The working of the fiber material takes place in the refining gap formed between the refining elements on two opposed refining discs rotating relative to each other. The material is thereby subjected to mechanical action by working means on the refining elements, and it moves simultaneously by the effect of the centrifugal force. The working means can be formed as continuous or discontinuous bars, teeth or in some other way.

At the defibering of fiber material in the form of chips the chips bits are desired to be disintegrated to individual fibers with a minimum of fiber shortening. Experiments have proved that the configuration of the refining elements at the inner portion of the refining gap is of great importance for the feed of the material through the refining gap as well as for the defibering process. At the dispersion of recycle fiber pulp a working is desired which does not cause any fiber shortening or reduction in the freeness value (CSF) of the pulp.

Working, which causes fibrillation and fiber shortening, occurs above all when the refining means are formed with bars, by the effect of the edges of the bars.

Conventional refining elements with working means in the form of bars with inter- mediate grooves can also result in a non-uniform flow of the material through the refining gap. This implies at the same time that the load on the motor or motors driving one or both of the refining discs will be uneven. As a result thereof, the process will be difficult to control, and the energy consumption increases. It can also effect the quality of the worked pulp.

The present invention offers a solution of the aforesaid problems. Opposed co- operating refining elements shall be provided with projecting working means in the form of pins with circula cross-section. The pins on a refining element are arrange to extend into the interspace between the pins on the opposed co-operating refining element. The refining elements shall also be provided with flow restrictions in the form of strips extending substantially in the circumferential direction.

The characterizing features of the invention are apparent from the attache claims.

The invention is described in greater detail in the following, with reference to the accompanying Figures illustrating an embodiment of refining elements according to the invention.

Figs. 1 and 2 show a pair of co-operating refining elements according to the invention; Fig. 3 is a lateral view of the refining elements in working position; Fig. 4 shows an alternative configuration of a refining element.

The co-operating refining elements 10,11 are intended to be positioned on each of two opposed refining discs in a refiner where the refining discs are rotary relative to each other. The refining elements shown are provided with projecting working means in the form of pins 12,13 with substantially circula cross-section, which are arrange in several rows in the circumferential direction. The rows of pins are located radially spaced from each other across the entire surface of the refining elements. These pins 12,13 can alternatively be arrange only in an inner zone on the refining elements 10, 11. An outside located zone can then be provided with conventional working means, for example bars 14.

The pins 12,13 shall be arrange in at least two radially spaced rows and be cylindric with a diameter of 10-30 mm, preferably 15-25 mm, with rounded tops. Their length shall be 10-30 mm, preferably 15-25 mm. Alternatively, conical pins can be used. In working position the pins shall extend transversely across the refining gap almost all the way to the surface of the opposed refining element.

The refining elements 10,11 further are provided with flow restrictions in the form of strips 15,16, which substantially extend in the circumferential direction. Compare with the pins, the strips shall be low, suitably 4-12 mm, preferably 6-10 mm. The strips can be placed in connection to the pins along arcs. Alternatively, they can be given a direction slightly deviating from an arc, i. e. the radius increases or decreases along a strip. The strips can be continuous or discontinuous. Discontinuous strips can extend between two pins.

At the working of the material during its passage outward through the refining gap between the co-operating refining elements 10,11, the material will be acted upon by the pins 12,13 and strips 15,16 in a manner, which yields a very uniform feed. At the same time, an effective but mild start of the defibration and, respectively, dispersion is obtained. The strips 15,16 have the object to effect the staytime of the material in the refining gap. For this purpose, the height and direction of the strips are of decisive importance. This favorable effect on the material implies that even a non-uniform supply of material is balance in the refining gap which has a stabilizing effect on the entire working process.

By positioning the refining elements according to the invention on the inner portion of the refining discs, conventional refining elements can be arrange on the outer portion of the refining discs and thereby improve the stability of the material flow and motor load. This applies also when the refining elements according to the invention have an inner zone with pins 12,13 and an outer zone with conventional working means, for example in the form of bars 14.

The invention, of course, is not restricted to the embodiments shown, but can be varied within the scope of the claims.