doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Infrared Thermometer for Nitre Bluing.

OK, Thanks.

Excellent points by everyone. It appears to me, in order to achieve the correct temperature for annealing, (drawing the temper) a lead bath inside a digitally controlled oven or kiln would serve well, being more controllable and therefore not relying on "reading the metal". In addition, the infrared thermometer could be used to "shoot" the lead to insure the correct temperature was achieved. Correct or incorrect?

Damascus;
as far as I am concerned you can "CAN" your Goody-Goody Bit. This all started with "YOUR" correction of Jack Rowe.

I very politely, I thought, came to Mr Rowe's defence & simply stated the term he used was correct.


This could have all ended right here, "EXCEPT" you jumped in with both barrels about the Superior Intelligence of the Brits IE "IF" the Brits do it this way then it is Unquestionably right.

I will whip this dead dog no longer but simply stand firm that evidence has been given that to simply say one has tempered a piece of steel is correct usage of the word, while to say one has drawn the temper is Technically incorrect, regardless of how commonly used it may be (By the Brits).

Correct or Incorrect? The answer is maybe. If you look at tempering color charts for steel Ken, you will see different temperature ranges and colors for slightly different tool steels. If you know what you have for spring stock, and have used it successfully many times before at a given temperature or color to make a good spring, then what you are assuming is correct. If you anneal some unknown spring steel, shape a complex spring, harden it and temper it exactly as you did with another spring steel, your spring may or may not be satisfactory. Some folks refer to tempering as annealing, but generally in the U.S., annealing is the process of heating steel dull red for an extended period, usually in an inert gas atmosphere to prevent scale formation, and then very slowly cooling to achieve a dead soft state. I've seen annealing processes as long as 28 hours. Tempering is a partial annealing process that brings steel down from it's maximum hardness.

https://www.google.com/search?q=steel+tempering+colors+temperatures&tbm=isc

It is the clarity of molten Potassium nitrate that makes it nice for tempering or drawing springs, or for blueing small parts because you can actually see the color and quench when you get there. Going all the way to the 633 degree F melting point, or beyond, may not give you a good spring. When you coat a part in powdered graphite and immerse it in molten lead, you are relying on temperature alone, and a thermometer of some sort is necessary since you may not have 100% pure lead, and your lead pot can get much too hot. Using stump killer that is not pure Potassium Nitrate may slightly change the melting point just as different alloys of lead have different melting points. You can heat either lead or potassium nitrate far beyond their melting points, as their boiling points are much higher. In short, using an accurate temperature controlled oven or knowing the exact temperature of your molten lead or potassium nitrate bath will only be useful for known alloys of steel or prior success with a given steel. Confused enough?

OK Keith,

Annealing it is for type processes like preparing an action for polishing in preparation of case-coloring. Tempering for springs.

Thanks for the confusion. Looks like trial tests will be appropriate, I have a source for car battery lead at my local scrap yard.

Please people, let's not let semantics interrupt a very nice flow of information.

Regards
Ken

Well, no actually. Annealing a rifle action for example would alter it's heat treating by making it softer. You can spot anneal a case hardened action such as a Krag so you can drill and tap it for scope mount screws. I believe you can re-case color a shiny shotgun action without annealing it first. An engraver might want to anneal to make previously case hardened metal soft enough for his gravers. When the case colors are gone, the surface hardness is still there. Tempering is a partial annealing process that brings hardened steel down to a more useable state, but not dead soft.

A lot of car battery lead contains cadmium Ken. Pure lead is easy enough to come by, and a little safer when it comes to exposure without adding cadmium. Cadmium exposure has been linked to some mass murders. We like you just the way you are.

I worked w/a gunsmith that insisted the correct term was 'draw TO temper' and he corrected me every time I said 'draw the temper'.
Of course, I purposely from that point on said 'draw the temper' just because.

Whatever,,make it dead soft, make it glass hard and then draw it back to spring hard.
Works for me.

What about that infrared thermometer,,any better, more accurate than a regular thermometer?
I've gotten along with stick thermometer in a lead or niter pot. Or just judging by eye w/a torch heating the spring from below on a steel plate.

Either type of thermometer works fine as long as it is calibrated correctly. The only advantage to the infrared type is that it is non-contact and you can take accurate temperatures at a distance.

I have a couple 5 gallon buckets of various spring steel I have collected over the years. I have saved flat springs from everything from old clocks to heavy cable retrievers to truck leaf springs. I also did my electrical apprenticeship in a steel mill, and would often watch for when the cold rolling mills were running different grades of steel that might come in handy in the future. I would shear strips of different grades and thicknesses, and tag it with information from the Met-Lab analysis so I'd know what I had when I went to use it.

A few years ago, I needed to make a top lever spring for a Lefever, so I found some spring stock of suitable thickness in my little inventory. I noted that it was very hard right off the mill, so I decided to anneal it before bending and shaping my springs. I cut about a dozen short strips, as I was going to make several spares since broken top lever springs are somewhat common in Lefevers, and put them inside a short length of 2" pipe threaded and capped on both ends with a small vent hole drilled in one cap. I wrapped the spring stock in paper so it would burn off the oxygen to prevent scale formation, and put it on the log grate of my fireplace and cooked it dull red for several hours, then buried it in the hot coals before going to bed so it could slowly cool. I expected it to be dead soft the next day, but it still snapped like a pretzel when I tried to bend it. This is why I told Ken that it doesn't always go exactly by the book when you use different steels. You know you have a good spring when you compress it fully and it doesn't either snap or take a set after hardening and tempering. If it works, then you make notes. Life would be simpler if you could always use the exact same steel, but not as interesting.

I've received a PM from another member who states that it works very well. He considers it safer since you can shoot it at an angle, so as to avoid being over the pot.

My spring steel comes from an assortment of old leg-hold traps. They were very inexpensive at an auction. Lot's of different thicknesses on the different sizes.

Cadmium. Great. Just what I need.

OK, now, am I understanding you that annealing is not necessary before you polish for case-coloring?

Ken, that would be a good question for Doug (PA24)or someone else who actually does color case hardening, and does it well. But it is my understanding that if you are merely polishing to clean rust or patina off the action or parts before re-case coloring, then there is no need to heat that steel to an annealing temperature which is well above normal bone pack case hardening temperatures. We've all seen those guns that had those original mottled case colors polished off to a high shine by someone (notice that I did not say idiot!) who preferred that look.

OK,

Now, the question topic pivots back to either sand or nitre salts as a medium. Would packing the spring in sand, (or the salts) heating, and holding it for a short while in the kiln work? Am I correct in thinking that the spring needs to be quenched at that time? Using either lead, sand or salts as the medium?