Author Topic: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"  (Read 17389 times)

Offline petespaco

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For hightemp1----
  I am moving your last private message to the "public" area, since I think that most of the issues you bring forth are  of general interest to others.  I hope you don't mind----:
Your latest comments:
[/quote]Regarding melting copper, I seem to recall you really need a lot of power as you do not have the advantage of good heating before reaching curie-point, as there is is no curie-point for copper as its not a ferromagnetic material. So your only hope is lots of insulation to keep the heat in.[/quote]
You are correct.  There is also no "curie point" for graphite.

Call me a Doubting Thomas but .....   Knowing what I know about these heaters I don't want to be the 1st person to try and cast something useful, other than a ingot.  Ingots can and should be cast at lowest temp possible for best results.  Small intricate castings on the other hand require superheat temp of 200 degrees in excess of melt temp, else metal freezes/poor detail, etc.  I assume higher temps are exponentially difficult and that is why no one has tried/succeeded AFAIK.
I have been thinking about this.
I do have several sheathed thermocouple type K temperature meters that are capable of measuring temps up to at least 2200°F.
I have used them for years to measure hearth temperatures for  my woodgas to electricitly projects.
It would be easy to stick one into the molten copper to check temperature.  I would turn power off when I do this so the ferrous material in the T/C sheath wouldn't effect accuracy of the reading.  There is a bit of a concern that the molten copper would "poison" the T/C sheath, but I have a few older ones that I could sacrifice if it's true.
  Once, a long time ago, I sold several hundred sheathed thermocouples  (made by a friend of mine) at a time to Boeing to be used in particular foundry practice.  They dropped the T/C into the molten bath each time they wanted to know the temp.  They'd get one or two sample readings before the sheath melted.
  I don't think we'd have the same problem with copper though.


Offline hightemp1

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Some of those quotes were from Mads, buy yeah, no problem, I'm grateful again - you're the best!  I've heard many pyrometers are not very accurate at these high temps, but most are consistent so if you have a good pour with proper filling then you can repeat measured temp.  Color tests is also difficult and varies depending on day/night, clouds/sun.  Generally a very bright yellow boarding on white is supposed to be around 2200, I think.  Not sure where one needs eye protection so please know/understand or just use protection if you plan on testing and please be careful with hot metal Pete. 

I'm thinking if these 2500 watt heaters don't cut it for casting bronze, then scaling these up somehow, or using another design that puts out maybe 4 to 10KW - the most my home will handle safely. One of my previous post shows a link with bill of materials for a design that accepted 8-15 KW input, though I did not see a schematic.  The lower range could use 220 volt but the upper ranges needed 3-phase power lines -that would be prohibitively expensive.

Curious too, as to why I don't see people casting smaller aluminum items with these, or at least some of the easier to cast, Zamac zinc alloys.  Just my biased opinoion, but I think everyone should possibly have one of these in the kitchen ;)  Just speculating on copper for now.
« Last Edit: May 24, 2019, 12:05:15 AM by hightemp1 »

Offline hightemp1

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Don't know much about pryometers, but it may be large in relation to the copper load so preheating it with a torch somehow so that it does not cool the melt too much may help.  Those copper ingots can be easily cut & reused.  You may want to pour the molten metal load into water, this makes copper shot, not sure, but that may be better for next reheating melts.  Manufacturer recommendation of not topping off crucible (75% Max-?) will be safer and probably extend your crucible life?
« Last Edit: May 24, 2019, 12:07:01 AM by hightemp1 »

Offline badpeter

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I finally got to do the casting yesterday... ;D ;D ;D
So I can confirm that aluminium melts in about 15 minutes and copper indeed takes just an hour (my setup is unchanged from the specs that i mentioned).

Also I found out that 50/50 plaster/sand mold, pre treated in an oven DOES withstand thermal shock and doesn't explode like I worried. Great for ingots and other things. The dagger turned out crappy due to air bubbles - i forgot to make the air holes. I think I can use this mould one more time, although I kind of ruined it getting the piece out.

Now my power got even lower to a ridiculous 570 W (wtf!) I thought hard about it and realized something... crucible is withering away. It is much thinner now. Dont know where all that graphite is going but every firing i get slightly less and less power. This got to be the explanation.
The amount of metal inside seems to not affect power drawn. Looks like the amount of graphite is determining factor.

Now I am hearing people add borax to purify the alloy. Will have to do that for cleaner result.
I recorded my experiments, just got to cut the vid!= )

Offline hightemp1

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Badpeter, good stuff - cut that sucker - if you post a descent pic of the casting we might be able to tell exactly why it did not turn out (is surface finish & air bubble similar to last pour)?  Crucibles are by nature disposable especially if you have long melt times, and have lots of dross; also, using same crucible for different alloys can screw up castings easily - how many melts did you get out of it?  I used to cast mostly silicon bronze and it did not require a flux, only a good skimming before pour.  Other copper alloys did require both a flux and a skim, not sure about aluminum, though I heard many just skim and pour, as well.  Also not sure on this either, but borax/fluxes may contribute to shorter crucible life due to their corrosive nature. 

How many volts/amp did you start with on this last pour, how many amps did you finish with, and how much aluminum did you melt? 

I know copper can be melted at 2000 degrees with these, everyone is doing it - just looking for confirmation that the required super-heat temps of 2200 can be obtained with a pound or two of copper using these heaters (call me skeptical).

Update: possibly induction swirling melting action has eroded the soft graphite - no clue here???   Careful you don't get a pot of molten metal somewhere not wanted !!!
« Last Edit: May 24, 2019, 05:28:47 PM by hightemp1 »

Offline badpeter

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Finally! :)
The dagger didn't turn out pretty but the rest works okay. Hope it answers some questions!


Offline hightemp1

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I would never have believed it, but there it is right before my eyes.  A Kilo (?) of Aluminum Bronze cast in one hour using less than 1KW with these ZVS heaters.  Metal actually looked pretty fluid and did a descent job of filling the mold looking very sword-like - CONGRATULATIONS AND THANK YOU !!!

I am only guessing but here is what may have happened.  Aluminum was not skimmed and produced most  of the dross (prepare AL/Bronze ingots beforehand - they will be cleaner). Dross was not removed before pouring or was incorporated in melt (lower part of casting (blade) was filled with drossy metal because drossy metal is lighter and filled the mold first.  Upper part (handle) actually looks very good.  The air hole on the handle is normal shrinkage occurring at the thickest part (either pour directly at thickest part or have a separate riser there).  Other possible cause of the air hole is a mold breakage or mold halves were not clamped hard enough(did you notice the metal leaking out at the end?) Metal should be melted as quickly as possible so getting a 2500 watt PS or better would speed things up -not sure by how much.  Do you know the composition of the aluminum, I think most people use pure aluminum without other impurities, not sure though.  Wish I could analyse further but my better half is waiting for me.

Pete and others may have questions & suggestions too.  Regarding PS. coil, electronics, etc. they will have to advise, but again, I am amazed the power you got out of it.  Granted, you could have melted that same amount of alloy using gas in about 15 minutes with forced air, but the point as far as I'm concerned you have proven that bronze casting can be done with these heaters?   
« Last Edit: July 17, 2019, 07:27:32 PM by hightemp1 »

Offline petespaco

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badpeter:
  I think you did pretty good on that pour, for a first attempt.
But---
  You need a riser that acts like a "mold sprued cup" above your sprue.
https://www.researchgate.net/figure/Sprue-cup-shape-in-casting-mold_fig1_325985131

 This gives you a reservoir for material so it can fill in as the metal starts to freeze.
Also, you need a couple of vents in the top of the mold along its length to let gases out. This will also allow the metal to flow faster to the far end of the mold and reduce the pressure so the mold is a bit less likely to leak.  Finally, when those vents start to fill and/or overflow, you know you've got  enough material.

 With something that (relatively) small, you might need as much as 30 to 40% extra material  to fill that mold sprue cup and to make up for any leaks.

I am no experienced caster, but have done some aluminum, bronze and iron casting, being coached and guided by those who are.

hightemp1: The T/C's that I often use have sheath diameters of about 1/8" and I recommend preheating them with a propane torch just before inserting them into the molten metal for small melts.

OT:   Several friends and I have been doing iron ore to wrought iron smelts on an off for the last 15 years or so.  In this case, only the slag actually melts.

Also, when making blister steel, we toss broken used glass into the crucible.  It melts and sits atop the steel, preventing oxidation.  I think this will work well for copper, but probably not for aluminum bronze, due to its low melting temperature.

---Just a shade tree mechanic, looking on,
Pete Stanaitis
---------------

Offline hightemp1

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OTH, I did not realize that aluminum bronze had such a low melting point - 1900 F and such a high pouring temp of 2300.   Perhaps the temp was not hot enough to melt all the copper and mix homogeneously so the lower part (blade) was more aluminum and upper was more copper.  The molten metal did look more orange than yellow -what color did it look like to you?  The test ingot looked kinda striped - silver spots and gold spots indicating poor mix of copper and aluminum - did you do any kind or strength or hardness test?  Induction heating is supposed to mix the metal for you - or maybe not and you just had to mix it yourself ?  Have to think about it some more.  ???

Update: Just noticed in your description that you have 12% alum and no iron - I think most aluminum bronze normally contains 1-5 percent iron -   I would think without any iron the melting and pouring temps would go down from 1900 and 2300 making it easier to cast, not sure how much though.  Badpeter, what are all your opinions:

 pouring temp(color),
weight of metal load,
manual skim/stir before pouring or not ,
did it look like there was a lot of mixing of molten metal from the induction currents(some say this mixing can look like boiling),
ingot tests,
cause of problems in handle & blade area,
did metal get hot enough for proper mixing to occur,
using more metal for pouring sprue/risers/vents,
drossy or clean metal ?
 

Forgot to mention that the video itself was very professional - congrats there too.  8) 
Can't wait for Part 2...........



« Last Edit: May 25, 2019, 06:43:36 AM by hightemp1 »

Offline badpeter

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So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Power: something is going on with this! With the same setup, every run has less and less output. I tried a quick melt yesterday, max power decreased by another 100 w. I dont know whats going on except my theory with crucible getting thinner and thinner. Imagine if I could get all 1800 w out of this! I'd be able to melt iron (and add it to my alloy). Will have to wait until new crucible from ebay, if power goes high again, I d say that be the proof. Rather inconvenient that crucibles have such a limited life. I wonder if there are any other options beside graphite... 

Offline hightemp1

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So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Power: something is going on with this! With the same setup, every run has less and less output. I tried a quick melt yesterday, max power decreased by another 100 w. I dont know whats going on except my theory with crucible getting thinner and thinner. Imagine if I could get all 1800 w out of this! I'd be able to melt iron (and add it to my alloy). Will have to wait until new crucible from ebay, if power goes high again, I d say that be the proof. Rather inconvenient that crucibles have such a limited life. I wonder if there are any other options beside graphite...

Badpeter, I would redo the mold.  When plaster casting I always had "fins" at the parting lines especially with multi-part molds - seldom had leakage (ill fitting mold) though. Looks like you have some kind of hybrid sand/plaster type of mold.  How much water do you add to the mix (very little = sand, lots = plaster), also sand requires no baking to expel the water.  I used to get a ready-made metal casting plaster in 20 lb bags from a local aluminum plaster metal casting operation - worked fine for smallish copper alloys but since plaster of paris burns at 2200 F I could never reuse the molds.  Not very familiar with sand casting mechanics though most use it today - materials are cheaper than plaster, sand is naturally porous so venting is less of an issue, and resulting castings have better physical properties than plaster castings because the metal cools faster in a sand mold. Like plaster molds, sand molds can never be reused either, AFAIK.

Found this cool Foundry Manual produced by the Navy that has a lot of good practical info - it's huge but has lots of hyper links:
https://maritime.org/doc/foundry/index.htm

Crucible question is good one, unfortunately I don't know if the quality of graphite induction crucibles varies or not, but I do know graphite is very soft and I suppose very restive, hence the high temps we are getting.  I know gas fired salamander crucibles are more durable and less "chalky" therefore maybe less susceptible to induction erosion currents.  Wonder if they conduct as much heat or not, and if they available in cylinder form. 

How many melts have you had with that crucible?
What melt size  2,3 or 4 pounds did you have? 

Approximate color and what color changes if any did you notice that occurred from copper melting to right before you pouring?
These colors are a guide only:
Light orange 1800
Yellow 1920
Light Yellow 2010
White 2190*


*2190 give or take a few degrees is where I would cast smallish silicon bronze castings and most all other bronzes - white color.  Not sure what temps to cast this hybrid Al/Cu that does not contain iron as I could find no exact info on this alloy.  Normally Al/Cu with 3% iron, small castings pour at 2400 close to cast iron temps. What difference not having 3% iron makes I can only guess that 2200 or white hot would be best pouring temps for your 88/12 alloy.

To increase convection stirring action you might want make the coil thicker,shorter, wider-spaced???  Peter said that on his 1.2 pound melt the metal was boiling.  It was not actually boiling (4644 F is boiling point of Cu) -- he may have had too much convection stirring which I believe is also not good (too much turbulence caused oxidation/dross).  Petespaco, you don't by chance remember achieving white hot temps with the bigger melts do you?

You are on the right track I think and trust one way or another you will do it.

« Last Edit: July 17, 2019, 07:38:03 PM by hightemp1 »

Offline petespaco

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Quote
Peter said that on his 1.2 pound melt the metal was boiling.  It was not actually boiling (4644 F is boiling point of Cu) -- he may have had too much convection stirring which I believe is also not good (too much turbulence caused oxidation/dross).  Petespaco, you don't by chance remember achieving white hot temps with the bigger melts do you?

Okay, let's call it "bubbling", for lack of a more acceptable term.
I didn't notice any difference in radiated color between large and small melts.  They all "bubbled" a short while after melting. 
As far as videos go, the white balance setting and circuitry of still cameras and camcorders varies so much that what you see on a "screen" is NOT predictor of what the eye is seeing.  And, of course, different eye/brain combinations "see" color differently, too.
  I hate to have to dig into lens filtering, but might just give some a try  some day, to be able to show what the melt actually looks like.
You guys might want to look at the melting points for various alloys  of aluminum.
I just looked up a binary eutectic table for aluminum, just for starters.  the eutectic of aluminum and  copper is only 1018°F, for instance.

Also, badpeter,--- I noticed a current shunt in your latest video, but I don't see any wires connected to it.  Did I miss something?  Are you reporting mains current or are you reporting current into the heater driver board?  And, are you reporting gross or net current?
 

Offline hightemp1

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I just tried melting some more copper with the 2500 watt unit.
It went well despite my making a newby mistake by putting to much cold metal into the molten copper in the crucible.
The video is here:
/>
Interestingly, the current dropped more than in previous melts as the copper first melted.  I think I have some ideas about that, which will require further testing, one of these days,  But, even at 24 gross amps, (18 amps net) and 48 volts or (864 watts),  the full  crucible sure did melt well.

Peter, Just watched your video again.  At one point you said the copper was boiling.  I think that may have been induction stirring of the metal because copper boils at 4644 degrees.  This stirring action produces what is called a meniscus where the top of the melt raises in center and lowers at crucible edges.  Sounds like there may have been  some pretty vigorous stirring, to the point of bubbling?  Stirring is good for alloying to a point, but too much, I would think, causes excessive oxidation/dross.  So maybe a lower frequency would be better for melting (longer or thicker or wider-spaced coil)?  BTW, how is your crucible holding out?

Noticed again that when you dumped in the extra copper the noise level dropped by what sounded like a factor of two.  I thought maybe you blew out one of the fans, but that would have been impossible since you have them hooked up separately.   I think you said the extra load caused that.  So some parts from the heater caused the noise, like transformers make noises for some reason, so noise is emitted from the coil, and load is like a single turn transformer that varies with load/sound somehow?  Just curious again.

Also wondering if you noticed a significant color change from your melt temp of 2000 (light yellow) to pour temp?  2190 is white hot and is where I used to pour small bronze alloy castings.



« Last Edit: May 25, 2019, 08:25:25 PM by hightemp1 »

Offline hightemp1

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You guys might want to look at the melting points for various alloys  of aluminum.
I just looked up a binary eutectic table for aluminum, just for starters.  the eutectic of aluminum and  copper is only 1018°F, for instance.

Also, badpeter,--- I noticed a current shunt in your latest video, but I don't see any wires connected to it.  Did I miss something?  Are you reporting mains current or are you reporting current into the heater driver board?  And, are you reporting gross or net current?

Ok, that is a low eutectic so I take from that nice tidbit of info, that maybe proper mixing took place shortly after everything melted and melting point was far lower than I thought.  So evidently, there is a huge gap between melt temp 1100 and possible target pouring temp of 2200.  Should have been a rainbow of color changes from melt to pour?

Good question on the amps - no clue here but hope to know.

Update: Badpeter, not sure on alloying, but I think you are supposed to melt the metal with the higher melting point first then add lower melting point metal???  Also, I think you should make some ingots of Al/Cu first, whatever size(s) best fits in your crucible.  For smaller melts, you could pour a load into water producing Al/Cu shot.
« Last Edit: May 26, 2019, 01:32:22 AM by hightemp1 »

Offline badpeter

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Molds: I use 50/50 plaster / sand mix, also 2 plasters for 1 water. Found information suggests that pure plaster cannot stand heat shock very well so sand makes it softer (although weaker) so it doesnt crack. Oven treatment is super neccessary so the mould doesn't explode on contact with hot metal from steam forming throughout. (it dries for couple days too before that but it is not enough)
Pure sand casting doesnt have this issue, but it is a chore to work with. I ve used it in the past for my other propane vids.
Transformer would hum only slighlty louder on overload. The massive fan under it drowns any possible sounds. It is not a part of the system in any way and connects separately to mains power.
The shunt does nothing at the moment. Crappy ebay meter burnt out and i left the shunt until I get a new one. As I explained in the description, to measure DC current just divide power (blue meter) by DC voltage (orange multimeter) (aka 700w/46v=15a dc.) So I have about 15 amps dc going in the induction unit. It can also be calculated the long way by utilizing turn ratios on transformer and ac current on mains, but thats the long way.
The hot metal is yellow to white, and is quite bright. It even shine through thick insulation. It loses brighness quickly when crucible is extracted.

So basically now I am going to wait until i get another different crucible from ebay (also ammeter). If i see increased power with new crucible, it will be conclusive that graphite is responsible for the most power draw. 
Meanwhile I may cut the existing crucible in half and plug a small coil, see how that goes. 
 

Offline hightemp1

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Molds: I use 50/50 plaster / sand mix, also 2 plasters for 1 water. Found information suggests that pure plaster cannot stand heat shock very well so sand makes it softer (although weaker) so it doesnt crack. Oven treatment is super neccessary so the mould doesn't explode on contact with hot metal from steam forming throughout. (it dries for couple days too before that but it is not enough)
Pure sand casting doesnt have this issue, but it is a chore to work with. I ve used it in the past for my other propane vids.
Transformer would hum only slighlty louder on overload. The massive fan under it drowns any possible sounds. It is not a part of the system in any way and connects separately to mains power.
The shunt does nothing at the moment. Crappy ebay meter burnt out and i left the shunt until I get a new one. As I explained in the description, to measure DC current just divide power (blue meter) by DC voltage (orange multimeter) (aka 700w/46v=15a dc.) So I have about 15 amps dc going in the induction unit. It can also be calculated the long way by utilizing turn ratios on transformer and ac current on mains, but thats the long way.
The hot metal is yellow to white, and is quite bright. It even shine through thick insulation. It loses brightness quickly when crucible is extracted.

So basically now I am going to wait until i get another different crucible from ebay (also ammeter). If i see increased power with new crucible, it will be conclusive that graphite is responsible for the most power draw. 
Meanwhile I may cut the existing crucible in half and plug a small coil, see how that goes.

Using plaster, OK.  If you cut 2 keys in each half before pouring the other half you should not have alignment problems. For a two-part mold it seamed like I always did 3 halves, the first half was disposed of and only used to scrape a good parting line to limit parting flash lines.  Not sure what ration of plaster to sand I was using and not sure of other additives they used, but the molds were very strong after air dried and still pretty strong when bone dry though much lighter.  You can skip the air drying and just oven dry vented between 300 and 450 timing it such that molds are 450 all the way through when ready to pour.  Yes, they must be bone dry - witness the king of random video - he pours into a wet plaster mold and it sounds like popcorn popping. :o
 
Yellow to white so maybe between 2000 and 2100 - Nice.  Not sure on your alloy but that may or may not have been the correct pouring temp. Eye protection is necessary somewhere thereabouts?

I just paid $50 for a 3000w PS though I have no clue if it will work.  It will be four 750w server PS's wired in series.
/>Would like to hook up so that input power is switchable between 12,24,36 &48 volts giving at least some sort of way to adjust power for whatever that is worth. Basically I want more power for melting, not ways to adjust to lower power.  Adjustable may have some unforeseen use, but not still sure if I can get it running stably with all four in series.  I have seen similar HP power supplies with 1200w @ 12v so if you put 4 in series you'd get 4800 watts, maybe useful somewhere down the road.  Or maybe 2 of these 3000w supplies everyone is using could also be combined in some way giving 6000 watts - now were talking!!  Supposedly, they work in series fairly easily, though Mads says in the video that large smoothing caps may be required to balance things out?  I guess I'll find out one way or another.  Also, no clue clue if hooking em up in parallel if possible?

That is a big crucible so maybe that's a good idea.  May have some life yet for testing at least, but be very careful with worn crucibles, they are fragile enough and even more so when 2000 degrees plus. Not sure what happens when a pot of molten metal exposes a coil but know it will burn right through most everything else.
« Last Edit: May 26, 2019, 12:38:42 AM by hightemp1 »

Offline petespaco

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hightemp1"
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Noticed again that when you dumped in the extra copper the noise level dropped by what sounded like a factor of two.
The change in noise came from the power supply.  When the current increases to some specific point, the fan's speed is increasesd and vise-versa when current goes down.  And that's what you heard.   My  comment at that time wasn't all that accurate, was it?

Nailing down colors to exact temperatures:
  I am not sure that all metals glow with the same colors at the same temperatures. Some googling does not help to clear this up.
But,  even the amount of backlight can have a huge effect on any particular metal.
That's why a blacksmith shop is often dimly lit.  When I am demonstrating the heat treating of fire strikers to the public, outdoors, it's tough to see the curie point, unless I sorta hide the part under the forge.  Even then, I miss it occasionally.
But just to give you an extreme example. when forging titanium, It gets unbelievably white-white-white in a short period of time.  I have never seen any other metal do that even when forge welding or watching them pour 15 or 20 tons of steel.  And, again, people have widely varying color perception abilities.
  I suppose I better get back out there with a thermocouple.  I am also going  to fool around with home made camera filters, but don't hold your breath.

Offline hightemp1

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Noticed again that when you dumped in the extra copper the noise level dropped by what sounded like a factor of two.
The change in noise came from the power supply.  When the current increases to some specific point, the fan's speed is increasesd and vise-versa when current goes down.  And that's what you heard.   My  comment at that time wasn't all that accurate, was it?


Noise Level:  Your comment was plenty accurate, I'm just, you could say "electrically challenged".

TC & Filters: screw the TC and Filters -- I'd just like to know what you see, with proper eye protection, when you melt a pound of copper for half an hour, but I expect, and rightly so, to not be holding my breath.    As I said before, I am in no hurry at all and I am just amazed how gracious you are with sharing your time and knowledge.
« Last Edit: May 26, 2019, 01:27:31 AM by hightemp1 »

Offline hightemp1

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So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Here are some links from that foundry manual on curing casting defects:
https://maritime.org/doc/foundry/part3.htm#pg149
https://maritime.org/doc/foundry/pg157.htm
https://maritime.org/doc/foundry/pg159.htm
https://maritime.org/doc/foundry/pg161.htm
https://maritime.org/doc/foundry/pg163.htm
https://maritime.org/doc/foundry/pg165.htm
https://maritime.org/doc/foundry/pg167.htm
https://maritime.org/doc/foundry/pg169.htm
https://maritime.org/doc/foundry/pg171.htm

The color effect is such that some metals dominate color much more easily, I don't understand that either.

By weight, I think you want 88 percent Cu and 12 percent Al

 A primitive hardness test is just nailing it with a screwdriver and comparing marks with soft copper ingot or other metals you have lying around. Stength is putting it in a vice, if it does not brake after a few good wacks, your good to go.  Bending without weakening may be ok depending on use - just means it is malleable.


« Last Edit: May 26, 2019, 03:08:17 AM by hightemp1 »

Offline T3sl4co1l

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FYI, gypsum (the active ingredient in plaster) dehydrates in two stages: first to hemihydrite around 170°C, and then to anhydrite around 700°C.

Actually, looking it up, it seems it goes straight to anhydrite around 170°C, at least that's what the text claims.  But the amount lost is just less than the total.  But more than hemihydrite.  It's like it's... quintahydrite, as it were (i.e., 1/5th of an H2O). The final total is plausibly correct (the exact figure is 20.93% water in stoichiometric gypsum).  So now I really wonder if this paper is missing something, or if it has to do with material purity (it was only "90% pure"), or if no one really knew the truth about gypsum dehydration and just kind of went along with it all these years because, who cares it's just gypsum, right?

Anyways-- I've never had problems when heating it to dull red hot.  But I've always seen exactly the bubbling you describe: not violent, but still too much for the material porosity and venting to handle without leaving bubbles.

FWIW, I usually use 1:1 to 2:1 sand (fine or sifted sand preferred) and plaster, for simple casting investment.

Protip: when the metal has fully solidified, drop the mold in a bucket of water.  The plaster will spall off, freeing the casting in no time. :)

Plaster-based investment is also reusable, just dehydrate in the oven to get back to the active hemihydrite form (hardens when water is added).  Needs to be smashed up finely, of course.

Tim

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