Doctor blade for a fiber web machine and doctor arrangement in a fiber web machine

1. A doctor blade for a fiber web machine, the doctor blade comprising:

a fastening detent section terminating in a blade attachment end;

a blade section, the blade section terminating at a tip, opposite the attachment end;

wherein a cross-sectional plane is defined with respect to the doctor blade which extends in a width from the blade section tip to the blade attachment end and in a thickness perpendicular to the width;

wherein an axis of symmetry is defined which lies in the cross-sectional plane of the doctor blade, and extends from the attachment end toward the tip, and about which the fastening detent section of the doctor blade is substantially symmetric;

wherein the blade section is asymmetric about the axis of symmetry;

wherein the doctor blade has a first part of the blade section at least above the axis of symmetry, and a second part of the blade section at least mostly below the axis of symmetry;

wherein the first part has a first surface which originates at the tip and extends away from the axis of symmetry at a first angle a first distance in a direction toward the attachment end, and a second surface which joins the first surface and extends in relation to the axis of symmetry at a second angle in the direction toward the attachment end, the second angle being less than the first angle, wherein the first surface and the second surface form the first part which is arranged to function as a doctor blade; and

wherein the second part has a foil blade surface which originates at the tip and extends away from the axis of symmetry in the direction toward the attachment end a second distance which is greater than the first distance, said foil blade surface being arranged to function as a foil blade and defines an asymmetric bulge extending from the axis of symmetry, and wherein the foil blade surface forms an angle with the second surface of the first part of the blade section of between 10°-30°.

2. The doctor blade of claim 1 wherein the doctor blade is a unitary seamless machined part of plastic material.

3. The doctor blade of claim 2 wherein the doctor blade is a unitary seamless machined part of HD or LD polyethylene.

4. The doctor blade of claim 2 wherein the doctor blade is a unitary seamless machined part of polypropylene.

5. The doctor blade of claim 1 wherein the doctor blade is a unitary plastic pultrusion.

6. The doctor blade of claim 1 wherein the foil blade surface forms an angle with the second surface of the first part of the blade section of between 15°-20°.

7. The doctor blade of claim 1 wherein the first part of the blade section first surface extends 10-20 percent of the width of the doctor blade.

8. The doctor blade of claim 1 wherein the doctor blade is dimensioned to have a width of about 100 mm, and a doctor blade minimum thickness of approximately 2.5 mm, and wherein the fastening detent section terminating in the blade attachment end is formed by said minimum thickness part forming a neck which has shoulders extending to a total thickness of at least four millimeter, said neck and shoulders being symmetric about the axis of symmetry so the doctor blade can be positioned in a blade holder in a first position and in a second position where the doctor blade is arranged rotated 180 degrees about the axis of symmetry in the blade holder.

9. The doctor blade of claim 1 wherein the foil blade surface has an effective length of 30-50 mm along the width.

10. The doctor blade of claim 1 wherein the foil blade surface has an effective length of 35-45 mm along the width.