PRE-PRESS FOR A PAPER WEB

Abstract: The present invention relates to a pre-press for a paper web (W). The pre-press comprises a load shoe (10) pressed against a backing element, preferably a vac roll (11), at a pressure providing load pressure by a medium, preferably liquid, said medium acting at the same time as lubrication medium.

Description: Pre-press for a paper web The present invention relates to a pre-press for a paper web. So-called pre-press equipment are known of prior art in paper drying in which a separate load shoe is used, preferably in conjunction with a vac(uum) roll. The vac roll is a roll design provided with a vacuum box thereinside, with the aid of vacuum directed whereat water is drawn off from the web as the roll comprises perforation in its shell and preferably also a separate circumferential grooving. A drawback in the pre-press arrangements has been how to find an appropriate operating system for the load shoe. Use of oil as the operating liquid of the load shoe causes that the apparatus arrangement is required to be well housed in order to prevent leakages of oil. In the present application an apparatus design of novel type is disclosed for using the load shoe of a pre-press for paper web. It is suggested in the application that for the operation liquid of the load shoe, the same liquid is used as for lubrication of the shoe. Preferably and most preferably it is water which is used, that is, the very same liquid which is being removed from the web. Therefore, the system can be open and there is no need to house and shelter it outwards. The spilled water is gathered in a gathering trough in the adjacency of the shoe and is conducted back into circulation. In the pre-press design, in the wire section the water removal is intensified by pressing the load shoe against the vac roll. The web is conducted between the press shoe and the vac roll preferably between two wires or felts. For the load liquid of the shoe press, water is used in a design according to the invention. In the design of the invention, the water serves thus both as lubrication medium and as a medium producing simultaneous load pressure. With the aid of water the shoe is pressed against the back roll. The wire on the side of the shoe may be water-permeable, slightly water-permeable or water-impermeable. The water is pumped from a water container along the pipes at load pressure into one or more loading chambers, whereby the pressure of the water exerts an effect on the load shoe, pressing it against the backing surface. The water acts at the same time as lubrication medium. From the pressure volume in conjunction with the load shoe, a passage is provided to the front surface of the load shoe and preferably to a groove on the front edge of the load shoe relative to the propagation direction of the web. So, the lubrication medium, preferably water, is conducted to the front edge of the load shoe and a mobile felt transfers the lubrication medium in the form of film to the surface of the load shoe. On the other side of the load shoe, the lubrication medium is gathered into a trough and conducted further back into water circulation. The pre-press of the invention is characterized in that the pre-press comprises a load shoe which is pressed against a backing element, preferably a vac roll, at a pressure of a medium, preferably of liquid, providing load pressure, said liquid acting at the same time as lubrication medium. The invention is described below referring to certain preferred embodiments presented in the figures of the accompanying drawings, whereto the invention is not, however, intended to be exclusively restricted. Fig. 1 presents a pre-press of the invention as cross-section image. Fig. 2 presents the lubrication medium / load medium circulation arrangement of the pre-press as shown in Fig. 1 in machine direction. Fig. 3 presents the apparatus design in a more comprehensive context. In the design shown in Fig. l a nip N j is produced between the load shoe 10 and the back roll, preferably vac roll 11. The wires / weaves H j and H 2 and web W therebetween are conducted via nip N j . Water removal occurs in nip N j into an internal vacuum space O in the vac roll. The suction effect is intensified by pressing the load shoe 10 against the surface 11 'a of the shell 11a of the vac roll 11. In the design presented in the figure, the load shoe 10 is connected to a seat 13. The load shoe 10 comprises a cross-section profile which is provided with a web plate part 10a and branch parts lOb^lOd^ The seat 13 comprises a web plate part 13a and branch parts 13b l 5 13b 2 , and on the ends of the branch parts, inward edges 13d l 5 13d 2 . In the middle of the web plate part 13a, a neck 13c has been furthermore provided, whereby in the spaces E j and E 2 defined between the neck and the side walls 13b j , 13b 2 , a load shoe 10 has been disposed at side branches lOb^lOb^ Medium, preferably water, is conducted by pressure via channel 15 into a space between the neck 13c of the seat 13 and the load shoe 10; into chamber D and from said space D it is conducted onwards via channel 16 into groove 17 on the front surface 10' of the load shoe. The medium is liquid, preferably water or aqueous mixture. The groove 17 has been arranged to pass on the length of the entire load shoe. In space D the pressure of the medium affects at a force on the undersurface of the web plate part 10a of the load shoe 10, pressing the load shoe 10 against its abutting surface, preferably against the outer surface 11a' of the shell 11a of the vac roll 11. Web W and the wires / weaves H j and H 2 pass via said surfaces; via the nip N j between the front surface 10' of the load shoe 10 and the outer surface 11 'a of the shell 11a of the vac roll 11. The medium, being preferably water, is con¬ ducted via branch channel C 1 ,C 2 ... of the manifold J within the frame beam P into space D. The spilled water and the water leaving the load shoe are conducted into trough 20 and onwards back into water circulation. The pre-press shown in Fig. 1 comprises a vac roll 11 as a second backing element. Another roll may also be used instead of vac roll 11, such as a roll provided with recessed surface. Fig. 2 presents a liquid circulation arrangement of a pre-press according to the invention. Via the branch channels C 1 ,C 2 ... of the manifold J within the frame beam P, the medium is conducted to one or more chambers D between the undersur¬ face of the load shoe 10 and the seat 13, and the load shoe 10 is pressed in line with the surfaces of the branch parts 13b 1 ,13b 2 of the seat 13 towards the backing element 11, e.g. especially towards the vac roll 11. The water discharged from the load shoe 10 with felt H 2 is conducted into a collector tank 20 and then along a channel 21 into a liquid container 22 and furthermore, pumped by pump 23, along channel 24 back into manifold J to be back in the adjacency with the load shoe 10. Fig. 3 shows the means design in a wider context. The travelling of web W is presented by arrows L j and the circulation directions of felt transfers with arrows 1^ and L 3 . Web W is conducted from felt circulation H 3 and the web is transferred in line with felt H j between felt H j and felt H 2 , and into nip N j . The water is gathered in trough 20 and moved back into manifold J.

Claims: Claims 1. Pre-press for a paper web (W), characterized in that the pre-press comprises a load shoe (10) which is pressed against a backing element, preferably a vac roll (11), at a pressure of a medium, preferably of a liquid, providing load pressure, said medium acting at the same time as a lubrication medium. 2. Pre-press according to claim 1, characterized in that the medium is conducted from the conjunction of chamber (D) in association with the load shoe along a separate channel to the front surface of the load shoe to serve as lubrication medium and into a groove (17) of the load shoe (10), formed preferably on the front edge thereof, and preferably formed therein, when watching in the propagation direction of the web. 3. Pre-press according to any one of the preceding claims, characterized in that the chamber (D), into which the lubrication medium is first conducted, has been formed between the bottom of the web plate part (10a) of the load shoe (10) and the seat (13). • 4. Pre-press according to any one of the preceding claims, characterized in that the load shoe (10) comprises a web plate part (10a) and branch parts (lOb^lOb^, and that the load shoe (10) has been so fitted on the seat (13) that the branch parts (10b l 5 10b 2 ) of the load shoe (10) have been arranged to move in the spaces (E^E^ defined between the central neck (13c) of the seat (13) and the side walls (13b l 5 13b 2 ) and that the lubrication medium, preferably water, is conducted via a channel (15) formed in the neck (13c) into space (D) defined between the seat (13) and the movable load shoe (10). 5. Pre-press according to any one of the preceding claims, characterized in that the groove (17) on the front surface (10') of the load shoe (10) in which the channel (16) from chamber (D) ends, has been formed on the entire length of the load shoe (10). 6. Paper pre-press according to any one of the preceding claims, characterized in that in the area of the trailing side of the load shoe (10) a trough (20) has been provided to which the water carried by the felt from the load shoe (10) is conducted and from which trough (20) a water circulation arrangement is provided into a collector tank (20), and further, back to the load shoe to a manifold (J) in conjunc¬ tion therewith, from where the liquid is conducted onwards via one or more branch channels (C 1 ,C 2 ...) to one or more chambers (D) communciating with the load shoe, and that a pump means (23) is provided with which said liquid, preferably water, is circulated. 7. Pre-press according to any one of the preceding claims, characterized in that the medium is water or an aqueous mixture.

Inventors: HOLOPAINEN KARI, HOLOPAINEN, KARI
Applicants: VALMET PAPER MACHINERY INC, VALMET PAPER MACHINERY INC.
Application year: 1995
Main classification: D21F3
IPC codes: D21F3