Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,... – Making hole or aperture in article
Patent
1997-06-27
1998-10-13
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
Making hole or aperture in article
2643289, 26432811, 425566, 425577, B29C 4526
Patent
active
058208038
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improvement of a valve gate-type injection molding method and apparatus, wherein molten synthetic resin such as plastic is injected into a closed mold and then the mold is opened to take out a cooled and solidified product, thereby to attain a molded product which is the target product.
BACKGROUND ART
Before now, various types of injection molding methods and apparatuses have been proposed as injection molding methods and apparatuses to attain comparatively precise molded products from synthetic resin, such as plastic.
In particular, in recent years, an injection molding method and apparatus of valve gate type, has been proposed as one of the injection molding methods and apparatuses, in order to reduce the molding cycle time for a molded product.
This valve gate-type injection molding method and apparatus comprises a valve for temporarily holding molten resin to which prepressure is applied, and a valve pin extendably and retractably placed within the valve, wherein by releasing a gate formed in the mold by the valve pin, molten resin, to which prepressure was applied, fills the cavity in the mold at a high speed, and the gate is closed again by the valve pin after the filling of the molten resin.
This type of valve gate-type injection molding method and apparatus has the effect of eliminating the time wasted by the compression of the molten resin before its injection, and therefore shortening the molding cycle time for a molded product, because molten resin within the valve is compressed in advance during the opening of the mold to take out the molded product.
FIG. 18 is a cross section of the principal elements of a conventional valve gate-type injection molding apparatus 1, discussed above, and more particularly the valve gate-type injection molding apparatus 1 to mold a tubular molded product, such as a roller having an axial hole through its center.
The valve gate-type injection molding apparatus 1 comprises an upper mold 2 where a valve body, not shown, is installed, and a lower mold 4 where a tubular cavity 3 is formed. Therein, a first hole 5, having a sectional form of a cone, is formed inside the upper mold 2 at a position corresponding to the upper end 3a of the cavity 3, the inner surface of its lower end is a gate 6 for filling the cavity 3 with molten resin. Also, inside the upper mold 2, a second hole 7, having a sectional form of a cone and a diameter greater than that of the first hole 5, is formed and connects to the upper edge of the first hole 5. In the center thereof, a valve pin 8, of a valve which is not shown, is provided extendably and retractably in a vertical direction opposite to the gate 6.
The end of the valve pin 8 is in the form of a cylinder; its diameter L is substantially equal to that of the diameter M of the gate 6. The valve pin 8 is constituted in such a manner that the gate 6 is closed when the valve pin 8 drops to the position of the gate 6, and the gate 6 is opened when the valve pin 8 rises to the position shown in the drawing.
Meanwhile, a cylindrical core 9 for forming the central hole of a tubular molded product which is molded of molten resin that fills the cavity, is located at the center of the cavity 3 formed inside the lower mold 4. A protruding pin 10, to remove the molded product from the cavity 3, is inserted around the core 9. The protruding pin 10 is arranged to rise and fall with respect to the core 9.
Next, the operation of the valve gate-type injection molding apparatus 1 is explained. As shown in FIG. 19, in which the same portions as in FIG. 18 are shown with the same reference numerals or symbols, the gate 6 enters a state of release according to the position of the valve pin, which has retracted upwards. Therefore the molten resin, compressed in the valve, not shown, is injected by way of gate 6 and fills the cavity 3 as shown with the arrow A.
In this way, molten resin is injected by way of the gate 6 into the cavity 3. When the filling is complete, valve pin 8 drops and stops at the pos
REFERENCES:
patent: 4125352 (1978-11-01), Gellert
patent: 4521179 (1985-06-01), Gellert
patent: 4530654 (1985-07-01), Rose
patent: 5423672 (1995-06-01), Gordon
patent: 5460763 (1995-10-01), Asai
Heitbrink Jill L.
Takaoka Seiko Co., Ltd.
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