Trouble Shooting the Extrusion Process-Using the Scientific Method
Trouble Shooting the Extrusion Process
Using the Scientific Method
The scientific method
As defined by The Oxford Dictionaries Online;
“A method or procedure that has
Whether you are solving complex problems off line, or troubling shooting online, to resolve immediate process issues, make sure it is within quick reach.
The method simply put is;
Confirm or Deny
The procedure to follow when executing the method is as follows;
Make an observation.
Check your senses.
observe carefully ( use protective eyewear)
Sound; loud noise, grinding, scraping or more subtle…vibration, (old mechanics trick… touch the handle of a screw driver to your ear and touch the blade to the machine) to assess level of vibration.
(use care, some decomposing plastics, such as vinyl and urethanes for example, can be extremely dangerous if not lethal)
(use care, surface may be too hot)
Taste, (stay away from taste, too dangerous)
Define the Problem; is it a Defect or a process/equipment situation.
Gather information and resources.
Complex problems will require more time to gather information.
Trouble shooting on the fly, where a quick fix to maintain production may not offer the luxury of time.
Find out as much as you can.
Verify process parameters (set vs. actual)
Verify Recipe; Materials and regrind
and moisture content.
Take measurements where needed (parts and parameters)
Another term for a hypothesis is an educated guess.
Rely on your
Make a prediction based on the hypothesis.
Test the hypothesis and what you predict by performing an experiment and collecting data.
Select the easiest and fastest choice first
Adjust only one variable at a time
Only one person should make the adjustment
Allow ample time for the effect to take place
If no desired results occur, return conditions to previous settings
Analyze the data and if the data proves the hypothesis correct, then implement a fix.
Interpret the data and draw conclusions.
If fix seems to work,
carefully watch for undesirable side effect from factor interactions
If fix is successful then implement
Remove fix to ensure it addresses root cause (optional, time permitting)
If unsuccessful return factor to original set point
Rinse and repeat.
Don’t stop until you find what works.
If you are new to extrusion or have not seen many problems, it would serve you well to internalize a comprehensive list of potential problems and the solutions that are common to the extrusion process that you are involved with.
This will save
Next month, a post covering extrusion defects and process problems will be offered. Don’t miss it…it will be comprehensive!
Scientific Method Extrusion Example:
What is causing the variation recently experienced in the extruded profile part’s dimensions?
there are no feed issues (we can eliminate as possible cause)
Material is dried properly (we can eliminate as possible cause)
All temperatures are holding set point (we can eliminate as possible cause)
What is the Screw and barrel wear?
The Melt pump discharge pressure seems to vary more than usual, although no historical data is available to confirm this.
Melt pump suction
pressure varies considerably.
A hypothesis is a potential answer to the question, one that can somehow be tested.
This hypothesis is not necessarily the correct
A prediction is an outcome we'd expect to see if the hypothesis is correct.
To test the hypothesis, we need to make an observation or perform an experiment associated with the prediction.
If when we change the screw, after install it does run surge free, then the hypothesis is supported—likely correct.
If the screw doesn't eliminate the surging, then the hypothesis is not supported—likely wrong.
The results of a test may support or contradict—oppose—a hypothesis.
Analyze the data generated from the experiment.
If the data proves the hypothesis correct then
If the experiment disproves the hypothesis, then the investigation must continue.
This step of the scientific method is to reflect on the results and use them to guide the next steps.
Our first hypothesis was not supported
We can skip the screw removal.
On to the next hypothesis.
Iteration # 2
Report Final Conclusion
Remove melt pump and disassemble to verify that the pump has bad wear.
Rebuild or replace melt pump as needed.
Install new or rebuilt melt pump back on line.
Dimensions of the extruded part are now back, within tolerance.