MXPA99007017A - High speed infrared/convection dryer - Google Patents

Abstract

A combination infrared/convection dryer or oven (10) for drying travelling webs (W). A shutter assembly (8) is provided between the infrared radiation source (16) and the moving web in order to selectively expose the web to infrared radiation. Drying efficiency is optimized by adding heated impinged air at high velocity on the machine direction ends and between the infrared elements. The air being discharged on the web is heated as it is pulled across the elements to a centralized return air duct (42). The return air is pulled into the inlet of a close coupled supply fan (28) which then discharges the air to the nozzles. A portion of the air is alsoexhausted at atmosphere to maintain the oven enclosure in a negative pressure state, thus drawing fresh make-up air into the oven housing through the web inlet (12) and outlet (13) slots. Flotation nozzles (151, 152) can be used where contactless support of the running web is desired. Enhanced drying of the web and/or a coating on the web at high speed is achieved without a concomitant increase in dryer length.

Description

HIGH SPEED DRYER BY INFRARED / CONVECTION BACKGROUND OF THE INVENTION The present invention relates to a network drying apparatus. In the drying of a mobile network of material, such as paper, film or other sheet or flat material, it is often desirable that the network be dried quickly, and that the length of the dryer be limited in view of the constraints of space and cost. Various attempts have been made in the prior art to decrease the length and / or increase the efficiency and linear speed of the network dryers. To that end, infrared radiation has been used either alone or in combination with air to dry the network. For example, U.S. Patent No. 4,936,025 discloses a method for drying a mobile network, by passing the free contact network through various vacuum drying spaces. In this way, the network is passed through an empty space of infrared treatment in which the infrared radiation is applied to the network from a unit of REF .: 30846 infrared, and then goes to an air drying space inside which the network is dried by blowing with gas from a dryer unit of networks, which carries air, which simultaneously supports the network of contact . In addition, U.S. Patent No. 4,756,091 discloses an infrared radiant heated gas heated air drying oven, in which the arrays of infrared heaters are accommodated with hot air flow inlet nozzles therealong. US Patent No. 5,261,166 discloses a dryer in combination of infrared and air flotation, wherein a plurality of air bars are mounted above and below the network, for non-contact convection drying of the network, and they mount a plurality of infrared gas-lit burners between the air rods. In many conventional infrared dryers, however, much of the heat delivered by the infrared energy source is lost to the surroundings by transmission, reflection and radiation. In addition, the infrared elements must be continuously turned on and off to prevent the burn of the network. This reduces the efficiency and can reduce the life of the infrared element. It is therefore an object of the present invention to provide a more efficient infrared / convection combination oven or a dryer for drying mobile networks. A further objective of the present invention is to provide optimum control of an infrared / convection oven. Still another objective of the present invention is to provide infrared and convection drying, while floating support the mobile network. Yet another objective of the present invention is to eliminate the need to continuously turn the infrared elements on and off.

BRIEF DESCRIPTION OF THE INVENTION The problems of the prior art have been overcome by the present invention, which provides a combined infrared / convection dryer or furnace for traveling networks. A damper or shutter assembly is provided between the infrared radiation source and the mobile network, in order to selectively expose the network to the infrared radiation. The drying efficiency is optimized by the addition of hot air that collides at high speed, on the ends of the machine direction, and between the infrared elements. The air that is discharged on the network is heated as it is pulled through the elements towards a centralized return air duct. The return air is drawn to the inlet of a close coupled supply fan, which then discharges air to the nozzles. A portion of the air is also allowed to escape into the atmosphere to maintain the enclosure of the furnace in a negative pressure state, thereby pulling fresh air back into the furnace housing through the inlet and outlet slots of the network. The improved drying of the network and / or a coating of the network at high speed is achieved without a concomitant increase in the length of the dryer. In one embodiment of the invention, air rods are used for the floating support of the mobile network, to avoid contact of the network with the drying elements.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of the infrared / convection oven according to the present invention; Figure 2 is a top view of the gate or blind assembly for use in the dryer of the present invention; Figure 3 is a front view of the gate or blind assembly, taken along line 3-3 of Figure 2; Figure 4 is a side view of the gate or blind assembly, taken along line 4-4 of Figure 3; Figure 5 is a detailed view showing the connection of a damper or shutter of the control mechanism according to the present invention; Figure 6 is a front view of the furnace with a coupled fan assembly, close; and Figure 7 is a schematic cross-sectional view of an infrared / convection float oven according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Returning first to Figure 1, a dryer or furnace according to the present invention is generally shown at 10. The furnace 10 is defined by a housing 11, preferably insulated, having an opening 12 for entering the network to accommodate the entry of a network into the housing, and an exit opening 13 for the network, spaced from the inlet 12 for accommodate the network output from the host, as shown. The housing 11 can be constructed of any suitable material, preferably reflective, such as aluminum or stainless steel. A plurality of spaced apart idler rollers 14a-14n is provided to guide and support the network W as it travels through the furnace 10 from the inlet 12 to the outlet 13. It is preferred that the rollers 14 be placed at least below each source of shock air 15a, 15b, 15c as shown, since at the points of shock, the network W needs greater support to avoid distortion of the network, especially during cases of low voltage. A pair of infrared radiation elements 16, 16a are secured in the housing 11 to supply the drying of the network. The colliding air is preferably provided upstream and downstream of each infrared irradiation source 16, 16a, which in the embodiment shown, is near the inlet 12 of the furnace, near the outlet 13 of the furnace, and in a central site in the furnace. The air rods 15a, 15b and 15c are provided for this purpose, and are in combination with an air supply source, such as a fan, through the set of suitable conduits. The particular configurations of the air bars 15a and 15c are similar, and are designed to form air knives that provide mass transfer to the network, and cooling air to the shutter or gate assembly. The configuration of the central air bar 15b is designed to provide mass transfers to promote drying.

Positioned between the air shock sources 15a and 15b is the elemental source 16 of infrared radiation. Towards the input end of the network, the radiation source 16 is mounted to the source of shock 15a with the L-shaped sheet 7, and is preferably angular with an upward direction toward the center of the oven, as shown. This upward angle creates sufficient overlap on the idle non-drive roller to create a driving force for the roller, so that the network W proceeds properly through the furnace. Similarly, placed between the air shock sources 15a and 15c, there is a second infrared radiation source 16a, similarly mounted to the air shock source 15c with the L-shaped sheet 7a, and also angled in the upward direction towards the center of oven 10, as shown. The shutter or gate assemblies 8 and 9 are placed below the infrared elements 16a and 16, respectively, to allow control of the radiation allowed to reach the W network., without the need to turn off the infrared radiation source (s). With reference to Figure 2, each blind or gate assembly includes a plurality of aligned blades 20, each blade 20 slightly overlaps its adjacent blade when in the closed position, as seen in Figure 3. The number of blades 20 in each shutter or gate assembly may vary and depends on the particular dimensions of the infrared heating element used. Although the dimensions of each blade are not typical, it has been found that blades of 2.54 cm (1 inch) in width are suitable and that such blades can be placed at 2.38 cm (0.94 inches) center to center, to create overlap. necessary. Preferably, the damping blades 20 are designed with a reflective surface to reflect the infrared light back to the infrared elements, and direct it away from the network. Referring now to Figure 5, the blades 20 are coupled to the shutter or gate assembly using a spike arrangement, as shown. In this way, each end of each blade 20 is pivotally fixed to a clamp 32 on the end of the shank 30. The end of the shank 30 opposite the clamp 32 is fixed to the damping jib link arm 33. Each push link arm 33 for each damping blade 20 is then connected via a connecting link 34 (FIG. 4), which allows all of the dampers to be pivoted after actuation of an air cylinder 40 (located externally of the furnace) which is connected to a cylinder fork 37, and then to the connecting link 34 via the damping link pivot 35. Preferably, the opening and closing of the gates or blinds is based on linear velocity. At a predetermined linear speed adjustment point (which can be signaled by a suitable means, such as magnetic collection connected to the drive shaft of the coating line), the blinds or gates open and allow the exposure of the network to infrared radiation. In the case where the linear speed falls below the set point, the blinds close and prevent the burn of the network. As shown in Figure 6, a supply / exhaust fan 28 is in communication with the furnace, and in particular, with the air rods 15a, 15b and 15c, by means of suitable conduits 40, 41. The fan 28 it is adjusted to size to accommodate excess air that escapes, in order to keep the oven enclosure in a negative pressure state. This negative pressure causes the infiltration air to enter the furnace 10 through the slots 12 and 13 inlet and outlet of the network. The dampers 5 and 6 are provided with the ducts to regulate the flow of air to and from the fan 28. The return air is pulled from the return ducts 42, 43 in the furnace by the supply / exhaust fan 28. Since the return ducts are centrally located in the furnace 10, the return air is directed on the entire face of the infrared heating element, whereby the air in the recirculated supply is heated, to improve the efficiency. Figure 7 shows an alternative embodiment of the present invention which employs the flotation nozzles in place of the idle rolls in order to provide the support of the non-contacting network. Suitable flotation air rods include HI-FLOAT® air rods commercially available from Grace Tec Systems. In the embodiment shown, the air blades 15a and 15c are placed at the inlet and outlet ends of the network, of the dryer in a manner similar to that of the previous mode, and provide mass transfer to the network, and air from Cooling to blind mounts, as described above. An air flotation nozzle 150 is preferably located centrally between the air blades 15a and 15b. Similar air flotation nozzles 151 and 152 are placed below the network between the air blades 15a 'and 15c', and are displaced from the air flotation nozzle 150. The air exiting from the air flotation nozzles supports and dries the running net by flotation. The elemental infrared radiation sources 16 and 16a, together with the blind assemblies (not shown) are between each air blade, and the flotation nozzle 150 is above the network, analogous to the previous mode. Optionally, a source of infrared radiation 160 and the corresponding shutter assembly (not shown) can be located below the network, and between the flotation nozzles 151 and 152 to improve the drying efficiency. Those skilled in the art will appreciate that infrared radiation sources can be used above the network, below the network, or both, depending on the desired drying capacity. Similarly, the particular site of the flotation nozzles will depend on the drying capacity, provided that adequate support of the network is achieved. An infrared pyrometer (not shown) is incorporated into the control scheme to maintain the temperature of the output network. The opening / closing synchronization of the blinds is based on the percentage press speed. The opening / closing control of the blinds is also interlocked to a network break detector. In operation, the supply / exhaust fan 28 is turned on and a preheating cycle is started by activating the shutter assembly to the closed position. The infrared element is ignited and a desired temperature set point, such as 760 ° C (1400 ° F) is achieved. Once the set point is reached (which can be signaled by any suitable means, such as a light on a control panel) the temperature is subsequently controlled by means of a thermocouple and an SCR controller. At the set point temperature the oven is ready to dry. The blind assembly is open and closed by means of a linear speed control setpoint, such as 21.3 meters per minute (70 feet per minute). After reaching the linear speed set point, the blinds will open, whereby infrared energy is emitted to the network medium W. The elementary temperature control will now move to the network temperature via the infrared temperature pyrometer of the network, and the SCR controller. As the linear speed is reduced to an intermittent stop, the shutter assembly will again be closed, once it slows down beyond the linear speed control set point. The temperature control of the infrared element will be assumed, keeping the temperature setpoint fast. The same sequence occurs in the case of a network breakdown. Preferably, a safety interruption or stop is incorporated, which is based on the temperature of the infrared element. For example, in the event that the element temperature reaches 982 ° C (1800 ° F), a high temperature limit switch will be activated and the element will be turned off.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (14)

RE IVINDICATIONS Having described the invention as above, the content of the following claims is claimed as property:

1. An infrared / convection dryer for a mobile network, characterized in that it comprises: a dryer housing having an input slot of the network, and an output slot of the network spaced from the input slot of the network; the impact means in the housing, to cause the gas to hit the network; a fan in communication with the shock means to supply gas to the impact means; the infrared heating means in the housing, for irradiating infrared light and heating the network; the shutter means or gate in the housing, the shutter means is movable between an open position which allows the irradiated infrared light to strike the network, and a second closed position which prevents the irradiated infrared light from hitting the network; and the recirculation means in communication with the fan, for recirculating a portion of the gas from the dryer housing to the impact means.

2. The infrared / convection dryer according to claim 1, characterized in that it comprises a return duct in the dryer housing, for recirculating the hot air to the fan and back to the housing.

3. The infrared / convection dryer according to claim 1, characterized in that the shock means comprises a plurality of air nozzles.

4. The infrared / convection dryer according to claim 3, characterized in that the network is supported in the housing by a plurality of rollers, each placed below an air nozzle.

5. The infrared / convection dryer according to claim 1, characterized in that the shock means comprises a plurality of flotation nozzles.

6. The infrared / convection dryer according to claim 1, characterized in that the opening and closing of the shutter means is dependent on the speed of the mobile network.

7. The infrared / convection dryer for drying a mobile network, characterized in that it comprises: a dryer housing having an input slot of the network, and an output slot of the spaced network of the input slot of the network, the medium of shock in the housing, to cause the gas to hit the network; a fan in communication with the shock means to supply the gas to the shock medium; the infrared heating means in the housing for irradiating infrared light and heating the network; the means to measure the speed of the running network; the shutter means in the housing, which responds to the measured speed of the running network, to selectively direct the infrared light away from the running network, when the measured speed falls below a predetermined value; and the recirculation means in communication with the fan, for recirculating a portion of the gas from the dryer housing to the impact means.

8. The infrared / convection dryer according to claim 7, characterized in that it also comprises a return duct in the dryer housing, for recirculating hot air towards the fan and back towards the housing.

9. The infrared / convection dryer according to claim 7, characterized in that the shock means comprises a plurality of air nozzles.

10. The infrared / convection dryer according to claim 9, characterized in that the net is supported in the dryer by a plurality of rollers, each placed below an air nozzle.

11. The infrared / convection dryer according to claim 7, characterized in that the shock means comprises a plurality of flotation nozzles.

12. A method for drying a mobile network, characterized in that it comprises: the provision of a dryer housing having a network input slot and a network output slot spaced from the input slot of the network; causing the mobile network to travel through the dryer housing; the measurement of the speed of the mobile network; the shock of the gas on the mobile network in the housing; irradiating selectively the infrared light on the mobile network in the housing; and directing the infrared light away from the mobile network, when the measured speed of the running network falls below a predetermined value.

13. The method according to claim 12, characterized in that the infrared light is directed away from the running network, by reflection.

14. The method according to claim 12, characterized in that the infrared light is directed away from the network that runs through the shutter assembly lock placed in the housing, between the infrared light and the network. SUMMARY OF THE INVENTION A dryer or combi in infrared / convection combination (10) is described for drying mobile networks (W). A shutter assembly with door (8) is provided between the infrared radiation source (16) and the mobile network, in order to selectively expose the network to infrared radiation. Drying efficiency is optimized by adding hot, high-velocity air that collides at the machine's direction ends and between the infrared elements. The air that is discharged over the network is heated as it is pulled through the elements to a centralized return air duct (42). The return air is pulled towards the inlet of a close coupled supply fan (28), which then discharges the air from the nozzles. A portion of the air is also escaped into the atmosphere to maintain the oven housing in a negative pressure state, thereby pulling fresh fresh air, into the oven housing, through the inlet slots of the network (12) and output from the network (13). The rotation nozzles (151, 152) can be used where contactless support of the mobile network is desired. Improved drying of the network and / or a coating on the network at a high speed is achieved without a concomitant increase in the length of the dryer.