Seminar Report
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Medical Plastics :
Materials, Applications And Processing
For Medical Devices And
Pharmaceuticals Industries |
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SUCCESSFUL
INJECTION MOLDING FOR MEDICAL COMPONENTS
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Making
Moulding Successful.......
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Parameter
Material / Prt / Mld
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Shot
Size
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Injection
Rate
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Injection
Pressures
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Recovery
Rate
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Reqd.
Screw Torque
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High
MFI Mat.
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------
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▲
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------
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▲
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▼
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Tough
Mat.
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------
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▼
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▲
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▼
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▲
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High
Viscous Mat.
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------
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▼
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▲
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▼
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▲
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Ht.
Sensitive Mat.
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▲
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▼
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Monitored
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▼
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------
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Glass
filled Mat.
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------
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▼
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------
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▼
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▲
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Flame
Ret. Mat.
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▲
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------
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------
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▼
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------
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Thin
walled prt.
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------
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▲
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▲
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▼
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------
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Thick
walled prt.
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▲
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▼
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------
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▲
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------
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Fast
cycling prt.
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▼
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▲
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------
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▲
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------
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Improper
Venting
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------
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▼
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▲
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------
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------
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Long
flow path
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------
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------
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▲
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------
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------
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Making
Moulding Successful.......
| Cycle
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Speed
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Pressure
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Temperature
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Time
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Distance
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| Mould
Close
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▲ |
------
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------ |
------ |
------ |
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Mould
Safety |
▲ |
▼
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------
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▼
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▼
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| Tonnage
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------
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▼
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------
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------
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------
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Injection
Fill
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▲ |
Max.
Actual + 10 Bar
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------
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------
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Maintain
Cushion 3.10 mm
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Inj.
Pack
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------ |
▼
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------ |
▼
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------ |
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Inj.
Hold
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------ |
▼ |
------ |
▼
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------ |
| Barrel
Temperature |
------ |
------ |
As
low as possible
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Apply
Soak
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------ |
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Refilling
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Monitor
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------ |
Within
Cooling
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Shot
Size
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| Back
Pressure
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------ |
▼ |
------ |
------ |
------ |
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Suck Back |
------ |
------ |
------ |
------ |
▼ |
| Mould
Open |
▲
|
------ |
------ |
------ |
▼
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| Ejection
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▲
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▼ |
------ |
▼ |
▼ |
| Oil
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------
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------
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Bet. 40-45ºC
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------ |
------ |
| Mould
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------
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------
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Controlled
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------ |
------ |
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PORT CAP
27 X 7mm by 1.5mm thick
Part weight 0.76gms
Cavity 8
Shot weight : 11.87 gms
Mould cold runner
Cycle time 29 sec.
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SPIKE PORT
Dia 11x 25mm by 2mm thick
Part weight 0.75gms
Cavity 16
Shot weight : 20 gms
Mould cold runner
Cycle time 33.7 sec.
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Typical Soft PVC formulation.............
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PVC
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- 100
(Reon 5711 or Indovin 57GER068)
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DOP
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- 20phr onwards depending upon the
hardness required
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OTM
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- 2-3phr (FDA approved stabilizer)
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Epoxy
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- 2-3phr
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B-22 (KANEKA)
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- 4-6phr (impact modifier dosage will also depend upon
the requirement)
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PA-20 (Kaneka)
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- 1-2phr (processing aid)
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Oxidixzed PE Wax
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- 0.2-0.3phr (external lubricant)
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Pigment
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- as per requirement
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Process guideline for soft PVC......
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Nozzle
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Front
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Center
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Rear
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Barrel Temperature Deg. C
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165-170
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165-170
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165-170
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150-160
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Reco. Melt temp
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190-200 deg. C
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Reco. Mould temp
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40 deg. C
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Injection Speed
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Moderate to fast
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Injection Pressure
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1200-1500 bar
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Pack/Hold pressure
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750 bar
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Back Pressure
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150 bar (melt)
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Screw Speed
0.15-0.20 m/s
70 to 90 rpm for typical 40 mm screw dia
Clamp
force Typical 1.6 to 3.4 tons/Inch2
GP screw with chrome plating Comp.
Ratio : 2.0:1
Some times requires high screw
torque
Notes:
The processing window is narrow,
needs accurate & stable controls
Residence time should be aimed for 2
shot
Shut down
One completion of run turn off
heater and purge slowly special purging compounds of enhanced stability
are available or use PS or stiff HDPE
Never allow Material to hang up in
the barrel
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Thermo Plastic Elastomer - TPE
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TPE Processing Parameters
Screw Design
Special equipment is not required -
use a screw L/D ratio approximately 20:1 and a compression ratio of 2.5:1
Barrel capacity
No less
than 1.3 shots and no more than 4
shots
Clamp Pressure
3 to 5
tons/in2 of projected area.
Screw RPM
100 to 200 RPM
Screw cushion
3
to 6 mm
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Increase flow
TPE rubber is a shear-dependent polymer, which means the higher the
shear
ratge, the lower the viscosity. This implies it is more effective to
raise injection pressure
and speed rather than barrel temperature
Temperature
settings, °C (°F)
As low as possible. At lower melt temperatures less cooling is needed,
resulting in faster cycle times.
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