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

Molding PVC With a Cushion…

The basics of scientific molding is the same whether you are molding CPVC or PP as it is with large parts vs. small parts. Essentially, the difference between is in the range and scale of parameters and not the scientific approach.

Question: Isn’t it dangerous to mold PVC with a cushion since the extra material in front of the screw will degrade?
My Response: This has a negligible affect on the residence time since the cushion is a very small fraction of entire volume of material within the barrel. With PVC , it is vitally important to mold with a cushion since the performance and repeat ability of the smear tip is greatly influenced by the material viscosity. Frequent variation in part weight and quality will occur if a cushion is not used because viscosity of PVC is greatly influenced by small material temperature fluctuations.
Additional Information: Since the screw typically contains approximately 2 times the maximum shot capacity of the molding machine, a 5-10% cushion will not affect the integrity of the PVC within the barrel.
-Andy

Using Standardized Ejector Rods…

With the right mold preparation, you can use one set of ejector rods in every machine. One this is done, you can keep the rods in the machine and use the same ejection retract position for all your molds.

Issue: Most of your molds use ejector rods to push the ejection system and you always have to change and adjust ejector rods during each mold change.
Resolution: Spacers should be added to each mold which screw into the ejector plate and are flush with the back of the clamping plate. If ties ejection is used, all the spacers should have the same threading for the knockout rods. Then each machine can have ejector rods machined to be flush with the movable platen when the ejection retract is in the back-most position.
Additional Information: As for the rods and spacers, I recommend they be machined out of Col-Rolled Steel to ensure their strength and endurance.
-Andy

Temp, Time, & Part Dimensions…

A cooler mold tends to provide larger part dimensions, but this can often be offset by a reduction in cooling time. It is generally worth the effort to perform a quick DOE to verify.

Concern: During an on-site training session, we were discussing how a cooler mold typically provides the best potential for a lower cycle time. In this discourse, one of the participants was explaining that they typically use mold temperature to achieve specific part dimensions.
My Response: As a class, we used one of their dimensionally critical parts and performed a small DOE with 3 different cooling times at 3 different mold temperatures. Once complete, a part molded 4 seconds faster with a mold temperature set 20 degrees F lower had better dimensions than before. This goes to show that just because you made a good part, a better process is not impossible.
-Andy

Why Train Operators?

You should have training available to all your employees. This will give you the largest available pool of employees to choose from for advancement.

Question: Why would I want to include operators and part inspectors in my training plan?
My Response: You never know where your next technician could come from. Technical proficiency is something you can develop over time. When you expose your employees to more information, some will be indifferent, while others will want to learn more and expand their knowledge. Unfortunately, many of the people who want to learn more do not even realize it until the information is made available. Our customers are often surprised at whom wants to learn and improve.
-Andy

Cavity Imbalance for LCP…

Whether you are processing PVC, Nylon, PS, or LCP, the basic strategy for filling and packing the mold is fundamentally the same.

Question: I am having a problem on my connector mold having a short shot. I am using lcp as the material and my mold is 8 cavity mold with submarine gate.
My Response:
Regarding Imbalance – You can improve the cavity imbalance either through a different injection speed or a flow balancing technology such as the MeltFlipper®.
Regarding Processing – The following 4 steps will help you maximize the potential of the tool in its current state:
1) Measure the melt temperature and ensure it is within manufacturer’s recommendations.
2) Make all cavities short shot at time of transfer.
3) Use a packing pressure which will fill out the mold and give you acceptable parts.
4) Reduce the clamp tonnage to allow more venting (this must be done after the transfer and packing is complete).
Other aspects can be investigated once the balance and process issues are addressed.
-Andy

  • Recent Posts

  • Recent Comments

  • Archives

  • Categories

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