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Gifferboy

Yellow Vacuforms

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I have a 1/48 Classic Airframes Boulton Paul Defiant in my stash, which I was thinking of starting next. However, when I took a look amongst the box contents, I noticed that the vacuform canopies have got a yellow tint to them.

I have done a search on other forums, but I haven't come across any solutions to 'fix' the problem, other than reform a new one and I don't have any experience or confidence in doing this. There aren't any after market canopies for this kit either.

Has anyone found any secret 'cleaning' methods or an alternative canopy set that could be modified to fit?

Many Thanks

Sean

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I have a 1/48 Classic Airframes Boulton Paul Defiant in my stash, which I was thinking of starting next. However, when I took a look amongst the box contents, I noticed that the vacuform canopies have got a yellow tint to them.

I have done a search on other forums, but I haven't come across any solutions to 'fix' the problem, other than reform a new one and I don't have any experience or confidence in doing this. There aren't any after market canopies for this kit either.

Has anyone found any secret 'cleaning' methods or an alternative canopy set that could be modified to fit?

Many Thanks

Sean

Hi Sean

sounds like the original issue of the CA Kit, (see here about the differences http://kits.kitreview.com/defiantreviewse_1.htm) if it's the one with the sharkmouth plane it is...

You could try the yellowing decal fix, leave in sunlight for a few weeks, which is not going to be much use if you are in the UK at this time of year.

Smash moulding is a lot easier than you might think, look it up or ask here for details,

The moulds can be easily made from the existing parts, by filling and then filling with say, Milliput, adding a handle as well. (but suggest adding some form of release agent to existing canopies)

These will then make your moulds to make new canopy parts. This at least will not destroy the existing yellowed ones.

You have nothing to lose doing this, and a lot to gain, and as you are making a new part, you can keep trying until you succeed, or run out of clear sheet, get bored or burn your fingers... :)

HTH

T

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Hi Sean

sounds like the original issue of the CA Kit, (see here about the differences http://kits.kitreview.com/defiantreviewse_1.htm) if it's the one with the sharkmouth plane it is...

You could try the yellowing decal fix, leave in sunlight for a few weeks, which is not going to be much use if you are in the UK at this time of year.

Smash moulding is a lot easier than you might think, look it up or ask here for details,

The moulds can be easily made from the existing parts, by filling and then filling with say, Milliput, adding a handle as well. (but suggest adding some form of release agent to existing canopies)

These will then make your moulds to make new canopy parts. This at least will not destroy the existing yellowed ones.

You have nothing to lose doing this, and a lot to gain, and as you are making a new part, you can keep trying until you succeed, or run out of clear sheet, get bored or burn your fingers... :)

HTH

T

Thanks Troy

You're right, it is the original issue with the slightly fatter fuselage.

If I am to try smash molding, what thickness of sheet do you normally use? Also, will it be ok applying to Vacform without the heat deforming the original?

Any advice would be gratefully received.

Thanks

Sean

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I might be able to help here.

I think somewhere in my stash i have the old Tommy Atkins Vacform Defiant which has a vac canopy & turret.

Let me check , if i have it , if i have your wellcome to it.

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This is interesting topic as I have similar problems with canopies from other manufacturers.

So, is this inevitable process that will sooner or later hit all vacuformed canopies?

And is there a way to fix the existing canopy, without making the new one?

I am asking this because it is not always easy to remove canopy from the assembled model

(for example on biplane with enclosed canopy).

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Thanks Troy

If I am to try smash molding, what thickness of sheet do you normally use? Also, will it be ok applying to Vacform without the heat deforming the original?

Any advice would be gratefully received.

Thanks

Sean

I'm definitely no expert on this but I've just smash moulded a new canopy for my Boulton Paul PIIIa this morning.

I didn't have an original pattern to go from (I picked this kit up from the SMW kit-swap and it had no canopy) so I had to shape a new solid plastic part that looked and fitted as required, just slightly smaller than required to make up for the thickness of the plastic I was going to make the canopy from.

As for thickness of the plastic, this was just a guess as I was only able to use stuff I had to hand. As it happens I used some plastic packing from the Tom-Tom sat-nav I bought a few years ago. I think the plastic type is PET and it's fairly thin.

All I did was to mount the solid shape on a sturdy stick (a screw driver in this case) and gave it to the Mrs to hold steady. I then gently warmed up the thin plastic over the gas hob on low and just as you can see it start to sag, I put it over the and pulled it down over the solid shape and held it until it cooled (only a few seconds or so) Then I cut away the excess and removed the solid shape. After a bit of careful trimming I had a perfect canopy.

I guess what you would need to do is make a cast of the inside of your existing yellowing canopy, This should be the right size, more or less, depending on what thickness of clear plastic you use. You can't really use your existing vac canopy directly to smash mould over as it would be a bit too floppy and difficult to hold. You might be able to fill the inside of your yellow canopy to make it more solid and mountable but I would have though that this would make your new part slightly oversize.

What you can use to make the cast from I don't really know; it would have to be something that you can easily release from your yellow canopy and that is quite solid and you can mount somehow to enable you to pull your soft plastic over.

Hope this helps, good luck - I wish we could find a way to fix the originals!

EDIT: a link to a site showing plunge (smash) moulding in words and pictures

Karl

Edited by Karl

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So, is this inevitable process that will sooner or later hit all vacuformed canopies?

No, canopies made from PETG are OK - this is the material used by Falcon for their excellent canopies. Unfortunately, most older vacs use a less stable plastic which is prone to yellowing.

And is there a way to fix the existing canopy, without making the new one?

Not that I've ever discovered,

Cheers,

Bill.

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I might be able to help here.

I think somewhere in my stash i have the old Tommy Atkins Vacform Defiant which has a vac canopy & turret.

Let me check , if i have it , if i have your wellcome to it.

Hi Keith

If you do manage to find the spare canopy and turret, please let me know.

I can send you a box and P+P to return them, plus any cost that you would want for them.

Thanks

Sean

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I've got a few vac form canopies in the stash that have yellowed, however I built several models in the 90's using the Falcon sets and these don't appear to have yellowed at all, still look good.

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Which canopies other than Falcon's are yellowing-proof?

I know that canopies from Planet models go yellow for sure, as this happened on my built and unbuilt kits from them.

Also, which materials are safe against yellowing for use in home-making of canopies?

Thanks!

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I have a 1/48 Classic Airframes Boulton Paul Defiant in my stash, which I was thinking of starting next. However, when I took a look amongst the box contents, I noticed that the vacuform canopies have got a yellow tint to them.

Try leaving them in very bright sunlight, this works for decals, even if applied to models already.

worth a go

Dave

Edited by zero

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Leaving them in bright sunlight does not work. It is an irreversible change in the material. I have a stack of NA.16 variants with unusable canopies, all different from the later Texan/Harvard ones.

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Fascinating. I think it should be pointed out that the vacform transparencies are not the ABS used on Amigas, and I suspect that bromine plays no part in this yellowing. Like the man said, being an industrial chemist helps, and I'm definitely not. However, as a simple test buying a pot of hydrogen peroxide and dunking a canopy into it for minutes? hours? shouldn't be too difficult. Do tell us all. If it works, It'll be a great boost.

Like most aircraft enthusiasts, I tend to think of the effects of high-strength HP as in Me163 explosions, not in terms of the low strength stuff that girls put on their hair.

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Just a note for those attempting to create their own vacform canopies . A friend of mine is a vacform manufacturer and he told me that the first attempts or first "pressings" from a mould are rarely a success . It seems the moulds need to "warm up" . So if your early attempts don't work well just keep trying because they do improve .

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I have a 1/48 Classic Airframes Boulton Paul Defiant in my stash, which I was thinking of starting next. However, when I took a look amongst the box contents, I noticed that the vacuform canopies have got a yellow tint to them.

I have done a search on other forums, but I haven't come across any solutions to 'fix' the problem, other than reform a new one and I don't have any experience or confidence in doing this. There aren't any after market canopies for this kit either.

Has anyone found any secret 'cleaning' methods or an alternative canopy set that could be modified to fit?

Many Thanks

Sean

hi Sean,

You could remake the mould from the vac form you have, but it requires a bit of work!

If you create some walls to the flat area of the vac form using styrene and glue it to the edges and fill the vac form [inside face] with car body filler ensuring no bubbles or gaps are present, once set break off the vac form and then glue the plug you have created to a block of wood. If you take this to anyone who does vac forming it will be a really quick little job for them.

regards

Graham

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I think as they age and yellow they also go brittle as I have found out on some of my quarter scale gliders, that's 1/4 scale, not 1/48.

I have a large 2 seat ASK 21 where the canopy has yellowed quite badly and needs replacing, only problem is it is too large for me to do.

Andrew

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Posted (edited)
On ‎01‎/‎01‎/‎2011 at 15:49, MarkoZG said:

Which canopies other than Falcon's are yellowing-proof?

I know that canopies from Planet models go yellow for sure, as this happened on my built and unbuilt kits from them.

Also, which materials are safe against yellowing for use in home-making of canopies?

Thanks!

 

Like others here, I've read that this yellowing is irreversible and a result of the formulation of plastic used by the manufacturer.

 

Taking Marko's specific point above about Planet Models, this applies to some, but not all. I have a Planet 1/48 Ju388K/L with very badly yellowed vac parts, but also a Planet He 1077 Julia where the parts have remained as clear as the date they were purchased. Hopefully, they changed the formulation of the Vac plastic they use?

 

I must also add positive feedback for the good folks at Special Hobby/CMK/Planet, who supplied me with replacement transparencies for my kit Free of Charge earlier this year - thanks chaps!

 

SD

 

 

 

 

 

 

 

 

 

 

Edited by SafetyDad

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Hhhhmmm -

I have a 1/48 Czech Model Me. 309 kit that I bought cheaply a year or so ago off a stall at an airshow.  When I came to try to build it I found the vacform canopy to be yellowed. I left it on a windowsill for some weeks and it cleared a little.  Unfortunately I decided to do something else and now I find the canopy is back to yellow.

 

HOWEVER, sun /natural light *did* seem to improve the situation.  Whether it would if a built model is left in such a position I don’t know.  In my case such things are discouraged by SWMBO.

 

Does Czech Model still exist, does anyone know?  I suspect it’s now known under another name.

 

Jonny

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Posted (edited)

I believe the yellowing is due to the break down of fire retatdent releasing bromine into the plastic. The same happens to old plastic computer cases which go yellow. There's nothing you can do with a transparent material that's affected, other than replace it.

 

Edited by 3DStewart
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The main cause of of yellowing in plastics is oxidation, heat and UV light. They cause desaturation and conjugation. When all the available bonds on a carbon atom are occupied by hydrogen atoms it is ‘saturated’. When there are carbon to carbon double bonds, C=C, then the molecule is said to be unsaturated. That is the difference between saturated and unsaturated fats. The formation of these double bonds results in conjugation. Conjugation is simply a chain of alternating double and single bonds like so, C-C=C-C=C-C=C-C=. In conjugated systems the π bonding electrons delocalise. That means that the electrons are no longer associated with a single carbon atom. Delocalised electrons absorb light in the visible spectrum and it is that that leads to the plastic looking yellowish. The colour of many dyes is derived from this mechanism.

 

Most flame retardants are safe but aliphatic bromine compounds are sensitive to heat and UV light and breakdown to release bromine. This accelerates the yellowing process. Some manufacturers add a blue dye to counteract the yellowing.

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