US3406466A - Drying apparatus - Google Patents

Description

1953 H. 1 SMITH. JR 3,406,466

DRYING APPARATUS Filed July 12, 1967 5 Sheets-Sheet l j: 9 j a a 3 k K 3r 0/ 1 l 3 w 1 i 9 g Kg INVENTOR L Horace L. Sm/fh, Jr.

a H 7 %%%Z@%% 28 ATTORNEYS Oct. 22, 1968 H. 1.. SMITH, JR

DRYING APPARATUS 5 Sheets-Sheet 2 Filed July 12, 1967 ATTORNEYS Oct. 22, 1968 H. L. SMITH. JR 3,406,466

DRYING APPARATUS Filed July 12, 1967 5 Sheets-Sheet S- Horace L. Smith, Jr

/ I jwflgwyw/w ATTORNEYS United States Patent 3,406,466 DRYING APPARATUS Horace L. Smith, Jr., Richmond, Va., assignor to White Consolidated Industries, Inc., a corporation of Delaware Filed July 12, 1967, Ser. No. 652,887 5 Claims. (Cl. 34-155) ABSTRACT OF THE DISCLOSURE Drying apparatus for sheet and web type material including a belt type carrier having a material supporting leg disposed betwen the radiant heating-fluid impingement unit and an array of radiant heaters with the material supporting surface of the carrier facing the heating-impingemerit unit. This surface is polished and may have a release type coating thereon, and the opposite surface is treated to produce a high coefficient of absorption for radiant energy. Provision is made for pressing the material to be dried onto the carrier at one end and for separating it from the carrier at the opposite end.

Background, summary, and objects of the invention The present invention relates to apparatus for drying web, sheet, and like materials and, more specifically, to apparatus which is particularly adapted for drying materials having very low wet strength and materials which are coated to provide a smooth or glossy surface.

Heretofore, toilet paper, facial tissue, and similar lightweight products with a low wet strength have been dried on Yankee dryers. These are cast iron, steam-heated drums having polished or chrome-plated surfaces to produce a smooth surface on the product and are made in very large diameters (12-18 feet). This is because the product must be completely dried between the points where it is pressed onto and taken off the drum, which are approximately 270 apart.

Yankee dryers have an extremely high initial cost. In fact even the smaller dryers of this type may cost over $100,000.

Such dryers are also expensive to operate. This is in part because they must be operated at low temperatures (generally a maxium of 350 F.) because of the problems in handling the pressures associated with high temperature steam and because of the limitations on steam pressures imposed by insurance companies and various governmental regulation bodies. Drying operations conducted at low temperatures are notoriously inefficient and correspondingly expensive to conduct.

Also, devices known as doctor blades are employed to peel the dried product from Yankee dryers at the takeoff point. These wear grooves in the surface of the dryer so that its surface has to be reground to a smooth finish at frequent intervals.

The refinishing is itself expensive. In addition, repeated regrindings reduce the thickness of the dryer shell. This reduces the maximum pressure which the shell can withstand, which requires a decrease in the temperature of the steam employed with a corresponding decrease in the efficiency of the drying operation.

Glossy coated products are dried in much the same manner as low wet-strength products such as those described above except that the dryers are generally smaller in diameter. Accordingly, the previously known dryers for such materials have much the same disadvantages as Yankee dryers. In addition, these dryers often impart an objectional curl to the product because it is only dried from one side.

Another disadvantage of both Yankee dryers and the dryers heretofore employed to dry coated products is that drying temperatures (and accordingly, drying rates) and other process parameters cannot be changed during the operation of the dryer as a practical matter. This is a significant drawback since a superior product can be produced if the drying rate and other parameters can be altered to accommodate variations in the product delivered to the dryer.

It is an important and primary object of the present invention to provide novel, improved dryers for products of the type described above which do not have the disadvantages of the dryers by which they have heretofore been dried.

The novel dryers disclosed herein, by which the foregoing and other important objects of the present invention are attained, include an endless belt type carrier with a polished surface to which the product being dried is in elfect glued by a press roll or similar device. One or more radiant heating-fluid impingement units facing the exposed surface of the product dry it by a combination of radiant energy and impinging air or other fluid.

At the same time the product is preferably heated from the opposite side by conduction through the belt. The belt, in turn, is heated by radiant energy emanating from heaters disposed on the opposite side of the carriers material supporting leg from the radiant heating-fluid impingement unit.

One important advantage of the type of dryer just discussed over Yankee dryers and those of a similar nature is that its initial cost is much lower. At the same time it is capable of drying the types of products discussed above equally as well as the latter since the polished belt will impart as smooth or glossy a surface to the product as the cylindrical surface of Yankee and similar dryers.

Moreover, such belts may be easily and inexpensively provided with release type coatings on their material supporting surfaces to facilitate separation of the product from the carrier. This makes it possible to use an air knife or similar device to separate the dried product from the carrier rather than the doctor blade heretofore employed for this purpose. Accordingly, another significant advantage of the present invention is that the damage to the surface of the product suporting carrier caused by doctor blades and similar carrier contacting devices can be entirely eliminated.

Another important advantage of the dryers disclosed herein over those described above is that much higher drying rates and corresponding decreases in drying costs can be obtained since the radiant heaters of the present invention can be operated at much higher temperatures than steam heated dryers. Furthermore, the combination of radiation, impinging air, and conduction employed in the dryers of the present invention is much more efiicient than conduction alone as in steam-heated Yankee dryers and others of a similar nature.

A further advantage of the present invention over the prior art dryers described above is that, because the product is dried from both sides, it remains flat and does not curl. Accordingly, in applications where a curled product is objectionable, the dryers of the present invention are capable of producing a better product than the type of dryer just mentioned.

Yet another advantage of the dryers disclosed herein is that the temperatures of the radiant heaters in the radiant heating-fluid impingement unit and those on the opposite side of the carrier as well as the composition, temperature, velocity, and volume of the impinging fluid can be easily, quickly, and accurately varied to compensate for variations in the product delivered to the dryer. Accordingly, the dryers of the present invention are capable of producing a product of more uniform and higher quality than the type of dryer described above.

From the foregoing it will be apparent that other important but more specific objects of the present invention reside in' the provision of dryers in accord with the preceding object which:

(1) Have a much lower initial cost than Yankee and similar previously known dryers.

(2) Are capable of drying low wet-strength and coated products more efliciently, at higher rates, and at lower cost than the dryers heretofore employed for this purpose.

' (3) Are capable of producing products of more uniform and higher quality than Yankee dryers and other heretofore known dryers of a similar type.

(4) Include various ones of the novel features described above and different combinations of these features.

Other important objects and advantages and further novel features of the present invention will become apparent from the appended claims and as the ensuing detailed description and discussion proceeds in conjunction with the accompanying drawing.

Brief description of the drawing In the drawing:

FIGURE 1 is a generally diagrammatic side view of drying apparatus constructed in accord with the principles of the present invention;

FIGURE 2 is a plan view of the apparatus of FIGURE 1; and

FIGURE 3 is a pictorial view of a radiant heating-fluid impingement unit incorporated in the apparatus of FIG- URE 1.

Detailed description of a preferred embodiment Referring now to the drawing, FIGURES 1 and 2 depict in generally diagrammatic form an examplary dryer embodying and constructed in accord with the principles of the present invention. Dryer 10 includes an endless belt type carrier 12 trained around drive rolls 14 and 16 and over idler rollers 17 to provide product supporting and return legs 18 and 20, a radiant heating-fluid impingement unit 22 and radiant heaters 24 for drying a web of product 26 glued onto leg 18 of carrier 12 by a press roll 28, and an air knife 30 for separating the dried product from the carrier onto a roll 32 for delivery to a rewind stand or further processing station (not shown).

Endless belt 12 may be fabricated of any suitable material, but will typically be of mild or stainless steel, or high strength bronze. The outer or product supporting surface 34 of the belt is treated to produce a high polish, as by chrome plating it, so that it will impart a smooth or polished finish to the web of product 26 glued onto it by press roll 28.

The polished outer surface of the carrier is also preferably coated with Teflon or a similar release type material to facilitate separation of the dried Web 26 from the carrier at the discharge end of the dryer. As discussed above, this is an important feature of the present invention since it permits the product to be separated from the belt by an air doctor or air knife, eliminating the surface damaging contact appurtenant to the use of a conventional doctor blade.

The opposite or inner surface 36 of the belt is treated to produce a high coefficient of absorption for radiant energy. This is so the belt will absorb to the maximum extent the radiant energy emitted from radiant heaters 24. This surface treatment may be accomplished in any desired fashion. A number of suitable techniques for providing such a surface are described in my Patent No. 3,262,494, issued July 26, 1966.

The press and take-01f rolls 28 and 32 and the rolls 14 and 16 around which carrier 12 is trained together with air knife 30 are of conventional construction as is the drive mechanism (not shown) for rotating rolls 14 and 16. Since these components are conventional and as their details form no part of the present invention, they will not be described further herein.

Referring now to FIGURE 3, the fluid impingementradiant heating unit 22 incorporated in dryer '10 includes main supply and return ducts 38 and 40 extending lengthwise of dryer 10 and generally T-sectioned branch supply and return ducts 42 and 44 extending transversely across the main ducts. The branch and main supply ducts 42 and 38 communicate through openings 46, and similar openings 48 provide communication between the branch and main return ducts.

Air or other fluid is accelerated and directed at high velocity against web 26 through apertures 50 drilled in flow plates 52, which form one wall of each branch supply duct 42. The flow apertures are typically drilled through the flow plate at an angle of 15. The total area of the apertures will normally be from 1% or less to 5% of the total area of the plate.

The high velocity fluid impinging on web 26 scours evolved volatiles away from its surface, thereby preventing the formation of a stagnant boundary layer and increasing the efiiciency with which radiant energy is transferred from unit 22 to the web as explained in detail in my copending application, No. 654,838, filed July 20, 1967 for Apparatus for and Method of Drying Ink and Other Materials on a Carrier. Therefore, the use of impinging fluid in combination with radiant energy is one of the important features contributing to the superiority of the dryers disclosed herein over the heretofore known dryers described above.

The spent treating fluid, together with its burden of evolved volatiles, flows from adjacent web 26 into branch return ducts 44 through inlets 54. The inlets extend the length of the branch ducts and accordingly minimize resistance to the flow of the fluid and evolved volatiles into the return ducts.

The air or other impinging fluid is heated, delivered to, and exhausted from radiant heating-fluid impingement unit 22 by a fluid heating and circulating system including supply and return trunks 58 and 60. This system may be of any desired construction, but is preferably arranged so that the volume, composition, velocity, temperature, and/or other characteristics of the treating fluid can be varied to compensate for variations in the material delivered to the dryer. One suitable system of this type, especially designed for installations employing radiant heating-fluid impingement units of the type described in the preceding paragraphs, is disclosed in copending application, No. 615,966, filed Feb. 14, 1967.

In radiant heating-fluid impingement unit 22, flow plates 52 are heated to obtain the emission of energy in the infrared portion of the spectrum for evolving volatiles from web 26 or the coating thereon. This may be done by welding or otherwise fixing tubular type heaters 56 in heat conductive relationship to the inner or back sides of the flow plates. To increase the absorptivity of energy from tubular heaters 56 and the emissivity of the flow plates, the surfaces of the latter may be covered with a high emissivity coating. A number of satisfactory coatings are described in Patent No. 3,262,494.

The type of radiant heating-fluid impingement unit described briefly above is disclosed in more detail in copending application, No. 615,966. Reference may be had to the copending application if deemed necessary to a complete understanding of the present invention.

The remaining major components of dryer 10 are the radiant heaters 24 employed to dry web 26 from the conveyor or carrier side. Any desired type of appropriate radiant heater may be employed. One satisfactory type is that described in my Patent No. 3,258,204, issued June 28, 1966.

The type of radiant heater described in the foregoing patent has the advantage that it is capable of handling liquids which may be circulated in liquid form at temperatures of 1,000 F. and higher. Accordingly, such radiant heaters are capable of providing very high flux densities.

The combination of radiant heaters 24 and radiant heating-fluid impingement unit 22 typically results in from 15,000 to 20,000 B.t.u.s per square foot of web area per hour. This provides very high drying rates, which is one of the significant advantages of the present invention.

The liquid for the radiant energy emitting components of radiant heating-fluid impingement unit 22 and radiant heaters 24 can be heated and circulated by any appropri. ate system. Suitable systems are disclosed in application No. 615,966 and in Patent No. 3,258,408; and either or a combination of both of these systems can be employed, if desired.

One advantage of employing liquid circulating systems of the type mentioned in the preceding paragraph is that the temperature of the radiant energy emitting components in radiant heating-fluid impingement unit 22 and the temperature of radiant heaters 24 can be readily and easily varied. This, together with control over the composition, velocity, temperature, volume, etc., of the impinging fluid described earlier make-s dryers of the type disclosed herein capable of readily compensating for variations in the product delivered to the dryer.

The operation of dryer is thought to be apparent from the foregoing. Briefly, however, the web 26 of wet or coated paper or other product delivered to the machine around press roll 28 is glued onto the highly polished outer surface 34 of carrier 12 as it passes through the nip between press roll 28 and drive roll 14. Carrier 12 then carries the wet product between radiant heating-fluid impingement unit 22 and radiant heaters 24.

As the product passes between these components, it is dried from the exposed side by a combination of radiant energy and impinging fluid from unit 22. At the same time, energy emitted from radiators 24 and absorbed by carrier 12 is conducted through the latter to dry the product from the opposite side. This process of heating the product simultaneously from both sides not only provides very high drying rates but, also, eliminates the objectionable curl in the product which would result if it were heated from only one side.

As the product reaches the discharge end of dryer 10, it is separated from carrier 12 by air knife 30. As described above, separation is preferably facilitated by providing a Teflon or other release type coating on the polished outer surface 34 of carrier 12. The dried product separated from carrier 12 by air knife 30 is trained around roll 32. From here it is let to a rewind stand or further processing station (not shown).

It will be apparent to those skilled in the art to which the present invention pertains that many modifications may be made in the exemplary embodiment of the invention described above without exceeding the scope of the invention. For example, the principles of the present invention may equally well be applied to vertical instead of horizontal type dryers and to dryers configured to follow arcuate and other curved paths. Accordingly, to the extent that such modifications are not expressly ex cluded from the appended claims, they are fully intended to be covered therein.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description,

and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. Drying apparatus for web and sheet type materials comprising a belt type carrier for the material to be dried, the material supporting surface of said conveyor being highly polished; means for pressing the material to be dried onto said carrier comprising a press roll spanning said carrier and engaging said carrier at one end thereof; a radiant heating and fluid impingement unit for drying the material pressed onto said carrier, said unit comprising plural radiant heating elements disposed in closely spaced, parallel relation to and spanning said carrier, fluid supply and return duct means on the Opposite side of said radiant heating elements from said carrier, fluid impingement means for distributing a heated fluid from said supply duct means onto the material on said carrier, and means for returning fluid from adjacent said carrier to said return duct means; and means for heating the side of the material opposite the side against which the heated fluid is impinged by conduction.

2. The drying apparatus of claim 1, wherein said lastmentioned means comprises a radiant heater on the opposite side of the carrier from the radiant heating-fluid impingement unit, the surface of the carrier facing the radiant heater being treated to produce a high absorptivity coeflicient for radiant energy, whereby said carrier will absorb radiant energy emitted from said heater and transfer it by conduction t0 the material pressed thereon.

3. The drying apparatus of claim 1, wherein there is a release type coating on the polished surface of the carrier to facilitate the separation of the dried material from the carrier.

4. The drying apparatus of claim 1, together with means at the end of the carrier opposite the end where the material to be dried is pressed onto the carrier for separating the dried material from the carrier.

5. The drying apparatus of claim 1, wherein the fluid distributing and return means of the radiant heating-fluid impingement unit comprises branch supply and return ducts extending across said main supply and return duct means and communicating therewith; means at spaced intervals along said branch supply ducts and communicating therewith for directing said fluid from said branch supply ducts into contact with the material being dried; and at least one fluid inlet to each of the branch return ducts.

References Cited UNITED STATES PATENTS 1,595,478 8/1926 Minton 341 17 XR 2,022,593 11/1935 Fuykers 34160 XR 2,229,285 1/1941 Gehnrich 34160 XR 2,389,586 11/1945 Andrews 34'160 XR 2,747,583 5/1956 Frankenburg et al. 34155 XR 3,013,878 12/1961 Dessauer.

3,013,900 12/1961 Yezek et al.

3,084,448 4/1963 Dungler 34-155 3,266,169 8/1966 Smith 345 XR FREDERICK L. MATTESON, JR., Primary Examiner. A. D. HERRMANN, Assistant Examiner.

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