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'[EE] Need inexpensive mold material'
2012\02\13@225355 by Dwayne Reid

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Good day to all.

Not sure if this is [EE] or [OT] - trying for [EE].

I'm looking for an inexpensive sheet material that I can use for epoxy molds.  I have a product that is an epoxy blob about 1.5" x 1.1" by 0.5" thick.  I need to find a faster way of making these epoxy blobs.

What I'm currently using is a piece of acrylic with a couple of dozen pockets milled in it (all the way through).  I cover the back side with tape (for a seal), place my modules in the proper spots, then pour epoxy and bake in an oven.  The problem occurs when we go to remove the cured epoxy blobs from the form - its time consuming even though we swabbed the sides of the mold with mold-release compound.

What I'd like to explore is using a sacrificial material that I can break away from the epoxy blobs after the epoxy has cured.  This material must be capable of withstanding the about 100C cure temperature in the oven.

I have considered using 1/2" MDF - it machines quickly on a CNC router and 1/2" thick material breaks fairly easily.  But - I'd like to find something a little more fragile if possible.

I expect to have to make several thousand of these units.

Is anyone aware of an inexpensive sheet material that machines easily, can withstand 100C for an hour or so and breaks easily when I need to snap these modules out of the form?

I'm considering some form of high-density foam board but don't really have any idea of what to look for .

Suggestions gratefully accepted.

Many thanks!

dwayne

-- Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2012\02\13@231941 by Spehro Pefhany

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At 10:53 PM 2/13/2012, you wrote:
>Good day to all.
>
>Not sure if this is [EE] or [OT] - trying for [EE].
>
>Is anyone aware of an inexpensive sheet material that machines
>easily, can withstand 100C for an hour or so and breaks easily when I
>need to snap these modules out of the form?
>
>I'm considering some form of high-density foam board but don't really
>have any idea of what to look for .

Maybe "Ultra-machinable" polyurethane foam. McMaster carries it, for
example. Price varies greatly with density (0.04/in^2 to 0.12/in^2).

Have you considered re-usable flexible silicone molds?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2012\02\13@232637 by John Gardner

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If you're just milling a slot in the acrylic, try a bit of taper.
Very smooth surfaces help too.

If it works have your tool grinder modify an appropriate end
mill so you can bang out the slots.

Another ploy is to make the mold in pieces, fastened together
for the pour.

Teflon molds? Not much sticks to that stuff...Pricey, though.

Jac

2012\02\13@232939 by PICdude

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Could you use a supported latex mold?  It would be re-usable too.

Also, do you have to cure the epoxy in an oven?  Instead, couldn't you  add UV-cure additives and cure with UV light?

Cheers,
-Neil.



Quoting Dwayne Reid <dwaynerspamKILLspamplanet.eon.net>:

{Quote hidden}

>

2012\02\13@232942 by John Gardner

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....re-usable flexible silicone molds?

That's a good idea - Bet it'll work.

Jac

2012\02\14@022213 by IVP

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> Could you use a supported latex mold?  It would be re-usable too

Agree. I use it a fair bit (and silicone rubber - inert to almost everything)

I also use a type of rubbery compound that has to be melted in a sand
bath on the stove as a quick and cheap substitute for silicone

Don't recall if this is the name but it's the same stuff

http://www.maragon.co.uk/vinamold.html

And laminating film can be deformed by heat, ovbiously, and won't
interfere with the epoxy cure. If supported it should do the job, but
I've never cured epoxy as high as 100C

2012\02\14@023116 by IVP

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You might have to do a little experimenting to test that the material
you use is inert. Epoxy curing can be upset by some plastics (including
the binder in wood products), as any fumes or residual monomer given
off can interfere with the curing and leave the surface sticky. In extreme
cases the fumes can penetrate quite deeply and the result will be very
unsatisfactory. The reason I suggested laminating film and silicone, which
I use for both polyester, which is very aggressive, and epoxy, which can
be sensitiv

2012\02\14@045030 by alan.b.pearce

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> Have you considered re-usable flexible silicone molds?

My wife has a cake "tin" made out of that stuff. Maybe just go down the kitchen store to find a readymade version of what you want ???


-- Scanned by iCritical.

2012\02\14@045110 by alan.b.pearce

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> What I'm currently using is a piece of acrylic with a couple of dozen pockets milled
> in it (all the way through).  I cover the back side with tape (for a seal), place my
> modules in the proper spots, then pour epoxy and bake in an oven.  The problem
> occurs when we go to remove the cured epoxy blobs from the form - its time consuming
> even though we swabbed the sides of the mold with mold-release compound.

You do have a slight angle on the sides of the mold? I would have thought this would be enough to allow release with a small tap from a wooden hammer or similar on the back side, seeing you already have access to the back by taking the tape off. If it won't come out, just how smooth has the cutter left the sides of the pockets? It may just be a case of polishing them with a release angle.


-- Scanned by iCritical.

2012\02\14@051344 by KPL

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make a paper box, that fits inside the pocket? Most probably, some kind of
waxed or silicone paper would be required.

On Tue, Feb 14, 2012 at 05:53, Dwayne Reid <EraseMEdwaynerspam_OUTspamTakeThisOuTplanet.eon.net> wrote:

{Quote hidden}

>

2012\02\14@080314 by RussellMc

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> I'm looking for an inexpensive sheet material that I can use for
> epoxy molds.  I have a product that is an epoxy blob about 1.5" x
> 1.1" by 0.5" thick.  I need to find a faster way of making these epoxy blobs.

I'd second silicone rubber .
You can get high temperature versions but many standard type are
probably OK at 100 C.

Semi random thoughts:

- Somewhat lower temperature for longer would presumably work as well.

- Can you mold release early on when the epoxy has attained its basic
strength and can be handled reasonably well without deforming  - and
then place them on a flat sheet - eg Teflon cooking sheet - to final
cure. Early release may or may not help releasability. It would allow
a dearer mold material to be used to make more parts.

- Cure temperature and time sounds like 24 hour epoxy. Can you use a
faster setting epoxy. This usually has less bonding strength, but is
that an issue here?

- Might some mold release spray be acceptable. Not all would be. Silicone spray?



      Russell

2012\02\14@081343 by RussellMc

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> I'm looking for an inexpensive sheet material that I can use for
> epoxy molds.  I have a product that is an epoxy blob about 1.5" x
> 1.1" by 0.5" thick.  I need to find a faster way of making these epoxy blobs.

Various metal alloys melt at temperatures from 50C on up.
You could probably easily enough manage a positive - negative molding
sequence where you make a metal mold from an eg wood master by pouring
in liquid metal, then set the epoxy at 100C in metal, then melt out
the metal at a quick exposure to 110-120C.

Melting temperatures are quite precise.

Rose's metal melts at 98C and, as it is not a utectic mix, you can
probably move the temperature around a bit by changing percentages.

   http://en.wikipedia.org/wiki/Wood's_metal

Here's a nice range. Everything from about40C to 140 C seems to use
some Bismuth.

   http://en.wikipedia.org/wiki/Fusible_alloy

They are not mentioned but I'd guess some Gallium tin lead mixes may work.

Rose's metal has various temperaures shown for it from about 97 to 107
- probably because it is NOT a eutectic mix

   http://en.wikipedia.org/wiki/Rose%27s_metal

Newtonsmetal 97C

         http://en.wikipedia.org/wiki/Newton%27s_metal


  http://en.wikipedia.org/wiki/Fusible_alloy

2012\02\14@082143 by Spehro Pefhany

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At 04:48 AM 2/14/2012, you wrote:
> > What I'm currently using is a piece of
> acrylic with a couple of dozen pockets milled
> > in it (all the way through).  I cover the
> back side with tape (for a seal), place my
> > modules in the proper spots, then pour epoxy
> and bake in an oven.  The problem
> > occurs when we go to remove the cured epoxy
> blobs from the form - its time consuming
> > even though we swabbed the sides of the mold with mold-release compound..
>
>You do have a slight angle on the sides of the
>mold? I would have thought this would be enough
>to allow release with a small tap from a wooden
>hammer or similar on the back side, seeing you
>already have access to the back by taking the
>tape off. If it won't come out, just how smooth
>has the cutter left the sides of the pockets? It
>may just be a case of polishing them with a release angle.

Exactly- the draft angle has to be much larger in a mold that is not
well polished. A WAG might be 3-4° for a reasonably well polished rigid
mold material.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com


2012\02\14@085056 by Carl Denk

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I have made molds from fiberglass that work well. The surface must be very smooth, catalyzed paint (not solvent like mineral spirits) like a fine auto finish, and well waxed. In the craft area there are mold materials available of all varieties. Try searching internet for that.

You don't say how many you need to make, and how quickly. Careful of fast setting epoxies, they exotherm, and boil causing foaming in anything but thin layers.

What are using for epoxy and filler? I like the West epoxy with micro balloons,  milled glass fiber or flox (milled cotton) for filler depending on usage. If interested in this, I can supply more info.

Can you use Bondo (Polyester auto body filler). It's cheap, cures quickly, and is sand-able finish-able,

On 2/14/2012 8:13 AM, RussellMc wrote:
>> I'm looking for an inexpensive sheet material that I can use for
>> epoxy molds.  I have a product that is an epoxy blob about 1.5" x
>> 1.1" by 0.5" thick.  I need to find a faster way of making these epoxy blobs.
>>      
>

2012\02\14@194823 by Lee Mulvogue

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Get some proper moulding Addition-Cured RTV silicone, like Dow Corning
Silastic S-2 or similar.  They are initially expensive, I think I paid
about $80 for 1.1kg, but they would make a mould that is reusable
hundreds, if not thousands, of times, and readily flexible so your
parts just pop right out in 2 seconds flat.  Available in different
shore hardnesses, choose one that's flexy enough to pop your part out,
and has a high tear strength.  You don't even need a release agent,
but a quick spray of a proper release agent can greatly extend the
life.
       Do a youtube search and you'll find vids on how to make moulds, and
see them in action.  Well worth the initial cost if you are doing
thousands, only need to machine up the one initial set to base the
mould off, no more time required machining for each mould run.  And
1.1kg should make you a whole heap of moulds of your required size.
       some info:
www.erapol.com.au/english/Products/Silicone/Addition-Cured.html
[1]
Lee

-------------------------
Msg sent via Webmail - http://hosting.myob.com/

Links:
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[1]
http://www.erapol.com.au/english/Products/Silicone/Addition-Cured.htm

2012\02\14@203912 by Ariel Rocholl

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Agreed with all Lee said, it is my experience also. Dow Corning silicones
are among the best.

Just a note to add is they last for a limited time if not cured, so make
sure you buy it when you need it. In my experience 6 months may be already
too much wait as the silicone will start degrading fast.
Cheers,

-- Ariel Rocholl
http://www.rf-explorer.com



On Wed, Feb 15, 2012 at 1:48 AM, Lee Mulvogue <KILLspamleeKILLspamspambaudalign.com> wrote:

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>

2012\02\15@124803 by Adam Field

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On Tue, Feb 14, 2012 at 7:48 PM, Lee Mulvogue <RemoveMEleeTakeThisOuTspambaudalign.com> wrote:
>
> Get some proper moulding Addition-Cured RTV silicone, like Dow Corning
> Silastic S-2 or similar.  They are initially expensive, I think I paid
> about $80 for 1.1kg, but they would make a mould that is reusable
> hundreds, if not thousands, of times, and readily flexible so your
> parts just pop right out in 2 seconds flat.  Available in different
> shore hardnesses, choose one that's flexy enough to pop your part out,
> and has a high tear strength.  You don't even need a release agent,
> but a quick spray of a proper release agent can greatly extend the
> life.

We've used Smooth On Mold Max 60 to make some molds for urethane encase parts.

http://www.smooth-on.com/a59/Mold-Max%3D-60-Higher-Heat-Resistant-Silicone/article_info.html

They have lots of grades available (you may not need 60). I think it
was around $100 / gallon.

We used MDF that was then varnished to make the negative mold for the
silicone rubber.

2012\02\15@143030 by jim

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Try Alumilite.com

Regards,

Jim

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