US3246400A

US3246400A - Drying drum

Info

Publication number: US3246400A
Application number: US204930A
Authority: US
Inventors: Richard P Brown
Original assignee: Bell and Howell Co
Current assignee: IMO Industries Inc
Priority date: 1962-06-25
Filing date: 1962-06-25
Publication date: 1966-04-19
Anticipated expiration: 1983-04-19

Description

April 9, 1966 R. P. BROWN 3,246,400

DRYING DRUM Filed June 25, 1962 I N VEN TOR. fl/cA/Apo PB/POWN .4 r ram/5k.

United States Patent 3,246,400 DRYING DRUM Richard P. Brown, Monrovia, Calif., assignor, by mesne assignments, to Bell & Howell Company, Chicago, Ill., a corporation of Illinois Filed June 25, 1962, Ser. No. 204,930 7 Claims. (Cl. 34-110) This invention relates to an improved drying drum, and particularly to a drying drum adaptable for use in dynamic recording systems.

Dynamic recording systems, such as a recording system wherein a photosensitive recording medium is employed to record images produced by an oscillograph, normally require a very short access time. The term access time is used to indicate the time interval between the exposure ofthe photosensitive medium, which may be referred to as recording paper, to a light stimulus to be recorded, and the presentation of the recorded record for visual observation. Normally, a dynamic recording system wherein a drying drum is utilized includes apparatus wherein the recording paper, which is in the form of an elongated strip, is passed through a plurality of baths of developing solutions after exposure. After passing through the baths, the recording paper is placed into contact with a rotating drying drum for drying of the developing solutions. The drying drum is heated internally, and is arranged to rotateat such speed with relation to the speed of the strip of recording paper that there is no relative movement between the moving surface of the drying drum and the moving recording paper. After drying, the recording paper is passed from the apparatus for visual observation.

Heretofore, drying drums for use in such apparatus have comprised a cylindrical platen made of stainless steel, arranged to be engageable with the recording paper. The surface of such drying drums was smooth. Several problems have impaired satisfactory performance of these former drying drums.

Although the internal heating means are arranged to distribute the heat on the interior surface of the platen as evenly as possible, it is impossible to apply heat equally to all points on the platen. For-mer platen'constructions have comprised a relatively thin layer of a material such as stainless steel, which does not have a high coefficient of thermal conductivity. As a result, considerable diiferences in temperature have resulted over the platen surface, due to the inability of such thin layer of material to conduct heat laterally about the platen to equalize surface temperature. It is a characteristic of the recording paper ordinarily used with such systems that the paper contracts when dried, and the extent of such contraction is dependent upon the heat applied to the paper during drying. The non-uniform heating of the surface has therefore aifected the recording paper dimensionally, resulting in undesirable differences in the width of the paper throughout the length of the record.

A more serious problem has existed due to the formation of a boundary layer of air and steam between the paper and the platen surface as the wet paper comes into contact with the heated platen. The formation of such boundary layer causes a loss of intimate contact between the paper and the platen surface, and a corresponding reduction in the amount of heat transferable from the platen to the paper. The boundary layer has been found to occur at paper speeds of approximately ten feet per minute, and former dynamic recording systems of the type described have thereby been limited to paper speeds of ten feet per minute, or less, over the drying drum. The remainder of the dynamic recording system is capable of producing a record at a much higher speed, and thus the defects of former drying drums have reduced the effectiveness of the entire apparatus.

3,246,400 Patented Apr. 19, 1966 Certain dynamic recording systems which do not employ developing baths, and therefore concern themselves with substantially smaller quantities of developing solutions to be dried from the paper, include a stationary platen rather than a drying drum. Where a platen is stationary, it has been possible to provide large slots in the platen which scrape oif the boundary layer of air and steam as the paper moves across the platen, in order to insure intimate contact between the platen and the paper. Such slots have been impractical, however, in systems wherein there is no relative motion between the platen and the moving paper, for the reason that the'portion of the recording paper adjacent the large slot remains unheated and, therefore, undried. A permanent and undesirable impression is thereby left on the recording paper.

This invention resolves the foregoing difficulties by the provision of a drying drum so constructed as to provide substantially uniform temperature over the entire drum surface, and provided with means for venting the boundary layer of air and steam without the leaving of undried areas upon the recording paper.

Briefly, this invention provides a drying drum of conventional outer dimensions made from a material having high heat conductivity. A thick layer of such material is used in order to provide good lateral conduction of heat for substantially uniform surface temperature. It has been found that within certain critical dimensions, very small grooves may be provided upon the drum surface for venting of the boundary layer of air and steam. Such grooves are sufficiently small that the portions of the paper adjacent the grooves absorb sufficient heat from the surrounding paper and platen surface for satisfactory drying, especially where substantially uniform temperature prevailson the platen surface. Furthermore, as the recording paper contracts during drying, certain portions of 'its surface will be moved from positions adjacent grooves to positions adjacent the platen surface between the grooves, if the grooves are sufficiently small. Therefore, this invention provides a drum surface which defines a plurality of small parallel grooves. Each groove has a width of from 0.0005 inch to 0.002 inch, and the maximum depth of each groove is substantially equal to its width. Each of the lands, which are the areas on the drum surface between the grooves, must be at least as wide as the width of each of the grooves. In order to provide a sufficient total groove area for carrying off the air and steam, the grooves are disposed along the drum surface at a frequency of at least grooves per inch, but not more than 600 grooves per inch.

It has been found in practice that a drying drum in accordance with the present invention will permit drying of recording paper at speeds 'as high as fifty feet per minute. Such speeds may even exceed the capabilities of the remainder of the apparatus for delivering developed paper to be dried, but it has been found that satisfactory performance of the entire apparatus may be achieved at speeds up. to thirty feet per minute. Thus the drying drum, according to the present invention, has tripled the output capacity of this type of dynamic recording system.

This invention will be more clearly understood with reference to the following description and accompanying drawings, in which: 1

FIG. 1 is a perspective view of a drying drum in accordance with the present invention, partially cut away;

FIG. 2 is an enlarged partial cross-section view of the exterior surface of a drying drum in accordance with the present invention; and I FIG. 3 is an enlarged cross-section view, partially cut away, of another embodiment of a drying drum in accordance with the present invention.

Referring now to the drawings, FIG. 1 shows a strip of photosensitive recording paper 5 engaged with a drying drum indicated generally at 6, as a part of a dynamic recording system (not shown), wherein the recording paper 5 has been exposed to a source of light and. passed through a series of baths of developing solution. The recording paper 5 has a path of movement in the direction of the arrows and is held against the exterior surface of the drying drum 6, which exterior surface may be referred to as the platen 7, by guide roller 10. Guide roller is arranged at any desired location, and normally is at a point more than 180 around the platen 7 from the point where the recording paper 5 first engages the platen 7, in order to provide contact for a sufiicient time for drying.

In the preferred form, the drying drum 6 is formed by a platen 7 substantially in the shape of a hollow cylinder. The ends of the platen 7 are closed by suitable end pieces 8 each containing a central shaft" 9 or other suitable means for rotatably mounting the drying drum 6 Within the dynamic recording system (not shown). Heating means (not shown) are disposed within the hollow interior of the drying drum 6, and are arranged to distribute heat as evenly as possible around the interior surface of the platen 7. In the preferred form, the platen'7 is made from a material having a high coeificient of thermal conductivity, such as aluminum, and is of a suflicient thickness to insure good lateral thermal conduction around the circumference of the palten. In the presently preferred embodiment, the platen 7 has a diameter of ten inches, and is comprised of aluminum having a thickness of five-eighths inch.

Referring now to FIG. 2, the exterior surface of the platen 7 defines a plurality of elongated grooves 11. The grooves 11 are disposed substantially equidistant from and parallel to one another. In the preferred form, the

grooves 11 extend circumferentially around the drying drum 6 in the same direction as the direction of movement of the recording paper 5. However, the grooves 11 may extend longitudinally or angularly in any desired direction. The preferred circumferential direction for grooves 11 is selected because such grooves may be quickly and inexpensively formed by lathe turning. V

In the dynamic recording system with which a drying drum in accordance with the present invention is used, there is no relative motion between the surface of the platen 7 and the surface of the recording paper 5. The

lower surface of the recording paper 5 is normally in intimate contact with the platen 7, but, as illustrated in FIG. 2, a portion of the recording paper 5 directly adjacent the grooves 11 has no contact with the heated platen 7. The size and frequency of placement of grooves 11 therefore becomes critical for the reason that grooves 11 having too great a width will leave a permanent impression upon the portions of the recording paper 5 adjacent the grooves, which will be undried. V i

The purpose of the grooves is to provide a channel for carrying off the boundary layer of air and steam forming between the platen 7 and the recording paper 5 as the Wet recording paper 5 comes into contact with the heated platen 7. There must, therefore, be a sufficient total groove area for carrying oif all of the air and steam required to be carried off. For this reason, the selection of proper size and number for the grooves 11 requires a balancing of the requirements for providing the desired total groove area, and also providing the maximum possible area for intimate contact between the recording paper 5 and the surface of the platen 7.

In the preferred embodiment of this invention, therefore, this proper balance is achieved by providing grooves 11 having a width in the range of from 0.0005 inch to 0.002 inch, and optimum results are obtained when the groove width is substantially 0.001 inch.

In order to provide the required total groove area, there must be a large number of the grooves 11, and

it has been found that the frequency at which grooves 11 are disposed along the surface of the platen 7 must be at least one-hundred fifty grooves per inch, but not more than six-hundred grooves per inch. The frequency with which the grooves 11 are disposed is inversely proportional to the width selected for the grooves. When grooves 11 are utilized having the optimum width of 0.001 inch, the optimum frequency has been found to be threehundred grooves per inch.

To provide the desired total area for intimate contact between the recording paper 5 and the surface of the laten 7, it is necessary that the lands, indicated generally at 12, be of at least the same width as the width of the grooves 11. In the preferred form, the lands 12 are at least twice the Width of the grooves 11.

In operation, the steam is forced by its own expansion and the pressure of the recording paper 5 against the lands 12 into the nearest groove 11. As the drying drum 6 rotates, the steam in the grooves 11 passes out of the grooves 11 in the area between take-up roller 10 and the point where the recording paper 5 first engages the drying drum 6. No boundary layer is permitted to form, and the recording paper 5 is permitted to absorb heat from the platen 7 through the lands 12 substantially uniformly over the entire outer surface of the platen '7.

In the event chemicals are employed in the recording paper 5, or in the developing baths (not shown) which would be corrosive to the material from which the platen 7 is made, a thin layer of a non-corrosive material may be placed over the outer surface of the platen 7. Such an embodiment is shown in FIG. 3, wherein the platen 7A is comprised of a substantially thick layer of a material 14 which is a good thermal conductor, to the exterior of which is bonded a thin layer of corrosion-resistant material 15, such as stainless steel. The grooves 11 are formed in the exterior surface of the corrosion-resistant material 15. In the preferred embodiment, the layer of corrosion-resistant material is stainless steel having a thickness of approximately 0.015 inch, in order that its characteristics of poor thermal conductivity do not impair the even heat distribution of the material 14 having a high coefficient of thermal conductivity. The material 14 is aluminum in the preferred embodiment, having a thickness of five-eighths inch for a 10 inch diameter platen 7.

The invention claimed is:

1. Apparatus for drying elongated strips of photographic material of the class wherein the strip of material to be dried is moving and is engaged with the surface of a heated rotating drying drum which rotates about an axis transverse to the path of motion of the strip at such speed that the surface of the drum travels at substantially the same rate of speed as the strip, so that there is substantially no relative motion between the drum surface and the strip engaged therewith, an improved drying drum, comprising:

(a) a hollow cylindrical drum having closed ends and adapted to carry internal heating means,

(b) the drum being made from a material having a coefficient of thermal conductivity and having a wall thickness suflicient to provide a substantially uniform temperature at all points on the cylindrical drum surface,

(0) the drum having a plurality of substantially identical parallel grooves on its exterior surface, the grooves being equidistant from one another and separated by a distance at least as great as the width of each groove,

(d) the Width of each groove being in the range of from 0.0005 inch to 0.002 inch, and the maximum depth of each groove being substantially equal to its width,

(e) the parallel grooves being disposed at a frequency in the range of from to 600 grooves per inch along the surface of the platen.

2. A drying drum according to claim 1 wherein the width of each groove is at least 0.001 inch and the grooves are disposed along the platen surface at a frequency of at least three-hundred per inch.

3. A drying drum according to claim 1 wherein the width of each groove is at least 0.001 inch and the distance between adjacent grooves is at least twice the width of each groove.

4. A drying drum according to claim 1 wherein the grooves extend transverse to the axis of the drum, in the same direction as the path of movement of the strip of material being dried.

5. A drying drum according to claim 1 wherein the drum has a thin layer of a corrosion-resistant metal thermally bonded to the exterior surface of a thick layer of a material having a high coefficient of thermal conductivity, and the grooves are formed in the exterior surface of the thin layer of corrosion-resistant metal.

6. Apparatus for drying elongated strips of photographic material of the class wherein the strip of material to be dried is moving and is engaged with the surface of a heated rotating drying drum which rotates about an axis transverse to the path of motion of the strip at such speed that the surface of the drum travels at substantially the same rate of speed as the strip, so that there is substantially no relative motion between the drum surface and the strip engaged therewith, the apparatus comprismg (a) a hollow cylindrical drum adapted to carry internal heating means and made from a material having a coefiicient of thermal conductivity and a wall thickness sufficient to provide conduction of heat laterally in the wall of the drum for maintaining a substantially uniform temperature over the cylindrical drum surface engaged by the strip of material,

(b) the drum having a plurality of substantially identical parallel grooves on its exterior surface, the grooves being equidistant from one another and separated by a distance at least as great as the width of each groove,

(c) the width of each groove being in the range of from 0.0005 inch to 0.002 inch, inclusive, and the maximum depthof each groove being substantially equal to its width,

(f) the parallel grooves being disposed at a frequency in the range of from 150 to 600 grooves per inch, inclusive, along the surface of the platen, and

(e) means for maintaining a wet shrinkable strip of photographic material in intimate contact with the exterior surface of the drum over a selected extent circumferentially of the drum as the drum is rotated,

(1) the portions of the photographic material in contact with the drum between the grooves being dried by heat transferred from the drum,

(2) the portions of the photographic material spanning the grooves being dried by heat transferred thereto from the portions of the material in contact with the drum between the grooves,

(3) water vapor released from the material passing away from the material through the grooves,

(4) the photographic material within the selected extent of the drum thereby being maintained at substantially uniform temperature so that it shrinks substantially uniformly in a direction transverse to its path of motion.

7. Apparatus for drying a strip of wet photographic material of indeterminant length, comprising (a) a rotatable heated drum having a circularly cylindrical exterior surface maintained at a selected temperature substantially uniformly thereover,

(b) means for intimately engaging the wet strip with the drum around a portion of the periphery of the drum,

the strip shrinking as it dries in proportion to the heat applied thereto,

(c) the surface of the drum engaged by the strip defining a plurality of small closely-spaced grooves and lands for receiving and directing away from the strip vapors produced as the strip is dried,

the grooves being disposed and arranged on the drum so that the strip is maintained at substantially uniform temperature along lines transverse to its length so that the strip shrinks uniformly transversely of its length and the lands having a width at least twice the width of the grooves.

References Cited by the Examiner UNITED STATES PATENTS 2,299,662 10/1942 Thaler 34-122 2,519,105 8/1950 Blue 341 10 2,621,982 12/1952 Crosland 34-110 2,861,508 11/1958 Baumbach 34--155 FOREIGN PATENTS 872,3 62 7/ 1961 Great Britain.

WILLIAM F. ODEA, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

Claims

7. APPARATUS FOR DRYING A STRIP OF WET PHOTOGRAPHIC MATERIAL OF INDETERMINANT LENGTH, COMPRISING (A) A ROTATABLE HEATED DRUM HAVING A CIRCULARLY CYLINDRICAL EXTERIOR SURFACE MAINTAINED AT A SELECTED TEMPERATURE SUBSTANTIALLY UNIFORMLY THEREOVER, (B) MEANS FOR INTIMATELY ENGAGING THE WET STRIP WITH THE DRUM AROUND A PORTION OF THE PERIPHERY OF THE DRUM, THE STRIP SHRINKING AS IT DRIES IN PROPORTION TO THE HEAT APPLIED THERETO, (C) THE SURFACE OF THE DRUM ENGAGED BY THE STRIP DEFINING A PLURALITY OF SMALL CLOSELY-SPACED GROOVES AND LANDS FOR RECEIVING AND DIRECTING AWAY FROM THE STRIP VAPORS PRODUCED AS THE STRIP IS DRIED, THE GROOVES BEING DISPOSED AND ARRANGED ON THE DRUM SO THAT THE STRIP IS MAINGAINED AT SUBSTANTIALLY UNIFORM TEMPERATURE ALONG LINES TRANSVERSE TO ITS LENGTH SO THAT THE STRIP SHRINKS UNIFORMLY TRANSVERSELY OF ITS LENGTH AND THE LANDS HAVING A WIDTH AT LEST TWICE THE WIDTH OF THE GROOVES.