US2900273A - Method and means for continuously pretreating and coating vibrating metal objects - Google Patents

Description

Aug. 18, 1959 H. E. LINDEN 2,900,273 METHOD AND MEANS FOR CONTINUOUSLY PRE-TREATING AND COATING VIBRATING METAL OBJECTS Filed Sept. 26, 1955 2 Sheets-She et 1 IN V EN TOR. Hike/5R r t". Z lf/DE/V AI'wK/VEYS,

Aug. 18, 1959 H. E. LINDEN 2,900,273

METHOD AND MEANS FOR CONTINUOUSLY PRE-TREATING AND COATING vIBRATING METAL OBJECTS Filed Sept. 26, 1955 2 Sheets-Sheet 2 RELEASE OF BASE METAL FROM TAKE OFFSPIOOL vi BRATION OF BASE METAL HEATWG CLEANING OF BASE METAL COATING 0F BASE METAL To OTHER PROCESS sna s, coouue, ETC.

p 0F INVENTOR. FINISHED COATED aeer'. Z/A/DEA/ dtzan ya METHOD AND MEANS FOR CONTINUOUSLY PRE- TREATINGAND COATING VIBRATING NIETAL OBJECTS Herbert E. Linden, Los Angeles, Calif., assignor t American Mollerizing Corporation, Beverly Hills, Calif., a corporation of Nevada -"'Application September-26, 1955, SerialNo. 536,445

is Claims. (c1; 117-51 IThis invention relates to a method andme'a'ns of coating articles, s'tn'psfwires and the like, and.particular1y'has reference to the coating of metal objectswith a molten metal such as aluminum. 7

In the past, one of the chief problems in coating processes utilizing such metals as aluminum for the coating material has beenin obtaining a coating layer of uniform thickness on the object tofbe coated. Furthermore, ina continuous process for coating objects, the'p'roblem of obtaining a uniform and controlled thickness of coating material becomes increasingly important since, as greater quantities of material are being coated any given time, much. greater wastage of coatingmaterial and object can occur. I

Another problem in' coating with aluminum is the fact that molten aluminum oxidizes readily, thus forming an oxide film on the exposed surface of'the aluminum layer. In the past, various methods of breaking up this oxide film have been utilized, such as by agitating the surface of the aluminum bath at a point where the material emerges from the molten aluminum, or by directing a blast of air on the surface ofthe molten aluminum. However, metal strips, wires, and the like, at coating temperatures, are very ductile, and any substantial agitation produced thereon will easily deform or tend to elongate the hot strip. a

Another major problem in coating with materials such as aluminum is to obtain ahigh degree of adherence be tween the coating metal'and the object being coated.

These problems have been solved in largemeasure by the process disclosed in the Moller Patent No. 2,315,725 and the application of Moller entitled Method and Means for Cleaning and Coating Metal Objects, Serial No. 252,267, filed October 20,1951, 'now abandoned. The present invention is particularly adapted for and useful in combination with the above mentioned Moller processes to further improve the quality and speed of coating, particularly where continuous process means are utilized.

Bearing in mind the foregoing considerations, it is a major object of the present invention to provide a method and means whereby a continuous material to be coated is subjected to I a vibratory motion thereby obtaining a coating of finer grain size and greater uniformity'withoutdeforming or elongating the material to be coated.

It is another'object ofthis' invention to provide a method and means whereby a'continuous material to be coated with aluminum, aluminumalloys or other coating metal may be drawn through boththepre-treatment and coating phases of the coating process more rapidly than has been achieved in the past.

It is still another object of this invention to provide a method and meauswhereby a continuous process for coating material is utilized wherein said material is-precleaned in an improved manner byvibrato'ry means.

The foregoing and-additional objects and advantages of the invention will-be apparent from the following Un d W3 Per 2 description of one embodiment'thereof, andfrom the attached drawing, wherein:

Figure l is a partially sectioned elevational view showing one form of coating apparatus having means for continuously coating a moving strip of material'in accordance with the present invention;

Figure 2 is a plan view thereof; and I V Figure 3 is an enlarged view taken along the line 3 in Figure 1.

In general, the present invention relates to a method and means for coating a continuously moving material with a molten metal, such as aluminum, or an aluminum alloy. I v

The material to be coated has imparted to ita' vibratory motion just prior to its entry'into the pre-treating phase of the process, and, after passing through the pretreatment phase, enters the coating phase of the process where it is coated with coating material and then withdrawn. v

The pre-treating phase of the process consists of passing the material through a molten salt bath. The coating phase of the process consistsv of passing the" pretreated material through the molten coating metal. For this purpose, a salt bath' furnace is divided into two sections by a bafile plate which terminates above the floor of the furnace, so that two lower salt-connected sections are formed. A layer of molten metal is floated upon the salt bath in one section of the furnace. Material is passed into the purely saltbath section of the furnace, up into the molten coating metal section, and out of the salt bath furnace. A periodic vibratory motion is imparted to the continuous material by suitable means as it is passed into the salt bath, or pro-treating section, of the salt bath furnace.

For a greater understanding of the invention, reference should now be had to the following description and to the accompanying drawings.

The word strip or strip of materia "as-used in the specification and claims, includes only continuous material whether it be wire, sheet, tube, or thin ribbons of metal, which are ordinarily designated as strip in the art. The word strip is thus to be treated as the full equivalent of the words continuous material.

Referring first particularly to' Figures 1 and 2, the numeral 10 designates a rectangular crucible of a-salt bath furnace having a floor 13, elongated side walls- 14 and 15, and end walls 16 and 25. The crucible is split into two sections 18 and- 19 by a bafiie plate 12 which is affixed to side walls 14 and 15-andis parallel 'to end walls 16 and 25 of the crucible. The upper edgeof the baflie plate extends to the top edge of the side walls- 14 and 15; the lower edge terminates above the floor 13 of the crucible.

A molten salt bath 11, of greater density than aluminum, comprising for instance, such salts as cryolite, barium chloride, and sodium chloride is contained in the lower portion of crucible 10, and extends above the lower end-of the bafiieplate-IZ to form two lower saltconnected sections. The upper end of 'thebaifle plate extends preferably about siX-inches-abovethesurfaceof the salt bath and acts as one of the retaining'walls for a layer of coating metal 17, such as'aluminum, which lies on the surface of the salt bath in the-left hand section 18 of the crucible 10. The coating metal is' made molten by the heat conducted through the fused 'salt bath 11 and can be relatively thin, or for'example approximately onehalf inch in thickness. Section'18 of the crucible in which the molten'aluminum is placed can be designated as the coating section and the right-hand section 19 of the crucible the primary'pre-treatment section. The fluorides of the moltensalt llkeep-the coating metal 17 free from oxides by forming a thin protective layer on the exposed surface of the coating metal.

A cylindrical guide roller 20 is rotatably mounted on .a crossbar21 supported by two side frames 22 mounted to the floor 13 in the coating section 18 of crucible by means of locknuts or studs 22a. Guide roller 20 may be designated as the submerged guide roller for the sake of clarity. A second guide roller 23 is positioned above the crucible 10 and preferably approximately above submerged guide roller 20. Guide roller 23 may be rotatably mounted to any stable fixture (not shown) in a manner similar to that of submerged guide roller 20. Another guide roller 24 is positioned above the crucible 10 at approximately the same height as guide roller 23 adjacent end wall 25. Guide roller 24 may be rotatably mounted to any stable fixture (not shown) in a manner similar to that of submerged guide roller 20, and may be designated as the pretreatment guide roller for the sake of clarity.

A cylindrical spool 26 is positioned to the right of,

' and preferably at the same height as, the pre-treatment guide roller 24. A second spool 27 is positioned to the left of, and preferably at the same height as, guide roller 23. Spools 26 and 27, guide rollers 20, 23 and 24 all lie in a plane approximately parallel to side wall 14.

Referring now primarily to Figures 2 and 3, suitable driving means, such as an electric motor 28 connected to a current source, is stably mounted on or near the upper edge of end wall 25 of crucible 10 by conventional clamping means 28a. The shaft of electric motor 28 extends horizontally in a direction substantially parallel to side wall of the crucible. An octagonal plate cam 30 is centrally located on shaft 29 and tightly fitted thereto at a 90 angle.

A longitudinal follower arm 31 contacts the edge 32 of plate cam 30 through a follower disc 33 which is rotatably mounted at one end of the follower arm. The follower arm lies in the plane of the plate cam and is pivotally mounted, a short distance from the follower disc, to the electric motor 28 by means of a fulcrum crossbar 34 and .side frame assembly shown generally at 35. A stud 36 protrudes from the side frame assembly 35 at a point directly beneath the follower arm 31 and on the side of the frame assembly closest to the follower disc 33. One end of an open helical spring 37 is attached to stud 36 and the other end is attached to the follower arm 31 and forms a 90 angle with said follower arm. 7

The pre-treatment guide roller 24, the free end of the follower arm, designated as the rocking end 38, and the submerged guide roller lie generally in a plane approximately parallel to the side wall 15 of crucible 10. Also, the guide rollers 20 and 24, and the follower arm 31 are elevated relative to each other in a manner such that a continuous strip or wire 39, guided by said guide rollers, contacts the rocking end 38 of the follower arm when the follower arm is in the horizontal position shown in Figure 3. If desired, the wire 39 may be constructed in the form of an endless chain (not shown) having intermittent carriers or hooks thereon, whereby individual articles may be carried continuously down through the pre-treating section 19 and upwardly through the coating section 18. Also, if desired, a strip or any other shape of continuous material may be utilized in place of wire 39.

In operation, the wire 39 to be coated is fed from the supply spool 26 over pre-treatment guide roller 24, then downwardly in contacting relation with rocking end 38 of follower arm 31 and into salt bath 11, thence under submerged guide roller 20, and upwardly through the salt bath and into the molten metal 17. After the wire emerges from the molten metal .17, it is wound onto a take-up spool 27 via second guide roller 23.

Therotation of shaft 29 of electric motor 28 imparts a. rotating motion to the octagonal plate cam 30. As

. 4 the plate cam 30 rotates the follower disc 33 receives a vibrating up-down motion which, in turn, is imparted to the rocking end 38 of the follower arm 31. The magnitude of the vibratory motion of the rocking end 38 may be controlled by means of spring 37.

Rocking end 38 periodically drops on the continuously moving wire 39, thus imparting a vibrating motion to the wire. Higher frequency vibrating motion may be imparted to the wire by means of conventional electromagnetic devices, thus eliminating the need for such mechanical devices as herein described. Ultrasonic frequencies may also be imparted to the wire by means of magnetostrictive devices. While the period of vibratory motion imparted 'to the wire may be varied Within large limits, frequencies as low as cycles per minute have been used with a great improvement in coating uniformity. It should be understood that the means of producing vibratory motion in the wire 39 need not be restricted to a use of direct mechanical force upon the wire itself but includes mechanical and electromagnetic forces acting upon the salt bath, which cause a periodic movement or turbulence of said salt bath, to be transmitted to said wire.

The intensity with which the wire 39 is hit by the rocking end 38 is also a factor in obtaining improved coating and may be varied within large limits. A stroke of the rocking end 38 of as low a magnitude as a few inches, has been used with consequent improvement in the quality of the coating. When coating a continuous wire, a stroke of 3 to 4 inches is preferable.

It should be noted that imparting a vibratory motion to the wire 39 after it has been coated would not be feasible. In order for a true aluminum-metal alloy to form during the coating phase of the process, the temperature of the wire must be raised to at least the melting point of the coating metal. In the case of pure aluminum, the wire temperature would necessarily be about 1218 F., and in the case of base aluminum alloys, about 1000-1200 F. At these temperatures, the wire is easily deformed and stretched. Thus, if a vibratory motion were imparted to the strip or wire 39 in this highly ductile state, deformation and elongation of the wire would result. For this reason the wire is struck while it is still cold, thereby minimizing deformation and elongation, while retaining the advantages herein set forth.

The vibrating motion of the wire is considerably damped upon being passed through the molten salt bath 11 and consequently, upon emergence from the coating metal 17, the vibratory motion is almost imperceptible being of the order of 10- -40 inches.

Without meaning to be bound by any particular theory for the improvements described herein, the following explanation is advanced.

The molten salt bath, being between 1400-1600 F., lies above the critical temperature of the predominantly iron article introduced therein. The vibration of the wire in the critical temperature range may produce a molecular re-arrangement making it more susceptible to an adherence with a coating metal such as aluminum.

The vibratory motion described may produce an improvement in the pre-treating phase of the coating process by causing removal of some salt adhering to the wire. This, in effect, produces a cleaner surface for coating. By the time the wire has reached the molten metal, its vibratory motion is greatly damped, and any slight vibratory motion remaining is probably sufficient to produce a finer grained and more uniform thickness of coating metal, without at the same time, causing any possible deforma tion or elongation of the material. Since coating processes, in general, must err on the side of overabundance, any improvement in uniformity of the coating layer leads to a more rapid continuous process.

schematically, the process steps are shown in Figure 4. Boxes 50, 52, 54, 56, 58 and 60 denote respectively the steps of take-oft of base metal from spool 26, vibration of the base metal, heating and cleaning of the base metal, coating of the base metal, cooling etc., and wind-up of the finished aluminum-coated metal.

While the forms of the device and the processes shown and described herein are fully capable of achieving the objects and providing the advantages hereinbefore stated, it will be realized that they are capable of some modification without departure from the spirit of the invention. For this reason, I do not mean to be limited to the forms shown and described, but rather to the scope of the appended claims.

I claim: I

1. A method of coating a continuously moving material with a molten coating metal which includes the steps of: passing said material into a molten salt bath; vibrating said material while in said salt bath, the vibratory motion imparted to said material being substantially dampened by said salt bath prior to the eXit of said material from said salt bath; and thereafter passing said material from said salt bath directly into said molten metal.

2. A method of coating a continuous metal strip with a second molten metal which includes the steps of: floating a molten coating metal on a portion of the surface of a molten salt bath, said salt bath having a higher specific gravity than said molten metal; passing said strip into the uncovered portion of the surface of said salt bath; imparting vibratory motion to said strip, as it enters said molten salt bath; and passing said strip from said salt bath directly into said molten metal bath.

3. The method of claim 2 characterized in that the vibratory motion of said strip is essentially completely damped during the course of its passage through said molten coating metal.

4. A method of coating a continuous metal strip with a second molten metal which includes the steps of: floating said molten coating metal on a portion of the sur- 7 face of a molten salt bath, said salt bath having a higher specific gravity than said molten metal; passing said strip into the uncovered portion of the surface of said salt bath; periodically striking said stn'p prior to its entry into said molten salt bath, thereby imparting vibratory motion to said strip; and passing said strip from said salt bath directly into said molten metal bath.

5. The method of claim 4 characterized in that the frequency and intensity with which said strip is struck prior to its entry into said molten salt bath is such that the vibratory motion of said strip is barely perceptible at the surface of said molten metal bath.

6. A method of coating a continuous ferrous metal strip with a molten metal selected from the group consisting of aluminum and aluminum alloys which includes the steps of: floating said molten metal on a portion of the surface of a fluoride containing salt bath, said salt bath having a temperature above the critical temperature of said strip and having a higher specific gravity than said molten metal; said salt bath preventing said molten metal from being oxidized by forming a protective fluoride layer on the surface of the molten metal; passing said strip into the uncovered portion of the surface of said molten salt bath; periodically striking said moving strip at least 120 times per minute prior to its entry into said molten salt bath thereby imparting vibratory motion to said strip, the vibratory motion of said stripbeing barely perceptible at the surface of said molten metal; and passing said strip from said salt bath directly into said molten metal- 7. A method of preparing a continuously moving metal strip for coating with a molten metal which includes the steps of: preparing a molten bath of salts; and vibrating said strip prior to its entry into said molten salt, thereby imparting vibratory motion to said strip while said strip is in contact with said molten salt.

8. The method of claim 7 characterized in that the temperature of said salt bath is above the critical temperature of said strip.

9. A method of coating material with a molten coating metal which includes the steps of: passing said material into a molten salt bath, vibrating said material while in said salt bath the vibratory motion imparted to said material being substantially dampened by the salt bath prior to exit of said material from said salt bath; and thereafter passing said material from said salt bath directly into said molten metal.

10. An apparatus for pre-treating with a molten salt and coating with a molten metal a continuously moving strip which comprises a furnace containing a crucible; a downwardly projecting baflie plate dividing said crucible into a pre-treating section to contain molten salt and a coating section to contain molten metal, said baflie being positioned with its lower edge in spaced relationship from the floor of said crucible whereby said crucible is adapted to contain a unitary lower body of one of said molten materials in both sections and an immiscible upper body of the other of said molten materials floating upon the lower molten material and confined to a single section; means for passing the continuously moving strip to be treated through said pre-treating section, thence underneath said baffle and through said coating section; and means acting on said strip prior to its entry into the coating section for continuously imparting vibration to said strip for at least a portion of its travel through said pretreating section, whereby the vibration of the strip is substantially dampened by the molten salt bath prior to its entry into the molten coating bath.

11. The apparatus of claim 10 wherein said vibratory means comprises an arm mechanically adapted periodically to strike said strip as said strip moves adjacent said arm.

12. The apparatus of claim 10 wherein said means for imparting vibration comprises a motor stably mounted adjacent said pretreating section, a polygonal cam centrally located on the driving shaft of said motor; a longitudinal follower arm-disc assembly, said disc being rotatably attached to one end of the longitudinal follower arm and adapted to' contact the edge of said cam, said follower arm being pivotally mounted at a point along its length, and having its other end positioned to strike said moving strip when a downward motion is given to said end of said follower arm; and a spring having one end aflixed to said follower arm to restrict the vibratory motion of said ends of said follower arm when said arm is in motion.

13. An apparatus for pro-treating and coating a continuously moving strip which comprises a crucible; a

baffle plate dividing said crucible into a pre-treating sec- 7 tion and a coating section, said baffle being spaced from the floor of said crucible; a molten salt bath in both the pretreating and coating sections of said crucible; a molten coating material floating on the molten salt and confined to the coating section by said baflie; means for passing said strip through said pre-treating section, thence underneath said baffle and through said coating section; and means acting on said strip prior to its entry into the coating section for imparting vibration to said strip for at least a portion of its travel through said salt bath; said salt bath acting as substantially the sole dampenmg means.

References Cited in the file of this patent UNITED STATES PATENTS 2,315,725 Moller Apr. 6, 1943 2,686,135 Butler Aug. 10, 1954 2,790,736 McLaughlin Apr. 30, 1957

Claims (1)

1. A METHOD OF COATING A CONTINUOUSLY MOVING MATERIAL WITH A MOLTEN COATING METAL WHICH INCLUDES THE STEPS OF: PASSING SAID MATERIAL INTO A MOLTEN SALT BATH; VIBRATING SAID MATERIAL WHILE IN SAID SALT BATH, THE VIBRATORY MOTION IMPARTED TO SAID MATERIAL BEING SUBSTANTIALLY

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