Crucible Tempering Revisited: To use borax or not? or something else?
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- Опубликовано: 26 сен 2024
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Today I have an interesting situation. 2 crucibles in need of tempering, and a bag of something that could potentially substitute for borax. Why is this important? Because borax can greatly shorten the lives of crucibles, though it can help them through the tempering process.
I can control my new little kiln pretty well, so i'm testing, back to back, crucibles with no treatment, and a treatment that could be considered like borax, but less likely to ruin my crucibles. Maybe. It's just an excuse to play with fire, really.
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"a vaguely scientific" video is the best video
I cant pretend to be a scientist but maybe I can be a bad scientist if I try really hard
Paul, Ah, myths and legends of ages past! How they plague the foundry industry.
I am not too sure about any of this! SOME crucible manufacturers recommend a preheat to above working temp by perhaps as much as 200 deg C for very large crucibles (300 kg plus!) before first use and indeed before any subsequent use if it has been allowed to cool down. These crucibles are very heavy and 2 to 3 inches thick, they are made for continuous use. Note that not all manufactures recommend this treatment and they NEVER suggest any sort of fluxing treatment - the impracticality of this repeated preheat after each cool down for us and our small crucibles is I am sure obvious.
In 60 years of using crucibles, I have NEVER bothered with any sort of tempering and this has never caused me any problems. I think that a temper just robs you of a melt - more than one if it is a very hot temper as you seem want to do. Crucibles are expensive, why waste part of their life on an unnecessary procedure? Now, I speak from a point of always buying good quality crucibles - some of the rubbish one sees from various online sources I would not use and if a crucible of mine caught small pox like yours seem to have or the often seen on YT extensive surface crazing I would be having some harsh words with its supplier. Also, if I got graphite all over my hands when handling a new crucible, I would not buy from there again - good crucibles have a glaze on the outside which prevents this and stops (well, slows) oxidation (burning out of the graphite). Note that the glaze is not on the inside for were it to be fluxing with metal oxides would occur and drastically shorten life. The unnecessary use of ANY flux like Borax salt lime et al is sacrilege, fluxes destroy crucibles and should be used very sparingly as rarely and for as short a time as possible for melt treatment only, all residue to be removed ASAP.
Perhaps the worst thing you can do to a crucible is dunk it in water!!!!!!! Manufactures are so concerned about water pick up that they say NEVER even stand a crucible on a concrete floor. My wife nearly had to call an ambulance when I saw you dunk that crucible!
If you think a crucible has got wet dry at 90 deg C and then 150 deg C for about 2 hours at each but any higher temp tempering waste of time, fuel, and crucible life!
In short NO fluxes, NO water and I strongly recommend NO tempering.
Martin
Hi Martin! Good info here, if you don't mind im going to pin this post so people find it more easily
Paul, I am honoured that you have chosen to pin my comment.
A little story about a wet crucible;- I once was given a largish furnace, it had a BC75 crucible fitted (75 Kg of aluminium). Unfortunately it had been out side in the rain for months and the crucible contained about 2 inches of grotty corroded aluminium and about 3 inches of water. I was desperate to save the crucible as a new one was about $800.00! (Ouch!) So I turned it upside down and the aluminium fell out (with a little help). I sat it, still upside down, a little up off the floor on some wood and I had a 100 watt light globe going on the floor under it. After about 2 weeks the bottom of the crucible (uppermost) felt warm and dry so I returned it to the furnace and lit a small gas burner in the furnace. I ran it on and off for a week or so slowly increasing the flame until I got to about 400 deg C then I put the proper burner in place and took it to red heat. It did not crack or explode and in fact it has melted about 600 kg of aluminium since - $800.00 saved - Phew! But I do not recommend this sort of thing!... Martin
@@olfoundryman8418 interesting to see your experienced opinion.
Do you believe it matters if the crucible is heated in one spot over and over again versus spreading it out? I might get one of those with the indent as a spout. So I'd be able to tell which side I exposed to the heating element. So would occasional or frequent rotation have any meaningful effect to the crucible's life?
@@olfoundryman8418 oh, wow! You have a lot of videos that I'm gonna have to watch.
@@konstellashon1364 , Please do 😊.... Martin
Zero flux given.
The one crucible gave precisely zero flux
This comment is highly underrated
I definitely enjoyed "not learning anything". (But i feel informationalized)
"Vaguely informational, maybe" should be a video category. Id fall into that one for sure
I have 3 crucibles. 1 small 2 kg and 2 6 kgs. Did not treat any. Only used the small one 1 and the 1 of the big ones twice. The other I have done 10 burns in. They crackle. Sure would hate to have one rupture and spill molten brass on my foot as I am pouring 4Kgs. Another youtube video said expect 30 to 40 pours in a crucible's life. By your video proper treatment could extend longevity of crucible a great deal. Thank you. I love all the advice I get from my fellow metal heads.
armed with this new knowledge we go forth
into the fire.
The best videos are those that are fun to watch and you learn absolutely nothing! Actually there was plenty of interesting information. So I feel like I learned something...
I'm sure somebody learned something, hopefully it wasn't wrong! The important part, however, is I got to play with fire. And in the end, isn't that what this is really all about?
@@PaulsGarage yes, exactly!
This is one of the better explained videos on how to treat a crucible. I just got my first furnace and am watching videos before I get started.
Glad I can help! Good luck!
Thanks, I will try. I'm building my first furnace over the weekend. I've watched a heap of your videos and hopefully I can get it done. Best wishes, from Australia, Keep up the good content.
Thanks and good luck! For more good metal casting info I would suggest swdweebs channel also
I made due with a DIY and finally gave up - just spend the money for a Devil Forge as those trashcan furnaces take a while to heat up and can barely handle aluminum so for the amount of time and money you'll waste building it and then the extra gas you'll use, it's cheaper and easier in the long run to simply purchase a real one.
It doesn't make sense to me to coat the inside of a crucible with borax if you're going to be melting aluminum in them, the borax is just gonna re-melt and contaminate the aluminum forming aluminum borides. As far as fluxes go, there are two different major kinds. "Drossing" flux and "covering" flux. Drossing flux pulls together impurities and brings them to the top, making them easier to scrape away. Covering fluxes cover the melt in a sheet of molten glass, preventing gas from getting in to the metal, preventing oxidation, and preventing the metal itself from burning away. Other things can be added to the fluxes like fluoride to help draw magnesium out of aluminum, and titanium as a grain refiner. All fluxes chemically attack the crucible and shortens their lives. Silicon carbide crucibles are the most resistant to this chemical attack, but are also more expensive. There is no flux that modifies the melting point of a metal or alloy, or make a metal "flow" better. That would have to be another metal added to the alloy itself. There are other things that can be added to the alloys for the purposes of grain refinement, such as silicon or titanium to aluminum. There is no one universal flux for all metals, since one flux may help a certain metal, but may just further contaminate another, as with the case of borax in aluminum.
I don't believe tempering achieves anything useful. I have never seen anything mentioned about it in any real literature, only online forums where it's people doing things but they don't know why, because they saw someone else do it or someone else told them to do it, and are now passing that information on in an authoritative manner. When I receive a new crucible I just put it in the oven at 200 degrees for a couple hours to make sure all the water is driven out of it so it doesn't turn into a bomb in the furnace. These chinese crucibles are cheap, but of horrific quality. I'd want to get all the life I can out of them by using as little flux as possible. Just enough to help the melt. As far as glazing goes, the only things I have seen regarding it is if the crucible is going to be used for melting low temperature metals that won't re-melt the glazing, like precious metals. However, I believe that professionally, they just use very smooth ceramic non-wetting crucibles for that purpose.
Casting forums and youtube videos are mostly useless for finding out real, useful information. It is definitely a struggle.
Thank you for the information. I just got a small graphite crucible that I'm going to melt aluminum in for small pendants and stuff. Do you think I need to glaze it or add any flux at all? Do you have any recommendations? Or would I still achieve good results without any tempering/fluxing whatsoever?
Great vid for a guy like me. Always appreciate the education.
Great video and whiting experiment Paul, thank you!
You're welcome!
Ha, now I begin to understand my question. Thanks for another 'highly informative' video.
I'm glad I could help!
First time I've seen you. I like. Great job. Very entertaining and educational...even though I learned NOTHING! lol
The textures of these vases triggered some phobias in me that I didn't know I had
Paul you are Awesome in a vaguely scientific way :o) Thanks for sharing!!!
Your awesome. Thanks for sharing your knowledge. And you totally inspired me to get into this.
Calcium Carbonate, when burnt (around 1500 F) becomes Calcium Oxide. Cooled calcium oxide, particularly when made wet, turns back into calcium carbonate (lime). This reaction is the basis for making vaguely scientific concrete, but it also is used as a fluxing agent in iron smelting work. So perhaps your non-scientific meanderings accidentally trod into established scientific processes. A true shame that you actually did something non-random. Maybe next video.
I didnt know know that about iron smelting, but it makes perfect sense. CaO's fluxing power requires a lot of heat but it should be at full force at iron melt temps.
@@PaulsGarage In steel making, they don't bother with pulverizing the limestone, it is just crushed and shipped in by hopper car.
Hey, Paul! I'm back! Gonna be doing some tempering of crucibles myself soon, so this helps a lot. Thanks for the video!
Hallo all
To sum it up.
Borax is bad for my crucible and I should slowly heat it to 500deg and then to red hot and let it slowly cool down
(Its a 6kg silicon carbide graphite)
And advice will be appreciated
Thanks
I'm from Vietnam. Hello Paul's Garage. I like your video
Hello! I've never been to Vietnam but my wife has and she said Its a beautiful country
@@PaulsGarage Really? it's really a poor country, I aslo like life ' your country (euro )
Ok, now that I've watched the whole thing, I'm glad to hear a couple of things, 1) we basically have the same philosophy on tempering, just stick it in there and heat it up. 2) what you said about borite and flaking makes sense. I've never used any of the borite stuff and I've never seen my crucibles...what was the phrase?.. "turn to rubble". I have seen plenty of other RUclipsrs with crucibles that appear to just fall apart. I always attributed it to a different material, but I also know that some of them do the borax thing.
I think the most telling result here was just how vitrified the unfluxed crucible got at 2100. If its that melty at 2100, borax would be way too overpowered. Some natural borates are full liquid by 1650. The only benefit might be that borates will form a glassy surface on their own unlike other fluxes, but thats not necessary for crucibles I think.
I learned that I should cook my raw crucibles before using and fluxing, which I had no idea about, is pointless for medium heat melts and quite damaging for higher heats
So thanks :D
I will not flux crucibles at all, ever
I made the mistake of using borax once and it made a mess of the crucible - never again.
For tempering, stick it in the over at 400 for a bit and then set the over to the lowest setting and allow it to slowly cool overnight - that'll bake out all of the moisture and temper it just fine.
Not sure where you got your crucibles from though as I've never had one get that glassy look on the outside even when I've melted several pounds of spent shell casings.
As for how long they'll last, depending on how you handle, treat and store them, on average you're going to get 20-30 good sessions out of them so yours still looking good after what sounds like maybe half a dozen light uses is nothing exceptional - mine are still looking good as new after a dozen sessions and I'll go for several hours as I process one or two forty gallon trashcans full of crushed soda cans.
Hey Paul member when you melted cast-iron there is a crucible that you can buy that’s rated for 2900° maybe you should buy it and re-tried melting cast-iron again I bought that crucible and I want to try melting cast-iron with it I have several of them that are rated for that temperature basically all of them my furnace gets up to 2600° but I coded it would say at night
Hello! These crucibles are rated to 2900, actually. When I did the iron melt I started with a bad crucible, but even good ones (and furnaces for that matter) became expendable at iron temperatures. While my setup melted the iron no problem, I havent had a desire to cast anything with it, mostly do to the extreme heat and fuel usage it requires
What the flux?
The crucible done with whiting looks better to my untrained eye.
I think so too, the surface looks a little better up close. Hard to tell in the video, but it looks more consistent up close
@@PaulsGarage time will tell if it actually is better. Perhaps it will only be a cosmetic difference though? In which case the better looking one is better.
Cool. That would make an interesting glazing I would think.
I'm sure if I'm wrong, I'll hear about it soon. 😎
Oh! Woops. XD I just used it and it worked out. Mine did turn out like yours though.
you should research what it takes to make your own graphite crucible. there's a few out there that do it. awesome vid. thx.
Is it possible for graphite to be an electrical conductor in this way? I want to make a graphite column like the one found in batteries.
Borax is banned in the uk as it’s classed as a poison, I’m yet to use borax on my graphite crucible, would adding borax prevent metal adhering to the crucible when pouring
Salam qardaş,bronza əritmək üçün tiqelin qatqılarını bilirsizsə yazardızda mənə,Potanı hansı maddələrdən hazırlamaq olur?
Enjoyed this, thanks :)
great info. Just tempered my crucible
thanks, i enjoyed learning 'absolutely nothing'
I think I missed it. What was in the bag that you put into water?
How is mgo a flux? It melts at 5200f? They use it in electro refractory for electric arc
I tempered mine in an oven, never used any. But I got bits of what looked like molten glass in my metal from my crucible
It's not a clay mix, it's a two part resin with graphite fibers mixed in. You can burn it with an oxygen flame.
Good morning sir I m from India and I m automobile engineer...
Just wanted to know that ist waste oil is chipper then coal...thanks
Could you theoretically use some sort of sort of baking soda mix?
Where did he get inexpensive calcium carbonate from?
My next kiln build will be from a stainless steel beer keg, and it will be huge, but I can't seem to find a larger crucible, like the ones he has here.
From his link I found a #14 that should work.
Pottery supply places. It's comes pure, ground to #325 mesh, and it's cheap. Potters use it in glazes as a flux. You can get all kinds of stuff from pottery supply places 😉
Did you dip it in cold water after you heated it up or naturally let it cool down without water?
No water, air cool
What happens if you temper it upside down, will it make a difference, as the glazing will move to the lip and not the bottom? Then when right way up and used the glazing will eventual start flowing back down.
If you haven't already, please consider recording a video that demonstrates the different sizes of crucibles like #3,#4 and others you may have. I'd like to create small bars of copper and brass, but have no way to gauge the size of the crucible I'd like to use without having something to compare them with. Also, what do the numbers on some crucibles represent? Cheers
The number of kilograms of metal they can fit, so a #10 can hold 10 kg of molten metal with the density of metal obviously varying by volume - ie/gold is denser than aluminum so 10 kg of aluminum would fill the crucible almost completely while 10 kg of gold only partially.
As such, if you're looking for a specific weight then that's how to figure out how large a crucible you're looking for.
You said "small" bars so if you're just talking an ounce or two you could likely get away with one of those ceramic jewelry crucibles and simply use a blow torch - check out videos on pouring silver and gold bars to see what I mean.
@@seanfoltz7645 Thank you for all the great information. Very helpful. Cheers
Thank You for the video. How long do you hold the crucible at the max temperature. I have tried a couple of crucibles and do not get the same results
What about cement powder and then firing it?
Interesting video! I will add nothing to the crucible while tempering it 😁✌🏻✌🏻
Why did they end up 2 different sizes? I saw they were both marked 8, so I assume they started at the same size, it is interesting that one shrunk significantly more than the other.
What! No fire & destruction! Am disappounted!😢😢😢😢
Fire and destruction will come eventually, hopefully not when I'm using these expensive crucibles!
I think there are call and there are graphite from my research.
Propane and propane accessories
Fired using clean burning propane and propane accessories... Hank Hill would be proud.
Why does mine not look like your tempered one.
13:02 is that a bluetooth gas hose?
Interesting video. I didn't see the propane burner coming in what was obviously an electric kiln. I like that. I really like that burner setup w the standoff between the gas nozzle and the "siphon" body/flame holder.
"We don't talk blasphemy here." 😁 The metric system was created for sissies who can't do math, fractions, or unit conversion.
So why the factory does not produce them already like this?
$$$ is my guess
Very good video….I like to see a video that explain what you are doing ,so I can learn as you explain. Always try to learn something that why I love U Tube.👏👏👏👏👏👏👏🇺🇸🇺🇸🇺🇸🇺🇸🍻🍻🍻🍺🍺🍺💕💕💕
What about a ceramic slurry like pottery clay
Pottery ceramic would break off while it's cooling. Pottery ceramic has a much higher expansion rate than graphite clay and it can't handle temperature swings like graphite clay
Does the Tempering process relieve some of the internal stresses making the material less hard & less brittle?
What is that bag of white powder that u put into?
Just like middle school science fair! Vaguely scientific with no real results!
Just wait, ill do a baking soda volcano next 🤣
I watched a video on manufacturing the crucible they are fired at 1800°
Could you dry it in an electric stove for an hour or so?
well you learn something every day, not here.. today but, hopefully somewhere
Exactly!
I have finished tempering my crucible(same one in video) Do I now treat the inside of it with borax?
No I wouldn't use any borax, it can damage the crucible and shorten it's life. Most of them come ready to go other than the potential moisture issues
What kind of crucible would you use for cast iron?
nice video
speaking of salt, could it be an effective flux for this purpose? i know some blacksmiths use it for forge welding.
Yes! Salt would work as well, but like calcium carbonate, you would need higher temperatures than a typical aluminum melt. Im just going to not add a flux, as the unfluxed crucible still showed a lot of vitrifixation (glass melting)
sodium chloride (table salt) and potassium chloride (table salt substitute) are used as covering fluxes for aluminum.
Omg you are awesome.. 5 mins in and you've summed up my dad's master's in chemistry explanation to my 7yr old self.. I totally get it and the concept is way more important than the details.. rock on dude.. you can, fyi, use that borax, a and hammer washing soda and a bar of fels naptha soap to make a bad ass laundry detergent..
My brand new crucible has couple of small pieces chipped off.
Is it still good or it has to be smooth all the way ?
I'm not sure it matters, but you would probably want to contact the place that sold them to you to be sure. My crucibles get pretty nasty by the time i stop using them and it usually doesn't cause problems until stuff starts falling off
How can you do this same or similar process without a kiln and thermocouple?
I used to just heat it glowing red and let it cool. It isn't as exact as this but it does a similar thing
Know any websites for bar molds
G’day Paul I’m really enjoying your videos I just thought I would mention l Believe that there is no need to use borax on a graphite Crucible it will deteriorate regardless of what you do you only need to put borax on ceramic crucibles 🤠💛😎👍
I just got a new #3 crucible. Are you saying I can make mine last hopefully indefinitely longer if I just go down to the drug store and buy a bottle of pure calcium carbonate supplement powder and mix it with water?
You don't even have to do that. Temper it with heat alone, no need for added flux
No - the crucibles will last 20-30 castings on average, depending on how well you treat and store them - if you want to make your crucible last just make sure that whenever you use it, you get it back into the furnace as soon as you finish your pour and then allow it to sit inside with the lid shut so that it cools down slowly.
Also, make sure to warm up your tongs so you aren't grabbing it with cold/cool metal and avoid putting it down on a cold or wet surface when swapping tongs after removing it from the furnace.
Are you going to melt some thing again
Thanks for the suggestion!
Once the crucible has dried you are going to heat it up in the foundry, how many deg about and how long?
Thanks so much!
Where do you get your K - type probes for your thermometer ?
A pottery supply place. Most kilns today use type K thermocouple and frequently see temps around 2300f. So the probes have to be very durable and even then they are wear and tear items. Replacements are frequent. Any place that sells pottery stuff/kiln stuff, even glass art should have the probes
Hey Paul can you try to make lava
How long it last ?
Any additive that results in the formation of a Eutectic system is a flux?
Is that the definition? That sounds so much simpler than the rambling i found everywhere else. Makes sense
@@PaulsGarage I'm not a metallurgist or ceramics technician but that was what my reading on the topic distilled down into. It does seem like the sort of explanation that is workable, a concept that lets you make predictions etc. If you want the details there is a pretty deep rabbit hole starting with a google search for "OpenCALPHAD".
So, why not concrete lime and soak the crucible in it?
PS. Oh, it did nothing, okay, don't worry about it. :P
Still good video, now I know what not to do.
More of those nothing learning moments. Thank you in advance.
Why nobody using hydrogen foundry? Hho
Anybody have an opinion whether a couple of cheap, used propane weed burners, one large, one small will be of any use building and operating a propane kiln-foundry-furnace or whatever the heck they're called?
كيف تصنع بودقة الذهب وما هي المواد التي تصنع منها بودقة الذهب ... أرجو الرد
Do you attualy know what your talking about ?
11:33 get some shoestrings, hippie! ;)
My therapist always told me to better control my temper
Better get some calcium carbonate then! Eat eggs with the shells, that'll do it.
@@PaulsGarage chalk it up to the heat of the moment
borax as a flux is for metals like copper brass silver, its used only to stop oxidation of metal and give the metal a clean flow, the quality of the metal is of more importance than a crucible, all crucibles have a life span and need replacing, the flux is for clean metal not crucible care, the flux reduces fire stain in the metal, and stops metal sticking in the crucible
Can I say first?
Can confirm first!
This video could have been 3 minutes long.
BORING
350F for an hour is sufficient. Compliments I believe was BigStackD.
Am I the only one who has an idea that is actually his wife who edit the videos and write the yellow texts? It's funny. Sometimes 🤣
I like to think I have multiple personalities, they are all the same but they think the other personalities are idiots. One of them does the editing 🤣
@@PaulsGarage It was also a thought I had. 😝
where do you get the crucibles ?
PMC supplies. They have a website and also sell on Amazon
@@PaulsGarage Thanks Paul!
I tried melting cast-iron and almost did it Paul if you buy a silicon carbide and crucible those crucible‘s are rated for 3200° but they’re expensive a 5 inch one is like $31
You can melt cast iron using a charcoal furnace with a hair dryer - found out by accident as my first DIY furnace used a old cast iron pot for my crucible and I actually melted out the bottom of the pot.
I use very small fireclay / alumina crucibles for jewellery purposes and those are seasoned with borax before first use. They just get gradually heated with a blowtorch to drive off moisture, then brought up to red heat and sprinkled with powdered borax which glazes the surface. Borax is used with most gold and silver melts to help remove impurities and prevent gas absorption. I don’t think there would be any benefit to using borax as a glaze on a graphite crucible.