US2801604A

US2801604A - Processed drawn implement

Info

Publication number: US2801604A
Application number: US204152A
Authority: US
Inventors: John J Russell; William A Beck
Original assignee: National Glaco Chemical Corp
Current assignee: National Glaco Chemical Corp
Priority date: 1951-01-03
Filing date: 1951-01-03
Publication date: 1957-08-06
Anticipated expiration: 1974-08-06

Description

AugJ-i, 1957 J. J. RussELL 'ErAL n PROCESSED DRAWN IMPLEMENT Filed Jan. 3. 1951 2 Sheets-Sheet 1 exam sunzmce 5 v COATING OXIDE sum-Act! 5 I COAT MG oxwe sunnce 6 COAT! u a oxloe sum-Ac: 6

COATING OXIDE SURFAC 6 coATluG oxm: sun cs6 COAT" N G 1 imam/5: Joly/z J/MAZZ 2 Sheets-Sheet 2 HEIGHT OF BREAD PAN az o/n HEIGHT \N \NGHES OF SAMPLE- J. J. RUSSELL ET AL PROCESSED DRAWN IMPLEMENT GRAPH OF SnO THICKNESS vs:

Aug. 6, 1957 Filed Jan. 3. 1951 Z i m Q P m M mm s N F EwA o N P S aw e ML H O c AR C B N.- Wm M Ts l F T H H 0N6 6 HA1 a p a A H H @T m w w w w United States Patent G PROCESSED DRAWN IMPLEMENT John J. Russell, Des Plaines, and William A. Beck, Itasca, Ill., assignors to National Glaco Chemical Corporation, Chicago, 111., a corporation of Illinois Application January 3, 1951, Serial N 0. 204,152 4 Claims. (31. 113-420 This invention relates to a composite tin coated metallic structure, which may be fabricated into shaped metallic articles provided with processed outer surfaces in order to facilitate deep drawing of the article and to exhibit a relatively high absorption to convective and radiant energy.

An object of this invention is the provision of a practical process for chemically treating tin and tin base alloys in order to provide the outer surfaces with a compound of tin coating to substantially reduce the amount of friction produced between the tin plated structure and the drawing tools during the deep drawing operations.

Another object of this invention is to provide a compound of tin intermediate to the tin layer of a tin plated structure, wherein said compound of tin iscapable of supporting a lubricating film during the drawing operation.

A more specific object of this invention is to provide a tin plated structure with an oxide of tin intermediate to the tin layer of said tin plated structure wherein said oxideof tin, capable of being deformed, remains as an. extended continuous coating throughout the drawing operation.

Another specific object of this invention is to provide a process for forming a deep drawn baking pan having a continuous oxide of tin coating covering the outer surfaces of said baking pan, wherein said oxide of tin enhances the drawability of the tin plated steel structure, and in addition, provides the baking pan with exterior surfaces capable of absorbing radiant energy.

Other objects and advantages of this invention will become apparent as this description proceeds, particularly when considered in connection with the accompanying drawings in which:

Figure 1 is a. face view of a processed tin plated blank for making a drawn baking pan;

Figure 2 is a perspective view of a partially fabricated processed tin plated baking pan, which has been subjected to the first 'step in the drawing operation;

Figure 3 is a perspective view of a partially fabricated baking pan, which has been subjected to a subsequent drawing operation;

Figure 4 is a perspective view of a finished baking pan made from a blank as thatshown in Figure 1, and with the outer edges trimmed and formed;

Figure 5 is a graphic diagram showing the relative ratio of the combined oxide coating, tin and tin-iron alloy layerthicknesses versus the corresponding height of a drawn tin plated bread pan;

Figure 6is a graphic diagram showing the relative ratio of the oxide of tin coating versus the correspondingheight of a drawn tin plated bread pan;

Figure 7 is a photomicrograph cross-sectional view of a portion of atin, plate area, not subjected to deformation, of the bottom of a drawn bake pan showing the relative thicknesses of oxide coating, tin layer and alloy layer (2500Xmagnification) and c Figure 8' is a photomicrograph cross-sectional view showing the relative thicknesses of the oxide coating tin layer and alloy layer of a corresponding tin plate area wherein said area has been subjected to deformation.

Referring now more particularly to the drawings, Figure 1 illustrates a tin plated baking pan blank 2 wherein prior to the blanking operation said tin plated structure was subjected to a chemical process. In this process a continuous oxide of tin is formed on the exterior surfaces of the tin plated structure. This tin plated structure comprises a steel core having a tin-iron alloy layer intermediate to a tin layer, which may be deposited either by the conventional hot dip process or the electrolytic plating process. The steps illustrated in the chemical process for converting a portion of the tin layer to an oxide of tin coating are described in our copending applications Serial No. 156,671, filed April 18, 1950, now Patent No. 2,738,897 and Serial No. 156,672, filed April 18, 1950, now Patent No. 2,724,526.

The configuration and dimensions of the blank 2 are designed so as to afford sufficient metal during the drawing operation. This blank 2 is blanked in the conventional manner using standard press, tool and die operations. The irregular shaped corner contours 4 are designed so as to give sufficient metal to the body of the formed metal article during the successive drawing operations. The outer surfaces of the blank 2 have been chemically treated having an oxide of tin coating, generally designated by numeral 6, formed thereon.

The blank 2 is treated with a drawing lubricant prior to insertion into the first operation drawing die set, which has been specifically designed for drawing a bake pan. Although the specific design and construction of the die set does not constitute any part of this invention, the specific skills required in the fabrication of drawn lightgauged metal articles shall be considered unique in the fabrication of drawn processed tin plated articles. The drawing lubricant which has been applied to the blank 2 may consist of numerous compositions such as metallic soaps, oils, greases, water soluble compounds, and combinations thereof. We have found numerous compositions of drawing lubricants that may be used in the drawing operations. Although we have found that the water soluble compounds and the metallic soaps are superior, the steps in the fabrication of a drawn bake pan shall not be limited to the type or composition of the drawing lubricant.

Figure 2 illustratesthe result produced in the first step in the drawing operation of a processed drawn bake pan 10. The upper flange 12 has been deformed to produce a rectangular cavity 14 having side walls 16 and a botminds. The depth of draw, which may be defined as the height of the side wall 16, will be approximately 60% of the final height of the side wall obtained in the final drawing operation, as shown in Figure 3.

Figure 3 illustrates the configuration of a processed drawn bake pan 10, which has been subjected to the final drawing operation wherein the height of the side wall 16 has been elongated by the drawing operation to approximately an additional 40% of the final depth. Hold-down grooves 20 have been formed on the outer flanges 12, in order to facilitate the flow of metal from the contour edges 4 of the drawing blank 2, so as to acquire sufficient metal. We have found that the hold-down grooves 20 tend to restrain the flow of metal along the side walls 16 and direct the flow of metal along the corners 22.

Figure 4 illustrates the final fabricated shape of a processed drawn bake pan 10 wherein the outer flanges 12 have been trimmed, formed and curled, so that the bake pan 10 may be inserted into a conventional multiple baking pan set.

Drawing, forming and similaroperations require pressures sufiicient to exceed the elastic limit of the base metal stock and effect permanent changes in its contour and size. The pressures so exerted must not exceed the ultimate strength or the breaking point of the material or the result will be scrap. For instance, in these operations the plasticity of the metal permits it to flow into shapes quite different from those existing originally. However, the pressures on the punch and the die must be definitely controlled while blank holding pressures must be lessened at times or even completely released. In addition, die considerations relative to drawing, such as die clearances, must be carefully determined for drawing, forming and related operations, because the clearance vitally affects the success of the draw. For example, insufficient clearance or improper radii may .cause tearing of the stock, cracking of the work at corners, damage to the dies and other difliculties; while excessive clearances may lead to too much metal in the corners, cracking or bursting of the die, incomplete filling of the die, and generally poor draws. Improper clearances also have an effect on the tonnage requirements of the press operation. A change in the physical characteristics of the stock is likely to have a marked effect on the behalf of the dies. Difiiculties due to clearances in certain instances may be somewhat alleviated in the press room by various lubrication expedients.

We have found that in the fabrication of tin plated articles it has been extremely difiicult to obtain a continuous coating of the tin layer over the entire drawn surfaces of the drawn bake pan 10. In addition, we have found that our percentage of rejects, such as breakage, tears and the like, has been extremely high, in the neighborhood of 18 to 23%. We have taken into consideration the various drawing parameters in these drawing operations and successful production runs have not been obtained. In addition, many types of lubricants and drawing compounds have been used without beneficial results.

The reason for such varying results may be attributed to the nature of tin plate. The tin layer is extremely soft and plastic as compared to the intermediate tin-iron alloy layer and the steel basis. By subjecting the tin plate to deformation, the continuous tin layer, being extremely fluid under drawing pressures, tends to break down and separate leaving the alloy layer and steel basis exposed. Since the alloy layer and steel basis are subject to a high corrosion rate, it is highly desirable to retain a continuous layer of tin over the outer surfaces of the drawn article in order to substantially reduce corrosion.

By the introduction of a compound of tin coating contiguous to the tin layer, we have been able to obtain excellent results in the fabrication of deep drawn tin plated articles. We have found that the percentage of rejects has been substantially reduced to approximately 3 to 5%; there has been a substantial reduction in the consumption of power in the deep drawing operation due to the decreasing amount of friction between the article and the die; the speed of the drawing operation has been enhanced; and there has been a substantial increase in the life of the tools and dies due to a reduction of galling action on the dies.

The compound of tin coating 6 may be generally defined as the metastable form of the oxide of tin, although we have found other tin compounds, such as the phosphates and sulfates, are adaptable in this operation.

We have found that the oxide of tin exhibits superior drawing properties relative to the tin plated article than do other compounds of tin coatings; and in addition, the oxide of tin coating performs an additional function insomuch that it exhibits a high degree of heat absorption when subjected to radiant energy.

The chemical process utilized in converting a portion of the tin or the tin alloy surfaces to a compound of tin coating, preferably the metastable form of an oxide of tin, is set forth in the aforesaid copending applications. This process consists of an-odically converting the tin or tin alloy surfaces electrolytically to a metastable form of the oxide of tin. Numerous process solution parameters, such as composition, concentration, temperature and time of immersion are set forth; and the chemical process shall not be limited to any specific composite group of parameters.

The metastable oxide of tin composition exhibits interference colors when the coating is less than about seven microns thick. We have found that satisfactory results are obtained when we use a coating thickness greater than seven microns and less than about 40 microinches. Figure 7 illustrates a photomicrograph showing an opaque oxide coating 6a which has a thickness of approximately 18 microinches thick. The oxide coating was formed on one and one-half pound tin plate, using the previously disclosed chemical treatments. It shall be noted that the oxide coating 6a is substantially greater in thickness than the tin-iron alloy layer 28. Intermediate to the tin-iron alloy layer 28 and the opaque oxide coating 6a is the tin layer 30. The steel base metal is identified by numeral 32; and the copper mounting 34 is used to, back' up the tin plate so that a well defined boundary may be secured while preparing these photomicrographic samples.

One and one-half pound tin plate generally is defined as having a tin and tin alloy layer of combined thickness of approximately 90 microinches. Since a portion of the tin layer 30 has been converted to the metastable form of the oxide of tin 6a, Figure 7 illustrates the relative proportions of these various compositions and their relative thicknesses. The photomicrograph illustrated in Figure 7 is a sectional area taken from the bottom of the drawn pan 10, wherein this area has not been subjected to deformation.

As can be noted from the illustration, the tin layer 30 constitutes a substantial thickness of the combined tintin alloy layer and coating. The thickness of the tin layer 30 approximates from about 60 to microinches.

Figure 8 illustrates an oxide coated one and one-half pound tin plate area, which has been subjected to deformation. This photomicrograph was taken from a sectionalradius area 36 as shown in Figure 4. The composite tin plate structure in Figure 8 comprises a copper mounting plate 38, the oxide coating 6b, tin layer 42, tin iron alloy layer 44, and the steel base 46. It shall be noted that the combined thickness of the oxide coating 6b, tin layer 42 and the alloy layer 44 have been substantially reduced from a thickness of about microinches to about 65 microinches. There has been approximately a reduction of one-third of the total thickness of the combined composition. It further shall be noted that the tin layer 30 has been substantially reduced in thickness. Since these photographs were taken at a magnification of approximately 2500X, the relative thicknesses of the oxide coatings 6a and 6b and the tin iron alloy layers 28 and 44 do not illustrate a substantial, reduction in thickness. Although there has been a substantial reduction of approximately 50% in the thickness of the oxide coating 6a, the variation may be interpreted to poor definition and focus in the photomicrograph.

Figure 5 is a graph illustrating the variation in the combined thicknesses of the oxide coating, tin layer and iron alloy layer, taken along the side wall 16 of the drawn bake pan 10 from the upper bead 17, around the radius 36, to the bottom 18 of the pan 10. These combined thicknesses were ascertained by two methods, namely, chemical analysis and relative non-magnetic thickness.

With reference to the graph as shown in Figure 5,,the abscissa defines the relative height of the side 16 of the bread pan 10 and the ordinate defines the combined thicknesses of the oxide coating, tin layer and tin-iron alloy layer. In following the curve along the bottom 18, the combined thickness is approximately 90 microinches and gradually decreases along the bottom radius 36 t0 approximately 65 microinches, gradually increases and obtains the maximum thickness of approximately 90 microinches and decreases along the bead 17 to approximately 65 microinches, and then increases to the maximum thickness along the flanges 12. In interpreting this diagram, it shall be noted that the bottom 18, the sides 16 and the flanges 12 have been subjected to substantially no deformation. The combined thicknesses along the bottom radius 36 and the head 17 have been reduced to approximately two-thirds of the original thickness. It shall be noted that the photornicrograph illustrated in Figure 8 still retains over the bottom radius 36 a substantial amount of the tin layer 42, and other photomicrographs, not illustrated, indicate that similar results were obtainable along the bead 17.

Figure 6 illustrates the curve of the relative thickness of the tin oxide layer 6 versus the relative height of the bread pan 10. It shall be noted from the diagram that the maximum thickness of the oxide layer 6 of about 15 microinches along the bottom 18, side 16 and flange 12 has been reduced in thickness, due to deformation, to about 8 microinches along the bottom radius 36 and the bead 17. It shall be noted in comparing the photomicrographs that there is a greater percentage reduction in the oxide coatings 6a and 6b as compared to the tin layers 30 and 42, and this may be based upon the relative degrees of plasticity of the higher melting oxide of tin composition as compared to the lower melting point of tin.

In interpreting these relative results, we have found that the presence of the oxide coatings 6a and 61) have greatly enhanced the drawability of tin plate because the oxide coatings 6a and 6b, due to a higher melting point and toughness, afford an intermediate stratum between the low melting tin layers and the punch and die used in the drawing operation. Since tin has a melting point of approximately 449 F. We have found that there has been a considerable amount of galling of the dies because tin of itself has an extremely high tendency to wet metal surfaces when no oxide interface is present. In addition, due to the relatively high temperatures created in the drawing operations, tin without the presence of the oxide interface tends to disperse unevenly over the entire drawing area so that in areas of greater deformation we have found that practically no tin remains on these surfaces. It is well known in the art that tin affords substantial corrosion resistance and it is highly desirable to retain the tin uniformly over the entire surface of the drawn article, such as a cooking utensil or baking implement. The tin-iron alloy, as well as the steel base, are subject to rapid corrosion rates.

In addition, the oxide of tin coating 6 performs another function. We have found that by preferably using the metastable form of the oxide of tin coating 6 during the drawing operation, and then subjecting the drawn bake pan 10 to an elevated temperature, less than the melting point of tin, the black metastable form of oxide of tin can be converted to an opaque olive-green stable form of oxide of tin. In addition, there are numerous scratches and draw marks produced over the entire surface area during the drawing operation. However, during the conversion cycle from the metastable to the stable form of the oxide of tin, these imperfections are cured so that the final product exhibits a continuous oxide coating of tin 6 over the entire surface. We have found that satisfactory results have been obtained by first converting the metastable oxide of tin to the stable form, and then producing the drawn article or implement. These forms of oxide of tin coatings 6 exhibit superior absorptive properties when the article is subjected to convective and radiant heat, such as required in the baking of bread.

While for the purposes of illustrating and describing the present invention certain preferred embodiments have been shown in the drawing, it is to be understood that the invention is not to be limited thereby since such variations are contemplated as may be commensurate 7 with the spirit and scope of the invention set forth in the accompanying claims.

We claim as our invention:

1. A method of fabricating a tinned blank consisting of a base metal having a tin or tin alloy layer deposited thereon into a processed drawn tinned article comprising the steps of chemically treating the tin layer so as to partially convert a portion of the tin layer into an oxide of tin coating, coating a portion of said oxide of tin coating with a drawing lubricant and then subjecting the treated tinned blank to a drawing operation whereby the metallic tin layer is substantially intact between said base metal and said oxide of tin coating.

2. A method of producing a processed drawn baking implement comprising the steps of chemically treating a tin plated steel base blank whereby a portion of the tin layer is partially converted to the meta-stable form of the oxide of tin, coating a portion of said oxide of tin coating with a drawing lubricant, deforming said treated blank into a shaped implement whereby the remaining metallic tin layer is substantially intact between said steel base and said oxide of tin layer, trimming said deformed shaped implement and then forming the flanges of said deformed shaped implement into a baking implement.

3. A method of producing a processed drawn baking implement comprising the steps of chemically treating a tin plated steel base blank whereby a portion of the tin layer is partially converted to the meta-stable form of the oxide of tin, coating a portion of said oxide of tin coating with a drawing lubricant, deforming said treated blank into a shaped implement whereby said remaining metallic tin layer is substantially intact between said steel base and said oxide of tin layer, trimming said deformed shaped implement, forming the flanges of said deformed shaped implement into a baking implement, and then subjecting said baking implement to elevated temperature whereby the metastable oxide of tin is converted to the stable form of the oxide of tin.

4. A method of fabricating a sanitary deep drawn inetallic baking pan structure free of interior folds and crevices, having heat absorptive tin oxide outer coatings comprising the following steps: chemically treating a tin coated steel core blank so as to form a tin oxide coating coetxensive with the remaining corrosion resistant tin layer, coating a portion of said tin oxide coating with a drawing lubricant, subjecting the oxide coated steel core blank having corrosion resistant metallic tin interposed between said oxide coating and said steel supporting core to a deep drawing operation, whereby the metallic tin is substantially intact between said steel core and said oxide coating.

References Cited in the file of this patent UNITED STATES PATENTS 436,883 Wagandt Sept. 23, 1890 499,359 Hall June 13, 1893 2,024,951 Schutte Dec. 17, 1935 2,152,516 White Mar. 28, 1939 2,215,165 Sumner Sept. 17, 1940 2,245,561 Nelson et al. June 17, 1941 2,346,714 Wobbe Apr. 18, 1944 2,391,660 Ward Dec. 25, i945 2,462,728 Debs Feb. 22, 1949 2,471,500 Stewart et al May 31, 1949 FOREIGN PATENTS 300,641 Great Britain Apr. 7, 1930 OTHER REFERENCES Tinplate, by W. E. Hoare and E. S. Hedges, published in 1945 by Edward Arnold and Company, London, page 243.

Metallurgy of Deep Drawing and Pressing, by J. Dudley Jevons, Second Edition, published 1942 by John Wiley and Sons, Inc., New York, page 117.

Claims

1. A METHOD OF FABRICATING A TINNED CONSISTING OF A BASE METAL HAVING A TIN OR ALLOY LAYER DESPOSITED THEREON INTO A PROCESSED DRAWN TINNED ARTICLE COMPRISING THE STEPS OF CHEMICALLY TREADING THE TIN LAYER SO AS TO PARTIALLY CONVERT A PORTION OF THE TIN LAYER INTO AN OXIDE OF TIN COATING, COATING A PORTION OF SAID OXIDE OF TIN COATING WITH A DRAWING LUBRICANT AND THEN SUBJECTING THE TREATED TINNED BLANK TO A DRAWING OPERATION WHEREBY THE METALLIC TIN LAYER IS SUBSTANTIALLY INTACT BETWEEN SAID BASE METTAL AND SAID OXIDE OF TIN COATING.