US2688155A

US2688155A - Apparatus and method for controlling the application of plastic material to casting surfaces of sheeting machines

Info

Publication number: US2688155A
Application number: US342326A
Authority: US
Inventors: Gale F Nadeau; Walter R White
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1953-03-16
Filing date: 1953-03-16
Publication date: 1954-09-07
Anticipated expiration: 1971-09-07
Also published as: GB775880A

Description

Sept. 7, 1954 1 APPARATUS AND METHOD FOR CONTROLLING THE APPLICATION Filed March 16, 1953 G F NADEAU ETAL 2688,155

OF PLASTIC MATERIAL TC CASTING SURFACES 0F SHEETING MACHINES 2 Sheets-Sheet l GALE F NADEAU WAL rm P. WHITE INVENTORS amwx A I ATTORNEYS Sept. 7, 1954 G. F. NADEAU ET AL 2,638,155

APPARATUS AND METHOD FOR CONTROLLING THE APPLICATION OF PLASTIC MATERIAL TO CASTING SURFACES OF SHEETING MACHINES Filed March 16, 1955 2 Sheets-Sheet 2 GALE i WADE AU WALTE/EN RN WIgZTE E T0 04m! Q1 flTTOR/VEYS Patented Sept. 7, 1954 APPARATUS AND METHOD FOR CONTROL- LING THE APPLICATION OF PLASTIC MA- TERIAL T CASTING SURFACES OF SHEETING MACHINES Gale F. Nadeau and Walter R. White, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 16, 1953, Serial No. 342,326

7 Claims. 1

This invention relates to an improved method and apparatus for casting an evaporative-type dope on a surface to form sheeting. Such sheeting may be used for packaging, for film base, and for other purposes.

In this art it has always been diflicult to form sheeting which is perfectly smooth and of an accurate thickness throughout, largely because relatively slight air disturbances or vibrations may tend to ruin the sheeting by causing wrinkles, waves, or the like, in the surface of the sheeting before it sets. While some of these imperfections may smooth out before setting, it is usually difficult or impossible to prevent a permanent deforming of the sheet.

Our invention is particularly directed to a method and apparatus for overcoming these and other difficulties and to provide a means which reduces or entirely eliminates vibrations in the fluid dope being deposited upon a dope-receiving surface by a suitable hopper. It has been recognized that it is desirable to reduce eddy and other air currents about the dope as it passes from a hopper, as is indicated in Patent 2,592,319, Casting Apparatus for Film Support or Sheeting, G. F. Nadeau and A. M. Glasoe, granted April 8, 1952. It has not, however, been recognized that beneficial results could be obtained by reducing the usual air currents on that side of the hopper from which the casting surface approaches to have the dope laid on the wheel. As is pointed out in the above patent, the usual type of casting machine employs an endless surface, such as the periphery of a wheel or a belt, which is provided with an accurate, smooth surface and which moves constantly past the hopper so that a plastic sheet may be spread on the surface, set or dried until it is self -supporting, at which time the sheet may be stripped from the casting surface. Where wheels are used, they are frequently of large diameter, such as, for instance, from 10 to 18, and an enclosure is built about the wheel to carry off solvent vapors and to control the temperatures. Because of the nature of these enclosures and the large size of the machine, it is difiicult if not impossible, to build up a casing which can be streamlined to such an extent that the air will follow exactly the desired path. Ducts, supporting rollers, and even the sheet being formed all contribute to the difficulty of obtaining smooth even air circulation.

An object of our invention is to overcome the difficulties above pointed out. Another object of our invention is to provide a method of breaking up air currents atthe portion of the machine where they appear to be the most harmful. A further object of our invention is to provide a bafliing system which causes the air to follow a path in which it will not materially affect the dope being laid on the casting surface. A still further object of our invention is to provide an apparatus in which no additional air circulation, other than that already present in the casing of the apparatus, is required to produce the desired effects. Still another object of our invention is to provide a means of protecting the head of dope passing from the hopper to the casting surface against unwanted circulation of air. A still further object of our invention is to prevent a thin layer of air which is believed to follow the surface of the casting member from passing into the bed of dope being laid on the wheel. Other objects will appear from the following specification, the novel features being particularly pointed out in the claims at the end thereof.

The invention, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of the specific embodiments when read in connection with the drawings in which:

Fig. l is a greatly simplified view showing a casting wheel in elevation and certain parts in section of a typical embodiment of our invention. It may be pointed out in this figure that the scale of the parts is deformed in order to better illustrate the invention;

Fig. 2 is a top plan View showing a portion of the side walls in section of an improved air baiile constructed in accordance with, and embodying a preferred form of, our invention and showing on an enlarged scale the baffle shown in Fig. l. Unessential details of the apparatus are omitted in this View;

Fig. 3 is a fragmentary detail section, parts being shown in elevation of a second embodiment of our invention. Here again the scale of the parts is distorted to better illustrate th invention; and

Fig. 4 is a, part side elevation and part section showing schematically a slightly dilferent embodiment of our invention.

We found that one of the disturbing air currents which affects the laying of a head of plastic material on a casting surface is a thin layer of air which appears to follow the casting surface as it passes toward the hopper. While it had been previously recognized that air on the freshly laid layer of dope could readily disturb its surface, it was not thought that the air on the opposite side of the bead passing from the hopper to the casting surface was materially affected, particularly since the distance of the coating blade to the casting surface was often quite small, such as, for instance, .05. It is to be understood that this figure is by way of example since, of course, the distance from the blade to the casting surface is altered for various different thicknesses of sheeting.

Referring to Fig. 1 showing a preferred form of our invention, a wheel I may be mounted on trunnions 2 and may be turned in any well-known manner. In this view, the wheel turns in a clockwise direction so that a casting surface 3, which preferably is highly polished, may move beneath a hopper 4 having casting blades 5 and 6. These blades may be adjusted in known manners to and from each other and the casting surface 3. As pointed out above, the hopper blade 5 may be spaced from the casting surface a distance of .030 to 1.000". This hopper may contain a fluid or plastic dope l of the evaporative type which may flow down between the hopper blades 5 and 5 to the casting surface, after which it may be carried around the wheel and stripped off after setting and reaching a selfsupporting stage. It may be received from the casting surface 3 by passing it about a roller 8 and leading it away from the casting surface 3 and over suitable rolls 9, I0 and l I. There is a casing broadly indicated at l6 having an air inlet [1 in the top and an opening 18 through which the set sheet 20 passes out and over a guide roller l 2. To prevent solvent vapors from collecting in casing l6, air may be circulated to draw them away from the casting surface 3 and the sheet laid thereon. There is a partition 2| leading from the hopper 4 to an air duct 22 from which air is drawn through the duct 23 by suitable means, such as an air pump 24. The solvent vapors may be reclaimed by passing through the pipe 25 to a suitable recovery apparatus and if desired, the purified air may be recirculated to duct 28. There is a partition 26 dividing the air duct 22 into two sections, one of which 2'! passes around the periphery of the wheel I and leading to an air duct 28 into which air passes to practically encircle the wheel. There is an opening 29 into the chamber I 5 through which the sheeting passes before it is stripped from the wheel over roller 8. Thus, the chamber I6 is subjected to air currents which cannot pass smoothly in the shortest path or in a streamline manner through the casing from the inlet I! to air exit [3 connected by duct [4 to exit duct 25. The air must pass about the edges of the sheeting and various other parts. of the casing and machine such as roller supports, ducts, hopper, and the like, and it is therefore broken up in variable speed components.

In order to prevent these air currents and others from reaching the stream of dope 3| passing downwardly from the hopper blades to the casting surface 3even though this distance is exceedingly smallwe have provided an air baffle 32. This air baille, as best shown in Fig. 2, may lie between

side walls

33 and 34 of the casing and it may be, and preferably is, supported by such walls.

It may comprise a box-like frame consisting of

end pieces

35 and 36 mounted on the

walls

33 and 34 with a plurality of partition plates 31 extending between the end members and front and

back frame members

38 and 39. The plates or

slats

31, 38 and 39 are preferably spaced apart to provide flue-like openings 40 between the slatlike members and, to maintain these in correct alignment, we prefer to provide a series of rods 4| with spaced members 42 so that the air baffle plates will be held in position. Different numbers of baffle plates may be used and we have found that from three to six or more is usually satisfactory, although this may depend in part on the amount of air circulation which must be dispersed.

For average materials, the air circulation in the chamber l6 may be from 300 to 1500' per minute. It is believed, however, that a principal cause of disturbance of the bead 3| is a thin layer of air which follows the surface of the casting wheel or belt.

As will be noted from Fig. 1, the

baffle plates

31, 33 and 39 may be applied in parallel relationship with the bottom edges spaced from the wheel from, for instance, .055" to .065. This spacing is not too critical, and may be varied. In fact, it sometimes does vary slightly even between the air bafiles because the slats or baffle plates are made in a generally rectangular form for convenience, and such a bafile does not, of course, exactly follow the curvature of the casting surface where a wheel is used. However, where the wheel may be, say, 18' in diameter, the curvature does not depart far from a straight line in a distance of perhaps 3 or 4". By way of example, such a baflle may be, for instance, 3 or 4 wide, and perhaps 4" high, and the length of the baffle will preferably extend from wall to wall on each side of the casting surface.

It may be also desirable but not essential to provide another air baflie strip 43 which may have a plush or soft cloth 44 mounted along the bottom edge, as indicated. Such a strip may be spaced some distance from the casting surface 3 as, for instance, .020". Thus, with the air ballie plates and the air baffle strip 43 mounted as shown in Fig. 1, any layer of air following the casting surface must pass beneath the narrow openings between these members and the casting surface. It has been found that the reduction in the velocity of air around the dope casting unit with the construction above described is very beneficial. The air baflle generally shows a material up-draft between the first and second air baffles counting the baffles from left to right. Between subsequent baffles, there appears to be only a slight up draft, indicating the escapement of air that had managed to pass under the first one or two baffles.

It is very difficult to determine exactly what occurs with this construction, but the resulting effect is quite obvious-that there is far less disturbance with the labyrinth air baffle than is present without it. Where there is considerable air circulating in various directions, it is particularly difficult to describe accurately the exact path the air takes with such an apparatus as there are so many contributing factors which may vary somewhat at different times. Nevertheless, a labyrinth-type baffle has been quite successful.

In Fig. 3, there is a slightly different embodiment of our invention in which the hopper is mounted on rails 5| and 52 and the

hopper blades

53 and 54 lay the plastic coating 55 on a casting surface 56 of a wheel 57. Here, there i a casing plate 58 with a second plate 59 extending over the top of that surface of the wheel upon which the plastic material has been flowed, and this plate may be attached or taped at 60 to plate 58. In this form of the invention, there may be a suction chamber 6| witha suction pipe 62 leading to an air evacuating apparatus so that air in the chamber 6| may pass out through the suction box 64. The chamber 6| will be held under a somewhat different pressure than the pressure in a casing, similar to casing I6 shown in Fig. 1, and this pressure may be from 3 to 10" of water. In this case, there is an air baffle strip 65 having a bottom edg 66 spaced from the wheel a distance of perhaps .020, and the labyrinth or air baffle may consist of a series of spaced plates 61 with flues 68 extending between the baffle plates. Thus, air which may tend to follow the surface 56, either due to the turning of the wheel 51 or to the suction in chamber 63, in passing under labryrinth baffle and air baffle strip is broken up and is at least partially passed up through the fines 68 so that very little passes into the chamber 6| and so that the vacuum line 62 may draw off air evenly from the bead 69 of plastic dope being laid upon the wheel. In other words, the air in the chamber 6| will not be disturbed by eddy currents, even though the air is being constantly drawn out by the vacuum apparatus. Presumably, this causes an even pressure on the length of the bead 69 and prevents uneven air currents from reaching this bead and, consequently, wrinkling it. If desired, the air baffle strip 65 may be made a part of the air baiiles or may be entirely omitted.

Fig. 4 is still another embodiment of our invention wherein the casting surface ID is a polished belt mounted on wheels ll with a hopper 12 above the belt. The hopper has blades 13 and [4 so that a bead 75 of material can be laid on the belt. In this instance, there is an air baffle 16 and, if desired, an air baffle strip 1'! which may be spaced from the casting surface as in the embodiments shown above.

It should be stressed that under the dope hopper, it is necessary to minimize to the greatest extent possible any movement of air whether the air stream be more or less uniform and streamline or whether it be turbulent and made up of eddy currents. It is only by maintaining a fairly static air condition under the hopper and near the dope hopper orifice that slugging of the dope on the hopper blades can be prevented. The use of th labyrinth bafiie in addition to preventing air flow up the surface of the wheel and under the dope hopper also has the virtue of accomplishing this result without contacting the wheel surface. The mechanism by which a multiple slot labryrinth type baffle works is generally considered to be a result of frictional loss of energy in the air stream as a result of its flow up through the narrowly spaced members of the bafiie. Because of the number of them and their relative closeness, the air velocity is decreased due to typical viscous energy considerations. It follows, therefore, that there will be some exhaust of air from the tops of the bafile under most conditions of operation. It is conceivable that with very high impingement velocities against the baffle, some down draft or aspirator effect at the first or second slot could be realized. This situation, however, under our conditions of operation and with the air velocities involved does not exist.

The air baffle or labyrinth is quite simple and it may be made of wood, metal or other suitable material. It may be desirable to cover the bafiie plates with material which can be readily laundered or cleaned as, for instance, linen sheeting or the like.

While we have illustrated a preferred form of our invention, it is obvious that many changes will suggest'themselves to those skilled in the art, and we contemplate as within thescope of our invention all such changes as may come within the scope of the appended claims.

Having thus described our invention, what we claim is new and desire to secure by Letters Patent of the United States is:

1. Apparatus for casting plastic sheet material comprising a movable casting surface, a hopper for depositing a uniform layer of evaporativetype plastic dope on the casting surface, a chamber through which air is circulated over at least a portion of the casting surface before it reaches the hopper, means for controlling the circulating air moving over the casting surface and toward the hopper comprising a plurality of closelyspaced bafile plates extending across the casting surface out of contact with the casting surface but lying close thereto, said bafile plates extending in a direction away from the casting surface to provide narrow flue-like spaces between the baffle plates to resist eddy currents in the air adjacent the hopper whereby an even layer of plastic dope may be spread on the casting surface. 1

2. Apparatus for casting plastic sheet material of the type defined in claim 1 characterized in that the movable casting surface is carried by a wheel and in that the baffle plates may extend away from the wheel casting surface in a generally radial direction.

3. Apparatus for casting plastic sheet material of the type defined in claim 1 characterized in that the baflle plates are parallel to each other, in that at least one baffle plate extends radially away from the casting surface of the wheel, and in that the fines between the bafile plates are many times the height of the separation of the plates.

4. A method of minimizing irregularities in spreading a thin even layer of plastic dope upon a moving casting surface comprising passing circulating air over the casting surface adjacent an area where the plastic dope is applied to the casting surface and dividing a portion of the circulating air into a plurality of thin parallel streams substantially as wide as the casting surface and as it approaches the dope applying area to prevent substantial amounts of air from moving toward the application area at which the plastic dope is applied.

5. A method of minimizing irregularities in spreading a plastic dope of an evaporative-type on a casting surface comprising circulating air about the area where the dope is applied to a casting surface, and dividing a portion of the air into a plurality of parallel streams extending across the casting surface as it approaches the dope-applying area to prevent eddy currents of air from contacting flowing dope.

6. A method of minimizing irregularities in spreading a plastic dope sheeting on a casting surface comprising circulating air thereabouts, restricting air circulation in a direction toward an area in which fluid dope is applied to the casting surface by dividing the air into a plurality of parallel layers directed at substantially right angles to the casting surface and adjacent the area where the dope is applied to the casting surfaces to prevent eddy currents from contacting the flowing dope to the casting surface.

7. A method of minimizing irregularities in spreading a plastic dope sheeting on a moving 2,688,155 I 7 a casting surface comprising circulating air therecarried along by the casting surface or other air abouts to carry off solvent vapors, said casting currents from coming into contact with and desurface tending to carry a layer of air along with forming the dope flowing to the casting surface.

the surface as it moves, restricting air circulation in a direction toward an area in which fluid 5 References Cited in the me of thls patent dope is applied to the casting surface by divid- UNITED STATES PATENTS ing the air into a plurality of parallel layers ad- Number Name t jacent to and leading away from the casting sur- 2,051,201 Davidson Aug. 18, 1936 face as it approaches the area where the dope 2,201,747 Staudt May 21, 1940 is applied thereto to prevent eddy currents, air 10 2,226,186 Van Derhoef Dec. 24, 1940