Electrically Heated Rotarv Kiln J
4
E. P. BARRETT, Rletallurgical Division, U. S. Bureau of Mines, Minneapolis, Minn., W. L. BARRETT, U. S. Bureau of Mines, Pittsburgh, Penna., AND P. R. PORATH, U. S . Bureau of Mines, Rlinneapolis, Minn.
A
inches long, are tapped for 0.3125-inch standard thread and screwed onto the cap screws projecting through the shell. Grooves are cut with a round file in two of the heating-element refractories to fit around the Allegheny tubes and the thermocouple protection tube. The spaces between the heatingelement refractories are filled with Alundum cement.
S ELECTRICALLY heated rotary kiln was constructed for studying the relative reducibility characteristics of small amounts of various iron oxide materials a t temperatures less t h a n 1000" C. The use of such a large, alloy-lined rotary kiln should be considered where cheap porrer is available.
The dimensions and the arrangement of the parts of the kiln can be seen in Figure 1. -4n end view of t h e kiln is shown in Figure 2.
The kiln consists of a steel cylinder fitted with tires and supported on two pairs of flanged wheels. Rotation is imparted by one pair of wheels mounted on a shaft connected to a speedreducing unit driven by a '/a-horsepower motor. The steel shell is lined with 2.5 inches of refractory insulating brick laid in a slurry of RA-162 Alundum cement plus 10 per cent of sodium silicate. It is essential that this lining remain rigidly in place in the kiln, as the soft insulating brick wear rapidly when free to move as the kiln is rotated. Four metallic resistor heating elements are placed within the refractory insulating lining and outside of an Allegheny 55 alloy retort. Three 0.25-inch holes are drilled through the shell and insulating brick in line with the contacting edges of two heating-element refractories. A thermocouple installed through the hole midway between the ends of the kiln touches the outer surface of the retort and is connected to brass slip rings surrounding t,he central portion of t'he kiln. Carbon brushes touching the rings are connect,ed to a recording potentiometer. The temperature indicated on the recorder probably is slightly higher than the actual temperature of the charge within the retort; however, it serves as a control of the maximum operating temperature. The holes 3 inches on each side of the thermocouple hole are tapped for 0,3125-inch standard thread. Cap screws, 0.3125 X 1 inch, are screwed into the holes from the outside of the shell. Two pieces of Allegheny 55 0,125-inch pipe-size tubing, 3.25
Heating Elements Each heating element contains 42 feet of N o . 16 B. &. S. gage Sichrome V wire wound on a 0.25-inch rod and pulled to 65 inches. Each helical coil is threaded into six parallel holes approximately 0.5 inch in diameter extending lengthwise through a refractory cast on the form shown in Figure 3. Semicylindrical form A , 5.75 inches in diameter by 10.75 inches in length, is made by nailing thin sheet iron to three semicircular pieces of 1-inch board which are attached afterivard to baseboard D . The semicircular pieces of 20-gage sheet iron, B and C, are fastened to A with screws and are 7.75 inches in diameter with a slot a t the top to hold a power hacksaw blade or ot,her piece of flat iron to separate the quadrants. On each side of this slot' are six holes 0.531 inch in diameter, spaced 0.878 inch center to center on arcs 0.5 inch from the outer edges of B and C. Form A is covered with waxed paper. Each of the cold-rolled iron rods, E , 0.5 inch in diameter by 13 inches inlength, is wrapped in a strip of waxed paper 10.75 inches long by 3 inches wide. The overlapping edge is fastened with rubber cement. A mixture of equal parts of RA-162 Alundum and Thermolith cements plus 10 per cent of >35-mesh Carbofrax cement No. 3 is plastered on
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A"
$"by brass slip rings -for thermocouple connection
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FIGURE 1. SECTION THROUGH KILN ON DIAMETER 684
NOVEMBER 15, 1940
ANALYTICAL EDITION
685
TABLE 11. IRON CONTENT OF ORES AKD SPONGE IRONS 7 -
Test No.
Size, hIesh
Material Mill scale Magnetite Limonite Hematite Hematite Hematite Hematite
135
>35 >28 >48 >48 >48 > 48
As charged 72.4 67.1 60.2 68.6 68.6 68.6 68.6
Iron, Per Cent -Sponge IronTotal Metal Zletallized 97.0 96.9 99.9 95.1 97.4 92.6 91.4 99.0 90.5 96.5 98.7 955 95.2 99.8 95.0 94.1 98.8 93.0 94.6 99.4 94.1
d with 500 grams of >4-
