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NEngineer (Chemical) (OP)
4 Oct 07 17:55
How to find optimum injection speed on electric machine?
Helpful Member!  dwightdixon (Materials)
4 Oct 07 18:40
Injection speed is dependent on the type of material and its ability to shear thin as well as the potential for surface defects caused by filling too fast thru sharp flow transitions. Start by consulting the materials supplier and then let the machine tell you when you are going too fast and limiting out the injection pressure. Slow it down, if you are getting jetting or surface delamination.
NEngineer (Chemical) (OP)
8 Oct 07 15:13
Dwightdixon,

As you mentioned "let the machine tell you when you are going too fast and limiting out the injection pressure" How to find it that we are going too fast or too slow? Are you referring to any viscosity curver? if so please explain in detail.
Helpful Member!  mjh368 (Chemical)
8 Oct 07 15:30
check out www.injectionmoldingonline.com.

also check out www.plastics.com/communities

read articles on www.immnet.com

These will give you a lot of information about plastics processing.  After you got your basics down let us know if you have a specific questions.
Helpful Member!  patprimmer (Publican)
8 Oct 07 17:15
Injection speed is always a compromise.

Basic rule of thumb is to inject as fast as possible without causing problems.

Filling to fast can cause:-

Burns from shear.
Burns from gas traps.
Poor surface from jetting.
Poor surface from turbulence over sharp edges.
Over pack and flash from hitting the mould full point with to much inertia in the screw.

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mauriciob (Mechanical)
15 Oct 07 17:00
The question is what the injection speed is to fill the cavities. If it is a hydraulic or an electric machine is irrelevant.

The injection speed depends, as mentioned above on the material rheology. It also depends on the part design and requirements and the mould design, specially the type of gate and dimensions. A mould flow analysis may help.

For the part of "let the machine tell you", I agree, but there should also be a way to determine it theoretically while the mould is in its design face. I would like to see a post with some formulas. When the mould is already built, visit http://www.fimmtech.com/ (no affiliation). They have free and paid stuff to come up with the right injection speed and other set up parameters.

Mauricio Benavides
Injecnet Solution Inc
www.injecneering.com

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