Instructables
Picture of microwave smelter
03.jpg

Remember how your parents used to say "don't put metal in the microwave"? Prepare to throw that cardinal nugget of advice straight out the window because we're going to do just that. We're going to use a domestic, unmodified microwave to melt metal! 

I happened upon an article in an old Popular Science magazine (c.2003) about microwave smelting and thought it was so awesome I had to try it for myself. So, just what happens when you try to smelt metal in the microwave? Turns out, it works!

Also, if you do it wrong you end up with a fiery microwave disaster:
Want to see how it's not done? Let's go!
 
Remove these adsRemove these ads by Signing Up

Step 1: Tools + materials

Picture of tools + materials

tools:
  • oven mitts
  • safety goggles + face shield
  • metal tongs / grips
  • old microwave
.
materials:
  • stainless steel measuring cup (crucible)
  • silicon-carbide block (details in step 2)
  • ceramic casserole dish / fire bricks
  • tin / lead / silver solder (details in step 2)
  • mold for metal ingots (pancake mold)


Step 2: Science + disclaimer

How does it work?
In it's most basic form the microwave is being used to generate heat to an element which then melts the metal, while not arcing the magnetron to the metal to be melted.

The microwave I used was an 850W microwave (model: GE 3850W3W081A), I used regular bricks to build the hearth to keep the crucible and a silicon-carbide material as the heating element (I also used building insulation to try and keep the heat directed inwards, a terrible terrible mistake). The insulation was an addition I incorporated after reading another smelting article and attempting to blend methods to achieve more effiecient results. However I didn't anticipate the reactions of all the elements together in my microwave. The outcome was a success, and a failure.

Next, I had to choose metals that I were readily available to anybody and wold have a low enough melting point to be melted in a regular microwave. For this experiment I chose 2 types of common plumbing solder, 50/50 blend of tin/lead and silver solder, having a melting point of 180-190 °C (360-370 °F) and 450 °C (840 °F) respectively. There's other metals that could be smelted this way, like zinc (and plutonium?). Maybe you can find other metals with low melting points, here's a good place to start.

To help focus the energy of the microwave I used silicon-carbide, which is a microwave susceptor: meaning it absorbs microwave energy and turns it into heat energy. Silicon-carbide can be found in block-knife sharpeners, but I found they were too expensive. Instead, I used a silicone-carbide rubbing stone for under $14 found at the hardware store.

The crucible I used was metal with a higher melting point that the melting I was attempting to smelt. My crucible was a regular stainless steel measuring cup (melting point of 1510°C [2750°F])

To recap:
Microwave: 850W
Tin/lead solder: 180-190 °C (360-370 °F)
Silver solder: 450 °C (840 °F)
Microwave susceptor: silicon-carbide rubbing stone

Step 3: Safety (seriously)

Smelting in a microwave isn't a bad idea, but does require some precautions to be safe.

It should go without saying that molten metal, hot bricks, radiation and fire can cause harm you you and everything around you., Be aware of your surroundings and always use appropriate safety measures when dealing with hazardous methods and materials. 

Here's my setup:
  • Face shield
  • Eye protection
  • Oven mitt
  • Metal tongs/grips
  • Fire extinguisher
  • Bucket of water
  • Outside environment
The water bucket shown here was our emergency backup. As you can see from the video we ended up using it. Always unplug your microwave and other electrical equipment before introducing any water. Electrical equipment and water do not mix!

Step 4: Build hearth

The Popular Science article I read mentioned using a casserole dish for the hearth, but then went on to say that the glass top of the dish cracked due to thermal stress after being heated then removed from the microwave. Not wanting to have shattered glass in my face I opted to skip this step and go right for brick as the hearth.

Knowing that I would be reaching tempertures of  500°C (900°F), I wanted something that could handle the heat stress and fracture if it failed and not splinter. I chose brick. There's a specific dense brick used in fireplaces called fire-brick that would have been ideal, however I used think regular bricks and no fractures occurred in over 40 minutes of heating. I also (erroneously) added an additional layer or insulation to the inside of the brick to try and create more heat in the hearth. Do not do this! Brick on it's own will suffice.

Stack your bricks into a simple house-like configuration. Leaving anough room in the middle to have your silicon-carbide slab to sit on teh base of your brick-house with the stainless steel crucible on top. Lay bricks over roof of brick house.

Step 5: Prepare metal and crucible

Picture of prepare metal and crucible
12.jpg
14.jpg
I used a stainless steel measuring cup for my crucible, which has a meting point of 1510°C (2750°F)
 I knew that I was only going to reach about 400/900, so using this as my crucible was a fine choice. Glass would have also worked, as it melts at around the same point as stainless steel (and higher, depending on the type of glass).

Find your metals and coil or snip into your crucible.

Step 6: Timing

Picture of timing
The wattage of your microwave will dictate the length of time your smelter will need to be timed for. It's smart to start with a short time duration to ensure your hearth and insulation are assembled correctly, then work your way up from there. The silicon-carbide heating slab will stay warm for a long time, so minimal loss occurs if you open the microwave to check on your smelter.

Here's the data from my 850W microwave:
  • 50/50 lead/tin
    • 5 minutes - mostly melted
    • 10 minutes - completely molten
  • Silver
    • 15 minutes - completely molten

Step 7: Pour ingots

Picture of pour ingots
04.jpg
00.jpg
If all goes well, after a few minutes you'll notice that your crucible has heated up and smelted the metal. Grab your crucible with tongs and pour it into your mold. I used a cast aluminum pancake mold found at a local houseware store. The melting point of cast aluminum is 660.32 °C (1220.58 °F), well above the molten temperature of the lead/tin and silver solder.

Pour molten metal into mold and allow to cool, then gently tap reverse side of mold to release the cast ingot.

Step 8: How not to

You've watched the video, you saw the inferno. That was caused by double-whammy of not paying attention and using inappropriate materials being used. Using insulation is sound, provided it's rated to be used in high-heat situations. In my effort to keep things accessible and open I chose to use a rigid-type foam building insulation. Bad idea. The heat from the crucible in combination with the duration I had set caused a corner to the foam to ignite. I shut off the microwave and waited to the flame to die out, but it was only getting worse. Fearing a backdraft if I opened the microwave door, I risked it anyway. Yup, huge fireball.


We were able to get our cameras running just when the flames died down from reentry temperature to just immolation inferno. 
The lesson here is to use just bricks to create the hearth and wait the amount of time required to to the job effectively, without trying to accelerate the process with insulation.

Science can be messy and dangerous, so be safe and have fun!
1-40 of 165Next »
irongus11 months ago
this is not smelting. its just melting metal and u do not need the silicon carbide susceptors to create the heat. arcing in the solder material would provide heat. smelting as far as I understand it is the reduction of ore...iron oxide or other ore bearing material into metal. its a chemical process. heating up ore will not reduce it to metal. I have safely melted steel in my microwave without external suceptors to create the heat and there are some good patents in the uspto that describe microwave remelting techniques it is a a good first try.
ehhdean1 year ago
Any idea what temperature it gets up to? I'm looking at melting down some bismuth.
well silver melts around 1,762 F. and bismuth around 520. i think you'll be good. ;D
kelseymh1 year ago
You do not want to use water to douse the sort of fire you caused in your microwave!
Instead of the bucket of water, keep a bucket of dry sand on hand. A small 1-gallon bucket like you have will have enough sand to fill the microwave, and will be light enough (about two to three times as heavy as the water) to pick up and throw.

You don't want to have to remember to unplug the burning oven before using the water -- stop the flames FIRST! When you forget, you'll have bigger problems on your hands. Also, throwing water on molten metal is going to generate superheated steam and droplets of boiling water coming back into your face.

Once you have the flames suppressed, you can unplug the unit, or throw the breaker, or whatever you need to do to finish cleaning up the mess.
mikeasaurus (author)  kelseymh1 year ago
Good safety tips.
The video doesn't show the full dangerous hilarity of the unprepared attempt: The microwave was unplugged after the insulation caught fire and there was a good moment of panic when we couldn't decide to close the door to starve the fire, or open it to extinguish. We left it closed, and the fire started melting the microwave, opening the door made it worse and the fire extinguisher had no pressure (dial indicated it was full). The water was only meant to be used as a last resort, which quickly became our only resort. I had my doubts that the microwave would get hot enough to work, and didn't prepare adequately.

I think I covered safety well enough in written form, but people draw all kinds of conclusions from watching the video without reading the narrative.
Never forget the last words of many a Darwin Award winner, "Hey, guys! Watch this!"

:-D
mikeasaurus (author)  kelseymh1 year ago
With borderline projects like this, I'm sure my name will make that list someday. At least now I know what I'll say!
Either that or, "Hey bro, hold my beer..."
anasdad1 year ago
Very nice !!! But, a simple warning from a paranoid fireman... Always have a good fire extinguisher on hand, the bucket of water worked, but could have electrocuted someone. Even unplugged, there's a threat of stored electricity hurting you.
Ken

PS: I will be trying this... Thanks!
Hilarious. You got my vote.
dlivings3 years ago
Funny to read all the scaredy cat comments. People are so misled. Actually water is not very conductive nor dangerous as folks think around water. When you add soap / or salt to it , it becomes conductive. I saw mythbuster stooges tell everyone that a toaster in a bathtub is lethal. I will jump into a bathtub with a toaster and smile all the while and jump out unphased, (because I know not to touch any metal with my hands) It takes 2 poles to be shocked.. When people die, is when they have their fingers wrapped around a metal conductor. The electricity contracts your muscles and makes it impossible to let go. If electricity has caused your house to catch fire, you'd better get some water on it! If you're scared, then put on a dress. Also, you can never put FOIL into a microwave. nor the plates with gold painted fancywork. As a rule of thumb, you should not put silverware in the micro unless there is 1& 2/3 more mass of water. And never with the silverware against the side of it, because it can create a pocket that traps microwaves and will spark which burns holes in the paint.
finton dlivings2 years ago
Tee hee. "I will jump into a bathtub with a toaster ... and jump out unphased". You mean "unfazed", but "unphased" is an apt misspelling when talking about electricity!     :]
soundmotor2 years ago
mikeasaurus: although they did not cause any problems for you, you might want to try firebrick next time. Firebrick is not porous like red brick so it does not retain moisture. If your red brick is stored outside they may. Mosture in red brick + heat could = steam with a resulting.....KABOOM!
KneXtreme2 years ago
Do you reckon I could melt silver coins?
bonpierce3 years ago
You do realize this contains LEAD right? Lead is a carcinogen whether it is being melted or held in your hand a a charm or around your neck as a necklace.

You don't want long exposure of any kind to this stuff. Seriously.
Lead isn't a carcinogen. It's a toxic, heavy metal - a poison. That's different. It isn't going to hurt you unless you ingest it, either by eating it, chronically getting lead paint (which isn't sold anymore) on your skin or by inhaling the fumes after it reaches it's vaporization point which is a whole lot higher than it's relatively low melting point. If one were to smelt lead every day, there would be danger. One time isn't dangerous if you are the least bit careful.
Do you remember good old time of tetraethil lead in gasoline ? I guess some of that stuff is stil spread all around
So why is there this huge push away from it for consumer (and most other) electronics?
Because it if it ends up in landfills it contaminates the water table. Of course, every public waste disposal site that I know of keeps electronic junk out of the landfill and recycles it properly but because it once did end up there; politicians created the legislation to eliminate lead in all forms. Makes for good campaign bragging rights. "Senator Jones drafted legislation to eliminate lead and protect our children."
Then why do we still use Lead Acid Batts for vehicles?
Because there is no acceptable substitute. It's pretty much as simple as that. No other type of battery can stand up to the thousands of cycles of charge / discharge, put out as much current and withstand the environmental conditions that vehicles are subject to. At least not in that price range. How would you like to have to pay $350 to $700 for a car battery (installation not included)?
skaar terpodion2 years ago
i've read that iron acid batteries are better for lifespan and resiliency, but they're low capacity. now ni-mh could be used, they have low size, high current and capacity. at least acid iron could be built at home.
Lead Acid batteries are still being use for vehicles because an all around substitute hasn't been created. The hazards of using them have been mitigated to a large degree on both the manufacture, and consumer end. The salvage price for lead has always been constantly high enough that persons in the know, never sent them to the land fill. The high deposits we see now on new batteries is to keep the ignorant, and lazy from sending them to the landfill.
Also, due to the large deposits encouraging battery exchanges, something like 98% of car batteries are recycled.
I think too there is a certain paranoia about lead. This paranoia is, in part, spread by certain legislators who, in an effort to look as though they are actually earning their salaries, play up the supposed dangers of "demon Lead" and pass legislation against it. If the web site I looked at earlier is correct, easy flow silver solder contains cadmium which is definitely something you don't want to breathe the fumes. I have read cases of jewelers killed by melting cadmium and breathing the fumes. I have yet to see anything about anyone dying from melting lead. If melting lead was that dangerous plumbers should have been dropping like flies before legislation banned it in plumbers solder. I believe the effects lead has on the brain and nervous systems of immature humans is the main thing we must be careful of when dealing with lead and that is more likely to incur through ingestion.
AMEEN!
This is a good point. It's easy enough to find "Lead Free" solder these days (Sn-Ag-Cu), people should just use that if they plan on handling their ingots (as a paperweight, etc) created here.
You realize however that lead-free solder is actually worse for you.
*citation needed.
I had originally heard about a Danish study through a television program, so I had to do some quick research to get you facts you can read yourself.

Heres a pdf from a company called OK International, who is a global supplier of soldering products. In it they reference the study and explain the results. Obviously being a supplier, they have no reason to manipulate the results either way...
Wow thats really quite the paper I said to myself I'm just going to skim it than I got to the end and was like wow that was informative. I reccomend that to anyone who wants the real scientific answer to whether or not LeadFree Solder is More harmful to you. Which apparently it is.

Que instructable about making an effective deskmounted airfilter for your soldering station.
I'm glad you found it informative. Too often people just assume that lead-free means safe and they use it without proper ventilation, doing god only knows what to their lungs...

In fact, an Instructable member has already made an inexpensive air filtration system that was intended for use with soldering.

You can see it here.
Well thats handy, I dont exactly work in a production environment where I'm soldering ALL day. But this is good to know I also was under the same assumption.

I've been using this stuff the "Special Blend" at Sparkfun, http://www.sparkfun.com/products/10243 enjoying it quite a bit I will definitely look at that Ible though I do really appreciate my lungs. :)

The area I work in is a pretty open area but its probably still insufficient.
If you read the MSDS, it has basically the same ingredients and warnings as other non-lead solders. What I would be concerned about is two statements;
  1. Prolonged inhalation of fume may result in lung complications.
  2. This product may contain lead. (So much for being lead-free...)
It's important to read it if you haven't already. :)
Actually the MSDS is not a datasheet for the Sparkofun product. The data sheet is for Indium solder products that Sparkofun lazily points customers to. Early on the data sheet states the warnings concerning lead apply to those Indium products containing lead. The datasheet is usable, but you need to know what it is you are looking at, and how to apply it to the Sparkofun solder product. A thousand lashes of Ann Landers wet noodle for Sparkofun, for confusing people about their products.
While I find the linked PDF interesting, I can't give it much credibility because of their inability to correctly quote the name of the largest occupational safety organization in the US. It seems like a miniscule detail, but they're making a lot of claims, and citing a lot of other works, not to have done their research, or at least proofread the work before publishing.
Yes, I see too that they referenced OSHA incorrectly as OHSA.
I only chose this source because (someone here wanted me to back up my statement and) Ok Int. references the Danish Study that I had heard about from a TV program.

If anyone wants to read the full Danish Study for themselves they can read it here.
Certainly is. Always read the material Data Staftey Sheets about any of these things.
Lead free solder was used in a lot of volkswagons, xbox, and pretty much everything else where the environmentalist went on a rampage to get rid of lead. that is why you get the red ring of death in an xbox and your airconditioner in your volks wagon. Especially in deisel. Environmentalist did not think ahead about all the crap going into a landfill because it can't stand up to any heat and or vibration.
Would appear that not all lead free sold alloys are created equal. Who knows exactly why they weren't properly researched by manufacturers, or those specifying manufacturing specifications prior to their use? This is not the first time a change(for any reason) in manufacturing methods created problems, and it will not the last. Of course it's all the fault of the environmentalists.
1-40 of 165Next »