US2982312A - Tubing and method of making coated tubing - Google Patents

Description

May'Z, 1961 l. cAPLAN ErAL TUBING AND METHOD oF MAKING COATED TUBING Filed sept; 4, 1958 s y mm@ w m GW whim Y@ 4v f f A may I, d Z d a l .n ,wow/m@ M f iii- A wm H| |V @Sk RNQ NA QSS Tw* .wwwwvww LVV Q \\vb NMS QMMQQ f uw. LWN ik l G 0 Q Q Q D o C D D e D O O G o o o o o o o G NIT D NR n G A A Q G TA A Q s NNW .I 3f TY |L K TM. MMI .Nhkw lwvnu MASQ m35 H N Nmwww NAD MQ YN NN YN w the drawing,4 in which:

TUBING AND METHOD OF MAKING COATED TUBING Isadore Caplan, Bernard E. Frank, and Gerard T. Ruflin, Rochester, N.Y., andV Robert F. Thomson,v Grosse Pointe Woods, Mich., assgnors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Sept. 4, 1958, Ser. No. 758,986

11 claims. (cl. 13s- 145) This `invention relates to the manufacture of interiorly coated welded steel tubing. A primary object of the invention is to provide a method of making welded steel tubing While simultaneously coating the inner surface thereof with a permanent coating of an aluminum-zinc alloy which is securely bondedlto the surface of the tubing.

The invention comprehends making steel tubing from a cleaned flat strip of steel which is continuously moved longitudinally through a tube-forming mill. The tubeforming mill transversely bends the strip of steel into a tubular configuration. An alloy of aluminum and zinc is progressively introduced into the tubing during its formation. Prior to the complete formation of the tubing and about at the same point on the. tube-forming mill where the aluminum-zinc alloy is introduced into the tubing, the small diameter pipe which discharges a non-oxidizing gas enters the tubing and extends longitudinally therein. After the alloy is introduced into the interior of the tubing the formation of the tubing is completed and the tubing is passed through a' suitable welding device. It is subsequently passed through sizing means which impart the desired finish cross-sectional configuration of the tubing.Y 'After the tubing has .been

sized, it is passed through a heating means where the` causes the vaporized alloy to condense `as a uniform coating on the inner surface of the tubing. If desired,

`the Vtubing can then be given asuitablek coating on its outer surface, resized, and cut to useful lengths age or coiled on reelsfor storage.

Further objects, features and advantages of the present invention will become more apparent through the followfor stora suitable cleaning compound, a rinse 18, a pickling bath 20 and a subsequent rinse 22. After passing through the cleaning unit 14, the strip S is dried by an air blowoff 24 and directed into the tube-forming mill 12.

The tube-forming mill 12 is composed of a group of forming devices 26, each of which includes a pair 4of rolls 28 and 30. A sulicient number of forming devices 26 are included in the forming mill to impart the desired circular cross-sectional configuration to the flat steel strip S. The forming devices progressively bend the flat steel strip S into a tube T having an open seam Y 32 at the top where edges 34 and 36 of the strip abut.

Prior to the complete formation of the tube T, a small diameter Vpipe' 38 for conveying a non-oxidizing gasis introduced into the tubing interior as shown more clearly in Figure 2. An aluminum-zinc alloy may also beintroduced into the tubing at this point as a wire 40 through the small diameter pipe 38. The formed tube T then passes between welding rolls 42 or other suitable welding apparatus to close the seam 32 formed by the abutting edges 34 and 36 of the steel strip S. The formed tube then passes between sizingrolls 44 which further impart desired cross-sectional configuration of the tubing and then through a swaging device 46 for a final sizing operation. i

From the mill 12 the formed tubing T passes into a suitable heating chamber 48 where the aluminum-zinc alloy which was placed in the tubing is vaporized. The

ing descripton of preferred embodiments thereof and from vaporized alloy penetrates the inner surface 50 of the tubing and forms alstrong alloy bond therewith. The specific construction Yof the means by which the tubing is heated is not material to this invention. It may be of any construction which will suciently raise the tubing to a temperature which is suicient to vaporize the aluminum-zinc alloy and preferably simultaneously anneal the tubing. Although the annealing operation can take place after the vaporization operation, it is generally preferred to accomplish both simultaneously. Satisfactory results have been obtained using annealing rolls such as are described in the- United States Patent No. 2,822,291, Rea

I. Hahn, patent February 4, 1958, and which is 'assigned to the assigneeof the present invention.

VFrom the heating chamber 48 the tubing T passes Vthrough a=cooling chamber S2Which serves to solidifythe vaporized alloy to'form a coating 51 on the inner sur" can also bei'used. Whenrthe tubing is cooled in this i Figure" l is a diagrammatic Vview showing a Vtubeform- 'i -in`g' n 1i1l provided with suitable apparatus for carrying out thepresent invention; t

As shown' in Figure 1 the a dat steel strip S "of AISLlOlO, AISI` 1020, AISI 1008 `steel or'the like, which is coil'edon' a reel 10- positioned L adjacent one end of`a "tube-forming mill 12. Between.

is another-'enlarged sectional viewfalong the Y' line 5-5 of Figure l. l '-1 tubing T is formed frommanner, the alloy" coating 51 solidiesso rapidly that there is substantially no tendency Vfor the coating metal to run toward the bottom of the tubing. lt has been Y observedthatthe alloy coating` formed by this invention bottom of the'tubing with the thickness at the bottom being only negligiblyY greater. Y

A protective atmosphere is preferably "maintained around the outside ofthe tubing when it is in a heated condition 4to'prevent oxidationof the outer surface of the I r'tubing-'and to insure against oxidation within the tubing. a Accordinglyfthe `heating and" cooling means are Vprefer'- ably housed in the closed chambers 48 and 52 to facili-y tatethisfend.v After cooling, the V.tubing can then be is afclaning .unit 14 whichprepares the surface of the:

otating circular wire brushesl lwhiichiare liooded'with vresized, gif desired, and" cut into'whatever lengthsar desired] lf cut into extremely long lengths, the tubing is' coiled onto'long reels but it can Ybecutinto short `lengths''and' stored in straiglit'A pieces, rif desired.` `f1j Priorl to' enterig th`e Vtube'mill theflat steel Ystrip S is preferably continuously cleaned lof Vall dirt,v steel, ox

des, oils or other materials by the cleaning unit 14, shown in the drawing. The cleaning unit consists of two motor driven contra-rotating wire brushes 16 which scrub the side of the strip which is to form the inner surface Si) of the tubing T. The brushes 16 of the cleaning unit are Hooded with a hot alkaline cleaning compound to carry away the loosened soil. One such alkaline cleaning solution which may be used is an aqueous solution which is saturated with sodium silicate and sodium hydroxide. The steel strip then passes under a water spray or rinse 18 to remove any cleaning compound which may be adhering to its surface. After rinsing, the steel strip can be passed through a pickling bath 20, such as an aqueous solution containing 30%, by volume, hydrochloric acid. After the pickling treatment, the strip is passed through the rinse 22 to remove any traces of the pickling solution which may be adhering to its surface after the pickling treatment, and is then subjected to an air blow-oft` 24 to dry it.

Other methods of cleaning, such as sand blasting, spray washing, electrolytic cleaning, etc.. may be used in some instances to prepare the steel strip for use in accordance with the invention. However, We have found that the hereinbefore described method of cleaning provides especially beneficial results when used in combination with the coating method of the invention. The internal coatings applied to tubing surfaces which are cleaned in this manner are particularly more adherent and permanent.

The coating metal can be introduced into the interior of the hollow and annular cylindrical tubing T in any convenient form. Our invention is especially more conveniently practiced, however, if the coating metal is introduced into the tubing in a wire form 40, as shown in the drawing. Generally it is preferred to introduce the coating metal into the tubing immediately before it is fully formed. The wire 40 may be coiled on a roll 54 mounted on the tube-forming mill 12 and fed through a directing tube 56 into the interior of the tubing by means of a pair of driving rolls S8. As shown in the drawing, the aluminum-zinc alloy wire 40 can be introduced within the tubing through the small diameter pipe 38 which is used to introduce the protective atmospherel into the interior of the tubing. The specic construction of this mechanism is not aipartvof this invention and any suitable device can be used to introduce the'coating metal at a substantially uniform rate. The particular rate at which the metal is introduced is variable to some extent and is governed by the size and speed of movement of the tubing being formed.

As shown in United States Patent No. 2,771,669, filed in the names of J. W Armstrong, R. W. Spears and R. D. Williams and which is assigned to the assignee of the present invention, particles of metal such as zinc can also be uniformly introduced into the interior of the tubing employing a suitable hopper or funnel having a narrow outlet which extends into the tubing prior to its complete formation.

Obviously, in order to provide a uniform coating, the amount of aluminum-zinc alloy which is introduced into the interior of the tubing must vary inl direct proportion with both the size and speed of movementv of the tubing which is to be alloy coated. Moreover, coating compositions of varying proportions can be produced by varying the amount of coating material introduced into the interior of the tubing. In general, highly satisfactory As a specific example, steel tubing having an outer diameter of approximately "ta inch and a wall thickness of approximately 0.028 inch can .be successfully coated using an aluminum-zinc alloy wire, approximately 0.032 inch in diameter, which is moving at the speed of the tubing being formed. Similarly one can use an aluminumzinc wire, approximately 0.047 inch in diameter, which is moving at the speed of the tubing to coat tubing having an outer diameter of approximately inch and a wall thickness of about 0.035 inch. In general, highly satisfactory results are obtained when a weight of approximately 0.0025 pound per-foot of tubing and 0.0053 pound per foot of tubing are, respectively, used.

A non-oxidizing gas from a suitable reservoir (not shown) passes through the small diameter pipe 38 which is introduced into the tubing at approximately the same point on the tube-forming mill where the coating metal is introduced into the tubing. As shown in the drawing, this small diameter pipe 38 has a part (not shown) which extends axially within the interior of the tubing towards the swaging device to a point where the tubing is completely formed. The discharge end of the pipe is located at a point where the tubing is completely formed so that the reducing atmosphere emitted therefrom will be substantially contained within the interior of the tubing. Thus, a protective atmosphere is established within the tubing as it moves along the various following operations.

It is also desirable to employ a protective atmosphere outside the tubing in the operation following tube formation. Heating the tubing in an oxidizing atmosphere may cause a deleterious corrosion and spalling of the outer surface which is detrimental to subsequent outer coating operations. Thus, as shown in Figure l, the heating and cooling of the tubing can be done within closed chambers in which a protective atmosphere is established. The non-oxidizing gas can be introduced into the chambers by means of additional piping from the source of supply (not shown).

A gas which protects the interior and exterior of the tubing is preferably 20% to 25% reducing in nature. For example, highly satisfactory results are obtained with a gas which has the following analysis: 10% carbon monoxide, 18% hydrogen, 41/2 carbon dioxide, 1% methane and the balance nitrogen, all proportions by volume. However, substantially pure mixtures of hydrogen, carbon monoxide, nitrogen, helium, argon, can also be used.

From the swaging device or sizing device the tubing passes into the heating chamber where it is heated above the vaporization temperature of the aluminum-zinc alloy which was deposited within the tubing during its formation. The vaporization of the aluminum-zinc alloy permits the alloy to penetrate the inner surface of the tubing to some extent to produce an exceedingly uniform tenacious alloy coating. The vaporization of the alloy and the annealing of the steel tubing can be accomplished simultaneously, if desired, and in such instance the tubing should be heated to a temperature which is not only sufin thickness. InV most instances, the coating of approximately 0.001 inch. in thickness is preferred.

ficient to vaporize the zinc but also to anneal the tubing. It has been found that satisfactory alloy coatings are obtained when the tubing is heated to a temperature beween 1700 F. and 2400 F. In general, highly satisfactory annealing and coating results are obtainable in the temperature range of approximately 2000 F, to 2400" F.

After the tubing has been cooled, if desired, it may be coated on its outer diameter and subsequently passed Vthrough a pull-out unit to resize the outside of the tubing.

In some instances the various coating and heat treatments to which the tubing is subjected may affect the outer dimensions of the tubing so that resizing is required. Should resizing be required, the tubing can be passed through a pull-out unit which is, in general, similar to the final sizingdevices employed on the tube mill which g pose the base metal.

l the surface of the steel.

the -white corrosion products of a pure zinc coating which would spall or flake from the surface and subsequently deleteriously aiiect the fuel system. Moreover, steel tubing which isused to convey especially corrosive materials must-be `correspondinglyV of especially high corrosion resistance.

It has been foundthat when 'vaporizing pure zinc metal in accordance with the method` set forth in the aforementioned Armstrong et al. patent, `the zincmetal forms dendritic structures on the inner surface of the tubing with-pure base `metal exposed therebetween. Thus, the coating formed, 1unlike an immersion coating, is

somewhat discontinuous ands contains pinholes at which corrosion can occur. The galvanic or sacrificial properties of the zinc will protect these bare spots to some extent but yover extended periods of time the corrosion resistance of the coating is seriously aected.

Moreover, due to the dendritic structure and the formation of ferro-zinclintermetallic compounds, the pure zinc coating tends to be undesirably brittle/for some applications. Where the tubing is subjected to an exces- :sive amount of bending, the harder and more brittle zinc coating is not Vsufficiently ductile to resist cracking and delamination and therefore exhibits especially poor cor' rosion resistance.

It has now been found thatby adding rather large, amountsxof aluminum to-zinc an especially satisfactory coating can be formed that is bright, ductile and more corrosion resistant. alloy wire onto the inner surface of the tubing no dendriticstructure is formed and` an exceptionally smoother, uniform, bright and shiny coating isy obtained. Since substantially no dendritic structure isV present in the aluminum-zinc coating, there are no pinholes present to ex- Moreover, the laddition of the aluminum minimizes the formation of the brittle ferro-zinc intermetalliccompounds which contribute to the brittlenessof the coating.

A further advantage of the coating formed with the aluminum-zinc alloy in the method hereinbefore vde-` scribed is that it contains a thin overlay of an aluminumrich alloy which virtu-ally eliminates the white` corrosion products common to a pure zinc coating This thin aluminum-rich overlay provides the coating with anexceptionally higher corrosion resistance than'that even obtained under a hot dip process employing a similar aluminumainc alloy. f In addition to the more ductile .and continuous characteristics of the coating, Vthis invention further provides corrosion protection by means of its ne sacrificial properties. Y

1The ductile, continuous, highly corrosion-resistant` will not even wet the surface onto which it is to be deposited and that it merely melts without evenalloying to We have Vfound especially satisfactory results' are obtainablewhen forming a coating in accord-ance with thev present invention'with a zinc base alloy containing, by weight, about 10% to 20% alu- /minum and 80% -to 90%V zinc. 'H owever, in some instances, it is preferable to employ a zinc base alloy con- By vaporizing analuminum-zinc weight, and as high as 30%, by weight. in general, highly satisfactory coatings can be obtained employing a zinc base alloy wire containing approximately 18%, by weight, aluminum and the balance zinc. 3

We have also found that highly satisfactory coatings are obtained with a sodium-aluminum-zinc alloy in which the sodium content is about 0.08% to 0.12%, by Weight. The addition of the sodium increases the fluidity ofthe aluminum-zinc alloy and contributes to the formation of an exceptionally adherent and more ductile coating. Y In general, we have Vfound that zinc base alloys containing 0.08% to 0.12%, by Weight, sodium and about 12% to 18%, by weight, aluminum and the balance zinc will provide highly satisfactory results. In some instances,

however, satisfactory coatings may be formed With'the abovementioned Yamount of sodium in zinc base alloys containing as low as 5%, by weight, aluminum andas high as 30%, by weight, aluminum. f

We have found that sodium in combinationV with Yaluminum and zinc provides a highly satisfactory smooth, brighttand ductile alloy coating. However, in some instances alloys containing another alkali metal, particularly lithium and-potassium, may also be used in place of a portion or even the entirety of sodium in the alloy described above to obtain highly satisfactory vaporized coatings. Moreover, it isalso contemplated that in certain instances the alkaline earth metals, particularly calcium, can be used in place o f a portion or all of the sodium in the aluminum-sodium-zinc alloy described above.

It is to be understood that the term abutment is used herein in its primary meaning; i.e. indicating touching or contacting. Thus, overlapping edges of a lap seam is also comprehended within the phrase abutting edges as well as non-overlapping contacting edges, such as shown in the drawing. Our invention therefore encompasses making tubing having `abutting edges from a metal strip having scarfed longitudinal edges, the surfaces thereof being non-perpendicular to the major surface of the steel strip, as well as from a steel strip having its longitudinal edges perpendicular to the major surface of the strip;

` It is to be'further understood that the term zinc base alloys asused herein, refers to those alloys which contain zinc in greater proportions than 50%, by weight.

Although our invention has been described in connecf tion with single wall tubing and other certain specific ex-V an adherent, uniform alloy coating during formation of'said tubing from a steel strip, said method comprising the steps of longitudinally moving a substantially'at steel strip while continuously transversely bending it into a tubular configuration having Yabutting edges forming a seam, introducing an alloy containing aluminum and vzinc into the interior of the tubing, after it is completely formed heating the tubing to a degree sufficient to vapor ize said alloy within the tubing and thereafter cooling the tubing sufficiently to cause said alloy to solidify so as to form a smooth and ductile alloy coating on the interior of the tubing. l

2. The method of coating the interior of steel tubing with an adherent, uniform alloy coating during formation 'of said tubing from a steel strip, said method comprising the steps of longitudinally moving a steel strip While continuously transversely bending it into aV tubular configuration having abutting edges forming a seam, introducing a `zinc baseall'oy containing approximately y 57% to 30% by weight aluminum into the interior of the tubing, after it is completely formed heating the tubing ,to agdegree suicient to vaporize said alloy within the tubing and thereafter cooling the tubing suiciently to cause said alloy to solidify so as to form a smooth and ductile alloy coating on the interior of the tubing.

with an adherent, uniform alloy coating during formation of said tubing from a steel strip, said method comprising the steps of longitudinally moving a steel strip while continuously transversely bending it into a tubular configuration having abutting edges forming a seam, introducing an alloy containing about to 30% by weight of aluminum and 70% to 95% by weight of zinc into the interior of the tubing, after it is completely formed heating the tubing to a temperature of approximately 1700 F. to 2400 F. to vaporize said alloy within the tubing, and thereafter cooling the tubing sufficiently to cause said alloy to solidify so as to form a smooth and ductile alloy coating on the interior of the tubing.

y 4. A method of coating the interior of steel tubing with an adherent, uniform alloy coating during formation of said tubing from a steel strip, said method comprising the steps of longitudinally moving a steel strip while continuously transversely bending it into a tubular configuration having abutting edges forming a seam, introducing a zinc base alloy containing aluminum and a metal from the class consisting of alkali and alkaline earth metals into the interior of the tubing, after it is completely formed heating the tubing to a degree suflcient to vaporize said alloy within the tubing, and thereafter cooling the tubing suiciently to cause the alloy to solidify so as to form a smooth and ductile alloy coating on the interior of the tubing.

5. The method of coating the interior of steel tubing with an adherent, uniform alloy coating during formation of said tubing from a steel strip, said method comprising the steps of longitudinally moving a steel strip while continuously transversely bending it into a tubular configuration having abutting edges forming a seam, introducing an alloy containing, by weight, about 12% to 18% aluminum, about 0.08% to 0.12% sodium and the balance substantially zinc into the interior of the tubing, after it is completely formed heating the tubing to a temperature of approximately 1700" F. to 2400 F. to vaporize said alloy within the tubing, and thereafter cooling the tubing suciently to cause the alloy to solidify so as to form a smooth and ductile coating on the interior of the tubing.

6. The method of coating the interior of steel tubing with an adherent, uniform alloy coating during formation of said tubing from a substantially flat steel strip, said method comprising the steps of longituldinally moving a substantially flat steel strip while continuously transversely bending it into a tubular configuration having abutting edges forming a seam, continuously introducing a wire of an alloy containing about 5% to 30%, by weight, aluminum and about to 95%, by weight, zinc into the interior of said tubing prior to the complete shaping thereof, discharging a non-oxidizing gas into the interior of the tubing at a point where it is substantially completely formed, after the tubing is completely formed heating the tubing to a temperature of about 1700 F. to 2400 F. to vaporize said alloy within the tubing, and thereafter cooling the tubing to cause said alloy to solidify so as to form a smooth and ductile coating on the interior of said tubing.

7. An article of manufacture comprising a steel tube having an inner surface, a coating on said inner surface of a vaporized zinc base alloy containing approximately 5% to 30% by weight of aluminum.

8. An article of manufacture comprising a steel tube having an inner surface, a coating on said inner surface of a vaporized alloy consisting essentially of approximately 5% to 30% by weight of aluminum and about 70% to 95 by weight of zinc.

9. An article of manufacture having a smooth and ductile zinc base alloy coating thereon comprising a steel tube and an interior coating on said tube of a vaporized alloy containing, by weight, about 5% to 30% aluminum and about 70% to 95% zinc, said coating being especially high in aluminum content at its outer surface.

10. An article of manufacture having a smooth ductile zinc base alloy coating thereon comprising a steel tube and an interior coating on said tube of a vaporized alloy containing, by weight, about 5% to 30% aluminum, about 70% to 95% zinc and about 0.08% to 0.12% sodium, said coating being especially high in aluminum content at its outer surface.

1l. An article of manufacture having a smooth ductile zinc base alloy coating thereon comprising a steel tube and an interior coating on said tube of a vaporized alloy containing, by weight, about 5% to 30% aluminum, about 70% to 95% zinc and about 0.08% to 0.12% of a metal from the class consisting of alkali and alkaline earth metals, said coating being especially high in aluminum content at its outer surface.

References Cited in the le of this patent UNITED STATES PATENTS 2,771,669 Armstrong Nov. w27, 1956

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