| Recorded: |
June 9, 2011 |
| Presented by: |
Dave Schmidt, Husky |
|
|
As molders strive to become more competitive, the systematic elimination of waste has become more critical and all aspects of the injection molding process must be examined for cost containment opportunities. An area of focus for scrap reduction is often the color change process. Improving the color change process can help injection molders reduce their resin costs and improve part quality, thereby improving their profitability.
Since color-change problems have always been considered inherent to hot runner design, the issues are not always well addressed. However, investigations into the root causes of extended color change times has yielded intriguing results. This Webinar reviews the basics of colorants and color change, the root causes of lengthy color changes, as well as the hardware and processing strategies used to improve color change. The discussion is supported with actual case studies of color change improvements.
Webinar follow-up: questions and comments
Download the Color Change Procedure PDF for more information.
1) The color change that is causing the most problem is white. We are running a hot runner with four cavities. The material being run is polystyrene GPS. We can spend an entire day purging. We have tried all the popular purging materials without a lot of success. We have gone up and down on the runner temps and some times this has helped. We still get a white bleed a couple days later.
a. Have you tried increasing your injection speed on your machine during the color change process? This will help increase the shear through the hot runner and should facilitate a faster color change.
b. Have you checked your entire system (machine, melt delivery system) for any possible hang up spots?
c. See attached Color Change Procedure.
2) 200 cycles could be considered an optimal number of cycles to pass from a Black color to crystal? I use a Valve Gate U500 to thinwall (PSGP).
a. 200 cycles is a reasonable average from black to clear. If you want to further improve we could review the Hot Runner to see if the was designed for color change, and review the system to see if there is anything we could do to help improve its color change performance. You mention the part is thinwall, this Hot Runner may have been designed with pressure in mind, channel sizes may have not been optimal for color change.
b. See attached Color Change Procedure.
3) Can you talk about the sensitivities of liquid colors?
a. We suggest that you contact your resin supplier regarding this question, assuming you are talking about temperature sensitivity of liquid colors. In general we have seen that liquid colorants are harder to change color.
4) Are tip insulators manufactured?
a. Yes tip insulators are manufactured from bar stock. They themselves are not injection molded.
5) The recommended 30°C reduction / increase are good for PP as well as for PE?
a. Yes this temperature reduction / increase should be good for both PP and PE.
b. See attached Color Change Procedure.
6) What is the impact of the surface roughness / quality of the channels to color change?
a. Any surface imperfections / tooling chatter marks create possible hang up spots for plastic. These hang up spots are not good for color change applications.
7) Which pigments are more common in food applications? Organic or mineral type?
a. We would suggest that you contact your resin supplier regarding this question.
8) Does Husky have the color change procedure automated or as an assistant in the machine SW?
a. Some models of our machines have this capability.
b. We are currently developing this type of option as part of our Altanium Hot Runner temperature controller offering.
9) Can the high flow eliminate weld lines when the front of two flows join together? It is especially visible when using pearlescent.
a. I am assuming you are referring to UltraFlow tips. If so, yes we have had success in eliminating flow lines with pearlescent colored resins by using UltraFlow tips.
10) Where can we get more info on the ultra flow tips?
a. Contact your local Husky Hot Runner sales representative.
11) Orica Mining Services - produces shock tube-3 layers, the last one is colored, we use different colors: red, yellow, magenta, green. The worse is magenta, we have too much scrap and its specifications is much different from another ones. We use pellets both plast and color pigments. Which parameters are more important to be taken for comparison and better results?
a. We would need to collect more information on this topic to discuss this particular issue in further detail to be able to suggest a solution. Please contact your local Hot Runner representative and if they cannot address your issue, they can put you in contact with the proper Hot Runner personnel to address your issue.
12) Our facility is on its way to beginning to use purging material. Can you advice what kind of purging material would be better to use?
a. We have had good luck with Ultrapurge – ultrapurge.com
13) Can you provide a formal color change procedure?
a. Download the Color Change Procedure PDF for more information.
14) Can the ultra flow tips be fitted into another system that is not a husky system?
a. No, Husky’s UltraFlow tips cannot be used on any other Hot Runner suppliers system.
15) Is there a greater pressure loss using the ultra flow tip?
a. The pressure loss increase with UltraFlow tips is application dependent. We have seen anywhere from 5-25% increase in pressure drop with these tips; it is application dependent.
16) Do you recommend any purging compound?
a. We have had good luck with Ultrapurge – ultrapurge.com
17) Is it necessary to change the temperatures in the moment of the change of color?
a. It is not always necessary to modify temperature settings during a color change. As a starting point normal process parameters can be used during color change. If that is not yielding acceptable color change time for you, you can progress to modifying temperatures (machine and HR) if you would like try and reduce your color change time.
b. Download the Color Change Procedure PDF for more information.
|
