PROCEDURE AND APPARATUS FOR CONTINUOUS PRODUCTION OF CORRUGATED/UNDULATED SHEETS IN A WINDABLE WEB; WINDABLE THERMOPLASTIC WEB WITH TRANSVERSE CORRUGATIONS/UNDULATIONS

Abstract: A continuous web of corrugated thermoplastic material sheet is produced with the wave or zigzag shapes disposed with their axes transverse to the direction of extrusion, or of travel, of said web, by passing it between a forming cylinder provided with grooves communicating with a suction means, and a drawing cylinder collaborating therewith. The corrugated sheet is windable and this facilitates application, storage and transport thereof.

Description: PROCEDURE AND APPARATUS FOR CONTINUOUS PRODUCTION OF CORRUGATED/UNDULATED SHEETS IN A WINDABLE WEB; WINDABLE THERMOPLASTIC WEB WITH TRANSVERSE CORRUGATIONS/UNDULATIONS DESCRIPTION The invention refers to the field of sheets or plates of undulated or corrugated plastic material, as are currently in widespread use in the construction industry, for packaging, for do-it-yourself and for numerous other uses. The corrugated thermoplastic materials currently on the market are produced continuously via a process which includes a step of plasticization of the thermoplastic material with an extruder, a step of rolling of the web through a flat head and a calender, a subsequent step of deformation of the web according to shapes with axes longitudinal to the web, through a series of roller trains which transform the section of the web from planar to longitudinally corrugated. It is obvious that this production system allows only the formation of corrugated sheets with longitudinal ribs (corrugations). Said webs, on account of their shape, cannot be wound into rolls, and therefore they are cut into sheets and stacked for storage and transport, with the drawback of requiring a greater percentage of overlapping in use. Also known to the art are windable corrugated webs of fibreglass material, which are produced with corrugations at right angles to the direction of production by means involving a process of impregnation of a textile support, which is then subjected to drying so that the resin hardens. Such a production process is not applicable to thermoplastic materials. The objects of the present invention are to obtain a windable corrugated web of thermoplastic material and allow production on an industrial scale of web products of corrugated thermoplastic material sheet that can be wound in a roll. These objects are achieved with the invention as set forth in claim 1, claim 2 and claim 8. Further advantageous features of the invention can be read in the dependent claims. In other words, the invention provides a web of thermoplastic material, however produced, which is corrugated transversely to the length thereof. It further provides a production process whereby a continuous web of thermoplastic material is extruded with simultaneous on-line extrusion, or alternatively produced separately and fed with a roll of pre-extruded thermoplastic material, in suitable conditions of temperature, and subsequently formed with corrugations having a transverse axis with respect to the direction of extrusion-feeding, namely to the longitudinal direction of the web, in a cylinder assembly which operates with the aid of a suction system. The web is then trimmed along the longitudinal edges thereof. The apparatus of the invention comprises a cylinder assembly, a forming cylinder of which has channel shapes extending substantially parallel to the axis of the cylinder and communicating with a vacuum system, and a so-called drawing cylinder that has elongated protrusions parallel to the axis of the cylinder and collaborates with the forming cylinder to form the corrugations of the web. The invention allows to overcome the drawbacks of the prior art, and in particular forms a windable corrugated web and allows production of a continuous web of corrugated sheet material that can be wound in a roll, with consequent advantages as regards transport and storage. Furthermore it provides a process for producing corrugated webs and panels that can be wound in a roll, with resulting advantages as far as transport and storage are concerned. Furthermore it provides a process for production of corrugated webs and panels that is economically competitive. Non-limiting embodiments of the invention will be described below with reference to the attached drawings, in which: Figures 1, 2, 3 and 4 are perspective views of portions of corrugated plastic web, as can be obtained by the present invention; Figure 5 is a perspective view of corrugated web according to the present invention, wound in a roll around a core; Figure 6 is a part sectional elevational view of a calender for shaping the web; Figure 7 is a diagrammatic side elevational view, with parts removed, of the calender of Figure 6; Figure 8 is a sectional view of a forming cylinder of the calender, taken along plane 8-8 of figure 9, perpendicular to the axis of the roller itself; Figure 9 is a side elevational view of the forming cylinder; Figure 10 is a broken off axial section through the forming cylinder; Figure 11 shows, in a broken-off sectional view taken in a plane perpendicular to the respective axes, a collaborating drawing cylinder and forming cylinder, for forming a fret-type corrugated web, Figure 12 shows, in a section similar to that of Figure 11, a collaborating drawing cylinder and forming cylinder, for forming wave-type corrugated web, Figure 13 is a broken off perspective view of a web of material leaving the calender, before longitudinal trimming of the sides along the dashed lines. Figures 1 and 4 show portions of wave shaped (Figs 1 and 2) or fret shaped (Figs 3, 4) corrugated web or panels, of extruded thermoplastic material, as can be obtained according to the present invention. The terms "undulated" and "corrugated", "undulation" and "corrugation" will henceforth be used indifferently with reference to one or the other type of configuration and the wave-shaped or zigzag (fret) shaped protrusion (undulation) will be called the "rib" or "corrugation". Whilst corrugated panels were per se known to the art prior to the invention, it was not known prior thereto to form said panels with the corrugations having their axis transverse to the direction of travel, or of extrusion, of the plastic material used for the panel. Said direction of travel and/or of extrusion is indicated by an arrow in Figures 1-4. The webs of said figures are designated with reference numerals la, lb, lc, and Id. Figure 5 shows a web lb wound in a roll around a core 2, and said figure shows both the arrangement of the undulations of the web, transverse to the longitudinal direction of said web, and one of the advantages of the invention, that is to say the possibility of winding the web produced. With reference now to Figures 6-12 a calender apparatus will be described, designated as whole with reference numeral 10. The apparatus 10 comprises, on a framework 12, a forming cylinder 14 having a horizontal axis, a cooperating cylinder 16 collaborating in forming, henceforth called "drawing cylinder" for the sake of brevity, having a horizontal axis, and an accompanying or cooling cylinder 18 having a horizontal axis. The three cylinders or rollers are carried on respective shafts designated with reference numerals 20, 22 and 24, respectively, and these are carried rotatingly on the framework in bushings that can be moved vertically thereon. The details of said assembly are not explained here in that they are well within the reach of a person skilled in the art. Each shaft has an articulated connection, 26, 28, 30 with respective drive means for the drive unit, which in the example in the figure comprises a motor 32 connected to reduction gears 34, 36, 38. A forming cylinder 14 is shown in greater detail in Figures 8, 9, 10. It comprises a casing 48 with its outer surface shaped with alternating grooves 41 and lands or ridges 42. As can be better seen in Figure 9, each groove is defined, in a longitudinal direction, by surfaces, shaped like an arc of a circle, for example; that is to say, the cylinder 14 has the axially outermost parts 43 smooth and not grooved, preferably at the same level as the land parts 42. The cylinder casing has a plurality of axially extending conduits 45, 46, for communicating with a vacuum source. Said conduits 45, 46 communicate through small holes 47, 48 with the grooves 41 and the lands 42. The suction or vacuum system is not further described because it can be of any known type. The shape of the forming cylinder with grooves or lands defines the shape of the web produced. The cylinder in Figure 8, for example, will produce a zigzag or fret shaped corrugated web. A preferred drawing cylinder 16 for collaboration with the corrugated cylinder 14 is illustrated in Figures 6 to 11 and is part of this invention. The drawing cylinder 16 comprises a plurality of cylindrical or tubular elements 52 having their axes parallel to the axis of the cylinder, supported and connected with cooling tubes 54 of a same length. The circumferential distance between the elements 52 is correlated to the distance and the shape of the grooves 41 of the forming cylinder with which the drawing cylinder is to collaborate. The length of the tubular elements 52 is about equal to the useful length of the grooves 41. Figure 12 illustrates a forming cylinder 14a, with grooves 41a and lands 42a, for forming a wave shaped corrugated web. The forming cylinder 14a has a shape in side view similar to that shown for the cylinder 14 in Figure 9, and has the same vacuum application system with small holes 47a and 48a. To collaborate with the cylinder 14a, a drawing cylinder 16a has a shape with lands 52a alternating with valleys 51a, of a shape and length correlated with the grooves 41a and the protrusions or lands 42a of the forming cylinder, and turns with the lands or protrusions 52a thereof alternating with the lands 42a of the forming cylinder. Alternatively, a cylinder with tubes like that described previously could be used equally advantageously. The cooling cylinder 18 can have a similar shape to that of the forming cylinder or can be smooth and serves to support and guide the web as it emerges. The production process will now be described. A smooth continuous web of thermoplastic material is extruded by a traditional extrusion head, referenced E in Figure 6. According to a characteristic of the invention, the extrusion head (or alternatively any means feeding a web of thermoplastic material in suitable temperature conditions) is positioned in the vicinity of the upper surface of the forming cylinder 14, so that the force of gravity acting on the web collaborates to dispose said web close to the surface of the forming cylinder. The extruded web thus settles on the uppermost surface of the cylinder 14 and is pulled against said surface by vacuum generated by the vacuum system and applied to the grooves 41 through the conduits 45, 46 and the holes 47, 48. It should be noted that vacuum application is made possible by the fact that the grooves 41 are closed at the ends, that is to say completely surrounded by the raised parts 42, 43. Forming of the web is completed by the collaboration of the forming cylinder and the drawing cylinder 16 which rotate in opposite directions. The lands of the drawing cylinder enter partially into the grooves 41 of the forming cylinder, further pushing the material against the surface thereof. The web emerging from the nip between the forming cylinder and the drawing cylinder is shaped as illustrated in Figure 13, that is to say it has smooth longitudinal edges and a corrugated longitudinal part with corrugations having a transverse axis. The web preferably then passes on the cylinder 18 which guides it to the outlet, possibly cooling it in a per se known manner. Downstream of the forming apparatus described, the web undergoes trimming along the longitudinal edges, that is to say, the side parts without grooves which were formed on contact with the raised parts 43 of the cylinder 14 are cut away from the web. Scrap material can be recycled. A product is obtained as shown in Figure 1, or in Figure 2 or in Figure 3 or 4 or other, according to the cylinder configuration used. It should be noted that while the outer shape of the forming cylinder central portion must correspond to the shape of the product to be obtained, the drawing cylinder with peripheral tubes can be used to collaborate with a plurality of forming cylinders with different shapes. Alternatively it is possible to use a drawing cylinder matched with the forming cylinder, as shown in Figure 12.

Claims: CLAIMS 1. A web of corrugated thermoplastic material (la; lb; lc; Id) characterized in that it has corrugations transverse to the longitudinal extension the web, so as to be windable in a roll. 2. A process for continuous production of a corrugated web of thermoplastic material, characterized in that it comprises the following steps: producing a continuous web of thermoplastic material, or alternatively feeding a web of thermoplastic material under suitable temperature conditions, forming said web into a shape with corrugations having their axis transverse to the longitudinal direction of the web with the aid of a suction type forming surface. 3. A process according to claim 2, characterized in that said forming surface is the surface of a rotating forming cylinder (14, 14a). 4. A process according to claim 3 characterized in that - the forming surface comprises grooved parts (41) and raised or land parts (43) following each other in the direction of travel of the web and raised or land side parts (43) to provide a vacuum seal, so that the longitudinal edges of the grooved web leaving the forming surface are not corrugated, - and that downstream of said forming step the web is subjected to trimming on the side edges to eliminate said ungrooved parts. 5. A process according to claim 2 characterized in that said step of forming the thermoplastic material comprises forming the web between a drawing surface and a forming surface. 6. A process according to claim 5 characterized in that said web forming step is done between a forming cylinder (14) with suction and a "drawing" cylinder (16), said cylinders being counter-rotating. 7. A process according to claim 6, characterized in that it comprises a cooling step for the formed web, downstream of said forming and drawing cylinders, by means of a cooling cylinder. 8. An apparatus for continuous production of a web of thermoplastic material corrugated transversely to the longitudinal extension of the web, characterized in that it comprises: a rotating forming cylinder (14; 14a), provided with a substantially cylindrical moulding surface with grooves (41) extending transversely to the direction of travel of the web and with means (45, 46) for generating a vacuum in said grooves to pull the web material toward the walls thereof. 9. An apparatus according to claim 8, characterized in that the forming surface comprises raised or land parts (43) between the grooves and on the side edges (43) of the cylinder, providing a seal for vacuum generated in the grooves. 10. An apparatus according to claim 8 further comprising a drawing cylinder (16) collaborating with the forming cylinder, counter-rotating therewith, and provided with ridges or lands able to penetrate at least partially into the grooves of the forming cylinder as it rotates therewith. 11. An apparatus according to claim 10, wherein said drawing cylinder (16a) has a shape matching the shape of the forming cylinder (14a). 12. An apparatus according to claim 10, characterized in that the drawing cylinder (16a) has a plurality of cylindrical or tubular bodies (52) spaced apart from each other circumferentially and supported by radial arms. 13. An apparatus according to claim 8, wherein the forming cylinder has a horizontal axis and an extrusion head (E) for extruding the continuous web is positioned upstream of said forming cylinder and near thereto, substantially level with the uppermost surface of the forming cylinder or a little higher, so that the force of gravity can collaborate to dispose the extruded web in contact with the forming surface. 14. An apparatus according to claim 8, comprising a cooling cylinder (18) downstream of the forming cylinder. 15. An apparatus according to claim 9 characterized in that it comprises trimming means downstream of the forming cylinder, to trim said grooved web along the edges thereof. 16. An apparatus according to any of the preceding claims wherein at least said forming and drawing cylinders are mounted on a single framework (12), with drive means thereof and means for adjusting the distance therebetween.

Inventors: LIATI GIUSEPPE, LIATI, GIUSEPPE
Applicants: DIPIEMME DIES AND PLASTIC MACH, LIATI GIUSEPPE, DIPIEMME DIES AND PLASTIC MACHINERY S.R.L., LIATI, GIUSEPPE
Application year: 2001
Main classification: B29C53
IPC codes: B29C53