Self-cleaning gravimetric and volumetric dosing equipment

Abstract

A self-cleaning quantitative feeding device comprises: a material hopper for accommodating material pellets; a feeding screw; a first material outlet, through which the pellets of material fall by gravity onto a first end of the feeding screw, for feeding the pellets into a processing machine. A second material outlet is located below the first end of the feeding screw, wherein a sliding door blocks the second material outlet. A pneumatic piston is provided for pulling the sliding door to open the second material outlet, and a venturi pump is located below the second material outlet for pulling the pellets through the second material outlet when the sliding door is opened.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to Israel Patent Application No. 268544, filed on August 6, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention belongs to the field of adding raw materials to production machines that produce products through industrial processes. In particular, the present invention relates to adding small amounts of masterbatches to production machines that produce plastic products. Background Art

[0004] In the modern world, plastics are the material of choice for making a seemingly unlimited number of products. These products are produced by various industrial processes such as injection molding, blow molding, extrusion and 3-D printers. The raw materials fed into the machines used to produce the final product are a mixture consisting of: polymers (called resins in the industry) in the form of beads, colorants and other additives (such as UV inhibitors). Colorants and other additives are supplied as masterbatches, which are concentrated mixtures of pigments and / or additives that are encapsulated into a carrier resin during heat treatment and then cooled and cut into pelletized shapes.

[0005]

[0026] The terms "beads," "pellets," and "pellets" are used interchangeably herein to refer to small pieces of material typically having a weight in the range of 0.01 g - 0.04 g.

[0006] In most plastic product manufacturing facilities today, resin is fed directly into the production machine in controlled quantities, and the desired color of the plastic product is achieved by feeding masterbatches, which are color additives and have the same chromaticity as the desired chromaticity of the final product, through a relatively small weight or volumetric dosing system mounted on the throat of the processing machine.

[0007] Patent US6,911,607 describes a typical weight dosing system of this type. The system includes a container filled with additive material. The additive material is dosed into and mixed with the basic material flow fed into the processing device by a dosing mechanism, which includes a motor that causes a worm screw to rotate in a cylindrical insert extending from the container. A weighing sensor weighs the additive material in the container, the dosing mechanism, and both of them. Weight loss measurement is used to calibrate the rotation speed of the worm screw to provide the desired dosing rate. As explained in the present application, the design of the system leads to weighing errors, which are compensated by using a calibration curve diagram determined experimentally for each different additive material. The weighing error is caused by the displacement of the center of gravity of the container and the dosing mechanism caused when the material is added to or removed from the container, as well as the nonlinearity between the rotation speed of the motor and the discharge mass per unit time of the dosing mechanism. One type of weighing error that cannot be compensated for is caused by noise and vibrations from, for example, the dosing mechanism, handling equipment and people moving around the dosing system, or by someone or something touching the container.

[0008] US6,688,493 of the inventor of the present invention describes a weight dosing system that provides a solution to the weighing errors inherent in the system described in US6,911,607. Figure 1 shows a schematic block diagram of the system of US6,688,493. The system includes a container 10, a material hopper 11 located inside the container 10, a weighing sensor 16 connected to the material hopper 11, and a controller 13 that calculates the weight based on the information of the weighing sensor 16 and commands the motor 14 of the screw feeder 12 to distribute part of the material to the molding machine 15. The inclined wall and parallel wall of the hopper 11 minimize the weight error and facilitate weight calibration by keeping the material pressure in the hopper 11 constant.

[0009] The material must be fed into the molding machine in portions of precise weight, and each portion must be fed at a given time and for a given duration. To achieve this goal, the controller 13 commands the motor 14 of the screw feeder 12 to start rotating at a specific rotation at a given time and for a given duration. Since the given time and duration of feeding are determined by the molding machine 15, the rotation of the screw feeder 12 is the only variable that can be used to control the weight of the fed portion.

[0010] FIG2 shows a cross section of the system with material in the material hopper and the system in a working or ready-to-work configuration. Material 17 filling the material hopper 11 is fed through the outlet 18 of the material hopper 11 to a space 19 created between the outlet 18 of the material hopper and the outlet 20 of the container 10. From this space 19, the material 17 is fed through the outlet 20 of the container 10 into the screw feeder 12. The outlet 18 of the material hopper is displaced from the outlet 20 of the container so that the material in the outlet shaft 21 is kept constant as long as the material level 22 is above the upper end of the outlet shaft 21 and the material hopper 11 is isolated. The portion of the material 17 located in the space 19 acts as a buffer, which isolates the material hopper 11 and limits the noise and vibration from the screw feeder 12 and its motor 14, so that the material hopper 11 can be accurately weighed by the load cell 16. When the material level 22 decreases to a threshold level, the controller 13 commands the refilling device 23 to refill the material hopper 11.

[0011] All known gravimetric and volumetric dosing systems designed for adding small amounts of additives (e.g., masterbatch) directly into the throat of a production machine have substantially the same structure as described with reference to Figures 1 and 2, and operate in the same manner. It should be noted that the volumetric dosing systems are also manufactured by the applicant of the present application. The volumetric systems are identical to the gravimetric systems shown in Figures 1 and 2, except that the volumetric systems do not include a load cell, and the feeding during a production run depends on the assumption that the properties of the material (e.g., specific gravity) and / or the material flow properties do not change after an initial calibration of the feed screw speed.

[0012] One of the practical disadvantages of working with a dosing system of the type described above is that a considerable amount of time is required to empty the material hopper and to clean all traces of material from the hopper and the auger each time a change of material is required to produce a product of a different colour.

[0013] It is an object of the present invention to provide a solution to this problem in the form of components added to conventional systems which can be activated to perform a self-cleaning function.

[0014] Further objects and advantages of the invention will appear as the description proceeds. Summary of the invention

[0015] Described herein is a self-cleaning dosing device comprising:

[0016] a) a material hopper for containing material pellets;

[0017] b) Feeding screw;

[0018] c) a first material outlet, through which pellets of material fall by gravity onto a first end of a feed screw;

[0019] d) a cylindrical insert surrounding the feed screw; and

[0020] e) A motor connected to a first end of the feed screw and causing the feed screw to rotate within the cylindrical insert to push the masterbatch pellets to a second end of the feed screw where the pellets of material fall out of the cylindrical insert.

[0021] The self-cleaning dosing system also includes:

[0022] i) a second material outlet below the first end of the feed screw;

[0023] ii) a sliding door blocking the outlet of the second material;

[0024] iii) a pneumatic piston, which pulls back the sliding door to open the second material outlet;

[0025] iv) a venturi pump located below the second material outlet; and

[0026] v) an air nozzle positioned opposite the second end of the feed screw and configured to generate and direct an air flow through the cylindrical insert.

[0027] In a self-cleaning metering device:

[0028] ai) the motor is configured to reverse the direction of rotation of the feed screw so that the material pellets between the threads of the feed screw are conveyed backwards towards the second material outlet;

[0029] aii) air flow generated by the air nozzle pushes the material pellets that have fallen into the bottom of the cylindrical insert backwards through the cylindrical insert towards the second material outlet; and

[0030] aiii) a venturi pump pulls all pellets of material that fall from the material hopper through the first material outlet and the second material outlet, out of the apparatus by counter-rotation of the feed screw and air flow from the nozzle to push the pellets of material out of the feed screw and the cylindrical insert;

[0031] As a result of the activities described in ai) to aiii), all traces of material are completely removed from the material hopper, feed screw and cylindrical insert.

[0032] Examples of self-cleaning dosing devices include:

[0033] a) a container surrounding a material hopper; and

[0034] b) A load cell attached to the material hopper, the load cell being configured to weigh the material hopper and material within the material hopper.

[0035] In an embodiment of the self-cleaning dosing device, the material is a masterbatch.

[0036] Embodiments of the self-cleaning dosing apparatus are configured to add small amounts of masterbatch to a resin introduced into a production machine to produce a colored product made from plastic.

[0037] Embodiments of the self-cleaning dosing apparatus are configured for use with injection molding, extrusion, and extrusion blow molding production machines.

[0038] In an embodiment of the self-cleaning dosing apparatus, the pellets of material removed from the material hopper, the dosing screw and the cylindrical insert by the venturi pump are returned to the container used to supply the material hopper with the material.

[0039] All the above and other characteristics and advantages of the invention will be further understood from the following illustrative and non-limiting description of embodiments thereof, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] - Figure 1 schematically shows a prior art gravimetric dosing system;

[0041] - Figure 2 is a cross-sectional view of the system of Figure 1;

[0042] - Figure 3 A self-cleaning gravimetric dosing device is schematically shown;

[0043] - Figure 4 A self-cleaning volumetric dosing device is schematically shown;

[0044] - Figure 5 Schematic diagram showing the Figure 3 and Figure 4 an enlarged view of a component of the device;

[0045] - Figure 6 schematically illustrates the direction of air flow through the device during the cleaning process;

[0046] - Figure 7 Schematically showing the direction of movement of masterbatch pellets out of the device through the outlet of the venturi pump during the cleaning process; and

[0047] - Figure 8 It is schematically shown how masterbatches removed from the device 30 or the device 130 during the cleaning process are returned to the supply container 72 . DETAILED DESCRIPTION

[0048] Described herein is a self-cleaning gravimetric and volumetric dosing device. The device is designed to add small amounts of masterbatch to a resin introduced into a production machine to produce a colored product made of plastic. The self-cleaning device enables all pellets of a first type of masterbatch to be automatically removed from the interior of the device before a second type of masterbatch is introduced. The device can be used with a production machine for any type of plastic manufacturing process, such as injection molding, extrusion, and extrusion blow molding.

[0049] Figure 3 An embodiment of a self-cleaning weight dosing device 30 is schematically shown. The device 30 includes a material hopper 32 located within a container 34. A load cell 36 is connected to the material hopper to weigh the material hopper 32 and the masterbatch introduced into the material hopper 32 by a material loader 38. In operation, pellets of masterbatch fall from the material hopper through a first material outlet 40 into a feed screw 42 by gravity. A reversible motor 44 rotates the feed screw 42 to push the pellets of masterbatch to the end of the feed screw 42, where they fall through a neck 46 (under the top of the neck) into the throat 50 of the production machine. Not shown in the figure is a controller that receives weight data from the load cell to determine the weight of the masterbatch dispensed by the device by using a weight loss method. After calibration, the controller activates the motor 44 and adjusts the rotation speed of the screw to dispense an accurate weight portion of masterbatch at a given time and for a given duration. If the material loader 38 is a venturi loader, for example, the controller activates the venturi loader to refill the material hopper 32 upon receiving a signal from a sensor inside the hopper indicating that the level of masterbatch has dropped to a threshold value.

[0050] Figure 4 An embodiment of a self-cleaning volumetric dosing device 130 is schematically shown. The device 130 and Figure 3 The apparatus 30 of is the same as that of except that the apparatus 130 does not include the load cell 36 and thus does not require the container 34 for isolating the material hopper 32 from vibrations and improving the accuracy of the weight measured by the load cell.

[0051] The components of the above-described apparatus 30 and apparatus 130 are structurally and functionally identical to those present in prior art gravimetric and volumetric dosing systems. The controller and the cables connecting the controller to the sensors and electric valves at various locations in the system are not included. Figure 3 and 4 or shown in the following figures, as they are not relevant to the present invention.

[0052] Now refer to the attached Figure 3 and 4 And especially Figure 5 Describe the new components of the apparatus 30 and 130 that enable the self-cleaning function, Figure 5 is an enlarged view schematically showing components of the apparatus 30 and 130 located below the material hopper 32.

[0053] Figure 5 Seen in the figure are the material hopper 32 and the first material outlet 40 at the bottom of the hopper. In operation, masterbatch falls from the material hopper 32 through the first material outlet 40 onto the feed screw 42 rotated by the motor 44. As the feed screw 42 turns inside the cylindrical insert 45, the pellets of masterbatch move one at a time to the end of the feed screw, where they fall into the space below the cover 48 of the neck 46 of the processing machine to which the apparatus 30 or 130 is attached. From the neck 46, the pellets fall through the throat 50 into the processing machine.

[0054] When it is desired to change from masterbatch having a first color to masterbatch having a second color, the motor 44 is reversed to reverse the rotation of the feed screw 42, causing the masterbatch pellets between the threads of the feed screw 42 to be transported backward toward the second material outlet 52. At the same time, a signal is sent to the solenoid valve 62, which opens to allow compressed air to enter the normally closed pneumatic piston 56 to pull the sliding door 64 back to open the second material outlet 52. At the same time as the second material outlet 52 is opened, compressed air is introduced into the venturi pump 54 via the air inlet, and the compressed air is introduced into the neck 46 of the processing machine via the nozzle 58. The air flow generated by the nozzle 58 enters the end of the feed screw 42 and pushes the masterbatch pellets that have fallen to the bottom of the cylindrical insert 45 backward through the cylindrical insert 45 toward the second material outlet 52. The venturi pump 54 pulls all of the masterbatch pellets (i.e., those that fall from the material hopper 32 through the first material outlet 40 and the second material outlet 52, as well as the masterbatch pellets that are pushed out of the feed screw 42 and the cylindrical insert 45 by the reverse rotation of the feed screw 42 and the air flow from the nozzle 58) out of the device in the direction indicated by the arrow 60. From the outlet of the venturi pump 54, the masterbatch pellets will return to the container used to supply the masterbatch to the material hopper 32 (see Figure 8 ). Thus, the combined action of the venturi pump 54, the counter-rotation of the feed screw 42 and the air flow generated by the nozzle 58 completely removes all traces of the masterbatch from the material hopper 32, the feed screw 42 and the cylindrical insert 45.

[0055] Figure 6 The direction of the air flow through the device during the cleaning process is schematically shown. Note that during the cleaning process, the sliding door 64 is pulled back to open the second material outlet 52. Reference numerals 68a, 68b and 68c schematically represent compressed air lines from a compressor (not shown) to the piston 56, the venturi pump 54 and the nozzle 58, respectively.

[0056] Figure 7The direction of movement of the masterbatch pellets out of the device through the outlet of the venturi pump during the cleaning process is schematically shown.

[0057] Figure 8 It is schematically shown how masterbatch is supplied to the material hopper 32 and how masterbatch removed from the device 30 or device 130 is returned to the supply container 72 during the cleaning process. The container 72 is a container for storing masterbatch supplied from a producer or a container for storing masterbatch in a manufacturing facility, and is usually located in a storage area at a distance from the production machine and the attached dosing device 30, 130. During a production run, if the level 76 of masterbatch in the material hopper 32 drops to a low threshold, the material loader 38 is activated to draw masterbatch from the container 72 until the material loader is deactivated when the level 76 reaches an upper threshold. After the production run is completed, the feed screw is rotated in the reverse direction and compressed air is introduced via air lines 68a, 68b and 68c to empty all the masterbatch pellets from the material hopper and feed screw 42, as described above. The pellets discharged through the outlet of the venturi pump 54 are then delivered to the container 72 by any method known in the art, for example, by a material loader (e.g., a venturi pump) attached to the container 72 pulling them through a tube connected to the outlet of the venturi pump 54. Figure 8 In FIG. 1 , arrow 74 symbolically shows the direction in which the masterbatch pellets fall from the end of the feed screw into the throat of the processing machine.

[0058] Although the embodiments of the present invention have been described by way of illustration, it should be understood that the invention may be susceptible to numerous changes, modifications and adaptations without departing from the scope of the claims.

Claims

1. A self-cleaning quantitative feeding device, comprising: a) a material hopper containing pellets of material; b) Feeding screw; c) a first material outlet through which pellets of material fall by gravity onto a first end of the feed screw; d) a cylindrical insert surrounding the feed screw; as well as e) a motor connected to said first end of the feed screw and causing the feed screw to rotate within the cylindrical insert to push the pellets of material to the second end of the feed screw where they fall out of the cylindrical insert; The self-cleaning dosing device is characterized in that it comprises: i) a second material outlet located below the first end of the feed screw; ii) a sliding door blocking the outlet of the second material; iii) a pneumatic piston, which pulls back the sliding door to open the second material outlet; iv) a venturi pump located below the second material outlet; and v) an air nozzle located opposite the second end of the feed screw and configured to generate and direct an air flow from the second end of the feed screw into and back through the cylindrical insert to the first end of the feed screw; in: ai) the motor is configured to reverse the direction of rotation of the feed screw so that pellets of material between the threads of the feed screw are conveyed backwards towards the second material outlet; aii) air flow generated by the air nozzle pushes the pellet of material that falls into the bottom of the cylindrical insert backwards through the cylindrical insert towards the second material outlet; and aiii) a venturi pump pulls all pellets of material that fall from the material hopper through the first material outlet and the second material outlet, and the pellets of material that are pushed out of the feed screw and the cylindrical insert by the counter-rotation of the feed screw and the air flow from the air nozzle, out of the self-cleaning dosing device; All traces of pellets of material are thereby completely removed from the material hopper, feed auger and cylindrical insert.

2. The self-cleaning dosing device according to claim 1, comprising: a) A container surrounding a material hopper; as well as b) A load cell attached to the material hopper, the load cell being configured to weigh the material hopper and a pellet of material within the material hopper.

3. The self-cleaning dosing device according to claim 1, wherein the pellets of material are masterbatches.

4. The self-cleaning dosing device of claim 3, wherein the self-cleaning dosing device is configured to add a small amount of masterbatch to a resin introduced into a production machine to produce a colored product made of plastic.

5. The self-cleaning dosing device according to claim 4, wherein: The self-cleaning dosing device is configured for use with injection molding, extrusion and extrusion blow molding production machines.

6. The self-cleaning quantitative feeding device according to claim 1, wherein: Pellets of material removed from the material hopper, feed screw and cylindrical insert by the venturi pump are returned to the container used to supply the pellets of material to the material hopper.

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