Troubleshooting Focus: Sprue Sticking

Material sticking can bring processing to a standstill, regardless of its source. When troubleshooting, keep in mind that the location of a sticky part in the mold is not necessarily the area of the mold that is the cause. Different sections of the mold can hang onto the part and exerted force can cause the part to bind in another section. Carefully evaluate what happens as the mold opens with special attention to four possible causes for sticking at the sprue. 

Sprue sticking

If you have more questions about sprue sticking, talk with your Eastman technical service representative and ask for a free copy of our Injection Molding Troubleshooting Guide.

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In case you missed our small appliance acoustics webinar—it’s now available on demand.


Noise is a turn-off. Quiet is a value-add. Consumers are willing to pay a premium for small appliances that provide robust performance—and do it with less noise.

This 1-hour webinar shows where noise comes from and how a material change can help reduce it. 
Reducing noise without reducing performance.
In our free webinar, Tritan experts discuss the source of noise in motorized small appliances, how to test the acoustic properties of materials, and how Eastman Tritan copolyester can help reduce noise and create more satisfied customers. 

Sound design with Tritan can add significant value to small appliances by:
•  Allowing more powerful motors
•  Increasing customer satisfaction
•  Receiving positive online reviews
•  Achieving product differentiation
•  Creating opportunities for higher margins
 
TMI TIP: For more information about the acoustic properties of Tritan, download this brochure. 

 
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Hot runner molding systems #1

Introduction and advantages

Eastman receives many questions about molding Eastman Tritan copolyester with hot runner systems. It can be a complex topic, loaded with variables that include not only mold design, but also part size, polymer formulation, and part design. Success depends on early collaboration and clear communication between Eastman, molders, tool builders, and hot runner suppliers.
 
We’re usingTritanMoldIt.com as a platform to jumpstart this communication between stakeholders.  During the next few months, the Tritan experts will post a series of blogs, beginning with this overview and advantages of hot runners for amorphous copolyesters, including Tritan. 

We invite you to help shape our series of hot runner blogs. Send your feedback. Ask your questions. Share your success stories. We look forward to hearing from you.
 

Key advantages of hot runner systems

In a hot runner molding system, the runners are within the mold. They are heated to maintain the plastic resin in a liquid state (a temperature above the material’s softening temperature, Tg) within the tool until it passes through the gate into the mold cavity. Unlike a cold runner system, hot runners are not ejected with the finished part. Instead, they stay in the mold in a liquid state, ready to fill the cavity on the next shot.
 
Hot runner systems are popular for high-production runs or in high-cavity molds, where quality is critical and gate witnesses are objectionable. A hot runner system can offer these advantages:
• Less resin used because there is virtually no waste
• Shorter flow path
• Reduced injection time; reduced open-dwelling time
• Lower cost per part for high-volume production—especially small parts
• Higher part quality
• More design flexibility


 

In Part 2 of our hot runner series, we’ll start focusing on specific ways for getting the best results with Tritan in a hot runner system. 

 
TMI TIP: Help make this ongoing series on hot runners more relevant for your needs. Let us know your feedback or questions—and share your experience with hot runner systems and Tritan.  

For more information about hot runners, download the Eastman Tritan copolyester Processing Guide
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Troubleshooting Focus: Flowlines
Flowlines are wavy or rippling surface defects. They can appear as lines, streaks, or patterns, but are consistent with the material flow within the cavity of the mold. They occur when the molten plastic passes through the mold or gate and can have many causes and corrective actions. 

If you have more questions about flowlines or other molding defects, talk with your Eastman technical service representative—and ask how to receive your free copy of our Injection Molding Troubleshooting Guide
 

TMI TIPFor more information about getting the best results when you mold with Tritan, watch the webinar Copolyester Processing Solutions.
 
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Secondary Operations: Adhesive Bonding
Unlike solvents, which evaporate, an adhesive layer remains a functional part of the finished assembly. Therefore, the characteristics of the adhesive layer play a key role in the performance and appearance of the finished part.
 
Consider these characteristics when selecting an adhesive:
  • Chemical compatibility with parts being joined
  • Aesthetics of the finished joint
  • Expansion/contraction with temperature changes (NOTE: if expansion/contraction are a major concern, consider mechanical fasteners.)
  • Brittleness, rigidity, flexibility
  • Durability/service life
  • Adhesive strength (adhesion to the plastic)
  • Cohesive strength (resistance to internal tearing)
  • End-use requirements
 
Eastman Tritan copolyester offers outstanding chemical resistance and has been studied with many adhesives and different bonding procedures. 
Adhesive bonding procedures for Eastman Tritan copolyester     
When adhesive bonding parts made with Tritan, joining surfaces should:
  • Fit well without forcing
  • Have no visible gaps
  • Be smooth but not polished:
    • Sand the surfaces you wish to bond with a 120-grit or finer paper.
    • Diamond-wheel polishers, jointers/planers, or other mechanical devices can produce excellent results.
    • Do not use soft-polishing wheels or flame polishing, as they can round the edges, creating gaps and improper fit.
 
Before selecting an adhesive system, conduct a careful evaluation of the part application to ensure the adhesive provides both acceptable performance (bond appearance and strength) and that it meets all applicable regulatory requirements. See inset box for several recommendations.
 NOTE: This list of recommended adhesive systems does not include all products have been used successfully with Tritan. For best performance, always follow the guidelines provided by the adhesive manufacturer.
    
Recommended adhesive systems for use with Tritan
  • Dymax adhesives for medical devices 
  • Henkel adhesives for medical devices 
  • Weld-On® 55*
  • Lord® adhesives 7542 A/B*
  • Flex Welder 14345*
  • Lord adhesives 403/19*
  • Lord adhesives 406/19*
  • Lord adhesives 406/17*
  • Plastic Welder® II 14340*
*Tested according to ASTM D1002

For details about bonding Tritan to itself and to other materials, contact your Eastman technical representative. For more information about adhesive bonding as well as tips for decorating, painting, overmolding, and other tips, download a free copy of the Secondary operations guide
 
TMI TIP: Adhesives that contain a volatile component may shrink while curing. To compensate for shrinkage, cut the joint on an angle, thereby providing space for the joint to be slightly overfilled. Consult your adhesive supplier literature for specific information on shrinkage. 
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