US2421073A

US2421073A - Sheet making mechanism

Info

Publication number: US2421073A
Application number: US484634A
Authority: US
Inventors: Edouard M Kratz
Original assignee: Carbide and Carbon Chemicals Corp
Current assignee: Carbide and Carbon Chemicals Corp
Priority date: 1943-04-26
Filing date: 1943-04-26
Publication date: 1947-05-27
Anticipated expiration: 1964-05-27

Description

May 27, 1947. KRATZ SHEET MAKING MECHANISM 3 Sheets-Sheet 1 Filed April 26, 1943 [72 M97275? fczozzardfyl rafz.

)))))llllllllll|lllllllllllllv May 27, 1947. E. M. KRATZ 2,421,073

SHEET MAKING MECHANISM Filed April 26, 1943 3 Sheets-Sheet 2 1/ j fdouardfyfiazz y 194?. E. M. KRATZ 2,421,073

SHEET MAKING MECHANISM Filed April 2a, 1943 :5 Sheets-Sheet 5 mi "H jg I [III/Ill will! WWW w fdbzzarci/Yfizzi'i Patented May 27, 1947 SHEET MAKING MECHANISM Edouard M. Kratz, Gary, Ind., assignor, by mesne assignments, to Carbide and Carbon Chemicals Corporation, New York, N. Y., a corporation of New York Application April 26, 1943, Serial No. 484,634

Claims.

This invention relates to improvement in sheet making mechanism and has particular reference to mechanism for delivering a film of liquid to a surface on which a Web of sheet material is to be formed.

Among the troublesome problems encountered in attempting to produce a sheet of uniform thickness are those of preventing a more or less automatic build-up of thickness at the edges of the web (probably due to surface tension characteristics of the liquid coating delivered to the forming surface) the elimination or prevention of the formatign of ripple-like effects incident to the travel of the liquid coating under the edge of a doctor blade; the maintenance of uniformity of the depth of liquid coating and of resulting sheet thickness notwithstanding temperature changes which cause warping of the conventional metal doctor blade; the drying of the liquid on the doctor blade adjacent its operative edge and resulting interference with normal function thereof; and the maintenance of a substantially constant temperature of the liquid and of the doctor blade to obtain uniformity in the sheet production.

The main objects of the present invention are to provide improvements in the doctor blade and liquid depositing structure which will effectively overcome the difiiculties indicated in the foregoing statement of troublesome problems.

In prior art structures of which I am aware, attempts have been made to solve the indicated problems by relatively large, heavy and cumbersome hopper and doctor blade constructions which are also objectionable because of their excessively high cost.

It is also an object of the present invention to provide mechanism of the character indicated which will be of both simple and durable construction and which may be produced at very low cost.

Other objects and advantages will be understood by reference to the following specification and accompanying drawings (three sheets) wherein there is illustrated sheet forming mechanism embodying a selected form of the invention.

In the drawings:

Fig. 1 is a plan of an end portion of sheet forming mechanism to which the improved doctor blade structure is applied.

Fig, 2 is an end elevation.

Fig. 3 is a section on the line 33 of Fig. 1.

Fig. 4 is a section on the lines 4-4 of Figs. 1 and 3.

Fig. 5 is a section on the line 5-5 of Fig. 1.

Fig. 6 is a perspective of the improved doctor blade structure.

Fig. '7 is a perspective of the trough or hopper which is associated with the doctor blade for delivering liquid to the forming surface, and

Fig. 8 is a front elevation of the improved doctor blade.

The sheet or web forming mechanism herein disclosed embodies a sheet metal band or belt H] which is supported by suitable rolls or drums, one of Which i indicated at H. The drum H is carried by a shaft journalled in suitable bearings i2 supported by side frames l3 of the apparatus. The roll II is driven at the desired speed by any suitable means, herein illustrated as including worm wheel l4 secured to the shaft of the drum, and a Worm gear l5 carried by a driven shaft [6 and operatively meshing with the worm wheel I l. The drum II is preferably a hollow drum, and a, heating medium such as hot water is circulated through the drum for maintaining the drum and the forming belt [0 at a predetermined temperature. Hot water may be delivered to and may escape from the drum through the opposite end portions of the drum shaft, which may be hollow. Suitable couplings such as indicated at I! may be provided for connecting the necessary water piping to the ends of the drum shaft.

A doctor blade and liquid trough supporting frame It, embodying a transverse member l9 and longitudinally extending end arms 20, are pivotally mounted on a rod 2! which is suitably supported on the upper ends of posts 22 which extend upwardly from the frames IS. The side arms 20 of the member I8 are provided with rollers 23 rotatably mounted in suitable enlargements of the arms, and said rollers bear on the surface of the drum ll near its ends for supporting the member 18 in substantially fixed operative relation to the surface of the drum and to the surface of the forming band It].

A metal doctor blade 24 has end portions 2 5 (shown in this instance as being of reduced width) vertically slidably positioned in appropriately formed slots or ways 26 provided in upwardly extending enlargements 21 of the arms 20. The main, if not the only, functions of the last mentioned mounting of the doctor blade in the arms 20 are to support the doctor blade in an approximately vertically disposed position and to permit raising or lowering of the doctor relative to said arms 20 while preventing any substanti q rocking of the doctor blade about an axis extending in the direction of the length of the doctor.

The doctor blade 24 is adjustably supported in selected position relative to the surface of the forming belt or band by means of a pair of rolls 28 which engage the surface of the roll H (see Fig. 4), and are respectively associated with the opposite end portions of the doctor blade. Each roller 28 is mounted in the lower end of a clevis or forked member '29 which embraces the thickness of the doctor blade 24 (see Fig. and the doctor blade is vertically movable in said clevis. Guide bars 30-30 arranged at the sides of the arms of the forked member and secured to the doctor blade, and cover plates 3| extending over the clevis arms and secured to said guide bars 3ll30, serve to hold the rollers and their mounting members 29 against lateral shifting or wobbling relative to the doctor blade. Vertical adjustment of the doctor blade relative to the band I0, is effected by means of a screw 32 which is threaded through the bar 24 so as to cause its lower end to engage the cross part 33 of the roller mounting member 29. Turning of the screw in or out will efiect downward or upward adjustment of the roller. To facilitate repeated setting of the doctor blade in predetermined spaced relation to the band l0, the screw is provided with an adjusting arm 34 which serves as a pointer with reference to a suitable scale provided on an index plate 35. Th index plate 35 is fixedly mounted on the upper edge of the doctor blade 24 in any suitable manner.

The doctor blade 24 is preferably made of a very rigid and inflexible metallic bar, the lower edge of which is preferably beveled, as indicated at 36, to provide a thin lower edge portion 3l. The position of the lower edge 31 relative to the surface of the band It! determines the: thickness of the coating of liquid L (Fig. 3) which is carried forwardly by the band II]. By making the doctor blade 24 out of material which has a very low and substantially negligible coefficient of expansion within the range of temperatures to which the doctor blade is subjected, I have found that it is practicable to more or less arch the lower edge of the bar longitudinally to a very slight extent for the purpose of preventing a tendency of the liquid to increase its depth or thickness near the edges of the coating. As represented in Fig. 8, the length of the lower edge 31 of the doctor bar has its central portion, indicated by the dimension line C, recessed slightly from the normal plane of said lower edge. The extent of recessing is ordinarily very slight, usually only a matter of .001 or .002 inch. The end portions of the lower edge of the bar, such as indicated at D, incline downwardly to the normal plane of said lower edge 31 and, if desired, short end portions E may continue outwardly in said normal plane. By such formation of the lower edge of the doctor blade, the coating of liquid carried forwardly on the band It] has its marginal portions slightly tapered to conform to the thinning effect of the downwardly inclined portions D of the lower edge of the doctor blade. It has been found that in the normal operation of the apparatus, the liquid coating has a tendency to build up its thickness at its edges. This tendency may be the result of some characteristic surface tension, or it may be otherwise explained. In any event, by initially forming the liquid coating with margins of gradually reduced thickness as already indicated, it has been found that the final sheet product will be free from thickened edges or margins. This is a highly important advantage in the production of sheeting, first in that it avoids waste of material incident to trimming away the objectionably thickened portions, either because the thickened margins will not meet the specifications of the finished product or because satisfactory reeling of the web with such thickened portions is difiicult to effect if not impracticable. It may be observed that in attempting to reel sheeting in which the margins are thicker than the body of the sheet, the ends of the reel will build up to a much larger diameter than is required by the intermediate portion of the reel, thereby causing the reel to be too loosely wound intermediate its ends, too tight at its ends, and otherwise uneven and objectionable.

When the doctor blade 24 is made of thermostable material such as above alluded to, for example Invar steel, one commercial form of which is available under the trade name Fahralloy, the use of the described, slightly arched doctor blade edge is quite practicable in that variations in temperature and consequent changes in the blade due to expansion or contraction will not occur to alter the operative edge of the bar.

I have found that a doctor blade made of the said Fahralloy containing 37% nickel, a minor percentage of manganese (l /2%), and possibly 1% of silicon (the balance being iron), gives effective thermostability in the range of temperatures employed in the production of certain sheeting, the solution for which is preferably delivered to the forming band at about F. It will, of course, be understood that the doctor blade should be made of an alloy which provides the desired thermostability throughout the temperature range which is experienced in the production of a sheet from the particular solution to be employed.

The doctor blade 24 has detachably secured to it a trough-like structure 38, preferably made of sheet metal and embodying a temperature control chamber or jacket 39 at one side. The jacketed trough structure '38 embodies a front wall 40, the height of which is somewhat less than the height of the jacketed side of the trough. The liquid to be deposited on the band I0 is introduced to the trough, preferably at about the center thereof, through an inlet connection 4|. The trough has its ends closed by end walls 42, and the top wall 43 of the jacketed side thereof is extended rearwardly and then upwardly as indicated at 44 to form a small overflow tray. The ends of the trough are also preferably provided with wood or other end plates 45 suitably attached to the end plates 42. Hot water or other temperature controlling medium may be circulated through the jacket 39, the heating medium being delivered to the jacket through an inlet connection 46 and discharged through an outlet connection 41.

On the bottom of the trough or hopper 38 there is provided a pair of depending

ribs

48 and 49, between which there is frictionally positioned a flannel, felt or similarly wrapped wood or like bar 50. The soft, non-scratching covering on the bar 50 rests on the highly polished surface of the band l0 and serves to support the hopper on the band without danger of scratching the band incident to its travel under the hopper. The trough or hopper is detachably connected to the doctor blade 24 by means of a pair of spring clips Sl-Sl which are secured to the doctor blade and adapted to hook around the end members 45 of the trough structure to thereby hold the latter in predetermined juxtaposed relation to the doctor blade. The liquid material from which the sheeting is to be formed is delivered to the trough 38 at such a rate that the trough is filled to a point considerably above the top edge of the front wall t0, the liquid overflowing said front wall 483 and finding its way downwardly between said front wall 4!] and the doctor blade to be deposited on the band ill. The space between the front wall 411 of the trough and the adjacent face of the doctor blade 24 is effectively closed by portions of the side members 15 which extend forwardly from the front edges of the end members 42 of the trough into substantially abutting relationship to the adjacent wall of the doctor blade, in which position said end members 115 are held by the clips The slight space beneath the lower edges of the end members 4'5, and between the lower edge of the doctor blade and the front edge of the felt covered strip 50, may conveniently be closed at each end by means of a side member such as 5.2 which is secured to the doctor blade.

The tension with which the clips 5| hold the trough in the described relation to the doctor blade is not suificient to prevent the trough from maintaining its described supporting engagement with the surface of the band Iii, notwithstanding any vertical adjustment of the doctor blade. The weight of the trough and its contents is sufiicient to cause the trough to remain stationary when the doctor blade is adjusted up or down, the clips slipping vertically over the respective end portions of the trough.

It will be apparent that because of the small exposed area of the pool of liquid in the trough 38, the loss of solvents by evaporation from the trough will be held to a minimum. It may be further reduced by applying a cover to the trough if desired, and in the formation of sheeting from certain types of solution, for example from a vinyl resin solution, it has been found that a sheet or film of the material will be formed across the top of the pool extending from the forward edge of the top wall 43 to the doctor blade and from end to end of the trough. The formation of such a film is, of course, aided by the small extent of the area to be covered. In one practical embodiment of the structure, the dimension of the film between the trough and the doctor blade is between 1 and 2 inches, and in that case the formation of the covering film as referred to has been found to occur very quickly after the apparatus is set in operation. The formation of such film effectively seals the trough against further evaporation of solvents, and hence insures delivery of the solution in the desired condition to the forming band ID.

On the front upper portion of the doctor blade 2 there is fixedly mounted a wood or other suitable bar 53, the same being secured by screws or otherwise directly to the blade 24. An adjustably mounted bar 55, also of wood or other suitable material, is associated with the lower front portion of the doctor blade so as to cooperate with the beveled face 35 of the latter to form a chamber 55. The bar 54 may be vertically adjustably connected to the upper bar 53 by means of an adjusting screw 55, which has its threaded end threaded into an angle member 51 secured to the bar 54 and its upper end rotatably anchored in an angle bracket 58 which is secured to the upper bar 53. It will be apparent that by appropriately rotatin the screw 56, the bar 54 may be adjusted up or down to thereby regulate the position of the lower edge 59 of said bar 54 with reference to the band In and the coating L thereon. Suitable bowed springs, such as indicated at 60, may be employed for resiliently holding the lower bar 54 in place against the front face of the doctor blade 24. Such bowed springs 60 may be secured to the upper bar 53 by means of screws such as indicated at 6!, by means of which the pressure of the springs 68 on the bar 54 may be adjusted.

The chamber 55 may be closed at its ends by suitable means such as plates 52 secured to the ends of the doctor blade. Said chamber serves to entrap some of the solvent of the liquid solution to thereby prevent starting of the drying process until the liquid coating on the band has had an opportunity to achieve a smooth, non-wavy surface, which is highly desirable in the formation of most sheeting. Specifically, the solvent retaining chamber 55 appears to provide the required time interval for the smoothing out of ripples which would otherwise appear on the surface of the liquid coating incident to the passage of the unquid under the lower edge of the doctor blade. This feature is particularly important in connection with the formation of sheeting from liquid which embodies a highly volatile solvent and which tends to take a surface set almost immediately upon exposure to air. In the drawings, particularly in Fig. 3, the thickness of the band i0 and the depth of the liquid coating L are considerably exaggerated for purposes of illustration, and it will be understood that the depth of the liquid coating is usually only a matter of a few thousandths of an inch, so that the tendency of certain liquids to set rapidly is pronounced.

In one example of the production of sheeting from one vinyl resin solution, the solution is preferably delivered to the trough at a temperature of about F. In order to maintain the pool of the solution in the trough at the selected temperature, hot water or other medium at the required temperature, for example at F1, may be circulated through the jacket 39. Such heating medium may be derived from any suitable source. Owing to the small body of solution which requires temperature control, a relatively small water jacket is required. Due to the relatively small size of the doctor blade 24, heat loss through that source is held down to a practical minimum so that the temperature controlling medium need not be heated to an excessively higher temperature than the desired temperature of the solution.

The vertical plane of the rear face of the doctor blade, and hence the vertical plane in which lies the operative edge 3'! of the doctor blade, is preferably disposed slightly rearwardly of the vertical plane of the axis of the drum H. By this arrangement the doctor blade edge 31 will be in operative relation to a portion of the band which is firmly supported by the drum and incapable of any material wavering therefrom which could impair the constancy of the space between the doctor blade edge 31 and the surface of the band As represented in Figure l, the band I!) carries the liquid coating from the casting or forming apparatus into an oven r dryer 63 of any suitable construction. Upon emergence of the sheet covered band from the dryer, the sheeting may be stripped from the band by any preferred mechanism so as to leave the band clean and free for continuation of the film casting operation. By circulating a heating medium through the drum ll, the temperature of the band is effectively controlled so that the liquid solution will not be congealed or frozen upon contact with the band but will retain its free flowing liquid form long enough for the proper formation of the sheet producing coating.

Changes in the described structure may be made without departing from the principles of the invention as above described and referred to in the appended claims.

I claim:

1. In film forming apparatus of the class described, the combination of an endless belt on which to form a film from a liquid solution, a doctor blade, means supporting said doctor blade, said means being adjustable so as to permit adjustment of the doctor blade toward and from said moving member, a trough for delivering the film forming solution to said endless belt, means for supporting said trough on said endless belt, and means carried by said doctor blade for slidably holding said trough against said doctor blade, said means permitting said doctor blade to be vertically adjusted while said trough remains supported on said endless belt.

2. Apparatus according to claim 1 wherein the means for supporting the trough on the endless belt comprises non-scratching means detachably secured to the bottom of said trough and engaging the film forming surface of said endless belt.

3. Apparatus according to claim 1 in which the means for supporting said trough on said endless belt comprises a cloth-covered strip detachably secured to the bottom of said trough.

4. In apparatus for forming a sheet from a liquid solution, a moving member having a surface to which the solution is delivered, a doctor blade having its lower edge spaced from said surface and co-operating therewith to determine the thickness of the film of solution carried past said doctor blade by said moving member, said lower edge having a substantially straight central longitudinal portion and elongated end portions extending downwardly and outwardly from said central portion to thereby efifect tapering of the marginal portions of the sheet forming solution passing under said edge, whereby the normal tendency of the film to build up its marginal thickness is counteracted and uniformity of sheet thickness is attained.

5. In apparatus for forming a sheet from a liquid solution, a moving member having a surface to which the solution is delivered, a doctor blade having its lower edge spaced from said surface and co-operating therewith to determine the thickness of the film of solution carried past said doctor blade by said moving member, said lower edge having a substantially straight central longitudinal portion and elongated end portions extending downwardly and outwardly from said central portion to thereby efi'ect tapering of the marginal portions of the sheet forming solution passing under said edge, whereby the normal tendency of the film to build up its marginal thickness is counteracted and uniformity of sheet thickness is attained, said doctor blade having at least such lower edge portion formed of an alloy which is substantially non-expansible within the normal range of temperatures encountered in the sheet-forming operation.

EDOUARD M. KRATZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 864,028 Peters Aug. 20, 1907 1,764,423 Stone June 1'7, 1930 410,898 Kattentidt Sept. 10, 1889 1,604,941 Hofmann Oct. 26, 1926 171,629 Owens Dec. 28, 1875 953,570 Zickerman Mar. 29, 1910 2 ,033,379 Jenkins et al Mar. 10, 1936 1,829,153 Pearl Oct. 27, 1931 328,958 Maxfield Oct. 27, 1885 1,033,282 Sleeper July 23, 1912 2,261,411 Rees Nov.-4, 1941 2,051,201 Davidson Apr. 18, 1936 1,961,025 Wickham May 29, 1934 2,011,354 Carver et al. Aug. 13, 1935