This Old Mold 1 - Cooling

Tips for optimizing existing molds to run Eastman Tritan copolyester
 

The success of Eastman Tritan copolyester—especially in medical devices—makes more brand owners want to try it. One challenge to even

greater success has been how to use molds designed for other plastics. Sometimes it works fine - sometimes not so much.

Successful molding of any polymer depends on the ability to fill the part, cool the mold, and "freeze" the melted resin. Failure to do

so can cause sticking and ejection molding difficulty—which can limit the number of parts per hour and the quality of the parts.

 

Since most competitive materials freeze off at a higher temperature than Tritan, the mold may now need to cool more efficiently and

quickly than the original design. Engineering solutions that are straightforward when a customer builds a new mold for a different resin

can become challenges when a molder wants to produce high-quality Tritan parts by optimizing “this old mold.”

 

 The basics

  1. The suggested mold temperature for running Tritan is 38°–66°C (100°–150°F).
  2. Uniform temperature throughout the mold helps ensure even heat transfer from both wall surfaces, which decreases residual stress and warpage and reduces cycle time. When optimizing an existing mold, keep this in mind so upgrades do not upset existing dynamics. 
  3. Tower water may be adequate, but we strongly recommend using chillers to ensure a proper supply of cool water to the molds. Properly sized pumps and supply lines are also critical.

Typical modifications
Here are the most common actions required when optimizing existing molds to run Tritan. 

1. Cooling the cavity walls
  • Consider the theramal conductivity of the mold material. This is one variable you can't change, so it's important to factor it into all changes you can make.
  • Evaluate the current cooling line layout, and make sure all changes are made to achieve uniform cooling.
  • Make sure you have a turbulent water flow in the lines-laminar flow only has ½ the cooling efficiency of turbulent flow. Changing flow dynamics may be more cost-effective than changing diameter of the coolant channel.
2. Cooling the cores
  • Use baffles or bubblers to achieve proper core cooling.
  • Consider circular cooling channels around the cavity and core inserts.
3. Cooling the gates
  • Injection molding gates typically have the highest heat load in an injection mold
  • Increased cooling efficiency here can pay big dividends.
4. Cooling around the sprues
  • Consider adding cooling lines adjacent to sprues.
  • Spiral cooling sprue inserts or high-conductivity sprue bushings can be cost-effective retrofits.
5. Don't forget venting.
  • Poor venting can result in incomplete fill, increased pressure heat, and bum marks.

 No old mold is typical
Every combination of existing mold properties and molding requirements is different. Because your needs are unique, we recommend involving Eastman as early in the planning as possible. Contact the Tritan Experts.

Eastman can review your tooling drawings and help you plan for uniform mold cooling. The Tritan experts can also help you evaluate the results of optimizing your old mold.