Naked Science Forum

General Science => General Science => Topic started by: chris on 21/08/2007 20:42:05

Title: How are plastic bottles made? Where is the join?
Post by: chris on 21/08/2007 20:42:05

Can anyone tell me how plastic bottles are made? Is it some kind of moulding process? If so, where is the join, and how do "they" get the screw cap bit on?

Chris

Title: How are plastic bottles made? Where is the join?
Post by: paul.fr on 21/08/2007 21:24:59

well i know plastic cups can be made by heating a round piece of plastic, then forcing a metal mould in to it. This expands the plastic in to the shape of the mould.

It is also why re-heating it can make the cup shrink back to a flat piece of round plastic, water pressure can also have the same effect. Take a plastic cup diving and see what happens to it, or heat it with a hair dryer.
that makes me think of an experiment to post

oops, that does not answer the question.

I suppose the above procedure would be no good for plastic bottles, so what else could they use?

there is a procedure called blow moulding where hot gasses are used to "blow" hollow shaped moulds. that's all i know.

over to those far more intelligent.........

Title: How are plastic bottles made? Where is the join?
Post by: DoctorBeaver on 21/08/2007 21:36:58

They're made by injection or blow moulding. With injection moulding, plastic is forced at very high pressure & temperature into a die. The die then opens and, lo, a plastic bottle (or whatever has been moulded) drops out.

The die for bottles is normally in 3 parts - 2 sides and a top; or body, top & bottom. The top goes between the sides to form the inside of the bottle so that the plastic is forced round it. Sometimes, if the die isn't an exact fit, you get what looks like a seam where the plastic has leaked into the gap.

Title: How are plastic bottles made? Where is the join?
Post by: paul.fr on 21/08/2007 21:40:37

Hay Doc,

could blow and injection moulding be the same thing with different names? The process you describe is what i remember as blow moulding.

maybe, maybe not?

Title: How are plastic bottles made? Where is the join?
Post by: DoctorBeaver on 21/08/2007 21:43:33

Blow moulding is different insofar as the inside isn't formed by part of the die; it is sheer internal pressure that forms the hollowness (the same as glass blowing).

Title: How are plastic bottles made? Where is the join?
Post by: paul.fr on 21/08/2007 21:44:40

Quote from: DoctorBeaver on 21/08/2007 21:43:33

Blow moulding is different insofar as the inside isn't formed by part of the die; it is sheer internal pressure that forms the hollowness (the same as glass blowing).

ah  [:I] goodbye..

Title: How are plastic bottles made? Where is the join?
Post by: eric l on 22/08/2007 09:18:26

In the case of PET bottles, the user (= the company that bottles water or whatever) receives small test-tube like "preforms".  These sites shows how these preforms are blown up to full scale bottles (click on "view animation" with the second one).
http://www.kenplas.com/project/pet/petblow.aspx
http://www.bpf.co.uk/bpfindustry/process_plastics_injection_blow_moulding.cfm

Title: How are plastic bottles made? Where is the join?
Post by: DoctorBeaver on 22/08/2007 10:02:52

And here's a link about injection moulding.

http://www.azom.com/details.asp?ArticleID=265 (http://www.azom.com/details.asp?ArticleID=265)

Title: How are plastic bottles made? Where is the join?
Post by: eric l on 22/08/2007 12:15:32

Quote from: DoctorBeaver on 22/08/2007 10:02:52

And here's a link about injection moulding.

http://www.azom.com/details.asp?ArticleID=265 (http://www.azom.com/details.asp?ArticleID=265)

No animation ???  [;D]  Good info, though !

Title: How are plastic bottles made? Where is the join?
Post by: DoctorBeaver on 22/08/2007 13:37:22

You want animation? Then watch The Simpsons!  [:(!]