Patent GB-858637-A (GB)
Title: Method for sorting composite scrap metal
IPC: B03B9/06
Filed: 1958-07-09
Abstract: 858,637. Washing granular materials; hammer mills. AMERICAN SMELTING & REFINING CO. July 9, 1958 [July 30, 1957], No. 22000/58. Classes 59 and 82(2) Composite metal scrap, particularly light metal and aluminium scrap is separated from contaminants by crushing in a hammer mill and subjecting the crushed mixture to a density separation to separate the scrap metal fragments from the contaminants. The composite scrap is crushed in hammer mill 1 to fragments less than eight inches in size, fines are removed by screen 8, magnetic fragments by magnetic pulley 9 and the scrap fragments are fed into a sink-float drum separator 2 containing a water suspension of magnetite or ferrosilicon maintained at a density of 2.8 to 3.5 gms./cc. A water suspension of galena or a heavy hydrocarbon liquid may also be used. The sojourn time of the float particles in the separating medium should be between one to ten seconds and the distance between the inlet and outlet of the floats in drum 2 should be between one to six feet. The floats containing the aluminium are transferred to side 24 of vibrating screen 21, washed with recycled water from sprays 25 and fresh water from sprays 26 and then re-treated in a second drum separator 3, heavy liquid from hopper 74 being recycled into drum 3 with the floats. The density of the separating medium in drum 3 is maintained between 1.8 and 2.5 gms./cc. and the sink fragments from this drum containing the aluminium and heavier constituents are washed and transferred to an inclined rotary hot air drier 71 containing a screening section 97. The solid ferrous medium attached to the dried aluminium is separated by the screen, removed by rotation of the drier and collected in box 98 for re-use. The aluminium is finally melted in furnace 102 and cast into ingots. The wash water from drums 2 and 3 is treated in separate magnetic separators 47 and 86 which recover the solid ferrous medium which after washing, dewatering and demagnetizing is passed to hopper 33 for further use. The scrap may be subjected to any number of sinkfloat separations. The sink-float drum separators '2 2 and 3 comprise a drum 165 (Fig. 6) supported by rollers 166 and rotated at 4 r.p.m., with sink lifter baffles 173 mounted around the drum periphery, and stationary longitudinal baffles which extend below the surface of the liquid and prevent the floats being removed by the lifters 173. A vibrating feed shoot 181 has an extensible leg 183 for adjustment of the distance between the feed inlet and the float discharge which controls the sojourn time of the float in the liquid. The floats are discharged into launder 186 and the sinks into launder 184 and in drums the recycled heavy liquid from hopper 33 (Fig. 1) is discharged into the liquid via pipe 36 while in drum 3 it is discharged on to shoot 181. An alternative apparatus is shown in Fig. 7 and comprises a cone shaped tank 198, vibrating shoot 199, air lift and agitator 189, sink launder 190, float baffle 191, float launder 192 and stirrers 197. A hammer mill for crushing the scrap (Fig. 2) comprises a feed shoot 117, a driven shaft 124 on which are mounted two pairs of arms 125, 126, and hammer members 130 mounted on pins 127 and 128. Hammer elements 132 project from the rim 131 and have dull edges 133 so that on rotation of shaft 124 at 600 to 2,000 r.p.m. the hammers crush the scrap against back plate 120, the crushed scrap discharging through grate 121. Oversize scrap pieces are ejected through the weighted closure members 137 pivotally mounted on shaft 136. The position of members 137 may be adjusted by a handle 138. In an alternative hammer mill (Fig. 4, not shown) a series of discs mounted on a driven shaft each carry three hammer elements which are mounted on the disc periphery so as to be free to swing about their mounting pins.