Belt

1 . A belt for a fiber web machine, the belt having an inner surface and an outer surface, wherein the belt comprises a plurality of parallel dewatering grooves extending in a machine direction beneath the outer surface of the belt, each dewatering groove having a width in a cross direction which is parallel to the machine direction, wherein each dewatering groove comprises:

shallow portions having a first depth which is recessed below the outer surface; and

deep portions having a second depth which is recessed below the outer surface an amount which is greater than the first depth, which first and second depths are determined from the outer surface of the belt in a depth direction, wherein the first depth is smaller than the second depth, wherein each dewatering groove defines a sequence of concave segments following one after another in the machine direction, with a discontinuity between adjacent concave segments.

2 . The belt of claim 1 , wherein a number of the shallow portions within each of the dewatering grooves is 1/m to 50/m, measured in the machine direction.

3 . The belt of claim 1 , wherein the second depth is in a range between 0.8 mm and 1.6 mm.

4 . The belt of claim 1 , wherein the first depth is 5 to 25 percent of the second depth, determined from the outer surface of the belt in the depth direction.

5 . The belt of claim 1 , wherein the first depth is in a range between 0.02 mm and 0.4 mm.

6 . The belt of claim 1 , wherein the belt has a thickness in the direction of the first depth, and wherein the first depth is at least 0.2% with respect to the thickness of the belt.

7 . The belt of claim 1 , wherein the belt has a thickness in the direction of the first depth, and wherein the second depth is equal to or more than 6% of the thickness of the belt and/or equal to or less than 30% of the thickness of the belt.

8 . The belt of claim 1 wherein the sequence of concave segments of each dewatering groove has a plurality of shallow portions spaced apart from one another by deep portions, and wherein imaginary central lines are defined passing through a center of each shallow portion running perpendicular to the first direction, and wherein a distance between central lines of two nearest shallow portions is at least 20 mm and not greater that 100 mm.

9 . The belt of claim 1 , wherein the shallow portions are arranged to taper so that a cross sectional area of the first groove taken along a plane perpendicular to the first direction increases running from a shallow portion to a deep portion.

10 . The belt of claim 1 wherein the shallow portions comprise one or more curved sides.

11 . The belt of claim 1 , wherein the shallow portions have an average length in a range between 8 mm and 25 mm, measured in the first direction.

12 . The belt of claim 1 , wherein the deep portions have an average length in a range between 20 mm and 60 mm, measured in the first direction.

13 . The belt of claim 1 , wherein the shallow portions are arranged in such a way that each shallow portion extends from a bottom of the first dewatering groove in a direction forming an angle of at least 5° and equal to or less than 90° to the bottom of the first dewatering groove.

14 . The belt according to claim 1 , wherein a width of the shallow portions is at least 8% of the width of the first dewatering groove.

15 . The belt of claim 1 , wherein at least 99% of dewatering grooves comprise the shallow and deep portions.

16 . The belt of claim 1 wherein the dewatering grooves are arranged to form a total volume for water of from 100 to 600 ml per m 2 of belt surface.

17 . A belt for a fiber web machine, the belt having an inner surface and an outer surface, wherein the belt comprises:

a plurality of parallel dewatering grooves which extend in a machine direction and which open on the outer surface of the belt, each dewatering groove having a width measured in a cross direction perpendicular to the machine direction;

wherein each of the plurality of parallel dewatering grooves has a plurality of concave groove segments, each groove segment having a central deep portion extending a second depth beneath the outer surface and shallow portions recessed below the outer surface, a shallow portion being positioned on either side of each deep portion, and each shallow portion extending beneath the outer surface a first depth that is less than the second depth, such that each concave groove segment has a deep portion between two shallow portions; and

wherein transition portions which extend in a continuous transition in depth from the first depth to the second depth of the deep portions on opposite sides of the shallow portion, the transition portions being a gradual change in depth below the outer surface in the machine direction, wherein the plurality of concave groove segments within each parallel dewatering groove define a sequence of concave portions following one after the other.

18 . The belt of claim 17 , wherein the shallow portions are arranged in such a way that each shallow portion extends from a bottom of its dewatering groove in a direction forming an angle of at least 5° and equal to or less than 90° to the bottom of said dewatering groove.

19 . The belt of claim 17 wherein the transition portions of each shallow portion define curved sides of said shallow portion.