WO2003097928A1

WO2003097928A1 - Impeller for paper pulp kneaders

Info

Publication number: WO2003097928A1
Application number: PCT/EP2003/005093
Authority: WO
Inventors: Giancarlo Dal Maso
Original assignee: Comer Spa
Priority date: 2002-05-17
Filing date: 2003-05-15
Publication date: 2003-11-27
Also published as: EP1511896A1; AU2003240650A1; ITVI20020097A1

Abstract

An impeller (1; 20; 30) for paper pulp kneaders is disclosed comprising an essentially plan bottom flange (2), a central shaft (4) which starts from the plane (K) defined by said bottom flange (2) in order to determine a longitudinal spin axis (X) of said impeller (1), one or more blades (5; 31) cross-wound around said central shaft (4). Each blade (5; 31) has an ending section (6) connected to said bottom flange (2), whose outer convex surface (7) is defined by a number of points (8) for each of them an (α) angle is being defined, which: has a width lower than 20°; lays on a parallel plane (TT) or coincident with the plane (K) defined by said bottom flange (2); is comprised between the tangent (9) to the contour or of said outer convex surface (7) and the tangent (10) drawn to a circumference (11) having the center in the longitudinal axis (X) and passing through the point (8).

Description

IMPELLER FOR PAPER PULP KNEADERS.

This invention is about an impeller for paper pulp kneaders.

As known, in the paper industry, devices named "kneaders" are used for the making of paper pulps, which basically consist of a container wherein an impeller is placed that carries out the making of the pulp by chipping wastepaper into an aqueous bath.

The action carried out by the kneader allows separating the cellulose fibres and making homogenous the water suspension of the same fibres.

Another important function of the kneader is that of separating the ink which soaks the cellulose fibres' paper so as to recover said fibres in order to remake new paper free of ink contamination.

The impeller of the kneader has a frustum conical shape with the major base placed on the. bottom of the tank and it is equipped with a number of blades cross-wound around a central vertical shaft which determines a longitudinal spin axis.

During the rotation, the impeller acts essentially as a pump which conveys the paper pulp towards the bottom through the channels formed between the blades and then makes it ascend continuously from the bottom upward along the walls of the tank, thus carrying out the pulping action. The separation of the paper from the ink takes place because of the rubbing among adjacent cellulose fibres and such rubbing occurs with consecutive steps of the mixture through the same impeller.

It must be noticed that in order to achieve an optimal rubbing among the fibres it is necessary to operate at high concentrations of the mixture because when the ratio between the amount of fibres and the water increases, the vertical motion of the mixture causes among the fibres a behaviour that evolves from a simple sliding into a rubbing due to the greater proximity between the same fibres.

The rubbing function is essential in order to achieve the intimate separation from fibre to fibre after a first phase of simple breaking of the paper into smaller pieces.

The state of the art impellers are of the multi-start type, usually equipped with three or more blades.

A state of the art kneader for paper pulps is described in the patent EP 0 775 233 registered under the name of the same applicant of this patent, and it exactly uses a triple-start impeller of a frustum conical shape, with a convergent taper towards the upper part of the tank which contains it. The impeller which is used in the kneader described in the previously cited patent, has however several inconveniences. A first problem consists in that the treated material which descends along the channels among the blades, when it reaches the lower part of the impeller is radially ejected at high speed. This involves a useless waste of energy which is transmitted to the mixture only as kinetic energy that is wasted without intervening in the pulping process because a piezometric excess head is formed thanks to the Bernoulli effect, relative to the head due to the level of the pulp of the tank.

Another inconvenience consists in that the ending section of the channels defined among the blades of the impeller where the material's discharge takes place, they are not fully loaded by the mixture which tends to be dispersed due to the increase of the abovementioned radial velocity. It follows that the pressure, already high as a result of the abovementioned phenomenon, is concentrated in a limited area of the blades by causing their accentuated wear. This causes high pressure on the blades that besides involving also in this case a power loss, it also generates an accentuated wear of the same blades. A further inconvenience consists in that on the lower ending section of the impeller, the blades have a sharp vertically. The presence of the abovementioned excessive pressure close to the discharge, forces the mixture to exit also in the upward axial direction. The phenomenon is completely negative because it supports the upper mixture by preventing its fall towards the impeller and by contributing to lock their motion, which is accentuated mainly in the presence of high concentrations. The present invention intends to remedy to said inconveniences. More specifically, a first object of the invention is that of making an impeller that would reduce the velocity of the mixture at the discharge from the channels next to the lower part of the same impeller.

It is another object that the impeller of the invention would allow reducing the pressure on the blades close to the output section of the ducts. It is a further object that the impeller of the invention would reduce the whirling motions of the mixture in proximity of the final area. Said objects are accomplished by an impeller for paper pulp kneaders that in line with the main claim, comprises:

- an essentially plan bottom flange connectable to driving means;

- a central shaft which starts from the plane defined by said bottom flange in order to determine a longitudinal spin axis of said impeller; - one or more blades cross-wound around said central shaft and is characterized in that each of said blades has an ending section, connected to said bottom flange, whose outer convex surface is defined by a plurality of points for each of them an α angle is being defined, which:

- has a width lower than 20°; - lays on a parallel plane or coincident with the plane defined by said bottom flange;

- is comprised between the tangent to the contour of said outer convex surface and the tangent drawn to a circumference having the center in said longitudinal axis and passing through said point. According to a preferred embodiment, the ending section of the blade has an essentially triangular shape with an outer convex surface, slanting and upward divergent in accordance with a direction that forms a β angle greater than 30° with the longitudinal axis of the impeller. Advantageously, the impeller of the invention allows a considerable saving on the used energy.

Yet advantageously, the impeller of the invention improves the volumetric performance of the kneader which is applied to because it reduces the reflux in the ending part of the impeller. In a further advantageous manner, the impeller of the invention reduces also the specific pressure in proximity of the bottom of the blades thus improving its life.

Said objects and advantages will be better highlighted in an explanatory but not limiting way during the description of a preferred embodiment of the invention with reference to the annexed drawings, wherein: - Figures 1 and 2 show the same isometric view of the same impeller of the invention;

- Figure 3 shows an isometric view of an embodiment of the impeller of figure

1 ;

- Figure 4 shows an isometric view of an operative embodiment of the impeller of the invention. The impeller of the invention is shown through an isometric view in figures 1 and 2, where is generally indicated with 1.

It is described that the impeller comprises an essentially plan bottom flange 2, connectable to driving means by means of through holes 3 and equipped with a central shaft 4.

The central shaft 4 starts from the plane K defined by the bottom flange 2 and where blades 5 are cross-wound around it.

It must be noticed that the central shaft 4 determines a longitudinal spin axis X of the impeller 1 which, in the case here described, has a frustum conical shape with the major base placed in the lower part and thus in proximity of the bottom of the container that holds it and that here is not shown.

Furthermore the impeller 1 is of the three-start type and thus is comprised of three blades as shown with greater details in figure 3.

It also must be noticed that the connection of the impeller 1 to the driving means, not shown in the drawings, can also take place through different systems than the screw like means, in which case the bottom flange 2 will be free of holes 3.

Furthermore it must be noticed that the number of starts of the blades which make up the impeller can be whichever number and these blades can have any angle of inclination with respect to the user's needs.

According to the invention each of said blades 5 has an ending section 6 which is connected to the bottom flange 2 and has the outer convex surface 7 which is defined by a number of points 8 for each of them an α angle is being defined, which: - has a width lower than 20°;

- lays on a parallel plane π or coincident with the plane K defined by said bottom flange 2;

- is comprised between the tangent 9 to the contour of said outer convex surface 7 and the tangent 10 drawn to a circumference 11 having the center in said longitudinal axis X and passing through the point 8.

In such manner an impeller is achieved, that compared to the state of the art impellers, has a lower output velocity from the material towards the bottom of the impeller.

This situation advantageously includes an energy saving because the power that the motorized means provide for the impeller, can be transferred in greater amounts to the mixture to be treated with resulting considerable energy savings.

It also described that the ending section 6 of the blade 5 is delimited by the following: - a first point 12 that corresponds to the intersection between the outer edge 5a of the blade 5 and the outer edge 6a of the ending section 6 which have different inclinations among them; - a second point 13 that corresponds to the intersection between the outer edge 6a of the ending section 6 and the bottom flange 2; - a third point 14 that corresponds to the intersection between the curve 15 defined by the intersection of the ending section 6 with the bottom flange 2 and the vertical plane Ω which passes through the longitudinal axis X of the impeller and through the first point 12.

More specifically it is illustrated in figure 1 that the tangent line 16 drawn to the outer convex surface 7 of the ending section 6 and passing through the first point 12 and the third point 14, forms a β angle greater than 30° with the longitudinal axis X.

In such manner a greater flaring of the ending section 6 of the outward blades is achieved, compared to the state of the art impellers which have the ending sections of the more vertical blades.

Therefore in the impeller of the invention, advantageously, the mixture can more easily exit from the ending section 17 of the channel defined among the blades, because the possibility of an axial ascent of the mixture along the direction X is reduced and thus the possibility that it would overflow from the outer edge 6a by causing vorticity and mainly a power loss.

In figure 3 an embodiment of the invented impeller is shown, generally indicated with 20, which differs from the impeller illustrated and shown in figures 1 and 2, because it has, in proximity of the outer edge 5a of each blade 5, a containment tab 5b that is developed for a stretch of the length of each blade 5 starting from the central shaft 4.

Preferably, when there is a containment tab 5b, it ends about one turn before the blade reaches the bottom flange 2 and it has an inclination towards the same flange 2. The action which the presence of the tabs 5b develops, is that of generating a centripetal component which acts on the pulp mass that is thus forced towards the longitudinal axis X of the impeller so as to be contained over the entire blades' surface by reducing the pulp mass that peripherally slides out due to the centrifugal effect. It must be noticed that the impeller of the invention shown in figures 1 and 3 is of the left-handed type and it develops the pulping action by rotating in the clockwise direction indicated by the arrow 18 in the figures 1 and 3. The same pulping action can be developed also by a further operative embodiment of the invented impeller, generally indicated with 30 and shown in figure 4, which has a right-handed winding direction 31 of the blades and is put in rotation according to the counter-clockwise direction shown by the arrow 32. Preferably, but not necessarily, it has the containment tab 33. As previously said, the impeller of the invention, regardless of the winding direction of its blades, it can be made with any number of starts. Furthermore, during the executive phase of the invented impeller, some modifications suitable for improving its operation or.for making its construction cheaper can be carried out that, if falling within the scope of the following claims, they should be doubtlessly considered protected by the present patent.

Claims

1 ) An impeller (1 ; 20; 30) for paper pulp kneaders comprising:

- an essentially plan bottom flange (2) connectable to driving means;

- a central shaft (4) which starts from the plane (K) defined by said bottom flange (2) in order to determine a longitudinal spin axis (X) of said impeller

(1 );

- one or more blades (5; 31 ) cross-wound around said central shaft (4), characterized in that each of said blades (5; 31) has an ending section (6), connected to said bottom flange (2), whose outer convex surface (7) is defined by a number of points (8) for each of them an α angle is being defined, which:

- has a width lower than 20°;

- lays on a parallel plane (π) or coincident with the plane (K) defined by said bottom flange (2); - is comprised between the tangent (9) to the contour of said outer convex surface (7) and the tangent (10) drawn to a circumference (11 ) having the center in said longitudinal axis (X) and passing through said point (8).

2) The impeller (1 ; 20; 30) according to claim 1 ), characterized in that said ending section (6) of said blade (5; 31 ) is delimited by the following:

- a first point (12) that corresponds to the intersection between the outer edge (5a) of the blade (5) and the outer edge (6a) of the ending section (6) which have different inclinations among them;

- a second point (13) that corresponds to the intersection between the outer edge (6a) of the ending section (6) and the bottom flange (2);

- a third point (14) that corresponds to the intersection between the curve (15) defined by the intersection of said ending section (6) with said bottom flange (2) and the vertical plane (Ω) passing through the longitudinal axis (X) of the impeller and through the first point (12). 3) The impeller (1 ; 20; 30) according to claim 2), characterized in that the tangent line (16) drawn to the outer convex surface (7) of said ending section (6) of said blade (5) and passing through a first point (12) and said third point (14), forms a β angle greater than 30° with the longitudinal axis (X). 4) The impeller (1 ; 20; 30) according to claim 1 ), characterized in that the outer edge (5a) of each of said blades (5; 31 ) has a continuous containment tab (5b; 33) which develops for a stretch of the length of every blade (5; 31 ) starting from said central shaft (4).

5) The impeller (1; 20; 30) according to claim 4), characterized in that each containment tab (5b; 33) is slanted towards said bottom flange (2).

6) The impeller (1; 20; 30) according to claim 1 ), characterized in that said impeller (1) has a frustum conical shape with the major base placed in proximity of said bottom flange (2). 7) The impeller (1; 20; 30) according to claim 1 ), characterized by being of the multi-start type.

8) The impeller (1) according to claim 7), characterized by being of the three-start type.