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PBT (SPESIN-PBT) |
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Processing of SPESIN-PBT |
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1. Injection
Molding |
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1-1 Selection of Molding Machine
For injection molding of SPESIN, a general-purpose
reciprocating
screw-type injection machine is used, and 1.2 to 4
times/shot of
capacity (ratio between product, sprue and runner
volume) may
be sufficient.
To obtain optimum product properties from SPESIN,
proper control
of injection machine temperature, time, and pressure
are essential.
When injection molding of SPESIN is completed,
residual resin
must be cleaned while the cylinder is still warm by
using HDPE, PP, or PS resin.
Before injection molding work, the injection machine
must be
heated to the required injection machine temperature
of SPESIN,
and a sufficient quantity of resin must be pumped
in.
2-2 Pressure Condition
The molding pressure setting varies and is
determined, considering the resin grade to be used,
the complexity of products, and the dimension of the
runner and gate.
Normally, minimum pressure is applied at the initial
stage of operation, which will be gradually
increased until optimum pressure conditions are
determined.
The proper holding pressure is 50~60% of the primary
molding pressure, and back pressure should be
determined in consideration of factors such as
kneading of resins, gas venting, etc.
2-3 Temperature Condition
Cylinder temperature of the injection machine should
be set 20 ~40 higher than the melting temperature
of SPESIN.
Normally, a range of 225~270 is appropriate for
injection molding, and temperatures over 280 are
not advisable.
For setting mold temperature, consideration should
be given to reduction of internal stress,
improvement of surface conditions, and prevention of
post-distortion.
Generally, 40 of the glass transient temperature (Tg)
of PBT resin is ideal for evenly dispersed
crystallization and for reducing cycle time.
For the glass fiber reinforced grade of SPESIN
(KP212G30), 80 is adequate.
2-4 Example of Injection Molding Conditions |
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Item |
KP211 |
KP213G30 |
KP212G30V0 |
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Weight |
25g |
115g |
80g |
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Injection
Machine |
FANUC
AUTOSHOT
35Ton |
ENGEL
ES150P
150Ton |
ENGEL
ES75P
75Ton |
Processing Conditions
Nozzle Temperature
Cylinder Temperature
Mold Temperature
Injection Pressure
Holding Pressure
Back Pressure
Infection Time
Holding Time
Total Cycle Time |
240
245/230/225
60
820kg/㎠
310kg/㎠
8kg/㎠
1.2sec
2.5sec
26sec |
255
265/260/240
80
910kg/㎠
355kg/㎠
10kg/㎠
2sec
23sec |
250
265/255/230
10
845kg/㎠
510kg/㎠
12kg/㎠
1.5sec
5sec
28sec |
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2-5 Defective Molding and Trouble
Shooting |
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Item |
Britt
leness
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Short
Shot
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Poor
Surface
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Stain
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Flash
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Void
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Flow
Mark
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Poor
Mold
Release
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Warpage
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Burning
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Cylinder
Temp |
↓ |
↑ |
↑ |
↓ |
↓ |
↓ |
↑ |
↓ |
↓ |
↓ |
Mold
Temp |
↑ |
↑ |
↑ |
↑ |
↓ |
↓ |
↑ |
↓ |
↓ |
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Nozzle
Temp |
↓ |
↑ |
↑ |
↓ |
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↓ |
↑ |
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↓ |
↓ |
Injection
Speed |
↓ |
↑ |
↑ |
↓ |
↓ |
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↑ |
↓ |
↑ |
↓ |
Injection
Pressure |
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↑ |
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↑ |
↓ |
↑ |
↑ |
↓ |
↑ |
↓ |
Holding
Pressure |
↓ |
↑ |
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↑ |
↓ |
↑ |
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↓ |
↑ |
↓ |
Back
Pressure |
↓ |
↑ |
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↓ |
↓ |
↑ |
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↓ |
Cooling
Time |
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↑ |
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↑ |
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Screw
rpm |
↓ |
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↓ |
Nozzle
Diameter |
↑ |
↑ |
↑ |
↑ |
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↑ |
↑ |
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↑ |
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Gas
Vent |
O |
o |
o |
o |
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o |
o |
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o |
o↑ |
Gate
Size |
↑ |
↑ |
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↑ |
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↑ |
↑ |
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↑ |
Gate
Position |
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o |
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o |
o |
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o |
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Drying |
O |
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o |
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o |
o |
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Note. |
↑: Need to Increase
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↓: Need to Decrease |
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O: Study for Effecting
Factors |
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2-6 Use of Scrap
Scrap (unsatisfactory parts, sprue, and runner) of SPESIN
can be used within 20% of mix ratio without degradation of
properties.
For using scrap, an even crushing must be done and any
foreign elements must be completely eliminated.
When equipped with a hopper dryer, scrap generated
immediately after injection molding can be used after
crushing without a re-drying process.
However, if the workplace is humid or if the crushing
process is delayed, it is necessary to monitor closely for
possible re-absorption of water or moisture.
Principally speaking, materials that have gone through the
crushing process should be re-dried before inputting for
ensuring satisfactory product properties.
For parts/products with special impact strength
requirements, it is best not to use scrap. |
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2. Product and Mould
Design
In designing injection molded parts, the maximum flow
distance for the thickness of each part to be molded is
crucial.
When the molten resin temperature is 265, the L/t is in the
250~300 range.
Flowability of SPESIN varies according to melting
temperature and injecting pressure.
As an example using KP211, with injecting pressure of
1,430kg/cm, L/t is 250 when melting temperature is 250, but
L/t rises to 300 when melting temperature is 270.
In designing molds, measures should be taken to minimize
flow resistance of molten resin and all unnecessary scrap
should be minimized in designing flow lead.
Optimum designing is now feasible by computer.
The proper gas vent should be considered for extrusion
molding of SPESIN, as the gas vent has a major effect on the
properties and appearance of molded parts.
For general gas vents, small grooves are provided at the
parting face opposite the gate.
With SPESIN, it is possible by making grooves of 0.02~0.05
cm depth at 3cm apart.
As burr (flash) can be generated, care must be taken not to
make the grooves too deep. In the case of gas venting on a
wide surface, and it may be advisable that several
diamond-shaped grooves are made by means of scraping.
A pricking or pushing pin can be installed to the part where
gas is gathered if it is difficult to install a vent line.
For the flameproof grade of SPESIN, it is advisable to
install a series of vent lines along the cavity surrounding.
In mold designing, the following general factors should be
considered for ensuring the highest properties during the
molding process of SPESIN. |
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a. Material for mould
b. Design of runner and sprue
c. Design of gate
d. Consideration for molding shrinkage |
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