FILAMENT PRODUCTION DEVICE AND METHOD

Abstract

A device that recycles thermoplastics for producing a filament for fused deposition modelling devices (FDM) and respective operating method is provided. The crushed thermoplastic is introduced into the hopper, pushed by a screw, driven by the motor, inside the barrel, whose axial force is sustained by the axial bearing. The thermoplastic is melted with the assistance of electrical heating resistors and passes through a degassing zone connected to the vacuum pump. The thermoplastic is forced through the die, being cooled on a cooling tray having a water circulation system. The diameter of the filament is controlled by the puller based on the data obtained in the measurement system of the filament diameter. A microcontroller controls the entire process.

Claims

1. A device for producing a filament, comprising: a screw, driven by an motor, said screw having at least, two phases, comprising in a first phase a feeding zone where the thermoplastic material enters, a compression zone and a metering zone; and in a second phase a decompression zone, a degassing zone, a compression zone and a metering zone; the zones having different channel depths, the feeding and degassing zones having the deepest channel, the metering zones having a shallower channel and the remaining zones gradually vary the depth of the channel to join the bordering zones; said screw inserted in a barrel along its length; a die, situated at the end of the screw opposite to the feeding zone; at least one electrical heating resistor installed on each of the said phases of the screw; a degassing system comprising a vacuum pump connected to the barrel by means of a vacuum plug, in the degassing zone of the screw, causing a decrease in pressure; a cooling unit; a filament diameter control unit, comprising a diameter measuring mechanism, a puller and respective motor; a microcontroller arranged to control: i. the operating cycle of the electrical heating resistors, by processing the data sent by at least one temperature sensor installed next to each of the electrical heating resistors; ii. the motor for driving the screw; and iii. control the speed of the motor for operating the puller of the diameter control unit, by processing the data sent by the diameter measuring mechanism.

2. The device according to claim 1, wherein the cooling unit comprises a cooling tray and a water circulation system.

3. The device according to claim 1, wherein the diameter measuring mechanism is a digital calliper.

4. The device according to claim 1, wherein the diameter measuring mechanism is of a laser type.

5. The device according to claim 1, wherein the diameter control unit additionally comprises at least two traction rollers disposed vertically, which are pressed against each other by an elastic placed on plastic bearings of the upper roller, and the movement of the traction rollers is controlled by the motor which acts on the lower roller.

6. The device according to claim 1, wherein the microcontroller controls the operating cycle of the electrical heating resistors by the control algorithm in a Proportional-Integral-Derivative closed loop.

7. The device according to claim 1, wherein the microcontroller controls the motor operation by pulse-width modulation.

8. The device according to claim 1, wherein the barrel is finned at the feeding zone of the screw.

9. A method of operating the device for producing a filament of claim 1, further comprising the following steps: a) receiving and processing the temperature data from the temperature sensors installed next to each of the electrical heating resistors, actuating until it reaches the steady state in the temperature of said zones; b) driving the motor of the screw which promotes the rotation of the screw compressing and pushing the flakes of thermoplastic material at the feeding zone of the screw along the barrel heated by the electrical heating resistors, resulting in the fusion of the thermoplastic; c) melted thermoplastic material arriving at the degassing zone, where the decrease in pressure caused by the arrangement of the screw and by the connection to the vacuum plug between the barrel and the vacuum pump causes the thermoplastic to bubble and consequently release volatile gases; d) compressing the thermoplastic against the die traversing the orifice thereof; e) in filament form but still in fused state, the thermoplastic traversing the cooling unit making it return to solid state; f) pulling of the filament in solid state by the traction rollers of the puller of the diameter control unit; g) calibrating of the filament diameter, by the diameter measuring mechanism, which sends this data to the microcontroller; h) processing the data sent by the diameter control unit and varies the motor speed of the puller to calibrate the filament diameter, increasing the motor speed of the puller to decrease the diameter of the filament, or lowering the motor speed of the puller to increase the diameter.

10. Method according to claim 9, wherein in the cooling unit, the thermoplastic passes through a cooling tray and through a water circulation system.

Description

DESCRIPTION OF THE DRAWINGS

[0049] For improved comprehension of the present application, the accompanying drawings represent preferred embodiments, but are not intended to limit the art disclosed herein.

[0050] FIG. 1: Schematic representation of a perspective view of the device developed, wherein (1) represents the motor that drives the screw; (2) represents the axial bearing; (3) represents the vacuum pump; (4) represents the hopper; (5) represents the barrel; (6) represents electrical heating resistors; (7) represents the vacuum plug of the degassing zone; (8) represents the die; (9) represents the cooling tray; (10) represents the filament diameter measuring mechanism; (11) represents the puller; (12) represents the water circulation system.

[0051] FIG. 2: Schematic cut-off representation of the device developed, wherein (13) represents the screw.

[0052] FIG. 3: Schematic representation of the filament diameter control unit wherein (14) represents the coupling with rollers pulling the filament trough the calliper measuring zone; (15) represents the motor of the puller; (16) represents the traction rollers; (17) represents the plastic bearings; (18) represents the calliper.

DESCRIPTION OF EMBODIMENTS

[0053] Referring to the drawings, some embodiments are now described in further detail, but are not designed to limit the scope of the present application.

[0054] The present application describes a device for producing a filament usable in FDM devices, from crushed thermoplastic residues, and respective operating method of the device, leading to filament production.

[0055] The device pertains to an extruder of thermoplastics, whose screw is designed so as to obey the characteristics of the thermoplastics to be extruded. The device operates after stabilization of the different temperatures in the respective zones of the device, enabling the achievement of an ideal temperature profile for extrusion of the thermoplastic and which is in accordance with that programmed in the microcontroller. These temperatures are achieved and maintained based on the Proportional-Integral-Derivative (PID) control method. Once thermal stability is achieved, the screw (13) is driven by the motor (1), whose speed may be controlled by Pulse-Width Modulation, but depending on the motor, other speed control methods may be used.

[0056] The motor (1) is coupled to the screw (13) by means of a gearbox, which enables the rotation speed of the screw to be decreased or increased and, consequently, the torque to be increased or decreased, respectively. Upon turning, the screw (13) pushes the crushed thermoplastic in flakes that are previously washed and placed into the feed funnel (4). These flakes are obtained by crushing thermoplastic residues with the use of external shredders, which are not an integral part of the technology now described. These devices shred the thermoplastic up to the point at which their size enables a smooth extrusion process.

[0057] The action of pushing the plastic gives the screw (13) an axial reaction force in the opposite direction to this displacement, which is sustained by an axial bearing (2), and the load is distributed to the supporting base of the device, not enabling the screw to move in the opposite direction to the flow of the thermoplastic. The thermoplastic is pushed against the barrel (5) which is heated by the electrical heating resistors (6), resulting in the melting thereof. Arriving at the degassing zone (7) a sharp drop in pressure causes the polymer to bubble and release humidity, whereby eliminating the need for pre-drying and enhancing the quality of the product obtained. Subsequently, the melted thermoplastic is compressed against the die (8) leaving with a diameter equal to that of the hole, plus elastic expansion, hole that may have various diameters, affecting the speed of extrusion, traction and cooling of the filament. The larger the hole diameter and the greater the extrusion speed, the faster the speed of the puller (11) relative to the speed at which the thermoplastic is extruded by the device; the greater the flow, the lower the cooling efficiency. The filament is cooled on a cooling tray (9) so that the thermoplastic returns to solid state quickly, tray (9) that is constantly fed with water by a water circulation system (12) constituted of a water pump and a flow-limiting tap. This feeding induces the water to overflow of the smaller tray to the tray on which it rests, and from there back again to the water circulation system, whereby generating a constant water layer, thus increasing the contact between the water and the filament extruded, increasing the efficiency of the cooling due to convection. Lastly, after being cooled, the filament is pulled by a puller (11), which is only possible if the filament is already in solid state. The puller (11) is driven by a motor (15), which operates by rotation of the traction rollers (16), said rollers (16) having an adherent surface, which may be made of rubber material to increase adherence. These rollers (16) are pressed against each other by way of an elastic or spring placed on the plastic bearings (17) of the upper roller. The diameter of the filament is measured on the extrusion line, immediately prior to the puller (11) using a coupling with rollers (16), that pulls the filament through the measuring zone (14) which uses a digital calliper (18) and a spring or elastic to maintain the calliper (18) closed on the filament, whereby detecting a possible decrease in diameter.

[0058] The control of the device is made based on a microcontroller which acquires the temperature values measured by the sensors next to each of the electrical heating resistors (6) and adjusts the power of the electrical heating resistors (6) based on this information, using a control that can be by PID using solid state relays to switch on/off the electrical heating resistors (6) according to the temperature and programming by the microcontroller. The barrel (5) is finned in the feeding zone to prevent premature fusion of the flakes, which would cause the device to clog. Should the fins not dissipate the necessary heat, air or water cooling may be added to increase dissipation of the heat in the zone. The value measured by the filament diameter control unit is also acquired by the microcontroller, and based on this measurement, the speed of the motor (15) of the puller (11) is varied, thus varying the speed at which the filament is pulled by the puller (11) through the cooling zone, that is, the greater the speed at which the filament is pulled, the smaller the diameter of the filament and vice-versa. The measurement on the extrusion line is obtained by the microcontroller and thus the system has a feedback of the diameter, based on which the speed of the puller (11) is adjusted until it reaches a point at which it is within the parameters required for an FDM device.

[0059] In concrete terms, the operating method of the device for producing a filament comprises the following steps: [0060] a) Introducing thermoplastic flakes into the hopper (4) after having reached the steady state in the temperature of the different heating zones of the screw (13); [0061] b) Starting the motor (1) that drives the screw (13), it being connected to the screw (13) by a gearbox; [0062] c) Upon turning the screw (13) compresses and pushes the flakes along the barrel (5) heated by the electrical heating resistors (6), resulting in the fusion of the thermoplastic; [0063] d) Arriving at the degassing zone (7), a drastic drop in pressure caused by the arrangement of the screw (13)the deepening channel means there is a greater volume for the same amount of thermoplastic, resulting in the decompression thereof and consequently contributes to lower the pressure in the zoneand by a vacuum plug (7) made from an orifice in the barrel (5) connected to a vacuum pump (3) causes the thermoplastic to bubble and consequently release volatile gases such as water vapour, which would diminish the quality of the filament; [0064] e) The thermoplastic is compressed against the die (8) traversing the orifice thereof; [0065] f) Once in the form of filament, but still in melted state, the thermoplastic is pulled by the puller, passing beforehand through a cooling tray (9) which upon forcing the filament to come into contact with water by virtue of a water circulation system (12) made it return to solid state, whereby enabling it to be grasped and pulled by the puller (11); [0066] g) So that the diameter of the filament can be calibrated, it is measured next to the puller (11) and its diameter is sent to the microcontroller; [0067] h) The microcontroller decides whether it has to maintain the speed of the motor (15) of the puller (11) to maintain the diameter of the filament, increase the speed of the motor (15) of the puller (11) to decrease the diameter of the filament, or lower the motor speed (15) of the puller (11) to increase the diameter; [0068] i) The microcontroller also decides when the electrical heating resistors (6) are switched on during the operation of the proposed device, so that the temperature in each of the heated zones is pre-set. This is made by comparing the values measured by the temperature sensors (one for each of the electrical heating resistors) with the pre-set temperature values.

[0069] Naturally, the present specification is not in any way restricted to the embodiments presented in this document and a person with average skills in the field may envisage many possibilities of modifying it without straying from the general idea, as defined in the claims. The preferred embodiments described above are obviously combinable with one another. The following claims additionally define preferred embodiments.