US 3150576 A
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Description (OCR text may contain errors)
spt 29, 1964 L. v. GEwlss 3 1 PROCESS A AP ATUS FORMING TRANSVERSE CORRUGATIOI0676 ALL MS A SH 0R BAND OF MALLEABLE MATERIAL Flled Aug. 8, 1962 l 3 Sheets-Snee l sigg.
32 /034 ,g3 Js A 32 34 ATTORNEYS Sept. 29, 1964 L.. v. GEwxss 3,150,576
PRocEss AND APPARATUS RoR FORMING TRANsvERsE coRRuGATIoNs oF ALL RoRMs 1N A SHEET oR BAND oF MALLEABLR MATERIAL Filed Aug. 8, 1962 3 Sheets-snee? 2 6C bl i OR 'l0 INVENT /ob w/y-V/craGfw/ss RR R/RR A L /c isi/2,. e!
Sept. 29, 1964 L. v. GEwl 3,150,576
PROCESS AND APPARATUS FOR FORMING NSVERSE CORRUGATIONS OF ALI.. FORMS IN A SHEET OR BAND OF MALLEABLE MATERIAL Filed Aug. 8, 1962 3 Sheets-Sheek 3 @11. Awww 1M M I llllli H Il H INVENTOR (/c/E/v-V/cro/r Gf n//ss ATTORNEY 5 United States Patent O PRCESS AND APPARATUS FOR FURMING TRANSVERSE CORRUGATIONS F ALL FRMS IN A SHEET 0R BAND 0F MALLE- ABLE MATERIAL Lucien Victor Gewiss, Ville DAvray, Seine et Oise, France, assignor to Marc Wood Societe Anonyme pour la Promotion des Echanges Techniques Internationaux, Paris, France, a company of France Filed Aug. 8, 1962, Ser. No. 215,567 Claims priority, application France Aug. 9, 1961 26 Claims. (Cl. S93-84) In applicants copending application Serial No. 514,171, filed June 9, 1955 (which application is hereby incorporated by reference herein and Which is based upon French Patents 1,106,780, issued July 27, 1955; 66,807, issued March 25, 1957; 67,078, issued May 13, 1957; and 68,479, issued November 12, 1957), is described a novel type of material which is currently known under the name of herringbone structure and which, in its more general appearance, has the form of a structure folded from a flat sheet or band whose folds, located alternately in one and then another limiting plane, are zig-zag or corrugated lines. As pointed out in said copending application, such herringbone structures are comprised of ruled elementary surfaces which join each other along lines having points at which they change direction and at each of Which points border lines of four of said elementary surfaces converge, the sum of the angles formed on said surfaces between said border lines at each of said points being equal to 360. The surfaces of this novel structure may be planar or curved in coniiguration, or both, but in all cases the structure meets the limitations set forth above. As set forth in said copending application, one of the peculiar characteristics of the herringbone structure is that its surface is in actuality the materialization of a more or less complex geometric configuration which is developable along a plane (although the structure itself is not necessarily effectively developable).
Such herringbone structures have a great range of utilities, many of which are pointed out in said copending application and in said French patents. One of the important uses of such structures, for example, is in the manufacture of cores of sandwic panels, and especially herringbone cores in which corrugated or grooved cardboard sheets are used as the starting material for their preparation. Such corrugated sheets may, by processes disclosed in said copending application, be readily converted into herringbone structures.
While the manufacturing techniques described in said copending application and in said French patents are for the most part of extreme utility in fabricating herringbone structures, however, such techniques are not completely satisfactory for shaping the grooves necessary for the manufacture of composite herringbone cardboards. This is primarily because, due to the relatively small dimensions of such grooves, the machines on which these techniques are carried out are generally not suitable to ensure a sufliciently large production of herringbone structures.
It is accordingly a primary object of the present invention to provide a method and apparatus for effecting the continuous formation of herringbone structures at an extremely high production rate, in a sheet or band of pliable material.
It is another object of the present invention to provide a method and apparatus for forming herringbone grooves at an extremely high production rate in a sheet or band of paper destined for the manufacture of composite herringbone cardboards.
It is still a further object of the present invention to provide a method and apparatus capable of producing ICC herringbone structures and which is eiective to handle 60 meters of material per minute.
It is an additional important object of the present invention to provide a method and apparatus for forming transverse corrugations of all forms in a sheet or band of malleable material.
Itis a further object of the present invention to provide a method and apparatus for forming corrugated structures having corrugations of small amplitude.
These and other important objects and advantages of the present invention will become more apparent upon reference to the ensuing description and appended claims and drawings wherein:
FIG. 1 is a schematic longitudinal section of one embodiment of a machine according to the present invention;
FIG. 2 is a longitudinal section on an enlarged scale of a portion ofthe machine represented in FIG. 1;
FIG. 3 is a geometric iigure destined to explain a functional detail of the machine represented in FIGS. l and 2;
FIG. 4 is a plan View partly broken away of a portion of an endless belt forming an essential element of the machine of FIGS. 1 and 2 on an enlarged scale;
FIG. 5 is a section taken along lines 5 5 of FIG. 2 illustrating a nozzle element which aids in the formation of the herringbone structures which may be fashioned by the machine of FIGS. 1 and 2;
FIG. 6 is a section taken along lines 6-6 of FIG. 1 illustrating the details of a feed element useable in connection with the machine of the present invention;
FIG. 7 illustrates a partially broken plan view similar to that of FIG. 4 but showing a different form of corrugating element useable in connection with the present invention;
FIG. 8 illustrates a section taken along lines 8--8 of FIG. 7;
FIG. 9 is a partially broken plan view similar to that of FIG. 4 illustrating still another form of the corrugation-forming element of the machine of the present invention;
FIG. 10 is a section taken along the lines 10-10 of FIG. 9;
FIG. 11 is an enlarged section taken along lines 11-11 of FIG. 1 illustrating the details a feed elements useable in connection with the machine of the present invention; and
FIGS. 12-15 are respectively top plan, side elevation, bottom plan and perspective views of still another form of corrugating element useable in connection with the present invention.
Generally speaking, the method of the present invention may be carried out by apparatus comprising a corrugating element to which is imparted a translational movement, means for bringing a band or sheet of malleable material which has previously been longitudinally folded or corrugated into contact with the corrugating element during the course of its translational movement and for making said malleable material adapt itself to the configuration of said moving corrugating element, and means for continuously ejecting the corrugated band or sheet from the corrugating element. Through the substitution of one type of corrugating element for another, the corrugations imparted to the sheet or band of malleable material may range from herringbone, either planar or sinuous in conguration, to a conventional transverse sinuous or V-shaped corrugation, or the like.
The invention will first be described through reference to FIGS. 1-6 and 11 of the drawings, which illustrate different aspects of an apparatus within the scope of the present invention particularly adapted for forming herringbone grooves in bands or sheets of malleable material.
In the apparatus represented schematically in FIG. 1, a sheet of pliable or malleable material (such as paper) Patented Sept. 29, 1964iv .5 in which herringbone grooves are to be imparted is released continuously from a feed roll (not shown). This sheet 1 has been previously folded or corrugated longitudinally (with respect to its direction of ilow, as indicated by the arrow in FIG. 1) by a technique utilizing apparatus not forming part of the present invention and which, accordingly, has not been shown in the drawings. Such a pleating method, for example, may be accomplished as shown in applicants Patent 2,950,656 or, for example, as shown in applicants copending application Serial No. 514,171, previously mentioned.
The paper sheet is frictionally entrained continuously between two grooved and mating rolls 2 and 3 each having a profile corresponding to t'ne surface of the corrugated sheet 1 into which it comes in contact, as shown more particularly in FIG. 11, and, following its departure from between rolls 2 and 3, sheet 1 is received between an inclined guide plate 4 and a guide roll 5. As shown more particularly in FIG. 6, guide roll 5 has a prole corresponding to the profile of the lower face of guide plate 4, both of such proles corresponding to the crosssectional configuration of the corrugated paper sheet 1.
Guide plate 4, with the aid of guide roll 5, aids in guiding sheet 1 into contact with a continuously moving endless belt 6 which serves to impart to said sheet the desired herringbone configuration as will be described more particularly below.
Belt 6 passes through a point immediately above the upper inclined end of guide plate 4 and is mounted on two wheels 7 and 3 above a receiving table 9 onto which the nished herringbone sheet 1 passes after being removed from belt 6 in a manner to be described below.
While belt 6 is shown schematically in FIG. l, details of this belt may be seen in FIGS. 2 and 4. As shown therein, belt 6 is comprised of three thin, flexible supporting bands 6a, 6b and 6c which are parallel to one another and to which are attached a plurality of spaced, rigid herringbone shaped elements 1t), which are mounted adjacent to but spaced from one another on said bands 6a, 6b and 6c by conventional means. The spaces are left between the individual herringbone elements to permit the passage of air or other gas or vapor through belt 6 for a purpose to be described in greater detail below. Alternatively, herringbone elements 1t) could be made of a porous material such as wire netting whose meshes are suitably dimensioned to make belt 6 permeable to air, etc., and yet which will impart suitable mechanical resistance to the endless belt to permit the belt to function properly in the process in question.
Belt 6 is mounted about wheels 7 and S in a conventional manner to permit said wheels to drive the belt, ie., through a sprocket chain-sprocket wheell arrangement, which may readily be accomplished by fixing sprocket elements to the underside of bands 6a, 6b and 6c and by using sprocket wheels for wheels 7 and S.
Positioned inside ot belt 6 and spaced slightly downstream of the end of receiving table 9 which is closest to guide plate 4 is an intermediate idler drum 11 which is arranged with respect to receiving table 9 so as to ensure the positioning of the portion of belt 6 which is between sprocket wheel 7 and itselr in a direction substantially parallel to the plane of receiving table 9. On the other hand, sprocket wheel 8 is arranged at such a level with respect to receiving table 9 that the portion of belt 6 which is between idler drum 11 and sprocket wheel 8 moves progressively away from the Areceiving table 9 in the course of its forward travel. The distance separating belt 6 from receiving table 9 at the point where the two are parallel to one another is slightly greater than the height of the herringbone elements 10, taking into account the thickness of the herringboned paper sheet interposed between them.
Adjacent the upper end of guide plate 4 and immediately opposite belt 6 is positioned the outlet of a nozzle 12 which is connected to a supply of suitable hot fluid under pressure (i.e., steam) and whose outlet orifice 30 (see FIG. 5) preferably has a cross-section corresponding :substantially to the profile of the herringbone elements 10 on belt 6. Nozzle 12 is so positioned with respect to v.belt 6 that outlet orifice 30 is arranged transversely with .regard to the direction of movement of the belt.
At right angles to nozzle 12 and extending a certain distance downstream of the nozzle (as shown in FIGS. 1 and 2), a suction hood 13 is positioned adjacent the inner surface of belt 6. Downstream of the intermediate idler drum 11, and again opposite the inner surface of belt 6 is positioned a hood 14 which is connected to a .source of air under pressuure.
As will be noted particularly in FIG. 2, guide plate 4, .as is the case with sheet 1 itself, has exactly the profile land the angle of inclination as the iianks of the herringbone element 1t? which face downstream with respect to the movement of belt 6, viz., those flanks which are designated by the numeral 32 in FIG. 2. Since the corrugated paper sheet 1 which is fed into the apparatus of FIGS. 1 and 2 will be converted into the herringbone configuration without any considerable elongation or contraction of the material, the respective linear velocity of displacement of the sheet 1 and of the belt 6 must be exactly in vthe ratio of the cosine of the angle at the base of the herringbone elements 10 on the portion of the beit 6 that is parallel to the receiving table 9 (such angle is marked a in FIG. 2). More specically, if CA (i.e., see FIG. 3) represents the length of paper that has been deposited on one of the flanks 34 of the herringbone elements 10 during a given period, the advance of belt 6 duuring that same period will have been AB, that is, AC cos a. Since this ratio is constant, the ratio of the velocity of displacement of sheet 1 with respect to the linear velocity of belt 6 will be constant. Thus, so long as the angle a at the base of each of the herringbone elements 10 remains the same, the respective feed velocities of the sheet 1 and of the belt 6 may be maintained constant regardless of the particular height of successive herringbone elements 10. This characteristic of the apparatus of the instant invention makes it possible to fabricate herringbone structure having flanks of varying height without complications resulting from the requirement of variations in feed velocities and the like.
Taking into account the particular arrangements discussesd above, the operation of the apparatus of the present invention is as follows:
After adjusting the relative velocities of belt 6 and the feed of paper sheet 1 in accordance with the relationship described above (as will be obvious, the ratio of the velocities of the belt 6 and sheet 1 may be maintained constant through the use of a common drive system and a suitable gear train), sheet 1 is fed between rolls 2 and 3, up between guide plate 4 and guide roll 5, and along the remaining portion of guide plate 4 into contact with the moving belt 6 which, as shown in FIG. 2, is moving in the direction indicated by F. As the corrugated paper sheet 1 abuts against the flanks 34 of the herringbone elements 10 which are inclined upstream with respect to the direction of movement of belt 6, the longitudinal folds of the corrugated sheet will reverse themselves in a sort of rolling movement along the ridges of anks 34. On the other hand, the sheet 1 will cover the flanks 32 which are inclined downstream in a single moment in time since such anks have exactly the same angular inclination and the same transverse profile as does the sheet.
In this connection, it will be noted that while the paper sheet will cover the Hanks 34 which are inclined upstream in a progressive manner over a period of time, the movement of the sheet from one flank 34 to the next flank 34 is an abrupt movement, with the sheet covering the downstream ank 32 in a single moment, the profile of the sheet passing at the instant of the transfer of the sheet from ank 32 to Hank 34 from its own profile to the inverse profile, the latter corresponding to the profile of the upstream flank 34. This sudden change of profile, which would normally seem impossible to realize, is effected with the instant apparatus without any difficulties, thanks to the remarkable properties of the herringbone structure, the mobile fold of transformation being nothing more than a normal edge of the herringbone struucture which advances by rolling on the upstream inclined flank without having any reason to change its form, since it explores a surface of which it is the natural intersection.
In principle, this covering of the upstream flanks 34 by the paper sheet 1 is produced quite naturally by a normal operation of the apparatus described in FIGS. 1 and 2, as the result of the maintaining constant the simple ratio of the relative velocities of the sheet 1 and of the belt 6. This operation presupposes, however, that the sheet material used to form the herringbone structure is of a particularly homogeneous pliability, since any non-pliable foreign element incorporated in the sheet would hinder the regular unwinding of such sheet.
In practice, however, due to possible irregularities of the type mentioned, it is of advantage to assist the contact of the corrugated paper sheet 1 with the surface of the upstream flanks 34 by means of a thrust of fluid directed toward the point at which the corrugated sheet contacts such flanks. For this reason, the nozzle 12, having an orifice 30 conforming generally to the configuration of the herringbone element 10, is positioned transversely of belt 6 and is adapted to eject fluid under pressure at the paper sheet 1 substantially at its point of contact with flanks 34.
In the situation in which cardboard is used as the material to be herringboned, the uid ejected from nozzle 12 is preferably steam, since the heat and moisture released are particularly favorable for the softening of such cardboard. However, compressed air which has first been brought to a suitable temperature can also yield desirable results if, preferably, the cardboard band is first folded or corrugated longitudinally under the action of steam and if it has a sufficient degree of moisture and pliability at the time it comes in Contact with the herringbone element 10 of belt 6. The suction hood 13 is provided on the other side of the belt 6 from the nozzle 1.2 to absorb the steam or moist air which is released from the herringbone paper or cardboard in the course of drying. lf desired, of course, the action of nozzle 12 may be supplemented through the provision of additional nozzles or the like which are placed downstream of nozzle 12.
The air or steam blast from nozzle 12 and the aspiration of suction hood 13 act from both sides of belt 6 to keep the paper sheet 1 in contact with the herringbone elements 10 up to a point at which receiving table 9 is able to support the assembly, as is seen more clearly in FIG. 2. Following the point of inflection of belt 6 beyond the point of `contact of the intermediate idler drum 11 with the belt, the herringboned paper sheet, suitably dehydrated, is slowly disengaged from the herringbone elements 10 of the belt through the pull of gravity and with the assistance of the air pressure from hood 14. From this position, the finished structure, which has at this point dried almost completely, follows a path on receiving table 9 in the direction of the arrow F', advanced continuously by the new herringbone folds which continuously emerge downstream of the idler drum 11.
The machine which has been described above lends itself to the shaping of herringbone structures of any dimension and any form, independent of the nature of the folded or corrugated sheet used as the feed material, provided, however, that this material can be made sufficiently pliable in the zone at which the reversal or rolling of the herringbone fold is produced. For example, not only may herringbone elements of the type shown in FIG. 4 be utilized, but sinuous elements of the type shown in FIGS. 12-15 may also advantageously be utilized. (Note the holes in the bottom of the element, as shown in FIGS. 14 and l5, which permit the element to be attached to support bands 6a, 6b and 6c. The other corrugating elements of this specification may be similarly constructed.) In addition, as has previously been pointed out, herringbone elements of progressively increasing or decreasing height may be employed, in which case herringbone structures having non-parallel enveloping planes and of a great variety of forms may be produced. The important consideration in such case is that the angle a at the base of the herringbone elements should remain constant so as to permit the use of a constant ratio of paper sheet velocity and belt velocity. In the event this angle is varied, it will in such case be necessary to vary the belt velocity in such manner that the ratio of the cosine of the angle a is maintained constant so that the machine will operate correctly.
The foregoing description has been set forth in terms of herringbone structures to this point primarily because the most amazing and surprising results of the carrying out of the method and apparatus of the present invention take place in the case of such herringbone structures, due to their great difficulty of formation relative to more simply configured structures. It is essential to point out, however, that the method and apparatus of the instant invention are equally effective to form ordinary structures having transverse corrugations which are not in herringbone form, in which case corrugating elements such as are shown in FIGS. 7-10 may be substituted for the herringbone elements 10 of the embodiment set forth in FIGS. l, 2, and l2-l5 and a plane sheet of feed material substituted for the preliminarily corrugated sheet 1 useable in the formation of herringbone structures. Thus, as shown in FIGS. 7 and 8, a corrugated structure having transverse pleats and planar flanks may be produced by utilizing corrugating elements 10a and afiiXing them to supporting bands 6a, 6b and 6c in the same manner in which herringbone elements 10 were attached to the corresponding support bands of belt 6. Similarly, FIGS. 9 and 10 illustrate elements 10b which are useful to form a transversely corrugated structure having a sinuous crosssection. In each of these cases, the method of operation will be substantially as previously indicated.
While the instant application has been described in terms of the use of an endless belt for imparting the desired folds to the material to be formed, other forming elements may be substituted for such endless belt. For example, the belt can be replaced by a flat table having a length approximately equal to the structure to be produced, such flat table having its surface which is in contact with the material to be transformed of the desired ultimate configuration, viz., similar to the configuration of the herringbone elements 10 illustrated in FIGS. l and 2, 7-9, l2-l5, etc. During the advance of the table, the table will pick up the transformed structure. At the end of the forward translational movement of the table, the table will deposite the folded structure and then return to its initial position to pick up another structure. Such a structure has eXtreme versatility and makes it possible to make all sorts of structures merely by changing a plate and by making certain adjustments in the angles and speed of movement of the table as well as the material to be processed. Still other substitutes for the endless belt of FIGS. 1 and 2 may suggest themselves to produce results analogous to those obtained in the instant application.
In addition, other modifications of the apparatus may be made. For example, it may be desirable to position a guide roll or rolls closer to the upper end of guide plate 4 to furnish additional support for the corrugated sheet at a point as closeas possible to the endless belt 6. In addition, idler drum 11 may be replaced with a simple angular element bearing against the inside face of belt 6 which 'will serve to change the angle of movement of such belt in a manner analogous to which idler drum 11 performs such function. If desired, the preliminary longitudinal corrugation of the sheet 1 may take place immediately adjacent the belt 6, as by substituting a corrugating-feed device for the guide plate 4-guide roll 5 combination. Still further, while the apparatus previously described performs most favorably when the angle of inclination of guide plate 4 and, correspondingly, of the feed sheet 1 is identical to downstream fianks 32, a tolerance of plus or minus several degrees will not seriously impair the operation of the apparatus or the carrying out of the process in question since the process of the present invention presupposes that the material being formed will be malleable enough at the point at which the angle becomes significant to lend itself to folding inversely through a rolling operation as previously described. Any minor deviations in such angle will, accordingly, be absorbed without complications. It is desirable, however, that such deviations should be limited, preferably to a degree such that the feed sheet 1 will always present itself within the angle of the fianks 32 and 34 so as to be certain that the apex of the angle formed by such fianks will be reached by the advancing feed sheet.
When used in the claims, the term herringbone structure, herringbone configuration, etc., shall be construed to define a structure comprised of ruled elementary surfaces which join each other along lines having points at which they change direction and at each of which points border lines of four of said elementary surfaces converge, the sum of the angles formed on said surfaces between said border lines at each of said points being equal to 360. The term sinuous herringbone structure or the like shall be construed to define a herringbone structure whose walls are composed exclusively of an infinite number of ruled elementary surfaces which can be reduced respectively to the generating lines of said surfaces, said surfaces joining each other along undulated lines all of whose points are points at which said undulated lines change direction.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
What is claimed is:
1. Apparatus for forming corrugations of herringbone configuration in a sheet of pliable material comprising: corrugating means, said corrugating means having a corrugation forming surface which has the herringbone configuration of the corrugated sheet which said apparatus is to form; means for feeding a sheet of pliable material onto the surface of said corrugating means; means for causing relative movement between said corrugating means and said feeding means; said corrugation forming surface containing corrugations which are transverse with respect to the direction of said relative movement; said feeding means being positioned with respect to said corrugating means so that said sheet of pliable material is fed onto the corrugation forming surface of said corrugating means with the plane of the sheet in substantial parallelism with said transverse corrugations.
2. Apparatus as defined in claim 1 wherein the walls forming said transverse corrugations are inclined alternately upstream and downstream in the direction of said relative movement, said feeding means being positioned with respect to said corrugating means so that said sheet of pliable material is fed onto the surface of said corrugating means with its plane in substantial parallelism with respect to one of said upstream and downstream inclined walls.
3. Apparatus as defined in claim 2 wherein the inclined wall with which the plane of said sheet of pliable material is to be in substantial parallelism is said downstream inclined wall.
4. Apparatus as defined in claim 3 wherein the angles of inclination of all of said downstream inclined walls U are substantially identical to one another and wherein the angles of inclination of all of said upstream inclined walls are substantially identical with one another.
5. Apparatus as defined in claim 4 wherein means are provided to maintain constant the ratio of the linear velocity of displacement of the sheet of pliable material as it is fed by said feeding means to the linear velocity of said corrugating means in proportion to the cosine of the angle formed by said upstream inclined walls and a plane parallel to the direction of said relative movement.
6. Apparatus as defined in claim 5 wherein means are provided to move said corrugating means and wherein said feeding means are stationarily mounted with respect to said relative direction of movement.
7. Apparatus as defined in claim 6 wherein said corrugating means is an endless belt.
8. Apparatus as defined in claim 5 wherein the corrugation forming surface of said corrugating means is permeable to fluids.
9. Apparatus as defined in claim 8 wherein said permeability is obtained at least in part through the interposition of spaces between the transverse corrugations of said corrugation forming surface.
10. Apparatus as defined in claim 5 wherein the corrugation forming surface of said corrugating means is permeable to fluids and wherein means are provided to apply a fluid force to said sheet of pliable material as it is fed onto said corrugation forming surface to aid in the formation of the corrugated sheet.
11. Apparatus as defined in claim 5 wherein means are provided to remove the pliable sheet from said corrugating means after the corrugations in said sheet have been formed.
12. Apparatus as defined in claim 11 wherein the corrugation forming surface of said corrugating means is permeable to fluids and wherein said pliable sheet removal means comprises means to apply a fiuid force through said corrugation forming surface and against said corrugated pliable sheet.
13. Apparatus as defined in claim 5 wherein the height of at least some of the corrugations in said herringbone configuration are different from one another.
14. Appanatus as defined in claim 5 wherein the cross section Aof said corrugation forming surface in a plane transverse to said direction of relative movement correponds substantially to that of the pliable sheet to be fed onto said surface by said feeding means.
15. Apparatus as defined in claim 15 wherein said feeding means is designed to enable it to feed a sheet of pliable material which contains longitudinal corrugations with respect to the direction of feed.
16. Apparatus as defined in claim 5 wherein said corrugation forming surface has a sinuous herringbone configuration.
17. Apparatus as defined in claim 5 wherein said corrugation forming surface has a herringbone configuration with planar walls.
18. A method of forming herringbone corrugations in a sheet of pliable material comprising: providing a corrugation forming surface which has a herringbone configuration of the corrugated sheet to be formed, said corrugation forming surface having a plurality of substantially parallel corrugations; feeding a sheet of pliable material onto said corrugation forming surface so that the plane of said sheet is in substantial parallelism with said corrugations; and causing said corrugation forming surface to move relative to the point of introduction of said sheet of material onto said corrugation forming surface and in a direction substantially normal to said transverse corrugations.
19. A method as defined in claim 24 wherein the walls forming said transverse corrugations are inclined alternately upstream and downstream in the direction of the relative movement of said corrugation forming surface and said point of introduction of said sheet of material, and
9 additionally comprising feeding said sheet of material onto said corrugation forming surface so that the plane of said sheet is in substantial parallelism with respect to one of said upstream and downstream inclined walls.
20. A method as dened in claim 19 wherein the inclined wall with which the plane of said sheet of pliable material is fed in parallelism is said downstream inclined wall.
21. A method as defined in claim 20 wherein the angles of inclination of all of said downstream inclined walls are substantially identical to one another and wherein the angles of inclination of all of said upstream inclined walls are substantially identical with one another.
22. A method as defined in claim 21 additionally comprising maintaining constant the natio of the linear velocity of displacement of the sheet of pliable material as it is fed to the linear velocity of said corrugation forming surface in proportion to the cosine of the angle formed by said upstream inclined walls and a plane parallel to the direction of said relative movement.
23. A method as defined in claim 18 wherein said sheet of pliable material is longitudinally corrugated with respect to its direction of feed at the time it is fed onto said corrugation forming surface.
24. A method as defined in claim 23 wherein the crosssection of said longitudinally corrugated sheet corresponds substantially to the crosssection of said corrugation forming surface in a plane transverse to said direction of relative movement.
25. A method as defined in claim 22 wherein said sheet of pliable material is conformed to the surface configuration of said corrugaition forming surface by applying a fluid force to said sheet at about the time said sheet is fed onto said corrugation forming surface.
26. A method as defined in claim 18 wherein at the time said sheet of pliable material comes in contact with said corrugation forming surface it is self-supporting.
References Cited in the file of this patent UNITED STATES PATENTS 1,150,805 Beran Aug. 17, 1915 2,166,749 Burrill July 18, 1939 2,238,251 Dahlrnan Apr. 15, 1941 2,335,313 Rowe et al Nov. 30, 1943 2,675,053 Clemens Apr. 13, 1954 2,896,692 Villoresi July 28, 1959