| WO/2001/068260 | REFINING ELEMENT FOR A REFINING DISC |
| JPH11179222 | PULVERIZER |
| JPH03279478 | PULPER FOR PAPERMAKING |
OBITZ LARS (SE)
| US4023737A | 1977-05-17 |
| 1. | A refining disc for disc refiners which is of the kind that includes ribs or ridges (3,4) that extend over the refining zones of said disc and that are intended for coaction with ribs or ridges on another refining disc as the discs rotate relative to one another in mutually opposite directions, characterized in that the ribs or ridges (3,4) have the shape of involute arcs with circular evolutes and have a uniform width over respective refining zones (5,6) on the refining disc. |
| 2. | A refining disc according to Claim 1, characterised in that rotation of the disc can be reversed so as to enable both edges of the ribs or ridges (3,4) to be used for refining purposes. |
| 3. | A refining disc according to Claim or 2, characterised in that the pitch of the ribs or ridges (3) on one disc is different to the pitch of the ribs or ridges (4) on the disc that coacts with said one disc. |
In disc-refiners fitted with such discs, the material is treated in a space defined between two refining discs and the fibres in said material are treated at the location where the ribs or ridges meet one another. Because the ribs meet at an angle to one another as the discs rotate, so-called clip refining occurs. This should be avoided, since it impairs the quality of the treated material Attempts have been made to solve this problem, by using spaced arcuate ribs or ridges; see US-A 3 674 217 and US-A 4 023 737 in this regard. It is stated in these prior publications that the fibre material will be worked uniformly when the ribs or ridges are arcuate and that defibration is achieved with the minimum of fibre clipping. These proposals, however, do not provide any real solution to the problem, since the ridges on the two counteracting discs do not meet each other along their full lengths, in spite of this.
The object of the present invention is to solve the aforesaid problem and to avoid clip-refining of the material being treated. This object is achieved in accordance with the invention with the aid of refining discs that have the characteristic features set forth in the following claims.
The invention will now be described in more detail with reference to the accompanying drawings, in which
Figure 1 illustrates from above a refining disc segment as seen from the material refining gap; and Figure 2 is a corresponding view of an adjacent refining disc segment as seen from the other side of said gap.
Shown in Figure 1 is a refining segment 1 which is disposed on the inside of a refining disc and which is intended for coaction with the refining segment 2 on an adjacent refining disc on the other side of the refining gap. The ribs or ridges 3 and 4 on the respective segments 1 and 2 are curved and follow involute arcs having a circular evolute.
This ridge shape has been found to have several advantageous effects. When the two discs rotate in opposite directions and constitute a mirror image of one another, the ridges 3 and 4 will meet each other along their full lengths simultaneously, regardless of their mutual angular positions. This completely eliminates so-called clip-refining, which otherwise occurs when the ribs or ridges meet at a certain angle to one another. This ridge configuration also results in ridges and grooves of constant widths in respective refining zones perpendicular to the tangent of the involute, regardless of the radius. In the illustrated case, the refining segments are divided into two refining zones, to wit a radially inner infeed zone 5 and a radially outer refining zone 6.
This ridge, or rib, configuration comprising involute arcs with a circular evolute also enables the refiner to function as a double-rotating refiner, i. e. enables the direction of rotation of the refining discs to be reversed, therewith allowing both edges of the ridges 3 and 4 to be used for refining purposes.
Another advantage is that one rotor feeds in the material while the other rotor acts as a counterpressure or anvil surface? This results in a shear force that acts radially on the material being worked and not solely in a tangential direction, as is the case with conventional refining segments.
Figures 1 and 2 also show separate finesse, whereby the pitch is slightly different in the two segments 1 and 2, such that not all ribs or ridges will meet each other simultaneously over the whole surface during refining of the material, thereby to more uniform loading of the system?