Coated sheet metal and method of forming the same

3,478,554

Patented Nov. 18, 1969

United States Patent Office

3,478,554

COATED SHEET METAL AND METHOD OF FORMING THE SAME

John N. Demsey, Zion, III., and Vernon C. Heffran, Toledo, Ohio, assignors to Aluminum Company of 5 America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed May 26, 1967, Ser. No. 641,475

Int. Cl. B21b 45/06; B21c 23/24

U.S. Cl. 72—46 6 Claims

ABSTRACT OF THE DISCLOSURE

Drawing metal sheet having a resinous coating containing a lubricant. The lubricant in the coating reduces the tendency of the sheet to ear in the drawing operation. ⁱ⁵

This invention relates to an improved formable metal sheet and the drawing of said sheet into hollow or cupshaped articles. In particular, this invention relates to sheet comprising a metal substrate having a resinous coating thereon containing a metal-working lubricant, and to the drawing of such sheet.

As is well-known, in the formation of drawn hollow articles from metal sheet, such as a sheet of aluminum and aluminum base alloys, one of the major problems is the formation of “ears” during the drawing operation. Earing is the name given to the formation of scallops (ears) around the top or free edge of a drawn hollow article as a result of differences in the directional properties of the sheet metal used. Earing can develop in various metals and in the formation of different shapes of drawn hollow articles. Earing of aluminum and aluminum base alloy sheet metal, particularly in drawing cylindrically shaped hollow articles, is particularly trouble- ° some. It is pointed out in “How To Determine Characteristics of Earing in Aluminum,” Light Metal Age, December 1953, page 12, the types of earing which develop in drawing of aluminum and aluminum base alloy sheet. 0-90 degree ears result from a predominance of the annealing texture, and 45 degree ears are caused by a predominance of the rolling texture.

Drawn metal containers are used for packaging a great variety of foodstuffs, beverages and other materials. In _4gmany applications it is desirable to provide the inner surface of such containers with a resistant lining or coating to prevent contact between the metal and the product in the filled container. Such coatings should adhere tenaciously to the underlying metal surface of the con- _g0tainer. Further, the coating should be free from harmful toxic or flavor conferring constituents and have a high degree of stability towards organic acids, fats and greases, alcohols, dilute inorganic acids, alkalies, and other constituents that may be present in the packaged products. _5gIn addition, the outside surface of the drawn containers are also coated with a protective or decorative finish. Commonly used coating materials are the resinous type such as epoxy, acrylic, and phenolic resin compositions, with or without other components such as stabilizers, θθ plasticizers, and pigments. It is common practice to produce the containers by drawing sheet metal having the coating material already applied to the sheet.

Procedures for applying resinous coatings to metal sheet are well-known and depend to some extent on the _6gnature of the particular resin or resins employed. In general, they consist of cleaning the surface of the sheet, coating the cleaned surface with a liquid containing the resin, and converting the coating to a dry film. Examples of such procedures are found in United States Pat- γθ ents 3,114,725 and 3,206,848.

Once the coating has been dried or hardened, the coated sheet is ready for the forming operation. From the coated sheet, a disc or circular blank is cut. The circular blank is then coated with an additional outside or external layer of a suitable drawing lubricant, such as mineral oil, and placed in a holder, over an annular die cavity within a hydraulic or mechanical press. A punch then forces the blank through the die cavity thereby forming a hollow article having a cylindrical side wall and an end wall. A second drawing operation is sometimes employed to obtain a deeper drawn article.

However, earing of the sheet during the drawing operation is a problem, since the ears must be trimmed from the drawn article, with attendant expense and waste.

It is an object of this invention to provide a procedure for reducing the tendency of metal sheet having a resinous coating to form ears during drawing operations thereon, and it is a further object of this invention to provide such coated metal sheet with less tendency to ear when drawn.

In accordance with this invention, it has been found that when a relatively small amount of metal-drawing lubricant is incorporated in resinous coatings applied to sheet metal substrates by mixing the lubricant and the resin together prior to applying the resin to the substrate, hollow articles such as containers and the like drawn from such coated sheet exhibit substantially less earing. The incorporation of lubricant in the resinous coatings is referred to herein as “internal lubrication.” Moreover, it is unnecessary to follow the pior practice mentioned above of having an outside or external coating of lubricant on the sheet when it is drawn. Such lubrication was employed because without it the high degree of friction involved in such a forming operation would result in the center portion of the coated blank being severed by the punch rather than forming a drawn article. This phenomenon is referred to as “breakout.”

In fact, we have found that the layer of external lubricant heretofore employed in drawing metal sheet contributes to the formation of ears in the free edge or open end of drawn hollow articles such as containers, and by eliminating the layer of external lubricant between the metal sheet and the forming tools by introducing a small amount of lubricant into the coating, the formation of ears in the drawing operation is substantially reduced. It will be appreciated that there will be a small amount of lubricant at the outer surface of the coating even though the lubricant is incorporated in the coating. This small amount of lubricant is sufficient to permit satisfactory drawing of the blank without breakout.

In general, the lubricant incorporated in the resinous coating should be one which is not adversely affected by heating, baking or other operations employed in producing the resin film on the metal sheet, and which is not harmful or otherwise objectionable in the use to be made of the drawn article. Lanolin, polyethylene, waxes, butyl stearate, fluorocarbon telomers, mineral oils and petrolatum are examples of lubricants which produce satisfactory results.

The lubricant in the resin coating on the metal sheet should constitute 2-6% by weight of the coating. For optimum results, the preferred amount of lubricant has been found to be from 3% to 5% by weight of the coating. With above 6% of lubricant in the coating the desirable result of minimizing earing is achieved; however, no significant improvement is imparted by using over 6%. The amount of lubricant to be added for best results depends somewhat upon the lubricating efficiency of the particular lubricant used, as well as on the compatibility of the lubricant with the resinous coating material. Also, the amount of lubricant should not be such that it detrimentally affects the drawn article in use, such as impart3,478,554 ³ ing an objectionable taste, odor, or appearance to material packaged in the article.

The proper amount of lubricant can be blended with the resin prior to coating the sheet. The blending process should be such that the lubricant is dispersed throughout the coating material before application of the resultant mixture to the metal sheet. Generally speaking, the more thoroughly dispersed the lubricant is throughout the coating material, the better. In the case of polyethylene as an internal lubricant for instance, it has been found that quite satisfactory results can be achieved by slowly adding the resinous material to the lubricant while agitating the mixture. When a sufficient amount of lubricant has been mixed with the resinous coating material so that the final coating will have the desired percent of lubricant therein, it is desirable to agitate the mixture severely for approximately 30 minutes, as by means of a high speed dispersion mill. This assures that finely divided lubricant particles are well dispersed throughout the coating material.

The resultant mixture of internal lubricant and coating material can be applied to flat sheet metal in any conventional manner, such as by spraying, dipping or roller coating. The term “flat metal sheet” as used herein means both separate sheets and coiled strip metal from which blanks may be cut. Except for minor differences in mechanical handling, the procedure for separate sheets or coiled strip is the same. It is generally cheaper and more convenient to used coiled strip, however. Applying the mixture of internal lubricant and coating material to both sides of the flat sheet metal has been found to be beneficial in obtaining drawn hollow articles with minimum earing.

The blanks cut from coated flat metal sheet are drawn into hollow articles, such as in conventional drawing apparatus, but without the addition of an external lubricant to the blanks. The drawn products may be trimmed if need be; however, by employing this invention the trimming operation may, in many cases, be entirely eliminated.

The advantages obtained by this invention are illustrated in the following example. In the example, the sheets selected were composed of one of the aluminum base magnesium alloys employed extensively in commercial sheet drawing applications and in the extra hard H19 temper. In the example the percent of earing was calcucated on the basis of the formula:

Percent earing=^'¹, ^²χΐ00 Λι /ii=the measured straight line distance from the closed bottom of the drawn article to the tip of the longest ear on the open end;

h₂=the measured straight line distance from the closed bottom of the drawn article to the lowest valley between the ears.

EXAMPLE

Thirteen .010 gauge sheets of 5052 aluminum alloy in the extra hard temper (—H19) were coated with resinous materials as indicated below, and were drawn in two stages to form 208 diameter x 207 height hollow articles, each having a cylindrical side wall and an end wall. All of the sheets were chemically cleaned prior to applying the coatings, and the coatings were applied to the sheets by roller coating. As used herein, when reference is made to coating the inside of the sheet, it means that side of the sheet which, when drawn, is the inside of the hollow article. Reference to the outside of the sheet means the side which forms the outside of the drawn article.

Sheet No. 1 was coated on the outside with a clear epoxy amine resin. The epoxy amine resin coating material was purchased from Midland Industrial Finishing Company under their product designation V683. The inside was coated with an epoxy phenol-aldehyde, and vinyl chloride copolymer vinyl dispersion resin coating which was purchased from Midland Industrial Finishing Company and sold under their trade name “Mark H.” No lubricants were incorporated or mixed into either the inside or outside coatings.

Sheet No. 2 was coated on the inside and outside exactly as Sheet No. 1.

Sheet No. 3 was coated on the outside with a mixture of Midland’s V683 clear epoxy amine resin and 2% lanolin. The inside was coated with Midland’s “Mark II” vinyl dispersion resin. No internal lubricant was mixed with the “Mark II” inside coating material.

Sheet No. 4 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous material and 2% lanolin. The inside of Sheet No. 4 was coated with the above-mentioned Midland “Mark II” coating with no internal lubricant mixed in with it.

Sheet No. 5 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous material and 2% lanolin. The inside of Sheet No. 5 was coated with a mixture of Midland’s “Mark Π” vinyl dispersion resin and 2% polyethylene lubricant.

Sheet No. 6 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous material and 2% lanolin. The inside of Sheet No. 6 was coated with a mixture of Midland’s “Mark II” vinyl dispersion resin and 5% polyethylene lubricant.

Sheet No. 7 was coated on the outside with Midland’s V683 epoxy amine resinous material. Sheet No. 7 was coated on the inside with an acrylic resin coating composition purchased from the Glidden Company and sold under the product designated “Glidden 66225.”

Sheet No. 8 was coated on the inside and outside exactly as Sheet No. 7.

Sheet No. 9 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous coating material and 3% polyethylene lubricant. Sheet No. 9 was coated on the inside with a mixture of Glidden’s 66225 acrylic resin coating composition and 3% polyethylene lubricant.

Sheet No. 10 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous material and 2% lanolin lubricant. The inside was coated with a mixture of Midland’s “Mark II” vinyl dispersion resin coating and 2% polyethylene.

Sheet No. 11 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous material and 3% polyethylene coating. The inside was coated with a mixture of Midland’s “Mark II” vinyl dispersion resin and 3% polyethylene lubricant.

Sheet No. 12 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous material and 2% lanolin. The inside was coated with a mixture of Midland’s “Mark II” vinyl dispersion resin and 3% polyethylene lubricant.

Sheet No. 13 was coated on the outside with a mixture of Midland’s V683 epoxy amine resinous coating material and 3% polyethylene lubricant. The inside was coated with a mixture of a vinyl resin purchased from Pittsburgh Plate Glass Company and sold under their product designation “PPG X786” and 4½ % petrolatum.

The coating solvents were driven off from all of the sample sheet coatings by means of a medium velocity air oven to produce a dry coating film. The oven temperatures were selected so that normal curing of the coating materials was obtained.

The amount of dry coating on all of the above sample sheets was approximately 3 mgs. per square inch on the outside and from 8 to 10 mgs. per square inch on the inside.

In all of the instances wherein polyethylene lubricant was incorporated into the coating material, the polyethylene lubricant was mixed thoroughly by slowly adding the coating material to the lubricant while agitating. The mixture was blended for 30 minutes by using a high speed Eppenbach dispersion mill.

All thirteen of the coated sheets were cut to a round blank size of 5.66 inches diameter. Each of the blanks were inserted into a conventional blank and draw press which first formed a shallow shell of 303 x 115 which was

3,478,554 then redrawn in another press to a final 208 x 207 size shell. Tn the first drawing operation, the clearance between the stationary post and cavity punch was approximately sheet gauge plus 25% of gauge per side. In the redraw press, the clearance between the post and punch was increased to sheet gauge plus approximately 35% of gauge per side. Outside or external lubricants normally used in prior sheet metal drawing operations were applied in the amount of between 4 and 8 mgs. per square foot to both sides of the blanks cut from sheet Nos. 2, 3, 8 and 10. The blanks cut from the rest of the sheets did not have any external lubricant applied to them or to the forming die faces prior to or during drawing.

The summary of the test results are set forth in the following table:

is is

<td> Outside</td><td> Inside</td>

<td> Coating</td><td> Coating</td>

<td> Internal</td><td> Internal</td>

<td> Lubri-</td><td> Lubri- .</td>

<td> cation °</td><td> cation ^a .</td>

0

2

2

0

3

3

0 0 0

5

0

2

3

4¼

External Lubricant Added

No________

Yes_______

Yes.......

No________

No.....—

No________

No________

Yes.......

No________

Yes_______

No________

No________

No________

Percent Earing

Sample Sheet Number

1_

2_

3_......

4_

5_

6_

7..

8_

9_

10_

11_

12_

13_ a Percent of dry film by weight.

•Breakout of blank, not able to be drawn.

5.8 (*) 2.5 2.7 (*) 5.7 3.0 7.3 2.4 2.4 4.1

3. The method in claim 1 wherein said resinous coating a vinyl organosol.

4. The method in claim 1 wherein said resinous coating an epoxy resin.

5. The method of making a drawn hollow article from metal sheet, comprising the steps of coating both sides of flat metal sheet of an aluminum base magnesium alloy in H19 temper which tends to ear upon being drawn with a mixture of resinous coating material and a metal-drawing lubricant selected from the group consisting of lanolin, polyethylene and petrolatum, the said lubricant constituting 2-6% by weight of the coating, the said coated sheet having less tendency to ear upon being drawn than it would have without the said lubricant in the coating, and drawing the said sheet into said hollow article.

6. The method of making a drawn hollow article from flat metal sheet, comprising the steps of coating flat metal sheet which tends to ear upon being drawn with a resinous coating having a metal drawing lubricant selected from the group consisting of lanolin, polyethylene and petrolatum dispersed throughout the coating, the said lubricant constituting 2-6% by weight of the coating, the said coated sheet having less tendency to ear upon being drawn than it would have without the said lubricant in the coating, and drawing the said sheet into said hollow article without adding external lubricant.

As will be apparent to those skilled in the art in the light of the foregoing disclosure, many modifications, alterations and substitutions are possible in the utilization of this invention without departing from the spirit or scope thereof.