On Sun, 22 Mar 2009 14:54:04 -0500, the renowned Bert
wrote:
engineman wrote:
On Mar 22, 9:00?am, F. George McDuffee gmcduf...@mcduffee-
associates.us wrote:
On Sat, 21 Mar 2009 22:28:21 -0700 (PDT), engineman
wrote:
I have a plastic bottle that once held Lipton's green tea.
when I looked at the threads on the bottle it looks like they consist
of segments.
The cap has similar threads.
I'm wondering what the reason for these strange threads?
Engineman
http://www.photoworks.com/photo-shar...sionid=7ED5DB6...
==========
Mainly so the parts can be molded without the need for a special
"unscrewing" core. ?
By segmenting the threads it is possible to greatly simplify the
mold construction. ?It also eliminates the parting line problem
on the threads where the mold closes greatly reducing
maintenance.
Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).
I sent the wrong link- sorry, here's the right one:
http://www.photoworks.com/members/engineman
I don't think that these threads were designed for pressure relief,
they seem to be very strong.
The bottle seems to have 3 parting lines and the parting lines are all
on the lands of the thread.
Also it appears that the length and positioning of the lands would not
permit removal of the thread from the mold without unscrewing.
Engineman
It is so the cap does not go flying off from the pressure.
Google Patent number: 4747502, plus there are a few others.
MikeB
Eg. 6234338
Bingo! So as you unscrew the cap, the pressure can vent safely out
through the slots, whilst the cap is safely contained on the bottle
threads.
The security ring is screwed on with the cap-- just it has fingers
that snap out into a groove in the neck and retain it, with far more
strength than the bits that get torn when the cap is removed. I think
I could make a tool to remove Dansani security caps without breaking
them.
Thanks for this question-- I actually have taken a course in design of
blow molds and this area was not covered (though there was endless
discussion of 'starts' and such like). The standard thread forms are
covered by a part of the SPI- the Plastic Bottle Institute, believe it
or not.
http://tinyurl.com/dl9nw4
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com