The present invention relates to a system and associated apparatus for the dosage and subsequent continuous mixing of a fluid (normally a polyol), with solid powders, better known as mineral fillers, and/or solid powders obtained by way of a mechanical recycling process, from discarded plastic materials, expanded and otherwise.

The technical peculiarity of the proposed system consists of the dosage of such solid powders by way of a gravimetric dosage unit and a dynamic mixer into which a liquid is loaded with the right weight proportions, thus optimally ensuring a precision and constancy of such mixture of liquid/ solid powders.

The use of solid powders, better known as mineral fillers, in various technological processes for the conversion of plastic materials is a technical solution that is now known in the state of the art. The aim of this use is to give the final manufactured article better physical/mechanical characteristics. Other solid powders, also known in the background art, are used in production processes to reduce the cost of the final manufactured article and at the same time to safeguard the environment; these are solid powders obtained by way of a process of mechanical recycling of discarded plastic materials.

In continuous or discontinuous process technologies of expanded polyurethane production systems, the use of solid powders, mineral fillers and/or finely-pulverized production discards is a very widespread technical solution and has been adopted for many years.

These solid powders are usually dosed and premixed in the polyol, or reactant liquid, by way of technical solutions that involve the use of a mixing tank, known in the jargon as a “batch system”, and/or with the use of a dynamic mixer directly in the production line, known in the jargon as an “in-line system”. The formed polyol and solid mixture, in both systems, is conveyed by suction to a dosage pump, the line of which feeds into the mixing head, where the other reactant liquid, called isocyanate, is present, for the formation of the polyurethane polymer. The mixing heads used can operate on the low-pressure or high-pressure principle.

Generally, for dosing solid powders “volumetric” or “gravimetric” systems are used. Such systems have a single or double screw, designed especially and with a consequent geometric shape, as a function of the type of powder to be dosed.

For a more accurate dosage, the choice falls on “gravimetric” dosage.

These conventional apparatuses, while useful and practical, have some drawbacks, which include the fact that, during drainage phases or production shutdowns, or in any case during transition phases, the pressures in the various parts of the apparatus drain toward the parts that are not (or are no longer) under pressure (for example from the mixing tank toward the hopper and/or toward the polyol tank) with obvious drawbacks.

Furthermore, in end-of-cycle phases, a certain amount of polymeric material is wasted, owing to the need to clear the conduits and also owing to the impossibility of keeping it - even when production is stopped - in conditions in which it can subsequently be used.

Other aspects that show room for improvement in these conventional apparatuses are the homogeneity of mixing, the speed of production, the precision with which the components are mixed, versatility, and reliability.

The aim of the present invention is to provide an apparatus for the production of polymeric products that is capable of solving the above- mentioned problems and overcoming the above-mentioned limitations of the background art.

Within this aim, an object of the present invention is to prevent disadvantageous backflow and abrupt changes in pressure in parts of the apparatus, in particular during transition phases.

Another object of the invention consists of providing an apparatus that reduces the waste of materials.

Another object of the invention consists of providing an apparatus that improves the speed of production and/or the precision with which the components are mixed, and/or versatility and/or reliability with respect to conventional apparatuses.

This aim and these and other objects which will become better apparent hereinafter are all achieved by an apparatus according to claim 1.

Further characteristics and advantages of the invention will become more apparent from the detailed description of a preferred, but not exclusive, embodiment of an apparatus for the production of polymeric products, illustrated by way of non-limiting example with the aid of the accompanying drawings wherein:

Figure 1 is a block diagram that shows the structure of a possible embodiment of the apparatus according to the present invention;

Figure 2 is a detailed diagram of a preferred embodiment of the apparatus, in which the conventional symbols of system layouts are used;

Figure 3 is a cross-sectional view of a possible embodiment of the mixing assembly;

Figure 4 shows a possible embodiment of the agitator device present in the preferred embodiment of the apparatus;

Figure 5 shows a possible embodiment of the dosage assembly.

With reference to the figures, the apparatus for the production of polymeric products according to the invention is generally designated with the reference numeral 1.

The apparatus 1 comprises a mixing assembly 40 configured to mix at least one fluid component (typically liquid polyol), which arrives from a tank of fluid 20, with at least one component in powder form (typically a mix of powders of variable composition according to the product to be obtained), which arrives from a powder feeding assembly 30, so as to form a mixed polymer in output from the mixing assembly 40. In more detail, the mixing assembly 40 comprises a mixing chamber 41 in which, during use, the above-mentioned components (fluid and in powder form) are introduced in order to be mixed.

The apparatus 1 also comprises at least one outflow duct 71a, 71b which is configured to convey the mixed polymer, which arrives from the mixing assembly 40, toward a dosage assembly 70.

The dosage assembly 70 is adapted to dispense the mixed polymer in a controlled manner toward one or more apparatuses for the production of polyurethane products, such as for example molds.

Preferably, the tank of fluid 20 is a tank under pressure, which is connected to the mixing chamber 41 by way of a fluid supply duct 29. Conveniently, in output from the tank of fluid 20, a fluid dosage pump 22 regulates the flow of the fluid component from the tank of fluid 20 to the mixing chamber 41 through the fluid supply duct 29.

Preferably, the fluid dosage pump 22 is a gear pump driven by a three-phase motor.

Even more preferably, downstream of the fluid dosage pump 22 there is a flow meter 23 functionally connected to an electronic control unit (PLC) that regulates the flow rate of the fluid dosage pump 22 as a function of the readings of the flow meter 23 and on the basis of a value that can be configured by an operator through an input interface.

In more detail, in the preferred embodiments, a self-regulating system for the fluid is provided by way of the flow meter 23 and a PID (Proportional Integral-Derivative) algorithm executed by the electronic control unit, so that the flow rate read by the flow meter 23 is sent in a signal to the electronic control unit, which, using the PID algorithm, produces a constant reference signal, sending it to an inverter associated with the three-phase motor of the fluid dosage pump 22.

In the preferred embodiments, the powder feeding assembly 30 comprises a hopper 31, positioned at a higher level than the mixing chamber 41, and a powder feeding duct 39 which connects the hopper 31 to the mixing chamber 41 and leads into this from above, so that the components in powder form which arrive from the hopper 31 enter the mixing chamber 41 by falling, passing through the powder feeding duct 39.

According to an optimal solution, the powder feeding assembly 30 also comprises a measurement device 33 for measuring the weight force generated by the at least one component in powder form added to the hopper

31 (for example one or more load cells) and a dosage device 32 for dosing the amount of powder introduced by the hopper 31 into the powder feeding duct 39 (which preferably comprises a screw feeder driven by a motor 34).

Advantageously, the measurement device 33 and the dosage device

32 are functionally connected to an electronic control unit which actuates the dosage device 32 as a function of the weight detected by the measurement device 33 in order to introduce an amount of powder that is determined on the basis of a value entered by a user by means of an interface (for example a conventional command panel).

The powder feeding assembly 30 as described herein is advantageous even if inserted into an apparatus that is conventional in other respects: therefore it is possible to provide an apparatus that does not form part of the present invention, that is missing the drainage and recirculation assembly 50 (which will be described below), and which comprises the powder feeding assembly 30.

In the preferred embodiments, the mixing assembly 40 comprises a dynamic mixer 400 which in turn comprises the mixing chamber 41 which extends (preferably along a longitudinal axis), defining a passage for the fluid and powder components, from two inlets (an inlet for the fluid component 48 and an inlet for the components in powder form 47) to an outlet 49, so that in the mixing chamber 41, the components are mixed while they are being conveyed from the inlets 48, 47 to the outlet 49 (it is in this sense that the mixer is defined as “dynamic” here: the mixing occurs continuously during the passage into the mixing chamber 41).

The outlet 49 has its axis preferably parallel to the longitudinal axis of the mixing chamber 41, being positioned at the distal end thereof.

At least one mixing and conveyance element 42, adapted to cause the movement and the mixing of the solid and liquid components, acts in the mixing chamber 41 and comprises preferably a screw feeder (or portion of screw feeder 42a) or the like.

In the preferred and illustrated embodiment, the mixing chamber 41 extends along a longitudinal axis and comprises a proximal chamber sector 41a and a distal chamber sector 41b.

In this embodiment, the details of which can be seen in Figure 3, inside the mixing chamber 41 a mixing and conveyance element 42 is provided which rotates about the longitudinal axis of the chamber.

Such mixing and conveyance element 42 comprises a proximal screw feeder portion 42a which is positioned in the proximal chamber sector 41a and a distal portion 42b which is positioned in the distal chamber sector 41b. The above-mentioned distal portion 42b is provided with pins 43 which protrude radially (outward) and are interleaved (at least during the rotation) with complementary contrast pins 44 with which the distal sector 41b of the chamber 41 is provided and which protrude (inward) from a perimeter wall of the mixing chamber 41 toward the longitudinal axis. In other words, the pins 43 during the rotation pass through spaces that separate the contrast pins 44 from each other.

In practice, the mixing and conveyance element 42 is composed of a trapezoidal screw, which forms the screw feeder portion 42a, in the proximal portion 41a, to which the shaft from which the pins 43 protrude is coupled coaxially in rotation. The mixing and conveyance element 42 can also be composed of a single shaft from which the trapezoidal screw protrudes in the proximal portion, and from which the pins 43 protrude in the distal portion. Both the inlet for the fluid component 48 and the inlet for the component in powder form 47 lead into the proximal sector 41a of the mixing chamber. The inlet for the fluid component 48 preferably has a horizontal axis, transverse with respect to the longitudinal axis of the mixing chamber 41, while the inlet for the component in powder form 47 preferably has a vertical axis, perpendicular with respect to the longitudinal axis of the mixing chamber 41.

Advantageously, the mixing chamber 41 is not under pressure and therefore the mixing assembly 40 is configured so that, during operation, there is a pressure in the mixing chamber 41 that is substantially equal to atmospheric pressure. Among other things, this prevents the backflow of material toward the powder feeding assembly 30 and/or toward the tank of fluid 20 when the processing cycle is interrupted and also during transition phases.

Optionally, the presence of a casing welded externally on the mixing chamber 41 and a temperature probe make it possible to control the temperature of the material during the mixing phase.

The mixing element 42 is obviously driven rotationally by a motor 46. It is possible to vary the number of revolutions of the mixing element 42 via the installation of an inverter associated with the motor 46, which is therefore preferably an electric motor.

The mixing assembly 40 as described herein, and in particular the dynamic mixer 400, is advantageous even if inserted into an apparatus that is conventional in other respects: therefore it is possible to provide an apparatus that does not form part of the present invention, that is missing the drainage and recirculation assembly 50 (which will be described below), and which comprises the mixing assembly 40 as described herein, and in particular the dynamic mixer 400.

According to the invention, the apparatus 1 comprises a drainage and recirculation assembly 50, interposed between the mixing assembly 40 and the at least one outflow duct 71a, 71b.

Such drainage and recirculation assembly 50 is connected via fluid dynamics to the mixing chamber 41, to both an entrance and an exit thereof, and is selectively configurable at least in an active dispensing condition and in a recirculation condition.

In the active dispensing condition, the drainage and recirculation assembly 50 conveys the mixed polymer, in output from the mixing assembly 40, toward the outflow duct 71a, 71b; this condition is therefore the normal condition which allows operation at speed during the production cycle.

In the recirculation condition, the drainage and recirculation assembly

50 redirects the mixed polymer, which arrives from the mixing chamber 41, to the mixing chamber 41; this condition therefore makes it possible to ensure the continuity of operation of the dynamic mixer 400 even when the flow downstream is interrupted, for example during clearing or cleaning, or shutdown of the parts of the apparatus 1 downstream of the mixing assembly, or when the accumulation tank 60 (which will be described below), if present, is full.

The drainage and recirculation assembly 50 comprises a drainage tank

51 which is configured so that, in the active dispensing condition, it is passed through by the mixed polymer that arrives from the mixing assembly 40 and is directed to the outflow duct 71a, 71b. To this end the drainage tank 51 is connected to the outlet 49 of the mixing chamber 41 by way of an arrival duct 59 and is connected to the outflow duct 71a by way of a delivery duct 58.

The drainage tank 51 preferably is vase-shaped, having a lower part with a downwardly-decreasing cross-section.

Furthermore, the drainage tank 51 is adapted to accommodate the mixed polymer returning from the at least one outflow duct 71a, 71b when the active dispensing condition is interrupted, so as to clear at least partly the outflow duct 71a.

In more detail, preferably, the drainage and recirculation assembly 50 can also be configured in a drainage condition, in which the mixed polymer that returns from the outflow duct 71a is directed to the drainage tank 51 by way of a drainage duct 55 so as to allow the venting of pressure of the at least one outflow duct 71a. Such drainage duct 55, preferably, branches off from the delivery duct 58 (downstream of the pump 54 that pumps in output from the drainage tank 51 and which will be described below), connecting the delivery duct 58 to an entrance to the drainage tank 51.

A return duct 56 connects the delivery duct 58 to the mixing chamber 41, leading into the proximal chamber sector 41a in order to allow the return of the mixed polymer fluid from the drainage tank 51 to the mixing chamber 41 in the recirculation condition.

In the embodiment illustrated, the return duct 56 branches off from the delivery duct 58 downstream of the drainage duct 55.

The transition from the active dispensing condition to the recirculation condition, and optionally to the drainage condition, is determined by means of a system of valves 18 conveniently arranged downstream of the drainage tank 51, along the delivery duct 58 and/or the outflow duct 71a and/or the return duct 55 and 56.

According to an optional and particularly advantageous characteristic, the drainage and recirculation assembly 50 comprises a pressure maintenance device 15, which is positioned between the mixing chamber 41 and the drainage tank 51 along the arrival duct 59. Such pressure maintenance device 15 is configured to maintain, within the polymer being mixed inside the mixing chamber 41, a minimum pressure which is higher than a threshold value, both in the active dispensing condition and in the recirculation condition.

In more detail, in the preferred embodiment, the pressure maintenance device 15 comprises a membrane valve 52 which is actuated by a pressure switch 53: the pressure switch 53 reads the pressure upstream of the membrane valve 52 and actuates the latter in retraction so as to keep that pressure constant or in any case within a predefined range.

In practice, the function of the pressure maintenance device 15 is to ensure a minimum counter-pressure against the mixing assembly 40 upstream, so as to obtain an optimal filling of the mixing chamber 41 (in particular of the distal portion 41a) and as a consequence improve the homogeneity of the fluid/powder mixture.

Conveniently, the level of the mixed polymer inside the drainage tank 51 is controlled through three vibrating levels (start loading, stop loading, precautionary control super max).

Preferably, the drainage and recirculation assembly 50 comprises, downstream of the drainage tank 51, a pump 54 (preferably a membrane pump) which is configured to pump the mixed polymer in output from the drainage tank 51, along the delivery duct 58, so as to direct it toward the at least one outflow duct 71a, 71b (in the active dispensing condition) or toward the return duct 56 to the mixing chamber 41 (in the recirculation condition).

In some embodiments, including the one illustrated, the apparatus 1 comprises an accumulation tank 60 for accumulating the mixed polymer, which is interposed between the drainage and recirculation assembly 50 and the dosage assembly 70.

In these embodiments, the at least one outflow duct 71a, 71b comprises at least one a first outflow duct 71a, which connects the drainage and recirculation assembly 50 to the accumulation tank 60, and a second outflow duct 71b, which connects the accumulation tank 60 to the dosage assembly the first outflow duct 71a conveys the mixed polymer into the accumulation tank and the second outflow duct 71b conveys the mixed polymer from the accumulation tank 60 to the dosage assembly 70.

According to a particularly advantageous characteristic, the accumulation tank 60 comprises an agitator device 61 (which preferably comprises a rotating element) configured to agitate the mixed polymer inside the accumulation tank 60 so as to keep it in a usable condition.

In some particularly advantageous embodiments, the agitator device 61 comprises at least one first blade 63 configured to generate, in the fluid mixed polymer, an axial motion and at least one second blade 62 configured to generate, in the fluid mixed polymer, a radial motion. Optionally a lower disc is provided.

In the particular embodiment shown in Figure 4, there are two horizontally extending first blades 63 connected to two vertically extending second blades 62. There can be a larger number of blades 62, 63.

Conveniently, the agitator device 61 is actuated rotationally by an electric motor 64 provided with inverter which makes it possible to adjust the rotation speed.

Optionally, the accumulation tank 60 is provided with a thermostat control system which is configured to maintain the temperature of the mixed polymer inside the accumulation tank 60 within a predetermined interval of temperatures and comprises heating means and cooling means (for example electric resistance heaters) and cooling means (for example cooling ducts passed through by a cooling fluid, preferably water).

For an optimal operation, the accumulation tank 60 is pressurized, preferably provided with a casing, made in conformance with Directive 2014/68/EU (PED, Pressure Equipment Directive), provided with a safety valve and with devices for controlling the level (preferably load cells).

The accumulation tank 60 as described herein is advantageous even if inserted into an apparatus that is conventional in other respects: therefore it is possible to provide an apparatus that does not form part of the present invention, that is missing the drainage and recirculation assembly 50, and which comprises the accumulation tank 60.

The dosage assembly 70 comprises one or more casting heads 7A, 7B, 7C which are adapted to dispense the mixed polymer into a product forming apparatus (for example a mold).

In the non-limiting example shown, there are three casting heads 7 A, 7B, 7C, but there can be any number thereof according to requirements.

Advantageously, for each casting head 7A, 7B, 7C there is a respective dosage pump 72 which is configured to pump the mixed polymer to a casting head; all of this is done with a brushless motor 74 coupled to the corresponding pump 72.

The brushless motor 74 has the advantageous peculiarity of being able to operate at a constant torque at any number of revolutions; this makes it possible to handle a vast range of flow rates while not requiring any speed change drive units/gear motors and the technical constraints associated with them.

The coupling between the pump 72 and the brushless motor 74 can be with an elastic or magnetic connection 75. The advantage of the latter is that the entrainment of the pump occurs by a magnetic field, without the need for guide bearings/seals on the shaft of the pump body, which over time (especially for uninterrupted prolonged use) can be the focus of criticalities and breakages that require maintenance and consequent shutdown of the apparatus.

Preferably, the dosage assembly 70 comprises, for each casting head 7A, 7B, 7C, a respective flow-rate measurement unit 73 (a flow meter), which is functionally connected to the respective brushless motor 74, the brushless motor being configured to adjust the flow rate of the adjustment pump 72 as a function of the flow rate detected by the flow-rate measurement device 73.

The correct dosage flow rate can be obtained using a PID which retroactively connects the flow rate values read by the flow-rate measurement device (flow meter) 73 located after the dosing and the brushless motor. The dosage assembly 70 as described herein is advantageous even if inserted into an apparatus that is conventional in other respects: therefore it is possible to provide an apparatus that does not form part of the present invention, that is missing the drainage and recirculation assembly 50, and which comprises the dosage assembly 70 having the characteristics described herein.

Further implementation details of the preferred embodiment can be clearly deduced from the system diagram of Figure 2, in which the conventional symbols known in the technical sector are used, and which therefore will not be discussed further.

The operation of the apparatus 1 is clear and evident from the foregoing description.

In practice, in the operation of the preferred and illustrated embodiment, by virtue in particular of the presence of the drainage and recirculation assembly, by passing from the active dispensing condition to the drainage condition and then to the recirculation condition, by means of the valves 18, it is possible to carry out three cycles, i.e.:

- loading the accumulation tank 60;

- venting the pressure in the outflow duct 71a that feeds the accumulation tank 60 (the pressure will be vented into the drainage tank 51 once the loading cycle described above is finished);

- returning to the mixing chamber 41 of the dynamic mixer 400.

In practice it has been found that the apparatus for the production of polymeric products according to the present invention fully achieves the set aim and objects, in that it makes it possible to prevent disadvantageous backflow of material in parts of the apparatus and abrupt changes in pressure, in particular during transition phases.

Another advantage of the apparatus according to the invention consists in that it reduces the waste of material.

Another advantage of the apparatus, according to the invention, consists in that it improves the speed of production, as well as the precision with which the components are mixed, and also the versatility and reliability, with respect to conventional apparatuses.

The apparatus for the production of polymeric products thus conceived is susceptible of numerous modifications and variations all of which are within the scope of the appended claims.

Moreover, all the details may be substituted by other, technically equivalent elements.

The disclosures in Italian Patent Application No. 102022000017169 from which this application claims priority are incorporated herein by reference.

Where the technical features mentioned in any claim are followed by reference numerals and/or signs, those reference numerals and/or signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference numerals and/or signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference numerals and/or signs.