A DOCTOR ARRANGEMENT FOR ROLL PRESSES

Abstract: A doctor arrangement for roll presses includes for each press roll (1, 2) a web transfer device (6, 7) which lies in abutment with the barrel surface of its respective roll or in abutment with a wire mounted on said barrel surface. The web transfer device (6, 7) comprises doctor sections (13) having doctor blades (8, 9) and included in a module system. The sections (13) are supported by a coarse shredded trough (5) arranged above the press roll nip (3) and forming, together with the doctor sections (13), a rigid construction in the longitudinal direction of the rolls (1, 2).

Description: A DOCTOR ARRANGEMENT FOR ROLL PRESSES The present invention relates to a doctor arrangement for roll presses which includes for each roll a web transfer device which lies against the barrel surface of a respective roll or against a wire mounted on said barrel surface. A roll press includes two mutually coacting press rolls that define a press roll nip therebetween. The rolls are arranged in a trough into which a suspension of material, for instance pulp suspension, is delivered. The rolls have liquid pervious barrel surfaces and the suspension is de-watered by pressing the liquid through said surfaces with the aid of an overpressure. Final de-watering of the suspension to a desired dry content of the material is achieved in the nip between the rolls. The barrel surfaces of the press rolls are comprised of perforated sheet metal attached to a roll body. In order to obtain a sufficiently large capacity, the combined open area of the holes shall be large whilst, at the same time, the holes must be small so that fibres will not accompany the liquid through the holes. Wires may be mounted onto the barrel surfaces of the rolls to this end. Located downstream of the roll nip is a doctor arrangement which functions to remove the de-watered pulp web from the rolls or from the wires mounted thereon. The doctor arrangement includes a web transfer device for each roll. Hitherto, the web transfer device has comprised a doctor beam that includes a doctor blade for abutment with the barrel surface of the roll or with the wire. The present invention has its basis in a problem encountered with doctor beams and doctor blades. This problem is one of maintaining the doctor blade and the wire surface at a particular distance apart, and is particularly manifested by the greater lengths of such roll presses. With the intention of obtaining maximum possible rigidity, the doctor beam has been given a box-like construction. The boxlike construction coupled with the temperature differences of the different plates in the beam structure make it impossible to retain the doctor blade setting. Consequently, the doctor blade has been placed firmly against the roll in practice, in order to reduce fibre transfer in the pulp. In the case of presses that do not include wires, this practice has been more or less successful and results in lower fibre transfers. In the case of rolls that are fitted with wires, however, it has not been possible to adjust the doctor blade to a zero setting without risk of cutting the wire to pieces. The object of the present invention is to eliminate the aforesaid problem and to enable the doctor blades to optimally abut the press rolls. This object is achieved with the inventive doctor arrangement having the characteristic features set forth in the following Claims. The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 is a cross-sectional view of the central part of a roll press equipped with an inventive doctor arrangement above the roll nip; Fig. 2 illustrates part of Fig. 1 in larger scale; Fig. 3 illustrates a web transfer device in a longitudinal plane through the press; Figs. 3a-c illustrate three alternative embodiments of a part of Fig. 3 in larger scale; Fig. 4 is a cross-sectional view of an alternative embodiment of an inventive doctor arrangement; and Fig. 4a illustrates part of Fig. 4 in larger scale. The roll press illustrated in Fig. 1 includes two rolls 1 and 2, which include a perforated barrel and possibly a wire for allowing water pressed from the pulp to pass through. The roll 2 of said rolls 1 , 2 can be moved laterally to adjust the setting of the roll nip 3. The pulp is pressed up towards the nip 3 between the rolls 1 and 2 where the pulp is de-watered, and is then pressed up from the nip 3 against a shredder screw 4 arranged in a coarse shredder trough 5 and extending parallel with the rolls. The shredder screw 4 disintegrates the pulp and conveys it axially out of the press. Each roll 1 and 2 is equipped with a respective web transfer device 6 and 7. The web transfer devices 6, 7 are comprised of doctor sections 13 forming part of a module system. Doctor blades 8 and 9 are provided at the bottom of respective doctor sections, for scraping respective roll surfaces or wire surfaces. Fig. 2 is an enlarged view of that part of the doctor arrangement belonging to the moveable roll 2. Each doctor blade 9 is carried in the web transfer device 7 by a clamping strip 10. Division of the web transfer device, doctor blades and clamping strips into modules 13 in the longitudinal direction of the press will best be seen from Fig. 3. The doctor sections 13 are carried by the coarse shredder trough 5 by means of supports 14, which in the case of the illustrated embodiment have the form of bottlescrews. As will be seen from Figs. 2 and 3, a support element 14 is provided for each section 13. Each support element 14 is pivotally mounted to an arm 15 fixed to the module 13 and said arm is, in turn, pivotally mounted on a pivot shaft 16. Because the doctor sections are pivotal about the pivot shaft 16, the doctor blades 8, 9 can be pressed against their respective roll surface 1 , 2 with an appropriate force, by shortening the support element 14. That part of the doctor arrangement belonging to the moveable roil 2 includes a setting device 19 on each support element 14, for changing the position of the support mounting at the coarse shredder trough 5. This enables the individual modules to follow the moveable roll. Also shown in Fig. 3 is a suspension device 20 provided at the boundary between two doctor sections 13, therewith to connect the sections 13 end-to-end. The suspension can be made eccentric in accordance with Fig. 3b with the aid of an eccentric pin 21 , or eccentric in accordance with Fig. 3c with an eccentric sleeve 22, so that adjustments can be made to the suspension points of said modules when necessary. Figs. 4 and 4a illustrate an alternative embodiment of the supports 14. In the case of this embodiment, there is used instead of a bottle screw for instance a spring device that includes a compression spring 23 housed in a sleeve 24. A setting rod 25 is connected to the sleeve 24 and loads the spring 23 downward in Fig. 4a to an extent which depends on the position of the setting nut 26. Upward movement of the setting rod 25 is limited by a stop screw 27. This arrangement enables the doctor beam to be set positionally in four different ways. When the setting rod 25 is spaced from the stop screw 27 there will be spring abutment with the roll, and when the sleeve 24 is spaced from the trough plate 28, i.e. the resting surface of the spring, the doctor beam can be moved away from the roll. On the other hand, in the absence of any space between the setting rod 25 and the stop screw 27, there will be no spring abutment with the roll and if there is no distance between the sleeve 24 and the trough plate 28, there will be no movement of the doctor beam away from the roll. This arrangement thus allows the support element 14 to operate in any one of four different ways, namely fully resilient, i.e. movement in both directions is permitted, resiliency against the roll, i.e. only movement towards the roll is permitted, resiliency away from the roll, i.e. movement is only permitted away from the roll, and full rigidity, i.e. no movement is permitted either towards or away from the roll. The coarse shredder trough, which was earlier used solely to transport pulp, is also used in accordance with the invention as reference points for the doctor sections. The coarse shredder trough already has the form of a beam construction and the additional use of the trough to suspend the doctor sections means that the trough must be strengthened with stronger side-beams. The trough 5 thus becomes the rigid part and transfer of the web is effected by doctor sections that are suspended individually from the trough 5. The module construction also enables the doctor arrangement to be used with presses of mutually different sizes where the number of presses is the sole parameter. Because the doctor section is thus short and constructed from a single plate, the temperature problems existing with traditional box constructions no longer occur. The doctor construction can be given any length along the press and no interspaces need be provided to compensate for thermal expansion. The system of modules means that each web transfer device will be thin but nevertheless strong and provides better geometrical conditions with respect to the roll body, i.e. provides better clearance angles to the roll, therewith reducing the risk of pulp packing beneath the doctor blades. The inventive doctor arrangement provides significant improvement to the longest presses. The doctor beams earlier used have required a centre support fastened in the press trough. This construction required the press trough to be made stronger so as to prevent outward deflection of the press trough as a result of the trough pressure affecting the centre support, i.e. the centre of the doctor beam, and therewith cause the doctor blade to penetrate into the roll. Since this support can now be eliminated, the press trough can be calculated for a different outward deflection of the trough and is not restricted by the position or attitude of the doctor blade relative to the roll.

Claims: CLAIMS 1. A doctor arrangement intended for roll presses and comprising for each press roll (1 , 2) a web transfer device (6, 7) which lies in abutment with the barrel surface of its respective press roll or in abutment with a wire mounted on said barrel surface, characterized in that the web transfer device (6, 7) is comprised of doctor sections (13) which include doctor blades (8, 9) and which are included in a module system, wherein the web transfer device is supported by a coarse shredder trough (5) located above the press roll nip (3) and forming together with the doctor sections (13) a rigid construction that extends in the longitudinal direction of the rolls (1 , 2). 2. A doctor arrangement according to Claim 1 , characterized in that the doctor sections (13) are supported by the coarse shredder trough (5) through the medium of a pivot shaft (16) and an adjustable support device (14) between the doctor sections (13) and respective sides of the coarse shredder trough (5). 3. A doctor arrangement according to Claim 2, characterized in that the support devices have the form of bottle screws (14). 4. A doctor arrangement according to Claim 2, characterized in that the support devices (14) are comprised of spring means (23, 24) for enabling resilient loading of the doctor sections towards and/or away from respective rolls (1 , 2) or to obtain a rigid, fixed position relative to the roll. 5. A doctor arrangement according to any one of Claims 2-4, characterized by a suspension device (20) disposed between the coarse shredder trough (5) and the doctor sections (13) at the border between each pair of sections, said suspension device (20) connecting mutually adjacent sections (13) together. 6. A doctor arrangement according to Claim 5, characterized in that the suspension device (20) is connected pivotally to the sections (13) by an eccentric pivot means for adjustment of the section suspension points.

Inventors: OEDMARK LEIF, OEDMARK, LEIF
Applicants: OEDMARK LEIF, VALMET FIBERTECH AB, OEDMARK, LEIF, VALMET FIBERTECH AKTIEBOLAG
Application year: 1999
Main classification: D21G3
IPC codes: D21F3, D21G3