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PostPosted: Fri Jul 26, 2019 9:54 am 
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I believe many have anchored a cast resin hull to avoid the possibility of a "memory" return to the original warped shape. I have corrected a wl hull using a very hot water soaking method and will share the technique I used but am reluctant to begin kit construction until I am sure of the apparent success of my method.

So here are my questions:

1, Who has experienced a return to the original warped shape once the hull has cooled (assuming heat was used)? What method was used to attempt to initially correct the warping and was another method used to finally correct the warping?

2. Who has had a success in correcting the problem using any technique and not experienced a memory return to the original warped condition over time and further has not anchored the hull to hold the corrected hull flat?

3. Who has not been able to correct the problem at all using any technique and what was the technique used and the probable reason it did not work?

I am sure there are answers out there but if you are reluctant to share yours on an open post please send me a PM and I will keep your response confidential.

Thanks
Steve


Last edited by Timmy C on Sat Jul 27, 2019 2:53 pm, edited 1 time in total.
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PostPosted: Fri Jul 26, 2019 10:12 am 
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The few time I've had to correct resin parts worked out well for me. Dip the part into boiling water for about 10 sec (not with your fingers, though!), or until you can straighten the part. Thinly cast parts will require less time than large solid pieces. When straightened, plunge or soak immediately into cold water and leave there for a few minutes until the resin has completely cooled and set. Resin doesn't have the memory that styrene has and so will keep it's new shape. I haven't had to straighten ships' hulls, but I think you would have to fasten it to a piece of flat metal to ensure a flat straight shape.
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PostPosted: Fri Jul 26, 2019 11:22 am 
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I had experienced that recently several times with resin hulls.

As far as I understand it, resin cannot be reshaped by heat (because of the crosslinking of the polymers), i.e. it is a thermoset polymer.

If a hull is warped, there are two options:

it was warped during removal of the hull from the mould, i.e. the resin was completely cured only after leaving the mould. In this case it should be impossible to correct the hull and the producer should offer a replacement hull. The wrong form is "memorised".

it was warped e.g. by severe temperature stress during transport. In this case it is possible to cure it by heat. The correct form is "memorised".

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PostPosted: Fri Jul 26, 2019 1:00 pm 
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maxim wrote:
I had experienced that recently several times with resin hulls.

As far as I understand it, resin cannot be reshaped by heat (because of the crosslinking of the polymers), i.e. it is a thermoset polymer.

If a hull is warped, there are two options:

it was warped during removal of the hull from the mould, i.e. the resin was completely cured only after leaving the mould. In this case it should be impossible to correct the hull and the producer should offer a replacement hull. The wrong form is "memorised".

it was warped e.g. by severe temperature stress during transport. In this case it is possible to cure it by heat. The correct form is "memorised".


Maxim

Were you able to correct the hulls using heat and if so what technique did you use?

Steve


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PostPosted: Sat Jul 27, 2019 1:15 am 
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I was able to correct some hulls using heat, but not others - see the for me most likely explanation why above.

I put them into boiling water, then fix them to a flat surface and let them cool down slowly.

Fast cooling in a freezer appears to be dangerous, because it causes massive stress to the material.

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PostPosted: Sat Jul 27, 2019 2:08 am 
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Quote:
As far as I understand it, resin cannot be reshaped by heat (because of the crosslinking of the polymers), i.e. it is a thermoset polymer.


I'm afraid it is not that simple: "resin" may refer to rather various plastics, for instance polyurethane (PUR). The buff colored resin in many kits seems to be PUR in most cases. As this PUR is thermoplastic and not thermosetting, it may be formed vary well with heat. While others like grey resin may not.

So there is no final answer that works for all resin kits, depending on the material in case.

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PostPosted: Sat Jul 27, 2019 2:37 am 
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Polyurethane is used for similar casting methods, true, they are often called resin kits.

My comment refers to kits, which I think are made from thermosetting resins.

I cannot remember to have had a warped polyurethane hull.

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PostPosted: Sat Jul 27, 2019 4:47 am 
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My last attempts to correct some hulls:

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Yangwu, Fupo,and Volta, the first two Oceanmoon kits, the last one Doggy Industries. All from the 1884 Sino-French War.

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PostPosted: Sat Jul 27, 2019 6:50 am 
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In regards to most resins used by cottage industry manufacturers,

First, cured resin doesn't melt, it will get soft, but it will catch on fire before it melts at approx 220f

Second, resin warps due to uneven cooling. This can be caused by a number of factors like being pulled from a mold too soon or a breeze from a fan.

Third, you don't need water to transfer heat. It doesn't hurt, but it doesn't help much either.

Fourth, putting a large thick warm piece in a freezer is risking uneven cooling. It's not necessary.

Fifth, resin does not retain a 'memory'.

Sixth, different colours are simply dyes added to the resin. Color doesn't change how the resin reacts.

So, keep it simple.

Secure your piece to a flat wood board. Use screws in the bottom, or clamps on flat areas. Or weights. Avoid details and edges. Use only enough pressure to flatten the item. If you feel it takes too much pressure, do it in stages. Flatten a little, then do it again flattening a little more.

Do not flatten your piece after its heated. Clamps and weights will be cold and could cause uneven cooling.

Place in cold oven.
Place on rack or sheet, it doesn't matter.
Turn oven on to 130-160f it doesn't matter if it's gas or electric. The temp matters.
Leave in for 30-40min after it is at temperature.
Remove and place somewhere it won't be touched or be in a breeze. I usually just leave on the stove.
Walk away.
Next morning, remove from board.
If happy with results, resume building.
If not, do it again.
It will not warp again unless exposed to high temps and uneven cooling.
If you have super glued any parts, the glue will most likely be crumbly and have to be scraped off. SG.doesnt like heat. The part will most likely come of with a little pressure. I work a knife blade into the joint and give a little twist.

That's it.
Good luck!

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Last edited by Admhawk on Mon Jul 29, 2019 7:35 pm, edited 1 time in total.

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PostPosted: Sat Jul 27, 2019 2:44 pm 
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Admhawk's answer should be saved in the Tips section

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PostPosted: Sun Jul 28, 2019 1:59 am 
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@ Admhawk: thank you very much for your detailed explanation!

I would have two questions:
a) how do you clean the oven afterwards? Resin and food are not really compatible and some resins smell quite strongly even after a long time.

b) You wrote that resin has no "memory". A thermoplastic as polystyrene has clearly no "memory", it can be reformed by heat to any form, because there is no cross-linking between the polymers.

In contrast, in resins the individual polymers are cross-linked. They cannot be reformed into any form. I experienced very often that bended small parts (e.g. missiles, cranes, parts of masts) themselves went back into the correct form after a short time in hot water. I think that is referred to as the "memory" of the correct form.

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PostPosted: Mon Jul 29, 2019 7:35 pm 
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Hi Maxim, Sorry for the delay in answering, my computer decided it didn't want to listen to me anymore. I finally convinced it otherwise.

To answer your first question, I have run across some foul smelling resins. Fortunately, none required oven treatment. Anything I've put in the oven hasn't caused much odor. If it did, I'd probably run a clean cycle to burn it out. Any oven cleaner I've smelled is much worse than most resins.

As far as memory goes, I'm not a chemist, but this is what I've learned. (Full Disclosure, Some of the fancier words/sentences have been plagiarized)

There may be many resins that exhibit Memory traits. However, I don’t believe many in our hobby do.

Crosslink density varies depending on the monomer or prepolymer mix, and the mechanism of crosslinking. The higher the crosslink density and aromatic (organic compound) content of a thermoset polymer, the higher the resistance to heat degradation and chemical attack. Mechanical strength and hardness also improve with crosslink density, although at the expense of brittleness. They normally decompose before melting.

The degree of crosslinking and resulting physical type (elastomer or plastic) is adjusted from the molecular weight and functionality of isocyanate resins, prepolymers, and the exact combinations of diols, triols and polyols selected, with the rate of reaction being strongly influenced by catalysts and inhibitors.

Thermosetting polymer mixtures based on thermosetting resin monomers and pre-polymers can be formulated and applied and processed in a variety of ways to create distinctive cured properties.

Conventional thermoset plastics or elastomers cannot be melted and re-shaped after they are cured. However, Some thermoset polyurethanes have transient properties, which allow moderate reforming. Some hard, plastic thermosets may undergo permanent or plastic deformation under load. Most Formulas used in our hobby undergo permanent deformation when heated and under load.

One thing to keep in mind, there are so many formulas out there that someone might use a different kind of resin than we are used to. One that may not deform under heat or might retain a strong memory.

So to sum it up, The better resins used are formulated in such a way to allow a bit of reforming. Heating and cooling need to be done slowly for best results. And finally, there are many variables that can interfere and cause issues, but some people are just luckier than others. :smallsmile:

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