Electrochemical and metallurgical industry . iiere are otherconsiderations which arc fatal to the construction of the fur-nace if we attempt to use a graphite rod as resistor. Let itbe assumed that to carry out the furnace v/ork, we kilowatts per square decimeter of resistor surface. Thenif the length of ilie resistor is 1, as before, and the radius ofthe resistor is t, we have the following equations to determineits dimensions. To fulliil the requirements as to resistanceequation (2) becomes 1 -=164 (3) ?trr and the equation for the surface is a —5000 X 100 = 2500 (4) 2Tt1 From (3)
Electrochemical and metallurgical industry . iiere are otherconsiderations which arc fatal to the construction of the fur-nace if we attempt to use a graphite rod as resistor. Let itbe assumed that to carry out the furnace v/ork, we kilowatts per square decimeter of resistor surface. Thenif the length of ilie resistor is 1, as before, and the radius ofthe resistor is t, we have the following equations to determineits dimensions. To fulliil the requirements as to resistanceequation (2) becomes 1 -=164 (3) ?trr and the equation for the surface is a —5000 X 100 = 2500 (4) 2Tt1 From (3) and (4) we find 1 = = cms. While carbon rods of these dimensions might he ol)tained, theywould be found very unsatisfactory, for they would be toodelicate to handle without breaking. A closer approach to a practicable resistor might be madeby using one having a rectangular cross-section, for this shapewould give a greater heating surface for the electrical resis-;ace of a given length. Assume, for examijle, that we de-. FIG. 7.—OUTER I.\RT OF RESISTOR. cide to use a plate cm. thick. Then if the width of theplate is b, equations (3) and (4) may be written as follows:1 = 164 , (4) X 100 = 2500 (5) 2(+ b)lir<)ni (4) and (5) we get 1 = = cms. This is somewhat l)etter, but the plate would be a \ er.\- deli-cate article to handle, and even if successful)}- i)nt in place inthe furnace, would probably be broken while in use. Some examples of improved forms of resistors are shownin Fig. 8. These may easily be made from graphitizedarticles with the help of a hack-saw. The forms shown in thefigure have been made and used in the laboratory for va-rious purposes and were found to give satisfactory results. Itshould be noted here that in connecting the resistors havinga rectangular cross-section to the terminals a good methodis to cut slots in the latter, the dimensions of the slots beinggreater than those of the section of the resisto
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectmetallurgy
