Patent GB-637537-A (GB)
Title: Apparatus for coating or impregnating metal strip stock with metal
IPC: C23C2/00
Filed: 1947-07-31
Abstract: 637,537. Tinning. GENERAL MOTORS CORPORATION. July 31, 1947, No. 20783. Convention date, Jan, 29, 1941. [Class 82(ii)] [Also in Group XXII] Apparatus for the coating or impregnation with metal of metallic strip comprises a pair of end chambers adapted to be partially filled with molten metal, through which chambers the strip successively passes, an intermediate chamber adapted to be avacuated and connected with each end chamber by a throat which fits closely round the strip, and a supply tank and pump to supply molten metal to each of the end chambers so as to maintain the level of the metal therein above the surface of the strip and to seal the two end chambers from the intermediate vacuum chamber. In Fig. 2, which shows the apparatus diagrammatically, the strip passes through coating chambers 24, 28, an intermediate vacuum chamber 26 and a casting gate 128. Reducing gas is supplied to the chambers 24, 28 and the chamber 26 is connected to a vacuum pump by the pipe 32; the latter chamber also includes a vibrator 54 to assist in dislodging occluded air from the strip. Metal is continuously circulated through the chambers 24, 28 by pumps 40, 42 from a melting chamber 38 to which it returns through pipes 48, 50 connected to weirs 44, 46. Metal escaping into the chamber 26 returns through a pipe 36, the length of which is greater than the barometric head, to a sump 34, the level in which is maintained by an automatically operated pump 52 which returns excess metal to the chamber 38. The chambers 24, 26, 28 are separately heated. The strip is guided through the chamber 26 by means of perforated tubes separated at the centre of the chamber, and is maintained in this chamber at a temperature above the melting point of the impregnating metal. The chambers 24, 26 28 have a common insulating jacket, filled with heat insulating material or comprising a dead air space and the chamber 38 is also insulated. The throat 70, Fig. 4, through which the strip passes from chamber 24 to chamber 26, is carried by a tube 84 secured to the outer throat 86 so that both throats may be withdrawn for changing when different sized strips are operated upon. The bottom of the chamber 24 slopes towards a drain 94 connected through the pipes 96 to the pump 40. An inspection window is provided. The throat between chambers 26, 28 is also connected to the outer throat of the chamber 28 for withdrawal: this throat comprises a series of serrations to allow restricted flow of metal out of the chamber 28 on to the top of the strip. The bottom of the chamber 28 is constructed similarly to that of chamber 24. The height of the weir 45 is adjustable by means of a handwheel 116 which actuates a semi-cylindrical weir level 118, Fig. 9: a hand-wheel 124 is used to operate a valve 126 when it is desired to drain the chamber 122 between the weir and pipe 50. The casting gate 128, Fig. 8, comprises a wire brush 130 to remove molten metal from the underside of the strip and laterally adjustable, side rails 132 spring pressed against the sides of the strip: resiliently mounted levelling plates are also provided, being carried on blocks 140, Fig. 14, longitudinal chambers 174 extending therethrough to supply gas and and air to burners 180 to heat the rails 132: other longitudinal chambers 182, 184 serve for the circulation of cooling water. The molten metal is caused to set by water jets 150, Fig. 8, gas jets 152 being provided to heat the corners of the rails 132 to prevent sticking. The casting gate also comprises spring-urged rollers 154, 155. In a modified form of casting gate, Fig. 17, spaced, internally heated, laterally adjustable rollers 190, 192 rotate in opposite directions on either side of the strip, to prevent metal running off the sides of the strip. The depth of metal is controlled by an internally heated transverse roller 200 driven in synchronism with a grooved roller 208 and pivotally mounted for adjustment of coating thickness. Water jets play on the under surface of the strip before and after the rollers 200, 208, the first jet cooling and the second freezing the coating metal. A hood may be provided over the rollers 190, 200 to contain a non-oxidising atmosphere. The strip is pretreated by passing over burners 241, Fig. 22, and beneath a hood 250 to which reducing gas such as hydrogen, carbon monoxide or mixtures thereof, is fed, immediately before entering the chamber 24. Alternatively, pretreatment may be effected by passing between spring pressed rollers 275, 277, Fig. 26, current being passed along the strip between the rollers and the molten metal in the chamber 24, reducing gas being again supplied to the hood 250; or heating may be effected by induction. In a further modification, Fig. 24, the strip is fluxed by means of a liquid fed from tank 260 by sponge rubber rollers 256, 255, 254. The level of liquid in the tank 260 is float controlled: the flux may be zinc chloride solution.