Greystoke's Workshop - Vacuum/Pressure Casting

[Tarzan]

I've decided to stop thread-crapping on Domo's far superior casting efforts, and create a separate thread to track my custom keycap efforts.

So far I've accumulated a vacuum pump, vacuum chamber, air compressor (untested, but warned that it is loud...), and a 5-gallon paint pressure pot (being reconditioned).

I'm planning on using the pressure pot in a similar setup to the one below (pic lifted from a model warships forum):



The paint pot I got from a CL seller started off looking like this:



And currently looks like this:




Previous owner had left quite a crust of dried paint on the pot, but it seems to be coming off okay using a mixed approach of paint stripper and glass bead blasting. 

More pics to follow.

[SpAmRaY]

Awesome, more DIY/Custom work!

/Turn on mom voice

     Just be careful using things under pressure!

[Tarzan]

Awesome, more DIY/Custom work!

/Turn on mom voice

     Just be careful using things under pressure!

I hear that.  I used to change the tires on my dad's farm truck, big old 80psi split-rim jobs.  Had it drummed into me from a very early age; "If that thing lets go it'll take your head off, so be careful!" 

Based on Domo's experience and from reading up on resin casting forums, I'm only going to pressurize castings to 40psi, nowhere near the 110psi the pressure pot is rated to handle.  Exercising due caution, of course.

Next step; build some sort of ventilated sound-abatement box for the compressor.

[SpAmRaY]

Awesome, more DIY/Custom work!

/Turn on mom voice

     Just be careful using things under pressure!

I hear that.  I used to change the tires on my dad's farm truck, big old 80psi split-rim jobs.  Had it drummed into me from a very early age; "If that thing lets go it'll take your head off, so be careful!" 

Based on Domo's experience and from reading up on resin casting forums, I'm only going to pressurize castings to 40psi, nowhere near the 110psi the pressure pot is rated to handle.  Exercising due caution, of course.

Next step; build some sort of ventilated sound-abatement box for the compressor.

I had a good friend as a kid who almost lost his arm and part of his face because he was airing up a small scooter tire....

[The_Beast]

*Waits for kawa's post about this*

[mkawa]

Awesome, more DIY/Custom work!

/Turn on mom voice

     Just be careful using things under pressure!

I hear that.  I used to change the tires on my dad's farm truck, big old 80psi split-rim jobs.  Had it drummed into me from a very early age; "If that thing lets go it'll take your head off, so be careful!" 

Based on Domo's experience and from reading up on resin casting forums, I'm only going to pressurize castings to 40psi, nowhere near the 110psi the pressure pot is rated to handle.  Exercising due caution, of course.

Next step; build some sort of ventilated sound-abatement box for the compressor.

even if you could do ventilate and still sound-abate, you'd be screwed by all the damn vibration. just buy the extremely quiet off-brand compressor from amazon (it's a pretty standard unit but with one of the newer motor designs that are particularly quiet -- a lot of 12vdc tire-inflators use these motors now). resell the big noisy compressor to a contractor who doesn't give a crap.

otherwise it looks like you have your bases covered recovering the pressure pot. after bead blasting and meking the crap out of it, i would pressure test it in an abandoned field, even to 40psi. when these things go, especially if there's heat involved (which naturally there is) they're likely to go like pipe bombs. very uncool if you'd like to continue living without pieces of metal in you. the things to watch out for are basically any elastomer seals and metal fatigue. elastomer seals are easy to test. metal fatigue is not. you just have to pressure it, exerting the force the clamps and pot are supposed to live through and hope they live through it. you're totally doing the right thing in being very dubious of a well well used pot of unknown origin obtained from CL.

[Tarzan]

Awesome, more DIY/Custom work!

/Turn on mom voice

     Just be careful using things under pressure!

I hear that.  I used to change the tires on my dad's farm truck, big old 80psi split-rim jobs.  Had it drummed into me from a very early age; "If that thing lets go it'll take your head off, so be careful!" 

Based on Domo's experience and from reading up on resin casting forums, I'm only going to pressurize castings to 40psi, nowhere near the 110psi the pressure pot is rated to handle.  Exercising due caution, of course.

Next step; build some sort of ventilated sound-abatement box for the compressor.

even if you could do ventilate and still sound-abate, you'd be screwed by all the damn vibration. just buy the extremely quiet off-brand compressor from amazon (it's a pretty standard unit but with one of the newer motor designs that are particularly quiet -- a lot of 12vdc tire-inflators use these motors now). resell the big noisy compressor to a contractor who doesn't give a crap.

otherwise it looks like you have your bases covered recovering the pressure pot. after bead blasting and meking the crap out of it, i would pressure test it in an abandoned field, even to 40psi. when these things go, especially if there's heat involved (which naturally there is) they're likely to go like pipe bombs. very uncool if you'd like to continue living without pieces of metal in you. the things to watch out for are basically any elastomer seals and metal fatigue. elastomer seals are easy to test. metal fatigue is not. you just have to pressure it, exerting the force the clamps and pot are supposed to live through and hope they live through it. you're totally doing the right thing in being very dubious of a well well used pot of unknown origin obtained from CL.

I appreciate the feedback, Mkawa!  I'm having the paint pot cleaned at a sandblasting outfit, when I get the lid openings closed up I'll take it back to them for pressure testing.  I talked to the shop owner when I dropped it off, he said he has a couple of ones just like it, they use them in the powder-coating booth.

Not quite sure what to do about the larger openings in the lid, figured I'd ask around for a good aluminum welding shop (used to know all these places back when I restored motorcycles...) and get some quotes on having plates welded/brazed to the lid.  I haven't checked since the hardware was removed from the lid, if I'm lucky the openings might be threaded, so I could get some 1.5"-2" brass pipe plugs to fit, with a retaining nut on the inside (outside?) for extra strength.

Plans for the weekend are to clear some space in the garage and set up some shelves.  And check out Amazon for a quiet air compressor.   

[mkawa]

it's aluminum? i'd be double careful about it then and have them pressure test it all the way up to 110psi for like 20-30 minutes. have them do it AFTER you get the alum welding done. if there are pluggable nibbles, i would go with JB welding the threads together and probably a material harder than alum, not softer. i'd also JB weld or straight up weld a huge cap over the threaded cap.

lemme link the quiet air compressor (that omg i want so badly)

http://www.amazon.com/GMC-SYCLONE-Ultra-Oil-Free-Compressor/dp/B0038MWDXY/ref=sr_1_1?ie=UTF8&qid=1377266093&sr=8-1&keywords=quiet+compressor

[mkawa]

another way to keep yourself safe is to build a gigantic box out of really really thick acrylic. like 1.5". this stuff is expensive as crap if it's fresh and custom cut, so raid the alley behind an acrylic store for scraps. a 1.5" block of acrylic not only weighs like 20lbs/ft2 but will stop or significantly slow a very high velocity piece of metal

[Tarzan]

Some updated pics.

Pressure pot back from powder-coating, with fresh piping and gauge


Used a large dial gauge mostly for style, but also to help see it better indoors


Interior of lid, showing the fittings used to close the two large openings. 

Pipe plugs, installed backwards so the plate side is inside the lid - better security against blowouts.  Some pitting in the metal, but none of it serious.  Seal was in good shape, apart from embedded paint residue, but I used almost a whole tube of aquarium sealer to run a bead along both sides of the seal for maximal air sealing.

Big old pressure pot

Galvanized finish was flaking off in some areas, the paint shop media blasted it before powder-coating

Air compressor.  Loud.


In the garage, going to try a pressure test later today, once the neighbors are all awake.   

[Tarzan]

Just out of curiousity, I stood on the bathroom scale holding the pressure pot.  32.4 kilos/71.4 pounds seems to be the differential in weight.  Massive bit of kit.

[Tarzan]

After some re-plumbing, and another run to Home Depot for some PFTE (?) paste, the pressure seems to be holding.  I'll let it set for a few hours, maybe overnight, to see if there is some really slow leak I haven't spotted.


It took quite a bit of clamping force to seal the lid, I cranked those six clamps pretty hard to get it air-tight.

[MOZ]

How did I miss this up until now?

Looking forward to this.

[mkawa]

i bet it's your silicone actually. you want a really dense silicone RUBBER, high quality name brand to form that gasket. look at the momentive line and the permatex line. momentive 159 in particular is the highest tensile strength RTV silicone rubber on the market. HOWEVER most of the datasheeted gasket makers can only handle 5-6mm of thickness without compromising their mech specs. the other way to do it is to measure things out pretty precisely and pick up a properly cast high temp high pressure silicone rubber gasket from mcmaster. their selection is good, and as far as i know their own their cast tooling so you can't get their better gaskets (eg, the fluorinated viton FKMs) from other places.

[mkawa]

other than the gasket, the pot looks great!

[Tarzan]

other than the gasket, the pot looks great!

Thanks!  The gasket is actually pretty fresh, it's just the surface that rides on the pot rim that's got bits of dried paint embedded in it.  I suspect the PO was pretty careless with it, there's no excuse for not cleaning the pot thoroughly in between paint jobs.

I do appreciate the tip re: McMaster-Carr!  So far the pressure pot is holding a steady 47psi, after slathering all the threaded joints with pipe paste.  There was even air leaking out around that huge clean-out plug, I put a bead of paste around the inside thread seam and it seems to have sealed it.  Knock on wood, I'll know for sure tomorrow.

[The_Beast]

the pot looks great!

kawa, pushing k and inspecting pot!

[mashby]

Can't wait to see what you do with this Greystoke. Very, very inspiring.

[Binge]

 

The work you did on that pressure pot is astounding

Great find and superior work, friend.

[Tarzan]

Good news on the sealing front; 24 hours later the pot pressure gauge still shows 47psi. 

Looks like all systems go for an actual live casting test.  Soon^TM

Spent a few hours today making a cradle for the pressure pot, so I can use it on it's side.





Still need a strap to secure it, for peace of mind, I've got a couple of motorcycle tie-downs that should do the trick.

Was going to try casting a couple of caps, but ran out of energy.  Shifting that pot around all afternoon was a real workout.   
 

[metalliqaz]

Amazing refurb job!

[Tarzan]

Amazing refurb job!

Thanks!  Most of the credit is due to the paint shop, they really made it look like new.  Hard to believe it's 70 years old...

[tufty]

Big compressors are loud, you can make a near-silent setup for small volumes using a fridge compressor (and you can go *waaaaaaay* past 50 psi), for bigger volumes you can use 2 in parallel.

See this, for example : http://hackaday.com/2013/09/17/high-pressure-air-compressor-using-a-pair-of-refrigeration-compressors/

I can get 500psi from my fridge compressor.

[Tarzan]

Big compressors are loud, you can make a near-silent setup for small volumes using a fridge compressor (and you can go *waaaaaaay* past 50 psi), for bigger volumes you can use 2 in parallel.

See this, for example : http://hackaday.com/2013/09/17/high-pressure-air-compressor-using-a-pair-of-refrigeration-compressors/

I can get 500psi from my fridge compressor.

I appreciate the tip!  So far the compressor I've got is working well, since I'm doing pretty low-volume casting I only power it on once a week or so, but down the road I could definitely use a quieter compressor.   )