All melt channels together are called runner or runner system.
For these names, there is no distinction between hot and cold runner.
A good runner is responsible for a balanced filling of the cavity and less material and pressure loss.
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The pressure at different positions inside the cavity/runner is called “Pressure Distribution”.
Ideally in injection molding process, the pressure distribution should be uniform throughout the cavity after the molten plastic completely fills the cavity. In this case the molded part shrinks uniformly.
In reality due to the different cooling behaviour of the part there is always a difference in pressure distribution.
Injection molding simulation is a great tool to predict the pressure inside the cavity, which can help to achieve uniform pressure distribution as good as possible.
The unheated melt channel from machine nozzle / hot runner up to the cavity is called cold runner.
In the injection molding cycle the cold runner is cooling down and freezes.
The gate geometry is very flexible, like umbrella gate, cashew gate, ring gate.
The cold runner is ejected together with the part.
The separation from the part is done automatically or manually.
The collected cold runners will be recycled or disposed as waste.
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In an injection molding tool, the melt channel between cylinder and cold runner / cavity is called hot runner.
The difference from a cold runner is that the hot runner has at least one heater band to keep the hot runner at temperature.
The melt inside the hot runner stays fluid during the complete cycle and will be used directly for the next shot.
No waste is produced.
Hot runners are used to save material or to avoid weld lines (sequential injection).
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The hot runner system can be separated in different components.
The area, where the melt is divided into the different hot runner gates, is called manifold.
For molds with multiple cavities, a homogeneous melt temperature and pressure distribution are necessary.
Therefore, the manifold should be preferably symmetrical.
In the injection molding, the melt is injected inside the cavity through a gate.
Therefore, the gate position has an essential influence on the quality of the part.
The route of weld lines, the existence of air traps and the fiber orientation depends on the gate position.
Different flow length affects the pressure that is needed to fill the cavity.
The wall thickness at gate position leads to a longer or shorter packing time.
Moreover, the gate position might change the warpage of a part considerably.
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A group of experts in the plastic industry founded the company PLEXPERT, 2006 in Germany, in order to save resources, providing a positive impact on budget and environment.
There are two divisions within the company. One is focusing on finite element simulations (FEM) like injection molding simulation and structural analysis.
Based on decades of practical experience DFM conform results are given by the consultant service of PLEXPERT to decrease part costs and increase quality in the production of plastic parts.
The second division is focused on the development and supply of soft- and hardware to the plastic industry. With the state of the art products PLEXPERT contributes to secure production and reduce the need of precious resources.
Today PLEXPERT has offices in Canada, Germany, Thailand and China in order to support its customers fast and effectively.
Due to a close network of plastic experts, partners are available in many other countries as well and offer PLEXPERT products and services.
PLEXPERT Company Logo.
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The space between the two mold halves, which should be filled with melt, is called cavity.
The shrinkage of the material needs to be considered for the production of the cavity to get dimensionally accurate parts.
In the injection molding simulation, it is important to use the cavity size for the warpage calculation.
