Selection of Injection Molding Machine

SUMIKAEXCEL PES can be molded using standard in-line type injection molding machines and plunger (preplasticating) type injection molding machines.

Screw and Cylinder

• Since the filler reinforced grades of SUMIKAEXCEL PES are filled with glass fiber, etc., it is recommended to use wear-resistant materials for screws and cylinders.
• A standard full flight type screw is good for SUMIKAEXCEL PES. Sub-flight screws and high mixing screws are not recommended because the residence time in the cylinder may become longer, or the resin temperature may rise above 400°C due to shear heating.
• A typical screw design suitable for SUMIKAEXCEL PES is as follows.
  • L/D (screw length [L]/screw diameter [D]) : approx. 20
  • Compression ratio : around 2 to 2.2
  • Ratio of each zone :
    Feed zone : around 55%
    Compression zone : around 25%
    Metering zone : around 20%
• Screw heads for in-line type injection molding machines are recommended to be equipped with backflow prevention mechanism.

Nozzle

• For the material of the nozzle, the same as those in "Screw and Cylinder" can be used.
• Use of the open type nozzle is suitable. Shut-off nozzles are not preferable because they have a lot of dead space and resin tends to retain in it.
• For the nozzle heater, it is recommended to use an independent temperature controller with PID control.

Injection Unit and Its Control System

• Due to the high melt viscosity of SUMIKAEXCEL PES, it is recommended that injection molding machines with a maximum injection pressure of 200MPa or higher be used.
• Screw rotation torque during metering tends to be large also due to high melt viscosity, so it is recommended that injection molding machines with high power plasticizing units be used.

Injection Capacity

• It is recommended to select a molding machine whose shot size is about 1/3 to 3/4 of its maximum injection capacity. If the shot size is too small, the residence time of resin in the high temperature cylinder will be longer, and various molding defects are more likely to occur.

Mold Design

As PES has high melt viscosity and low mold shrinkage, the following factors must be taken into account when designing molds.

Mold Materials

• Molds used for making prototypes and for small production lots can be composed of carbon alloy steel for machine structural use (S55C). However, these molds should be hardened by quenching if they are to incorporate sliding core parts.
• When mass production and high dimensional precision are required, it is recommended that steels having greater rigidity be used, such as chrome molybdenum steels (SCM435 and SCM440) or alloy tool steels (SKD11 and SKD61).
• Before using a material other than the above, carefully consider whether there are any problems. (Cu alloys, etc., are not recommended as mold materials.)

Sprue

• The length of the sprue should be designed as short as possible, and it is recommended that the taper angle be enlarged (up to 5°).
• A sprue lock should be installed in order to secure better sprue release, as shown in Figure 4-3-1.

Figure 4-3-1 Sprue Diagram

Runner

• Runners are preferred as thick and short as possible. The thickness and length should be determined with consideration of resin flowability.
• Runners should have a circular or trapezoidal cross-sectional shape.
• Considering the gate balance is also important.

Gate system

Side gate

• For rectangular gates, it is most efficient to use deep lands with short lengths. The appropriate land length is 1mm or less, and the land gate depth should be about 70% of the wall thickness of the molded products.

Figure 4-3-3 Side Gate Diagram

Pinpoint / Submarine Gate

• The gate diameter should be between 0.8 to 1.2mm, with land lengths of 1mm or less. If flow length are long, it is preferable to have multi gates rather than to enlarg the gate diameter.

Figure 4-3-4 Pinpoint/Submarine Gate Diagram

Film gate

• The preferred gate depth should be equivalent to "the wall thickness of the molded products × 0.5". The land length should be 1mm or less.

Figure 4-3-5 Film Gate Diagram

Draft Angle

• As PES has low mold shrinkage, draft angle should be in the range of at least 1° (1/60) to 2° (1/30). For deeper cavities, a larger draft angle would be recommended.
• As thin-walled products tend to be overfilled, a larger draft angle is recommended.
• Larger draft angles are also recommended for glass fiber reinforced grades.
• If adequate draft angles cannot be utilized due to the shape of the molded products, it may be necessary to install slide cores or devise some good ejection methods.

Air Venting (Gas Drainage)

• The recommended depth for air vents ranges from 0.01 to 0.05mm. SUMIKAEXCEL PES has high melt viscosity, so flash defects will not easily occur even when 0.05mm air vents have been installed.
• Air vents must be installed for the molding of thin-walled products.