Not applicable
Not applicable
This invention relates to plastic recycling and and plastic manufacturing processes and more specifically relates to a plastic recycling system that processes post-consumer plastic waste into uniform structural mono filament to be used in plastic additive manufacturing.
Plastic extrusion systems are commonly used by existing plastic manufacturers that produce plastic mono filament. Current plastic manufacturers intake new plastic material in a uniform pelletized form factor and melt the material through their extruder to produce the mono filament made out of previously unprocessed plastic resin. Conventional extrusion systems are not capable of processing post-consumer and contaminated plastic waste. Post-consumer plastic waste as a feedstock is inherently non-uniform as it is sourced from municipalities whose constituents utilize materials from any number of producers. Since the waste also comes from waste sorting facilities the feedstock also contains non-trivial amounts of non-plastic contamination that consists of material ranging from but not limited to dirt, debris, glass, metal, and organic material.
Specifically pertaining to the extrusion process, conventional extruders rely on feedstock consistency to dictate the uniformity of the output extrudate. Conventional extruders typically operate at a single flow and feed rate that is predetermined before the extrusion process begins and remains running at the same rate until the process ends. Granulated waste plastic consists of flakes with a size variation of roughly 0.1 mm to 2 mm, which is not suitable feedstock for current extrusion systems. Because of the fluctuation in material flow and pressure that is caused by the size inconsistencies, conventional extruders will produce low-quality mono filament with a high variance in diameter. Additionally, any trace of contaminant in the extruder feedstock will likely cause clogging issues due to insufficient material screening and filtering processes in traditional extrusion.
Specifically pertaining to the current recycling infrastructure, existing recycling systems do not process post-consumer plastic waste due to factors such as technological barriers in which existing technology is not equipped to process inconsistent and contaminated material. Additionally, a lack of resources prevents current recyclers from investment in further developing the recycling infrastructure to enable proper handling of post-consumer plastic. Conventional recyclers focus primarily on sorting of plastics to be sold on the scrap plastic market rather than actual processing of said material.
In these respects, the process of this present invention fulfills a unique need for a system that accepts contaminated post-consumer plastic waste and produces reliable and structural plastic mono filament that can be reused in downstream plastic manufacturing processes. Additionally, this invention serves as a proof of concept and creates a pathway for utilizing post-consumer plastic material as useful feedstock material, which can therefore encourage further recycling infrastructure development.
In view of the shortcomings of existing recycling and extrusion technology, the present invention is uniquely positioned to efficiently process post-consumer plastic material, that would otherwise be land filled, into reliable additive manufacturing feedstock with properties and performance characteristics comparable to their raw material equivalents.
The general purpose of this invention is to provide a closed-loop methodology for recycling post-consumer plastic material to be used as direct substitution for existing raw materials currently used in additive manufacturing to reduce the reliance on crude oil for producing more plastic resin as well as to reduce the volume of plastic waste that is currently being land filled and causing plastic pollution.
A combination of manual sorting, filtered granulation, gravity separation, washing, and mesh sifting eliminate contaminants and impurities from the input material throughout several steps in the recycling process. The effluent water produced from the system is further purified and reintroduced into the system to supply the other water-reliant processes, such as the washing, drying, and extrusion steps, thereby creating an additional closed-loop water management system. The cleaned and reground plastic material that feeds into the extrusion machine passes through additional melt filtration in its molten state to remove additional micro-contaminants, resulting in a purified extrudate that is monitored by an active programmable control logic mechanism that utilizes the extrudate's diameter to dynamically adjust the rate at which the extruder produces filament as well as the rate at which the belt puller pulls the material onto a spindle through a winder.
An object of the present invention is to provide a methodology and means for recycling heavily contaminated post-consumer plastic waste material that is currently being land filled due to the shortcomings of existing recycling infrastructure.
Another object of the invention is to produce uniform plastic mono filament from non-uniform plastic regrind using an integration of software technology with industrial hardware to alter conventional extrusion in order to accommodate for variance in quality or properties of the feedstock material.
Another object is to provide a system that utilizes its own closed-loop water management system that filters and repurposes effluent water in order to reduce water consumption of recycling and extrusion processes and eliminate industrial waste water typically produced in manufacturing.
The following detailed description of the invention details with accompanying drawings are not intended to limit the scope of the invention, but rather illustrate the preferred embodiment of the invention.
The granulation step 300 utilizes a conveyor belt to transfer material into a granulator with a wide hopper to receive material that is then reduced in size into reground flake material. The granulator may comprise a staggered blade screened granulator, generally known in the industrial arts, that receives the material from the hopper discharge port. The granulator may typically include sharp blades extending from a rotating shaft and arrayed therealong in staggered, angularly offset fashion. As ground material is shredded sufficiently it falls through a mesh screen and into a downward chute leading to a bin that holds the flake material.
The granulated flake material 306 resulting from granulation step 300 is filtered through an eddy current separation mechanism 400 (
Gravity separation 500 eliminates coarse non-plastic material that comprises but is not limited to sand, food waste, and powder residue. The gravity separation phase constitutes two stages of gravity separation.
Stratified material 501-502 resulting from the secondary gravity separation step illustrated in
Dry flake material 703 is further sifted for final removal of loosened micro-contaminants that were dislodged from the flake during the washing 600 and drying 700 processes.
The extrusion process 900 illustrated in
Prior to operating the extruder, several components need to be primed for efficient operation such as the four heating zones 903, the hot water tank 905, and the cold water tank 906. Each heating zone 903 is set to a specific temperature based on the heat pro file of the material being processed. Unique heat pro files are determined based on the material melt temperature. The temperature of the hot water tank 905 and cold water tank 906 are additionally determined based on the material melt temperature such that when the material enters into the water bath the temperature differential does not cause the material's shape to deform.
Material is fed into the extruder's hopper 901 using a flood feeding strategy, in which the material is fed into the hopper to a certain capacity, or a starve feeding strategy, in which the material is fed into the hopper at a metered rate such that the hopper does not accumulate material. The particular method of loading material into the hopper is largely dependent upon material properties.
The programmable logic controller (PLC) 910 is used to determine the initial speed at which the extrusion screw 902 revolves and therefore the speed at which material is moved through the extruder. The overall throughput is additionally impacted by the speed at which the belt puller 911 pulls the material onto a spindle, which is also controlled by the PLC 910. The rotation of the extrusion screw 902 in combination with the heat from the heating zones 903 melt, compress, and compound the material such that a single thread of compact mono filament is formed. The extrudate material is filtered through a mesh screen pack 904 consisting of multiple layers of mesh screens of varying grades for a final filtration of decontaminants before exiting the nozzle 912 of the extruder.
The molten extrudate is immediately fed into the hot water tank 905 to initiate the material cooling process. A pump is utilized in the hot water tank 905 to generate movement in the water and distribute the heat from the extrudate evenly in the tank and maintain its equilibrium temperature. The hot water tank 905 precedes the cold water tank 906 where the material is further cooled so that the extrudate material is now hardened mono filament. Similarly to the hot water tank 905, the cold water tank 906 also utilizes a water pump to facilitate distribution of heat and maintain the tank's temperature. An air wipe system powered by the air compressor 909 dries the material of any surface water remaining from the water tanks 905-906.
A laser micrometer 907 measures the diameter and ovality of the resulting mono filament and provides this data to the PLC 910 that then utilizes the input data according to the dynamic control logic illustrated in the flowchart in
Given a target diameter, the PLC 910 will accept the diameter read by the micrometer 907 as input data to process. A diameter larger than the target diameter will trigger the PLC 910 to decrease the speed of the extrusion screw 902. After allowing the material behavior to absorb the alteration, the PLC 910 will subsequently decrease the speed of the belt puller 911 to reach equilibrium with the extrusion screw 902. Alternatively, if the diameter is smaller than the target diameter the PLC 910 will increase the speed of the extrusion screw 902, followed by the increasing the speed of the belt puller 911 after the appropriate delay. A diameter matching the desired target diameter will result in no change to the behavior of the extrusion screw 902 or belt puller 911 speeds.
The PLC 910 also monitors the pressure of the extrusion chamber for the entirety of the extrusion process to ensure safety of the equipment and the operators. A maximum operating pressure specification is provided by the equipment manufacturer; the PLC 910 has an automatic fail safe when the machinery reaches 60% of the maximum pressure.
With regard to
Finally, the mono filament is wound onto a spindle by the winder 908. The resulting spool of mono filament can then be used directly for fused filament fabrication (FFF) or optionally further processed into plastic pellets through a pelletizer to meet form factor needs of other forms of plastic manufacturing such as injection molding.
The invention as described above illustrates the principles of the invention and a preferred embodiment of the invention, but are not meant as limitations. There are many possible variations resulting from potential alterations in sizing, material, and the like made by those skilled in the art.
This application claims the benefit of filing date priority of U.S. Patent Application No. 63/013,110, filed on Apr. 21, 2020.
Number | Date | Country | |
---|---|---|---|
63013110 | Apr 2020 | US |