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    reference, etc. of the runner). Therefore, ASU composes 1-
    cavity mold; the GSU of combination and transfer of basic
    attributes of the ASU composes 2-cavity and 3-cavity mold;
    similarly, CSU composes multi-cavity molds, which are the
    combination of GSUs, namely, 2-cavity and 3-cavity molds.
    III.   KNOWLEDGE DRIVEN MECHANISM OF HOT-RUNNER
    STRUCTURE DESIGN
    As a special component of a hot-runner plastic injection
    mold, hot-runner system is used to deliver thermoplastic melt
    to a mold or into the cavity. A hot-runner system consists of
    hot-runner components (including gate, hot-runner plate and
    nozzle), heating system, temperature control system and
    auxiliary parts. During design process of a plastic injection
    mold hot-runner, these parameters must be considered,
    namely, technical parameters of product raw material, weight
    of the plastic piece, wall thickness of the product, number of
    cavities, preset gate number and position, plastic injection
    machine type (mechanical, hydraulic, or manufacturer), preset
    clamping force (ton), preset injection pressure (kg/cm3
    ), preset injection velocity(cm3
    /sec), preset injection period,
    temperature (including molten plastic temperature, injection
    nozzle temperature, and mold cavity temperature), pressure
    (including plastication pressure, injection pressure, and mold
    cavity pressure), and corresponding operation time (including
    injection time, dwell time, and cooling time) etc..
    Applying rheology law, hot-runner should be able to
    keep balance naturally. Mechanical equilibrium spreader plate
    is usually applied to design hot-runner for multi-cavity mold.
    In other words, the runner length of each gate between nozzle
    and cavity of the plastic injection machine is the same, so is
    the diameter. No matter how the cavities are laid out in a
    multi-cavity mold, only continuous melt can guarantee
    product quality.
    The volumetric velocity of melt flow Q is calculated as:
    3
    /(/sec) QQ s cm pm ρ =  
    Where, Qp is the weight of plastic piece (g); s is the injection
    time (sec); m is the melt density, and
    23
    ()/[10'()](/) m P RT P g cm ρπ ωπ −IF plastic flowability = [poor],
    THEN gate dimension = [more than the estimation]
    For runner design of a hot-runner plate, less heat loss,
    less injection pressure loss, and less runner volume are main
    requirements, by which the corresponding rules are organized
    for section shape selection and hot-runner plate structure
    design. For example, the difficulty of manufacturing and the
    heat loss can partially determine the design rules of the section
    shape selection of a runner.
    Rule5. IF heat loss = [small],  
    THEN runner section shape = [round] or [regular hexagon] or
    [combination of semicircle & trapezoid]
    Rule6. IF processability = [good],  
    THEN runner section shape = [round]
    Nozzle is at the end of a hot-runner system. As a key
    part, a nozzle connects to the cavity directly. A nozzle consists
    of a body equipped with heating system, and an insert at the
    end. Nozzle design must meet these requirements: constant
    melt temperature during flowing to avoid solidification when
    under-heating at the end, or, to avoid degradation at internal
    over-heating; even temperature distribution; heat insulation
    between nozzle and mold to reduce cavity cooling time, and to
    reduce internal stress between molds caused by temperature
    rising; leak-free nozzle insert, which is a precise component in
    the runner system; leak-free between nozzle and runner plate;
    and maneuverability. Moreover, the nozzle and the runner
    plate fixing, plastic material, shape and height of the gate
    should be considered as well.
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