Filtering device for solid wastes

A filtering device is provided for solid wastes which includes a rotating drum having longitudinal rows of separating holes located through its outer surface. Plates are located between these rows and extend from the drum at a predetermined height in proportion to the radial dimensions of the holes. The plates can be continuous of discontinuous and can extend either perpendicularly relative to the drum or slightly inclined relative to the drum in a direction opposite the rotation of the drum. If desired, transversely extending plates may also be employed. The plates prevents clogging due to the phenomena of winding wherein fibers exit a hole and re-enter another hole as the drum rotates.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
This invention relates to solid waste disposal and more particularly to 
filtering devices for solid wastes. 
2. Discussion of the Related Art 
It is known that solid urban wastes must be subjected as a preliminary step 
to volumetrical separation and then to qualitative separation where they 
can be subjected with the necessary treatments to recycle recoverable 
portions and dispose of the non-recyclable portions. 
Volumetric selection is usually done by means of rotating filters which 
comprise drums or cylinders having mantles provided with holes of various 
shapes and dimensions. The drum is rotated about its longitudinal axis and 
this rotation causes material placed inside to be separated according to 
the size of the material pieces. 
In operation, the material pieces which are smaller than the dimensions of 
the holes pass therethrough, thereby discharging to the outside. On the 
other hand, the material pieces which exceed the hole dimensions continue 
across the free end of the drum for subsequent filtering or for final 
treatment or discharge. 
In the case of solid urban wastes, the material placed in the rotating 
filter often contains scraps, fibers, plastic film, iron filings, and 
similar elongated bodies. These materials tend to wind themselves around 
the zone of the mantle of the cylinder between two contiguous holes, 
thereby clogging the separating holes. 
This phenomenon of winding is caused by a filamentary or fibrous material 
landing across the drum segment between two adjacent holes and partly 
sticking out from them when these holes are at the lowest point during the 
rotation of the drum. During this rotation, these fibrous materials are 
carried in such a way as to move from the lowest to the highest zone. In 
this highest position, these materials tend to re-enter the drum interior 
due to the combined effect of the force of gravity ad the centrifugal 
force of the cylinder created by the aerodynamic effect in the direction 
opposite to that of the rotation of the drum. This re-entry occurs via 
both the hole from which they previously exited and from the hole adjacent 
beside the exited hole in the direction of rotation. This dual re-entry 
creates tangles around the two holes, thereby obstructing them. 
This winding phenomenon is principally observed in the zones between the 
holes arranged longitudinally relative to one another. The transverse 
zones are less susceptible to winding, since in that radial direction the 
effect of the aerodynamic centrifugal force has little influence. 
Accordingly, the scraps and strings have the tendency to re-enter through 
the same holes they came out, thereby rendering the holes self-cleaning. 
Experience has shown that approximately 95% of the winding between two 
holes is observed in the longitudinal inter-spaces and 5% in the 
circumferential spaces. 
Winding causes a rapid and progressive clogging of the holes with a 
consequent reduction of the efficiency of the filtering and the need for 
frequent and costly cleaning, with significant increase in cost. 
In the Italian Patent No. 1,126,918, commonly assigned, winding is 
prevented by providing appendices in the form of cylindric or conical 
collars corresponding to all or part of the holes of the filtering surface 
and the outside of the cylinder. Although satisfactory, the solution 
envisioned by this patent shows significant inconveniences. 
For example, considerable manufacturing costs are incurred, especially due 
to the fact that the collars are conical. Also, an appropriate projecting 
of the machines is needed on account of the machine weight, which in turn 
adds additional weight and therefore requires a greater power source. In 
spite of the cone shape of the collars, there is a tendency for a moderate 
quantity of material to re-enter the inside of the filtering cylinder in 
the phase of passing through some of the holes and the collars. In 
addition, the determination of the dimensions of the holes requires 
proceeding through successive approximations case-by-case, thereby 
frustrating any attempts to improve the filtering process. This is 
particularly true regarding filtering plants for solid urban waste. 
Finally, the perforated surface must be periodically changed after 
abrasion caused by the material, thereby increasing plant operational 
costs. 
Accordingly, it is an object of the present invention to eliminate the 
phenomena of winding of scraps and/or strings around two contiguous holes 
of a filtering cylinder via a simple means which does not require special 
operations to clean the filter itself. 
Other objects and advantages will become apparent from these drawings and 
specification which follow. 
SUMMARY OF THE INVENTION 
According to the present invention, partitions or channels are placed on 
the outside of the filtering cylinder perpendicular to the outside surface 
of the mantle itself and arranged between rows of holes. Preferably, the 
channels have a height proportionate to the dimensions of the holes. These 
heights extend perpendicularly to the external surface of the cylinder or 
transversely inclined with respect to the radial direction of the 
cylinder, this inclination being in the direction opposite to that of the 
rotation of the filtering cylinder. Transverse channels or plates may also 
be provided in addition to the longitudinal plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A filter according to the present invention comprises a rotating filter 
cylinder or drum 2 equipped on its mantle with longitudinal rows of holes 
6. The material to be filtered enters the interior of cylinder 2 via a 
feed hopper 1. When the cylinder 2 is rotated about its longitudinal axis, 
any material contained therein which is smaller than the dimensions of the 
hole 6 exits the cylinder 2 and is collected in the discharge hopper 3. 
Residual material which is larger than the hole dimensions passes out of 
the free end 4 of the cylinder 2. 
The cylinder 2 is provided on the outside with longitudinally extending 
plates 5 set between one row of holes 6 and an adjacent row. Plates 5 
create an aureole around cylinder 2, as shown in FIG. 2. If desired, 
additional plates 7 may be provided in the transverse direction. Plates 5 
and/or 7 may be continuous or discontinuous. 
These plates 5 extend from the outside of cylinder 2 with a radial 
orientation and can be slightly inclined in the direction opposite to that 
of the rotation of cylinder 2, as shown in FIG. 3. Also, they have a 
height which is determined as a function of the radial dimensions of the 
holes, wherein this height is proportionately increased when the radial 
dimensions of the holes are larger. 
With the use of plates 5, there is a self-cleaning action of the holes 6. 
In conventional filters, all the scraps or fibrous bodies which penetrate 
into two or more holes 6 and extend across them would tend at every 
rotation to become wound going in and out of the holes. During rotation, 
the plates 5 and 7 of the present invention prevent these bodies from 
entering into a hole other than the one or the ones from which they 
exited, thereby forcing them back into the cylinder 2. 
As previously discussed, the movement of the scraps and fibrous bodies is 
guided by an aerodynamic force acting centrifugally to the rotating 
cylinder 2. Thus, the prevention of deviation of the trajectory in this 
direction suffices to obtain the desired self-cleaning action. 
Accordingly, the present invention simply and economically reduces plant 
operation costs. 
Although the present invention has been described in reference to preferred 
embodiments, various modifications and improvements will become apparent 
to one skilled in the art without departing from the spirit and scope of 
the invention as defined in the following claims.