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View Full Version : Tried Mold Warmer & half wave rectifier



HangFireW8
11-23-2010, 11:14 PM
All,

I've been using a propane torch to warm up iron molds, and dipping aluminum molds in the pot, but both methods have their drawbacks. I can't dump in sprues and rejects with a mold on top of the pot, sometimes the mold falls off (or falls in), plus on a Lee 6 Cavity it is more important to warm the sprue plate, which I am hesitant to dunk.

Besides, I have too many fiddly things to fiddle with, without lighting and handling a propane torch, even if I get the tanks cheap 1/2 full at yard sales, it is one expense and one more set of things to drag out to the casting bench.

So, last week I picked up myself a 1000W Single Burner at Rite Aid (no Walgreens near by), and after testing it to see if it worked, I put together a half wave rectifier to run it at 500W (cut off one half of Alternating Current wave). It boils water in 8 minutes flat and truly draws 1000W, which I thought was a bit much, so I put together a bridge rectifier using both sides in a switched socket, so I can run the socket under the switch at 500W or 1000W.
http://castboolits.gunloads.com/picture.php?albumid=440&pictureid=2949
500W will melt an ingot on the scrap metal quite handily (and messily, I might add), so I have to stay on my toes or maybe moderate heat a little more with the plate's bimetallic strip control.
http://castboolits.gunloads.com/picture.php?albumid=440&pictureid=2950
Anyway, the results are pictured, not a huge amount but I was more concerned with quality and trying out a new routine than quantity. Practically 100% of what you see are keepers, and it was a real joy to switch between two iron molds and have the standby be hot and ready to go. This is much faster than using a propane torch, and I can switch whenever a mold gets too frosty or I just want to change production.
http://castboolits.gunloads.com/picture.php?albumid=440&pictureid=2951
Plus both molds are ready to go after new ingots, sprues and rejects have melted.

My thanks to those here on the Forum promoting electric mold warmers, it has greatly improved my production and quality, and I recommend it to all.

-HF

lwknight
11-24-2010, 12:13 AM
Electric mold warmers and PID controllers are the best things to come to casting in generations.

montana_charlie
11-24-2010, 02:17 PM
I don't understand why you thought the 1000W needed to be cut in half.

CM

HangFireW8
11-24-2010, 04:27 PM
Electric mold warmers and PID controllers are the best things to come to casting in generations.

I haven't gone PID yet, but I see the temptation. Right now I've gotten a sufficient boost in productivity and quality that I'm pretty happy. Plus, at a very low cost + effort.

When I first measured my Lee pot temperature swings, I was starting to think a better controller was needed. Then I held the thermometer just off the pot wall in the melt, and I saw that it was only swinging less than 30 degrees, not the full 200 on the walls. Right now boolit consistency is more than enough for my needs.

When it gets a little colder outside I'm going to try the Lee pot on the half wave circuit and see where it holds temp at continuous heat (knob on "10").


I don't understand why you thought the 1000W needed to be cut in half.


Because 1000 Watts is insanely hot.

I wanted it to be an ingot warmer as well, without actually melting the ingot. As it turns out, it still melts ingots, so I will have to use a pot to "warm" ingots and then just pour them in.

However a pot on the warmer (even a small one like the RCBS 10#) is not very compatible with warming molds; not much room for both. So, I may need to cut it back to 300 Watts or so.

Right before I switch molds I just switch it to 1000W (bypass rectifier). For Lee aluminum 6 Cav molds I also flip them over to heat up the sprue plate, the mold stays warm enough.

-HF

montana_charlie
11-24-2010, 05:50 PM
I don't understand why you thought the 1000W needed to be cut in half.

Because 1000 Watts is insanely hot.

I wanted it to be an ingot warmer as well, without actually melting the ingot. As it turns out, it still melts ingots, so I will have to use a pot to "warm" ingots and then just pour them in.

1000 watts is not a temperature, but 1000 degrees is 'hot'.
1000 watts is an amount of power which can bring the hotplate to a given tenperature faster than 500 watts can.

The temperature the hotplate will reach might be 100 degrees (not enough to preheat a mould) or 1000 degrees (enough to boil lead). Whatever the temperature will be, it's controlled by the thermostat.
That would be the knob on the hotplate.

If it's still melting ingots, you need to turn the heat down by turning that knob...not reduce the amount of power reaching the appliance.
Your hotplate is trying to draw 1000w. If your rectifier is only capable of providing 500w (or 300w) the hotplate may soon suck all of the smoke out of it.

CM

HangFireW8
11-24-2010, 06:35 PM
The temperature the hotplate will reach might be 100 degrees (not enough to preheat a mould) or 1000 degrees (enough to boil lead). Whatever the temperature will be, it's controlled by the thermostat.
That would be the knob on the hotplate.

The heat on my hotplate is NOT controlled by a thermostat. It is controlled by a bimetallic strip, which works on its own thermal properties, not the burner's thermal properties. I could substitute a refrigerator motor for the burner and the bimetallic strip will still cycle based on its own load, temperature and environment, not its load's temp. So, it is not a thermostat.



If it's still melting ingots, you need to turn the heat down by turning that knob...not reduce the amount of power reaching the appliance.


Patently false. By turning down the knob, the hot plate at 1000W and 0W will alternately melt the ingot, then let the puddle cool, then melt it again. This has been discussed before.



Your hotplate is trying to draw 1000w. If your rectifier is only capable of providing 500w (or 300w) the hotplate may soon suck all of the smoke out of it.


I'm not such a Noob that I underspec'ed the diodes. They are running at about 75% of spec and don't even get very warm. They also get to cool off 30 times a second. I expect they should last a few decades.

-HF

94Doug
11-24-2010, 06:36 PM
I like the Bullplate lube shown in its normal position: spilled.


Doug

HangFireW8
11-24-2010, 06:41 PM
I like the Bullplate lube shown in its normal position: spilled.


Thanks! Yeah, it was spilled some months ago, but I'm still using the dregs. :grin:

Notice the melt mark on the side of the bottle? That's my own unique contribution.

-HF

leftiye
11-24-2010, 10:37 PM
Instead of warming ingots, melt sprues and ingots in a second pot (Iron) that you can pour (sitting on a hot plate) and replenish your casting pot from this. No waiting for the casting pot to come back up to temp. A lighting rheostat can control the power supplied well enough to heat this pot (mine does). You might be able to warm molds over this pot.

HangFireW8
11-24-2010, 10:56 PM
Instead of warming ingots, melt sprues and ingots in a second pot (Iron) that you can pour (sitting on a hot plate) and replenish your casting ot from this. No waiting for the casting pot to come back up to temp. A lighting rheostat can control the power supplied well enough to heat this pot (mine does). You might be able to warm molds over this pot.

Well, that's the question, isn't it... do I make the one hot plate do double duty, or do I have it do one thing (say, warm molds) and get another hot plate (or whatever) to preheat lead?

If I try to crowd everything on one hot plate, I'll need something better than the chunk of Aluminum I have now to manage it all. Sometimes I have 3 molds going at once, and once the pot is reloaded with hot lead, the point of having warm molds is to get right back to casting, so now I'm thinking I might just need another hot plate.

I really don't want molds and preheat pots competing for time or space.

But at the moment, the real priority is to turn that piece of plywood into a casting tray, with carry handles, spill stopping edges, and some hold-downs. This is as much a safety issue as a productivity issue.

-HF

montana_charlie
11-25-2010, 02:21 PM
The heat on my hotplate is NOT controlled by a thermostat. It is controlled by a bimetallic strip, which works on its own thermal properties, not the burner's thermal properties. So, it is not a thermostat.
It's a 'mechanical' thermostat meant to control the temperature of the hotplate by manipulating the on time/off time of the circuit.
All of our hotplates and most of our casting pots use the same basic device.

Patently false. By turning down the knob, the hot plate at 1000W and 0W will alternately melt the ingot, then let the puddle cool, then melt it again. This has been discussed before.
Does your knob only have two positions...'Hot' and 'Off' ?
Hundreds of us use hotplates to warm ingots, preheat moulds and soften ingredients for bullet lube, and melt lead.
A small amount of trial and error is needed to find the right knob position for a given activity.

Back to my original question...
Why is it that only you need a special power supply to make yours do the same kinds of jobs?

CM

HangFireW8
11-25-2010, 03:59 PM
Back to my original question...
Why is it that only you need a special power supply to make yours do the same kinds of jobs?

I dunno, I'm special? I like to experiment? I like to combine my hobbies? Why do you need to make your own special boolits, why don't you buy them like everyone else?

The real reason is I want the mold to have a consistent pre-heat, just like the guy who built the PID controller for his pot. I guess he's special, too.

When the controller knob is turned down, the burner spends significant amounts of time on the Off cycle. If I pull the mold off to use near the end of the off cycle, it is measurably cooler than at the end of an On cycle.

I just used it today to run the lube heater in my 4500. Instead of turning it on and off, on and off, with a power strip switch, I just put it on 1/2 wave and ran it until I was done. Lube stayed warm but never ran or dripped. I suppose I could go back to doing manually, but it worked so well, I don't think I will.

I'm going to experiment some more with different plates on top of the burner. If I can't get exactly what I want, I may build myself a Triac controller. It won't be A/C activated, though, as RF interference can play havoc with activation, so I'll use some kind of timer or waveform generator. Then, I'll be extra-special.

-HF

BOOM BOOM
11-25-2010, 05:15 PM
HI,
IFIRC it takes 1740 deg. F . TO BOIL LEAD, so no worry there.

alamogunr
11-25-2010, 08:55 PM
The hot plate in your picture looks exactly like the one I bought at Fred's. The aluminum plate I use looks about twice as big as yours but mine is .375 tk and yours looks to be about .500 tk. When I set my mold on the plate I twist the knob up a bit and turn it back down when I pick up the mold. Also the aluminum plate should moderate the fluctuations somewhat even though aluminum doesn't retain heat like iron or steel. I don't do this more than once or twice a session. I also don't use the hot plate to warm sprues or ingots. Those are put into the pot during one of my pauses in casting.

My point is that we each have ways of doing things and we each fixate on different things that bug us. I may try your bridge rectifier circuit someday when I'm in an experimental mood.

John
W.TN

markinalpine
11-25-2010, 11:05 PM
Harbor Freight has a Speed Control that is rated at 15 Amps for$19.99, and they're having holiday sales. http://www.harborfreight.com/router-speed-control-43060.html
Mark :coffeecom