Author Topic: By Jupiter  (Read 60572 times)

Offline Brian Rupnow

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Re: By Jupiter
« Reply #75 on: March 01, 2018, 01:23:02 AM »
Mike--You are doing some marvelous work there. I understand the science behind what you are doing, but the practical application is way beyond my skill set. Thank you for the great pictures and documentation.--Brian

Offline petertha

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Re: By Jupiter
« Reply #76 on: March 01, 2018, 07:21:00 AM »
Looks like you have it nailed

I used to do quite a bit of composite work (high performance RC models, molds & such). I already had a vacuum pump for bagging & read about people reconditioning kitchen pots with gaskets & such. Eventually I landed on some ebay suppliers, likely Asian made & re-distributed. I bought one like below & they are dead simple plug & play. Depending on your molding fluids (resins, urethanes, silicones...) you likely have to allow for the bulk foaming effect. It rises like a sponge, then collapses into a bubble free degassed mix, which is what you want. Also its nice (mandatory?) to have a relief valve & see through lid. I've attached video below. Particularly with faster cure time mixtures, you want to get your goop properly mixed, straight into the chamber, de-gas & commence application. The more viscous the mixture, the higher propensity to hold bubbles. If you don't mix the A&B properly trying not to create bubbles , you have bigger headaches.

https://www.ebay.ca/itm/BACOENG-2-Quart-Mini-Stainless-Steel-Extraction-Degassing-Vacuum-Chamber/162328539488?hash=item25cb88f160:g:i-oAAOSwmRFaZVVf

There are decent vac pumps out in ebay land too. Yes the oil is something to be aware of, depending on the specific compressor & how you've rigged it, any carryover as small vapor mist can mess up your mixture chemistry & adversely affect cure properties so beware. Also, the hardener/catalyst component of some mixtures, particularly epoxy's & urethanes can adversely react with some of the pump internals. I used to hear this a lot with 'repurposed' compressors, either the seals breaking down or other issues hey weren't service rated for. Again, more money but decent vac pumps are available & generally cheaper than they were years ago,
https://www.ebay.ca/itm/5CFM-Vacuum-Pump-2-Stage-1-2-Hp-Rotary-40Miron-Wine-Degassing-HVAC-Auto-AC/292433929614?hash=item44166ba58e:g:6kEAAOSwWEZadCS1


« Last Edit: March 01, 2018, 07:26:08 AM by petertha »

Online Vixen

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Re: By Jupiter
« Reply #77 on: March 01, 2018, 10:22:59 AM »
Hello petertha,

Thanks for your reply. I now have a much better understanding of the degassing process, thanks to the video.  :ThumbsUp: :ThumbsUp:

I appreciate that the equipment I put together is very rudimentary, but I only have one more set of silicone moulds to make. Hopefully it will last long enough for that.

I have checked on evil-bay and can find similar pots and vacuum pumps, all manufactured in China, often with 'free' delivery to the UK. If I get serious and find I need better equipment, then I know it is easily available.

Thanks again

Mike
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.

Online Vixen

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Re: By Jupiter
« Reply #78 on: March 06, 2018, 12:14:40 PM »
The lost wax casting saga continues.

The snow has long gone and I am out of hibernation again. So, time to construct some one-shot mould boxes out of Plasticard and to mix and pour the silicone resin around the three core patterns for the Jupiter's Induction Manifold.

Also a chance to try out the new degassing rig made from a modified, oil-less tyre inflation pump and a recycled pressure cooker pot.

The degassing worked very well. The improvised vacuum pump pulled a good vacuum. I do not know how many inches or pounds because the vacuum gage had not yet arrived in the post. I degassed the silicon in the mixing jug several times until the goop stopped expanding and most of the bubbles had burst. When the degassing had slowed, I gently poured the silicone into the three mould boxes and degassed again. The silicone resin is very stiff and so the entrapped bubbles take a long time to rise to the surface by their buoyancy. It is amazing to see how much air there is in the mixed silicone resin.



The Silicone resin takes 12 hours to cure and this is done at normal atmospheric pressure, which collapses any remaining microscopic air bubbles to zero.
Here are the three mould boxes next morning. Together, they hold a kilogram of silicone. the triangles at the corner of each box are to economise on the quantity of expensive silicone. The white plastic tubes sticking out of the moulds will be used to align both mould halves after they have been cut open.



You will all have to wait to see if the patterns release from the silicone, or whether I have three, big, expensive, pink, blocks of rubber with the patterns firmly glued inside.

Mike



« Last Edit: March 06, 2018, 10:47:36 PM by Vixen »
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Offline Hugh Currin

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Re: By Jupiter
« Reply #79 on: March 06, 2018, 05:03:40 PM »
Mike:

Great work and beautiful parts. The mold making and investment casting is very interesting. I've always thought of investment casting as way too expensive to consider. Nice to see there are some firms who will do small volume orders. Food for thought.

I haven't done any of this but did a little bit of research. I think one can use pressure during cure to "shrink" bubbles. Just compressing them decreases their size. This may have been for resin parts in a silicone mold. Should work for the mold itself though? May be ahead applying vacuum during cure as you did, I don't know. But might work to pull a vacuum on the poured mold followed by pressure?

I remember seeing vacuum pumps for fiberglass work. Vacuum bagging mainly. Of interest because they are made to work with resin fumes. I looked at my old source, FiberGlast, and found some. But they are commercial and really expensive. I remember they had a less expensive unit, but that was 20 years ago. They do have a venturi vacuum generator. Hook it up to a air source and it generates a vacuum. Don't know how well they work, and this one still expensive, but they do exist.

Again, thanks for the build log. Am following along.

Hugh
Hugh

Offline Jasonb

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Re: By Jupiter
« Reply #80 on: March 06, 2018, 06:02:45 PM »
Hope they come out alright in the morning.

I have one of the small vac pumps from Bagpress which I use for veneering and laminating.



And also the odd bit of thermo forming of corian.




Offline petertha

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Re: By Jupiter
« Reply #81 on: March 06, 2018, 08:34:58 PM »
I think one can use pressure during cure to "shrink" bubbles. Just compressing them decreases their size. This may have been for resin parts in a silicone mold. Should work for the mold itself though? May be ahead applying vacuum during cure as you did, I don't know. But might work to pull a vacuum on the poured mold followed by pressure?
Hugh

Yes, that is something you see quite often in composites work, very often as a combination of other processes.
- Vacuum: to conform the layup resin/cloth to the mold, particularly complex shapes. Also in the case of sandwich construction where the cloth is bonded to an intermediary core material, foam, balsa, hex etc. It also works in conjunction with peel ply, a porous fabric or film that bleeds excess resin through in a regulated manner into a sacrificial wick layer for a light layup.
- Pressure: to assist the vacuum which max's out at atmospheric 14.7 psi. So an added 20 psi gives net 34 psi
- Temperature: to assist cure (or absolutely required in the case of pre-pregs) & give added strength to resin

But getting back to pressure, for anything of volume like the unit shown, you start to get into some engineering. It has to have sufficient wall thickness to withstand pressure, typically compressed air. A typical air compressor tank is quite thin, but it just has small flange inlets for air in/out vs. a big opening to get your mix in & out of. So unless you want to be unscrewing lots of nuts on a flange, you are probably limited to lower pressures. When you see industrial autoclaves they are very substantial, essentially heavy wall pipe with domed end bells that look like submarines :) From a hobby standpoint a 'leak' in a vacuum is an aw shucks fssst... & some wasted resin. A leak in a pressure vessel can be more dramatic. I know we are talking 'low' pressure but just for fun, Google exploding 'home compressor tank' one day.

The issue with bubbles in a silicone or urethane semi-flexible mold is more about surface blemishes. Because its so viscous it makes it hard for gas (air) to escape. In the case of epoxy resins for layups, its more serious. it can compromise strength. But we can use a few tricks. Essentially the bubbles want to go 'up' to the lower pressure source. So its better to have lower hydrostatic head. That could mean flat dish with 1" height of resin, vs. a jar with 4" of resin. Or if space is a concern, do them in batches (providing you have sufficient cure time).

Looking forward to the metal bits. You are doing a fantastic job!

Online Vixen

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Re: By Jupiter
« Reply #82 on: March 07, 2018, 07:30:34 AM »
Hugh,
Thanks for calling by. Yes you are correct, lost wax casting of larger items can be a very expensive process. It is not just the expense in time to make the patterns and moulds, there is the expense of the materials, the silicone rubber, the soluble and hard waxes. Then comes the cost of the foundry. Lost wax casting for the model maker works best for small items such as steam fittings etc. Sometimes, there are larger parts, which are impossible to machine (like these Jupiter manifolds), then there are few options other than lost wax casting.

I think Petertha has answered the questions of vacuum then applying external pressure. It is good to hear how things are done in the big bad commercial world. That sort information is useful to the hobbyist, knowing that it can be done encourages further experimentation. It does emphasise what I said about the expense of this sort of work. A good commercial vacuum pump alone will cost several hundred pounds, dollars, whatever. Even that little 'Minipress' pump that Jason uses costs several hundreds.

Back to the Jupiter mould making. After degassing the silicone rubber with my ultra low cost modified tyre pump and pressure cooker pot. The silicone was allowed to cure overnight at normal atmospheric pressure. Next morning, the silicone had fully cured and it was time to open the mould boxes and cut open the moulds to remove the patterns. I was a little concerned that he silicone would not release cleanly from the patterns. I had used beeswax furniture polish as the release agent and was unsure how well it would work, if at all. I started by pulling apart the mould boxes and withdrawing the plastic alignment tubes. The mould boxes were made from plasticard sheet and the pieces will get recycled,




The moulds were cut open along the centre line to remove the pattern pieces. The jagged cut line is intentional, the rough cut edges together with the two tubes, accurately realign the two halves


I was very pleased with the results. The silicon moulds were very crisp and sharp, without any sign of an air bubble. The pattern pieces released without the slightest problem. My rudimentary vacuum pump and degassing rig had achieved everything expected of it. It proves to me that a little ingenuity can be mightier than the cheque book.

Mike

« Last Edit: May 27, 2018, 11:12:12 PM by Vixen »
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Offline petertha

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Re: By Jupiter
« Reply #83 on: March 08, 2018, 12:49:12 AM »
Beautiful! I'm glad everything worked. Just a few links for the notebook.

I don't work with silicones much, but have worked with their urethane cousins in various durometers. Both have their place which I wont get into. But both can be very fussy about what kinds of releasing agent one chooses. And I'm not talking about partial sticking, I mean the wrong choice can adversely affect the entire cure & become a real mess. You probably have some euro equivalent of places like this, they tend to be sculpture / special effects / jewelry making / bronze art casting type suppliers.
http://www.sculpturesupply.com/list.php

Finally found the place I got my vac chamber. Looks +/-$ similar to the ebay links from before
https://www.bestvaluevacs.com/categories/vacuum-chambers/aluminum-chambers.html

Maybe more composites orientated, but closer to home for you
http://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/rtv-silicone-rubber/condensation-cure-mould-making-silicone-rubber-rtv.html

There are other vendors like Smooth-On & Alumilite that offer proven & compatible resins, sealers, release agents etc. But I think we beat this subject to death now. Molten metal time! :)


Online Vixen

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Re: By Jupiter
« Reply #84 on: March 08, 2018, 12:22:26 PM »
Hello Peter,

Thanks for all the insight into alternative materials, equipment and all the other techniques. It is all helpful in understanding the possibilities and alternative techniques. This understanding helps me refine my methods and equipment.

Here is a short summary the lessons I have learned so far, which may be useful to others contemplating making this journey.

I am using Polycraft GP-3481-F RTV Silicone Mould Making Rubber Shore A27. It is a Condensation Cure silicone rubber and therefore very tolerant of other materials. I have shown it is compatible with my perspex pattern materials, with grey primer paint, with Plasticard, liquid poly cements and beeswax furniture polish. This silicone will also self degas to a limited extent but can be improved with vacuum degassing.

I use a modified domestic pressure cooker pot as the degassing pot with a polycarbonate lid. It is almost identical to the $118 two gallon pots on your list.

I use a modified truck tyre inflation pump as the vacuum pump for my degassing rig. It  cost me 12 off evil-bay and it works well enough. If it should fail, the cost of a replacement is so low compared to a commercial vacuum pump, that I could replace it 10 times over. Commercial vacuum pumps can cost upwards of 200 -300.

I hope this will help others and show that with a little ingenuity, we can achieve similar results to much more expensive commercial equipment.

Thanks to all of you who have contributed to this project. I have learned so much, including how a vacuum bag will be useful (indispensable) when the time comes for me to laminate the airscrew.

Mike



« Last Edit: March 08, 2018, 05:55:45 PM by Vixen »
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Online Vixen

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Re: By Jupiter
« Reply #85 on: March 14, 2018, 05:14:57 PM »
It's soluble wax injection time for the cores of the Jupiter's Induction Manifold.

I obtained some different soluble wax for this batch of wax injection. As you can see, I bought 1lb block of Freeman Jewelers soluble wax from a UK supplier; Walsh's Jewellery Supplies. The new wax has a slightly lower melting point 165 to 170*F (75*C). It melts quickly, solidifies slowly and is very hard when at room temperature. It seems to be a good choice.



The colour takes a bit of getting used to but the finished waxes are very clean and precise. Warning, Children, please do not try to eat the engine parts.






While all this has been going on, I have made the external master pattern for the Induction Manifold using the same laminated perspex sheet method as before. The individual laminations were milled from 5.0mm perspex, The end flanges were similarly machined and everything cemented together with Tensol 12 cement in the same jig that was used to build the core patterns






The laminated block was then carefully carved and filed to shape. It's a long, slow and messy process. Here are the external and core master patterns side by side.






I used 3mm and 5mm tall plasticard letters and numerals to add some detail to the casting.




This shot should give you an ideal of the size on the Induction Manifold. The wide angle lens distorts the image somewhat. The final image shows the master pattern sitting in the plasticard mould box awaiting the Silicone resin to be mixed and poured.






Mike

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Offline petertha

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Re: By Jupiter
« Reply #86 on: March 14, 2018, 06:58:32 PM »
They look fantastic, Mike.

When you got your casting quote(s) do you get the impression it was mostly of a function of volume like 3DP jobs, or is there a 'complexity' factor in there as well?

Online Vixen

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Re: By Jupiter
« Reply #87 on: March 14, 2018, 08:17:13 PM »
Hi Peter,

I use a company called 'Just Castings' located in the jewelry district in central London. They make two charges, one if for your share of the investment flask and the other is for the exact amount of metal used. Being a jeweler they charge for each gram of metal used. My Inlet Manifolds each consume 50.2 grams of aluminium. I am so glad I did not choose gold or platinum. Sounds strange, as we all buy our aluminium, or steel or bronze by the foot or metre length rather than by weight.

The investment process is quite involved and uses some specialist equipment. First your wax model is attached to a central wax Tree along with all the other wax models. The Tree is immersed in a flask filled with a ceramic investment slurry, (similar to Plaster of Paris), where it is degassed and allowed to set. The flask is then placed in a burn-out furnace and brought up to red heat over a period of twelve hours. The wax melts and the residues are vapourised by the heat. The metal for the casting is melted in an induction furnace, part of the vacuum casting rig. The red hot flask is transferred to the vacuum caster. The molten metal is automatically poured and a strong vacuum applied to the flask. The molten metal cools slowly filling every corner of the cavity in the investment flask. After a few minutes, to allow the metal to solidify, the hot flask is immersed in cold water which shatters the ceramic investment . High pressure water jets remove the remaining investment. The individual cast items are then cut from the Tree, the metal Tree is later recycled.

Just Castings prepare and cast several batches in different metal each day, sometimes you will wait a few days for a cost effective batch in aluminium, which is not a common jewelry material

Mike
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Offline Tennessee Whiskey

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Re: By Jupiter
« Reply #88 on: March 14, 2018, 08:54:23 PM »
Seems as if you are dealing with craftsman in the correct district; as this build is heirloom quality mechanical jewelry  8).

Cletus

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Re: By Jupiter
« Reply #89 on: March 14, 2018, 08:56:55 PM »
Hi Cletus,

The only problem is they charge jewelry prices.

Mike   :'(
It is the journey that matters, not the destination

Oh! sod the journey, lets hit the bar and pool instead.