The invention concerns an improved filtering basket suited to be installed in systems for filtering fibres in water dispersion.
As is known, in the paper industry water dispersions containing cellulose fibres—mainly those derived from recovered paper—before being used in the production process must be properly filtered in order to eliminate all the impurities contained therein.
Filtering is carried out by means of the known strainers that substantially comprise a fixed filtering basket made of stainless steel and constituted by a plurality of metal bars that develop mainly in a longitudinal direction, positioned side by side in order to define a tubular structure.
The bars are provided with shaped edges that are substantially in the form of a trapezium, circumferentially spaced from one another in such a way as to define, on the inner lateral surface of the basket, a plurality of properly sized longitudinal slots whose widths are in the order of fractions of millimetre.
The inner lateral surface of the basket thus becomes the filtering surface.
Outside the bars there are annular elements coaxially spaced from one another that block them and maintain the tubular shape of the basket unaltered.
Inside the basket there is a rotor that sets the dispersion moving, so that the dispersion, while passing through the sized slots, releases the impurities present therein.
The filtering baskets having the characteristics described above and belonging to the known art, however, pose some recognized drawbacks.
A first recognized drawback lies in that their filtering action cannot exceed certain maximum values.
It is known, in fact, that, with reference to
The formation of such vortex V, in combination with the converging-diverging profile of the channel C defined by the profiles of the bars at the level of the slots F, produces the filtering action due to the known Venturi effect.
Furthermore, it has been found out that in order to obtain the formation of an optimal vortex the dimensions of the shaped edges of the bars must not be below certain pre-established values and therefore they are carried out in substantially standard sizes.
There is therefore a limit for the maximum thickness of the slots present in the basket per unit of length of the lateral surface and this represents a limitation to the filtering capacity of the baskets of known type.
Another limitation is represented by the fact that all the slots F present the same inlet angle γ as shown in
The present invention intends to overcome the drawbacks described above.
In particular, it is a first object of the invention to manufacture a filtering basket for filtering fibres in water dispersion that compared to filtering baskets of known type having the same size features thicker filtering slots.
It is another object of the invention to manufacture a basket that, compared to filtering baskets of known type, has a differentiated filtering capacity, such as to obtain better selection of the fibres to be accepted and to be rejected.
The objects described above have been achieved through the construction of a filtering basket whose characteristics are in accordance with the contents of the main claim.
Other characteristics of the basket of the invention are described in the dependent claims.
Advantageously, the basket that is the subject of the invention ensures more efficiency and better filtering quality than the baskets of known type having the same size.
The objects and advantages described above will be highlighted in greater detail in the description of preferred embodiments of the invention that are illustrated as examples without limitation in the enclosed drawings, wherein:
The filtering basket that is the subject of the invention is shown in axonometric view in
It is applied to machines for filtering fibres in water dispersion and, as shown also in the partial cross section of
Each profiled bar 2, 3, with reference also to
When the profiled bars 2, 3 are arranged side by side, one against the other, so that the respective prismatic bodies 6, 7 are in contact with each other, the corresponding shaped edges 4, 5 are spaced from each other in such a way as to define a plurality of longitudinal slots F that transform the inner lateral surface of the basket 1 into a filtering surface.
A plurality of annular elements 8 coaxial with one another and spaced from one another according to the longitudinal axis X defined by the basket are coupled by interference to the outside of the profiled bars 2, 3, in such a way as to maintain the tubular geometric configuration of the basket 1 unaltered.
It is useful to observe that the annular elements 8, which in the case shown in
According to the invention, the profiled bars 2, 3 comprise a plurality of main bars 2, each provided with a shaped edge 4 whose cross-section is in the form of a trapezium, with the long side 4a facing towards the inside of the basket, and a plurality of secundary bars 3, each provided with a shaped edge 5 whose cross-section is in the shape of a curve, with the convex side facing towards the inside of said basket.
As shown in
It can also be observed that each main bar 2 is included between two secundary bars 3 and that between each pair of main bars 2 there is a secundary bar 3.
Substantially, therefore, the profiled bars are arranged so that each main bar 2 is followed by a secundary bar 3, in a continuous sequence according to the circumference that defines the lateral surface of the filtering basket.
In particular, in the cross-section of the filtering basket shown in
Furthermore, it is possible to identify a first circumference C1 tangential to the shaped edge 4 of the main bars 2 and a second circumference C2 tangential to the shaped edge 5 of the bars 3, both having their centre on the longitudinal axis X, wherein the radius R2 of the second circumference C2 is longer than the radius R1 of the first circumference C1.
In this way a plurality of recesses 9 is defined in the basket 1, said recesses being included between the sides of the shaped edges 4 of each pair of main bars 2 adjacent to each other and the circumferences C1 and C2.
Each recess 9, indicated by a broken line in
Tests performed on prototypes have shown that in each recess 9, indicated by a broken line in
The profile 5a of the shaped edge 5 of each secundary bar has the shape of an arc of a circle and is housed approximately at the height of the short side 9a of the trapezium-shaped recess 9, thus allowing the main bars 2 to be moved near each other.
Furthermore, the thickness of the secundary bars 3 can be reduced to a minimum value compatible with the mechanical resistance conditions, thus obtaining slots F that are very near each other and are both affected by a single vortex V.
In this way the invention also achieves the object to increase the number of slots F per unit of surface compared to the known art, thus increasing the filtering capacity of the basket even if it has the same size as the filtering baskets of the known art.
The prototypes that have been constructed have made it possible to verify, as is shown in
It can also be observed that in each recess 9 angles β1 and β2 are created for the inlet of the fluid in the respective slots F, said angles being different from each other, so that it is possible to differentiate the filtration of the fluid in two separate slots instead of in a single slot, as is the case with the baskets constructed according to the known art shown in
Each profiled bar 2, 3, as can be observed also in
In this way between each pair of profiled bars 2, 3 a conveying channel 12 is defined, which is delimited by the intermediate sections 10, 11, diverges towards the inside of the basket and communicates with a corresponding slot F.
In particular, each intermediate section 10, 11 is delimited by lateral walls 10a, 11a parallel to each other and the thickness Sa of the intermediate section 11 of each secundary bar 3 is equal to the diameter of the arc of a circle 5a that defines the shaped edge 5.
The prismatic bodies 6, 7 of the profiled bars 2, 3 present concavities 6a, 7a and protrusions 6b, 7b that can be matched to each other as shown in
A construction variant of the filtering basket of the invention, indicated by 100 in
In this way, between each pair of main bars 2 three slots F are defined, which are all affected by a single vortex V created between the main bars 2 adjacent to each other.
Also in this case the thickness of the secundary bars 103 can be reduced to very low values compatibly with the possibility to guarantee the necessary mechanical resistance, in such a way as to further concentrate the number of filtering slots F per circumferential unit of length of the basket.
Experimental tests have shown that, as illustrated in
Furthermore, the three slots F included between each pair of main bars 2 present three different fluid inlet angles β1, β2 and β3.
Therefore, also this construction variants achieves the object to further differentiate the filtration of the fibres on three different slots with three different inlet angles.
The filtering basket carried out according to any of the described variants is constructed so that the profiled bars 2, 3; 103 have different cross-sections along the longitudinal axis X of the basket.
Thus, in
This particular embodiment can be carried out both in the case where in each pair of main bars 2 there is a single secundary bar 3 and in the case where said secundary bars 103 are two.
In this way, draining chambers 13; 113 are defined inside the basket, thus improving the filtration of the fibrous suspension as regards both the filtering quality and the flow rate of the filtered fluid.
In fact, the presence of the draining chambers 13, 113 allows each slot F to be restricted while maintaining for the basket in its whole a satisfying flow rate of solution filtered through the filtering surface.
The hollow areas 3a, 103a of the bars are obtained in such positions that the draining chambers 13, 113 are included between the annular elements 8 when these are arranged so as to encircle the bars 2, 3; 103 externally.
According to the above, it can thus be understood that the basket that is the subject of the invention, in both the embodiments described, achieves the set objects and offers the described advantages.
In particular, it has been observed that the special configuration and arrangement of the shaped edges of the shaped bars makes it possible to increase the number of slots per circumferential unit of length compared to the baskets carried out according to the known art.
The invention also ensures the advantage that said differentiated slots have differentiated inlet angles, in such a way as to obtain the differentiated and selective filtration of the fibres of the solution.
Furthermore, the creation of hollow areas in the secundary bars makes it possible to maintain good values of flow rate even though the width of the slots is reduced as much as possible, by thinning the bars until reaching the minimum limit compatible with their mechanical resistance.
In the construction stage of the basket that is the subject of the invention changes may be made that are neither described herein nor illustrated in the figures.
It is understood, however, that if these changes fall within the scope of the following claims, they must all be considered protected by the present patent.
Where technical features mentioned in any claim are followed by reference signs, those reference sings have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.
Number | Date | Country | Kind |
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VI2007A000209 | Jul 2007 | IT | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/060103 | 7/31/2008 | WO | 00 | 2/26/2010 |