Thermoplastic Construction

This thread is to discuss thermoplastic boat construction.

Thermoplastics are plastics that can be melted or heat formed. In contrast typical epoxies and styrenated resins are themosetting plastics. Once "formed" or cured they cannot be reshaped.

Thermoplastics are formed in processes such as rotomoulding, VARTM and oven forming. Some companies can provide standard product that the builder can use to build boats. This is like buying plywood. If the builder has a suitable oven, an air oven that can operate up to 250degC, they could build parts using standard vacuum bag process and buying polypropylene (PP) or PET material which is interleaved with glass or carbon. or they can buy cloth such as Twintex which has the plastic mingled with the glas, ready for processing.

Simon has a couple of questions that I shall answer here.

1) Crane Composites, no you will have to continue the search if Crane are not responding
2) Yes you need to build an oven as big as you require or like crane use heated rollers for fabrication. I recommend a vacuum approach which merans batch manufacture.
3) Yes this is done with theroplastics and thermoset sandwich construction
4) You would need to build a lap joint. The joint would have a batton or strip behind the joint. More sophisticated is to build panels with a joggle in them so the joint is flush and the strap is not required. Look for typical sheet metal joggle joints as examples. Epoxies, polyurethanes and methacrylates can be used to for the join, speak to adhesive suppliers about the base materials and they will have several structural adhesives suitable.

Regards Peter

 

To whom is interested:

This thread is continuation of a thread in the metal department,
( http://www.boatdesign.net/forums/showthread.php?t=20801 )
where I was asking for alternatives to aluminium surfaces that will have similar or even better qualities like abrasion-resistance, strength, corrosion resistance, low maintenance, no painting and fairing.
Peter has provided the input to look at thermoplastics, as he has experience with the use of it.

Apparently they top the aluminium's qualities and are even lighter.

One option is to produce thermoplastic sheets that can be glued onto the hull to form a surface.

The other option would be to melt fibers with thermoplastics to produce a thermoplastic laminate with any fiber you choose, like carbon, Kevlar, glass, etc.

Both ways mean that you have to bake the thermoplastics yourself in a oven.

I was looking around the web a bit and have found a site that was describing
Continuous Fiber Reinforced Thermoplastic Composites Panels

http://www.cranecomposites.com/zenicon.asp

It is a common term and Crane Composites is selling a ready thermoplastic laminate sheet that is 2,6m wide and up to 150m long, with various specifications.

Under:

http://www.cranecomposites.com/pdf/6881_zen_tech.pdf

you will find an example of the laminates properties

I would be interested to find out if the below described solution is doable, a progress and cost-effective.

Building large sandwich panels that could be used for building methods like
Kelsall's and Hugh's or for hard chined hulls. These panels would be in one full size so no need for scarfing or joining.

The thermoplastic composites can be glued to the core on both sides.
This would eliminate the need of touching any fibers and laminating several layers. Just put three layers together and that is it. The surface would be fair, without the need to paint.

The following issues come to my mind.

1. I have no idea how costly the panels are and if they are appropriate for this kind of use. I do not know about the surface quality. Crane Composites has not answered yet. What are the alternatives? Peter suggests batch building smaller panels and joining them together. My first thought is that I want an even and homogeneous surface on the outside without visible joints. Is this make-able with several panels joined together?

2. As the panels are 2.6m wide, how can they be joined in the case of chined hulls. Peter has suggested joggle or lap joints. Maybe there is a way to weld the panels together.

What do you think? Is this a possible solution in composite boatbuilding and would satisfy my wish for an alternative to aluminium boatbuilding.

I think that it smells like an interesting technology although I have very little knowledge about it.

Simon

 

I thought that I would share a bit of the scale model project I'm working on.

I looked at aluminum coated corrugated plastic for my hovercaft hull (floats like a boat with engine/fan off) but it was too heavy and expensive, so I am using the cheap non-laminated corrugated plastic (sign board).

Heat gun bending plastic (for hull): test sample


This is a very crude experiment, but I now have a 4-1/2 foot long model. I'm not posting it until I get some testing done, and I still have to install the motors, fans, batteries and RC gear.
..............................................................

Here is another thermo-product which some people may be interested in. It was first posted in the boatdesign.net forum for use as a possible sliding hatch material.

Kydex
http://www.kydex.com/default.asp

........................................

http://www.kydex.com/applications_miscellaneous.asp

Illuminated signs, somehow one of the more interesing uses.
http://www.kydex.com/applications_signagehousings.asp

 

I have built hulls using Twintex, I am very impressed, they are incredibly tough.

The down side is nothing will stick to them so you have to do everything in one shot. And you can't stick panels together.

The most widely used thermoplastic for hulls would be Royalex, which is quite common in open canoes.

Gareth

 

Gareth:

how did you use Twintex in your hull construction? What kind of finish?
Do you think that it could be use for larger hulls and how would you propose to set it up in a sandwich construction?



kach22i:

Kydex seems to have interesting surface properties, it is very tough and has a high notch resistancy. As they are prefabricated panels they need to be glued to a structural underground like a laminate.

Royalex: I have not found any manufacturers website. The references I have found were by canoe producers. It seems to a all-in-one composite that is "ripens" in a oven.


What kind of sandwich structure could be defined with these materials?
Inside skin:?
Core:?
Outside skin:? Twindex
Surface: ? Would it need a seperate surface like kydex?

Simon

 

Hi Grob and Simon,
1) Twintex can be joined together with acrylic, methacrylic and polyurethane structural adhesives, probably more. Speak to any major adhesive supplier and they will provide something suitable for the grade of Twintex. Twintex is available in Polypropylene and PET plastic. I've used a 3M product on melamine and polypropylene sheets which we used for a mould. When we found that the inserts where in the wrong place and had to remove them we destroyed the mould in the attempt. The joints did not fail! The melamine or the PP came off in big chunks. So much for not being able to be bonded! See
http://www.stealth316.com/2-dp8005.htm

2) See
http://www.oldtowncanoe.com/canoes/anatomy/materials/royalex.html

for a discription of Royalex. Its a thermoplastic laminate optimised for vacuum forming. Mainly PVC outer for cosmetics and UV resistance, then ABS inners for structural perfomance. Some canoe manufacturers also get grades that have ABS foam in it to create a lighter structure yet still be vacuum formable. It does not get "ripened!" most plastics need to be dried before they are vac formed. Moisture in the plastic will degrade the surface finish if the plastic has been stored in high humidity. The plastic supplier will provide moisture content specs for the process. Water is a plasticiser in most plastics ie it acts as an internal lubricant. If you dry the plastic too much it will crack when formed.

Regards Peter S

 

Peter,

with ripening of Royalex I meant that that the core will expand and create a foam. Ripen might not be the right word.

I have found some other products that could be interesting:

Honeycomb with thermally fused face sheets in sizes up to 13,6m x 2,75m

http://www.omniapanels.co.uk/thermoplastic_panels_technical.html

and

"Foamed in-situ thermoformable Sandwich"

http://www.fits-technology.com/

I, personally prefer to buy (if not to expensive) panels instead of building them, even if this limits me in hull shapes. I would like to build a boat without too much laminating.

One thing I still did not get: How is Twindex's surface? Does it need additional treatment like painting? Is it just like a raw laminate?

Simon

 

Hi Simon,
The omnipanel looks good. The FIT panel looks to be a low modulus product probably not suitable for hulls. The twintex finish looks just like a laminate, tends to be a bit glosser.

Personally if you want to build a boat but not laminate then you are looking at infusion. You could build flat panels and "cold mould" you could build foam strip plank and infuse. Thermoplastic amatuer construction of boats is in its infancy and you will have to have the right technical and physical resources. Whereas infusing a hull is easy, minimises wet laminating and hugh variety of solutions are available of the shelf. Heres a guy building a triamaran using strip foam/infusion.

http://www.fram.nl/workshop/controlled_vacuum_infusion/cvi.htm

Peter