Patent Application
20090039106
The present invention regards a device and a process for processing mixtures of a number of granular materials, in particular granules of plastics material.
Before being subjected to a process of transformation or reuse, the plastics materials, upon reduction or grinding into granules or flakes of desired granulometry or size, are added with other granular or powder materials, typically granular (ground) or powder plastics materials and, if needed, small or very small quantities of one or more additives, typically colorant powder, a lubricant agent and the like, as is well known to a man skilled in the art of plastics material transformation. The metering devices or dosing apparatuses of granular materials, both of volumetric and gravimetric type, which are currently available on the market result unsatisfactory above all from the standpoint of metering precision.
The volumetric dosing apparatuses in general consist of a containment container of granular material to be metered and a motorized screw feeder set to dispense or extract granular material from the container. The amount dispensed in the unit of time or batch of granular material extracted by the screw depends on the rotation time, the rotation speed and on the size of the screw. The batches coming from different granular material containers fall into a mixer-homogenizer device or mixer. The usable mixers can be of various types: horizontal, vertical, fountain and overflow, all intended to closely mix together the different quantities of granular plastics materials and possible additives so to obtain the most uniform mixture possible.
The gravimetric dosing apparatuses have two or more flanking storage hoppers, which are set to feed granular material by gravity to an underlying weighing hopper, which is in turn intended to discharge the material fed therein into an underlying mixing/homogenization hopper. Typically, the feeding, weighing and mixing/homogenization operations are controlled by a program electronic control unit.
The dosing apparatuses proposed up to now, nevertheless, while satisfactory from many standpoints, have drawbacks which are due in particular to the use of a mixer or stirrer. There exist, in fact, granular material transformation processes in which the hourly quantity of granular plastics material mixture to be transformed is relatively low, less than 20 kg/hour and for which the percentage amounts of additive can be very small, on the order of 0.2-0.3%.
The dosing machines currently available on the market are in general made for very high productions, typically greater than 50 kg/hour of mixture to be fed to a transformation machine of the granular plastics material, e.g. an injection press, arranged downstream of the dosing apparatus. Moreover, the amount of material contained in the mixer is usually closely tied to the productive capacity of the dosing apparatus. It follows that, when the transformation machine requires low hourly quantities of plastics material mixture, the mixture quantity waiting to be consumed by the machine remains in the mixer for a relatively long time period, sometimes equal to or greater than 30 minutes. During this waiting period, due to the different nature and different granulometries of the mixed granular materials and hence different specific weight of the same, the mixture undergoes demixing. In other words, the materials with greater specific weight are separated from the other components of the mixture, with consequent creation of non-uniformity in the mixture and worsening of the chemical-physical characteristics of the final product molded by the transformation machine. The vibrations transmitted by the transformation machine also significantly favor the spontaneous demixing of the granular materials present in the mixture.
The main object of the present invention is to provide a new process for the metering of granular material to apply to those dosing devices of said granular material which can be utilized without the use of a mixer.
Another object of the present invention is to provide a metering process of said granular material capable of making a uniform mixture and a higher precision metering with respect to the current state of the art.
A further object of the present invention is to provide a granular material metering process applicable to respective metering devices in a flexible manner and at competitive production costs.
Another object of the present invention is to provide a multiple metering device of granular material capable of carrying out metering for very low percentages, less than 0.2% for each metered granular material.
These and other objects which will be better appear below are attained with a metering process of a number of granular materials comprising the steps of:
According to another aspect of the present invention, a multiple metering device of granular material is provided to implement the abovementioned process, comprising a plurality of loading hoppers of a respective granular material to be metered equipped with a respective extractor device and a program electronic control unit intended to control said extractor devices, and characterized in that it comprises at least one conveyance zone, set to receive metered amounts of different granular materials from said extractor devices, at least one holding container set downstream of said conveyance zone and intended to receive metered amounts of granular material from said conveyance zone and to dispense it to a user unit, and sensor means set to control the attainment of a pre-established level in said at least one holding container in order to send a control signal to said program electronic control unit upon attainment of said pre-established level.
Further aspects and advantages of the present invention will be clearer from the following detailed description of a currently preferred embodiment thereof, illustrated as merely exemplifying and non-limiting examples in the accompanying drawings, in which
a, 4b and 4c illustrate the opening-closing functions with respect to time of three dispenser devices of the same number of hoppers containing different granular materials for the obtainment of a mixture with different percentages of the respective granular materials.
With reference to the above-listed Figures, it will be noted how a process for the preparation of mixtures of granular material according to the present invention can be made by means of a multiple metering device DM, which is formed by a plurality of upper hoppers, removably installable in the same number of housing seats delimited by a fixed support frame TL. In the drawing, three hoppers T1, T2 and T4, are illustrated, the hopper T3 having been omitted to better illustrate the internal part of the multiple metering device DM, it being understood that the multiple metering device can comprise a number of hoppers which is greater or less than four.
The hoppers T1-T4 can have the same size or different sizes from each other according to requirements and are intended to contain a respective granular material to be transformed, typically a virgin granular plastics material or a ground scrap or sprue material in the form of rough pieces or a colorant and/or another granular additive to be added in a metered manner to another or other granular materials.
Every hopper T1-T4 is equipped with a lower discharge mouth interceptable by a respective extractor-dosing device DE1-DE4 of any suitable type, preferably an extractor-dosing apparatus formed by an oscillator rotor of the type described in the patent U.S. Pat. No. 6,981,619 B2 in the name of the same applicant of the present application. One such extractor-dosing device DE1-DE4 is therefore preferably constituted by an oscillating rotor controllable by a linear actuator AL of any suitable type, to dispense metered amounts of material contained in the respective overlying hopper.
Optionally, the extractor device DE1-DE4 according to one particular advantageously variant thereof can be composed of a “eyelid” mechanism, as described in the U.S. Pat. No. 7,137,729 B2 in the name of the same applicant of the present invention, which by repeatedly and rapidly opening and closing dispenses by gravity, in a pre-established fraction (thousandth) of a second, a predetermined amount of granular material with a very high precision.
Below the discharge mouth of each hopper T1-T4, a conveyance zone ZC is provided with sloped walls converging towards an underlying holding container CP of any suitable type to convey the granular material extracted by the hoppers T1-T4 therein by gravity. The holding container CP is preferably composed of a duct delimited between two terminal flanges: upper FA and lower FB, respectively, fixed in use to a lower flange Fl of the conveyance zone ZC and to an attachment flange FMT of a transformer machine or press of plastic granular material (not shown in the drawings).
Level sensor means MS are advantageously provided for, at the holding container CP, e.g. constituted by a radar probe or by a pair of photocells, which are preferably adjustably locatable at different levels along the holding container CP and are set to detect the attainment of a predetermined mixture level of granular materials conveyed in the holding container CP. Once the mixture of granular materials has reached the pre-established level, the level sensor means MS will send an input signal to a program electronic control unit CPU, which will send a control signal to the extractor devices DE1-DE4, thereby interrupting the dispensing of further granular material. The dispensing will automatically restart as soon as the mixture level of granular material in the holding container CP descends below the pre-established threshold level.
In
At the beginning, in the preliminary calibration or set-up step, the operator manually prearranges a tray container VS (
The quantity of granular material extracted from the containment hopper T1 and transferred into the container VS is weighed (block 120) on weighing means, such as a high-precision electronic weighing balance of any suitable type, placed outside the multiple metering device DM. The weight value is then stored (block 130) in the program control unit CPU. The operation is repeated (block 140) for the remaining hoppers T2-T4 containing the other materials to be metered.
Once the calibration step has terminated, the operator stores, in the program control unit CPU, the data (block 150—
Once the percentage is known of each granular material which must be present in the desired mixture, the program control unit CPU calculates (block 160) the cyclic period of every opening-closing operation of each extractor device DE1-DE4 of the hoppers T1-T4, maintaining the opening time interval constant, in a manner such that the opening-closing period of every extractor device DE1-DE4 is directly proportional to the respective percentage of each granular material to be metered for obtainment of the desired mixture. An actual example of calculation of the cyclic opening-closing operation associated with each extractor device will be reported in more detail below.
The subsequent step consists of sending a signal processed by the program electronic control unit CPU to all or some of the extractor devices DE1-DE4, which will be energized (blocks 170DE1, 170DE2, . . . , 170DEn) to be opened and closed with a respective period X, Y, . . . , Z correlated with the specific percentage of the granular material extracted by each of these and which must be present in the desired mixture. The material extracted by all or part of the hoppers T1, T2, . . . , Tn is collected in the conveyance zone ZC and discharged into the holding container CP (block 200), where the level sensors MS are in operation. If the height of the mixture level exceeds a pre-established value VP (block 210), the program control unit PCU will store the state of each extractor device (block 220) so to immediately stop (block 230) all extractor devices DE1, DE2, . . . , DEn.
As soon as the granular material mixture level contained in the holding container CP descends below the pre-established level VP, each extractor device will be activated (blocks 240DE1, 240DE2, . . . , 240DEn), starting again from the previously stored state, so to continue the opening-closing sequence with the same period, X, Y, . . . , Z, respectively, of the previously interrupted step (blocks 170DE1, 170DE2, . . . , 170DEn). The end of the process can be manually controlled by the operator, who can turn off the multiple metering device DM (blocks 270 and 280), e.g. by pressing a suitable stop button (not shown in the drawings).
In the diagrams illustrated in
Two dashed lines parallel to the y axes indicate an interruption in the operation of the extractor devices DE1-DE3 following the attainment of the predetermined threshold level of mixture collected in the holding container CP. It will be noted how the functions F1-F3 associated with the extractor devices DE1-DE3, after every operation interruption, start again from the state which immediately preceded the interruption, so to continue the programmed opening and closing sequence with the same period. In other words, upon interruption of each extractor device DE1-DE3, i.e. at the attainment of the pre-established level in the holding container CP, the program electronic control unit CPU stores the state and the precise instant corresponding with the stored opening-closing cycle state previously carried out by each dispenser device DE1-DE3. With the lowering of the mixture level in the holding container (CP), each dispenser device DE1-DE3 is reactivated by the program electronic control unit (CPU) so to restart to carry out the same number of opening-closing cycles already previously executed in the pre-established time interval or period P, thus maintaining continuity in the metering and mixing process.
In the example illustrated in
With the process according to the present invention, it is possible to obtain a precise metering and a mixing of static type of various granular materials, without the use of a special mechanical mixing device for the granular materials themselves, thus drastically reducing the demixing problems during the dwell time of the mixture in the holding container CP, problems which instead occur when the mixture is stirred with a mixing device.
To confer further flexibility to the system, as well as for the obtainment of a more energetic mixing of the various granular materials which form the final mixture, a phase displacement Δt can be provided for between the functions F1, F2, . . . , Fn associated with the various extractor devices DE1, DE2, . . . , DEn, as will be easy to understand by a man skilled in the art.
Moreover, if one uses extractor devices DE1, DE2, . . . , DEn having a constant opening time, the program control unit CPU, when the interruption due to having attained the filling level in the holding container CP coincides with the opening instant of one or more of the extractor devices DE1, DE2, . . . , DEn, will delay the interruption of the extractor devices themselves by a time interval such that those extractor devices which are found in the opening step complete the dispensing of the material. Consequently, the interruption will occur when all extractor devices DE1, DE2, . . . , DEn are found in the closed step.
The present invention, as described above, is susceptible to numerous modifications and variants within the protective scope as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07113956.2 | Aug 2007 | EP | regional |
