One such sprue system is known as the hot runner, which is also referred to as the hot runner system. Specifically, it is utilized for the mechanical injection molding of thermoplastics, which is a procedure that involves the processing of a variety of polymers. In addition to having a greater temperature, the hot runner system is thermally isolated from the rest of the injection molding tool. This allows it to maintain a higher temperature.
Building a hot runner system
The hot runner nozzle is the final component of the hot runner system. It serves as the boundary between the heated and unheated areas of the injection molding tool. The hot runner nozzles and distributors are adjusted to a specific temperature range that allows for the plastic to be processed effectively. Hot runner control cabinets serve this purpose. They closely monitor the target and actual temperatures, making adjustments as needed.
Hot runner systems are typically categorized as open or closed systems. In a closed system, the injection point can be sealed using a unique technology. A closure needle is typically used for this purpose. They can be operated by an independently adjustable mechanism. Typically, this can be operated using electrical, pneumatic, or hydraulic power. Hot runner systems are commonly bought as pre-made components rather than being manufactured in-house by the toolmakers.
How hot runner systems work
Disadvantages of injection molding without a hot runner
When it comes to the injection molding of thermoplastics, the plastic melt is transported into the mold cavity or mold cavities using a plasticizing unit. Traditional injection molding tools lack thermal separation between the gating system and the rest of the tool. It is important to ensure that both the sprue system and the tool are tempered at a temperature lower than the processing temperature of the plastic.
The processed plastic solidifies in the sprue system, even during the production of the component. This leads to drawbacks for the shape of the sprue system. As an expert in materials engineering, one often encounters the need to separate the sprue from the component. This can be achieved by incorporating extra functional components into the tool or by performing post-demolding procedures. This can be do both manually or mechanically. When the sprue is separated, a mark may be left on the component.
Using this particular sprue system ensures that no raw material goes to waste and is fully utilized in the final product. The sprue piece must then be either recycled or disposed of, just like any other material. Due to this, the shot volume also increases, resulting in the need to plasticize more plastic than necessary for the component. This could potentially affect both energy consumption and the performance of the machinery involved.
Advantages of injection molding with a hot runner system
When using a hot runner, the gating system is consistently kept thermally isolated from the rest of the tool. It is heated in a separate manner. Consequently, the plastic melt stays in a flowable state within the sprue system throughout the entire production process. Thus, the plastic in the sprue system does not solidify and there is no remaining sprue on the component that requires separation afterwards. Furthermore, the functionality and design of a hot runner enable the achievement of longer flow paths during injection molding. This occurs because the molten material does not undergo sufficient cooling in the sprue channel. As a consequence, the viscosity rises, leading to a decrease in pressure within the sprue system.
Cascade injection molding can be utilized to produce large components using the hot runner system.
Disadvantages of injection molding with a hot runner system
One drawback of this kind of construction is the potential for higher investment costs. The tool should be specifically designed to be compatible with a hot runner system. The system itself can be quite expensive, and there is also the additional effort required to operate and maintain the machines that control and regulate the hot runner system. Nevertheless, it is important to consider these expenses in relation to the potential cost savings that a hot runner system can offer. Significant amounts of raw materials can be conserved, particularly when dealing with high-cost technical thermoplastics. Furthermore, the expenses associated with post-processing the completed components are decreased.
Insulating channel tools, unlike hot runners, have a different structure and functionality, but they serve a similar purpose to hot runner systems. Using this technique, the sprue is expanded to ensure that a plastic core remains, preventing complete solidification. For the molding of thermosets and elastomers, which involve the hardening of plastic through temperature, cold runner systems are commonly employed.
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