Temperature questions

[Marlin Junky]

Since I don't have an infrared temperature sensor, perhaps someone out there with one can help me out 'cause I'm getting tired fiddling with my cheesy hot plate controls.

Before my last casting session, I laid my 1000F casting thermometer on the hot plate burner along side my aluminum mold an it reached 510F or so while I was doing other stuff and waiting for the pot and the mold to reach their operating temps. So I thought, too hot, gotta lower it before trying to cast. My question that I couldn't answer was, I wonder what the actual mold and sprue plate temps were when the surface of the hot plate was 500+F. Has anyone with an infrared device ever checked the temp differentials. If the mold set on the 500F hot plate long enough I don't think it would ever reach 500F because of the difference in the specific heat between aluminum and steel and the steel sprue plate couldn't get any hotter than the heat sink underneath it, right?

Are these any good?:

http://www.harborfreight.com/non-contact-laser-thermometer-96451.html

Thanks,
MJ

P.S. Here's one that's even less $$ but it only goes to 482F:
http://www.harborfreight.com/infrared-thermometer-93984.html

[Catshooter]

Marlin,

I do have one. It's a Fluke and it doesn't really like reflective surfaces. I can get readings of 250 degrees off the top of my lead pot, off the molten wheel weights.

It will read fairly well on my iron moulds as they're not polished. You're correct in that the mould can't get to a higher temp than the hot plate element. The temp of a mould on the plate can surprise you. The very bottom may only be ten or fifteen degrees less than the element, but as you read up the mould the temp drops off fast. I've seen 430 to 280, top to bottom.

Now if you leave the mould on the plate long enough it will soak well and the temp will come up pretty well. The top still never seems the same as the bottom though.

A silver impregnated heat transfer grease between the mould and the sprue plate makes a huge difference. Danged expensive though (silver is over $40).


Cat

[Marlin Junky]

catshooter,

I've got a KINTREX IRT0421 in my amazon shopping cart right now. How about if just the sprue plate temp is tested?

What happens when you check your melt temp before fluxing; i.e., while it's still covered with oxides? Does the Fluke's thermometer read properly then?

MJ

[Ervin]

I invested in a sears infared and it has been very accurate. It only measures surface temp but has been a big help. You have to learn how to use it on your own. I still use a a dial therm. for bottom temps. ERVIN

[Marlin Junky]

I invested in a sears infared and it has been very accurate. It only measures surface temp but has been a big help. You have to learn how to use it on your own. I still use a a dial therm. for bottom temps. ERVIN

Mold surface temps is what I want it for. Basically, I was just asking Catshooter if he has tried his Fluke on non-shinny surfaces; i.e., oxidized casting alloy.

MJ

[Catshooter]

Sorry for not seeing your question until today Marlin.

I've found it to be a definate maybe on surfaces like that. However, if you can afford one, buy it. You'll use it plenty for casting and elsewhere. It reads well on my iron moulds.


Cat

[cbrick]

Marlin, try this.

NOE Casting Thermometer (http://castboolits.gunloads.com/showthread.php?t=100997)

I use a 1/2 inch thick aluminum pate on my hot plate and have it drilled to hold the probe. You can also drill your molds to hold the probe while pre-heating or casting. Works like a charm and not expensive.

Rick

[Marlin Junky]

Rick,

That looks pretty cool... less money than the gizmo (KINTREX IRT0421) I bought yesterday from Amazon too. Nevertheless I want a reading on the top surface of my sprue plate. BTW, what is a good temp for the sprue plate? I like my sprue plates hot enough so the alloy rolls off like it's oppositely charged and the sprues take a couple seconds to set up... I love that temp, whatever it is.

MJ

[geargnasher]

MJ, the problem is heating the mould evenly all the way through in the open air. Tough to do, especially the sprue plate. I copied Montana Charlie's mould oven concept and it works like a charm: Get a solid steel electrical workbox, the kind with as few knock-outs and holes as possible, get the cover for it, and cut a hole in the side that you can sneak the mould blocks through, leave enough lip on the bottom of the hole to suppor the mould handles while the bottom of the blocks lay flat on the bottom of the oven, drill a hole through the top and install a grill thermometer obtained from the grill parts dept. of any home improvement or hardware store, set the oven on the hot plate, put the mould inside with the blocks slightly apart and turn it on high. Once the air in the oven is up to the temp you think you want, wait ten minutes for the mould to heat evenly (it's like cooking meat). I find this method extremely effective on heavy, brass moulds and on the six-cavity Lee and NOE moulds.

As far as infrared, I agree with Catshooter. I have a Fluke infrared also and it's iffy on lots of things. At work I use a thermal contact probe with a temperature transducer that plugs into my Fluke DVOM, much more accurate. I only use the infrared for determining radiator inlet and outlet temps, or for tuning alcohol engines by measuring header pipe temp.

Gear

[cbrick]

leave enough lip on the bottom of the hole to suppor the mould handles while the bottom of the blocks lay flat on the bottom of the oven, Gear

I should have mentioned the electric box as an oven when I posted the link to Swede's thermometer. It really does trap heat around the sprue plate and top half of the mold, works well.

Another trick is that in the half inch aluminum plate I use on the hot plate I drilled it for a 1/4 inch by 5/8 coarse thread bolt. Place a bit of anti-sieze on the treads and turn the bolt in or out as an adjustment for the mold handles. I have most brands of molds and the handles for them, they are all a different distance from the hinge pin to the aluminum plate so to get the mold to sit flat I simply adjust the height of the bolt. The MP 4 cav brass molds are heavy enough to sit flat with or without handles but for everything else except 6 cav iron the bolt works great.

Rick

[Catshooter]

Marlin,

Radio Shack carries a silver inpregnated heat transfer paste that will help you get and keep the sprue plate up to temp. Works well. Not cheap though, a tiny little tube of about one millionth of an ounce was ten bucks.


Cat