The present invention relates to a fluidification device for granular material, particularly useful for fluidifying granular plastics contained in a loading hopper.
In the field of processing plastics materials, the raw material is a loose material, i.e. in granules, and is stored in storage containers of large size for being delivered by a supplier. The granular material is then transferred into containers of medium and small size, e.g. a loading hopper, for continuously feeding molding or processing machines arranged in a working plant to process or transform plastics granular material through various transformation stages.
In the various working stages, as a matter of fact, various needs are to be met, e.g. dehumidification of the granules, such as for a number of hours, while the same are at rest, mixing of the granules with additives and/or dyes, as well as transfer of the granules to the load mouth of a processing machine. In all these stages, a medium-small container (hopper or conveyor) has to be used for containing the granular material waiting to undergo transformation processing. In some working methods, such medium-small containers must be more than one in number, as is required in the dehumidification step, for which both a hopper, in which hot and dry air is caused to flow, and a feeder (conveyor) designed to keep the hopper always full, are to be provided.
More particularly, loading hoppers have in common the fact that, in order to facilitate withdrawal of granular material contained therein, at lower portion thereof a tapering is provided, that reduces its size from a larger cross-section to the size of a lower discharge mouth. In other words, into the same hopper a conveying system with convergent sloping walls is provided which forces granular material to move towards the discharge mouth.
Some loose materials, in those cases in which their granules have uniform size and low cohesion and/or friction among them, can advance with no problems from the top of the hopper to the discharge or drawing mouth thereof.
However, the granules of the loose material may have an irregular shape, e.g. a flat shape, high friction and/or large volume/surface ratio, i.e. configuration features that contribute to make flowing within a loading hopper difficult and sometimes impossible.
In the specific case of granules of plastic materials having an high volume/surface ratio, e.g. granules with an extended or laminar shape, the material as a whole flows with much more difficulty, even because the various granules are by far more subject to electrostatically adhere one to another than the granules with a lower volume/surface ratio, e.g. granules having spherical, cylindrical, cubic or slightly parallelepipedic shape.
Moreover, in case of high friction between stored granular material and the walls of the loading hopper, a substantial wall effect is generated with consequent increase in falling rate differancies between the granules close to the hopper walls, especially when the walls are convergent, and the granules relatively far away from the walls.
In the following description the materials having the above-mentioned problems will be indicated as poorly flowing materials.
To facilitate falling or downward movement of poorly flowing materials contained in loading hoppers so-called “bridge breaker” systems have been suggested in the state of the art. The most common “bridge breaker” systems comprise electrical or pneumatic vibrators installed in the storage hopper, which are usually energized every time a withdrawal of granular material occurs.
Moreover, conventional “bridge breaker” systems have a number of undesired drawbacks in that they cause irregular delivery of granular material from the discharge mouth of the loading hopper, i.e. at a flow rate highly variable in time. Furthermore, vibrations generated by the “bridge breaker” system are transmitted not only to the loading hopper, but also to the rest of the working plant, and thus, if for example the plant comprises a weighing system, measured altered, and thus not reliable values are obtained.
It has already been proposed to solve the above-mentioned wall effect problem by energizing one or more continuous blades or jets of compressed air, to assist in the fluidification of the granular material owing to the feeding in of compressed air that acts as a fluidification agent. Air supply is activated in the very moment in which granular material delivery begins and goes on until delivery is stopped.
Materials also exist, however, that are insensitive to conventional “bridge breaker” systems and thus make it impossible delivery through the discharge mouth of the loading hopper. Such materials typically comprise coarse ground films or thin wall laminar pieces of plastic material. On the other hand, it is impossible to subject such materials to a grinding operation that could result in a finer granular size, as this would cause excessive degradation of the polymeric material.
Flowing problems in storage containers also arise in plants for processing granular materials of a nature different from plastics.
The main object of the present invention is to provide a new fluidification device for fluidifying poorly flowing granular materials, which is suitable for eliminating or drastically reducing the drawbacks referred to above with reference to the state of the art.
Another object of the present invention is to provide a fluidification device to be installed in a container or loading hopper for a granular material, which allows regular fall or descent of the granules in the hopper, thereby assuring a regular and continuous withdrawal of granular material from a lower discharge mouth without generating vibrations that would damage any handling or measuring systems associated with, or adjacent to, the loading hopper.
Not least object of the present invention is to provide a fluidification device which is highly reliable, easily installable in a loading hopper and can be obtained at competitive production and service costs.
These and other objects, which will better appear below, are obtained through a fluidification device for granular material having a loading hopper for said granular material provided with at least one lower discharge mouth and a opening-closing device for said at least one discharge mouth, and comprising jet means designed to direct at least one jet of a pressurized fluid into said loading hopper, and intermittent supplying means of pressurized fluid in fluid communication with said jet means to generate intermittent jets of pressurized fluid.
Advantageously, a fluidification device according to the present invention comprises an electronic control unit to control and synchronize said opening and closing device for the discharge mouth of the loading hopper and the intermittent supplying means of pressurized fluid.
Further features and advantages of the present invention will better appear from the following detailed description of some presently preferred embodiments of a fluidification device for granular material, given with reference to the accompanying drawings, in which:
Referring first to
Preferably, the actuator 16 can be controlled by an electronic control unit CU, typically a programmable electronic board.
More particularly, as illustrated in
To obviate this serious drawback, according to a first embodiment of the present invention illustrated in
The compressed air is delivered by any suitable compressed-air source (not shown in drawings), such as a compressor of any suitable type, through a suitable supplying duct 8, which can for example pass in a suitable way through the lower discharge mouth 4. Preferably, the nozzle 7 is seated into a suitable seat or through opening (hole) 9 formed in a side wall 14 of the loading hopper 1, preferably close to or at the discharge mouth 4.
The supplying duct 8 is interceptable by a valve means, preferably a two way-two position solenoid valve 11 controlled by a timer 12, controlled at its input by an opened-state detector for the gate valve 5, e.g. a limit switch 13 or any other suitable type of position sensor.
During the operation of the fluidification device illustrated in
Because of the delivery of granular material 3 through the lower discharge mouth 4, in the remaining granular material 3 in the upper portion of the hopper 1, mainly owing to the descent motion towards the discharge mouth 4, a series of bridges or resistant zones are generated at different levels, e.g. bridges 6a and 6e as shown in
Opening of the gate valve 5 is detected by the limit switch 13, which transmits an input signal to the timer 12 that in turn generates an output control signals to cause intermittent opening of the solenoid valve 11. Such an intermittent operation of the solenoid valve 11 generates intermittent feeding of compressed air to the nozzle 7 through the duct 8, which results in a sequence of jets g1-gn suitable for moving and shaking the granular material 3 in the inner zone above the discharge mouth 4 to be generated within a predetermined range. The sequence of jets g1-gn is suitable for breaking any so treated bridge or resistant zone of material 3, i.e. both the material subject to the breaking action of the jets g1-gn and that portion of material that above the bridge or resistant zone 6a when this is been destroyed, is thus free to fall towards the discharge mouth 4 and pass through it with no problems.
Obviously, the range of action of each jet in the sequence of jets g1-gn at the output of the nozzle 7 depends from the pressure of the compressed air fed to the nozzle, the characteristic features of the granular material 3, the load of granular material 3 present in the hopper 1, and other factors.
When a desired or programmed amount of granular material 3 is delivered from the lower discharge mouth 4 of the loading hopper 1, the gate valve 5 is closed by its actuator 16, and thus the limit switch 13 is opened, which also results in the cutting-off of the timer 12 and thus of compressed air feeding to nozzle 7.
It was found in practice that by suitably choosing the opening and closing times for the solenoid valve 11 controlled by timer 12 typically on the base of the parameters detected during experimental tests made with various types of material, including the “poorly flowing granular” material (in the sense specified above), storable in loading hoppers 1 depending upon the power of the jets g1-gn, it is possible to obtain an almost continuous and regular delivery of granular material 3 throughout the discharge mouth 4. A particularly preferred value of the opening and closing time of the solenoid valve 11 has been found to be about 0.3 seconds.
The nozzles 70a-70f are designed to generate intermittent jets against the granular material 30, which is stored in the loading hopper 10, whereby pressure waves are generated (as schematically indicated in
Six jets 70a-70f are illustrated in the drawings, each jet being designed to be energized onto a wall in an asymmetrical way with respect to another wall, and is alternated with respect to the other jets on the same wall.
Particularly, as shown in
The feeding ducts 80a and 80b are intercettable by a suitable valve means, preferably a five-way and two-position solenoid valve 110, which is controlled by a timer 120. The timer 120 is controlled at the input by an opened state detector of a gate valve 50 designed to open-close the discharge mouth 40 of the loading hopper 10, e.g. a limit switch 130 or other suitable position sensor.
When the fluidification device is in use, the opening of the gate valve 50 is detected by the limit switch 130, which sends a control signal to the timer 120, which, in turn, alternately switches the solenoid valve 110 between a first and a second operation state. More particularly, in its first operation state (
Alternating, asymmetrical and to a certain extent opposite jets qa, gc, ge, and gb, gf, which are suitably distributed, e.g. along the entire length of the inclined side walls 140a, 140b of the loading hopper 10, act at different levels within a determined range of action, and in a whole specified area about and above each nozzle, thus carrying out their shaking and/or pulsating action onto parts of granular material 30 which are adjacent to the inclined walls 140a and 140b. Owing to such a shaking action the single granules 110 are de-compacted, i.e. the various granules are released one from the other and thus they are fluidified, i.e. they freely fall towards the discharge mouth 40.
It was practically found that, for that most of the granular materials, an optimum opening time of the solenoid valve 110 by means of the timer 120 in order to generate jets ga-gf is, preferably, of the order of 0.3 second for each nozzle group. Such an optimum time permits compressed air jets having a very high flow rate, i.e. provided with an efficient jet energy, to be created by each group of nozzles.
Moreover, the solenoid valve 110 generates pulsations having a relatively low amplitude, whereby undesired vibrations on any sensors, for example weight detectors installed at the loading hopper 10 or in any structure mechanically connected thereto, are not transmitted.
If the jets ga-gf are uninterrupted, i.e. continuous, instead of intermittent and alternating, the granular mass state would soon become static, i.e. such that at the zones near the nozzles 70a-70f the granules would be hit in a reduced and almost ineffective way, since a regular flow towards the discharge mouth 40 would not be ensured.
The embodiment illustrated in
Advantageously, opening and closing times, respectively ta and tb, of the solenoid valves 110a and 110b by the respective timers 120a and 120b, can be the same or different. If the operation times ta and tb are different, a condition occurs in which, at some time, e.g. at time ta, the nozzles 700a-700f simultaneously work, whereas at other time, e.g. at time tb, they work in an alternating and asymmetrical way, as above explained.
The number of usable solenoid valves, jets and timers is not limitative and can changes depending on loading hopper size and features of the granular material to be fluidified. In practice, it has been demonstrated that one solenoid valve, which switches in order to alternatively feed two series of jets located on two different (inclined) walls of the hopper, is, in the most case, sufficient to achieve a regular descent also of “poorly flowing” granular materials along the loading hopper.
A preferred configuration of a loading hopper 1, designed to contain material which has to be dosed on a suitable weighing device (not shown), is illustrated in
In
In
The present invention, as described above is susceptible to numerous modifications and variations within the scope as defined by the accompanying claims.
Thus, for example, an electronic programmable control unit (CU), typically a programmable electronic board, can be provided in substitution or addition to the control timer/s of the solenoid valve/s designed to modulate the jets. Owing to the electronic programmable control unit, opening-closing times of the solenoid valve/s can be varied depending on the nature of the granular material stored in the loading hopper.
Moreover, instead of by opening the gate valve 50, the intermittent pressurized fluid feeding to the jets can be controlled by a remote control, such as an infrared ray, via radio, or similar remote control.
Number | Date | Country | Kind |
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VR2005A000050 | May 2005 | IT | national |