| 摘要 |
914,823. Automatic control systems for tube mills. BABCOCK & WILCOX Ltd. March 13, 1959 [March 14, 1958], No. 8355/58. Class 38 (4). In a pulverizing mill of the kind including a rotary casing containing a charge of free pulverizing elements as in Specification 832,404 [Group II] in which the driving power decreases with increase of speed and pulverization is effected with a relatively low energy consumption per pound of ground material, electric strain gauges measuring the vertical strain on the support for the mill automatically control the feed to the mill. Fig. 4 shows one of the four corners of a framework 15 carrying a tube mill (not shown) for pulverizing coal. Each corner is supported partly by a bolt 150 screwed into the framework and resting on a sole-plate 153 and partly by a bolt 141 also screwed into the framework and resting on a strain gauge unit 121. Each of the strain gauge units is filled with water-repellent material and comprises two pairs of strain gauges (not shown) mounted at right-angles to each other and connected to form a temperature-compensated bridge circuit. Thin metal strips 161 are arranged horizontally and interconnect blocks attached to the framework and the sole-plate to prevent horizontal movements, and permit vertical movements, of the framework. The four bridge circuits 121, Fig. 6, are connected in series so that a D.C. signal representative of the total weight of the mill and its contents is applied through an electronic device 173 to control a two-phase servomotor 195. Servomotor 195 adjusts, through a pneumatic system, the speed of an electric motor (not shown) operating a coal feeder so that the amount of coal in the mill is maintained constant. Follow-up is provided by a potentiometer 177 adjusted by servomotor 195 and the amount of coal maintained in the mill is determined by the setting of a potentiometer 171. The mill, as in Specification 832,404, is of the type in which (a) the mill is driven by an electric-hydraulic unit at a speed which is dependent on the rate of flow of air to the mill and (b) the rate of feed of coal is also made dependent on the load on a steam generating unit supplied with fuel from the mill. |
