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Spiral Flow Test…

I received a follow-up question regarding a post earlier this year, The Uses of MFI…, 

KJ
You mentioned the spiral flow, what is this test?

My Response
The spiral flow test uses a mold with a long spiral flow channel emanating from the center. Notches are etched along the flow path to help identify the length the polymer has flowed within the mold. The mold can be filled using either a constant velocity (constant shear) or constant pressure (constant strain) to determine the polymer behavior.
The behavior of the polymer can be evaluated based on process output data such as flow length, part weight, and pressure at transfer. When using the spiral flow test, it is best to use a mold which has a channel thickness similar to the parts actually being molded.
Additional Thoughts
You might want to consider purchasing a small, inexpensive, molding machine to conduct spiral flow tests on every incoming batch of material.
-Andy

Thermoplastics vs. Thermosets…

I have read some industry discussion groups lately and have noticed some confusion on the difference between Thermosets and Thermoplastics, so I will use this post to help clarify these points…

Thermosets
Thermosets are polymerized during processing while thermoplastics are polymerized before being processed. During processing, the polymer chains in thermosets fuse together, or cross-link. Once these polymers cross-link, they undergo a chemical change which prevents them from being melted and reprocessed. An egg is an example of a natural polymer which thermosets. Once the egg is heated, it solidifies and cannot be melted again.
Thermoplastics
Thermoplastics are long polymer chains that are fully polymerized when shipped by the resin manufacturer. Thermoplastics can be re-ground, melted and re-processed while retaining most of their original properties. An example of a natural thermoplastic material is wax. It can be melted and formed. Once cooled, the hardened wax can be melted and formed again. Unlike thermosets, most plastics companies prefer thermoplastic materials because they can be reprocessed and recycled.
-Andy

Drop Packing Pressure and Time…?

This question came in from a molder overseas…

HM
During process optimization, which is best, keep both the packing pressure and packing time to zero OR only holding pressure?
My Response
This is based on your machine. On most machines, you can turn the pressure down to zero and the pressure will turn off. Before you make this assumption, you should verify this by turning off the time and ensure the part looks the same.
Additional Thoughts
For some related reading, please review some of the following: 
-Andy

Why Commit to Training…?

I was on a call the other day and was asked this question…

Caller
What type of commitment should I make to training, and why?

My Response
An in-house training initiative gives you a competitive edge in today’s fast-paced plastics industry. Well trained employees can better cope and adapt to changing product lines, customer requirements, and production strategies. Today’s customers are sensitive to quality, economy and efficiency. Most customers are impressed with a job delivered on time and on budget, and from a safe plant.
Additional Thoughts
Imagine being able to boast that all of your production workers have gone through a comprehensive in-house training program and that your company has a system in place for continually improving the skills of its workers. Not only does his boost confidence and security among your employees, but it also tells your customers that you’re committed to raising the bar.
-Andy

Retaining Defects…

I was recently visiting a molder who was having a specific problem…

Supervisor
We are having trouble with our employees properly identifying and naming part defects… any suggestions as to how we can improve this?
note: After a couple questions, it was determined that they do not retain defective parts as they are all discarded, reworked, or reground.
My Response
It is critical that you retain current samples of each part defect your company encounters. These defects should be placed in a visible area to ensure the employees will walk by and see them on a routine basis. This make a great training tool and will help provide a common ground when defect-related questions arise.
Additional Thoughts
Please review your defect board a few times a year to ensure the parts are up to date and still defects. I have seen many parts that are so old that factors such as dust and dimensional creep will make the intended defect invisible.
-Andy

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