Mix Plastic

  • LD, LLDPE and HDPE film coming from shopping bags, packaging etc. and few bottles.
  • Heavy printed PP film that's the eye catching wrap of most food products.
  • PVC film and blister pack that's still around.
  • Multi-layers films used in the food industry to preserve perishable food.
  • PS trays both vacuum molded and foamed.
  • Same trays out of PET
  • Leather, cleaning pads, cotton fabrics, wood, other materials.

 

So, with a "raw material" like this not much should be expected and here is why:

First, to make a system delivering a good quality product at the end will cost a fortune, and nobody will make any money out of it.

Second because even thinking to the most sophisticated unit for the separation of whatever you expect as normal contamination, there will always be something not expected  and quality will be spoiled anyway.

The matter has many variables and a lot depends from the starting point.

 

Even with the very best, sophisticated set up that will remove all PVC, PET, PS and other sinkable plastics, with a set of washing machines and dryers to remove all paper, foamed materials, some wood etc, what remains is still contaminated by some multi-layers film, cleaning pads, foamed Polyurethane that will not break apart and surely something else. Pelletizing and filtration will take care.

And this is only what's related to separation while, like any other film washing line, the other two difficult points are cutting and drying.

Cutting because heavy contamination will require a frequent maintenance of the cutting system and drying because films are getting thinner day by day and, as one may understand, the thinner it is, the more difficult is to dry.

Cutting first: the only approach in this case will be the single shaft shredder that's described in the machinery section of this site, because it is, specially for high production rates, the less expensive machine in terms of "currency" per Kg.

This kind of system should be sized for production rates not less than 1 ton/hour and, if more, much better.

Drying is the other issue; mechanical centrifugal dryer are performing well if thickness of film is over 40/45 microns, while if thickness is less, as it normally is in this case, together with the high throughput required, residual moisture content to expect at the end is well over 10%, meaning no extruder will handle it.

You will say hot air drying system will fix the problem and you're surely right but how much it cost ? (we don't like it)

In our opinion, the best ratio energy/drying effect is achieved by the agglomerator that's described in the machinery section of this site.

Let's go now to the final stage of the line that's filtering and pelletizing.

Which kind of extruder should be used for this purpose ?

This must be evaluated each time according with the starting material.

The best way to go, is a combination of  two extruders; first a twin screw extruder will provide for compounding and first filtration ( backflushing filter with a screen 0,5 mm) a second single screw, a short L/D one, for further filtration, down to 0,2 mm and pelletizing.

This, of course, if the customer will pay for the higher quality.


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