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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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Coloring Water Line Connections…

One molder asked me this question the other day…

Manager
Our setup techs always seem to connect the water lines incorrectly. We have diagrams to show the setup, but they seem to mess it up anyways.

My Response
Companies who use individual water lines rather than a manifold should color-code everything using blue lines for incoming water, red lines for outgoing water, and extra colors such as yellow for line which exit and re-enter the mold.
Once you have this established, place colored plaques on each connection of the mold. This will ensure that your employees cannot accidentally connect an in-line to an out connector.
-Andy

Setting Final Cushion…

During some classroom training the other week, a student asked me the following question…

John
What value should you set the cushion at?

My Response
A good rule of thumb is 10% of the initial shot size. For example, if the overall shot size is 100mm, then the cushion should be about 10mm. This avoids pressure losses from too much material in front of the screw, yet provides enough room in front of the screw for normal variability.
Related Posts:
-Andy

Teaching Tolerances…

I was asked this question during a recent on-site visit…

QA Manager
What is an easy was to explain tolerances to new employees?
My Response
Focus on the fact that tolerances are commonly expressed in a way which can be easily broken up into simple math equations.
Dimension: 1.00 ± 0.01
Upper Limit: 1.00 + 0.01 = 1.01
Lower Limit: 1.00 – 0.01 = 0.99
Additional Thoughts
When possible break ideas into their simplest form such as an equation or concept. Keep in mind the issue is very often math not tolerances. In this case, focus the attention on basic math and calculator usage first before moving on to part tolerances.
-Andy 

How Much Training a Week…

As a trainer, this is one of the more common questions I receive…

Manager
How much training a week should I give my employees?

My Response
We typically recommend between 1 and 2 hours a week. It is always much better to provide your employees a slow, steady, & consistent stream of information over an extended period of time. One hour a week for 40 weeks can be much more effective than one 40-hour week in altering the behavior and improving the skills of your employees.
Additional Thoughts
There is always a place for multi-day training sessions, but they are most effective in teaching a specific skill rather than relaying general knowledge.
-Andy

PBT in Hot Runner Systems…

I was asked this question by a molder who was having trouble balancing a hot runner system…

Bob
We have this new mold which is running 16 cavities in PBT. Usually we can balance the mold using the drop temperatures, but that does not seem to work on this mold. Any thoughts?
My Response
Essentially, semi-crystalline polymers with a high degree of crystallinity such as PBT and nylon are not highly affected by temperature. In such a case, you will have to adjust the gates or the hot runner system itself to balance the shear of the mold.
Additional Thoughts
Cold runner systems are the best for these materials. I know many molders who use a press-side low-RPM grinder to effectively grind up the material and re-introduce PBT back into the process.
-Andy

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