Injection Molding Conditions for SUMIKAEXCEL PES

Selection of Injection Molding Machine

SUMIKAEXCEL PES can be molded by standard inline type and plunger type (ram fed) injection molding machines.

Screws and Cylinders

  • As filler reinforced grades of SUMIKAEXCEL PES contain glass fiber and other materials as filler, it is preferable that materials with good abrasion resistance be utilized.
  • Standard full flight screws are preferable for their low shear heating. Sub-fight screws and high mixing screws are not recommended for avoiding degradation of resin due to high shear heating.

Typical screw designs are as follows:

  • L/D: screw length (L) / screw diameter (D) = a value of approximately 20 is preferable.
  • Compression ratio: compression ratio = a value of 2 - 2.2 is preferable.
  • Zone length ratio
    e.g.)
    • Feeding zone: approximately 55%
    • Compression zone: approximately 25%
    • Metering zone: approximately 20%
  • Screw heads with check valve are recommended.

Nozzles

  • Nozzle materials must be suited to the particular screw and cylinder utilized.
  • Open nozzles should always be used. Shut-off nozzles should not be used, as they have excessive dead space that can trap and retain resin.
  • The nozzle heaters used must have independent temperature control employing the PID control method. The PID control method provides good controllability.
  • When extension nozzles are used, they should be designed with consideration for consistent temperature distribution.

Injection Unit and Control System

  • As SUMIKAEXCEL PES possesses high melt viscosity, it is preferable to utilize molding machinery that is capable of supplying an injection pressure of 200 MPa or greater.
  • As SUMIKAEXCEL PES possesses high melt viscosity, large amounts of torque are produced within the metering zone. Therefore, it is recommended that a high power injection unit is used.

Molding Machine Capacity

  • Although capacity depends upon the size of the moldings, the best results are obtained from a combination of cylinder diameter and mold clamp pressure that allows for continuous metering of 1/3 - 3/4 of the total injection capacity. If there is inadequate continuous metering capability, then any excess residual resin may result in a variety of molding defects.

Pre-drying

As SUMIKAEXCEL PES is susceptible to water absorption, it must be dried thoroughly prior to usage. SUMIKAEXCEL PES resin should be dried at temperatures ranging from 160 - 180 deg C for 5 - 24 hours, using a hot air circulation oven or a dehumidifying dryer. When drying using oven trays, SUMIKAEXCEL PES resin should be spread on the trays to a thickness of 50 mm or less. In particular, for molding large sized moldings, it is recommended that SUMIKAEXCEL PES resin is dried at a temperature of 180 deg C.
In addition, the use of a dehumidifying dryer is recommended for non-reinforced grades and for large sized moldings. If a hopper dryer is used, it is important to ensure that it contains both adequate resin capacity and large heat capacity. If sufficient pre-drying does not occur, then silver streaking may appear on the surface of the molding. If this kind of phenomena occurs, then further drying of the resin is necessary.
As SUMIKAEXCEL PES is not susceptible to hydrolysis, it will not deteriorate during the drying process, if dried in accordance with the abovementioned conditions.

Figure 1 Relation of Drying Temperature / Time and Water absorption

Figure 1 Relation of Drying Temperature / Time and Water absorption

Molding Conditions

Standard molding conditions for SUMIKAEXCEL PES are as follows:

Grade 3600G
4100G
4800G Glass Fiber
Reinforced Grades
Drying Conditions 160~180 deg C×5~24hr 160~180 deg C×5~24hr 160~180 deg C×5~24hr
Cylinder Temperature (deg C) Rear 300~340 320~340 300~340
Center 320~370 330~370 320~370
Front 330~380 340~390 330~380
Nozzle 330~380 340~390 330~380
Tool Temperature(deg C) 120~180 120~180 120~180
Injection Pressure(MPa) 100~200 120~180 100~200
Holding Pressure(MPa) 50~100 80~150 50~100
Injection Speed Low speed - medium speed Low speed - medium speed 50~100
Screw Rotation Speed(rpm) 50~100 50~100 50~100
Back Pressure(MPa) 5~10 5~20 5~10

Resin Temperature

A resin temperature of 330 - 380 deg C is recommended. As SUMIKAEXCEL PES possesses high melt viscosity, the resin temperature tends to increase to a value somewhat higher than the cylinder temperature setting, thus may result in a temperature difference of more than 40 deg C. The resin temperature must be carefully monitored while molding operations are performed.

Figure 2 Flow Lengths of SUMIKAEXCEL PES

Figure 2 Flow Lengths of SUMIKAEXCEL PES

Tool Temperature

The tool temperature should be set in a manner such that the surface temperature will be between 120 - 180 deg C. Also, ensure that the surface of the mold has a uniform temperature distribution.
If the tool temperature is excessively low, moldings may warp and crack (rupture) due to residual stresses. Residual stresses may also cause glass fibers to be visible on the surface of moldings using glass fiber grades. Moldings having low residual stresses can be obtained by using a high tool temperature. However, if the tool temperature is excessively high, deformation may occur during mold release.
With respect to the methods used for tool heating, both heaters and oil temperature control are recommended. However, for the following tools, oil temperature control should be implemented in order to ensure the most uniform tool temperature distribution: tools that have complex shapes; deep tools; and tools that have slide cores.
In particular, when molding large sized products and when using non-reinforced grades, additional precautions must be taken to ensure that proper tool temperatures are maintained.

Injection Pressure and Maintained Pressure

In general, the molding of SUMIKAEXCEL PES requires a high injection pressure. Over 150 MPa of injection pressure is required for the molding of thin-walled products; the use of glass fiber reinforced grades; and for moldings that have long flow lengths.
It is recommended that the maintained pressure is set to 1/2 - 1/3 of the injection pressure. Lower maintained pressures will result in moldings that have less residual stress.

Injection Speed

In general, SUMIKAEXCEL PES should be molded at low - medium injection speeds. However, the optimum injection speed will vary depending upon the shape of the molding.
As SUMIKAEXCEL PES has a high melt viscosity, an excessively high injection speed will result in burning and silver streaking, due to the heat produced from shearing and adiabatic air compression. However, high injection speeds are required for the molding of both thin-walled products (1 mmt or less) and products having long flow distances.
In general, lower injection speeds result in moldings that have less residual stress.

Screw Rotation Speed and Back Pressure

It is recommended that screw rotation speed is between 50 - 100 rpm in order to prevent increases in resin temperature due to shear heat.
The application of the appropriate back pressure allows for consistent melting of resin. The recommended back pressure is 5 - 10 MPa.
When using PES grades that have high molecular weights, ensure that a greater back pressure is applied. However, if back pressure becomes excessively high, the resin may overheat and overcharging may occur.

Purging

The following materials are suitable for usage in purging : polyethylene that has a high molecular weight of approximately MFR 0.05;
polycarbonate; or more preferably, these same materials yet containing glass fiber.
After shooting out any resin remaining within the cylinder, set the cylinder temperature to 280 - 300 deg C. Once the temperature has dropped to 340 deg C or less, feed in high molecular weight polyethylene, then continue the purging operation until the preset temperature has been reached.
If molding is operated with SUMIKAEXCEL PES after purging, shoot out all purging agent that remains within the cylinder, then set the initial cylinder temperature to a relatively low temperature (300 - 320 deg C) and feed in the SUMIKAEXCEL PES. After the purging agent has been completely displaced with SUMIKAEXCEL PES at this temperature, raise the cylinder temperature to the molding temperature. If SUMIKAEXCEL PES has been fed in after the temperature of the cylinder has already risen to the molding temperature, then some purging agent may tend to remain inside the cylinder. This may lead to thermal deterioration of the purging agent, possibly resulting in molding defects.
Whenever the molding process is paused for a short period of time, set the cylinder temperature to 250 - 260 deg C, in order to prevent thermal deterioration of the resin. If the resin decreases to a temperature lower than 250 deg C, the screw surfaces and internal walls of the cylinder may be damaged and lumps of hardened resin may be formed after the molding process has resumed. When the molding process is to be paused for a long period of time, reduce the cylinder temperature only after the inside of the cylinder has been purged with purging agent.

Purging Method

The purging method for SUMIKAEXCEL PES is explained here.

Recommended purging agents : Polyethylene that has a high molecular weight of approximately MFR 0.05 ; polycarbonate; or more preferably, these same materials yet containing glass fiber.
  • As SUMIKAEXCEL PES requires high processing temperatures, generating smoke, gas emission and resin scattering may occur during the purging process.
  • Ensure that none of the purging agent is left within the cylinder.
1 End of molding Shoot out all preceding resin (from within both hopper and cylinder).
Set the cylinder temperature to 280 - 300 deg C.
2 Feeding of purging agent Once the temperature has decreased to 340 deg C or less, feed in the purging agent, then continue the purging operation until the preset temperature is reached.
As soon as all purging agent has been shot out, if polycarbonate is being used, feed in the polyethylene to displace the polycarbonate in the cylinder.
3 End of operation Turn OFF the power. (It is OK to power down while the temperature is decreasing.)

Replacement with SUMIKAEXCEL PES

1 End of molding Shoot out all preceding resin (from within both hopper and cylinder).
2 Raising of cylinder temperature Set the cylinder temperature to the molding temperature for SUMIKAEXCEL PES.
3 Displacement of resin After completely displacing the resin with SUMIKAEXCEL PES, resume the molding process.
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