Tube Furnace 3: Tabasco
Construction
The minimum goal to reach with the tabasco iteration of the tube furnace is to reach 1000C with no more than a calculated 1000 Watts of power. The ideal goal would be to reach this temperature with around 500 Watts of power. Maintaining this temperature for long periods of oxidation is also important.
The tube of the furnace is a 2 inch quartz glass tube, with a center covered in refractory cement, and approximately 20 loops of double twisted 24g kanthal wire wrapped over the cement portion. This is wrapped in several layers of ceramic wool insulation, and then covered with sheet metal. The sheet metal is held together with shelf brackets and a handle. On the back of the tube is an attached thermocouple for temperature measurement. Other parts of the setup include a programmable circuit breaker to protect the local circuit from overloading, a motor control to control the voltage/current flowing into the furnace, and a voltmeter attached to the thermocouple for temperature readings.
Shelf brackets, sheet metal, kanthal wire, refractory cement, ceramic wool, quartz glass tube, nuts and bolts, refractory bricks, ceramic weave insulated copper wiring, motor control, thermocouple, ceramic beads, voltmeter, controlled power box, handle
Item
Specifications
Quartz Glass Tube
14” long, 2” diameter, 2 mm thickness
Sheet Metal
Folded into a 9.5” x 9.5” x 10.5” box
Kanthal Wire
24g, 20’+, wrapped into 20 loops around glass tube
Ceramic Wool
1” thick, cut to wrap once around the tube and to wrap around refractory bricks 5” x 5” x 1” refractory bricks
Thermocouple
8” long, mount has less than 2” diameter
Refractory Bricks
5” x 5” x 1” each, 2” hole cut through middle for glass tube, approximately 5 used and held together by refractory cement
Shelf Brackets
Approximately 8’ of bracketing used, each bracket side is 1.5” wide with about 2 mm thickness
1. Coat outer mid section of glass tube in refractory cement, score lines to allow for shrinkage during curing, let cure for several hours
2. Measure kanthal wire using the desired number of loops around the tube, with some extra length, then double the total length. Fold in half and twist the entire wire tightly using a power drill and tension. Carefully wrap wire around the cemented area of the tube, holding firmly. Hold with rubber bands and cement on top, let cure.
3. Wrap tube with wire in ceramic wool. Connect ceramic wiring to the extra kanthal wiring.
4. Bend sheet metal into a box, drill hole to fit tube through as it sticks through insulation. Place the tube through sheet metal box. Drill holes for wires, use ceramic beads to prevent contact between wiring and the sheet metal box.
5. Bracket the edges of the box, leaving extra bracket to allow the furnace to stand up. Fix in thermocouple.
Successful for oxidation purposes
Can maintain heat for long periods
Despite this, doesn’t hit power goal of 500 W for 1000oC (~1400w)
Can be more efficient in trapping heat and power usage
Heavy and bulky
Thermocouple could be mounted better
Glass used was too thin
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