US2817312A - Hot dip coating apparatus - Google Patents

Description

T. H. WESTBY HOT DIP COATING APPARATUS Dec. 24, 1957 Filed April 11, 1955 IN! I INVENTOR. 7% Wssray United States Patent HOT DIP COATING APPARATUS Thor H. Westby, Chicago, Ill. Application April 11, 1955, Serial No. 500,431

7 3 Claims. (Cl. 118-122) The present invention relates to improvements in apparatusifor hot dip coating with molten metals and concerns itself more particularly with apparatus suitable for use in theapplication of aluminum on continuous steel strip or wire operation;

. The present application is related to applicants earlier filed co-pending application, Serial No. 203,565, filed December 29, 1950, now Patent Number 2,706,161.

The application of aluminum on to continuous strip or wire in mill type operation has been found to present several problems in order to achieve commercial production speeds as well as ductility, adherence and various other required coating characteristics. The covering of. iron and steel with aluminum has been undertaken with other processes before, it being regarded as a more durable corrosion resistant material for most purposes than zinc or lead. In order to be successful in a commercial sense a process should achieve all of. the foregoing and be capable of execution at cost rates which are competitive with known protective coating methods.

The preparation of the base metal, in order to receive the bond with the coating metal, has been considered one of its more diflicult obstacles. Foregoing processes have undertaken various expedients which necessitated greater cost for one reason or another. Where the cleansed base metal has had to be confined to a non-reactive atmosphere, the cost of maintaining the inert atmosphere conditions together with the attendant reduced speed of operation have brought the selling price out of the range of the competitive market.

Under some processes the bonding flux has to be kept in contiguous relationship to themolten coating metal. This is attended by a high rate of coating metal deterioration through contamination and results in consequent time loss for replenishment and ladling. Thus notwithstanding the attractiveness of aluminum as a coating deposit, its use has continued to be retarded because of the inability to maintain comparative cost positions in respect to galvanizing or lead coating as typical examples.

In my co-pending' application referred to above, there is disclosed a composition of water soluble bonding flux which will effectively promote the instantaneous adhesion of pure and alloyed aluminum to iron or steel as a base metal under conditions which may be executed in ordinary atmospheric surroundings "and under speeds of operation comparable to those of galvanizing. As a consequence there may be performed an effective and total coating of properly-cleaned and previously prepared steel and iron wire as well as sheet and strip stock under efiicient continuous mill type operation. Also, because of the instantaneous bonding action,the coating layer may be applied with an attendant shallow interfusion between the mutual contacting surfaces, thereby avoiding the consequent brittle alloy characteristics which are the result of a deep interfusion between the two metals. This permits the coated material to exhibit remarkable facilities in subsequent metal working. It has been found to have sufli- Qicnt ductility to permit over 15% in drawing and prac- 2,8 1 7,3 l 2 Patented Dec. 24, 1957 tically total freedom in respect to forming and bending.

In practicing my process, the base metal, whether wire or sheet, is first prepared by preheating or annealing and thereafter by pickling in conventional hot acid solution. The distance between the preheating and pickling stations are advantageously maintained moderately close so that the pickling operation will be assured full effectiveness, and for the additional reason of providing abundant heat reserve to carry over beyond the fiuxing operation so as to induce brisk evaporation before entering the molten metal bath.

In the accompanying illustrations,

Fig. 1 illustrates diagrammatically an arrangement of apparatus under which the present invention may be prac ticed; and

Fig. 2 is an enlarged detailed diagrammatic sectional view of the apparatus at the dipping and wiping stages where sheet or strip material is coated.

At 11 there is indicated a preheating or annealing oven at which the wire or strip stock coming from a coil is elevated to a suitable temperature for pickling. As the stock emerges from station 11 it may be directed over a guide roller or shafting 12 into a conventional acid pickling bath 13 which should remove film and surface oxidation.

As the stock emerges from the pickling tank 13, it is redirected over a guide 14 to enter a vat 15 which contains the aqueous fiuxing solution described in my referred to co-pending application. It is not necessary to wash the pickling solutionbefore entering the fiuxing vat 15 under normal conditions of operation since any carry-over of the pickling acid into the fiuxing solution innormal quantities will sustain the acid level and compensate for depletion. The replenishment of the flux ingredients may as a consequence involve the addition only of the chloride components.

In the flux vat the stock is weighted down assuring total immersion as at 16, and leaving this tank it again passes over a guide 17 and is directed into the coating metal container 18 which is heated as at 19 in order to maintain a proper molten condition of the aluminum 21 and in order to restore heat losses which are inherent in the operation due to conduction and also to-normal radiation.

The space interval between the fiuxing station 15 and the aluminum coating station 18 is advantageously one of significant magnitude since it is necessary during this transit to achieve a substantial evaporation of the aqueous traces of the flux from carrying over into the aluminum bath. This may be achieved by providing a regulation in the level of guide 17 in a vertical direction so that the interim span of the stock may be made to travel a sufficient distance to achieve a substantial drying of the flux solution. Spacing between preceding stations may be kept at a minimum in order that the traveling stock may retain sufiicient of its initial heat induced in the preheating or annealing oven to promote the just described evaporation. Alternatively this evaporation may also be assisted by a hot gas blower or similar drying expedient which does not afiect the chemical deposit borne by the stock.

In the case of wire, it has been found that sutficient drying takes place by passing the Wire over guides 17 with an intervalic span of about 10 to 12 feet. As the wire or other stock is directed downwardly into the aluminum bath 18, it passes under a sinker bar 22, the location of which, lengthwise of the bath, is advantageously adjustable.

For the purpose of providing means for varying the period of immersion within the metal bath 18 for stock of greater density or thickness requiring a proportionately greater immersion interval, the sinker bar 22 may be ad;

which are driven at rates of speed correspondingly from 200 feet per minute to 60 feet per minute. Suitable provision in the burner 19 or induction heating implements should be made to restore heat losses carried away by the stock, or a sufficient volume of molten metal 21 should be maintained so that this recovery corresponds to the rate of heat loss. 1

As the stock emerges beyond the sinker bar 21, molten metal will adhere to its surfaces in excess quantity, requiring a process of removal which will now be described.

This step in the procedure is particularly critical in respect to to aluminum and various of its alloys because of the brief range of proper fluidity characteristic inherent in this material. In the case of wire, it has been found advantageous to provide a frame 23 of substantial stability mounted on an inclined support bed 24 which should slope at an angle as nearly as feasible corresponding to the angle of the emergent span 25, as it leaves the surface of the bath 21. The frame 23 is a support structure for a series of clampingly adjustable asbestos packed wipers each of which is disposed in longitudinal alignment with a related wire strand as it emerges from beneath the sinker bar 22 out of the surface of the molten aluminum 21.

An apparatus should also be provided whereby the support structure or frame 23 may be adjusted on its bed 24 in respect to distance from the aluminum bath 18. This adjustment will be influenced by the size of Wire under treatment as well as by the ambient temperature conditions which may prevail. By regulating the adjustment of the support 23 along the inclined supporting bed 24 as the line is in operation, the attendant will be able to locate precisely the rightplaceat which the ideal fluidity prevails for performing the excess coating removal or wiping operation. This adjustment also provides a means, together with the degree of clamping of the individual wipers, for regulating the thickness of coating. The overall range or latitude of adjustment to be provided for on the bed 24 should be from 6 inches to 54 inches, the lighter gauge wires carryingtheir latent heat through shorter distances beforereaching wiping fluidity, and the heavier wires doing so over longer distances. As the wire passes over the terminal guide 26 it may be quenched by water spray if desired, and is thereafter in readiness for reeling.

In the case of sheet material as indicated in Fig. 2, the arrangement in respect to the wiping operation should follow the general teachings already described. As the stock passes over the weighted sinker bar 22 and emerges from the .surface of the aluminum bath 21, it may be passed between mutually adjustable wiping rollers 31 and 32. The latter members should also be mounted on a support structure which will permit them to be adjusted after the manner indicated between dotted outlines 31a and 32a in order to perform their roller wiping action at the instantof ideal fluidity. This support arrangement may require that for the lighter gauges of sheet stock the lowermost wiping roller 32 be able to approach conditions of partial submergence in the aluminum bath as designated.

While the present invention has been explained and described with reference to certain specific embodiments, it will be understood nevertheless that this is by way of illustration and not limitation. For scope of invention, therefore, reference should be had solely to the appended claims.

The invention claimed is: I

1. In a continuous line coating operation, a bath for containing molten aluminum at from 1200 to 1250 F., a sinker bar adjustably positionable in said bath for directing a continuous line of stock into immersion within said bath, apparatus for pulling said stock out of said bath at an angle in accordance with the position of said sinker bar, a supporting way inclined to correspond sub- 7 stantially with said angle, a series of wiping implements and a rack for mounting said wiping implements for the removal of excess aluminum from said stock, said rack including adjustment means for anchoring itself at variable distances from the bath onto said supporting way.

2. In a hot-dip coating system, a container for a bath of molten metal including heat replenishment means for maintaining a predetermined heat reserve in the molten metal bath, a sinker bar for depressing a continuous line of base metal material into the molten metal bath of said container as it progresses from a flux application station in said system, and a wiping apparatus including a supporting bed inclined to approximately the egress angle of a base metal material as it emerges from said container beyond said sinker bar, a plurality of wiping elements, a support for holding the excess coating metal wiping elements carried by said supporting bed, and means for adjusting the position of said support on said bed and thus regulating the distance between the wiping elements borne thereby and the point of emergence of said base metal material from said bath whereby to effect a controlled removal of coating metal excess at a precise instant of fluidity.

3. In a continuous hot dip aluminum coating system for wire or flat stock base metal, an open-vat heated container for molten aluminum, a sinker bar immersed in said container beneath and around which the base metal is trained to travel from preceding base metal preparatory stations, a wiping apparatus for removing excess quantities of aluminum coating from the base metal as it emerges from said container, and a supporting bed for said wiping apparatus comprising an inclined bedelement disposed to parallel the flight of the base metal as it emerges from said container, and means for adjustably securing said wiping apparatus at different positions along said inclined bed element whereby to regulate the instant of wiping to coincide with the suitable fluidity of the coating aluminum with regard to retentive heat characteristics and ambient atmospheric conditions.

References Cited in the file of this patent UNITED STATES PATENTS 1,512,371 Sommer Oct. 21, 1924 1,942,121 Potter Jan. 2, 1934 2,497,119 Fink Feb. 14, 1950 2,5 69,097 Grange et a1 Sept. 25, 1951 FOREIGN PATENTS 352,911 Great Britain Ian. 9, 1930

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