US3779056A

US3779056A - Method of coating steel wire with aluminum

Info

Publication number: US3779056A
Application number: US00213048A
Authority: US
Inventors: J Brugger; G Padjen; R Helman
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1971-12-28
Filing date: 1971-12-28
Publication date: 1973-12-18
Anticipated expiration: 1990-12-18
Also published as: CA958291A

Abstract

A heavy aluminum coating ranging in thickness from 10 to 15 per cent of the as-coated radius of a wire is provided on steel wire having a nominal diameter of from 0.08 to 0.25 inches by a combination of heating the wire to a temperature within a predetermined range, passing the wire at a predetermined speed related in a substantially inverse ratio to the temperature of the wire through a molten aluminum bath having a predetermined temperature and depth inversely related to each other. The particular operating conditions of the process provide a coating of the desired thickness while operating on a plateau in a curve representing the relationship between the coating thickness and the various combined parameters of the process to provide a readily controllable process of making an easily reproducible, uniform heavy aluminum coating with a very thin interfacial alloy layer on long lengths of ferrous wire. The coated wire is readily redrawable if necessary to attain a desired final gage and strength.

Description

United States a Patent [191 Padjen et a1.

[ METHOD OF COATING STEEL WIRE WITH ALUMINUM [75] Inventors: George Padjen; Robert W. Helman;

Joseph A. Brugger, all of Bethlehem, Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

[22] Filed: Dec. 28, 1971 [2]] App]. No.: 213,048

[52] US. Cl 72/47, 29/l83.5, 29/l9l.6, 29/1962, 117/51, 1 17/1 14 C, 117/1 19.4, 117/128, 118/7, 118/63, 118/69, 118/420, 118/429 [51] Int. Cl. B2lc 23/24, C230 H08 [58] Field of Search 117/51, 114 C, 119.4, 117/128; 72/47 [56] References Cited UNITED STATES PATENTS 2,166,510 7/1939 Whitfield et a1. 117/51 2,203,606 6/1940 Whitfield et a1. 1 17/51 X 2,354,459 7/1944 Harris et al. 117/128 UX 3,057,050 10/1962 Hodge et a1 ll7/l 14 C X 3,227,577 l/l966 Baessler et a1. 117/114 C X 3,468,695 9/1969 Federman 117/51 3,470,939 10/1969 Coad 117/114 C X 3,224,037 12/1965 Nickola et a1. 117/51 X 3,523,815 8/1970 Baxter 117/128 X Dec. 18,1973

Pierson et a1. 1 17/51 Dion et a1. 117/114C [57] ABSTRACT A heavy aluminum coating ranging in thickness from 10 to 15 per cent of the as-coated radius of a wire is provided on steel wire having a nominal diameter of from 0.08 to 0.25 inches by a combination of heating the wire to a temperature within a predetermined range, passing the wire at a predetermined speed related in a substantially inverse ratio to the temperature of the wire through a molten aluminum bath having a predetermined temperature and depth inversely related to each other. The particular operating conditions of the process provide a coating of the desired thickness while operating on a plateau in a curve representing the relationship between the coating thickness and the various combined parameters of the process to provide a readily controllable process of making an easily reproducible, uniform heavy aluminum coating with a very thin interfacial alloy layer on long lengths of ferrous wire. The coated wire is readily redrawable if necessary to attain a desired final gage and strength.

17 Claims, 9 Drawing Figures METHOD OF COATING STEEL WIRE WITI-I ALUMINUM BACKGROUND OF THE INVENTION The present invention relates to the production of aluminum coated wire and particularly to as-coated and redrawn aluminum coated wire having a relatively heavy but less than the maximum obtainable aluminum coating equal to between to per cent of the coated radius of the wire.

Numerous attempts have been made to coat steel wire with heavy coatings of aluminum and zinc in order to simultaneously take advantage of both the strength of the steel and the corrosion resistance and in the case of an aluminum coating the better conductivity of the coating metal. It was previously a serious problem to even attain a very heavy coating of these molten metals upon a wire. The broad problem of obtaining maximum coatings was solved, however, for zinc coatings by processes such as disclosed by US. Pat. No. 2,294,750 to Harris and for aluminum coating by the process disclosed by US. Pat. No. 3,468,695 to Feder man who applied the process disclosed by Harris to the coating of wire with heavy coatings of aluminum.

While the process disclosed by Harris and Federman effectively coats wire with heavy coatings of either zinc or aluminum, it has proved to be a problem to successfully coat wire with less than a maximum coating particularly when the coating is aluminum. Harris and Federman taught that in order to attain a maximum molten metal coating upon a base wire the wire must be drawn very quickly through a molten coating bath while the wire is still relatively cold with respect to the temperature of the bath. Under these circumstances the body of the wire acts as a heat sink to extract heat from the bath metal immediately surrounding the base wire as it passes through the bath. The maximum amount of coating metal is thereby frozen to the wire surface. Harris discovered that in order to attain the maximum coating the wire base must be quickly withdrawn from the coating bath before the heat of the bath begins to remelt the outer layers of the solidified coating from the wire surface. It might appear in view of these prior teachings that the only thing which need be done to readily attain any desired amount of coating metal up tothe maximum attainable upon the wire base would be to effectively vary the temperature of the wire entering the molten bath. It has, however, unexpectedly proved to be extremely difficult to provide a given intermediate amount of coating metal upon a steel wire base and virtually impossible to dependably reproduce any particular desired coating thickness uniformly on a long length of wire or from time to time on different lengths or diameters of wire. Considerable difficulty has also been encountered in obtaining coatings having good adherence to the wire when operating in accordance with the prior art teachings.

It has proved in particular to be a problem to produce aluminum coated wire for conductor strand for electric power transmission purposes. This strand may be comprised of either single aluminum coated wires or several such wireslaid together into a multiwire strand. In such strand the aluminum coating on the individual wires must fall within the limits of 10 to 15 per cent of the total as-coated radius of the wire in order to meet standard specifications which call for both a certain minimum thickness for the aluminum coating in order to attain a desired corrosion resistance and electrical conductivity and a minimum total strength to allow the wires to be self-supporting over long spans between supports. Since the specifications call for a wire strength significantly greater than the maximum attainable strength ofaluminum per se, the solidified outer coating of aluminum contributes virtually no strength to the wire as a whole. Since the strength specifications and requirements are based upon the outside, or ascoated, diameter of the coated wire, it will readily be seen that having too much coating material deposited upon the surface of the wire reduces the net area of the strength providing steel andthereby renders achievement of the required tensile strength a virtual impossibility. The coating thickness must, therefore, conform with the specified coating thickness within rigid limits. In addition the usual economic considerations require that the relatively expensive aluminum not be applied to the steel base in an amount excessively greater than that actually required to provide the proper conductivity and to effectively eliminate corrosion.

It is quite important in aluminum coated conductor strand for the aluminum coating to be extremely uniform because a large portion, if not all, of any high frequency current of electricity passing through the strand will be carried through the aluminum and any significant variation in the thickness of the aluminum with respect to the underlying ferrous base, which has a lower conductivity, may very significantly affect the relative conductivity of the aluminum coated wire or strand from one section or strand to another. It is also important in conductor strand not to have more than a very thin or minimal amount of interfacial iron-aluminum alloy layer between the aluminum and the ferrous base metal because the iron-aluminum alloy interferes with the high frequency conductivity of the coating.

Since it is possible where desired to readily attain aluminum coatings of up to per cent of the wire diameter by following the principle of allowing the wire to act as a heat sink and then withdrawing the wire before significant remelting occurs, a substantial problem is presented in attempting to reliably and uniformly attain a coating in the range of only 10 to 15 per cent of the coated wire diameter. In fact wires coated with aluminum in the range of 10 to 15 per cent of the diameter of the wire have exhibited, in the experience of the inventors, very poor uniformity, because the prior processes of coating have been very sensitive and subject to wide variations in results due to small and often unknown changes in the coating conditions.

It has also proved to be a problem in molten aluminum coating to coat a steel wire previously treated to attain the maximum combination of strength and due tility by a so-called patenting treatment without destroying or adversely affecting the patented metallurgical structure of the wire. While a cold patented wire could be quickly passed through an aluminum bath to pick up a maximum thickness of coating without adversely affecting the metallurgical structure, i.e. causing the fine pearlitic particles to spheroidize, if the wire became too hot in the bath due to long coating remelting times or the like, the fine pearlitic structure of the patented wire would often be adversely affected by a coating operation applying a molten coating of aluminum constituting 10 to 15 per cent or so of the ascoated radius of the wire. Destruction of the fine pearl itic structure of the patented wire would then prevent the subsequent redrawing of the wire to high strengths. Since redrawing of aluminum coated conductor strand is almost invariably necessary after coating to attain the required strength of the finished wire, any treatment which prevents effective redrawing seriously impedes the production of such conductor strand.

It is difficult in any molten metal coating process to hold the conditions of coating at a constant level. For instance, in a molten coating bath it is quite difficult to hold the bath level within approximately plus or minus one eighth of an inch and the molten bath temperature within closer than about plus or minus two degrees. lt is also difficult to maintain the speed of the wire through the bath at closer than plus or minus one foot per minute of the desired speed, and it is in particular extremely difficult because of varying emissivity of the wire surface due to varying roughness or cleanliness and slight variations in diameter of the wire to maintain the temperature of the wire within closer than approximately plus or minus ten degrees of the desired temperature as the wire passes into the molten bath.

SUMMARY OF THE INVENTION The aforementioned difficulties encountered in prior art processes have now been obviated by the invention of the applicants. The present applicants have discovered that the difficulties of the prior art have been largely caused by attempts to operate molten aluminum coating processes for coating wire in operating regions where a small change in operating conditions is liable to cause a very large change in the amount of coating material applied or remaining upon the as-coated wire. In addition previous processes have tended to cause various detrimental changes in the applied coating and base wire. The applicants have discovered, furthermore, that there are critical ranges of combinations of operating conditions wherein the process of coating assumes a substantially stable pattern and where a fairly large change, relatively speaking, in operating conditions will not greatly or seriously disturb the properties of the resulting coated product. The applicants, furthermore, have determined these operating ranges with respect to the production of hot-dip aluminum coated steel wire having a coating of to per cent of the as-coated radius of the wire upon a wire base having an initial diameter of from 0.08 to 0.25 inches, a type of product with which particular difficulty has previously been encountered.

The applicants have also discovered that there is a range of coating conditions which result in a slip phenomena in applied molten aluminum coating processes just prior to normal remelting phenomena in the coating. Such slip phenomena must be avoided to produce usable coated material. It is a feature of the present invention, therefore, to arrange the parameters of the coating operation to avoid the area of slip.

The inventors have discovered that a combination of certain interrelated ranges of operating variables in a process of aluminum coating ferrous wire will provide an aluminum coated wire product of the proper dimensions with very superior uniformity, having a very thin interfacial alloy layer and exhibiting no damage to the metallurgical structure of the underlying ferrous wire. These operating variables are the following:

1. the initial temperature of the wire.

2. the speed at which the wire passes through the aluminum bath.

3. the temperature of the aluminum bath.

4. the depth or length of the bath portion through which the wire passes.

5. the particular ratio relationship of the temperature of the wire with the initial diameter of the wire.

6. the particular ratio relationship of the initial diameter of the wire with the distance the wire passes through the molten aluminum bath.

7. the particular ratio relationship of the speed of the wire through the bath to the initial diameter of the wire.

The process of the invention provides interrelated ranges of operating conditions to attain a stable coating operation which is readily controllable. This is accomplished by operating within the following critical ranges with appropriate variations of inversely and directly related operating variables. Broadly speaking the critical ranges of the invention call for a previously cleaned ferrous base wire of the proper dimensions to be preheated to a temperature range of 980 to 1060 degrees Fahrenheit in a reducing atmosphere, passage of the preheated wire at from to 135 feet per minute into a substantially pure molten aluminum bath held at from 20 to degrees above the melting point of the molten metal, passing the wire through the molten bath for a distance of from 0.5 to 4 inches, and controlling the temperature of the wire as it enters the molten bath in inverse ratio to the initial wire diameter with a predetermined ratio relationship effective to avoid the initiation of coating slip. The inverse ratio relationship should be such that a wire having an initial diameter of 0.08 to 0.15 inches enters the bath at a temperature between 1,000 and 1,060 Fahrenheit, a wire having an initial diameter of 0.15 to'0.215 inches enters the molten bath at a temperaturebetween 980 and 1,040" Fahrenheit and a wire having an initial diameter of 0.215 to 0.25 inches enters the molten bath at a temperature between 980 and 1,020 Fahrenheit. The distance traveled by the wire through the molten bath is also controlled within a range of 0.5 to 4 inches in a direct ratio relationship with the initial diameter of the wire within a range of 0.08 to 0.25 inches. The ratio relationship of the distance traveled to the diameter of the wire is such that a wire having a diameter of approximately 0.08 to 0.15 inches passes through the molten bath for a distance of 0.5 to 1.5 inches, and a wire having an initial diameter of 0.15 to 0.25 inches passes through the molten bath for a distance of 1.5 to 4 inches. The speed of the wire through the molten bath is also controlled within the range of 70 to 135 feet per minute in inverse ratio to the initial diameter of the wire within a range of 0.08 to 0.25 inches. The ratio relationship of the speed of the wire to the wire diameter is such that a wire of from 0.08 to 0.15 inches passes through the molten bath at a speed of from to feet per minute, a wire of from 0.15 to 0.215 inches passes through the molten bath at from 72 to 128 feet per minute and a wire of from 0.215 to 0.25 inches passes through the molten bath at a speed of from 70 to 100 feet per minute in inverse ratio with the initial diameter of the wire. In each case the particular ratio relationship will bepredetermined to avoid initiation of coating slip. Preferred ranges set forth within the following specification will in general provide even more desirable results so far as the production of an aluminum coated wire for conductor strandis concerned. The use of certain of the above critical ranges in combination with other elements of the broad basic invention, such as controlling the temperature of the wire as it enters the bath in inverse ratio to the initial wire diameter within the range of approximately 980 to 1,060 Fahrenheit, controlling the distance traveled by the wire through the molten bath in direct ratio with the initial wire diameter within the range of 0.5 to 4 inches, and controlling the speed of the wire through the bath within the range of 70 to 135 feet per minute in inverse ratio to the initial diameter of the wire, will also provide superior results if proper ratios are adhered to.

By operating in accordance with the teaching of the present invention within the foregoing ranges an aluminum coated wire is provided within the desired specifications which wire has greatly superior uniformity and reproducibility, has superior adhesiveness of the molten coating to the base wire and which has substantially the same metallurgical structure in the ferrous base both at the surface and internally as the initial uncoated wire even when the initial starting structure is the fine pearlitic structure of a patented wire.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional elevation of a coating line suitable for the practice of the coating method of the invention.

FIG. 2 is a schematic cross-sectional elevation of a preferred coating apparatus for the practice of the method of the invention.

FIG. 3 is an elevational view of a suitable apparatus for redrawing the coated wire to finalstrength and dimensions.

FIGS. 4, 5 and 6 are illustrative plots of the coating thickness obtained versus the aluminum bath depth for various wire preheat temperatures under various bath conditions.

FIG. 7 is a graphic representation of the heat history of an aluminum coated wire coated by the method of the applicants compared with the heat history of a wire coated with aluminum in a more conventional manner such as taught by a typical process of the prior art.

FIG. 7A is a table summarizing the information shown. by the curves inFIG. 7.

FIG. 8 is a graphic representation of the effect of redrawing upon the tensile strength of heavy aluminum coated wire plotted with respect to the diameter of the coated wire versus the tensile strength of the wire.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown a coating line apparatus suitable for the practice of the method of the invention. A wire 11 is unwound from a payoff reel 13 and drawn through the coating line by the drawing action of a takeup block 15 at the opposite end of the coating line. As the wire 11 is drawn off payoff reel 13 it passes first around and between a pair of bridle sheaves 17 and 19 which establish the proper tension in the coating line between the takeup block 15 and the bridle sheaves l7 and 19. The wire 11 passes from the bridle sheaves 17 and 19 into a molten lead bath 21 held at approxi mately 900 degrees Fahrenheit to burn any deleterious organic substances such as lubricating oils or the like from the surface of the wire. The wire 11 is submerged in the lead bath 21 as it passes under sinker rolls or

sheaves

23 and 25. The wire 11 then passes from the molten lead bath over a guide sheave 27 and down into a hydrochloric or other suitable acid type pickling bath 29 where it passes back and forth in the bath over large guide sheaves 31 and 33 and then passes from the pickling bath 29 over guide sheave 34 and into a rinsing station 35 where substantially all acid residue is washed I from the surface of the wire by cold water sprays or like means for rinsing the wire with cold water. A suitable temperature for the pickling bath 29 will be 140 Fahrenheit and the cold water of the rinse may suitably be about 60 Fahrenheit. Fromthe cold water rinse station 35 wire 11 passes to a sulfuric acid type anodic cleaning cell 37 where any remaining contamination or corrosion is substantially completely removed from the surface of the wire 11. After passing through. anodic cleaning cell 37 the wire 11 passes first through a rinse station 39 where the wire is rinsed with a spray or stream of cold water which may suitably be about 60 Fahrenheit and then, because sulfuric acid tends to cling rather tenaciously to a metal surface, through a hot water rinse station 41 where any remaining residue of acid from either prior acid treatment is removed from the surface of the wire by hot water sprays or the like having a temperature which may suitably be somewhat more than 150 Fahrenheit. After wire 11 passes from hot water rinse station 41 it passes through a drying station 43 where blasts of hot or cold air serve to remove substantially all moisture remaining from the preceding rinsing steps from the surface of the wire. Immediately after passing from the drying station 43 wire 11 then passes into a rnufile tube furnace 45 where the wire is heated in a reducing atmosphere composed of to 100 per cent hydrogen and the balance some effectively inert gaseous diluent. Wire 11 passes into the muffle tube 47 of muffle tube furnace 45 through a suitable small aperture or opening at the entrance to the muffle tube 47 and then continues through the muf fle tube 47 and a muffle tube'extension 49 into a gas tight sheave housing 51 into which muffle tube extension 49 opens. Wire 11 passes over guide sheaves 53 and 54 within housing 51 and is directed by said sheaves through a hollow gas tight extension 55 of housing 51 into a coating chamber 57 submerged within a molten bath 59 of substantially pure aluminum contained in a ceramic coating po't 61. Wire 11 passes within chamber 57 about sinker guide sheave 64 and then about guide sheave 63 positioned within an extension or shelf 65 of the chamber 57 which shelf is completely submerged within the'molten bath 59 to provide a shallow section 67 of the bath 59 only a few inches deep.

The sinker guide sheave 63 directs the wire 11 upwardly through a gas tight die 69 which fits tightly enough about the wire 11 to prevent seepage of either the gaseous atmosphere out of the submerged coating chamber 57 or of molten aluminum into the chamber 57 but not tight enough to mar the surface of the wire 11 in any way as it passes through the die 69. The exact dimensions of the die 69 which are necessary to prevent such seepage will depend upon the materials from which the die is made, the depth of the die below the surface of the molten aluminum bath and the speed of the wire through the die. The depth of the die 69 below the surface of the molten aluminum bath 59, or stated another way, the depth of the shallow section 67 of the aluminum bath, may be adjusted by changing the level of the chamber 57 within the aluminum bath by suitto control the amount of coating deposited upon the wire 11 since the level of the bath may be changed more quickly than the temperature of the incoming wire or the temperature of the bath.

After passing through the die 69 wire 11 passes through from 0.5 to 4 inches of molten aluminum in the shallow section 67 of the molten aluminum bath 59. A heavy aluminum coating is deposited on the clean wire surface as it passes through the molten aluminum. 1m-

mediately after the wire passes from the molten alumi- 4 num it is exposed to a cool air stream from an air orifice 75 to precool the surface of the molten aluminum and is then preferably passed upwardly through a water quench 77 where the wire is quenched by sprays of water to solidify the aluminum coating quickly before the wire passes over a guide sheave 79 and then downwardly to takeup block 15.

FIG. 2 shows in cross-section an alternative and preferred form of coating apparatus. In FIG. 2 the wire 111 preferably first passes through a cleaning and heating section of the coating line substantially similar to .the arrangement shown in FIG. 1. After passing through a muffle tube furnace such as shown at 45 in FIG. 1 the wire 111 continues through a muffle tube extension 113 into an interconnected sheave housing 115, about a sheave 117, through a housing extension 1 19 into a second interconnected housing 121 in which a guide sheave 123 directs the wire 1 1 1 into the bottom of a die 125 mounted in a die housing 127 in the floor 129 of a shelf 131 extending from the side of an induction heating type molten metal coating pot 133 in which there is contained a substantially pure molten aluminum coating bath 135. The molten aluminum bath is kept at a temperature approximately to 80 Fahrenheit above its melting temperature and preferably 20 to 40 Fahrenheit above its melting temperature by induction heating coils 137 mounted peripherally about interconnecting passageways 139 in the bottom of the coating pot 133. The die 125 is secured in the die housing 127 by a threaded screw cap 139 which fits down over the top of the housing. The level of the molten aluminum 135 in the coating pot 133 and thus the level of the molten bath above the die 125 is controlled by a ceramic displacement block 141 which is movable up and down in the molten coating bath 135 by any suitable mechanism such, as, for instance, the rocker arm 143 positionable by the interaction of the rack 145 and screw 147 rotatable by motor 149 which serves to position the displacement block 141 through linkage 151.

The muffle tube furnace, the muffle tube extension I 113 and

sheave housings

115 and 121 are all filled with a reducing atmosphere and preferably with an atmosphere comprised of 50 to 100 per cent hydrogen and the rest an effectively inert diluent such as nitrogen, argon or the like. It would be possible to merely have the

sheave housings

115 and 121 filled with an inert or non-oxidizing atmosphere so long as the wire is heated in a reducing atmosphere, but it will be found usually preferable to surround the wire with one interconnected uniform reducing atmosphere in all the chambers.

The molten coating pot 133 will preferably be lined with high alumina refractory bricks or the like 134. The bath level adjusting motor 149 may be automatically operated by any suitable automatic bath level detection device, not shown, or may be manually operated by the operator when necessary.

The wire 111 after passing through the die passes up through 0.5 to 4 inches of molten aluminum, the depth of which is predetermined to pick up a heavy coating of aluminum and then passes through an air stream emitted from dual air nozzles 153. After passing through the air stream from nozzles 153 where the still molten coating has its surface layers cooled and preferably partially solidified, the wire 111 preferably passes up into a suitable quench 155 where the coating on the wire is still further cooled by water streams or sprays of water to a state of solidification where it can be safely contacted by a guide sheave 157 to change the direction of the wire and also steady the wire to prevent excessive vibration in and along the length of the wire. it is very desirable that the wire 111 be quenched as quickly as possible after it leaves the coating bath so that it can be contacted with a sheave 157 or other steadying device as soon as possible to damp out undesirable vibrations which can cause surface unevenness and eccentricity of the molten coating on the wire if the vibrations become too severe or long continued prior to substantially complete solidification of the molten coating upon the surface of the wire. While it is difficult to know how much vibration in the wire can be tolerated, and all the sources of such vibration, it can be said in general that it is usually advantageous to contact the wire with a vibration damper of some sort as quickly as possible after coating so that the span of the vibrating section of wire is reduced so far as practical. Lumpy and eccentric coatings are thereby prevented by the combination of prompt quenching in water quench 155 and prompt contact of the wire 111 with damping sheave 157. While the quench 155, therefore, is not an absolutely necessary part of the basic process of the invention, it is, as can readily be seen, a very desirable addition to the process.

After passing around the vibration damping guide sheave 159 the wire 111 passes through a weir type quenching bath 159 where the coating and wire is cooled to substantially ambient temperature conditions prior to passage over guide sheaves 161 and 163 and onto takeup block 165. An electronic coating thickness detector 167 of any suitable type may be positioned between

guide sheaves

161 and 163, if desired, to continuously monitor the applied coating thickness. The reading from the micrometer may be used by the operator to adjust the bath depth or any suitable automatic feedback loop type control system, as described hereinafter, may be installed to automatically control the bath level, wire speed, or other suitable parameters of the coating process to control the coating being deposited according to the coating thickness detected. A suitable immersion type thermocouple 169 may also be mounted in the molten coating bath to continuously monitor the temperature of the molten metal. A suitable radiation pyrometer 181 having a sight tube 183 may be aimed at the wire 111 through the wall of the housing extension 119 to monitor the temperature of the wire. Water overflow or drainage from

quenches

155 and 159 pass through

suitable conduits

171 and 173 to drain 175. A reducing atmosphere comprising 50 to 100 per cent of hydrogen and the balance some effectively inert gaseous diluent such as nitrogen, argon or the like is injected into the

housings

115 and 121 through gas conduits 177.

If desired a suitable feedback type electronic control 185 having a set point potentiometer circuit 187 to set the desired coating thickness and a lead 189 to transmit the detection signal from the electronic coating thickness detector 167 and use it either to control the speed of the wire by sending wire. speed signals to the tapeup 165 through lead 191 or bath level signals to the dis placement block motor 149 through lead 193, or both. A power source 195 may serve to activate the control 185 and also, if desired, to power motor 149 and takeup 165 through the controller.

A suitable apparatus for drawing or redrawing the ascoated aluminum covered wire as received from the ap paratus shown in FIGS. 1 or 2 to final size and strength, if such redrawing is necessary, is shown in FIG. 3. While a full hard wire can be aluminum coated according to the coating procedure of the present invention if a full hard wire is desired, if the coated wire is to be used as conductor strand meeting American Society for Testing Specifications, and particularly specification B4 16, for such conductor strand, it has been found impossible for most, if not all, sizes of aluminum coated wire to meet the strength specifications without subsequent redrawing of wire having an initial coated diameter greater than that required down to the final size and strength required. (The amount of redrawing necessary will presently be more fuly explained in connection with FIG. 8). In order to effect proper redrawing it is necessary to start with a wire having a patented or fine pearlitic structure which combines the maximum strength. and ductility attainable simultaneously in a wire. This wire must then be redrawn by suitable apparatus such as shown in FIG. 3 after it has been coated with aluminum. In order to effect a proper redrawing it is extremely important that the fine pearlitic structure of the wire not be affected by the coating process.

In FIG. 3 a coil or series of coils 211 of wire 213, which have been removed after coating from the takeup blocks or 165 in FIGS. 1 or 2, are supported on a mandrel 215 extending from a support 216. The wire 213 is drawn or pulled through a guide ring 219 supported on base 221 and then into a guide 222 leading into a lubrication reservoir 223 supported by bracket 225 on base 227 and connected to a drawing die 229 mounted on a bracket 231. The wire is drawn down to a smaller diameter in the die 229 which is preferably a pressure lubrication type die. The tensile strength of the wire based upon the redrawn overall coated diameter will increase substantially after passagethrough the die 229 because of the work hardening of the ferrous base metal by the drawing operation. The relative thickness of the aluminum coating upon the surface of the wire will remain the same with respect to the coated diameter of the wire because the coating and the base wire are drawn down proportionately to smaller absolute dimensions while still maintaining the same relative dimensions with respect to each other. After the wire 213 passes through the die 229 it passes around drawing block 233 which provides the pull or tension to draw the wire 213 through the die. Wire 213 passes around drawing block 233 for several turns sufficient to grip the block and then passes from the block to and through a second lubrication reservoir 235, drawing die 237 and onto a second drawing block 239. As the wire 213 passes through the second drawing die 237 it is again decreased in size and attains a higher tensile strength due to work hardening. After passing about the second drawing block 239 the wire 213 passes into still another lubrication reseroir 241 and a third drawing die 243 and then is collected upon atakeup block 245 from which it is ultimately removed for storageand use. lt will be readily understood that the wire may be drawn through as many drawing stages as necessary to attain its final desired size and tensile strength. Three drawing stages are shown in FIG. 3 by way of example only.

The present inventors have discovered that a ferrous metal wire having a diameter between 0.08 and 0.25 inches and especially apreviously patented wire which must be redrawn, can be successfully coated with a uniform, reproducible aluminum coating with the range of 10 to l5 percent of the coated radius of the wire by the use of the foregoing apparatus or similar suitable apparatus if the coating operation is carried out within the following critical per cent of operation. While the coating applied may range from 10 to 15 per cent of the coated radius of the wire it is even. more preferable to operate within the. ranges of coating conditions which will result in the attainment of a preferred coating within the range of 12 to 14.5 percent of the coated radius of the wire.

According to thepresent invention the wire must first be thoroughly cleaned to remove all extraneous contamination including oxidation from its surface. The wire may be from 0.08 to 0.25 inches in diameter and preferably for best operation will be within the range of 0.145 to 0.22 inches in diameter. The wire 11 or 111 after a thorough cleaning will be passed through the coating line, or at least the molten coating bath, at from to l35 feet per minute and preferably for best results at approximately to feet per minute by the drawing action of the takeups 15 or after having been first heated in suitable heating means such as muffle tube furnace 45 to a temperature of between 980 to l,060 Fahrenheit. The molten coating bath will be held within a temperature range between 20 to 80 Fahrenheit above the melting temperature of the mol ten aluminum in the coating bath and preferably for best results between 20 to 40 Fahrenheit abovethe melting temperature of the molten bath. The molten bath will be composed of substantially pure or commerically pure aluminum so that the bath will have a melting temperature of approximately Fahrenheit or possibly somewhat less due to very small amounts, or traces, of impurities. For best results in coating the aluminum should be at,least commerically pure. However, regardless of the purity, the tempera ture of the bath should be within the range of 20 to 80 Fahrenheit above the melting temperature of the alt:- minum of which the molten bath is composed.

The effective depth of the molten aluminum bath must be within the range of approximately 0.5 to 4 inches and for best results the coating portion of the bath will be approximately 1 to 3 inches deep.

Within the foregoing ranges the temperature of the wire as it enters the bath will be controlled so that the temperature will be related inversely to theinitial wire diameter of 0.08 to 0.25 inches within the range of 980 to l,060 Fahrenheit. The wire will be heated to this temperature in a reducing atmosphere and preferably in a reducing atmosphere composed of approximately 50 to 100 per cent hydrogen and the balance some effectively inert gaseous diluent such as nitrogen, argon, or the like. It has been found that because of the relatively low temperature the reducing atmosphere must be fairly reactive to effect proper cleaning of the wire surface. At concentrations of hydrogen less than 50 per cent the cleaning effect of the reducing atmosphere upon the wire surface tends to become spotty.

The inverse ratio relationship between the temperature of the bath and the initial diameter of the wire should be such that a wire between 0.08 and 0.15 inches in diameter will have a temperature between l,000 and l,060 Fahrenheit-approximately inversely related, a wire having a diameter between 0.15 and 0.215 inches will have a temperature between 980 and 1,040 Fahrenheit approximately inversely related and a wire having a diameter between 0.215 and 0.25 inches will have a temperature of from 980 and 1,020 Fahrenheit approximately inversely related to the diameter. For best results in coating it is preferred to operate within the range of 980 to 1,040 Fahrenheit upon a wire having a diameter of between 0. l to 0.215 inches. However, good results will also be obtained within the foregoing range of wire sizes and temperatures if the larger or smaller sizes of wire are used.

The distance traveled by the wire through the molten aluminum bath must also be controlled in a direct ratio with the initial wire diameter within a range of 0.5 to 4 inch bath depth. The depth of the aluminum bath in carefully designed apparatus may be fairly easily controlled to within approximately one eighth of an inch of the desired depth by movement of the submerged coating chamber 57 by means of the adjusting apparatus shown in FIG. 1 or in FIG. 2 by movement of the ceramic displacement block 141 by operation of motor 149.

The direct relationship between the depth of the molten bath and the initial wire diameter should be such that a wire having an initial wire diameter of 0.08 to 0.15 inches will travel through a molten aluminum bath having a depth of 0.5 to 1.5 inches, and a wire having an initial diameter of 0.15 to 0.25 inches will pass through a molten aluminum bath having a depth of 1.5 to 4 inches. For best operation, furthermore, it is preferable for the process to be operated within a range of initial wire diameters of from 0.145 to 0.22 inches in approximate direct ratio with a molten coating bath having a depth of between approximately 1.5 to 2.5 inches. As will be explained hereinafter, in each of the foregoing ranges the particular ratio relationship must also be predetermined to avoid initiation of coating slip. v

In addition tothe foregoing requirements of the process it is necessary that the speed of the wire through the bath of molten aluminum coating metal be accurately controlled so as to be within the range of 70 to 135 feet per minute and preferably within a range of speed of 90 to 120 feet per minute and to be in inverse ratio relationship with the initial diameter of the wire being coated. The speed of the wire can, of course, be readily adjusted by adjusting the speed of the takeup blocks or 165 shown in FIGS. 1 or 2 respectively.

The inverse relationship between the speed of the wire and the initial diameter of the wire should be such that a wire having an initial diameter of 0.08 to 0.15 inches has a speed related approximately inversely to the diameter within a range of 100 to 135 feet per minute, a wire having an initial diameter of from 0.15 to 0.215 inches has a speed related approximately inversely to the diameter within a range of 72 to 128 feet per minute, and a wire having an initial wire diameter of from 0.215 to 0.25 inches has a speed through the molten bath approximately inversely related to the initial diameter of the wire within a range of to feet per minute. For best operation'of the process of the invention it is preferred to coat a wire having an initial diameter of from 0.145 to 0.22 inches approximately inversely related to a speed of from 90 to feet per minute through the molten coating bath.

By operating the coating process within the above parameters and ranges in accordance with the present invention not only will a desirable coating within the required ranges be attained but in addition a patented wire having the maximum attainable combination of strength and ductility byreason of the fine pearlitic structure attained during a patenting treatment of the wire will not be detrimentally affected by the application of the coating process. Thus although the process of the present invention is applicable to the coating of a full hard wire or the like if such a coated wire is required for some subsequent use to which it is to be put, the process is particularly useful and applicable to the coating of a patented wire which is to be later redrawn to a smaller size and very high strength.

It will be found after the coating of a patented wire that no detectable change in the fine pearlitic structure of the patented wire can be discovered microscopically or otherwise either internally or on the surface of the wire. It will be seen, therefore, that coating by the process of the invention is particularly effective and useful in the coating of a wire which must subsequently be redrawn to attain its final strength or dimensions. The reason for this minimization of any metallurgical change in the physical structure of a patented wire can be seen in FIG. 7 which is a graphic plot of the heat history of both a wire coated by the process of the instant invention and of a similar wire coated in a conventional flux type molten aluminum coating process for comparison. The dotted curve in FIG. 7 is the heat history of a wire coated by a conventional coating process. Here the wire is first heated in a flux and drier to 200 Fahrenheit as shown by the initial portion of the curve and then passed into a molten aluminum bath where it reaches a temperature of about 1,2l0 Fahrenheit in a period of 3.6 seconds while it is in the bath before beginning to cool on a descending curve after leaving the molten bath. In the process of the present invention, however, as shown by the dashed line in FIG. 7, the wire is heated from ambient mill temperature upwardly along a relatively. smooth curve to a temperature of around 980 to l,040 (the two temperatures being shown by the split ascending curves) prior to entrance of the wire into the molten aluminum bath where it is raised in the about 0.08 seconds while it remains in the bath to only approximately 990 to 1 ,050 Fahrenheit. The wire is then cooled quickly back to less than 200 Fahrenheit. The relatively short time at the highest temperature which the wire attains is insufficient to effect the metallurgical structure of the patented wire and the cooling period from the elevated temperature is in addition not long enough to encourage any metalordinate and the diameter of the coated wire is shown onltheabscissa. The minimum strength which will meet cthe publi'shed specifications of the American Society forTesting Materials for a :85 carbon wire coated withaheavy layer ofaluminum is shownby the dashed line 201. As indicated agraphically by the dashed line ll any wire having a finished diameter less than 0.129 inches'musthave aminimum tensile strength of at least 195,000 poundsper square inch. For sizes of wire larger than 0.129 inchesfinished diameter the tensile tstrength can be proportionallyless as shown by the descending portion of the dashed line down to the maximum ifinished size of an aluminum coated conductor .strand wire size of 0.204 inchesdiameter which diamelter-of wire'must have a minimum tensile strengthof at .least 155,000 pounds per square inch. As aluminum "coated wire of -variousinitial sizes is progressively retdrawnit=will decrease in size and increase in strength .along the solid curvesshown in FIG. 8 as examples. The *redrawingof thealuminum coated wire may be accomplished inlany suitable manner such as by the apparatus showninlFlG. 3.

It will be'found that as the wire is redrawn both the aluminum coating and the base wire are reduced in size proportionately with respect to each other so that a wirehaving an initialaluminurn coating before redrawing of, for instance, 11 percent of the cross sectional area of the coated wire, will after redrawing still have an aluminum coating equal to 11 per cent of the cross sectional area of the coated wire. As can be seen from FIG. 8'redrawing of the wire to meet specifications as to strength requires a fairly severe redrawing particularlywithrespect to the smaller sizes of wire so it is of upmostimportance that the metallurgical structure of the wire not be adversely affected by the process of coating the wire. The process of coating according to theipresent invention is particularly effective in maintaining this prior patented metallurgical structure and thus facilitating effective'redrawing of the coated wire.

FIGS. 4, 5, and 6 are graphs showing for three representative diameter wires of 0.150inch, 0.200 inch, and 0.235 inch the relationship between the aluminum coating thickness of the as-coated wire and the bath depth of the molten aluminum coating bath in inches.

Each graph has a series of curves each of which records Societyfor Testing Materials and particularly specifications B416.

In FIG. 4 the initial wire diameter of the green, or uncoated, wire is 0.150 inches, the carbon content is 0.85 carbon, the speed of the wire through the aluminum bath is 115 feet per minute and the temperature of the molten aluminum bath is held at l.,290-Fahrenheit. It can be seen that a good working plateau area is attained when the initial temperature of the wire just prior toentrance into the molten bath is from approxi- .mately 1,000" to l,060 Fahrenheit and the depth of the molten aluminum bath is from about 0.5 to .2 inches. In this area of the curve a smallchangein the conditions of coating will not cause a large change in the final coating thickness deposited upon the wires A wire thus may be coated when operating within this area of the graph both uniformly over long lengths and reliably from one coating run or from one wire to the next. A curved line marked slips begin" indicates the point at which the conditions of coating are such=that after the wire emerges from the molten bath a cylinder of coating tends to separate and slip down the wire until it freezes onto the wire as the wire leaves the coating bath causing an interrupted nonuniform coating upon the finished wire. The slip is believed to occur on the threshold of the remelt cycle-when the temperatures of the wire and the molten coating metal approach equilibrium with respect to each other. Slip may be described as a very unstable condition in which the-residency time of the wire in the bath has caused the wire temperature to rise. This rise in temperature causes the aluminum coating adjacent to the wire surface to either remain or become molten while an outer cylinder of the coating metal freezes. As the slip area is entered the outer cylinder of solidified aluminum will separate and slip down the wire until it freezes onto the moving wire at a lower level.

Any longer residency time in the bath results in a slumped coating in which the entire coating collapses into a lumpy mass In order to avoid the initiation of slipping the slips begin area or line in FIG. 4 mustnot be crossed. Anyone knowledgeable in the art of hot dip coating can establish these limits for any size wire by replotting the illustrative curves in FIGS. 4, 5 and 6. At times it may also be desirable to obtain a few experimental points. In effect slipping defines the practical upper limit of bath depth in some areas to produce a coating of acceptable quality. Slipping tends to occur at shallower bath depths with increasing wire temperature and appears with deeper bath depths with increasing wire diameter.

The horizontal solid line at the bottom of FIG. 4 indicates the thickness of coating which will be attained with a wash of aluminum deposited from a hot bath upon a wire left in the bath long enough to reach a more or. less equilibrium temperature. As shown in FIG. 4 by the scattered points about and along this line a wire preheated to 1,100 to l,l20 Fahrenheit will attain a final coating within this general range of wash coatings if the other conditions of coating remaimthe same.

In FIG. 5 there is shown as a further example a graph similar to the graph of FIG. 4 with the exception that the initial diameter of the green uncoated wire is 0.2.00 inches and the speed of the line or the passage of the wire through the molten bath is feet per minute.

The bath temperature remains at 1,290 Fahrenheit and the carbon content of the wire remains at 0.85 carbon.

In FIG. 6 there is shown as a still further example a graph similar to those of FIGS. 4 and 5 but wherein the initial diameter of the green uncoated wire is 0.235 inches, the speed of the wire through the molten bath is 92 feet per minute and the molten aluminum bath is held at a temperature of 1,300" Fahrenheit. It can be seen that a good plateau working area is attained with the wire preheated to around 980 to l,040. The high bath temperature in this example is detrimental to the maintenance of a very thin iron-aluminum alloy layer between the aluminum coating and the ferrous base metal. A very thin alloy layer may be defined as an alloy layer which constitutes less than 2 per cent of the total coating thickness. It is particularly important to obtain a thin alloy layer because a thicker alloy layer of say greater than 2 per cent of the total aluminum coating thickness will have a very detrimental effect upon the electrical conductivity of aluminum coated conductor strand. The minimum alloy layer attained by the process of the invention results from the relatively low temperatures attained by the coated wire and the short time at maximumtemperature. The very thin iron-aluminum alloy later at the interface between the aluminum coating and the ferrous base metal is attained without the need for any alloying additions to the bath which might also deleteriously affect the conductivity of the final wire or strand.

It will be noted that in FIG. 6 the slips begin line is not shown. This is because with the heavier wire gage in FIG. 5 the slips begin line has been moved far to the right.

It will readily be recognized from the graphs shown in FIGS. 4, 5 and 6 that the present invention provides a method of coating wire with aluminum which operates in a stable coating zone where changes within the ranges of coating conditions or parameters do not result in unacceptable changes in the coating applied to the wire. Unavoidable changes in the coating conditions due to the usual apparatus limitations which have previously made uniform, reproducible coating in this general area of high wire temperatures and superior coating adherence to the base wire impractical, if not impossible, to attain are eliminated by operating within the various ranges of coating conditions defined by the invention where small changes in the coating conditions produce small and not large changes in the aluminum coating applied to the base wire.

We claim:

l. A method of coating steel wire having an initial diameter of from 0.08 to 0.25 inches with a substantially pure aluminum coating having a thickness of approximately 10 to per cent of the coated wire radius with not morethan a very thin iron aluminum alloy layer between the pure aluminum coating and the base metal comprising:

a. cleaning the surface of the wire,

b. heating the wire to between 980 to l,060

Fahrenheit within a reducing atmosphere,

c. passing the heated wire at a speed of from 70 to 135 feet per minute into a molten aluminum bath below the surface thereof without intermediate contact with oxidizing conditions, said bath being comprised of at least commercially pure alluminum held at a temperature of from approximately to 80 Fahrenheit above the melting point of the molten metal,

d. passing said wire through said molten bath for a distance of approximately 0.5 to 4 inches at a speed of from to feet per minute,

e. passing the wire from the molten bath,

f. maintaining the temperature of the wire as it enters the bath in inverse ratio with respect to the initial wire diameter within the range of approximately 980 to 1,060 Fahrenheit,

g. maintaining the distance traveled by the wire through the molten metal bath in direct ratio with respect to the initial diameter of the wire within the range of 0.5 to 4 inches of travel through the molten aluminum bath with a ratio predetermined as to the deeper limit of the molten bath to avoid the initiation of coating slip, and

h. maintaining the speed of the wire through the molten aluminum bath within the range of 70 to 135 feet per minute in inverse ratio with respect to the initial diameter of the wire.

2. A method of coating steel wire with a substantially pure aluminum coating according to claim 1 additionally comprising:

i. quenching the wire immediately after it passes from said molten bath to solidify at least the surface of the molten coating upon the wire and contacting the wire with a vibration damping means before significant vibration appears in the wire.

3. A method of coating steel wire with aluminum according to claim 2 wherein said vibration damping means is a contacting guide sheave.

4. A method of coating steel wire with aluminum according to claim 2 wherein the wire has an initial fine pearlitic metallurgical structure and additionally comprising:

j. drawing said coated wire through a die to reduce the size of the wire and increase its tensile strength.

5. A method of coating steel wire with aluminum according to claim 1 wherein the wire has an initial fine pearlitic metallurgical structure prior to passage through said molten aluminum bath and additionally comprising:

j. drawing said coated wire through a reducing die to reduce the size of the wire and increase its tensile strength.

6. A method of coating steel wire with aluminum according to claim 1 wherein the wire has an initial uncoated diameter of 0.145 to 0.22 inches and is coated with an aluminum coating equal to 12 to 14.5 per cent of the coated radius of the wire.

7. A method of coating steel wire with aluminum according to claim 1 wherein the temperature of the wire is controlled within the range of 980 to l,060 Fahrenheit as it enters the molten aluminum bath in inverse ratio with respect to the initial wire diameter within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of 0.08 to 0.15 inches is controlled to have a temperature of between 1,000 and 1,060 Fahrenheit inversely related to the diameter,

ii. a wire having an initial uncoated diameter of 0.15 to 0.215 inches is controlled to have a temperature of 980 to 1,040 Fahrenheit inversely related to the diameter, and

iii. a wire having an initial uncoated diameter of 0.215 to 0.25 inches is controlled to have a temperature of between 980 to l,020 Fahrenheit inversely related to the diameter. 8. A method of coating steel wire with aluminum according to claim 7 wherein the distance traveled by the wire through the molten metal bath within a range of 0.5 to 4 inches is controlled in a direct ratio with the initial uncoated wire diameter with a ratio relationship such that i. a wire having a diameter of approximately 0.08 to 0.15 inches will travel through the molten coating bath for approximately 0.5 to 1.5 inches, and 1 ii. a wire having a diameter of approximately 0.15 to 0.25 inches will travel through the molten coating bath for approximately 1.5 to 4 inches. 9. A method of coating steel wire with aluminum according to claim 7 wherein the initial uncoated diameter of the wire is 0.145 to 0.22 inches and the distance traveled by the wire through the molten bath is controlled in .a direct ratio with the initial diameter of the wire within a range of 1.5 to 2.5 inches of travel such that the coating applied is equal to 12 to 14.5 per cent of the coated radius of the wire.

:10. A method of coating steel wire with aluminum according to claim 8 wherein the speed of the wire through the molten bath within the range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of from 0.08 tp 0.15 inchs will have a speed of travel through the molten bath of 100 to 135 feet per minute,

ii. a wire having an initial uncoated diameter of from 0.15 to 0.215 inches will have a speed of travel through the molten bath of 72 to 128 feet per minute, and

iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a speed of travel through the molten bath of from 70 to 100 feet per minute.

1 1. A method of coating steel wire with aluminum aecording to claim 8 wherein the initial uncoated diameter ofthe wire is 0.15 to 0.215 inches and the speed of travel of the wire through the molten bath is controlled within the range of 90 to 120 feet per minute in inverse ratio with respect to the initial diameter of the wire in inches.

12. A method of coating steel wire with aluminum in accordance with claim 10 wherein the wire has an initial finepearlitic metallurgical structure prior to passage through said molten aluminum bath which remains unchanged after passage of said wire through said bath and additionally comprising:

j. drawing said coated wire through a reducing die to reduce the diameter of the wire and increase its tensile strength to specifications.

13. A method of coating steel wire with aluminum according to claim 1 wherein the distance traveled by the wire through the molten metal bath within a range of 0.5 to 4'inches is controlled in a direct ratio with the initial uncoated diameter of the wire being coated with a ratio relationship such that i. a wire having a diameter of approximately 0.08 to 0.15 inches will travel through the molten coating bath for approximately 0.5 to 1.5 inches, and

ii. a wire having a diameter of approximately 0.15 to 0.25 inches will travel through the molten coating bath for approximately 1.5 to 4 inchesb 14. A method of coating steel wire with aluminum according to claim 13 wherein the speed of the wire through the molten coating bath within the range of to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within" the range of 0.08 to 0.25 inches with a ratio relationship such that:

i. a wire having an initial uncoated diameter of from 0.08 to 0.15 inches will have a transit speed through the molten bath of from to feet per minute in inverse ratio to the initial diameter of the wire,

ii. a with having an initial uncoated diameter of from 0.15 to 0.215 inches will have a transit speed through the molten bath of from 72 to 128 feet per minute in inverse ratio to the initial diameter of the wire, and

iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a transit speed through the molten bath of from 70 to 100 feet per minute in inverse ratio with the initial diameter of the wire. I

15. A method of coating steel wire with aluminum according to claim 1 wherein the speed of the wire through the molten coating bath within the range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that 1 i. a wire having an initial uncoated diameter of from 0.08 to 0.15 inches will have a transit speed through the molten bath of from 100 to 135 feet per minute in inverse ratio to the initial diameter of the wire,

ii. a wire having an initial uncoated diameter of from 0.15 to 0.215 inches will have a transit speed through the molten bath of from 72 to 128 feet per minute in inverse ratio to the initial diameter of the wire, and

iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a transit speed through the molten bath of from 70 to 100 feet per minute in inverse ratio with the initial diameter of the wire.

16. A method of coating steel wire with aluminum according to claim 1 wherein the temperature of the wire is controlled within the range of 980 to 1,060 Fahrenheit as it enters the molten aluminum bath in inverse ratio with respect to the initial wire diameter within the range of 0.08 to 0.25 inches with a ratio relationship such that I i. a wire having an initial uncoated diameter of 0.08 to 0.15 inches is controlled to have a temperature of between 1,000 and 1,060 Fahrenheit inversely related thereto,

ii. a wire having an initial uncoated diameter of 0.15 to 0.215 inches is controlled to have a temperature of 980 to 1,040" degrees inversely related thereto,

iii. a wire having an initial uncoated diameter of 0.215 to 0.25 inches is controlled to have a temperature of between 980 to l,020 Fahrenheit inversely related thereto, and

wherein the speed of the wire through the molten coating bath within the range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of from 0.08 to 0.15 inches will have a transit speed through the molten bath of from 100 to 135 feet per minute in inverse ratio to the initial diameter of the wire,

ii. a wire having an initial uncoated diameter of from 0.15 to 0.215 inches will have a transit speed through the molten bath of from 72 to l28 feet per minute in inverse ratio to the initial diameter of the wire, and

iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a transit speed through the molten bath of from to feet per minute in inverse ratio to the initial diameter of the wire. 17. A method of'coating steel wire with aluminum in accordance with claim 16 wherein the wire has an initial fine pearlitic metallurgical structure prior to passage through said molten aluminum bath, which structure remains unchanged after passage of said wire through said bath and additionally comprising:

Claims

1. A method of coating steel wire having an initial diameter of from 0.08 to 0.25 inches with a substantially pure aluminum coating having a thickness of approximately 10 to 15 per cent of the coated wire radius with not more than a very thin iron aluminum alloy layer between the pure aluminum coating and the base metal comprising: a. cleaning the surface of the wire, b. heating the wire to between 980* to 1,060* Fahrenheit within a reducing atmosphere, c. passing the heated wire at a speed of from 70 to 135 feet per minute into a molten aluminum bath below the surface thereof without intermediate contact with oxidizing conditions, said bath being comprised of at least commercially pure alluminum held at a temperature of from approximately 20* to 80* Fahrenheit above the melting point of the molten metal, d. passing said wire through said molten bath for a distance of approximately 0.5 to 4 inches at a speed of from 70 to 135 feet per minute, e. passing the wire from the molten bath, f. maintaining the temperature of the wire as it enters the bath in inverse ratio with respect to the initial wire diameter within the range of approximately 980* to 1,060* Fahrenheit, g. maintaining the distance traveled by the wire through the molten metal bath in direct ratio with respect to the initial diameter of the wire within the range of 0.5 to 4 inches of travel through the molten aluminum bath with a ratio predetermined as to the deeper limit of the molten bath to avoid the initiation of coating slip, and h. maintaining the speed of the wire through the molten aluminum bath within the range of 70 to 135 feet per minute in inverse ratio with respect to the initial diameter of the wire.

2. A method of coating steel wire with a substantially pure aluminum coating according to claim 1 additionally comprising: i. quenching the wire immediately after it passes from said molten bath to solidify at least the surface of the molten coating upon the wire and contacting the wire with a vibration damping means before significant vibration appears in the wire.

4. A method of coating steel wire with aluminum according to claim 2 wherein the wire has an initial fine pearlitic metallurgical structure and additionally comprising: j. drawing said coated wire through a die to reduce the size of the wire and increase its tensile strength.

5. A method of coating steel wire with aluminum according to claim 1 wherein the wire has an initial fine pearlitic metallurgical structure prior to passage through said molten aluminum bath and additionally comprising: j. drawing said coated wire through a reducing die to reduce the size of the wire and increase its tensile strength.

7. A method of coating steel wire with aluminum according to claim 1 wherein the temperature of the wire is controlled within the range of 980* to 1,060* Fahrenheit as it enters the molten aluminum bath in inverse ratio with respect to the initial wire diameter within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of 0.08 to 0.15 inches is controlled to have a temperature of between 1,000* and 1,060* Fahrenheit inversely related to the diameter, ii. a wire having an initial uncoated diameter of 0.15 to 0.215 inches is controlled to have a temperature of 980* to 1,040* Fahrenheit inversely related to the diameter, and iii. a wire having an initial uncoated diameter of 0.215 to 0.25 inches is controlled to have a temperature of between 980* to 1,020* Fahrenheit inversely related to the diameter.

8. A method of coating steel wire with aluminum according to claim 7 wherein the distance traveled by the wire through the molten metal bath within a range of 0.5 to 4 inches is controlled in a direct ratio with the initial uncoated wire diameter with a ratio relationship such that i. a wire having a diameter of approximately 0.08 to 0.15 inches will travel through the molten coating bath for approximately 0.5 to 1.5 inches, and ii. a wire having a diameter of approximately 0.15 to 0.25 inches will travel through the molten coating bath for approximately 1.5 to 4 inches.

9. A method of coating steel wire with alumInum according to claim 7 wherein the initial uncoated diameter of the wire is 0.145 to 0.22 inches and the distance traveled by the wire through the molten bath is controlled in a direct ratio with the initial diameter of the wire within a range of 1.5 to 2.5 inches of travel such that the coating applied is equal to 12 to 14.5 per cent of the coated radius of the wire.

10. A method of coating steel wire with aluminum according to claim 8 wherein the speed of the wire through the molten bath within the range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of from 0.08 tp 0.15 inchs will have a speed of travel through the molten bath of 100 to 135 feet per minute, ii. a wire having an initial uncoated diameter of from 0.15 to 0.215 inches will have a speed of travel through the molten bath of 72 to 128 feet per minute, and iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a speed of travel through the molten bath of from 70 to 100 feet per minute.

11. A method of coating steel wire with aluminum according to claim 8 wherein the initial uncoated diameter of the wire is 0.15 to 0.215 inches and the speed of travel of the wire through the molten bath is controlled within the range of 90 to 120 feet per minute in inverse ratio with respect to the initial diameter of the wire in inches.

12. A method of coating steel wire with aluminum in accordance with claim 10 wherein the wire has an initial fine pearlitic metallurgical structure prior to passage through said molten aluminum bath which remains unchanged after passage of said wire through said bath and additionally comprising: j. drawing said coated wire through a reducing die to reduce the diameter of the wire and increase its tensile strength to specifications.

13. A method of coating steel wire with aluminum according to claim 1 wherein the distance traveled by the wire through the molten metal bath within a range of 0.5 to 4 inches is controlled in a direct ratio with the initial uncoated diameter of the wire being coated with a ratio relationship such that i. a wire having a diameter of approximately 0.08 to 0.15 inches will travel through the molten coating bath for approximately 0.5 to 1.5 inches, and ii. a wire having a diameter of approximately 0.15 to 0.25 inches will travel through the molten coating bath for approximately 1.5 to 4 inches.

14. A method of coating steel wire with aluminum according to claim 13 wherein the speed of the wire through the molten coating bath within the range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that: i. a wire having an initial uncoated diameter of from 0.08 to 0.15 inches will have a transit speed through the molten bath of from 100 to 135 feet per minute in inverse ratio to the initial diameter of the wire, ii. a with having an initial uncoated diameter of from 0.15 to 0.215 inches will have a transit speed through the molten bath of from 72 to 128 feet per minute in inverse ratio to the initial diameter of the wire, and iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a transit speed through the molten bath of from 70 to 100 feet per minute in inverse ratio with the initial diameter of the wire.

15. A method of coating steel wire with aluminum according to claim 1 wherein the speed of the wire through the molten coating bath within The range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of from 0.08 to 0.15 inches will have a transit speed through the molten bath of from 100 to 135 feet per minute in inverse ratio to the initial diameter of the wire, ii. a wire having an initial uncoated diameter of from 0.15 to 0.215 inches will have a transit speed through the molten bath of from 72 to 128 feet per minute in inverse ratio to the initial diameter of the wire, and iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a transit speed through the molten bath of from 70 to 100 feet per minute in inverse ratio with the initial diameter of the wire.

16. A method of coating steel wire with aluminum according to claim 1 wherein the temperature of the wire is controlled within the range of 980* to 1,060* Fahrenheit as it enters the molten aluminum bath in inverse ratio with respect to the initial wire diameter within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of 0.08 to 0.15 inches is controlled to have a temperature of between 1,000* and 1,060* Fahrenheit inversely related thereto, ii. a wire having an initial uncoated diameter of 0.15 to 0.215 inches is controlled to have a temperature of 980* to 1,040* degrees inversely related thereto, iii. a wire having an initial uncoated diameter of 0.215 to 0.25 inches is controlled to have a temperature of between 980* to 1,020* Fahrenheit inversely related thereto, and wherein the speed of the wire through the molten coating bath within the range of 70 to 135 feet per minute is controlled in inverse ratio with respect to the initial diameter of the wire within the range of 0.08 to 0.25 inches with a ratio relationship such that i. a wire having an initial uncoated diameter of from 0.08 to 0.15 inches will have a transit speed through the molten bath of from 100 to 135 feet per minute in inverse ratio to the initial diameter of the wire, ii. a wire having an initial uncoated diameter of from 0.15 to 0.215 inches will have a transit speed through the molten bath of from 72 to 128 feet per minute in inverse ratio to the initial diameter of the wire, and iii. a wire having an initial uncoated diameter of from 0.215 to 0.25 inches will have a transit speed through the molten bath of from 70 to 100 feet per minute in inverse ratio to the initial diameter of the wire.

17. A method of coating steel wire with aluminum in accordance with claim 16 wherein the wire has an initial fine pearlitic metallurgical structure prior to passage through said molten aluminum bath, which structure remains unchanged after passage of said wire through said bath and additionally comprising: j. drawing said coated wire through a reducing die to reduce the diameter of the wire and increase its tensile strength to specifications.