Process and system for heating a semi-finished product

Abstract

Process and system (3) for heating a semi-finished product (99), the system (3) comprising a support surface (4), one or more electrically conductive elements (5) fixed in distributed way onto the support surface (4) and a control unit (9), wherein the process comprises: arranging the semi-finished product (99) facing the support surface (4) and heating the semi-finished product (99) by the heating system (3), and wherein heating the semi-finished product (99) comprises, by the control unit (9): applying a respective electrical voltage (Vr) in alternating regime to opposite ends of each electrically conductive element (5), detecting in continuous a respective electrical current (i) flowing in each electrically conductive element (5) and adjusting overtime applying the respective electrical voltage (Vr) as a function of a comparison between a time-averaged value (iRMS) of the respective electrical current (i) and a respective threshold value (itres).

Description

[0001] DESCRIPTION

[0002] Title: PROCESS AND SYSTEM FOR HEATING A SEMI-FINISHED PRODUCT

[0003] Technical field of the invention

[0004] The present invention relates to a process, and a system, for heating a semi-finished product, for example a semi-finished product belonging to a process for producing composite products for the interior finishes of motor vehicles (e.g., trim panels for doors, dashboards, posts, instrument panels, top roofs, etc.), boats, aircraft, and / or furnishing components.

[0005] Prior art

[0006] For the production of composite products, such as for example for the aforesaid interior finishes, it is known to coat a preformed substrate (typically in rigid plastic material), i.e. already formed before being coated, with (at least) one coating layer. Such a coating layer provides the desired tactile and / or aesthetic properties to the finished product.

[0007] Summary of the invention

[0008] “Activation temperature” referred to an adhesive is understood to mean a temperature at which the adhesive assumes properties such as to wet the surfaces to be glued and determine the adhesion between the components (typically the adhesive maintains these properties even in a range of temperatures above the activation temperature).

[0009] “Semi-finished product”, in the present context, is understood to mean a product (as a single body or composed of several mutually coupled parts / layers) that has reached any time step of realization within a process for producing the respective finished product, including a final step, that is, it can be understood to mean any semi-finished product taken at any step of the realization process, up to the (substantially) finished product itself. For example, in the aforesaid process for producing composite products, semi-finished can be understood to mean any of the following (non-exhaustive list): the preformed substrate only, the coating layer (preferably with three-dimensional shape) with or without an adhesive layer, the preformed substrate coupled to the coating layer with a non-active adhesive layer in the middle (therefore before the actual mutual gluing), the finished composite product (e.g. after compression).

[0010] In the aforesaid context, the Applicant has realized that it is particularly advantageous to introduce, in the process for producing a composite product, one or more infrared heating steps for a semi-finished product, in order to obtain various results depending on which semi-finished product is heated. For example, in the case of heating the preformed substrate only, the heating can act as a preheating of the substrate in order to avoid thermal changes during the gluing step. Or in the case of heating the semifinished product comprising the preformed substrate, the coating layer and the interposed adhesive layer, the heating may serve to activate the adhesive layer suitably arranged to adhere the coating layer to the substrate.

[0011] In order to achieve a desired efficiency and / or homogeneity in heating of the semifinished product, which is provided with its own three-dimensional shape (typically non- planar), the Applicant considers it equally advantageous that the infrared irradiation surface substantially reproduces the shape of the semi-finished product, so that the distance between the semi-finished product and the irradiation surface is maintained constant, along the entire surface extension of the semi-finished product.

[0012] It therefore follows that the shape of the irradiation surface is adapted to the morphology of the semi-finished product, for example by presenting ridges and / or valleys suitably arranged to match the shape of the semi-finished product.

[0013] In this situation, the Applicant has also realised that, in order to realize the aforesaid irradiation surface by means of electrically conductive elements that are spatially distributed on a suitably shaped support surface, it is necessary, for geometric and / or use purposes (for example to avoid hot spots), to provide electrically conductive elements of different lengths to be suitably arranged on the surface.

[0014] However, the Applicant has observed that having, on the same support surface, electrically conductive elements of different lengths entails numerous problems from the point of view of the electrical voltage supply (e.g. expressed in Volts [V]) of said electrically conductive elements. In fact, with the same input voltage, elements with shorter length offer less overall electrical resistance, with consequent greater passage of electrical current (e.g. expressed in Amperes [A]) and potential greater risk of incurring overheating and burning phenomena, as well as damage to the element and therefore relative non-operation.

[0015] On the other hand, the Applicant notes that adapting the grid electrical voltage to desired values as a function of the specific length of each electrically conductive element, for example by using transformers, cannot be realized since such an adaptation would be too complicated to carry out, as well as expensive, as it would potentially be necessary to provide a dedicated transformer for each element. The Applicant has therefore addressed the problem of heating a semi-finished product efficiently, for example in terms of effectiveness and / or homogeneity in heating, and at the same time simple and economical, for example in terms of equipment used and / or operations required.

[0016] According to the Applicant, the aforesaid problem is solved by a process, and a system, for heating a semi-finished product in accordance with the appended claims and / or having one or more of the following characteristics.

[0017] According to one aspect the invention relates to a process for heating a semi-finished product.

[0018] Preferably the process comprises providing said semi-finished product.

[0019] Preferably the process comprises providing an infrared heating system comprising a support surface and one or more electrically conductive elements fixed in distributed way onto said support surface.

[0020] Preferably the process comprises arranging said semi-finished product facing said support surface of the infrared heating system.

[0021] Preferably the process comprises heating said semi-finished product by said infrared heating system.

[0022] Preferably said heating said semi-finished product comprises:

[0023] - applying a respective electrical voltage in alternating regime to opposite ends of each electrically conductive element of said one or more electrically conductive elements;

[0024] - detecting in continuous a respective electrical current flowing through each electrically conductive element as a consequence of said applying said respective electrical voltage in alternating regime;

[0025] - adjusting over time said applying said respective electrical voltage as a function of a comparison between a time-averaged value of said respective electrical current and a respective threshold value.

[0026] According to another aspect, the invention relates to an infrared heating system of a semi-finished product.

[0027] Preferably the system comprises a support surface and one or more electrically conductive elements fixed in a distributed way onto said support surface.

[0028] Preferably the system comprises a control unit.

[0029] Preferably said control unit is programmed for:

[0030] - applying a respective electrical voltage in alternating regime to opposite ends of each electrically conductive element of said one or more electrically conductive elements;

[0031] - detecting in continuous a respective electrical current flowing through each electrically conductive element as a consequence of said applying said respective electrical voltage in alternating regime;

[0032] - adjusting over time said applying said respective electrical voltage as a function of a comparison between a time-averaged value of said respective electrical current and a respective threshold value.

[0033] According to the Applicant, infrared heating (e.g., which exploits a radiation having a substantial part - e.g., at least 70% or 80% - of the emission power falling in the spectral band comprised between 0.7 pm - preferably 1 pm, and 8 pm - preferably 5 pm, more preferably 3 pm, extremes included) is particularly advantageous for heating the semifinished product as it is able to provide heat while avoiding at the same time direct contact between the semi-finished product and the heat source, which could result in damage to the semi-finished product. For example, when the semi-finished product comprises or consists of the coating layer aimed at conferring aesthetic qualities to the finished product, a direct contact could result in the occurrence of aesthetic defects such as for example opacity, shine, burns, loss of colour, etc., on the coating layer, especially if made of natural leather and / or fake leather (e.g., TPO, PVC, Alcantara™, etc.).

[0034] The application of electrical voltage in alternating regime to the electrically conductive elements makes it possible to use the same type of supply with which the distribution of electricity in the grid is normally made. This is preferable to the use of the supply in continuous regime since complex, bulky and above all expensive equipment aimed precisely at converting the grid supply voltage from alternating (AC) regime to continuous (DC) regime are not required.

[0035] Furthermore, adjusting over time said applying the respective electrical voltage to the respective electrically conductive element, that is, adjusting over time the time intervals of application of the alternating electrical voltage to the ends of the electric resistors for infrared heating (e.g. alternating switch-on periods, in which there is applied electrical voltage, to switch-off periods, in which the applied voltage is zero), as a function of the aforesaid comparison between the time-averaged value of the electrical current flowing in the element and the threshold value, allows, on the one hand, to limit the average electrical current flowing in each electrically conductive element (as if the element were crossed at the ends thereof by an average electrical voltage lower than the grid supply voltage actually applied), without necessarily having, on the other hand, to vary the intensity (e.g. amplitude) of said grid supply voltage (i.e. without having to use transformers and / or similar equipment). In this way, it is possible to limit the aforesaid average electrical current (to avoid overheating phenomena of the electrically conductive element) independently of, and capable of adapting autonomously to, the specific length of the given element, and keeping the supply apparatus of the heating system simple and economical.

[0036] The present invention in one or more of the aforesaid aspects can have one or more of the following preferred characteristics.

[0037] In one embodiment said semi-finished product consists of a preformed substrate, for example of rigid plastic material. In this way, the heating can act as a preheating to avoid thermal stress of the semi-finished product.

[0038] Preferably, arranging said semi-finished product facing said support surface comprises arranging a first face of said substrate, intended to be in contact with an adhesive layer, directly facing said support surface. In this way, heating is directed only where it is useful, limiting time and / or costs.

[0039] In one embodiment said semi-finished product consists of a coating layer (for example in natural or artificial leather) and of an adhesive layer arranged at a face of said coating layer. In this way the heating activates the adhesive (i.e. brings the adhesive layer to a temperature greater than or equal to the activation temperature of the adhesive).

[0040] Preferably said coating layer comprises a plurality of pieces sewn together. Preferably said coating layer is provided with a three-dimensional shape substantially reproducing a surface shape of at least one face of the preformed substrate.

[0041] Preferably arranging said semi-finished product facing said support surface comprises arranging said adhesive layer directly facing said support surface. In this way the activation of the adhesive is particularly quick and simple, as it is possible to directly expose the adhesive layer to the irradiating surface.

[0042] In one embodiment said semi-finished product comprises (more preferably consists of) a preformed substrate, a coating layer superimposed on said preformed substrate, and an adhesive layer interposed (in contact) between said preformed substrate and said coating layer. In this way the heating activates the adhesive keeping the process simple and with steps limited in their number, since the package comprising all the layers included in the final product is already heated.

[0043] Preferably, arranging said semi-finished product facing said support surface comprises arranging said coating layer directly facing said support surface. In this way, the heating of the adhesive is further facilitated since the part of the semi-finished product typically having less thermal resistance is exposed. It is noted that infrared heating is particularly suitable for penetrating the coating layer up to the adhesive in an effective way even if the adhesive layer is not directly exposed to the irradiating surface.

[0044] In one embodiment said semi-finished product consists of a finished composite product comprising a preformed substrate, a coating layer glued to said preformed substrate by means of a heat-activated adhesive layer. In this way it is possible to improve a desired aesthetic performance of the product. For example, in the case of an Alcantara™ coating layer, a (further) finished product heating step may contribute to returning an improved aesthetic performance sometimes lost as a consequence of a step of compression exerted on the coating layer in order to carry out the gluing (better described below).

[0045] In one embodiment (for example in any of the aforesaid embodiments of the semifinished product except when the semi-finished product consists of said finished composite product) the process comprises, more preferably subsequently to said heating said semi-finished product, providing a further semi-finished product (distinct from said semi-finished product).

[0046] Preferably said further semi-finished product may consist of one or more of the following (compatibly with the embodiment of the semi-finished product): a preformed substrate; a coating layer and an adhesive layer arranged at one face of said coating layer; an assembly comprising a preformed substrate, a coating layer superimposed on said preformed substrate, and an adhesive layer interposed (in contact) between said preformed substrate and said coating layer; a finished composite product comprising a preformed substrate, a coating layer glued to said preformed substrate by means of a heat-activated adhesive layer.

[0047] In one embodiment said further semi-finished product comprises said semi-finished product. For example, if the semi-finished product consists of the aforesaid preformed substrate, the further semi-finished product may instead comprise the assembly comprising the preformed substrate, the coating layer superimposed on said preformed substrate, and the adhesive layer interposed (in contact) between said preformed substrate and said coating layer.

[0048] Preferably said process comprises arranging said further semi-finished product facing said support surface. Preferably arranging said further semi-finished product facing said support surface comprises one or more of (all) the characteristics of said arranging said semi-finished product facing said support surface.

[0049] Preferably said process comprises heating said further semi-finished product. In this way, several distinct heating steps can be provided, in order to pursue different results, as for example described above depending on which elements can be included in the further semi-finished product.

[0050] Preferably said heating said further semi-finished product comprises one or more of, preferably all of, the characteristics of said heating said semi-finished product. In this way, the process is rational and simplified.

[0051] Preferably said heating of said further semi-finished product is performed by said infrared heating system. In this way the equipment remains limited and is exploited efficiently.

[0052] Preferably applying said respective electrical voltage comprises applying a (respective) electrical supply voltage. Preferably the (respective) electrical supply voltage is variable over time, typically with signal over time having a sinusoidal shape.

[0053] Preferably each electrically conductive element is connected to a power supply source in an electrically independent manner from remaining electrically conductive elements. In this way, the adjustment over time of the respective electrical voltage is facilitated.

[0054] Preferably adjusting over time said applying said respective electrical voltage is performed so that said time-averaged value of the respective electrical current is less than or equal to said respective threshold value. In this way, each electrically conductive element is operated in a safe regime.

[0055] Preferably, adjusting over time said applying said respective electrical voltage comprises applying to each electrically conductive element said electrical supply voltage intermittently over time (e.g. according to a respective time program). The respective time program of each element may or may not differ from that of other electrically conductive elements of the heating system.

[0056] Preferably, adjusting over time said applying said respective electrical voltage comprises modulating said electrical supply voltage by phase angle control (phase cutting or phase-fired control - PFC). In the phase angle control of a periodic signal, only determined portions of the input periodic signal (in the specific case of the supply voltage) corresponding to predetermined intervals of phase angles of the input periodic signal (i.e. corresponding to limited portions of an entire signal waveform in a given period) are transmitted to the load (in this specific case the electrically conductive element). This is repeated for each period or even half-period of the input signal. In other words, in the phase angle control, at least a portion of the input signal is transmitted to the load for each period, or even half-period, of the input signal. In this way, the average electrical voltage perceived by the given electrically conductive element has a stable trend over time and is less prone to oscillation phenomena and / or peaks. Without wishing to be bound by any theory, the Applicant considers that the modulation with phase angle control is particularly advantageous for the present invention in order to limit voltage peaks on the given electrically conductive element following the adjustment over time of the application of the electrical voltage applied to the ends of the element (and therefore to limit the flowing electrical current, to the advantage of the protection of the element). This is particularly true in case of comparison with a control of the “zero crossing" type, where the signal, when transmitted, is transmitted for one or more entire periods, and, when it is not transmitted, it is not transmitted for one or more respective entire periods, resulting in a more oscillating supply over time as there are entire transmitted periods interspersed with one or more entire non-transmitted periods and where the transmitted signal always reaches the respective peak value. Instead, in case of modulation with phase angle control, the transmitted signal does not necessarily include the peak of the input signal. According to the Applicant, therefore, the modulation with control of the “zero crossing” type is worse for the element in terms of undergone voltage peaks compared to the modulation with phase angle control.

[0057] In an alternative embodiment, adjusting over time said applying said respective electrical voltage comprises modulating said electrical supply voltage by “zero crossing" type control (described above).

[0058] Preferably, adjusting over time said applying said respective electrical voltage is performed by means of a controller device. Preferably said heating system comprises, for each electrically conductive element, a respective controller device electrically connected to the respective electrically conductive element, more preferably electrically interposed between said power supply source and the respective electrically conductive element.

[0059] Preferably said control unit is operatively connected to each controller device to control each controller device independently. In this way each electrically conductive element is supplied independently of the remaining elements.

[0060] Preferably said (each) controller device comprises (or consists of) a diode interrupting device, such as for example a thyristor, in particular a SCR (silicon controlled rectifier also known as semiconductor controlled rectifier). In this way, the supply circuit of each electrically conductive element is simple and functional.

[0061] Preferably adjusting over time said applying said respective electrical voltage is performed by said control unit by means of said respective controller device.

[0062] Preferably said time-average value of said respective electrical current corresponds to a root mean square (RMS) of said respective electrical current. In this way, the time- averaged value of the electrical current is advantageously correlated to the power delivered by the electrically conductive element (to which the threshold value is preferably also correlated, as described below).

[0063] Preferably said process comprises calculating said respective threshold value as a function of one or more of the following parameters: material of the respective electrically conductive element, cross-section of the respective electrically conductive element (e.g. rectangular cross-section), desired (electrical) power per unit length to be generated by means of the respective electrically conductive element. In this way the respective threshold value is representative of the desired process conditions to be obtained with the given electrically conductive element. In general, each electrically conductive element can in fact correspond to a respective threshold value. With the same power to be generated, cross-section and material of all the electrically conductive elements, the respective threshold values are all equal.

[0064] Preferably said process comprises adjusting said respective threshold value as a function of a (electrical) power value per unit length to be generated by means of said respective electrically conductive element. For example, the adjustment of the respective threshold value can be performed as a function of the spatial position of the given electrically conductive element with respect to the geometry of the support surface, for example by making sure that the spatially innermost elements deliver less power than the outermost ones, so as to limit the occurrence of temperature peaks on the semi-finished product and ensure a uniform temperature of the semi-finished product.

[0065] Preferably said support surface is (substantially) counter-shaped to said semi-finished product. Preferably, where provided, said support surface is (substantially) countershaped to said preformed substrate (preferably to a first face of said preformed substrate intended to be coated by the coating layer).

[0066] Preferably each electrically conductive element is a metal strip (or thin strip). In this way, the element is particularly suitable for use as an infrared heater and is at the same time economical.

[0067] Preferably said strip is deformable (e.g., plastically). In this way, the strip can be adapted to the three-dimensional shape of the support surface.

[0068] According to a further aspect, the invention relates to a method for producing a composite product comprising said heating process.

[0069] Preferably said production method comprises compressing said semi-finished product by pressing said preformed substrate and said coating layer against each other.

[0070] In one embodiment (for example when the semi-finished product does not consist of the aforesaid finished composite product) said compressing said semi-finished product is performed subsequently to said heating said semi-finished product.

[0071] In one embodiment (for example when the semi-finished product consists of the aforesaid finished composite product) said compressing said semi-finished product is performed prior to said heating said semi-finished product.

[0072] Optionally, the production method may further comprise (in addition or alternative to the compression of the semi-finished product) a step of compression of the further semi-finished product (when compatible with reference to the composition of the further semi-finished product).

[0073] In one embodiment compressing said semi-finished product (and / or further semifinished product) comprises cooling at the same time (at least) said coating layer. In this way, the mutual substrate-coating layer adhesion is stably fixed.

[0074] Preferably said cooling is performed by keeping a temperature of a half-mould in contact with said coating layer lower than said activation temperature of said adhesive layer.

[0075] Preferably said compressing said semi-finished product (and / or further semi-finished product) is performed by pressing against each other a first and second half-moulds of a mould with said semi-finished product (and / or further semi-finished product) interposed between compression surfaces respectively of said first and second halfmoulds.

[0076] According to a still further aspect, the present invention relates to a plant for producing a composite product, said plant comprising said heating system.

[0077] Preferably said plant comprises a mould structured to compress said semi-finished product (and / or further semi-finished product). Preferably said mould comprises a first and second half-moulds each having a respective compression surface.

[0078] Brief description of the figures

[0079] Figure 1 partially and schematically shows a production plant according to the present invention; figure 2 shows a detail of a heating system according to the present invention; figures 3-5 partially and schematically show some steps of a method for producing a composite product according to the present invention performed by means of the plant of figure 1 ; figure 6 schematically shows some types of modulation over time of a time-dependent signal, figure 7 schematically shows a supply circuit of an electrically conductive element of a heating system according to the present invention.

[0080] Detailed description of some embodiments of the invention

[0081] The features and advantages of the present invention will be further clarified by the following detailed description of some embodiments of the present invention, presented by way of non-limiting example, with reference to the attached figures.

[0082] In the figures, reference numeral 100 indicates a plant for producing a composite product according to the present invention.

[0083] The plant 100 exemplarily comprises a first heating station 101 and a second compression and cooling station 102. Preferably the second station 102 is arranged immediately downstream of the first station 101 (fig. 1 ).

[0084] The first station 101 comprises an infrared heating system 3 for a semi-finished product 99.

[0085] In the following, for the sake of clarity, it is specified that an exemplary embodiment will be described in which the semi-finished product 99 consists of a preformed substrate 10, a coating layer 60 superimposed on the substrate 10, and an adhesive layer 70 interposed between the preformed substrate 10 and the coating layer 60. Exemplarily, the substrate 10 is as a single piece and of rigid polymeric material, for example polyurethane.

[0086] Exemplarily, the preformed substrate 10 is in fact preformed, i.e. it has a three- dimensional shape conferred prior to the heating process, for example by means of a moulding process (not shown) for a raw material to form the substrate 10. The aforesaid shape of the substrate 10 exemplarily comprises portions with complex geometry (in the illustrated and simplified example, it has a recess with two oblique side walls).

[0087] Typically the coating layer 60 comprises at least one aesthetic sheet 61 which remains visible during use of the finished composite product and which, for example, can be made of: natural textile fabric, synthetic textile fabric, natural leather, fake leather (i.e. a material having mechanical and / or tactile and / or aesthetic characteristics that recall natural leather), etc.

[0088] The coating layer may further comprise a functional layer, e.g. a polymeric (e.g. polyurethane) foam layer, which, in the finished product, is interposed between the substrate and the aesthetic sheet to impart particular properties to the finished product (e.g. hard-touch / soft-touch tactile properties). In the example, the coating layer 60 comprises an aesthetic sheet 61 made of Alcantara™, and a functional layer 80, e.g. of open-cell polyurethane foam, arranged between the substrate 10 and the aesthetic sheet 61 , preferably directly in contact with the aesthetic sheet 61 , to impart to the finished product a soft-touch property.

[0089] For example, the adhesive layer 70 may comprise a polyurethane hot melt reactive adhesive.

[0090] Optionally, the adhesive may be applied only at some portions respectively of the substrate and / or of the coating layer, and / or following a pattern, such as for example by lines or by dots. Alternatively, the adhesive may be applied along an entire surface extension of respectively the substrate and / or the coating layer. The adhesive can also be applied uniformly or by providing areas with a greater amount of adhesive (for example where stronger gluing is expected to be necessary).

[0091] In other embodiments (not shown) the substrate may consist of only one or more of the aforesaid components.

[0092] Exemplarily, the heating system 3 comprises a support surface 4 and a plurality of electrically conductive elements 5 fixed (e.g. by means of metal clips, wire, etc.) in a distributed way onto the support surface 4, for example as shown in figure 2.

[0093] Exemplarily, each electrically conductive element 5 is made by means of a metal strip, exemplarily in a single piece. The strips are exemplary deformable in such a way that they can adapt, during the fixing step, to the three-dimensional conformation of the support surface 4, and have a wavy pattern with ridges that develop away from the support surface 4 (e.g. in order to compensate for any thermal expansions), as for example shown in Figures 1 and 3 (not to scale).

[0094] Advantageously, the support surface 4 is made of electrically and thermally insulating material, for example ceramic arranged in contact with the strips.

[0095] Typically, each electrically conductive element 5 (when electrically supplied) has an infrared emission band, which may comprise one or more between near infrared (NIR), with wavelengths for example comprised between 0.75 pm and 1.4 pm, short wave infrared (SWIR), with wavelengths for example comprised between 1.4 pm and 3 pm, and medium wave infrared (MWIR), with wavelengths for example comprised between 3 pm and 8 pm.

[0096] For example, each electrically conductive element can be made of Kantal A1TM, FeCrAI alloy, or Nikrothal™, NiCr alloy.

[0097] Exemplarily, the support surface 4 is substantially counter-shaped to the semi-finished product 99, more precisely to an external shape of the preformed substrate 10, exemplarily to a first face 15 of the preformed substrate 10 intended to be coated by means of the coating layer 60 (as better described below).

[0098] Exemplarily, it is observed, as shown in figure 2, that the electrically conductive elements 5 (exemplarily shown in a number equal to four in figure 2) arranged on the support surface 4 have different lengths (along a respective direction of greater extension) from each other, precisely in order to faithfully follow the specific conformation of the support surface 4. Exemplarily, each heater has a rectangular cross-section with a width equal to about 3 mm and a thickness equal to about 0.5 mm. Exemplarily, the first station 101 further comprises a rest body 30 shaped to support the semi-finished product 99 in such a way that the preformed substrate 10 can be conveniently arranged in relation to the heating system 3.

[0099] Optionally (not shown), also the rest device can be heated, for example by means of a series of tubes for a heat transfer fluid (e.g., diathermic oil, air or water), or by means of electrical resistors, to contribute to the heating of the semi-finished product, as better described below.

[0100] Exemplarily, the heating system further comprises a power supply source 6 connected to the electrically heating elements 5 for supplying the elements. Exemplarily, the power supply source 6 is structured to provide an electrical supply voltage Va in alternating regime, for example the grid electrical voltage. Exemplarily, the electrical supply voltage is variable over time with sinusoidal trend.

[0101] Exemplarily, each electrically conductive element 5 is connected to the power supply source 6 by means of a respective supply circuit 7 (figure 7).

[0102] Preferably (not shown) the electrically conductive elements 5 are connected to the power supply source 6 independently of each other.

[0103] Exemplarily, the heating system 3 further comprises a respective controller device 8 for each element 5. Figures 1 and 3 show, in a purely schematic and symbolic way, a single controller device 8. Exemplarily, each controller device 8 is part of the respective supply circuit 7 of the respective electrically conductive element 5 and is electrically interposed between the power supply source 6 and the respective electrically conductive element 5.

[0104] Exemplarily, the controller device comprises a diode interrupting device, such as for example a thyristor. In detail, each controller device 8 is an SCR. Such devices will not be described further in detail as for example of known type. By way of example, it should only be reminded that an SCR can allow or prevent conduction towards the load downstream of the SCR (in this specific case the electrically conductive element 5) as a function of a given command.

[0105] Exemplarily, the heating system 3 further comprises a control unit 9 operatively connected to each controller device 8.

[0106] Exemplarily, the second station 102 comprises a mould 50 comprising a first 11 and a second half-mould 12 each having a respective compression surface 13 and 14. Exemplarily, each compression surface 13 and 14 is substantially counter-shaped to the semi-finished product 99 (in particular to the preformed substrate 10), preferably each compression surface is counter-shaped to a respective one between the first 15 and the second face 16 of the preformed substrate 10.

[0107] Optionally, the second half-mould 12 can coincide with the rest body 30, or be distinct and separate from the rest body 30 (as shown in figure 1 ). Exemplarily (not shown) the first half-mould 11 may be cooled in use.

[0108] In use, the plant 100 may implement a method for producing a composite product, the method comprising a process for heating the semi-finished product 99, as will be exemplarily described below with reference to figures 3-5.

[0109] First of all, it is exemplary envisaged to provide the semi-finished product 99.

[0110] It is therefore exemplary provided for arranging the semi-finished product 99 facing the support surface 4 of the infrared heating system 3. In detail, the semi-finished product 99 is exemplarily arranged above the rest body 30 with the preformed substrate 10 proximal to the rest body 30 and the coating layer 60 turned towards the heating system 3. Exemplarily, arranging the semi-finished product 99 facing the support surface 4 comprises arranging the coating layer 60 directly facing the support surface 4.

[0111] At this point, it is exemplarily provided for heating the semi-finished product 99 by the infrared heating system 3, exemplarily to activate the adhesive layer 70. For example, a hot melt polyurethane adhesive having an activation temperature comprised between about 60-65 °C may be brought to a temperature of about 70 °C. The activation temperature is characteristic of the particular material or mixture of materials of which the adhesive is composed.

[0112] Exemplarily, heating the semi-finished product 99 comprises applying a respective electrical voltage Vr in alternating regime to opposite ends of each electrically conductive element 5, exemplarily by application of the electrical supply voltage Va by the power supply source 6.

[0113] It is therefore exemplary provided for detecting in continuous a respective electrical current (i) flowing through each electrically conductive element 5 as a consequence of applying the respective electrical voltage Vr.

[0114] Exemplarily, the process therefore comprises adjusting over time the application of the respective electrical voltage Vr as a function of a comparison between a time-averaged value iRMS of the respective electrical current (i) and a respective threshold value itres. Exemplarily, it is provided for calculating the respective threshold value itres of electrical current for each electrically conductive element 5. The respective threshold value itres can for example be calculated as a function of a desired linear electrical power to be generated with a given electrically conductive element, of the material and cross-section of the electrically conductive element. In this way the threshold value does not depend on the length of the electrically conductive element.

[0115] Advantageously, the linear electrical power to be generated is established on the basis of safety limits of the electrically conductive element, that is, in a conservative way so as to avoid overheating, and therefore burning, of the element.

[0116] In detail, the control unit 9 acts exemplarily on the controller device 8 by operating the controller device 8 in such a way as to supply the electrically conductive element 5 intermittently over time (i.e. by opening and closing the circuit intermittently), in such a way that the time-averaged value iRMS, exemplarily the root mean square (RMS), of the electrical current (i) flowing through the element 5 when the circuit is closed is maintained less than or equal to the respective threshold value itres.

[0117] Exemplarily, adjusting the application of the respective electrical voltage Vr comprises modulating the electrical supply voltage Va acting on each electrically conductive element 5 by phase angle control. The modulation with phase angle control will not be described further as for example of known type.

[0118] Exemplarily, the control unit 9 is suitably programmed for selecting the phase angle intervals of the signal of input supply voltage Va as a function of which to operate the controller device 8 in order to transmit the voltage to the load (i.e. element 5) in such a way that the average value iRMS of the electrical current (i) is maintained in relation to the respective threshold value itres.

[0119] Figure 6 graphically shows an example of modulation of a source signal S1 with sinusoidal trend, such as for example the aforesaid electrical supply voltage Va can be, respectively with “zero crossing” type control (on the left), and with phase angle control (on the right).

[0120] As can be observed, in the presence of phase angle control, the complete input signal S1 is modulated such that there is at least one portion of signal transmitted to the load for each half period of the input signal. In figure 6 the signal portions transmitted are those represented in darker colour above the original waveform of the signal S1 depicted in lighter colour. The four signals represented respectively at the percentages from 25% to 100% represent by way of example only different modulations of the signal S1 , in which, for each half-period, 25%, 50%, 75% and 100% of the input signal S1 is transmitted respectively.

[0121] In a comparison with the modulation with “zero crossing” control, it can be observed how the modulation with phase angle control is able to obtain a more homogeneous and stable transmitted signal (as for example there is a portion of signal transmitted for each half-period unlike the “zero crossing” control where it may happen that for some entire periods there is no transmission).

[0122] Finally, it is exemplarily provided, after heating the semi-finished product 99, for compressing the semi-finished product 99 by pressing the preformed substrate 10 and the coating layer 60 against each other by means of the mould 50. Exemplarily, the composite product 99 is thus obtained (exemplarily, the composite product is indicated with the same reference numeral as the semi-finished product as it can also be considered a semi-finished product with regard to the heating process according to the present invention, as described above).

[0123] Exemplarily, the process also comprises adjusting the respective threshold value itres of each electrically conductive element 5 as a function of the linear power (e.g. W / m) to be generated with the element, for example as a function of a spatial position of the element 5 on the support surface 4. For example, elements 5 occupying more central positions can be adjusted so as to generate less linear power, resulting in a lower threshold value itres compared to a value calculated only as a function of the aforesaid safety limits.

Claims

CLAIMS1 . Process for heating a semi-finished product (99), the process comprising:- providing an infrared heating system (3) comprising a support surface (4) and one or more electrically conductive elements (5) fixed in distributed way onto said support surface (4);- arranging said semi-finished product (99) facing said support surface (4) of said infrared heating system (3);- heating said semi-finished product (99) by said infrared heating system (3); wherein said heating said semi-finished product (99) comprises:- applying a respective electrical voltage (Vr) in alternating regime to opposite ends of each electrically conductive element (5) of said one or more electrically conductive elements (5);- detecting in continuous a respective electrical current (i) flowing through each electrically conductive element (5) as a consequence of said applying said respective electrical voltage (Vr) in alternating regime;- adjusting over time said applying said respective electrical voltage (Vr) as a function of a comparison between a time-averaged value (iRMS) of said respective electrical current (i) and a respective threshold value (itres).

2. Process according to claim 1 , wherein adjusting overtime said applying said respective electrical voltage (Vr) is performed so that said time-averaged value (iRMS) of said respective electrical current (i) is less than or equal to said respective threshold value (itres).

3. Process according to any one of the previous claims, wherein applying said respective electrical voltage (Vr) comprises applying an electrical supply voltage (Va), and wherein adjusting over time said applying said respective electrical voltage (Vr) comprises applying to each electrically conductive element (5) said electrical supply voltage (Va) intermittently over time.

4. Process according to claim 3, wherein adjusting overtime said applying said respective electrical voltage (Vr) comprises modulating said electrical supply voltage (Va) by phase angle control.

5. Process according to any one of the previous claims, wherein adjusting over time said applying said respective electrical voltage (Vr) is performed by means of a controller device (8), and wherein said controller device (8) comprises a diode interrupting device.

6. Process according to any one of the previous claims, wherein said time-averaged value(iRMS) of said respective electrical current (i) corresponds to a root mean square of said respective electrical current (i).

7. Process according to any one of the previous claims, comprising calculating said respective threshold value ( itres) as a function of one or more of the following parameters: material of the respective electrically conductive element (5), cross-section of the respective electrically conductive element (5), desired power per unit length to be generated by means of the respective electrically conductive element (5).

8. Process according to any one of the previous claims, comprising adjusting said respective threshold value (itres) as a function of a value of power per unit length to be generated by means of said respective electrically conductive element (5).

9. Process according to any one of the previous claims, wherein said semi-finished product (99) comprises a preformed substrate (10), a coating layer (60) superimposed on said preformed substrate (10), and an adhesive layer (70) interposed between said preformed substrate (10) and said coating layer (60), wherein said support surface (4) is substantially counter-shaped to said preformed substrate (10), and wherein each electrically conductive element (5) is a metal strip.

10. Infrared heating system (3) of a semi-finished product (99), said heating system (3) comprising:- a support surface (4) and one or more electrically conductive elements (5) fixed in distributed way onto said support surface (4);- a control unit (9) programmed for:- applying a respective electrical voltage (Vr) in alternating regime to opposite ends of each electrically conductive element (5) of said one or more electrically conductive elements (5);- detecting in continuous a respective electrical current (i) flowing through each electrically conductive element (5) as a consequence of said applying said electrical voltage (Vr) in alternating regime;- adjusting over time said applying said electrical voltage (Vr) as a function of a comparison between a time-averaged value (iRMS) of said electrical current (i) and a respective threshold value (itres).

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