- KNOWN WAYS FOR PREWASHING
let's see what is useful to pre-wash
and what's useless divided by scrap
- (You can go
directly to the one is of interest to
- What is common
to all pre-washing system is a GOOD
sounds very dirty because coming from
garbage selection and consequently,
is provided mainly when granulator blades
can wear rapidly because of the amount
and type of dirt, but here a single
shaft shredder is the machine to use
and wearing is not critical.
- As we said it
its dedicated page, the problem here
is mainly separation and two, sometimes
three, sink-float tanks are required
to deeply separate, at least, olefins
from sinkable plastics.
- Just because the best way to achieve
results is using clean water, each tank
should "separated" from the
following one by a washing/drying step
so, while material goes forward, water
- This apply to almost all systems,
surely to all "no chemical"
washing lines but, in this particular
case, it is very important.
- Back to the pre-washing matter,
it goes by itself this system already
has a pre-washing and nothing else is
needed, at least from cleaning point
of view. (while the separation problem
- On FILM
WASHING LINES the matter can be
- For film scraps coming from
collection we do not suggest a pre-washing
treatment of any kind because amount
of dirt is generally little and granulator
should handle this pretty easily.
- If contamination is not this "little"
but still scraps are coming from scraps
collection, we do suggest a single-shaft
shredder that will last very many days
- If film scrap is agro-film, silage
film or stuff like that, the pre-washing
step should be seriously taken into
- The film we just mentioned is clearly
contaminated by sand, hearth, stones,
you name it and any blade of any cutting
machine wears out in no time therefore
a pre-washing of some sort is kind of
- Specially for film, there are many
ways to carry out this depending by
which material you're feeding in and
what you need at the end. (pellets to
blow film, pellets for pipes or profiles
extrusion, blow molding, injection molding,
- For agro-film, for example, a low
energy consumption wet trammel will
do the job and removes 95% of dirt
just spraying some water in a tumbling,
perforated screen; with a washer/dryer
just after it, dirt will be almost completely
gone and for the rest of the washing
line it will be like eating a piece
- In case of silage film, where contamination
is not only sand but also grass, hay,
leaves and other floating contamination,
it will be better to use a pre-washing
machine that makes friction as well
to release most of this dirt.
- This machine will consume more energy
but it is the only way to get rid of
bottles washing, most of the times,
doesn't require pre-washing.
- Of course, unless scrap bottles
are not coming from a landfill pick
up or something similar to this and
unless we are not talking about oil
- If this is the case, we do suggest
to go with a double shaft shredder that
with little energy opens and shred the
bales of bottles (or lose) and doses
pieces to a pre-washing machine that
will remove surface dirt, most of paper
labels and most of soap, milk oil or
whatever dirt is inside. (the most,
not all the dirt)
- After this a wet granulator will
easily handle what's left into it and
a final deep washing will do the rest.
- This, once again, only in the case
bottles are more than dirty because
for every machine you add to the system,
there will be a bigger investment cost,
maintenance, energy etc. (it means,
do not complain if at the end the system
costs too much !)
- For the pre-washing of the PET
bottles washing line, we need a
little bit of your patience to go through
what it means.
- Let's make an introduction first:
- It is quite important the way PET
bottles are cut; this effects the way
line will perform, the amount of fines,
the amount of PET flakes floating on
to of water and some other few things.
- Therefore a sharp edge flakes will
make the washing line to run much better
than a jagged one.
- All this at the end means blades
of granulator should be sharp all the
- As everybody knows, PET is abrasive
by itself, paper isn't less and dirt
doesn't help much so how we do it ?
- A lot depends, once again, by the
way bottles are arriving at the very
- If you operate in a country where
it never rains, we do suggest to skip
the pre-washing process all together
and put a second granulator so you can
switch from one to the other and have
the line running 24/7 with no downtime.
- Why this ? Because a second dry
granulator cost less than the pre-washing,
takes less space, consume less energy,
is more productive than the wet process,
granulator will never rust and
all these good things.
- After this pre-washing of flakes
is much easier, more effective
- But we should be talking about pre-washing,
isn't it ?
- Because most of countries have rain,
snow etc. pretty often and bottles are
already wet, most of the times, we do
suggest to go with a wet process all
- After bales-breaker, so after bottles
are in single form, we go into a trammel
with continuous hot water spray to detach
all labels and get rid of most of them,
together with some glue and most of
- Keeping water very hot the process
has the big advantage to turn PVC
bottles opalescent, so way easy to recognize
and remove from the PET stream.
- More than this, being in a country
where electricity doesn't cost a fortune,
a second trammel, running with hot air,
can get to the point to shrink all bottles,
making the average thickness higher
and easier to wash, dry etc..
- Does this sound good ? Yes it does
also because, back to PVC bottles, they
will definetly get brown and very easy
to recognize and remove.
- After all this, your bottles will
be pretty clean, shrunk, labels and
dirt free and without any PVC content
so granulator blades will last very
long and its maintenance cost not high
- On the other side you should keep
in mind that hot water cost a bit and
hot air even more so you should run
the numbers in the country where you
are and see if this is convenient to
- Each piece of the equipment cost
money from investment and operating
costs point of view.
- Keep this always in mind.