Method of manufacturing a screen cylinder and a screen cylinder
The present invention relates to a method of manufacturing a screen cylinder, and a screen cylinder that is particularly suitable for screening, filtering, fractionating, or sorting cellulose pulp or fiber suspensions of the pulp and paper making industry, or other similar suspensions. The present invention relates more particularly to screening or filtering devices of the type comprising a plurality of screen wires ( 10 ) positioned at a small spacing parallel to each other, the screen wires ( 10 ) being fastened into notches in the support elements ( 20 ) by means of shrink fitting the screen wires ( 10 ) into the notches by heating the second rim area ( 26 ) of the support ring ( 20 ) after the screen wires ( 10 ) have been inserted into the notches.
1. A method of manufacturing a screen cylinder, said screen cylinder formed of at least a number of screen wires, wherein pairs of adjacent screen wires provide a screening slot therebetween, and substantially circular support rings, said support rings having a first rim area provided with notches into which said screen wires are installed, and a second rim area opposite to said first rim area, the method comprising:
a) after installing some of the screen wires into said notches of said support rings, evenly and uniformly heating the second rim area of at least one of said support rings such that a temperature of the first rim area remains lower than a temperature of the second rim area, and whereby the second rim area is deformed, and
b) allowing at least one of said support rings to cool to decrease a diameter of the at least one of said support rings, whereby the first rim area is deformed and the screen wires are clamped in said notches.
2. The method as recited in claim 1 , wherein heating the second rim area comprises raising the temperature of the second rim area of the support rings locally to between 450 and 1100 degrees Celsius.
3. The method as recited in claim 1 , wherein the heating is practiced by one of a heating torch, inductive heating, resistance heating, conductive heating, and laser.
4. The method as recited in claim 1 , wherein heating the second rim area comprises at least one of heating a surface of the second rim area and heating opposite side faces of the second rim area.
5. The method as recited in claim 4 , wherein heating the second rim area and allowing the second rim area to cool is practiced in several successive stages.
6. The method as recited in claim 4 , further comprising dividing the second rim area of one of the support rings into annular zones, and wherein heating the second rim area comprises heating the annular zones in separate stages.
7. The method as recited in claim 6 , wherein heating the annular zones in separate stages comprises allowing one annular zone to cool before heating another annular zone.
8. The method as recited in claim 3 , further comprising dividing the second rim area into angular segments, and wherein heating the second rim area comprises heating the annular segments in separate stages.
9. The method as recited in claim 1 , wherein heating the second rim area of at least one of said support rings comprises one of heating the second rim area of all support rings, heating the second rim area of some of the support rings, and heating the second rim area of some of the support rings with a reduced power.
10. The method as recited in claim 1 , wherein the method further comprises, while heating the second rim area of at least one of said support rings, one of moving the cylinder and keeping a heating element stationary and moving the heating element and keeping the cylinder stationary.
11. The method as recited in claim 1 , wherein the notches are adapted to allow form locking of the number of screen wires in the support rings.
12. The method as recited claim 1 , wherein the diameter of the support ring is reduced at least 0.2%.
13. The method as recited in claim 1 , wherein the method further comprises constraining thermal expansion of the at least one of said support rings during heating with an adjacent structure.
14. The method as recited in claim 1 , wherein heating the second rim area evenly and uniformly comprises heating the second rim area symmetrically in relation to a radial centerline plane, C L , of the support ring.
15. The method as recited in claim 1 , wherein heating the second rim area evenly and uniformly comprises raising the temperature of the second rim area of the support rings locally to between 450 and 1100 degrees Celsius.