| JP2003105685 | METHOD FOR PRODUCING PULP SHEET |
| JP04370286 | DISK FILTER APPARATUS FOR PULP TREATMENT |
| WO/1999/011357 | APPARATUS FOR FILTERING SUSPENSIONS |
Lundberg, Jörgen (Idrottsgatan 21, Sundsvall, S-856 43, SE)
| 1. | A roll body for a press roll for dewatering pulp, comprising a central drum and several frame rings, to which at least one perforated roll plate is intended to be attached, the frame rings being distributed along the length of the central drum, characterized in that each frame ring is attached directly to the central drum, and is provided with at least one recess, whereby a passage in the axial direction is provided for the transport of liquid to the ends of the roll body. |
| 2. | A roll body according to claim 1 , characterized in that each recess is adjacent to the central drum. |
| 3. | A roll body according to claim 1 or 2, characterized in that the recess of each frame ring is axially aligned with the recess of the adjacent frame ring, whereby an axially continuous passage through the frame rings is provided. |
| 4. | A roll body according any of the claims 1 to 3, characterized in that each frame ring is provided with several recesses distributed along the circumference of the frame ring. |
| 5. | A roll body according any of the claims 1 to 4, characterized in that each frame ring is attached to the adjacent frame ring by at least one intermediate member. |
| 6. | A roll body according any of the claims 1 to 5, characterized in that the central drum is covered with a surface of stainless steel. |
| 7. | A roll press for dewatering pulp, comprising two press rolls, between which the pulp is passed, and in the press nip of which the pulp is pressed, the roll body for each press roll comprising a central drum and several frame rings distributed along the length of the central drum, at least one perforated roll plate being attached to the frame rings, characterized in that the roll body for at least one of the press rolls comprises the special features mentioned in any of the claims 1 to 6. |
| 8. | A roll press according to claim 7, characterized in that the roll press is arranged to pass the pulp between the two press rolls in a vertical direction from below upwards, and that the roll body of both press rolls comprises the special features mentioned in any of the claims 1 to 6. |
| 9. | A roll press according to claim 7, characterized in that said two press rolls form a lower press roll and an upper press roll, respectively, of the roll press, and that the roll body of the lower press roll comprises the special features men tioned in any of the claims 1 to 6. |
Technical Field
The present invention relates to a roll body for a press roll for dewatering pulp, comprising a central drum and several frame rings, to which at least one perforated roll plate is intended to be attached, the frame rings being distributed along the length of the central drum, and to a roll press comprising at least one press roll provided with said roll body.
Background of the Invention
When producing cellulose-based products, a roll press is frequently pre- sent for dewatering the cellulose-based pulp. The pulp is passed between two cooperating press rolls in a roll press, the press rolls having a perforated envelope surface, whereby the envelope surface is permeable to water pressed out of the pulp, and is pressed in the press nip between the press rolls, whereby water is pressed out of the pulp. One example of such a roll press for dewatering pulp is disclosed in SE 505 539, e.g., where the central axes of the press rolls are lying in substantially the same horizontal plane, and the pulp is passing the press nip between the press rolls in a vertical direction, from below upwards.
SE 519 753 describes a sealing of a press roll in a roll press having two co-operating press rolls for dewatering material suspensions. The above mentioned roll presses have in common that their roll bodies have a conventional structure, where the roll body comprises a longitudinal central drum, which can comprise a drum or an inner drum covered with a covering plate, or the like. The central drum is provided with several supporting ribs arranged longitudinally along the longitudinal axis of the central drum and evenly distributed along the circumference of the central drum. The purpose of these supporting ribs is to strengthen the structure, and also to provide channels which axially guide liquid pressed out of the pulp to the ends of the press roll. On these supporting ribs, several circumferential frame rings are attached, surrounding the roll body along its whole length, the purpose of which is to be a supporting structure for the perfo- rated roll plates which are positioned utmost on the press roll, since the roll plates are abutting the frame rings around their whole circumference, and to allow expressed liquid, which has passed through the roll plate, to fall downwards after the passage through the apertures of the roll plate. This is important in order to reduce
the rewetting, i.e. the liquid which after the press nip flows back through the roll plate and dilutes the pressed pulp, especially for roll presses where the pulp is passed through the press nip between two press rolls in a vertical direction from below upwards, such as in SE 505 539, and also regarding the lower press roll for roll presses, where the pulp is passed in a substantially horizontal direction through the press nip between an upper and a lower press roll, the central axes of which are lying in different horizontal planes. The result of this rewetting is that the resulting dryness of the pressed pulp from the roll press is lower, and that the pulp is contaminated by lye or liquid previously pressed out. However, a drawback to prior art roll bodies is that this passage of liquid downwards in a vertical direction, inside the perforated roll plate, is limited due to the longitudinal supporting ribs, whereby the reduction of the rewetting is not effective enough. Further, the construction of prior art roll bodies is complicated and consists of several construction articles, which results in a complicated manufac- turing of the roll body, involving several welding and shrinking steps, and consequently, also a complicated manufacturing of the press roll, and a high manufacturing cost due to this.
The Object of the Invention
The object of the present invention is thus to provide a roll body which pro- vides a press roll having a minimized rewetting, and which is less complicated and less expensive to manufacture compared to conventional roll bodies, especially for roll presses where the pulp is passing the press nip between two press rolls in a vertical direction from below upwards, and regarding the lower press roll of a roll press where the pulp is passing the press nip between an upper and a lower press roll in a substantial horizontal direction. Further, the purpose is to provide a roll press which achieves a minimized rewetting and which is also less complicated and less expensive to manufacture compared to conventional roll presses.
Summary of the Invention
The above mentioned objects are achieved by providing a roll body of the kind defined in the preamble of claim 1 , and a roll press of the kind defined in the preamble of claim 7, where a roll body comprises the special features that each frame ring is attached directly to the central drum, and is provided with at least one recess, whereby a passage in the axial direction is provided for the transport of
liquid to the ends of the roll body. If the central drum comprises a covering sheet, naturally, each frame ring is attached to the covering sheet. By this roll body according to the present invention, a press roll is provided, having minimized rewet- ting since the construction makes it possible to omit the supporting ribs, whereby the fall downwards of expressed liquid, inside the perforated roll plates, no longer is restricted by said supporting ribs, especially for roll presses where the cellulose- based pulp is passing the press nip between two press rolls in a vertical direction, from below upwards, and regarding the lower press roll of roll presses where the pulp is passing the press nip between an upper and a lower press roll, in a sub- stantial horizontal direction. Further, by this roll body according the present invention, a roll press having a minimized rewetting is provided. The roll body of the present invention is also less complicated in its construction, and has fewer construction articles, which results in fewer manufacturing steps, which in turn results in lower manufacturing costs of the roll body, the press roll and, consequently, also of the roll press.
According to an advantageous embodiment of the roll body according to the present invention, each recess is adjacent to the central drum, which results in that liquid pressed out of the pulp is more easily transported in the axial direction, and thereby further reduces the rewetting. According to another advantageous embodiment of the roll body according to the present invention, the recess of each frame ring is axially aligned with the recess of the adjacent frame ring, whereby an axially continuous passage through the frame rings is provided, which further facilitates the transportation of liquid in the axial direction. According to yet another advantageous embodiment of the roll body according to the present invention, each frame ring is provided with several recesses distributed along the circumference of the frame ring. By this, the transportation of liquid in the axial direction is made yet more effective.
According to an advantageous embodiment of the roll press according to the present invention, the roll body of at least one of the press rolls comprises the further special features mentioned in any of the claims 2 to 6.
According to a further advantageous embodiment of the roll press according to the present invention, the roll press is arranged to pass the pulp between the two press rolls in a vertical direction from below upwards, where the roll body
of both press rolls comprises the special features mentioned in any of the claims 1 to 6.
According to another advantageous embodiment of the roll press according to the present invention, said two press rolls form a lower press roll and an up- per press roll, respectively, of the roll press, where the roll body of the lower press roll comprises the special features mentioned in any of the claims 1 to 6. The central axis of the upper press roll is lying in a horizontal plane above the horizontal plane in which the central axis of the lower press roll lies, whereby the pulp is fed more horizontally than vertically between the press rolls. This roll press can also comprise a conveying belt for the pulp, which runs between the press rolls.
Brief Description of the Drawings
The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which: Fig. 1 is a schematic cut-away view of a conventional press roll having a conventional roll body,
Fig. 2 is a schematic partial sectional view of a conventional roll body, Fig. 3 is a schematic partial sectional view of an embodiment of a roll body according to the present invention, Fig. 4 is a schematic partial top view of the frame rings of the roll body of
Fig. 3, and
Fig. 5 is a sectional view of an embodiment of the roll press according to the present invention.
Detailed Description of Embodiments Fig. 1 shows in section a conventional press roll comprising a conventional roll body. The roll body comprises a longitudinal central drum 1 , to the ends of which attachment means 2 are attached for the pivotal mounting in a roll press. To the envelope surface of the central drum 1 , several longitudinal supporting ribs 3 are attached by welding. Several flat bars 4 are welded to several frame rings 5 at the inside of said frame rings 5, so that the frame rings 5 are positioned in succession with a suitable distance apart and distributed along a distance corresponding to the length of the central drum 1. The flat bars 4 are extending transversely to the frame rings 5 at their inside, and form, together with the frame rings 5, a kind
of "cage". This "cage" is then shrunk into its position on the supporting ribs 3. The distances between the frame rings 5 allow the liquid, pressed out of the pressed pulp, to pass. Onto the frame rings 5, around their whole outer circumference, several perforated roll plates 6 have then been shrunk into position, and welded edge to edge.
Fig. 2 shows a partial sectional view of a conventional press roll, illustrating in more detail the attachment of the frame rings 2.5 to the central drum 2.1 , by means of the longitudinal supporting ribs 2.3 and the flat bars 2.4.
Fig. 3 shows a partial sectional view of an embodiment of a roll body ac- cording to the present invention. Several frame rings 7 are attached directly to the central drum 8 of the roll body, and each frame ring 7 is provided with several through holes/recesses 9.1 , 9.2, 9.3 distributed over the circumference of the frame ring 7, which provide a passage in the axial direction for the transport of liquid to the ends of the roll body. The extension of the frame rings 7 in the radial di- rection is considerably greater compared to conventional frame rings, which in the roll body according to the present invention results in an effective "height of fall" of the expressed liquid after the passage through the perforated roll plate, due to the absence of the conventional supporting ribs. The recesses 91 , 9.2, 9.3 are adjacent to the central drum 8, which facilitates the axial transport of liquid. The re- cesses 9.1 , 9.2, 9.3 of each frame ring 7 are in axial alignment with the corresponding recesses of the adjacent frame ring, whereby an axially continuous passage through the frame rings 7 is provided. The central drum 8 is covered with a surface of stainless steel 10. The roll plates are then affixed to the outside of the frame rings 7. Fig. 4 shows a schematic partial top view of the frame rings of the roll body of Fig. 3. Each frame ring 7, 7.1 , 7.2, 7.3, 7.4 is attached to an adjacent frame ring 7, 7.1 , 7.2, 7.3, 7.4 by means of several welded intermediate members 11.1 , 11.2, 11.3, 11.4 to provide a rigid construction. However, the frame rings can be fixed in relation to each other in any other way, by screw joint reinforcement, shrinking etc., for example.
Fig. 5 shows an embodiment of the roll press according to the present invention, comprising a first press roll 12 and a second press roll 13, the longitudinal central axes of which are lying in substantially the same horizontal plane, each press roll comprising a roll body according to the present invention, where respec-
tive frame ring 14, 15 is attached directly to respective central drum 16, 17. Perforated roll plates 18, 19 are abutting against the frame rings 14, 15. The pulp 20 is fed in through an inlet 21 and pressed up towards a press nip 22 between the first and the second press roll 12, 13, the rotation of which is indicated by vertically pointing arrows, the pulp 20 being dewatered and further pressed vertically upwards. By means of this roll press, the liquid pressed out of the pulp 20 in the press nip 22, which has permeated through the holes of the roll plates 18, 19, can more easily fall downwards compared to conventional roll presses, whereby the rewetting is effectively reduced.
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