US2023904A - Process of finishing metallic sheets - Google Patents

Description

Dec. 10, 1935. L. SCHULTE PROCESS OF' FINISHING METALLI C SHEETS Filed June 6, 4952 flvvzwroe: Zoo/s 509w 7:5 gym [2% Patented Dec. 10, 1935 UNl'lED STATES PATENT, OFFICE PROCESS OF FINISHING METALLIC SHEETS Louis Schulte, Cleveland,

Ohio, assignor to Schulte Grinding and Polishing Machine Company, Incorporated, Cleveland, Ohio, at corporation of Qhio Application June 6, 1932, Serial No. M55843 5 Claims.

the sheets must have a maximum capacity of ice-- ing formed or drawn to the desired shape and where a smooth and uniform surface finish is essential. 35 In order to more clearly point out the novel features of my invention and their advantages. '1 shall first briefly describe the present process of sheet manufacture and its defects and deficiencies, with particular reference to the manu- 249 facture of sheet steel of the low carbon type.

Low carbon sheet steel is made from sheet bars by a hot rolling process in any suitable rolling mill. These sheets are rolled substantially to the desired thickness and are known as hot rolled or 25 black sheets. These sheets are then pickled, that isthey are immersed in a suitable acid, such as dilute sulphuric acid, for the purpose of removing the scale and other oxides and surface impurities, after which the sheets are washed, rinsed m and dried. These sheets are then annealed by any desired process and in any suitable apps. ratus. These sheets are then cold rolled to the desired thickness in any suitable type of cold rolling equipment. After this, the sheets are fiattened by a series of rolls or stretched by suitable equipment and sheared to size. f In some cases the order of pickling and annealing is reversed and other modifications and additions are frequently made in the above process for (3o 7 the manufacture of sheets. These sheets are generally known in the trade as full finished automobile or furniture stock. I

After the cold rolling above referred to, the sheets are inspected for visible surface defects as and signs of Weakness such as slivers, oxides, blemishes, pin holes, cracks, fissures, and other indications of defects and weaknesses.

I have found that from 30% to 60% of the cold rolled or full finished" steel sheets manufacgo tured substantially in accordance with the above described usual process are rejected by the inspectors. These rejected sheets have heretofore been sold as seconds at a substantial reduction in sales price entailing a considerable loss to the sheet manufacturer.

Among the causes for rejections on account of defects are minute cracks or pin holes originating from the sheet bar or billet and produced in the hot rolling and roughing process or produced by defects of the mill or by impurities or scale 5 adhering to the hot roll. Further causes for rejection are scratch marks resulting from the handling or transporting of the sheets in rolling,

. pickling, and annealing. Further causes for rejection are the presence of slivers formed either 30 in the hot rolling or in the cold rolling process. Many sheets are also rejected because of etch ing or corrosion marks produced in the pickling tank by contact of one sheet against another or other causes.

it should be noted that many defects of this type just pointed out are microscopic only and are not, visible to the eye of even a trained in spector and many sheets are approved which later fail during the drawing or forming process by cracking or tearing. It should also be noted that the above defects, and particularly the invisible defects, are purely surface defects and rarely penetrate more than a fraction of a thousandth of an inch below the surface of the sheet. It should also be noted that the surface of the metal is coated with a strain hardened film of relatively greater brittleness and less elasticity than the body of the metal which film is invisible to the eye as a defect and which has a deleterious efiect on the working properties of the metal.

One object of this present invention is therefore, to produce a sheet having a smooth pure metallic surface which is homogeneous in structure and uniformly smooth in appearance and which is free from visible and microscopic slivers, cracks, pin holes, fissures, oxides, blemishes and discolorations.

A further object of this invention is to provide a sheet which has a surface of uniform annular I structure free from visible and invisible dfiects and free from films of strainhardened metal, which will permit deeper drawing, bending, and/or forming with a minimum of breakage, tearing or cracking of the surface of the metal and which therefore has, superior drawing, forming, and spinning qualities.

A further object of this invention is to produce sheets which are free from surface defects, both visible and microscopic, which act as sources of w corrosion and eventually cause the lifting and cracking of the preservative or decorative coating of paint, enamel, or other material applied thereto.

A further object of this invention is to develop a M method of producing sheetswhich eliminates much loss and spoilage in the manufacture of the sheet and in the fabrication of the sheets into articles of the desired shape.

A further object of this invention is to provide a method of salvaging the large number of sheets which are rejected as seconds when manufactured by present processes and make sheets from these seconds which'are superior in appearance and'quality to the usual prime sheets, with a minimum of expense and with no commercially objectionable reduction in the thickness of the metal.

A further object of this invention is to produce a sheet of metal which has a smooth cold rolled finish superior in respect'to smoothness and texture to any finish obtainable with processes of the same efficiency and economy heretofore used and which sheet at the same time has superior drawmg and forming properties.

A further object of this invention is to produce a sheet of steel which has a smooth uniform texture and improved drawing and bending qualities and which at the same time has superior properties for the adhesion of paint, enamel, or other decorative coatings, and which will resist the flaking off and cracking of mnallic protective coatings.

Further and more specific objects of. this in- 3q vention will become apparent from the following description, and claims. This description sets forth in detail certain products and methods embodying this invention, such disclosed methods constituting, however, but a few of the methods 35* in which the principle of this invention may be applied.

In the producing of my improved product and i in the carrying out of my improved process I utilize the above enumerated generally used steps :0 of the present process of producing cold rolled sheets, or any other steps or processes for producing cold rolled or full finished steel sheets devised for this purpose in the industry. In order to correct the deficiencies and to correct the de- 15 fects of the present processes, however, I add a novel step to the present process of manufacture. This step comprises a novel grinding method which is effected on my improved apparatus disclosed in my pending application for patent en- 50 titled Method of and apparatus for grinding and polishing flexible sheets, Serial No. 583,960, filed December 30, 1931.

An explanation of certain features of this application is necessary for the full understanding 55 of the hereinafter described process and in the annexed drawing only so much of this machine is illustrated as is necessary to such full understanding.

Referring to the drawing:

60 Figure 1 is a side elevation of my improved apparatus adapted to perform the novel step of grinding flexible metallic sheets required for producing my improved sheet andcarrying out the 65 hereinafter described process.

' Fig. 2 is a plan view of the apparatus shown in Fig. 1.

Fig. 3 is a very much enlarged transverse sectional view taken on the plane indicated by line 7 3, I in Fig. 2, showing the relation of the grinding element and supporting rollers of one of the grinding units or stations.

' I shall first briefly describe the apparatus shown in the drawing and shall then describe the process 75 in which this apparatus is used for performing one of the steps, and shall then point out the advantages which result from this process.

Referring to the drawing, this improved apparatus comprises a conveyor which preferably consists of an endless relatively flexible belt I. a made of duc k, rubber fabric or other suitable material. This belt is mounted at one end on a driving or head pulley 2, and at the other end on the driven or tail pulley 3. This belt travels through a plurality of grinding units or stations, 1 three in the embodiment illustrated as shown at 4, 5, and 6. Each of these grinding units or stations is provided with a grinding or abrading element, a grinding wheel 'I being shown in the units 4 and 5 and a grinding belt 8 mounted on pulleys lb 8a and 8b being shown in the unit 6. As will be evident from an inspection, the upper strand of the conveyor belt passes through the upper portion of the grinding units adjacent to the grinding elements, and the lower or return strand 20 passes through the lower portion of the grinding units.

The driving or head pulley 2 for driving the conveyor belt is rotatably mounted in a pair of bearings 9 supported in floor stands l0 and is driven through suitable gear reducer mechanism and sprocket chain drive, by means of a motor H. The bearings 9 are adiustably mounted on the =fioor stands I0 and adjusting screw devices I2 are provided for the purposeof maintaining the desired tension on the sprocket chain drive and belt I.

The driven or tail pulley 3 is similarly rotatably mounted in a pair of bearings l3 adjustably mounted on floor stands l4. 1 Adjusting screw de- 85 vices l5 are provided for the purpose of regulating the tension on the endless flexible belt I.

This apparatus includes a series of grinding units or stations when the apparatus is of the continuous type as illustrated at Figs. 1 and 2, in 40 which a sheet is fed in at one end of the apparatus and moves continuously in one direction the upper side of the sheet successively engaging the various abrading elements until the sheet is finished and removed at the other end of the apparatus.

The above continuous type of machine is especially well adapted for quantity production. Where less production is required a machine having only a single unit is employed, this machine being equipped with an automatic device for reversing the direction of travel of the conveyor belt.

Each grinding unit or station consists of three floor stands I6, I1, and I8. Fixedly mounted on 65 each of thesefloor stands is a bearing IS in which a shaft 20 is mounted. Upon this shaft in units 4 and 5 is mounted the grinding element 1 and also a suitable pulley adapted to be driven by means of a belt 2| from a motor 22. The shaft 20 is adapted to be reciprocated axially, as it rotates, by means of a motor 23 mounted on the floor stands [8.

As has been pointed out, the belt passes through the upper portion of the grinding unit adjacent to the rotating grinding surface of the grinding element. As will be evident from Fig. 3, this belt is supported by a pair of spaced bed rollers 24 each mounted in a pair of arms 25. The arms 25 are supported on shafts 26 and 21 which are, in turn, mounted on vertically adjustable bearing blocks 28. Suitable means are provided for raising and lowering the bed rollers 24 and for vary-'- ing the spacing of these rollers, as is pointed out in my co-pending application Serial No. 583,960. (6

Pivotally mounted on each end of the bed rollers 24 is an angularly shaped bracket 29. Each bracket supports a pair of pinch rollers 30 and 3 I. The lower pinch roller 30 is rotatably mounted in the bracket 29 and in a flxed position in the bracket and the upper rubber covered pinch roller 3| is adjustably mounted in the bracket for movement toward and from the lower roller 30.

The grinding unit or station 6 is identical in construction with grinding units 4 and 5 just described except that in the grinding unit 6 a grinding belt 8 is used for the grinding element instead of the grinding wheel. This grinding belt is mounted on a pair of pulleys 8a and 8b, the lower one of which is mounted on the shaft 20 and the upper one of which is mounted on the shaft 20a which is rotatably supported in suitable bearings mounted on columns 32 which are in turn supported on the floor stands l6 and H, as will be readily understood.

The periphery of the grinding wheel and the outer surface of the grinding belt are coated with a suitable abrading material secured in place by means of cement, glue, or other suitable adhesive.

In order to protect the belt I from abrasion or wear by contact with-the grinding wheel or grinding belt when no sheet is mounted on the belt under the grinding elements, a metallic apron sheet I a, preferably made of relatively thin, inexpensive, flexible steel, fibre, or the like, may be mounted on the belt. I have found that a hot rolled soft annealednon-pickled sheet with heavy scale, is best adapted for use as an apron sheet and wears a relatively long time. This apron sheet may be made in sections and may be secured to the belt i by rivets or in any other approved manner when the apparatus is of the continuous type.

In the use of the apparatus just described, the sheets to be ground, indicated at 33a, 33b, 33c,

and 33d, are loosely placed on the apron sheet on the traveling belt i. When the sheets reach the pinch rollers 30 and 30, the sheet, apron sheet and belt will be pressed between the pinch rollers and the sheet will be held frictionally to the surface of the belt 9 by these pinch rollers, the intensity of this frictional engagement being adjustable as may be required. These pinch rollers are preferably provided at points just ahead of and just behind the point where'the grinding or polishing element engages the sheet and they are provided for the purpose of preventing the sheet from being shifted or otherwise thrown longitudinally of the belt by the force of the grinding action on the sheet. I

As will appear from Fig. 3, belt 8 is supported on the bed rollers 28 which are symmetrically spaced about a vertical plane passing through the grinding wheel '21 and the belt together with the superimposed sheet 33a is slightly flexed downwardly concavely toward the grinding wheel at the point where the grinding surface contacts the sheet. It will be understood that the intensity of contact pressure of the grinding surface on the sheet 33a may be varied either by changing the tension on the belt or by changing the spacing of the rollers 26 or by raising or lowering the rollers 26. V

The nature of the abrasive used on the grinding element, as well as the intensity of contact pressure of the grinding surface on the sheet, and the speed of the grinding element and the speed with whichthe sheet traverses the grinding surface will determine the amount of ma terial removed by one pass of the sheet on the wheel. The texture of the finished surface desired also determines the abrasive to be used as will behereinafter pointed out. 7 It willbe evident that certain novel and very 5 desirable advantages result from the use of this apparatus. It will be evident, for instance, that the conveying belt which supports the sheet is relatively soft and yielding, and, from this, it will be understood that if there is any varia- 10 tion in the thickness of the material of the sheets being ground or if there is any variation in the contour of the surface of the grinding element, or if there is any unevenness in the surface of the supporting belt, the belt will flex sufliciently to absorb this or any other irregularities, this yielding of the belt to irregularities being afiected by the softness of the material of the belt as well as by the resilience of the belt in a y direction at right angles to the grinding surface. It will'further be apparent that the flexing of. the sheet concavely toward the grinding or abrading element at the abrading surface will produce a substantial increase in-the length of the arc of contact of the sheet on the abrading element, thereby causing the abrading element to contact a larger area of the sheet at any instant than would be possible on a flat sheet.

A further result of this concave flexing of the sheet toward the abrading element is that the unit of pressure per square inch against the abrading element is very much smaller than this pressure would be if the sheet were flat or bent concavely outwardly, for the removal of the same amount of material from the surface of the sheet, the longer are of contact of the sheet against the abrading element resulting in the same amount of removal of material. Another decided advantage of the flexing of the sheet concavely toward the grinding element 40 is the fact that the sheet, when flexed in this manner, tends to assume a truly cylindrical form in which all' of the elements in the flexed portion are straight lines parallel to the axis of the abrading element. This property of the flexing actually serves to straighten sheets which are normally wavy and have high spots when laid on a flat table, these sheets, when thus flexed, presenting a true cylindrical surface to the abrading element. As a result of shaping these so sheets into the cylindrical form producing straight line elements parallel to the axis of the grinding element, a contact of the abrading element across the entire face of the sheet and at every point of the face is assured.

A further advantage of the flexing of the sheet concavely toward the abrading element is that there is a minimum of heating of the sheet during the grinding operation and, due to the fact that no high spots on the sheet are forced into an the abrading surface of the abrading element, no blue spots or other discolorations occur in the sheet due toan intensive contact with the abrad ing element on high spots.

A' further advantage of this flexing of the g sheet is that, if any heat is generated in the sheet at any point by the abrading element for any reason, this heating, local or otherwise, will instantly cause the sheet to buckle or bulge under Y the influence of the heat and, as is well known, 7

As pointed out above, the abrading or grinding element is axially reciprocated during the grinding operation and this axial reciprocation facilitates the production of a uniform texture of the surface of the'sheet.

In carrying out my improved process for the production of the improved sheet, which fulfills the objects of this invention set forth at the beginning of this specification, I start with the cold rolled or full finished sheet produced by hot rolling, pickling, annealing and cold rolling in any suitable type of cold rolling apparatus, or cold rolled sheets having characteristics similar to those pointed out above and produced by any desired process. As pointed out above, these sheets have many defects, some of them visible and others only microscopic, which cause their rejection and/or failure in subsequent fabrication operations. Among these defects are cracks, slivers, pin holes, fissures, etchings, corrosion marks, strain hardened surface films, etc. Many of these defects, as was pointed out, penetrate only a microscopic distance into the body of the metal, in many cases not to exceed onehalf of one-thousandth of an inch, but this microscopic depth of these defects is sufiicient to start cracks which cause failure in fabrication. The cold rolled sheets, such as prepared above, are at present accepted by the trade .and the failures resulting from the use of these sheets condoned as an unavoidable evil.

I have found, however, that by grinding the microscopic film from the surface of the sheets in the novel manner in the improved grinding apparatus described above, I am able to produce sheets which are substantially free from visible defects and which substantially entirely eliminate failures in subsequent fabrication. By selecting the proper abrasive, glued or cemented to the abrasiveelement, I find that a single pass of the sheet through a number of units or stations such, for instance, as illustrated in Figs. 1 and 2, is usually suflicient to produce the desired results. In this apparatus the sheets can be treated in a continuous manner, entering one end of the machine and discharging from the other end; If, however, only a single unit is provided in the machine, the direction of travel of the conveying belt may be reversed either automatically or manually, and in this manner several passes will be sufficient to produce the desired texture of finish on the surface of the sheet and the desired freedom from injurious surface defects.

In order to secure this rate of production on low carbon steel sheets, I have found that it is necessary to use an emery of about grit or an artificial abrasive of about grit with a conveyor belt speed of from 30 to 40 feet per minute.

It should be pointed out that with an apparatus including a plurality of units, my process contemplates the use of different grades of abrading material on the several units, a coarser grade on the first unit or units engaging the sheet and a finer grade or grades on the units which engage the sheets at the end of the grindingoperations. When the apparatus is only provided with a single unit it will be understood that the sheets will be finished in batches, all of the sheets of one batch being first ground with a coarse grinding element. The grinding element is then removed from the housing preferably with shaft, bearings and pulley, and a finer abrading element is put in place in the unit and the sheets in the batch are then given a second finer ing, for sheets which have to be used for decoraproduced by polishing or bufiing the sheets in 8.

grinding, and so on until all the sheets have been surfaced to the desired degree of fineness.

It is distinctly pointed out that this grinding or abrading process does not contemplate the removal of all of the hot rolled surface scale, oxides, 5 or other impurities by grinding as this is not economically feasible. The herein described process contemplates starting with a sheet from which these surface impurities have been removed by commercially eflicient processes and sheets 10 which have been smoothed by the coldrolling process.

This novel manner of performing the abrading operation has enabled me to secure results which it has been impossible to obtain by grindl5 ing the sheets in any other manner.

This process produces a smooth, pure metallic surface which is uniform in structure and ap pearance and is free from the visible and microscopic defects and strain hardened films of metal. 20

The practicing of this process has enabled me to produce a sheet which will permit deeper drawing and bending or forming and which is much superior inthis respect to any sheets produced with any other commercially feasible processes. 26 This process has further enabled me to produce sheets which are free from those surface defects such as pin holes, cracks, etc., which serve as incipient sources of corrosion due to the entrapping of moisture when a protective coating is 80 applied. This process has further enabled me to eliminate spoilage in the manufacture and fabrication of the sheets and has provided a process of salvaging large numbers of sheets which have heretofore been rejected as seconds, 8 thesesalvaged sheets being superior in appearance and quality to the usual prime sheets and the salvaging having been effected with a minimum of expense.

The hereindescribed process may to one or both sides of the sheets depending on the use for which the sheet is intended as will be understood.

It frequently happens that a smoother finish or polish is required than that produced by grindtive purposes and such smoother sheets may be machine, such as described above, without injuriously affecting the drawing properties of the 50 steel sheets. Such a uniform polished surface may be produced by passing the sheet several times into abrading engagement with a grain emery with grease or oil, or a composition comprising stearic acid mixed in a moltencondition with other lubricants or finer abrasives such as pumice powder, fine emery, tripoli powder, rotten stone, or the like.

For-certain purposes where a high polished steel is required and where it is important to have a sheet free from surface cracks, pin holes, slivers, oxides, fissures and other defects, which injuriously affect the drawing properties of the steel and where it-is essential that these sheets be produced with a minimum of expense, I employ a few additional steps to produce a superior I product at a low expense. These steps consist of subjecting the surface of the cold rolled steel ground in accordance with the above described novel method, to a slight acid treatment and 70 afterwards giving the sheet one or two light passes of cold rolling on a highly polished cold rolling mill, preferably equipped with hardened heat treated alloyed type of rolls. This combined process produces a surface on the sheets which ll be applied 40 rolled sheet produced in any other manner, with the same economy. Such sheets are particularly useful for articles which are to have "a highly decorative surface.

As explained above, the cold rolled sheets treated with my improved method of grinding have superior qualities for preventing the starting of corrosion under the surface of the coating. For some purposes, however, a surface is desired which forms a greater adhesion to or bond with the coating material, and where a deep drawing steel is required for such purposes, I use the following steps; the cold rolled sheet surface treated with my special grinding method is subjected to an acid treatment or pickling which produces a surface on the sheet which is uniform in texture but which has greater properties for bonding with a paint or enamel protective or decorative coating. Such a sheet is also well adapted for hot galvanizing and when so coated will withstand the flaking oil or cracking of the zinc coating much more effectively than any other types of galvanized sheets, especially in drawing or forming operations. These sheets, if annealed after galvanizing, producing what is known as galvano-annealed sheets, will be still better adapted for forming or drawing without flaking.

A steel sheet ground on both sides by my improved process is also particularly well adapted for the production of tin plate. Such a sheet can be immersed in the fluxing liquid and tinned immediately after it leaves the grinding apparatus, and will produce a superior tin plate especially in respect to corrosion resisting properties.

Another very advantageous use of steel sheet ground by my process results from white annealing such a ground sheet in the presence of a reducing gas, which is known as a deoxidized sheetl Such a sheet is very useful in the trade, having a fine, uniform white-grey appearance and is excellent for deep drawing.

While the above processes and products produced therewith have been described very largely with respect to the manufacture ofsteel sheets, it will be understood that in its broader aspects this invention is not limited to any particular material and is equally applicable to other metals.

Many other modifications of this invention and its application will naturally occur to those skilled in this art, and the present disclosures should therefore'be considered as typical only and I do not desire to be limited to the exact process shown and described.

What I claim is:

1. The process of producing a metallic sheet suitable for deep drawing and having a surface of uniform texture, consisting of pickling the sheet, cold rolling the sheet, progressively fiexing the sheet concavely and yieldingly engaging the concaved surface of the sheet with a cushioned rotating grinding surface, and grinding only suiiicient metal from the surface of the sheet to remove the surface defects and strain hardened film imparted to the sheet by the preceding steps of manufacture.

2. The process of producing a metallic sheet provided with a highly finished homogeneous surface, consisting of pickling the sheet, cold rolling the sheet, removing the microscopic defects from the surface of the sheet by progressively flexing the sheet concavely and by yieldingly engaging the progressively concavely flexed surface of the sheet with a rotating grinding element and subjecting the surface of the sheet to an acid treatment and lightly cold rolling the sheet subsequent to the grinding operation.

3. The process of producing a low carbon steel sheet suitable for drawing purposes from a black steel sheet which consists of annealing the sheet, pickling the sheet, cold rolling the sheet, and grinding the skin defects from the surface of the sheet which are imparted to the sheet by the pickling, annealing and cold rolling steps, by progressively flexing the sheet concavely toward, and yieldingly holding the concave portion of the sheet in engagement with, the periphcry of a cushioned rotating grinding surface.

4. The method of reclaiming rejected cold rolled sheets which consists of removing only so much of the surface of the cold rolled sheet so as to remove the microscopic strain hardened film by progressively lightly contacting the sheet witli the periphery of a rotating abrading element, the area of contact being substantially greater than a line contact, subjecting the sheet to a washing treatment and again lightly cold rolling the sheet, whereby no commercially ob-' jectionable reduction in thickness is effected.

5. The method of reclaiming rejected cold rolled sheets which consists of abrading only. so much of the surface of the cold rolled sheet as will remove the microscopic strain hardened film. subjecting the sheet to a slight acid treatment and lightly cold rolling the sheet, whereby the entire surface of the sheet is treated and whereby the thickness of the sheet is not reduced more than two one-thousandths of an inch. I

LOUIS SCHULTE. 5

Images