Small Qty Injection

[Painter1]

I would welcome advice on how to shoot a small quantity with an injector. 

My current typical procedure for a single color using injection molds;

1.) Make at least 4 cups heated in the microwave, tinted and poured into Presto Pot.
2.) Mix in PP until temp is stable as required, 325-340
3.) Open valve on PP and place injector, sans tip, under the flow to fill point.
4.) put on nozzle/tip and purge the injector of plastic. 
5.) Purge solid plug of plastic at end of injector (sets up due to cold injector)
6.) Refill injector and start shooting. 

I know some folks suck up the plastic from a container into the injector,but I hate having the plastic on the outside of the injector. 

I am interested in doing 1/2 cup and 1 cup quantities.

 

[sim]

I only ever shoot in 'small quantities' compared to that - usually 4oz (1/2 cup) - the plastic on the outside of the injector will peel right off, I just add it to my sprue pile for re-melt.... it also gives you an idea of how the thin portion of the bait will look.

so - 4oz in microwave until temp - stick the injector in enough to get a solid fill  - inject into mold - clean/repeat.

[Painter1]

After struggling with it a bit, I have recently had good success with small quantity injection.  I placed the injector in my toaster oven (the one I use to bake jigs in) after removing the rubber ball at the handle.

I made about 3/4 cup of plastic, poured it into the preheated injector, put on the injector tip, and shot the baits.

Just had to figure out how much plastic would fit in the injector and only make up up that much.  The pre-heated injector allowed me to use all of the plastic without a cold plug at the end.

I have had a problem with color change in the hot plastic with this last box, so small batches and quick shots are the only way I can get my whites to be pearly bright. 

[MO QWACK]

The key with white is every time you reheat add stabilizer and some fresh raw plastic with a few new drops of white 

[tboxfish]

The key with white is every time you reheat add stabilizer and some fresh raw plastic with a few new drops of white

Great tip that will be put to use!

[Jerry V]

The key with white is every time you reheat add stabilizer and some fresh raw plastic with a few new drops of white

Great tip that will be put to use!

This also works for Chartreuse and other powerful/light colors...

[ctom]

Something else to keep in mind when re-heating just enough to keep the plastic workable is that you do NOT have to bring to 350 degrees each time you hit the heat switch. 320-340 degrees is plenty good for all but the fussiest of shots and molds.

[Jerry V]

I think another key is to heat in small increments and stir frequently.  There is a fine line between good to go and flat out burnt when it comes to the lighter colors... stir,heat,stir,heat, stir,stir,stir  They are tempermental that way.

[ctom]

OR you can power down to 80% too. As Jerry mentions, some of the lighter colors and fluorescents can be temperamental. They require some special handling to prevent discoloring and/or burning. Play around with a very small bowl of white or clear with some glitter using the various ideas mentioned here to see which works best for you, taking time to shoot the colors. Now take the baits you just shot and use those for practice in re-melting. Be sure to use stabilizer to help you keep clean colors on re-melts.

[TTDuckman]

I think Ctom hit it on the head, the reheat temp should be just enough to get the plastic back to an injectable viscosity.   One question that I have is how many and what type of molds are you using?  For example, this week, I made about 350 white skinny carrotts.  My recipe was as follows:
Bear in mind, I made 3 batches identical to this to get to 350.
4 cups CCM medium
5 tablespoons salt
4 tablespoons softener
15-20 drops of stabilizer
2 tablespoons of non-CCM white colorant

I was shooting 6 5" skinny carrot molds ( I use 2 6oz injectors)
Heat plastic, stabilizer, salt and softener to completion (I don't use a thermometer for a couple of reasons).
Add colorant, stir and put in micro for another 30+seconds.
Stir, suck up and inject 3 molds with each injector, purge liquid plastic back in the 4-cup pyrex
Demold, stir and shoot them the same way and purge.
While demolding, heat the plastic for for the opproximately 60-90 seconds while demolding.
Stir inject the molds and purge. 
At this point, I don't have enough plastic in the pyrex to shoot the molds the last round.
Take scraps from from the tops of the sprues (not the sprues themselves as the baits are hanging) and the plugs and place them in the pyrex
Stir the pyrex and microwave these scraps, at this point, you can add 5 drops or so of stabilizer if you wish
Demold, stir reheated plastic and inject the 4th round.

To get to 350, I make 3 batches identical to this.  24 hours later, I pull the baits off the sprues, put the plugs and cut up discs that are left at the bottom of the pyrex and add about 15 drops of stabilizer and heat the plastic to an injectible viscosity and shoot my final 4 shoot round as was detailed above.

In my experience (8 years), white is a fairly resiliant color and I almost never get yellowing.  Pearl is another story and smaller batches are often neccessary when dealing with it, as is chartreuse. 

I am not looking for an arguement on the thermometer issue, and will merely state my reasons for not using one.  Others feel a different way and different ways of doing things make the world go round:

Shooting plastics is about feel, experience is your greatest teacher
Understanding the 3 major phases of plastic preparation (liquid, gel, back to liquid), is necessary
Temp guns measure surface temperatures, even after stirring, you are getting a surface temperature
By the time you get to the majic 350 on the gun, your plastic in the lower 1/4 of your pyrex is well beyond that. 
In my opinion, a lot of yellowing has to do with a reliance on taking a temperature of plastic instead of going by feel. 
Overheating is one of the most encountered problems that new shooters encounter and I firmly believe that is directly related to the use of a thermometer.


That is my two cents.

Tim

[Denny Welch]

Great post, Tim.  If you are pouring that many baits I'm curious why you don't use a presto pot.  What are your thoughts re pros and cons.  Call me stupid (many people do), but I never use salt or HDA with carrots...don't know why, just don't.  I'm going to try it now.

Again, great post.  Thanks for sharing.

[TTDuckman]

I don't use a pot, due to lack of molds.  I shoot a round (4 shoots) and then start another round another set of molds that is almost always a different color.  Cool the first molds, then rotate back to them. 

If I was shooting several different styles of baits with the same color and salt or softness combinations, I definitely would use my pot (I have one, just don't use it very often at all). 

I typically have 20-24 cavities of the molds I am shooting, one mold I only have 10. 

Tim

[matt]

When I do lams most of my scerws I can melt down and a great color that I can use again

[ctom]

Per TTDuckman...."In my experience (8 years), white is a fairly resiliant color and I almost never get yellowing.  Pearl is another story and smaller batches are often neccessary when dealing with it, as is chartreuse."

I think some of this is due to what goes into the plastic: in this case the pearl whether it be in liquid or powder form. Pearl is an additive that gives a lot of internal "reflection" not only with light but in heat. The strongest  pearl I make is for the pro blue color and it is the most unpredictable color I make.

White, in and of itself, is a very heavy, dense colorant. It adds a whole bunch of weight to plastic. Perhaps some of the issues that arise in using it come from the pigments used in its manufacture?

Clear and some of the clear colors are also tricky especially if the have glitter.

The microwaves are all different even in identical units. Take time to find out what your oven does at high and 80% at identical times and whether there are predictable hot spots within in during use. Plastic problems are generally not a single issue type of thing. There are usually a couple small contributing factors that add up to trouble. This is why I think play time with plastic is so essential....not only can some great colors come from it but you learn a lot about the little things that can pop up and mess with plastic handling.

[Botanophilia]

I might do a batch as small as 2 oz in the microwave.  Useful for playing with new colors or if I have a color that I use only occasionally and don't need a lot of baits.