EP1592921A2

EP1592921A2 - Device and method for gas-flow heat treating strip material

Info

Publication number: EP1592921A2
Application number: EP04710875A
Authority: EP
Inventors: Domenico PERCIVALLE SPECIAL CONV. SAS PERCIVALLE
Original assignee: Percivalle Special Converting Sas Di Percivalle Barbara E C
Current assignee: Percivalle Special Converting Sas Di Percivalle Barbara E C
Priority date: 2003-02-14
Filing date: 2004-02-13
Publication date: 2005-11-09
Also published as: WO2004072552A2; ITMI20030273A1; WO2004072552A8; WO2004072552A3

Abstract

In a device (1) for gas-flow heat treating strip material, and which may be used in particular as a drying device in a coating machine or flexographic or rotogravure printing press, a treating unit (13) has a high-speed dispenser (28) for directing a main gas flow (11) onto a surface (26) of a work strip (4) by means of a delivery slot (34) positioned crosswise to a feed direction (D) of the strip (4) and of a width of less than approximately 0.5 mm; and a low-speed dispenser (38) is located downstream from the high-speed dispenser (28) to direct an additional gas flow (12) onto the surface (26) of the strip (4) at a speed slower than the speed of the main gas flow (11).

Description

DEVICE AND METHOD FOR GAS-FLOW HEAT TREATING STRIP MATERIAL

TECHNICAL FIELD

The present invention relates to a device and method for gas-flow heat treating strip material, and in particular for drying, heating, cooling, polymerizing strips of flexible materials in coating or flexographic or rotogravure printing processes and machines.

BACKGROUND ART

Numerous processes call for treating, with a heated or cooled flow of gas (air or inert gas) , a strip material (such as paper, polymer films, flexible packing materials, . thin strips of metal, such as aluminium, copper, steel, etc.) to which substances of various types have been applied, e.g. by printing, coating, impregnation, etc.

Flexographic or rotogravure printing presses, for example, are normally equipped with driers for removing volatile components from the strip of printed material, in particular solvents or water from the inks or coatings applied. This is done using a heated flow of gas supplied by nozzles of various shapes and sizes. In particular, driers are known in which the flow of gas is emitted by a succession of slots having relatively large openings (of about a few millimetres) , or which comprise nozzles with an orifice of over a millimetre in diameter.

These solutions, however, are not altogether satisfactory in terms of energy efficiency, and in particular by only permitting effective heat transmission to the material being processed at the expense of considerable energy consumption. Particularly problematic is the presence, on the surface of the work strip, of a laminar gas layer, which greatly reduces the heat exchange coefficient between the flow of gas directed onto the material and the material itself. DISCLOSURE OF INVENTION

It is therefore an object of the present invention to provide a device for gas-flow heat treating strip material, which may be used in particular as a highly effective drying device on a coating machine or flexographic or rotogravure printing press. In particular, it is an object of the invention to provide a high-performance device which, at the same time, is compact and cheap and easy to produce. It is a further object of the invention to provide a versatile device which can also be used in modular form, and for equipping a variety of different machines or production lines.

According to the present invention, there is provided a device for gas-flow heat treating strip material, as claimed in Claim 1.

By virtue of the characteristics claimed, the work strip is subjected to a high-speed flow of gas defining a very thin fluid blade capable of penetrating deep down into the laminar gas layer on the surface of the work strip to break up and/or significantly reduce the thickness of the layer. Eliminating or reducing the thickness of the laminar gas layer covering the surface of the strip results in improved heat exchange and a high degree of efficiency of the device. Using the solution according to the invention therefore improves the heat exchange coefficient between the flow of gas and the work material, and consequently the efficiency of the device for a given thermal and drive power capacity. The device preferably embodies the auxiliary characteristics defined in Claim 3, which, on the one hand, further improve heat exchange efficiency, and, on the other, increase total gas supply to permit adjustment of the concentration of evaporated substances in the outflow gas from the device. This solution is particularly advantageous when, on account of low highspeed gas supply, the solvent or water concentration in the outflow gas is too high. The low-speed gas flow provides the additional supply required to obtain the desired concentration.

By virtue of the further characteristic of the invention defined in Claim 6, the gas flow remains substantially in contact with the surface of the strip along the whole length of the channel defined about the strip, thus enabling highly effective heat transfer to the strip.

The invention also relates to a method as defined in Claim 13 and, preferably, in the dependent Claims 14 to 21.

In short, as compared with existing systems of equal performance, the solution according to the present invention is more efficient and requires less drive and thermal power. For a given drive power capacity, gas flow speed is higher, so that the gas supply required for heat treatment can be reduced. A number of treating units may obviously be installed in series to form, for example, drying chambers which, given the improved efficiency of the device according to the invention, will be shorter in length as compared with known solutions .

BRIEF DESCRIPTION OF THE DRAWINGS

A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows, schematically, a machine for applying substances to a strip material, and featuring a device in accordance with the invention;

Figure 2 shows a schematic section of one embodiment of the device according to the invention;

Figure 3 shows a partial view in perspective of the Figure 2 device;

Figures 4 to 8 show respective alternative embodiments of the device according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows, schematically, a machine 1 for applying substances to strip material, e.g. a coating machine or a rotogravure or flexographic printing press.

Machine 1 comprises a known station 2 for applying the necessary substance/s (e.g. a flexographic or rotogravure printing unit, or a coating or impregnating unit) ; known conveying means 3 for feeding a strip 4 of work material (paper, flexible packing material, polymer film, a thin strip of metal such as aluminium, copper, steel, etc.) along a path 5; and a treating device 10 located downstream from station 2 along path 5, and for treating strip 4 with a main gas flow 11 and, optionally, an additional gas flow 12.

In the non-limiting example shown, device 10 defines a drying device of machine 1, in particular for removing solvents or water remaining on strip 4 after the substances (ink, pigments, coating substances, etc.) are applied at station 2.

With reference to Figures 2 and 3, device 10 comprises a treating unit 13 having a box 14 defined by a box body having an inner chamber 15 for the passage of strip 4. At opposite longitudinal ends 16, 17, chamber 15 comprises an inlet 18 and an outlet 19 formed through respective end walls 21, 22 of box 14, and through which strip 4 is inserted; and a feed direction D of strip 4 is defined between inlet 18 and outlet 19. Obviously, feed direction D of strip 4 may be opposite to that shown in the accompanying drawings (as illustrated by the dash line in Figure 3) .

Treating unit 13 comprises first blow means 25 for blowing main gas flow 11 onto a surface 26 of work strip

4; and second blow means 27 located downstream from first blow means 25 along path 5 of strip 4, and for blowing additional gas flow 12 onto surface 26.

First blow means 25 comprise a high-speed dispenser 28 housed inside box 14 and having an overpressure chamber 29 with an inlet connected to a gas flow (air or inert gas) supply circuit 30. Along circuit 30, upstream from overpressure chamber 29, are installed a fan 31 or a compressor or other suitable apparatus for circulating a gas flow, and a heating or cooling member 32 of any known type for heating or cooling gas flow 11. Member 32 may be installed inside overpressure chamber 29.

Overpressure chamber 29 comprises a nozzle 33 having a delivery slot 34 crosswise to direction D and through which gas flow 11 is emitted onto surface 26.

Delivery slot 34 is a continuous, elongated, substantially rectangular slot extending over substantially the whole width of strip 4 (i.e. of a length substantially equal to the width of strip 4) , and has an opening (i.e. width) of less than approximately 0.50 mm, preferably ranging between approximately 0.20 and 0.50 mm, and even more preferably of approximately 0.30 mm. Nozzle 33 is located at end 16 of box 14; and supporting means 35 are provided to support strip 4 inside chamber 15 so that surface 26 faces nozzle 33, and delivery slot 34 is located close to surface 26, and in particular at a distance (measured in the direction 'of gas flow 11 from delivery slot 34) of approximately 5 to 10 times the opening of delivery slot 34.

In the Figure 2 and 3 example, supporting means 35 comprise two rollers 36 located respectively at inlet 18 and outlet 19; a surface 37 of strip 4, opposite surface 26, rests on rollers 36; and nozzle 33 and delivery slot 34 are inclined with respect to the perpendicular to surface 26. More specifically, nozzle 33 and delivery slot 34 are designed so that gas flow 11 strikes surface 26 at an angle (with respect to the perpendicular to surface 26) of approximately 20° to 40°, and preferably of approximately 30°.

Clearly, supporting means 35 may comprise rollers 36 differing in number and arrangement from those described purely by way of example.

Second blow means 27 comprise a low-speed dispenser 38 housed in box 14, downstream from high-speed dispenser 28, and having an overpressure chamber 39 with an inlet connected to a gas flow (air or inert gas) supply circuit 40. In the Figure 2 example, low-speed dispenser 38 is connected to circuit 30 by a branch line 41 fitted with a valve 42, though a circuit 40 independent of circuit 30 may obviously be used. Overpressure chamber 39 has one or more nozzles 43 with an orifice and/or slot, and so sized as to deliver additional gas flow 12 at a slower speed than main gas flow 11 from delivery slot 34 of high-speed dispenser 28. The speed of main gas flow 11 is over approximately 50 m/s, and preferably ranges between approximately 50 and 200 m/s, while the speed of additional gas flow 12 is below approximately 50 m/s, and preferably ranges between approximately 10 and 35 m/s.

Treating unit 13 also comprises conducting means 45 for defining about strip 4 a gas flow channel 46 substantially parallel to strip 4. More specifically, channel 46 is defined inside chamber 15, and is bounded by a conducting wall 47 facing and substantially parallel to strip 4, and by two sides 48 extending substantially perpendicularly from respective lateral edges of conducting wall 47 towards and beyond strip 4. In the example shown, sides 48 are portions of respective lateral walls of box 14. On the opposite side to conducting wall 47, channel 46 is bounded by strip 4 itself supported on rollers 36. Preferably, though, as shown in Figure 2, channel 46 is bounded by a bottom wall 49 substantially parallel to strip 4 and to conducting wall 47, and located on the opposite side of strip 4 to conducting wall 47, between rollers 36 and between sides 48, and close to, but not contacting, surface 37 of strip 4.

At end 17, i.e. outlet 19, treating unit 13 has extraction means 50 by which the gas flow along channel 46 is extracted from the channel. Extraction means 50 comprise an opening 51 formed in conducting wall 47 and connected by a chamber 52 to an extraction circuit 53 having a suitable (known) suction apparatus 54. Opening 51 is substantially rectangular, extends parallel to delivery slot 34, substantially over the whole width of strip 4, and is defined by a baffle 55 sloping with respect to strip 4 and defining a portion of end wall 22. As shown in Figure 1, extraction circuit 53 may be connected to a stack 56 directly or via a (known) unit 57 for recovering and/or eliminating the substances contained in the extracted gas flow. Whichever the case, extraction circuit 53 is not connected to supply circuits 30, 40, and the extracted gas flow is not recirculated to treating unit 13. Treating unit 13, and in particular high-speed dispenser 28, is always supplied with a fresh gas flow.

Device 1 implementing the method according to the invention operates as follows. After travelling through station 2, strip 4 is fed to treating unit 13 to undergo a treatment stage in which main gas flow 11 is fed onto surface 26 by high-speed dispenser 28, and specifically through delivery slot 34 of the width defined previously. After gas flow 11, additional gas flow 12 is fed onto surface 26 by low- speed dispenser 38 downstream from gas flow 11 along path 5. Gas flow 12 is fed onto surface 26 at a lower speed than gas flow 11. Gas flows 11, 12 flow along channel 46, are extracted by extraction means 50, and are fed to recovery and/or removal unit 57 and to stack 56. Alternatively, the method according to the invention does not include additional gas flow 12, in which case, low- speed dispenser 38 may be eliminated.

In the Figure 4 variation, otherwise similar to what has already been described, low-speed dispenser 38 is located upstream from high-speed dispenser 28, so that additional gas flow 12 is fed onto strip 4 before main gas flow 11. It is understood that low-speed dispensers 38 may be provided both up- and downstream from highspeed dispenser 28.

In this variation, supporting means 35 comprise a powered belt 60 mounted on rollers 61; strip 4 lies on belt 60 with surface 37 downwards and the opposite surface 26 facing dispensers 28, 38; in which case, channel 46 is bounded by conveying wall 47 and sides 48, and also by belt 60 which in fact replaces bottom wall 49. In the Figure 5 variation, supporting means 35 comprise a cylinder 62; surface 37 of strip 4 rests on a lateral surface 63 of cylinder 62, which lateral surface 63 defines the bottom wall of channel 46; and cylinder 62 may be heated or cooled in any known manner. Box 14 defining chamber 15 is shaped to follow the curvature of cylinder 62, so that channel 46 is curved, conducting wall 47 being a curved wall with substantially the same radius of curvature as cylinder 62. Obviously, chamber 15, i.e. channel 46, may extend along a long or short portion of lateral surface 63 of cylinder 62.

In the Figure 6 and 7 embodiments (which relate, in particular, to drying devices 10 located downstream from a flexographic and rotogravure printing station 2 respectively) , device 10 comprises a number of treating units 13 (of the type described previously) located in series along path 5 of the work strip 4.

Treating units 13 are housed inside a box 14 having a curved inner chamber 15 substantially parallel to strip 4 and having an inlet 18 and an outlet 19; strip 4 is supported, substantially curved, inside chamber 15 by supporting means 35 comprising, in this case, a series of rollers 65; and each treating unit 13 comprises a high- speed dispenser 28 and a low-speed dispenser 38 having the characteristics described previously.

Treating units 13 have respective channels 46 bounded by respective conducting walls 47 and, laterally, by the lateral walls of box 14 (not shown in Figures 6 and 7) . In the Figure 6 variation, channels 46 are bounded, on the opposite side of strip 4 to conducting walls 47, by bottom walls 49 located between rollers 65. In the Figure 7 variation, rollers 65 are closer together, and there are no bottom walls 49. Treating units 13 also comprise respective extraction means 50. More specifically, each treating unit 13 comprises an opening 51 formed in respective conducting wall 47; and openings 51 may be connected to a common extraction circuit (not shown) having a suitable suction apparatus (not shown) .

Each treating unit 13 may have its own supply circuit and own gas flow extraction circuit, or a common supply circuit and common extraction circuit may be provided connecting all the treating units in parallel.

Obviously, if a number of treating units 13 are provided, the method according to the invention comprises a number of series treating stages performed in respective treating units 13.

Figure 8, in which any details similar to or identical with those already described are indicated using the same reference numbers, shows a variation of high-speed dispensers 28 employed in accordance with the invention. In this variation, each dispenser 28 comprises a substantially cylindrical shell 70 crosswise to direction D; shell 70 is bounded by a substantially cylindrical lateral wall 71 defining overpressure chamber 29 inside; lateral wall 71 has a longitudinal through opening 73 bounded by two facing edges 74 and defining delivery slot 34; and delivery slot 34 is advantageously bounded by one or two blades 75 fitted to edges 74 of opening 73, as shown respectively in the two dispensers 28 in Figure 8. A channel 76 for recirculating gas flow 11 is provided radially outwards of shell 70 and about lateral wall 71, so that gas flow 11, after striking surface 26 of strip 4, is partly recirculated about shell 70 inside channel 76, and partly continues along channel 46, as described previously.

Clearly, other changes may be made to the device as described and illustrated herein without, however, departing from the scope of the present invention.

For example, each treating unit 13 may comprise a number of high-speed dispensers 28 arranged in succession and having respective delivery slots 34 parallel to one another, and/or a number of low-speed dispensers 38 in series .

Nozzles 33 of high-speed dispensers 28 may be variously oriented. If a number of dispensers 28 are employed, respective nozzles 33 may all be inclined in the same direction or not. Treating units 13 may even be located on both sides of strip 4 to treat both opposite surfaces 26 and 37 of strip 4.

Claims

1) A device (1) for gas-flow heat treating strip material, and which may be used in particular as a drying device in a coating machine or flexographic or rotogravure printing press, the device comprising at least one treating unit (13) having first blow means (25) for directing a main gas flow (11) onto at least one surface (26) of a work strip (4) by means of a delivery slot (34) positioned crosswise to a feed direction (D) of the strip; and the device being characterized in that the delivery slot (34) is a continuous elongated slot, and is of a width of less than approximately 0.50 mm.

2) A device as claimed in Claim 1, characterized in that the delivery slot (34) is of a width ranging between approximately 0.20 and 0.50 mm, and preferably of about 0.30 mm.

3) A device as claimed in Claim 1 or 2, characterized in that the treating unit (13) comprises second blow means (27) located downstream and/or upstream from the first blow means (25) along a path (5) of the strip, to feed an additional gas flow (12) onto the surface (26) of the strip.

4) A device as claimed in Claim 3, characterized in that the second blow means (27) supply an additional gas flow (12) at a speed lower than the speed of said main gas flow (11) supplied by the first blow means (25) .

5) A device as claimed in Claim 3 or 4, characterized in that the second blow means (27) comprise nozzles (43) with an orifice and/or slot, and so sized that the speed of the additional gas flow (12) is lower than that of the main gas flow (11) . 6) A device as claimed in any one of the foregoing Claims, characterized in that the treating unit (13) comprises conducting means (45) defining about the strip (4) a gas flow channel (46) substantially parallel to the strip . 7) A device as claimed in Claim 6, characterized in that the channel (46) is bounded by a conducting wall (47) substantially parallel to and facing the surface (26) of the strip (4), and by two sides (48) extending substantially perpendicularly towards the strip from respective lateral edges of the conducting wall.

8) A device as claimed in Claim 7, characterized in that the channel (46) is bounded by a bottom wall (49) substantially parallel to the strip (4) and to the conducting wall (47) , and located on the opposite side of the strip to the conducting wall.

9) A device as claimed in one of Claims 6 to 8, characterized in that the treating unit (13) comprises extraction means (50) by which the gas flow along the channel is extracted from the channel (46); said first blow means (25) and said extraction means (50) being located at opposite longitudinal ends of the channel.

10) A device as claimed in any one of the foregoing Claims, characterized by comprising a number of treating units (13) in series.

11) A device as claimed in one of the foregoing Claims, characterized in that the delivery slot (34) is located close to the surface (26) of the work strip (4), and in particular at a distance, measured in the direction of the gas flow (11) from the delivery slot (34) , ranging between approximately 5 and 10 times the opening of the delivery slot (34) .

12) A device as claimed in one of the foregoing Claims, characterized in that the delivery slot (34) is inclined with respect to the perpendicular to the surface (26) of the work strip (4), preferably at an angle ranging between approximately 20° and 40°, and preferably of approximately 30°. 13) A method of gas-flow heat treating strip material, in particular for drying strips of flexible material in coating or flexographic or rotogravure printing processes, the method comprising at least a first treating stage, in which a main gas flow (11) is fed onto at least one surface (26) of a work strip (4) by means of a delivery slot (34) positioned crosswise to a feed direction (D) of the strip; and the method being characterized in that the main gas flow is supplied through a continuous elongated delivery slot (34) of a width of less than approximately 0.50 mm.

14) A method as claimed in Claim 13, characterized in that the delivery slot (34) is of a width ranging between approximately 0.20 and 0.50 mm, and preferably of approximately 0.30 mm.

15) A method as claimed in Claim 13 or 14, characterized in that, at said treating stage, before and/or after said main gas flow (11) , an additional gas glow (12) is fed onto the surface (26) of the strip upstream and/or downstream from the main gas flow along a path (5) of the strip.

16) A method as claimed in Claim 15, characterized in that the additional gas flow (12) is fed onto the surface (26) of the strip (4) at a speed slower than the speed of the main gas flow (11) .

17) A method as claimed in one of Claims 13 to 16, characterized by comprising a step of providing about the strip (4) a gas flow channel (46) substantially parallel to the strip.

18) A method as claimed in Claim 17, characterized by comprising an extraction step, in which the gas flow along the channel (46) is extracted from the channel.

19) A method as claimed in one of Claims 13 to 18, characterized by comprising a number of treating stages in series.

20) A method as claimed in one of Claims 13 to 19, characterized in that the main gas flow (11) is supplied through said delivery slot (34) close to the surface (26) of the work strip (4) , and in particular at a distance, measured in the direction of the gas flow (11) from the delivery slot (34) , ranging between approximately 5 and 10 times the opening of the delivery slot (34) . 21) A method as claimed in one of Claims 13 to 20, characterized in that the main gas flow (11) is supplied inclined with respect to the perpendicular to the surface (26) of the work strip (4) , preferably at an angle ranging between approximately 20° and 40°, and preferably of approximately 30°.