Torsten's Training Tip: Thermal Properties

Understanding the thermal properties of polymers is important for evaluating the heating and cooling behaviors of molded parts. Since polymer injection molding is a process of heat exchange, thermal properties play a key role in this process.

During the injection molding process, a polymer is heated in different ways, beginning inside the machine cylinder. Electric heater bands around the cylinder create heat which is transferred through convection from the cylinder to the polymer. Then, the rotating screw creates shear heat which transfers to the polymer on top of the convection transfer.

In addition, when the material is rapidly injected through the machine nozzle body, nozzle tip, runner system and gate, more shear heat is generated. As the shear heat energy increases, the temperature of the polymer continues to increase, driving up the temperature of the material inside the cavity.

The two most important material properties are specific heat capacity and thermal conductivity.

Understanding the concepts of specific heat capacity and thermal conductivity is key to understanding how they affect part and mold design. Specific heat capacity is how much heating energy is required to bring a polymer to its process temperature range. Thermal conductivity is a property that will indicate how quickly heat will move through the polymer material during the heating and cooling phase. 

By understanding these behaviors, decisions can be made that will influence the overall quality of the molded part, from wall thickness versus flow distance capability to location and number of gates to overall cycle time.

Kruse Training offers a full section of Polymer Materials lessons. You can purchase individual lessons or the full set.

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Kruse Analysis, Inc. has been providing CAE simulation services to the plastic injection molding industry since 1995. By using advanced Moldex3D technology, Kruse helps customers troubleshoot from product design to development, optimize design patterns, shorten time-to-market, and maximize product return on investment (ROI). For more information, visit www.kruseanalysis.com

Kruse Training, Inc. offers a state-of-the-art online knowledge and training solution that use 3D process simulation technology to demonstrate cause and effect of molding behavior. This interactive training program illustrates how "The Circle of Knowledge" between the part designer, mold designer, and process engineers works in the real world of plastic mold and design. For more information, visit www.krusetraining.com