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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.

Safety Glasses on the Production Floor

I was recently asked a question which has been debated for many years…

Jennifer
What is the proper rule for safety glasses? Some say they are not always needed, others say they should be work at all times, what is your opinion?
My Response
Before I relate my opinion, I first want to bring up three important factors…
1) Virtually all machine and equipment manufacturers suggest that eye protection be worn at all times.
2) Virtually all safety regulatory groups recommend of require safety glasses to be worn at all times on the production floor.
3) Virtually all safety training recommends safety glasses to be worn around any piece of production equipment.
First… anyone violating a safety guard, servicing a machine, purging, grinding, or opening the safety gates for any reason must wear safety glasses.
Second… I strongly feel that anyone on the production floor should be wearing safety glasses.
Third… I also feel that the tool room, maintenance area, quality lab, and warehouse should also be included. 
Additional Thoughts
In all stages of my professional development, I have been taught the importance of personal protection equipment and specifically… eye protection.
I have personally seen safety hazards such as fragments and fluids travel hundreds of feet across the production floor… all being serious hazards to everyone on the production floor.
As always, I am interested in hearing your opinion on this matter.
-Andy

Can High Clamp Tonnage Cause Flash?

In a recent seminar, I received this interesting question…

Participant
Can high clamp tonnage actually cause flash?
My Response
Yes, it actually can. High Clamp Tonnage can block the vents, causing gases to become trapped in the mold during 1st stage injection. Although, these gasses most often heat and cause burning or short shots… these gasses can also force the parting line to open allowing the gases and some polymer to escape.
This rare flash resulting from high clamp tonnage tends to be very thin and wispy since it often tightly clamped immediately after it is formed. Often, this flash remains with the mold and builds up on the parting line.
Additional Thoughts
Excessive clamp tonnage is never a good practice as it will often cause damage to the vents, parting line, and may even stress the mold components.
-Andy

Article on ‘Talent Management’

I recently read a great article entitled ‘Profitable Manufacturers Focus on Talent Management‘…

In this IndustryWeek article, the author cites a new study released by Deloitte, The Manufacturing Institute and Oracle to explain that top manufacturers are still investing in their workforce… regardless of the financial times.
Article Excerpt
The study shows that surveyed manufacturers, especially the most profitable, rank employing a top-notch workforce high on their priority list. Many companies assigned a higher importance to implementing people management practices compared to increasing customer service orientation.”

Article Link

20-page Report Link

-Andy

Rules for a DIII Process

A frequent blogger asked this question the other day…
MJ
I know, the rules for DII process as follows:
 
•  A process that uses one injection speed to fill – whenever possible 
•  The mold fills 95 to 98 percent full during first stage 
•  All cavities are short shot during first stage 
•  First stage fill is velocity-controlled and not pressure limited 
•  Second stage pack is pressure-controller and not velocity limited 
•  Process uses only 20 to 80 percent of the machine’s available shot size 
•  The final cushion is approximately 10 percent of the overall shot size
 
Do you have something like this for DIII process?
My Response
As with above, the following items are also rules of thumb, and are not set in stone.
•  A process that uses one injection speed to fill – whenever possible 
•  The mold fills 80-90 percent full during first stage 
•  All cavities are short shot during first stage 
•  First stage fill is velocity-controlled and not pressure limited 
•  Second stage pack is velocity-controlled and not pressure limited
•  Second stage transfers at approximately 95-98 percent full
•  Second stage transfer is controlled using post-gate cavity pressure
•  Third stage hold is pressure-controller and not velocity limited
•  Process uses only 20 to 80 percent of the machine’s available shot size 
•  The final cushion is approximately 10 percent of the overall shot size
Additional Thoughts
A DIII process requires cavity pressure transfer capabilities, and should only be used if you and your technicians have a high level of competence. Such a process gives you excellent control, but may be overkill for many applications with good processing windows.
-Andy

The Affect Of Screw Diameter On Shear Rate

One of our customers brought up this question…
Jim M.
How does shear rate vary for the same fill rate going from a small screw to a large screw?  The volumetric flow rate being the same of course, but is there a difference in shear rate caused by the barrel / screw size differences?
My Response
With respect to shear during first stage injection, virtually all the shear occurs in the nozzle, runner, gates, and mold cavity. The diameter of the barrel, in comparison, is inconsequential.
If you used the same rotational speed (RPM) with a larger diameter screw, then you would create more shear during recovery since the circumferential speed would increase. For this reason… you should try to match the recovery times to help balance the shear caused during screw recovery.
Additional Thoughts
What is usually overlooked is the ID and length of the nozzle which may change from machine to machine as well as the resulting melt temperature due to recovery… These oversights often make people think it’s the barrel that is causing the difference.
-Andy