US2573883A - Metal coating process and oil finishing composition therefor - Google Patents

Description

Patented Nov. 6, 1951 METAL COATING PROCESS AND OIL FINISH- ING COMPOSITION THEREFOR George W. Waters, Wood River, 111., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application April 12, 1947, Serial No. 741,002

17 Claims.

This invention relates to metal coating or alloying of metals. More particularly this invention pertains to oil compositions used in tinning, terne coating, lead coating, and the like, in order to facilitate and aid in coating or alloying a base metal with a uniform and tenacious metal coating.

This process, for example, the tinning process comprises essentially coating base metals by dipping and the like said metals into a bathof molten tin thereby coating the base metal with a thin film of metallic tin. .The tinning process is carried out at elevated temperatures and when skillfully done with the aid of good fluxing agents and proper tinning oils actually forms an alloy of tin and the metal being treated which is generally iron, steel and other ferrous metals.

To insure strong adherence of the tin to the metal surface being coated, the metal must be absolutely cleaii and free of any grease, dirt, oxide film and rust. This is necessary to insure intimate contact of the metal with the molten tin, terne composition and the like. Metals which are to be coated with tin and the like are therefore carefully prepared by being properly mechanically and chemically treated, pickled and kept in slightly acidic solution in order to prevent oxidation of the metal surface prior to entering the tinning bath or the like.

Briefly stated, for example, one method of tin coating of base metals comprises dipping or passing a properly cleaned metal into a bath of molten tin, on to an oil bath and then through cleaners toremove excess oil and polish the tinned metal surface. The general procedure is to pass a mildly pickled metal plate from a slightly acidified storage tank into a tin pot usually divided into a series of compartments. Each compartment contains a series of rollers through which the metal can pass during its various stages of tin coating. The molten tin occupies the lower or bottom part of the tin pot. On the feed end of the pot floats a layer of flux and on the exit end floats a much deeper layer of oil.

The flux serves to give final preparation of the metal surface before being immersed into the molten tin. It consists generally of zinc chloride or mixtures of zinc chloride and sodium chloride or ferric chloride or ammonium chloride and the like. The function or purpose of the flux is' to clean thoroughly the metal surface, remove moisture, absorb any oxide film, pickling scum and control more or less the wettability'of the metal by the tin'so that the molten tin would react and adhere uniformly and tenaciouslyto the metal surface treated. a

From the fluxing bath the metal proceeds on through a series of rollers through a molten tin bath kept at a temperature of between about 525 F. to above about 750 F. depending upon the operating conditions. The tinned metal then proceeds through an oil bath while passing through rollers where excess tin is removed, better distribution of the tin coating is secured and oxidation of the tin is inhibited. The tinned metal having a thin film of oil on it proceeds on out of the oil bath and receives a, cleaning treatment where excess oil is removed. Any remaining oil left on the metal aids in polishing the metal to a desired surface finish.

Articles of odd shape can be tin coated by mechanical or hand dipping into a flux coated tin pot and then redipped into an oil coated tin pot which on withdrawal comes in contact with the oil and receives its beneficial treatment. If desired the metal can then be immersed into a hot oil bath for final oil treatment in order to more closely control the thickness of the tin coating and also such oil treatments act to some degree as a quenching medium.

Tinning oils play a vital role in the tinplating art for they serve to secure better distribution of tin on the basemetal being coated,.aid in removal of excess tin and protect the tin from oxidation or discoloration while being cooled. To accomplish these and other features a good tinning oil must be capable of adsorbing oxides so as to keepthe metal surface clean; it must have a suitable interfacial tension with molten tin and with the atmosphere and it must be stable and not tend to deteriorate or polymerize even after longperiods of use under extremely high temperatures. Efficient tinning oils should in addition form a uniform film on the coated metal surface while in the tin pot but on immersing from the pot drain ofi easily and quickly. Oils which do not drain off easily must be continuously replaced which is quite an expense. Such oils alsotend to form globules or isolated patches on the tinned surface which produce depressions on the tin coating, resulting in localities which are very thin and which form grease marks on the tinned surface.

One main criterion of a good tinning oil as stated above is its ability to drain off rapidly from the tinned article as it emerges from the hot oil bath. From this aspect. straight mineral oils and even palm oil after relatively short periods of use are not satisfactory. This desirable phenomenon of rapid draining seems to be associated with the presence of certain polar bodies in the oil. An oil containing a plurality of these polar bodies drains off rapidly and leaves the tinned surfaces clean and bright. It is assumed that such on films tend to form one or more aggregates which move continuously over the surface in an apparently random fashion. As the activity of the aggregates becomes reduced owing to reduction of these polar bodies, the draining rate of the oil is reduced and-eventually a continuous film state is reached "where the draining properties of oils are considerably tretarded and the oil is no longer suitable .for

use. It is postulated that the efficiency "of such oils is due to the formation of .a monomolecular absorbed layer over the surface of the tin.

Generally oils used in tinplating are subjected to elevate temperatures of at least 60" and higher for long intervals. It is therefore essential that such oils be chemically stable at such temperature, without undue volatilization, decomposition or polymerization.

Palm oil is known to be an efficient tinning oil.

However, it has .several serious drawbacks in that it is costly, difficult to obtain and above all polymerizes readily at temperatures above 470 resulting in sludging and high -oil losses. Also .other beneficial tinplate properties of palm oil are destroyed at temperatures above 470 F. At this elevated temperature palm oils leave on the tinplate streaks of oil resulting .in a dull, lustreless coated surface. Other known tinning oils such as hydrogenated cottonseed oil present even more difilcult tinningoil problems than palm oil and generally are not as efiicient.

It is an object of this invention :to produce an excellent tinning oil having a petroleum hydrocarbon -base. Another objectof this invention is to produce a new and improved tinningoi'l which is stable .at extremelyhigh temperatures for long periods of time. Another objectof this invention is to produce a new and improved tinning oil having .the ability to take up oxide, to readily absorb flux residue and to promote the spreading of tin and other molten metals. Still another object of this invention is to produce a tinning oil which does notstain or have bad efi'ects on the coated surface if left on. Furthermore, it is another object of this invention to produce a tin- .ningoil which d-rainsand cleans easily and which .is not a fire hazard.

The above and other objects may be attained in accordance with the present invention by admixing with a mineral .oil base a suitable amount of partially hydrogenated high molecular weight fish and/or marine oil .distillates. The amount of partially hydrogenated high molecular weight fish and/or marine oilcdistillates which can be added to a mineral oil base should be .suificient to maintain the acid number .of the tinning oil composition at not less than 3 and .not above about 15, and preferably between about 4 to 10. In order to maintain the acid number of the composition at these values, a replenishing agent or fish oil stearine pitches.

can be added to the oil at determined intervals.

adjust the .acid number of the .base composition to not less than 3 and not above about 15.

The partially hydrogenated fish and/or marine oil distillates .and their :mixtures can be obtained from codfish oil, codliver oil, vdogiish oil, dolphin body oil, dolphin fish oil, herring oil, Jap fish oil, menhaden oil, porpoise body and jaw oils, salmon oil, sardine and sardine liver oils, seal oils, shark and shark liver oils, sperm whale body and head oils, whale oil and the like.

The fish and/or marine oildistillate products of this invention, can be removed from such oils by a conventional means and then hydrogenated or the oils can be hydrogenated first and the product then split and the overhead distillate fraction .removed by distillation, extraction and the like. For example a fish oil such as herring oil, menhaden oil and the like, can be hydrogenated and split and subsequently distilled to produce .an overhead distillate of hydrogenated fish oil. The residue product is generally referred to in the trade as fatty acid residuum products The pitch can be further split, subjected to distillation, the overhead distillation fraction recovered, hydrogenated and combined with the first overhead distillate product and used as additive products in this invention. Another method of producing the desired distillate fractions is to split the oil first, remove the distillate fraction and then hydrogenate it preferably in'the "presence of a suitable catalyst and at elevated temperatures.

The overhead distillate product obtained from fish and/or marine oils and their mixtures which are used as the additives for tinning oils of this invention are not to be confused withithe residue product generally referred to as stearine pitches or residuum products. The two materials are entirely separate and distinct and the stearine pitches are not contemplated for use in this invention since test results indicate, as will be hereinafter shown, that they are inferior to the distillate fractions as tinning oil additives.

The mineral oil base used can be any suitable refined petroleum hydrocarbon stockhaving high flash and fire points and which are substantially stable 'at tinning temperatures of between about eon-490 F. Suitable petroleum hydrocarbon base stocks which-can be used are solvent extracted Mid-Continent Bright stock, acid treated Mid-Continent Bright stock, acid treated naphthenic neutral stock and blends of these oil stocks. Preferably however solvent extracted Mid-Continent Bright stock having .a Saybolt Universal viscosity at 210 F. of -170 is used as the oil base stock because of the superior tinplating results obtained when using this type of To more fully and clearly illustrate this invention a series of identical and parallel comparative tinning tests were conducted in which the tinning performance as to flux removal, drainage characteristic, ease ofcleaning and spreadability characteristics of mineral oil, palm oil, mixture of palm .oil and mineral oil, a composition comprising a mixture of mineral oil and hydrogenated fish oil residuum or stearine pitches and a mixture of mineral oil with hydrogenated fish and/or marine oil distillate products were compared.

One test was conducted as follows:

A. Bickled sheets of black plate, stored in 0.5

;-percent H01. were dipped in flux (3 pounds .-..ZnClz plus 5 ounces NH4C1 per gallon) and tinned "at temperatures between about 530-560 F., and preferably at 550 F. The tinning pot surface was covered with flux. Sheets were tinned so that very little, if any, flux adhered to the sheets upon withdrawal. Immediately after withdrawal, thesheets were transferred to a finishing pot f'containing tin at 530-545" F. and a superimposed layer of oil at 460-490 F. and preferably at 470 The relatively high temperature was necessary to maintain the desired oil temperature. Here the sheets were immersed inthe tin and then drained in the oil layer. Metal strips tested were given a tinning and oil treatment at regular intervals and the test was conducted for a period of 72 hours. The properties as indicated in Table I were graded in descending order, (l)v "kept at "a temperature of 460-475" F. 'To'simulate the oil-tin interface encountered in tinplate manufacture, a small amount of tin was poured into the bottom of the oil pot; Tests were conducted for a '72 hour period with the same compositions as indicated inJTable I and the results were substantially the same as indicated in oil pot and the flux and oil tested put in the feed and end or exit compartments of the machine respectively. The oil temperature was kept in hour interval and the tinning performance of the oils as to flux removal, draining characteristics, ease of cleaning and spreading characterbein he s (2) n x t, c. The r sults of 2 istics were noted. The results again were similar the test were as follows: to those disclosed in Table 1, showing the su- TABLEI [The rating as here given is an arbitrary figure which is based on the figure'l as being excellent and as being unsuitable for tin coating and the like] Draining Spreading Code No. Flux Removal Characteristics Ease of Cleaning Characteristics Total Remarks 1 10. Poor flux re- 10.Streaked badly. i0. Flux spots, 10. Stained, Strip- 40 Mineral alone was found totally unmoval. Stained, sticky ped, Heavy tinsuitable. At the end of 24 hours and ditiicult to ned. sludge formations were high and clean. losses heavy so that testhad to be discontinued. 2 3. Showed good 5. Good drawing 4. Easy but flux 3. Good at early Although the tinning characteristics of v flux removal for characteristics spots noted. stage but spanpalm oil were good for 24 hours, oil 72 hour test. for early part of. gle about 24 losses were. heavy at the end of the hrs. 72 hour test.

3, Palm 6 8. Poor through- 8. Easy to remove 7. Stained 29 After 24 hours the tin plate was stained oilinminout test period. but flux spots and Spangled. Stripping was noted l il, noted. and drainingwas poor throughout test.

I p At the end of 24 hours test was discontinued.

do. 8. Good draining 4. Fair 21 Fluxremoval and spreading were good. early period of Draining and cleaning were poor and test but became became increasingly worse.

' worselater.

3. Good for 48 3. Same 2. Good 10 Fluxremovaland spreading were good. hours, but at Exhibited a pronounced stabilizing and of test peefieot on the composition and gave riod SihOWOd good tinning performance at the end signs of poor of 48 hours and fair tinning performming. ance at the end of 72 hours. Oil losses were only t5; of that of palm oil after 72 hrs.

Code No. 1-Mineral Code No. 2Palm oil. Code N 0. 32050% by wt. of palm oil in mineral oil base.

oil (Solvent extracted Mid-Continent oil (150-170 BUS at 210 F.)).

Code No. 4-Mixture of hydrogenated fish oil residuum or stearine pitches in mineral oil having an acid number of 3 to 15. Code N o. 5Mixture of hydrogenated fish oil distillates in mineral oil having an acid value of 3 to 15. 1

7 .3. Another test was conducted in which the tinning technic was slightly modified. Two tinning pots were used as before, and the tempera- "ture of the first tin pot was kept at 535 F. and the final pot at 4'75- F. Instead of the oil layer on the second pot, a small amount of tallow just sufficient to form a ring covering the bath edges was used to keep the surface clean. Im-

TABLE II periority of mineral oil-hydrogenated fish oil 'distillates over other oils tested as tinning oil.

number of mineral oil-hydrogenated fish'oil distillates between about 3 to 15. The following results were obtained.

Comparative rating as to the following characteristics.

Draining Spreading Flux Re- Ease of Agent Charac- Charac- Total Remarks mwal teristlcs Cleaning teristics 1 Mineral oil-hydrogenated fish oil distillates having an 8 I 7 6 30 Drained very poorly and unacid number less than 3. V stable.

2 .Mineral oil-hydrogenated fish oil distillates having an 3 6 7 p 4 20 Cause etching of metal surface acid number greater than 15. and diflicult to clean.

3 Mineral oil-hydrogenated fish 011 distillates having an 2 3 3 2 10 Good spreading characteristics acid number between about 4-10. vand stable.

d t'lllheigating as here given is an arbitrary figure which is based on the figure 1 as being excellent-audio as being unsuitable for tin coating an e e. v ,7

-mediately upon withdrawal of the sheet from ,the second pot,

as has beenrepeatedly polntedout the acid it was-transferred to an oilpot .number of tinning oil compositionof thisinvention must be kept at not less tha'n.3 and not over 15. Since compositions of this invention are modified due to the elevated: temperature at 'which they are maintained, readjustment of the acid value within the desired limit must be made at certain intervals. This is done by replenishing the composition with a concentrate comprising approximately 50% by weight mineral oil and 50% by weight partially hydrogenated fish oil distillates in amount sufficient to maintain the acid number of the composition between about 3 to 15, and preferably 4.to 10. By replenishing composition of this invention with'the above concentrate such tinning oils can be used with excellent results for many months.

The amount of partially hydrogenated fish and/or marine oil distillates added'to a mineral f'trolytic means is greatly improved by dipping such metal treated. surfaces. into a hot bath it an" peatedly dipped in the various oils during a 24 hour interval and the characteristics of the oil film remaining on the plate were preserved by printing oil on a hard filter paper and observations made.

TABLE III Composition Observations and Remarks 1 Mineral Oil "l Drained poorly throughout 7 test period. Filter paperggvered with a heavy oil 7 m.

2 by wt. of Palm Oil in min- Drained poorly, paper covineral oil. ered with an oil film.

3 Mineral oil-hydrogenated fish oil Do.

distillates having an acid number less than 3.

4 Palm Oil Drained very well, few oil spots on paper. 5 Mineral oil-hydrogenatedfish oil Equal to, if not superior to,

distillates having an acid numpalm oil in draining charber between 3 and 15. acteristics.

minor amounts of high molecular'fatty acids such as oleic, stearic and. the like can be added to compositions of this invention to improvethe lustre of the tinplate, and spreadability ofthe tinning composition. Also'animal and vegetable oils such as cocoanut oil, castor oil, cotton- 2 seed oil, peanut oil and the like as well as synthetic lubricants produced by polymerizationof olefins can be admixed with compositionv of this invention.

Compositions of this invention are not re-' stricted to use in tinplating only butare equally applicable for terne coating, lead coating and the like. Neither are these compositions restricted to use where metal plating is done only by dipping and the like. Compositions of this invencomprising. an oil composition of this invention.

In. addition to being equal to and in most properties superior to palm oil, compositions of this invention have a particular advantage over palm oil in that they reduce to a minimum the danger of Tim hazard.

' It is to be understood thatwhile the features of the invention have been described and illustrated in connection withfspecific compositions, the invention isnot to be limit'ed thereto or otherwise restricted exceptby the prior art and the scope of the appended claims.

I claim as my invention:

1. A method of coating ferrous metal which includes cleaning and pickling said metal, passing the metal through a'fiux bath consisting essentially of a zinc chloride amrnonium chloride solution; followed by passing the metal into a molten tin loath maintained at a temperature between about 530-560 F. and finally passing said tin treated metal through an oil composition maintained at a temperature between about 460-490 F. consisting essentially of a mixture of mineral oil and partially hydrogenated fish oil distillates,

said oil mixture having an acid number of not less. than 3 and not more than about 15.

2. A method of coating ferrous metal which includes cleaning and pickling said metal, passing the metal through a flux bath consisting essentially of a zinc chloride-ammonium chloride solution,- followed by passing the metal into a molten tin bath'maintained at a temperature between about 5302560" F. and finally passing said tin treated metal through an oil composition, maintained at a temperature between about 460-490 F., consisting essentially of, a mixture of mineral oil and partially hydrogenated fish oil distillates,

tion can be used to improvethe metalcoating---- surface and deposition of metalson metal base by electrolytic methods as well as any other known metal plating method. The appearance of surfaces having tin deposited thereon by elecsaid oil mixture being replenished at desired intervals with a concentrate comprising approximately a 50-50 mixture of hydrogenated fish oil distillates-mineral'oil, in amounts sufiicient to maintain the acid number of said oil composition between about 3 to 15.

3. A method of coating ferrous metal which includes cleaning and pickling said metal, passing the metal through a flux bath consistingessentially of a zinc chloride-ammonium chloride solu tion, followed by passing the metal into a molten tin bat-h maintained at an elevated temperature and finallypassingsaid tin treated metal through an oil composition, maintained at an elevated temperature, consisting essentially of a mixture i of mineral oil and partially hydrogenatedfish oil desired intervals with a concentrate comprising approximately a 50-50 mixture of hydrogenated fish oil-'distillates-mineral oil, in amounts sufiicient to maintain the acid number of said oil composition between about 3 to 15.

4. A method of coating ferrous metal which includes cleaning and pickling said metal, passing the metal through a flux bath, on through a molten metal bath selected from the class con sisting of molten tin, tin-lead alloy and lead and finally passing said metal through an oil composition, maintained at an elevated temperature,

.consistinghessentially of ,a blend of mineral oil and partially hydrogenated marine oil distillates,

said oil -blend having an acid number of not less than 3 and not more 'than'about passing said metal through an oil composition,

maintained at an elevated temperature, consisting essentially of a blend of. mineral oil and partially hydrogenated fish oil distillates, said oil blend having an acid number of not less than 3 and not more than about 15. V '7. A method of coating ferrous metal which includes cleaning and pickling said metal passing the metal through a flux bath, on through a molten metal bath of lead and finally passing said metal through an oil composition, maintained at an elevated temperature, consisting essentially of a blend of mineral oil and partially hydrogenated fish oil distillates, said oil blend having an acid number of not less than 3 and not more than about 15.

8. A mineral oil composition suitable for aiding the formation of an adherent metal coating on another metal, consisting essentially of a mixture of a mineral oil and a hydrogenated fatty oil distillate, said blend having an acid number of between about 3 to 15. I

9. A mineral oil composition suitable for aiding in the formation of an adherent metal coating on the surface of an article of another metal, consisting essentially of amixtureof a mineral oil and a hydrogenated marine oil distillate, said blend having an acid number of between about I 3 and 15.

10. A mineral oil composition suitable for aiding in the formation of an adherent metal coating on the surface of an article of another metal, consisting of a mixture of a mineral oil and a hydrogenated marine oil distillate, said blend having an acid number of between about 3 and 15.

11. A mineral oil composition suitable for aiding in the formation of an adherent metal coating on the surface of an article of another metal, consisting of a mixture of 2% to 20% of a hydrogenated marine oil distillate and the balance mineral oil.

12. A soap-free, non-emulsifiable mineral oil composition suitable for aiding in the formation of an adherent metal coating on the surface of an article of another metal, consisting of a mixture of from 5% to 15% of a hydrogenated marine oil distillate and the balance mineral oil.

13. A mineral oil composition suitable for aiding in the formation of an adherent metal coating on the surface of an article of another metal, consisting of a mixture of a mineral oil and a hydrogenated fish oil distillate, said blend having an acid number of between 3 and 15.

14. A mineral oil composition suitable for aiding in the formation of an adherent metal coating on the surface of an article of another metal, consisting of a mixture of 2% to 20% of a hydrogenated fish oil distillate and the balance mineral oil.

15. A soap-free, non-emulsifiable mineral oil composition suitable for aiding in the formation of an adherent metal coatin on the surface of an article of another metal, consisting of a mixture of from 5% to 15% of a hydrogenated fish oil distillate and the balance mineral oil.

16. A mineral oil composition suitable for aiding in the formation of an adherent metal coat ing on the surface of an article of another metal, consisting of a, mixture of 2% to 20% of a hydrogenated fatty oil distillate and th balance mineral oil.

17. A method of coating ferrous metal which includes cleaning and pickling said metal, passing the metal through a fiux bath on through a molten metal bath selected from the group consisting of tin, tin-lead alloy and lead and finally passing said metal through an oil composition, maintained at an elevated temperature, consisting essentially of a mineral oil and a hydrogenated fatty oil distillate, said oil blend having an acid number of not less than 3 and not more than about 15.

' GEORGE W. WATERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 2,356,863 MacLaren et a1. Aug. 29, 1944

Claims (2)

1. A METHOD OF COATING FERROUS METAL WHICH INCLUDES CLEANING AND PICKLING SAID METAL, PASSING THE METAL THROUGH A FLUX BATH CONSISTING ESSENTIALLY OF A ZINC CHLORIDE-AMMONIUM CHLORIDE SOLUTION, FOLLOWED BY PASSING THE METAL INTO A MOLTEN TIN BATH MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 530*-560* F. AND FINALLY PASSING SAID TIN TREATED METAL THROUGH AN OIL COMPOSITION MAINTAINED AT A TEMPERATURE BETWEEN ABOUT 460*-490* F. CONSISTING ESSENTIALLY OF A MIXTURE OF MINERAL OIL AND PARTIALLY HYDROGENATED FISH OIL DISTILLATES, SAID OIL MIXTURE HAVING AN ACID NUMBER OF NOT LESS THAN 3 AND NOT MORE THAN ABOUT 15.

8. A MINERAL OIL COMPOSITION SUITABLE FOR AIDING THE FORMATION OF AN ADHERENT METAL COATING ON ANOTHER METAL, CONSISTING ESSENTIALLY OF A MIXTURE OF A MINERAL OIL AND A HYDROGENATED FATTY OIL DISTILLATE, SAID BLEND HAVING AN ACID NUMBER OF BETWEEN ABOUT 3 TO 15.