METHOD TO PRODUCE RADIATING TUBES AND RELATIVE RADIATING TUBES FOR RADIANCY HEATING LINES

Abstract: Method to produce radiating tubes, and relative radiating tubes, for radiancy heating lines for premises (12), said radiating tubes defining a forced-circulation circuit of a thermal carrier gas fluid for heating purposes, said radiating tubes being formed by shaping from an aluminium-coated steel strip, said aluminium-coated steel strip being subjected, during one step of the production cycle of the radiating tube (10), to at least a heat treatment step made at a temperature above the melting temperature of aluminium, said heat treatment having the function of improving the intrinsic characteristics of heat emissivity of said tubes (10).

Description: "METHOD TO PRODUCE RADIATING TUBES AND RELATIVE RADIATING TUBES FOR RADIANCY HEATING LINES" * * * * * FIELD OF THE INVENTION This invention concerns a method to produce radiating tubes used in radiancy heating lines for heating civilian, industrial or commercial premises, mainly large-size, such as warehouses, store houses, gymnasiums, green houses, churches, etc. The invention also concerns the radiating tubes obtained by the method as above . BACKGROUND OF THE INVENTION The state of the art includes radiancy heating plants comprising lines of tubes arranged inside the premises to be heated, generally on the ceiling; the tubes make a circuit inside which a high temperature thermal carrier gas fluid is made to circulate, which heats the tubes and, by radiancy, the surrounding environmen . The radiating tubes are associated at one end to a heat generator, such as a burner using air which is either blown or sucked in, suitable to produce the thermal carrier gas fluid, and at another end to a suction and/or recircling unit, such as a fan, which achieves the forced circulation of the gas fluid inside the radiating tubes. The radiating lines usually comprise two tubes, one associated with the burner and the other associated with the suction and/or recircling unit, connected to each other by connection elements which close the circuit wherein the gas fluid circulates . In the state of the art, the radiating tubes are associated with heat insulating elements, which at least partly surround them, the function of which is to direct the radiated heat and limit heat losses. In tubes installed on the ceiling, the heat insulating elements are placed above and partly to one side of the tubes, and direct the heat substantially downwards. Radiating tubes of this type are normally obtained starting from a strip of aluminium steel, that is, coated with aluminium, generally supplied in coils, which is unwound, shaped and then jointed to obtain the final configuration . The aluminium plating process gives the steel greater malleability, facilitating the shaping of the strip to obtain the tubular shape, and provides protection from corrosive and/or oxidizing elements transported by the gases which circulate inside the radiating tubes . Compared with zinc plating, aluminium plating does not cause polluting emissions into the atmosphere. Radiating tubes produced with aluminium coated metal do however have a limited coefficient of heat emissivity which considerably limits the radiancy and therefore lowers the performance of the heating plants . To increase the coefficient of heat emissivity, normally, the tubes are painted on the outside, at least in the part not associated with the heat insulating elements, that is, in the part facing towards the premises to be heated. The painting process requires specific working equipment and, above all, specific plants to purify and dispose of the noxious emissions deriving from the painting process. This operation also entails longer cycle times and greater running costs. The present Applicant has devised and embodied this invention to overcome the shortcomings of conventional tubes and to obtain further advantages as explained hereafter. SUMMARY OF THE INVENTION The invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the invention. The purpose of the invention is to achieve radiating tubes for radiancy heating plants characterized by a high intrinsic coefficient of heat emissivity, and therefore considerable performance, without the need to paint the radiating tubes . The radiating tubes to which the invention refers preferentially, though not necessarily, have a diameter of at least 200 mm, and are mostly used to heat large premises such as industrial warehouses, store houses or similar. The tubes typically have only one part of their surface, normally the lower part in the typical case of a ceiling application, which actually radiates heat towards the environment; the other part is normally covered by a partly surrounding lining which, in most cases, comprises a heat insulating element . Another purpose of the invention is to provide a method which allows to achieve said radiating tubes in a single step and in the same plant, thus reducing production costs and times . According to the invention, the term tube should be taken to include different sections, not only circular, for example elliptic or polygonal in general. The invention provides to achieve radiating tubes of the type disclosed above by shaping a strip of aluminium-coated steel which, in at least one step of the production process, is subjected to a heat treatment in a furnace. In a first preferential embodiment, the heat treatment in the furnace is done after the shaping step which leads to the formation of the tube. In another embodiment, the aluminium-coated steel strip is subjected to the heat treatment in the furnace before the shaping step. The furnace treatment is made by making the tubes, or the coil from which the tubes are later obtained, pass inside a furnace with a temperature higher than the melting temperature of aluminium, and for a pre-defined period of time. In a preferential embodiment, the treatment temperature is between 600 and 900 °C, and the time the radiating tubes or coils are kept inside the furnace is between 5 and 20 minutes. The furnace treatment with these temperature and time parameters causes a mutual penetration of the particles of the aluminium coating and the particles of steel which achieves a considerable and intrinsic increase in the characteristics of heat emissivity in the tubes. A first advantage of the invention is that the furnace treatment allows to obviate the need to paint the tubes, since it takes the coefficient of heat emissivity to values comparable to those which are obtained with said painting treatment. Moreover, the increase in the coefficient of heat emissivity affects the whole surface of the radiating tubes homogeneously, both inside and outside, which entails a further improvement in the heat yield of the tubes . In fact, the heat radiated on the side where there is the cover and the insulation, which in radiating tubes of this type, during use, has an extremely low value due to the presence of the insulated lining, is reflected inside the tube towards the part of the surface of the radiating tubes facing the premises to be heated and then given up to those premises . The heat radiated towards the premises from the side of the tube which is not lined is continuously re-integrated by the heat arriving from the other side of the tube radiated inside the tube itself. This heat cannot propagate towards the outside due to the presence of the lining; therefore it is transmitted naturally towards the part of the tube which, since it is in contact with the premises to be heated, has a temperature lower than that of the remaining part of the tube. This phenomenon does not occur in painted tubes, since in this case the treatment which increases the heat emissivity is only superficial and external, and does not affect the inner face of the tube. Nor does it occur in those tubes which do not have at least a lined and/or insulated part, and which therefore do not have diversified conditions of radiancy on the surface of the tube. The radiating tubes according to the invention can thus be achieved entirely in line by means of the same plant, with a considerable reduction in production times and costs, and also of the costs to purify and dispose of the noxious substances connected with painting. The tubes can be obtained also by roller levelling or with another appropriate procedure . In a preferential embodiment, the tubes are obtained by joining the adjacent edges of a plurality of tubular elements, wherein the heat treatment in the furnace, causing the aluminium coating said edges to at least partly melt, causes reciprocal penetration and welding. According to a variant of this embodiment, it is provided to use weld material to improve the welding of the adjacent edges. BRIEF DESCRIPTION OF THE DRAWINGS These and other characteristics of the invention will become clear from the following description of a preferential form of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein: Fig. 1 shows a transverse section of a line of radiating tubes according to the invention in a simplified form; Fig. 2 is a flow chart of the two possible variants of the method to produce radiating tubes according to the invention; Fig. 3 is a prospective view of a segment of tube according to the invention; Fig. 4 is a section from A to A of Fig. 3; Fig. 5 shows the enlarged detail B of Fig. 4; Fig. 6 shows a variant of Fig. 5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to Fig. 1, the number 10 denotes generally a radiating tube according to the invention of a radiancy line 11 employed to heat premises with a civilian, commercial or industrial use, such as warehouses, sports installations, assembly rooms or otherwise, indicated generally with the number 12. The line 11 comprises, in the case shown and in a conventional manner, a pair of tubes 10 defining a closed circuit inside which a thermal carrier gas fluid is made to circulate produced by a generator, for example a burner. The tubes 10 may extend parallel and close to each other, or separate and distanced, provided that they always converge towards the generator . These features are already known in the state of the art, and therefore they are neither described nor illustrated in any further detail here. The radiating tubes 10, in this case, are associated with a cover 14, attached in this case to the ceiling 13 of the premises 12, which enfolds them and substantially covers them above and at the sides. The cover 14 is shaped substantially like an upside down U, and in this case comprises a sheet metal shell 15 and a heat insulating lining 16 substantially in contact with, or in any case very close to, the affected surface of the tube 10. The shell 15 may be omitted, however. The conformation and the structure of the cover 14 and the heat insulating lining 16 considerably limit and annul the radiancy of the heat from the upper part of the radiating tubes 10; thus, the only part which radiates heat is the one facing downwards and towards the premises 12 to be heated. The radiating tubes 10 according to the invention are made from a strip of aluminium-coated steel which is normally supplied in coils. The method to produce the tubes 10 according to the invention is shown according to two possible variants in the diagram in Fig. 2. In a first embodiment, the method provides to unwind the coil of aluminium-coated steel strip and shape it to form the tube . At the same time the strip is shaped, or in co-ordination therewith, the various joints are made to weld together the segments of tube obtained from the shaping operation. Subsequently, after optional operations to shear the strip to size and/or bend back the terminal segments, the tubes are made to pass inside a furnace, for example a tunnel furnace, where they are subjected to heat treatment. To be more exact, the tubes are introduced and kept inside the furnace for a pre-determined period of time at a temperature above the melting temperature of aluminium; these conditions cause a mutual penetration of the aluminium particles and the steel particles. In a preferential embodiment, and according to the dimensional and technological characteristics of the basic material, the period the tubes are kept inside the furnace is between 5 and 20 minutes, and the processing temperature is between 600 and 900 °C. After exiting from the furnace the radiating tubes 10 thus produced are cooled and then discharged to be possibly completed with connection elements in correspondence with the joints, for example flange means, and then assembled on the insulated covers 14. According to a variant, the shearing to size is done at the end of the cooling step after the furnace treatment. In a second solution, the invention provides for the furnace treatment to be done directly on the coil of aluminium-coated steel before the shaping operation and before the joints are made; the coil is then cooled, unwound, shaped to form the segments of tube, and then the various joints are made to obtain the tubes 10. The mutual penetration of the aluminium and steel obtained by the furnace treatment as described above gives the tubes 10 a considerable increase in their intrinsic characteristics of heat emissivity, and obviates the need to paint them. The considerable heat emissivity extended to the inner surface of the tubes 10 gives them a further improvement in performance . In fact, since the heat (indicated schematically by the line of dashes in Fig. 1) radiated by the radiating tubes 10 from the side facing the cover 14 cannot exit towards the outside due to the presence of the cover 14 with the relative insulation 16, it causes on this side an increase in temperature with a consequent continuous irradiancy in the direction of the side facing the premises 12 to be heated; this side is constantly at a lower temperature due to the free emission of heat towards the premises 12. This additional heat is in turn given up to the premises 12, thus improving the performance of the radiating tubes 10 and guaranteeing maximum heat emissivity by the entire surface of the tube 10, at the same time reducing production costs and times . In the solution shown in Figs. 3-5, the joints 17 between various segments of tube to obtain the tube 10 are made by crimping the respective end edges 18a and 18b, bent back and laid adjacent to each other. In this case, the furnace treatment made at a temperature above the melting temperature of aluminium causes the material coating the edges 18a, 18b to melt, and hence the mutual penetration and welding in correspondence with the lines indicated by the number 19. Therefore, the furnace treatment increases the efficiency of the joint and reduces the risks of the segments of tube becoming detached, even partly. The variant shown in Fig. 6 provides to use weld material 20 to further increase the welding hold. Obviously, it is possible to make modifications and additions to the method to produce radiating tubes and the relative radiating tubes as described heretofore, but these shall remain within the field and scope of the invention.

Claims: CLAIMS 1 - Method to produce radiating tubes for radiancy heating lines for premises (12), said radiating tubes defining a forced-circulation circuit of a thermal carrier gas fluid for heating purposes, said radiating tubes being formed by shaping from an aluminium-coated steel strip, the method being characterized in that said aluminium-coated steel strip is subjected, during one step of the production cycle of the radiating tube (10), to at least a heat treatment step made at a temperature above the melting temperature of aluminium, said heat treatment having the function of improving the intrinsic characteristics of heat emissivity of said tubes (10) . 2 - Method as in Claim 1, characterized in that said heat treatment step is made after the tube (10) has been formed by shaping from the aluminium-coated steel strip. 3 - Method as in Claim 1, characterized in that said heat treatment step is made directly on the aluminium-coated steel strip before the tube (10) has been formed by shaping. 4 - Method as in Claim 1, characterized in that said heat treatment step is made for a time of between 5 and 20 minutes according to the dimensional and technological characteristics of the aluminium-coated steel strip. 5 - Method as in Claim 1, characterized in that said heat treatment step is made at a temperature of between 600 and 900 °C according to the dimensional and technological characteristics of the aluminium-coated steel strip. 6 - Method as in Claim 1, characterized in that said tubes (10) are formed by shaping a plurality of segments of tube which are then connected in correspondence with joining points (17 ) . 7 - Method as in Claim 6, characterized in that said joining points (17) are obtained by placing respective edges (18a, 18b) of segments of tube adjacent and obtaining the connection in correspondence with welding lines (19) during said heat treatment step by melting the relative aluminium coating. 8 - Method as in Claim 7, characterized in that it provides to use weld material (20) in correspondence with at least part of the coupling zone of said adjacent edges (18a, 18b) to improve the hold of the welding. 9 - Radiating tubes for radiancy heating lines for premises (12), said tubes defining a forced-circulation circuit of a gas heating fluid, said radiating tubes made from an aluminium-coated tubular steel strip, the radiating tubes being characterized- in that said aluminium-coated steel strip is subjected, during at least one step of the production cycle, to at least a heat treatment made at a temperature above the melting temperature of aluminium. 10 - Radiating tubes as in Claim 9, characterized in that they comprise segments of tube connected together in correspondence with joining points (17), said joining points comprising respective adjacent edges (18a, 18b) of two adjacent segments of tube and connected together in correspondence with welding lines (19) obtained by the melting of the aluminium coating during the heat treatment step in the furnace. 11 - Radiating tubes as in Claim 9, characterized in that said radiating lines (11) comprise at least partly heat insulating covering means (14) suitable to cooperate at least partly with the part of the surface of said tubes (10) which does not face the premises (12) to be heated.

Inventors: CARLI VITTORIO, MARTOREL GASTONE, CARLI, VITTORIO, MARTOREL, GASTONE
Applicants: CARLI VITTORIO, EUKLIMA SRL, MARTOREL GASTONE, CARLI, VITTORIO, MARTOREL, GASTONE
Application year: 1999
Main classification: B21C37
IPC codes: B21C37