US2983990A - Paper mill roll - Google Patents

Description

y 1961 J. J- STEVENSON ET AL 90 PAPER MILL ROLL Filed Sept. 29, 1958 G INVENTOR-f [5 B dq PAPER MILL RoLL James Joseph Stevenson and Philip Ralph Dowden, Erie, Pa, assignors to Continental Rubber Works, Erie, Pa., a corporation of Pennsylvania Filed Sept. 29, 1958, Ser. No. 763,870 4 Claims. (11. 29-132 This invention is a roll for paper machines which is particularly useful as a top press roll in the press section where the paper web is so weak and tender that it must be supported on felts which carry it through the nip of the rolls. The top press roll is critical because it comes into direct contact with the paper Web and must be free of any tendency to pick up the paper fibers or the web will be damaged and may even break and interrupt the continuous operation. Granite has been considered the best known material for top press rolls although rolls of hard rubber with granite or rock like particles bonded therein are used. These hard rubber rolls all provide an active surface of rock which simulates the action of granite at lower cost and weight.

Although the roll of this invention is made of hard rubber and rock particles, unlike the prior rolls, the rock particles are not bonded in the rubber and fall out when the outer surface of the roll is finish ground or as the outer surface wears. The resultant surface is uniformly peppered with pits so fine as not to spoil the surface of the paper which act to break the water film on the roll and to provide minute ai-r cushions releasing the web from the roll. The absence of rock particles in the surface also eliminates scoring of the doctor blade.

In the drawing, Fig. l is an elevation of a roll and Fig. 2 is an enlarged fragmentary section of the rubber covering of the roll.

The roll has the usual metal roll body 1 bonded to a hard rubber (e.g. Pusey and Jones plastorneter reading of 1 with 4; ball) covering 2 which is finish ground to provide the paper Web contacting surface 3. The parts so far described follow the prior :art such as Patents 1,563,943; 1,537,439; 1,787,890; Re. 18,111; 2,062,317; and 2,280,208. In the prior art, as represented by these patents, granite rolls remained the best in performance and the hard rubber rolls used were those which had an active surface of granite or equivalent rock.

In most of the prior art hard rubber rolls, the rock particles were relatively coarse and in all of the rolls the rock particles were bonded. Because these particles were intended to be firmly bonded in the hard rubber, they were preferably crushed or powdered so as to have jagged edges rather than having the rounded surfaces usual in sand. In amount, the particles were at least equal to the weight of rubber and ranged up to five times the weight of rubber.

In the present application, use is made of fine rock particles 4 in amount having a weight of about A; the weight of the hard rubber. A readily available commercial rock material is natural crystal quartz grade 1/0 having particles which will pass through a 94 mesh screen and will be retained on a 115 mesh screen. Although these fine particles are uniformly dispersed in the hard rubber, as shown at the left in Fig. 2 which shows the condition of the rubber at the end of the molding operation, they are not bonded to the rubber. When the roll is subjected to the usual finish grinding operation, the particles fall out or are knocked out of the rubber surface leaving-the ground surface peppered with small pits.

nited States Patent ice These pits appear only where the particles have been eX- posed by the grinding operation. Beneath the ground surface, the particles are still embedded in the rubber and provide a solid subsurface. The resultant active surface of the roll, instead of being predominantly rock, is predominantly rubber with small diameter pits which trap air and aid in releasing the paper web from the roll surface. Because the rock material does not form the active surface of the roll, it need not be selected for its paper releasing properties as has been the case in the prior hard rubber rolls. Neither the material nor its size or shape is critical. The particles should not be so large as to provide pits which would make the active surface of the roll too rough for the grade of paper. It will be noted that the depth of the pits on the active surface averages less than the diameter of the particles and that below the active surface the rubber covering is solid and substantially rock hard, as shown by the plastometer reading given above.

Because the particles do not form any substantial part of the active surface of the roll, the material is not critical. Silica is a readily available material which might be considered preferred because of its cheapness.

For the hard rubber covering 2, butadiene copolymer elastomers are preferred because of their oil resisting and heat resisting properties. When a roll bearing overheats, the temperature rises rapidly and the ability of the hard rubber covering to stand temperatures up to 200 F. without softening or cracking is important. At these temperatures, granite rolls crack. Another advantage of the butadiene elastomers is that they can be applied in much greater thicknesses if desired. While other hard rubber coatings have practically been limited to thickness of /2", the butadiene rubber can be applied in thicknesses up to 2 /2" and more. The rubber should not bond to the rock particles although a tendency to bond may be overcome by using a releasing agent which will prevent bonding. Non-wetting or water repellent properties are desirable because the purpose of the rolls is to remove water from the paper web.

The action of the roll on the moist paper web is better than granite which has heretofore been considered to have the best action. There is almost no tendency for the paper web to stick to the surface. Another advantage is that water does not form in a continuous film around the roll so as to interfere with the removal of water from the paper web. The minute pits formed by the removal of the fine particles act to break the water film which would otherwise follow around the roll and be returned to the paper web. The butadiene rubber has very little tendency to stick to paper fibers. While paper fibers drying on other rolls must be scraped off, scraping is not necessary with the butadiene rubber.

Not only does the roll surface have a better action on the paper web, but it does not heat or wear or score the doctor blade because there is essentially no rock in the active surface. The active surface of the roll also Wears longer before needing refinishing. When substituted for commercial hard rubber paper rolls, the present rolls run from two to three times as long before requiring regrinding. Wear of the active surface does not change the action. As the surface wears, fine particles which had previously been embedded are exposed and fall out continuously renewing the pitted surface.

The roll can be used with all kinds of paper even including ground wood pulp, which is considered one of the most diflicult to handle.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A paper machine roll comprising a roll body and a covering bonded to the body comprising hard butadiene copolymer rubber having uniformly dispersed therein fine silica particles of substantially 100 mesh unbonded to the rubber and said roll having a finish ground surface in which the great majority of the particles exposed by finish grinding have fallen out so said finish ground surface is a smooth essentially silica free active surface with fine pits throughout promoting release of paper fibers while the unexposed particles remain in the rubber to provide a hard subsurface.

2. A paper machine roll comprising a roll body and a covering bonded to the body comprising hard rubber having uniformly dispersed therein fine rock particles of substantially 100 mesh unbonded to the rubber and said roll having a finish ground surface in which the great majority of the particles exposed by finish grinding have fallen out so said finish ground surface is a smooth essentially rock free active surface with fine pits throughout promoting release of paper fibers while the unexposed particles remain in the rubber to provide a hard subsurface.

3. A paper machine roll comprising a roll body and a covering bonded to the body comprising hard butadiene copolymer rubber having uniformly dispersed therein fine rock particles unbonded to the rubber and said roll having a finish ground surface in which the great majority of the particles exposed by finish grinding have fallen out so said finish ground surface is a smooth essentially rock free active surface with fine pits throughout promoting release of paper fibers while the unexposed particles remain in the rubber to provide a hard subsurface.

4. A paper machine roll comprising a roll body and a covering bonded to the body comprising hard rubber having uniformly dispersed therein fine rock particles unbonded to the rubber and said roll having a finish ground surface in which the great majority of the particles exposed by finish grinding have fallen out so said finish ground surface is a smooth essentially rock free surface with fine pits throughout promoting release of paper fibers while the unexposed particles remain in the rubber to provide a hard subsurface.

References Cited in the file of this patent UNITED STATES PATENTS 1,563,943 Adams et a1. Dec. 1, 1925 1,787,890 Woodward Jan. 6, 1931 2,062,317 Joseph Dec. 1, 1936 2,168,233 Millspaugh Aug. 1, 1939 2,280,208 Wilkie Apr. 21, 1942 2,332,514 Holtzclaw Oct. 26, 1943 2,569,546 Treue Oct. 2, 1951

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