Lost PLA processes, products, knowledge.

[kadora]

Hello
ABBY thank you for your excellent explanation of casting process but you know people will always TRY to find new easier way for making anything under the sun.
I have found this video Portland cement mould
RAVIV do you have two spare cylinder head castings for sale ? I would like to build V twin engine .

 

[abby]

I guess that if you live in a place where the real thing is unavailable or hard to get then you will try all the possibilities , genuine Mansfield moulding sand is dug from a quarry not far from me and it is much cheaper than cement...............and it works !
Dan.

 

[Richard Carlstedt]

Thank You Dan !
You are the first person I've heard to state what really happens
"The plaster component contains water of crystallization which will only be driven off at 550°C.:"
You will see in my post ( #5) that temperature is critical. Even the two gentlemen that taught me Lost Wax used the wrong term .."Burn-out", ....its not, its conversion of molecules that release water. Had a two piece mold ( no wax) that was dried in a oven for 3 days at 200 C then immediately raised to 590 C in 2 hours and due to the shop closing rushed to pour Bronze and it blew apart-- I should have known as I saw spirals of water vapor leaving the Sprue and condensate on the Kiln Door when removing the mold. Sorry for the rant , but I wasted months on a failed project before discovering the error in terms and think Newbies deserve the truth, and not fairy tales.
Rich

And yes, I now only pour at 1300 F ( 700 C) even with "no Wax paterns"

 

[abby]

Rich , I only use Goldstar Omega investment cement which I have found to be the most reliable for my way of working.
My burn-out kiln holds 4 x 6" dia flasks 12" deep which is around 12 lbs each in weight of investment powder and can mean between 4 and several hundred castings.
The heating cycle starts with a five hour soak at 180°C , the moulds are upside down for most of this time and the molten wax runs out into a collection tray.
Near the end of the 5 hours the moulds are turned upright.
Over the next 90 minutes the temperature is ramped up to 350°C and soaked for an hour before ramping to 550°C over the next hour and again soaking for an hour.
These temperature transitions are not fanciful , they are actually needed.
The first soak is to do with a change in state of the refractory component , the second is the water of crystallisation.
At this point there should be no water present either free or combined but there may still be wax and soot.
The final ramp is to 725°C and the soak can be from 2 - 5 hours , I have found that some of my moulds have still had traces of wax after 3 hours soak.
Good ventilation should help any soot to disappear.
Final casting temperature will depend upon the metal and the thickness of the castings.
For aluminium I allow the moulds to cool to 150°C or less , for copper based alloys I cast at 400-500°C.
Casting wax has no inert fillers and residue is less than 0.1% , presumably the new "lost plastics" are the same.
I have "burned out" insects , cloth , wood and even Airfix model kits, these can leave ash residue so a catchment area should be made in wax and attached to the pattern.
Molten metal can flush the ash out of the mould and into the catchment.
You may find more information on my website http://www.unionsteammodels.co.uk/
Dan.

 

[Raviv]

Hi kadora
i can cast a few more and have them available.
if you need a specific head volume, let me know, currently these are design to have approx 6-6.5cc in order to achieve a static compression ratio of approx 8.5:1 (50cc for each cylinder).

 

[kadora]

Excellent I have sent you personal message.

 

[Richard Carlstedt]

DAN
You had more valuable information in your last posted paragraph than most any book or article
Thank You !
I have done wax, pine cones and permanent (aluminum patterns ) split molds and have only poured in Brass, Bronze and Silver
Rich

 

[creast]

Rich , I only use Goldstar Omega investment cement which I have found to be the most reliable for my way of working.
My burn-out kiln holds 4 x 6" dia flasks 12" deep which is around 12 lbs each in weight of investment powder and can mean between 4 and several hundred castings.
The heating cycle starts with a five hour soak at 180°C , the moulds are upside down for most of this time and the molten wax runs out into a collection tray.
Near the end of the 5 hours the moulds are turned upright.
Over the next 90 minutes the temperature is ramped up to 350°C and soaked for an hour before ramping to 550°C over the next hour and again soaking for an hour.
These temperature transitions are not fanciful , they are actually needed.
The first soak is to do with a change in state of the refractory component , the second is the water of crystallisation.
At this point there should be no water present either free or combined but there may still be wax and soot.
The final ramp is to 725°C and the soak can be from 2 - 5 hours , I have found that some of my moulds have still had traces of wax after 3 hours soak.
Good ventilation should help any soot to disappear.
Final casting temperature will depend upon the metal and the thickness of the castings.
For aluminium I allow the moulds to cool to 150°C or less , for copper based alloys I cast at 400-500°C.
Casting wax has no inert fillers and residue is less than 0.1% , presumably the new "lost plastics" are the same.
I have "burned out" insects , cloth , wood and even Airfix model kits, these can leave ash residue so a catchment area should be made in wax and attached to the pattern.
Molten metal can flush the ash out of the mould and into the catchment.
You may find more information on my website http://www.unionsteammodels.co.uk/
Dan.

Dan,
What has happened to your website??
Keep getting iffy ads.
Rich

 

[abby]

Sorry Rich but we closed the website down , it was being hosted on a pal's PC but there was so many attempts at hacking - thousands per day - that he decided to shut it down.
I have been renovating my house for some time now and have had very little time for model making or casting but a few years ago I came across a process being used by a local foundry to produce cold end rotors for automotive turbos.
This was once the largest foundry in England casting magnesium aircraft engine parts , now a shadow of it's former size but very high tech .
The process was secret at the time and still under development but it solved a problem that I had encountered when investment casting aluminium and it's alloys.
Gypsum based investment powder has up to 40% crystobalite refractory content and is very strong, my moulds have to withstand 27 ins Hg vacuum which will suck the molten metal through the smallest crack.
If the casting is hollow , like a tube for example , it will have an investment core , as the casting cools and solidifies it contracts but it cannot crush the strong investment inside it and a crack often occurs ruining the casting.
To overcome this problem and entirely new form of investment has been developed and is now commercially available.
In addition an entirely new idea for forming the moulds has been developed which although obvious when explained is very clever thinking.
I believe the process would be game changing for model engine castings in light alloy and intend to try it out , possibly next summer , when I have finished my house DIY.
If successful I will of course give the community the details.
Dan.

 

[creast]

Sorry Rich but we closed the website down , it was being hosted on a pal's PC but there was so many attempts at hacking - thousands per day - that he decided to shut it down.
I have been renovating my house for some time now and have had very little time for model making or casting but a few years ago I came across a process being used by a local foundry to produce cold end rotors for automotive turbos.
This was once the largest foundry in England casting magnesium aircraft engine parts , now a shadow of it's former size but very high tech .
The process was secret at the time and still under development but it solved a problem that I had encountered when investment casting aluminium and it's alloys.
Gypsum based investment powder has up to 40% crystobalite refractory content and is very strong, my moulds have to withstand 27 ins Hg vacuum which will suck the molten metal through the smallest crack.
If the casting is hollow , like a tube for example , it will have an investment core , as the casting cools and solidifies it contracts but it cannot crush the strong investment inside it and a crack often occurs ruining the casting.
To overcome this problem and entirely new form of investment has been developed and is now commercially available.
In addition an entirely new idea for forming the moulds has been developed which although obvious when explained is very clever thinking.
I believe the process would be game changing for model engine castings in light alloy and intend to try it out , possibly next summer , when I have finished my house DIY.
If successful I will of course give the community the details.
Dan.

Dan,
Many thanks for replying... I really appreciate that.
Thanks also for the insight to the process you described which sounds intriguing.
I have been trying to lost wax/PLA deep finned engine parts in aluminium alloy for some time now. Brass works fine but Aluminium seems to give me more grief. I do use commercial SRS Industrial A plaster and vacuum during casting.
Wax seems more encouraging despite the fumes which are far worse than PLA.
3D printing takes hours and I won't go into the pains of removing support materials or layer orientation so I am pursuing machined wax for patterns.
Anyway, I wish you all the best with the DIY!
Rich

 

[Richard Carlstedt]

Dan
I am still on "hold" with my engine Lost PLA project .
Need to get my Kiln wired to a new controller (Multi-step Programing ) yet
Will look into that new investment Dan when I am ready ( Thanks !)
I have Satin Cast now, but the right investment is very important .

I did want to comment on Aluminum Casting that no one mentioned to my knowledge.
At work, We had/and used Aluminum Castings with CRITICAL machined airflow surfaces. ( ie no porosity )
We used 356 Al for most parts, but this is what we learned from our foundry sources

Cover the crucible during heat
De-Gas the melt and pour IMMEDIATELY ! They actually measured the time in seconds !
DO not attempt to cast during rain or higher humidity days

In degassing, you are releasing Hydrogen that has been absorbed by the liquid Aluminum
They have tremendous affinity for each other ! Our parts were so critical, that the foundry even flew an expert in from the UK to help with the procedures

When cooling, the hydrogen atoms coagulate and form hydrogen bubbles which is porosity
in the finish part and when machined, you have a poor surface
So if your castings have bubbles, you have a Hydrogen problem
Rich

 

[GreenTwin]

Polycast is the filament that many are using in lieu of PLA for lost-3D-printed castings.
Polycast supposedly burns out more cleanly than PLA (I have not used Polycast, and have not tried lost-PLA casting).

For investment material, a lot of hobby folks are using this material, and casting parts in gray iron with it.

 

[GreenTwin]

It should be noted that pla-printed patterns most likely can be heated so a softened state (not liquid), and removed from a fully hardened resin-bound sand mold, to basically recreate the precision of a ceramic shell casting, without all the trouble of creating a ceramic shell.

I intend to use the removable pla pattern method to make helical gears for a Frisco Standard marine engine.

.

 

[Richard Carlstedt]

My ****oo
I should have correctly responded with my project material, sorry about that
I have liquid resin casting wax patterns made for my next project. not PLA.
I just used the term because i was more focused on burn out and investment procedures
The resin patterns need very precise steps in burn out and I am waiting for a friend to help program
the controller ...or confirm i have it right.
Thanks for the info ! Never hurts to know more
Rich

My grandson does PLA models and has a 3D printer so I will be bugging him later for some of the
support parts for my intricate resin patterns
( trying to hold +/= .001 " ) ykes!

Rich

 

[abby]

I have a controller made by Vertex , it uses fuzzy logic to control temperature to within 2 deg centigrade and can be easily programmed for multi-step process.
It can be loaded with more than one program so the kiln could be used for burn-out and heat-treatment by selecting the relevant programme.
Output is 5v so solid state relays can be switched , cost was about £100 including 2 relays .
Dan.

 

[ajoeiam]

Sorry Rich but we closed the website down , it was being hosted on a pal's PC but there was so many attempts at hacking - thousands per day - that he decided to shut it down.

snip

I haven't done it yet but it is possible to have an online web presence for not too much $$$/month.

Found one that will let me use postgresql and doesn't change in price from some paltry sum to a pricey amount after initial payment and its like about $100 canuckistani or a trifle less per year. If you get lots of hits daily it might be a bit more but still within reasonable bounds imo.

HTH

 

[lohring]

Here's a really simple method.

Lohring Miller

 

[dnalot]

Here is an example of how to do lost foam casting at home the right way. The vibrater is a must as it compacts the sand without damaging the foam part. You can find these on Amazon but do your search for pneumatic vibrater or you will get some intersting sugestions. Ant to make it more interesting the parts being cast are of engine parts.



Mark T