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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 separation.
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 the other.
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 flakes.
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, water filtration.
If you can just dump it, good for you, but this is not common so let's see what can be done about it.
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 system.
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 water.
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.