Plastics Training: June 2010 Archives

Although there are many regulations, and interpretations, most manufacturers and regulatory groups can agree that safety glasses should be worn under the following machine conditions...

1) Whenever a safety gate is opened, it is considered violated, and eye protection is required. This includes mold or die changes, machine maintenance, mold or die cleaning, clearing a stuck part, and semi-automatic operation.

2) Whenever polymer is purged from the barrel, high pressures and temperatures are being released. Both eye and face protection should be used in the form of a face shield.

-Andy

There is much information available online, but there are a few things that you can also investigate in-house and with your supplier.

1. Any additive will change the melting characteristics of the polymer. You should always perform a tact temperature study as well as check and document the temperature of your melt with each polymer/additive combination. Some additives may cause the polymer to stick to the screw rather than the barrel, requiring an unnecessarily high screw speed to recover the shot. Adversely, one colorant may cause the polymer to melt very smoothly, resulting in a lower melt temperature. To better explain this, one of my customers (who processes only one base resin) showed me a screw with different colored stains along the transition zone. Each stain indicates the melting characteristic of that material/colorant combination. Some colors caused softening near the feed zone, while others softened closer to the metering zone with a rainbow of colors in between.

2. In additional to documenting the process outputs such as fill weight, peak pressure at fill, back pressure, etc. you should also consider taking a picture of the short so that you can visually match the appearance of the colored first stage short shots to the natural first stage short shot. Although most additives act as plasticizers, some additives will actually increase the viscosity of the polymer melt... especially if it reduces the melt temperature. This consequence can be improved by optimizing the screw recovery for each formulation you use.

3. Contact your material supplier and request any Technical Service Bulletins regarding acetals and/or the colorants you use. Also request drying specifications and annealing suggestions. In many cases, materials like acetals will provide more consistent dimensions when annealed.

In semi-crystalline polymers, such as nylon, colorants and additives can also affect semi-crystalline site nucleation and growth. 

For, more information about tact temperature studies, please read: Optimizing Screw Recovery...

For free multimedia presentations on process documentation, scientific molding, and in-mold rheology, please visit:  http://www.traininteractive.com/free/webinar/player/

-Andy

Definitely, the more quality knows about production, the better off you are. They usually don't need to know all the technical information... but an increase in knowledge will always improve overall communication.

You should include your production employees in the education effort so that they have some responsibility in teaching your quality employees about what they do.

Keep in mind, this is not a one-way street. Cross-training your production employees about quality is an equally critical step.

-Andy