US3460467A - Wet presses - Google Patents

Description

O. B. NYSTROM WET PRESSES Aug. 12, 1969.

2 Sheets-Sheet 1 Filed Dec. 27, 1966 Fl 6.1 v

FIG.5

United States Patent 3,460,467 WET PRESSES Olof Birger Nystrom, Sundsbruk, Sweden, assignor to Sunds Aktiebolag, Sundsbruk, Sundsvall, Sweden Filed Dec. 27, 1966, Ser. No. 604,857 Claims priority, application Sweden, Jan. 25, 1966,

921/ 66 Int. Cl. 133% 9/20, 3/04; B01d 33/06 US. Cl. 100-121 12 Claims ABSTRACT OF THE DISCLOSURE In connection with the thickening of fibrous pulp suspensions of cellulosic material, for example, mechanical wood-pulp, and similar materials in wet presses of the kind comprising two or more roll-shaped press members, which are provided with perforations, slots or the like and which are adapted to rotate in a vat, tightening against the press members (rolls), considerable rewetting of the web of pulp takes place after the press roll nip, which is due to the fact that part of the liquid, entering through the perforated shell of the roll during the pressing opera tion, is sucked back into the web of pulp while the web is expanding after the press roll nip. The high pressure often occurring in the press roll nip also results in the life of the perforated shell of the roll becoming so short that the press-in spite of its functional suitability for the dewatering to high consistenciesmay become too eX- pensive to maintain and may cause too frequent stoppages.

The present invention has for its object to eliminate the aforesaid drawbacks. The improvement according to the invention is characterized in that at least one of the press rolls is provided with one or more groups of channels arranged one after the other with respect to the axial direction of the roll, each of said channels extending all around the roll and being preferably unbroken, radially extending partition walls being provided between said channels, said partition walls constituting, at their outer peripheries, supports for a pervious, preferably perforated shell plate, each of said groups of channels being separated from the neighbouring groups of channels by radially extending walls, to which the respective appertaining shell plate of each group of channels is secured by means of an unbroken, or substantially unbroken, weld which is common to every two juxtaposed shell plates.

The invention will be described below in greater detail in connection with the accompanying drawings, in which FIGURE 1, partly in cross-section, shows a known wet press of the type to which the present invention refers primarily, FIGURE 2 showing a partial cross sectional view of the press rolls, on an enlarged scale as compared with FIGURE 1, FIGURE 3 showing a cross sectional view along the line 33 of FIGURE 2, FIGURE 4 showing a cross sectional view of a particular way of joining, in accordance with the invention, the two ends of a shell plate, and FIGURE 5 showing a cross sectional view of a special scraping device according to the invention.

The invention refers to the type of wet presses, appearing from FIGURE 1, i.e. presses of the kind having two, or more, roll-shaped press members, each of which ex- 3,460,467 Patented Aug. 12, 1969 "ice poses part of its surface towards one (or more) chamber, or vat, which tightens against the rolls and which, under an excess pressure, amounting to 0.22.0 kg./sq. cm., is kept filled with a fiber suspension of 0.56% consistency. Good operating results have been obtained at an initial consistency of about 4% of the fibrous suspension and at an excess pressure, amounting to about 0.5 kg./ sq. cm., and also at initial consistencies of about 2, 3 and 5% and at about 69% and at about 942% in the press, shown in FIGURES 1 and 2, which is provided with two rolls 1 and 2 and the vat of which is designated by 3. The fibrous suspension is supplied to the vat through the short feed pipe 4. Upon rotation of the rolls 1, 2 in the directions of the arrows each roll picks up a layer of pulp, not shown in the drawing, said layer during its upward move ment being compressed by the rolls to form one single web of pulp. It is then important that the pressed out liquid, which flows into each roll through the perforations provided therein, be led away in such a manner that it will not re-wet the web of pulp after the nip. For that reason the rolls 1, 2 are equipped with rings 6 extending all around the rolls and serving as supporting or carrying members, channels 7 being formed between said rings, said channels likewise extending all around the rolls and preferably having outwardly widening walls extending from a bowl-shaped bottom at a clearance angle of, for example, 20. Within the channels the pressed out liquid flows downwards and moves on into openings provided in the body 9 of the roll and extending about radially thereof or, as shown in FIGURE 2, into openings 8 directed obliquely downwards at an angle of a and further into the interior 10 of the body of the roll, from where the liquid is led away through the openings 11.

The channels 7, extending all around the roll, may, however involve that a support, which is not so good, is obtained for the perforated plate. Due to the high surface pressures in the nip (of the order 300-400 leg/longitudinal centimeter) in wet presses of the type in question the envelope of the body of the roll normally displays a square-net pattern of peripherally and axially extending fillets, the surfaces of which that are in contact with the perforated plate are tooth-shaped, the plate being spot- Welded to a number of the teeth. The spot-welding idea results in a durability which is not quite satisfactory in the above described embodiment and it is not suitable for use in connection with the embodiments of the rolls in accordance with the present invention, which thus has for its object to eliminate also this drawback. Therefore, a more reliable way of securing is proposed and is shown, in principle, in FIGURE 3. The perforated plate 5 is applied to the body of the roll, is tightened around the latter and is welded together by one or more welds. After that a V-shaped, or similar chamfering is turned for the weld 12, which will thereby join two shell plates at the ring 6 and which preferably is made to extend continuously all the way around. The V-shaped, or similar, cham-fering may also be made in the plates before applying them to the body of the roll. It is possible also to do completely without the chamfering, when thin plates are concerned, for example, plates of 2 mm. thickness, if the edges of the plates are placed in contact with each other or, when thick plates are concerned, for example, plates of 4-6 mm. thickness, if the edges of the plates are placed at a distance from each other. In order to increase the durability of the plate an edge zone 13 of 2-8 mm., preferably about 3, 4 or 5 mm., of the plate may be left unperforated near the weld. The axial length of each plate should be of the order 500 mm., preferably 200-400 mm. and preferentially about 200 mm.., when the diameter of the roll amounts to about 600-1000 mm., or more,

and said axial length should extend over a group of about -40, preferably about -25 and preferentially about channels 7 and partition walls 6. By means of the above described Way of fixing the plates their durability has become multiplied.

FIGURE 4 shows how the two ends of 'a shell plate may be joined together. The axial weld 14 is made against a fillet 15, which is mounted in a groove 16 in the ring 6. The inevitable rolling out (increase in length) of the plates, which occurs after some time of use but which becomes greatly reduced because of the above described way of fixing the plates along their circumferential edges, by welding, by this way of performing the joining together of the ends of the plates will be distributed all around the roll and will result in a small increase of the diameter of the shell plate, such increase being uniform all the Way around.

The thickness of each perforated plate must be adapted both to the demands for strength and to the demands for filtering properties. An example of a suitable embodiment is as follows: thickness of plate=2 mm., or 4 mm., diameter of perforation=1 mm., distance between the perforations=2 mm., which means that the diameter of each perforation amounts to 50% of the distance between the perforations, a divergence of 125%, possibly of 250%, being permissible.

As will appear from FIGURE 1 the web of pulp is removed from the roll 2 by means of a doctor 17, is then conveyed, by means of the roll 1, to the right in the figure and after that is led away by way of the receiving table 18. It has been found that difficulties may arise in respect of the doctor 17 because of the fact that on account of the high surface pressures, fibers are pressed into the perforations, which will result in a breakage of the doctor. In order to eliminate this drawback the doctor may be constructed in the manner shown in FIGURE 5. The doctor blade 19 is mounted in a holder 22, actuated by the spring 20 and turnable on a spindle 21. In case there is formed, on the roll 2, a layer of fibers, which it is diificult to remove, the doctor blade 19 will swing upwards and outwards, the pressure of the spring 20 increasing gradually, until the spring force has become great enough for causing the doctor blade to cut through the layer of fibers and remove it in its entirety.

I claim:

1. In a pair of press rolls in which at least one of the rolls is provided with a plurality of generally parallel peripheral channels extending continuously around the periphery of the roll and adapted to contain a stream of filtrate, said channels being confined in the axial direction by radially extending walls and by rings arranged peripherally around the roll, each said ring at its outer periphery constituting a supporting surface for a pervious shell plate, the improvement according to which the shell plate consists essentially of a number of section plates, each section plate covering a number of channels in the axial direction, said number being lower than the total number of channels on the roll, and in that each section plate is secured to the supporting surface of an adjacent ring by means of a substantially unbroken weld along the peripherally arranged sides of said section plate.

2. Improvement according to claim 1, in which the weld constitutes a common joint for two adjacent section plates.

3. An improvement according to claim 1, in which the sides of each channel diverge in the radial outward direction, the angle between said sides being within the range 3-30.

4. An improvement according to claim 3, in which each channel has a bowl-shaped bottom.

5. An improvement according to claim 1, in which the channels are arranged in groups comprising from about 10 to about 40 channels, all of which are separated from each other by said walls.

6. An improvement according to claim 1, in which each channel has a number of outlet passages directed inwards, preferably radially inwards, relatively to the roll, said passages serving for leading away to the interior of the roll the filtrate entering the passages.

7. A pair of press rolls as defined in claim 6, in which the outlet passages are directed obliquely backwards with respect to the direction of movement, at the press roll nip, of the material being treated.

8. An improvement according to claim 1, in which an edge zone, of a width of 2-8 mm., of the shell plate embracing the roll is unperforated.

9. An improvement according to claim 1, in which a fillet is provided under each axial weld, said fillet resting in a matching axial groove in the wall of the channel.

10. An improvement according to claim 1, in which the perforated plate is provided with a great number of regularly distributed holes, each having a diameter of 0.8-1.2 mm., and the pitch amounting to the double diameter of the hole, the thickness of each plate being from about 2 to about 6 mm.

11. An improved press roll pair in which at least one of the rolls is provided with a plurality of channels arranged after each other in the axial direction of said roll and adapted for a stream of filtrate and extending continuously around the periphery of the roll, said channels being confined in the axial direction by radially extending walls and peripherally around the roll arranged rings, said rings at their outer periphery constituting a supporting surface for a pervious, preferably perforated shell plate, sai'd pair of press rolls being associated with a doctor which is adapted to yield outwards with respect to the center of the roll and which is under an elastic pressure, whereby fibers pressed into the perforations are removed therefrom.

12. An improvement according to claim 11, in which the elastic pressure is obtained by means of a spring.

References Cited UNITED STATES PATENTS 1,787,937 1/1931 Dunn 174 2,972,378 2/1961 Nuyens 100-121 X 3,105,043 9/1963 Rich et a1 210402 3,217,554 11/1965 Stalker 29129 X PETER FELDMAN, Primary Examiner US. Cl. X.R.

29l2l; l00174; 162-289; 210402

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