Glove Box for bubble free casting??

[mangozac]

[Anvils Hammer]

Im an engineer in this life!! I just cant do maths.. which is a requirement for "normal" engineering and getting any kind of qualification.. so I have to keep it as a hobby and never went into the feild properly.

The bubbles in the helmets were approx 0.75 to 1mm in diameter. Any bubble is unacceptable.

I want to be the first miniatures manufacture to replace

"due to the nature of the casting process, your parts may contain small bubbles blah blah blah"

with

"Our parts are always flawless, if you find any defect or bubble of any size, we will refund the money and you can keep the part"

But to do that, I need a state of the art set up which can consistently produce parts with no bubbles at all, which is why im so interested in casting in a total vacuum..

I can get an electronic guage for £150, or a regular guage for £20.. Im going to stick to the cheap one for the time being!!

reguarding the pump, eventually I want this-

http://www.javac.co.uk/vector-high-vacu ... 16245.html

I have no idea how much it is, but it can pump down a 20L chamber to 0.01mbar in 45 seconds..

thats 99.999% of the air removed.. in less than a minute.. air bubbles? what air bubbles?

Ive been running anvil industry for about 9 months now. Its incredibly hard work, and im still not making enough money to move out of my parents house yet, but Im confident I will, and I know I want to run the company long term, at least 5 years. Which means its well worth investing in state of the art vacuum technology, as soon as I can afford to.

I will order the vacuum gauge tommorow and try and leak proof the chamber a bit better..

AH

[mangozac]

[Anvils Hammer]

haha, how old is the average caster?

My skill level when I started AI was the same as it was when I was 19.. if id started it a few years back, Id never have had to do minimum wage bar work while at uni! never mind though Ive started now..

Updates-

Im thinking polycarbonate for the design of the box, you can get special gloves designed for glove box use, but I suspect they will be very expensive, so im going to go about making my own.. it has to withstand 14psi, which I think I can mange. Im currently thinking the thickest gardening glove I can find, reinforced with somthing to stop any expansion.

I tested my pressure pot today by pressurising it and dunking it a water tank.

The main rubber seal is good, the leaks are around the valves, the main leak comes from the emergency release valve, so im guessing this is how air is getting in.

I will seal these leaks, rig up the guage when it arrives and repeat my experiment.

If I see an improvement ie smaller/no air bubbles, I will start building the box!!

AH

[mangozac]

Most of the casters I know are in their 30's or older....

Polycarbonate is good, but can be expensive at the thicknesses you'd be after. Could be worth replacing the emergency release valve with a plug for further testing of the vacuum technique...

[mangozac]

Hey Joel check this out: . At 1:46 there is a shot of a vacuum casting machine that look like it's doing exactly what we've been discussing here.

We're actually working with the company at work to produce some injection moulded polycarbonate lenses for an automotive product.

[Anvils Hammer]

Cool!!

Yep thats what I need.. but A. costing a few hundred instead of thousands, and B, filling 10-20 molds at a time instead of one!

Done some more research-

The Vector pump I mentioned is about £2000.. slightly out of the price range at the moment. My current pump can pull the vacuum I need no problem, I just need to get a leek proof pot!!

The polycarb is not so expensive, Im intending a double layer design which is self reinforcing under vacuum, made of 2x8mm plate, for a total 16mm thickness of polycarb, The ammount I need is less than £100 and I already have all the tools I need to precision cut it.

The pouring mech is more difficult, I rang a company today who sell glove box glove spares and was quoted about £350 for the cheapest glove/ring combination!! way out of the price range, and also not particular suited to waht I want to do.

Having to put a gloved hand in there is a pain as it means the box has to be quite a bit bigger than If I just have a mechanism in it..

My current line of thought is to have the resin cup on a rod which leads out the box, I could rotate the rod to pour, and push it in and out to move it back and forth along the rows.

The only problem with this method is that I have to vacuum seal the hole. thats not a problem for a static/rotating rod, but to move it back and forth requires an expanding/contracting membrane of some sort, which is more problematic.

Ive been having so much trouble casting my bases the past few days that Its just not worth selling them untill I can figure out a reliable, quick method of casting them. So im going to withdraw the range till I can sort my box out. Bah!

AH

[Anvils Hammer]

Further thoughts and research..

sticking a sealed rod through the box wall is going to be a massive pain.

Its very easy to create a solid polycarb box which will allow a perfect vacuum, but as soon as I cut the polycarb to allow anything through, I am instantly going to have a massive problem maintaining the vacuum!

One option is to build trays which hold the resin above the molds, I can then tip the entire box on its side a bit to pour the resin into the molds. By using a rotating device in the chamber, The molds could remain horizontal, only the resin trays would rotate to pour.

This approach is mechnicacally quite simple, but its a pain to arrange the trays in the correct places, fill each tray with the required ammount of resin, and then have to tip the box up.

Im leaning toward the mechanical solution again..

I would need a rubber cup with I can pour the resin into, and which is moldable, thats no problem..

The cup is mounted on a rack and pinion, so it can move back and forward over a row of molds, the rack could be set at different possitions in the box to accommodate different molds.

a wire runs into the box through a single small hole, sealed with araldite. Inside the box would be-

one geared motor, for transverse back and forward.
one solenoid, for opening the valve which pours resin into the molds.

The controls would be outside.

pour the mixed resin into the cup, close the lid, apply the vacuum, then move it along the row, opening the solenoid for a few seconds over each mold.

Mechanically, its quite simple, I would build it with lego.. assuming a lego mindstorms DC motor will operate under vacuum. then I just need to order a suitable solenoid.

this approach means I can quickly and easily pour precice ammounts of resin into the molds, and can use molds of varying size but keep the mold box small.

So the problems, as Lane pointed out-

Lubricants exposed to vacuum. Lack of air cooling under vacuum.

air cooling im not concerned about, as the motor will only run intermittantly for 20 seconds or so before re-pressurisation, so I dont think cooling is an issue.

Lubricants is an issue.. I need motors which dont have any! which is probably quite specialised..

guess what.. more research!!

All thoughts on the robotic approach proposed, very welcome!

AH

[mangozac]

Now we're talking!

Most of your thought pattern sounds pretty feasible to me. It will indeed be easier to seal some wires into the box rather than the mechanical links.

When you talk about using a solenoid will that be a solenoid valve to let the resin flow through or a solenoid plunger to push the cup over? Neither technique is very suitable: the plunger setup does not provide enough fine control and the valve type really needs the fluid to be pressurized as the orifice is only very small. Plus it would need to be cleaned out before the resin clogs it up. You may need something more akin to a servo motor tipping the cup.

For the lateral movement I would pick up a cheap inkjet printer and hack it apart. The rail and carriage assembly would be perfect for this. Plus it comes with the stepper motor already attached: simply hook up a cheap stepper driver board and you're good to go!

The grease issue is not so much to do with the motor but rather the gearing. Using stepper motors with belts (like used in the printer) will minimise the need to lubricate. Belts aren't as good for cnc routers and stuff but for this there's fine as there's no real load being placed on the assembly.

You're right, at the duty cycle you're running at heat won't be a problem.

This is exciting!

[Anvils Hammer]

If I didnt need it for printing out packing slips, my printer would already be in peices on the floor!!

Thats an idea which is very worth exploring, though I was hoping I could just plug two wires into a battery to make the motor go round.. whats a stepper driver board?
Will get my hands on a printer and have a play around..

If you can help me with the wiring etc that would be great.. I basically need to be able to push a button to run it one way, and push another button to run it the otherway.. nothing more complicated than that..

I have no objection to just dunking the motor in the vacuum and crossing my fingers, Isnt there a chance the lubrication in tha motor itself will evaporate and the motor will tear itself apart? It would be a shame to build a printer based unit only to have the motor pack in after a few weeks/months..

For the resin flow. I was thinking of a "bath" for the resin with a nozzel in the bottom blocked by a rubber ball. The solenoid would pull the rubber ball up a few mm. The resin would flow through under gravity, same as emptying a cup..

I can experiment with different shapes/sizes of bath/nozzel.

I need this equipment set up as soon as possible, but I also want it to actually work so its worth putting in the effort to design and build it properly.

AH

[mangozac]

[blind pig]

[Lane]

[blind pig]

[mangozac]

I was under the impression that he would laminate the perspex sheets together for strength?

@Bec: I should get myself a clear lid for vacuuming one day...

Oh and on the subject of vacuums, I was cleaning out my office at work today and realised I have a new vacuum pump sitting there! It was provided by a potential client who wanted us to build a control system to go with it but they turned out to be time wasters so the project never went ahead. The pump has been sitting in a box for 6 months - I figure if they don't ask for it then in 6 months time it becomes mine and I can use it for casting. It's rated at 110 litres per minute and 60mBar, which is not bad at all!