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#105 Molding Conditions of an Injection Molding Machine (4)

Category : Technical Information
December 9, 2011
1. Screw Rotation Speed

The screw rotation speed in plastic injection molding is the speed of rotations of the screw for mixing the pellets. Its unit is rpm (revolutions per minute).

If the screw rotation speed is too high, air gets mixed inside the molten plastic which can make gas generation to occur easily. Also, if the screw rotational speed is too low, sufficient kneading will not be made and the material quality can fluctuate.

2. Screw Back Pressure

The screw back pressure is the pressure at the time that the screw moves back for measuring the material. Its unit is MPa or kgf/cm2. The kneading state of the material changes due to changes in the back pressure.

3. Mold Opening and Closing Speed

The mold opening and closing speed is the speed at which the mold is opened and the speed at which the mold is closed. The unit is mm/s. Although the time required for opening and closing the mold being small is effective in shortening the cycle time, if the opening and closing speed is too high, the danger becomes high of the molds colliding with each other, and hence it is necessary to put a brake just before the molds meet.

Also, if the mold opening speed is too high, the mold releasing state fluctuates which can cause fluctuations in the quality.

4. Mold Clamping Force

The mold clamping force is the force for closing the parting surface, and its unit is kN (kilo Newtons) of tf (tons force). Although this unit is usually expressed merely as "tons" while speaking, in mechanics it is correct to append the weight unit "f".

5. Ejecting Speed

The ejecting speed is the speed of forward movement by the ejector rod, and its unit is mm/s. If the ejecting speed is too high, the product may get deformed or the surface may become white. If the ejecting speed is too low, the molding cycle time becomes long.

6. Ejection Count

The ejection count or the number of times of ejection is very often set in the range of 1 to 3. Although ejecting once is enough if the mold is one with good mole release property; however, if it is bad, it may not be possible to take out the molded product from the mold unless ejection is made several times.

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