presto pot with stir

[dlaery]

do these do a good job of keeping the plastic from burning?

 

[Fern]

I have 3 of them that i use to keep remelt plastic hot.  I typically hand dip tubes and I am left with a lot of scrap after I cut the tails so i have a ton of plastic i remelt in the microwave, place into the presto and keep re-melting until i fill it up. I then shoot the re-melt into swimbait molds. 

I will say that it does keep the plastic from burning. I have not had any issues with the plastic burning, please note though that i don't typically separate the plastic by color when i re-melt so it usually turns into a greening brown color. I have attempted to separate all the chartreuse i had at one point and the time i did that, the chartreuse started out really bright and as i got towards the bottom, the green started getting kind of dull. I am sure i could've prevented this by adding heat stabilizer, however when it comes to burning the plastic, i have not had that issue.  

[ACAMACIAN]

I have used the presto pot and what I have found is as the paddle goes around the side of the pot ends up burning the plastic. I have a tendency of scraping it off and ruin the rest of the plastic. Not a fan yet.

 

[bryanmc]

2 hours ago, ACAMACIAN said:

I have used the presto pot and what I have found is as the paddle goes around the side of the pot ends up burning the plastic. I have a tendency of scraping it off and ruin the rest of the plastic. Not a fan yet.

 

If you put a PID controller on your pot you will never burn your plastic.  Th PID controls the temp of the element in the bottom of the pot.  The plastic can never get hotter than the element.

[dlaery]

hey thanks!, that helps. I will do the PID, i haven't decided how to mount the thermal coupler. I guess I could take the thermostat apart on the presto and see if I can see some wires  to connect to the thermocouple post on the PID.

 

[bryanmc]

3 hours ago, dlaery said:

hey thanks!, that helps. I will do the PID, i haven't decided how to mount the thermal coupler. I guess I could take the thermostat apart on the presto and see if I can see some wires  to connect to the thermocouple post on the PID.

 

Throw the whole plug in power thing away and connect the SSR directly to the pins that come from the element.  As far as the thermocouple, I drilled a little divot in the bottom of the pot (not a hole, really just an indent for the nose of the t-couple to sit in).  Then I took a piece of metal bar and ran it diagonally across the bottom of the pot.  I drilled a hole in it corresponding to the divot in the middle and mounted the t-couple there.  You just need to make sure the nose of the t-couple is snug against the bottom of the pot.

[dlaery]

5 minutes ago, bryanmc said:

Throw the whole plug in power thing away and connect the SSR directly to the pins that come from the element.  As far as the thermocouple, I drilled a little divot in the bottom of the pot (not a hole, really just an indent for the nose of the t-couple to sit in).  Then I took a piece of metal bar and ran it diagonally across the bottom of the pot.  I drilled a hole in it corresponding to the divot in the middle and mounted the t-couple there.  You just need to make sure the nose of the t-couple is snug against the bottom of the pot.

ok, thanks!

[bryanmc]

Should have mentioned that the ends of the bar that hold the t-couple fit in between the legs and the pot on either end.

 

[dlaery]

On 7/5/2023 at 7:44 PM, bryanmc said:

Should have mentioned that the ends of the bar that hold the t-couple fit in between the legs and the pot on either end.

 

so a thermocouple with a probe? or a surface mount like this https://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=273

 

[bryanmc]

The thermocouple I used looks like this picture.   Imagine running a thin metal bar from corner to corner on the picture you supplied.  You drill a hole in the center of the bar and the t-couple goes through the bar and the nose contacts the bottom of the pot in the location of the divot mentioned earlier.  You can thread a nut on the thermocouple to adjust the depth and / or hold it in place as necessary.

 

Edited July 8, 2023 by bryanmc

[dlaery]

ok thanks, that makes sense.

[The Plastics Man]

On 7/6/2023 at 4:34 AM, bryanmc said:

Throw the whole plug in power thing away and connect the SSR directly to the pins that come from the element.  As far as the thermocouple, I drilled a little divot in the bottom of the pot (not a hole, really just an indent for the nose of the t-couple to sit in).  Then I took a piece of metal bar and ran it diagonally across the bottom of the pot.  I drilled a hole in it corresponding to the divot in the middle and mounted the t-couple there.  You just need to make sure the nose of the t-couple is snug against the bottom of the pot.

Great Information. I am thinking with the element, as most electric pots have "hot spots" around certain areas on the element ring,  each pot will have different characteristics,  finding that and placing the T coupler as close as possible to the hottest spot ? Just a thought 

[bryanmc]

11 hours ago, The Plastics Man said:

Great Information. I am thinking with the element, as most electric pots have "hot spots" around certain areas on the element ring,  each pot will have different characteristics,  finding that and placing the T coupler as close as possible to the hottest spot ? Just a thought 

My thinking was if you read off the hottest spot, the rest of the base might never get to temp or might take a long time.   In the center of the pot you read more the plastic temp than element heat.   

[The Plastics Man]

6 hours ago, bryanmc said:

My thinking was if you read off the hottest spot, the rest of the base might never get to temp or might take a long time.   In the center of the pot you read more the plastic temp than element heat.   

True. However, as most stirrers may not scrape from the surface of the pot as there's usually a millimetre or so gap , if there is a hot spot, it could scorch. I found that my pots , after years of use have evidence of hot zones and if I do not work that particular spot when reaching temp, it does scorch and results with burnt flaky bits.

It's a double edge sword IMO

I am thinking of spending $ on a set of larger presto pots and converting with PID's with taps to drain out a quart at a time. But ultimately , I would love to have a heat exchanger unit/ pump designed to constantly feed my hotrunner machine or have an heat exchange/ injection unit designed for a series of multi cav hobby molds and move away from the hotrunner and microwaves all together

 

[SlowFISH]

Use a PID as recommended and don't get caught up with over thinking the pot is hotter here than there, etc etc and if your paddle is scraping the bottom - since the first use of my pots after setting them up with PID controllers I haven't burnt ANYTHING - NADA - those things just flat out work. 

  The PID's once up and stabilized just tickle the element constantly to keep temp - once it's up and running - you'll be fine... only time plastic has a chance of getting cooked is if you don't use a motorized stirring paddle.  Seriously - stirring with a PID is about as dummy proof as you can get.   The only time plastic has chance to get too hot is when your at the very bottom of a shoot.... as there is so little plastic in the pot it can mess with the temp a bit - but I'm talking the last 1/8"=1/4" left - its even hard to suck the plastic up without air with that little plastic.

I bought 7" long thermocouples and have them mounted on the same plate that holds my stirring motor going down into the pot so I can remove them easy to clean.  They are about 1" inboard from the outside of the pot.  I set them up to be about 1/32"-1/16" off the bottom (They don't touch the pot metal).

 J.

[dlaery]

28 minutes ago, SlowFISH said:

 don't get caught up with over thinking the pot is hotter here than there, etc etc and

that's gonna be hard to do.

 

[bryanmc]

16 hours ago, SlowFISH said:

I bought 7" long thermocouples and have them mounted on the same plate that holds my stirring motor going down into the pot so I can remove them easy to clean.  They are about 1" inboard from the outside of the pot.  I set them up to be about 1/32"-1/16" off the bottom (They don't touch the pot metal).

 J.

I had originally thought about doing it that way, but it would have required me to build (not my strong suit) or find a top plate and stirrer paddle that would stir without contacting the t-couple.  I still think about doing it now and then so I wouldn't have to stop the motor to load an injector.

[SlowFISH]

9 hours ago, bryanmc said:

I had originally thought about doing it that way, but it would have required me to build (not my strong suit) or find a top plate and stirrer paddle that would stir without contacting the t-couple.  I still think about doing it now and then so I wouldn't have to stop the motor to load an injector.

It's a double edge sword - I offset my paddles so I can leave the injection in the pot with it running.  It doesn't stir as well as it would if I had full coverage - but it's really only noticeable in two conditions - when adding glitter - I make sure to pull my injector out and let it stir fully and when I start tossing in runners/remelts.... sometimes they can get unhung up on the thermocouple or injector.  The best solution is the "Shooting Star" manifold - but for a hobbyist - I can live with paying attention when I toss in remelts/glitter and deal with it.

[Tlyons]

Do you all heat the plastic in microwave first then put into pot ? i tried to pour in the pot and heat that way and it just burns the plastic