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Don’t Forget to Move the Temperature Probe…

I was discussing the measurement of the polymer temperature with an engineer and he explained a problem he is encountering…

Joe
Each of our technicians are getting different results when we they measure the melt temperature… especially when we measure high temperature materials like polysulfone.

note: I asked one of their techs to demonstrate how they measure the melt temperature and he purged the material, inserted a thin-style probe, and recorded the highest temperature reading. I then asked the technician to repeat the process, but when he inserted the probe I asked him to move is around slowly. The result was a temperature which was 15 degrees higher than his previous measurement.
My Response
When measuring a melt temperature, it is important to move the probe around a little. When the probe is inserted into the melt, a skin of cooled polymer forms around the probe. To ensure you are getting the temperature of the melt, you need to use the surrounding material to soften this skin and get some of the interior polymer melt in contact with the probe.

-Andy

Making Significant Changes…

As a follow-up to a previous post, I was asked to expand in the second rule of processing…

The 5 Basic Rules of Processing (from before):
Rule 1 – Make one process change at a time
Rule 2 – Make significant changes
Rule 3 – If a change does not help, change it back
Rule 4 – Document the process
Rule 5 – Document all changes to the process
Rule #2
The idea behind this is that you always want to know you are making a change which is important. Too often people will tweak different parameters without any direct knowledge as to the effectiveness of the change.
When you make a change, you want to ensure it is large enough to make a difference. Remember any change to the process can be reversed either completely or partially.
Additional Thoughts
I have seen many molders who make small adjustments with the belief it will improve the situation. A symptom of this behavior is a control panel with a large amount of numbers which do not end in either 5 or 0. For instance, if the injection profile looks like the following… V1=11.1 mm/s, V2=30.3 mm/s, V3=23.4 mm/s, V4=28.4 mm/s, and V5=12.7 mm/s. It is very unlikely that each of those velocities have been optimized and each speed in the profile can be properly justified. This type of profile is almost always the result of someone tinkering with the process until a good part came out of the machine.
-Andy 

PPE for Purging…

I have seen many variations on this principle…

Steve
Here we only require our employees to wear safety glasses when purging… is that fine?

My Response
Purged plastics can cause some of the most debilitating injuries because they have a tendency to not only burn, but stick to or inject under your skin as well. When purging goes well, the conditions are relatively safe, but it is not uncommon for a explosive discharge to occur as a result of nozzle blockage or gas buildup.
If you are not wearing a face shield, heat resistant gloves, and long sleeves while purging; you are opening yourself up for serious injury.
Additional Thoughts
In all our training courses, we stress the same PPE recommended by most machine manufacturers which includes the wearing of the following when purging:
  • Face Shield
  • Heat Resistant Gloves
  • Long Sleeves (Cotton)
-Andy

5 Basic Rules of Processing…

I was asked this question yesterday via email…

Manager
What should I be looking for when my guys process?

My Response
There the 5 things that I always look for:
Rule 1 – Make one process change at a time
Rule 2 – Make significant changes
Rule 3 – If a change does not help, change it back
Rule 4 – Document the process
Rule 5 – Document all changes to the process
These rules apply to injection molding, extrusion, and blow molding alike.
Additional Thoughts
This list seems pretty simple, but I have found that most molders skip at least one or two of these steps whenever they process. 
-Andy

More on Robots vs. Automation…

This question came up as a follow-up question to a recent blog about robotics and automation…

GH
Would a part diverter be classified as robotics or automation?
My Response
The general rule I always follow is: If it is programmable, it is a robot… if not, it is automation.
Therefore, if the diverter acted as a sort device where acceptable parts were sent one way, while defective or questionable parts were sent another way based on process or inspection data, then it could be considered robotics. If a sensor was just placed on a conveyor to sense different parts and automatically divert of orient parts in a specific manner, then it might be considered automation.
Additional Thougths
Under such a definition, a simple device such as a sprue picker which needs to be mechanically adjusted to alter the speed, length, and movement of the arm might be considered automation.
-Andy

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