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Injection Molding Machines
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2 Selection
of Injection Molding Machines
2.1Selection
of Injection Molding Machines
Commercial
molding machines can be used to mold Duracon :
specialized machinery is not required.
In
selecting a molding machine, the injection weight per shot must
be determined, along with the projected area of the molded product.
The following two points must be taken into account : |
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Injection weight per shot = Machine
capacity 20-80%
(preferably 30-50%) |
| Clamping force>Projected area
of a molded product49-69MPa |
2.2Plasticization
Mechanism
Although
it is desirable to select a screw which can perform plasticization
with sufficient kneading to keep the range of material temperature
distribution as narrow as possible, general purpose screws
are used and specialized screws are usually not required for
injection molding of Duracon.
One
of the most important elements in screw construction is the
non-return valve, which is used to prevent molten resin from
returning to the hopper side during the dwell stroke and to
apply sufficient pressure to the cavity. If the prevention
of reverse flow is not sufficient, defects such as sinks,
voids, reduced dimensional accuracy, and deterioration in
the strength of moldings may arise.
Therefore,
it is necessary to carefully monitor the movement and stoppage
of the screw.
Machines
used to mold glass fiber reinforced plastics require wear
resistant screws and cylinders. Usually, wear resistance is
ensured by the selection of the proper type of steel and various
after treatments of the screw and cylinder. |
2.3Injection
Mechanism
Major
factors concerning the injection mechanism include the injection
rate and the pattern control of injection speed.
When
the wall is thin or a multi-cavity mold with thin runners
is used, a molding machine with a high injection rate may
be required but high injection speeds are not always needed.
There is an optimum injection speed for any given molding,
and this speed depends upon the shape of the mold. For example,
to prevent flow marks, a slow filling speed through the
gate is preferable. |
2.4Nozzle
Structure
| Nozzles
are classified into open-type and valve-type nozzles.
Duracon can easily be molded by the open-type
nozzle. The open-type nozzle may sometimes cause drooling,
but this can be prevented through use of a reverse tapered
nozzle or a valve-type nozzle. Among the various valve-type
nozzles, a nozzle with a mechanism which allows the valve
to be opened by pressure generated in the cylinder allows
easy molding of Duracon. |
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The data shown in this home page
are based on our accumulated experience and laboratory data, and
not always directly applicable to your products used under different
conditions. Therefore, we can not guarantee that the contents
of this home page are directly applicable as they are to the specific
condition in our customers, and we appreciate your final decision
on the use of these data.
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Molding technology for Duracon