Groove configuration for a press belt in an extended nip press

The grooves of a grooved press belt are formed with an improved configuration which reduces groove closure under pressure and which reduces cracking and tearing of the belt. The improved groove configuration consists of a curved bottom and two upwardly diverging side walls. In a first embodiment the bottom wall is semi-circular and has a diameter which is equal to about one half of the width of the groove opening. The upwardly diverging side walls preferably include radiused upper edges. The side walls preferably have an angle of divergence between about five degrees and about fifteen degrees from a vertical plane. In a second embodiment, the bottom of the groove is substantially flat, and the bottom corners are radiused to provide a smooth transition between the flat bottom and the upwardly diverging side walls.

BACKGROUND AND SUMMARY OF THE INVENTION 
The instant invention relates to grooved press belts for use in paper 
making machinery, and other like machinery, and more particularly to an 
improved groove configuration for such press belts. 
Press belts are used in various press devices, such as shoe-type presses, 
as used in paper making machines and calendars, to transport a continuous 
sheet through a press nip. The prior art press belts typically comprise a 
polyurethane or rubber material having a reinforcing fiber weave imbedded 
therein. In the paper making art, it is well known to provide grooves in 
the outer surface of a press belt in order to provide a channel to carry 
water away from the sheet as it is being pressed. In this connection, 
grooves are usually formed with a rectangular cross-section. However, 
there are two significant problems with conventional rectangular groove 
configurations. The first problem is that rectangular shaped grooves have 
a natural tendency to close under pressure of the nip. The pressure of the 
nip deforms the lands between the grooves forcing the sides of the grooves 
toward each other and thereby closing the groove. Several solutions have 
been proposed for the problem of groove closure. However, none of the 
proposed solutions appear to be satisfactory. U.S. Pat. No. 4,880,501 
discloses a groove configuration wherein the tops of the lands are formed 
with a concave shape. This concave formation is believed to reduce the 
deformation of the land. However, this type of machining is very difficult 
to accomplish, and furthermore it does not completely eliminate groove 
closure. U.S. Pat. No. 4,908,103 discloses a press belt having an outer 
surface which is constructed of a harder material which is not as likely 
to be elastically deformed. However, the use of two different elastomers 
leads to problems with delamination or separation of the two elastomer 
layers. British Patent No. GB 8818992.3 discloses a press belt wherein 
cross-pieces extend between the lands to provide to support the lands. 
However, reinforcing cross-pieces reduce the efficiency of the grooves by 
hindering the flow of water once in the grooves. Furthermore, the 
cross-pieces are difficult to machine. 
The second problem associated with conventional rectangular groove 
configurations is the tendency for the lands to break off at their base. 
Cracking of the belt leads to shortened life span, increased belt 
replacement, and increased machine down time. In this regard, it has been 
found that the cumulative stress of repeatedly passing through the nip 
causes the lands to crack at their bottom edges. The sharp corners of the 
rectangular grooves create stress points in the material wherein the 
maximum stress often exceeds four times the stress elsewhere in the 
material. In order to remedy this problem, it is has been suggested to 
make the grooved surface of the belt from a harder elastomer. However, 
there is the problem of delamination, as indicated earlier. In addition, 
harder elastomers generally have less tolerance for repeated bending as 
would be required in an press belt. One solution which has been suggested 
is to provide the elastomer with reinforcing threads (U.S. Pat. No. 
4,946,731). However, when a plurality of filaments are used to reinforce 
the elastomer, cutting of the grooves exposes the matrix of fibers and 
opens paths for water to get inside the belt and cause failure. Yet 
another solution is to provide filaments located within the lands (GB 
8818992.3). However, precise location of the filaments and machining of 
the grooves so that the filaments lie within the lands is extremely 
difficult, leading to a high percentage of substandard belts or belt 
rejections. 
Accordingly, among the objects of the instant invention are: the provision 
of a groove configuration for a press belt which effectively reduces 
groove closure; the provision of a groove configuration which reduces 
cracking of the belt; and the provision of a groove configuration which is 
simple and inexpensive to machine. 
The above objects are accomplished by providing a groove configuration 
wherein the grooves are formed with an arcuate bottom and two upwardly 
diverging side walls. The arcuate bottom is preferably semi-circular and 
has a diameter which is equal to about one half of the width of the groove 
opening. The upwardly diverging side walls preferably include radiused 
upper edges which provide a smooth curved transition between the side 
walls and the outer surface of the press belt. Each side wall preferably 
has an angle of divergence between about five (5) degrees and about 
fifteen (15) degrees from a vertical plane. In a second embodiment, the 
groove is formed with a substantially flat bottom and radiused corners 
which provide a smooth transition between the flat bottom and the upwardly 
diverging side walls. 
Other objects, features and advantages of the invention shall become 
apparent as the description thereof proceeds when considered in connection 
with the accompanying illustrative drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, a first embodiment of the press belt of the 
instant invention is illustrated and generally indicated at 10 in FIGS. 
1-3. As will hereinafter be more fully described, the belt 10 includes a 
groove configuration which reduces groove closure under compression and 
which reduces cracking of the belt at the bottom corners of the grooves. 
Press belt 10 comprises a continuous loop of elastomeric material which is 
formed by known belt forming techniques. Press belt 10 includes inner and 
outer surfaces generally indicated at 11, 12, and further includes a 
lengthwise spiralling groove generally indicated at 14. In use, the outer 
grooved surface 12 of the belt 10 makes contact with a sheet 18 (FIG. 3) 
to be pressed. The spiral groove 14 actually forms a plurality of 
lengthwise longitudinal grooves which are separated by lands 16. Press 
belts 10 are generally formed with a thickness between about 3-6 mm. 
Groove 14 is generally 0.5 to 1.0 mm wide with the lands 16 generally 2-5 
times the width of the groove 14. While groove 14 has been illustrated as 
extending lengthwise to the direction of belt 10, it is to be understood 
that the direction of the groove(s) is not critical to the operation of 
the belt. Accordingly, grooves 14 may alternatively extend either 
crosswise, or at an angle to the direction of the belt. The groove 14 is 
formed with an arcuate bottom 20, and two upwardly diverging side walls 
22. Arcuate bottom 20 preferably has a diameter (D) which is equal to 
about one half of the width (W) of the groove opening (See FIG. 2). 
Diverging walls 22 are preferably formed with radiused top edges 24 which 
provide a smooth transition between side walls 22 and outer surface 12. As 
illustrated in FIG. 2, each side wall 22 preferably has an angle of 
divergence between about five (5) degrees and about fifteen (15) degrees 
from a vertical plane, although both smaller and larger angles of 
divergence are acceptable. 
Referring now to FIG. 3, press belt 10 is shown in conjunction with sheet 
18 which is being pressed in a shoe type pressing device, i.e. an extended 
nip press device as shown in FIG. 5. While the side walls 22 of groove 14 
still tend to deform inwardly under compression, the diverging 
configuration of the side walls 22 compensates for the compression. The 
resulting groove 14 (FIG. 3) is thus generally rectangular in shape. 
Curved bottom 20 of groove 14 more evenly distributes the stress of the 
nip compression, and therefore reduces cracking and failure of the belt 
10. It has been found that the stress at the transition points between the 
bottom 20 and side walls 22 has been effectively reduced to about 1.1 
times the normal stress on the material elsewhere in the belt. As 
discussed previously, the maximum stress caused by a sharp corner often 
exceed four times the normal stress. The life of press belt 10 is thus 
extended by a significant amount of time over the prior art press belts. 
Referring now to FIG. 4, a second embodiment of the press belt is 
illustrated and generally indicated at 26. Press belt 26 includes inner 
and outer surfaces generally indicated at 27, 28, and lengthwise 
spiralling groove generally indicated at 30. Unlike press belt 10, grooves 
30 are formed with a substantially flat bottom 34, upwardly diverging side 
walls 36, and radiused bottom corners 38 which provide a smooth transition 
between the flat bottom 34 and the diverging side walls 36. The side walls 
36 are preferably formed with radiused upper edges 40. Each side wall 36 
preferably has an angle of divergence between about five (5) degrees and 
about fifteen (15) degrees from a vertical plane. 
In use, the diverging side walls 36 of the grooves 30 compensate for 
elastic deformation of the lands 32 under compression thereby resulting in 
a rectangular groove. The radiused corners 38 more evenly distribute the 
stress of the nip compression and therefore reduce cracking and failure of 
the belt 26. 
It can therefore be seen that the instant invention provides a unique and 
novel groove configuration for a press belt. The groove configuration 
includes rounded or radiused corners which effectively reduce structural 
stress at the transitions between the bottom and side walls of the groove. 
The outwardly diverging walls of the grooves compensate for elastic 
deformation of the press belt and thus provide a generally rectangular 
groove for carrying away water from the sheet being pressed. For these 
reasons, the instant invention represents a significant advancement in the 
art which has substantial commercial merit. 
While there is shown and described herein certain specific structure 
embodying the invention, it will be manifest to those skilled in the art 
that various modifications and rearrangements of the parts may be made 
without departing from the spirit and scope of the underlying inventive 
concept and that the same is not limited to the particular forms herein 
shown and described except insofar as indicated by the scope of the 
appended claims.