US3082119A

US3082119A - Method of and apparatus for hot-dip coating strands

Info

Publication number: US3082119A
Application number: US10639A
Authority: US
Inventors: Arch W Harris
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1960-02-24
Filing date: 1960-02-24
Publication date: 1963-03-19
Anticipated expiration: 1980-03-19

Description

3,082,119 METHOD oF AND APPARATUS FOR HOT-DIP coA'rING STRANDS Filed Feb. 24, 1960 *March 19, 1963 A. w. HARRIS 2 Sheets-.Sheet 1 March 19, 1963 A. w. HARRIS 3,082,119

METHOD OF' AND APPARATUS FOR HOT-DIP COATING STRANDS Filed Feb. 24, 1960 2 Sheets-Sheet 2 A fior/rey Filed Feb. 24, 19.60, Ser. No. 10,639 .6 Claims. (Cl. 117-114) This invention relates to an i-mproved method and apparat-us for hot-dip coating a continuous lmetallic strand with a metal or `alloy having a substantially lower melting point than the metal or alloy of the strand and more particularly to an improved method for the continuous hot-dip coating ofV a steel strand with a molten metal, such as aluminum, which does. not readily wet steel.

Conventional processes of hot-dip coating are of two general varieties. The first is characterized Iby passing .the cleaned base metal through a ux and then into a molten bath of the coating metal. InV the second, the cleaned metal is heated in a reducing atmosphere and passed into the molten coating metal while still under the protection ofthe atmosphere. The aim in both instances is to bring clean metallic surfaces into contact and thus achieve a complete wetting of the base metal with the molten coating metal. Complete wetting is essential .to .avoid black-spots, (uncoated areas). It is Well recognized that the use of ux, either liquid or gaseous, for -this purpose presents several disadvantages. Moreover, this critical objective is not attained by either `c`:onventional procedure when applied in the coating of ,a continuously moving strand except at rather low rates of strand movement. In the case of aluminum .coated ,steel wire, black-spots are not completely eliminated even at impractically low strand speeds.

Accordingly it is an ,object of the present invention to provide an improved continu-ous hot-dip coating process wherein smooth coatings free .of even minute uncoated areas-can .be produced at highspeed without use of fluxes or preheating in a reducing atmosphere.

Another disadvantage of prior art practices has been the inability to produce a perfectly valuminum coated `strand having .high tensile strength. This derives from the fact that the coating bath must tbe maintained ata temperatureof 1100 to `1300 F. dependingupon the purity Vof aluminum used and the steel brought to this temperature by fthe bath itself or by preheating. Thus in conventional practices `:because of the relatively slow rates of strand travel, the steel is substantially annealed, and the ,desired effects of prior cold Working or heat treatment to raise tensile properties of the steel are largely lost. Similar diiliculties, .but to a somewhat lesser degree are encountered in `continuous hot -galvanizing and tinning operations.

Accordingly another object of the invention is the provision of hot-dip coating process in which time at coating temperature is so short that physical properties of .the base metal are not substantially reduced thereby; a .particular object being production of hot-dipaluminum coated steel strands having tensile strength in excess 4of 2001,000i,p.s.i.

Another problem encountered in adapting conventional 4procedures of hot-dip aluminum coating of steel strands has been .the cont-rol of thickness of the alloy Vlayer -produced ,during the passage ofthe strand through the molten 4coating bath. The development of some intermetallic .compounds between the base and coating metals is 'beneficial, increasing adherence, improving soldering charac- `teristics and the like. Excessive alloy however is detrimental, consequently control ofalloy formation has been the subject `of intensive investigation. Since maximum speed of travel in conventional hot-dip procedures is Xed arent O "ice by `other considerations, 'the conventional solution to alloy control has been to alloy the coating bathwith a metal which tends to suppress alloy formation. While such practices have been successful to a considerable degree, they introduce certain undesirable limitations, for example, the use o f a feW percent of silicon in the aluminum bath reduces the alloy formation but at the same time adversely affects other characteristics of the coating itself.

Accordi-1q1gly, it 4is a further object of 4the invention to provide ,an improved Vprocess which permits the use of unalloyed coating baths.

Other objects will appear vas the description proceeds.

Heretofore control of black-spots to even `a reasonable Vdegree inthe hot-dip aluminum coating of steel has required limi-,ting strand speed v.to a maximum of about 4G feet per minute; the maximum varying somewhat with Athe dimensions of the str-and beingcoated. Even at such Aslow speeds vsome `black-spots or holidays are caused by gas evolution from the steel base through the molter coating -just before or just after emergence from the c-oating bath.. l have found this speed limitation is removed and black-spots and the like, completely eliminated b3 `imparting, inV combination with certain other practicef .hereafter .,described, vibratory forces of a particular nature tothe strand as it enters the aluminum bath. Moreover, 1 have found that these practices make an unexpectedly large reduction in the time o f immersion anc' that the strand leaving the coating bath not only `carries la completeI coating but little or no alloy is formed thereor during its passage `through the .-bath.

I am aware that the use of vibration to promote wettability in soldering operations and the like has been proposed. However, such earlier proposals have in general been concerned with ultrasonic vibrations and `have never been successfully applied in the continuous coating operations outlined above. I have found that success in the `latter operations requires strict adherence to the following principles:

Firstly, the vibratory forcemust be applied in such manner as to develop a transient, random vibration in the strand, such being characterized by innumerable frequen cies inexcess ofASO: cycles per second and an overall ac .celeration in excess of 2.0 g. Secondly, the vibratory forc V .must-be appliedtothe `strand as near its entry into the po as -is practical; the vibrations or vibratory energy imparte( tothestrand mustbe substantially dissipated or dampener .out-before the stra-nd is discharged from the coating po 4into-the atmosphere and the strand must be moved at sub stantially no tension. The foregoing conditions are es .sentialto .avoiding `the development of standing waves ir `.the .exiting strand` which cause rough, uneven coating and even extensive uncoated areas.

The lterm substantially no tension as used herein i understood to mean not-substantially more tension lthai is required to move the strand through the apparatus anc excludes the application of appreciable back tension.

The required transient, random type Vof vibrations an produced in the strand by ,applying shock impulses a ,regular intervals while restraining movement of the strani in the direction of the blow. The aim is to produce 1 ,slight random movement of the strand `rather than move mentof apar-ticular amplitude in aparticular plane. Ac Ycordingly, results are not associated with development i1 `the strand of motion having a particular frequency am level-of acceleration but rather with the development o an extremelycomplex motion in which substantially al `frequencies over fa -relatively wide range falling withii the audible frequency band are present at about the sam` ,levellofacceleration I have not, for example, been abL Ato produce coatings at high speeds `completely free o black-spots by inducing a pure sinusoidal vibration in th| strand. A minimum of 40 to 60` shock impulses pe4 encountered; the optimum rate within this range depending on the mass of strand, the degree with which movement of the strand in the direction of impact is limited, and to some extent on lthe design of the vibrator itself. The lowest frequency developing in the strand should be of the order of 80 c.p.s. but may be as high as about 400 c.p.s. without adverse effect. Absence of frequencies below about 300 c.p.s. requires higher overall accelerations which while not detrimental is wasteful of vibrating power. The highest frequency developing in ythe strand may be in excess of 16,000 c.p.s. however the absence of frequencies over about 3000 c.p.s. is not detrimental. The intensity of the induced vibrations is important and is conveniently defined in terms of acceleration as multiples of g, the acceleration of gravity, 32.172. ft./sec./sec. In Ithis regard, the value of acceleration associated with the full range of frequencies present in the motion, i.e., the overall acceleration, is the determining factor. The required motion being both transient and random, the acceleration associated with any particular component (frequency) thereof may vary considerably from moment to moment; the overall acceleration however, remains relatively constant and must be maintained at at least 20 g for satisfactory coating results. Overall accelerations as high as 5000 g have produced good results, but I prefer to use the lowest acceleration commensurate with good results since more eicient use of vibrating power with least wear of the vibrator is achieved. The important point in this regard is that the vibrations and vibratory energy imparted to the strand must be substantially above that which would be absorbed or dissipated by the passage of the strand through the coating bath. A minimum acceleration of 20 g achieves this result. Optimum value of acceleration varies with the material, temper, shape and dimensions of the strand, the design of the imparting vibrator and its associated motion limiting device and thus must be determined experimentally for each installation. The presence of discrete peaks in the frequency-acceleration curve are not detrimental, although extremely high level peaks toward the lower end of the frequency range may, under some conditions, contribute to the formation of standing waves in the exciting strand, which condition must be avoided if smooth, black-spot free coatings are to be produced.

Control of motion in the strand is conveniently accomplished by regulating the rate of application of the shock impulses. Other factors being equal, the range of frequencies developing in the strand can be shifted upwardly and, more importantly, the overall acceleration associated therewith can be increased by increasing the impact rate. The frequency range and acceleration can also be altered by increasing the restriction of strand movement in the direction of impulse application. Restricting strand movement increases the energy imparted per blow and contributes to randomness of the motion achieved, for example, using an impact rate of 300 impulses per second against a restricted No. l gage low carbon steel wire moving at 75 f.p.m. induced vibrations having an overall acceleration of 1000 g and produced an excellent aluminum coating; removing the restriction however altered the characteristics of the motion in the wire sufiiciently to adversely affect the coating and required increasing the impact rate to 900 impulses per second to restore coating quality. Accordingly, it is preferable in practicing my invention to use a fixed degree of restriction at the imparting vibrator and adjust the impact rate if required.

Characteristics of the vibratory motion required in the present method were determined using an Endevco accelerometer and amplifier, a tape recorder, and a Bruel & Kiaer frequency analyzer and graphic level recorder.

A tape recording of the amplified output voltage of the accelerometer was made while the vibration pick-up of the instrument was held manually against the vibrating strand. A loop of the tape was then played back continuously on the tape recorder and the electrical voltage produced was -fed through the analyzer into the graphic level recorder to produce a graph of vibration level as a function of frequency. The overall acceleration was computed from the graphed data.

In addition to greatly promoting wettability, induced vibratory motions of the character described, greatly increases the rate of heat transfer from the coating bath to the strand. The magnitude of the latter effect is such that time of immersion in the bath must be limited to a maximum of about 8 seconds if the benefits of the invention are to be obtained. Immersion time is a function of length of immersion and speed of strand travel through the bath and is fixed in design of the coating pot and rigging. A minimum immersion of about 0.5 second must be provided to produce satisfactory coating. Where minimum alteration of physical properties of the base metal is required, the immersion time should be as short as possible and preferably not more than about 3 seconds. The maximum in -this regard varies somewhat with mass of the strand and bath temperature.

A preferred arrangement of processing steps and apparatus suitable for the practices of my invention is shown in the attached drawing, in which:

FIGURE 1 is a schematic side elevation, partly in section of a coating line embodying the principles of my invention; t

FIGURE 2 is an enlarged longitudinal section of the coating pot of FIGURE l;

FIGURE 3 is a partial end elevation of the coating pot;

FIGURE 4 is a plan of the vibration imparting mechanism;

FIGURE 5 is a sectional view taken along plane IV IV of FIGURE 4;

FIGURE 6 is a side elevation of the hold-down mechanism;

FIGURES 7 and 8 are respectively, a front elevation and a plan View of a gas Wipe particularly adapted to the practices of my invention; and

FIGURE 9 is a sectional View thereof taken along the plane IX-IX of FIGURE 8.

With particular reference to the drawing, the numeral 2 designates a coil of strand or wire S disposed on a pay-off reel 4 which is power driven and provided with conventional controls, not shown, for automatically regulating the speed thereof. Located at the other end of the line is a power-driven take-up reel or recoiler 40 also provided with conventional controls, not shown, for automatic speed regulation. Reels 4 and 40 are operated to feed and gather strand S at the same lineal rate so that the strand will be moved through the apparatus at substantially no tension. From the pay-olf reel, the strand S may be fed through cleaning tank 6, preferably a tank of molten caustic and then through a water rinse 8. Alternately or sequentially the strand may be conducted through a tank 10 containing a dilute aqueous sulphuric or hydrochloric cleaning solution followed by a water rinse 12. Cleaning arrangement shown is particularly adapted to the removal of the lubricants and .drawing compounds conventionally used in the cold drawing of wire. The molten caustic breaks down the drawing lubricants to a readily removable form and complete neutralization and cleansing is effected by the acid bath. Methods better adapted to other materials can, of course, be substituted. Preferably the strand is next conducted through a hot Water rinse tank 14 to further rinse the strand, expel as much adsorbed gas as possible, and promote drying thereof. Drying is substantially completed by a hot-air or similar drier 16, after which the strand is passed into contact with a rotary impact-imparting mechanism V for inducing vibratory motion of the required character in the strand. An adjustable, resiliently mounted hold-down sheave 18 located just ahead of the mechanism V maintains the strand in suitable contact therewith to restrict strand movement in the direction `of application of impact; the yamount of such restriction being regulatable by adjustment of spring pressure on the sheave. From vibrator V the strandpasses through an elongated tube22 havingone end submerged in a bath 20 of molten coating metal. A gas inlet 24 is provided adjacent the lower end of the tube and a nonoxidiz'ing or reducing gas is continuously introduced to maintain a nonoxidizing atmosphere in contact with the bath-surface at the point of entry of the strand. If the gas is combustible, it may be burned at the `upper end of .the tube as it exits therefrom. Vibrator-y motion induced in strand S rapidly dissipates any absorbed gas or Water films from the `strand and 'disrupts any oxide `films formed on the bath surface, however, exceptionally heavy top dross is produced; accordingly, the steps `for vdrying the strand and. maintaining the bath surface free of oxide while not essential tin the present methodto the production of a quality aluminum coating, are included lfor economic reasons. The flow of gas through tube 22 carries away the gases and any water vapor evolved from the strand by the `imparted vibration and maintains the surface `of the coating metal rat the point of strand entry -completely free of oxide, accomplishing this objective without lthe formation of any deleterious side reaction products. In coating withzinc or tin, drying of the strand is, of course, a `necessary 'safety measure. The strand is submerged inthe coating metal by `a sinker 26, passing therefrom in a substantially vertical pass-line to a de- Viiector rol-l 34 located a suicient distance above the bath to -avoid contacting the strand -prior -to complete solidification of the coating thereon. ranged to direct a blast of -cool air or atomized Water against the strand to arrest alloy formation, may be positioned below sheave 34. Means 35 should be supported in an ladjustable manner to `bepositionable in the pass as may be required. The coated strand leaves the bath through a specially constructed gas wipe 30, lpartially submerged in `the molten coating metal. Wipe 30, shown yin detail in FIGURES 7, 8, and 9, comprises an open-bottom, box-like chamber A having in the top thereof, an opening 431 for the passage of the coated strand and a gas inlet 32. A combustible gas, e.g. natural gas, Ais introduced at inlet 32 and burned Vat opening 31. The latter should be restricted to `a `size permitting a free dow of the gas completely around `the exiting strand but preventing 4back-flow of air into -the chamber. The -burning gas promotes flow-back of excess `coating metaland maintains `the bath surface yfree of oxides Yand dross at the 'point-of strand -exit toinsure bright, uniform coatings. Extending the width of .chamber 30A several linches above the bottom thereof and disposed below opening 31"soas to contact-a strand :exiting therethrough Vis a rod '-28 of Alundum or like material supported at one end by the blind recess in boss 127A- and` by `the threaded opening in-boss 327B at `the other, threaded plug `27C serving 4to -clamp the rod iin thisposition. Rod ZS is :preferably grooved 4to tprevent strand S from rubbing the side walls .of opening 311. Projecting from 4one side of chamber 39A and aligned to permit observation of the contact .of strandSand .bar 28 isa sight tube 29, the end of which is .closed to the latmosphere by a suitable sgiass disc 29Aanddclamping ring 29B. Support ar-m 30B weld-ed .or .otherwise attached to the back-of chamber 39A, :is slidably disposed in a `clamp rwhich lin turn isr-slidably attached .to vertical standards 25 carriedby the bac-k `wallZA of the coating pot.

As previously mentioned, the .present invention .contemplates prevention `of standing waves in the strand leaving the coating .pot by maintaining `the strand substantially untensioned and dissipatingza substantial portion of the energy limparted by vibrator V before discharging the Acoated strand into the atmosphere. The

Cooling means ar- I latter is accomplished by `positioning, wipe 30 so that bar 28 bears against strand S at a point ll/z to.3 inches above -the surface of the molten .coating metal to deflect the strand from the positionit would, by reason of its substantially untensioned condition, otherwise normally assume in passing lfrom sinker 26 to sheave 34. The degree of deflection must be such as will develop sufficient pressure to maintain a positive contact of strand and bar at all times, but insuicient to remove the coating at the point of contact.

Since for any given deflection, the pressure of contact depends upon the resilience of the strand which in turn varies with such factors -as strand composition, its crosssectional dimensions and prior treatments Vaffecting its mechanical properties, the position of wipe 30 must be adjusted for diiferent strands. Itis impossible to assign numerical limits of either deflection or pressure, accordingly, necessary adjustments must be made by Observaion of results.

Location of contact bar 28 is of `critical importance tc the practical achievement of the results of my invention Complete submersion favors dissipation of the vibratory energy from the strand and does so Without damage tc 4the coating. A completely submerged bar, however, :be haves erratically; such ibars frequently disintegrate in exceedingly short times. Moreover, adjustment of a sub merged bar is very diiiicult and time consuming. On the other hand, rough, oxidized streaks and other coating defects resulting from contacting the molten coating can not be tolerated. I have found the foregoing diflicultie: are completely avoided and the required dissipation o: vibra-tory energy achieved only if the contact is mad within the gas Wipe a few inches above the bath surface Due to the upward drag of molten metal by the rapidly moving strand, the coating at this location lis abnormally thick, is fully molten and is protected against` oxidatior by the atmosphere of the wipe. Under these condition: the disturbance of the coating lby the squeegeeing actioi of the contact bar has no permanent elfect and the coat ing produced is uniform and free of oxide streaks. Fo: effective dampening, however, contact must be made with in l-/z and 3 inches of the bath surface, depending some what on the speed of travel, size, :and mechanical prop erties of the strand. The bar is easily adjusted sincl contact-can be observed through the sight tube Z9;

From sheave 34 the'coated strand may be conveyed bj suitable arrangement of rolls or sheaves, through con ventional means indicated at 36 and 38 to further cool treat, or ylubricate the product as desired. Thereafte' the strand is wound on talre-up reel 40 previously de scribed. Since it is essential to the purposes of my in `vention that the strand does not ybecome taut during it passage through the equipment, care must be taken in de sign -to minimize friction at, as well as the number oi `conveying rolls or sheaves. Straightthrough-type 4treat ing tanks should be used wherever possible.

A preferred embodiment of the vibrator V is shown i1 FIGUR-ES 4 and 5 of the drawing. lt is` comprised of variable speed motor A50 connected to a pair of oppose discs v52. Disposed `between the discs are la plurality o equally spaced pins or bars 54 spaced inwardly a sligh distance from Ithe periphery of the :discs as shown i1 FIGURE 5. The assembly is supported on va plate 5i from the'forward wall of `coating-pot 2A)` withwthetop edge of the discs 52 projecting above lthe normal pass line o the strand. Thus, the str-and rides loosely between th discs and is subjected ytofan impact by each pin as th discs rotate. Hold-down sheave v18 positioned to'rideeth surface of the strand a `slightfdistance ahead of disc 52 is carriedyby a bearing bracket 58 which is tit-ted t slide y'freely on a pair -of supportrods `60. A spring 6.' is positioned bet-Ween the bracket 58Hand a retainer ba 64; the latter being `adjustafbly secured to supports Y6 Thus, sheave 18 resiliently -urges the strand -into contac with the pins and resiliently restricts the movement o the strand in the direction of the impacts applied by the pins. Spring pressure determines the amount of restriction and is regulatable by adjusting the position of the retainer bar `64. Lateral displacement of the strand by the impacts is prevented by the projecting edges of discs 52. Conventional means (not shown), for controlling -the speed of the motor S` are provided so that the impact rate may be regulated. Direction of rotation of motor 50 is selected to drive discs 52 in the direction of strand travel to aid strand movement through the coating bath and thus minimize tension build-up. Thus, the described arrangement is particularly suited to the purposes of the present invention.

The following specific examples serve to illustrate the practices and results of the invention.

Example A Cold drawn, high-carbon steel wire, size 0.103, grade SAE C-1085 having a tensile strength in excess of 200,000 p.s.i., was hot-dip coated with aluminum containing 3% silicon at a speed of 130 fpm. to provide a defect free coating without affecting the tensile proper-ties of the steel by the -following sequence of treatment:

The wire was continuously fed from a pay-off reel 4 and passed successively through molten sodium hydroxide, maintained at between 800 and 950 F. in tank 6, Water rinse 8, a cold dilute muriatic acid bath y and a cold water rinse 12 to remove the drawing lubricant and any foreign material from the surface thereof. The cleaned wire was dried by passing it through hot water tank 14 and hot-air drier 16'. Hold-down sheave 18 was adjusted to provide a medium level of resilient restriction and the vibrator V, which consisted of ten 10) Vs" diameter pins 54, equally spaced about a 5%" diameter circle on discs 52, was rotated to impart 360 impacts per second to the wire. These particular conditions induced vibrations in the wire having frequencies continuously distributed over the frequency range 80 to 10,000 c.p.s. at an overall acceleration of 1200 g. The wire was introduced into the coating pot through tube 22 in which a small flow of natural gas was maintained through inlet 24, the gas being allowed to burn at the upper end of the tube. The bath was maintained at about 1200 F. and the length of wire immersion therein was about 4 feet, thus, provided an immersion time, at 130 f.p.rn., of 1.85 seconds. After passing around sinker 2.6 the wire left the bath through gas wipe 30 wherein a small flow of natural gas was maintained through inlet 32 and allowed to burn around the strand at the opening 31. With the strand moving at speed (130 fpm.) the position of wipe 30 was adjusted to bring bar Z8 into a uniform and positive contact with the Wire at a point about 11/2 inches above the baths surface with a pressure just short of -tha-t which will cause -a dry-streak or other damage in the coating. The wire was -allowed to cool naturally to the solidication temperature of the coating in its upward passage to sheave 34. Temperature of the Wire was further reduced by passing through Warm water in tank 36', a film of oil `applied in tank 3S and the coated wire recoiled by take- -up reel 40. A clear, bright aluminum coating amounting to 0.36 oz. per square foot of wire surface was 0btained. The coating was completely free of black-spots and could be formed into the standard wire Ibut-ton test without cracking or peeling. The alloy layer formed was uniform and slightly less than normal. Tensile tests of the wire showed substantially no change in the physical properties of the base metal.

Example B Materials and conditions were the same as in Example A except that the use of the hot water rinse 14, the drier 16 and the bath entry tube ZZ was eliminated. insofar as product was concerned, results were the same as in A but, a large amount of top dross was produced at the entry end of the coating pot. While the dross did not interfere with coating, it represents a substantial loss of coating metal.

Example C Cold drawn wire, size 0.103, grade SAE C-1060 was coated using the same sequence as Example B except that acid cleaning 10 Was also eliminated, the vibrator was operated to impart 450 impacts per second and the speed of the line reduced to f.p.m. At this speed a coating of 0.295 oz. per square foot was produced. Overall acceleration of motion in the wire was 1000 g, immersion time in bath was 2.4 seconds. Coating was bright and completely free of black-spots, although the wire entering the coating pot carried a visible brown film.

Example D The wire of Example C was coated using an impact rate of 175 impacts per second at a speed of 136 f.p.m. The overall acceleration of the vibratory motion imparted was about 400 g and immersion time in the bath was about 1.75 seconds. Again, clear, bright, black-spot free coatings of unsually high adherence were achieved.

Example E Low carbon steel wire, size 0.0625, was coated using the sequences utilized in Example A. In this instance a vibrator consisting of sixteen (16) diameter pins equally spaced about a 5% diameter circle on discs 52 was rotated to impart about 600 impacts per second and the line operated at f.p.m. Hold-down sheave 18 was adjusted to provide light pressure and three levels of overall acceleration (25, 60 and 100 g) in the motion induced in the Wire. Time in the coating bath was 2.0 seconds. In all instances bright, clear, black-spot free coatings were produced.

Example F Low carbon steel wire, size 0.135 inch was coated using the sequence outlined in Example A at 75 f.p.m. using a vibrator consisting of twelve (12) 1%" diameter -pins equally spaced about a 5% circle on discs 52. Hold-down sheave 18 was adjusted to apply a medium restrictive pressure. The vibrator was rotated to apply impact rates varied 200 to 800 per second, inducing random trransient motion in the wire at levels varying from 2000 to 2750 g. Immersion time was 3.2 seconds. Exceptional coatings were obtained over the entire range.

-In general wires as small as 0.04" in diameter and as large as 0.238" have been coated successfully and all advantages of the present method achieved. Aluminum coatings amounting to 0.50 oz. per square foot have been applied to 0.080 size wire at 200 fpm.; also to 0.148 size wire at and 220 f.p.m. In the case of large diameter wire, it has proven advantageous to use a rotating sinker and remove the wire from the bath at an angle rather than in a vertical pass; this reduces dragging at the sinker and aids in avoiding deleterious standing waves in the exit pass.

Speeds up to 250 f.p.m. (about six times the maximum speed possible heretofore), have been used. Operations at high speed permit reduction of the immersion time to less than 1 second. The latter, coupled with the fact that vibrating in the manner described greatly increases the rate of heat transfer, affords a degree of control of alloy formation not heretofore available. This may be illustrated by the fact that the coated wire of Example A can be produced substantially free of alloy layer by quenching the coated strand as it emerges through the gas wire by passing it through the cooling device 35 wherein it is sprayed with steam, atomized water or s1mply with a blast of cold air. This result is obtained even with a bath of substantially pure aluminum maintamed at a temperature of about 1235 F. By regulating the position of cooler 35 in relation to the speed of travel of the strand, the optimum amount of alloy layer consistent with good adhesion, brightness of coating and other desired characteristics can be produced.

As used in the foregoing description, the term strand includes single Vcontinuous lengths of metallic strip "or wire as well as a plurality Vof lengths twisted or otherwise grouped together.

This application is a continuation-in-part of my copending application Serial No. 743,616, led June 23, 1958, now abandoned.

While the foregoing examples have illustrated application of my invention to the aluminum coating of steel, it is not limited thereto but can be applied with advantage in the continuous hot-dip galvanizing and tinning of steel and other basis metals.

I claim:

1. A method of producing cold drawn aluminum coated steel wire having a high tensile strength characterized by freedom from black spots from cleaned, cold drawn wire comprising continuously advancing the cleaned wire in a substantially untensioned condition through a fluxyfree bath consisting essentially of molten aluminum at -a speed in excess of 40 fee-t perminute and with an immersion time of not more than about 3 seconds, applying at least 40 shock type impulses per second to the wire adjacent the entry portion of the bath while restricting movement of the wire in the direction of application of the shock type impulses adjacent the point of application thereof to produce transient random vibrations in the strand characterized by the presence of innumerable frequencies in excess of about 80 c.p.s. and an overall acceleration value in excess of 20 g whereby the surface o-f the lwire is continuously wetted to form an uninterrupted molten sleeve `of coating metal thereon, said vibrations having sufcient intensity to dislodge the coating metal from the wire as it emerges from the bath if not dampened, the shock type impulses being applied to the wire in the direction of travel thereof to maintain the wire in said substantially untensioned condition, positively dampening the vibration of said substantially untensioned coated wire before it contacts the air to prevent the molten coating metal being dislodged therefrom, withdrawing said wire from the bath in an upward directionand quickly quenching the molten coating metal to minimize the alloy layer formation before changing the direction of movement of the coated wire.

2. A method of producing cold drawn aluminum coated steel wire having a tensile strength in excess of 200,000 p.s.i. characterized by freedom from black spots comprising cleaning the cold drawn wire to remove the cold drawing lubricants therefrom, continuously advancing the cleaned wire in a substantially untensioned condition 4through a flux-free bath consisting essentially of molten aluminum with an immersion time of not more than about 3 seconds, applying at least 40 shock type impulses per second to the wire adjacent the entry portion of the bath while resiliently restricting movement of Ithe strand in the direction of application of the shock type impulses adjacent the point of application thereof to produce transient random vibrations in the strand characterized by the presence of innumerable frequencies in the range of about 80 to 10,000 c.p.s. and an overall acceleration value in the range of 100 to 1000 g whereby the surface of the wire is continuously wetted to form an uninterrupted molten sleeve of coating metal thereon, said vibrations having sufficient intens-ity to dislodge the coating metal from the wire as it emerges from the bath if not dampened, withdrawing said substantially untensioned wire from the bath in a vertical direction through a nonoxidizing atmosphere, positively dampening the vibration of said wire suiciently as it leaves the ba-th and While in said nonoxidizing atmosphere to prevent the molten coating metal being dislodged therefrom and continuing the vertical travel of the wire for a sufficient d-istance to permit the molten metal to freeze with a smooth surface before changing the direction of movement of the coated wire.

3,. A method of producing aluminum coated steelwire having good physical properties Vcharacterized by freedom from black spots from cleaned, cold drawn steel wire comprising continuously advancing the cleaned Wire in a substantiallyuntensioned condition through a substantially molten aluminum flux-free coating bath at a speedin excess ofA 40 feetperrninute and with an im- 'mersion time of not'more thanabout 8 seconds, applying at least 40 shock type impulses per second to the wire adjacent the entry portion of the bath while restricting movement of the wire in the direction of application of the shock .type impulses adjacent the point of application thereof to produce transient random vibrations in the strand characterized by the presence of innumerable frequencies in excess of about c.p.s. and an overall acceleration value in excess of 20 g whereby the surface of the wire is continuously wetted to form an uninterrupted mol-ten sleeve of coating metal thereon, said vibrations having sufficient intensity to dislodge the coating metal from the wire as it emerges from the bath if not dampcned, positively dampening the vibrations .of said substantially untensioned coated wire before it contacts the air to prevent the mol-ten coating metal from being dislodged therefrom, withdrawing said wire from the bath in an upward direction and continuing the upward travel of the wire for suicient distance to permit .the coating metal to freeze with a smooth surface before changing the direction of movement of the coated wire.

4. Apparatus for continuously hot-dip coating strand comprising means for continuously advancing strand through a bath of molten coating metal, vibrating means at the entry end of the bath for imparting at least 40 shock type impulses per second to the strand and produce random, transient vibrations in the strand traveling lthrough the molten coating metal characterized by the presence of innumerable frequencies in excess of about 80 c.p.s. and an overall acceleration value in excess of 20 g, positive vibration dissipating means at the exit end of the bath adapted to contact said strand prior to its discharge into the air, and means adjacent the vibrating means for resiliently restricting movement of the strand in the direction of application of the shock type impulses.

5. Apparatus for continuously hot-dip coating strand comprising means for continuously advancing strand through a bath of molten coating metal, rotary vibrating means at the entry end of the bath for imparting at least 40 shock type impulses per second to the strand and produce random -transient vibrations in the strand traveling through the molten coating metal characterized by the presence of innumerable frequencies in excess oi abou-t 80 c.p.s. and an overall acceleration value in excess of 20 g, positive vibration dissipating means at the exit end of the bath adapted to contact said strand prior to its discharge into the air, adjustable means for urging the strand into contact with the vibrating meansi and variable speed driving means for the vibrating means, said driving means being adapted to rotate the vibrating means so that the impact is applied in the direc-tion ol movement of the strand.

6. Apparatus -for continuously hot-dip coating strane' comprising means for continuously advancing strand through a bath of molten coating metal in a substantially untensioned condition, rotary vibrating means a the entry end of the bath for imparting at least 40 shocl type impulses per second to the strand and produce random transient vibrations in the strand traveling througl the molten coating metal characterized by the presence of innumerable frequencies in excess of about 80 c.p.s and an overall acceleration value in excess of 20 g, posi tive vibration dissipating means at the exit end of the bath adapted to contact said strand prior to its discharg into the air, and driving means. for the rotary vibrating means, lsaid driving means being adapted to rotate the rotary vibrating means so that the impact is applied in 2,731,362 Brondyke Jan. 17, 1956 the direction of movement of the strand. 2,895,845 `Jones et al July 21, 1959 2,900,273 Linden Aug. 18, 1959 References Cited in the le of this patent 2,906,018 Baker Sept. 29, 1959 UNITED STATES PATENTS 5 1,770,910 Byrd July 22, 1930 1,933,401 Ward Oct. 31, 1933

Claims

1. A METHOD OF PRODUCING COLD DRAWN ALUMINIUM COATED STEEL WIRE HAVING A HIGH TENSILE STRENGTH CHARACTERIZED BY FREEDOM FROM BLACK SPOTS FROM CLEANED, COLD DRAWN WIRE COMPRISING CONTINUOUSLY ADVANCING THE CLEANED WIRE IN A SUBSTANTIALLY UNTENSIONED CONDITION THROUGH A FLUXFREE BATH CONSISTING ESSENTIALLY OF MOLTEN ALUMINUM AT A SPEED IN EXCESS OF 40 FEET PER MINUTE AND WITH AN IMMERSION TIME OF NOT MORE THAN ABOUT 3 SECONDS, APPLYING AT LEAST 40 SHOCK TYPE IMPULSES PER SECOND TO THE WIRE ADJACENT THE ENTRY PORTION OF THE BATH WHILE RESTRICTING MOVEMENT OF THE WIRE IN THE DIRECTION OF APPLICATION OF THE SHOCK TYPE IMPULSES ADJACENT THE POINT OF APPLICATION THEREOF TO PRODUCE TRANSIENT RANDOM VIBRATIONS IN THE STRAND CHARACTERIZED BY THE PRESENCE OF INUMERABLE FREQUENCIES IN EXCESS OF ABOUT 80 C.P.S. AND AN OVERALL ACCELERATION VALUE IN EXCESS OF 20 G WHEREBY THE SURFACE OF THE WIRE IS CONTINUOUSLY WETTED TO FORM AN UNINTERRUPTED MOLTEN SLEEVE OF COATING METAL THEREON, SAID VIBRATIONS HAVING SUFFICIENT INTENSITY TO DISLODGE THE COATING METAL FROM THE WIRE AS IT EMERGES FROM THE BATH IF NOT DAMPENED, THE SHOCK TYPE IMPULSES BEING APPLIED TO THE WIRE IN THE DIRECTION OF TRAVEL THEREOF TO MAINTAIN THE WIRE IN SAID SUBSTANTIALLY UNTENSIONED CONDITION, POSITIVELY DAMPENING THE VIBRATION OF SAID SUBSTANTIALLY UNTENSIONED COATED WIRE BEFORE IT CONTACTS THE AIR TO PREVENT THE MOLTEN COATING METAL BEING DISLODGED THEREFROM, WITHDRAWING SAID WIRE FROM THE BATH IN AN UPWARD DIRECTION AND QUICKLY QUENCHING THE MOLTEN COATING METAL TO MINIMIZE THE ALLOY LAYER FORMATION BEFORE CHANGING THE DIRECTION OF MOVEMENT OF THE COATED WIRE.