Russell
Painted? Do you know a paint which will adhere to PET?
All the ones I have seen have been in the natural colour, or in the case of AndyTs probably the best colour in the world.
With the wisdom of hindsight I should probably have run some bright PVC tape along the hull on the inside to help the Ogre see it - when I think about it praps I should have added a few dozen flashing surface mount LEDs of different colours - now THAT would make her noticeable!
FWIW the fact that Cyanos are not waterproof - like most of the glues we use is really not material, since with impervious materials like PET the water can only access the glue line edge, and the effect (as was found in WW1) is to soften the glue and this forms a wonderful crack-stopper. PVAs aren’t , nor any contact glue but in practice they work better than theory suggests:D
In all these glue/bond tests, did anyone try any of the Cyano-epoxy systems that use a glue and a primer? Here in the US there’s a brand called Cyanopoxy, that reportedly bonds slippery engineering acetal plastics like Delrin, which is all but impossible to glue using other methods. It would offset the cost factor of using recycled bottles though, since it is rather expensive.
Bill,
thanks for that - worth a try.
and anything that bonds delrin must have a good grasp on van der Waals forces
It’s not so much the cost that would affect my thinking, but it might be getting in the way of Fun:D
Bottle boats are fast and fun, even if we have to forego the 10c return bonus :mad:
Bonding tests (optimised for joining halves of a hull) are proceeding well:
having done some tests I realised that the adhesive join was perfectly effective, but decidedly unhandsome, so a 2-bead applicator was designed and made - it is offered to you in case it helps with another adhesive application.
It may LOOK LIKE a tiling adhesive spreader but its actually derived from FEA, intense CAE work and honest copying-and-adapting
Trial hull join (surfaces abraded, not degreased) was completely successful - I would use that joint happily. Adhesive was again FIAT gasket silicone - it is a acid cure silicone and I don’t think that there is anything special about it.
I have assembled another 4 silicones - all, I think, acid cure RTV types (bathtub sealant) and will get a series of test pieces done this weekend.
I’m also going to make and photograph some more shrunk hulls, and try garage vacuum forming in styrene.
andrew
In the interest of rigorous honesty I have to report the results of my silicone glueing of PET bottles tests:
Didn’t work
There, that didn’t hurt as much as expected:p
I had lined up four common types of Silicone RTV glues/mastics, and many, many sample pieces of PET bottle. Having started the process I discovered that two of the silicones had completely cured in the tube/cartridge, so that left only two viable silicones
Half the PEt samples were abraded with fine sandpaper, half were degreased with alcohol (specifically methylated spirit - mostly ethanol)
I made a 2-bead spreader - which worked brilliantly so I am sure that the silicone was applied evenly and repeatedly.
all the samples were clamped and left for 3 days indoors to cure (they were both acid-cure types)
all the samples peeled apart easily!
My first trials were carried out with the same adhesive - but I both abraded and degreased the surface,and the test pieces are still very strong and permanently bonded.
So a battle lost, but the war continues - I will be bottle-shrinking again over the holiday period and will carry out more tests until I understand what the crirtical processes are.
Then you will know, & I will have FLEETS of the things
BTW - if you mix soda bicarbonate into an acid-cure RTV silicone (one that smells of vineger on curing) you will produce a foam silicone rubber that is skinned on the outside and has myriad closed-cell bubbles (filled with CO2)
andrew
Have you considered that perhaps the sort of joints you are trying to create will not subject the glues to peeling load.
In the diagram you published on 6th November the main loads would be bending and perhaps tension of the hull shell as a whole which would put the joint in shear. There may have been a possibility of the two hull sections trying to separate at deck level, but this will be constrained by the deck itself being glued to both sections effectively preventing peeling loads. A stategically placed inwale located with its upper edge a deck’s thickness below the hull edge would form an effective ledge onto which to glue the deck itself - also with no peeling tendancies.
This is certainly what I found in my tests on Sticks Like Sh*t. Peeling, with loads at 90 degrees to the joint - rubbish. Shear, with loads parallel to the joint - very strong, 20 to 30 lbf/in^2 even in creep over several hours with no failure.
As an addendum, you can thin silicone with any of the light solvents (zylene is often suggested) like cellulose thinners - this will make for a pourable and more easily mixed foaming mix
possibly a good way of making the bow of a shrunk bottle foooty?
andrew
“foamed with my own importance”
Yesterday I tried a technique which is probably called stitch welding. It is easy to do, and is quite strong. A pair of 3-liter ginger ale bottles were attached with this method. A series of spot-welds is made along the seam. It has the drawback of leaving a set of thru-holes, which must be filled, as well as a set of small protrusions at each weld, which must be trimmed off.
The method is described below:
Tools - a soldering-iron type of tool designed for cutting sail fabric (it probably has a lower tip temperature than a normal soldering iron), with a sharp pointed tip.
Operation - the two pieces must overlap, and be held in close contact (they were temporarily taped together); the iron is poked through both pieces and withdrawn quickly. It is necessary to make sure that the pieces are lying flat together before proceeding to the next stitch. Each weld will leave a small hole (perhaps a skilled operator could do it without making a hole), and a little plastic will ooze outward, which must later be trimmed off.
I have done this from the outside of the bottles; perhaps the resulting deformity would be less if done from the inside (by a very small person). The welding was done at the curved shoulder of the inner bottle. I was concerned that some wrinkling might occur because of the high residual stress in this region, but it did not happen.
The overall seam is quite strong, but not water-tight, so it must be caulked afterward.
CORRECTION
While playing with it today, all the welds popped loose when I twisted the forward section to get a sharp prow shape. So maybe this isn’t such a good idea after all.
Yesterday I found a new product in the drug store. It is a 2-sided tape, called Uglue, which comes in several forms (individual pieces, or a roll about an inch wide).
Two sections of bottle were prepared by sanding with a fine grit, then cleaning with an alcohol swab. The tape was applied, and allowed to sit for a day. It appears to work, and survives significant twisting. The adhesive is quite agressive, and when I tried to peel it, it was obvious that it was adhering to the surfaces, and the adhesive was stretching. A stretchy adhesive is the cure for peeling, since it spreads out the force; it remains to be seen whether this adhesive will remain stretchy through its life.
One obvious disadvantage: the adhesive is about 0.020 inches (0.5 mm)thick, which will create a discontinuity. However, this might not be too terrible, since my 3-Liter Torpedo has a similar discontinuity at the aft end of its false prow (partially taped, not glued), and is still competitive with the local V-12’s.
I havn’t come across uglue, but adhesive names don’t cross the atlantic well.
Like you I don’t worry too much about a step in a hull, so long as is in the trailing direction,
Its timely that you have raised this now, as I have a cunning plan to get moulding again in the near future. I now believe that I will be able to fit two plugs into a pop bottle and get two hulls per shrink!
I have used sail reinforcement tape as part of the structure of my hull and deck of my bottle boats, and have found it very difficult to remove (I probably made modifications every few weeks in the past year). When it is removed, it leaves a residue on the bottle, which implies reasonably good adhesion. The Uglue may have a similar adhesive.
Another factor in peeling, is that the stress is concentrated along the peel line. A relatively thick adhesive layer will spread the stress a little. So the Uglue may have hit the sweet spot for our purpose.
In the past, I had tried 2-sided sail tape, which worked for a while before it peeled. This may have a similar adhesive, but perhaps not thick enough for our purpose. The sail tape is also relatively narrow (1/4 inch), which increases the peeling stress.
Reading through past posts on this thread, there have been some other 2-sided tapes suggested, but I don’t think any of them had actually been tested. So there may be other similar useful items.
