Warped stitched papermaker's forming fabric with fewer effective top MD yarns than bottom MD yarns

1. A papermaking fabric, comprising a series of repeat units, each of the repeat units including:

a set of top machine direction (MD) yarns;

a set of top cross machine direction (CMD) yarns interwoven with the top MD yarns;

a set of bottom MD yarns;

a set of bottom CMD yarns interwoven with the bottom MD yarns; and

a set of stitching yarns, the stitching yarns being disposed in pairs, at least one of the yarns of each of the stitching yarn pairs being interwoven with the top CMD yarns and the bottom CMD yarns, wherein when a first stitching yarn of a pair is interweaving with the top CMD yarns, a second stitching yarn of the pair is passing below the top CMD yarns, and when the second stitching yarn of the pair is interweaving with the top CMD yarns, the first stitching yarn of the pair is passing below the top CMD yarns, such that each stitching yarn pair forms a composite top MD yarn;

wherein the set of top MD yarns includes a first number of top MD yarns, and wherein the set of stitching yarns comprises a second number of composite top MD yarns, and wherein the set of bottom MD yarns includes a third number of bottom MD yarns; and

wherein the ratio of the sum of the first and second numbers to the third number is 2:3.

2. The papermaking fabric defined in claim 1 , wherein one of the set of stitching yarn pairs is positioned between each adjacent pair of top MD yarns.

3. The papermaking fabric defined in claim 1 , wherein a first yarn of each of the stitching yarn pairs stitches on one side of a bottom MD yarn, and a second yarn of each of the stitching yarn pairs stitches on the other side of that bottom MD yarn.

4. The papermaking fabric defined in claim 1 , wherein each of the stitching yarns of a pair passes below at least one bottom CMD yarn.

5. The papermaking fabric defined in claim 1 , wherein the sum of the first and second numbers is eight.

6. The papermaking fabric defined in claim 1 , wherein the diameters of the top MD yarns and the stitching yarns are substantially the same.

7. The papermaking fabric defined in claim 1 , wherein the diameters of the top MD yarns and the stitching yarns are between about 0.10 and 0.20 mm.

8. The papermaking fabric defined in claim 1 , wherein the top MD yarns, stitching yarns and top CMD yarns interweave with each other to form a plain weave pattern.

9. The papermaking fabric defined in claim 1 , wherein the set of top CMD yarns comprises twice as many yarns as the set of bottom CMD yarns.

10. The papermaking fabric defined in claim 1 , wherein the mesh of the top surface of the fabric is between about 20×30 and 30×50.

11. A papermaking fabric, comprising a series of repeat units, each of the repeat units including:

a set of top machine direction (MD) yarns;

a set of top cross machine direction (CMD) yarns interwoven with the top MD yarns;

a set of bottom MD yarns;

a set of bottom CMD yarns interwoven with the bottom MD yarns; and

a set of stitching yarns, the stitching yarns being disposed in pairs, at least one of the yarns of each of the stitching yarn pairs being interwoven with the top CMD yarns and the bottom CMD yarns, wherein when a first stitching yarn of a pair is interweaving with the top CMD yarns, a second stitching yarn of the pair is passing below the top CMD yarns, and when the second stitching yarn of the pair is interweaving with the top CMD yarns, the first stitching yarn of the pair is passing below the top CMD yarns;

wherein the set of top MD yarns includes a first number of top MD yarns, and wherein the set of stitching yarns comprises a second number of stitching yarn pairs, and wherein the set of bottom MD yarns includes a third number of bottom MD yarns; and

wherein the ratio of the sum of the first and second numbers to the third number is 2:3.

12. The papermaking fabric defined in claim 11 , wherein one of the set of stitching yarn pairs is positioned between each adjacent pair of top MD yarns.

13. The papermaking fabric defined in claim 11 , wherein a first yarn of each of the stitching yarn pairs stitches on one side of a bottom MD yarn, and a second yarn of each of the stitching yarn pairs stitches on the other side of that bottom MD yarn.

14. The papermaking fabric defined in claim 11 , wherein each of the stitching yarns of a pair passes below at least one bottom CMD yarn.

15. The papermaking fabric defined in claim 11 , wherein the sum of the first and second numbers is eight.

16. The papermaking fabric defined in claim 11 , wherein the diameters of the top MD yarns and the stitching yarns are substantially the same.

17. The papermaking fabric defined in claim 11 , wherein the diameters of the top MD yarns and the stitching yarns are between about 0.10 and 0.20 mm.

18. The papermaking fabric defined in claim 11 , wherein the top MD yarns, stitching yarns and top CMD yarns interweave with each other to form a plain weave pattern.

19. The papermaking fabric defined in claim 11 , wherein the set of top CMD yarns comprises twice as many yarns as the set of bottom CMD yarns.

20. The papermaking fabric defined in claim 11 , wherein the mesh of the top surface of the fabric is between about 20×30 and 30×50.

21. A papermaking fabric, comprising a series of repeat units, each of the repeat units including:

a set of top machine direction (MD) yarns;

a set of top cross machine direction (CMD) yarns interwoven with the top MD yarns;

a set of bottom MD yarns;

a set of bottom CMD yarns interwoven with the bottom MD yarns; and

a set of stitching yarns, the stitching yarns being disposed in pairs, at least one of the yarns of each of the stitching yarn pairs being interwoven with the top CMD yarns and the bottom CMD yarns, wherein when a first stitching yarn of a pair is interweaving with the top CMD yarns, a second stitching yarn of the pair is passing below the top CMD yarns, and when the second stitching yarn of the pair is interweaving with the top CMD yarns, the first stitching yarn of the pair is passing below the top CMD yarns, such that each stitching yarn pair forms a composite top MD yarn;

wherein the set of top MD yarns includes a first number of top MD yarns, and wherein the set of stitching yarns comprises a second number of composite top MD yarns, and wherein the set of bottom MD yarns includes a third number of bottom MD yarns; and

wherein the sum of the first and second numbers is less than the third number.

22. A method of making paper, comprising the steps of:

(a) providing a papermaking fabric, the papermaking fabric including a series of repeat units, each of the repeat units comprising:

a set of top machine direction (MD) yarns;

a set of top cross machine direction (CMD) yarns interwoven with the top MD yarns;

a set of bottom MD yarns;

a set of bottom CMD yarns interwoven with the bottom MD yarns; and

a set of stitching yarns, the stitching yarns being disposed in pairs, at least one of the yarns of each of the stitching yarn pairs being interwoven with the top CMD yarns and the bottom CMD yarns, wherein when a first stitching yarn of a pair is interweaving with the top CMD yarns, a second stitching yarn of the pair is passing below the top CMD yarns, and when the second stitching yarn of the pair is interweaving with the top CMD yarns, the first stitching yarn of the pair is passing below the top CMD yarns;

wherein the set of top MD yarns includes a first number of top MD yarns, and wherein the set of stitching yarns comprises a second number of stitching yarn pairs, and wherein the set of bottom MD yarns includes a third number of bottom MD yarns; and

wherein the ratio of the sum of the first and second numbers to the third number is 2:3;

(b) applying paper stock to the papermaking fabric; and

(c) removing moisture from the paper stock.