Welcome!

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.

VISIT OUR STORE
VISIT OUR WEBSITE

Improving Mixing…

Screw speed is not the most consistent method of improving mixing within the barrel. Back Pressure and Melt Temperature are more consistent and reliable methods of mixing your polymer.

Question: I read your post on using a slow screw for long cycle time for processes like ours. My techs tell me they need to use a high screw speed to get the material properly mixed, is this true?
My Response: High rotational speeds will add shear to the material. Excessively high speeds will also cause heating due to excessive polymer chain breakage and degradation, especially if semi-crystalline polymers are being forced through the transition zone before they are ready to melt. Both of these results are not consistent & reliable, and will add variability to your process. Good mixing typically requires shear, temperature, or both. If you need more back flow & shear, then you should add back pressure to the process. If the material needs more heat to mix or melt properly, then you should increase the middle and front zones to increase the melt temperature. In any case, you should document the Melt Temperature (probe inserted into purge), Back Pressure (in plastic pressure), and Recovery Time (in seconds) when the mixing is adequate so your melting profile can be easily duplicated in the future.
-Andy

Slow Screw Speeds…

On the newer electric injection molding machines, there is typically no detriment to using a slow screw speed for longer cycle times. This will just result in a more uniform and consistent melt.

Question: Your training states that recovery should consume 80% of the cooling time. Some of our cooling times are almost 2 minutes, will this put excessive strain on our new electric machines?
My Response: This actually adds no additional strain on your servo motor. As long as the machine can maintain a consistent recovery time, you should use a slow screw speed when possible. I have seen all-electric molding machines capable of maintaining consistent recovery times with rotational speeds lower than 10 RPM.
-Andy

Sustaining Proper Documentation…

The employees need examples of how the documentation makes their job easier and reduces process shift. If they do not understand how the training helps themselves, they are less likely to document the process changes.

Question: I need advice as to how to better enforce the use of process sheets and track/record any changes made. I am hoping that somebody in the blog an contribute as well.
1) The employees need examples of how the documentation makes their job easier and reduces process shift.
• No doc example: Shift 1 gets flash and increases tonnage, shift 2 sees burning and reduces injection speed, shift 3 gets sinks at the end of fill and reduces mold temp, shift 1 then finds large dimensions and decreases packing, shift 2 gets sinks and decreases melt temperature, etc.
• Doc example: Shift 1 gets flash and increase tonnage, shift 2 sees burning and cleans the vents and reduces the tonnage a little and the process runs well for the next few days.
2) They also need to know how it helps them identify non-processing problems and bring them to the attention of management. For example, if a mold keeps having burning issues, then they can easily justify the need to invest in venting improvements to the tooling.
3) The employees are never reprimanded for documenting their changes. Employees are trying to do a good job, and when they are attacked for documenting their changes and following procedures, they lose all motivation to document any further changes. (ie. Never let management paw through the logs to determine who made the change last night which causes bad parts)
4) The management needs to reprimand those who do not document changes, including engineers and managers. Ultimately, management needs to back the effort for it to succeed. I had this policy instituted at a company I worked for and was deservedly reprimanded a week later for not documenting my changes during an overnight troubleshooting session.
When we do on-site training we constantly reinforce the benefits and helpfulness of documentation with respect to easing the job of processors and technicians.
All readers are welcome to comment with their experience as well.
-Andy

Sort vs. Standardize

There are many variations in 5S, and many people get confused between some of the terms. Since the terms all revolve around the same Lean Manufacturing principles there is often a confusion of concepts.
Question: How do I explain the difference between Sorting and Standardizing?
My Response: Sorting involves the organization of workplace and the elimination of unwanted materials. Standardizing typically takes place afterwards to make similar workplaces look alike. For example, Sorting may determine that machine #1 and #2 both require a melt temperature probe at the machine; Standardizing will place the melt temperature probe next to the control panel on both machines so it can be easily found.
-Andy

General Purging Procedure

I am often asked which method is the best way to purge. Unfortunately there are so many different types of compounds and applications that there no specific method which is best, but most procedures include the following aspects.
Preparation: One of the most important aspects of purging is the preparation. This includes obtaining and mixing your materials, acquiring the processing parameters, and reviewing the recommended procedures.
Initial Cleaning: The old material must be vacuumed and wiped out to avoid cross contamination.
Initial Purge: The purging material must be run through the machine to remove the old material from the barrel, screw, nozzle, and hot runner system.
Final Cleaning: A second cleaning operation is typically needed to clear out the purge form the hopper and material delivery system.
Final Purge: The final material is run through the barrel, screw, nozzle, and hot runner system to push out the purging compound.
Production: The last step involves getting the machine back into production mode while making acceptable product.
I understand there are many purging products which have specific requirements, but you will find these steps involved in most purging procedures you encounter.
-Andy

  • Recent Posts

  • Recent Comments

  • Archives

  • Categories

    • © 2016 All Rights Reserved | Powered by Wordpress | Made with ❤ by Themely