- What it should be considered
setting up a film washing line
scraps out of olefins is the most common
scrap that can be found on the market
so one of the easy part of the job is
sourcing the raw material. Unfortunately
the easy part of this job is only
- Into bales of film scraps, doesn't
matter if your supplier did swear it
was deeply sorted, you should expect
what an unrestrained fantasy mind can
think of and, may be, it's not enough.
- The motto "do it yourself"
is what should apply here, meaning you
can forget to load the whole bale into
the best and powerful shredder you just
bought because is not going to work,
at least for a long time.
- Scrap bales need to be opened and
sorted not only for that reason but
removing of wood, foamed materials,
an entire piece of carton etc, is compulsory if
what you're looking for is a pellet
good for film application.
- Not to talk about steel or other
metals that will be into bales, no question.
- Therefore, manual sorting will not
be good only to protect your shredder
but also for the quality of your final
- We always mention "shredder"
and not granulator on purpose; again
because you should expect everything
and because we're talking about dirty
material, we strongly suggest to go
with a single shaft shredder rather
than a granulator to save maintenance
first and consequently (a lot of) downtime.
- If you'll need a small size flake
because of your force-feeder, you can
always go into a granulator at the end
of the line because, after material
is clean and dry, your blades will last
- Of course we are talking about an
industrial system working 24/7 because
if you have spare time here and there
the story can be very different.
- So, we got our material shred, using
a grid of about 50 mm in order to not
create lots of fines during washing
- Even if it is true shredder delivers
material constantly, we like to go into
a buffer silo anyway to be sure the
quantity of flakes we feed to the line
is what we want and, just in case, operator
should state how much material goes
to the line and not the shredder itself.
- Buffer silo extraction screw speed
can be adjusted to deliver to the line
what operator think is the best for
the efficiency of the line. (because
it is a screw conveyor, dosing will
be by volume and not by weight, remember
- Separation into a sink-float tank
should take place first to get rid of
sinkable that surely is contamination.
- A lot of guys out there call them
"washing tanks" but you try
yourself to dip a flake into water,
leave it there for a couple of hours
and check how clean it is after that.
You judge it yourself.
- Anyway, after separation by flotation,
giving to dirt the time to absorb water,
material need to be washed, meaning
removing dirt for its surface.
- What we do is to go to a "centrifuge
like" machine to apply a lot friction
in presence of water, like my grandma
was doing long time ago because, by
the way, it still works.
- The combination of a sink float
tank and a washer is what separates
and clean plastic film flakes.
- Now, if your material has a little
amount of dirt, one sink float tank
and a washer will do the job, if it
not enough, you should add another set
to get it more clean, and so on.
- No machinery manufacturer knows
about your material so it is customer
responsibility to show what will be
the worse scrap coming to the line and
to suggest what you need.
- This means if you change your scrap
characteristic, line will perform differently,
may be better, may be not, up to you.
- And this is normally why customers
complain after putting a line in operation;
may be it is a machinery supplier fault
but, most of the time. material is not
the one it was supposed to be, and nothing
works or, if it does, it comes out to
be too expensive, throughput too low,
lower quality than expected and so on.
- You may not like it but the sentence "shit
in, shit out" is what applies here.
- Back to film washing line, let's
talk a bit about what effects the most
production rate besides contamination.
- This is the data you should know
very well because it is what states
the throughput of the line.
- As we said before, starting from
first screw conveyor extracting flakes
from buffer silo, everything goes by
volume and the fact you need production
rate expressed in Kg/hour doesn't match.
- In other words, if you feed a 40
micros average thickness film and you
get, let's say, one ton per hour, with
exactly the same line you'll get 750
Kg/hour with a 30 microns film, 500
Kg with a 20 microns and so on.
- On the other side, problems (cutting
and drying) will increase proportionally
with the decrease of thickness so, not
only you get less production but your
machinery will not perform as well as
they are supposed to.
- We'll make another example for the
"non conosseur" about drying.
- Let's assume the centrifugal dryer
leave one drop of water every one square
meter of a 40 microns film that weight
about 3,5 grams that represent .
- Because the dryer removes water from
a surface you'll find the same drop
(same weight of water) on the same square
meter of film that, this time is only
20 microns, therefore you have twice
as much in term of moisture content.
- Got the point ?
- So, at the end, thickness is the
issue and the line should be configured
accordingly, keeping in mind film makers
are daily trying to decrease thickness
to save money and you'll be more and
more in trouble.
- And we, as machinery manufacturer,
- If you like some more technical
details please drop a line to: