Efficient multicavity processing of small medical parts


There’s a big incentive for molders of small medical parts to increase production efficiency by going to 16, 32, or even more cavities using hot runner/valve gate systems. Molders have always had great success with Eastman Tritan copolyester for medium-to-large components of medical devices and electronic instruments. Recently, our commitment to small, multicavity solutions began delivering big results. 

We are working with designers and engineers to introduce Tritan into small, precision, multicavity injection molded components as a bisphenol-free alternative to polycarbonate (PC) and acrylic.

Here are a few issues to consider when designing molds for multicavity production.   

Residence time
  • As cavitation is increased, the distance from the machine nozzle to the cavities increases. This results in a greater volume of resin in the hot runner manifold and, subsequently, longer residence times. For example, in a recent 32-cavity mold, the weight of the material in the hot runner system is 22 times the weight of all 32 parts combined.
  • Eastman's guideline for design residence time with copolyesters is 5 minutes.  

Pressure drop
  • Higher pressure losses through the runner system are typical of higher-cavitation tooling, because the increased distance from the machine nozzle to the cavities results in longer flow-length requirements for the resin.
  • Eastman's guideline for maximum fill pressure for a runner/part/gate is 20,000 psi.

Balance
  • Higher-cavitation tooling can make it more difficult to achieve cavity-to-cavity balance during the filling process. This can affect part quality and increase scrap rate.
  • Recently, we solved this problem with a synchro-plate system that mechanically actuates all valve gates simultaneously. Contact Eastman for more details. 

Venting and cooling
  • Inadequate cooling and venting can result in high levels of residual stress and increased warpage.
  • Increasing cooling channel diameters without maintaining velocity can actually result in a decrease in the total heat removed in a given channel.
  • When molding Tritan, it is critical to freeze the outer skin thoroughly before ejection to prevent sticking and deformation of the part. (See Jan. 5 blog on “Proper Cooling.”)

Mold finish
  • Some engineering polymers are very sensitive to mold finish, making mold polishing critical.
  • In some cases, surfaces polished smoother than required for ejection only add to the mold cost. What’s more, highly polished surfaces can create a vacuum in low-or no-draft areas and actually hinder ejection.
  • Tritan is less sensitive to mold finish—and in some cases has run successfully with less thorough mold polishing

You can see more information about mold design under either the MEDICAL or DURABLES tab above.

 

TMI TIP: As always, early collaboration helps ensure best results from high-cavity molds. Watch this unique collaboration video



You can learn more about how Eastman is helping customers achieve optimal tooling, processing, and manufacturing results in the August 2015 issue of Plastics Technology.  
 
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Join us at MD&M West!

You can speak with a Tritan expert in person at MD&M West. 

Eastman will be exhibiting in Booth 2407, February 9 to 11. Stop by to see how Eastman Tritan copolyester and other medical-grade polymers are helping device makers meet regulatory requirements, improve patient safety, and ensure confidence in end-product performance.
 
While at our booth, you can pick up two white papers with great information about important roles chemical resistance plays in preventing health care-acquired infections and complying with best practices for oncology drug delivery devices.  


MD&M West will be the center of the medtech world in early February. It’s a great place to discuss possibilities our whole portfolio of medical-grade polymers. You’re invited to talk with Tritan experts about specific advantages for medical devices, including:   
•  Toughness    
•  Crystal clear or opaque
•  Chemical resistance
•  Sterilization stability
•  Made without bisphenol A (BPA)
•  UL V2 flame rating
•  Successful secondary operations 
 
TMI TIP: To schedule a private appointment during your booth visit, go to www.Eastman.com/MDMW2016.   

 
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Why devices are failing in oncology drug delivery applications

Some traditional polymers used in drug delivery devices are not compatible with modern oncology chemotherapies—including the cancer drugs and the carrier solvents that help make them effective.
 
Device manufacturers have more reasons than ever to understand the chemical resistance of the materials they use in devices, including:
•  The widespread use and growing economic importance of oncology drugs
•  A recent FDA Safety Alert* concerning infusion devices made with polycarbonate (PC) or acrylonitrile-butadiene-styrene (ABS)

Polymers that have a low level of compatibility with chemicals such as lipids, disinfectants, and specific oncology drugs and solvents can experience environmental stress cracking (ESC) or premature device failure in the presence of applied or residual stress. 
 
All stakeholders are working together to reduce product failure and improve safety through:
•  Vigilance by regulatory agencies
•  Chemical resistance research by polymer manufacturers
•  Informed polymer selection for oncology drug delivery devices
 
For its part, Eastman has conducted a series of chemical resistance tests on Eastman Tritan copolyester and competitive polymers. The test results are presented and discussed in a recently posted webcast titled “Why Devices are Failing in Oncology Drug Delivery Applications”.



Eastman also offers a free white paper that will give you more details of the testing.
 
 


 
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Proper cooling saves time, improves quality

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


 

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Designing for Manufacturability Webinar Tomorrow!

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.
 

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