With any polymer, poor and uneven cooling can result in:
•  Increased cycle time
•  High levels of residual stress
•  Increased warpage
•  Sticking and difficulty in ejection 

Considering the unique properties of Eastman Tritan^™ copolyester, a few important guidelines will improve efficiency and part performance. 

Because of the relatively low flex modulus of Tritan, uniform and efficient mold cooling—especially in the cores— is critical for the successful molding and ejection of parts.
 
When working with Tritan, you need to make sure you are cooling the resin enough to set up the outer skin of the part in order to get good release from the mold. This initial skin formation can take 10 to 20% longer than normal engineering resins, but cooling time throughout the rest of the part will be approximately the same.
 
Here are a few tips to improve cooling efficiency:
•  Design ample mold-cooling channels with proper spacing and sizing.
•  Use properly sized pumps and supply lines to deliver a good turbulent flow of water around the cavity. (The flow rate should be high enough to reach a minimum Reynolds number (Nr) of 6,000 in those areas where cooling is desired.)
•  Use chillers, if practical, to ensure a proper supply of cool water to molds. 
•  Remove heat uniformly to avoid hot spots that can cause sticking and local deformation.
•  Provide ample cooling near potential hot spots such as sprues and hot runners.
•  Pay special attention to cooling heat sinks in pins and thin areas, and around slides.
•  The mold should be cooled to 60°C (140°F) before ejection.
                       
For more information, see May 29, 2014 Blog “Tooling design — keys to success” 

For best results, involve an Eastman tech services engineer or design services engineer early in your planning. We’re prepared to discuss mold design, including line spacing and core cooling techniques such as baffles and bubblers, and much more. 

 

TMI TIP: For more information download the Eastman polymers Processing and mold design guidelines.

 

The Tritan experts at Eastman are hosting a live webinar on December 10, 2015, from 11:00 to 12:00 EST. This webinar will cover these important considerations to help you design for manufacturability:

• Material selection criteria
• Part design for injection molding
• Tool design for injection molding
• Molding workcell design 
• Processing tips for Tritan

Join us live! Register now to participate in “Designing for Injection Molding Manufacturability,” offered by Eastman from 11:00 to 12:00 pm EST on Thursday, December 10, 2015.
 

Proper mold design provides a giant step toward reducing problems like flashing when injection molding with Eastman Tritan^™ copolyester and other Eastman copolyesters. Collaborating with an Eastman technical service representative early in your project can help ensure you’re off on the right foot.

To help ensure continued molding success, this blog focuses on three different types of flashing problems, their possible causes, and corrective actions you can take for each.


General Flashing:

Possible cause	Corrective action
1. Poor mold spot	Spot mold to ensure fit and vent depths at ~0.025mm (0.001in).
2. Injection Pressure too high	Reduce pressure. This may require higher melt temperature or lower injection speed.
3. Coost time too long	Shorten boost time, lower boost pressure, or move transfer to an earlier position.
4. Insufficient clamp tonnage	Increase clamp pressure or move to a machine with more tonnage.

 


Flash and Short Shot in Different Shots:

 

Possible Cause	Corrective action
1. Core shift	Check wall thickness for core shift. Investigate for source of core shift and repair mold.
2. Inadequate clamp tonnage	Increase clamp pressure or move to a machine with more tonnage.
3. Fill speed or pressure too high	Reduce speed or fill pressure.
4. Melt temperature too low	Check and raise melt temperature if needed.
5. Sprue too long too small, "O" dimension	Install correct-size sprue.

 

New medical-grade Eastman Tritan™ copolyester delivers peace of mind without sacrificing performance in medical-device applications. The unique combination of properties allows Tritan to satisfy a set of customer needs that previously have not been met by other polymers available to the medical-device industry.
Expect a balance of important advantages with Eastman Tritan™ copolyester MX711.  
 

• Processability
• Chemical resistance
• Toughness
• Hydrolytic stability
• Compatibility with sterilization methods
• Clarity
• BPA-free
• Secondary operations and assembly
• Heat resistance

 
Eastman Tritan™ copolyester MX711 is well-suited for medical-device applications that demand superior chemical resistance, clarity and hydrolytic stability, including:
 

• IV system components
• Blood therapy devices

Find more information here about the advantages of Tritan for a wide range medical applications.

 

Proper Gating Selection
 
  •Select a compatible gating style for the selected resin. Most conventional cold gating styles work well with copolyesters. For hot runner systems, valve gates should be used.
 
Design Tooling with good Cooling/Thermal Control
 
  •Copolyesters require good thermal control throughout the cavity for optimal processing.
 
Design Tooling with a plan for venting
 
  •Poor venting can result in burn marks and incomplete fill.
 
Design Tooling with a plan for ejection
 
  •Parts should be adequately supported during ejection to avoid part deformation/breakage
 
Click here for more successful processing tips