US2671491A - Method for forming sheet metal and sheet metal formed thereby - Google Patents

Description

' March 9, 1954 A s BIORDI ET AL 2,671,491

METHOD Fok F'oRMING SHEET METAL AND SHEET METAL FORMED THEREBY Original Filed Jan. 20, 1951 7 She ets'-Sheet l ,Higl. T

flLaaerfi. .B/ORDI AZ zinc/r M TVTQRNER IN V EN TORS- flTTORNE Y- A. S. BIORDI ET AL METHOD FOR FORMING SHEET METAL AND March 9, 1954 2,671,491

SHEET METAL FORMED THEREBY Original Filed Jan. 20, 1951 7 Sheets-Sheet 2 mm fl 3 6 5% w SW T E E/ mm 3 w 2 fl v. J B F 4 T ll! w w 3. E 6 Z a m ww w H MWQ 6 3 a t ATTORNEY.

March 1954 A. s. BIORDI ET AL METHOD FOR FORMING SHEET METAL AND SHEET METAL FORMED THEREBY Original Filed Jan. 20, 1951 7 Sheets-Sheet 3 JqLBL-RT EB/0RD) & tin CK M. Mm/ER 7 INVENTORS.

March 9, 1954 s, BIORDI ETAL 2,671,491

METHOD FOR FORMING SHEET METAL AND SHEET METAL FORMED THEREBY Originai Filed Jan. 20, 1951 7 Sheets-Sheet 5 229.16. fi'w'giz E 918.

ALBERT SIB/0RD: (hi/1m J'I. WERNER m\\\\\\\\\ IN V EN TORS.

March 1954 A. s. BIORDI' ET AL 2,671 9 "METHOD FOR FORMING SHEET METAL AND SHEET METAL FQRMED THEREBY Original Filed Jan. 20, 1951 '7 Sheets-Sheet 6 a7 as 87:

INVENTORS.

A T TOENE y.

March 1954 A. s. BIORDI ET AL 2,671,491

METHOD FOR FORMING SHEET METAL AND SHEET METAL FORMED THEREBY Original Filed Jan. 20, 1951 7 Sheets-Sheet 7 EgJZ. 32 3 I 3 84: 2 83 92 INVENTORfi.

Patented Mar. 9, 1954 UNITED STATES- ATENT OFFICE METHOD FOR FORMING SHEET METAL AND SHEET METAL FORMED THEREBY tion of California Original application January 20, 1951, Serial No. 207,044. Divided and this application May 5, 1952, Serial No. 286,046

7 Claims. 1

This application is a division of application Serial No. 207,044, filed January 20, 1951.

This invention relates to a method of forming an insulation and acoustical blanket and to the method of forming the foil employed in the manufacturing of the envelope for such insulation or acoustical blanket, and also to machinery for making such foil for such use.

Blankets now primarily employed for high temperature insulation for surfaces of jet and gas turbine engines are constructed of layers of batting of silica or glass fibers encased in a metallic foil envelope. The envelope formed of thin sheets of metal foil is used as a reflective surface to act as a radiation shield to cut down the loss of heat from the heated surfaces which are insulated by the blankets.

Since there is danger of fuel leaks from such jet engines, foils of sheet stainless steel, formerly sheet silica foil, are employed to form envelopes with sealed edges to seal the porous batting and prevent the accumulation of fuel in the batting which otherwise would create a severe fire hazard. Such envelopes also give added strength to the blanket, particularly when glass fiber or envelope which is to be placed closest to the surface to be insulated'by the blanket, called the hot side. The grooves or corrugations are placed parallel to the generating element of the surface. Thus, for cylindrical surfaces, the grooves are parallel to each other and for conical surfaces they form an acute angle with each other related to the angle of the cone which is to be covered.

It is a feature of our invention that the edges of the corrugated blanket are so formed that the blanket is of substantially uniform thickness to its edges. This is accomplished by so forming the edge of the sheet that it may be overfolded to form a sealed edge without substantially compressing the fibers of the batting. This is accomplished by pleating the foil adjacent the ends of the groove and bending the adjacent foil along its longitudinal edge into an arcuate form to pro vide room for the batting when the longitudinal edges of the foil are overfolded.

By so forming the envelope we may overfold grooves at the desired angular relation to each other. We also provide means for pleating the edges of the. sheet at the ends of the grooves, and

provide means for forming the adjacent portions of the foil to form an arcuate edge to the sheet.

For such purpose we have devised a grooving, pleating, and forming press containing a grooving die in whicha foil groove is formed and an indexing slot means to receive the grooved foil and to hold the sheet to form the desired angle between successive grooves so that they shall be along the generating lines of the developed surfaces. We also provide an edge-holding and pleating die to form the arcuate ends referred to above.

These and other objects of our invention will be described in connection with the drawings, in which Fig. l is a vertical front view of the forming press of our invention;

Fig. 2 is a section taken on line 2-2 of Fig. 1;

Fig. 3 is a perspective of the die assembly;

Fig. 4 is a detail section taken on line 44 of Fig. 1, showing the positioning of the female dies and indexing slots;

Fig. 5 is an exploded view of the male pleating die;

Fig. 6 is an exploded view of the female grooving, pleating, and indexing dies;

Fig. 7 is a section taken on line of Fig. 1;

Fig. 8 is a fragmentary side view of Fig. '7;

Fig. 9 is a bottom view of Fig. 8;

Fig. 10 is a section taken on line Ill-I0 of Fig. 1;

Fig. 11 is a section taken on line HH of Fig. 12;

Fig. 12 is a side view of Fig. 10;

Fig. 13 shows a perspective view of a modification of the holding die;

Fig. 14 is a view similar to Fig. 10, showing the positioning of the die of Fig. 13;

Fig. 15 is a somewhat schematic showing of the mechanism in position in the first stage of the grooving operation;

Fig. 16 is a somewhat schematic and fragmentary view showing the second stage of the operation showing the engagement of the edge holding mechanism; I

Fig. 1'7 is a sectional view similar to Fig. 16, showing the engagement of the pleating die;

Fig. 18 is a somewhat schematic view show ing the last stage of the cycle of operation of formation of the pleat and curved edge;

Fig. 19 is a section taken on knew-19 of Fig.

Fig. 20 is a side view of Fig. 21;

Fig. 21 is a view taken on line '2 l-2I of Fig. 1 showing the engagement of the pleating die;

Fig. 22 is a plan view of a fragment of the foil showing the groove in its initial form;

Fig. 23 shows the position of the succeeding grooves;

Fig. 24 is a section taken on line 2424 of Fig. 22;

Fig. 25 is a section taken on line 25-25 of Fig. 23;

Fig. 26 is a section taken on line 26--25 of Fig. 23;

Fig. 27 shows an enlarged. detail of the pleate arcuate end of the grooved foil;

Fig. 28 is a section taken on line 28-48 of Fig. 2'7;

Fig. 29 is the same view as Fig. 2'7, but showing the position of the section lines of the succeeding figures;

Fig. 30 is a section taken on line 3l)--3ll of Fig. 29;

Fig. 31 is a section taken on line 3i-3l of Fig. 29;

Fig. 32 is an end view of Fig. 29;

Fig. 33 shows the developed corrugated foil for use in a blanket to cover a conical pipe;

Fig. 34 shows the blanket'formed from the foil of Fig. 33 and curled for illustrative purposes;

Fig. 35 shows how the blanket may be positioned in a conical tail pipe of a jet plane;

Fig. 36 is a section taken on line 35-36 of Fig. 34;

Fig. 37 is a section taken perpendicularly to the section on line 31-41 of Fig. 34;

Fig. 38 shows a formed sheet such as may be employed in forming a blanket for a cylindrical pipe; and

Fig. 39 illustrates a blanket formed from such sheet and positioned on such a cylindrical pipe.

The press is formed of a bed i, suitably supported on ends 2. The bed carries the female grooving die 4, shown in Figs. 2, 3, and 4. This is formed of an elongated bar carrying a longitudal groove 1 and a flange 8. Suitably slotted clamping bars placed on the flange and held to the base clamp the die to the bed. The align larity of the die and its position on the bed may thus be adjusted by moving the die with respect to the clamping bars on the bed.

Extending longitudinally of the bed (see Fig. 1) is a slotted horizontal vertical bar or flange i I which is affixed to the bed by suitable bolts. A plurality of die blocks carry a groove :8 between the top flat surfaces of the die block l2. These blocks are assembled side by side between clamping plates I3 with notch I2a on the flange II and held in place on the flange .l l by the bolts M which pass through suitably provided slots in the die blocks, clamping plates and the flange. An elongated female die is thus obtained, Mounted on the flange at each end of the assmbled die blocks 12 is a pleating die I5 .(see Figs. 2, 4, and 6) having a curved groove 11, having a vertical section which is convex upwardly, which registers at one end with the groove N3 of the die block I2. Flanking the groove is a curved surface 11' of like curvature but disposed at a higher elevation than the base of the groove H. The flat top face I5, formed as a flat extension of the pleating die 15, is at a lower level than the top face IQ of the die blocks l2 to meet the downwardly curved faces 16 of the block l5, between which faces the curved groove I1 is positioned. The position of the die blocks [2 and the pleating dies may be altered by moving them on the flange 11 to the desired location.

The holding dies 20 and 2| are mounted on each side of the female pleating die l5. They are coplanar and conform to the surface I5 and I1, respectively. The dies are assembled and held in place on the flange 1 by the pins 22 which pass through the dies and the flange II. It will be observed that there are two pleating dies of the same construction, one at each end of the die block assembly, and that each of these dies 15 is flanked by holding dies.

The indexing dies 23 are grooved and formed in identical fashion to the pleating dies I5 with a curved face 24, like It, curved groove 25, like I7. and flat face 26, like l5. This die is mounted on a bracket 21. It is grooved to slidably fit over the flange 21' and is held by the set screw 23. The bracket 21 carries a pivot hole 28. A hub plate 29 carrying bolt holes 30, a hub 31, and a bore 32 may be clamped to the flange I l by means of suitable bolts, and a pin 33 passes through the bores 32 and 28. An index 34 and a protractor 35 may be provided to measure angular adjustment of the bracket 27 and the index die 23 about the axis of the pin 33. The position of the die longitudinally of the flange may be adjusted by positioning the bolts 36, and the an gular relationship of the slots 25 with respect to the face of the flange H may be adjusted by rotation of the bracket 21 about the pin 33. The position of the index block along the flange 21' may also be adjusted by sliding the block along the flange. It will be observed that two such index block assemblies are provided, one adjacent each female leating die ii.

The male grooving die 31 (Figs. 2, 3, '7, and L5) is mounted on a bracket 38 between clamping blocks 38 on the vertical slide 40. The edge ll of grooving die enters the groove of the female grooving die I. The lateral position of the male grooving die in respect to the bed of the press is adjusted by positioning the male grooving die on the bracket 38 which extends along the length of the slide 40 and is provided with suitable transverse slots positioned at intervals. The slots being elongated, the angular position of the die 31 with respect to the face of the slide 40 may also be adjusted. The male grooving die I! may thus be fixed parallel 'to and mating with the female grooving die I.

The male holding die (see Figs. 2, 5, 6, '7, 10, and i5) is formed of a plurality of abutting blocks, shown as four, to wit, 43a to Mid, inclusive, each provided with a T head 43 and a squarefaced knife edge 44 and adjacent faces 44 between which the knife is positioned. The square-faced knife edge 44 of each block is such as to mate and register with the grooves I8 of the die blocks I2 and with adjacent faces 44 registering with faces IQ of the die block 12.

The end die'blocks 43a and 43d have vertical slots 42 formedin their outer faces. The blocks are slid nto the 1' slots 53' formed in the T slide B3. The pleating die 46 is formed with a T head extension bracket 42a carrying a suitable bore so as to fit into the T slot 53. The vertical rib 42a is formed in the outer face of the pleating die 46 to enter and engage with the slots '32. By passing a stud through the bore 420 and suitably disposed bore in the T slot, the dies are fixed in the slot and hold the die blocks in a fixed position in the slot.

The pleating die 46 positioned at each end of the die 42 has a knife 44 similar to 45', the vertical section of which is convex upwardly, and forms a curved extension of the knife edge 45 to form the curved pleating knife 44 which is the pleating die 45 (see Figs. 11 and 12) and fiat surfaces 15 positioned at the end of the knife so that it conforms with the surfaces 15 and Hi and the groove I! of the female pleating die. Thus, when the pleating and holding dies are placed in the die blocks 62, the l-znife edge 44 enters the groove 18 and the knife edge #55 enters and conforms with the groove H which has a like curvature to the knife edge 45, and the flat surfaces 44' (see Figs. 18 and 19) rest on the surfaces I8 of the die block I2 and the surface 46 on the surfaces !5 and 15. The knives referred to above are not formed to have a cutting edge, but have a cross section which conforms with that of the mating female die.

The sides of the holding blocks 4'! (see Figs. 5, 6, 10, 1i, and 12) are grooved at 8 so that they slide over the slides 45 formed on both sides of the pleating dies. The holding blocks 47, at their lower ends, are curved at 49 to conform with the curved surfaces 2| of the holding dies 25. These holding blocks have a flat surface 59 which conforms with the flat surface H of the holding dies 20. Compression springs 5| are mounted in the bores 52 of the sliding holding blocks All and underneath the T slot 53 in which the T head 43 is mounted. The blocks ll are provided with a slot 54 so that they can slide over a pin 55 which passes through the bore 55 in the slide 46.

Figs. 13 and 14 show a modification of the construction wherein a groove 48' is provided in the face of the holding die on the other side of the groove 48. An elongated slot 54 is provided and two pins 55 are employed to hold the plate as in the groove. This construction prevents any tipping of the die about the pin.

The T slide 53 is mounted longitudinally of slide 40 on brackets 57 positioned at the ends of the rods 58 which are carried in bearings 59 psitioned on the slide it. The rods are clamped in brackets 58 positioned on the slide 45! by means of heavy tension springs i, bolts 62 and adjusting bolts 63 on threads B formed in the rods 58.

The slide all is reciprccated by the link 55 (see Fig. 2) which is pivoted on the slide at 5 and on the frame by means of the link 6% pivoted on the frame at 6'! and on the link 65 at pivot 63. The link 65 is pivoted to the piston red It! at 69 and the cylinder 7! is pivoted on the frame at T2.

Having erected and leveled the press so that the bed plate I of the press is level, the die blocks I2 and the holding and pleating dies l5 and 36 are assembled in the T slot 53 so that the female and male dies register. nuts 133 are adjusted so that the T slot is level and uniform cornpression of the male and female die occurs across the longitiudinal length thereof. The clamping blocks 9 are adjusted so that the angle which the center line of the die groove 1 of the grooving die 4 makes with the center line of the slot [8 of Figs. 22-24).

the assembled die block i2 is the required angle for the surface elements of the developed sur-' face being grooved. Thus, it may be an acute angle for the form shown in Fig. 33 or parallel for form shown in Fig. 38. The brackets 21 are adjusted on the flange H so that one index die is adjacent each female pleating die and the in-' dex dies are longitudinally separated on thecenter line passing through the groove of the indexing die at a distance equal to the longitudinal separation of the female pleating die on the center line passing through the grooves. The brackets 27 are adjusted about their pins 32 and the blocks 23 are positioned on the flange 21, so that the center line of the grooves of each of the index dies 23 at both ends of the die 52 are on one line, which bears the same angular rela-,

of the die 43.

The operation of this press will be described when employed in forming the corrugated elongated foil with cupped longitudinal ends which we have developed for use with insulating blankets. It will be understood that sheet metal of various thicknesses may be employed, depending upon the power of the press to form these sheets.

The cross sectional form of the grooves may be altered and the angular relationship thereof also altered, depending upon the function forwhich the sheet is designed.

Thus, sheet material, such as stainless steel sheet of about 0.002" thickness (such sheets are herein referred to as foils l3) formed into an elongated sheet, of width preferably not less than the length of the male grooving die, is fed ina direction of the length of the sheet and transversely to the die. One end is positioned over the die 4 and a switch (not shown) may be manually actuated to start the hydraulic pump to actuate the piston in cylinder H. The piston ascends, causing the slide to descend, and the male die 31 enters the female grooving die 6 (see Fig. 15). When fully entered the pin 13 which has been previously adjusted for such purpose opens the circuit and cuts off pressure in the cylinder 1. When the circuit is again manually closed. the pump is actuated to cause the piston 10 to descend and the slide thus ascends. The maxi.

mum upper limit of the stroke is controlled by the position of the contact 8| which trips the notch 13.

A groove 83 is thus formed which extends across the width of the sheet 84 from edge to edge (see The groove has a u shaped cross section, as shown in Fig. 26. When the groove 83 is formed the sheet 84 is lifted from the grooving die 4. The sheet 84 is now advanced and the groove 83 is positioned in the die blocks l2, the groove fitting inside the grooves l8. next descent of the slide, a second groove 85, similar to 83, is formed in the female die 4. Simultaneously the holding and pleating dies 43 and 4'! and the female dies I 2 and I5 function in the following manner. When the slide descends the blocks 41' first contact the sheet 84 at 86, i. e., in the area of 84 (see Fig. 26) adjacent to and on both sides of the groove, which is thus clamped between the curved surface 49 of the block 41 and the curved surface 2| of the holding On the block 8 and between the not surface 24' of the block 20 and the flat surface in of the block 41. Thus. at the corresp d ng l n tu dg th sheets are curv d downwardly into a portion at Fig. 25) curved transversely of the longitudinal edge of the sheets, and a fiat, i. e., horizontal, flange portion at 88. As the slide 40 con tinues to descend, the springs .5! compress, holdthe edges 8.6 .on both sides of the groove 83 ainst displacement on the holdin urfaces and thus smooth. However, since the portion of the sheet between the blocks 20, i. e., between the inner faces B9 and 3 of the blocks 41 .(see Figs. 10, 11, and 15). is not restrained it tends to cup due t the curlin o the curved flange formed when the holding dies meet. The transverse section of the cupped flange is thus convexed upwardly. As the slide 60 continues in its descent. he blade 44 and the curved blade 48 enter the oove .83 and force it into the gro ve 8 and the curved groove H, The excess metal in the cupped port on s thus ocally pleat d betw e the me ns surfa es of l5 a d 6- Th f rm of the pleat is a box pleat, as illustrated in Fig. 31, Since there is a greater excess of metal at the curved surface 8.! than at the horizontal surfaces of the flange positioned over of the pleating die [.5 or over 19 of the longitudinal holding .die, the pleat is wider over the curved surface and becomes triangular in shape as it progresses outwardly in both directions away from the curved surface in the form of a generally diamondshaped pleat. Thus (see Fig. 29) the pleat is wider at 92 and narrows down to disappear at 94 and narrows down to a narrow pleat at 93 where it intersects the edge. The result is a local constriction in the groove at the curved surface 31.

The sheet may now be advanced to form the succeeding grooves at equal predetermined intervals and angular relation throughout the length of said sheet "by again setting the grooves formed in the grooving die 4 in the die block .12 which function thus as registering dies to regulate the advance of the sheet and the angular disposition of the succeeding grooves, II the ud nal length 0.1 the sheet t r ugh an acute angle equal to that between the center lines of the die blocks 12.- This is s m what inc nveni nt and a slow per tion. We have incr ased th peed of the peration by u ing the index ng dies 3 which are adjusted as described a ove by setting the curved grooved foil sheet after formi in the blocks [5 and 20 in the dies 23. The sheet is automatically advanced and rotated through the desired angle described above to place the roove formed in the die 4 in the die blocks 12 and L5,. Thus, the die blocks I2 index the posi, tion of the first roove formed the front edge of the sheet and the index blocks 23 position ach succeeding groov in 12 and automatically index the sheet to form the groove at the desired spatial and angular relation to the preceding grooves.

It will be observed, because the width between the outer faces of the holding and forming blocks 41 are at least equal to the interval between the center line of the grooves of the female die blocks l2 and ,4. that the sheet is continuously formed into a compound flat and urved flange alum? each longitudinal edge. The rooves will be on the surfaces which are developed, since they hear he n cessary relation to each other equivalent to the generating lines of these surfaces. Thus, if the grooves are at an equal angle to each other. the sheet is rotated angularly as the groove is moved from the die groove N to the indexing die 23, the angle of rotation being equal to the angle between these die grooves.

The grooves form rigidifying reinforcements extending across the width and along the length of the sheet. The pleated ends cause local stillening at the edges and at both sides of thecupped curved flanges to hold the shape of the curved flange during fabrication and further handling. A foil sheet such as one described above is flimsy and distorts easily and is easily cracked in bandling by cold working. The fact that the curved surfaces between the pleats are smooth and substantially unwrinkled and. therefore are not coldworked between the pleats is a material factor in reducing the number of sheets that show cracks at these localities after fabrication into blankets. This is a matter of utmost importance, since even a minute crack will permit entry of fuel into the interior of the blanket when used as a blanket for the tail pipe of a jet engine. The

fuel may gasify and ignite, causing an explosion within the confines of the blanket and a disastrous fire.

The use of the grooved sheet with curved end 81 will be illustrated by reference to its function in the fabrication of blankets with fibrous material such as fiber glass or siliceous fiber batting.

As is illustrated in Figs. 34-39, the blanket is formed by using a flat foil 91 and placing batts 93, which may be siliceous or glass fibers, and a batt 9! of either of the two or any number of such batts with intermediate foil sheets, as the nature of the blanket requires,

The sheet 83 is laid on top of the batt 91 with the bottom of the groove 86 against the batt and with the grooves extending in the direction of the generating line of the developed surface of the form to be covered by the blanket. All of the lateral edges 86 and the ends 95 and the edges of the foil 99 are tack-welded, seamwelded, and over-folded, and welded in similar manner to form a completely enclosed and sealed envelope for the fibrous batting. In so doing, the grooves 86 are pressed into the batting so that the batting puffs up and fills in between the grooves 86. At the lateral edges the curved portion 8'! permits the batting to maintain its full thickness to the lateral edge. This is important because the insulating quality of the blanket is diminished by the compression of the edges of the batting where, except for this cupping, the ends would be so compressed as to cause a crushing of and powdering of the fibers. The blankets between the cupped edges are flat and may be stacked one on top of the other smoothly.

It will be observed that the blanket can now be placed over the surface of which it was a development. By allowing for the depth and the number and spacing of grooves in laying out the sheet, when laid with the grooved foil against the surface to be insulated, the blanket and foil bend without wrinkling or cracking of the foil to contact the surface, the foil bending at the grooves which act as hinged joints extending the full width of the blanket.

We may also provide openings I00 suitably sealed for passage of any structural projecting part and also provide lacing hooks 1.08 and Ill] fo un ng o e onical pipe. as in Fig. 35,

or the cylindrical pipe, as in 38, or on any other structure of desired shape.

It will be observed that at the ends of the blanket where no extra precautions are taken to form a curved end at the seal, the blanket is over-folded when laced so that an extra thickness of blanket is provided for added insulating efiect.

While we have described a particular embodiment of our invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

We claim:

1. A method for forming a foil sheet having a developed surface to cover a curved structure, which comprises forming a plurality of grooves in said sheet extending transversely between the longitudinal edges of said sheet and across the width thereof, downwardly and curvaceously bending the said sheet, adjacent the longitudinal edges of said sheet, to form a curved flange along the longitudinal edge of said foil sheet, holding a portion of said sheet at said curved flange and on each side of said grooves against displacement, leaving another portion of said foil sheet on each side of said grooves and between said first-mentioned portion and said grooves unrestrained, and pleating said sheet at said unrestrained portions.

2. A method for forming a foil sheet having a developed surface to cover a curved structure, which comprises forming a plurality of grooves in said sheet extending transversely between the longitudinal edges of said sheet and across the width thereof, downwardly and curvaceously bending the said sheet adjacent and along the longitudinal edges of said sheet, forming a transversely curved flange along the longitudinal edge of said foil sheet, holding a portion of said sheet at said curved flange and on each side of said grooves against displacement, leaving another portion of said foil sheet on each side of said grooves and between said first mentioned portion and said grooves unrestrained, and pleating said sheet at said unrestrained portions.

3. A method for forming a foil sheet having a developed surface to cover a curved surface. which comprises corrugating said sheet and forming a plurality of grooves in said sheet extending transversely between the longitudinal edges of said sheet and across the width of said sheet, positioning said grooves at equal acute angles to each other, bending said sheet along the longitudinal edges downwardly into a curved flange, forming a flat-edge flange positioned along the longitudinal edges of said sheet, holding said curved and said fiat flange on each side of said grooves against displacement while leaving another portion of said sheet on each side of said grooves and between the first mentioned portion and said grooves unrestrained, and locally pleating said sheet at said unrestrained portions.

4. A method for forming a foil sheet having a developed surface to cover a curved surface, which comprises corrugating said sheet and forming a plurality of grooves in said sheet extending transversely between the longitudinal edges of said sheet and across the width of said sheet, positioning said grooves at equal acute angles to each other, bending said sheet along the longitudinal edges downwardly into a curved flange, forming a flat-edge flange positioned at and along the longitudinal edges of said sheet, holding said curved and said flat flange on each side of said grooves against displacement while leaving another portion of said sheet on each side of said grooves and between the first mentioned portion and said grooves unrestrained, and locally pleating said sheet at said unrestrained portions.

, 5. A method for forming a foil sheet having a developed surface to cover a curved surface, which comprises corrugating said sheet to form a groove extending transversely between the longitudinal edges of said sheet, shifting the longitudinal length of said sheet through an acute angle, corrugating said sheet transversely between the longitudinal edges of said sheet to form a groove at the above acute angle to said first mentioned groove, repeatedly shifting said sheet through said angle and corrugating said sheet in a plurality oi grooves disposed longitudinally of said sheet and extending transversely between the longitudinal edges of said sheet at spaced intervals and at equal acute angles to each other, bending said sheet along the longitudinal edges downwardly into a curved flange, forming a flatedge flange positioned at and along the longitudinal edges of said sheet, holding said curved and said flat flange on each side of said grooves against displacement while leaving another portion of said sheet on each side of said grooves and between the first mentioned portion and said grooves unrestrained, and locally pleating said sheet at said unrestrained portions.

6. A method for forming a foil sheet having a developed surface to cover a curved surface, which comprises corrugating said sheet to form a groove extending transversely between the longitudinal edges of said sheet, shifting the iongitudinal length of said sheet through an acute angle, corrugating said heet transversely of the longitudinal length of said sheet to form a groove extending between the longitudinal edges of said sheet at the above acute angle to said first mentioned groove and spaced from said first mentioned groove, repeatedly shifting said sheet through said angle and corrugating said sheet in a plurality of grooves, each disposed transversely between the longitudinal edges of said sheet and spaced longitudinally of said sheet at equal intervals and at equal acute angles to each other, bending said sheet along the pleated longitudinal edges downwardly into a curved flange, forming a flat-edge flange positioned at the longitudinal edges of said sheet, holding said curved and said fiat flange on each side of said grooves against displacement while leaving another portion of said sheet on each side of said grooves and between the flrst mentioned portion and said grooves unrestrained, and locally pleating said sheet at said unrestrained portions.

7. A method for forming a foil sheet having a developed surface to cover a curved surface, which comprises corrugating said sheet to form a groove extending transversely between the longitudinal edges of said sheet, shifting the longitudinal length of said sheet through an acute angle, corrugating said sheet transversely of the longitudinal length of said sheet to form a groove at the above acute angle to said first mentioned groove, repeatedly shifting said sheet through said angle and at a spaced interval from said first mentioned groove, corrugating said sheet in a plurality of grooves disposed longitudinally of said sheet at spaced intervals and at equal acute angles to each other, downwardly curvaceously bending the longitudinal edges of said sheet, holding said curved and said flat flange on each side of said grooves against displacement while leaving another portion of said. sheet on each. side of said groove and between the first mentioned portion and said grooves unrestrained, and locally pleating said sheet at said unrestrained portions.

ALBERT S. BIORDI.

JACK M. WARNER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Williams Dec. 12, 1893 Number Number m 95,866

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