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Standard Injection Molding
Successful molding of Ticona’s engineering resins begins with
an appropriate choice of machine and screw. Using an unsuitable molding machine or screw design
can lead to poor material homogeneity, an inconsistent molding process and machine and/or screw wear.
All of these factors can adversely affect the quality of the molded parts.
Incorrect pre-drying, atypical machine settings, or machine and
mold problems can lead to surface defects or part failures. As the properties of injection-molded
parts are also very dependent on material handling and processing conditions, we provide the following
tools to help you achieve satisfactory molding results:
Clamp Force Calculation:
Viscous
polymers require high pressure to force the melt through the nozzle, runner system, and gate into the
mold cavity. The pressure that develops in the mold cavity tends to push apart the mold plates.
The clamping unit must have adequate locking force to keep the mold fully closed during the several
injection steps. Insufficient locking force leads to flash on molded parts, dimensional variation,
and can even damage the mold parting line or accelerate mold wear. Depending on the polymer being
processed, a reasonable estimate of required clamping force is three to five tons per square inch times
the total projected area at the parting line of part(s) and runner(s). Higher viscosity grades,
such as, highly filled compounds, may require higher pressure.
Screw Speed Calculation:
Screw
rotation speed (rpm) has a major effect on the quality of the polymer melt. Too low a speed increases
the cycle time, while high screw speed may thermally degrade the polymer. The required screw speed
for a specific polymer depends on the polymer viscosity and the screw diameter. Our Product Tool
(link located on the upper right site of this page) contains recommended screw speeds for each grade. Injection
molding recommendations for our products:
Celcon® and Hostaform® Acetal Copolymers
Celcon
and Hostaform acetal copolymers can be processed on all current standard injection molding machines
(presses).
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of six, and a metering zone of four diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 3:1
- For glass-fiber reinforced grades, both barrel and screw should
be made from a wear-resistant grade of steel
- Due to the short residence time, suitable shot volumes range between
30 and 70 % of the maximum metering capacity of the machine
- A free flow nozzle is best for these resins
Celanex® PBT, Vandar® PBT, Riteflex® COPE, and Impet®
PET Polyester Products
Celanex PBT, Vandar PBT, Riteflex
COPE, and Impet PET polyester resins can be processed on all current standard injection molding machines.
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of six, and a metering zone of four diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 2.5:1
- For glass-fiber reinforced grades, both barrel and screw should
be made from a wear-resistant grade of steel
- Due to the short residence time, suitable shot volumes range between
30 and 70 % of the maximum metering capacity of the machine
- A free flow nozzle is best for these resins
Fortron® Polyphenylene Sulfide (PPS)
Fortron
PPS resins can be processed on all current standard injection molding machines.
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of six, and a metering zone of four diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 2:1
- Wear and corrosion protective measures are recommended. A hard
material coating or powdered metal coating should be used on the screw. It could also be boronized.
The cylinder should also have interior armouring or a bimetallic coating. The arm parts of the non-return
valve should be coated with powdered metal steels
- Due to the short residence time, suitable shot volumes are from
30% to 70 % of the maximum metering capacity of the machine
- Fortron PPS can be processed using a free flow nozzle, but this
usually requires a reduction of the machine nozzle temperature. Shut off nozzles are recommended where
large orifices are required.
Vectra® Liquid Crystal Polymer (LCP)
Vectra
LCP resins can be processed on current standard injection molding machines.
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of five, and a metering zone of five diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 2:1 for small machines or about 3:1
for large machines.
- Wear and corrosion protective measures are recommended. Boronize
the screw or use a hard material or powdered metal coating. Use interior armouring or apply bimetals
to the cylinder. Use powdered metal steels on parts of the non-return valve
- Due to the short residence time, suitable shot volumes range between
50 and 75 % of the maximum metering capacity
- Vectra LCP can be processed with a free flowing nozzle, but this
usually requires a reduction of the machine nozzle temperature. Shut-off nozzles are recommended where
large orifices are required
- Due to the low viscosity of LCPs, the non-return valve must be
operating flawlessly. The melt cushion should be monitored to insure this is the case
- High plastication temperatures are used due to the fast cycling
of this material
- Where short metering paths are required, a pressure accumulator
may be advisable in order to achieve high injection speeds
Celstran® Long Fiber Reinforced Thermoplastics (LFRT)
Celstran
LFRT products may be processed using current standard injection molding machines having screw diameters
greater than 40mm (1.6 inches).
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of six, and a metering zone of four diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 2:1. Screw flight depth should be
at least 4.5mm (0.18 inches)
- Wear and corrosion protective measures are recommended. Use
a boron treated screw or one with a hard or powdered metal coating. Use interior armouring or
a bimetallic coating on the cylinder and arm parts of the non-return valve with powdered metal steels.
Additional corrosion protection of the melt carrying components in the plastication unit is recommended
when working with Celstran LFRT nylon or PPS products
- Due to the short residence time, suitable shot volumes are from
30% to 70 % of the maximum metering capacity of the machine
- Celstran LFRT is usually processed using a free flow nozzle, but
it requires an orifice diameter greater than 0.16 inches (4 mm) and preferably larger than 0.125 inches
(6 mm). A shut-off nozzle may be advisable if a large orifice is used
- An easy flowing, three-part, check-ring type of non-return valve
with a large cross section is recommended
Topas® Cyclic Olefin Copolymer (COC)
Topas
COC resins can be processed on current standard injection molding machines.
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of six, and a metering zone of four diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 2.3:1
- Due to the short residence time, suitable shot volumes are from
30% to 70 % of the maximum metering capacity of the machine
- Topas COC is best processed using a free flowing nozzle
GUR®/Hostalloy® Injection-moldable ultra-high molecular
weight polyethylene (UHMW-PE)
GUR UHMW-PE 5113 and Hostalloy
731 UHMW-PE products can be processed on current standard injection molding machines.
- A three-zone screw should be used, having a feed zone
of approximately ten diameters, a compression zone of six, and a metering zone of four diameters. It
should have an L/D ratio of 20:1 with a compression ratio of about 2:1and preferably less than 2.5:1
- Due to the short residence time, suitable shot volumes are from
30% to 70 % of the maximum metering capacity of the machine
- These injection-moldable GUR/Hostalloy UHMWPE products are best
processed using a free flow nozzle
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