JP3280320B2 - Screws with vent grooves in the flight - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw for plasticizing and / or injecting a molding material such as a synthetic resin or rubber into a cylinder and having a gas vent groove. .

[0002]

2. Description of the Related Art Water vapor or volatile gas generated during plasticization of a molding material adversely affects the quality of a molded product and becomes defective. Therefore, a hygroscopic resin or a resin that easily generates gas during plasticization is used. In molding, the molding material is dried beforehand.However, in the case of insufficient resin or thermosetting resin or rubber that cannot be dried by heating alone, a molding machine equipped with a vent is required. It is adopted to forcibly discharge gas generated during plasticization.

As means for discharging gas other than the vent,
A screw flight provided with a gas vent groove is known from Japanese Utility Model Publication No. 53-3250. In this conventional structure, a gas vent groove is provided only on the tip end surface of the flight located in the compression zone, and an exhaust hole is formed in the compression zone from the rear end of the screw to communicate with the gas vent groove, and gas is vented from the exhaust hole. The gas flowing into the groove was exhausted to the outside from the rear end of the screw.

[0004]

In the adoption of a screw having a normal configuration, water vapor and volatile gas in a heating cylinder generated from a molding material during plasticization pass between semi-molten or unmelted molding material in a supply zone. The gas is naturally or forcibly evacuated to the outside through the gap around the material drop port or the rear end of the shaft, but in the metering zone closer to the nozzle than the compression zone in the molten state, the flow gap required for gas exhaust is Because of the lack of the gas, it is considered difficult to exhaust the gas that has been entrained in the molten material and reached the metering zone from the supply zone.

[0005] In the above-mentioned conventional structure, in addition to the exhaust gas in the supply zone, the gas generated during the plasticization and moved to the compression zone side is removed together with the gas degassed from the molten molding material.
The gas is trapped and exhausted by the gas vent groove of the flight, and the gas is prevented from moving to the measurement zone. However, there is a problem that it is not enough to prevent gas from entering into the measuring zone, and it is extremely difficult to return the gas in the molten material in the metering zone to the compression zone and exhaust the gas.

The present invention has been conceived in order to solve the above-mentioned conventional problems, and an object of the present invention is to exhaust gas through a gas vent groove provided on the top surface of a flight. It is an object of the present invention to provide a screw having a gas vent groove in a flight having a new configuration capable of sufficiently exhausting gas in a metering zone.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a screw for plasticizing and / or injection in a heating cylinder, which is located immediately before a material drop opening of the heating cylinder when the screw retreats from the screw tip. A gas vent groove having a groove width d of about 1/3 of the lateral width D of the top surface is continuously formed on the top surface of the flight to the site.

[0008] In the screw having such a configuration, an exhausting operation is performed by the gas vent groove in a zone in the heating cylinder immediately before the material dropping port of the heating cylinder from the tip of the screw. The gas vent groove in those zones acts as an exhaust path for gas in the metering zone, degassing and discharging gas in the metering zone efficiently, and the remaining gas This prevents the occurrence of defective products.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, reference numeral 1 denotes a screw for a thermoplastic resin, and a flight 3 is continuously formed around a shaft portion 2 from the tip of the screw to the vicinity of the rear end. On the top surface of the flight 3 of the screw 1, a gas vent groove 4 is formed continuously from the flight tip 3 a at the screw tip to the flight end 3 b at the rear end of the shaft 2.

As shown in FIG. 2, such a screw 1 is rotatably and removably inserted into a heating cylinder 7 having a nozzle 5 at a tip and a material dropping port 6 on a rear part.
The molding material supplied into the heating cylinder from the material dropping port 6 is plasticized while retreating by screw rotation, is measured in the tip of the heating cylinder 7, and the measured material is moved forward from the nozzle 5 into the mold (see FIG. Is omitted).

The screw 1 in the heating cylinder has a clearance between the top surface of the flight 3 and the inner wall surface of the heating cylinder 7 for slight rotation and sliding in which the molding material is difficult to enter even in a molten state. Through the clearance, the gas vent groove 4 communicates with any of the supply zone A, the compression zone B, and the measurement zone C in the heating cylinder. It communicates with the outside through the surrounding gap.

When the internal pressure of the heating cylinder 7 increases due to plasticization of the molding material, a pressure difference occurs between the side of the gas release groove 4 communicating with the outside and the inside of the heating cylinder, and water vapor and volatiles generated during plasticization are generated. Flows into the gas vent groove 4 from the clearance and is discharged from the material dropping port 6 to the outside via the hopper 8 or from the gap around the rear end of the shaft portion 2 to the atmosphere.

Although the exhaust in the supply zone A is also performed between the semi-molten or unmelted molding material as in the past, in the measuring zone C, since the molding material is completely melted, Although there is no gap between the materials as in zone A, there is a gas vent groove 4 on the top surface of the flight 4 facing the inner wall surface of the heating cylinder 7 with a clearance, and in the measurement zone C, the inner wall surface and the screw 1 Is narrowed, the molten material from the compression zone B is stretched thinly, and the measurement zone C is in a state where it is easily degassed by the internal pressure.

From such a situation, the gas entrained in the molten material in the measuring zone C naturally flows into the relatively low-pressure gas vent groove 4 from the clearance by communicating with the outside, and flows backward in the gas vent groove. Become fluid. In the supply zone A in which the molding material is in an unmelted state, the pressure difference in the gas vent groove 4 is not as large as that in the measurement zone C, so that the gas vent groove 4 becomes closer to the material drop port 6 communicating with the outside air.
A part of the gas flowing backward through the gas flows out to the supply zone A.

The gas that has partially flowed out flows to the material dropping port 6 together with the gas generated in the supply zone A, and the remaining gas that continues to flow through the gas vent groove 4 is the material dropping port 6 or the shaft 2. Will be released to the atmosphere from the surrounding gap at the rear end. In any case, the gas flowing into the gas vent groove 4 is finally released into the atmosphere and does not remain in the gas vent groove 4.

Therefore, the gas vent groove 4 of the flight 3 located in the supply zone A and the compression zone B is provided with an exhaust passage for the gas in the metering zone C because the exhaust to the compression zone B is mainly performed with a gap of the molding material. Therefore, it is only necessary to continuously form at least the gas vent groove 4 from the tip of the screw to the flight 4 at a position located in the vicinity of the material drop port 6 of the heating cylinder at the time of screw retreat. Often, the gas in the molten material will be degassed while passing through the metering zone C and metered into the tip of the heating cylinder 2, and will be exhausted from the gas vent groove 4.

In the screw 1, the flight end 3 b at the rear end of the shaft portion 2 extends from the flight end 3 a at the screw end to the flight end 3 b at the rear end of the shaft 2.
Since the gas vent groove 4 is formed continuously up to the whole, if the material particles are smaller than the groove width of the gas vent groove 4 formed there, the material particles enter the gas vent groove 4 and the gas Since there is a possibility that exhaust will be impaired by closing the extraction groove 4,
As a preventive measure, the gas vent groove 4 is limited to a flight located immediately before the material drop port 6 of the heating cylinder at the time of screw retreat.

As shown in FIG. 3, the groove width d of the gas release groove 4 is set to about 1/3 of the lateral width D of the top surface of the flight 4 because its purpose is to serve as a gas exhaust passage. The cross-sectional shape is preferably a semi-elliptical shape, a semi-circular shape, or the like.

In the flight 3, the temperature of the tip end surface closest to the inner wall surface of the heating cylinder 7 is high, and the temperature decreases as it approaches the shaft portion 2. Is cooled, and cooling water or the like is easily generated, and this flows to the top surface side by the screw rotation, is gasified again, is taken into the molten resin, and the exhaust efficiency may be reduced. The groove 4 is preferably limited to a depth within a range in which the flight 3 maintains a high temperature by heating from the heating cylinder side.

The screw 1 shown in FIG. 1 is for a thermoplastic resin and has a valve at the tip of the screw. However, the screw 1 can be applied to molding of thermosetting resin or rubber. Only the valve at the tip is omitted and no other changes are required.

In the molding of the thermosetting resin, the surface gloss of the molded product is improved, the appearance is not deteriorated, the structure is dense, and the physical strength is improved as compared with the case of using a normal screw. In addition, dirt on the mold part surface and the gas venting portion is reduced. As a result, the mold is hardly corroded, the management is easy, and the extra time for cleaning and the like is reduced.

[0022]

【Example】

 Screw shaft diameter 30mm Flight diameter 40mm Width of flight top surface 6mm Width of gas vent groove 2mm Depth of gas vent groove 1mm

[Brief description of the drawings]

FIG. 1 is a side view of a screw in which a gas vent groove is provided continuously from the flight tip at the tip of the screw to the flight end at the rear end of the shaft.

FIG. 2 is a schematic vertical sectional view of a heating cylinder of an injection device provided with the screw according to the first embodiment.

FIG. 3 is a partial longitudinal sectional view of a flight having a gas vent groove provided in the screw of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw 2 Shaft part 3 Flight 3a Flight tip 3b Flight end 4 Gas vent groove 6 Material drop port 7 Heating cylinder 8 Hopper

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B29C 45/60 B29C 47/60-47/64 B29B 7/42

Claims (1)

(57) [Claims] 1. A screw for plasticizing and / or injecting in a heating cylinder, wherein the screw is provided on a top surface of a flight from a screw tip to a portion located immediately before a material dropping port of the heating cylinder when the screw is retreated. A screw having a gas vent groove on a flight, wherein gas vent grooves having a groove width d of about 1/3 of the lateral width D of the surface are continuously formed.