FI69138B - REFERENCE TO A CENTER FOR CENTRAL FUGAL MATERIALS - Google Patents

Description

1 69138

Method and apparatus for centrifuging wood material

The present invention relates to a method 5 and an apparatus for grinding paper wood and / or wood chips, in which the force forcing the sanding surface against the wood increases from centrifugal. The present method and apparatus also includes other features and advantages, which are discussed in detail below.

A conventional method of producing sanded paperwood for making paper products involves pressing a pile of paperwood (round wood or wood chips) against a rotating grindstone, simultaneously feeding a jet of water into the grinding chamber, especially by spraying water directly onto the stone surface at a location separate from the grinder. The dam or barrier keeps the formed ground wood mass, which is an aqueous ground mass, in the grinding chamber at a slightly higher level than the lower end of the stone for cleaning, lubricating and cooling the stone. The ground wood mass flowing over the dam is removed due to its own weight for further processing. A variation of the above is a “tubeless” method in which the stone is not immersed in a liquid and in which the use of additional water jets is provided.

25

Another known method utilizes a disc shredder in which the material to be comminuted or ground is machined between two opposing plates placed close to each other and rotating relative to each other.

30 As a result of recent developments, wood is sanded at a higher than atmospheric pressure, which allows higher sanding temperatures than standard stone-wood sanding (SGW).

U.S. Pat. Nos. 3,808,090 and 3,948,449 describe a process for improving wood pulp 25 in which wood is ground in a closed 2,691 38 grinding chamber in a pressurized gaseous atmosphere. In the two patents mentioned above, the wood is fed into the grinding chamber and the over-atmospheric pressure can be maintained in the grinding chamber only for as long as it takes to grind the wood pile. However, when a new pile of wood needs to be fed into the magazine, the magazine needs to be opened and the grinding surface pressure drops to atmospheric pressure. Thus, the sander does not work continuously in a pressurized atmosphere.

In an attempt to overcome the problem just defined 10, Oy Tampella Ab has made further developments, as exemplified by Canadian Patent No. 1,097,118, published March 10, 1981, and U.S. Pat. in Patents 4,270,702 and 4,274,600, issued June 2, 1981 and June 23, 1981, respectively. Oy Tampella's 15 manufacturing methods have two pressure seals in the feed chamber upstream of the grinding chamber, one facing the outside air and the other facing the grinding chamber. Thus, the feed chamber acts as a double seal, allowing the pressure in the grinding chamber to always be kept higher than the air-20 circumferential pressure. When using this method, the pressure in the grinding chamber can rise to several bars, the temperatures on the surface of the grindstone can rise much above the boiling point of the standard pressure.

Due to the considerable size and complexity of the SGW method and the pressurized wood chip (PGW) method developed to date, it would be desirable to reduce the complexity and size of the installation required to produce wood pulp that can be used in papermaking. In both the PGW and SGW manufacturing methods, 30. very large compression sensors must be used to hydraulically force the round wood against the grindstone, and there must be a storage for incoming sanding wood above the main location of the pressure sensors.

Another approach to sanding wood chips 35 is where the sanding pressure between the wood and the sanding surface is obtained

II

3 691 38 centrifugal, by making a cylindrical inner sanding surface, and "centrifuging" the wood outwardly against a stationary sanding surface by centrifugal force. The centrifugal motion would not only provide an appropriate increase in compression between the wood and the abrasive surface, but could also pressurize the amount of water that travels with the wood, thus allowing higher temperatures than the maximum temperatures achievable with the standard SGW manufacturing method.

An earlier Canadian patent, 2834, issued October 24, 1873, defines a rudimentary version of a wood centrifugal grinder having a stationary inner cylindrical grinding surface and a rotor that pivots vertically about an axis and centrifuges the feeder wood centrifugally outwardly in contact with radial paths. The water needed to cool the grinding surface and make the ground mass-like is simply sprayed into the housing with a simple hose or pipe.

20 Due to the rudimentary structure used by Moore, his equipment does not meet today's requirements for high-speed grinding.

Accordingly, it is an object of the invention to provide a method and apparatus which is improved over Moore's apparatus 25 and which operates in accordance with the principle of rotation to provide a uniform and pressurized water jet against an inner grinding surface.

The features of the method and device according to the invention are set out in claims 1 to 17.

According to the invention, there is provided a grinding method which utilizes an internal grinding surface in the form of a rotating surface. The method involves having a rotating material on the periphery of the inner abrasive surface to generate a centrifugal abrasive force between the material and the surface, simultaneously applying water to the abrasive surface through openings which also rotate very close to the periphery of the surface.

4,691 38

Essential for a centrifugal grinder according to claim 1, nozzle means communicating with other water passages for spraying water against an internally rotating inner grinding surface 5 with the motor. Positioning the second waterway further away from the rotor shaft than the first waterway is particularly important precisely because the rotational movement of the rotor causes an increase in pressure in the nozzle means and an increase in pressure against the grinding surface by the centrifugal force, thereby naturally increasing the grinding power of the wood.

The accompanying drawing illustrates two embodiments of the present invention, in which like parts denote like parts at several points, and in which: Figure 1 is a partially vertical and partially sectioned view of a centrifugal grinder of a first embodiment of a paper wood constructed in accordance with the present invention; Figure 2 is a partial plan view and a partial horizontal sectional view Fig. 3 is a schematic sectional view showing generally means by which water can be introduced into injection holes near the grinding surface; Fig. 4 is an axial sectional view of another embodiment of the present invention; Fig. 5 is a cross-sectional view taken along Fig. 4; line 5-5, Figure 6 is a cross-sectional view taken along the line 6-6 in Figure 4, 30 Figure 7 is an elevational view of the rotors shown in Figure 6 copolymer in view of the direction of the arrow 7.

Attention is first drawn to Figure 1, in which the left part is an axial sectional view of a paper-wood centrifugal grinder 10 comprising a domed upper frame 12, a cylindrical outer stone mounting frame 14 with two outwardly extending flanges 15 and 16 at opposite ends 11 69138, and a bottom frame 18, which is described in more detail below. A plurality of stone segments 20 are firmly attached to the stone mounting frame, forming a radially symmetrical, curved, cylindrical inner grinding surface 22. The stone segments may be hexagonal in shape.

Central to the grinding chamber 24 is a drive shaft 27 mounted on conical bearings, one of which is shown in Figure 1 by reference numeral 26, to which a rotor hub 28 is fixed by means of a wedge 29.

Extending substantially radially away from the hub 28, at least one, and preferably two or three concave arms 30 are adapted to convey the paper-wood circumferentially along the circumference of the grinding surface 22.

15, as shown in Figure 2, arm 30 rotates about axis 31 in the direction of the arrow 32, and is gradually curved such that the distal part 34 is inclined relative to the direction of running backwards. As can also be seen in Figure 2, the off-center portion 34 has a plurality of gripping teeth 36 along its front surface, which teeth 36 are adapted to grip the piece of paper wood 38 to stabilize it as it rotates against the sanding surface 22 and to minimize bumping and rolling of the paperwood 38. The concave shank 25 has an adjustable finger beam 40 at an end spaced from its center, which may be a stainless steel casting adapted to run very close to the grinding surface 22 to ensure that the water and wood pulp near the paperwood 38 should also be wiped circumferentially along the grinding surface 2. and thus "centrifuged" outwardly against the grinding surface 22 due to centrifugal force.

It should be noted that where only one arm 30 is used, the hub 28 must be balanced by additional weights placed opposite the single arm. Using 35 two opposite arms, or three identical arms 69138 placed at 120 ° intervals, the balancing board is eliminated.

Returning to Figure 1, it can be seen that the base frame 18 includes a ripper, generally designated 5 43, which ripper 43 comprises a stator 45 and a rotor 47, the rotor being a sauna piece with a plate-like rotating bottom wall 48 integral with the hub 28. The rotor 47 is provided with a plurality of slots as well as a stator 45, and the openings 46 of the two sets of slots pass over each other at high speed, thereby tearing the wood chips through like scissors or cutters.

The purpose of tearing is to break chips that otherwise tend to cause increasing clogging downstream.

The base frame 18 includes a wall 50 defining a helically formed discharge zone for the pulp. An opening (not shown) is provided to remove the pulp from the discharge zone. »The bearing seal is generally indicated at 53 and includes an L-shaped 20 stationary ring 54 forced upwardly by a spring 57 against the bottom of an annular downwardly directed protrusion 56 which is cohesive with hub 28.

At the upper end of the concave arm 30 there is an annular plate 59 which, together with the part 48, defines a drawing zone 25 for the aqueous grinding mass resulting from the grinding process.

Connected above the upper frame 12 is a paper wood supply pipe 60 along which pieces of paper wood 38a can pass. It should also be noted from Figure 1 that while the arm 30 30 is connected to the hub 28, it also has a free inner edge 61 which abuts the inner circumference 62 of the annular plate 59.

Thus, a central opening 64 is defined from which pieces of paper wood 38a can fall in.

7,691 38

It has been investigated that the hub 28 need not be as long as shown in Figure 1 and that it may terminate closer to the wedge 29. It has also been investigated that the entire grinding chamber 24 could be further pressurized to a higher atmospheric pressure using single or double seals (not shown). ), so that the pressure under which the aqueous mass is centrifuged along and against the grinding surface 22 would become higher than atmospheric pressure due to both centrifugal force and additional pressure.

The embodiment shown in Figures 1 and 2 is arranged in a vertical position, i.e. the axis of rotation extends vertically, the arrangement schematically shown in Fig. 3 is shown in a horizontal position. The actual purpose of Figure 3 is to show how water can be conducted close to the grinding surface 22a 15, and that the central exhaust effect of the rotational movement of the arms 30 also causes an increase in pressure in the water coming from the nozzles 67.

Using purely mathematical methods, it is simple to show that within a radius of 30.5 cm, measured from the position of the 20 nozzles 67 to the center line of rotational motion, and at a rotational speed of 120 radians per second, a pressure increase of 0.63-0.70 MPa occurs from the center line to the nozzles. This allows a relatively low water pressure to be used at the initial feed point 25 70. Because the pressure varies with respect to the square of the radius and also the square of the rotational speed, significant increases in water pressure can be achieved with fully controllable dimensions.

In Kuya 3, an electric motor 71 rotates the input shaft 72 of the reduction gearbox 74, the power take-off shaft 75 of the gearbox 30 rotating the concave arms shown in Fig. 3 only by the water pipes 77.

To achieve grinding pressures in the range of 0.70 MPa, which are considered typical for conventional grinders, mathematical calculation shows that a centrifugal grinder with a diameter of 69,138 feet and a diameter of 203 cm has the required rotational speeds in the range of 7 k / s. This would correspond to a surface velocity of about 45 m / s.

Attention is now directed to Figures 4-7, which show 5 second embodiments of the present invention.

In Figures 4 and 5, the cylindrical inner grinding surface 90 is defined by portions of the cylinder of suitable stone 92 which are held in place by the stone support frame 94.

A housing 1Q 96 is sealed to the stone support frame 94, which is sealed to the left of the bearing frame 99 in Figure 4 and sealed to the bearing frame 101 in the right of Figure 4.

In Fig. 4, the bearing frame 101 on the right is connected to a steering shaft bearing frame 104, which includes a set of roller bearings 105 supporting the steering shaft 107 for central rotation about a central shaft 109.

In Fig. 4 on the left, a bearing frame 99 is connected to a drive shaft 112 of conventional construction supporting two roller bearings 113 and 115, 2Q which centrally support a low speed rotating drive shaft 117 which, together with the steering shaft 107, stably supports the rotor 120 rotating about an axis 109.

As best seen in Figures 4 and 5 taken together, the rotor 120 essentially comprises two end plates 122 and 123 supporting two axially extending sickle-shaped members 125 and 126 (see Figure 5). In more detail, each of the sickle-shaped members 125 and 126 includes an outwardly extending portion 129, and a substantially partially cylindrical portion 31 located eccentrically with respect to the axis 109 of said rotor.

In even more detail, looking at Figure 5, the center of curvature of the left-hand semi-cylindrical portion 1?] Is at 134, while the center of curvature of the right-hand part 9 691 38 or the cylindrical portion 131 is at 136. Of course, the locations of these centers of curvature are not. since what matters is not where the centers are located, but rather that the surface defined by part 131 131 is such that at one end it is located closer to the actual axis of rotation 109 than at the other end. To illustrate, when looking at Figure 5, it can be seen that the portion 139 of the partially cylindrical portion 131 adjacent to the portion 129 is closer to the axis 109 than the region 141. As can be seen in Figure 5, the space between the two members 125 and 126 is filled with different thick logs. It should be noted that as the rotor rotates relative to the shaft 109, the centrifugal force thus generated tends to cause the logs 15 to "lower" along the curvature of the portion 131, as if this were a downward slope in the gravitational field. In fact, the centrifugal force generated by the rotational motion of the rotor, provided the rotational motion is fast enough, is significantly greater than the gravitational field, 20 so that the logs between members 125 and 126 mainly "see" only centrifugal force as they seek exit from the rotary shaft 109. and 126, because their portions 131 extend further and further away from the shaft 25 109 when counterclockwise, as also shown in Figure 5, the supports tend to roll or counterclockwise relative to the members 125 and 126, thus approaching their end regions where the members 125 and 126 There is a space therebetween that allows the logs to move outward 30 by centrifugal force and to contact the cylindrical inner surface 90 of the grindstone segments 90. The rotor structure shown in Figure 5 forms a "temporary center" to avoid the development of a situation where the second tray is fully loaded at the same time, 35 another, which may be empty, cannot receive logs because its inlet is closed.

10,691 38

At the edge of the parts 131 at the point furthest from the axis of rotation 108, a guide plate 143 abuts close to the inner grinding surface 90. At the outermost point of the portion 129 of each member 125,126, a finger bar 145 is attached to hold an aqueous pulp formed of wood pulp and of water added thereto, rotating around and against the inner abrasive surface 90. Preferably, the finger beams 145 are shaped to assist in removing the mass 10 to the sides of the stone. A suitable shape for the finger beam shown at 145 is disclosed in Canadian Patent No. 947,555, issued March 21, 1974 to Koehring-Waterous Ltd. and inventor G.W. Cryderman.

The outer plates 122 and 123 of the rotor 120 are shaped as shown in Figure 5, the shape being substantially circular with two outwardly extending lugs 147. The lugs 147 are intended to limit the escape of unwanted chips. This ensures that the chips remain in the grinding zone and 20 ensures that they are completely ground,

It should be noted that the nominal outer circumferential diameter of the plates 122 and 123 is smaller than the diameter of the inner sanding surface 90, leaving a gap 152 between which paper pulp can exit the inner sanding surface 90. However, the lugs 147 extend outwardly beyond the radius of the inner sanding surface 90 and thus they extend over the grindstone segments. This allows the determination of two "grinding cavities", as they could be described, each grinding cavity being defined in the transverse direction by two lugs 147, an abrasive surface 90 on the outside, a plate 143 on the front of the second members 125 and 126, and a part on the back of the second members 125 and 126. 129 and a finger bar 145. The logs are centrifuged or forced from the centrifuge into these grinding holes, where 35 they are ground to a mass.

> 1 11 69138

Returning briefly to Figure 4, it can be seen that the bearing frames 99 and 101 are delimited on the outside by two annular pulp / oil mechanical seals 156 which are internally opposed to the slowly rotating drive shaft 117 and the steering shaft 107, respectively.

Thus, the housing 96 defines the top of the chamber within which the rotor 120 rotates, which chamber retains the paper pulp and directs it downward. The lower part of the chamber, as shown in Figures 4 and 5, can be placed in a pulp basin 160 provided below the factory floor level 158, the pulp basin 160 has a pulp discharge passage 162 leading to the next pulp treatment step (this is not related to the present invention). ).

Attention is now directed to Figures 6 and 7 to illustrate a particular feature of the present invention in connection with the desirability of forcing the pulp surface 90 towards the axial ends of the paper pulp in order to promote the pulp to leave the grinding surface.

Figure 6 shows an external end view of the plate 123, 20 on the left in Figure 4. Figure 6 shows that the outer circumference of the left plate 123 has a recess 171, but that the plate 123 is otherwise similar in shape to the plate 122 shown in Figure 5. Between the two plates 122 and 123 are connected an inverted V-shaped finger beam support 173 25 in which an additional finger beam 175, which is also inverted V-shaped, is firmly bolted or crimped. Figure 6 shows three sets of fasteners 178, which may be in the form of bolts or clamps.

Figure 7 shows a straight elevational view of the rotor 120 as viewed from a direction showing the actual shape of the additional finger beam 175 and its bracket 173. The additional finger bar 175 consists of two plate elements, each with a curved outer edge 181 having the same curvature as the inner grinding surface 90. Since the direction of rotation, 12 691 38 as seen in Figure 6, is clockwise (as in Figure 5), which means that the additional finger bar 175 moves as shown in Fig. 7 during normal rotational movement of the rotor 120, it can be seen that the wood pulp adhering to the grinding surface 90 but escaping from under the finger bar 145 is guided into two arms and forced axially towards the ends of the inner grinding surface 90 so that it can exit from there and drop down into the mass pool 160.

The additional finger beam 175 is preferred in that it avoids the formation of an excessive pile of wood chips on the inner sanding surface. Such a formation could impair the grinding action.

Attention is again directed to Figures 4 and 5 to illustrate water passageways that allow water to enter the grinding chamber along the slow rotating drive shaft 177 and that water is available in a plurality of nozzles adjacent the inner grinding surface.

In more detail, looking at Figure 4, the jet feedwater is seen coming from the left along the feed pipe 184, through a rotating seal 186 and into a central passage 189 located axially on the low speed drive shaft 117. From the axial passage 189 extend a plurality (in this case 4) of radially outward passages 191 are connected by aisle 189, in which case aisles 191 are defined by appropriate or other conductors. The passages 191 are connected at their outermost ends or at the ends furthest from the center to corresponding jet tubes 193 extending axially relative to the rotor 120 and supported between the plates 122 and 123. As can be seen in Figure 4, each of the removable nozzles 193 is closed at its right end 35 by a tube cover 195, and each nozzle 38 has a plurality of nozzle openings 196 near the inner grinding surface 90.

As previously described in this shipment, the rotational movement of the rotor 120 increases the pressure in the detachable nozzles 193 relative to the pressure in the passage 189, allowing the supply water pressure along the pipe 184 to be lower than the design pressure in the detachable nozzles 193.

The design of the grinder as defined herein has 1.0. numerous advantages, and these are outlined below.

First, the grinding assembly defined herein can be used to create pressure effects without the need for a pressure-lock mechanism.

15 Secondly, it has been thought that this structure makes it possible to grind wood chips as well as logs by means of an additional screw feeder or other transfer element for the chips.

Further, by feeding spray water through the rotor 20, an essential component of its final pressure can be created centrifugally. Likewise, the pressure of the water coming from the orifices 196 increases with the rotational speed, as does the grinding pressure.

Compared to disc grinders, the grinding device of the present invention rotates more slowly than the grinder on the chip feed-cutting surface (where the chips are accelerated from stops to rotational motion). The grinder according to the present invention can rotate in the speed range of 8 k / s compared to the speed of the disc shredder at 30 k / s.

30 Thus, less power is consumed than in the grinder (in this particular area), and the chip reaches the machining surface of the grinder under better conditions due to the previous speed.

14,691 38

While the rotors with two opposite pockets or abrasive cavities are illustrated in the drawings of this specification, it will be appreciated that one, three or more such abrasive cavities may be used.

It is further understood that the grinding pressure 5 can be precisely adjusted by providing the means for changing the speed of the rotor, as this controls the generated centrifugal force.

Although not described, a screw feeder could be used to move logs or wood chips 1Q to the center of the rotor through the inlet on the control shaft 107. It is clear that the structure defined in the description results in its uninterrupted loading, which is the main improvement over traditional single-feed grinders. By using an uninterruptible feed or conveyor system, it is possible to automate loading with the present invention, thus reducing the need for manpower and improving safety.

These are clear advantages over conventional type grinders.

20 An alternative that may be added to the structure described herein in the future is to rotate the inner grinding surface in the opposite direction to the rotor. This increases the speed at which the wood travels over the grinding surface without changing the grinding pressure (which depends only on the centrifugal force, i.e. the rotational speed of the rotor 120).

Yet another alternative would be to use a grinding stone surface having a non-cylindrical shape, for example a conical surface with a profile as shown by dashed line 197 in Figure 1. This could be used to assist in both mass removal and saving the distance between the rotor and the rock. Such an alternative could well be used especially in the chip grinding process, where the distance between the stone and the rotor is more decisive, and where the change in circumferential speed due to the variable diameter is less important.

tl 15 691 38

Since the stone structure is fixed in the present structure, the stresses are considerably lower. The stone structure of the present construction consists of glaze * supported parts placed in a steel rim or 5 in a frame 94. This allows the use of a stone with a lower weight and which is not as complicated as in conventional structures. Another option is the possible design of the stone frame so that it forms a jacket for cooling.

While specific embodiments of the present invention have been shown in the accompanying drawings and the foregoing description, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the scope of the present invention as set forth in the appended claims.

Claims (17)

A method for grinding wood material against an inner sanding surface in the form of a rotating surface, characterized in that it comprises the steps of a) rotating the material around the inner sanding surface in a plurality of separate and circumferentially separated pockets to generate a centrifugal sanding force between the material and the surface; ) spraying water on the grinding surface from the nozzle means behind each pocket in the direction of rotation to remove wood fibers and form a slurry; and c) using a centrifugal effect to increase the water pressure in the nozzle means. A method according to claim 1, characterized in that it further comprises the step of rubbing the grinding surface with a finger bar placed between each pocket and the corresponding nozzle means. A method according to claim 2, characterized in that it further comprises the step of cleaning the grinding surface with a herringbone finger bar following the nozzle means to cause the slurry to move towards the axial ends of the grinding surface. A method according to claim 1, characterized in that the grinding surface is in the grinding chamber and the material is rotated around the grinding surface by a rotor coaxial, and that the water application step is performed by passing water into the rotor axially and passing water to the nozzles away from the rotor shaft. direction. Method according to Claim 1 or 4, characterized in that the material is paper wood. Method according to Claim 1 or 4, characterized in that the material is paper wood which is fed axially into a chamber containing a grinding surface. A method according to claim 1 or 4, characterized in that the water applied through the nozzles is introduced around the grinding surface with the material and pressed by centrifugal force, whereby the boiling point of the water rises and the grinding process proceeds above the boiling point of the water at atmospheric pressure without evaporating . A centrifugal grinder (10) comprising an inner grinding surface (22) in the form of a rotating surface, a rotor (28, 30) mounted to rotate concentrically with the grinding surface, having a central cavity and defining at least two pockets through which the material in the central cavity 10 can pass in contact with the grinding surface and distributed around the rotor and separated in intermediate areas, first means (60) for supplying the material to be ground to the central cavity, second means (27) for rotating the rotor and third means (189, 15 191, 193, 196) connected to the rotor the third means comprises a first water passage (189) in the rotor adjacent to its axis, and for each pocket a second water passage (193) in the rotor adjacent to the grinding pin-20 nan, which passage follows the respective pocket in the direction of rotation, water conveying means (191) , which connect the first path to the second path , and nozzle means (196) in communication with each second passageway for spraying water against the grinding surface, each second passageway being farther from the rotor axis than the first passageway, wherein rotation of the rotor increases water pressure in the nozzle means relative to the pressure in the first passageway. Device according to Claim 8, characterized in that the surface of rotation tapers in the other direction along its axis. Device according to Claim 8, characterized in that the axis of the grinding surface (22) is substantially horizontal. Device according to Claim 8, characterized in that the grinding surface (22) is substantially cylindrical. 18,691 38 Device according to Claim 8, characterized in that two of the pockets are arranged in opposite places on the rotor (28, 30), the intermediate areas being larger in circumference than the pockets. Device according to Claim 8, characterized in that the first water passage (189) is coaxial with the rotor (28, 30). Device according to claim 12, characterized in that each nozzle means has a plurality of nozzles for spraying water against the grinding surface (22). Device according to Claim 8 or 14, characterized in that the primary finger beam (40) is arranged on the rotor in the direction of rotation behind each pocket 15 and in front of the corresponding second water path and runs substantially parallel to the rotor axis and that the secondary finger beam (173) is arranged on the rotor in the direction of rotation. behind each primary finger bar and is in the shape of a fishbone above, so that the function of the second finger bar is to force the abrasive surface towards the axial ends of the grinding surface in the paper wood. Device according to Claim 8, characterized in that the primary finger bar (40) is arranged on the rotor in the direction of rotation behind each pocket and in front of the corresponding second water path (193) and runs substantially parallel to the axis of the rotor (28, 30) and the secondary finger bar (173) is placed on the rotor in the direction of rotation behind each primary finger bar (40) and is in the shape of a fishbone above, so that the secondary finger bar serves to force the pulp towards the axial ends of the grinding surface, the grinder further comprising a housing (96), defines a grinding surface at each end of the pulp evacuation chamber, and a pulp outlet in communication with the pulp evacuation chambers. 16,691 38 Device according to Claim 9, characterized in that the inner grinding surface (22) is conical. 691 38 1 9