View Full Version : Temperature and Thermometers
August 15, 2010, 08:10 AM
As far as thermometers go, I have a couple of questions.
1. How do you keep the thermometer off the sides of the pot and from giving you a false reading. I'm thinking that the closer the thermometer is to the bottom of the pot, closer to the heat source that is (and especially if it's touching the iron), then conduction will cause the thermo to give a false reading. Or, am I being too technical? (I'm a science teacher, so I might be analyzing this too much).
2. Anyone ever use those digital infrared thermometers while casting. My Pop uses one with hot oil when he's frying stuff. Would one of those work for reading Pb temperature?
August 15, 2010, 09:32 AM
My casting thermometer has a clip that holds the tip where I want it and keeps it away from the side of the pot. I'm thinking about IR but not sure it will give a good reading on molten Pb, read an interesting post about that around here somewhere yesterday. I may wind up with IR someday for other applications but I think I'll get better results from the conventional thermometer.
10 Spot Terminator
August 15, 2010, 10:12 AM
On my Lee magnum pot I just took a length of bailing wire and wrapped one end several times around a pencil to make a coil appx. 1/2 in. tall and ran the other end around a support post on the back of the pot draping the coil over the edge of the pot. I set it so it suspends appx. 1 in. above the rim of the pot and at an angle to keep the gauge away from the middle of the pot and the stem near the middle. The gauge angles away from you but I dont have to check it all that often anyway. Works great for me . I got my thermometer from Roto Metals. Are the same as the RCBS but less money . Dont know anyone using digitals at this time . 10 Spot
August 15, 2010, 11:02 AM
Personally I have not see much difference and "perhaps", you are being too technical. In use, I find that there is an optimum span that makes for a good "RUN". I let the finished product, talk to me and can tell how my run is doing at that time. I then note the temp. and try to work within that span. I do my runs outside where there are other variable in play such a breeze and ambient temperatures. Just do it and observe your results. Frankly, once you get into your run, you will hardly pay any attention to the temp. indicator.
The digitals work well but should be compared to a more rliable standard, from time to time. The respose time is quicker and you will see faster swings when compared to the analogs. Keep in mind that regarless of your pot or temp. indicator, you will always see temp. swings. Either will work just as well for your work.
Be Safe !!!
August 15, 2010, 12:43 PM
shiney lead & an infared thermometer don`t work ,I think the lead reflects the feed back away or summtin.
I started hot & worked down for yrs. before purchasing a thermometer!!
August 20, 2010, 03:08 PM
The IR emmisivity of lead is low and you need an IR thermometer that lets you adjust emmisivity to accurately read it or other things that aren't flat black.
I use a digital thermocouple thermometer. These are very fast and reliable. They have higher useful resolution than the analog thermometers. (Harbor Freight used to carry one, but they're gone now.) I don't care if the absolute accuracy is off a few degrees, as long as the instrument is repeatable. So, I make thermocouples out of stranded, glass cloth insulated thermocouple extension wire, and coil it like a phone cord and insert it into the head of a drilled-out 3/8" 10-32 brass bolt, then silver braze the junction to the tip of the bolt. I drill and tap mold blocks to accept the thermocouple bolt. This lets me read the temperature of the blocks until I find what they like to be when I pour. After sprue cutting, and dropping bullets, then I close the mold and just wait for the thermometer to tell me when to pour again? It's very consistent. It stops the block temperature from wandering up and down.
Top to bottom temperature gradient will depend on convection some, but, in general, the thermal conductivity of metals are so much higher than air, even moving air, they tend to equalize their temperature toward being isotherms. I don't recall measuring the gradient in one of my melts? Don't know why not. Next time I think of it, I will, but basically I set and forget my melter and just worry about mold block temperature.
August 20, 2010, 08:43 PM
I think you are reading too much into it. It's not that techinical. Put the thermometer in and keep the melt between 650 and 700 for the smelt and the zinc weights will float to the top with the clips. Now for my casting pot with already clean lead I usually go around 750 or a little higher.
August 20, 2010, 10:33 PM
lately I`ve ran across so many that I actually took em back & traded em for a peice of bucket of "lead" ones ????
I sort em out as best I can before ingotizing em.
This is my regular Tire guy I trade em to , so I help him he helps me !!!!!
August 20, 2010, 10:42 PM
I use a PID controller with a thermocouple on the bullet casting machine I built. As others have pointed out IR thermometers don’t work.
August 21, 2010, 02:08 PM
I'm only asking this because I'm too lazy to measure myself or look at a periodic table...
I too sorted out about 15-20 lbs of Fe and Zn weights. If I offer to trade them for Pb weights, am I getting roughly the same poundage per volume? (that's a terrible phrase to use I know... "poundage per volume") I don't have my periodic table in front of me, and I don't have the densities of either metals memorized to make a guestimate on the mass.
Anyone can chime in. Which has the higher density, Pb or Fe?
August 21, 2010, 03:23 PM
I use a thermocouple with a long stainless probe so I just stick it in the pot to the bottom and it's long enough that it does not interfere with casting. The first thing I did was to check the calibration of my Lee pot and my RCBS pot. I was amazed at how close those thermostats are! Even with my probe up against the side of the pot 7 = 700 within a few degrees except the Lee pot tops out at 950 set for 10. Noteably, the Lee was closer than the RCBS pot even though the RCBS is close enough for gubmint work.
August 21, 2010, 06:28 PM
I've posted this before, but here's my PID.
You won't know how important temp is until you KNOW EXACTLY what the temp is. Each and every mold will have a temp that works best for every given alloy. Add to that the method used to pour, you have a lot of variables to keep tract of.
I'm NOT trying to turn casting bullets into an exact science, but the more you are in control of, the better the finished product.
Here's where the thermocouple enters the pot.
August 28, 2010, 10:54 PM
Thanks, Unclenick. I was thinking about your post when I was casting today. I now know that mould temp is as important as alloy temp. Also helped to know that moulds may have temperature preferences different even from similar moulds. Didn't install sensors but it was helpful to know anyway.
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