Shoe press belt

Details Shoe press belt Shoe press belt

2002-07-29

2004-05-18

Chin, Peter (Department: 1731)

Paper making and fiber liberation

Apparatus

Running or indefinite length product forming and/or treating...

C162S358400, C162S901000, C428S217000, C428S312200, C428S314400, C428S318600

Reexamination Certificate

active

06736939

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a belt for a shoe press in the press part of a papermaking machine. In particular, the invention relates to improvements in the durability of a shoe press belt.
BACKGROUND OF THE INVENTION
Shoe presses used in recent years in the press parts of papermaking machinery are classified roughly into the two types shown in
FIGS. 8 and 9
. Each of these shoe presses includes a press roll P and a shoe S. The shoe S has an arcuate top recess conforming with the bottom of a roll P. An endless upper felt
92
and an endless lower felt
93
run between the roll P and the shoe S, and a wet web W runs between the felts
92
and
93
. An endless press belt B runs between the lower felt
93
and the shoe S, and follows the felt
93
. The shoe S urges the belt B upward to press the felts
92
and
93
against the roll P. The effect of the shoe is to form a wide nip zone, which improves the water squeezing effect of the pressure exerted between the roll P and the shoe S.
The press belt B of the shoe press
91
shown in
FIG. 8
is relatively long, and runs under constant tension over guide rollers
94
, there being four such guide rollers in the apparatus of FIG.
8
. The press belt B of the shoe press
91
shown in
FIG. 9
is relatively short, and its path is a small circle.
In general, as shown in
FIG. 10
, the press roll P of each shoe press
91
includes both a cylindrical central portion, and end portions P′ tapering in the axial outward direction. The shoe S of each shoe press
91
has chamfered round ends S′.
In the older shoe presses of the foregoing types, the nip zone N, that is, the zone underneath the middle portion of the press roll not including the tapered end portions P′, was wider than the shoe width S″, the shoe width being the width of the middle portion of the shoe, not including the chamfered round ends S′. On the other hand, in some current shoe presses, as shown in
FIG. 10
, the nip zone N formed between the roll P and the shoe S is narrower than the shoe width S″. The zones above the end portions of the shoe outside the nip zone N may be referred to as non-nip zones N′.
In the shoe press shown in
FIG. 10
, a shearing force acts continuously on the press belt B at the boundaries P″, between the nip zone N and the non-nip zones N′, at the inner ends of the tapered end portions P′ of the press roll. As a result of the shearing force, cracks are liable to develop along the boundary P″ in the belt B. These cracks adversely affect the durability of the press belt, making it unsuitable for long-term use.
In view of the foregoing problem, the object of this invention is to provide a durable shoe press belt, in which the shearing force acting at the boundary between the nip zone and the non-nip zones is either non-existent or sufficiently weak that it causes minimal damage to the press belt.
In accordance with the invention, a specially constructed shoe press belt is used in a shoe press which comprises a press roll and a shoe, and in which the nip zone formed between the press roll and the shoe is narrower than the shoe. In this press, therefore, there is a nip zone, and at least one non-nip zone, meeting at a boundary, which will ordinarily coincide with the outer end of a cylindrical part of the press roll. The press belt, which extends through the nip zone and the non-nip zone, has a body comprising a hard portion and a portion of less hardness, and a part of the portion of the belt having less hardness is directly opposite the boundary between the nip and non-nip zones.
In one preferred embodiment of the invention, the hard portion of the belt body comprises a high molecular weight elastic material, and the portion of the belt body having less hardness comprises a high molecular weight elastic material having a hardness less than that of the high molecular weight elastic material of the hard portion of the body.
In another preferred embodiment, the hard portion of the body comprises a dense, high molecular weight, elastic material, and the portion of the body having less hardness comprises a high molecular weight elastic material having voids formed therein.
In still another embodiment, the belt body comprises a thin portion and a thick portion, so that a part of the thin portion can be positioned directly opposite the boundary between the nip and non-nip zones.


REFERENCES:
patent: 4330023 (1982-05-01), Cronin
patent: 4877472 (1989-10-01), Rodal
patent: 4944844 (1990-07-01), Marcinko
patent: 5766421 (1998-06-01), Aufrecht
patent: 5943951 (1999-08-01), Muellner et al.
patent: 6030503 (2000-02-01), Matuschczyk
patent: 6042695 (2000-03-01), Ishino
patent: 6116156 (2000-09-01), Schiel et al.

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