure was increased considerably.

(Object of the Invention) The present invention was made in view of the above circumstances, and it is possible to smoothly send pressurized air into the molding material that is in the solidification process within the cavity, and also to reduce the pressure of this pressurized air. It is an object of the present invention to provide an injection molding nozzle device that can be lowered.

(Structure of the Invention) In order to achieve this object, the present invention is configured such that during the injection process of the molten molding material, the pressure inside the mold cavity is once reduced and then pressurized air is introduced. That is, a body heated to a temperature equal to or higher than the solidification temperature of a thermoplastic molding material, a cylinder portion formed in this body and having one end communicating with an injection port, a molding material flow path and an air flow path opening in the inner circumferential wall of this cylinder portion, a plunger that moves forward and backward within the cylinder portion,
The plunger has a second molding material flow path that communicates the molding material flow path with the injection port at the forward movement position toward the injection port side, and a second molding material flow path that communicates the molding material flow path with the injection port at the exit movement position. A second air flow path is formed, and the injection port is configured to be depressurized once during the retreating process of the plunger. Based on the example shown below,
The present invention will be explained in detail.

(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 view showing pressurized air supply. be.

In FIG. 1, reference numeral 10 denotes a body of the injection nozzle device, and the body 10 includes a casing 12, a bearing 14, a housing 16, a bush 18, and a nozzle cover 20. The bearing 14 and the casing 12 have a cylinder portion 2 that penetrates in the vertical direction.
2 is formed, and the upper end of this cylinder portion 22 communicates with an injection port 24 formed in the nozzle cover 20. This injection port 24 has a smaller diameter than the cylinder portion 22. 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 hot water channel 32 is provided between the fitting surfaces of the housing 16 and the bearing 14, and a heated water channel 32 is provided between the fitting surfaces of the housing 16 and the bearing 14, and a heated water passage 32 is provided between the fitting surfaces of the housing 16 and the bearing 14, and a heated water passage 32 is provided between the fitting surfaces of the housing 16 and the bearing 14, and a heated water channel 32 is provided between the fitting surfaces of the housing 16 and the bearing 14, and a heated water channel 32 is provided between the fitting surfaces of the housing 16 and the bearing 14, and a heated water channel 32 is provided between the fitting surfaces of the housing 16 and the bearing 14.
A warm water channel 34 is formed between the two surfaces.
The hot water pumped from the plurality of hot water channels 36 surrounding the wax flow path 28 of the L fitting 26 is transferred to the hot water channels 32, 34.
This discharged hot water is heated by a heating device (not shown) and circulates through each of the hot water channels 36, 32, and 34. As a result, the area passing through the molten wax is heated above its solidification temperature.

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

44 is a plunger, and the cylinder portion 22
A piston 46 that slides within the cylinder tube 42 is fixed to the lower end thereof. A passage 50 is provided in the upper air chamber 48 within the cylinder tube 42 defined by the piston 46.
However, passages 54 are opened in each of the lower air chambers 52. 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.

The plunger 44 has a second wax passage 56 as a second molding material passage and a second air passage 58.
is formed. Second wax channel 56
communicates the wax flow path 28 with the injection port 24 at the raised position of the plunger 44. At this time, the second air flow path 58 is closed by the inner wall of 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 flow path 56 is cut off from the wax flow path 28 on the body 10 side, and the second air flow path 58 communicates with the air flow path 30 on the body 10 side. In FIG. 1, reference numeral 59 is a guide pin that engages in a long groove 59a formed in the plunger 44 to restrict rotation of the plunger 44.

Reference numeral 60 designates a mold that is divided into upper and lower parts, and a mold cavity 62 (62a, 62b) and an injection path 64 are formed in this mold 60, and the opening of the injection path 64 to the mold cavity 62 has a small diameter. Squeezed spout 66
(66a, 66b) are formed. In this mold 60, the injection path 64 is located at the injection port 2 on the body 10 side.
4 and is pressed and held by the body 10 so as to communicate with the body 10. 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. aisle 54
When the plunger 44 is brought to the raised position shown in FIG. 2 by supplying pressurized air, the upper and lower ends of the second air passage 58 are closed by the inner wall of the cylinder portion 22. When molten wax is force-fed into the wax flow path 28 in this state, the wax passes through the second wax flow path 56 of the plunger 44, the injection port 24, and the injection path 64, and enters the mold cavity 62 from the small-diameter injection port 66. Sprays well. Since the mold 60 is cooled below the solidification temperature of the wax, 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, creating cavities 68 (68a, 68) inside.
8b) is formed. During this process, the wax in the center of the cavity 62 is still in a molten or semi-molten state.

When the amount of wax flowing into the cavity 62 becomes a fraction of the volume of the cavity 62, for example, about 1/3 to 2/3, the pressurized air supply to the passage 54 is cut off and the passage 50 is pressurized. The air supply is switched using a solenoid valve (not shown) or the like. Then, the plunger 44 starts descending. During the descending process of the plunger 44, the second wax flow path 56 is first cut off from the wax flow path 28, and the pumping of wax into the cavity 62 is stopped. As the plunger 44 further descends, the plunger 44
Since the two flow paths 56 and 58 remain closed by the inner wall of the cylinder portion 22, the internal pressure of the injection path 64 and the cavity 68 is reduced. and plunger 44
3, the second air passage 58 communicates with the air passage 30 on the body 10 side, and the pressurized air previously supplied to the air passage 30 flows through the injection passage 64 and the nozzle 66. and flows into the cavity 68 within the cavity 62.

The wax passing through the injection passage 64 in the mold 60 solidifies from the part that contacts the inner wall of the injection passage 64, and the actual cross-sectional area of the passage through which the molten wax passes becomes small. is difficult to pass through the injection path 64. However, in this device, the pressure inside the cavity 68 is reduced once, so the air passages 30, 5
The differential pressure between the air pressure in 8 and the air pressure in cavity 68 increases. Therefore, the moment the air passages 30 and 58 communicate with each other, a large amount of air flows forcefully into the cavity 68, and this initial air flow ensures that a narrow air passage is formed in the injection passage 64 and the nozzle 66. . Therefore, the air pressure of the air passages 30, 58 is applied sufficiently to the inside of the cavity 68 from now on.

With the cavity 68 pressurized in this manner, the wax within the cavity 62 is completely solidified. As a result, the wax model inside the cavity 62 does not have any surface deviation, making it possible to efficiently create a highly accurate model. When the mold 60 is dismantled and the model is taken out, the cavity 68 is communicated with the atmosphere through the passage through which pressurized air passes, so even if the model cools, the inside of the cavity 68 will not become under negative pressure. There is no chance of the model breaking.

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 polystyrene, urea resin, and other thermoplastic molded products. In addition, in this embodiment, the machine is a wax model molding machine, and the spout 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 spouted from the spout 66, and the model is It is best to do this every time to make the wall thickness uniform. However, it goes without saying that the present invention can achieve the intended purpose even if the nozzle orifice is provided at another position.

Furthermore, in this embodiment, a smaller volume of molten wax is injected than the mold cavity 62.
Since the cavity 68 with a large volume is formed inside, the effect of saving wax is large, but the present invention injects the molding material in an amount that almost fills the inside of the cavity.
Pressurized air may be introduced into a gap created in the center by contraction during cooling.

(Effects of the Invention) As described above, in the present invention, the injection of molding material and the supply of pressurized air are switched by the forward and backward movement of the plunger, so that the pressure inside the mold cavity is reduced once during the switching process. Therefore, the difference between the cavity internal pressure and the pressurized air pressure increases, making it easier for pressurized air to enter. Moreover, since this pressurized air initially flows in a relatively large amount, an air passage is reliably formed within the injection path, and the injection path can be prevented from being blocked by the molding material.
Therefore, pressurized air can be reliably sent to the center of the cavity, and the molding material can be solidified with sufficient pressure applied from the inside, improving the precision of the product. Furthermore, since pressurized air can be sufficiently fed even at relatively low pressure, the air pressurization device becomes simple.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIGS. 2 and 3 are explanatory diagrams of operations during injection and pressurized air feeding. 10...Body, 22...Cylinder section, 24...
... injection port, 28 ... molding material flow path, 30 ... air flow path, 44 ... plunger, 56 ... second molding material flow path, 58 ... second air flow path.

Claims (1)

[Claims] 1. A body heated to a temperature equal to or higher than the solidification temperature of a thermoplastic molding material, a cylinder portion formed in this body and having one end communicating with an injection port, a molding material flow path and an air flow path opening in the inner circumferential wall of this cylinder portion, and the above-mentioned Equipped with a plunger that moves forward and backward within the cylinder,
The plunger has a second molding material flow path that communicates the molding material flow path with the injection port at the forward movement position toward the injection port side, and a second molding material flow path that communicates the molding material flow path with the injection port at the exit movement position. An injection molding nozzle device, characterized in that the injection nozzle device is formed with a second air flow path, and the injection port is once depressurized during the retreating process of the plunger.