- Sorting is the very step of plastic recycling.
- Sorting is compulsory in some applications and surely
is if final product needs to be of very high quality.
- Here a description of some sorting methods of both
manual and automatic with advantages and disadvantage
of each of them.
- The sorting method suitable for you depends a lot
by the country you're living in or, in other words,
how much man power cost.
- To see exactly how much it is costing to you download
the following file:
- Running cost excel file.
- (Right click and save as)
- Sorting can be set up
in many different ways.
can be manual, automatic or, and it
is what we do suggest, a mixture of
lot depends about the scrap you're dealing
with and the kind of system it is afterworlds.
example, in a LDPE film washing line
a piece of wood is extremely dangerous,
because it will go all the way together
with PE making the guy working on extruder
filter very busy indeed.
the same piece of wood goes into a PET
washing line, nobody cares because it
will be floating while PET sinks, therefore
separation is very easy.
means the same contaminant can be a
nightmare for one application and nothing
for another one.
- To make a good example of what we're
talking about, we'll take in consideration
a PET bottles washing line where sorting
must be very effective.
- Let's talk about manual sorting
- The simplest, and less effective
way of sorting is the "negative
- It means a conveyor belt where people
pick up whatever is not a PET bottle
just by visual recognition.
- Unfortunately, this way of sorting
is not very effective first because
PVC bottles look if not identical, very
similar to PET bottles and second because
people get bored with this kind of job
and after a little while, pay little
attention on what they're doing.
- (this is the difference between
theory and practice)
- The alternative is "positive
sorting" meaning people standing
beside a conveyor belt pick up each
and every plastic bottle and toss it
on another conveyor going to granulator;
this way personnel is somehow obliged
to pay a lot more attention on what
they're doing and sorting is much more
- There are some more aids to increase
the efficiency of manual sorting.
- Polarized light and UV light are
the most common.
- Automatic sorting uses NIR rays
detection and/or X-ray detectors.
- First one has the advantage to recognize
all different plastics (PS-PA-PVC etc.)
while X-ray detectors can scan, and
remove, only PVC.
- Keeping in mind most of manufacturer
of NIR detectors guarantee about 96%
separation, according with the initial
level of contamination, you should install
one, two or whatever number of pieces
to get at the end a residual contamination
of less than 30 PP total.
- And this kind of device is pretty
- An X-ray detector can guarantee
99% PVC separation but careless about
- So, the best deal for automatic
separation will be one NIR and one X-ray
detector combined together and you'll
be on the safe side.
- Now, if you combine some manual
sorting (it can also be a final inspection
after automatic separation) and some
automatic you're done.