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Injection Molding

Injection Molding 

 Injection machine 
The injection machine is a machine that melt plasticize the molding material inside the heating cylinder and inject this into the mold tool to create the molded product by solidifying inside it. The injection machine is constructed of a mold clamping device that opens and closes the mold tool, and device that plasticize and inject the molding material. There are several types in the injection machine, and the difference is made by how these two devices are arranged. 
  • Horizontal injection machine ： Both mold clamping device and injection device compounded horizontally 
  • Vertical injection machine ： Both mold clamping device and injection device compounded vertically 
  • Two-color injection machine 
  • Rotary injection machine 
  • Low foam injection machine 
  • Multi material injection machine 
  • Sandwich injection machine 
 Selection of injection machine

 Select by injection volume  
        As a guide, generally the injection machine should be selected so that molded product volume will become 30% to 80% of the machine's injection volume. When molding, the relation of the machine's injection volume Q(g) and one shot weight (sprue and runner weight included) W(g) should be in the range indicated below. 
                      Q ＝ （1.3～1.5）×W 
    If the injection volume is too small, plasticization will not make it, and might lose its original physicality as a molded product because the resin will be sent without enough plasticization. On the other hand, if the injection volume is too big, residence time inside the cylinder will be longer and cause degradation by more chance. 
Select by mold clamping pressure 
       Both toggle type and direct pressure type is suitable when molding NOVADURAN. The relation of molded product projected area A(cm2) and required mold clamping pressure P(ton) should be in the range indicated 
below. 
 P ＝ （0.5～0.7）×A

Nozzle structure 
      Open nozzle is common when molding NOVADURAN. The nozzle of commercially-supplied injection machine can be open nozzle or shut-off nozzle  but in any type, it is necessary to have a temperature control. If drooling from the nozzle is concerned, use the shut-off nozzle. However, it might cause burn and sunspot object by resin retention at the slide part, so be careful.

Injection mechanism 
     NOVADURAN can be molded by the basic injection machine which has the function of constant injection speed and two-stage injection pressure control, but when molding the product which severe measurement, appearance, and moldability (liquidity and demoldability) is required, it is effective to use the machine that has a program control of injection speed and injection pressure. 

 Backflow prevention ring 
        Backflow prevention ring is necessary at the screw, because NOVADURAN has relatively low melt viscosity. If this backflow prevention ring is damaged by wear or corrode, cushion volume cannot be kept because of the resin backflow from the cylinder to the hopper when injecting (pressure keeping), and injection pressure (holding pressure) might not be put properly to the cavity. In this case, good molded product cannot be made, so cushion volume and its stability must be well controlled and maintained when molding. Corrosion and abrasion resistance steel grade is preferable for the back flow prevention ring. 

 Drying machine 
     Preliminary drying is necessary before molding NOVADURAN, and the condition below is general. 
 120℃ 5～8 hours 
 130℃ 4～6 hours 
Shelf-type hot air circulation dryer, hopper dryer, or dehumidification dryer is preferred when drying. To prevent the dust and the dirt getting inside, a filter should be placed to air intake of the drying machine, and its maintenance against clogging is also necessary.

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