Glove Box for bubble free casting??

[blind pig]

[Anvils Hammer]

Blind Pig,

basically, if there is no air in the mold, then there are no air bubbles. The resin flows into the entire part exactly like filling a cup with water. The resin surface tension will cause voids, probably, but those voids will be empty, so when the vacuum is released, they are instantly filled with resin instead of nothing, under normal air pressure.

The problem is getting ALL the air out, at the moment Im removing maby 98%, but the 2% remaining is still causing bubbles in my tests.

Lane- see below.

Further experimenting has been done!

My vacuum gauge arrived today, pretty usefull.

The pump is rated for 15 microns, but when it was pulling on JUST the guage, it was reading just under 10 mbar, which is about 700 microns! no good at all! However I suspect its the guage which is inaccurate, rather than the brand new pump, as the difference between 0mbar and 10 mbar is only a few mm on the dial!

When I hook the pump up to the pot, it pulls it down to about 20mbar in a minute or so.

Tommorow Im going to test to find the leaks, I was advised to wipe leak spots with thinners as apparently its volatile to the point of making the needle budge if there is a leak.

What I really need is the £2000 pump with an electronic gauge, but for the time being I have to make do.

Im hoping if I can find and plug the leaks, I can get 10mbar in the chamber (on my gauge anyway..) which is half the ammount of air as before, so Ill then retry the vacuum pouring test I did and see what difference it makes.


Building the box-

the "reinforcing" I was talking about- I mean overlapping tha plates in such a way that every plate is supported on all 4 sides by another plate. So that when the box is emptied, the crushing force is applyed only to the polycarb. This means that while there will still be screws and glue, they will not be nessecary for the boxes structural integrity.

I cant use a tube because they are just to expensive for what I need. For a future, larger vacuum chamber, a large peice of polycarb tube would be well worth looking at!

6mm acrylic will distort horrifically under vacuum.. which I why Im using 12mm polycarbonate- its 30X stronger!
The lid will be a single peice, 12mm thick, 25cmx20cm approx, Ive not done the final designing yet.

The box will be 15cm deep, giving an internal volume of 7.5L which will help with pump time, but which is still large enough to fit bigger molds and my resin mechanism.

The internal mechanism-

I rang up a "proper" solenoid company and was quoted £20-40 for one, so I bought 4 from ebay for £5!, when all 4 have broken, Ill consider the pricy one!

Im going to go with lego for the slider mech. Simply because i already have all the parts including the control mech, built into my lego MINDSTORMS kit from when I was younger, and I can build the whole thing with lego in a fraction of the time of modifying a printer set up.
It also means I can quickly make any changes I need to.

Im going to use an un geared lego motor, which should be ok in the vacuum, I will then use a load of lego technic gears to get a usefull speed on the rack and pinion set up, and I have to build in the resin cup and valve.

Ill post pleanty of pictures once I start work.

Cheers for all advice.

AH

[Eltnot]

I wouldn't use screws or glue. If I was to make a glove box, I'd be looking at welded plate with reinforcing on the inside. A good welding job will mean that the only leaks will be potentially around your opening and piping. I'm going to have a chat to my father about the cost of building such a box over the Christmas break.

[mangozac]

[blind pig]

[mangozac]

Speed was my understanding. If you can leave the moulds to cure at air pressure after pouring in a vacuum then you can cast at a suitably higher speed.

[Anvils Hammer]

Ive realised once again im over complicating things massively!

In the long run I want a semi automated custom built set up with 20L internal volume and the worlds most awesome vac pump hooked up.

in the short term, I Just need to get a "proof of concept" set up, so as you suggest, Im going to buy a peice of polycarb and use it to make a lid for my existing pressure pot.

That should provide a totally leak free seal and allow me to pull a really good vacuum, as it will just be the lid, and a hose running to the pump via a valve.

So I need a polycarb lid, and the lego mech.

Mango, Yeah I have 4 of the new motors, which are mine, and one old one which I inherited from my dad! I have pleanty of the long wires but will probably make my own leads as the circuitry isnt complicated. The RCX will be staying well outside the box!!

Once Ive got the mech built and the lid, I can start casting using this method straight away, and if it works like I hope, I can look at building a dedicated higher spec system in a few months time.

Blind Pig, the reason im doing this is, as mango said, speed.

The way most of you do it-

pour resin
sqeeze each filled mold individually to get some air out initially.
vacuum for a minute
change to pressure and leave under pressure for 20 minutes
remove from pot and de mold

now that does work great, but compare to the proposed system-

vacuum for a minute,
pour resin,
remove from pot.

pouring under hard vacuum also gives garanteed perfect parts, assuming the vacuum is good enough. So I dont need to individually check each part as I am at the moment.

At the moment Im pulling at around 10mbar, which is 99% of the air, I really need to get that to about 99.9% which im hoping is acheivable.

The vacuum pressure method works perfectly, but I can only do one tray at a time, perhaps 30 molds per hour tops

Using just pressure casting, I can fill around 100 molds per hour (with a mate helping)

Using my proposed vacuum system, there is no reason I cant fill and demold 400 molds per hour. So potentially much much quicker!

That speed of casting will allow me to make my entire weeks worth of sales in an afternoon, which gives me the rest of the week to work on awesome new products!

I think I might make a test lego mech this afternoon..

AH

[blind pig]

Could you not try a second pressure vessel and see what that does to your turn-around times?

Although it wouldn't be as much fun as playing around with LEGO, it seems like a cheaper and easier option.

[Anvils Hammer]

[Anvils Hammer]

Money Money money.

I need to spend some..

Been doing a lot of thinking and testing..

Tried to make my own pot lid.. could only pull down to 500 mbar. If I continue to experiment, I could potentially get somthing that works but it will cost a few hundred quid in materials and potentially weeks of time wasted, to end up with something which may or may not do the job..

The conclusion Ive come to is that Im not an expert, and Im better off spending money on some proper equipment which is garanteed to work perfectly first time.

So, Im planning to purchase one of these-

http://island-scientific.co.uk/vacuumfilling.aspx

A Chamber with a 17L capacity, perspex lid and a "pouring arm" which can rotate and move in and out of the chamber. I can pour the resin into a custom designed cup and then move it along a line of molds in the chamber.

Total cost- £1000

Which is an eye watering ammount of money, but its garanteed to work, requires no mechanisms or electronics, and has a large capacity which will happily take virtually any size molds.

On top of this, I then need a vacuum pump which can empty the chamber in a reasonable ammount of time.

My current pump is 5.3CFM, and gets my 10L pot empty in just over a minute, however I know the pot leaks like crazy, so Im going to test the current pump on the new pot when it arrives.

The pump is rated for a final vacuum of 25microns, but I only actually need 100 microns to cast with, so Im hoping as the vacuum pot is totally sealed, it should pump down to a workable pressure inside the resins curing time.

If the current pump cant reduce the pressure quick enough, I will have to purchase a new pump.. but can shop around so hopefully will not cost to much.

The upside of spending all this money is that my chamber will have a built in mechanical casting arm, and will definatly hold a perfect vacuum!

AH

[mangozac]

Ouch that is pricey, but you're right - in the scheme of things probably not too bad. It will take a LOT of casting to pay for itself though - you don't think maybe you should wait a little while before committing to something like that?

Larger capacity is good and bad - yes you can fit bigger moulds but it also means longer to evacuate the air. I would expect the moulds to be relatively small the majority of the time?

[Anvils Hammer]

Now that Ive seen the quality of the split molds, I refuse to produce anything in a two part mold again.. so I need to vacuum cast.

I estimate that the equipment will pay for itself, in saved labour, in around two years, and I plan on running Anvil Industry a lot longer than that! So its well worth the investment, even if in the short term, its a lot of money.

At the moment, I only really require a 10L container or even less than that, as my molds are small.

The reason Im getting the 17L container is to allow for extra capacity if and when I need it.. I dont want to buy a small tank and then have to buy another one and enormous extra cost in six months time!

AH

[Anvils Hammer]

ouch time.... Ive ordered the Chamber.

Ive spoken to a couple of people and no one seems to be able to tell me which pump will pull the chamber down to 1mbar or less in the time I need it to.. there are to many variables and basically they say I need to experiment, and spending more money will not nessecarily help matters.

Ive purchased a load of very dense blue insulation foam, which im going to seal with a coating of resin after cutting it into circules.

by dropping two circles into the bottom of the chamber, I can reduce the volume from 17L to 10L, Which is the same as my current pot.

My existing vacuum pump can pull the current pot down to 1mbar in around a minute, so if I can achieve that performance on the new chamber, which has a guaranteed vacuum seal, it should be possible to cast under.

A larger pump which would pump it down faster will set me back over £1k, which I cannot justify at the moment, so the back up plan, if my current pump is to slow, is to use a slower resin!

Ive still got a sample of FC10 Im yet to use, which I believe has a 6-7 minute pot life.. pleanty of time to pull a perfect vacuum!

Now I just have to wait for the chamber to arrive.. which could be up to a couple of weeks.. In the mean while I shall jsut have to work on new master parts..

AH

[blind pig]

A few of us in the past have used kiddies play sand to fill a vacuum chamber if a smaller volume was needed with an inadequate vacuum pump. Easy to get a level surface with a bit of MDF cut to size too.

[mangozac]

Beach sand for me

That's a big step Joel and should be an exciting progression! I'm sure we'll all be eager to see the results!