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Soda Bottles are pressure tested but water bottles are not! Don't use water bottles for
pressurized rockets. Water Rocket Pop! does not recommend pressurizing above 100 psi for safety
reasons. Some people have tested burst pressures using other launch pads.
This note is from an expert in pressure testing soda bottles:
I was reading a piece on a trade site for carbonated beverage bottles that said
the industry has settled on a standard of two times the fill pressure for
carbonated beverages (60 psi), so 120 psi would appear to be the current minimum
acceptable burst pressure for the industry. When I left the industry (1986) the
QA standard was a minimum burst test of 160 psi (if my memory serves me - I know
that's in the range at least).
Having been lucky enough to be involved in the development of PET bottle
production (1980) I would like to give you some insight into the confusion you
experienced as to how your bottle failed (exploded). Relative to the neck breaking, ... the neck is not the "strongest" part of the
bottle. The process of blowing the bottle from a preform orients the molecules
of the PET along the axis of greatest stretch (the length), thus making the
thinner areas of the bottle enormously stronger (by weight) than the thicker
neck area which experiences almost no molecular orientation. Thus the neck is
tougher in some aspects than the oriented material; however, it is a quite =
brittle.
Also although your bottles neck failed it probably was not the first point to do
so. Your picture that shows the whole bottle is a bit difficult to see details
in, but having witnessed literally thousands of such tests to failure I feel
pretty confident in saying that your bottle first split along the longitudinal
axis. Then the forces generated by the nearly instantaneous release of
pressure from the bottle most probably caused pieces of the more brittle neck
to run off in all directions (to paraphrase Eugene Ionesco).
I hope this clarifies your results a little.
Best regards,
Chris Bonner
flarecrafter@aol.com
Reprinted with permission. Clarification in italics added.
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Recycle / Reuse
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Earth911.org is a very good source of knowledge
to recycling plastic, and so many other things. |
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