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joelhains

Keeping Your Molds Cool...and Plastic Hot?

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Anybody here ever "ice" your molds to make demolding faster? I have only been injecting plastics a short time and most of my molds are just single cavity. This makes filling larger orders very time consuming. I've been trying to think of ways to make my production more efficient. One thing I've cone up with is "icing" the mold. It seems to be working fine do far but I've only shot about 30 baits thus way so far.

Another question I have is for the guys heating plastic in the microwave. Is there a good way of keeping the plastic hot longer? It seems I only have time to shoot 3-5 baits before I have to heat the plastic again. I was thinking of trying an electric skillet and heating the plastic in the microwave and then putting the plastic in the glass containers directly on the skillet. Has anyone done this? If so how well does it work?

Thanks for all the help guys!

Edited by joelhains
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As much as you'll hate me saying this, the best answer is always molds, molds, and more molds.  The better you get, the more molds you'll want.

 

As for keeping the plastic hot after the initial microwave burst, hot plates and burners are always best.  Place them on mid-temp, transfer your cups from micro to burner, and you're good to go.  Keep in mind that all burners are temperamental and will heat at different intervals.  Once you learn the burner(s) you have, you should be good to go. 

 

Hope this helps a lil' 

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Agree with the above, more molds, but as you need to start somewhere, I've found some options.

1. Clamp your mold being shot between some that aren't, they will cool it down, while reheating plastic, lay the halves down and sit cold ones on it.

2. Ice packs can be handy too.

3. have a break and throw it in the freezer for 5 minutes.

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I did not think you were actually using ice. That may work for a bait with large appendages but if you have a mold with thin ones they will be hard to fill. Your best bet is to keep them at a warm working temp. Setting them in front of a fan will keep them from over heating. Clamping them with other molds not being used will work to but when they get hot it will still take awhile to cool down. As for putting your Pyrex cups on a griddle, I have been doing that for awhile. Does not work unless you stir it once in awhile to keep the skin off the top. My main cups I never reheat just remelt the sprues and add them back in the main cups. Give the ones on the griddle a little temp boost. I use a high sided one in case of a spill and it won't get knocked off. I have a bunch of videos on you tube showing how I do it. Look me up and watch a few. My channel is Franksrooty2 , a couple of them are in the tutorials section on this site too.

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Five years ago I started injecting baits using a microwave and Pyrex cups. I gave up after a few months because it was so time consuming. But recently I tried it again but this time a bought a presto pot and I'm telling you it has been so much better. I just leave the injector in the pot so it stays warm and I don't have to clean it before every shot. I would strongly recommend not cooling your mold in ice water.

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It comes to more cavities.  I have two 7 cavities and a 3 for my frog. I use 4 cups of plastic and a microwave.  Once to temp t takes me about 5 seconds to pour, minute to let set up, when I pull the worms I heat for 30 seconds and start over.  I can do around 80-100 in an hour and 60-75 for the frog.

Edited by Mudd Butt Baits
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I use an air hose from my compressor to cool a mold with compressed air so I can demold more quickly.  It's like blowing on hot coffee to cool it a little.  Aluminum transfers the heat away pretty quickly this way.

But I'm a hobby pourer.  If I were doing it for a living, I'd buy more molds, so I could do production with the minimum amount of sets.  Time is money.

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One method some have used for cooling molds is a heavy tile (stone or ceramic) kept in the freezer, and they just put the mold on the tile.  When the tile starts to warm up they swap tiles.  Don't ever set a hot glass cup of plastic on the tile though.  It will crack or shatter and dump hot plastic all over.  Heck I once set a cup on my drill press table on a cool day.  When the plastic finally cooled and I peeled it up my drill press table slots where the cleanest I had ever seen them.  LOL.  

 

One I made was a small clamping press for molds that you circulate chilled water through with a pump from a bucket of icewater.  I think I saw that somebody has made one like that for sale.  Instead of having a water jacketed mold the clamp that holds the mold has is the water jacket.  

 

I don't think I would do anything like you show where water could easily come in contact with molten plastic by accident.  It can spatter and have a steam explosion throwing throwing molten plastic everywhere including into your face and eyes.  

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As alsworms says.....more molds.....period.

or....don't prepare as much plastic....

You should have enough molds to pour out the batch you make up. Putting them in front of a floor fan helps allot after filling them.

I think the bottom line is ....you are NEVER going to have enough molds and ALWAYS going to have left over plastic.

If you you do buy a bunch more molds and really get into it....if you are married find a good Divorce Attorney!

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One method some have used for cooling molds is a heavy tile (stone or ceramic) kept in the freezer, and they just put the mold on the tile.  When the tile starts to warm up they swap tiles.  Don't ever set a hot glass cup of plastic on the tile though.  It will crack or shatter and dump hot plastic all over.  Heck I once set a cup on my drill press table on a cool day.  When the plastic finally cooled and I peeled it up my drill press table slots where the cleanest I had ever seen them.  LOL.  

 

I would add that because aluminum transfers heat so well this works better than you might think.  

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I make my molds out of a urethane resin - so it insulates the bait ALOT more than aluminum.... which makes for long wait times to demold.  

 

Three things that I've found that help which haven't been mentioned...

 

1. After kicking the plastic over at 350 - I try to shoot the baits at temps closer to 300 - this drastically reduces how hot the molds get and how fast I can get the baits out.

 

2. I remove my baits and immediately drop them in a cold water bath (Some people frown against this - some people do it).  I've found if I keep my molds lubricated well the baits will almost fall out of the mold once I open them - this lets me demold while they are still VERY soft which cuts down on time and since i dump them straight into the water - I don't get any deformities.  (I hope that makes sense).

 

3. I nuke my plastic when I'm making 12 oz or less instead of using a presto.  I've found that when the plastic is just sitting - keeping it in the microwave keeps it warmer than leaving it out on the counter.  I've also made a small insulated "box" out of extruded insulation foam to keep the plastic in (and hot).  It worked well in keeping the plastic hot longer as well.

 

  J.

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2. I remove my baits and immediately drop them in a cold water bath (Some people frown against this - some people do it).  I've found if I keep my molds lubricated well the baits will almost fall out of the mold once I open them - this lets me demold while they are still VERY soft which cuts down on time and since i dump them straight into the water - I don't get any deformities.  (I hope that makes sense).

 

Still on the sprue? Do you recycle sprues?

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There are some great ideas here!I really like the idea of keeping tiles in the freezer. I have piece of granite counter top left over from a kitchen remodel I just finished that is about 18x24 inches. I think it would be perfect fit freezing and keeping mold cool.

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There are some great ideas here!I really like the idea of keeping tiles in the freezer. I have piece of granite counter top left over from a kitchen remodel I just finished that is about 18x24 inches. I think it would be perfect fit freezing and keeping mold cool.

 

When I first heard of it I wondered about it, then I recalled that rocks are used as heat sinks for other things as well.  One high efficiency solar home I know of uses a huge mound of buried boulders as heat sink.  I forget the particulars, but they credited it with a measurable portion of their heating and cooling budget.  

 

I would think that in order to make the most out of it as a heat sink for molds you would need several pieces, and maybe an insulated pad to set them on when you remove one from the freezer so less heat intrudes from the surface it is resting on.  

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boulders are generally used in saunas and steam baths because they hold heat well , Heatsinks are units which are designed to dissipate heat  .Aluminum makes a good heatsink because it drops the heat quicker than most materials . Heat and wet stone is a dangerous combination , the old school meathod of breaking up rock was to heat it then throw water on it , then the rock would shatter . I've seen  rocks pop in camp fires because they were holding in moisture  . My boss had his lip sewn up because someone threw a beer bottle into the fire pit ,  it basically exploded and a chunk of glass cut his face wide open

I'm sure a warm mold wouldn't be enough to shatter a piece of tile , but a cold tile that has condensation from being in a freezer may very well shatter if any hot plastic gets dropped on it . It would probably have a similar effect as putting a measuring cup of plastic on a cold metal surface

If I was to use anything to rapidly cool down a mold then I'd probably use a cooler ice pack . it would keep the mold dry , and it would stay cold for a fair amount of time

Edited by curt k
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A beer bottle thrown into a fire would need to have liquid in it and be sealed in order to explode in the manner you describe.  Much in the same manners as soda bottle bombs using vinegar and baking soda.

 

Perhaps the tile might break if suddenly exposed to high heat.  I have seen volcanic rock in a fire pit explode with hotter burning woods like ironwood.  

 

The guys I know who use tiles are not suddenly placing a preheated mold on a cold tile.  They are starting with the mold in shelf state on a cold tile.  (Not all molds will shoot well cold, but many will).  When the tile stops working they swap it for another cold tile.

 

As to moisture a frozen cold pack is no less likely to condense moisture out of the air than a frozen tile. 

 

Personally I like my chill plate vise.  The mold can still potentially be exposed to some condensation from the chill plates, but all liquid water is pumped in and out unexposed to the micro environment around my mold.  My biggest problem with using is that I have a lot of molds that require drill vents instead of edge vents, and I just haven't gotten around to making a textured surface plate for it so I can be sure those will all vent properly.  A textured surface plate of course has the issue of less contact surface.  Actually, when I have time I plan to totally redesign the chill plate vise so it will hold the mold halves making opening and closing the mold part of opening and closing the clamp.  The problem with that of course is that I have different sizes of molds, so more machining and more mechanical planning is in order.  

 

Anyway you raise some valid points perhaps, but I like to more fully understand exactly what is happening if I can.  

 

A heat sink is anything that draw draws heat away from something else.  Rocks can be used as a heat sink for solar energy.  They have the benefit, in that they can slowly release it back when solar energy is reduced.  A finned aluminum plate on a CPU is a heat sink.  A solid welding table is a heat sink.  A rock in the sun is a heat sink.  Its just an object at a lower temperature that can store some heat energy from something else.  If it is has a surface not exposed to the heat source and it transfers heat efficiently like aluminum it can help more rapidly bring the heat energy level of something else down closer to the general ambient more quickly by transferring the heat energy into the surrounding area.  

 

People have the tendency to think in narrower more specific terms and absolutes with stuff like this, but in nature (and I don't mean just in the woods) all of these things are continuously interacting on a huge cosmic scale.  The larger the scale we choose to try and encompass in our understanding the more we can control or atleast guide those things within our grasp.  

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the exploded beer bottle was an empty bottle ,and it obviously it would have still had moisture in it since it was freshly drank and thrown in the pit . The impact of it was pretty clear to me .and actually a bit surprising to me cocidering the number of bottles I've seen thrown into the fires while in my youth

The mold isn't going to get hot enough to crack up a tile , my point was that if hot plastic got spilled on it then it very well may .

And yes a cooler pack will create condensation and more so than most things that come out of of a freezer and for sure it would create more than a tile  , but I could throw one of those against a wall and chances are that it would stay intact

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Still on the sprue? Do you recycle sprues?

 

I open the mold and lift the sprue sightly and cut it either with a scissor or x-acto depending on the mold - then reheat them.  I try not to reuse anything I've dumped in the water unless it's sat out for a day to dry.

 

    J.

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I open the mold and lift the sprue sightly and cut it either with a scissor or x-acto depending on the mold - then reheat them.  I try not to reuse anything I've dumped in the water unless it's sat out for a day to dry.

 

    J.

Makes sense, sorry I was thinking if they were still red hot  your plastic might still be molten inside, and cutting would cause issues.

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You'll think everything is fine and then one day you'll get a drop or two of water in the hot plastic and your whole world will change in an instant.

 

Once you feel the pain you'll stop using ice.

 

I could not have said it better.  Save yourself a nasty burn and keep all moisture away from hot plastic.

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Makes sense, sorry I was thinking if they were still red hot  your plastic might still be molten inside, and cutting would cause issues.

 

Yeah - I wish I could demold that fast!!!! LOL!!  

 

I still wait a decent amount of time - but I can see by the crater in the sprue how much the bait has cooled - if it looks like a volcano - it's good to open.... It's never too hot to handle - just in some cases too hot to hold shape if you try to hold or sit it down where it will deform on it's own weight.  This condition is mostly the case after I've shot a bunch where the molds start getting hot over time and don't have enough down time to cool.

 

            J.

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