US3051080A - Architectural finish - Google Patents

Description

United States Patent Ofiice 3,051,080 Patented Aug. 28, 1962 3,051,080 ARCHITECTURAL FINISH Francis J. Clarke, Leechburg, Pa., assignor to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania No Drawing. Filed Nov. 8, 1960, Ser. No. 67,889 6 Claims. (Cl. 101-32) This invention relates to improvements in the surface finishes for stainless steel and is particularly directed to a new architectural finish for austenitic stainless steel panels.

In modern architectural design of buidings and particularly commercial oifice and business buildings in metropolitan areas, there is an increasing demand for stainless steel building panels for exterior application. This metal possesses the desired and required corrosion resistance for long-time outdoor atmospheric exposure plus the required formability and the desired mechanical strength. Also, this metal exhibits a particularly desired bright and lustrous attractive metallic appearance that may be modified by surface treatment to effect a multitude of reflective or of non-reflective surfaces that are ideal for either indoor or outdoor building panel applications. In consequence, it may be seen that stainless steel is an ideal material from which one may produce building panels. For outdoor building panel applications it is, of course, necessary to employ relatively dull or non-reflective finishes, in that if such a finish is too bright its reflection of sun rays will prohibitively blind on-lookers and may actually be responsible for damage to adjacent property. The stainless steel most frequently employed for such panels generally exhibits what is known in the industry as a #2D or #2B sheet finish. A #2D finish is a dull cold rolled finish or one in which the flat rolled stainless steel has been cold rolled, heat treated and pickled. This finish is relatively unattractive and consequently has fallen from demand since the primary purpose of employing stainless steel is to provide an attractive finish as well as one that will resist corrosive attack. A #ZB finish is somewhat brighter than a #2D in that it has been bright cold rolled or pressed between ,the relatively smooth rolls of a cold rolling mill after annealing and pickling, but it does not have as high a luster as a polished finish. This material, however, is generally considered to be too reflective and is also not particularly attractive for the desired application.

In addition, both a #2D and #2B sheet finish exhibit directional stripes on their surfaces, or in other words, show the imperfections of the cold rolling in one direction, hence requiring proper alignment of the panels both during fabrication and installation. A particularly desirable finish is a grit blasted finish or a finish wherein relativelyhard particulate material of a grit size of from about 3.0 to 50 grit has been propelled in a relatively uniform manner against the surface of the stainless steel so as to effect a substantially uniform 30 to 50 grit blasted finish. T effect ,such a finish by presently known commercial means would be prohibitively expensive in that each panel would have to be individually grit blasted, and additionally, it would be impractical to attempt to device means to effect the required uniformity of the panels appearance, in that in grit blasting the grit material is generally and gradually broken down ,into finer grit particles; consequently, one may not elfect a uniform 30 to 50 grit finish by grit blasting the stainless steel, and attempts to accomplish such a finish by this means have not been successful in that architectural requirements and specifications demand a completely uniform finish for each panel and deviation from such uniformity is readily observable on installed panels of this type. Other attempts to secure a uniform finish of this type have been to grit blast rolls of the cold rolling mill to effect the desired finish on the metal surface of the relatively hardened rolls. The stainless steel is then passed through such a mill and the desired finish is embossed on the surface of such stainless steel. This method has also proved to be relatively unsatisfactory in that, although the finish imposed is one that is highly desired, reproducibility has been found to be impractical in that the rolls lose their ability or wear smooth far before a commercial product may be efiected. In other words, once again the manufacturer is unable to meet the desired architectural specifications of a uniform surface, and consequently such a method has proved to be unsuccessful except as modified in accordance with the method of the present invention.

It has now been found that by employing rolls that possess a Rockwell C hardness of at least 60 and which have been given a substantially uniform 7 to 90 grit finish by grinding or polishing and subsequently grit blasted so as to effect a substantially 14 to 18 grit finish and then grit blasted a second time to effect the desired 30 to 50 grit finish, such rolls may be successfully employed to produce a strip product that exhibits a surprisingly uniform 30 to 50 grit finish throughout the lengths of numerous austenitic stainless steel coils.

It is accordingly the object of the present invention to provide a method wherein a substantially uniform 30 to 50 grit blasted finish may be produced on the surface of austenitic stainless steel strip.

It is also an object of the present invention to provide a new and useful architectural finish for stainless steel building panels that may be reproduced effectively so that panels produced by the present method on one lot may be subsequently and independently produced on another lot of austenitic stainless steel.

A still further object of the present invention is to provide a method of reproducing austenitic stainless steel building panels with a 30 to 50 grit blast finish in a substantially uniform manner.

Other objects and advantageous features will be obvious from the following specification:

In general, the present invention relates to the production of a stainless steel fiat rolled product that possesses a substantially uniform 30 to 50 grit blast finish that inyolves the steps of initally providing one or more cold rolling mill rolls that possess a hardness of at least 60 'Rockwell C, grinding the surface of such a roll with an abrasive so as to effect a substantially uniform to grit finish thereon, grit blasting the ground surface of the said roll with a grit that will effect a substantially uniform 14 to 18 grit blast finish, grit blasting the surface of said roll with a grit that will effect a substantially uniform 30 to 50 grit blasted finish on the surface thereof and finally cold rolling the stainless steel with the said roll so as to emboss the resulting roll finish on the surface thereof.

The reason for the reproducibility of the embossed finish of the present invention is not readily understood, in that to effect the grit blasted finish to the roll without first interposing the grinding and preliminary grit blasting steps does not effect a roll that will uniformly reproduce the desired finish. This is particularly true for reproducing the finish from lot to lot where it is necessary to employ new rolls of this nature or to re-face the original roll where the grit blasted finish deteriorates from use. The roll itself may be manufactured from any of the hardenable steel grades that are capable of being hardened on the surface thereof to a Rockwell C 60 or greater; for eX ample, such rolls are known to be fabricated from steel of the following analyses:

Analysis N0. 1 Analysis No. 2

Carbon .93 Carbon .83 Manganese .40 Manganese .34 Silicon .29 Phosphorous .012 Chromium 2.34 Sulfur .017 Vanadium .10 Silicon .27 Iron Bal. Nickel .20 Chromium 1.97 Vanadium .10 Molybdenum .22 ron Bal.

The roll, of course, is ground in a circular manner so that the grind marks parallel the peripheral face of the roll in contrast to the horizontal axis thereof. The grinding media may be any conventional grinding apparatus, such as a grinding wheel or a grinding belt, and the abrasive material itself may be any of the conventio-nl abrasive materials employed for such purposes or any other abrasive so long as it is capable of effecting the 70 to 90 grit finish thereon. Particularly satisfactory results have been obtained by employing an 80 grit number C80L10ES National Grinding Wheel (manufactured by the National Grinding Wheel Company of North Tonawanda, New York) on a cold rolling roll 28-inch diameter-56-inch face that exhibits a roll hardness of 66/67 Rockwell C. This grinding wheel is used to give a smooth uniform finish to the roll without brightness which must be free from roll chatter, wheel marks, grit marks, etc. The grinder employed may be any of the conventional apparatus. Particularly satisfactory results have been obtained by employing a Farrel Roll Grinder (manufactured by the Farrel Birmingham Company, Ansonia, New York).

The grit blasting may be accomplished by any of the commercially available apparatus designed for this purpose. Excellent results have been obtained by employing the Pangborn Rotablast Machine (manufactured by the 'Pangborn Corporation, Hagerstown, Maryland), wherein the roll is placed within a carriage within a machine which revolves the rolls as it enters the grit blast cabinet. As the carriage enters the cabinet, the door closes and a power driven wheel that includes a spout, impeller, vanes and impeller case impels the grit striking the rolls and breaks up the surface thereon. Other commercially available machines propel the grit through means of an air blast that picks up the grit through an applicator similar to the principle of a spray gun; however, best results hve been obtained by the Pangborn type machines. The initial grit used in the second step of the method should be substantially 14 to 18 grit. The preferred particles are 16 grit in size, and this size grit is available commercially. Particles of 16 grit size are about .049/ .050 inch in diameter. It is preferable to employ an angular type of grit. The G-l6 or 16 grit Mallabrasive (trademark of Pangborn Corporation applied to a hard metal abrasive) is used to roughen the surface and imparts a rough texture to the roll. It is, of course, understood that the roll must have a hardness of at least 60 Rockwell C in order to maintain the grit blast surface during processing and while embossing the ultimate cold-rolled article. The exact function of the initial or roughening grit blasting with the 16 grit material is not precisely understood, although such grit blasting may serve in some manner to further cold work the already hardened surface of the roll.

The length of time in which the roll is grit blasted with a 16 grit material is that length of time required to effect a substantially uniform 16 grit finish to the roll surface. It has been found to be preferable in obtaining optimum results to effect four passes in the Pangborn machine at 2 feet per minute rotation of the roll to get the desired effect.

The third step in treating the roll is to substantially uniformly grit blast the already grit blasted surface with 30 to 50 grit material that will effect a 30 to 50 grit blasted finish on the surface. 40 grit material has been found to be preferred and will be most often used, since it is a standard grit used in commercial grit blasting prac tices. The 40 grit material will preferably be an angular heat treated grit. The approximate size of this material is .010/ .015 inch diameter and is preferably a sharp angular grit which will retain the sharpness as it breaks up into smaller particles. I have found this to be an ideal grit material to use to impart to the roll the surface texture that has the desired attractive appearance, smoothness and uniformity. Usually one pass at four feet per minute will have the desired effects. The roll is now in condition for embossing stainless steel and may be inserted into the cold rolling mill to treat stainless steel.

It is, of course, understood that if both rolls through which the strip or sheet stainless steel passes have been given the treatment of the present invention, both surfaces of the strip will be embossed with the desired architectural finish; however, it will generally be desired to effect such a finish to only one side of the strip since only one side will be employed as an architectural finish, and consequently, generally will be desirable to eflfect such a finish to only one of the opposing work rolls in the cold rolling mill.

Any conventional cold rolling equipment that is capable of reducing the gauge of austenitic stainless steel strip or sheet may be employed, it. being understood that the embossing roll will be one designed to fit such a mill. We have employed such rolls in a two-high Lewis mill (manufactured by the Lewis Foundry Company of Pittsburgh, Pa.). The strip is threaded to the tension reel with the mill open (with the rolls apart). When the end is secured in the reel, the tension is applied and the rolls brought down and pressure applied. A lubricant, such as alcohol. should be used on the rolls; the strip is rolled in the regular manner. It has been found to be desirable to omit the use of rolling oils. The rolls should be kept moist by dripping and keeping the strip Wet with a material such as methyl ethyl or butyl alcohol. One pass on the mill is generally all that is required.

The method of the present invention has been found to be applicable only to the austenitic type stainless steels. These steels contain from about 10% to 30% chromium, less than 1% carbon, and various quantities of austenite stabilizers such as nickel, manganese and nitrogen that are designed to be present in such amounts as required to maintain an austenitic structure at room temperature. These materials are given an AISI designation as Types 200 and 300 stainless steels. Typical examples of such steels are AISI Types 201 and 202 and AISI Types 30 1, 302 and 304 stainless steels. Many grades contain incidental additions, such as molybdenum, columbium and titanium that affect the mechanical properties to some degree but do not basically afiect the austenitic structure nor fundamental mechanical properties. Such steels should be distinguished from ordinary low alloy and ferritic steels and from ferritic and martensitic type stainless steels which contain chromium within the same range as the austenitic steels but which do not contain suflicient quantities of austenite stabilizers to retain a room temperature austenitic structure and consequently do not have the same basic mechanical properties as the austenitic steels. Apparently, the unique mechanical properties inherent in austenitic stainless steels are required for the material to be amenable to the present process.

The grit employed in the initial grinding operation and in the subsequent grit blasting steps are the standard grit sizes as designated by the Society of Automotive Engineers (S.A.E.). The following Table I is a standard SAE grit size table giving the high and low limit screen sizes and the minimum and maximum percentages of grit retained and passed for a given number. The grit sizes 30, 70 and 90, as set forth in the present specification and claims, are not set forth in the table since these grit sizes are not standard commercially available particles and consequently are not set forth in the table; however, appropriate interpolation will evolve the appropriate measurements.

6 finishes, the standard polished black Carrara glass was used as a standard at 5.6% reflection at 45 and with the refractive index of 1.542.

It should be noted that all of the standard finishes exhibit different reflectivity from the longitudinal to the transverse readings, while the architectural finishes showed an identical reading in both the longitudinal and trans- TABLE I High limit screen Nominal screen Low limit screen Grit number Max. Screen Min. Screen Max. Screeen grit number grit number grit to number retained, and retained, and pass, and

percent aperture percent aperture percent aperture The 14 to 18 grit material may be composed of particles of any material, regardless of how hard or soft, that will impart the desired 14 to 18 grit finish to the steel roll. A particularly fit material has been found to be a Pangborn Mallabrasive material (Pangborn Corporation, Hagerstown, Maryland). Such material is composed of a hard brittle iron base product which has been reduced to the 14 to 18 grit size.

The 3.0 to 50 grit blast finish also may be accomplished by any material with sufiicient mechanical properties to impose such a 30 to 50 grit blast finish. I have obtained particularly desirable results by employing Pangborn Angular grit (trademark of Pangborn Corporation, Hagerstown, Maryland), such angular grit providing an abrasive with hard, sharp cutting edges.

Gloss meter readings were taken on various grades of standard finished sheet material commonly employed as architectural panel finishes on Type 302 and Type 202 stainless steels. Similar readings were also taken on the architectural finish applied to Type 302 stainless steel in accordance with the method of the present invention. Table II below shows the results of such readings.

The gloss meter employed was a photoelectric gloss meter, Model 660, manufactured by Photovolt Corporation, 95 Madison Avenue, New York 16, New York. To establish 100% reflectivity, a micropolished Type 302 stainless steel that was ground and polished with felt pads was regarded as having 70% reflectivity which is considered standard in the industry. For the lower reflected surfaces, #ZD, #2B and the present architectural verse directions. It is also to be noted that the architectural finish of the present invention ranges in reflectivity to from less than to more than a #2D finish. This is significant in that the architectural finish is far more attractive than the #2D finish and yet may possess either slightly less or slightly more reflectivity than that finish. It is to be noted that a #213 finish possesses higher reflectivity than a #3, and in fact, higher reflectivity than a #4 finish which is known to be a relatively bright and reflective finish.

I claim:

1. The method of providing an architectural finish to the surface of flat cold rolled austenitic stainless steel which comprises the steps:

(a) providing a steel roll that possesses a hardness of approximately 66/67 Rockwell C,

(b) grinding the surface of said roll with an grit abrasive so as to effect a uniform 80 grit finish thereon,

(c) grit blasting the surface of said roll with No. 16 grit particles so as to effect a uniform 16 grit, grit grit blasted finish thereon,

(d) grit blasting the surface of said roll with No. 40 grit particles so as to effect a uniform 40 grit, gri blasted finish thereon,

(e) inserting said roll as a work roll in a cold rolling mill and rolling said flat cold rolled austenitic stainless steel through said cold rolling mill so as to enrboss on the surface of said stainless steel the surface finish of said roll.

2. The method of providing an architectural finish to the surface of flat cold rolled austenitic stainless steel which comprises the steps:

(a) providing a hardenable steel roll that possesses a hardness of at least 60 Rockwell C,

(b) grinding the surface of said roll with a 70 to grit abrasive so as to effect a uniform 70 to 90 grit finish thereon,

(a) grit blasting the surface of said roll with particles of from 14 grit to 18 grit so as to effect a uniform grit finish thereon,

(d)grit blasting the surface of said roll with No. 30 to 50 grit particles so as to effect a uniform 30 to 50 grit finish thereon, and

(e) inserting said roll as a work roll in a cold rolling mill and rolling said flat cold rolled austenitic stainless steel through said cold rolling mill so as to emboss on the surface of said stainless steel the surface finish of said roll.

3. The method of providing an architectural finish to 7 the surface of flat cold rolled austenitic stainless steel which comprises the stepsz (a) providing a hardenable steel roll that possesses a hardness of at least 60 Rockwell C,

(b) grinding the surface of said roll with a 70 to 90 grit abrasive so as to effect a uniform 70 to 90 grit finish thereon,

(c) grit blasting the surface of said roll with particles of from 14 grit to 18 grit so as to effect a uniform grit finish thereon,

(d) grit blasting the surface of said roll with No. 30 to 50 grit particles so as to effect a uniform 30 to 50 grit finish thereon, and

(e) inserting said roll as a work roll in a cold rolling mill and rolling said flat cold rolled austenitic stainless steel through said cold rolling mill While applying alcohol as a lubricant so as to emboss on the surface of said stainless steel the surface finish of said roll.

4. The method of providing an architectural finish to the surface of fiat cold rolled stainless steel which comprises the steps:

(a) providing a pair of hardenable steel rolls, each of which possesses a surface hardness of at least 60 Rockwell C,

(b) grinding the surface of each of said rolls with a 70 to 90 grit abrasive so as to effect a uniform 70 to 90 grit finish on the surface of each of said rolls.

() grit blasting the surface of each of said rolls with grit particles of a grit size of from 14 to 18 grit so as to effect a uniform grit finish on the surface of each of said rolls,

(d) grit blasting the surface of each of said rolls with No. 30 to 50 grit particles so as to effect a uniform 30 to 50 grit finish on the surface of each of said rolls, and

(e) inserting said rolls as the opposing work rolls in a cold rolling mill and rolling said fiat cold rolled austenitic stainless steel through said cold rolling mill so as to emboss on the opposing surface of said stainless steel the surface finish of said rolls.

5. The method of providing an architectural finish to the work surface of hardened sheet or ship mill rolls and which surface shall impress complimentary finishes on sheet or strip during continued use thereof, the method comprising:

(a) grinding the surface of said roll With a 70 to 90 grit abrasive so as to effect a uniform 70 to 90 grit finish thereon,

(b) grit blasting the surface of said roll with particles of from 14 grit to 18 grit so as to effect a uniform grit finish thereon, and

(c) grit blasting the surface of said roll with number 30 to grit particles so as to effect a uniform 30 to 50 grit finish thereon.

6. The method of providing an architectural finish to the work surface of sheet or strip mill rolls having a hardness of at least Rockwell C and which surface shall impress complimentary finishes on sheet or strip during continued use thereof, the method comprising:

(a) grinding the surface of said roll with a to grit abrasive so as to effect a uniform 70 to 90 grit finish thereon,

(b) grit blasting the surface of said roll With particles of from 14 grit to 18 grit so as to effect a uniform grit finish thereon, and

(c) grit blasting the surface of said roll with number 30 to 50 grit particles so as to effect a uniform 30 to 50 grit finish thereon.

References Cited in the file of this patent UNITED STATES PATENTS