US2069658A - Method of coating strip steel and product - Google Patents

Description

Feb. 2, 1937.- v R. F RENKIN I I METHOD OF COATING STRIP STEEL AND PRODUCT Filed Dec. 9, 1933 INVENTOR JZFHezz/tzn XORNEYS Patented Feb. 2, 1937 UNITED STATES METHOD OF COATING STRIP STEEL AND PRODUCT Robert F. Rankin, Sharon, Pa., assignor, by

mesne assignments,

'town, Ohio Application December 9, 1933, Serial to himself, Henry A.

Roemer, and John M. Hughes, both of Youngs- 9 Claims. (01. 91-102) The invention relates broadly to coated metal products and methods of making the same, and more particularly to hot coating metal strips,

' sheets and the like, such as strip or sheet steel,- with a protective metallic coating, akin to but different from a galvanized coating, for making a ductile product having a longer life than the usual galvanized product. Y In other words, it is an object of the present 10 invention to provide a coated metal product, and a method of making the same, which efiiciently resists corrosion and heat and which is ductile enough to be severely formed, bent or pressed, deep drawn, or cold rolled to extreme reductions, without flaking or powdering the coating thereof, and this application is a continuation in part of my application for patent for Method of coating strip steel and product, filed March 22, 1933, Serial No. 662,054. I It has been customary to galvanize by employing a bath of zinc, or zinc alloys such as zinc and tin; zinc, lead and tin; zinc, lead, tin and aluminum; zinc, tin and aluminum; or zinc and.

aluminum; the bath being maintained at a term perature of 840 F. and upwards, and the coated product sometimes being subsequently heatedand/or rolled to produce a galvanized heat and/or corrosion resisting product, which will withstand forming at right angles without fiaking the coating thereof.

Authorities state that the addition of tin to the bath helps bring out the spangles or accelerates crystallization of the zinc, but caution that the addition of tin gives a less durable coating and caution'against the use of more than 2 to 3% of tin in the bath. l

Present day specifications require coated metal products for many purposes to be free from spangles, but to have a velvety grey frosted apthat the use of tin in a spelter bath, which authorities state brings out the spangles, should be eliminated according to prior experiences if a ciable amounts of tin and aluminum tothe spelter bath produces a tight, rust-resisting coating that may be formed at right angles',.or may be' rolled, without flaking. However, the aluminum apparently causes a reaction in the bath, which produces a black scum at the surface of the bath and dea'dens the flux. Moreover, a coating of uniform color cannot be produced because of unaccountable discoloration of the coated prodpea-rance, or to be capable of being polished to have a bright silvery or nickel appearance; so

coated "material is desired free from spangles..

I have discovered that the addition of appre-- uct. And finally, the rolling and forming of the product causes a fine powdering of the coating so that the powder gathers on the rolls or dies, which ultimately marks the rolled or formed product.

However, I have discovered that the addition of from 10 to 30% of tin to the zinc or spelter bath maintained at a critical temperature of approximately 800 F. produces acoating that is far more ductile than a straight spelter coating. In utilizing a straight spelter coating, a substantial layer of zinc-iron alloy is formed, which, under corrosion tests, stands up very well, but powders under forming operations. This appar- 'ently. occurs because when the zinc-iron alloy freezes, the mass as a whole undergoes an expansion rather than a contraction, which when frozen consists of a porous mass of individual crystallites having virtually no cohesion; and when iron is combined with zinc above a few hundredths of l per cent, it is very ,brittle and greatly affects the ductility of the material.

On the other hand, I have discovered that by the addition of an appreciable amount of tin, of from 10 to 30% to a spelter bath maintained at a critical temperature of approximately 800 F., the zinc iron. alloy in the coated product is greatly reduced or substantially eliminated, while a zinc-tin-iron alloy is formed, which is very ductile and cohesive.

I havelikewise discovered that when a bath of zinc with 10 to 30% of tin is utilized, together with a critical bath temperature of approximately 800 F., great savings in fuel used and in maintenance and replacement costs for the molten bath pot result, and a much longer pot life is obtained.

It would normally be expected that coating costs would be materially increased when a spelter bath containing a high percentage of tin is used, because the cost of tin is approximately five times that of zinc. However, I have discovered that for some unaccountable reason, when say a 20% tin, 80% zinc bath is utilized, the resultant coating on the material isonly approximately l tin and approximately 92 /g% zinc, when a critical bath temperature of approximately 800 F, is maintained.

I have likewise discovered that the bath temperature materially afiects thepercentage of tin in the resultant coating, for when a spelter bath containing 18% tin is operated at 860 F., a coating having only approximately 4% tin results, while when the same spelter bath containing 18% tin is operated at 790 F.,' the resultant coat- 65 termined only be anticipated, Moreover, with a given percen'tage of tin in the bath, the increase of pot replacement costs incident, to 860 F. bath temperature operation over 790 F. bath temperature operation may more than oifset themin the resultant coating with 790 F. operation according tothe above illustration.

However, although the bath temperature is one of the elements materially affecting the percentage, of tin in the resultant coating, in no case is the percentage of tin in the coating the same as the percentage of tin in the bath; and in no case is the percentage of tinin the coating decritical temperature .for coating material, the I resultant coating has substantially uniform thickness and therefore has the same or better corrosion resisting properties than theusual galvanized coating, and weighs only from 0.3 to 1 ounce per square footof material coated; while the usual galvanized coating weighs materially above 1 ounce per square foot 'of material coated, but

. has a non-uniform thickness-because of the spangles with very thin Joints between the span'gles.

The result is that the cost of coating in accordance with the present invention, using ap-- preciable amounts of tin in a zinc bath, taking into consideration raw material costs, pot maintenance and replacement costs, fuel costs, and

resultant coating thicknesses, is actually reduced from one-fourth to one-half of the cost of makin the usual galvanized coated material.

It appears from cost and production standpoints, that the lowest practical limit of the percentage of tin in the spelter bath is about 10% tin, in order to produce the improved results of the present invention; although this percentage may be slightly varied under certain circumstances. From the same standpoints, the improved product should havefrom 3 to 15% of tin in the coating thereof in order to obtain the improved results of the present invention.

It appears that a 20% tin zinc bath is preferable from all standpoints, and that a resultant coating on the product of approximately 7 tin is preferred, which is produced when the preferred bath is operated at the critical temperature of approximately 800 F.

The exact preferred percentage of tin in the bath or in the coating of the resultant product cannot be stated because the same may be varied in accordance with the product desired to be produced for the reason that the higher the percentage of tin in the bath or coating, the better .is the product, the lower is the melting point of by the percentage of tin in the is not intended to limit the scope of the present 1 invention to the preferred tin percentages stated.

It likewise appears thata critical bath temperature of approximately 800 F. is preferable from many standpoints, although with an increase of the tin content in the bath, the bath temperature may be reduced to approximately 775 F., or when an increase in the tin content of the resultant coating is desired, the bath-temperature may be reduced to approximately 775 F. However, the exact bath temperature cannot be stated because the same maybe varied within the limits stated herein, in accordance with the character of the resultant coating desired to be crease in high cost tin of from 4% to 8% present produced on the finished product; and it is not intended to limit, the scope of the present invenout flaking or 'powdering the coating thereof.

Moreover, the coated product will withstand heat up to 1250? Fl without affecting or deteriorating the coating thereof and the product is suitable for enameling at temperatures of from, 450 F, to 500 F.

And finally, the improved coatedproducts have a coating'which is free from spangles and which presents a uniform velvety, grey frosted appearance without polishing, and presents a bright nickel-like or silver-like appearance when polished. I

Accordingly, a general object of the present invention is toprovide coated metal products or articles having the improved characteristics stated, and to provide a method of coatingby which the described advantageous results are obtained.

These and other objects, results and characteristics' maybe obtained by the improved products and methods described herein in detail and claimed; and a preferred arrangement of apparatus which has been successfully used for carrying out the improved methods of coating and for making the improved product, is shown in the drawing, in which:-

The figure is adiagrarnmatic side elevation of a pickle tank, wash tank, scrubber, flux tank, coating pot, cooling zone, pull-up, and reels, which may be utilized for carrying out the improved method to make thedmptoved product.

Similar numerals refer to similar parts throughout the drawing. l A pickle tank, indicated generally at'A, contains the desired pickling solution, and the pickle tank A is preferablyprovided, with an entry roll I, hold down rolls 2 and 3, and an exit roll-l. A wash tank B is pickle tank, and the wash tains cold water and is the hold down ,roll'i.

A scrubber C is located adjacent to the exit end of the wash tank 3 and the scrubber C is preferably provided with scrubber, rolls and steam or hot water sprays which may act upon the surfaces of the material passed therethrough. A

tank preferably conpreferably provided with flux tank Dis preferably located at the exit end of the scrubber C, and

erably equipped with an roll 'I'and an exit roll 8.

tains preferably a bath of liquid flux, such as zinc chloride or other commercial flux. Immediately after the flux tank D, there is preferably provided air blower means E for drying the liquid flux the flux tank D is 'prefentry roll-'8, a hold'down The flux tank D conlocated immediately after the an which adheres to the surface of the material -the entry end of the coating pot F through a passed through the flux tank D;

A coating pot F is located beyond the air blowers E, and the coating pot may be heated by any usual means diagrammatically indicated at 9. The coating pot F is preferably provided with the usual entry roll Hi and hold down rolls II and II.

A molten bath is' maintained in the coating pot F, containing commercially'pure zinc or spelter and commercially pure tinin the desired proportions, including from to of tin, the proportion of tin in the bath being less in proportion by weight than the zinc.

The bath temperature is preferably maintained at a critical temperature of approximatey 800 F. and preferably not above 825 F., although the bath temperature may be controlled or varied, preferably downward to 775 F., when the percentage of tin in the bath is increased, or if the tin content of the resultantcoating on the article 4 to be coated is desired to be increased, to control the tin content of the coating on the article. Thus, when a critical temperature'of approximately 800 F. is referred to herein, the same is intended to include bath temperatures of from 775 F. to 825 F.

Wiper rolls I3 are provided adjacent the exit end of the coating pot for wiping from the surfaces of the material passing therethrough excess molten bath metal adhering thereto; and means is preferably provided for adjusting or controlling the pressure exerted by the wiper rolls, for controlling the thickness of the resultant coating on the coated material.

Immediately following the wiper rolls 13, there is preferably provided air blowers G for cooling the coated material, or in some cases the coated material may be passed through a water cooling tank, not shown, when it issues from the wiper rolls l3.

A pull-over roll H is preferably provided above the wiper rolls l3, and a cooling duct I leads from the pull-over roll H to. the pull-up tensioning device J. The cooling of the coated material may be controlled in any desired manner by circulating air or other cooling medium through the cooling duct I. A series of reels K, KI and K2 are preferably located adjacent the exit end of the pull-up tensioning device J, three reels being shown in the drawing to indicate that a plurality of strips may be passed in parallel, side by side, continuously through the described apparatus.

In operating the apparatus for carrying out the improved process to make the improved product, the steps are as follows:---

Hot or cold rolled preferably strip material S is pulled continuously at a uniform speed from coils thereof located in any suitable coil box (not shown) and passes over the roll I into the pickle tank A and under the rolls 2 and 3 thereof, whence it passes upwardly outof the pickle tank over' the roll 4 and down into the wash tank B underneath the roll 5 mounted thereon. The cold water in the wash tank removes acid salts which may have formed as a result of pickling. The strip S then passes through the scrubber C wherein steam or hot water is used to remove the film that may exist on the surfaces of the strip. The

strip then passes over the roll 6 and into'the flux tank D- underneath the roll 1 thereof, wherein liquid flux is applied to the surfaces of the strip,

thence outwardly over the roll 8 and between'the air blowers E where the flux is dried.

The strip then passes over the roll l0 and into dammed inlet, wherein the flux is permitted to collect on top of the molten bath. In passing through the molten bath in the coating pot, the strip is subjected to the action of the molten bath therein by passing beneath the rolls II and I2, and thence outward through the outlet portion of the bath. The intermediate portion of the bath between the dammed inlet and outlet portion is preferably covered with charcoal to retain heat and reduce oxidation.

The strip then passes between the wiper rolls l3, the pressure of which is adjusted to obtain.

the desired thickness and uniformity of coating, thence between the cooling blowers G, or in some cases through a water cooling tank, not shown. The strip S then passes over the roll H, through the cooling duct 1, and through the pull-up tensioning device J, thence to one of the reels K, Kl or'K2. Coils L of coated material are thus produced having a steel or iron base provided with a coating of an alloy of zinc, with tin as the main alloying agent, the tin being present in proportions to the zinc by weight of 3% or more in the.

coating, but being less inproportion by weight than the zinc.

The improved methodaccordingly,provides for the coating of metal strips, sheets and the like, with a protective coating, akin to, but different from a galvanized coating. Moreover, the coils L, which constitute the improved material pro duced comprise material which successfully resists corrosion, which is ductile enough to be.

severely formed, bent or pressed, or deep drawn, or cold rolled to extreme reductions without flaking or powdering the coating thereof, which will withstand heat up to 1250 F., and which is suitable for enameling at temperatures of from 450 F. to 500 F. Moreover, the coating is free from spangles, but presents a uniform velvety, greyfrosted appearance without polishing. And finally, the coating may be buffed and polished. to a high luster without a previous cold rolling treatmentof the coated material, as is necessary in accordance with prior practice.

The terms zinc or spelter. used herein and in the appended claims, refer to pure zinc, or to commercially pure zinc which may contain slight amounts of impurities such as iron, lead, cad-- mium, tin, copper and arsenic.

Likewise, the term tin", used herein and in the appended claims, refers to pure tin, or to commercially pure tin which may contain slight amounts of impurities, such as iron, copper and bismuth.

Moreover, in referring herein and in the appended claims to percentages of tin and/or zinc in the bathor in the coating on the product,- percentages by weight are meant.

It is not intended to limit the scope of the present invention to the coating of. strip steel, or to the continuous coating of a continuous strip, since it is clear that stripsheets, sheets and the like may be coated in the same manner; so that the terms ferrous strip metal, strip or strip steel used herein and in 'the appended claims. refer to strips, stripsheets, sheets, sheet steel, sheet iron and the like.

I claim:

1. In a method of coating ferrous strip metal, the steps of subjecting a strip to the action of 'a molten bath of zinc and the remainder from 10 to 30% tin maintained at a critical temperature of approximately800 'F., and then wiping the coated strip, to produce a coated strip product having a ductile and cohesive zinc-tin-iron alloy coating thereon. 4

2. In a method of coating ferrous strip metal, the steps of subjecting a strip to the action of a molten bath of zinc and the remainder 20% tin maintained at a critical temperature of apwithin the limits specified, and then wiping the' coated strip, to produce a coated strip product having a ductile and cohesive zinc-tin-iron alloy coating thereon. i

4. In a method of coating ferrous strip metal, the steps of subjecting a strip to the action of a molten bath of zinc and the remainder from 10 to30% tin, and maintaining the bath at a temperature of approximately 800 F. and not above 825 F., and varying the bath temperature downward to 775 F. when the percentage of tin in the bath is increased, within the limits specified, and then wiping the coated strip, to produce a coated strip product having a ductile and cohesive zinc-tin-iron alloy coating thereon.

5. In a methodor coating ferrous strip metal with a zinc-tin-iron alloy coating containing from 3 to 15% tin, the steps of subjecting a strip to the action of a molten bath of zinc and the remainder i'rom' 10 to- 30% tin, and controlling the bath temperature at from 775 F, to 825 F. to control the tin content of the coating on the coated strip, the temperature of the bath being varied downward to increase the tin content of the resultant coating on the strip, within the limits specified, and then wiping the strip, to produce a coated strip product having a' ductile and cohesive zinc-tin-iron alloy coating thereon.

6. In a method of coating ferrous strip metal; thesteps of continuously passing a strip through a molten bath of zinc and. the remainder from to 30% tin maintained at a critical temperature of approximately 800 F., and then wiping the strip, to produce a coated strip product having a ductile andcohesive zinc-tin-iron alloy coating thereon.

7. In a method of coating ferrous strip metal, the steps of continuously passing a strlpat a uniform speed through a molten bath of zinc and the remainder from 10 to 30% tin, controlling the bath temperature at from 775 F. to 825 F'., and controlling the speed of passage of the strip through the bath to control-the tin content of the coating on the strip, and then wipingxthe strip, to produce a coated strip product having a ductile and cohesive zinc-tin-iron alloy coating thereon.

8. A corrosionresisting coated metal product,-

coated by the method of claim L comprising a ferrous strip metal base, and a 'zinc-tin-iron alloy coating on the base having a substantially uniform thickness containing zinc and from 3 to tin; said coating being characterized by being ductile enough to be severely formed, bent or pressed, deep drawn or cold rolled to extreme re- I ductions without flaking or powdering; being further characterized by its ability to withstand heat up to 1250 F. without deteriorating, and by being suitable for enameling at a temperature offrom 450 F. to 500 F.;' and said coating being further characterized by being free from spangles, by having a velvety grey frosted appearance without polishing, and by presenting a brightnickellike. or silver-like appearance when polished.

9. A corrosion resisting coated metal product, coated by the method of claim 2, comprising a ferrous strip metal base, and a zinc-tin-iron alloy coating on the base having a substantially uniform thickness containing zinc and 7% tin; said coating being characterized by being ductile enough to be severely formed, bent .or pressed,

' deep drawn or cold rolled to extreme reductions without flaking or powdering; being further characterized by-its ability to withstand heat up to 1250 F. without deteriorating, and by being suitable for enameling at a temperature of from 450 F. to 500 F.; and said coating being further characterized by being free from spangles, by having a velvety grey frosted appearance without polishing, and by presenting a bright nickellike or silver-like appearance when polished.

ROBERT F. RENKIN.

Images