| 摘要 |
<p>576,331. Heat - treatment furnaces. McDONALD, J., FINLAYSON, A., and G.W.B. ELECTRIC FURNACES, Ltd. Nov. 2, 1943, Nos. 18100 and 19515. [Class 51 (ii)] [Also in Group XXXV] In heat-treatment furnaces in which air is circulated by means of a fan or the like the temperature is controlled by varying the heat derived from the friction of the circulating air. The regulation may be effected by varying the speed of the circulating fan or by varying the cross sectional area available in the furnace for the circulating air. Fig. 1 shows a heat-treatment furnace c having heating elements a and a fan f driven by an electric motor g for circulating air through the furnace and treatment chamber e. A thermocouple h is connected by leads j, l to controlling devices k, m for varying the speed of the motor g. Figs. 4 and 5 show the electric circuits for a two-speed motor M for driving the circulating fan. Current from the mains MS passes through a main contactor C1 provided with an operating coil C1 and thence through the high speed contactor C3 'having an operating coil C31 or a low speed contactor C2 provided with an operating coil C21 to the motor M. The operating coils C11, C21, C31 are supplied from mains CS and normally current flows through the coil C31 of the high speed contactor C3 and a relay switch R which is operated by a relay coil R1 under the control of a thermostat T. When the temperature rises to a predetermined level, the thermostat T operates the switch R to cut out the high speed contactor C3 and close the low speed contactor C2 to run the motor at a lower speed. As shown in Fig. 3, the thermocouple h operates through a control device k and leads l a motor m which actuates through wires r a baffle plate o to vary the cross sectional area of the path for the air circulated by a fan f. Specifications 477,607 and 519,675 are referred to.</p> |
