Gravimetric blender with operatively coupled bar code reader

Details Gravimetric blender with operatively coupled bar code reader Gravimetric blender with operatively coupled bar code reader

1998-05-14

2001-02-13

Gordon, Paul P. (Department: 2786)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Nonreactive mixing process

C700S052000, C700S065000, C700S164000, C700S266000, C700S215000, C700S217000, C222S057000, C222S058000, C222S075000, C222S077000, C366S018000, C366S020000, C366S021000, C366S141000

Reexamination Certificate

active

06188936

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to automated management, control and optimization of methods and apparatus for providing or otherwise processing precisely measured amounts of granular materials and, optionally, precisely measured amounts of coloring agent(s), particularly pigment in liquid form, preparatory to further processing of the combined granular materials and, optionally, liquid coloring agent(s). The invention relates more specifically to automated management, control and optimization of gravimetric blenders, optionally in combination with color addition pumps, providing precisely measured amounts of plastic resin material, and, optionally liquid coloring agents, and mixing these components prior to supplying the blended mixture to plastics manufacturing and processing equipment such as plastic injection molding, compression molding and extrusion equipment.
FIELD OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART
The modern gravimetric blender was essentially originated by one of the applicants of this invention and is widely used throughout the world by industries concerned with precision feeding of granular material, especially plastic resin material.
Gravimetric blenders operate by blending solid plastic resin material components and additives, by weight, in batches. Typically batches of material may consist of several solid material components. One of these may be “regrind”, consisting of ground plastic resin which had previously been molded or extruded and which either resulted in a defective product or was excess material not formed into a desired product.
Another component may be “natural” plastic resin which is virgin in nature in the sense that it has not previously been processed into a molded or extruded plastic part.
Yet another component may be a solid color material, typically flakes or freeze dried material, used to produce a desired color of the finished plastic part.
Still yet another component may be an additive used to adjust the blend to provide required performance characteristics during molding, extrusion or subsequent processing.
The gravimetric blender as originated by one of the applicants and as copied widely throughout the world typically includes hoppers for each of the components of the solid material to be blended together. Typically several hoppers or several compartments in a hopper may be provided, such as one compartment for “regrind” material, one compartment for “natural” material, one component for solid color additive material and one compartment for “additive”.
When the gravimetric blender operates, the unit desirably operates automatically, adding each of the component solid materials in the proper, desired percentages. Each solid material component is dispensed by weight into a single weigh bin. Once the proper amounts of each component have been serially dispensed into the weigh bin, all of the components are dropped together into a mixing chamber from the weigh bin.
Mixing is performed preferably continuously, and preferably even as additional batches of components are dispensed into the mixing chamber. When mixing is complete, the resulting blend is preferably provided directly to the desired molding or extrusion machine.
It is known to provide feedback control of the dispensed amounts of each solid material component provided to the weigh bin and measured by weight so that in the event of an error in the amount of a dispensed component, the succeeding batch may have the blend adjusted to account for the error detected in the preceding batch of blended material.
As one of the components forming a part of the resulting blend, it is known to supply solid color additives to the blend in order to provide a blend of a desired color. These color additives may be flaked pigments on wax carriers or in freeze dried form. It is also known to provide the color as pigment powder constituting one component of the resulting blend.
When preparing blends of resinous plastic material for molding or extrusion, when color amounts are too low the error is visible and a correction to increase color may be effectuated by an operator. However, when color amounts are too high, the problem is not visible and operators manually operating the process normally do not make any adjustment in the amount of color. Hence adjustments are frequently made to increase the amount of color materials supplied to a blend but almost never is the amount of color supplied to the blend reduced.
Liquid color material cannot be pre-blended into one of the solid material components and stored because of the danger inherent and difficulties attendant to clean-up in the event of component failure. Hence, liquid color, when used in plastics material processing heretofore, has been metered directly into the throat of a molding press or an extrusion machine, at a position to join the solid resinous material blend just prior to the molding or extrusion operation. This approach creates difficulties, among them being compensating for addition of pre-colored regrind solid material to the material mix.
When regrind is added to the blend of plastic resin materials, the regrind already contains the necessary color; such regrind need not be colored a second time. When metering resinous material at the throat of a molding press or an extrusion machine, such metering is conventionally performed volumetrically. Hence, the presence of already colored regrind, not requiring additional coloration, cannot be detected. As a result, excess liquid color is typically added to the blend, sometimes producing an unacceptable product and always resulting in the use of unneeded color material, which is undesirable and results in unnecessary expense.
Gravimetric blenders typically use one or more load cells to detect the weight of the weigh bin and material contained therein. Vibrational and shock loading of the load cells may result in erroneous measurements of the weight of the weigh bin and the material contained therein. These erroneous measurements may result in addition of excess material or an insufficient amount of a material component in a subsequent batch thereby producing a batch of blended material deviating from the desired specifications. The load cells are subject to some vibration and shock loading due to the presence of pneumatic piston-cylinder combinations typically connected to the frame of the gravimetric blender and used to dispense solid granular resinous material from a hopper downwardly into the weigh bin.
Further, vibrational and shock loading of the load cells may result from use of typically pneumatically driven piston-cylinder combinations to empty the weigh bin when the weight measurement is complete. Yet further vibrational and shock loading of the load cells may result from operation of the mixing chamber and the motor driving mixing means within the mixing chamber.
Because the frame of the gravimetric blender must be a rigid, high strength structure to provide the required strength to support the material storage hoppers and other components of the gravimetric blender, the gravimetric blender frame is typically steel. Since the frame is steel and rigid, shock and vibrational loads applied to the frame are readily transmitted along the frame and received by the various components of the gravimetric blender connected to the gravimetric blender frame.
When the gravimetric blender is mounted directly on a plastics material processing machine such as an extruder or, more particularly, an injection molding machine, the load cells of the gravimetric blender can be subjected to very substantial shock and vibrational loading. Injection molding machines have heavy steel platens and molds which open and close as parts are molded and ejected. There is a considerable amount of movement in an injection molding machine and the parts which move are heavy. Hence shock loads, which continuously propagate throughout injection molding machines and hence propagate through the gravimetric blender when the blender frame is bolted to the injection molding machine,

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