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[raflaunches]

Hi everyone


I don’t know if it’s been asked before but I’ll ask anyway...


How long does plastic hulls/sheet retain its flexibility?


To explain my enquiry, today I handed over a model I was asked to build but the kit was rather old by plastic kit standards (it was only a year younger than me! 34) by a company I know of called Billings. To be honest it was a kit I had never heard of and research on the internet revealed very little information. The kit in question was the Hover Port Of Rotterdam manufactured in 1985. The kit owner liked the look of it but didn’t have the skill or knowledge to build it to a standard he was happy with. Speaking to other club members we did have doubts whether the hover part of it would work due it’s design but we went with it and modified it with a more powerful motor, a bigger pulley wheel, and a more powerful battery (a 11.1v LiPo). Due to the lake at Wicksteed being flooded today we couldn’t test it but he took it home and put in the bath to see if the mods actually worked. He sent me a message with both good news and bad news- the model actually works quite well but it leaks (about a teacup full every 3 minutes). When I tested it a few weeks back with the unmodified model it didn’t leak but didn’t hover either! We put the new mods in at the park (we didn’t know the lake was flooded until we got there!) and turned it on and the model was pumping out a lot of air compared to the previous setup but it vibrated a lot.
When I attached the air blower parts to the hull I used plenty of glue and ensured there was plenty squished around them as I knew that could be a potential entry of water into the hull so I was rather surprised to hear that was leaking around them. My current theory is plastic fatigue but the kit was kept inside the box by the looks of things- my reasoning was that the injection moulded plastic parts when I removed them from the sprues were actually quite brittle and I often had to carry out repairs when constructing the model. I’ve seen plastic sheet become brittle when exposed to sunlight but does plastic become brittle if kept in its box? It’s the only thing I can think of that would possibly cause this and the age of the particular model kit has made me wonder if this is the case or not.
Does anyone know how long a plastic hull or parts last without any form of protection?

[Colin Bishop]

Interesting point Nick.

Some years ago I read an article published in the USA concerning the longevity of styrene for model making. I think it was something to do with whether models constructed in plastic were suitable as long term museum exhibits - the conclusion was that they are not. From this and some other information I have gathered over the years it would seem that:

Styrene and similar plastics are affected by UV light if not protected by paint or coating and will go brittle in a relatively short time.

Some early plasticard was prone to 'self destruct' although I have some on a model made back in the 80s which is still OK although the model hasn't been sailed for 35 years! I dare not touch it...

Modern plasticard is a lot more chemically stable than earlier versions.

Most styrene type plastics will ultimately self destruct and crumble due to their chemical hydrocarbon makeup.

The most durable material appears to be a natural one - wood in a dry climate - see pic below.

Colin

[raflaunches]

Hi Colin


That’s what I’m worried about because of the era of the model kit. The injection moulded parts for the mast were so fragile that that I snapped the supporting structure several times with the most minor of touches.
The hull was incredibly thin and twisted very easily, and thinking about now it could have introduced micro cracks at the weak points in the hull when using the kit parts to stiffen it up. Looking through some of the parts in the kit the clear plastic sheet has yellowed, which is why I decided not to use it on the build and go with the decals instead. I’ve just tried it and it shattered which seems to confirm that plastic parts even kept in its original packaging will deteriorate. As you say it must be the 1980s plastic chemical make up compared to modern plastics.
I’m thinking of repairing the hull by using epoxy resin and a fabric gauze type matting to reinforce the plastic but maintain some form of flexibility to dampen out the vibration.
I hope...

[phil_parker]

With my pedant hat on, can I point out that "Plastikard", note the K, is a specific product made by Slater's and not a pure styrene (I think there is some rubber in it). The correct term is plastic card if it's not the Slater's product.

The only reason I'm being pedantic is that there is a tendency for modellers to treat all plastic sheet as though it's the same - it isn't. Vac-formed hulls are very likely to be made form ABS rather than styrene. It's going to be important when comparing the long-life of one material against others.

[RST]

Hmm, I'm not sure if "rubber" is compatable with styrene constituents but I would agree totally there are different characteristics from different suppliers.  Even if it's extruded or rolled makes a difference not all PS is the same -just like EPS/XPS!  I would also argue there's probably as much PS hulls out there as ABS (aren't Billings known for ABS though?).


I'm envious of your sidewall hovercraft though.  Saw one on Ebay recently but I don't buy on auction even though I've wanted one for years!

Personally I notice that some folk who model in plastic would leve a white plastic component unpainted, whereas others (like me) would still prime it and paint it white.  I haven't had much problems over 30 years but then it's all painted and not left sat in the sun.

...There will be some variation in production runs though.  I know myself sculpting some PS sheet with a heat gun for something for work last week, when you het it like in vac-forming, it changes properties.  I'm sure I took my sheet past the glass transition point last weekend -but don't care, I just wanted to impression something.

There's folk on RC groups advocate reinforcing vac-formed hulls with epoxy and matting.  I don't see the point over the full thing personally.  Use doublers and solvent in the damaged area, or thoroughly rough-up, de-grease and use some adhesive and reinforcing.

Rich

[RST]

Apologies only:  Looking bck (not able to edit my posts) -I found out tonight a couple of buttons on my laptop are not working properly.  "a" especially, I'm getting tired re-editing things to correct LoL!