US3227577A - Metal coating of long lengths of metal bodies - Google Patents

Description

Jam 4, 1966 K. I-I. BAEssLER ETAI. 3,227,577

METAL COATING OF LONG LENGTHS OF METAL BODIES Filed Sept. 18, 1962 4 Sheets-Sheet 1 HYDROGEN 3837 FIG. I

METAL COA'IING OF LONG LENGTHS OF METAL BODIES Filed sept. 18, 1962' Ja- 4, 1956 K. H. BAESSLER ETAL 4 Sheets-Sheet 2 .rom E32-E344 Jm mJ E32-2344 2950.2

Jan' 4, 1966 K. H. BAESSLER ETAL 3,227,577

METAL COATING LONG LENGTHS OF METAL BODIES Filed Sept. 18, 1962 4 Sheets-Sheet 5 WIRE FROM THERMOSTAT APPLICATOR ARRANGED TO W l2\} T TURN ON HEATER 62a IF TEMPERATURE IS LOW,OR COLD 63 WATER IF TEMP- Q ERATURE ls HYDROGEN HIGH @D i ,|19 w TEMPERATURE Jan- 4, 1965 K. H. BAr-:ssLER ETAL 3,227,577

METAL COTING OF LONG LENGTHS OF METAL BODIES Filed sept. 18, 1962 4 Sheets-Sheet 4 T .m R S RE m w um R m .E M F 2 WH/ T R F B F. 4 L V 3 EU 0 0 2 RB DE wE El mw Mm .H O N PS Cw E 4 3 cMN... Ml E O 3 T5 UT R m 2 2 NA D W W E Y D 2 o UR H E O O O 1. LI .m 2 2,2 M Aw 02 L. W k m L.; 2` E1; w m 2 ww EL 1 www S 2l 5 En G. 2 M Il v .m Tw... AP ww ms 1(\ United States Patent O 3,227,577 METAL `ClOAllNG F LQNS LENGTHS 0F METALL BDlES Karl Hurst Eaessler, Walnut Creek, Calif., and Harry Robert Gardner, Jr., Trenton, Howard .lohnson- Godfrey, Pennington, and Dartrey Lewis, Trenton, NJ., assignors to The Colorado Fuel and lron Corporation,

Denver, Colo., a corporation of Colorado Filed Sept. 1S, 1962, Ser. No. 224,349 18 Claims. .(Cl. 117-102) This invention relates to coating of long lengths of metal bodies, such as wire and strip, with molten metal; the molten metal being caused to solidify to form a coating on the metal bodies. More particularly the invention relates to coating long lengths of metal wire or strip with molten aluminum and causing the molten aluminum to solidify as a coating upon the wire or strip.

According to the invention the metal strand to be coated with a coating metal is passed through an aperture die in a bath of the molten coating metal; the aperture in the die being slightly larger than the cross section of the strand so that as the strand passes through the die the outer surface of the strand is in contact with molten metal occuping the annular space between the strand and wall of the die and simultaneously as the strand continuously moves through, and outwardly from the die, the thickness of molten coating adhering to the strand may be controlled by a confined fluid pressure, i.e. static pressure, applied at the outlet end of the die against the molten metal in said annular space in a direction opposite to the direction of travel of the strand.

The process of the invention will hereinafter be described in connection with typical embodiments involving the coating of steel wire with aluminum but it will be understood that the principles of the process may be used for coating of metal products other than steel wire with molten metals other than aluminum, such as, for eX- ample, coating with zinc, zinc containing minor amounts of aluminum, tin, alloys of aluminum, and the like.

In general, the process of this invention, according to one manner of carrying it out, involves thorough cleaning of the steel wire, and removing any oxide if present on the surface by heating it in a hydrogen atmosphere or by other suitable method, and then passing it into a bath of molten aluminum, preferably in a downward direction, and out of the bath through a die which serves to control the ow of the molten aluminum onto the surface of the wire as a concentric coating of uniform and controlled thickness. After emerging from the aluminum bath the wire is passed, preferably in a downward direction, through an elongate chamber containing a gas, preferably a non-oxidizing gas such as hydrogen, under pressure which also serves to control thickness and surface characteristics of the coating, and then through a cooling bath, preferably water, under controlled conditions to further cool and solidify the coating. The wire emerges from the cooling bath as aluminum coated wire.

The invention also provides certain novel method steps and apparatus which is useful in carrying out the steps of the process, as described in further detail hereinafter.

Although the novel features which are believed to be characteristic of the invention are pointed out in the annexed claims, the invention itself as to its objects and advantages and the manner in which it may be carried out may be better understood by reference to the following more detailed description, taken in connection with the accompanying drawings, forming a. part hereof, in which FIG. 1 is a view primarily diagrammatic showing apparatus and illustrating the various steps for carrying out the process of the invention;

3,227,577 Patented Jan. 4, 1966 lFlGf.. 2 is a partial and semi-diagrammatic sectional View on a larger scale showing the apparatus for passing the wire in a guided path downwardly through the molten aluminum 'bath and more particularly the coating die arrangement for controlling the flow of molten aluminum onto the wire;

FIG. 3 is a view somewhat similar to FlG. 2, but showing a modified form, including a wire guide and floating die',

FIG. '4 is a partial and semi-diagrammatic sectional view of a modified form of cooling apparatus for cooling the coated wire after the molten coating has been applied; and

FIG. 5 is a partial 'and semi-diagrammatic sectional View of a different form of apparatus for controlled cooling of the lwire after the molten aluminum coating has been applied.

Referring now to the drawings, in which like reference characters denote like parts throughout the several views, the cleaning apparatus sometimes called the cleaning line and the other units of one form of plant for practicing the invention are shown diagrammatically in FIG. 1. As shown, there is a payoff reel, or swift 11 upon which the wire to be coated is wound and from which it is unwound and passed continuously through the various units of the plant where various treating steps are carried out. The wire, designated generally by reference character NV, after passing through the system is finally wound on a driven reel or take-up block 12. It will be understood that the block is equipped with the necessary guide rolls, driving mechanism, indicators and other equipment known to those skilled in the art. rl`he wire W in its various stages as it proceeds successively through the various units of the apparatus is designated by refe-rence character W coupled with an identifying numeral, as for example: W1, W2 etc. The wire W in the illustrative embodiment is steel wire having a diameter of 0.146 which was drawn from hot rolled rod stock made from carbon steel having specifications as follows: C O20-0.25%, Mn .20-.55%, P 0.040% max., S 0.050% max. lt will be understood that the specification of the wire is given `as one illustrative example.

In the process as illustrated, the wire W1 from reel 11 passes through a tank 13 containing a molten lead bath 13a maintained at about 850 F. to decompose soap which has been picked up by the wire from the dies in the previous drawing operation. The emerging wire W2 passes through a Water dip' 14a in tank 14 to partially cool the wire before it enters a hydrochloric acid bath 15a in tank 15. The hydrochloric acid bath is maintained at about 15% acid and at about 130 F. Til-ence the wire W4 passes through a cold water wash 16a in tank 16.

The emerging wire W5 then passes through alternating anodic, cathodic and anodic cold sulfuric acid baths 17a, 18e, 19a respectively in tanks 17, 18, 19, the electrolysis system `being designatedby reference numeral 20. The sulfuric acid is approximately 50% by volume yat a temperature maintained preferably between F. and 100 F. An anodic current of about 1500 xcoulom'bs per square foot is maintained. The wire W6 is then w-ashed in hot water 21a maintained at about 150 F. in tank 21. The emerging wire W7 is then 1subjected to an ultrasonic water wash 22a :at about 150 F. in tank 22. The ultrasonic wash consists -of applying 1000 watts per wire at about 40 kilocycles frequency. The emerging wire W8 is `then dried in hot air dryer 23. The construction of suitable cleaning apparatus as mentioned above is known to those skilled in the art.

lt is essential that the cleaning steps employed produce a chemically clean `surface on the wire which is free from dirt, smut or other contaminating substances. However, in some instances the cleaning need not be done exactly as described Iabove. For example, an alkali cleaner may be substituted for the hot lead bath, or the wire may be heated in a furnace yto decompose the soap film on the wire. If the soap on the wire which may have been picked up in the prior wire drawing opera-tions is not -too heavy the hot lead may be omitted. Also, the hydrochloric acid step may be omitted if the wire has been cold drawn and is reasonably free from excessive soap, scale or rust. The anodic sulfuric acid cleaning step is useful for removing carbonaceous smut from lthe surface of the wire. The ultrasonic cleaning is useful for removing loose dirt from the wire surface and to some extent serves the same purpose as the anodic sulfuric acid. One or more of these steps may be omitted if otherwise the wire is thoroughly cleaned. The significant point is that the cleaning steps produce a wire surface that is thoroughly free from dirt, smut, or other con- -t-aminating substances.

After thorough cleaning, the Wire is heated in hydrogen to a temperature between 1300 F. and 1800 F. The purpose of heating in hydrogen is to react with any i-ron oxide film, that may be present on the surface `of the wire to reduce the iron oxide to be metallic iron. If desired, the wire may be exposed to air during the early stages of raising its temperature to the range stated above, so that a visible (yellow, blue or gray) oxide film is formed on the wire. Then when the wire is sufficiently hot the oxide film is then reduced to iron by the hydrogen. The hydrogen is preferably passed in a confined stream enveloping the wire and in a direction -counter to the direct-ion of the movement of the wire. Preferably, the hydrogen is introduced at a point near the surface of the molten aluminum bath through which the wire passes ina downward direction, as described in further detail hereinafter. The significant point is that the surface of the wire be thoroughly cleaned and freed from oxides or other contaminant-s.

As illustrated in the drawings, t-he wire is heated by passing an electric current through the wire while exposing the wire to a hydrogen atmosphere. In the arrangement shown, one phase a of a three-phase supply is connected with the travelling wire at and 25a by means of contact pulleys 26, 26a. The other two phases b and c are connected with the wire Iat intermediate points 27 and 2S by similar contact pulleys 27b and 28C. This arrangement constitutes a delta -three-phase circuit in which the wire W9 forms the connection between the three phases. Since the portion of the wire entering and the portion of wire leaving the heating zone are both at the same potential and since the wire at Ithese points is connected to grounded objects, there is no potential above ground on the payoff lor take-up reels. Other methods of heating the wire may be employed, if desired. For example, the wire may be heated in a tube furnace.

In the apparatus, as shown, the wire during heating is passed through an elongate heating tube having a confining wall '30; thus provid-ing a tunnel 31 through which `the wire may travel while hydrogen may be and is, passed in a counter direction in a confined stream enveloping ythe wire. The wire passes over a pulley 32 mounted in the tunnel and thence in -a downward direction, through a vertically disposed length 33 of the tubular tunnel 31. This forms a pipe section 34 of lthe tunnel which extends into the chamber 35 of a heated furnace 36 which contains a pot of molten aluminum. The vertical section 33 of the tunnel is provided with connecting hollow conduit 37 which 'is connected -to a source 60 of hydrogen under pressure. 'This conduit 37 provides a port 38 near the surface 39 of the molten aluminum 40 in furnace 36, later -to be described. It will be observed that the lower end 41 of the vertical tube section 33 extends to 'a point below the surface 39 of the molten aluminum bath 40. Thus, hydrogen under pressure introduced through port 38 will be constrained to dow through the tunnel in a direction counter to the direction of travel of the wire. The hydrogen may be vented through a wire guide or aperture 42, in the closure piece 43 or through other suitable vent mean-s at the forward end of the tunnel 31.

After heating the wire and while it is still enveloped in a hydrogen atmosphere, the wire W10 passes over rotatably pulley 32 and thence downwardly through the tube section 33 which may be in the form of a pipe. The wire then passes vertically downward int-o the molten aluminum 40, entering the bath at a point below the surface 39 rof the molten aluminum. The distance between the wire heating zone and the aluminum ba-th is chosen so that the wire W10 enters the molten aluminum 40 in furnace 36 at a temperature near to the tempera-ture of the molten metal, which is maintained at 'about 1275 F.

The aluminum bath 40 may be maintained at the required temperature by any suitable means. As shown in the illustrative embodiment (FIG. 1) this is done by heating elements 45, known in the art as Globar heating elements. Preferably, the furnace 36, and as shown, is lined with a liner 46 of silicon carbide bonded with silicon nitride. Or the furnace may beV lined with other suitable material which is not attacked by the molten aluminum. Solid or liquid aluminum may be added to the aluminum pot 36a in the furnace by any suitable means to maintain the level of the bath reasonably constant and to replenish molten aluminum that is removed from the bath as the coating operation proceeds. As shown in FIG. 1, the aluminum is replenished by feeding aluminum rod 47 through an appropriate aperture 48 in the furnace wall into the bath by driven feed rolls 49. If desired, the feed rolls may be driven automatically in response to a bath level sensing device in order to maintain a constant level of the molten bath 40.

The tube section 33, extends vertically downward through an appropriate aperture 50 in the roof 51 of the furnace, to a point 41 beneath the surface 39 of the bath. A bafiie partition 52 having its lower edge above the bottom of the pot 46 and its upper edge above the surface of the bath permits clean aluminum only to pass underneath the baffle to the coating section 53 of the pot.

The wire W10 passes downwardly through the molten aluminum in the coating pot section 53 of the furnace and passes downwardly through an applicator die 5S. The die, which is described in further detail later on, permits the molten aluminum to ow downwardly from the aluminum pot around the wire in the form of a continuous coating which is attached to the steel wire by alloying with it and the amount of coating is limited by the size of the orifice 56 in the applicator die 55. As shown in FIG. 1, the applicator die has an annular shoulder 57 from which concentrically depends a neck portion 57a fitting into a hollow boss 58 depending from the bottom wall 59 of the furnace.

In coating steel wire of .146" diameter, for example, it has been found that if the thickness of the coating exceeds about .005, it is difficult to obtain a smooth coating. Also it is difficult to maintain an orifice on the applicator die having a diameter less than .010 larger than the wire diameter. However, it has been found that the hole or orifice diameter in the applicator die can be increased to about .030 larger than the wire diameter without obtaining an excessive flow of aluminum by applying hydrogen, or other suitable gas, confined under pressure against the outiiowing aluminum at the outlet end of the die as the wire travels continuously through the die. For example, in coating wire of the size mentioned above, the preferred orifice 4size is .020" larger than the wire diameter. For various sizes of wire the minimum orifice size is about 7% larger and the maximum orice size is about 21% larger than the wire diameter, and the preferred orifice size is about 14%V larger than the wire diameter.

As shown in FIG. 1, hydrogen 60a under pressure, from a suitable source 61 is introduced into pipe 62.

This pipe at its upper end is sealed around the boss 58 and depends vertically downward' with its lower end below the surface 63 of a water bathV 64' maintained in a suitable tank 65 located below the aluminum bath'. Thus, the upper end of the chamber providedr by pipe 62 communicates with the annular space between the wire W2 and the peripheral boundary of the orifice S6 and the lower endv of this chamber communicates with the water bath 64. This is described in further detail later.

The coated aluminum Wire W12 travels downwardly within vertical pipe 62. Hydrogen is introduced into this pipe through a port 65a under sufhcient pressure to cause it tobubble out of the water 54 in tank o5. The gas pressure in pipe 62 is therefore maintainedr constant and equal to the head 66 of water between the lower end 67 of the pipe and the surface of the water. The gas pressure in the pipe may, of course, be adjustably varied by raising or lowering the lower endv of the pipe' in relationto the surface 63 of the water bath; for example, by raising or lowering the surface of the water which may be done, by adjusting the height of overflow conduit 68 in the water tank.

It has been found that with a constant diameter orifice 56' in the applicator die of about .020'H larger than the diameter of the wire (which in the case now being describedA is .146 diam.), the thickness of the aluminum coating on the wire can be controlledV by varying the pressure head e6. For example, with a molten aluminum bath in applicator pot 53 which is 11/2 deep, the thickness of coating on` the .146 diam. wire may be varied between .0005 and .005 by changingy the head 66- from l to 4 of water pressure with a substantially constant linear travelling speed' of the; wirev within the range of about 8O feet to 130 feet per minute. It will be understood, of course, thatY the hydrogen static pressure in-pipe 62 is equal to the water head.

It has beenV found that the thickness of the coating depends upon the head of molten aluminuml in the aluminum furnace above the level of the applicator die, the clearance between the wire and the die, the length of the cylindrical portion of the die, the speed' of travel of the wire, aridthe back pressure exerted by the gas at the outlet end of the die. The back pressure ofthe gas counteracts the gravitational force or pressure of the molten metal due to its head in the furnace' and the' velocity head caused by the speed of travel of the wire as affected by the length and width of the die oriiice. The back pressure may be varied between i) and 6 inches of water pressure according to the required coating thickness for a 11/2 head of molten aluminum in the furnace. lf a deeper aluminum bath is used the maximum back pressure on the gas at the outlet of the die should be increased at the rate of about 21/2 of water pressure for each inch of additional aluminum head..

ln the process now being described, it will be seen that gravity is used to assist in controlling the` coating; Since the wire emerges vertically downward, the molten aluminum, as the wire leaves the applicator die, tends to form a concentric coating, and: since gravity is pulling the aluminum downwards, a much heavier coating can` be produced on the wire than would be the case' if the Wire were to emerge from the molten aluminum` bath' horizontally or upwardly.

In order to assist the formation of a concentric coating it has been found that a oating die has advantagesV over a die that is fixed or stationary. One form' of floating die arrangement is shown in FIG. 2. It comprises a centrally apertured die member mounted for limited lateral movement within a cylindrically shaped cage 7i) which is secured in stationary fashion to the bottom refractory liner wall 71 of the furnace. The cage has av central cylindrical inverted cup-shaped space '72' of a diameter larger than the outside diameter ofthe cylindrically shaped die' 55a. The cage has an inwardly extending annular shoulder 73 which provides an opening 74 inthe upper'end of the cage. This shoulder' serves as -a retainer member to coniine the extentV of vertical movement of the floating die 55a which normally rests upon the upwardlyl extending hollow boss 75 inthe bottom wall '71 of thecoating section 53 of the aluminum pot. The iioating die 55afhas a central cylindrically shaped diev hole 56a, a bevelledhollow throat portion 76 at its upper end and a flared eXitportion 77 at its lower end. lt will be observedZ that the wire W11 travels downwardly through the pipe section, through the central opening 'id` of the cage, then through the die hole 56a into pipe section 62, in which hydrogen' is maintained under pressure correspondingV to4 the water head 66 (see FIG. 1). It will now' be seen that: the die 55a is free to move laterally within a limited, range and vertically within a small tolerance and oats inthe molten aluminum which enters the cage through opening 74. Hence, if therev is a deviation in' the vertical path of travel of the wire the die will move so that the die hole 56a will assume a position concentric with the wire, thus aiding in assuring that a concentric coating ofaluminum of uniform thickness is deposited on the wire because the die is self-centering. The gas press re in the pipe 62 puts suhicient back pressure upon the molten aluminum around the periphery of the die to prevent unwanted leakage of the liquid around the die. And, as mentionedabove, the gas pressure is alsoV utilized to control the thickness of coating adhering to the wire.

Another modication of a iioating applicator die arrangement is illustrated in FIG. 3'. ln this arrangement the cage is provided with a wire guide arranged above and in vertical alignment with tthe applicator die. The cage 7h12 comprises a hollow refractory member of generally cylindrical shape secured, by refractory gasket 94a, at its bottom end tothe bottom of the coating section 75-of the aluminum' pot. lts upper end 80 extends above the surface 39 of the molten aluminum. The central inverted cup-shaped'portion 72b provides a cylindrical space within which is mounted an applicator die 55h similar in shape to die 55a. It has an upwardly fiaredk throat 75h, a cylindrical portion 56e, anda downwardly flared exit portion 7'7b. This applicator die may be made: of a size fittingV snugly within the inverted cupy portion, as shown in FIG. 3. Or the applicator die may be' made to have a diameter as shown in dotted lines 81, smaller than the diameter of inverted cup 72b to'provide a floating die. Horizontally disposed bores 82, 83',` 34 connecting with each other and with the molten `aluminum bath' 49 permit entry of the molten aluminum containedr in the potv into the centralk hollow portion of the cage and' thence into the flared throat 761; of the applicator die. Mounted within thevertical central opening 854 of the cage member-'7013 is a hollow adapter member having an'annular shoulder 87 and a depending guide-retainer portion 8S in which is. mounted a. centrally bored wire guide die S9 resting uponv inwardly extending annular shoulder 9i?. The upper' end of the adapter is secured by means of a refractory gasket 94' and sealed to the lower end of the' conduit 34, through4 which the wire W10 travels downwardly. ln this arrangement the wire is` guided bythe centrally bored guide die S9 which is mounted in vertical alignmentI with the' central boreV Sec of applicator diei 55h. The guide die 89 is made of a suitable wearresisting material suchy as tungsten carbide. The die, as shown is made of tungsten carbide sold under the name Carboloy; The guide die is advantageous because it insures that the running position of the Wire as it travels downwardly is kept in a' vertical path. The lining for the aluminum furnace and other parts of the apparatus withv which. the molten aluminum comes into contact shouldv be made of a material-which is not soluble inthe aluminum so that the coating is contaminated to minimum extent by such metals as iron and silicon. In this connection suitable materials for the aluminum pot are silicon carbide bonded with silicon nitride, and aluminum oxide refractories. Suitable materials for the applicator and guide dies are tungsten carbide, aluminum oxide refractory, certain silicon carbides, and oxidized Type 304 stainless steel. Silicon carbide bonded with silicon nitride has been found to have advantages as a material for constructing the pot and applicator die and the related apparatus.

One of the problems in coating steel wire with 'aluminum is caused by the fact that there is likely to be a very rapid formation of a brittle aluminum-iron alloy at the interface between the aluminum and the steel. If this alloy layer is too thick it will crack when the wire is bent and cause spalling of the coating. Also, if the coated Wire is subsequently to be reduced in diameter by drawing through dies, the alloy layer, if too thick, will crack and cause the coating to peel off. In order to overcome this diiculty it has heretofore been common practice in the art of coating steel wire with aluminum, to alloy the aluminum applied as a coating with 3% to 5% of siliconwhich markedly reduces the rate of formation of the aluminum-iron alloy layer.

The thickness of the aluminum-iron alloy layer also depends upon the time allowed for its formation. This time includes the time in the molten aluminum bath and the time after emerging from the bath until the coating is solidified. According to one feature of the process of this invention, the time that the wire is in the molten aluminum is very short due to the fact that the depth of the bath is only a few inches and the time until the coating solidies is reduced by cooling the wire under controlled conditions after it leaves the aluminum coating bath. In the apparatus, as shown in FIG. l, the wire is given a preliminary cooling in the pipe G2 and then is further cooled to insure desired solidication in the water bath 64 in tank 65. The usual operating speed for the process is a controlled linear speed within a range of from 60 to 300 f.p.m. (feet per minute). Thus, for example,- at a speed of 120 fpm., or two feet (2') per second, and an aluminum coating bath two inches (2) deep and a distance of three feet (3') from the aluminum bath to the water bath, the time of the wire in the aluminum bath is one-twelfth (1/12) second and the time from the aluminum bath to the water bath is one and one-half (l1/z) seconds and these times are so short that the aluminum-iron alloy layer that is formed is less than .0004" thick and usually in the neighborhood of .0002 thick when using pure aluminum for the coating material. Consequently the process is capable of producing pure aluminum coatings on steel wire which are suiiiciently ductile to permit the coated wire to be wrapped on its own diameter without spalling the coating. Furthermore such a coated wire may be cold drawn through dies of smaller diameter without stripping oi the coating.

It has been found that the appearance of the coating depends upon the rate and manner of cooling. Hence, it is important in practicing the process to control the ternperature of the water bath in tank 65 so that the surface of the coating will have a desirable smooth and shiny appearance. With the arrangement as shown in FIG. 1, it has been found that, if cold water, say at a temperature somewhat below 90 F. is used, the surface of the aluminum coating has a cratered appearance whereasat temperatures above about 90 F. the surface becomes smooth at about 115 F. and above this temperature the surface produced is smooth and shiny. At temperatures higher than about 115 F. the coating may still be liquid or at least too soft by the time the coated wire W13 reaches the guide sheave 92 in the water bath. In such case the guide sheave is arranged to allow the wire to have further time in the coolant before reaching the sheave. The guide sheave is mounted for rotation in a position to cause the wire to travel vertically through the aluminum pot and pipe 62. The time of exposure of the wire cit 8, W13 to the cooling water 64 may be regulated by raising or lowering the position of the guide sheave. However, 'there is an upper limit for the water temperature above which the cooling of the wire and adhering aluminum 'coating is too slow for practical use. Consequently, it has 'been found desirable to control and maintain the temperature of the water cooling bath at a temperature within the range of to 200 F. After passing over the rotatable guide sheave 93, the aluminum coated wire is taken up by any suitable arrangement, such as rotatable :receiving block 12.

A modified form of apparatus for water cooling the coated wire is illustrated in FIG. 4. In this arrangement the wire from the applicator die passes through a hydrogen-containing pipe 62a, corresponding, in general, to pipe 62 of FIG. 1. Pipe 62a extends into a Water tank a distance below the surface 102 of water 103 in the tank at least suflicient to provide the maximum head of hydrogen which it is intended to use in pipe 62a. A hydrogen inlet nipple 63 is provided which is connected to a source of hydrogen under pressure. An outlet nipple 63a is connected by a conduit 104 to a tube 105 which extends into a pressure-regulating tank 106 below the surface 107 of water therein by a distance d. The outlet of tube is adjusted to a distance a' below the surface of the water which will provide an adjusted pressure of hydrogen within the tube 62a corresponding to distance d as desired and the tube may be held in adjusted position by clamp 108. As mentioned above the pressure is regulated in pipe 62a to control thickness of coating applied to the wire.

The tank bottom is provided with an outlet nozzle 109 in vertical alignment with pipe 62a. Water may flow from tank 101 through the nozzle, through which also passes the coated wire W12 which is cooled by the water as the wire passes through the tank 101. Water from nozzle 109 is caught in a sump tank 110. A water pump 111 takes suction from the tank 110 through suction pipe 112 and circulates it back to tank 101 through discharge conduit 113, through a water heater 114, thence through conduit connected to the tank. Make-up cold water is supplied through a pipe 116 having a manually operated valve 117 and a solenoid valve 118 which is operated automatically by a thermostatic controller 119 connected to the valve 11S and a temperature sensor 120 in the water in cooling tank 101. An overflow pipe 121 maintains a constant level of water in tank 101; the overow passing into sump tank 110 which is provided with an over- :tiow pipe 122 which carries away superuous water. Thus the temperature of the cooling water in tank 101 may be adjusted and kept constant at desired temperature. In order to promote the formation of a smooth coating, the tank is provided with a vertical baie 123 terminating at its upper end below the surface 102 of the water 103 and at its lower end above the bottom of the tank to reduce turbulence of the water yin the section of the tank through which the wire passes.

The coated wire after passing through nozzle 109 is carried over a rotatable sheave 124 to a reel, such as take-up block 12, as shown in FIG. l.

The appearance of the coating also depends upon the nature of the gas in pipe 62. If air is used a rough and poor-appearing coating may result; if a non-oxidizing gas, such as hydrogen, is used a bright-appearing coating can be obtained. Other suitable gases for obtaining a bright coating include nitrogen, argon, helium and air from which the oxygen has been removed.

An alternative apparatus and method for freezing the aluminum coating on the wire, after the wire leaves the applicator die is illustrated in FIG. 5. In this method the coated wire after it passes through the hydrogen gas in vertical pipe 62, depending from the aluminum pot, is further cooled in a vertical water column supported by water flowing through an annular orifice. Apparatus for doing this, as shown in FIG. 5, comprises a water cooling tank 200 into which extends the hydrogen-containing pipe 62 which depends from the aluminum pot (see FIG. 1). As shown the tank 200 has a cylindrical side wall 201 and an open upper end 262. The water tank 2% is mounted concentrically within an overflow water tank 203 providing a reservoir. The reservoir tank 293 has an open upper end 204 and a bottom closure wall 295 having a central opening 206 from which depends a hollow neck portion 207. Mounted on the hollow neck is a. jet or nozzle device 298; As shown, this nomle device comprises a T, similar to a .pipe T, having .a hollow body portion 209 from which extends upwardly one leg 210 of the T and from which extends downwardly another coaxial leg 211 and from which extends outwardly the third leg 21.2 of the T. A centrally apertured plug 213 is secured in the hollow leg 210;. The Iplug has a cylindrical bore 214 terminating in an outwardly flared end 215. The upper end of the bore is, securedl to the depending hollow neck 207 of the cooling tank 200 in axial alignment therewith. Extending into and secured to the lower leg 211 of the T is a hollow plug 215 having an upwardly extending nipple portion of smaller diameter than the hollow body 209 of the T. The nipple 217 at its upper end terminates in a taperededge 21S compl.,- rnentary to the ared hollow portion 21S of the upper plug 213, this tapered edge terminaing short of the ii'ared wall 215. The lower plug has a central bore 19 in axial alignment with the bore 21d of the upper plug. Hence, there is provided an annular orice 2211l between the upper and' lower plugs; this orice extending upwardly and inwardly toward the vertical axis of the aligned bores 214, 219. Consequently the wire W12 may pass vertically downward' from the applicator die in the aluminum pot, through 4hydrogen-containing pipe 62, through cooling water 221 in the water tank and thence through the bores 214 and 219:.

The bottom wall 205 of overiiow-reservoir tank 203 has: an outlet port 222, connected to the intake conduit 223` of a suitable pump, such as a centrifugal pump 224. The pump discharge is connected to a discharge pipe 225, in tum connected to water heaterV 226 through which water pumped from overiiow tank 206 by pump 224 is forced. Water passed through heater 226 passes through a` connecting discharge conduit 227? into the hollow body portion 209 of the T 208; a hollow plug 22S connecting the conduit 227 to the third leg 212 o the T. The outer or reservoir tank 203- is provided with an overflow drain pipe 229, the upper end of which is open and may be vertically adjusted to` maintain a constant water level in reservoir tank 203'y at any desiredk height.

Cold water, as needed,V may be supplied to the water cooling system through a pipe 23) connected to a suitable source (not shown). The supply pipe 230 is provided withl an openable and! cl'oseable manually operated valve 231 and a solenoid operated' valve 232. The supply pipe 230 discharges into. tank 203. The solenoid valve may be automatically operated ttutough-` a; thermostatic control operative in response to changes inA temperature; of the water in tank 203A through a heat-sensing device 233V connected: through settahle thermostat 234 electrically corn nected by suitable wiring 235, to the. solenoid valve in a knowny manner. Hence, the; temperature of the water 221 which circulates through the nozzle device 298Y and thercooling tank 200 may be maintainedI at desired' operating temperature.

It may now be observedfrom the foregoing description that water in overflow reservoir 203` is pumped through heater 225through the annular orice, 226, upwardly through bore 214, into-Water cooling chamber 201. The water then ows over the top endv 262 of the cooling tank into reservoir 203; The water is forced through the annular oriiice 220 under sufficient pressure that the velocity head or pressure of the water in an upward direction in bore 214, is sulcient to support the hydrostatic head of theV column of water above the orifice so that the 'water willnot' fall by gravity into bore 219 while the coated wire W is travelling downwardly therethrough from the .aluminum pot which is, as hereinbefore described, located above the hydrogen-containing pipe 62.

The temperature of the water is controlled by thermostat control 234 which is set to open solenoid valve 232 to admit cold water to the system whenthe water gets too hot. Also heater 226 may be used, if desired', to aid in adjusting the Water temperature ir it is too cold. Excess water flows `out from overilow pipe 229.

This unit of the apparatus as illustrated in FIG. 5, causes the coated wirev emerging from pipe 62 to be cooled by a column of water from the top of cooling tank 206 tov the annular oriiice 22h. Such an arrangement may be used when it is desired to heat-treat high carbon wire for wireY drawing of the aluminum coated wire. In this case the wire is heated in hydrogen prior to passing it through the aluminum coating bath, which operation may be carried out in apparatus such as illustratedv in FIG. 1. However, the cooling system, as illustrated in FIG. S, is used in place of the water tank arrangement illustrated in FiG. l. The wire is heated in hydrogen to above the critical temperature (1350o F.) to take the carbides into solution', it is then cooled to approximately the temperature of the moltenv aluminum bathI (about 12"'5" F.) and then coated with molten aluminum as described above. The coated aluminum wire is then cooled' to 1G00" to l=l5tl F. by the wat-er 221 in tank 201 which is circulated as described in connection with the apparatus of FlG. 5, after which the coated' wire emerges from bore 219 into the atmospheric air. At this ternperature (l0G0'-1l50 F.) the aluminum coating is solid and` the carbides on exposure to the temperature of the atmosphere' come out of solution as very tine pearlite, producing what is known as a patented structure. The purpose of' having the coated wire emerging into atmospheric air after leaving the water cooling device of FIG. 5, is to retard the rate oi cooling to allow time for the carbides to come out of soiution'. The time required is in the neighborhood of l() seconds so it is desirable that the coated wire W14 is not cooledv more rapidly thanv by exposure to atmospheric air for thisv length of time. The air patented aluminum coated wire W14' may then be subsequently wire drawn', through suitable dies to desired smaller dian eter.

Apart from the. desirability of patenting for further wire drawing, it isY to be. pointed out that ifV high carbon wire (carbon over 6.35%) were heated' above the critical temperature. (l350 F.) inA hydrogen and then aluminum coated andl subsequently Icooled in water as described in connection with tank 65, FlG. l, it would become brittle and might break instead or" passing around pulley 92. Consequently the arrangement as shown' in' FIG. 4 or in Fl'G. 5 is very advantageous when it is desired to prevent embrittlement of high carbon wire where it is heated above l35(`1`o F. in hydrogen tunnel. 31 (see FIG. l).

All alternate way of processing high carbon wire is to (a) heat theV wire to below l350 F. (the critical temperatures) inthe hydrogen tunnelY 31. Inl this case cooling in water willA not cause brittleness. Another way is to cool in air (or hydrogen) after emerging. from the aluminum bath 4d untilv the temperature is not higher than 1G00 F. In this alternative, the water cooling would bel omitted altogether and suiiicient distance would be provided between thel aluminum pot and guide pulley 92 (FIG. l) to permit the requiredA cooling prior to winding the wire on takeup block 12. But this method has the disadvantage of allowing' more time for an undesirable thickness of aluminum-iron alloy layer to form at the interface between they outside aluminum Icoating layer and the surface of the wire.

Other coating metals than aluxninurnrriayl be used for coating metal products in accordancewith certain' featuresY of the process of the invention. The process lends itself to the use of aluminum silicon alloys in the. coating bath, and the process is particularly suitable for coatings of zinc since this metal forms a brittle Zinc-iron alloy in a manner analogous to the formation of an aluminumiron alloy when aluminum is used as the coating. In the case of zinc, the operating temperature of the molten zinc coating bath should be about S5 0 instead of about l275 the temperature adapted for the aluminum coating bath. Also in the case of zinc sufficient distance should be provided between the wire heating zone and the molten zinc bath or coating zone to permit the wire temperature to drop to about 850 when it enters the molten zinc bath. The process also may be used for coating other metals than steel with a coating other than aluminum or zinc. Although the process has been described in detail in connection with the coating of steel wire by way of illus trative example, it will be understood it may be used for coating strip or any body of elongate character of uniform cross section which may be caused to travel as a continuously travelling wire or strip. Accordingly, it will be understood than when the term strand is used in the claims it is intended to include wire and strip. Also, the process is adapted for coating various kinds of elongate metal products which can be alloyed with a coating metal such as wire or strip made of copper, stainless steel and the like.

While there has been disclosed herein, for purposes of illustration, one Way of treating the strand for the application of the molten coating metal, it will be understood that other treating methods may be used prior to applying the molten coating metal; the significant point being that the surface of the strand must be thoroughly clean and free from oxide or other contaminants when the strand is passed through the metal coating bath. For example, the wire or strip may be cleaned and coated with a flux prior to coating; or any other means known in the art for causing molten coating metal to coat a travelling metal strand may be used. Also, in some instances, certain features of the invention may be used in an arrangement whereby the strand may be caused to travel horizontally, vertically upwards or at an angle through the die, in a manner such that a confined fluid gas pressure may be exerted against the outlet end of the die for controlling coating thickness.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modications are possible within the scope of the invention claimed. In the claims the term downstream will be understood to mean the direction of travel of the strand and the term upstream, the opposite direction.

What is claimed is:

1. In a process of coating a metal strand with a coating metal wherein the strand is continuously passed through a molten bath of the coating metal, the method of controlling the thickness of the coating metal applied to the strand which comprises continuously passing the strand through a die positioned in the body of said bath of molten metal and having an orice diameter greater than the diameter of the coated strand and thence through an enclosed elongate chamber having one end communieating with the die oritice and owing molten coating metal by gravity flow in a downward direction from said molten bath through the annular space between said die and strand in the direction of travel of said strand whereby to apply coating metal to said strand and controlling the amount of coating metal applied to said strand as it emerges from said die by a controlled positive static gas pressure maintained within said chamber and exerted against the outlet end of said die in a direction opposite the direction of travel of said strand and at the same time not permitting gas within said chamber to flow through said die.

2. A method according to claim 1 in whichY said strand as it emerges from said die is passed through a chamber communicating with the outlet end of said die at one end and with a liquid cooling bath at the other end in which a non-oxidizing atmosphere is maintained to exert said controlled pressure against the outlet end of said die and the coated strand is passed through said non-oxidizing atmosphere into and through said liquid cooling bath to cool said coated strand, while maintaining said cooling bath at a temperature to insure that the cooled coated strand emerging from said cooling bath has a smooth surface.

3. A method of coating a metal strand with a metal coating which comprises treating a continuously travelling length of said strand to render its surface amenable to alloying said coating metal therewith, passing the so-tre'ated continuously travelling strand through an applicator die having an oriiice communicating with a molten'bath of said coating metal and having a diameter greater than the diameter of the coated strand so that there is an annular space of predetermined size around said strand as it travels through said die, causing molten coating metal to iiow by gravity from said bath through said annular space in the direction of travel of said strand, thereby applying a coating of said molten metal on to said strand, continuing the movement of said strand through an enclosed elongate chamber communicating with said annular space at the outlet end of said die and controlling the thickness of coating adhering to said strand as said strand passes into said chamber by maintaining a controlled positive static gas pressure maintained Within said chamber whereby only a controlled static gas pressure is exerted against the molten metal in said annular space at its outlet and at the same time maintaining the pressure sutliciently low in said chamber to prevent any of said gas from owing through said applicator die in a direction opposite the direction of travel of said strand.

4. A method of coating a steel strand with a metal coating such as aluminum and aluminum alloys which comprises treating a continuously travelling length of said strand to render its surface amenable to alloying said coating metal therewith, passing the so-treated continuously travelling strand in a downward direction through an .applicator die having an orifice communicating with a molten bath of said coating metal through which said strand passes and a diameter greater than the diameter of the coated strand so that there is an annular clearance space of predetermined size around said strand as it travels through said oriiice, causing molten coating metal to ow from said bath in a downward direction through said annular space in the direction of travel of said strand in contact with the surface of said strand, thereby applying a coating of said coating metal to said strand, continuing the movement of said strand having the molten coating metal applied thereto downwardly .through an elongate chamber communicating at its upper end with said annular space at the outlet end of said die and closed at its lower end by a liquid seal and controlling the thickness of the coating adhering to said strand as it emerges from said die by maintaining a gas under controlled positive pressure in said chamber which exerts only a static pressure against the outer end of said die at said annular space in a direction opposed to the direction of travel of said strand, and cooling said coated strand after it emerges from said die to solidify said coating metal.

5. A method according to claim 4 in which a nonoxidizing gas is maintained in said chamber for exerting said gas pressure against the outlet end of said die and to provide a non-oxidizing gas through which the coated strand passes and is cooled after it emerges from said die.

6. A method according to claim 5 in which the strand as it emerges from said chamber is passed throughtan aqueous cooling bath maintained at a controlled temperature adjusted to insure that the coated strand emerg- 13 ing from said cooling bathv has aA smooth surface7 solidified coating.

7. A method according to claim 6 in which the gas maintained under pressure in: said chamber is hydrogen and said liquid cooling bath is water between- 90 F. and ZG" F. and maintained at a temperature which insures both a smooth coating and a bright appearing surface.

8. A method according to claim 7 in which the diameter of the die orifice through which the strand passes is within the range of 7% to 21% larger than the diameter of the strand.

9. A method according to claim 8 in which the time of travel of the strand from the time it is brought into contact with the molten coating metal to the time it reaches said water cooling bath is not substantially greater than 2 seconds.

19. A process for producing a steel wire coated wlth a coating metal such as aluminum and aluminum alloys capable of being reduced in diameter by drawing through dies without cracking or peeling the coating metal which comprises heating a continuously travelling length of high carbon steel wire, after it has been cleaned, to a temperature above 1350 F. at which the carbides in said steel go into solution and removing any oxides present on the surface of said wire, causing said wire to travel through a molten bath of said coating metal maintained at a temperature about 1275 F., applying a predetermined thickness of molten coating metal to said strand by passing said strand through an applicator die having an orifice mounted in communication with said bath, said orifice having a diameter greater than the diameter of the coated wire, then passing the coated wire through a confined atmosphere of non-oxidizing gas maintained under positive pressure which is exerted as static pressure against the outlet end of said applicator die orifice and adjusted to control the thickness of molten coating metal adhering to said wire, causing said coated wire to travel through said confined non-oxidizing atmosphere and thence through a water bath maintained at a temperature to cool said coating to a temperature between 1000 F. and 115 0 F. thereby solidifying said coating metal and then cooling said coated wire at a rate to cause the carbides to come out of solution as very ne pearlite.

11. A process for producing a steel wire coated with a coating metal such as aluminum and aluminum alloys capable of being reduced in diameter by drawing through dies without cracking or peeling the coating metal which comprises heating a continuously travelling length of high carbon steel wire, after it has been cleaned, to a temperature above 1350 F. at which the carbides in said steel go into solution, removing any oxides present on the surface of said wire by passing it through a surrounding atmosphere of hydrogen in communication with an aluminum metal coating bath maintained molten at about 1275 F., cooling said wire to about the temperature of said coating bath while still surrounded by said hydrogen atmosphere, then causing said wire to travel downwardly through a molten metal applicator die having an orifice the diameter of which is larger than the diameter of said wire by at least 7% but not more than 21% so that there is an annular clearance space of pre-determined space in said die surrounding the wire, which annular space at its entrance end is in communication with said molten metal coating bath, causing said molten coating metal to ilow by gravity in a downward direction through said annular space in contact with the wire as the wire passes through said orifice thereby causing the molten metal to adhere to said wire, then passing the coated wire as it moves downwardly through an elongated chamber communicating at its upper end with said annular space and containing a confined atmosphere of nonoxidizing gas, maintained above atmospheric pressure, which is exerted as positive static pressure against the outlet end of said annular space and adjusted to control the thickness of molten coating metal adhering to said wire, causing said coated wire to travel through said nonoxidizing atmosphere and thence through a water bath and therein cooling said coating to a temperature between 1000 F. and 1150` F. thereby solidifying said coating metal' and. then. further cooling said coated wire at a; rate to cause the carbides in the steel wire to come out. of solution as very line pearliter 12i Apparatus for coat-ing a metal: wire strand of given diameter with a coating metal comprising means for cleaning the` surface. of a continuously moving length of strand travelling in a direction herein designated as downstream, a furnace having a pot holding a molten bath of said coating metal positioned downstream from said cleaning means; heating means positioned upstream from said molten bath to heat said wire strand; means for applying molten coating metal to said heated strand which comprises an applicator die having a cylindrical orilice through which said strand travels, said orifice having a diameter greater than the diameter of the coated strand of given diameter whereby an annular clearance space of predetermined area is provided in said die around said strand as it travels through said orice, said die being mounted on the bottom wall of said pot with the upstream end of said annular space communicating with said bath and in such position that molten coating metal tiows downwardly by gravity from said bath through said yannular space in the direction o ftravel of said strand and in contact therewith as said strand travels through said orifice, means defining an enclosed gas chamber positioned downstream from said die and connected to provide communication between said chamber and said annular space at its downstream end whereby gas pressure within said chamber is exterted against the downstream end of said annular space; means of introducing gas into said gas chamber under pressure; gas pressure regulating means to maintain a regulated positive pressure within said gas chamber whereby a controlled static gas pressure is maintained against molten metal fiowing downwardly in said annular space around said wire to control the thickness of molten metal coating applied to said wire as it passes through said die orifice; and means positioned downstream from said chamber for cooling the coated wire.

13. Structure according to claim 12 in which said applicator die is mounted for floating lateral movement and a cage surrounds said die preventing substantial longitudinal movement of said die and limiting the distance of said lateral movement.

14. Structure according to claim 13 which includes guide means causing said strand to travel through said molten metal coating bath and die downwardly in a substantially vertical direction, and said gas chamber is mounted in vertical alignment with said orifice downstream from said applicator die.

15. Structure according to claim 14 which includes a guide member having an opening therein through which said strand passes in a downward direction, said guide member being connected to said cage and mounted upstream from said applicator die with said opening in alignment with the orifice of said applicator die and said gas chamber is mounted in vertical alignment with said orifice downstream from said applicator die.

16. Structure according to claim 14 in which the means for cooling said coated strand downstream from said gas chamber comprises a tank having a bottom mounted below said gas chamber and containing a moving cooling liquid, means having a cylindrical wall defining an elongate hollow bore below said tank through which said strand passes downwardly in a substantially vertical direction and vertically aligned with said gas chamber, an annular opening in said cylindrical wall providing an upwardly and inwardly extending annular nozzle and liquid pumping means connected with said nozzle adapted to force water through said nozzle upwardly through 15 said bore and tank in a direction counter to the direction of travel of said wire therethrough with suiicient force to prevent substantial ow of liquid downwardly in said bore below said nozzle.

17. Apparatus according to claim 16 in which said cooling tank is surrounded by a reservoir into which cooling liquid forced through said tank overows and said pumping means is connected to take suction from said reservoir and circulate the cooling liquid back through said nozzle. Y

18. Apparatus according to claim 17 which includes means for automatically controlling the temperature of the cooling liquid circulated through said cooling tank.

References Cited bythe Examiner UNITED STATES PATENTS Underwood 118-420 X Girard et al.

Cook 118-68 X Dahlstrom.

Keller 11868 X Nystrom.

Knapp 118-125 X Stalson.

Eliot 22-200.1

RICHARD D. NEVIUS, Primary Examinar,

Claims (1)

1. 4. A METHOD OF COATING A STEEL STRAND WITH A METAL COATING SUCH AS ALUINUM AND ALUMINUM ALLOYS WHICH COMPRISES TREATING A CONTINUOUSLY TRAVELLING LENGTH OF SAID STRAND TO RENDER ITS SURFACE AMENABLE TO ALLOYING SAID COATING METAL THEREWITH, PASSING THE SO-TREATED CONTINUOUSLY TRAVELLING STRAND IN A DOWNWARD DIRECTION THROUGH AN APPLICATOR DIE HAVING AN ORIFICE COMMUNICATING WITH A MOLTEN BATH OF SAID COATING METAL THROUGH WHICH SAID STRAND PASSES AND A DIAMETER GREATER THAN THE DIAMETER OF THE COATED STRAND SO THAT THERE IS AN ANNULAR CLEARANCE SPACE OFPREDETERMINED SIZE AROUND SAID STRANDAS IT TRAVELS THROUGH SAID ORIFICE, CAUSING MOLTEN COATING METAL TO FLOW FROM SAID BATH IN A DOWNWARD DIRECTION THROUGH SAID ANNULAR SPACE IN THE DIRECTION OF TRAVEL OF SAID STRAND IN CONTACT WITH THE SURFACE OF SAID STRAND, THEREBY APPLYING A COATING OF SAID COATING METAL TO SAID STRAND, CONTINUING THEMOVEMENT OF SAID STRAND HAVING THE MOLTEN COATING METAL APPLIED THERETO DOWNWARDLY THROUGH AN ELONGATE CHAMBER COMMUNICATING AT ITS UPPER END WITH SAID ANNULAR SPACE AT THE OUTLET END OF SAID DIE AND CLOSED AT ITS LOWER END BY A LIQUID SEAL AND CONTROLLING THE THICKNESS OF THE COATING ADHERING TO SAID STRAND AS IT EMERGES FROM SAID DIE BY MAINTAINING A GAS UNDER CONTROLLED POSITIVE PRESSURE IN SAID CHAMBER WHICH EXERTS ONLY A STATIC PRESSURE AGAINST THE OUTER ENDOF SAID DIE AT SAID ANNULAR SPACE IN A DIRECTION OPPOSED TO THE DIRECTION OF TRAVEL OF SAID STRAND, AND COLING SAID COATED STRAND AFTER IT EMERGES FROM SAID DIE TO SOLIFIGY SAID COATING METAL.

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