Mold Preheater

[wimms]

(I'm reposting as my previous thread was deleted due to linking to ebay.. Hopefully google image search link is okay.)

Did you know that hair-straighteners have 2 PTC temperature controlled plate heaters that maintain 220C-230C (430F-450F) surface temperature?

Like these: https://www.google.com/search?safe=off&dcr=0&tbm=isch&q=PTC+heating+plate+element+constant+temperature

Thats a mold preheater right there, isn't it?

They are made in different sizes, wattage, set temperatures, many work direct from mains and need no PID controller.
They run around $5 for a pair on ebay.

They are so cheap that could be permanently attached to the base of the mold.

[oteroman]

Have a pic of your project/set up?


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[KenH]

I think that would work like a champ!

[Mal Paso]

Very Cool! Thanks for the post!

[KenH]

Only thing I might mention, with only 100 watts (the 110vac one I found) it would be pretty slow heating a mold from room temp. I use an old hotplate which works pretty good.

[OS OK]

My 1,200W hot plate set at 50% heat will heat a 6 gang aluminum mold to 400*F in the same time my 20 lb. Lee pot can melt a pot full of Pb.

I'm guessing 5~600 watts is what you'll need given the same time frame.

[wimms]

My 1,200W hot plate set at 50% heat will heat a 6 gang aluminum mold to 400*F in the same time my 20 lb. Lee pot can melt a pot full of Pb.

I'm guessing 5~600 watts is what you'll need given the same time frame.

My hopes are higher. Lee pot is 700W and can heat up 20 pounds of lead to 700F in reasonable time. Heating up 1/4 pounds of aluminum mold to 400F would need much less than that.

https://www.engineeringtoolbox.com/heat-up-energy-d_1055.html
Using formula there, assuming mold is 200grams and dT is 200C, for heat-up time of 20 minutes the necessary average heat transfer rate is 30Watts.
https://www.google.com/search?safe=off&dcr=0&q=0.2kg*0.9(kJ%2F(kg*C))*200C%2F1200sec

100W of heat is nothing to sneeze at, most soldering irons are below that.

Even if initial heatup time is slow, later it should be able to keep the mold from dropping below the desired temp.

I also hope that these aluminum plate heaters have better heat transfer and power density. But we'll see, I have a few coming my way, have a Lee 6 ganger and a spare termocouple.

[OS OK]

Well, I'm just looking at the problem from a blue collar point of view...from out in the field so to speak. I've seen a lot of pencilwork that didn't make it even though the numbers say it will.
For instance...trying to use a small braising tip on an acetylene rig to cherry up a 1" round bar for a 90* tight bend...the torch was plenty hot...just not enough 'volume' of that plenty hot. There was too much mass.
Heat travels quickly in metals, especially aluminum and those moulds are just little radiators giving it up to the ambient air.

Good luck though....it's the inventor in this world that makes life easier for others!

[wimms]

Heat travels quickly in metals, especially aluminum and those moulds are just little radiators giving it up to the ambient air.
Yes, convective heat loss is what keeps molds from overheating during casting, and it may exceed 100W in open air.
It's rather tricky to estimate, so I'll try 100W and 260W plates and see. Will add thermocouple to the mold too.

[OS OK]

Well, don't forget that you need to get that sprue plate up to the same temperature also, otherwise it will act as a chiller to the Pb you pour into the mould...wrinkles will appear even though the mould blocks appear to be hot enough.

I ended up putting an old can over my hot plate and tie wired it to the skill saw blade to make a sort of oven...that got things heated evenly...


207863

[Stilly]

That is a very nice setup.

In my opinion attaching anything to a mold besides a thermocouple (why even do that?) is not a good idea. You need to be able to move that mold around, it gets banged on possibly and dunked in water and then you have to deal with wires getting in the wrong place and melting out or being careful where you set it down. I think it would be better to build a nice mold garage that sits on top of a hot plate with a roof and side walls and heats the molds that way. OR, instead of a hotplate, it could have a couple of these things jammed up inside it to heat the molds as you sit them on it.

[lightman]

I won't thumb my nose at your idea. Every thing we do or use started off as someone's idea! But my hot plate that came from Walmart cost less than $12 works really well. For the cost and the fact that it's "plug and play", it's going to be hard to get away from it.

When you get your idea up and running, please post some pictures.

[wimms]

Well, don't forget that you need to get that sprue plate up to the same temperature also, otherwise it will act as a chiller to the Pb you pour into the mould...wrinkles will appear even though the mould blocks appear to be hot enough.

I ended up putting an old can over my hot plate and tie wired it to the skill saw blade to make a sort of oven...that got things heated evenly...

I wanted the hot plate to be both heat source and heat sink, so I "soldered" a chunk of aluminum stock onto the plate and added PID. The cover is just a sheet of stainless steel acting as a reflector lens. Not ideal but seems quite enough. I painted the aluminum black so it both radiates heat and can be read by infrared thermometer. I can rest the mold on this plate at any time and it will stabilize to desired temp rather fast. So I don't really need any PTC, but I wanna try it.

208232

[OS OK]

That setup looks like it'll geterdone...thanks for the idea about the black paint, I'd like to use that thermometer to read surfaces and verify that another thermometer is close or correct.
Recently someone mentioned floating a small piece of black metal in the melt to read the melt temp.

We have some good thinkers around here, I enjoy hanging out around people like that. Just as soon as you think you have all the bases covered, along comes a forum member with a new proven solution....sometimes I have to just smack myself in the forehead and exclaim..."No Duh! Why didn't I think of that!"

[Retumbo]

I use these, about 250 watts https://cloudfront.zoro.com/product/full/Z-0_p0fo5oy.JPG

[Mike W1]

Hate to rain on anybody's parade but if you do a bit of searching on here about infrared thermometers you will find that they're not accurate enough to tell you anything useful. Perhaps with an expensive one calibrated to the task but not the cheap ones we're likely to buy. I didn't just take somebody's word for that as I had one too and black paint, washers or whatever they don't read accurately.

[OS OK]

Yes...I think most everyone is aware of that by now but, the darker the surface the closer you get. We started some time ago trying to read the melt with pitiful success.
Even our thermometers are off, some by a great deal. After acquiring a PID I realized that too.

They might have done better making the digital Harbor Freight unit read...'cold, luke warm, warmer, hot, real hot.

[Mike W1]

Yes...I think most everyone is aware of that by now but, the darker the surface the closer you get. We started some time ago trying to read the melt with pitiful success.
Even our thermometers are off, some by a great deal. After acquiring a PID I realized that too.

They might have done better making the digital Harbor Freight unit read...'cold, luke warm, warmer, hot, real hot.

Can't disagree with that. My luber heater is PID controlled with the TC placed quite close to the luber itself. So one of the things I did was clear a small portion of paint on the luber as close to the TC as I could and painted that flat black. Also a small section next to the TC, again painted flat black. The readings were not reliable to say the least. Only thing I ever found it useful for was watching the hoses in a car to see if the thermostat opened up. Mine gave up the ghost and I've not missed it. "Luke warm", etc. would have been as useful as a degree reading that didn't really tell me much.

[wimms]

thanks for the idea about the black paint, I'd like to use that thermometer to read surfaces and verify that another thermometer is close or correct.
Recently someone mentioned floating a small piece of black metal in the melt to read the melt temp.

Thanks for your kind words. The paint I used was stove paint spray. I left the area of the mold placement unpainted for better heat transfer.

When I was playing around with electrolysis I quickly discovered that metal electrodes suck so I went ahead and bought few graphite electrode plates. They are made in all kind of sizes like this: https://www.google.com/search?safe=off&dcr=0&biw=1001&bih=508&tbm=isch&q=+graphite+electrode+plate and cost almost nothing.

The 50x50x3 cm I got work very well for floating on the melt, and being good heat conductor and ideal black body it is also large enough for infrared thermeter to take a good reading.

Very cheap infrared devices do not allow you to compensate for emissivity of material and do not have sharp enough focus to read from small areas.

It is very interesting to move infrared thermometer over that aluminum block from painted area to the unpainted and see how much the reading goes off immediately. Like hundreds of degrees off. The painted area matches TC reading of the PID within few degrees.


Retumbo - what are these?

[wimms]

Hate to rain on anybody's parade but if you do a bit of searching on here about infrared thermometers you will find that they're not accurate enough to tell you anything useful. Perhaps with an expensive one calibrated to the task but not the cheap ones we're likely to buy. I didn't just take somebody's word for that as I had one too and black paint, washers or whatever they don't read accurately.

It's not that bad. Sure, there are products that are more like toys, but there are some from china that are very usable. Just have to understand how IRT works and respect D/S optical ratio to get the readings. When I researched IRT for my needs, I found Benetech GM900 was quite good fit for me. I've never regretted getting one. Totally worth its price.

You have to know the emissivity of the material, or make it into a known one which is typically much easier.
Aluminum for eg has widely different emissivity depending on alloy, but also depending on the surface finish.
And the optical spot must be filled completely for the reading to be repeatable, so you can't really measure very small areas with low optical resolution devices.

Sure, I wanted some high-temp high-res Fluke, but the cost..

[AllanD]

To heat my mold all I do is set atop my Coal Stove which I also use to do any "smalting and I put my top-up pot inside it.

I cast with a 20lb Lee bottom pour pot, but when the mold is up to temp and I'm making good bullets sometimes I don't
want to stop to wait for ingots added to the Lee pot to melt. The coal stove is always hot this time of year anyway and any
fumes generated go up the chimney with whatever is in coal flue gasses.... which I am told includes mercury and Hydrogen Sulfide
which all things considered Lead fumes might as well be "the breath of life" by comparison...

[oger]

Been using old toaster ovens from garage sales forever. You can find them cheap if you look and they do last a long time.