Yellowing plastic

[Fudd]

I know this has been beat to death and I have reviewed most of the questions and answers, but would like some guidance.  I am using Bear's twinjectors system (shooting star).  I have 2 presto pots with stirrers.  I use a lot of light colors (white, pearl, glow, etc.) and cannot keep them from yellowing before I can get halfway through.  I put 4 cups of CC plastic in the pots, turn the pots and stirrers on then add my color and glitter.  I have the temp set so as it is a low as I can get by with drawing and shooting the plastic (310-320).  The stirrers stay on all the time.  I do add stabilizer, which helps some, but not in a measured quantity.  I would like to be able to do larger batches, but cannot due to the yellowing.  The plastic is about 6 months to 1 year old.

Thanks,

Scott

[Jason]

I need to scoot out the door but will respond to this in detail in just a bit.  Jason

[DARRYL]

I have some trouble with that also. I turned my power setting down to 70% on my microwave and that helped alot. My problems are occuring on about the 3rd reheat. I also use about 10 drops of stabilizer to 4 ounces of plastic. Should I be using more stabilizer?

[ctom]

I shoot mainly small baits and lots of transparents and lighter colors. I do tons of re-melts/re-heats. In 4 ounces of plastic I am using more stabilizer than 10 drops, but I am adding a small amount of raw plastic each time I re-melt. I also chop up the re-melt stuff so I am heating smaller pieces.

As far as the pots and 4 cups of product, I haven't been down that road. I have done a bunch of 1 cup batches and what I have found is that the one cup stuff is harder for me to control than a 4 ounce batch. I think a lot has to be considered when doing big batches especially if you are using a pot with a wide area of open plastic and stirrers since the surface of the plastic is always losing heat to the air. If that air is cold air, you might be thinking the product is not hot enough when it might actually be to hot down at the bottom. Keeping the plastic in motion all the time keeps that surface exposed to outside air continually. Your environment plays a huge factor in how your plastics gets worked and that environment does not stay static....what worked yesterday may not hand you the same results today.

I'm assuming you are using a quality thermometer to accurately determine the temp of the plastic. Never rely on a pot's thermostat.

Another thing I do is to add additional stabilizer as I re-heat and shoot. If I am looking at my third or fourth re-heat during a shot I will add more stabilizer. Stabilizer does not stay with the plastic. It will cook out and needs to be re-plenished as you work to keep the colors viable and your plastic from turning. I will also add maybe a half ounce of raw plastic when I add this stabilizer at mid-shoot. If my color weakens I use a toothpick tip dipped in colorant to adjust my color back. 

[Jester]

I'm not sure if this will help or not but here is what I am doing. I can reheat Chartreuse 8 times before it changes the color with no heat stabilizer. I am using a cheap microwave from Home Depot 700 watt I think. I heat 4oz. of plastic for 2 min to bring it up to temp. I add my color and stir it in. Reheat the colored plastic for 15-20 sec then add the glitter stir and shoot. I put the left over plastic back in the Pyrex cup and put it on a hot plate on med heat. I cut the runner up and put it back in the Pyrex cup and stir. Here is what I feel is the important part. When I reheat my plastic I never reheat it for more than 20 sec. without taking it out and stirring. My microwave heats in 1 min or 30 sec increments. So I reheat 20 sec take it out and stir then put it back in  for the remaining 10 sec take it out and shoot. Any time I have reheated plastic for more than 20 sec without taking it out and stirring it has either yellowed the plastic or stripped the color off of the glitter. Hope this helps.

Dennis

[fsh4fun]

I do exactly the same thing as Jester,except I leave my my leftovers out until I`m low on plastic,than remelt those.That being said,too many reheats and my plastic will start to yellow.I have never tried stabilizer yet,but I should.

[andrewlamberson]

Try mixing in just a little more virgin plastic...that can really help. I normally mix in a little virgin and 1 drop of X2 colorant to keep it on target.

And get a good digital (not IR !) thermometer  and microwave in 20-30 intervals and don't let the temp get above 350.

If you search previous posts..you'll see I'm big on CDN thermometer...and at $18...how wrong could I be?? !

http://www.amazon.com/CDN-DTQ450X-ProAccurate-Quick-Read-Thermometer/dp/B0021AEAG2/ref=sr_1_1?s=home-garden&ie=UTF8&qid=1353867035&sr=1-1&keywords=digital+thermometer

Temperature control is SUPER critical...but it seems to be the most overlooked by many folks.

While you are ordering the thermometer...check out the 14oz cast iron melting pot that T-Billy turned us on to. That on a single burner electric plate...and your plastic will stay hot a long time! Pre-warm it up...and I made a lid from some aluminum plate...but even using a square kitchen heat pad thingy (they kind you use to grab something out of the oven) works great.

http://www.amazon.com/Lodge-Pre-Seasoned-Cast-Iron-14-Ounce-Melting/dp/B0002CX9FE/ref=sr_1_5?s=home-garden&ie=UTF8&qid=1353867211&sr=1-5&keywords=cast+iron+pot

Order the scrapers also....so you can quickly clean out your pot without scratching it.

[Fudd]

Just to make everyone understand what I am doing.  I am not using a microwave, I am using Presto pots.  I am not remelting, this is virgin plastic.  I am using an IR gun, but only getting the plastic up to a temp that it will just barely flow.  I cannot go any colder and the IR gun is saying 310-320 degrees.  With the shooting star system 2 cups is as small a batch as you can use.

Thanks,

Scott

[Frank]

I get what you are saying. The problem I see happens to me also but only when I get down to a small amount in a presto. You see when the tstat say to turn on it goes all in till the heat is back up to temp. That is where the yellowing happens. Not sure what you could do to prevent it. I make a gallon at a time and stop when it is about 1/2 to 1" on the bottom. Which is where you are starting. Kitchen products work but are made for cooking, not plastic. Temp spikes are a killer of good plastic. Now get that system to fit the cast pots or pots made for plastic and you got something. I use prestos alot and really want to replace them asap. And I will soon. Dont have a fix for you though. Frank

[Jason]

I typed up most of what I know here:

http://www.caneycreekmolds.net/index.php?topic=2518.0

Please take a look and let me know if you have any questions, or if I forgot something.

Thanks,

Jason

[Fudd]

Frank,
     I have a full machine shop so I can build whatever I want to make this work better.  Would getting some heavy cast iron pots and building my own heating system be better?  The heating elements are still just on/off so work it be better?  Or would the heavy cast iron pot distribute the heat better/more even?

Thanks,

Scott

[Jason]

A cast iron pot, heat bands from McMaster Carr that wrapped the pot as well as covered the bottom, a stirring system built into a lid, and a digital probe thermostat would be an ideal solution.  If you start taking orders, put me down for one.

Jason

[Fudd]

That is what I am thinking.  Help me find a good cast iron pot of the size similar to a presto and we will have a go.

Thanks,

scott

[basshunter5]

I've read a lot about the bears system and it seems to be a good system but it also seems to me that it is better for very high production rather than the average small lure makers. I'm not saying it can't be used that way but from what I've read it will only suction properly if there are at least 2 cups of plastic in the pot or pots. 2 pots means at least four cups of plastic at the least to work properly. I'm not saying this is a bad thing  just that from my experience with lighter colors you either have to do small batches or have a lot of molds/cavitys in order to keep the colors from changing .  I know everyone has different opinions and experiences this is just from my experience with light colors.

[Frank]

Frank,
     I have a full machine shop so I can build whatever I want to make this work better.  Would getting some heavy cast iron pots and building my own heating system be better?  The heating elements are still just on/off so work it be better?  Or would the heavy cast iron pot distribute the heat better/more even?

Thanks,

Scott

Yes it would. Something with a side and bottom that are thick enough to NOT make a hot spot on start up. If you build it they will come. One of my ideas was a hot plate that goes up the sides. The reason for this is you can change pots fast and they are cheap enough to buy a bunch of them. There is alot of heat loss out the sides and top. I have two ritehete pots that are the cats meow. The plastic does not get yellow like the prestos but i cant use it with the twinjector. If you have a full machine shop why did you not build your own system? But then now you will. Frank