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  • Advantages of hot runner molds

    The hot runner mold has been very widely used in today's industrial countries and regions. This is mainly because the hot runner mold has the following features:

    Shortening the molding cycle of parts
    Due to no time limit from runner system cooling, the part can be timely ejected out after being cured. For most thin-walled parts, their molding cycle is less than 5 seconds in a hot runner mold.

    Saving plastic materials
    The pure hot runner mold has no cold runner, so there is no production of waste. This is especially significant for the application projects whose plastic materials are expensive in price. Indeed, internationally, the major hot runner manufacturers have their rapid development during the periods with expensive oil and plastic materials. The hot runner technology is an effective way to reduce wastes.

    Reducing waste materials, and improving product quality
    In the molding process of the hot runner, plastic melt temperature is accurately controlled in the runner system. Plastics are able to flow into the mold cavity in a more uniform state, resulting in consistent quality parts. There is good quality of the molded part at the gate of the hot runner with low residual stress after ejection and less distortion in parts. So, many high-quality products on the market are produced by the hot runner molds. For example, a lot of plastic parts produced through the hot runner molds have been used in MOTOROLA mobile phones, HP printers, and DELL laptop computers which are familiar to our hot runner molds.

    Eliminating the follow-up process and being conducive to automation
    The finished product is directly from the molding of the hot runner without a need to go through gate pruning, cold-runner material recycling, and other processes. This is conducive to automation. In foreign countries, many manufacturers have integrated the hot runner into the automation line to significantly improve production efficiency.

    Expand the application range of the injection molding process
    Many advanced technologies in plastic molding have been derived from the hot-runner. These include PET pre-molding production, mold multicolor co-injection, multi-material co- injection, STACK MOLD and so on.

     

    Composition of hot runner system

    In the world, there are a variety of hot runner product lines and their manufacturers. However, a typical hot runner system is composed of several major parts as below:
    • Hot runner manifold
    • Nozzle
    • Temperature controller
    • Auxiliary parts

    Key technology of hot runner applications

    For a hot runner mold, its successful application projects are required to be ensured through the multiple links. The most important are two technical factors: One is the plastic temperature control, and another is the control of plastic flow.

    Plastic temperature control
    In the applications of the hot runner mold, the plastic temperature control is very important. During the production, many issues concerning processes and product quality are directly related to the poor temperature control of the hot runner temperature system. For example, the hot pin gate method used in the plastic injection molding may result in a product whose gate quality is poor; the valve gate method used in molding may result in a problem where the valve pin is difficultly closed; the multi-part cavity mold may result in such problems as part-filling time, and inconsistent quality. It is the best to choice a hot runner system with multiple areas in which the temperatures are respectively controlled, in order to increase operational flexibility and application capability.

    Plastic flow control
    Plastic flow shall be balanced in a hot runner system. Gates shall be opened simultaneously, so that the plastic synchronically fills each cavity. For the FAMILY MOLD whose parts are significant different in weight, there shall be a balanced design in the runnel channel. Otherwise, some problems may occur, for example, insufficiency or excess in mold filling and pressure keeping for some parts; too much flash, and poor quality. The design in the hot runner size shall be reasonable. If the size is too small, then the filling pressure loss is too large. If the runner size is too large, then the hot runner volume is too large; in the case, the plastic stays so long in the hot runner system that the material properties are damaged, which results in a problem that the molded part cannot meet functional requirements. Now, there are professional CAE software products that assist the customers to design the best runner in the world, e.g. MOLDCAE.