"Purging the purge"

[Jorge Villegas]

Hello guys, this time i`ve been working with purging agents to improve changeover times.

So far excelent result with almost every material, but i`m still missing something with transparent materials. the purging materials manages to clean the whole barrel and screw, but i´m having a hard time "purging the purge". I´m working with a Ionomer and it`s just not able to clean the purge so I still get white streaks in my articles. I´ve tried with different "transparent" purges but I still get the same white streaks,

Any experience here on purging the barrel for Transparent materials?

[rickbatey]

I've preferred PDQ liquid purging compound for many years as I can mix it into the production resin and run it through the hot runner and valve gates. Buy the premeasured packets, knead them, and just drop into feed throat. No messes.
Many years ago we ran clear PC or white PC/PA in a single press at all times. Now we weren't working with your resin that I hear is a bear to run, but it worked wonders for scrap.
Rick.

[Jorge Villegas]

Thanks Rick for your feedback.

My coworker already tried with PDQ on transparent Polymers, The first thing the sales agent said was, drop the whole bag into the feeding throat. My coworker droped the whole bag into the feeding Throat. BAAAAAD idea. I had to unmount the screw to clean the mess the PE made.

I´m working on the method to work better with the PDQ, because for other materials it works excellent. Right now i`m working with 2 purging compund, dynapurge M (this does`sn work in hot runners and static mixers) and the PDQ. I didn´t like that much ultrapurge. Haven`t tried ASACLEAN, because we don`t have a sales agent here in Colombia.

I haven´t tried mixing the PDQ with the ionomer before feeding it to the machine. I think I will try that next.

[Airwinghma]

Greetings;

Used to run a rubber modified acrylic in transparent colors and were pulling screws to clean them during color changes. Ran trials of purging compounds and purgex worked the best, stopped pulling screws. Did a trial of a moldable purging agent safe for hot runners, ran it on a 48 cavity detergent cap, took the whole 55 lb bag and went from purple to clear in about 12 shots. But since it used the whole bag it was way cheaper to run natural material until it cleared.

Scott

[3NGLENN1889]

Hello all- after being in the trade for 30 years I've come across every "snake oil" for purging there is. Just recently I came across a product called ASA Clean. Very simply its glass filled polystyrene. The stuff is amazing. Just follow the directions to a tee. Black specs, residual colors, brown streaks, or just plain barrel scrubbing,
this stuff shows no mercy. Only small amounts are required. It's sold by the Polyone Corp. Hope this helps. G.P.

[pjhall]

Purge compound works to get the color / black specks out. There are some transparent material that will be milky for a long while until the purge comes out. Here are a couple of "transition after purge compounds" I use"

TPX (poly methyl Pentene). Purge compound then PP then TPX. If you use PC in the transition it will be very milky
Isoplast (TPU) - Purge compound then PC at 520 (no higher) then Isoplast. Be careful! The isoplast will purge like water at that temp. Lower barrel temps to 450-470 and you are all good!
Transparent ABS - I have yet to find a transition that works...

[Jorge Villegas]

Thank you all for the responses!

@3NGLENN1889. I`m trying to get a sample of the ASACLEAN. I hope to have it bynext week. I hope it doesn`t work, because i would have to import it directly, and for a purging agent, that would be waaaayyy to expensive ( remember our colombian "peso" is going through though time".

@pjhall Thanks for the reply, i`m going to try using PP to clean the purge and see how it works (i`m guessing it works best with a Random copolymer?) and the use the ionomer.

[joeprocess]

I have had the best success with following up our Dynapurge with Cleanplaspurge to remove much of the cloudiness. http://www.cleanplastpurge.com/

Kathy Baker also has a new product (Purge Right) she claims can do this as well, but I have not had the time to test it yet. Kathy Baker <kbaker11@rochester.rr.com>

[Jorge Villegas]

A quick Update on this Topic.

For anything outside clear materials, i`ve been using Dynapurge M and so far it works great for our needs, I improved the method (backpressure, rpms, and fans/short shots). By doing this It takes now a maximum of 10 minutos to clean the screw of those difficult colors. What i don´t like of the Dynapurge M is that it´s not suitable for hot runners. i´m evaluating anothe purge for this.

For the clear materials such as SAN or the Ionomers I´ve been "cleaning the purge" with PE, and so far I think this would be "the way". But i still need another couple fo test to determine if it really works. This would be a huge money saver. Everytime we change to clear materials we have to dismount the screw to clean, last week, doing the cleaning with purge and PE it actually worked, it took 30 minutes, 2kg of purge and 5 kg of PE to have clear products, instead of 7 hours to clean the screw. That`s something.