Gas injection mold structure for a gas auxiliary injection...

Details Gas injection mold structure for a gas auxiliary injection... Gas injection mold structure for a gas auxiliary injection...

1999-03-01

2001-11-13

Nguyen, Nam (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Means feeding fluent stock from plural sources to common...

C425S546000, C425SDIG002

Reexamination Certificate

active

06315542

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a gas injection mold structure and a gas injection device for use with the mold structure, in particular to a gas injection mold structure and gas injection device to be implemented in the field of gas auxiliary injection molding technology. This invention greatly reduces material consumption and production cost, and enhances accessibility in assembling and maintenance.
2. Description of the Related Art
Currently available Injection molded products that are manufactured by conventional molding, in particular that have immense size and diverse configurations (such as front casings of monitors, shoe lasts, and bicycle cranks), usually require relatively high production cost and extensive secondary manufacturing processes in order to attain satisfactory quality. However, to contend in the international settings that are short of manpower, cost conscious, and quality demanding, injection molds featuring gas channels are now frequently implemented in the field of advanced gas auxiliary injection molding to manufacture injection molded products that are of low cost, high rigidity, and fine appearance, and to solve technical flaws that cannot be addressed by conventional plastic injection molding. Therefore, how to engineer gas channels in molds now plays a primary role in the field of gas auxiliary injection molding (GAIM) technology. Since the key to successfully control passages of the gas channels relates to the mechanism for injecting gas into cavities, the gas injection device being provided in a mold is generally complicated in structure and requires high precision. These are reasons why the manufacturing and assembling/disassembling costs for the gas injection devices being adopted in the market can yet to be reduced to a satisfactory level.
The structure of a conventional gas injection device implemented in a conventional mold structure is described as follows. With reference to
FIG. 1
, a conventional gas injection mold structure
1
, a gas injection device
2
is provided within a male mold
3
. The gas injection device
2
includes an upper insert
4
being threaded in the male mold
3
and a lower insert
5
being affixed beneath the upper insert
4
. The upper insert
4
and the lower insert
5
are formed with a gas injection passage
6
therethrough. A running stick
7
is provided within the passage
6
. After or roughly when molten plastic material is injected into a cavity through sprues and runners, gas (generally being nitrogen gas) is injected through the passage
6
so as to push the running stick
7
upwards and to disengage a tapered closing face between the running stick
7
and the lower insert
5
such that the gas is injectable into the cavity
8
by passing a gap formed between the running stick
7
and the upper insert
4
. After the gas is completely released, an upper tapered end and a lower tapered end of the running sick
7
urge against tips of the upper inert
4
and lower insert
5
to seal the passage
6
as a result of resiliency of a spring
9
externally provided around the running stick
7
.
It is shown from
FIG. 1
that the conventional gas injection device
2
comprises numerous components and is complicated in structure. In the event of malfunction, maintenance, or replacement of the gas injection device
2
(such as replacing O-rings
10
that are provided around the upper insert
4
and that are intended to avoid gas leakage, wherein the O-rings are easily damaged due to prolonged compression and thus require frequent replacement), the procedures of assembling the upper and the lower inserts
4
,
5
into the male mold
3
require disassembling the overlaid laminated plate, crown block, crown plate, crown pin, and support block (not shown) that are located beneath the male mold
3
in order to replace components of the gas injection device
2
. Such time-consuming procedures are one of the significant technical flaws of the conventional gas auxiliary injection molding equipment.
Furthermore, using the passage
6
of the above conventional gas injection device
2
to inject pressurized gas results in collective expulsion of gas in a longitudinal direction such that the gas directly impacts mold walls
11
and penetrates plastic products thereby resulting in gas leakage and defective products. In the conventional gas auxiliary injection molding equipment, gas the passage
6
trails predetermined gas channels to urge molten plastic material flowing towards locations of lower pressure and lower viscosity; pressure is then preserved for a fixed interval to eliminate forming of contractions and sinks on the surfaces of the plastic products within the cavity
8
during the cooling process, and to prevent, particularly, the immense products from bending, deformation, and short-shot. However, slight contractions formed during the cooling process causes a gap forming at a contact surface between a tip end of the running stick
7
and the plastic material thereby subjecting gas being injected into the mold to discharge from the gap due to contraction or forming micro cracks between the tip end of the running stick
7
and the plastic material, wherein the micro cracks ultimately cause gas discharge. Blockage formed by the plastic material at an outlet of the passage
6
that communicates the cavity
8
also greatly reduces effect of gas injection into the cavity
8
. Furthermore, in such a conventional gas injection construction, repetitive impacts as a result of gas pressure between the running stick
7
and the plastic product within the cavity
8
also causes serious leakage and reverse discharge of pressurized gas.
Hence, it is desired to provide one or more gas injection devices and gas injection mold structure cooperated with the devices that solve the above limitations, reduce production cost, and enhance accessibility in assembling and maintenance. This invention discloses a creative gas injection mold structure for use in the field of gas auxiliary injection molding technology and a gas injection device as follows.
BRIEF SUMMARY OF THE INVENTION
It is a primary object of this invention to provide a gas injection mold structure for use in the field of gas auxiliary injection molding, in which the structure implements a specially engineered gas injection device that is threaded into a male mold, to evenly conduct pressurized gas towards opposing sides of a cavity so as to urge forward flow of plastic material whereby such flaws as penetration and surface sinks of plastic products are eliminated. The specially engineered gas injection device further eliminates blockage of gas passage to attain an ideal pressure preservation and eliminates gas discharge in the process of pressure preservation and cooling provide excellent air tightness. Furthermore, this invention helps to manufacture plastic products of excellent appearance because it eliminates impacts resulting from relative motion between the gas injection device and the cavity.
It is a secondary object of this invention to provide a gas injection mold structure for use in the field of gas auxiliary injection molding, in which the gas injection device is of a simple single-unit construction and is directly threaded into and affixed to the mold from a top of the mold. The gas injection device may be optionally assembled in the bosses of products (such as monitor housings), which have bosses, to perform gas injection so as to greatly reduce production cost of the gas injection device and the mold, to enhance usage and to facilitate replacement and maintenance of the gas injection device.
It is another object of this invention to provide a gas injection mold structure for use in the field of gas auxiliary injection molding that implements a single-unit, removable construction to allow the device to be assembled in various sets of gas auxiliary

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