Help needed building a expandable frame for moulds

[SMaund]

What resin are you planning to use? And what thickness?
If its for thin sheet in epoxy, make the biggest size, pour your sheet and cut the sizes you need..... probably easiest

EPDM rubber granules will be put in at a thickness of 4mm and then the wetpour Resin PU binder.

They will be made to the size required upon order, so the frame would be set to the size of sheet the customer would require

Which would be the best base plate to use? Assuming the resin would adhere to plywood, would a sheet of rubber over it be okay?

 

[baldkev]

You'll have to google this to confirm, but i believe its polyethylene that resin wont stick to

 

[Inspector]

HMWP (High-molecular-weight phthalates) like the white stuff cutting boards are made of. Resin doesn't stick to it and resin casting molds are made from it but even then it is advisable to spray the mold with a silicone or PTFE (polytetrafluoroethylene) mold release. It will need a flat support under it as it will sag and you will want to have it perfectly levelled or the resin will flow to even it self to gravity.

Pete

You could get away with a sheet of plywood or MDF that has plastic laminate on both sides and you coat the stuff with mold release.

 

[baldkev]

Hi pete, good points regarding support and levelling.... over here they use the polyethylene sheets for catering areas ( wall cladding ) and its pretty cheap. It could be bonded to ply etc, but i suspect by the time its been used in different sizes and sealed each time, it'll degrade with each use.... silicone doesnt like to stick to it, foil tape works though, but basically resin likes to escape, like water, so it needs sealing well.

 

[SMaund]

HMWP (High-molecular-weight phthalates) like the white stuff cutting boards are made of. Resin doesn't stick to it and resin casting molds are made from it but even then it is advisable to spray the mold with a silicone or PTFE (polytetrafluoroethylene) mold release. It will need a flat support under it as it will sag and you will want to have it perfectly levelled or the resin will flow to even it self to gravity.

Pete

You could get away with a sheet of plywood or MDF that has plastic laminate on both sides and you coat the stuff with mold release.

https://www.bearingboys.co.uk/UHMWPE-/UHMWPE-Natural-Sheet-2000-x-1000-x-5mm--46632-p
Would this be suitable for PU resin applications? Would I still need to use a mold release agent with this? Thank you

What about Polypropylene? Asking because the sheets for the same size are a lot cheaper

 

[Inspector]

My wife makes feather pen blanks cast in tin cured silicone molds using polyester resin. It doesn’t need a mold release. I make the molds and use paste wax to ensure the silicone doesn’t stick to the aluminium and PVC mold I use. The tin cured molds are pink. Blank makers using polyurethane and especially epoxy resins use platinum cured silicone, it’s blue, usually use silicone mold release and have to with epoxy or it pulls off bits of silicone when removed. Many people use the HMWP molds and all recommend mold release. I don’t know of anyone using polypropylene for molds. Most people making river tables make sacrificial molds using melamine or plastic laminate that is paste waxed or they use mold releases.

I suggest you buy some pieces of all the material candidates you may want to use and try them without and with wax or several kinds of mold releases to see what works with the casting materials you are working with. I’ll also suggest that you seek out resin casting forums or Facebook groups as they will have the answers for you. As great as this forum is we don’t have much more than a passing knowledge of resin work.
Best of luck with your enterprise.
Pete

 

[Keith 66]

^^^^^ This, There is no point making a nice mould to then have a stick up & have it fail to release, working in the boatbuilding trade with grp for 40 years I have seen a few & had a few myself, Its an awful feeling when a part sticks & you realise that somethings going to break before it comes out! worst one i did it came out eventually but i had a lot of little repairs to do
One i heard of was a mould for a 26ft fishing boat, they ended up scrapping the new hull & the mould itself at a cost of around 50k (at the time).

 

[Sporky McGuffin]

I've had a slight rethink of my design proposal - instead of the little triangles at the ends, run a flat board all the way along the beam. Then you'll be square in all directions, and you'll have a clamping surface to g-clamp (or similar) the beams to the edge of the base plate no matter the length of the mould.

Again, hopefully that makes sense...