Hi all
Just thought I would email you with the results of my experiment so far and trying to overcome the results of PET shrinking when heat is applied.
The object is to try and allow the pressure to over come the shrinking effect and to put a rocker on the lower side of the hull
Experiment No1. ~ Fizzy water Lr bottle clear with straight sides
A car tyre valve was fitted to the screw top of the bottle and the pressure increased in stages to 50psi.
At this point the skin of bottle was very tight and high pitched when tapped with finger.
[b]Attempt No.1[/b] ~ not wishing to apply much heat to start with, I decided to commandeer my good ladies hair dryer that just happens to have a variable heat control.
At all speeds and heat settings this had no effect and the bottle remained the same shape. ~ I had recently tried a non pressurised bottle and it seceded in getting the PET to shrink. So despite this initial disappointment, I decided to try with a hotter device.
[b]Attempt No.2[/b]~ The blow torch was ignited and the heat gently played over the Bottle from an arms distance ~ this started to have the desired effect to put a bow in the bottle ~ at this point and without any warning, the bottle was ripped from my hand by an invisible force and thrown so violently across the garage that the whole top of the bottle was embedded in through the side of an empty large cardboard box and with an accompanying explosive sound, the loudness of which I had not heard since I was in the Forces.
Having extracted the bottle from the side of the box, I could see a 5" split had ripped the bottle apart and there was sadly no rocker left to speak of.
Experiment No2. ~
The second bottle was again a 2ltr clear bottle however this time it used to contain still water and was of a much thinner material, so as a precautionary measure I only pressured it to 25Psi
Attempt No.1 ~ More hair dryer and when this had no effect Attempt No.2 ~ back to the blow lamp the result was another catastrophic failing as the 2nd bottle went the same way of the first.
Has any one got any bright ideas that will hopefully not result in me trying to blow my self up?
It might as well be TommoHawk ~ very grey and overcast.
I am trying to prepare a bottle boat for the Chris Dicks Award but my Bottle Footy requires a rocker and hence why I have been experimenting I think I need to have something a little hotter that a hair dryer but not a fierce as a blow torch ~ I think I am going to try a Halogen heater I have and try from 3 or 4 psi
I may be entirely mistaken as to what a “rocker” is with regards to a footy, but have you considered using the shrink to create the rocker, rather than trying to get it to expand? I’ve seen/heard of people molding canopies for RC aircraft using plastic bottles… they find one that’s a little bigger than the male mold, jam the mold up into the bottle, and heat it till the bottle shrinks down around the mold. If you had a mold of what you wanted the bottom of your bottle-footy to look like, could you stick it inside a bigger bottle, and shrink the bottle till it fit the mold?
-Rick (who’s advice, as usual, is worth less than you paid for it)
Hi Rick
thanks for the idea ~ I did try shrinking the top in the hopes of inducing a curve in the bottom, however all it did was to tension the bottom and flatten it.
Hi Rusty
Like your lateral thinking
I am going to try the halogen heater and a low psi this morning and will let you know how I get on
Have you considered those newish 2-liter CocaCola bottles with that build-in curve? Dunno if that’s the right shape or size… wonder if they do the same thing in 3-liter?
I have been playing in the garage and hey presto have a look at the result.
I have placed the bottle on a flat shelf so you can see the rocker more clearly against the cutting mat.
The observant among you will also note that I was also able to extend the bottle by inflating the end (normally the base)
Ok how?
well the tyre valve is self explanatory ~ I used a halogen heater with 3 x 400w elements
I started at about 5psi with the bottle about 100mm away from the heat gradually moving it closer till I saw the moulded ridge in the bottle start to contract.
I then started to gradually increase the pressure in the bottle until I got the opposite reaction at about 45psi ~ after each heating I had to re-pressure the bottle and then re-heat.
The base re-modelling was an experiment but it just goes to show it is possible.
The obvious next step was to contract the contract the deck so as to get more of a banana shape ~ so having taken photos of the first phase, I gradually released the pressure and heated the deck.
As it contracted creases started to form so I re-pressured the bottle and worked the heat so as to remove them.
Now before anyone says anything rude all I will say is that it is just your mind that thinks its phallic.
Walt, I am cock-a-hoot (no pun intended) about this the fact that I can now manipulate the bottle into the shape I want is very exciting
I have done a couple of other tests to try and answer your questions as best I can
The new shape with the neck cut off and ping pong ball inserted would be 340mm as it stands at present
Now I appreciate that this does not fit the box ~ but I did use a 2ltr bottle and blew the base out to form the shape ~ so I think some more PET moulding could produce an acceptable shape.
My latest thoughts are that it may be possible to cut the neck off so that you can just squeeze a ping pong ball into it ~ drill the base and put the tyre valve through ~ then insert the P/P ball and shrink the hole slightly - glue the P/P ball in the hole with Zap-a-Dappa - then inflate to 1 or 2 psi this would have the effect of pushing the P/P ball into the glue while it set.
Now the bottle can be manipulated so as to get the bow shape ~ Oh the possibilities are endless
The water line length with a total hull + weight of 456g (the closest I could get was exactly 300mm see attached photo
Once you started on the oxy-acetylene route I thought we were going to have to call out the Footy Thermal Polis - “raise your hands SIR and back away from that tactical nooclear device”
Great experimentation and results - thanks for making it available, dead ends and all:D
I can see Gary latching on to the curccurbitic aspects of your creation, especially if it were green:D
(I will have to see if Google or Babel can do a translation service from andrew to english)
Following the previous sucess, I have decided to experiment with a smaller bottle in the hopes that I can repeat the process but gain the advantages I have discovered.
To such I have scoured a couple of supermarkets and come up with a likely candidate for my application of Footy Plastic Surgery
