1. SINO www.cnmould.com
MOULD
Gas Assist Injection Molding
Gas assist injection Molding is a creative process which is gradually
applied to a variety of plastic products. It empties the interior of the thick wall
by gas, overcomes the limitations of traditional injection molding and foam
molding, and shows the incomparable advantage when compared with
traditional injection molding method.
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Compared with traditional injection molding method, gas assist injection
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molding technology can reduce workpiece weight, quicken cooling rate,
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decrease clamping force, simplify mold design and reduce the cost greatly. In
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the matter of products quality, gas assist injection molding technology can
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clear up surface marks, reduce product innerstress and warpage, and
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increase product strength and stiffness by setting stiffener with airway and
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keeping the product weight at the same time.
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Test below lists the gas assist injection molding advantages briefly:
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Elimination of sink marks.
Avoidance of plastic packing from the molding machine.
Reduced in-mould pressures by up to 60%, and therefore reduced
press lock forces enabling larger
• The use of gas assisted injection molding as a means of transmitting
pressure uniformly throughout the molding.
• Moldings on much smaller machines.
• Reduced power consumption.
• Reduced molded in stress, and therefore improved dimensional stability
with no distortion
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2. SINO www.cnmould.com
MOULD
Gas assist injection molding generally includes several major steps such
as melt injection, gas injection, gas holding, gas recovery, product ejection.
First, inject the pre-set viscous fluid (usually molten polymer) which occupies
a certain percentage of whole cavity by the gate. Then inject a certain
pressure of non-viscous fluid directly or through the mold gate and runner.
The non-viscous fluid is usually the inactive gas, generally is the N2. Because
the melt which contacted with the mold surface temperature is low, and in
thick-wall part (such as
reinforcing), the temperature
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is high, viscosity is small, high
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pressure gas promote the
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molten polymer to the end of
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the cavity, accordingly
promote hot fluid to fill the
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air road in the thick part of a
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product. Gas assist injection molding technology is mainly used in the
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manufacture of pipe shaped parts, large pallet and plastic product which
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consist of sections in different thickness, is widely used in home appliance,
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auto, office supplies, other daily necessities and many other fields.
wA few basic points on gas assist injection mould:
• First of all, consider where need to be emptied by gas, and then decide
how to connect them by air road.
• The air road should be balanced distributed and can’t form a loop.
• The air road should be distributed in a same direction with the main
material flow, and use a large radius at the corner.
• Gas nozzle should be placed further away from the plastic filling
location, and locates in wall thickness department, maintain a distance
of 20 with the gate.
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3. SINO www.cnmould.com
MOULD
• There must be clear of the flow direction and the ability of sneaking
into the end of the air road when injecting gas.
• The size of air load is very important, usually 2 or 4 times of the wall
thickness. It will create fusion line and gas trap if the air road is too big.
Too small will make the gas flow out of control.
• Cooling equably as far as possible, temperature difference between
inside and outside wall should be small as far as possible.
• Place a reasonable radius closure block in the runner, control the speed
of gas flow in different directions.
(edit by market02@sinogroupe.com )
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