Plastic Injection Gate Types - 2편

Gate Types

 

♣  Automatic Trim

• Submarine
• Cashew
• Pin
• Hot drop
• Valve

 

Submarine Gate

 

 

     ●   Tapered round gate that intersects the part below the parting line

     ●   Very Common

     ●    Nominal orifice diameter 25% to 75% nominal wall

 

 

Cashew Gate

 

     ●   Curved tunnel gate

     ●   Difficult to machine

    ●    Possible maintenance problem

 

 

Pin Gate

 

    ●   Used in 3 plate molds

    ●   Very small orifice

    ●   Modeled with beams

    ●   Nominal orifice diameter 0.25 to 1.5 mm

 

 

 

 

Hot drop

 

    ●   Delivers hot material to the part directly

    ●   Gate geometry and size dependant on type of hot drop desired

    ●   Orifice size can be critical so the nozzle will not drool

    ●   Modeled by beams

 

 

 

Valve Gate

 

 

    ●   Similar to a hot drop but the gate orifice is closed by a pin

    ●   Pin can be opened and closed several times during the cycle

    ●   Modeled by beams

 

 

 

 

Elements in a Gate

 

   ●   Gates should have a minimum of 3 elements across the gate to accurately predict

          ·  Gate freeze time

          ·  Shear rate

          ·  Pressure

 

 

Setting the Cross Section

 

   ●   Select the elements

   ●   Assign properties

        ·   Choose the type of property

        ·   Set the properties

        ·  Or . . .

    ●   Edit properties

        · If property type correct but dimensions must change

 

 

 

Gate Sizing

 

   ●   Gates should be sized using shear rate as a guide to refine the gate size from nominal values

   ●   Shear rate guidelines are found in the material database

   ●   Keep the gate shear rate below the material limit

   ●   If the gate geometry allows, reduce the shear rate further, to about 20,000 1/sec.

   ●   Large gates this is easy; edge, fan, flash

   ●   Difficult for sub gates and hot drops

   ●   Impossible for pin gates