anyone had any experience with casting stuff into resin ?

I couldn't find an LED back light for my electric bike that I like, so decided to make my own

was going to make a small one first to test, but with having to re-install windows last night (twice) I built a bigger one while I was waiting

rough plan was 2 lines of yellow, then 2 lines of red, then mixmatch of flashing red, then 2 lines of red, then 2 lines of yellow
(the flashing ones flash themselves, you just feed constant power and they flash)

pictures...


rear view


clear resin (from ebay)


mixed the first pour, 100ml resin, 1ml hardener, poured into old ice cream tub


wait for it to set, but still be tacky/sticky (like gel), mix and pour another 200ml in,  the put the LEDs in face down, pour another 100ml in ontop


I know resin gets hot when it sets... but this got crazy hot, it melted the bottom of the ice cream tub, so I took it out as soon as I could


closer inspection... and most of the LEDs have melted (the crask in the resin was me taking it out too soon)


but... they (mostly) all still work ok :-)



vid of flashing LEDs
http://imageshack.us/clip/my-videos/534/4hsfwkjiispeinfnnsokpw.mp4/



any ideas to stop the LEDs melting ?  I could try to cast it the other way up, so I leave the LEDs sticking out... but I'm not sure how well it will work

I thought most modern superbright LEDs came installed with heatsinks? certainly the ones in all my torches have.

Or are you saying the resin is melting the LEDs? Either way check how much heat the LEDs will actually crank out when they're on!

I can't get any super super bright LEDs in red

these are just the brightest red ones I can get

the resin got crazy hot while it was setting, melted the bottom of the ice cream tub it was in - and the hottest part is right in the center, where the LEDs are :-:


I've got super bright LEDs for the front, there's only 6 of them but when you tun the light on it's more like a light from a police helicopter than a bike light!   apparently those 6 are equal to 600 of these red ones :-o

p.s. just tested the light from it in the dark, and they're pretty bright / bright enough for what I need

just need to stop them melting nos :s

could you let it set on top of some ice? I guess it would take a lot longer

You could apply the resine in stages and layer it, it will generate less heat then.

What resin are you using? Epoxy?

Polyester or polyurethane?

Polyester resin is usually much cheaper, it's essentially fibreglass resin. It can have issues though with moisture content in the air so doing it over ice wouldn't be so good potentially. I've encapsulated insects in polyester resin, and the moisture in the air is enough to make the top air exposed layer remain tacky.

Polyurethane resin is more expensive.

I think polyurethane resin is quite particular about the mix ratio (usually 1:1) of the two parts. However if you are using polyester, which is usually 1-2% catalyst to the resin, it's less fussy. You can limit the exothermic heat output by putting less catalyst in. It'll take longer to cure, but generate less heat. The stuff I've used I've usually put about 1.2-1.5% in. The opposite is also true, more catalyst = quicker and more heat, to the point that the heat can make the resin crack, and even combust. 2% made an encapsulation of mine crack badly.

If you can't get superbright LEDs in red you could use a red filter? As long as you don't melt that too

You can get superbright red leds in smd form. Easier to use imo to

the LEDs I got are 8000mcd, which is pretty bright for a red led... but they're nothing compared to a cree torch etc... unless I'm looking in the wrong place ? (ebay/google) got any links DEViANCE ?

i think a filter would just filter out most of the light

Zpyder, I used 1% hardener so it must be the polyester stuff... can I use less than 1% ?  I don;t care how long it takes to set ? the bottle said min 1% max 2% so I went with 1%

I could try building it up in layers, the problem is I'd have to do it upside down, (with the leds pointing up) and the top surface isn;t as clear at the bottom, bottom surface is like glass.... top surface is like 100yr old glass... still clear'ish but not as good

Are you using weight or volume to measure? Using a decent scale, measuring by weight would be more accurate.

The amount of catalyst you need can vary based upon the volume of resin you're casting, larger pieces typically use less catalyst for the reason you encountered, it heats up too much. Rather than sacrifice another block of LED's, I'd be tempted to mix the volume of resin you need and do some blank, LED-less test casts with less catalyst, try 0.8%, wouldn't go below 0.5%.

Deviance's suggestion for doing it in layers is also a safe bet. If you do this though, make sure each new layer is poured into the mould whilst the previous layer is still tacky. To add further confusion, there are two kinds of polyester resin, one has a wax or something added to it, which is meant to create a barrier to air so it sets without staying tacky, typically used for single-layer casts. If you've got that resin you *might* find the layers could split from each other as they won't bond properly.

Quote from: knighty on July 12, 2013, 15:14:13 PM
the LEDs I got are 8000mcd, which is pretty bright for a red led... but they're nothing compared to a cree torch etc... unless I'm looking in the wrong place ? (ebay/google) got any links DEViANCE ?

i think a filter would just filter out most of the light

Zpyder, I used 1% hardener so it must be the polyester stuff... can I use less than 1% ?  I don;t care how long it takes to set ? the bottle said min 1% max 2% so I went with 1%

I could try building it up in layers, the problem is I'd have to do it upside down, (with the leds pointing up) and the top surface isn;t as clear at the bottom, bottom surface is like glass.... top surface is like 100yr old glass... still clear'ish but not as good

RS components have 9300, 14000 and 24000 mcd smd red leds.
http://uk.rs-online.com/web/c/displays-optoelectronics/leds-led-accessories/visible-leds/?searchTerm=smd+led&sort-by=Luminous+Intensity&sort-order=desc&view-type=List&applied-dimensions=4294380283&lastAttributeSelectedBlock=4294382446&sort-option=Luminous+Intensity

doh! I didn't check RS... bloody hate there catalog system / search function

I'll buy a few of each to play around with.... want them to be bright... but can't go blinding people behind me :-o

I've never used surface mount LEDs before... they any good / ok to work with ?

through whole is a piece of cake with the protoboard....

I weighed the resin and used the a syringe for the catalyst

I'll do some more tests I think....

poured 100ml the first time, then 300ml the second time

:-)