Method for manufacturing press felt with seam, press felt, and base fabric

1. A method for manufacturing a press felt with a seam for the press section of a paper machine, the method comprising:

weaving in a weaving machine in one go a one-base three-layer base fabric that comprises a web-side surface layer, an intermediate layer and further a bottom layer on the roll-side surface,

weaving in the base fabric several machine direction yarns in three layers and several cross-machine direction yarns that are arranged to cross with the machine direction yarns,

forming in the base fabric at least a first and a second cross-machine direction connecting end,

forming at the connecting ends by means of the machine direction yarns of the intermediate layer and bottom layer several seam loops for forming a seam,

fastening after weaving at least to the web-side surface of the base fabric at least one batt fibre layer,

arranging the yarn density ratio of the surface layer machine direction yarns to be at least double in comparison with the yarn density of the intermediate layer machine direction yarns and that of the bottom layer machine direction yarns, respectively,

using as the surface layer machine direction yarns those having an essentially smaller cross-sectional area in comparison with the machine direction yarns forming the seam loops, and arranging for the surface layer machine direction yarns a long free run over at least five cross-machine direction yarns.

2. A method as claimed in claim 1 , comprising

weaving the base fabric cross-machine direction yarns by using one cross-machine direction yarn system.

3. A method as claimed in claim 1 , comprising

weaving the base fabric cross-machine direction yarns by using two cross-machine direction yarn systems.

4. A method as claimed in claim 1 , comprising

turning the machine direction yarns running in the surface layer at the connecting end into a direction opposite to their direction of travel without forming seam loops.

5. A method as claimed in claim 1 , comprising

turning the machine direction yarns running in the surface layer at the connecting end into a direction opposite to their direction of travel to form connectable seam loops at the same time.

6. A method as claimed in claim 1 , comprising

turning the surface layer machine direction yarns at the connecting end around at least one cross-machine direction edge yarn into a direction opposite to their direction of travel.

7. A method as claimed in claim 1 , comprising

turning the surface layer machine direction yarns at the connecting end around at least one cross-machine direction edge yarn into a direction opposite to their direction of travel,

and removing said edge yarn after weaving and before attaching the batt fibre.

8. A method as claimed in claim 1 , comprising

extending the surface layer machine direction yarns over the seam area during weaving,

and cutting the surface layer machine direction yarns at the seam area after weaving.

9. A paper machine press section press felt comprising:

a one-base woven base fabric with three layers on top of each other, namely a web-side surface layer, intermediate layer and bottom layer on the roll-side surface,

several machine direction yarns and several cross-machine direction yarns that cross each other,

at least a first and a second cross-machine direction connecting end,

several seam loops at the connecting ends for forming a seam, the seam loops being formed by at least some of the machine direction yarns of the intermediate and bottom layers,

at least one batt fibre layer fastened to the at least the web-side surface of the base fabric,

and wherein the yarn density ratio of the surface layer machine direction yarns is at least double in comparison with the yarn density of the intermediate layer machine direction yarns and that of the bottom layer machine direction yarns, respectively,

the cross-sectional area of the surface layer machine direction yarns is smaller in comparison with that of the machine direction yarns forming the seam loops,

and the surface layer machine direction yarns have a long free run over at least five cross-machine direction yarns.

10. A base fabric of a press felt of a paper machine press section which comprises:

a one-base woven base fabric with three layers on top of each other, namely a web-side surface layer, intermediate layer and bottom layer on the roll-side surface,

several machine direction yarns and several cross-machine direction yarns that cross each other,

at least a first and a second cross-machine direction connecting end,

several seam loops at the connecting ends for forming a seam, the seam loops being formed by at least some of the machine direction yarns of the intermediate and bottom layers,

and wherein the yarn density ratio of the surface layer machine direction yarns is at least double in comparison with the yarn density of the intermediate layer machine direction yarns and the bottom layer machine direction yarns, respectively,

the cross-sectional area of the surface layer machine direction yarns is smaller in comparison with that of the machine direction yarns forming the seam loops,

and the surface layer machine direction yarns have a long free run over at least five cross-machine direction yarns.

11. A base fabric as claimed in claim 10 , comprising

the yarn density ratio of the surface layer machine direction yarns is at least triple in comparison with the yarn density of the intermediate layer machine direction yarns and the bottom layer machine direction yarns, respectively.

12. A base fabric as claimed in claim 10 , comprising

the yarn density ratio of the surface layer machine direction yarns is at least fourfold in comparison with the yarn density of the intermediate layer machine direction yarns and the bottom layer machine direction yarns, respectively.

13. A base fabric as claimed in claim 10 , comprising

the base fabric has one cross-machine direction yarn system.

14. A base fabric as claimed in claim 10 , comprising

the base fabric has two cross-machine direction yarn systems.

15. A base fabric as claimed in claim 10 , comprising

the surface layer machine direction yarns are turned at the connecting end into a direction opposite to their direction of travel without forming a connectable seam loop at the connecting end.

16. A base fabric as claimed in claim 10 , comprising

the surface layer machine direction yarns are turned at the connecting end into a direction opposite to their direction of travel without forming a connectable seam loop at the connecting end,

and the turned machine direction yarns return from the connecting end in the surface layer.

17. A base fabric as claimed in claim 10 , comprising

the surface layer machine direction yarns are turned at the connecting end into a direction opposite to their direction of travel without forming a connectable seam loop at the connecting end,

and the surface layer machine direction yarns are turned at the edge of a seam loop channel without extending on top of the seam loop channel.

18. A base fabric as claimed in claim 10 , comprising

the surface layer machine direction yarns are turned at the connecting end into a direction opposite to their direction of travel without forming a connectable seam loop at the connecting end,

and the surface layer machine direction yarns are turned at the seam loop channel as seen from the machine direction.

19. A base fabric as claimed in claim 10 , comprising

the surface layer machine direction yarns are turned at the connecting end into a direction opposite to their direction of travel without forming a connectable seam loop at the connecting end,

the surface layer machine direction yarns extend at the first connecting end further than the midpoint of the seam loops, whereby they form a seam flap protecting the seam loop channel,

and the surface layer machine direction yarns are turned at the second connecting end before the midpoint of the seam loops and in relation to the length of the seam flap.

20. A base fabric as claimed in claim 10 , comprising

the surface layer machine direction yarns are extended over the seam area during weaving,

and the surface layer machine direction yarns are cut after weaving to open the seam area.