The invention relates to an apparatus for defibration of reclaimed paper or the like, presented in the preamble of the appended claim 1. The in¬ vention relates also to a method for defibration of reclaimed paper or the like, presented in the preamble of the appended claim 8.

For example from Finnish Patents No. 56416 and No. 63075, a horizon- tal rotating drum is known, into which a paper material to be defibred is supplied together with water required for defibration. In the inner wall of the drum, plates are provided for lifting the mass to be defibred to the top of the drum, from where it falls to the bottom of the drum. The fibre bonds are thus broken up by the impact caused by falling.

A problem with such apparatuses lies in that although an effective breakage of fibre bonds is achieved by the drop at the time of the im¬ pact, the material to be defibred is otherwise guided by the plates in such a movement along the periphery of the drum that it is not subject to forces breaking up the fibre bonds.

It is an aim of the invention to eliminate the above-mentioned disadvan¬ tages and to provide an apparatus where the energy obtained by rota¬ tion of the drum can be used for defibration in a more efficient manner. For achieving this aim, the apparatus according to the invention is primarily characterized in what is presented in the characterizing part of the appended claim 1.

The apparatus of the invention is constructed in such a way that the elements guiding the movement of the material to be defibred induce rotation of the mass as a uniform accumulation in the lower part of the drum. The guide elements on the periphery of the drum, which may have variable shapes and distribution, must fulfil one requirement: they must move the material in the direction of the rotating movement only to the height of the centre part, from where the mass flow is returned. The continuous relative movement of the mass particles will rub the mass and generates forces which break up fibre bonds in the reclaimed paper or the like and detaches plastic from the fibre material.

As for the other advantageous embodiments of the apparatus, refer¬ ence is made to the appended dependent claims as well as to the de¬ scription below.

The method, in turn, for implementing the invention is characterized in what is presented in the characterizing part of the appended claim 8.

As for the other advantageous embodiments of the method, reference is made to the appended dependent claims as well as to the description below.

In the following, the invention will be described in more detail with ref¬ erence to the appended drawings, in which

Figure 1 shows the apparatus in a cross-section,

Figure 2 shows the apparatus in a longitudinal section,

Figure 3 shows the sorting means of the apparatus in a cross-sec¬ tion, and

Figures 4 — 6 show parts to be fixed on the inner wall of the drum.

Figure 1 shows a defibration drum in a cross-section. The inner wall of the drum 1 is provided with protruding guide elements 4 for guiding the movement of the material M to be defibred according to the rotational movement P of the drum. The guide elements 4 move along a circular path around the rotational axis of the drum and move with them the mass M to be defibred, placed in the lower part of the drum, however in a manner that they begin to release the mass not later than when they are at a 90° angular distance from the lowermost point of the rotational movement P. For achieving this, the guide elements 4 are plates pro¬ truding against the direction of the rotational movement P from the inner wall of the drum at an angle of less than 90°. Thus the guide elements 4 can entrain the mass in the quarter following the lowermost point of the rotational movement, wherein the mass will rotate as a uniform accumulation in the lower part of the drum 1 approximately within the

sector — 60°...+100°, when the lowermost point of the rotational path is taken as the zero angle. The mass will be ground by the action of the internal friction in a way that the fibres become detached from each other. At the same time plastic is separated from the fibre material.

Depending on the shape of the guide elements, part of the mass may be conveyed also to the upper part of the drum and fall from there. However, this part is insignificant for the defibration, and the uniform mass in the lower part of the drum will always be at least 95 wt-% of the total mass to be defibred.

The accumulation of mass M does not rotate regularly in the lower part of the drum 1 but the flows of single portions in it may vary. Conse¬ quently a certain portion, carried by the rotational movement P on the uppermost point of the accumulation, may start to migrate down either along the upper surface or through the inner parts of the accumulation, as illustrated by broken lines in the figure. Flows of single mass portions can be influenced by the placement and shapes of the guide elements 4.

Pieces of plastic and metal foil from the material to be defibred are fur¬ ther rolled into spherical pieces which can later be easily separated as reject.

Figure 2 shows the apparatus in a longitudinal section, and in the figure I — I indicates the section of Fig. 1 and III — III indicates the section of Fig. 3. The actual defibration drum 1 is in the inlet end of the apparatus, and it is continuously supplied with reclaimed paper to be defibred, via an inlet 2 in the front end wall of the drum. From inside the drum 1 , the defibred mass M is removed via an outlet 3 in the rear end to a sorting section 10. For this purpose, the rear wall can be provided with a lifting trough 11 which scoops the mass driven to the rear wall during defibra¬ tion and allows it to flow, as it turns upwards along the rotational move¬ ment, to the sorting section 10, to the innermost or centre part 12 around its rotational axis. There can be also several lifting troughs, e.g. three troughs, on the periphery of the outlet 3.

Figure 3 shows the sorting section in a cross-section. The sorting sec¬ tion rotates together with the drum, because it is formed inside the same outer housing as the drum 1 itself. A cylindrical centre part 12 around this common rotational axis comprises a spray pipe 14 inserted from the back of the apparatus, with the purpose of flushing the accept or the fibres through the sieve formed by the wall if the centre part. Coaxially with the centre part 12, around the same, there is a cylindrical intermediate part 13, whose wall consists of a material with such a mesh size, such as a dense wire, which will hold the accept but let water pass through it, which will thus flow to the outermost part limited by the housing of the drum 1 extending backwards. The reject which has not passed through the meshes of the innermost part 12 will be conveyed backwards by the action of a screw thread 12a placed inside the wall. The walls of the inner part 12 and the centre part 13 are, in turn, connected with a screw thread 13a which will move the accept backwards by the action of the rotational movement of the drum 1. The reject, which may consist of plastic or foreign objects, as well as the accept, which consists of fibres entering ink separation, can be re¬ moved from the rear end of the sorting section 10 by suitable transpor- tation means. Further, the water used in the sorting section can be con¬ nected to the water circulation system of the apparatus.

Further, Fig. 2 illustrates the placement of the guide elements 4. The guide elements 4, which in this case are plates, may have extension in the axial direction of the drum 1. Moreover, the guide elements in the rear part of the drum can be placed in a way that their longitudinal di¬ rection is at an angle to the rotational axis so that the end on the side of the inlet 2 is lower in the area of the rising part of the rotational move¬ ment P, wherein these means slightly resist the migration of the mass M towards the outlet 3, thus increasing the retention time. This angle can be arranged to be adjustable. In other respects, the mass M migrates in the axial direction of the drum 1 in a way that the supply of material at the front end will continuously push the mass towards the outlet 3, at which point a discharging means, such as the lifting trough, will continuously make room for fresh mass. The rotational axis of the drum is horizontal, but it can also be placed in a gentle slope, e.g. at an angle of 1 °, so that the end on the outlet 3 side is lower.

Figure 4 shows some feasible guide elements seen in a cross-section and in a longitudinal section of the drum. The elements are elongated plates whose outer edges, i.e. the edges closest to the rotational axis, consist of successive triangular portions 4a. The figure shows also plates 9 perpendicular to the rotational axis, protruding from the inner wall of the drum and placed between the above-mentioned plates, in¬ tended for penetrating the accumulation of the mass M in their longi¬ tudinal direction, thus shearing it in the direction of the rotational movement, and for generating more internal flows in the mass.

The guide elements 4 can also consist of separate triangular patches fixed at a suitable angle to the inner wall of the drum.

Figure 5 shows an alternative where the guide elements 4 are plates fixed to arms 5. The arms protrude from the inner wall of the drum, and the plates are placed in a manner that flow gaps are formed between them and the inner wall of the drum. The mass M to be defibred can flow on both sides of the plates, either on the side of the rotational axis or between the opposite side and the inner wall of the drum. The plates have additional means for influencing the rotation of the mass. The plate is provided with flow holes 6 passing through the plate and elements 7 protruding from the surface of the plate towards the inner wall. All these generate supplementary flows to the mass M, deviating from the regular rotational movement.

Finally Fig. 6 shows how the guide elements 4 can be journalled rotat- ably on the arms 5 protruding from the inner wall of the drum. Thus the cylinder journalled on the arm is provided with radially protruding ele¬ ments 8, such as blades, which come into contact with the mass, when the corresponding guide element circulates back to the lower part of the drum, and induce rotation of the guide element on the arm 5. This rota¬ tional movement generates additional flows to the mass, when the guide element is in its area in the lower part of the drum.

Naturally, all the above-mentioned guide elements can also be used in combination so that elements of a certain type are placed in an area se¬ lected for them in the axial direction of the drum.

One requirement for good operation of the apparatus is the fact that the reclaimed paper or the like to be defibred in the drum is sufficiently wet. This is secured by supplying a sufficient quantity of water and possibly additional chemicals to the inlet end of the drum. According to an ad- vantageous alternative, the reclaimed paper or the like is pre-wetted before supplying it inside the drum, whereby it has immediately a suit¬ ably low dry matter content to give at once a good start to the defibra¬ tion process. This can be conducted by a separate pre-wetting device placed upstream of the inlet 2 for wetting the material so that it will ab- sorb fluid already in advance, to a dry matter content of 30 weight-% or more. The invention can also be applied without pre-wetting, and also in this case reduced retention times will be achieved. The rotational frequency used in the drum is to be selected according to the dimen¬ sions of the drum and the consistency of the mass to be defibred in a manner that at the highest consistencies, the rotational speed or pe¬ ripheral speed of the drum required for achieving the defibration friction can be lowered. The defibration consistencies are usually in the range from 10 to 20 %. For example with a drum with an inner diameter of 2 m, a speed of ca. 28 r/min can be used for a consistency of 10 to 15 %, and a speed of ca. 15 r/min will be sufficient for a consistency of 18 to 20 %. Higher consistencies, e.g. in the range of 15 to 20 %, are advantageous, because the inner friction of the fibre material will thus be more efficient.

The invention allows a reduction of the retention time in comparison with normal defibration by dropping. When the retention time with con¬ ventional techniques is 20 min, the apparatus according to the invention will give the same defibration results with retention times of 7 to 15 min. This means a considerable increase in the defibration efficiency and energy savings per mass unit to be defibred.