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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.

Verifying a Consistent Silicone Process…

I was asked this question the other day…

Quality Manager
What is a good way to ensure a silicone molding process is consistent?

My Response
One good way to check the consistency of the process is to routinely measure the part weight. A consistent part weight indicates the same amount of material is injected and packed each cycle. This wont necessary tell you what is wrong or has changed, but will be a good indicator of process shift.
-Andy

Differential Cooling…

I was recently in a discussion with someone who was heavily involved in a molding trial…

Engineer
We just went through a series of trials to reach the correct molded part dimensions on a part, and it turned out we needed to use four different temperatures to achieve this. What mold cooling information should we be documenting for this?
My Response
Regarding the mold cooling, you should first have a detailed diagram of the cooling line/themolator layout. This diagram should document the coolant temperature entering and leaving the mold for each temperature profile. Over time, you should consider adjusting the tooling to accommodate these complications.
-Andy

Spiral Flow Test for PP…

I received this question as a follow-up to a previous blog posting…

YM

Is there any standard (ISO or ASTM) that can be reference
for a polypropylene spiral flow test?

My Response

Yes, there is a standard for this within ASTM D-4101. If you are looking to publish the results, then this can be very helpful. Unfortunately, the conditions, flow rates, and pressures used may not directly replicate your processing conditions. In practice, most of the companies I have dealt with create their own procedure based on the conditions of their process.

For example, if they are looking to compare the viscosity of two grades of material. they might replicate the melt temperatures and flow rates of the actual product, and measure the difference in pressure at transfer to represent viscosity.

Another company I have worked with uses many older, pressure-controlled, molding machines. This company uses a constant pressure with position transfer. The change in injection time and flow distance provides excellent information for comparing one material grade to another.

Additional Thoughts

Basically, I recommend you review the standard procedures for the spiral flow test, but adjust the test parameters to meet the specific needs of your production facility. The key factor is to perform a test which provides information which helps the production department.

-Andy

 

Restarting Your Training…

I was approached during NPE the other week by a manager…

Manager
We used to do On the Job training, but now we do nothing for our employees. How do we get started again?

My Response
The first step is to start training, even if it is something as simple as cross training. For example, you could have a technician assist in some mold PM’s to learn more about tooling.
Your employees will never get into the mindset if you never do any training. Employees want to do a good job, but they need the necessary intellectual tools to succeed.
Additional Thoughts
I understand that there is much more to effective plant-wide employee development than this, but any training is better than no training at all… and you have to start somewhere.
-Andy

Part Sticking and Machine-Independent Documentation…

I received a detailed request for help from a blog reader last month. Below if a distilled rendition of the discussion…

Issue
The mold has run without issues for years. Now the parts stick in the mold almost every shot, there is more flash, and the cushion is much lower than recollection. All the machine and temperature settings are the same, but the result is much different. Could this be a check ring issue?

My Response
The check ring is more commonly an issue if the sticking is intermittent… which this seems not to be the case. My initial suspicion is that there is too much material being injected or packed into the mold. Second, the mold or melt temperature might be higher than usual. There are a wide host of items which could contribute to this problem… but investigating these first might give a good idea as to the cause of the defect.
Additional Thoughts
This could also be chalked up as a documentation issue. Since we don’t know the melt temperature, 1st stage fill time, part weight, or other machine-independent parameters during the good runs, we cannot quickly identify ‘what changed’ between then and now. 
If you or anyone you work with would like to learn more about process documentation… we have some free multimedia webinars on scientific molding which can be viewed at http://www.traininteractive.com/free/webinar/player/
-Andy