SELF-CLEANING GRAVIMETRIC AND VOLUMETRIC DOSING APPARATUSES

Abstract

A self-cleaning dosing apparatus includes a material hopper for containing pellets of material, a feed screw, a first material outlet through which pellets of material fall by gravity onto a first end of the feed screw for the feeding of pellets to a process machine. A second material outlet is located beneath the first end of the feed screw, with a slide gate blocking the second material outlet. A pneumatic piston is provided for pulling the slide gate to unblock the second material outlet, and a Venturi pump is located under the second material outlet for pulling pellets through the second material outlet when the slide gate is opened.

Claims

1. A self-cleaning dosing apparatus comprising: a) a material hopper containing pellets of material; b) a feed 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 that surrounds the feed screw; and e) a motor that is connected to the first end of the feed screw and rotates the feed screw inside of the cylindrical insert to push pellets of masterbatch to a second end of the feed screw where the pellets of material fall out of the cylindrical insert; the self-cleaning dosing apparatus characterized in that it comprises: i) a second material outlet located beneath the first end of the feed screw; ii) a slide gate that blocks the second material outlet; iii) a pneumatic piston that pulls the slide gate back to unblock the second material outlet; iv) a Venturi pump located under the second material outlet; and iv) an air nozzle located opposite the second end of the feed screw and is configured to create and direct a stream of air through the cylindrical insert; wherein: ai) the motor is configured to reverse the direction of rotation of the feed screw, thereby causing the pellets of material between threads of the feed screw to be transported backwards towards the second material outlet; aii) the stream of air created by the air nozzle pushes pellets of material that have fallen to the bottom of the cylindrical insert back through the cylindrical insert towards the second material outlet; and aiii) the Venturi pump pulls all pellets of material that fall from the material hopper through 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 reverse rotation of the feed screw and the stream of air from the nozzle out of the apparatus; thereby completely removing all traces of the material from material hopper, the feed screw, and the cylindrical insert.

2. The self-cleaning dosing apparatus of claim 1 comprising: a) a container surrounding the material hopper; and b) a load cell attached to the material hopper, the load cell configured to weigh the material hopper and material inside the material hopper.

3. The self-cleaning dosing apparatus of claim 1, wherein the material is masterbatch.

4. The self-cleaning dosing apparatus of claim 3, wherein the apparatus is configured to add small quantities of masterbatch to resin introduced into production machines to produce colored products made from plastic.

5. The self-cleaning dosing apparatus of claim 4, wherein the apparatus is configured to be used with injection molding, extrusion, and extrusion blow molding production machines.

6. The self-cleaning dosing apparatus of claim 1, wherein the pellets of material removed from the material hopper, feed screw, and cylindrical insert by the Venturi pump are returned to a container used to supply the same material to the material hopper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 schematically shows a prior art gravimetric dosing system;

[0040] FIG. 2 is a cross-sectional view of the system of FIG. 1;

[0041] FIG. 3 schematically shows a self-cleaning gravimetric dosing apparatus;

[0042] FIG. 4 schematically shows a self-cleaning volumetric dosing apparatus;

[0043] FIG. 5 schematically shows an enlarged view the components of the apparatuses of FIG. 3 and FIG. 4 that are located beneath the material hopper;

[0044] FIG. 6 schematically shows the direction of air flow through the apparatus during the cleaning process;

[0045] FIG. 7 schematically shows the direction of motion of granules of masterbatch out of the apparatus through the outlet of the Venturi pump during the cleaning process; and

[0046] FIG. 8 schematically shows how the masterbatch removed from the apparatus 30 or apparatus 130 is returned to the supply container 72 during the cleaning process.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0047] Described herein are self-cleaning gravimetric and volumetric dosing apparatuses. The apparatuses are designed to add small quantities of masterbatch to the resin introduced into production machines to produce colored products made from plastic. The self-cleaning apparatuses enable automatic removal of all pellets of a first type of masterbatch from their interiors before a second type of masterbatch is introduced into the apparatus. The apparatuses can be used with production machines for any type of plastic manufacturing process, e.g. injection molding, extrusion, and extrusion blow molding.

[0048] FIG. 3 schematically shows an embodiment of self-cleaning gravimetric dosing apparatus 30. Apparatus 30 comprises a material hopper 32 located inside a container 34. A load cell 36 is attached to material hopper to weigh material hopper 32 and masterbatch introduced into it by means of material loader 38. In operation, pellets of masterbatch fall by gravity from material hopper through first material outlet 40 into feed screw 42. A reversible motor 44 rotates feed screw 42 to push pellets of masterbatch to the end of feed screw 42 where they fall through the neck piece 46 (under the roof of the neckpiece 48) into the throat 50 of the production machine. Not seen in the figure is a controller that receives weight data from load cell to determine the weight of masterbatch that is dispensed by the apparatus by using the loss-in-weight method. After calibration, the controller activates the motor 44 and adjusts the speed of rotation of the screw to dispense accurate weight portions of masterbatch in a given time and for a given duration. If material loader 38 is for example a Venturi loader, then the controller activates it to refill the material hopper 32 upon receiving a signal from a sensor inside the hopper indicating that the level of masterbatch has fallen to a threshold value.

[0049] FIG. 4 schematically shows an embodiment of a self-cleaning volumetric dosing apparatus 130. Apparatus 130 is identical to apparatus 30 in FIG. 3, with the exceptions that apparatus 130 does not comprise a load cell 36 and therefore does not require a container 34 to isolate the material hopper 32 from vibration and to improve the accuracy of the weights measured by the load cell.

[0050] The components of apparatus 30 and apparatus 130 described above are identical structurally and functionally to those found in the prior art gravimetric and volumetric dosing systems. A controller and the cables that connect it to sensors and electric valves at various locations in the system are not shown in FIGS. 3 and 4 or the following figures because they are not relevant to the present invention.

[0051] The new components of apparatuses 30 and 130 that enable the self-cleaning function will now be described with reference to FIGS. 3 and 4 and particularly FIG. 5, which is an enlarged view schematically showing the components of apparatuses 30 and 130 that are located beneath the material hopper 32.

[0052] Seen in FIG. 5 are material hopper 32 and a first material outlet 40 at the bottom of the hopper. In operation, masterbatch falls from material hopper 32 through first material opening 40 onto feed screw 42, which is rotated by motor 44. As feed screw 42 turns inside of cylindrical insert 45 pellets of masterbatch are moved one at a time to the end of the feed screw where they fall into a space below cover 48 of the neck piece 46 of the process machine to which apparatus 30 or 130 is attached. From the neck piece 46 the pellets fall through throat 50 into the process machine.

[0053] When it is desired to change from a masterbatch having a first color to one having a second color, motor 44 is reversed to reverse the rotation of feed screw 42 causing the pellets of masterbatch between threads of the feed screw 42 to be transported backwards towards second material outlet 52. At the same time a signal is sent to solenoid valve 62 that opens to allow compressed air to enter normally closed pneumatic piston 56 to pull back a slide gate 64 opening a second material outlet 52. Simultaneously with the opening of second material outlet 52, compressed air is introduced into Venturi pump 54 via air inlet 52 and compressed air is introduced into neck 46 of the processing machine via nozzle 58. Nozzle 58 creates a stream of air that enters the end of the feed screw 42 and pushes pellets of masterbatch that have fallen to the bottom of cylindrical insert 45 back through the cylindrical insert 45 towards second material outlet 52. The Venturi pump 54 pulls all pellets of masterbatch, .i.e. those that fall from the material hopper 32 through first material outlet 40 and second material outlet 52 and the pellets of masterbatch that are pushed out of the feed screw 42 and cylindrical insert 45 by the reverse rotation of feed screw 42 and the stream of air from nozzle 58, out of the apparatus in the direction indicated by arrow 60. From the outlet of Venturi pump 54 the pellets of masterbatch will be returned to a container used to supply masterbatch to material hopper 32 (see FIG. 8). Thus, the combined efforts of Venturi pump 54, reversal of rotation of the feed screw 42 and the stream of air produced by nozzle 58 thoroughly remove all traces of the masterbatch from material hopper 32, feed screw 42, and cylindrical insert 45.

[0054] FIG. 6 schematically shows the direction of air flow through the apparatus during the cleaning process. Note how during the cleaning process the slide gate 64 is pulled back to unblock the second material outlet 52. Reference signs 68a, 68b, and 68c schematically represent compressed lines from a compressor (not shown) to piston 56, Venturi pump 54, and nozzle 58 respectively.

[0055] FIG. 7 schematically shows the direction of motion of granules of masterbatch out of the apparatus through the outlet of the Venturi pump during the cleaning process.

[0056] FIG. 8 schematically shows how masterbatch is supplied to material hopper 32 and the masterbatch that is removed from the apparatus 30 or apparatus 130 is returned to a supply container 72 during the cleaning process. Container 72, which is the container in which the masterbatch is supplied from the producer or in which it is stored in the manufacturing facility is normally located in a storage area a distance from the production machines and attached dosing apparatus 30,130. During production runs, if the level of masterbatch 76 in material hopper 32 drops to a low threshold value, then material loader 38 is activated to draw masterbatch out of container 72 until level 76 reaches an upper threshold value when material loader is deactivated. After the production run is completed, the feed screw rotation is reversed and compressed air is introduced via air lines 68a, 68b, and 68c to empty all pellets of masterbatch from the material hopper and feed screw 42 as described herein above. The pellets that exit through the outlet of the Venturi pump 54 are then transported to container 72 by any means known in the art, for example they are pulled through a tube connected to the outlet of Venturi pump 54 by a material loader, e.g. a Venturi pump, attached to container 72. In FIG. 8, arrow 74 symbolically shows the direction of pellets of masterbatch falling off the end of the feed screw into the throat of a process machine.

[0057] Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.