Recycling Systems
The Recycling sector is an extensive field within the Environmental sector in which we want to recycle a wide variety of waste, aiming to enhance their direct re-use, or processing raw materials for their re-use in the production of new goods.
An important part of this waste is plastic origin, appearing in various forms: packs of various sizes and origins, film or other agricultural sources, and other home appliances, with the common feature of its previous use and the inability of the same form, being used again. We also included the waste or waste production industry from the processing of plastics.
In order to serve the objectives of this recycling activity, we have developed recycling systems for all types of recyclable plastics, whether plastic containers from small dimensions up to containers with 1 cubic meter, domestic bottles, dairy products packages, plastic film, and cans up to 200 litres…
A recycling System defines itself as an installation of several equipments, connected in series, allowing the full treatment of the waste/residue, to obtain a product which can be used as a raw material. This installation is composed by modules with independent functions, but interacting themselves to achieve the desired result. We shall now proceed to exemplify a base installation for the recycling of used plastics with contaminants.
We are going to discuss the following stages of the process:
1 – Grinding
2 – Washing or decontamination
3 – Drying
4 – Granulation
Depending on the materials being treated, we can use two or three phases of grinding, classifying them as: Pre-grinding or Shredding, middle grinding and final grinding.
When the waste has large dimensions, or is presented in bales, it’s used, in a previous phase, a guillotine, to cut the material in chunks that will facilitate the pre-grinding or shredding.
In the Pre-Grinding or Shredding, we shred the material, reducing his dimensions in a way that it can suffer a first washing or decontamination treatment. In this phase, we use a machine that we designate as pre-shredder, shredder, pre-grinder, primary grinder or primary shredder.
Depending on the characteristics of the material, it will be used a machine that are appropriate to these characteristics, like a low rotation single-shaft shredder for example.
The middle grinding is intended to reduce the material previously washed to a particle size that allows the second phase of washing or decontamination. In this phase and in the final grinding phase, it will be used a conventional machine that we designate as grinder, high-speed grinder, shredder or granulator.
For some materials that do not have high percentages of contaminants, we can suppress the phase of middle grinding, passing from pre-grinding to final grinding.
In this phase we intend to free the material of the contaminants, whether it’s dirt, products leftovers on the packages, paper, glues, or non-matching plastic materials. The equipments used on this phase vary depending on the treated material and they can perform alone or together, to achieve the best result. We are referring to tubs for washing and decantation, centrifugal washing machines and washing “trommels”.
The washing and decantation tubs, when placed in line next to pre-grinding, have to execute an immersion, swirling and decantation pre-wash, having rolling-drums that force the material to dive in the water, forcing it at the same time, to the way-out. In the tub, this process is repeated normally three times until the final exit of the material to the next phase, which allows to remove a large portion of contaminants. The same equipment is placed in a more advanced location of the process, normally after middle grinding. In that location, it performs a washing and separation function by decantation, process in which the more heavy materials go to the bottom, and the lighter materials float.
The centrifugal washing machines are used specially in the decontamination of packages with higher levels of contaminants, and also because these packages have large amounts of glued paper. They are also used in the plastic film washing (when they have large amounts of contaminants).
The “Trommel” is a rotation machine which (in some cases mixing water) produces a good washing effect. It’s used specially in recycling lines of metallic packages (like oil drums for example), but it can also be used in plastic film recycling lines or any other recycling system installation. His primal function is to loosen up and separate the material and to shake the sands or other residues at the same time. When placed before the pre-grinding, it protects the cutting elements of the shredder or grinder from premature worn.
The shredded and washed material carries large amounts of water and, although most of that water is going to be lost in the worm conveyors (because their inferior body is built in perforated sheet-metal), the remaining water has to be removed, for the posterior treatment in the extrusion machine or granulator.
This operation is carried by high-speed centrifugal drying machines. The rotor is involved all around by perforated sheet-metal, forming a round drum, allowing the exit of liquids and other impurities released during the process.
It’s intended that the material, after this operation, would not give degrees of moisture content above 5%, varying between 2% and that maximum value. In some materials, especially plastic film, it’s necessary to use more than one centrifugal drying machine, putting them online to obtain the desired result. After this process, the material is deposited into big-bags or transported to storage silos or sent directly to the extruder that will make its granulation or pelletization. This process completes the cycle of recycling by providing material with a purity that allows their re-use in the production of diverse goods.
The recycling line, as we describe it, has a fully automated operation, with human intervention only in feeding the first phase of treatment. The transport between the elements is made by conveyors and worm conveyors. The entire line is controlled by a powerful electronic unit, programmed according to the material being treated and the desired result. Metal detectors can be introduced in the line, with automatic stop of the element where the detection takes place, or, if we want to remove the bits of metal automatically, “overbands” can be introduced also.
The same principal may be used for recycling metallic cans (oil drums for example). In this case, the machines being used are the Low-Rotation Double-Shaft Shredders, with more or less cutting teeth, depending on the required dimensions for the next phase. In this line, the normal conveyors are replaced by metallic conveyors.
The washing is done with the use of washing “trommels”.
Plasmaq has ensured the representation of this equipment, available in various models, with different transformation capacity.
