thermometer question

[tommag]

I broke down and bought 340# of wheel weights yesterday. I sorted through 75# and then tried to melt them at low temp just in case I missed some zincs. My thermometer (brownells) showed only 580 when the stuff melted. The ingots looked sort of like particle board on the surface, kinda like galvanized sheet metal sometimes does.

What the heck does one use to calibrate a thermometer? 580 is lower than the melting point of lead as far as I know, I thought it was about 620.

Does zinc produce that flaky look, or is it due to something else?

The more I learn, the more I realize how litttle I know.

[ron brooks]

ou could boil some water and put the thermometer in the boiling water and see what it reads. Since water boils at 212' at see level that should let you know how you are doing.

Good luck,

Ron

[imashooter2]

I used boiling water to calibrate my thermometer. I'm near enough sea level that I can call boiling 212 degrees F. Here's a calculator in case you live on the top of a mountain:

http://www.biggreenegg.com/boilingPoint.htm

[NVcurmudgeon]

tommag, thermometers seem to vary wildly in calibration. I have an RCBS, and typical readings when temperature is "right" by looking at the glow of the grille on my Coleman stove, the freeze time of sprues, and when Vulcan is willing, a light frosting on castings with no smearing of alloy on the top of the mould, are between 650 and 750 degrees. I THINK that my thermometer is deadly accurate.
A freind of mine gets indicated temperatures of 800+ on his Lyman under the same conditions, using the same alloy and equipment. I guess you could send your thermometer back to brownell's for replacement, or just learn what it reads when everything is going well. After all, the main thing we are looking for is a means of returning to a successful temperature that has worked well with a particular mould and alloy.

On the zinc question, I have only found one weight that I suspected of being zinc. When sorting weights I set the funny looking ones aside. I melt the normal looking ones and if any don't melt readily, they join the funny looking pile. Obvious very soft tape-on weights are melted separately and saved for bore slugging, or traded to muzzle loader fans. Back to the funny looking pile, a magnet quickly eliminates the iron/steel weights, and a simple "heft test" culls out the all-plastic ones. Then I attempt to melt the rest separately. Most melt readily, and those that don't are carefully thrown away on the grounds of zinc suspicion. This procedure has kept my alloy contamination-free for years.

[grumpy one]

Tommag, the most practical way I know of to calibrate a lead-casting thermometer is to melt pure linotype and measure the temperature when it goes from solid to liquid, which is 462 degrees F. Of course most of what is described as linotype isn't, so don't expect the first sample to mean anything, but there is a simple way to tell whether you have pure linotype or not. Linotype is the only lead-tin-antimony alloy (it's 4% tin, 12% antimony, 84% lead) that transforms from solid to liquid without changing temperature. This is because it is a eutectic alloy - it consists of only one phase, not two or more. Non-eutectic alloys have a "solidus" temperature (where they transform from solid into mush) and a "liquidus" temperature (where they transform from mush into liquid). If you get some alleged linotype that actually transforms from solid to liquid at a single temperature, you can rely on that temperature being 462 degrees F, whatever your thermometer says. Then try it half a dozen times, both on rising and falling temperatures. If your thermometer always shows the same melting temperature, at least it works, whatever that temperature shows as. If it shows different temperatures rising and falling, which mechanical thermometers pretty much always do, toss it in the skip and buy a thermocouple and readout.

For what it's worth, the solidus temperature (where it goes from solid to mush) is always 462 degrees F for all tin-antimony-lead alloys - it is only the liquidus temperature that varies with the specific alloy. Unfortunately it is pretty difficult to measure the solidus temperature, unless the alloy is pretty close to pure linotype. For non-eutectic alloys, what happens at 462 F is that whatever proportion of the total mass can make up pure linotype melts, and the remainder melts at the melting point of whatever alloy the leftovers happen to constitute. This is actually very useful information, because it can be used to figure out just what alloy you have - but there are always two or more possibilities, so you have to have some idea to begin with. However that has nothing to do with solving your immediate problem. If you can get hold of some decent linotype, check whether it has a mush-mode or not as it melts. If it melts instantly, it's true eutectic lino and you can calibrate your thermometer from it. If it gets mushy first, it isn't true eutectic lino and you can learn just how unreal it is by checking how much the temperature has to rise between when it goes mushy, and when it finishes turning liquid.

The printing industry copes with the issue of non-eutectic lino by calling a bunch of different alloys lino. Hence if you buy some and find it has a mush mode, don't rush into calling the vendor names - he may win the resulting lawsuit.

[Jon K]

tommag,

OK, here goes.........

Here are several different things you can do, some of which depends on who you know, and how well you are recieved, when asking for help.

1. Find a local welder, best one you know. Get or ask for a Tempilstik(whatever temp he may have, or be able to get. Or better yet, if he has access to a Powerweld Infrared Temperature Indicating Thermometer(these are nice digital -58 to 923 degrees F). Use either of these in conjunction with your thermometer to calibrate.
2. If you can't find a welder with access to these, check your local community college, that has a welding class. They will surely have these, but will they help you?
3. Find an Instrument repair srvice and have them test and calibrate. Usually without a Calibration Certificate, it might cost $18-30 with cert add $25+. although at this point, you might want to buy a new thermomoeter. Or if you have a friend in this business, who will do it for free.
4. Find someone who has a thermometer, and check side by side.

I had a Brand X thermometer which I was always leary of. When I bought my
RCBS I checked it with X and tossed X into the trash.

Jon

[Edward429451]

I use a bunch of different thermometers in my work and only some of them are able to be calibrated. I test them against each other and calibrate the ones I can and make notation of which thermometer is off by how many deg. I use plain ice water to calibrate them. Pack a glass with shaved/chipped ice, fill to rim with cold water, pack more ice in until more ice will not fit, Temp should read a constant steady 31.5 deg F. Put all probes in at once and you'll see real quick whats what.

One or two is always right on and others always are off so you learn which to trust.

[tommag]

I have to leave tonight for a couple of weeks for work, so I'll try to digest all this when I get back.

I have used ice-water and salt to cal. my pulp thermo, but this one doesn't go below 200.

I will try boiling water, but that is on the low end of the scale. I don't have lino, so I don't know about that, even though it seems to be the best method. Maybe I should spring for a pot-ful for calibration if not for shooting.

I thought maybe I should SLOWLY bring up some pure pb and use that for a calibration. I have about 300 lbs of pb., so maybe that would be the answer. Does lead melt and freeze at consistent temps?

Again, I have to leave for a while, so please don't think me rude if I don't say thanks in a timely fashion.

Tom

[trk]

As an engineer involved in building and calibrating test equipment as well as an avid caster, let me add a few comments.

First, consitancy is the issue. Can you repeat the process that worked last time?
From this perspective it matters not if you're 5 or 10 degrees high or low, just is it the SAME - repeatablity!

Second, look to the linearity of the instrument. IF by it's nature it is linear, then calibrating by taking TWO known measurements (freezing and boiling points of water are most commonly available - note altitude corrections for boiling).

Third, there are many companies that will provide calibration services for 'nominal' fees IF you really require it. (Useful if you use the melting points of alloys as an indication of %lead and %tin.)

[grumpy one]

I thought maybe I should SLOWLY bring up some pure pb and use that for a calibration. I have about 300 lbs of pb., so maybe that would be the answer. Does lead melt and freeze at consistent temps?

Again, I have to leave for a while, so please don't think me rude if I don't say thanks in a timely fashion.

Tom


Tom,
Pure lead melts at 621 degrees F, and that is both the liquidus and solidus temperature, just like linotype. The reason I didn't recommend that route is if your alloy is impure the temperature could be quite a bit off before you could easily notice that you were measuring liquidus, and solidus was substantially different. However if you are pretty sure of the purity, you can do an accurate calibration by measuring the temperature it melts on the way up, and freezes on the way down. Those two should be the same, of course, or it proves your thermometer is inaccurate. If you have a fairly reliable provenance for the lead, and if you've done a hardness test, it is a reasonably accurate way to calibrate. Impurities are likely to affect the hardness if they affect the liquidus temperature much.

[melw]

I have been reading the board and learning a lot. I tried casting bullets years ago and did not have much luck. Friday I received a two cavity mold from a seller on eBay.
It is a Lee 200 grain SWC in .45.
So this weekend I decided to try again. I smoked it while the pot came up to temp. By the way smoking the mold with matches is kind of difficult. (You can read that as a major Pain) I preheated the mold and started casting. I had some problems with the process. Not getting sharp castings. I had to remelt about 50% of the drops for this. I also had many that have a frosted look. From what I have read here both of these problems are temperature related. I have seen the posts talking about using the digital thermometers to help monitor and control this.
I was looking at a local electronics store and they had some digital multi meters that would do temperature readings with a K type thermocouple. They come with a bare thermocouple.
Can I use this?
They also only seem to read in degrees C.
Have others used this type of equipment?
Thanks for any help!
Mel W.

[NVcurmudgeon]

Mel, no clue on thermocouples here, I never use anything electronic if there is any other way to achieve the same result. For smoking your mould, I agree that matches are a major PITA, and butane cigarette lighters burn fingers. The long butane barbecue and candle lighters are perfect for smoking moulds safely.

[montana_charlie]

I will add two things to this discussion...

- Another eutectic alloy is 63/37 solder. It goes from solid to liquid at 361° with no 'mush' stage.
- Pure lead is not eutectic, but it can be used to check the calibration of a thermometer. The method is described here http://www.bulletmetals.net/thermometry.htm .
CM

[lurch]

I have been reading the board and learning a lot. I tried casting bullets years ago and did not have much luck. Friday I received a two cavity mold from a seller on eBay.
It is a Lee 200 grain SWC in .45.
So this weekend I decided to try again. I smoked it while the pot came up to temp. By the way smoking the mold with matches is kind of difficult. (You can read that as a major Pain) I preheated the mold and started casting. I had some problems with the process. Not getting sharp castings. I had to remelt about 50% of the drops for this. I also had many that have a frosted look. From what I have read here both of these problems are temperature related. I have seen the posts talking about using the digital thermometers to help monitor and control this.
I was looking at a local electronics store and they had some digital multi meters that would do temperature readings with a K type thermocouple. They come with a bare thermocouple.
Can I use this?
They also only seem to read in degrees C.
Have others used this type of equipment?
Thanks for any help!
Mel W.


The bare thermocouple can work but not for the long haul. You can melt the insulation off of it at normal casting temperatures. To be useful, most of the plain wire thermocouples are insulated with teflon and depending on the particular stuff will melt anywhere from mid 400'sF to about 620F. The most likely candidate for the thermocouple insulation is PTFE which melts at around 620F. Some of the low temperature thermocouples are made with a PVC insulation that will leave in a heartbeat in molten lead - possibly accompanied by a visit from the tinsel fairy if you just jam it in the molten metal. I'd check the advertised temperature range for the multimeter and if it is 150C or better, it probably has a PTFE insulated thermocouple. You can probably get away with using this short term (for calibrating another thermometer designed for casting temperatures) if you keep an eye on the temperature and don't go above 600F or so.

If you get one and try, go easy (very slow) putting the thermocouple in the melt and look for the insulation shrinking back as it nears the metal surface. If ti shrinks back a lot, stop. It's PVC. If it doesn't shirk back, its probably PTFE and you can proceed. Calibrate a nromal casting thermometer against it and use that for normal operation.

If the meter accepts a standard thermocouple plug, you can get high temperature probes with that plug on the end that are designed for operation at the temperatures we cast at. These can be used with the meter as the main thermometer for casting temperature indication. I've not used one, but would not hesitate to if I did not have my pot on a PID controller.

[quack1]

Tommag- I have seen exactly the "particleboard" look on my ingots. Sort of looks like shiny silver flakes on the surfaces that touch the mold. As far as I can tell, it is from the type of ingot mold and rate of cooling. I see the flakes more when using steel muffin pans and cooling the ingots faster by setting them on cold concrete, like when I melted wheelweights last week. The concrete on the back porch was too cold to sit on for any length of time as the ground was frozen until 5 or 6 days before I smelted. Got lots of flakes in the ingots. I don't notice the flakes as much when I smelt in the summer. For whatever reason, I don't see the flakes as much with aluminum muffin pans. I keep the temp of the melted wheelweights below 650 to avoid zinc contamination so I don't think the flakes are zinc. I have also used these ingots and cast completely filled out bullets, also ruling out zinc contamination. The bullets don'tshow any of the flakes, either. For what it's worth, I also melted down a bunch of pure lead flashing and pipe last week, and saw the same flakes in the ingots. Any metallurgists care to take a guess?