- HDPE WASHING LINE
- Scrap sources of
HDPE are mainly from:
- Milk packaging,
shampoo and farmaceutical bottles, drums,
oil jars, crates, some fibres, nets
and some other few items, in less quantity.
- Let's see what's
good and bad of each one of them and most
of problems connected.
- Milk jugs are very
popular in many countries, specially the
US where most of milk has this kind of packaging.
- Natural material,
with an MFI ranging around 0,15 (extrusion
grade) after washing can be used for very
many applications in the field of extrusion.
- Contamination of
this product is milk (of course) paper labels,
some dust collected in the open air, the
very common orange skin, that can be found
for some unknown reason in all plastic scraps,
some coffee cup, a PET bottle here and there
and this is about it.
- What bother most
of everybody is the fact caps are colored
and material cannot be natural color any
more after grinding, washing and pelletizing.
- If it is done in
industrial quantity not much can be done
about it, unless you have a couple of hundred
thousands dollars to spend for a flakes
color sorter, but this your choice.
- Another system
that works pretty well about this subject
is a roll, mounted on top of a conveyor
belt, to flatten all bottles and a "shaker"
to make caps to detach from the bottles,
going then to a trammel for further
- You don't have
a 100% guarantee all caps are gone,
but most of them are.
- If bottles have
colored plastic labels, that will go
all the way into washing line, can be
removed at the end of it by a well working
labels separator, may be two, one after
- Unless you apply
for the FDA approval, you cannot sell
your pellets for blowing bottles for
food application but shampoos are very
common and market is wide open for any
good quality material.
- As we said before,
washing HDPE is pretty simple, the line
is not very costly (compared to a sophisticated
PET washing line) and anybody can run
the system understanding few basic things
in a very short time.
- The components
of a system for washing milk jugs:
- A conveyor belt
with a metal detector (you never know)
a good, oversized, dry granulator, a
buffer silo in the middle to match granulator
throughput and the one of the washing
line and the washing line itself.
- The most common
washing line composition will be a washing
machine that will remove ALL dirt, a
sink float tank to get rid of the always
present PS coffee cups and some PET
- A final dryer
will deliver flakes with a moisture
content of less than 1%, good enough
for the extrusion process.
- Now the big
point is, as for any other washing system,
- If you can just
dump it, good for you, but this is not
common so let's see what can be done
- As we said before,
most of contamination will be bad-smelling
milk that, into hot water will smell
even more nasty.
- First put your filtration unit outside
the building, if your neighbour doesn't
complain much, and try to set your filtration
system in the easiest possible way.
- The one that works best in this
situation is a combination of mechanical
filtration and DAF (Dispersed Air Flotation)
- The mechanical filtration for paper
that has been converted to pulp and
the DAF will remove most fat of milk
delivering a water good enough to be
re-used into washing machine.
- Because in the mix you'll find also
soap bottles, you may want to add to
your water some de-foaming agent to
avoid foam formation that creates trouble
to pumps and to the whole water circuit
- If final application of your flakes
is, for example, lumbers, a glass of
diesel fuel is a beautiful de-foaming
agent and doesn't cost anything.
- For rinsing purposes, you will need
some fresh water anyway.
- This washing way applies also to
drums, oil jars and the other items
we listed before.
- What changes is the size of washing
machine that, in case of drums should
be bigger, to give flakes more
washing time and more friction because
dirt is normally much more sticky and
difficult to remove.
- What changes, again, is the way
you should remove contamination from
- For the drums, situation is pretty
difficult because contamination here
can be really everything, including
dangerous chemicals and something else
you never though it was existing.
- In this case we do suggest to go
to a local water treatment company and
beg them to solve the problem; it will
not be easy and inexpensive but it's
the only way to go.
- In fact, if you tell to water treatment
companies which kind of contamination
you have inside, it will take a nanosecond
for them to solve the problem while
if what you should remove is "everything"
they will start scratching their head
and you're in trouble.
- If you have any other scrap we didn't
mention, let us know what it is and
it may be way to clean it.