What is a dual mold? Dual molds are different from conventional injection molds

What is a dual mold? Dual molds are different from conventional injection molds

Dual mold is different from traditional molds commonly used in injection molding. It is a type of mold with a unique structure. The dual mold consists of multiple separated surfaces, and each separated surface can have one or more cavities. These cavities are arranged within a mold in a controlled mold-clamping system. The metal injection mold includes the sprue, mold cavity, cooling system, guide pins, two-way ejection system, and a system to link the opening and closing modules.

The basic structure of the dual mold.

Dual mold includes movable mold, middle mold, and fixed mold.

What is a dual mold?
What is a dual mold?

The fixed mold component is placed on the right side of the mold. It is positioned on the machine’s fixed plate. A part of the pumping system is connected to the mold machine. The fixed part of the runner is thermally controlled, ensuring that the material flowing through the fixed mold maintains a stable melt temperature. When the mold is closed, it is connected to the inlet of the mold machine. Therefore, the extended part of the thermal runner must be long enough to ensure no leakage when the mold is opened.

The middle component consists of a frame with a hot runner system and cavities on both outer surfaces of the mold. Its injection system has heated nozzles on both sides. The middle mold section needs to be heated and supported, and the ejection mechanism is provided on each side of the movable mold and fixed mold components. Throughout the demolding process, the middle plate moves with the movable element, placing the middle mold section between the movable and fixed components. The heating system of the middle mold is similar to a conventional hot runner system, including nozzles, pipes, hot plates, and heating devices.

The movable component is located on the right side of the mold. This component moves along the mold’s rolling axis during operation. A linking device controls the middle plate. Both separated surfaces open simultaneously.

Features of dual mold:

  1. Productivity: Dual mold has double the capacity of traditional molds. It significantly reduces molding costs and increases the output of plastic components within a given time frame.
  2. Compatibility: Dual molds can be assembled with the same mold machine on a similar mold. There is no need to purchase additional equipment, saving costs on machinery, workshops, and labor.
  3. Production Requirements: The basic production requirements for dual molds are similar to those of traditional molds. However, the production time is shorter by 5-10% compared to single molds.
  4. Suitable for Large-Scale Production: Dual molds are suitable for large-scale production with large plastic parts. They offer high quantities and low production costs.

Hot Runner System: The dual mold can incorporate a hot runner system and a cooling channel system. The hot runner system can transfer pressure, improving the quality of plastic components and facilitating automation. However, specific requirements and higher costs may apply to certain types of plastics.

Cold Runner System: When using a cold runner system, the quality of plastic components may not be as good, and automation may not be possible. However, this process is simpler and more cost-effective. Due to the multi-layer injection mold design, the main runner needs to be longer to reduce casting time and increase productivity. Currently, hot runner gate systems are commonly used.

Temperature control system:

The mold temperature is one of the important factors that affect the product quality and the molding time of plastic components. When designing a dual mold, it is necessary to ensure that the temperature of all layers is the same. To reduce heat loss due to thermal conduction in the hot runner system, the contact area needs to be reduced, and insulation pads must be used. An important aspect of dual mold design is the cooling system:

  1. The cooling time should be minimized.
  2. The final plastic components need to be cooled to limit deformation.
  3. Auxiliary cooling channels can be added to the core and additional core parts.
  4. Cooling channels can also be installed in the middle mold layer to extract heat from the gate system.

Mold opening mechanism:

To ensure proper shrinkage of the plastic product, the time it remains in the cavities should be equal. Therefore, the dual mold should ensure that the parting surfaces of all cavities open at the same time. There are typically three cases:

  1. Rack and pinion drive
  2. Link drive
  3. Hydraulic cylinder drive

Gear and mechanical linkage mechanisms are often used in metal molds for die casting. These types of molds are more cost-effective and have better technical performance. However, they may be less flexible. Hydraulic mold opening mechanisms facilitate easier control of the mold opening time but require a larger structure and the use of oil passages, which can lead to environmental pollution.

Ejection system

The product release mechanism is the same as a regular mold. Plastic parts are pushed by push rods. Fix the mold using a hydraulic drive, tie rod, chain, and other methods.

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