Patent GB-486584-A (GB)
Title: Improvements in and relating to a method and apparatus for coating metals by dipping
IPC: C23C2/36
Filed: 1936-10-06
Abstract: 486,584. Coating with metals. HERMAN, J. L. Oct. 6, 1936, No. 27149. [Class 82 (ii)] To obtain a coating free from oxides on articles coated with metal by dipping, the articles are withdrawn from the molten metal into a non-oxidizing atmosphere through a part of the surface of the metal that is being constantly changed by movement of the metal to render it free from oxides &c. The movement of the metal is preferably in the same direction as that of the emerging article, e.g. it may comprise a stream of metal erupting from the surface. To prevent the inclusion of a large amount of iron in the coating when galvanizing iron or steel articles, the duration of immersion is preferably small, e.g. 3-5 seconds, and the bath temperature is kept low, e.g. 800-838‹ F. In the apparatus shown, Fig. 2, for galvanizing wire, a pan 11, comprising a central compartment 15, an inlet compartment 16, and an outlet compartment 18, is supported in the coating bath. The inlet and outlet compartments are open at the bottom and are bounded by side and end walls and top walls or covers. The central compartment is closed at the bottom except for a passage 26 in which is a pump or propeller 25 which draws molten zinc from the bath into the compartment 15 and forces it through a passage 31 into a shield 35 located partly in the bath and partly in the compartment 18, the zinc overflowing at the top of the shield. The pump or propeller also forces zinc through a trap 32 into the compartment 16 to create a surface movement of the zinc in this compartment to prevent accumulation of oxides, &c. Non-oxidizing gas is admitted to the compartments 16 and 18 through pipes 23 and 36 respectively. The wire passes through the inlet compartment into the zinc bath, under a roll 21, and up through the shield 35, the movement of the zinc in the shield in the same direction as the wire being stated to produce a thick even coating, free from oxides. The non-oxidizing gas in compartment 18 is preferably cooled to prevent the coating from running down the wire, which is passed rapidly up through an extension 38, filled with the gas, which terminates in a slit or nozzle 40 at which the gas escapes and may be burnt, the gas or flame enveloping the wire and preventing oxidation. The coating is then set by jets of water issuing from one or more nozzles 41, which may be on one or both sides of the wire, the water being supplied to the nozzles from a pressure tank 42. The wire is again sprayed by jets from nozzles 51 while passing over a roll 49 into a water bath 43 from which it passes to the take-up blocks or reels. In a modification the central and inlet compartments of the pan 11 are omitted, the pump or propeller being situated in a casing adjoining and communicating with the shield but closed on the top by a sloping wall. In the form shown in Fig. 5 no pump or propeller is employed, the upward movement of the zinc at the point of discharge being produced by arranging the shield 77 within a casing 73 with side walls extending above the level of zinc in the bath, the top of the shield being below this level so that the pressure of the zinc in the bath produces the upward flow. The casing 73 forms part of a compartment 67 which is filled with non-oxidizing gas. Zinc overflowing from the shield into the casing 73 is removed continuously or intermittently by means of a pump attached to an outlet 79, and returned to the bath. The galvanizing of wire for various purposes, e.g. for telephone and telegraph wires, fencing, door and bed springs, and garment hangers, and of buckets and utensil handles is referred to.