US2831269A - Drying apparatus - Google Patents

Description

' 2 Sheets-Sheet 1 April 22, 1958 J. K. BRUCE DRYING APPARATUS Filed Feb. 2. 1953 INVENTOR. JOHN K. BRUCE April 22, 1958 J. K. BRUCE DRYING APPARATUS 2 Sheets-Sheet 2 Filed Feb. 2, 1953 3 5mm 9E wmommmq INVENTOR.

JOHN K. BRUCE v vm mm wm M W W A T TORNE V United tates Patent DRYHNG APPARATUS John K. Bruce, South Pasadena, Calif., assignor to Albert Van Luit & (30., Los Angeles, Calif., a corporation of California Application February 2, 1953, Serial No. 334,567

6 Claims. (Cl. 34-155) tinuous or discontinuous paint, ink or other coating which.

requires drying.

The invention is excellently suited to wallpaper drying and is described in this application, although in no way so limited. At present, wallpapers are dried after painting or printing either by festooning the elongated strips thereof on racks built for such purpose or by carrying the paper over very large internally heated drums. Each of these'methods has significant and characteristic disadvantages. Festooning requires an inordinate amount of handling and drying time and also, as a consequence, an excessive amount of plant space if any appreciable footage production is involved. Heated drum drying has a tendency to adversely affect the color values of the paper coating and to reduce the moisture content of the paper itself. Such reduction in moisture content may i be the cause of color instability, and, in addition, it makes the paper difficult to handle, store and apply. A great deal of time and money has been expended in the past in an effort to develop a rapid non-destructive method of drying wallpapers, and I have now discovered such a method. The invention lies in a method of drying coated materials which comprises passing the material through a drying zone, while circulating through the zone and in contact with the coated surface of the material, a volume of moist, warm air. The method is unique in that drying does not depend upon contacting the paper with a heated object or surface, nor does it depend upon superheated steam or high temperature gases, both of which techniques have been shown to be unsuited for this purpose.

In its preferred embodiment the drying method of the invention comprises circulating in contact with the coating to be dried a large volume of air which has been heated to a temperature in the range of about 180 F. to about 200 F. and humidified to a relative humidity of between about 75% and 95%. For drying wallpaper, 85% relative humidity is preferred. The temperature of the air is carefully maintained below the boiling point of water so as to prevent water loss from the paper itself. As a consequence of the sub-boiling temperatures and relatively high moisture content of the drying media, the dried paper still has a moisture content, after drying, within the so-called mill tolerance range of approximately to 7%. This water content is apparently quite important in maintaining color stability, shelf life and workability.

Drying is accomplished in accordance with the described method in a fraction of the time required for rack drying, which is the only other presently known method of drying without adversely affecting moisture content and color stability. By way of example, a water Patented Apr. 2-2, 1958 base wallpaper paint will rack dry in approximately onehalf hour and is dried in accordance with the invention in approximately one to two seconds. The so-called transparent base wallpaper paints require upwardly of three hours for rack drying and something less than twenty seconds by the method of the invention. In addition to this appreciable time saving, the method affords a tremendous economy of space. A single installation for carrying out the method of the invention occupying approximately 40m 50 square feet will, in a days time, accommodate a quantity of paper requiring hundreds of square feet of rack drying space.

The invention is also directed to apparatus for drying coated materials in accordance with the described method. In this aspect the invention comprises a housing having side walls, a conveyor having a delivery flight and a return flight passing through the housing, means for admixing steam and air, means for heating the air either prior to, during or after mixing with steam, and means for circulating the air in the'housing and in the vicinity of the surface of the conveyor and preferably concurrently to the direction of conveyor travel. To minirnize heat load, in a preferred embodiment of the incention, the air is recirculated through the mixing and heating means for redelivery into the enclosed chamber.

The invention will be clearly understood in relation to both method and apparatus aspects thereof from the following detailed description taken in conjunction with the accompanying drawing, in. which:

Fig. l is a plan view of one form of apparatus of the invention;

Fig. 2 is a side elevation of the apparatus of Fig. 1;

Fig. 3 is a longitudinal vertical section taken on the line 3-3 of Fig. 1; and

Fig. 4 is a vertical section taken on the line 44 of Fig. 1.

Referring to the drawing, the illustrated apparatus comprises a framework 10 including longitudinally extending I beams 11 and 12 supported on pedestals as illustrated. A conveyor 14 includes a section 14A extending between pulleys 15, 16 mounted between the beams 11 and 12 and respectively adjacent opposite ends thereof, and a section 14B beneath section 14A and over a third pulley 18 mounted beneath the beams 11 and 12 and approximately below the pulley 15. A housing 20 is supported by the framework 10 substantially enclosing a major portion of the conveyor 14. The housing includes a first longitudinal extending compartment 22 overlying the upper surface of the conveyor 14, a horizontally disposed partition 22A forming the upper closure of the first compartment 22 and the bottom closure of asecond longitudinally extending compartment 23 overlying the compartment 22 and giving access thereto at one end through a port 24 in the partition 22A and a third section 28 underlying the conveyor section 14A.

The port 24 is provided with a screen 26. In preferred practice, as illustrated, the conveyor section 14B is carried through the lower section 28 of the housing between pulleys 16 and 18. The conveyor need not be sealed through the housing walls but the openings therein through whichthe conveyor passes in ingress and egress are held at a practical minimum size to minimize breathing. A pair of ducts 30, 32 communicate between the upper chamber 23 and the lower chamber 28 and provide means for gas flow from the upper to the lower chamber.

An air heater and mixer 34 in the form of a generally rectangular chamber is supported on the framework adjacent an end of the housing 20 designated as the input end, and, as shown in Fig. 4, opens at one face 34A into the lower chamber 28. A blower 36 is mounted above 3 .the housing 20 and adjacent the input end thereof, the

blower being driven in a conventional manner by a motor 37. The blower 36 takes suction through a duct 40 opening into the top of the heater and mixer 34 and delivers through a duct 42 into compartment 22 of the housing.

The heater 34 includes heating coils 44, which may be steam coils, an electric heater, or the like, to maintain the temperature of the air drawn from the lower chamber 23 through the heater and into the duct 4% at a predetermined value. A water heater is mounted adjacent the air heater 34 and includes conventional immersion-type heating elements ShA, 5GB for heating a body 52 of water contained in the heater St). A trap 54 is mounted above the heater 5G and includes a chamber 54A, an inlet 56 opening into the upper end of the chamber and communicating with the water heater and a drain 57 opening between the bottom of the chamber 54A and the water heater 50, the drainpipe 57 extending below the level of water in the heater 50. An outlet 58 communicates between the upper portion of the chamber 54A and the air heater 34.

The air heater 34 serves the double purpose of maintaining the desired temperature of the air stream passing therethrough and also as a mixer for mixing steam entering through conduit 58 and air entering from the housing chamber 28 to maintain the proper moisture content in the circulating air.

A rewind roller 60 is supported on a shaft journaled in pillow blocks 62, 63 on opposite members 11 and 12 of the framework 10. A torque motor 64 is mounted on the side of the framework to drive the shaft 133i and to maintain a predetermined take-up tension on the roller 60.

Between the outlet end of housing 29 and the rewind roller 60 a tube 66 is supported transversely above the conveyor 14 and is provided with a linear slot 56A directed downwardly toward the upper surface of the conveyor. A second blower 63 is connected through a conduit 69 to deliver dry air to the tube 66 from which it escapes through slot 66A against the surface of material passing along the conveyor 14. Some types of coating compounds are fusible at the drying temperature within the housing and with such compounds it is important that they be cooled prior to rewind. Such cooling is elfectuated by the auxiliary dry air source furnished by the blower 63 and distributing tube 66.

The conveyor 14 is preferably perforated to take advantage of the pressure drop between the upper and lower housing compartments. Since blower 3h effectively takes suction on compartment 28 and discharges into compartment 22, material carried on the perforated conveyor is held firmly thereon as a consequence of the inherent pressure differential.

The operation of the apparatus as illustrated is as iollows:

Air circulation within the housing is initiated by starting the blower 36, the circulation being in the path indicated by the arrows, i. e. through the lower section 22 of the upper portion of the housing from inlet to outlet ends of the housing escaping from compartment 22 at the downstream end through port 24 into the upper section 23 of the upper portion of the housing, flowing therein in the reverse direction to and through ducts 30, 32 into the lower section of the housing. The air passing into the lower section of the housing flows through the open face 34A of the air heater 34 into the heater wherein it is mixed with steam entering the heater from the steam drier 54, the moist air mixture being maintained at the proper temperature by means of the heating element 44 in the heater 34. Blower 36 takes suction on the heater 34 through duct 4% to complete the air flow cycle.

The volume of air flow is determined by the capacity of the blower 36 and any escape of air from the system is automatically compensated by drawing new air into the system. In other words, the housing breathes" to a certain extent through the ports of entry and exit of the conveyor 14. When the air temperature and saturation are within the desired range, conveyor 14 is started and coated material to be dried is supplied thereto at the right-hand end as viewed in Fig. 3.

As previously mentioned, the conveyor is perforated to take advantage of the pressure diiferential existing between the lower portion 28 of the housing and the section 22 of the upper portion of the housing to hold the coated material against the surface of the conveyor. The rewind roller 16 automatically pulls the paper through the drier at a rate corresponding to the rate of introduction. Introduction of coated paper may be continuous, or intermittent and the rewind roller may be operated accordingly.

Intermittent feed is required, as for example where the coated material, say wallpaper, is coated by a process of silk screening. In the silk screening process a section of paper is coated with a predetermined design and color and it is thereafter released into the drier while an immediately following section is similarly coated, so that the paper progresses through the drier in stages and at a rate determined by the silk screening process. in a typical operation involving the drying of wallpaper as coated by silk screening, paper is passed through the drier as described and taken up on the rewind roller 16, and after a given length of paper has been coated in a first operation it is returned from the rewind roller 60 to pass through a second silk screening procedure and again through the drier for applying a second portion of the final design which, in the silk screening process, is applied in increments.

If the material to be dried is being roller coated, it may be fed through the drier in a continuous manner and by means of the torque rewind motor at a synchronous speed with the coating speed.

Port 24, through which air circulates between the lower and upper portions 22 and 23 respectively of the upper portion of the housing, is provided with a screen 26. This screen prevents any paper from being sucked through the system in event of breakage within the drier and greatly facilitates quick resumption of operation in the event of such breakage.

The desired aim in drying the coating superimposed on any base material is to avoid, to the greatest possible extent, any change in the moisture content of the mateial itself. For example, wallpaper stock has a so-called mill tolerance of from 5% to 7% moisture. That is, suitable wallpaper stocks have a moisture content in this range when delivered from the paper mill. Any drying process which disturbs this moisture content, either by increase or decrease thereof from the specified mill tolerance range, is objectionable as materially affecting the properties of the paper itself and as apparently being responsible for changes in color values of the coating as occurring in such processes. The only drying process now known in the wallpaper art which satisfies the requirement with respect to effect on moisture content of the base stock is the process of racking or festooning. As pointed out, this process involves an undue amount of time and requires a great deal of space. By selection of operating conditions, as herein specified, drying with moist heated air in the manner described is accomplished in a minimum amount of time and without disturbing the moisture content of the paper stock.

The process is highly economical, the heat load being extremely small because of the very low specific heat of the material being dried. At the same time the process eifectuates considerable saving because of the amount of racking or festooning space it replaces and because of the racking or testooning time and labor that is eliminated.

I claim:

1. Apparatus for drying coated material comprising a substantially enclosed housing having side walls, a conveyor passing through the housing from a feed end to a discharge end and extending transversely substantially from side wall to side wall, the conveyor dividing the housing into end to end extending upper and lower sections, means providing a passageway for gas flow between the discharge end of the upper section of the housing and the lower section of the housing, a mixing chamber communicating with the lower section of the housing, heating means disposed in the mixing chamber, means operable to introduce water vapor into the mixing chamber, and means operable to circulate air from the lower section of the housing through the mixing chamber into the upper section of the housing adjacent the feed end to flow concurrently in contact with coated material carried through the housing on the conveyer.

2. Apparatus for drying coated material comprising a substantially enclosed housing having side walls, a conveyor passing through the housing from a feed end to a discharge end and extending transversely substantially from side wall to side wall and between end to end extending upper and lower sections of the housing, an air duct communicating with the discharge end of the housing at the upper section and extending between the upper and lower sections of the housing, means for introducing warm moist air into the upper section of the housing adjacent the feed end thereof to circulate the air in concurrent contact with the upper face of the conveyor, and means for withdrawing air from the lower section of the housing, said conveyor being pervious to gas flow therethrough, the pressure differential between the upper and lower sections of the housing biasing the coated material toward the conveyor.

3. Apparatus for drying coated material comprising a substantially enclosed housing, a conveyor passing through the housing from a feed end to a discharge end, the conveyor dividing the housing into upper and lower sections and being pervious to gas flow therethrough, a partition in the upper section of the housing dividing that section into lower and upper compartments, the lower compartment overlying the conveyor and the upper compartment overlying the lower compartment and communicating with the lower compartment by means of a port in the partition located near the discharge end of the housing, ducts communicating between the upper compartment of the upper section of the housing and the lower section of the housing at a point spaced from the discharge end of the housing, means operable to pass warm moist air into the lower compartment of the upper section of the housing adjacent the feed end thereof, and means operable to withdraw air from the lower sec tion of the housing.

4. Apparatus for drying coated material comprising a substantially enclosed housing having side walls, a conveyor passing through said housing having a delivery flight and a return flight, said delivery flight extending from a feed end to a discharge end of said housing and extending transversely substantially from side wall to side wall, said delivery flight defining end-to-end extending first and second sections of said housing, an air duct communicating with the discharge end of the housing at theupper section and extending between the first and second sections of the housing around said delivery flight, means for introducing warm moist air into the first section of the housing adjacent the feed end thereof to circulate the air in concurrent contact with the face of the delivery flight of the conveyor, and means for withdrawing air from the second section of the housing.

5. Apparatus in accordance with claim 4 and wherein said conveyor is pervious to gas flow therethrough, the pressure diiferential across the delivery flight between the first and second sections of the housing biasing the coated material toward the delivery flight of the conveyor.

6. Apparatus for drying coated wallpaper comprising a substantially enclosed housing having side walls and a feed end and a discharge end, moving means for moving wallpaper to said feed end through said housing and out said discharge end, support means within said housing contacting the uncoated side of said wallpaper, the support means and the wallpaper in contact therewith extending substantially from side wall to side wall of said housing thereby dividing the housing into end to end extending first and second sections, means providing a passageway for gas flow between the first section of the housing and the second section of the housing, a mixing chamber communicating with the second section of the housing, heating means disposed in the mixing chamber to heat the air to a temperature of about between 180 F. to about 200 F., means operable to introduce water vapor into the mixing chamber to humidity the heated air to a relative humidity of between about and and means operable to circulate air from the sec- 0nd section of the housing through the mixing chamber into the first section of the housing to cause drying of the coating material on the wallpaper.

References Cited in the file of this patent UNITED STATES PATENTS 507,304 Barney Oct. 24, 1893 734,949 Prince July 28, 1903 1,034,112 Hopkins July 30, 1912 1,463,923 Nelson Aug. 7, 1923 1,591,102 Randolph July 6, 1926 1,979,346 Rappolt et a1 Nov. 6, 1934 2,012,115 Woodrufi Aug. 20, 1935 2,128,697 Ettl Aug. 30, 1938 2,306,607 Horton Dec. 29, 1942 2,677,900 Mann May 11, 1954

Images