US2390440A - Lead coating - Google Patents

Description

Dec. 4, l1945. E, J, KALIL 2,390,440

LEAD COATING Filed may 29, 1942 2 sheets-sheet 2- 1 IN VEN TOR. EUGENE Jos EPH frm.

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HTTORNE'Y Patented Dec. 4, 1945 UNITED ISTATES PATENT OFFICE 2,390,440 i g v 4 LEAD COATING Eugene Joseph Kam, nimunmn, w. vs.,ass1gnor to The International Nickel Company, Inc.,

New York, N. Y., a corporation of Delaware Application May 29, 1942, Serial No. 445,399

8 Claims.

The present invention relates to lead coating. and, more particularly, to a novel ux and proc 'ess for coating metals and alloys with lead preparatory to a metal drawing operation.

It was known that a coating of soft metal, e,'g., lead, on the surface of a harder' metal such as steel and nickel base alloys facilitated the drawing of wires, bars, tubes and other'shapes. A

number of diiferent processes for applying such coatings had been proposed, including various hot dip methods. In the hot dip methods a bath of molten lead or other soft metal was ordinarily covered in whole or in part with a molten ilux through which the article to be coated was passed into the molten metal bath. While the functions of the flux were not completely understood, it

the metal being coated, such a clean metallic surface was obtained by grinding, pickling, gas reduction etc. Despite care in pickling or otherwise cleaning the surface, drawing difllculties frequently occurred, particularly on the inside surfaces of tubes. The most common drawing dimculty appeared as scoring marks on the surface ofthe drawn article and in some cases there would be actual. metal pick-up on the mandrel or die. Attempts to overcome these diiilcultiea which appeared to be traceable to uncontrollable pickling and leading practice,.were unsuc cessful.

I have invented a new ilux and process for coating metals andv alloys which not only overcomes the difficulties of prior art practice but also makes itV possible, when desired, to omit the pickling or cleaning steps and still get satisfactory lead coatings and satisfactory drawing characteristics. y

It is an object of the present invention to provide a process of producing a lead coating on metals and alloys `which adheres firmly to the underlying foundation.

, The present invention embraces supercially oxidized metallic shapes having an adherent lead coating and a process of coating metallic shapes with lead which can be carried out without a preliminary pickling or cleaning operation so that supercially oxidized shapes, e. g., hot rolled articles, may be coated directly with an adherent lead coating.

Further objects of the present invention include a flux and a process for lead coating metals and alloys which will insure a coating of lead having good covering power and rmadherence to the foundation.

'I'he present invention also contemplates coating metalsand alloys as a step preparatory to a drawing operation, which coating will be of such character as to prevent metal pick-up on the dies and mandrels' employed in the drawingV operation.

Other objects and advantages of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the drawings in which:

Fig. 1 is a ternary chart showing the composition' of the ux embodying the present invention; Fig. 2 depicts schematically the structure of a short metal object that has been coated with lead by the process of the present invention without removing the oxide layer;

Figs. 3 andV 4 reproduce, respectivelm'a photograph of a section of a two inch alloy tube after being coated with lead by the method of the present invention and a section of 1% inch. tube of a different alloy after being so coated and subsequently drawn to effect about 46% reduction in area in two passes, a portion of the lead coating in each case having been dissolved olf with dilute nitric acid to reveal the underlying oxide layer and a part of the oxide layer having been pickled off to show the foundation or base metal; and

Fig. 5 is a schematic reproduction of a photomicrograph of a cross section of a tube coated with'lead by the process of the present invention taken adjacent to thesurface thereof and showing the lead coating adhering-to an oxide coating which in turn strongly adheres tothe foundation or base metal.

Generally speaking, the present invention contemplates the production of an adherent coating Y of lead on harder metals and alloys by a hot dip sents the operable flux compositions which fall within the ranges: v

Per cent ZnCls 20 to 95 FeCls i 5 to 55 Niif'l.. 0 to 4o Preferably the flux composition lies within the field bounded by lines F G H I F corresponding to the ranges:

Per cent ZnClz f 35 to 90 FeCla 5 to 35 NH4C1 5 to 30 Other metal halides may also be` present withtained about 70% zinc chloride, 25% ferric chloride (FeClaHzO), and 5% ammonium chloride. The ferrie chloride content of the ux, while .it may be as high as about 55%,; preferably should not exceed about 35%. Above 35% FeCla the flux gives of! brown -fumes that become especially pronounced at about 55%. If FeCia is increased above 55%, there results an increased viscosity and excessive volatilization of FeCla. It is dimcult to obtain consistent lead-l ing results when more than about 35% FeCls is used, the fluxusually becoming stiff, mushy and pasty which is not conducive to good leading. The minimum amount of ferrie chloride which may be satisfactorily used in the process contemplated by the present invention is critical andy depends somewhat upon the .temperature of the flux, less ferric chloride being required as the temperature increases. Thus, when the temperature of the flux bath is within the range of about 670 to 700'y F., at least about '8% ferrie chloride is necessary, whereas good results can be had with about l5% ferrie chloride when' the temperature of the bath is within the range of about 825 to 850 F;

Ammonium chloride preferably is used to the extent of at least about 5%, although satisfactory results have been obtained when the flux within the ltemperature range of about 630'I".

by conductionfrom the molten metal bath and A as the temperature of the flux rises above the boiling point of water, the water used in preparing the flux paste evaporates and the flux becomes molten on further heating. After the flux has reached the temperature of the metal bath, 'the articles to be coated are passed through the molten ux into the molten metal. Tubular articles must be introduced in such a manner that the flux ows through the interior and wets all parts of the inner surface. When this .is done -a satisfactory adherent lead coating of good covering power -is obtained regardless of the condition 'of the surface of the articles, i. e., whether the hot rolled finish has been removed by pickling or not. 'I'his is a new result of great f commercial importance since it makes it `possible to produce drawn products without the necessity of pickling or otherwise cleaning the metal blanks prior to the drawing operation.

For the purpose of acquainting those skilled in the art with the benefits and advantages of the present invention, the results obtained in leading 7732 inch hot rolledrounds of a nickelchromium-iron alloy under various fluxes are given in Table 1. This alloy which is sold under the trade mark Inconel contains about 79% nickel, about 13% chromium and the balance iron and minor constituents and impurities. In the hot rolled conditi-on, this alloy is covered :Vith a n,superficial dark brown to black oxide ayer.

Table I E Flux composition (weight percent) Leading x Cleaning treati 7gg ment Tem Tim Coating zncl, reci, Nmoi others FP g (ming Pickled 7l 5. 5 23.5 NaCl I700 5 Batisiector 71 5. 5 23.5 NaCl 700 5 No coatings.' 4 5-8 Satisfactory. 80 5 Do. 80 5 N o coating. 67 5-8 Satisfactory. 79. 5 5 Do. 79. 5 5 Do. 55 l0 D0. 55 10-15 D0. 6l. 5 5 Do. 6l. 5 10-15 D0. 73. 5 5 Do. 73. 5 11.5 CuCl 5 D0. 72. 8 18.2 NaCl, 9.0 CuCl- 5 Very poor.

was free from this salt. The eiect of ammonium chloride is to facilitate a clean separation of flux from the leaded article vwhen it is removed from the bath and to maintain the uidity of the flux bath. As ammonium chloride is increased above about 20%, there is a slight increase in thefuming tendency of the vbath and above about 40% there is excessive fuming of NH4C1, the flux becomes crusty and cakes at the surface of the lead bath.

In coating wires, bars, tubes and other shapes by the process of the present invention, a molin leading operations on a commercial scale. The

4 rounds of Examples Nos. 9 and 10 were very well covered with lead but the flux fumed considerably at the temperature employed. The flux used in Example No. 12 required a higher temperature to coat unpickled materialsl than the fiux of Example 6, for example. The flux of Examples Nos. 13 and 14 was much more viscous than the other fluxes and is less desirable inasten bath of soft metal such as lead is heated much as the higher viscosity made it dimcuit 'lwithout impairing its activity.

In Table II are summarized the results obtained in coating Inconel rods and tubes. These blanks had oxide coatings of various charac-V teristics, depending upon the prior treatment. Thus, rods and tubes in the hot rolled condition or which had been subjected to an oxidizing anneal were covered with an oxide coating having a brown to black cast. On the other hand, articles which had been subjected to a reducing anneal following hot rolling were covered with an oxide coating having a greenish hue. The

' rod of Example No. 15 had a inch diameter and the ux employed contained about 20% FeClz, 75% ZnCln and 5% NHaCAl. The tubes of Examples 16, 17 and 18 were 8 gauge, 2 inches in diameter and i1/ feet long and they were coated using a flux of the same composition as Examples 7 and 8.

to obtain perfect coatings on the vinsides of tubes showed no signs of injury. The tube was given l a second draw resulting in a further reduction in area of 30.5% without an intermediate anneal and celient drawing characteristics and the mandrely without further lead coating. Again .the tube had excellent drawing characteristics and the mandrel showed no sign of damage. After a total reduction in area of about 45.6%, close inspection of the inside and outside of the tube showed that the surface was unscratched and completely satisfactory.

'I'he tube of Example No. 17 was drawn in the same manner as Tube No. 16. 'I'he outside surface was completely satisfactory but there were some scoring marks on the inside of the tube due to the fact that the reaction time had not been quite sumcient completely to coat the inner surface of th'e tube. By employing a somewhat higher temperature, a'longer time, or both, this dimculty can largely be overcome.

'I'he tube of Example No. 18 was also drawn in thev same manner as Examples No. 16 and 17 and it also had excellent drawing characteristics and both the inside and outside surfaces of the drawn tube where excellent. a

An Inconel wire covered with a er was coated with lead in the same manner as t Table 11 Leading Example Oxide coat- Cleaning v N0. shape i115 treatment Temp" Time Cting F. (min.)

l5 Rod Green None.- d70-700 5-8 Satisfactory. 16 Tube l0..... Pickled... (Hl-700 5 Satisfactory on both surfaces. 17 .do do None Gal-700 10 Satisfactory outside, inside not entirely coated in this time.

18 ado Black d0 v 700 i0 Satisfactory on both surfaces.

It is more difficult t0 get a Satisfactory adher- 40 Example No. 8. It was then given a reduction in ent lead coating of good covering power on articles covered with a green oxide coating than on those having the black to brown oxide coating. The reaction between the flux and the green oxide coating is much more sluggish than the reaction with the brown to black oxide. Satisfactory. results in coating Inconel articles cov- -ered with the green oxide coating ordinarily can .be obtained by allowing a. longer time for the reaction to take place or by raising the temperature of the bath or both.

lTable III summarizes the results obtained in coating rods of an age hardenable nickel-copperalumin-um alloy sold under the trade mark K- Monel." These rods were given no cleaning treatment following hot rolling and the surfaces therefore were covered with a layer of oxide h'aving a blue-black to black cast.

Table m Articles coated with lead by the process embodying thel present invention lend lthemselves readily to drawing operations.

The lead coated tube of Example No. 16, for exl ample, was given a ilrst draw resulting in au'eduction in area of about 32%. The tube had excharacteristics.

area of about 52.3% in 2 passes through a wire drawing die. The wire had excellent drawing Thereafter it was subjected to a second draw resulting in about 98.7% reduction in area in 6 passes, without intermediate anneal and without recoating with lead. Minute inspection after the second draw showed that the surface was very smooth and uniform and the results were highly satisfactory,

The new flux has given remarkable improvement in the drawing characteristics of certain iron-nickel-chromium alloys of the Elinvar type which require heavy cold reduction in order to produce substantially constant modulus of elasticity. In prior art practice in which a flux corresponding substantially to that used in Example No. 1 was used, it was necessary to carry out the drawing in 2 steps of three passes, each separated by an intermediate anneal followed by releading. When the new flux was used, vthe material was drawn to iinished siZe with 93.5% reduction in black oxide layarea in 7 passes without intermediate anneal and Without releading.

The leading coating process of the present invention, as will be clear from the foregoing specic examples, can be carried out on metal articles that have been cleaned by pickling or otherwise to' remove the oxide or other surface article of manufacture is depicted schematically in'Fig. 2, in whichl the vthicknesses of the lead coating and the oxide layer have been exaggerated for purposes of illustration. Fig. 3 is a reproduction of a 'photograph taken of a lshort section of a 2 inchfK-Monel tube which had been coated .in accordance' with the present invention with'out removal of the oxide surface which was formed during the conventional process of manufacturing the tube. 'I'he zone at the left shows lead coating had been removed with dilute nitric acid. The zone at the right shows the'foundation or'base metal after pickling off the Aoxide layer. oxide layer which kin turn adhered very strongly to the base metal. s

. Fig'. 4 is a reproduction of a photograph of a l1%4 inch Inconel tube which had been coated Vthe tube in the as leaded condition. I'he` dark middle zone shows the black oxide layer after the.V

'I'he lead coating was very adherent to the without pickling in accordance with the process of the present invention and then drawn to effect 45.6% reduction in area in two passes. The zone at the left shows the lead coating which is still were excellent despite the presence of the oxide layer under the lead.

While the mechanism of the action of the new v flux is not thoroughly understood, it is believed that when articles which have snot been cleaned or pickled are introduced into the new flux, a re-l action takes place between theux and the oxide layer. This reaction apparently does not completely remove the oxide coating from the surface of the article because articles which have l* been satisfactorily coated and drawn and from which the lead has been removed by deleading' in Y dilute nitric acid still have an adherent coating of oxide, as may be seen in Fig; 4. It may be that .the oxide layer is penetrated by the flux to provide al plurality of tenacles oflead on the under side of the coating extending into contact withuA the base metal itself but definite evidence in support of this theory is lacking. Whatever the mechanism of the reaction may be, the results of the reaction based upon a large number of experiments have been found to produce a Very definite improvement in the lead coating obtained and in the drawing characteristics of the coated article, as compared with prior art practice, particularly where the material was not cleaned or pickled prior to the leading operation.

Ferrie fluoride may be used to replace ferric chloride either in whole or in part in the flux embodyingthe present invention. Experiments made with FeFs indicate that this compound is less reactive than FeCl3 since a longer leading time is requiredunder comparable conditions to get equivalent results. Itl also has a higher melting point and is more expensive than ferric chloride. The following are typical examples of satisfactory fluxes in which FeFs was used instead of FeCls:

fmetal layer, an adherent oxide layer and an adherent lead coating. The structure of this new' FEF: ZnCl: NHO] Per cent Per cent Per cent Although the present invention has been de` scribed in connection with lcertainspeciflc mbodiments, it `is to be clearly understood that these examples have lbeen given by way of 'illustration and not by way of limitation. Modifications and variations in the flux composition and Vleading practice are possible, as those skilled in the art` will readily understand, and are contemplated as being within the vscope of the present invention, as def-ined in the appended claims.

I claim:

1. A lead coating bath characterized by 4the Y Y 60% of the total composition of the ilux.

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2. A ilux adapted for preparing metal articles for an adherent lead coating which comprises about 5% to 35% .of ferric chloride, about 5% of ammonium chloride, and the balance substantially all zinc chloride;

3. A metal halide fiuxfor use as a molten covgroup consisting of alkali metal and ammonium halides.

4; A lead coating flux consisting ,essentially of zinc chloride, ferric chloride and ammonium chloride, being present in proportions bounded by the curve F G H I F of the drawings.

5. A lead coating flux consisting of zinc chloride 79.5%, ferric chloride 15%, and ammonium chloride 5.5%.

Y 6. A lead coating ilux consisting of zinc chloride 67%, sodium chloride 17%, and ferric chloride 16%.

7. A lead coating flux consisting of zinc chloride 70%, ferric chloride 25%, and ammonium chloride 5%.

8. The method of lead coating articles made of nickel and nickel alloys without cleaning and removal of the hot rolled oxide surface, compris-

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