GB816623A - Improvements in or relating to screening apparatus - Google Patents

Abstract

816,623. Sifting apparatus. BURSTLEIN, E. M., and SOC. DES ACIERIES DE LONGWY. March 15, 1957 [July 21, 1956], No. 8672/57. Class 117 A screen, electrically heated by the flow of current therethrough, is divided into an even number of panels, one half of which is supplied from one phase of a two-phase source, and the other half is fed from the other phase. The source may comprise a 3 to 2 phase converting transformer fed from a 3 phase network, and the secondary voltage may be adjustable up to a maximum of 24 volts. Panels in each group may be connected in series, parallel, or series-parallel relation. To provide differential heating of the two groups the impedances thereof may be different or the groups may be supplied with different voltages. To provide a balanced differential heating of the groups, the impedance per unit area of one group may differ from that of the other, whilst the lengths of the panels in each group may also differ so that the overall impedance of both groups is the same. A high current connection to a screen gauze 46 is shown in Figs. 7 and 8, and includes a plate 43 forming part of means for stretching the the screen and compensating for the expansion thereof, slidably mounted over a guide secured to the screen frame. Threaded rods 44 arranged in two parallel rows are secured to the plate and project through a bus-bar 45, the gauze 46 and a clamping plate 47, and nuts 41 secure the assembly. Fig. 10 shows an electrical connection between adjacent gauze panels, and includes a plate 52 insulated from the screen frame and attached thereto by two rows of threaded rods 53 and nuts. Threaded rods 58, in two parallel rows, pass through a bus-bar 45, the two gauze panels 46 and 59 and a clamping plate 42. Nuts 41 secure the assembly. In both of the electrical connections described nut locking means 42 are provided. An intermediate support for large screens consists of a cross-member 60, Fig. 11, extending between the sides of the screen frame and carrying a channel shaped element 61 in which is resiliently secured an insulating member 62 e.g. of ceramic, held by nuts and bolts 65, 66. Specification 726,197 is referred to.