Dryer housing for floatingly drying a travelling web and method of floatingly guiding a travelling web

Abstract: Drying apparatus including pressure control of air supply feeding an air bar and subsequently impinging upon a web, so as to avoid or compensate for web shift without disturbing the cushion pressure and flotation techniques necessary for adequate web flotation and drying, as well as a method of regulating the pressure of supply air to such air bars. A damper or valve (18) is positioned in the header system (at 33) between first and second ducts (30, 31) feeding each air bar. Proper adjustment of the damper (18) regulates the pressure of supply air in each duct (30 and 31), and compensates for web shift, or minimizes said web shift, or prevents it from occurring.

Description: BACKGROUND OF THE INVENTION The present invention relates to a dryer housing for floatingly drying a travelling web and a method of floatingly guiding a travelling web. Conventional air bars and air duct delivery systems are designed to obtain even air flow to the web occurs notwithstanding minor disturbances in duct delivery systems. Uneven air distribution is generally considered to be undesirable, since the same can result in drying streaks on the web, improper clearance of the web from the air bar surface, and/or improper flotation of the web (e.g., web flutter). Thus, in a conventional air bar having more than one air receiving port in communication with a duct delivery system, if one port is supplied air at a pressure different from that at which another port is supplied air, the air bar is designed so that the two different air supplies mix in an internal chamber of the air bar, allowing even pressure air delivery to the web. In addition, as a floating web approaches the edge of an air bar, the pressure pad which allows web flotation collapses, causing web flutter. This phenomenon is similar to the edge of an unattached sail on a sail boat, and in flotation drying, is undesirable. Accordingly, webs are typically positioned about 2,5-10,2 cm (1-4 inches) from the air bar edges. It would, however, be desirable to continuously control or compensate for web shift occuring during the drying operation, regardless of the cause thereof. It is therefore an object of the present invention to compensate for such web shift. It is a further object of the present invention to provide apparatus to control the pressure differential between two ducts feeding a given air bar. US 5,199,623 discloses a web flotation dryer on which the pre-characterising portion of claims 1 and 5 is based. US 5,105,562 discloses a web dryer having upper finger ducts feeding air bars. Damping means are separately provided in each upper finger duct rather than in the crossover duct connecting the finger ducts. SUMMARY OF THE INVENTION The problems of the prior art have been overcome by the instant invention, which provides for pressure control of air supply feeding air bars and subsequently impinging upon a web, so as to avoid or compensate for web shift without disturbing the cushion pressure and flotation techniques necessary for adequate web flotation and drying. More specifically, a damper is positioned in the header system feeding first and second ducts, which ducts in turn feed each air bar. Proper adjustment of the damper regulates the pressure of supply air in each duct, and compensates for web shift or minimizes or prevents web shift from occurring. Accordingly the present invention provides a dryer housing for floatingly drying a travelling web, said housing comprising: an upper header assembly comprising a pair of upper ducts arranged to feed air to a plurality of upper air bars for floatingly drying a travelling web; said plurality of upper air bars each being in air-receiving communication with said pair of upper ducts; an upper crossover duct in air-receiving communication with a supply fan and in air-supplying communication with said pair of upper ducts; upper damper means for controlling the pressure differential between said pair of upper ducts whereby web shift can be compensated; characterised in that said upper ducts are finger ducts and in that said upper damper means are in said upper crossover duct; said dryer housing further comprising: a lower header assembly comprising a pair of lower finger ducts arranged to feed air to a plurality of lower air bars for floatingly drying a travelling web; a plurality of lower air bars each in air-receiving communication with said pair of lower finger ducts; a lower crossover duct in air-receiving communication with said supply fan and in air-supplying communication with said pair of lower finger ducts; and lower damper means in said lower crossover duct for controlling the said pair of lower pressure differential between finger ducts whereby web shift can be compensated. Further the present invention provides a method of floatingly guiding a travelling web, comprising: providing a supply of air to an upper header assembly including an upper crossover duct; feeding said air from said upper crossover duct to a pair of upper ducts in air-supplying communication with a plurality of air bars; floating said web on a cushion pressure of air created by said plurality of air bars; and regulating the amount of pressurized air fed to said upper ducts in response to shifting of said floating web so as to create a pressure differential between said pair of upper ducts; characterised by: providing a supply of air to a lower header assembly including a lower crossover duct; feeding said air from said lower crossover duct to a pair of lower finger ducts in air-supplying communication with a plurality of air bars; floating said web on a cushion pressure of air created by said plurality of air bars; and regulating the amount of pressurised air fed to said lower finger ducts in response to shifting of said floating web so as to create a pressure differential between said pari of lower finger ducts; whereby said pair of upper ducts are finger ducts and in that said pressure differentials are created using damper means in said upper and lower crossover ducts. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side cross-sectional view of a header assembly having an adjustable damper in accordance with the present invention; Figure 2 is a front cross-sectional view of the header system of Figure 1 in accordance with the present invention; Figure 3 is a cross-sectional view of a portion of the damper actuating assembly taken along line F-F of Figure 2; Figure 4 is a cross-sectional view of another portion of the damper actuating assembly taken along line E-E of Figure 2; Figure 5 is a cross-sectional view of the damper vane shown coupled to the damper actuating assembly in accordance with the present invention; Figure 6 is a bottom cross-sectional view of the upper header assembly of Figure 1 in accordance with the present invention; and Figure 7 is a front cross-sectional view of the header system of Figure 1 in accordance with another embodiment of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Turning now to Figures 1 and 2, there is shown generally at 10 an upper header assembly 11 and a lower header assembly 12, each adapted to receive and be in air flow communication with a plurality of air bars via a pair of finger ducts 30, 31 for floatingly drying a running web. Although the present invention is not limited to any particular type of air bar used, preferably the air bar is of the Coanda type such as the Hi-Float air bar commercially available from W.R. Grace & Co.-Conn. Each air bar has a pair of air receiving ports adapted to be sealingly connected to the header assembly 11 or 12 via ports 19a, 19b, 19c, etc. in each of the finger ducts 30, 31. Each air bar extends over and is fed by two finger ducts, and thus each air bar includes two ports, each corresponding to a port in each of the two finger ducts. Each upper and lower header assembly includes two finger ducts 30, 31 which directly feed the air bars as described above. The finger ducts 30 are proximal to the gear side A of the dryer, and the finger ducts 31 are proximal to the operator side B of the dryer. Located behind each pair of finger ducts 30 and 31 is a crossover duct 33. The crossover duct 33 is in communication with a supply fan (not shown) which provides pressurized air to the crossover duct, which in turn provides pressurized air to the finger ducts 30, 31 and ultimately to the plurality of air bars. Located on the operator side B of the dryer and accessible to the operator is damper actuator 13 having a moveable lever 14. As best seen in Figures 3 and 6, the lever 14 is coupled to a first rigid round rod 15 which extends into the dryer enclosure. Movement of the lever 14 causes rotational movement of the first round rod 15. At its distal end, the first round rod 15 is coupled via miter gears 17a, 17b to a second round rod 16 positioned perpendicularly to the first round rod 15, as best seen in Figure 4. The aforementioned rotational motion of the first round rod 15 causes a similar movement of the second round rod 16 via the miter gears 17a, 17b. Coupled to second round bar 16 is a damper vane 18, which is preferably a low carbon tabulated sheet. A V-shaped groove is formed along the length of the damper vane 18, as shown in Figure 5, to accommodate the round bar 16 and to which it is secured such as by welding. Rotational movement of round bar 16 causes rotational movement of damper vane 18 secured to it. A damper vane 18 is positioned in each crossover duct 33 which is in air supplying communication with finger ducts 30 and 31. When the damper vane 18 is in the fully open or horizontal position, the supply of air to the crossover duct 33 and subsequently to finger ducts 30 and 31 is substantially unaffected by the damper vane 18. However, in the event of web shift, movement of the damper vane 18 towards vertical will cause a pressure differential between finger duct 30 and finger duct 31, which compensates for the web shift. Accordingly, the amount of air supplied to each finger duct 30 and 31 can be regulated based upon the occurrence of web shift, either observed manually or sensed automatically. Although not shown in Figures 1 and 6, the lower header assembly 12 also has a damper vane 18' controllable in the same way. It should be understood by those skilled in the art that the respective relative positions of the first and second round rods 15, 16 are dictated by the location of the ducts in the dryer enclosure and by the location of the actuating assembly therefor; the actuating assembly including lever 14 should be readily accessible to the operator. Both of the upper and lower header assembly include a damper assembly, and that they can be individually controlled or can be controlled with a single actuator. For example, Figure 7 explicitly shows the embodiment wherein both the upper and lower header assembly are equipped with a damper assembly. Thus, upper header assembly includes damper vane 18 coupled to a rigid round rod 16, which in turn is coupled to rigid round rod 15 as in the embodiment of Figure 2. Similarly, lower header assembly includes a damper vane 18' coupled to a rigid round rod 16', which in turn is coupled to rigid round rod 15'. Each rod 15, 15' is coupled to an actuator 50 as shown. The damper assembly can be driven automatically using conventional actuator motors, which respond either to manual input or to an electrical signal generated as a result of web shift. For example, a conventional web guide optical sensor, such as an infrared sensor, can be used to sense when the web shifts. Upon the occurrence of a web shift requiring correction, such as a 30% or greater shift, the infrared sensor can send a signal to the actuator motor or motors, which causes movement of the dampers, preferably in steps, until the shift is less than the set point value, such as less than 30%. The upper and lower dampers can be moved as a result of the same signal, or can be moved independently by receiving separate signals. Alternatively, the dampers can be manually controlled. The operator would watch the web guide indicator and manually control a switch that activates the actuator. The switch would be released when the web guide indicator indicates that correction of web shift is no longer necessary.

Claims: Dryer housing for floatingly drying a travelling web, said housing comprising: an upper header assembly (11) comprising a pair of upper ducts (30, 31) arranged to feed air to a plurality of upper air bars for floatingly drying a travelling web; said plurality of upper air bars each being in air-receiving communication with said pair of upper ducts (30, 31) ; an upper crossover duct (33) in air-receiving communication with a supply fan and in air-supplying communication with said pair of upper ducts (30, 31); upper damper means (16, 18) for controlling the pressure differential between said pair of upper ducts (30, 31) whereby web shift can be compensated; characterised in that said upper ducts (30, 31) are finger ducts and in that said upper damper means (16, 18) are in said upper crossover duct (33); said dryer housing further comprising: a lower header assembly (12) comprising a pair of lower finger ducts (30, 31) arranged to feed air to a plurality of lower air bars for floatingly drying a travelling web; a plurality of lower air bars each in air-receiving communication with said pair of lower finger ducts (30, 31) ; a lower crossover duct (33) in air-receiving communication with said supply fan and in air-supplying communication with said pair of lower finger ducts (30, 31); and lower damper means (16', 18') in said lower crossover duct (33) for controlling the pressure differential between said pair of lower finger ducts (30, 31) whereby web shift can be compensated. A dryer housing according to claim 1, wherein said lower damper means comprises a lower damper vane (18') rotatingly secured in said lower crossover duct (33). A dryer housing according to claim 1 or 2, wherein said upper damper means comprises an upper damper vane (18) rotatingly secured in said upper crossover duct (33). A dryer housing according to either of claim 2 or 3, further comprising means (14, 15, 16, 14', 15', 16') for actuating said lower and/or upper damper vane(s) (18, 18'), said actuating means comprising a first rod (15, 15') extending into said dryer housing and rotatingly coupled to a second rod (16, 16') secured to said damper vane (18, 18'). A method of floatingly guiding a travelling web, comprising: providing a supply of air to an upper header assembly (11) including an upper crossover duct (33); feeding said air from said upper crossover duct (33) to a pair of upper ducts (30, 31) in air-supplying communication with a plurality of air bars; floating said web on a cushion pressure of air created by said plurality of air bars; and regulating the amount of pressurized air fed to said upper ducts (30, 31) in response to shifting of said floating web so as to create a pressure differential between said pair of upper ducts; characterised by : providing a supply of air to a lower header assembly (12) including a lower crossover duct (33); feeding said air from said lower crossover duct (33) to a pair of lower finger ducts (30, 31) in air-supplying communication with a plurality of air bars; floating said web on a cushion pressure of air created by said plurality of air bars; and regulating the amount of pressurised air fed to said lower finger ducts (30, 31) in response to shifting of said floating web so as to create a pressure differential between said pair of lower finger ducts; whereby said pair of upper ducts (30, 31) are finger ducts and in that said pressure differentials are created using damper means in said upper and lower crossover ducts (33) A method of floatingly guiding a travelling web, according to claim 5, further characterized by the step of sensing a position of said floating web; and effecting said regulating of the amount of pressurized air fed to said pair of upper and lower finger ducts (30, 31) in response to said sensed position of said floating web. A method according to claim 6, characterized by sensing said position of said floating web with an optical sensor.

Inventors: ROCHELEAU MICHAEL O, ROCHELEAU, MICHAEL O.
Applicants: MEGTEC SYS INC, MEGTEC SYSTEMS, INC.
Application year: 1996
Main classification: F26B13
IPC codes: F26B13, D06F58, D06B15