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This informative blog allows plastics professionals to discuss plastics training and technology. Brought to you by Routsis Training: the plastic industry's premiere training provider.

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Practice what you Learned

Just because you know the parts is supposed to 90-95% full does not mean you are actually practicing it. In a recent on-site training session the participants all understood the importance of molding a part short during 1st Stage Injection, but learned an important lesson in the lab.

Situation: In lab, we were establishing the first stage fill. We made a part which was just full and weighed the shot. In increasing the transfer position, they made a part which they thought was 90-95% full and weighed it. It turned out to be 98.5% full. They were amazed and learned a valuable lesson about why it is important to measure the parts and not just assume. The lesson is, you must practice what you learned so that you understand the application.
-Andy

Check the Melt Temperature

Unless you actually measure the melt temperature, you really do not know what is happening with the material. Recently at a molding facility, we encountered a 65 F (36 C) difference between the melt temperature and barrel temperature.

Comment from Technician: We always have to to run this mold with a hot material to get it to fill. Typically , we have to run the Polypropylene around 500°F (260°C).
Response: When measured, the melt temperature was actually only 434°F (223°C). In reality, this machine as designed with improperly located heater bands giving the impression that the material is actually much hotter than it really is. In fact, the material is being processed at a much lower temperature than most of their other machines.
-Andy
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Is MFI Better than Nothing?

Having the Melt Flow Index of a material does not provide a real picture of how the polymer will actually process, but it can be a helpful indicator in some cases. This post will outline an example of how the data can be of use to a technician.

Question: MFI is not supposed to be an accurate measurement of viscosity, so should we stop testing it?
My Response: The melt flow index is a low pressure & low shear rate test with a single data-point as a result ( grams extrudate per 10 minutes). Injection molding is a very dynamic process which typically involves very high shear rates and shear stresses. The only real value MFI data provides is for relative use in material comparison for material selection. 
Example: Let’s suppose you are making good parts with one lot of material which has a MFI of 40 g/10min. If you are running out of material and have to change lots and you can choose between one grade with a 45 MFI and another which has a 25 MFI. You might choose the 45 MFI material because it has the highest likelihood of molding similar to the 40 MFI lot.
-Andy
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Rear Zone Temperature Study

It is critical that your perform a rear zone temperature study on each of your molding machines. Just because two machines have the same brand and are running the same material, the optimal rear zone temperature is most often different.

Question: We run the same grade of PP on all our jobs and all the machines are the same brand. Do I really need to perform this test on each machine?
My Response: Yes, each machine may or may not be the same optimal rear zone temperature. I have seen a difference of 50°F using two similar machines with the same grade of material. Keep in mind, you also need to check the melt temperature since the temperatures are likely to be different.
-Andy
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Monitoring Power Consumption

One great way to get your employees excited about energy reduction is to provide a method of monitoring energy consumption. If your employees can actually see that a change, such as increasing 1st stage injection speed or reducing 2nd stage packing time, actually reduces the power consumption it can become a very empowering experience. There are many options available for this, but one which allows you to track consumption for individual machines over time would be most helpful.

-Andy
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