Metal Melting Furnace

Goals

Melt aluminum and copper-based alloys
Expand internal working volume from 381 cu. in. to 890 cu. in. by adding in additional side sections.

Materials

Scrap steel mixing tank
20 ft. of #3 rebar
Cardboard, wood boards, scrap wood for pouring forms (i.e. for the internal cavity of the furnace)
Homemade castable refractory ingredients (from [[1]])

  -silica sand (aka Silver Sand)
  -perlite, not Pearlite or Vermeculite
  -fire clay (aka Mortar Clay)
  -Portland Cement

Various steel and brass pipe fittings for the Ron Reil propane burner (from [[2]])

  -1 1/2" NPT to 3/4" NPT Galvanized steel reducer
  -3/4" NPT x 8" Black steel nipple
  -1" NPT x 3" Black steel nipple
  -#8 UNC size set screws
  -1/8" MIP x 4" brass nipple
  -1/8" FIP brass cap
  -1/8" FIP to 3/8" FIP brass bushing
  -3/8" MIP to 3/8" Flare brass bushing

Minimum 10 ft. "High Pressure" LPG hose
0-40 psi "High Pressure" Propane regulator
20lb. tank of propane

Notes on the materials

Scrap steel mixing tank

-Obtained (for free!) from an awesome fellow member.
-The tank is powder coated on the inside and outside.
-40, 60, and 80 grit flap discs were used with a 4 1/2" angle grinder, but the powder coating quickly loaded up the discs. Rate of removal: slow.......
-Grinding disc was used with the same angle grinder. The finish was ugly, but rate of removal was high! I cleaned up any missed spots with the 80 grit flap wheel.
-Crimped wire wheel was used as a last resort. Wire wheels are effective at removing paint and rust when the wheel is in good condition. This wheel was not. Wire shrapnel flew at a kajillion mph and the wheel was off balance. The angle grinder (a decent Makita brand) vibrated as bad as a broken Harbor Fright grinder. Solution: Armored up with full protection (minus a full face shield) and took 5 min breaks between 30 min intervals to regain feeling in my hands. Finish was weld-ready and beautiful. Rate of removal: medium, but probably could have been faster with a better wheel. Crimped wire wheels and wire cup brushes are an option I might look into.
-Quick Strip disc (i.e. abrasive bonded to a polymer sponge matrix) with the same angle grinder. Just bought it. Will try it out and report my results.
-Update 3/24/15: The quick strip disc performed excellently for the entire 30 minutes of its life. The powder coating came off very easily and the shiny metal underneath had a nice well...shiny...finish. I was disappointed with its lifespan though. Corners and hard-to-reach areas were impossible to reach once the outer edge wore away.

"#3" rebar

  -Home Depot occasionally sells long, mangled up sections for up to 50% off.  I bought a straight one because the mangled up ones were gone that day.
  -Certain types of rebar weld fairly well.  Others do not.  The one I got welded very well to the tank.  Note: I have only had 4 hours total of experience on a flux-core welder, so take "welded very well" with a grain of salt.  I hammered at the weld with a sledge hammer from multiple angles to see if it would hold up.  And it did. So good enough for this application.
  -#3 is 3/8" diameter.  It bends very easily with a copper pipe, benchtop vise, and enough leverage.

Pipe fittings

  -National Pipe Taper (NPT) does not go with UNC/UNF/UNFC threads!  NPT creates a better seal the more it is tightened, but still required some sort of thread sealant.  UNC/UNF/UNFC are threads found on machine screws.  NPT is the standard thread for plumbing applications.  Rectorseal #5 was selected as thread sealant from Rectorseal's selection chart for propane.  Yellow, double thick, PTFE thread tape seals, but is not recommended because of the high working temps of the burner.

"High Pressure" Propane hose and regulator

  -The 20lb propane tank used in this project has a soft-nosed Prest-O-Lite (POL) output connection.  Various types of connections are used including NPT threads.  The fittings used in this project fit apply only to this project.
  -The hose and regulator used in this application are used for camping and bbq grills.  Industrial grade T hoses and regulators for oxy-propane cutting can be used, but have different threads (the propane connections are left-hand threads) and are expensive!!!

Progress

Edit 3/24/15:

  Most of the remaining powder coat has been taken off.  Any remaining powder coat will be cleaned off with a new wire wheel or new wire cup brush.  The rebar stub reinforcements were cut out.  First, a flat was ground into all the stubs with the bench grinder. Then, a total of 33 2 inch sections were cut with the abrasive chop saw.  Lastly, the ends were grounded round on the bench grinder.  Ceramics like the castable refractory then to fail at the location of the largest flaw.  Grinding the sharp edges round reduces the stress concentration at the stubs.

Pictures to follow.

Metal Melting Furnace

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