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Oh, wow, what a bummer.

 

So weird...  I'd expect a slightly slow pour to maybe affect the casting, but not make the whole melt freeze in the crucible!  How slow were you pouring anyhow?  How much do you trust your pyrometer?  I'm wondering if maybe the melt just wasn't as hot as you thought it was.  I'm out of my depth when it comes to this small stuff though.

 

Might be worth posting about this one on the casting forum to see if the lost wax/vac assist casting gurus there have any insight.  Or maybe Julia will pop in here with some suggestions.

 

Kang

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7 minutes ago, Kang said:

Oh, wow, what a bummer.

 

So weird...  I'd expect a slightly slow pour to maybe affect the casting, but not make the whole melt freeze in the crucible!  How slow were you pouring anyhow?  How much do you trust your pyrometer?  I'm wondering if maybe the melt just wasn't as hot as you thought it was.  I'm out of my depth when it comes to this small stuff though.

 

Might be worth posting about this one on the casting forum to see if the lost wax/vac assist casting gurus there have any insight.  Or maybe Julia will pop in here with some suggestions.

 

Kang

 

The electromelt is new.  I have no way of testing the pyrometer in it, though the bronze melted exactly when it was supposed to.

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Hi,

 

Sorry to hear about the cast gone bad. Have little knowledge about the electromelts, except that I'd like to have one :)

 

Like you said yourself, It looks like the metal was too cold: we usually overheat it a little, because once you're ready to pour and especially with precious metals, at the beginning you tend to be more careful and try to pour slowly, which makes it to cool even more. (By the way, it will become easier as you'll get rid of the idea of pouring silver...it's just the mental image of pouring something expensive that gets on the way. I had that at the beginning and having silver dust at my clothes ended to this atom search and could spent quite some time gathering every little bit I found...now I just pretty much dust my clothes like it's wood dust. Same goes with the casts, now it's just like bronze, but the color is different :D

 

I also like to use long cylinders and long trees for all of the casts, even if there's not too many items to be cast. I'll lose some investment in the process, but the casts turn out better because the poured material gathers speed along the way and the fill rate is much better, because at the end of the tree the velocity forces the material into the small cavities better than anything else.

 

Was the crucible coated before you started to melt the silver? Was it a new one? I've had a cast go nasty, because the crucible had too much sediment from previous casts: the metal didn't melt at all, it remained in this weird gummy state.

 

Anyway, the pink stuff is copper, I normally don't do anything about it. It might look like it's a big portion of the copper content, but it's not. It usually comes off by scrubbing with a brass brush. It would only make a difference if you'd keep on melting the same item over and over again. The copper would eventually burn away.

 

 

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38 minutes ago, Julia said:

Hi,

 

Sorry to hear about the cast gone bad. Have little knowledge about the electromelts, except that I'd like to have one :)

 

Like you said yourself, It looks like the metal was too cold: we usually overheat it a little, because once you're ready to pour and especially with precious metals, at the beginning you tend to be more careful and try to pour slowly, which makes it to cool even more. (By the way, it will become easier as you'll get rid of the idea of pouring silver...it's just the mental image of pouring something expensive that gets on the way. I had that at the beginning and having silver dust at my clothes ended to this atom search and could spent quite some time gathering every little bit I found...now I just pretty much dust my clothes like it's wood dust. Same goes with the casts, now it's just like bronze, but the color is different :D

 

I also like to use long cylinders and long trees for all of the casts, even if there's not too many items to be cast. I'll lose some investment in the process, but the casts turn out better because the poured material gathers speed along the way and the fill rate is much better, because at the end of the tree the velocity forces the material into the small cavities better than anything else.

 

Was the crucible coated before you started to melt the silver? Was it a new one? I've had a cast go nasty, because the crucible had too much sediment from previous casts: the metal didn't melt at all, it remained in this weird gummy state.

 

Anyway, the pink stuff is copper, I normally don't do anything about it. It might look like it's a big portion of the copper content, but it's not. It usually comes off by scrubbing with a brass brush. It would only make a difference if you'd keep on melting the same item over and over again. The copper would eventually burn away.

 

 

 

Thanks Julia.  That's what I needed to hear.

 

Oh, and I misspoke when I called it an Electro-Melt. I couldn't afford the Kerr.  Mine is actually a QuikMelt Tabletop Deluxe (which was about 1/2 the price of the Kerr and got decent reviews):

 

quikmelt_chrome-300x300.jpg

 

My crucibles are new.  This one I reserve for silver and it was my first use of it. It is graphite and looks similar to this:

 

graphite-crucible-250x250.jpg

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Awesome! I can't afford to buy a Kerr either, can only dream and drool ^_^ I've been looking for a used electric melting furnace, but people tend to ask for a same price as what you'd get by ordering brand new from China...

 

Those graphite crucibles don't need to be seasoned, right? I've only heard about tempering to make them last longer.

Do you have something to swirl the melted metal around to make sure it has liquefied completely? Like a charcoal stick or something?

 

~Julia

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28 minutes ago, Julia said:

Awesome! I can't afford to buy a Kerr either, can only dream and drool ^_^ I've been looking for a used electric melting furnace, but people tend to ask for a same price as what you'd get by ordering brand new from China...

 

Those graphite crucibles don't need to be seasoned, right? I've only heard about tempering to make them last longer.

Do you have something to swirl the melted metal around to make sure it has liquefied completely? Like a charcoal stick or something?

 

~Julia

 

I've only heated it up a few times, but so far I really like the QuikMelt.  It have the bronze liquid in about 10 minutes.  I think the silver would have been too, but I think I just started out with too low a temp.

 

According the MFG, you just need to heat them once first, then you should be good.  I use a graphite rod for stirring and skimming; same material as the crucible.

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Failed again. ::(:

 

IMG_E2957.JPG.66adac2361b54f4c7d7da7ef30d0317c.JPG

 

 

The pour seemed to go well.  The problem is likely one of the following causes:

 

  1. I didn't have the silver hot enough.  Sure it was melted and runny, but had it really come up to pour temp?  I think I rushed it.
  2. The mold wasn't fully burnt out.  I don't think this is the case, but I can add an extra 30 min on the burn out as a precaution.
  3. I suck at spruing the rings. From everything I read, the way I did them should have worked.  That said, I may try something different next time.
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Hi and ack! That's a real bummer and real odd is the way how the models are all only partly filled. I don't see any porosity or shrinkage due to temperature, the parts that has been filled looks solid, but there are a few things with the sprues that I need to take a closer look at. Looks like a flow issue. I'm a bit in a hurry at the moment, but I'll take a closer look of the model and sprues later today. What's your final kiln temperature and do you let the mold temperature set before pouring?

 

~Julia

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As you know, all of my vacuum/investment casting lore is merely theoretical as I have only worked with sand molds and larger scale castings in bronze and aluminum.  So I can only guess... that said, my money is on either the melt or the mold having been too cold at pouring time.   OR... is there any chance you maybe forgot to turn on the vacuum pump?  ::D:  Looking forward to Julia's expert diagnosis of the spruing!

 

Insufficient burnout would have meant there was still water chemically bound up in the investment, which would have boiled out when the metal hit the mold and turned your trunk into a hideous swiss-cheezy hellscape.  The sprue would have shown a lot of scary bubbling and spitting during the pour in that case, at least as I understand it.  If that did not happen, IMO you can probably rule that out (though see sentence #1 in this post).

 

Got any pix of the wax tree before you invested it?  May help if you could hack off a branch or two from the cast tree (the way it came out it really does look a fair bit like a tree) and show us some close-ups of the connections...

 

Anyhow, you'll get it next time!  Good luck,

 

Kang

 

 

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4 hours ago, Julia said:

Hi and ack! That's a real bummer and real odd is the way how the models are all only partly filled. I don't see any porosity or shrinkage due to temperature, the parts that has been filled looks solid, but there are a few things with the sprues that I need to take a closer look at. Looks like a flow issue. I'm a bit in a hurry at the moment, but I'll take a closer look of the model and sprues later today. What's your final kiln temperature and do you let the mold temperature set before pouring?

 

~Julia

 

Thanks @Julia and @Kang.

 

My sprues were 2 point connections, that I think were just too thin and long. The metal never got to the top half of the rings.

 

IMG_E2957.JPG.a8a202a83ca3cc985e86687572a4aa35.JPG IMG_E2976.JPG.cd5ad5724b2afcaf806b1752f9c7682d.JPG

 

My kiln regimen was as follows:

 

Stage 1: 350 deg, rate of change 500 deg/hr, hold 1 hour; this was to do the initial wax melt out.  I collect that in a tray and remove it after the hour hold.

Stage 2: 1350 deg, rate of change 500 deg/hour, hold 1.5 hours

Stage 3: 950 deg, rate of change 450 deg/hour, hold 3 hours

 

The whole burnout from starting the kiln to pouring the silver was about 7 hours.

 

I set stage 3 to 3 hours so I have a hot flask when I go to cast.  I let it sit in the kiln at 950 for the first hour, then I start melting the silver and cast when the silver is ready.

 

My flask is 6 inches tall and 4 inches in diameter, perforated.

 

I definitely did have the vacuum on and to full pressure. 

 

Silver Melt Kiln Temp: 1780 deg

 

Things I am thinking of doing to fix the issue for the next time:

  • Increase the Stage 2 hold to 2 hours, just to be certain that the wax is fully vaporized.  One reference I read said that the round ends I got on my cast can be caused by insufficient air escape caused by a film of un-vaporized wax in the mold.  The water may have been gone from the plaster, but maybe not everything.
  • Change my sprue attachments and number from 2 long and thin sprues per ring to 4 short sprues, attached equidistant on the inside of each ring, thereby delivering silver to 4 separate sections of each ring at the same time. I am even thinking of trying it with the ring encircling (but not touching) the center wax column with the 4 sprues being very short at that point. Like this:

 

IMG_E2975.JPG.272d1d52fcf127296ab7db3e71b86354.JPG

 

 

  • Finally.  I'm going to wait longer once my silver melts.  This time I cast almost as soon as it was runny.  I bet that it wasn't really up to the pour temperature and was too close to the solidus temp, thus it cooled too quickly in the thin rings.  I honestly think that this was the true cause of the failure.  To avoid excitement this time, I'm going to set a timer to wait once it melts.  How long do you suppose I should wait? 5 minutes? 10?
  • Do you think 950 deg is hot enough for the flask temperature?  Should I go up to 1000 deg? My reference says 900 to 1000 deg for sterling.

 

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17 minutes ago, TaleSpinner said:
  • Finally.  I'm going to wait longer once my silver melts.  This time I cast almost as soom as it was runny.  I bet that it wasn't really up to the pour temperature and was too close to the solidus temp, thus it cooled too quickly in the thin rings.  I honestly think that this was the true cause of the failure.  To avoid excitement this time, I'm going to set a timer to wait once it melts.  How long do you suppose I should wait? 5 minutes? 10?

 

Well that was one of my guesses, so I'll double down on the culprit being a cold melt.  A pyrometer that can be dipped into the molten metal is the best way to be sure you're up to a specific temperature.

 

My setup is much different than yours, but I've had good luck just cooking the melt for an extra minute or two (about the time it would take me to doff gloves and set up a timer probably, lol) when I've had to try again on thin aluminum castings that failed to fill.  No idea how well that timing would translate to your setup though, since I work with larger amounts of molten metal (mostly aluminum) in a fuel-fired furnace rather than an electric.  Also I do not have a real pyrometer to begin with, I use the hot rod dip test to gauge pouring temperature. (like it sounds - you dip a preheated steel rod into the melt.  If it pulls out clean, it's "normal" pouring temperature, so I wait an extra minute or so if it is a thin casting, otherwise I flux, skim, and pour right then.)

 

The hot rod dip test is obviously not very accurate and false readings do occur; one day I'll smarten up and spend the $50 on parts to build a real pyrometer that I can dip into the melt to get its actual temperature.  But it's still better than nothing and has worked well for me for casting bronze and aluminum on most occasions.  I use it every time I cast anything, even when it's not a casting with thin sections.

 

Kang

 

 

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10 minutes ago, Kang said:

 

 

Well that was one of my guesses, so I'll double down on the culprit being a cold melt.  A pyrometer that can be dipped into the molten metal is the best way to be sure you're up to a specific temperature.

 

My setup is much different than yours, but I've had good luck just cooking the melt for an extra minute or two (about the time it would take me to doff gloves and set up a timer probably, lol) when I've had to try again on thin aluminum castings that failed to fill.  No idea how well that timing would translate to your setup though, since I work with larger amounts of molten metal (mostly aluminum) in a fuel-fired furnace rather than an electric.  Also I do not have a real pyrometer to begin with, I use the hot rod dip test to gauge pouring temperature. (like it sounds - you dip a preheated steel rod into the melt.  If it pulls out clean, it's "normal" pouring temperature, so I wait an extra minute or so if it is a thin casting, otherwise I flux, skim, and pour right then.)

 

The hot rod dip test is obviously not very accurate and false readings do occur; one day I'll smarten up and spend the $50 on parts to build a real pyrometer that I can dip into the melt to get its actual temperature.  But it's still better than nothing and has worked well for me for casting bronze and aluminum on most occasions.  I use it every time I cast anything, even when it's not a casting with thin sections.

 

Kang

 

 

 

I think maybe I will get a pyrometer.  Not sure I'd build one if I were you.  On Amazon right now you can buy probe versions for $20 to $50 and a no touch laser model for $65.

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Yeah, in your situation, being in business and all, I'd probably look for a ready made option as you suggest; time is money as they say, and I suspect you'd probably rather be spending yours mashing putty.  ::D:  My situation is a little different since at this point in my life, casting metal is 100% just for fun, and a big part of that fun is building my own gear when possible.

 

I'd avoid laser pyrometers for measuring melt temp; they not only apparently cost a little more, but have frequently been said not to be particularly suitable for such applications, due to the reflective nature of the surface of the melt as well as the heat radiating from the furnace walls - hotter than the melt itself, causing confused readings.   For getting a quick temp reading on a burned out mold you're about to pour though?  Should be ideal for that sort of thing, assuming it's a type that'll read that high. 

 

The probe type is useful for dipping in molten metal to get a temp reading, but even the kind you buy premade may need something like a wand to hold the probe and a few (consumable) graphite sheaths to protect the probe from shorting out/corroding when repeatedly dipped in the melt, if the ones you mentioned don't already come with all that.  I was reading just this morning about one new who is guy to the foundry hobby and did not know any better, who dipped an unsheathed (purchased) TC probe in molten aluminum, destroying it on its first use...  I haven't fully researched all the details but I know there are several flavours of probes and thermocouples suitable for different temperature ranges and applications.  I believe the K type thermocouples are most appropriate for (nonferrous) foundry work, but there's a lot more than just that to know, and I'm sure I'd need to read up on it all to make an informed decision. 

 

I'll certainly make sure to check out various options in the price range you mention before pulling the trigger on ordering any components, which I'm in no real rush to do anyhow.  But like I said, I'm in only this for kicks: the diy equipment builds I get into are close to half the fun, and my projects don't come with deadlines.  Or profit margins for that matter. 

 

Here's a couple of links to cheap pyrometer build instructions other backyard metal casting hobbyists have thoroughly researched and posted, which may be useful to you even if you buy one ready made.  The first one actually covers pyrometer builds that use both premade (easier) and homemade (cheaper) thermocouples.  There is some good background info there that may be helpful to know when you're shopping around.  Things like how you can extend your probe's lifespan by preheating its the tip in the furnace before dipping in order to minimize the time it needs to stay submerged in the harsh molten metal environment.  Or how to fabricate a wand to hold your probe when dipping it, or tips for drilling out cheap graphite gouging rods for use as protective sheaths, and so on. 

 

http://www.alloyavenue.com/vb/showthread.php?11337-Original-Post-of-How-to-Make-and-Use-a-Pyrometer

http://forums.thehomefoundry.org/index.php?threads/cheap-pyrometer-parts-list.33/

 

Hope this is helpful,

 

Kang

 

 

 

 

 

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Hi,

like I said before, I do not have an electrical kiln for melting, so I asked around and here's what I got:  heat the metal at least 100F over the desired temperature, that way you'll ensure that the metal has melted completely. So in this case it'll be around 1880 deg, 1900 degrees also works and 2000 is a max before the metal is too hot to cause problems.

 

Your burnout temperature is ok,  950 sounds about right for a casting temperature, 1000 is for finer designs: filigrees and such. I've heard that it's recommended to heat the flask 75-100F hotter when using a vacuum, but I'm yet to test it myself.

 

There are two things that can cause partly filled casts: temperature and sprues. Like Kang said earlier, a failed burnout will leave evidence, the surface is like bad case of acne or a side of a moon with all those little craters and such. If it's too hot: it'll do craters, tiny holes, cavities, plus this stuff that looks like sand and if too cold, the metal doesn't usually even reach the sprues and looks kind of sluggish and sad. You don't have any of that, so my bet is in the sprues. With small objects like these, make them as short, even and straight as possible. Try to avoid curves, bumps and too much of tapering, because if the sprue gets too thin too fast, that kind of shape will act as a nozzle and it will sort of spray the metal around instead of moving it forward. The thickness should be around the same as the model's. If the sprue is too thick, I've noticed that not only does it slow the metal down, but it will act as a storage unit for heat and that'll cause porosity on the ring shank. One last thing is that I see that you're using a secondary sprue. Try to get it to fill at the same time as the main one; now what happened is that the main sprue started to fill ok, but the flow was suddenly cut by a secondary sprue which started to fill at a slightly different time than the main branch and without a good momentum, it solidified. Just a thought :)

 

To be continued tomorrow,

G'night!

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On Friday and Saturday, I cast new waxes and put them onto a wax tree.  I tried experimenting with one around the center column.  The rest I did more traditionally, but with short, stocky sprues, all about the same length and thickness.

 

IMG_E2977.JPG.7b322d09c7c876ecb25d44fc4cfade31.JPG

 

 

Yesterday, I invested it and did the burnout and casting.  I did not change my burnout procedure, but when I melted the silver, I waited a whole 10 minutes after it melted for it to come up to temperature.  Sterling silver melts at 1640 deg F.  Last time ,I cast almost as soon as it was liquid, so I doubt it was much more than 1700 deg F.  This time with the 10 minute timer, It likely got all the way up to the 1780 I had the melt furnace set at.

 

Anyway...IT WORKED!!!!!

 

IMG_E2990.thumb.JPG.e8c71b57a18d3001be34a8696e4a98fd.JPGIMG_E2987.JPG.30b61ee9a2ab6dadbf834513d32ee7c9.JPG

 

4 of the 5 filled perfectly.  The one I experimented with failed to fill, but the rest are great.  The failure was the ring I was making for myself, LOL. There are a couple of bubbles on the top one, but none obscure details and can be easily removed.

 

I pickled them and snipped the rings off of the sprue.  Now begins the task of filing, finishing, and polishing them.

 

IMG_E2992.JPG.74a9cbc67284b1187001320018b61371.JPG

 

 

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