CA1045005A - Process for manufacturing a two-piece steel can - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed is an improved process for manufacturing a tin-free, two-piece steel can. In accordance with the defined coating composition, and then drawn and ironed by one or more stages to effect reduction of at least 20% in the cross section of the side wall. The coating composition is organic phase and contains the reaction product obtained by combining a multivalent metal cation, a polyphosphoric acid and a fatty alcohol. The composition additionally contains an organic lubricant and a small quantity of water.
This process makes possible the production of two-piece steel cans in a much simpler and less costly manner than has hereto-fore been possible.

Description

S.~45~5 This invention relates to the art of manufacturing two- ,' piece steel cans. Steel is a much preferred material for can manu-facture as compared to aluminum in vieW of its lower raw material ~-cost~ However, serious problems have been encountered in the past ' '' when attempting to apply two-piece aluminum can manufacturing ~ methods to steel can manufacture.
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Cans manufactured by modern industry are generally one v of three types. Oldest is the three-piece can which is manufac- ', tured,in three pieces: top, body and bottom. The body or side wall is roll formed and the seam soldered or glued. The bottom and top are separately manufactured and attached to the body of ' , the can by crimping.
The use of the previously-mentioned two-piece aluminum cans has become quite widespread. These cans are manufactured by ~;,; ' first forming a cup from a suitably sized aluminum blank. The cup is then subjected to one or more ironing stages in order to stretch and thin out the body of the cup to form a unitary and seamless can body and bottom. The top is separately manufactured ',' and attached as in tin-can manufacture. The advantages of this '`~ ' process over that of the three-piece can reside primarily in elim- r'- :, ination of a number of steps in the manufacturing process. Further , , since the can is manufactured in two pieces, the chance of struc- ,;
tural failure is considerably reduced. '.
The third type of can, with which the present invention ',, is concerned, is the two-piece steel can. Attempts to apply the knowledge obtained in developing the process for manufacturing --' the two-piece aluminum can met with little success. This lack ' ,~
of success may be attributed primarily to the difference in mal- ,,-' leability of steel as compared to aluminu~. While only minimal lubricant was necessary in order to successfully cup and iron , aluminum can bodies, very complicated methods were required for ,r drawing two-piece steel cans. ~ '' - 1 _ r~

~s~s One method found technically acceptable for drawing steel can bodies requires the application of a phosphate coating and lubricant to the surface prior to each drawing and/or iron-ing stage. In addition, it is necessary to remove these layers after each drawing stage to obtain effective reapplication of the coatings. The use of a lubricant alone (without pretreatment to form a phosphate coating) does not provide sufficient lubricating power for steel. The expense and complication of this process has prevented two-piece steel cans from competing effectively with two-piece aluminum cans. In one modification of this known technique, the steel surface is coated with a thin layer of tin which serves to eliminate the phosphatizing steps in the first `
two stages of the can manufacture. Tin, however, has become a very expensive raw material and, as a result, steel cans manu-factured by this method have also been found too expensive to com-pete with aluminum cans.
In accordance with the present invention, two-piece --steel cans are manufactured without galling of the ca'n surfaces or dies by a simplified and less costly process. Steel strip sheet or blanks are contacted with a coating composition contain-ing a) from 5 to 60 weight % of the reac-tion product obtained by contacting a salt of a multivalent metal cation, a polyphosphoric acid, and an alcohol of 10 to 36 carbon atoms in a weight ratio of metallic cations: P2O~ equivalent: alcohol oE 1:3-60:14-510, b) from 30 to 94 weight % of an organic lubricant of at least 12 carbon atoms and c) from 0.5 to 10 weight % water. Except in cases of very extreme drawing, application of the coating composition prior to the cupping procedure will provide sufficient lubricating qualities so that no further lubrication need be applied even during the subsequent ironing steps in which the cup is drawn to its full extent.
Examples of suitable organic lubricants are the hydro-:: . . . .
-~ 10~51~S
carbon oils, fatty acids, naturally occurring animal and vege-table oils and the alcohol, ester and amine derivatives of the ., ~., .
foregoing. Preferred organic lubr:icants are the mineral oils, oleic acid and oleyl amine. The viscosity of the mineral oil should be between 2.4 and 15 Engler (50C). The fatty acids and animal and vegetable oils should have from 8-22 carbon atoms. The organic lubricant is preferably present in a concentration of 64 -89 weight %.
The water content of the composition is very critical. -- -While a small amount of water has been found necessary to catalyze and accelerate the reaction of the phosphate with the metallic surface, an excess of water results in an undue instability of the composition. If the composition becomes unstable and separates -into two phases, little reaction occurs probably because the phos- -phate components are removed from effective contact with the metal surface by virtue of their solubility in the water phase. Desired water concentration may be maintained either by separate addition or via the water content normally present in the other components employed in the composition. Excellent lubricating results are ~`
obtained while maintaining acceptable stability when the water content is maintained below 7% and even more preferably between about 1 and 2%. Higher water concentrations may necessitate in-cluding surfactnts in the composition to maintain,phase stabili-ty.
The third essential component of the coating composition is a product obtained by combining three specified reactants. The first reactant is a salt of a multivalent metal cation. A pre-ferred multivalent metal is iron. Other suitable cations include zinc, manganese, molybdenum, tungsten, aluminum, lead, magnesium and calcium. The cation is preferably added as the phosphate salt ;

although other salts such as sulfate, nitrate and halides may be employed. The second reactant is a polyphosphoric acid which is :, - 3 - ~

~s~os preferably 76 to 85 weight % P20S. The third reactant is an al-cohol of 10 to 36 carbon atoms and is preferably an alkyl or alkyl aryl alcohol. Most preferably, the alcohol comprises a fatty alcohol of about 18 carbon atoms such as oleyl alcohol.
Natural alcohols such as wool fat alcohol are also suitable. The reaction product obtained by combining the foregoing reactants should be present in the composition in an amount of 5 to 60 weight % and preferably in an amount of 10 to 35 weight /0.
In order to obtain the desired reaction product, the multivalent metal salt may conventionally be dissolved in the polyphosphoric acid. This reaction results in an exothermic heat of solution. Thereafter, the aforementioned solution is combined with the alcohol and maintained at a temperature of at least 50C and up to 150C or higher for a period~of at least 30 minutes. Preferably, the temperature is at least 60C and most preferably at least 70C. Higher temperatures speed the rate of reaction between the alcohol, the polyphosphoric acid, and the multivalent metal cation.
The reactants should be combined for reaction purposes in a weight ratio of metallic cation: P205 equivalent: alcohol of 1:3-60:14-150. On a mole basis, the corresponding ratios are about 1:1.5-15:3-300 Depending on the viscosity of the organic lubricant em- -ployed, the coating composition may vary from very fluid to pasty in consistency.
Application of the lubricant coating to the metallic surface may be accomplished in any conventional manner. In the dip technique, the composition is maintained at a temperature of from ambient to 100C or higher and the workpiece is immersed in the composition for a period of at least one minute. Prefer-ably a temperature of at least 37C is employed. The contact time will depend upon the concentrations of the reactants, the tempera-~450C)~;
ture of the composition, as well as the thickness of the deposit desired. Normally, contact periods in excess of 60 minutes are unnecessary. Best results have generally been obtained when the -weight of the deposit obtained is between 0.5 and 10 grams per square meter (about 2 - 10 minutes contact time). The composition may also be employed using other conventional techniques such as flooding, wiping, spraying or rolling. Ambient temperatures are suitable if longer contact times are employed. Of course, if it is desired to employ the composition primarily for its lubricat- -ing rather than reactive properties, contact times of less than one second may be employed.
Maintaining the water content at the desired level is critical to the stability of the coating composition. One means for controlling this concentration is to maintain the bath at an elevated temperature such that the rate of water evaporation equal the rate at which water is dragged into the bath on the surface of wet workpieces. `~;
It has been found possible to apply the lubricant to the original coil, or after blanking or prior to any drawing stage. Application of the lubricant-to the coil, e.g., at the steel mill, is particularly advantageous because rusting of the coil is inhibited and yet the dried coil may be cupped at a later time without providing further lubrication. However, where de-sired, the lubricant may be reapplied between stages or may be employed as a drawing lubricant at the die. If desired, a differ-ent but compatible lubricant (e.g., aqueous phase) may be employed at the die.
Since steel cans must be lacquered for health reasons, standard procedure has been to apply a conversion coating to the interior surface after formation of the can iq completed in order to improve paint adhesion. This has been necessary even where tin has been employed to avoid the need for conversion coatings ~;, .. .. . . ... .

104S~ S
prior to forming. On the other hand, the reactive lubricant of this invention provides a coating which, even after drawing, will impart acceptable adhesion characteristics as a paint-base.
In the examples, the followiny raw materials were employed:
ADOL 66 Trademark of Ashland Chemical Co.
for isostearyl alcohol ~mixture of 18 carbon methyl isomers) Iodine value = 12, Cloud point 8C

CARNEA 21 Trademark of Shell Oil Co. for ;-mineral oils of low pour point.
Viscosity 105 SSU at 38 SSU at 210F
Flash 325F
Pour -30F
Specific Gravity 0.915 VALVATA 85 Trademar~ of Shell Oil Co. for mineral oils of high viscosity.

Viscosity 4450 SSU at 210 SSU at Flash 580F
Pour 10F-KEMAMINE P989 Trademark of Humko Sheffield Chemical Co. for oleyl amine (94% primary) `
Polyphosphoric Technical grade, 85% P2~5 equivalent, specific gravity 2.05 ~-~
at 20C. ;
Technical Iron '~

r\ ;:

~ soo~ ` :
Phosphate Technical Grade :

Approx. 17 wt. % Fe+ .

Appro~.. 13 ~t. % Fe+

Approx. 33.5 wt.% Po4 EXAMPLE 1 . .

Two formulations embodying the Reactive Lubricant of ... ~:

the present invention were prepared as follows: ` :
:' :
Formulation - Wt. %
A B ~
Polyphosphoric Acid14.5 8.8 . ::.
Technical Iron Phosphate .9 1.0 .
ADOL 66 13.5 14.~
CARNEA 21 38.6 40.6 ~.
VALVATA 85 9.0 9.6 ..
Oleic Acid 18.0 19.2 ..
KEMAMINE P989 4.5 4.8 H20 1.0 1.6 .~.
100 . O 100 . O '' "Black plate" (tin-free) steel coil stock was hand .
coated with formulation A to form a thin coating on the surface.
The coil stock was then fed to a cupper which punched out the blanks and formed them into cup-shaped articles. The cups were .
then contacted with formulation B at a temperature of 110F and subjected to a three-stage wall-ironing via 3 dies so that the wall thickness was reduced from .012"to 0.009". The cans obtained were of commercially acceptable quality, exhibiting acceptable ~;; `
size and wall thickness dimensions and being substantially free of any galling of the can surface. The dies were undamaged.
Similar results were obtained when the lubricant com-position and temperature were varied within the scope of the in-" ' ~

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vention. When the reactive lubricant was employed as a water emulsion, serious galling and scoring of the surfaces was ob-served.

Formulation A of Example 1 was applied to coil stock at a steel mill. It was found that the shelf life of the thus- -treated coil was in excess of four months. By comparison, un-treated coils exhibited a commercially unacceptable rust forma-tion after about one month.
After the 4 month period, the dry coil was subjected to blanking and cupping without any further lubrication.

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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a process for manufacturing a tin-free two-piece steel can wherein a steel blank is first cupped and then ironed to form a unitary bottom and sidewall structure, the improvement comprising:
A. contacting the steel surface with a stable organic phase coating composition, comprising:
a) 5 to 60 weight % of the reaction product obtained upon mixing as reactants 1) a salt of a multivalent metal cation, 2) a polyphosphoric acid, and 3) an alcohol of 10 - 36 carbon atoms, in a weight ratio of metallic cation:
P2O5 equivalent: alcohol of 1: 3-60:
14-150;
b) 30 to 94 weight % of an organic lubricant of at least 12 carbon atoms; and c) 0.5 to 10 weight % water.
B. thereafter subjecting the thus-treated surface to a cupping and one or more ironing stages to form a unitary bottom and sidewall structure.

2. The process of Claim 1, wherein said reaction pro-duct is obtained by maintaining said reactants in contact for at least 30 minutes before combining with said organic lubricant.

3. The process of Claim 2, wherein said reaction product is obtained by maintaining said reactants at a temperature of at least 50°C during the contact period.

4. The process of Claim 1, wherein the organic lubricant is selected from the group consisting of the hydrocarbon oils;
fatty acids, naturally occurring animal and vegetable oils, the alcohol, ester and amine derivatives of the foregoing; and mix-tures thereof.

5. The process of Claim 1, wherein said coating composi-tion consists essentially of 10 to 35 weight % reaction product;
58-89 weight % organic lubricant; and 1-2 weight % water.

6. The process of Claim 1 wherein said multivalent metal cation is iron; the polyphosphoric acid is about 76-84 weight %
P2O5 equivalent; the alcohol comprises an alkyl or alkylaryl alcohol; and said organic lubricant includes at least one mem-ber selected from the group consisting of mineral oil of vis-cosity 2.5-15° Engler, oleic acid and oleylamine.

7. The process of Claim 1 wherein said coating composi-tion contains about 1-2 % water.

8. The process of Claim 1, wherein the coating compo-sition is contacted with the steel surface at least one addi-tional time subsequent to the cupping step.

9. The process of Claim 1, wherein said coating composi-tion is maintained at a temperature of at least 37°C.