US 1916393 A
Description (OCR text may contain errors)
July 4, 1933. R W SMH 1,916,393
PULP SCREEN PLATE Filed Sept. 23, 1931 /N VEN TOR @YM/WM Arron/vf: Ys
Patented July 4, 1933 PATENT oFFicE RICHMOND W. SMITH, OF WALPOLE, MASSACHUSETTS PULP SCREEN PLATE Application "filed September 23, 1931. Serial No. 564,561.
My invention yrelates to the paper making industry and particularly to improve. mentsin devices for screening pulp, paper stock and the like.
5 Heretofore, screens of this type have been made of metal plates, generally bronze, or other non-ferrous metals, having openings of precise sizecut therein by sawing or milling. Itis extremely important that the screen openings be maintained within a few thousandths of an inch of the size as cut. The life of a metal screen is therefore very short due to the rapidity .with which the small but maximum permissible enlargement of the 35 openings occurs through normal wear. Moreover` the openings in avmetal plate present comparatively sharp edges and rough surfaces which tendto catch the passing bers y causing the formation of strings which re- 29 sult in slime spots in the finished paper. p
lIt has been proposed to eliminate these difficulties by electroplating a metal base plate with rubber, thereby covering the sharp edges and rough surfaces of the openings and utilizing the low friction coefficient of the rubber, when wet, to increase the capacity of the screen. minutesize of the openings required and because of the extremely small permissible U0 variation in the .size thereof such screens are difficult to makeand therefore very expensive. Y
Y The principal object of my invention ris to provide a pulp screen plate of rubber having openings of precise dimensions therein and which can be constructed at reasonable cost. Another object is to provide a screen plate having a greater capacity per unit of area and a very much longer life than the metal screens now inuse. Another object is to provide a screen in which the possibility of clogging is reduced to a minimum.
lVith these objects in view, my invention includes the novel elements and the combinations and arrangements thereof described below and illustrated in the accompanying drawing in which Fig. l is a fragmentary plan view of my pulp screen plate;
Because of the comparativelyl Fig. 2 is an enlarged fragmentary section in the plane 2-2 of Fig. l;
Fig. 3 is an enlarged fragmentary section in the plane 3 3 of Fig. l; and
Fig. 4 is a fragmentary perspective view of the screen yon an enlarged scale.
Referring to the drawing, l represents the screen which comprises two elements, a backing or stiening plate 2, and the rubber ,screen 8 which are secured together, preferably by cementing and vulcanizing, to form a unitary structure. Y
In making the screen, the metal plate is lirst slotted with a relief saw of thickness somewhat O'reater than the desired width of the finished slots. This cut does not go en-V tirely through the plate but extends only Vto about the depth indicated at 4. The next operation is to cut entirely throughthe plate with a saw only slightly thicker than there- 7U quired width of the finished slot, as shown at 5. The metal walls surrounding the openings are thus free or exposed. f
Since rubber does not vulcanize well to the bronze of which the plates are generally made, before applying the rubber 3 to the plate, the plate is sand blasted and then coated with brass 6 by spraying it thereon in a molten condition as is well understood in the art. This step ispreferably but not necessarily carried out prior tothe cutting through of the plate. After sand blasting and spray-y ing, the rubber is cemented tothe plate, as shown at 7, and vulcanized thereon. A slotting saw of the proper size operating through the slots already made in the metal plate is thenused to cut to exact size the screen open# ings proper in the rubber. These openings, depending upon requirements, generally vary in width between the approximate limits of 0.006 inch and 0.090 inch depending upon-conditions such, for example as the nature of the pulp and the ycharacter of the sheet required. It is understood of course that all the openings in any one screen should be the same size and it is extremely important that the slotsin the rubber be out squarely and very accurately.V
By reference to Fig. 4 which is an enlarged fragmentary perspective view of the screen, 100
Vdecrease the size of the openings, but the" rubber should project slightlylbeyond the edges of the openings in the metal plate as shown in Fig. 4. p
The met-al backing'for the screen should be of suliicient thickness to provide the requisite stability and, as a material therefor, bronze is preferred. The rubberscreen itself may be about 116 inch thick and of a density around twenty plastomcter although it is to be understood that the invention is in no sense limited in these respects.
Screens made according to my invention arc not only substantially inore'eliicient than all metal screens but are extremely resistant to wear. The life of such a screen is indefinitely long and cannot be accurately estimated at this time. One specimen which has been in operation over a year indicates no enlargement of the openings. On the other hand a comparative test of a rubber and bronze screen, respectively, extending'over a period of two months showed no enlargement whatever in the openings in the rubber screen whereas the openings in a bronze screen showed an average enlargement of 0.004 inch.
While I have described my invention in its preferred embodiment it is to be understood that thewords which I have used are words of description andnot of limitation and that changes within the scope of the appended claims may be made without departing from the true scope and spirit of my invention in its broader aspects.
What I claim isy 1. A pulp screen plate comprising a layer of rubber having openings therein, and a stilening plate substantially coextensive with the perf-orate portion of said rubber and having openings therein ycommunicating withthe openings in said rubber but slightly larger in size. y
2. A pulp screen plate comprising'a rigid metal plate having a layer of rubber'secured to one side thereof to orm a unitary struc` ture and provided with a multiplicity of passages extending therethrough.
V3. A pulp screen plate comprising a rigid metal plate having a layer of rubber secured to oneV side thereof to form a unitarystruci ture and provided with a multiplicity of pas sages extending therethrough; said passages being of larger cross sectional area in the metal than in the rubber.
4L. In a pulp screen plate, the combination with a rubber plate having slotted openings therein forming the screen proper, of means on one side thereof for stiffening said plate around the edges of said openings to prevent deformation under liquid pressure.
A pulp screen plate comprising a metal base plate having slotted openings therein of substantially greater cross sectional area at one side of said plate than at the other, and a rubber plate vulcanized thereon and having slottedopenings therein communicating with but of smaller cross sectional area thanthe vminimum area of the openings in said plate.
6. A pulp screen plate comprisin a rigid plate of corrosion resistant metal aving a layer of brass thereon and provided wlth slotted passages therethrough, and a rubber plate vulcanized on said brass and provided with slotted passages communicating with the passages in said metal plate.
7. A pulp screen plate comprising a metal plate having slotted openings therein provided with free` edges, and a rubber facing connected to said plate ;v said facing having slotted openings therein the walls surround` ing which overlie and 'project slightly beyond the walls surroundin'githe openings in the plate.
8. Ay pulp screen plate comprisinga metal plate and a rubber plate secured together to form a unitary structure, and provided-with a multiplicity of slotted passages therethrough; the side walls of said passages through the metal being exposed and splayed outwardly. u
9. -A pulp screen plate comprising a metal plate and a rubber plate vulcanized together to form a unitary structure, and provided with a multiplicity of slotted passages there through; the side walls of said passages through the rubber portion of the structure being parallel and in precise spaced relation and 4theside walls of said passages through the metal portion of the structure being exposed and splayed outwardly. u
l0. A pulp screen plate comprising a metal plate having a layer of rubber on one side thereof and provided with a mutiplicity of slotted passages therethrough, the walls surrounding the openings in the metal being exposed, the edges of the openings to said passages on the rubber side of said screen being square and sharp whereby openings of a precise width are defined.
11. The method of making a pulp screen plate which comprises cutting slotted openings in a metal plate, cementing a sheet of rubber to said plate, and thereafter cutting slotted openings in said sheet communicating with the openings in said plate.
l2. The method of making a pulp screen face of the plate than the other, Vulcanizing a layer of rubber over the surface of said plate having the openings of lesser Width therein, and thereafter forming in said rubber, slots of precise, predetermined but smaller size than the plate slots by cutting the rubber through the passages in said plate.
RICHMOND W. SMITH.