Melting Metal

Rev. 2002-12-31, 2003-02-07, -04-17, 05-21, -06-01, -07-20, -21, -08-29, -09-14, -11-16
2004-06-27, 2005-02-24, -08-01, 2006-02-02, -02-5, -03-21, 2007-11-13,
2008-01-29, 2009-02-20 (layout), 2010-01-31, -11-14, 2012-06-27
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Melting Aluminum  Can Return

Using Insulating Castable Refractory

Outside protection


Bucket FoundryFirehole

Lead Melting

Molding Crucible

Sandbox Sand Casting

Tools for metal handling

Basic Steps of Foundry Work

Melting Temperatures for Casting

Related pages
Metal Center


A glory hole provides more than enough heat to melt most metals including copper (1981F), but not iron (2802F) (A list of metal specs) But a glory hole is awkward for melting trash (i.e. scrap metal with paint and key rings.).
Cast iron fry pan used to melt aluminumI melt aluminum from cans in a specially built melter (next) using a cast iron fry pan on a long metal handle. A relatively short 1/2" angle iron piece (about 24") is firmly bolted to the pan and fits inside the end of a longer piece of conduit, held by a single bolt. I also have a multipurpose foundry, glory hole, forge which is nothing more than a cylinder lined with insulating castable refractory with a burner port in the side. This unit uses small pots of the same material as is used for glass. Which metals can be melted in iron (lead and aluminum) and which require a pot (brass, bronze) can be judged by what is used for brazing.

TIL ALUMINUM MELT - Even if the flame is aimed directly at the pan (as below), if the overall temp is a bit low, the handle of this iron pan will suck enough heat out to produce a chilled lump of aluminum under the slag.  Raising the temp and stirring will melt the lump. 2006-02-02


Using Insulating Castable Refractory

Foam frame of insulating castable moldThis is the form for building a cast furnace for melting aluminum cans following a couple of others that didn't work as well. Although this is not the finest photo in the world several points are visible:

  • A burner port is provided as a cylindrical tube aimed at the camera. In one previous version, the burner was directed into the opening for the pan, but that did not give good direction to heating the metal or the pan.
  • Aluminum foil is used to seal the bottom and back joints. The thin pieces of beadboard foam are held together with nails as pins. The castable was made very stiff (see below)
  • The core of the furnace is a rounded block of styrofoam bead block set against the left wall to provide the pan opening. The wall thickness was estimated from experience and is about 1" to 2".
  • The vertical unit is both a flue and entry point for the cans. In a previous version, the flue was made by wrapping a stack of aluminum cans in several layers of newspaper. This provided too tight a fit, blocking flue action when a can jammed. This square block is about 1/2-3/4" bigger than a can.Castable in foam frame, partially made
  • The furnace was built with an open bottom on a board and is used on a flat cast slab of insulating castable. I thought casting the floor and sides together would be a problem and the floor might fail and be hard to replace. Using the separate floor has survived well.
  • The entry is blocked with scraps of fire brick and castable rather than having a functioning door.
  • After the castable was built up as shown at the right including the collar, the flat slabs of board were formed into an outer mold around the chimney, pinned to hold shape, and tied to keep from opening. Much more liquid castable was poured in to form an integral chimney/flue with about 3/4" thick walls.
  • The garden claw shown in the photo (lower right) is good for mixing the castable, which tends to form rigid masses around dry mix. The claws break this better than a trowel.
  • Eventually, the unit began to crack and was reinforced with wire. (below) It has stood up to about one firing a month for over a year.
  • In use, the burner is propped so its head is aimed at an angle into the opening and gas is provided from a propane tank along with air from a blower. The inside rapidly rises in temperature. The flame is set to be a bit blue (oxidizing) and as cans are dropped in, their paint provides addition heat and the fumes are burned rather than escaping.
  • Can melting furnace as usedThe cans first boil off any fluid (water from rain or soda) inside then heat further, the liner fumes inside igniting with a distinct pop, then the paint catches. As the cans melt, 2 or 3 may be in the stack at a time and the weight of the upper ones forces the stack down. The paint ash and aluminum oxide skin are remarkably strong. A straight rod occasionally urges them on. Eventually, the amount of aluminum and slag in the pan requires removal and pouring. I pour ingots in casting sand for later re-melt and use. [Most recently, I have been burying light beadboard rectangles in the sand and pounding the sand - pouring the aluminum melts/burns out the beadboard.]
  • The finished (and well used outfit) is at the right. The burner (below) is shown at the right of the picture and fits in the burner port on the right side. It is normally propped up with a fire brick. Note the flat deck of insulating castable in a metal pan. The burner is designed for this setup, right angle access, gas line parallel to the blower input. It is used inside a brick BBQ pit U-shaped space. A shelf of expanded steel welded to a frame custom fitted to the pit supports the melter here. On the same shelf can be placed a legged grill with tray for charcoal cooking and the top lid and removable front panels permit smoking. A slide out tray below holds charcoal and smoking wood and a space in the brick in back admits a small propane burner to enhance the temperature.
  • Night shot of can melter in BBQNight shot, which shows interior of BBQ pit. The aluminum melter is sitting on a flat slab of insulating castable in a bent metal tray, the burner is to the right. Above is the peaked roof lid that keeps out rain and allows smoking food. Two guide rails on the top if the brick keep it centered. It hangs off the back when grilling food or other uses. The melter is sitting on a legged expanded metal mesh shelf that is behind the metal enclosure - a similar shelf fits in the space shown for cooking food, it has a rack that holds charcoal below it at an adjustable height. There a two sheets of metal painted brown below the opening. The front one fits into the opening to seal all for smoking.
  • After a discussion on the net, I decided to measure what I was getting from the cans.  On the first more careful run, having carefully cleaned out the pan and the inside of the melter, I counted out 110 cans which was about half the wire basket and close to a usual melt.  The industry considers the rate to be 32 cans per pound.  On my rough scale, I found 12 cans seemed to weigh 6 oz. and 9 weighed 4.5 each of which calculates out to 16 ounces for 32 cans.  The 110 cans would weigh out to 3.4375 pounds (3# 7oz).  The yield on my melt was 1# 14oz aluminum and 1# 1oz of trash.  That totals 2# 15oz, so 8 ounces went up in smoke, the plastic lining and outside paint. So 55% of the original weight came out in aluminum, 31% as trash. (64% Al 36% trash in result )   Some aluminum remains in the trash and I have melted more in the same mix to get more out.  In a second run, without counting the cans and adding some aluminum foil and pie pans yielded 2# 7oz aluminum and 1# 8oz trash.  (62% Al  38% trash)  2005-02-24


Keeping equipment outside, especially refractory insulation, requires protection from the rain.  This shield gains strength from the curved conduit and corrugated sheet metal.  The pivot at the curved back conduit puts the cover evenly over the equipment and permits raising the cover enough to let hot gases by.  Metal lets the cover be closed if it starts to rain while stuff under it is still hot. 2003-11-16 Shield over foundry and wax working - pivots up.
This is the burner used with the aluminum melter and (without the flared head) with the Firehole [it has since been rearranged so the gas enters through the T where the elbow is in the picture, so the gas flow will preheat without the blower supplying air.] Burner for the aluminum melter, with a small burner.
Gloryhole/forge/foundry (click for bigger image)BUCKET FOUNDRY
[For instructions on building the insides, making a cleaner version, and using this go to Firehole ]
This is the first version I built. By the time this picture was taken it is clear that the metal "popcorn pail" type container was not a good choice for leaving out in the weather - or it should have been painted with high temp paint. Since the picture was taken, I have taken off the rusted shell and wrapped it with thicker, painted metal, held in place with stainless steel hose clamps. I also keep the unit covered, as it absorbs water and that probably contributed to the rust.

The lid in place is the one used for foundry work and the hole in the side is the entry for the burner. Unlike most of my burners, this one does not have a flared end, but the castable was shaped to provide that. The entry is low for foundry work, below the edge of the crucible, which sits on a fire brick.
There is no back to the unit. When used for foundry, it sits on a block or tray of castable, as shown. When used for forging a block is held against the back and the unit is laid on its side, with the option of removing the back or using this door, so long work can be heated in the middle. When used as a glory hole, the back is blocked. Inside diameter is about 6".
Go to Firehole


Lead Melting - I needed Full view of double ended small ladleto melt One end of double ended ladle with lump of cold lead in it.some lead for molding an insert weight in the whirly jig. Although I have a ladle shape on one end of my glass gathering ball/scoop, I didn't want to put a lip on that and it has a very long (6') handle. So I went in to my welding box for the pipe ends [which are sold a steel/welding supply places to weld to the end of high pressure pipe to seal the end] I had bought before and used on the scoop. I found I had more sizes than I remembered, so I took two out (2" & 3") and cut a short length of 1/2" square tubing about 20" long. I cut the tubing at a slight angle and filed the end with a half-round file to further match the shape of the dome, laid it on a flat surface and torch welded it. I heated the lip with the torch and pounded a lip with a ball peen hammer. Then I melted the lead. In the pictures, the small puddle of remaining lead has set in the ladle.

Lead is a relatively low melting metal that can be used to make small castings and to provide weight for balancing. It can be melted in iron and if not overheated will not solder to the material (like brass will.) Lead is toxic and if allowed to accumulate in the body can cause brain damage and other problems. It should be handled with respect and when hot should be used in a well ventilated space. Shavings of lead should be cleaned up and hands washed after handling and before eating. Lead used to be used in paint and gasoline and both were removed (in part) to protect kids from lead in the environment.


Mold form for small crucibleThe photo at right shows the pieces in making a new crucible for brass melting. A blank was made up by stacking Styrofoam 2" block glued with yellow wood glue. A disk of wood was also glued on and the wood was screwed to an adaptor plate with a nut to fit on my flat grinder. When the glue set, the cone was shaped with a rasp and cut free with a saw. The form was covered with thin (dry cleaning type) plastic. Old T-shirt material was dipped in plaster of Paris mix and wrapped around the form like making a cast for a broken arm. When the plaster was set, the form and plastic were worked out. Unfortunately, I was not careful enough and the plastic left wrinkles on the inside of the plaster. I relieved that by making some more plaster and coating the inside. The crucible mix was pounded out 1/2" thick on a flat counter, sealing the seams and making a sheet equal to the circumference of the mold. A piece was laid in the bottom and the sheet was rolled around my hand and put in place, sealed with pressure to the bottom and at the overlap. When the material had dried and shrunk, it was wiggled out of the (not completely smooth) mold.
Box of sand used for casting and laying out clay formsThis box was originally (over-) built to provide a strong step for a person to get into my van as well as holding some tools.  The lid is just 1/2" plywood resting on 2x6's with routed in end handles and a rope loop shoulder strap.
When I started casting, it dawned on me that I could do rough casting of extra metal using play box sand, plus set the invested molds for pouring with support of the sand around them, plus have a fire proof place to set down the crucible of molten metal when transferring to the pouring handle. Also used for shaping clay for sagging as shown. 2003-07-20  This sand or some in a smaller container can be used to support an aluminum foil mold.  I needed half an egg shape in plaster and had a full wooden egg.  When I tried forming heavy duty aluminum foil around the egg then holding it in my hand, it distorted.  When the egg plus foil was pushed into damp sand, then the egg removed, the foil was completely supported by the sand. 2005-08-01
For the record, here are the sand casting cope and the tool I built for pounding the sand.

This red sand is very fine and has resin in it for bonding together to make it stick.  I bought one bag years ago.  In theory, it would allow me to make split molds using sand casting techniques.  In fact, I have been unable to make it work, probably because I don't pound the sand firm enough so the molds I have attempted have collapsed during casting,  I have succeeded in a couple of cases doing open faced pouring with the item in the flat lower half.  One item was an aluminum "Property Line" sign.  Another was the puffer cone shown below - note the rounded top of an open pour (more) A third was a color powder cup from a plaster model.  I haven't tried very hard to make this work. 2010-02-01Cast aluminum puffer head

Sand casting box and packing tool
These are tools built for handling the crucibles and molds.  The upper unit, left end in the insert, is used for pouring crucibles, which are lifted with the lower unit and set inside the ring.  The left ring was originally too large and was cut and overlapped without re-welding it.
The lifting unit was originally too weak to easily lift a crucible full of brass, so the straight 1/2" square tubing was added for stiffening.  The lower (left hand) curved pieces have been reshaped to fit the fairly thin space between the crucible and Firehole wall and bent in to get under the edge. The pieces are also not aligned, one is under the other when closed, to permit picking up smaller shapes, like investment tubes. Looks ugly, works okay.
This is actually smaller than the stuff to the left, 5/16" rod, for picking up small muffin cup sized crucibles either from above (left) or the side (right)  On opposite ends of the same rod. 2003-07-21
Crucible lifting clamp and pouring loop Small rod crucible handler
 This iron pot was purchased just for the purpose shown: to melt aluminum in the glory hole for larger pours.  An iron rod U first built for lifting slabs for reheating glass was rebent to fit along side the pot under the side flanges, to permit removal and pouring. At this time, it has been used for one sand casting which came out flawed but closer. 2005-02-24. Iron pot in glory hole to melt aluminum

Basic Foundry Steps
You make a model, usually using modeling clay.
You make a mold of the model using latex or silicone rubber
You make copies of the model in wax from the mold.
For big items you make the waxes up in sections.
You add sprues and venting to allow bronze to fill the mold properly
You encase the model in heat resistant material - investment for small items, silica flour ceramic shell for large.
You have the foundry equipment to melt the metal and heat/fire the mold
You pour the melted metal into hot mold
You let it cool
You clean off the investment/shell
You cut off the sprues and vents and if done in sections you weld the pieces
You clean up the casting and patina it as desired.
Good brief video of process for large work

Link to Techspec.htm

Melting Temperatures for Casting
Alloy/Material Melting Temp (F) Ratio of Metal:Wax (Wt) Flask Temp (F)
Fine (Pure) Silver s 1761 10.5:1 800
Yellow Gold 18K s 1700 16:1 900
Gold (Pure) s 1945    
Brass b 1652 (melt) 2150 (pouring)    
Beryllium Copper s 1800 8:1 800
Platinum s 3224 22:1 1600
Aluminum s 1200 2.7:1 400
Silicon Bronze s 1850 9:1 900
Pewter s 585 8:1 Ambient
Casting temperature should be 100 to 150F above melting temp. (Src: s=Swest Catalog, back cover, b Budget Casting)

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