Plastic part with regrind 25%
Plastic part with regrind 25%
(OP)
What impact with using 25% regrind in plastic? How do identify the plastic part defect is due to regrind?
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Plastic part with regrind 25%
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RE: Plastic part with regrind 25%
Hope this helps.
Paul Kuklych
http://www.improve-your-injection-molding.com
RE: Plastic part with regrind 25%
any test can identify the part have regrind?
RE: Plastic part with regrind 25%
It's not that easy to detect in the case of PE and PP. You can try:
1. FTIR to look for oxidation as seen in the carbonyl band (probably not sensitive enough though)
2. Have an expert lab measure the antioxidant levels and their degradation products. Each pass through an extruder consumes around 200ppm of process stabilizer(this method is most likely to work)
If you go for the second option the only lab I know of that can do it is www.stabilization-technologies.com or maybe www.norner.no
Chris DeArmitt - PhD FRSC
Plastics & Materials Consulting
www.phantomplastics.com
Plastic Training Seminars
www.plastictraining.com
RE: Plastic part with regrind 25%
Rick Fischer
Principal Engineer
Argonne National Laboratory
RE: Plastic part with regrind 25%
RE: Plastic part with regrind 25%
Rick Fischer
Principal Engineer
Argonne National Laboratory
RE: Plastic part with regrind 25%
RE: Plastic part with regrind 25%
An issue with regrind is contamination. Any foreign matter that gets into the plastic can have a bad effect on impact resistance. If you know you are going to use reground runners, take care to keep them clean. Store them in covered containers, make sure the grinder is clean and free of dirt debris and other plastic, and keep the hopper covered. Only use runners from properly molded molded parts. Make sure that the regrind particles stay mixed with your virgin pellets. If they segregate because of different shape or size, you may get some parts made with very high regring content.
It may be that the parts a marginally acceptable in impact even without regrind, and the addition of regrind tips them over the edge. Make sure your process is optimum. There is one school of thought that says use a melt temp near the bottom of the recommended range and inject fast. The idea here is to get your reduction in melt viscosity from shear thinning rather than temperature. I saw data where two samples of I think PP were processed by molding parts ad grinding them up, checking melt flow, remolding, rechecking, and comparing results. One sample was molded fast and cool, the other slow and hot. Slow and hot had the same melt flow after one cycle as the fast and cool did after five molding cycles. Heat is the killer here. I think the suggestion about testing for antioxident levels is a good one if ABS is used. If the butidiene oxidizes, is will cross link and get brittle and you loose impact resistance.
Another issue with glass filled material is damage to the fiber from excessive shearing. I worked on a problem once where a glass filled polyester part was breaking at some hardened steel pins held captive in the assembly. The molder was inexperienced with glass filled part and was using a very fast screw speed. This was chopping the glass fiber into glass particles. We set the screw speed to a level recommneded by the resin supplier, and the part was so strong that the failure mode was now fracture of the steel pins. It may be that grinding the runners and the additional molding cycle are breaking the fibers.
If the failure is at a sharp corner, do what you can to remove the corner. PC is notch sentitve, meaning its a normally ductile material that will undergo brittle fracture in the presence of a stress concentration.
Rick Fischer
Principal Engineer
Argonne National Laboratory
RE: Plastic part with regrind 25%
In glass fiber filled systems the glass fiber dominates properties like modulus and strength and to some degree impact resistance. Just one extruder or molding pass can really break the fibers down into shorter ones dramatically reducing properties. A test for this would be to ash the sample (e.g. 500C in air) and look at the fibers to see if they are like new or ground up. A look at the fiber length will tell you if it's regrind or not.
Chris DeArmitt - PhD FRSC
Plastics & Materials Consulting
www.phantomplastics.com
Plastic Training Seminars
www.plastictraining.com