US3085347A

US3085347A - Web breaking control in drying apparatus

Info

Publication number: US3085347A
Application number: US13901A
Authority: US
Inventors: Edgar J Justus
Original assignee: Beloit Iron Works Inc
Current assignee: Beloit Iron Works Inc
Priority date: 1960-03-09
Filing date: 1960-03-09
Publication date: 1963-04-16
Anticipated expiration: 1980-04-16

Description

April 16, 1963 E. J. JUSTUS WEB BREAKING CONTROL IN DRYING APPARATUS 4 Sheetsheet 1 Filed March 9, 1960 'QY-Z A ril 16, 1963 E. J. JUSTUS WEB BREAKING CONTROL IN DRYING APPARATUS Filed March 9, 1960 4 Sheets-Sheet 2 .[UFEHfUP a a7' .7. ustus April 16, 1963 E. J. JUSTUS WEB BREAKING CONTROL IN DRYING APPARATUS 4 Sheets-Sheet 3 Filed March 9, 1960 [HI/EHJUF [Li ya? Jus us April 16, 1963 E. J.- JUSTUS WEB BREAKING CONTROL IN DRYING APPARATUS 4 Sheets-Sheet 4 Filed March 9, 1960 R &

[HI/E11 0!" Q fd 'arffustus Hff 5 3,085,347 WEE BREAKING CONTROL IN DRYING APPARATUS Edgar J. Justus, Beloit, Wis, assignor to Beloit Iron Works, Beloit, Wis, a corporation of Wisconsin Filed Mar. 9, 1960, fier. No. 13,991 it) (Ilaims. (Cl. 34-49) The present invention relates broadly to drying apparatus, and is more particularly concerned with a high velocity air dryer of the recirculating type especially suitable in the paper making art and featuring therein the provision of paper web break detection means effective to initiate a plurality of steps in which exhaust air flow is reversed to render essentially remote system contamination from broken web pieces and the ignition of said particles within the system.

Relatively recently high velocity air drying has been practiced to augment the drying effect of conventional cylinder dryers and thereby attain higher production rates in paper making machines. Current demands for coating of papers on the paper machine have required added drying capacity, as is well known, often where space is limited. One drying system having a high order of proven effectiveness is of the recirculating air type embodying air delivery duct means mounting a suitable nozzle pattern and exhaust duct means communicating with a hood beneath which the web passes during performance of the drying step. It is not infrequent that the web will break in the region of the hood, and the bits and pieces of web are then carried by the exhaust duct means into the blowers, into the heating means, and by the air delivery duct means, into the nozzle structure. Some of the broken web particles may remain in the ducting, and with respect to the nozzle structure, any bits and pieces of web therein can at least interfere with the uniformity of air flow to a degree sufiicient to cause uneven drying, and can under more severe conditions jam the nozzle structure and even the ducting. As well, the presence of relative fine web particles within the hood and adjacent thereto with continued hot air input creates a very serious fire hazard, endangering operating personnel.

It is an important aim of the present invention to provide improved drying apparatus which reduces to a minimum fire hazards and effectively solves other problems arising upon occasion of a web break.

Another object of this invention lies in the provision of a recirculating high velocity air dryer system, embodying therein means in control of an exhaust fan, air heating means, exhaust air flow path, fresh air supply, and hood position with respect to the web being dried.

Still another object of this invention is to provide a high velocity air dryer having air delivery duct means and exhaust duct means in association with means providing a unidirectional ilow path of essentially unheated air through the air delivery and exhaust duct means in response to a web break signal. 7

-A further object of the instant invention lies in the prosivision of apparatus for drying paper webs and the like, embodying a hood, duct means delivering air to the hood and exhausting air therefrom, means connecting the air delivery and exhaust duct means, means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, closure means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, and

sheet break detection means connected to the means closing the connecting means and to the closure means to close the closure means and open the means closing the connecting means and provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs.

Other objects and advantages of the invention will become more apparent during the course of the following description, particularly when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals designate like parts throughout the same:

FIGURE 1 is a more or less diagrammatic view of a dryer section of a paper machine illustrative of an exemplary environment for the present invention;

FIGURE is a vertical sectional view, with parts thereof in elevation, of one form of dryer hood means and duct means which can be employed in the present invention;

FIGURES 3 and 4 are fragmentary plan views of air delivery nozzle means suitable for use with this invention;

FIGURE 5 is an end elevational view of a high velocity air dryer embodying the novel concepts-of this invention;

FIGURE 6 is a side elevational view of the structure of FIGURE 5; and

FIGURE 7 is a more or less diagrammatic view of the drying apparatus of this invention with a circuit diagram indicated thereon to more clearly ilustrate the steps of the instant invention upon occurrence of a web break.

Referring now to FIGURE 1, there is shown somewhat diagrammatically a dry end section 10 of drying apparatus of a paper machine with which the instant invention may be employed. However, it will be readily apparent during the course of the description now to follow that the drying means and method herein disclosed is also effective when installed subsequent to paper coating apparatus and that this invention is not restricted to use on a paper machine dryer. The techniques herein disclosed are of equal application in textile drying and in the drying of particulate and sheet materials wherein it is important to rapidly obtain a reverse air flow and to terminate certain other functions in the normal drying cycle.

The dry end section 10 shown in FIGURE 1 comprises a first row of horizontally aligned drying cylinders or drums lla-d of which four are shown in the exemplary embodiment illustrated, and a second row of horizontally aligned drying cylinders 12ad staggered with respect to the drying drums 11 of the first row. A Web of paper W passes alternately about the drying cylinders 11 and 12, and is maintained in contact with the surfaces of the drying cylinders 11a and 11b by a felt 13, and against the surfaces of the drying drums 1241-41 by a felt 14. A suitable number of rollers 15 are arranged to guide the felt 13, and rollers 16 guide the felt 14. The drying arrangement as thus far described Will be recognized as of an essentially conventional construction, and the general-practice in the art is to Wrap the web W about drying cylinders 11 and 12. However, cylinders are not at all times required, and the instant invention can be practiced utilizing a hood positioned with its mouth portion relatively closely adjacent a paper web advanced along a generally straight line, rather than serpentine, path.

Drying apparatus generally designated by the legend A and as constructed in accordance with the principles of this invention comprises a housing or insulated hood cover 18 having a length preferably coextensive with the width of the web W and provided with a bottom opening 19 therein, so that When the housing is suitably supported it overhangs the cylinder 11c approximately to the distance shown. Stated otherwise, the housing or hood 18 extends a sufficient distance about the cylinder or drum 11c to be coextensive with the wrap of the web W during travel along the circumferential portion of the rotatable drum 110.

The housing 18 may be shaped to provide a pair of generally upright

opposed sidewalls

20 and 21, a pair of opposed endwalls 22 and 23', a generally flat top wall 24, and a generally arcuately curved bottom wall 25 providing a confined path of web travel for the web during its wrapping contact with the drum 11c.

In the exemplary form of housing 18 shown in the drawings, there is supported interiorly thereof a plurality of circumferentially spaced supply or air delivery plenums Zea-d, four of which are illustrated, although of course the number may vary. Each supply plenum 26 may be of generally semi-cylindrical shape, and the plenum means 26ad communicate, respectively, with conduit means 27ad leading to a header 28 which connects with branch portion 29a of air delivery duct means 29. To exhaust moisture bearing air from the housing 18, and to provide a reverse air flow or air delivery to the housing 18 when a sheet break occurs, the housing top wall 24 receives

branch portions

30a and 31a of exhaust du-ct means 30 and 31.

As will be described hereinafter, the air delivery branch portion 29a and

exhaust branch portions

30a and 31a may have slidable connection with other portions of the air delivery and exhaust duct means 2931 to permit the hood 18 to be raised along said

branch portion

29a, 30a and 31a when a sheet break occurs.

Each supply plenum 26 supports nozzle means 32a-d, which may take a number of diiferent forms having various air delivery patterns therein which, if desired, may be arranged as in FIGURES 3 and 4. The nozzle means 32 may have a plurality or array of spaced holes or perforations 33 (FIGURE 3) of a particular configuration, diameter and number in order to obtain maximum drying efficiency, or, the nozzle means 32 in the form of a plate may have spaced slots 34 (FIGURE 4) which may be straight walled or tapered and of a spacing, width and number to obtain the desired drying efiiciency. It may be noted from FIGURE 2 that the perforated or slotted plates 32 close the mouth portion of each supply plenum 26, and to assure that the air stream issuing therefrom impinge against the paper web W generally normal thereto, each plate 32 is of generally arcuate shape when viewed in end, or as may be otherwise stated, each plate or nozzle member 32 has a curvature corresponding to that of the cylinder or drum 11c.

As is best shown in FIGURES and 6, the air delivery branch portion 29a of the duct means 29 is telescopingly received in a branch portion 2%, while the exhaust

duct branch portions

30a and 31a may telescope Within branch portions 305 and 31b of the exhaust duct means 30 and 31. Further details of the means to raise and lower the hood 18 will be later described, although it may now be noted that the hood end walls 22 and 23'may mount brackets 35 to which are connected pistons 36 of pneumatic or hydraulic cylinders 37 secured in any suitable manner to a fixed structure, as indicated in FIGURES 5 and 6.

The air delivery duct branch portion 29b is generally vertically disposed and integral therewith or in some other suitably connected in a generally horizontal duct branch portion or run 29c leading to a generally upright or vertically disposed duct branch portion 290! terminating in a blower housing 38. The exhaust d-uct branch portions 361) and 3117, on the other hand, may be connected to inclined branch portions 300 and 31c connected to curved or elbow branch portions 30d and 31d which merge or combine into a common horizontal branch portion or run designated generally as 3012. The horizontal run or branch portion 36c leads to a generally upright branch portion 30 connected to the blower housing 38, and upstream therefrom is a reduced diameter branch portion 30g leading to an exhaust fan housing 39.

The drying apparatus A as thus far described is supported in any suitable manner by a fixed structure. The support means for the air delivery and exhaust ducting may include longitudinally extending beams 40 (FIGURE 5), while the blower housing may be mounted upon stand means 41 and the exhaust fan housing 39 upon stand means 42 erected from a wall portion 43. The blower housing 38 mounts interiorly thereof fan means 44 indicated diagrammatically as driven through belt means 45 from motor means 46. A similar arrangement is provided for the exhaust fan, and motor means 47 supported upon the wall portion 43 is connected by belt means 48 to fan means 49 within the exhaust fan housing 39. Fresh or makeup air is supplied to the system through duct means 50 communicating with the blower housing 38, and within the duct means 50 is a damper or bfle member 51 to control the amount of air admitted to the housing 38. In the system illustrated, the damper means 51 is normally in a partially open position, and when a sheet break occurs as will later be described in detail, the damper means 51 is fully opened. Of course, between the damper means 51 and the blower housing 38, a permanently open inlet vane structure could be provided.

T he exhaust fan housing 39 also mounts duct means 52 having damper means 53 therewithin which is normally in a partially open position to vent from the system moisture laden air drawn by the fan means 49 through the exhaust duct means 30 and 31. When a sheet break occurs, however, the damper means 53 is caused to move to a fully open position under control of the air flow control system herein provided, to permit the input of a maximum amount of fresh air to the system for porting through the air delivery duct means 2-9 and exhaust duct means 30 and 31.

Additional damper means are herein provided for actuation when a sheet break occurs to block return air fiow to the blower 44 and to provide a unidirectional air flow from the blower means 44 through the air delivery and exhaust duct means 29-31, A first such damper means is herein referred to as an isolation damper, and is designated in FIGURES 5 and 7 by the numeral 54. The isolation damper 54 is located in the common horizontal run We leading from the exhaust duct portions 39d and 31d to the vertical duct portion 30 which terminates in the blower housing 38. It may now be seen that when the isolation damper 54 is actuated to a closed portion, normal flow of moisture laden air from the exhaust duct means 30 and 31 to the blower housing 38 is blocked, so that hits and pieces of broken web are not permitted to contaminate the blower means 44 and exhaust fan means 49, nor the ducting leading to the blower and exhaust fans. The manner in which the isolation damper 54 is actuated will be later described in connection with FIG- URE 7.

A further damper means provided in accordance with this invention is herein termed a by-pass or blow-back damper, and is designated in FIGURES 5, 6 and 7 by the numeral 55. The damper 55 is positioned in a connecting duct 56 extending between the air delivery duct portion 290 and the common exhaust duct horizontal portion 302 The by-pass damper 55 is normally closed, however, when a sheet break occurs, the bypass damper 55 is automatically actuated to an open position to provide an air flow path from the blower housing 38 through the air delivery vertical duct portion 29d and through the air delivery horizontal run 29c through the auxiliary duct means 56 and through the air delivery and exhaust duct portions 30d, 31d, 29b-31b and 29a-31a to the interior of the hood 18. The damper actuating means and the automatic system provided therefor will be noted in detail in connection with FIGURE 7.

During normal operation of the drying apparatus A,

air directed through the air delivery duct means 29 is increased in temperature to a level sufficient for effective drying of the traveling paper web W. For this purpose, heating means 57 are supported'in the generally vertical duct portion 29d of the air delivery duct 25?, although of course this position can well be varied. The heating means 57 may take various forms, as for example, steam coils or combustion air heaters. The heating means 57 are indicated somewhat diagrammatically in FIGURE 7 as electrical heating means, although generally speaking resistanoe heaters may not be desired because of the fire hazards involved.

Referring again to FIGURE 7, there is shown a rapid acting, highly reliable and relatively simple air flow control system operable upon occurrence of a web break to stop operation of the exhaust fan 49, shut oil the heating means 57, close the exhaust air flow path to the exhaust fan 49 and blower means 44 through closing of the isolation damper 54, provide a unidirectional air flow path from the blower 44 through the air delivery duct means 29 and exhaust air duct means 36 and 31 by opening of the bypass damper 55, and to raise the hood 18 by actuation of the cylinders 37. Other functions are performed when a sheet break occurs, and these will now be noted in the succeeding paragraphs.

In accordance with the principles of this invention, the occurrence of a web break is detected by a photoelectric cell or like device 60 (FIGURE 7) preferably positioned relatively close to the drying cylinder 11c, and if desired mounted by the hood means 18 adjacent the mouth 19 thereof. The break detector 65 is electrically connected to a control circuit 61 operating on 115 volts and 60 cycle current from leads L-1 and L-Z. The control circuit 61 operates a relay 62 in control of a pair of normally open switches 63 and 64 and a normally closed switch 65. The switch 65 when closed completes a circuit to a relay 66 in control of the exhaust fan motor 47, which in turn is supplied with power through leads L-3, L-4 and N. As is indicated in FIGURE 7, the blower fan motor 46 operates continuously in the event of a web break, and its operation is terminated only under control of a master switch 67.

With the exception of the blower fan and exhaust fan motors 46 and 47, the various earlier named functions of shutting oil the flow of heating fluid to the heating means 57, operating the dampers and raising the hood 18 are performed by a pneumatic system, although it will be readily apparent that a hydraulic system could as well be employed. The pneumatic system under control of the illustrated circuitry includes a main compressed air line 68 serving valve means 69, 7t) and 71, which in turn are respectively controlled by solenoids 72, 73 and 74. The solenoid 72 is electrically connected to the control circuit 61 and to the normally open switch 63, while the normally open switch 64 leads to the solenoids 73 and 74. The valve means 69 served by the compressed air line 68 controls the flow of fluid through lines 75 and 76 leading to the pneumatic motors 37 and thereby control raising or lowering of the hood 1%. The pneumatic motors 37 are shown somewhat diagrammatically in FIGURE 7, four pneumatic motors 37 being provided for effective raising and lowering the hood.

Compressed air from the main line 68 leads by branch line 77 to the valve means 70 and 71. The valve means '70 is first. in control of air motors 78 and 79 connected to the bypass damper 5'5 and isolation damper 54, respectively. The valve 70 further controls fluid flow through a branch line 80 leading to an air motor 81 for the exhaust fan damper 53, and through a branch connection 82 to an air motor 83 for the makeup air damper 51. The valve means 71, on the other hand, upon actuation by the solenoid 74 controls an air motor 84 to terminate steam how to the heater means 57.

The operation of the instant control system may be described as follows. When a sheet break occurs, the absence of the web sends a signal to the control circuit 61, operating the relay 62 and generally simultaneously the solenoid 72 in control of the valve means 69. Actuation of the relay 62 opens the switch means 65 which operates the relay 66 in control of the exhaust fan motor 47 .to shut off said motor. Actuation of the relay 62 further closes the switch means 64 to operate the solenoid 74, which is in control of the valve means 71, causing compressed air flow to the air motor 84 to shut olf steam flow to the heater means 57. The switch means 64 upon movement from a normally open to a closed position actuates the solenoid 73 and in turn the valve means 70 to close the isolation damper 54 and open the bypass damper by means of the air motors 79 and 78, respectively. Opening of the valve means 7% further provides a compressed air flow path through the conduit 80 to the air motor 81 to open the exhaust fan damper 53, and through the conduit 82, to open the makeup air damper 51. By action of the relay 62, the normally open switch 63 is closed, to complete a circuit to the solenoid 72, opening the valve means 69 and permitting compressed air flow to the pneumatic motors 37 to raise the hood 18 upwardly from the drying cylinder 11c.

Closing of the isolation damper 54 blocks the exhaust air duct means 30 and 31 downstream of the by-pass connection 56, so that any bits and pieces of broken paper web cannot be drawn down the exhaust duct portions 30:: and 30 to the blower 44. This prevents contamination of the blower 44 and clogging or other contamination of the exhaust air duct means 30 and 31 and the air delivery duct means 29. The exhaust air damper 53 and the makeup air damper 51 are in a fully open position, as described, and accordingly the blower mo tor 44 draws through the ducting 52 and 50 a relatively large supply of fresh air for direction through the air delivery duct portion 29d to the bypass connection 56, and from said connection past the open by-pass damper and through the duct portions 29b-31b and 29a31a through the nozzle means 32 and around the plenums 26a-d and outwardly through the hood means mouth portion 19.

It is of course appreciated that the air heated by the heater means 57 is at a relatively high temperature for efiective web drying, and that even when the heat supply to the heater means 57 is terminated, a substantial amount of residual heat remains in the air and that there remains a possibility of ignition of the relatively fine web particles within the hood 18. However, by this invention, since substantial volumes of ambient air are directed into the hood 18 from the blower 44, and since the hood 18 is raised away from the drying cylinder 110, there is essentially no likelihood of overdrying of the web particles such that ignition of the particles could take place.

Raising of the hood means 18 by the pneumatic motors 37 upon detection of a web break also permits ready rethreading of the web W about the drying cylinder 11c, and when the web W is properly in location, the photoelectric cell 60 through the control circuit 6-1 (assuming the main switch 67 is closed) closes the switch 65 and opens the switches 63 and 64 under action of the relay 62. Generally the reverse sequence of steps takes place, as compared with the steps described in connection with a web break'condition, and the exhaust fan motor is again started, heat supplied to the heater means 57, the isolation damper 54 opened and the by-pass damper 55 closed. The exhaust fan damper is closed, the makeup air damper 51 placed in a partially closed position, and the hood 18 lowered by the pneumatic motors 37. The normal air flow path is thereby restored, and in this cycle a portion of the moisture laden air is withdrawn from the system through the exhaust air duct portion 30g under action of the exhaust fan motor 49. The remaining portion of the moisture laden air is circulated by the blower 44- across the heating means 57 and through the air delivery duct 29 from which it issues thorugh the nozzle slots or openings in the nozzle plates 32. The heated air issuing through the openings 33 or slots 34 impinges generally normally against the paper web W, and under action of the exhaust fan 49, the air is withdrawn from adjacent the nozzle plates 32 in generally the directions indicated by the arrows in FIGURE 2. This air is then withdrawn from the hood interior through the exhaust air duct means 30 and 31, to be recirculated through the system as described. Air issuing from the slots or openings in the nozzle plates 32 is at substantial velocities of the order of from 15,000 to 30,000 feet per minute, and it is believed readily apparent that any control system to effect a reverse air flow of the exhaust air must have quick response or be rapid acting. Of course, the air delivered through the air delivery duct 20 and through the nozzle plates 32 is at a first or relatively high pressure, greater than the air pressure within the hood 18 and greater than the pressure of the air being exhausted through the duct means 30 and 31. The pressure within the hood 18 is of course greater than the air pressure in the exhaust duct means 30 and 31, and when a web break occurs and the isolation damper 54 is closed, the air following a unidirectional flow path through the duct means 29, 30 and 31 is at a fourth pressure between the orignal air delivery pressure and the exhaust air pressure. Thus, as compared with normal operation of the drying apparatus A, when a sheet break occurs pressure in the air delivery duct 29 decreases and the pressure in the exhaust air duct means 30 and 31 increases.

The instant control system effectively prevents combustion of readily ignitable fibrous particles upon occasion of a web break, and further prevents clogging of the nozzle means and ducting so that at all times a uniform air flow and uniform web drying are provided. It has been noted hereinabove that the dampers and hood could be hydraulically actuated in response to a web break signal, and of course other variations and modifications can be effected without departing from the novel concepts of this invention. 7

I claim as my invention:

1. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said Web, duct means delivering air to the hood, duct means exhausting air from said hood, means connecting the air delivery and exhaust duct means, means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, damper means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, means mounted to detect a break in said web, and control means responsive to said Web break detection means and connected to the means closing the connecting means and to the damper means to close the damper means and open the means closing the connecting means and provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs.

2. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, means for raising and lowering the hood, duct means delivering air to the hood, duct means exhausting air from said hood, means connecting the air delivery and exhaust duct means, means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, damper means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, means mounted to detect a break in said web, and control means responsive to said web break detection means and connected to the means closing the connecting means, to the damper means and to the means for raising and lowering the hood to close the damper means and open the means closing the connecting means and provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs while raising the hood to permit ready access to the web.

3. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, a blower for supplying air to said hood, air delivery duct means connecting the hood and blower, exhaust air duct means connecting the blower and hood, junction conduit means between the air delivery and exhaust air duct means, closure means in said conduit means closed during normal operation of the drying apparatus, damper means in the exhaust air duct means open during normal dryer operation and closed when a web break occurs to provide with the conduit means and closure means therein an air flow path of Y configuration from the blower through the conduit means to the hood, means responsive to a sheet break signal, and control means connected to said last-named means to open the closure means and close the damper means to provide the named flow path from the blower to the hood.

4. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, duct means delivering air to the hood, duct means exhausting air from said hood, means connecting the air delivery and exhaust duct means, damper means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, closure means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, heater means in the air delivery duct means, motor means connected to the damper means and to the closure means, means mounted to detect a break in said web, and control means responsive to said web break detection means and connected to the heater means and motor means for the damper and closure means effective when a web break occurs to shut off heating fluid to the heating means and to close the closure means while opening the damper means to provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs.

5. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, duct means delivering air to the hood, duct means delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, closure means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, an exhaust fan connected to the exhaust air duct to withdraw air from the hood during normal operation of the drying apparatus, means for raising and lowering the hood, heater means in the air delivery duct means, motor means connected to the damper means and to the closure means, means mounted to detect a break in said web, and control means responsive to said web break detection means and connected to the heater means, exhaust fan, means for raising and lowering the hood, and motor means for the damper and closure means effective when a web break occurs to shut ofi heating fluid to the heating means, stop the exhaust fan, raise the hood and to close the closure means while opening the damper means to provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs.

6. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, duct means delivering air to the hood, duct means exhausting air from said hood, means connecting the air delivery and exhaust duct means, damper means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, closure means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, motor means connected to the damper means and to the closure means, conduit means connected to a source of pressurized fluid and to the motor means for the closure and damper means, valve means in said conduit means, solenoid means connected to said valve means, means mounted to detect a break in said web, and control means responsive to said web break detection means and electrically connected to the solenoid means to actuate the valve means and port pressurized air to the motor means, closing the closure means and opening the damper means to provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs.

7. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, duct means delivering air to the hood, duct means exhausting air from said hood, means connecting the air delivery and exhaust duct means, damper means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the exhaust duct means during normal operation of the drying apparatus, closure means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, motor means connected to the damper means and to the closure means, an exhaust fan connected to the exhaust air duct to withdraw air from the hood during normal operation of the drying apparatus, pneumatic means for raising and lowering the hood, conduit means connected to a source of pressurized fluid and to the motor means for the closure and damper means and to the pneumatic means for the hood, valve means in said conduit means, solenoid means connected to said valve means, means mounted to detect a break in said web, and control means responsive to said web break detection means and electrically connected to the exhaust fan and to the solenoid means to terminate operation of said fan and to actuate the valve means for porting pressurized air to the motor means and to the pneumatic means for the hood, closing the closure means and opening the damper means to provide a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs while raising the hood to permit ready access to the Web.

8. Apparatus for drying paper webs and the like, comprising means providing a well supporting surface, a hood supported adjacent said surface during drying of said web, duct means delivering air to the hood, duct means exhausting air from said hood, flow control means in the air delivery and exhaust air duct means controlling the admission of air to the air delivery duct and the flow of moisture bearing air from the exhaust air duct, means connecting the air delivery and exhaust duct means, damper means closing the connecting means during normal operation of the drying apparatus, blower means connected to the air delivery and exhaust duct means directing air to the hood through the air delivery duct means and receiving air from the hood through the eX- haust duct means during normal operation of the drying apparatus, closure means in the exhaust duct means between the connecting means and the blower means open during normal operation of the drying apparatus and closed when a web break occurs to block return of air from the hood to the blower means, heater means in the air delivery duct means, motor means connected to the damper means and to the closure means, an exhaust fan connected to the exhaust air duct to withdraw air from the hood during normal operation of the drying apparatus, pneumatic means for raising and lowering the hood, motor means connected to the flow control means in the air delivery and exhaust air ducts, first conduit means connected to a source of pressurized fluid and to the motor means for the closure and damper means, second conduit means connected to said source and to the pneumatic means for the hood, and third conduit means also connected to said source and to the motor means for the flow control means, valve means in each of said first, second and third conduit means, solenoid means connected to each of said valve means, means mounted to detect a break in said web, and control means responsive to said web break detection means and electrically connected to the exhaust fan and to the solenoid means, whereby upon a web break the exhaust fan is stopped, and pressurized air is admitted to the motor means for the damper and closure means to close said closure means and open said damper means, providing a unidirectional air flow path from the blower means through the air delivery and exhaust duct means to the hood when a web break occurs, the pressurized air also opening the flow control means in the air delivery and exhaust air ducts, shutting off the supply of heating fluid of the heating means and raising the hood upon occasion of a web break to permit ready access to the web.

9. In an apparatus for drying a fibrous web, a rotatable drum providing a Web supporting surface, a hood extending about a portion of the circumference of said drum, means for raising and lowering said hood, an air delivery duct delivering air to said hood and the fibrous web passing about said drum, an air exhaust duct for withdrawing spent air from said hood and fibrous web, air moving means directing air through the air delivery duct to said hood and for withdrawing spent air from said hood through said exhaust duct, control means effective to direct the flow of air delivered by the air moving means through the air delivery and exhaust ducts out It 1 through the hood including damper means in said exhaust duct andby-passing damper means for directing air from said delivery duct to said exhaust duct, web break detecting means for detecting a break in the Web passing about said drum, and means operative under the control of said web break detecting means for raising said hood and operating said control means to operate both of said damper means to effect the delivery of air to said delivery and exhaust ducts out through the raised hood upon the detection of a break in the Web.

10. Apparatus for drying paper webs and the like, comprising means providing a web supporting surface, a hood supported adjacent said surface during drying of said web, means for raising and lowering said hood, a delivery duct for delivering air to the hood and Web, an exhaust duct for exhausting air from the hood, a con necting duct connected between said ducts, damper means in said connecting duct closed during normal operation of the drying apparatus, air moving means directing air through the air delivery duct and exhausting air through the exhaust duct, normally open damper means in said exhaust duct, and control means effective when a Web break occurs, to raise the hood, open said damper means in said connecting duct and close said damper means in said exhaust duct, to thereby provide a unidirectional air flow through the air delivery and exhaust ducts and out through the raised hood.

References Cited in the file of this patent UNITED STATES PATENTS 2,166,379 Skagerberg July 18, 1939 2,268,988 Hess et al. Ian. 6, 1942 2,928,185 Drew Mar. 15, 1960 2,939,222 Svavar et a1. June 7, 1960 FOREIGN PATENTS 748,080 Great Britain Apr. 18, 1956 770,240

Great Britain Mar. 20, 1957