Process for manufacturing a thermal roller and corresponding thermal roller

Abstract

A process for manufacturing a thermal roller (1) of the type comprising a spiral heat-exchange chamber (10) at least partially delimited by walls of plastic material is described. The heat-exchange chamber (10) is defined in an annular cavity (2) formed between an inner tubular element (3) and an outer tubular element (4) of the thermal roller (1). The inner tubular element (3) has an outer surface provided with a plastic material coating (13) comprising a base layer (131) which contacts said outer surface and at least one rib (132) projecting from the base layer (131) and integrally formed therewith. The at least one rib (132) extends along a helical path in the longitudinal extending direction (X-X) of the thermal roller (1) thereby correspondingly delimiting at least one helical channel (11) of the heat-exchange chamber (10). The coating (13) is made by spirally winding, on the outer surface of the inner tubular element (3), an extruded elongate element (20) made of a plastic material which comprises a base portion (21) intended to contact at least partially said surface to form a portion of the base layer (131) of the coating (13), and a ridge portion (22) upstanding from the base portion (21) to form the at least one rib (132). A thermal roller (1) that can be obtained by this process is also described.

Description

[0001] Process for manufacturing a thermal roller and corresponding thermal roller

[0002] DESCRIPTION

[0003] Field of the Invention

[0004] The present invention relates to a process for manufacturing a thermal roller and a thermal roller obtained by this process.

[0005] Known Art

[0006] Nowadays, thermal rollers are used in a variety of industrial applications in which the temperature of films or webs, e.g., polymer films, metal films, laminated films, webs of paper or cellulosic material, webs of woven or nonwoven material, etc. has to be controlled or changed. Heat exchange to heat, cool, or maintain at a constant temperature the film or web takes places mainly by conduction, i.e., by direct contact between the film or web and the thermal roller.

[0007] For this purpose, thermal rollers basically consist of a cylindrical body provided with a heat-exchange chamber in which a heat-transfer fluid, usually water, aqueous solutions, such as water and glycol solutions, or diathermal oil can be circulated. The heat-transfer fluid is supplied / discharged to / from the heat-exchange chamber via a fluid inlet and a fluid outlet, respectively, which are formed in hubs combined with the cylindrical body at its opposite longitudinal ends. Generally, the fluid inlet is formed in one of the hubs and the fluid outlet is formed in the opposite hub, but configurations in which the fluid inlet and fluid outlet are formed in the same hub are also possible. Anyway, under the conditions of use, the fluid inlet and fluid outlet are connected to an external hydraulic circuit which comprises pumping means and heat-exchange means to circulate the heat-transfer fluid in the heat-exchange chamber and control, in particular, the temperature and flow rate of the heat-transfer fluid itself.

[0008] The cylindrical body typically has a double-shell configuration comprising an outer tubular element intended to contact the film or web to be processed, and an inner tubular element arranged coaxially within the outer tubular element. The inner tubular element and the outer tubular element are sized to form an annular space between them, which defines the heat-exchange chamber of the thermal roller. In order to achieve as homogeneous a distribution as possible of the heat-transfer fluid circulating in the heat-exchange chamber during the rotation of the thermal roller and, as result, as uniform a temperature distribution as possible on the outer surface of the thermal roller itself, it is known to create in the aforesaid annular space at least one channel which extends helically over the entire length of the cylindrical body and which is in fluid communication with the fluid inlet and the fluid outlet of the thermal roller (so-called "spiral" heat-exchange chamber). The at least one helical channel is created by providing, in the annular space, a corresponding helically extending deflector element, the coils of which laterally delimit the helical channel.

[0009] According to a known solution, the deflector element consists of a metal profile usually made of steel and having circular cross-section, applied to the outer surface of the inner tubular element of the cylindrical body which forms the thermal roller. The latter is manufactured, in this case, by helically winding the metal profile onto the outer surface of the inner tubular element, by fixing the wound metal profile to the inner tubular element by welding, by fitting the outer tubular element onto the inner tubular element, and finally by applying the hubs to the ends of the resulting cylindrical body.

[0010] Manufacturing thermal rollers having a spiral heat-exchange chamber as described above is quite complex and expensive, especially also because of the tight machining tolerances required to ensure proper coupling between the metal profile constituting the helically extending deflector element and the outer tubular element of the cylindrical body. In addition, since the heat-exchange chamber is formed only of metal material, typically steel, it is more likely to be subject to corrosion due to rust formation and to deposition of limestone or other sediments, phenomena that degrade the performance of the thermal roller and reduce its service life.

[0011] To overcome the aforementioned drawbacks, thermal rollers with a spiral heatexchange chamber at least partially delimited by plastic material walls have been proposed.

[0012] For example, Patent EP 3 152 057 Bl in the name of the same Applicant describes a thermal roller with this type of spiral heat-exchange chamber, in which the inner tubular element is externally provided with a coating layer of plastic material. The coating layer comprises at least one rib extending along a helical path in the longitudinal extent direction of the thermal roller. The rib is formed integrally in the coating layer and has a height in the radial direction such that it contacts the inner surface of the outer tubular element. This way, at least one helical channel is defined in the heat-exchange chamber and is delimited in the longitudinal direction by adjacent coils of the rib and in the radial direction by the base of the coating layer of the inner tubular element and by the inner surface of the outer tubular element, respectively.

[0013] The same Patent also describes a process for manufacturing the aforesaid thermal roller, comprising the steps of providing the inner tubular element, externally covering the inner tubular element with a coating layer of plastic material of predetermined thickness, removing, by material removal operations, a part of the plastic material of the coating layer so as to form therein at least one helical channel extending in the direction of longitudinal extent of the inner tubular element, providing the outer tubular element and fitting it onto the inner tubular element provided with the coating layer in which the at least one helical channel was formed, providing two hubs and combining them with the inner tubular element and the outer tubular element which are combined with each other.

[0014] The Applicant found that, although this manufacturing process allows thermal rollers with a spiral heat-exchange chamber at least partially delimited by plastic walls to be formed easily, it is not very efficient in terms of the use of raw materials. In particular, creating the at least one helical channel in the coating layer of plastic material applied to the inner tubular element by subtractive machining, a significant amount of plastic waste is produced: the larger the thermal roller to be manufactured, the greater the waste. Clearly, this has a negative impact on the production costs of the thermal roller.

[0015] Summary of the invention

[0016] In view of the above, the Applicant considered the problem of providing a process of manufacturing a thermal roller of the type comprising a spiral heat-exchange chamber at least partially delimited by plastic material walls, which allows the elimination, or at least a substantial reduction, of plastic waste used to make the spiral heat exchange chamber.

[0017] In addition, the Applicant considered the problem of providing a process of manufacturing a thermal roller of the aforesaid type which can also be implemented in a simple, flexible, and cost-competitive manner.

[0018] The Applicant also considered the problem of providing a thermal roller of the aforesaid type having a structure which allows the elimination, or at least a substantial reduction in the waste of plastic material used to make the spiral heat-exchange chamber, thus resulting in lower production costs.

[0019] According to the present invention, these problems are solved by a process for manufacturing a thermal roller and a corresponding thermal roller having the characteristics set forth in the appended claim 1 and claim 10, respectively.

[0020] Within the scope of the following description and subsequent claims:

[0021] - "longitudinal direction" or "longitudinally" means a direction, or along a direction, parallel to the direction of the axis of rotation of the thermal roller, typically coincident with the main extent direction of the roller itself;

[0022] - "radial direction" or "radially" means a direction, or along a direction, perpendicular to the longitudinal direction;

[0023] - "elongate element" means an element whose longitudinal dimensions are substantially greater than the transverse dimensions, that is, than the width and height, of the element itself.

[0024] Specifically, in its first aspect, the invention relates to a process for manufacturing a thermal roller comprising:

[0025] - a cylindrical body extending along a longitudinal direction and comprising an inner tubular element and an outer tubular element coaxially arranged around the inner tubular element and forming with the inner tubular element an annular cavity, wherein the inner tubular element has an outer surface provided with a plastic material coating, wherein said coating comprises a base layer contacting said outer surface and at least one rib projecting from the base layer and integrally formed therewith, and wherein the at least one rib extends along a helical path in said longitudinal direction;

[0026] - a heat-exchange chamber defined in the annular cavity and comprising at least one helical channel intended to be flown by a heat-transfer fluid, wherein the at least one helical channel is delimited in said longitudinal direction by lateral walls of the at least one rib of said coating, and

[0027] - a pair of hubs, each arranged at a longitudinal end of the cylindrical body and delimiting the heat-exchange chamber in said longitudinal direction, wherein, the process comprises the steps of:

[0028] - providing the inner tubular element;

[0029] - applying the plastic material coating onto the outer surface of the inner tubular element;

[0030] - providing the outer tubular element;

[0031] - providing the pair of hubs, and

[0032] - assembling together the inner tubular element provided with said coating, the outer tubular element, and the pair of hubs so as to obtain the thermal roller.

[0033] The step of applying the plastic material coating comprises spirally winding at least one extruded elongate element made of plastic material on the outer surface of the inner tubular element, and the extruded elongate element comprises a base portion intended to contact at least partially the outer surface of the inner tubular element to form a portion of the base layer of the plastic material coating of the inner tubular element, and a ridge portion upstanding from said base portion to form the at least one rib of said coating.

[0034] Advantageously, such a manufacturing process allows a structured plastic material coating, already having the configuration suitable to form a spiral heatexchange chamber, to be created on the outer surface of the inner tubular element of the thermal roller. This way, after the application of the plastic material coating, no material removing steps are required to create the desired final structure in the coating itself, in particular the bottom and sides of at least one helical channel. Thus, the manufacturing process according to the invention allows to prevent, or at least drastically reduce the production of plastic waste for producing a thermal roller of the type comprising a spiral heat-exchange chamber at least partially delimited by plastic walls, and the resulting better exploitation, i.e., saving, of raw materials has positive effect on production costs. Eliminating from the process all operations directly or indirectly related to removing steps of material from the applied plastic material coating also contributes to reduce production costs.

[0035] The manufacturing process mentioned above may have one or more of the preferred aspects described below.

[0036] Preferably, the extruded elongate element wound on the outer surface of the inner tubular element to create the plastic material coating is a continuous element.

[0037] The extruded elongate element can be advantageously fed by a feeding unit consisting of or comprising an extruder for producing the extruded elongate element simultaneously with the step of applying the plastic material coating.

[0038] As an alternative, the extruded elongate element can be fed by a feeding unit consisting of or comprising a storage reel on which a length of said extruded elongate element produced before said step of applying the plastic material coating is wound.

[0039] According to a preferred implementation of the process, the spiral winding of the extruded elongate element on the outer surface of the inner tubular element is carried out by subjecting the inner tubular element to a rotation about a rotation axis parallel to the longitudinal direction and, simultaneously, the feeding unit to a translation along said longitudinal direction.

[0040] As an alternative, the spiral winding of the extruded elongate element on the outer surface of the inner tubular element could be carried out by subjecting the inner tubular element to a rotation about a rotation axis parallel to the longitudinal direction and, simultaneously, to a translation along said longitudinal direction.

[0041] Preferably, said rotation and translation are set and controlled so that the extruded elongate element is wound on the outer surface of the inner tubular element thus forming overlapping regions between base portions of adjacent windings of the same extruded elongate element.

[0042] According to a possible implementation of the process, said rotation and translation are set and controlled so that the extruded elongate element is wound on the outer surface of the inner tubular element with a constant pitch.

[0043] According to another possible implementation of the process, said rotation and translation are set and controlled so that said extruded elongate element is wound on the outer surface of the inner tubular element with variable pitch.

[0044] In order to make a heat-exchange chamber having a single-start configuration, i.e., comprising a single helical channel, the pitch of the single extruded elongate element wound on the inner tubular element is preferably chosen to be less than or equal to the maximum transverse width of the extruded elongate element, particularly its base portion.

[0045] In order to make double-start or multi-start heat-exchange chamber, that is, comprising two or more helical channels running in parallel, the pitch of each of the two or more extruded elongate elements correspondingly wound on the inner tubular element is instead chosen to be greater than the maximum transverse width of the respective extruded elongate element, so as to allow the two or more extruded elongate elements wound on the inner tubular element to be mutually interposed in the longitudinal direction.

[0046] Conveniently, the process comprises, before the step of applying the plastic material coating onto the outer surface of the inner tubular element, a step of treating said outer surface to increase its adhesiveness. This treating step may comprise applying at least one layer of an adhesion-promoter material onto said outer surface. As an alternative, the treating step may comprise flame or plasma treatment.

[0047] Conveniently, the process comprises, after the step of applying the plastic material coating onto the outer surface of the inner tubular element, a step of curing the applied coating, implemented, for example, by autoclave treatment of the coated inner tubular element.

[0048] If the extruded elongate element is manufactured separately and the elongate element is fed from a storage reel during the step of applying the plastic material coating onto the outer surface of the inner tubular element, the curing treatment can be carried out on the extruded elongate element alone, for example before winding onto the storage reel.

[0049] According to a possible implementation of the process, the assembling step of the thermal roller may comprise the steps of - combining the outer tubular element with the inner tubular element provided with the plastic material coating so as to form the cylindrical body, and

[0050] - combining each hub of the pair of hubs with a respective longitudinal end of the cylindrical body so as to obtain the thermal roller.

[0051] According to another possible implementation of the process, the assembling step of the thermal roller may comprise the steps of:

[0052] - combining a hub of the pair of hubs with an end of the outer tubular element;

[0053] - combining the inner tubular element, provided with the plastic material coating, with the outer tubular element so as to form the cylindrical body, and

[0054] - combining the other hub of the pair of hubs with the other end of the outer tubular element so as to obtain the thermal roller.

[0055] In its second aspect, the invention relates to a thermal roller comprising:

[0056] - a cylindrical body extending along a longitudinal direction and comprising an inner tubular element and an outer tubular element coaxially arranged around the inner tubular element and forming with the inner tubular element an annular cavity, wherein the inner tubular element has an outer surface provided with a plastic material coating, wherein said coating comprises a base layer contacting said outer surface and at least one rib projecting from the base layer and integrally formed therewith, and wherein the at least one rib extends along a helical path in said longitudinal direction;

[0057] - a heat-exchange chamber defined in said annular cavity and comprising at least one helical channel intended to be flown by a heat-transfer fluid, wherein the at least one helical channel is delimited in said longitudinal direction by lateral walls of the at least one rib of said coating, and

[0058] - a pair of hubs, each arranged at a longitudinal end of the cylindrical body and delimiting the heat-exchange chamber in said longitudinal direction.

[0059] The plastic material coating is formed by at least one extruded elongate element of plastic material spirally wound on the outer surface of the inner tubular element, and the at least one extruded elongate element comprises a base portion intended to contact the outer surface of the inner tubular element to form a portion of the base layer of said coating, and a ridge portion upstanding from said base portion to form said at least one rib.

[0060] Such a thermal roller can be directly manufactured through the manufacturing process described above and shares its advantages in terms of saving the plastic material needed to make the spiral heat-exchange chamber and the related reduction in production costs.

[0061] The thermal roller may have one or more of the preferred aspects described below.

[0062] Preferably, the extruded elongate element has a cross section of substantially inverted-T shape.

[0063] Conveniently, the base portion of the extruded elongate element comprises a pair of branches extending on opposite sides relative to the ridge portion, and, in a cross- sectional view of the extruded elongate element, said branches taper, or comprise at least one length, preferably a distal length, which tapers away from said ridge portion.

[0064] Conveniently, looking at the extruded elongate element in a cross-sectional view, the ridge portion has a shape that tapers away from the base portion.

[0065] Preferably, the ridge portion of the extruded elongate element is delimited by a pair of opposite side walls having a concave shape.

[0066] Conveniently, the ridge portion of the extruded elongate element has a rounded tip.

[0067] Brief description of the drawings

[0068] Further characteristics and advantages of the invention, in its previously mentioned aspects, will be more evident from the following detailed description of its preferred implementations or embodiments, made herein below and illustrated by way of example only and without limitations with reference to the attached drawings, wherein:

[0069] - Fig. 1 is a schematic perspective view of a thermal roller according to the present invention;

[0070] - Fig. 2 is a longitudinal sectional schematic view of the thermal roller in Fig. 1;

[0071] - Fig. 3 is a schematic perspective view, in longitudinal section, of a longitudinal end portion of the thermal roller in Fig. 1; - Fig. 4 is an enlarged view of the detail IV in Fig. 2;

[0072] - Fig. 5 is an magnified schematic view of the cross section of an extruded elongate element used to make the plastic material coating of the inner tubular element of the thermal roller in Fig. 1, and

[0073] - Figs. 6a-d are schematic views of steps of a thermal roller manufacturing process in Fig. 1.

[0074] Detailed description of embodiments of the invention

[0075] Referring in particular to Figs. 1 - 5, a possible embodiment of a thermal roller according to the present invention is collectively denoted by the numeral reference 1.

[0076] The thermal roller 1 comprises a cylindrical body 2 that extends along a longitudinal direction coincident with the direction of the axis of rotation X-X of the thermal roller 1.

[0077] As shown in Figs. 2 and 3, the cylindrical body 2 comprises an inner tubular element 3 and an outer tubular element 4 which have respective substantially circular cross-sections. The outer tubular element 4 is arranged coaxially around the inner tubular element 3 and forms an annular cavity 5 therewith, the latter having a radial thickness corresponding to the difference between the inner diameter of the outer tubular element 4 and the outer diameter of the inner tubular element 3.

[0078] A heat-exchange chamber 10 is defined in the annular cavity 5 and its structure will be described in more detail below. The heat-exchange chamber 10 is intended to be flown by a heat-transfer fluid to heat, cool, or maintain at a constant temperature a film or web of material 300 (shown in Fig. 1) which, during a treatment, is brought into contact with the thermal roller 1, more specifically with the outer surface of the outer tubular element 4 of the cylindrical body 2.

[0079] The thermal roller 1 further comprises a pair of hubs 6, 7, each arranged at a longitudinal end of the cylindrical body 2 and combined with the latter preferably in a removable manner.

[0080] The hubs 6, 7 mutually lock the inner the tubular element 3 and the outer tubular element 4 of the cylindrical body 2 in place and allow the thermal roller 1 to be rotatably supported in a respective supporting frame (not shown) during operation. In addition, the hubs 6, 7 delimit the heat-exchange chamber 10 in the longitudinal direction and are configured to allow the heat-transfer fluid to be supplied and discharged to / from the heat-exchange chamber 10

[0081] In the exemplary embodiment shown in the figures, the hubs 6, 7 are configured so as to close the longitudinal ends of both the outer tubular element 4 and the inner tubular element 3. In alternative embodiments of the thermal roller 1, not shown in the figures, the longitudinal ends of the inner tubular element 3 can be closed by respective cap elements separate from the hubs, the latter being then applied to the cylindrical body 2 in a position longitudinally outside with respect to the cap elements.

[0082] Again in the exemplary embodiment shown in the figures, the fluid inlet and outlet for the heat-transfer fluid are formed in the same hub, specifically, herein, the hub 7. In alternative embodiments of the thermal roller 1, not shown in the figures, the inlet and outlet of the heat-transfer fluid can each be formed in a different hub.

[0083] More specifically, in this case the hub 7 comprises a longitudinal duct 71 extending, preferably coaxially, between its two longitudinally opposite faces, and at least one radial duct 72 extending between the longitudinal duct 71 and the outer perimeter edge of the hub 7. Conveniently, the hub 7 may comprise a plurality of radial ducts 72, preferably equally spaced angularly in the perimeter direction.

[0084] The longitudinal duct 71 has a variable passage cross section. Specifically, the longitudinal duct 71 comprises a first length 71a defining a maximum passage cross section and extending between a longitudinally outer opening of the longitudinal duct 71 and a connecting zone of the radial duct(s) 72, and a second length 71b defining a minimum passage cross section and arranged between said connecting zone and a longitudinally inner opening of the longitudinal duct 71. The terms "inner" and "outer" referring to longitudinally opposite portions or elements of the hubs 6, 7 are herein to be understood with reference to their arrangement when mounted on the cylindrical body 2.

[0085] A tube 8 is coaxially arranged in the first length 71a of the longitudinal duct 71, the tube having a smaller cross section than the passage cross section of the first length 71a itself, so that, between the inner wall of the latter and the outer wall of the tube 8, an annular cavity 710 is defined in fluid communication with the at least one radial duct 72. The tube 8 is inserted into the longitudinal duct 71 through its longitudinally outer opening and is removably connected, e.g. screwed, to the longitudinal duct 71 itself at the second length 71b thereof.

[0086] The hub 6 comprises a blind longitudinal duct 61 extending, preferably coaxially, from its longitudinally inner face, and at least one radial duct 62 extending between the longitudinal duct 61 and the outer perimeter edge of the hub 6. Conveniently, the hub 6 may also comprise a plurality of radial ducts 62 preferably equally spaced angularly in the perimeter direction.

[0087] The hubs 6, 7 are placed in direct fluid communication via a tube 9 that extends, preferably coaxially, into the inner tubular element 3. In detail, an end of the tube 9 is removably connected to a longitudinally inner opening of the longitudinal duct 61 of the hub 6, whereas the other end of the tube 9 is removably connected to the longitudinally inner opening of the longitudinal duct 71 of the hub 7.

[0088] The hubs 6, 7, the tubes 8, 9 and the heat-exchange chamber 10 described above define a closed loop for circulating a heat-transfer fluid in the thermal roller 1. In detail, the heat-transfer fluid is supplied to the thermal roller 1 via the tube 8, which defines the fluid inlet of the thermal roller 1 at the hub 7. From the hub 7, the heat-transfer fluid then directly reaches the hub 6 through the tube 9. In the hub 6, through the longitudinal duct 61 and the radial duct(s) 62, the heat-transfer fluid is directed to a first end of the heat-exchange chamber 10. The heat-transfer fluid then travels through the entire heatexchange chamber 10, where it exchanges heat with the outer tubular element 4 of the cylindrical body 2. When the heat-transfer fluid reaches a second end, longitudinally opposite the first end, of the heat-exchange chamber 10, the heat-transfer fluid is discharged from the latter through the radial duct(s) 72 and the annular cavity 710 at the longitudinal duct 71 of the hub 7, the annular cavity defining the fluid outlet of the thermal roller 1, again at the hub 7.

[0089] The heat-exchange chamber 10 of the thermal roller 1 is of the spiral type and comprises at least one helical channel 11 running longitudinally in the annular cavity 5 formed between the inner tubular element 3 and the outer tubular element 4 along the entire length of the cylindrical body 2. In the exemplary embodiment shown in the figures, the heat-exchange chamber 10, in particular, has a single-start configuration, that is, it comprises a single helical channel 11. In alternative embodiments not shown in the figures, the heat-exchange chamber 10 could have a two- or multi-start configuration and correspondingly comprise two or more helical channels running longitudinally in the annular cavity 5 in parallel with each other.

[0090] The helical channel 11 is at least partially delimited by walls of plastic material. For this purpose, the inner tubular element 3 is provided with a coating 13 of plastic material applied to its outer surface.

[0091] The coating 13 comprises a base layer 131 which contacts the outer surface of the inner tubular element 3, and at least one rib 132, in particular exactly one in the case shown herein of a heat-exchange chamber 10 with single-start configuration, projecting radially from the base layer 131 and formed integrally therewith. The rib 132 extends along a helical path around the inner tubular element 3 in the longitudinal direction thereof. Consequently, a generic passage cross section of the helical channel 11 is delimited in the longitudinal direction by adjacent coils of the rib 132 of the coating 13, and in the radial direction by the base layer 131 of the coating 13 and by the inner surface 14 of the outer tubular element 4, respectively.

[0092] The coating 13 is formed by at least one extruded elongate element 20 spirally wound on the outer surface of the inner tubular element 3.

[0093] The extruded elongate element 20 has a configuration such that its windings on the outer surface of the inner tubular element 3 directly create the desired spiral structure of the heat-exchange chamber 10, without the need for subsequent machining, particularly material removal machining, on the resulting coating layer 13. In particular, the extruded elongate element 20 comprises a base portion 21 intended to contact the outer surface of the inner tubular element 3 to form a portion of the base layer 131 of the coating 13, and a ridge portion 22 upstanding from the base portion 21 to form the rib 132.

[0094] As best seen in Figs. 4 and 5, the extruded elongate element 20 preferably has a cross section having substantially inverted-T shape, in which the ridge portion 22 is arranged to straddle a longitudinal center plane CP of the extruded elongate element 20 and the base portion 21 comprises a pair of branches 21a, 21b which extend on opposite sides relative to the ridge portion 22.

[0095] Preferably, the branches 21a, 21b of the base portion 21 taper or comprise at least one length, particularly a distal length, which tapers away from the ridge portion 22. Advantageously, this allows overlapping regions to be created between base portions 21 of adjacent windings of the extruded elongate element 20, herein particularly between the branch 21b of the base portion 21 of each winding and the branch 21a of the base portion 21 of the subsequently created winding, without locally increasing the thickness of the base layer 131 of the coating 13.

[0096] The ridge portion 22 preferably has a shape that tapers away from the base portion 21 and preferably ends in a rounded tip.

[0097] Fig. 5 shows in more detail an example of an extruded elongate element 20 that can be used to make the coating 13. Specifically, this figure depicts the cross section of the extruded elongate element 20 as directly resulting from the extrusion process and before the same is wound on the outer surface of the inner tubular element 3.

[0098] In this example, the base portion 21 is delimited by a lower surface 211 substantially flat and the two branches 21a, 21b are shaped as right triangles, so that the base portion 21 essentially takes the shape of an isosceles trapezium. The extruded elongate element 20 has an overall symmetrical configuration with respect to the longitudinal center plane CP.

[0099] The extruded elongate element 20 has a maximum transverse height H measured between the bottom surface 211 of the base portion 21 and the tip of the ridge portion 22, preferably between 5 mm and 50 mm. In any case, the maximum transverse height H is preferably at least equal to the radial thickness of the annular cavity 5 formed between the inner tubular element 3 and the outer tubular element 4. Conveniently, the maximum transverse height H can be slightly greater than the radial thickness of the annular cavity 5, so as to obtain a radial interference between the ridge portion 22 of the extruded elongate element 20 - that is, the rib 132 of the coating 13 - and the inner surface 14 of the outer tubular element 4. In this case, when the outer tubular element 4 is mounted on the inner tubular element 3, the tip region of the ridge portion 22 undergoes compression and / or bending that contribute to create a watertight seal between the latter and the inner surface 14 of the outer tubular element 4.

[0100] The extruded elongate element 20 has a maximum transverse width H measured between the transversally opposite ends of the base portion 21, preferably between 5 mm and 200 mm.

[0101] As a result of the winding of the extruded elongate element 20 on the inner tubular element 3 to form the coating 13 and the subsequent mounting of the outer tubular element 4, the cross section and respective dimensions of the extruded elongate element 20 may be subjected to modifications, which, however, do not alter its overall inverted-T shaped configuration.

[0102] Modifications that may occur due to partial overlap between base portions 21 of adjacent windings of the extruded elongate element 20 are shown schematically in Figures 2-4 for illustrative purposes only. As can best be seen in Fig. 4, as a result of this overlapping, an undercut region 214 is created in the branch 21a of the base portion 21 of each winding and has a shape corresponding to the underlying, itself partially compressed, i.e., flattened, end of the branch 21b of the base portion 21 of the adjacent winding previously created.

[0103] The extruded elongate element 20 is preferably continuous, that is, it has no joints or other discontinuities along its windings on the outer surface of the tubular element 3.

[0104] The extruded elongate element 20 can be spirally wound on the outer surface of the inner tubular element 3 with a constant or variable pitch p. This second option can be useful for creating a helical channel 11 whose passage cross section is variable, in particular converging or diverging in the extending direction thereof around the inner tubular element 3.

[0105] In the embodiment shown in the figures - which, as already mentioned, refers to a thermal roller with a heat-exchange chamber having a single-start configuration - the extruded elongate element 20 is wound on the outer surface of the inner tubular element 3 with a pitch p constant and less than its maximum transverse width W, such that overlapping regions are created between the branches 21a, 21b of the base portions 21 of adjacent windings of the extruded elongate element 20. As an alternative, the pitch p could be equal to the maximum transverse width W of the extruded elongate element 20, such that the windings are mutually adjacent without overlapping.

[0106] In other embodiments not shown in the figures, in which the heat-exchange chamber 10 has a two-start or multi-start configuration, the pitch p of each of the two or more extruded elongate elements 20 correspondingly spirally wound on the inner tubular element 3 is instead chosen to be larger than the maximum transverse width W of the respective extruded elongate element, in order to allow them to be mutually interposed in the longitudinal direction.

[0107] In any case, the coating 13 formed by spiral winding the extruded elongate element(s) 20 covers the outer surface of the inner tubular element 3 preferably in a continuous manner.

[0108] Referring in particular to Figs. 6a-d, a preferred implementation of a process to manufacture the thermal roller 1 will be now described.

[0109] In a first step of the process, the inner tubular element 3 is provided (Fig. 6a).

[0110] The inner tubular element 3 is preferably made of metal, e.g., steel, by known manufacturing processes, e.g., processes for making welded or non-welded metal tubes. As an alternative, the inner tubular element 3 can be made of a composite material, such as a material based on carbon fibers impregnated with resin, again by known manufacturing processes, e.g., sheet wrapping, filament winding, or pull winding processes.

[0111] The outer surface of the inner tubular element 3, particularly if the latter is made of metal, is preferably treated to increase its adhesiveness. Such treatment preferably comprises the application of at least one layer 31 of an adhesion-promoter material (primer) to the outer surface, such as by painting or spraying. As an alternative, a flame or plasma treatment could be carried out.

[0112] At a subsequent step, the plastic material coating 13 is applied onto the inner tubular element 3. The coating 13 is created by spirally winding at least one, in the example shown here exactly one, extruded elongate element 20 on the outer surface of inner tubular element 3 (Fig. 6b).

[0113] The extruded elongate element 20 is made of an extrudable plastic material preferably selected from thermoplastic materials, elastomeric materials, or combinations thereof.

[0114] Examples of preferred thermoplastic materials are PVC, POM, PU.

[0115] Examples of preferred elastomeric materials are: EPDM, silicone, NBR, fluoroelastomers such as VITON®.

[0116] As for the rest, the extruded elongate element 20 is configured and sized as already described above in relation to the structure of the thermal roller 1.

[0117] The application of the extruded elongate element 20 on the outer surface of the inner tubular element 3 is carried out by using a specially designed applicator unit 400 schematically shown in Fig. 6b.

[0118] The applicator unit 400 comprises a supporting frame 410 for the inner tubular element 3. The supporting frame 410 is configured to support the inner tubular element 3 during its rotation (arrow R) about its longitudinal axis, which is coincident with the axis of rotation X-X of the finished thermal roller 1.

[0119] The applicator unit 400 further comprises a feeding unit 420 to feed the extruded elongate element 20 to be wound. The feeding unit 420 is preferably linearly translatable (double arrow T) along a direction parallel to the longitudinal axis of the inner tubular element 3 in the condition of being mounted on the respective supporting frame 410. For this purpose, the feeding unit 402 is mounted on rails 422.

[0120] Preferably, the applicator unit 400 also comprises a guide unit 430 interposed between the feeding unit 420 and the supporting frame 410 of the inner tubular element 3. The guide unit 430 comprises at least one guide roller and / or diverter 431 acting on the extruded elongate element 20 fed from the feeding unit 420. The guide unit 430 can advantageously be used to define an appropriate path for the extruded elongate element 20 downstream of the feeding unit 420, before it reaches the inner tubular element 3, and, at the same time, to control its state of tension and, therefore, the application pressure on the outer surface of the inner tubular element 3. The guide unit 430 is preferably translationally integral with the feeding unit 420. The rotation of the inner tubular element 3 given by the supporting frame 410 and the operation and translation of the feeding unit 420 and, if present, of the guiding unit 430 of the applicator unit 400 are controlled and coordinated by numerical control, by means of a control unit 440.

[0121] According to a preferred implementation of the process, the feeding unit 420 is or comprises an extruder 421 and the extruded elongate element 20 is produced (extruded) during the step of applying the coating 13 onto the outer surface of the inner tubular element 3.

[0122] As an alternative, the feeding unit 420 could consist of a storage reel (not shown) on which a certain length of the extruded elongate element 20, produced (extruded) before the step of applying the coating 13, is wound.

[0123] According to a preferred implementation of the process, the spiral winding of the extruded elongate element 20 on the outer surface of the inner tubular element 3 is formed by subjecting the inner tubular element 3, which is mounted on the supporting frame 410, to a rotation about its own longitudinal axis and, simultaneously, the feeding unit 420 and, if present, the guide unit 430 to a translation parallel to this longitudinal axis.

[0124] Alternatively, the spiral winding of the extruded elongate element 20 on the outer surface of the inner tubular element 3 could be formed by subjecting the inner tubular element 3 mounted on the supporting frame 410 to a rotation about its own longitudinal axis and, simultaneously, the supporting frame 410 itself to a translation parallel to this longitudinal axis, while the feeding unit 420 and, if present, the guide unit 430 are stationary. In this case, the supporting frame 410 is mounted on respective rails (not shown), whereas the feeding unit 420 may have a fixed installation.

[0125] The spiral winding of the extruded elongate element 20 on the outer surface of the inner tubular element 3 is preferably carried out continuously.

[0126] During the spiral winding, the extruded elongate element 20 is preferably subjected to a predetermined tension, by means of the guide unit 430 and / or the combined action of the rotation of the inner tubular element 3 and the translation of the feeding unit 420, so as to obtain a predetermined application pressure on the outer surface of the inner tubular element 3.

[0127] The parameters of the spiral winding of the extruded elongate element 20, especially the helix angle P defined as the angle formed between the tangent to the extruded elongate element 20 and a plane perpendicular to the longitudinal axis of the inner tubular element 3, and the pitch p can be set and controlled by the initial positioning of the feeding unit 420 and / or the guide unit 430 with respect to the inner tubular element 3 mounted on the supporting frame 410 and by their mutual movements during winding.

[0128] The absolute value of the helix angle P can be within the range of 0° to 90°, excluding the endpoints, and it can be kept constant or vary during winding.

[0129] The pitch p can be less than, equal to, or greater than the maximum transverse width W of the extruded elongate element 20, the maximum transverse width being measured before winding the latter on the inner tubular element 3, particularly as it comes out of the feeding unit 420, and can also be kept constant or vary during winding.

[0130] Specifically, in order to obtain a thermal roller 1 having the characteristics previously described with reference to Figs. 1-5, the extruded elongate element 20 is spirally wound on the outer surface of the inner tubular element 3 with a constant helix angle P and a constant pitch p which is smaller than the maximum transverse width W of the extruded elongate element 20 itself, such that overlapping regions are formed between base portions 21 of adjacent windings of the extruded elongate element 20.

[0131] In all cases, the coating 13 of plastic material resulting from the application step described above completely covers the outer surface of the inner tubular element 3 and is already provided with a helical channel 11 intended to form the spiral heat-exchange chamber 10 of the thermal roller 1, without the need for further machining, particularly machining to remove material from the applied coating layer, to create the helical channel 11 itself. Specifically, the helical channel 11 is delimited laterally, i.e., in the direction of longitudinal extent of the inner tubular element 3, by adjacent coils of the rib 132 of the coating 13, corresponding to the ridge portion 22 of the extruded longitudinal element 20 spirally wound on the outer surface of the inner tubular element 3, as described above. By means of the process of the invention, thermal rollers having a spiral heatexchange chamber with a two-start or multi-start configuration can also be manufactured. In this case, the step of applying the coating 13 of plastic material onto the outer surface of the inner tubular element 3 provides the spiral winding of two or more extruded elongate elements 20 mutually interposed in the longitudinal direction. In order to allow such interposition, each of the two or more extruded elongate elements 20 is spirally wound with a pitch p greater than the respective maximum transverse width W. The spiral winding of the two or more extruded elongate elements 20 can be carried out in succession by iteratively repeating the spiral winding step previously described of a single extruded elongate element 20. Alternatively, if the feeding unit 420 is configured so as to be able to feed two or more extruded elongate elements 20 simultaneously, for example if the extruder 421 is equipped with a multiple porthole die, the spiral winding of the two or more elongate elements 20 can be carried out simultaneously, in parallel, in a single winding step.

[0132] Again, the resulting coating 13 on the outer surface of the inner tubular element 3 directly features two or more helical channels 11 running parallel to each other, without the need for any other machining to form them.

[0133] After the step of applying the plastic material coating 13 onto the outer surface of the inner tubular element 3, and particularly in the case where this step is carried out by simultaneous extrusion of the at least one extruded elongate element 20, there is preferably a step of curing the applied coating 13, which step is carried out, for example, by autoclave treatment of the coated inner tubular element 3.

[0134] If the extruded elongate element 20 is produced separately and is fed from a storage reel during the step of applying the plastic material coating 13, the curing treatment can be carried out on the extruded elongate element alone, for example before winding onto the storage reel. In this case, it may be advantageous to heat the extruded elongate element 20 fed from the storage reel to facilitate the spiral winding and adhesion onto the outer surface of the inner tubular element 3. For this purpose, the applicator unit 400 may comprise a special heating unit (not shown), for example interposed between the feeding unit 420 and the guiding unit 430 and possibly integrated into the latter.

[0135] In a further step of the process, which can be carried out independently of the above described steps, in parallel with them or even before them, the outer tubular element 4 is provided.

[0136] The outer tubular element 4 is also preferably made of metal, e.g., steel, by known manufacturing processes, e.g., processes for making welded or non-welded metal tubes. As an alternative, the outer tubular element 4 can be made of a composite material, such as a material based on carbon fibers impregnated with resin, again by known manufacturing processes, such as sheet wrapping, filament winding, or pull winding processes.

[0137] The outer surface of the outer tubular element 4, intended to contact the film or web of material 300 to be heated or cooled, may be subjected to one or more surface treatments, such as chrome plating, nickel plating, zinc coating, anodization, anodic oxidation, thermal spraying, to achieve specific performance in terms of adhesion, corrosion resistance and / or heat transfer. If the temperatures involved are such that the integrity of the plastic material coating 13 of the inner tubular element 3 is not jeopardized, these surface treatments can also be carried out at a later step on the already assembled thermal roller 1 or on the cylindrical body 2 formed by assembling the inner tubular element 3 and the outer tubular element 4.

[0138] In a further step, which can be carried out independently of the above described steps, in parallel with them or even before them, the hubs 6, 7 are provided.

[0139] The hubs 6, 7 are preferably made of metal, e.g., steel, and preferably in one piece, e.g., by conventional machining processes of chip removal carried out on semifinished parts formed by casting.

[0140] Next, the thermal roller 1 is assembled.

[0141] For this purpose, according to a possible implementation of the process, shown in the figures, the outer tubular element 4 is combined with the inner tubular element 3 provided with the coating 13 (Fig. 6c), so as to obtain the cylindrical body 2 of the thermal roller 1.

[0142] In detail, the outer tubular element 4 is fit longitudinally onto the inner tubular element 3. As already mentioned, the maximum height in the radial direction of the coating 13, measured at the rib 132 and substantially corresponding to the maximum transverse height H of the extruded elongate element 20 spirally wound, may be slightly higher than the difference between the inner diameter of the outer tubular element 4 and the outer diameter of the inner tubular element 3. In this case, the outer tubular element 4 and the inner tubular element 3 provided with the coating 13 are coupled to each other with a certain degree of radial interference, which advantageously causes the tip region of the rib 132 to be compressed and / or bent and helps to create a watertight seal between the latter and the inner surface 14 of the outer tubular element 4.

[0143] The hubs 6, 7 are then combined with, and properly fixed to, the longitudinal ends of the cylindrical body 2 (Fig. 6d).

[0144] During and / or after this step, any additional components, such as the tubes 8 and 9 for supplying and circulating the heat-transfer fluid to / in the thermal roller 1, are also mounted, so as to complete the manufacture of the latter.

[0145] According to another possible implementation of the process, first one of the hubs 6, 7 is combined with and attached to a first end of the outer tubular element 4, then the inner tubular element 3 is mounted into the outer tubular element 4 through the second end thereof, thus forming the cylindrical body 2 of the thermal roller 1, and finally the cylindrical body 2 is closed by applying the other hub 6, 7 to the second end of the outer tubular element 4.

[0146] In order to meet specific and contingent application requirements, modifications and variations may be made by a field technician to the previously described embodiments or implementations of the thermal roller and the respective manufacturing process, while still remaining within the protection scope of the invention as defined by the attached claims.

Claims

CLAIMS1. Process for manufacturing a thermal roller (1), wherein said thermal roller (1) comprises:- a cylindrical body (2) extending along a longitudinal direction (X-X) and comprising an inner tubular element (3) and an outer tubular element (4) concentrically arranged around the inner tubular element (3) and forming with the inner tubular element (3) an annular cavity (5), wherein the inner tubular element (3) has an outer surface provided with a plastic material coating (13), wherein said coating (13) comprises a base layer (131) contacting said outer surface and at least one rib (132) projecting from the base layer (131) and integrally formed therewith, and wherein the at least one rib (132) extends along a helical path in said longitudinal direction (X-X);-a heat-exchange chamber (10) defined in said annular cavity (5) and comprising at least one helical channel (11) intended to be flown by a heat-transfer fluid, wherein the at least one helical channel (11) is delimited in said longitudinal direction (X-X) by lateral walls of the at least one rib (132) of said coating (13), and- a pair of hubs (6, 7), each arranged at a longitudinal end of the cylindrical body (2) and delimiting the heat-exchange chamber (10) in said longitudinal direction (X-X), said process comprising the steps of:- providing the inner tubular element (3);- applying the plastic material coating (13) onto the outer surface of the inner tubular element (3);- providing the outer tubular element (4);- providing the pair of hubs (6, 7), and- assembling together the inner tubular element (3) provided with said coating (13), the outer tubular element (4), and the pair of hubs (6, 7) so as to obtain the thermal roller (1), characterized in that the step of applying the plastic material coating (13) comprises spirally winding at least one extruded elongate element (20) made of a plastic material on the outer surface of the inner tubular element (3), and in that said extruded elongate element (20) comprises a base portion (21) intended to contact at least partiallythe outer surface of the inner tubular element (3) to form a portion of the base layer (131) of said coating (13), and a ridge portion (22) upstanding from said base portion (21) to form said at least one rib (132).

2. Process according to claim 1, wherein said extruded elongate element (20) is a continuous element.

3. Process according to claim 1 or 2, wherein the extruded elongate element (20) is fed by a feeding unit (420) consisting of or comprising an extruder (421) for producing said extruded elongate element (20) simultaneously with said step of applying the plastic material coating (13).

4. Process according to claim 1 or 2, wherein the extruded elongate element (20) is fed by a feeding unit (420) consisting of or comprising a storage reel on which a length of said extruded elongate element (20) produced before said step of applying the plastic material coating (13) is wound.

5. Process according to any one of the previous claims, wherein spirally winding said extruded elongate element (20) on the outer surface of the inner tubular element (3) is carried out by subjecting the inner tubular element (3) to a rotation about a rotation axis parallel to said longitudinal direction (X-X) and, simultaneously, said feeding unit (420) to a translation along said longitudinal direction (X-X).

6. Process according to any one of claims 1 to 4, wherein spirally winding said extruded elongate element (20) on the outer surface of the inner tubular element (3) is carried out by subjecting the inner tubular element (3) to a rotation about a rotation axis parallel to said longitudinal direction (X-X) and, simultaneously, to a translation along said longitudinal direction (X-X).

7. Process according to claim 5 or 6, wherein said rotation and translation are set and controlled so that said extruded elongate element (20) is wound on the outer surface of the inner tubular element (3), forming overlapping regions between base portions (21) of adjacent windings of said extruded elongate element (20).

8. Process according to any one of claims 5 to 7, wherein said rotation and translation are set and controlled so that said extruded elongate element (20) is wound on the outer surface of the inner tubular element (3) with a constant pitch (p).

9. Process according to any one of claims 5 to 7, wherein said rotation and translation are set and controlled so that said extruded elongate element (20) is wound on the outer surface of the inner tubular element (3) with a variable pitch (p).

10. Process according to any one of the previous claims, wherein said assembling step comprises the steps of:- combining the outer tubular element (4) with the inner tubular element (3) provided with said coating (13) so as to form said cylindrical body (2), and- combining each hub of the pair of hubs (6, 7) with a respective longitudinal end of the cylindrical body (2) so as to obtain the thermal roller (1), or the steps of:- combining a hub of the pair of hubs (6, 7) with an end of the outer tubular element (4);- combining the inner tubular element (3) provided with said coating (13) with the outer tubular element (4) so as to form said cylindrical body (2), and- combining the other hub of the pair of hubs (6, 7) with the other end of the outer tubular element (4) so as to obtain the thermal roller (1).

11. Thermal roller (1) comprising:- a cylindrical body (2) extending along a longitudinal direction (X-X) and comprising an inner tubular element (3) and an outer tubular element (4) concentrically arranged around the inner tubular element (3) and forming with the inner tubular element (3) an annular cavity (5), wherein the inner tubular element (3) has an outer surface provided with a plastic material coating (13), wherein said coating (13) comprises a base layer (131) contacting said outer surface and at least one rib (132) projecting from the base layer (131) and integrally formed therewith, and wherein the at least one rib (132) extends along a helical path in said longitudinal direction (X-X);-a heat-exchange chamber (10) defined in said annular cavity (5) and comprising at least one helical channel (11) intended to be flown by a heat-transfer fluid, wherein the at least one helical channel (11) is delimited in said longitudinal direction (X-X) by lateral walls of the at least one rib (132) of said coating (13), and- a pair of hubs (6, 7), each arranged at a longitudinal end of the cylindrical body(2) and delimiting the heat-exchange chamber (10) in said longitudinal direction (X-X), characterized in that said coating (13) is formed by at least one extruded elongate element (20) made of a plastic material spirally wound on the outer surface of the inner tubular element (3), and in that said extruded elongate element (20) comprises a base portion (21) intended to contact the outer surface of the inner tubular element (3) to form a portion of the base layer (131) of said coating (13), and a ridge portion (22) upstanding from said base portion (21) to form said at least one rib (132).

12. Thermal roller (1) according to claim 11, wherein said extruded elongate element (20) has a cross section having a substantially inverted-T shape.

13. Thermal roller (1) according to any one of claims 11 or 12, wherein said base portion (21) comprises a pair of branches (21a, 21b) extending on opposite sides relative to said ridge portion (22), and wherein, in a cross-sectional view of the extruded elongate element (20), said branches (21a, 21b) taper or comprise at least one length which tapers moving away from said ridge portion (22).

14. Thermal roller (1) according to any one of claims 11 to 13, wherein, in a cross-sectional view of the extruded elongate element (20), said ridge portion (22) has a shape which tapers moving away from said base portion (21).

15. Thermal roller (1) according to any one of claims 11 to 14, wherein said ridge portion (22) has a rounded tip.

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