US 2264329 A
Description (OCR text may contain errors)
Dec. 2, 1941. B. OFFEN DRYING APPARATUS Filed July 24, 19:57
2 Sheets-Sheet 2 INVENToR. Bae/VA /ao OFFEN, BY MM A TTORNEY.
Patented Dec. 2, 1941 PUNETED V STATES PATENT OFFICE 2,264,329 DRYING PARATUS Bernard Oen, Chicago, Ill. Application July l24, 1937, Serial No. 155,5?14
This invention relates to the art of drying web materials 'and the like.
This application 'covers improvements upon the apparatus set forth in my copending applications Serial No. 6453, led February 14, 1935, Serial No. 51,563, iled November 26, 1935, Serial No. 73,197, led April 8, 1936 and Serial No. 139,831, led April 30, 1937.
' The general object of this invention Ais to provide an improved apparatus for drying 4Web materials, and 'more particularly for drying such inaterals 'as freshly inked paper Vand the like.
It is 'another object of the invention to pr'ovide an improved drying apparatus capable 'of eii'ecting highly eicient drying o'f printed 'survfaces and the like, which 'uses a relatively small quantity 'of drying air.
It vis another object of 'the invention to provide a drying apparatus for drying freshly printed surfaces and the like, in which provision is made for recirculatin'g 'through the apparatus at least a portion of the air Withdrawn from contact with the surface, all of the air-circulating apparatus being built into and comprising part f 'a drying hood.
It is another object of this invention to provide a drying apparatus for drying freshly printed surfaces and the like, in which vprovision is made for the recirculation of air having a relatively low solvent vapor content after Contact With the surface to be dried, While other air Which has contacted With the surface to be dried and having a higher solvent vapor content is exhausted to the outdoor atmosphere.
It is ranother object of the invention to provide an improved apparatus for drying Vfreshlyprinted surfaces and the like, having novel and improved means for controlling the lrecirculation of 'drying air which has contacted with the 4surface to be dried.
It is another object of the invention to kprovide a drying hood having integrally associated therewith a fan for circulating air through the hood and in contact with the surface to be dried, 'and means within the hood Aandjcomizirising 'a part thereof for recirculating tothe fana portion of the air Which has contacted with the surface to be dried.
It is another object of the invention to provide apparatus for drying material such as freshly printed webs Which is substantially self-ccntained and vextremely compact, While providing for recirculation of air 'which' has contacted with the surface to be dried and for desired en'trol of lsuch recirculation.
It is another object iof the vinvention to provide an improved apparatus for drying materials such as freshly printed Webs 'which substantially 're'- duces the hazards of nre and explosion.
' in spaces so limited as to preclude 'o'r seriously interfere with the installation 'of hoods `l"xeretoe fore known. p
Another feature of the invention resides' in the provision of a drying hood having a plurality of exhaust ports, different of 'the ports being 'bonnected to different exhaust passages, "o`ne ofsad exhaust passages being adapted to discharge air to the outdoor `atr'nosphenor to a solvent recovery apparatus `o`r the like, While another of said exhaust passages 'is adapted to deliver air for recirculationthrough the hood. y
Another feature of the invention 'resides 'i'nth'e provision `of a drying hood having a plurality of exhaust ports, dilerent of the ports being connected toY different exhaust passages, 'one of vsaid exhaustpassages being adapted to discharge air to the outdoor atmosphere While another 'of said exhaust passages is adapted to deliver 'air lier recirculation through the hood and/or for discharge to the 'outdoor atmosphere.
Another feature vof the invention 'resides :in the provision of a drying lioodhavin'g supply and exhaust ports across which 'are extended screens of Wire or the like, o'f'rela'tivelynne Inesh. Heret'oiore, the hazards of re and explosion "in connection with theop-eieiion oi drying hoods, particularly hoods used for drying `printed surfaces, have' been very great. These hazards lhave been increased by lthe fact .that explosive and combustible rgases Within the hood are necessarily present -in considerable quantities. Any sparks r'lfia'me's beneath the hood are very apt to fhave, and have had, the effect of 'ignitihg and exploding great volumes of gas `tv'ithinftlie hood, with disastrous consequences. Applicants screens placed across the ports of the hood effectively prevent any lflames from 'entering Within the hood, Vand thus give vassurance against the 'combustio'n and'explosion of gases therevvithin.
The 'safety of applicants hood "is increased iurther by his novel arrangement of exhaust ports and exhaust passages. According to the invention, the exhaust ports which receive most of the solvent vapors evaporated from the surface to be dried are connected with an exhaust passage which leads to the outdoor atmosphere, and thus these vapors are discharged. If desired, of course, these vapors may be recovered in a solvent recovery system, as is well known. This air having a highsolvent vapor content is not recirculated, and thus the concentration of solvent vapor in air circulated through the hood is kept well below the explosive range. The air which is recirculated through the hood comes from an independent exhaust passage which connects to other exhaust ports adapted to draw ol air having a lower concentration of solvent vapors than the air drawn off through the first-mentioned ports. The air of low solvent vapor concentration is suited readily to absorb solvent vapors from the surface to be dried upon recirculation in contact therewith; and furthermore, recirculation of this air, because of its low solvent vapor concentration, will not result in reaching an explosive concentration of solvent fumes. Thus, applicants provision of separate exhaust passages and separate circulatory systems in connection therewith results not only in safer operation but also in more eihcient drying.
Other objects, features and advantages of the invention will be more apparent from the following description to be read in connection with the accompanying drawings, in which:
Fig. 1 is an elevational sectional View through a drying apparatus in accordance with the invention, taken on the line I-I of Fig. 2;
4 Fig. 2 is a front elevational View of the apparatus of Fig. l;
Fig. 3 is a plan view ratus ,of Figs. 1 and 2;
Fig. 4 diagrammatically illustrates a supply nozzle having a screen through which all of the air passing to the supply nozzle passes, and
Fig. 5 illustrates diagrammatically a fire screen covering one of the exhaust ports.
of a portion of the appa- Referring now to the drawings, numeral I0 designates generally a drying hood. Formed in the face of the hood and extending substantially across the width thereof in substantially horizontal direction, at a point near the central portion of the hood, is formed exhaust port II. At opposite sides of the face of the hood and extending lengthwise of the hood are exhaust ports I2. This arrangement of exhaust ports and the considerations which render its utilization advantageous are set forth in copending application Serial No. 139,831, filed April 30, 1937, and above referred to. It is t0 be understood, however, that the present invention is not limited to this particular arrangement of exhaust ports, but for the reasons set forth in said copending application it is preferable to use this arrangement. Exhaust port I I connects with an exhaust passage I3 formed within the hoo-d, and exhaust ports I2 connect with another exhaust passage, I 4, formed within the hood. Formed in the upper portion of the hood is an exhaust chamber I5 into which exhaust passage I3 discharges. Exhaust chamber I5, in turn, discharges through exhaust connection I6 which is adapted to discharge to the outdoor atmosphere air passing therethrough, or to supply such air to a solvent recovery system. Since solvent recovery systems are well known in the art and do not, per se, form part of this invention, noV further description of or reference to them is deemed necessary here. It is to be understood, moreover, that whenever reference is made herein, in either the description or the claims, to exhausting air to the outdoor atmosphere, this expression shall be understood to include and cover supplying air to a solvent recovery or similar system.
Also formed within the upper portion of the hood Ill are supply chambers I6a and Ib. As shown in Figs. 1 and 3, supply chambers I6a and I6b are separated by a space forming part of exhaust chamber I5, so that throughout the width of the hood supply chambers Ia and |617 are independent of each other. As best seen in Fig. 2, the supply chambers Ilia and I6b taper gradually across the width of the hood. Thus, air delivered to supply chambers I6a and I6b through supply connection I'I is equally distributed across the width of the hood.
Supplychamber I 6a communicates with supply passage I8a and supply chamber |617 communicates with supply passage Ib. It will be noted that exhaust passage I3 is interposed between supply passages Ia and IBb, and that supply passage Ib is interposed between exhaust passages I3 and I4.
The freshly inked surface to be dried, I9, is routed upwardly adjacent the hood I0 over rollers 20. Preferably, sealing member 2| is provided to enclose the rollers in a manner well known and understood in the art. At the face of the lower portion of the hood are provided a plurality of nozzles 22h adapted to discharge air from supply passage Ib against the surface IS. Preferably, the nozzles are arranged to discharge air against the web and in an upward direction. At the face of the upper portion of the hood are provided a plurality of supply nozzles 22a. adapted to discharge air from supply passage I8a against the web and in a downward direction.
Thus, nozzles 22a and 22h both discharge air toward the central portion of the hood. In a preferred form of the invention, the nozzles 22a and 22h extend across the width of the hood to form relatively long narrow slots, but it is to be understood that, if desired, any other type of nozzle formation may be used.
Mounted upon the hoodY I0, and adapted to be rotated therewith upon rollers 23 of the supporting structure, is a pedestal base 24. Base 24 carries a fan 25 and a driving motor therefor, 26, the discharge of fan 25 being directed through supply connection II.
Exhaust passage III discharges into an exhaust passage 2l which preferably extends across the width of the hood at the top thereof. Exhaust passage 21 is separated from exhaust chamber I5 by a plate or the like, 28, which is preferably removable. An end of exhaust passage 21 is adapted to communicate with and to supply air to mixing chamber 29 at the inlet to fan 25. Mixing chamber 29 is also adapted to receive, through opening 30, air from the ambient atmosphere. Thus, there is no need for providing ducts as has been commonly done heretofore, although auxiliary supply ductwork may be used in connection with the invention, if desired. v.The supply of air through opening 30 is adapted to be controlled by adjustable dampers 3l, while dampers 32 control the supply of air from passage 21 to mixing chamber 29. Thus, by controlling the setting of dampers 3| and 32, the proportions of fresh and recirculated air supplied to the fan may be variably controlled.
Central exhaust port II, being relatively large,
I3 is `not adapted for recirculation. If desired,
'air exhausted through passage 13 may be throttled, vas -by suitable danipe'ls, so that a greater volume kof y"fair will be available "for recirculation.
If it is desired `to -recirculate air from passage I4, the removable plate 2"8 is positioned as shown 7 in Fig. l, to -provide,"separjtin vbetween passages 2'1 and t5, and thedam-pers "32 are opened. Thus, the air from passage 2l will be recirculat'ed at `a rate determined by the relative positions of -dampers and '32 ivllio'h control the intake to '-7 the fan '25. Fan 25 recirculate's to the hood air withdrawn from passage T21 and supplies thereto air withdrawn 'from `the `arn'b'ier'i't atmosphere. An auxiliary fan T2511, is preferably provided in duct VI6 to eielct the discharge through duct I5 i of vvapor-laden air passing through port vII and passages I3 and I5.
In applications where it isdesired to exhaust all of the air which has contacted the web and to recirculate none, the dampers 32 may be closed and the plate 28 removed. In this case, air vfrom passage 2l will be delivered into exhaust chamber I5 and passed therefrom to exhaust duct i6, along with air from exhaust passage I3.
Should it be desired to recirculate only a por- 5 tion oi the air from passage I4, while exhausting the remaining portion, plate 128 may be partially removed, and damper's 32 may be partially opened.
In 'systems heretofore known, the usual method of recirculating has been to rdraw off from a common exhaust chamber one portion of air to be exhausted and another portion of air tol be recirculated. This arrangement has proven unsatisfactory since it `necessarily pits the recirculation fan and the exhaust fan against each other.
To lillustrate the inadequacy of the common exhaust passage arrangement, let it be assumed that exhaust passages I-'3 'and II both feed into the exhaust chamber I5 and that chamber I5 is connected to both the exhaust duct I6 and theinl'et to `mixing `chamber 2`9. Under this condition, the exhaust fan, 'in order -to exhaust air from the system, would'have to create a negative pressure 'within 'the exhaust chamber I5. Thus, the fan supplying air to the hood would, in order to Veiiect recirculation, have to kdraw air from the chamber I5 which was ata negative pressure. Thus, the 2re'c'ir"culatil'ig fan would require an additional amount'of power vto jovercome the nega-tive pressure within `*exhaust chamber I5, if this fan is to circulate air through the hood in the intended manner. Y A
A further disadvantage of this arrangement would be 'the necessityA 'for `automatically controlling the recirculating damper's 32. It is general practice in the V'o'l'oeration of drying hoods to operate only the exhaust fan at the time when the presses 4from which the websisrfed to the hood are started up. 'The exhaust Afans are started before the presses in order to insure against the l V'accumulation ofY explosive gases within fthe hood.i The 'cir.culation 'offairfcreated by the' operation :of 'the `exhaust 'fans is's'ufc'ent,
vchamber and thence out through the exhaust duct, without being circulated lin `contact with the 'web to be dried, thus trapping the fumes 'under the hood along the web, permitting an 'explosive condition to develop. As the web travel increases in speed, however, andas the recirculation `fan becomes operative, the lrecirculating fdanpers may be open. But -such operation of the V'darnpers requires automatic control.
Another disadvantage -of using a common exhaust `chamber is that this arrangement renders it exceedingly diflicult 'to obtain desired rates of air exhaust through the various exhaust portsL of the hood. Thus, while it is desirable to maine tain "a relatively rgreat ra-teof 'air withdrawal vat that part of the hood where most of the fumes v`are given ofi", "it is also desirable to maintain 'a lower rate of air withdrawal through ports serving portionsgof the hood where Iless fumes'are given orf. When, however, a ycommon exhaust chamber is used to Vwllich all of lthe exhaust ports supply air, the pressure d'iierential across each -of these ports is approximately the same and hence the rate of air vwithdrawal through 'each port -is lapproxirnat'ely the same. While dampers at the ports may overcome this condition to an extent, to provide a degree of control, such construction necessarily complicates the d-esign of the hood, increases the cost of its inan-v ulfacture, renders its operation more complex, and should be avoided. a Y
By providing separate exhaust vpassages serv.. ing different and independent exhaust chambers, 'applicant eiectively overcomes the disadvantages just described. The exhaust fan and the recirculating fan, according to the inventiohgdo not buck each otherand thus the power input to applicants Vfan motors is considerably less than in systems where a commonexhaust cham'- ber is) used. Moreover, there is no need, inapplioants system, for providing automatic control of the recirculating dampers. These lmaybe left in `any'desired position throughout all phases of operation, including the starting-up periods. During the starting-up period, while the exhaust fan is operative, all of the air exhausted by Athis fan will be circulated in contact with the web to be dried. Furthermore, applicants arrangement provides for independently and closely controlling the rates at which air is withdrawn through the dilerentexhaust passages and at which the air travels ,through the various parts of the hood. Thus, the air supply may be delivered at the proper velocity and may be properly distributed, and this air may then be withdrawn through each of different exhaust circuits vin any ldesired proportions, for recirculation or for discharge from the'syst-em; and this may beaccomplished, if desired, without recourse to dampers atthe various exhaust ports but merely byvcontrolling the speed of the exhaust and supply fans or by controlling 'dampers in-passag'es 'I3 and 14. Applicants arrangement', in'tvhieh separate passages are used for exhaust and for recirculation, permits the recirculation and exhaust to be substantially independent of each other, with the results that operation is much more economical and that a much greater degree of ilexibility is provided than in conventional systems using common exhaust passages.
If desired, air at room temperature may be employed for drying the surface. However, it is preferred to provide heating coils 33a in supply passage I8a and heating coils 33h in supply passage I8b for heating air supplied to the surface I9, these heating coils being supplied with heating medium in any desired manner. The heating coils are preferably individually controlled. Individual control of the heating coils is of particular advantage where it is required to dry inks or varnishes or the like which tend t become tacky or sticky at temperatures above normal temperatures. In such applications only the coils 33h will be supplied with heating medium. Thus, the air delivered by nozzles 22h will be warm and effect rapid drying of the surface, while the air delivered from nozzles 22a will be of normal room 4temperature and will tend to set the inks and varnishes on the surface before the surface passes from beneath the hood. On the other hand, in drying materials which have a relatively great tendency to case harden, the reverse procedure might be used, heating coils 33a only being supplied with heating medium in such case. Thus, the material to be dried will be subjected rst to relatively low temperatures and then, after most of the drying has been accomplished, the remainder of the drying will be accomplished at slightly higher temperature. This procedure completely avoids any case hardening of the material, while accomplishing efficient and complete drying.
As shown in Fig. 4, which illustrates one of the nozzles 22a., all the air delivered to the nozzle is passed through a screen 34. Screen 34 is preferably formed of metal and is preferably of relatively ne mesh, and it may be of double thickness. Screen 34 may be secured to the hood in any desired manner, as by studs 34a. The purpose of screen 34 is to prevent flames from the vicinity of the web from extending into the interior of passage I8a. The nozzles 22h are similarly protected for the same purpose and so also are the exhaust ports I I and I2. The screen protection for exhaust port II is indicated at 35 and the screen protection for one of the ports I2 is shown at 36. Because air flows into the exhaust passages through these exhaust ports and because the air in the exhaust passages is, generally speaking, much more inflammable and explosive than air at the supply ports or elsewhere within and beneath the hood, it is extremely important that these screens be provided at the exhaust ports.
To provide for the withdrawal of air through all portions of exhaust ports I2 at a substantially equal rate, and to accommodate the volume of air withdrawn therethrough while conserving space, exhaust passage I4 is formed generally in the form of a rectangle, from the lower central portion of which there has been removed an isosceles triangular section. This is indicated by the dotted lines Ida in Fig. 2, which define the lower contour of passage I4.
By the term hood or drying hood is meant an organized assembly of apparatus as illustrated, for example, in Fig. l, comprising an enclosure including air supply ports, air supply passages serving 'said ports, exhaust passages for withdrawingiair from the enclosure, means for passingma'web through the enclosure, to be subjected tothe drying action of the air delivered and removed through said passages, air supply and exhaust fans, and related structure combining all of the parts into a workable unit for the drying .ofinked webs, substantially as described.
y Since many changes may be made in the invention without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not in a limiting sense, applicant limiting himself only as indicated in the appended claims.
Having described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:
l. In a drying hood of the character described, means for supplying air to a surface to be dried. rst exhaust port means adapted to withdraw air from said surface after it has contacted therewith, means forming a first exhaust passage connecting with said first exhaust port means, second exhaust port means adapted to withdraw air from said surface after it has contacted therewith, means forming a second exhaust passage connecting with said second exhaust port means, means for exhausting from the hood air from one of said exhaust passages, means for recirculating in contact with the surface air from the other of -said exhaust passages, means for providing communication between said rst exhaust passage and said second exhaust passage, and adjustable means for rendering inoperative said last mentioned means.
2. A drying hood of the character described, including means forming at least one air supply passage, means including a fan for delivering air through said passage to a surface to be dried, means forming a plurality of return ports, means forming a plurality of return passageways severally communicating with said return ports, a plurality of discharge chambers adapted respectively to receive return air from said diierent return passages, means for delivering air from one of said chambers to the inlet of said supply fan, an exhaust blower adapted to withdraw air from the other of said chambers, means providing communication between said exhaust chambers, and adjustable means in control of said last mentioned means.
, 3. A drying hood of the character described including means for supplying air to a surface of a web to be dried, first exhaust port means adapted to Withdraw air from said surface after it has contacted therewith, said rst exhaust port means extending through a wall of the hood and being arranged substantially crosswise of the hood and extending over substantially the entire width of the path followed by the web as it is moved through the hood to receive the greater portion of fumes evaporated from said surface by said air, means forming a first exhaust passage connecting with said first exhaust port means,
second exhaust port means adapted to withdraw air from said surface after it has contacted therewith, said second exhaust port means being arrangedA longitudinally of the hood and substantially. atthe edges `thereof and adjacent the ends of the first exhaust port means to receive air having a lower concentration of fumes evaporated from said surface, means forming a second exhaust passage connecting with said second exhaust port means, means for lexhausting from the hood air from said rst exhaust passage, and means for recirculating in contact with the surface air from said second exhaust passage, and means to move a Web through the hood.
4. In a drying hood of the character described means for supplying air to a surface to be dried, rst exhaust port means adapted to Withdraw air from said surface after it has contacted therewith, said first exhaust port means being arranged to receive the greater portion of fumes evaporated from said surface by said air, means forming a rst exhaust passage connecting with said rst exhaust port means, second exhaust port means adapted to Withdraw air from said surface after it has contacted therewith, said second exhaust port means being arranged to receive air having a lower concentration of fumes evaporated from said surface, means forming a second exhaust passage connecting with said second exhaust port means, means for exhausting from the hood air from said rst exhaust passage, means for recirculating in contact with the surface air from said second exhaustl passage, and adjustable means for providing communication between said first exhaust passage and said second exhaust passage.