At optimum draft angles (c. 2°, but at least 1°) and with well-polished molds, PLEXIGLAS® moldings can usually be demolded without any problems.If there are problems with demolding owing to unfavorable mold or molding design, PLEXIGLAS® molding compounds can also be supplied in special "le" grades for easy mold release. If the requirements to be met by the part allow it, grades of PLEXIGLAS® molding compound with higher impact strength can be used instead of standard molding compound.

For thin-walled parts, an increase in mold temperature, higher injection speed or increased melt temperature have a positive effect. If the thermal and mechanical requirements to be met by the molding allow it, a grade of molding compound with greater ease of flow can be employed. PLEXIGLAS® 6N shows particular ease of flow. Among the impact-modified grades, PLEXIGLAS® Resist zkBR or the PLEXIGLAS® Resist zkHF series are recommended, for example.

PLEXIGLAS® molding compound is dry when packaged and can be processed without predrying even after several weeks' storage, thanks to the polyethylene lining. We nevertheless advise our customers to use suitable drying equipment.

PLEXIGLAS® can be processed on injection-molding machines with 3-zone generel purpose screws for thermoplastics.

Predrying should generally be performed at the highest possible temperatures without causing the pellets to cake. Temperatures of 10 to 15°C below the Vicat softening temperature should therefore be observed. You will find the Vicat softening temperature in our product information leaflets on the respective material or in the CAMPUS database. We recommend the use of desiccant-type driers.

Plasticization should be performed as gently as possible (at low speed). The usual peripheral speed for processing PLEXIGLAS® is 0.3 m/s.

This fault points to various causes:

• Mold not optimally filled
• Shrinkage not adequately compensated for
• Air entrapment (fluctuations in material feed)

Remedies:

• Examine material feed
• Reduce melt temperature
• Extend hold time
• Increase holding pressure
• Reduce injection speed
• Increase mold temperature
• Reduce screw speed
• Raise back pressure
• Improve predrying
• Enlarge gates and possibly runners

Possible cause:

The melt is not optimally pressed against the mold surface.

Remedies:

• Increase melt temperature
• Raise mold temperature
• Increase injection speed
• Increase injection pressure
• Exchange material

This fault points to various causes:

1. Material is too damp

Remedies:

• Predry material
• Lower melt temperature
• Raise injection pressure
• Increase injection speed
• Increase back pressure

2. Decomposition due to overheating of melt

Remedies:

• Check melt temperature (cylinder nozzle and hot runner) and reduce if necessary
• Lower back pressure
• Reduce screw speed
• Reduce injection speed
• Enlarge gates and possibly runners

Possible cause:

Insufficient pressure / dwell pressure to compensate for shrinkage

Remedies:

• Check material feed
• Increase mold temperature
• Reduce melt temperature
• Raise holding pressure
• Prolong hold time
• Extend injection time
• Increase injection pressure
• Reduce injection speed
• Lower screw speed - Enlarge gates and runners

Possible cause:

Cold slug that protrudes into the mold

Remedies:

• Check that nozzles are tight
• With mechanical shut-off nozzle, check that the latter functions properly- Increase nozzle temperature
• Raise mold temperature
• Avoid sharp edges, particularly at the transition from the gate to the mold cavity
• Round off and gates polish well
• Polish the nozzle, which should be conical to allow reliable extraction of the cold slug
• Provide a blind hole in front of the ejector
• Raise melt temperature

Possible cause:

Sprue is overloaded or not optimally designed

Remedies:

• Polish sprue bushing
• Make sure sprue bushing is conical and oversized in comparison with the nozzle
• Enlarge ejector or the undercut around it
• Round off Z-shaped ejector slightly to prevent sprue from breaking at this point
• Prolong cooling time
• Reduce injection pressure
• Reduce holding pressure

Possible cause:

Unfavorable venting of mold

Remedies:

• Reduce injection speed
• Reduce cylinder temperature
• Install vent
• Change wall thickness in mold
• Optimize predrying

Possible cause:

Irregular shrinkage due to different molding section or contour (surface)

Remedies:

• Extend cooling time
• Control temperature of two mold halves separately; cool the "hollow" side, keep the other side warm
• Install heating / cooling channels just below the mold surface
• Lower melt temperature by reducing band heater temperature, screw speed and back pressure
• Decrease mold temperature
• Use a clamping device for the moldings