CA1050216A - Non-ferrous fasteners having ferrous metal core - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method of providing a member having a ferrous metal core with a nonferrous coating wherein the ferrous metal core affords strength and rigidity while the nonferrous outer coating provides a non-corrosive surface and wherein the coating is of such uniform thickness that final forming of the member may be perforated without penetrating or breaking the coating or exposing the core. The coating is applied by extruding the non-ferrous material in a die pocket and passing the ferrous metal core through the plastic nonferrous metal in the pocket with only the high extrusion pressure creating the heat to render the nonferrous metal plastic.

Description

2~L6 M HOD OF PRODUCING ~ NON-FERROUS COATING
ON A FERROUS METAL CORE
B _ GROUND OF THE INVENTION
It is quite common in the field where various types of fasteners are utilized in the assembly of materials that environmental conditions frequently result in rust or corrosion occurring on the fasteners or between the fasteners and the assembled materials. Many times this may be due in large part to the electrical current that occurs between different materials and especially where the work pieces held together by the fasteners may all be of different materials having different electrical potentials. The rate of decom-position and/or corrosion of the work pieces and the fasteners may also be affected by the nature of the connection of the fasteners and work pieces as a result of the stress level imposed on the connections which may increase the degree of corrosion. External forces applied to the work pieces or an improper or interference fit of the fasteners in the work pieces may also affect corrosion factor. ~
Heretofore, electroplated metals utilizing cadmium or zinc or any of various organic coatings have been utilized to inhibit corrosion and electrolytic action. However, thin coatings of these materials were relied upon and such coatings were easily ruptured and thus exposed the core metals to the environment. In such circumstances aluminum or plastic coatings would have been more satisfactory since these ma-terials would not readily permit corrosion to occur between the fasteners and work pieces While such materials may have been superior in many respects to cadmium, zinc and other electroplated materials they did not lend themselves readily to electrodede osi~ionon the fasteners. Further and more .~

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importantly, the degree of corrosion protection afforded by any coating on a fastener of any kind is directly proportional to the thickness of the applied coating and since electrodeposition of coating metal is typically limited to thin coatings fast-eners clad in this manner have been lacking in effective coating thickness and totally inadequate from the standpoint of corrosion resistance. In fact, such coatings were quickly destroyed and allowed corrosive reactions to develop between the fasteners and the work pieces.
Other problems incurred by electroplating coatings on fasteners include embrittlement of the coating as thus applied. Hot dipping of fasteners with zinc or aluminum may provide a coating of adequate thickness but coatings applied in this manner are frequently lacking in the uniform thickness of the coating necessary to provide the degree of corrosion protection for fasteners thus coated as normally required in the usual operating environment.
Mechanical coating by peen plating has been used to some extent but this type of coating process is restricted to the use of cadmium or zinc and for all practical purposes this prohibits use of this type of process for coating fast-eners for the purpose of inhibiting corrosion. Such peen plated parts often are sub~ect to excessive porosity to a prohibitive extent, if applied to fasteners and such that in-sufficient corrosion inhibiting protection is provided when fasteners coated by this process are utilized in their normal environment.
Fast~ners made entirely of aluminum, or other non-corrosive materials have been used in an effort to overcome the problem of excessive corrosion and to some extent this type ,,~ .

~V~6 of fastener may have been successful in meeting some of the problems. However, fastenings of this type have proved lacking in structural properties essential to the proper functioning of the usual fastening installation. These non-ferrous fasteners were fabricated from relatively soft ma-terial lacking the required strength and rigidity and when hardened became brittle to the point where even in the act of their installation they were subject to fracture.
SU~ARY OF THE INVENTION
This invention relates generally to a method of coating a member for use in metal work and more particularly to the provision of a method and apparatus for producing such member in the form of a corrosion resistant nonferrous wire having a ferrous metal core for strength and rigidity.
The nonferrous layer on the wire is of ample thickness to prevent rupture thereof in normal usage and such that forming operations may be performed thereon, as in the formation of a head portion and point on respective end portions of a wire section, or the forming of threads, as for a screw or a bolt, all without exposing the ferrous metal core to the atmosphere or to contact with other materials with which it may be joined, such as work pieces normally encountered in its usual en-vironment.
The invention contemplates a method and apparatus for producing the corrosion resistant nonferrous clad ferrous metal wire by a high pressure extrusion system wherein the heat generated by the extrusion process comprises the sole source of heat utilized in coating the ferrous metal core with the nonferrous corrosion preventing outer layer. This system utilizes a cross-head die in the high pressure extrusion process wherein the nonferrous metal being extruded, such as aluminum, is forced into the cross-head die under great pressure ' ,~
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2~6 which generates heat sufficiently to render the aluminum plas-tic. This comprises the only heat used with this system and while the aluminum is in the plastic state the ferrous metal core wire is passed through the nonferrous metal at its point of plasticity to be coated with the plastic metal and the coated wire emerges from the die through a passage of a size to control the thickness and uniformity o~ the non-corrosive outer layer surrounding the inner metal core.
The invention, in summary, is a method of forming a metal clad wire for the manufacture of fasteners by passing a ferrous metal wire through a plasticized portion of nonferrous metal, wherein said nonferrous metal is continuously extruded into a die under pressure to form said plasticized portion, said ferrous metal wire is passed through said di~ at sub-stantially a right angle to the passage of said nonferrous --metal and through the plasticized portion which forms around the said wire to provide a wrought aluminum structure enclosing the wire, the extrusion pressure comprising the sole source of heat generated to render the nonferrous metal plasticized 0 in said cer.tral cavity without application of lubricant.
OBJECTS OF THE INVENTION
It is the primary purpose of the invention to provide a metal clad wire wherein a ferrous metal core affords strength and rigidity and a nonferrous coating prevents corrosion.
The principal object of the invention is the pro-duction of a nonferrous metal clad ferrous metal wire formed by passing the ferrous metal wire through the nonferrous metal while the latter is in a plastic state.
An important object of the invention is to produce a corrosion resistant nonferrous metal coated ferrous metal wire by forcing the nonferrous metal into a die under great pressure whereby the nonferrous metal is rendered plastic and _ ik/ ;` `
' then passing the ferrous metal wire into the die and through the plastic portion of the nonferrous metal.
A further object of the invention is the production of a corroslon inhibiting wire by extruding a nonferrous metal under great pressure through one side of a cross-head die into a central cavity in a plastic state and passing a ferrous metal wire into another side of the die at substantially a right angle to the direction of entry of the nonferrous metal, through the plastic nonferrous metal and emerging at the other -4a- : -jk/~1 ~502~6 side of the die coated with the corrosion inhibiting coating.
Another object of the lnvention is to provide a corrosion inhibited coated wire by passing a ferrous metal wire entirely through a cross-head die into which a non-ferrous metal is extruded to provide a plastic portion in a central cavity through which the ferrous metal wire passes and wherein the entering opening in the die for the ferrous metal wire is of a diameter affording minimum clearance for the wire and the opening from the die for the coated wire is of a diameter to provide and control the desired thickness of the coating surrounding the wire core.
DESCRIPTION OF THE DRAWINGS
The foregoing and other and more specific objects of the invention are attained by the structure and arrangement illustrated in the accompanying drawings wherein:
Figure 1 is a general view of a cross-head die apparatus illustrating an opening in one side of the die for extruding a nonferrous metal into a central cavity in a plastic state and an opening through the die for entry of a ferrous metal wire at one side which passes through the plastic metal and emerges at the opposite side fully coated through an exit opening in the die;
Figure 2 is a longitudinal sectional view through a typically coated nail formed from corrosion inhibitng wire produced in accordance with the invention;
Figure 3 is a view similar to Figure ~, showing a ~-similarly coated nail where the surface of the coating is provided with deformations which afford greater holding power when the nail is driven;

2'~6 Fiaure 4 is a longitudinal sectional view of a bolt manufactured and formed in accordance with the invention;
Figure 5 is a sectional view similar to Figure 4, showing a typical screw manufactured and formed in accord--ance with the teachings of this invention, and Figure 6 is a sectional view through a staple formed from coated wire manufactured according to this in-vention.
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- 10 In the drawings, looking at Figure 1, a cross-head die 10 is illustrated having an opening 11 into which metal rod 12 is entered and extruded under great pressure into a central cavity 13 where the rod reaches a plastic state as indicated at 14. The rod 12 is formed from a nonferrouS
metal, such as aluminum and when it is forced into the cavity 13 during extrusion it is the high pressure of this operation that generates the heat resulting in the metal reaching a plastic state as it enters the cavity 13. An entering opening 15 is provided in a side of the die 10 and which leads into the central cavity 13. An exit opening 16 leads from the cavity 13 at the other side of the cavity and emerges through the opposite side of the die. The openings 15 and 16 are axially aligned and provide a continuous passage through the die yenerally at right angles to the opening 11 for the metal rod 12. By "fluid state" is meant that property of the nonferrous metal under increased temperature, as at 14, whereby the particles thereof have the ability to move easily and change their relative positions without departing from solid form, so that under pressure the heated metal, whether from pressure or by applied heat, is capable of plastic flow.

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~,o~Oz~6 A continuous length of a ferrous metal wire 17 is fed into the opening 15 and is forced through the plastic metal 14 in the cavity 13, which adheres to the wire and the wire 17 with this outer layer, or coating 18, is forced through the exit opening 16, which forces the coating layer into intimate engagement with the wire core to provide a strong bond. The entering opening 15 is dimensioned to the diameter of the wire 17, with a minimum clearance, whereby the wire is closely guided as it passes into the cavity 13 and through the plastic metal 14. The exit opening 16 is utilized to control the thickness and the uniformity of the coating 18 on the wire core and accordingly is dimensioned to the combined diameter of the wire core 17 and the surrounding outer layer 18. The diameter of the opening 16 is dimensioned to provide the desired predetermined thickness of non-corrosive metal to be deposited entirely around the wire core 17 and the resulting coated wire is extruded to an exact diameter in accordance with that desired for making fasteners of the type to be manufactured for a particular production run. The heat generated by extruding the nonferrous coating through the opening 16 maintains the state of the metal 14 for plastic flow so that themetal forms around the wire 17 and bonds with itself to envelop the wire and bonds effectively to the wire 17, as well, to form a wrought aluminum structure enclosing the ferrous metal core. The coated wire can be produced to any specified diameter with the wire core and outer coating layer in proper proportions so that subsequent drawing operations to provide coated wire of smaller diameter will produce wire having a desired ratio of ferrous metal core to nonferrous metal coating to provide the non-corrosive coating required.

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~050~6 The relative dimensions of the non-corrosive coating 18 with respect to the ferrous metal core 17 can be varied in accordance with the conditions to be met in the use to which the final product is to be put. If the size of the wire core 17 is relatively large in relation to the coating layer 18 the strength and rigidity of the fastener will be greater but the corrosion resistance will be reduced. On the contrary where the outer coating layer 18 is of relatively heavier thickness in relation to the diameter of the wire core 17 the corrosion resistance will be increased but the strength of the fastener will be reduced. The diameter of the wire core 17 can be varied of course, according to the predeter-mined strength of the fastener required for the intended appli-cation and of course, the corrosion resistance desired can be obtained to the degree necessary by varying the thickness of the outer coating layer 18. An optimum condition may be obtained where the corrosion resisting coating 18 is maintained at a mini-mum thickness in the range of .005" to .010" for fasteners where it is not necessary for the fastener to be threaded. If the fastener is intended to be threaded or if any other deformation of the fastener shank is to be resorted to then the outer coating layer 18 should be maintained at a thickness of about .020".
This inventive concept can be utilized in the manu-facture of corrosion resistant nails, screws, bolts, and staples, or the like and the relative proportions of the ferrous metal core 17 and the nonferrous outer coating la~er 18 will be varied accordinyly. The coated wire of this invention is dis-closed in Figures 2 and 3 as applied to two types nails in-corporating the anti-corrosive properties afforded by the use of the present coated wire core. In Figure 2 the nail 20 is shown as of the ordinary or usual type having a pointed driving end .~
_ ~ _ 21 and a head 22 for pounding the nail into its driven position.
Figure 3 illustrates a coated nail similar to that shown in Figure 2 but wherein the corrosion resistant coating 18 is provided with surface deformations 23 on the shank areas of the nail and on the point 21 and head 22 as well. These surface indentations provide greater holding properties for the nail when driven into the workpieces it is used to secure.
The final forming of the fasteners from this coated wire, as in the formation of thepoints 21 and the heads 22 on the nails 20 and 24 of Figures 2 and 3 respectively can be done in accordance with known processes that will assure a finished product where the ferrous metal core 17 will no~ be exposed by breaking the outer coating laver 18. One example of the techniques required for this purpose is taught by United States Patent No. 2,718,647 but other methods for performing these operations may be known to those experienced in this art.
As shown in Figure ~, the coated wire of this invention is applied to a bolt 25 having a head 26 and a threaded end 27. The outer coating layer 18 includes a flange 28 underlying the bolt head 26 so that when applied to connect workpieces no part of the bolt will come in contact with the workpiece. The head 26 of the bolt is formed by upsetting the core 17 in a suitable machine to form the -hexagonal shape re~uired for driving the bolt while the thickness of the corrosion resisting coating layer 18 is maintained of such thickness as to provide the anit-corrosion properties and to enable the threading 27 without destroying such properties.

0~6 Figure 5 illustrates the coated wire of this in-vention as applied to a typical screw 29 having a slotted head 30 and a threaded shank 31. Here again the outer coating layer 18 is maintained at a relatlve thickness in relation to the core 17 such as will enable the forming of the threads 31 without exposing the core metal 17 and providing - a finished screw having the required strength properties.
The coated wire of this invention is utilized in the manufacture of staples as shown in Figure 6. Here the re-lative proportions of the coating layer 18 and the wire core 17 are such that the bending the wire to form the staple 32 will not fracture the coating and expose the core. The points 33 of course, can be formed according to known processes.
In the method of this invention the core metal 17 may be formed of steel, other materials having the required structural strength and rigidity, as well as other properties, can be utilized :if preferred. The outer coating layer 18 may be made of aluminum, copper, or other materials that are resistant to corrosion inducing atmospheres and to galvanic action. ~ -~ .

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Claims (6)

WHAT IS CLAIMED IS:

1. The method of forming a metal clad wire for the manufacture of fasteners by passing a ferrous metal wire through a plasticized portion of nonferrous metal, wherein said nonferrous metal is continuously extruded into a die under pressure to form said plasticized portion, said ferrous metal wire is passed through said die at sub-stantially a right angle to the passage of said nonferrous metal and through the plasticized portion which forms around the said wire to provide a wrought aluminum structure enclosing the wire, the extrusion pressure comprising the sole source of heat generated to render the nonferrous metal plasticized in said central cavity without appli-cation of lubricant.

2. A method of forming metal clad wire in a cross-head die and wherein solid nonferrous metal is extruded continuously through one side of the die into a central cavity with a sufficient pressure to convert from a solid to plastic without application of lubricant, a ferrous metal wire is passed into another side of said die at an angle to the extrusion angle of the nonferrous metal, said wire passing through the plastic nonferrous metal in said central cavity which forms around the wire to provide a wrought aluminum struc-ture enclosing the wire and emerging through the opposite side of said die, said ferrous metal wire at the side where it passes into said die enters an opening in that side of the die having a diameter affording minimum clearance for the wire, said die at said opposite side having a larger opening whereby the coating will extrude through this opposite opening and form the coating on the wire, the heat of extrusion through the last named opening enabling the nonferrous metal to form a uniform coating thickness en-closing said ferrous metal wire according to the diameter of the last named opening, said extrusion pressure com-prising the only source for rendering the nonferrous metal in a state of plastic flow, the extrusion pressure on said nonferrous metal providing the sole source of heat.

3. A method of forming a metal clad wire in a die having a cavity, continuously extruding a nonferrous metal into said cavity of the die under extrusion pressure to generate the sole source of heat such as to render the nonferrous metal in a plastic state in said cavity without application of lubricant, passing a ferrous metal wire into an entering orifice of said die and through the plastic portion of said nonferrous metal generally at a right angle to the direction of extruding the nonferrous metal into the die which forms a nonferrous coating layer around the wire, whereby said coating layer provides a wrought aluminum structure enclosing the wire, and passing said coated ferrous metal wire through an exit opening in the die of larger diameter than said entering orifice to further extrude and bond the nonferrous coating layer around and on the ferrous metal wire to provide a pre-determined coating thickness of uniform diameter conforming with said larger diameter, said extrusion pressure being the only source of rendering the nonferrous metal in a state of plastic flow.

4. A method of forming a metal clad wire as set forth in claim 3 wherein said nonferrous metal is extruded into said cavity from one side of said die, said ferrous.
metal wire is passed into said entering orifice at another side of the die, and said coated wire passes through said exit opening in axial alignment with the wire at the enter-ing opening and exits through a third side of the die at substantially a right angle to said one side.

5. A method of forming a metal clad wire as set forth in claim 4 and locating said cavity centrally in said die coincident with the axis of the ferrous metal wire and the entrance of the nonferrous metal.

6. A method of forming a metal clad wire as set forth in claim 4 and providing minimum clearance for the uncoated wire, and further providing an exit of a diameter to force the plastic nonferrous metal into bonded engage-ment with said wire and defining the total diameter of the coated wire, and providing said die with an entrance to said cavity for said nonferrous metal of greater diameter than said orifice or said opening.