Flexible poylmers

[bdizzy]

Hey folks,

I'm looking to produce flexible household mouldings. I've got the equipment to make moulds from various types of wood (by creating 16' 'negatives' from my regular mouldings). I would like to be able to pour the resin into the mould, have it set up slightly, and remove it in order to bend it to the final shape before it fully cures. Does anyone have any suggestions on how to go about this and what products to use?

Thanks,
Mike

 

[patprimmer]

I don't like to sound negative, but it sounds to me like you are about to jump in way over your head.

Wood is not normally a suitable material for moulds unless you intend to thermo form.

What do you mean by flexible.

You say 16'' Do you mean 16 inches.

To catch the cure in a state where it is not to sticky to handle and rubbery enough to both handle without pulling it out of shape entirely, but still form into shape will be a challenge.

How complicated is the shape.

How will you get it to release from a wood mould.





Regards

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[MikeHalloran]

I'm pretty sure he means 16 feet.

Here in The Colonies, it's getting hard to find actual wood mouldings anymore, even the ones finger- jointed from short sticks. The big box lumberyards stock plastic mouldings that I think are made of polystyrene foam, with a skin that looks like ABS. It's a bit more limber than wood. Most of it will bend to a 2 foot radius the easy way without heat. It's easy to nail, but it doesn't hold nails well. Anyway, that crap is flexible enough to follow any wall I've ever seen. So if he's talking about just conforming to a warped wall, I don't see a market for a b-staged product.

If he's thinking about just forming it around corners, e.g. to zero radius, Poisson's Ratio works against the idea. I.e., a molding of any thickness, folded over a sharp corner, is going to bulge in a rather ugly way.




Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

OK

Now I see what he is getting at.

He wants to produce sheets of plastic to use in place of plywood panelling that he can bend into place for corners or to conform to irregularities in the wall.

That can possibly be done with sheet plastic. It will be expensive.

With some practice, sheet plastic can be formed into place with a hot air gun or strip heaters and a bending jig for tight straight bends. Acrylic, ABS or PVC can be used.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bdizzy]

Sorry for the vague description. I probably am jumping in to this head first however that is something that really must be done when reseaching new ways to do things. This has been done before, in many different configurations. Usually using a polymer resin of some sort. I'll attach a few pictures of what i'm trying to accomplish. I realize I may have to build a form that is made of a more suitable substance, does anyone have any suggestions? I'd like to be able to create a "wood grain" in the finished product and be able to apply a stain or paint to it. These moulding will be used to both curve along a wall and curve around window arches in order to create a solid looking moulding. Thanks for the suggestions so far!

Another note, I've seen this process done before however it was brief. The resin was poured into a form and let set up, and then they proceeded to release the mould and lay it out on the floor where they slowly pulled it around a teplate that was cut to match the window. (Something like a 12"r).

This product would go over very well in my state but no one wants to wait the 4-6 weeks it takes to ship from a current supplier, so I usually charge them an arm and a leg to turn the arches from MDF, which is time consuming and, well, MDF is not a pleasure to work with.

Pics:

http://www.flextrim.com/images/flexprod.jpg

http://www.corallight.com/images/shop/items/Flex.jpg

http://flexibletrim.com/images/Products/photo2.jpg

Thanks again,
Mike

 

[btrueblood]

The foam trim that Mike mentions is (I think) Reaction-Injection Molded (RIM) polyurethane foam (urethane resin with isocyanurate blowing agent?), in a fairly stiff and brittle formulation similar to insulation foam. The foam self-skins, IIRC. It will bend a bit, then snaps.

There are urethane and urethane foam systems with much greater flexibility. Suggest you google, or search on matweb for urethane and urethane foams, and talk to a supplier of these. Pat can probably give you a few ideas too. As pointed out by other posters, there is a limit to how far any material will bend without distorting the heck out of the trim shape.

The wood "forms" you are talking about will need a lot of reinforcement if you use them for a foam molding system, as these usually require a significant amount of internal mold pressure to work properly. Think many, many C-clamps and big backing boards.

A local company I interviewed with, Heat-Con Composites, makes a line of composite-curing electric "blanket" heaters and controllers. One use for these they are developing is to heat polyethylene-composite "boards" to allow them to be formed for curved decks/steps/stairs. This won't work with cured urethane foams, but might work with other thermoformed polymers/elastomers.

 

[MikeHalloran]

OR, if you're now turning window arches from MDF, you might look into getting a 3-axis CNC mill, which could make the arches, and attached tangent sections if you like, unattended.



Mike Halloran
Pembroke Pines, FL, USA

 

[bdizzy]

Thanks for the wealth of information this far.

Another thing that may spark some ideas...

When I saw these manufactured, first, the worker took a 2-part mixture and simply poured it into a 16 foot mold that was open along the top. He waited as it chemically heated and cured. Then he realeased it from the mold, still hot, and layed it on the ground. There was very little smell eminating. While on the ground, he slowly bend it around the template and blocked it as certain points to retain the shape. The material, when fully cured, it quite flexible. It can be nailed, filled, painted or stained in order to look just like the wood it is replacing.

I wish I knew the chemical he was using. It seems to be a gaurded secret. I am still contacting numerous suppliers in order to find a solution.

Thank you all for your continuing contributions.

Sincerely,
Mike