My turbine wheel

[larry cottrill]

Hi Alex,

Your propeller looks very nice. To my knowledge, investment casting method is good for parts which dia smaller than 200mm only, I guess your propeller is largely bigger than that.

This part will be cast in Inconel 713 (vacuum melted) by ordinary gravity method.

Horace -

The only way I have seen investment casting done was where you need to make a new pattern and a new mold every time you want to make a new part. This was custom jewelry work, and so the one-off process was quite acceptable. Is this also true of your turbine, or do you have some way of doing this with permanent, separable molds that can be re-used?

The way we did it was to pour a high-temperature 'plaster' around the pattern and let it harden, then evaporate the wax out of it in an oven. Finally, the gold was melted in a special crucible and the molten gold was rammed into the mold with a centifugal casting rig, and the plaster mold [weakened by the heat it had endured] was easily broken away. Then the piece was polished, plated, and otherwise finished up.

And Alex, yes, the screw [propeller] is very nice indeed.

L Cottrill

[skyfrog]

The only way I have seen investment casting done was where you need to make a new pattern and a new mold every time you want to make a new part. This was custom jewelry work, and so the one-off process was quite acceptable. Is this also true of your turbine, or do you have some way of doing this with permanent, separable molds that can be re-used?

Hi Larry,

Yes the process of casting my turbine is exactly the same with the said jewelry work. In investment casting, the only permanent mould is for making wax pattern, after wax is form injected, we then proceeding a metal casting process, ceramic shell is made around the wax pattern, during which wax is heated vaporized and disappeared, leaving an empty cavity for metal casting. For making each metal part we have to consume one wax pattern and one cermaic shell. In this process, Precision is the most obvious benefit, beacuse after casting the part is nearly net-shape, in my case the only machining need to be done is sizing and boring.

[AlexUA]

Good morning friends!
I think that for you a morning, as for us 5 o'clock in the evening.
Look a photo.
The form{*shape*} is executed{*made*} from jeweller gum, from this form{*shape*} it is possible to produce (approximately) of 5000 thousand
Wax patterns.
I pour out by a centrifugal inductive casting. But Casting under pressure more precise.
The kilogram of wax costs{*stands*} approximately 15 $, the gum costs{*stands*} 25-27 $ a kilogram.
The jewellers apply gum to, that from the form{*shape*} to drag composite model,..If the form{*shape*} was idle time on a design, then it is possible to apply (duralumin a matrix) - ((form{*shape*}))))And to pour the same wax.

One more way:
To use the machine CNC for milling model wax, accuracy very high! Very much!
By this machine it is possible not only to mill wax, but also mild metal of a type duralumin.
http://www.rolanddg.com/products/mdx650/index.html
This machine also is the scanner! That is, lay parts, scan, and to mill same
Matrix.

Probably I have helped to you...x.

[skyfrog]

Wow look at the parting surface ! It's so complicated I once thought it was wrapped paper :) Again, nice job.

I can't quite understand the RP concept of the Roland machine, what's the difference beween this one and the laser based rapid prototyping ?

[Hank]

Hello- Investment Casting has become a production tool over about the last fifteen years. Sturm-Ruger uses this process for the manufacture of frames and slides for their pistols in lots counted in tens of thousands.

This form of casting has been around a while. The Greeks were casting using this process about four thousand years ago.
Hank

[skyfrog]

This form of casting has been around a while. The Greeks were casting using this process about four thousand years ago.

You reminded me one thing. It could be very possible that the casting business will last another 4000 years or more. What about semiconductor (IC) industry ? Could it last for another 40 years ?

Casting is long lasting manufacturing process but it's dirty and danger manufacturing process too.

[skyfrog]

I wrecked my first wax turbine just now. It was kind of boring tonight, I decided to have a little fun with my wax turbine.

By boring a blind hole on the wax pattern, I then use a pencil as substitude for shaft, a short tube as substitude for bearing, electric fan as substitude for gas source. All substitutions are low tech w/o accurate alignment, so it was OK in low speed though seen wobbly, but when in high speed, the wax turbine lost control and fell down to the floor. Some blades were gone. This is my first gas turbine adventure :-)

Yes I'll be very careful balancing the real thing in the future.

[larry cottrill]

I wrecked my first wax turbine just now. It was kind of boring tonight, I decided to have a little fun with my wax turbine.

By boring a blind hole on the wax pattern, I then use a pencil as substitude for shaft, a short tube as substitude for bearing, electric fan as substitude for gas source. All substitutions are low tech w/o accurate alignment, so it was OK in low speed though seen wobbly, but when in high speed, the wax turbine lost control and fell down to the floor. Some blades were gone. This is my first gas turbine adventure :-)

Yes I'll be very careful balancing the real thing in the future.

For those who may not be familiar with it, the casting wax used for this is very fine-grained, hard and brittle. It can be worked with ordinary metal-working tools with no problem [which is why it is so useful for making patterns], and can even be milled, drilled and lathe turned. Very nifty stuff.

I just thought I'd throw this in for some who might imagine we're talking about something like beeswax. Casting wax is more like a hard plastic for workability and handling capability. I have no idea what the melting temp is, but it's reasonably high [for wax, that is]. A very hot oven will evaporate it cleanly out of the mold in minutes.

L Cottrill

[Al Belli]

I have used polystyrene filled pattern wax, with excellent results.

Try: Argueso, M., & Co., Inc. -- Mamaroneck , NY -- Vegetable Waxes & Fibers, Wax Refiners & Compounders

Technical info on pattern waxes. http://www.argueso.com/technical2.htm
Products http://www.argueso.com/Product%20Line.htm
Using pattern waxes properly http://www.argueso.com/technical1.htm

Al Belli

[skyfrog]

Thanks Larry, Ben and Al, for your helpful comments and useful links.

Last night I use melted candle wax to glue pencil onto the turbine, the candle wax works fine, but there was at least two obvious misalignments in the assembly caused the accident.

As to the design of the turbine itself, I am quite sure that it will do nice job extracting energy from hot gas.

[Bruno Ogorelec]

Does anyone have an idea how 3-dimensional printing compares in cost to the conventional wax pattern method?

[Al Belli]

Hi Bruno,

The cost of stereolithographic patterns is very high, but is competetive for a few parts since no mold or complex machining is required.

The part is drawn in a conventional CAD system that will output a .STL file. This type of file describes the part surfaces as thousands of triangles, with the direction and length of each side, given at each intersection point.
The .STL file is inputted to a machine-proprietary program which takes the tessellated ( .STL ) file and re-constructs the part as a series of 2D plots with a specified thickness ( Z axis ).
The machine then extrudes a semi molten wax from a precision width nozzle, and proceeds to draw the part as a series of layers of a specific thickness value.
The completed wax pattern may then be used for an investment pattern.
Polystyrene can also be used as a material in these machines.
This is a time intensive process, and requires a fairly expensive machine (~ $125,000.00 ), so You can see that the cost for each pattern will be based on an hourly shop rate of about $ 120.00 .

Al Belli

[skyfrog]

Hi Bruno,

The cost of stereolithographic patterns is very high, but is competetive for a few parts since no mold or complex machining is required.

The part is drawn in a conventional CAD system that will output a .STL file. This type of file describes the part surfaces as thousands of triangles, with the direction and length of each side, given at each intersection point.
The .STL file is inputted to a machine-proprietary program which takes the tessellated ( .STL ) file and re-constructs the part as a series of 2D plots with a specified thickness ( Z axis ).
The machine then extrudes a semi molten wax from a precision width nozzle, and proceeds to draw the part as a series of layers of a specific thickness value.
The completed wax pattern may then be used for an investment pattern.
Polystyrene can also be used as a material in these machines.
This is a time intensive process, and requires a fairly expensive machine (~ $125,000.00 ), so You can see that the cost for each pattern will be based on an hourly shop rate of about $ 120.00 .

Al Belli

Thanks Al, nice info.

Let me add a bit more regarding RP application. Yes the price is high no metter machine itself or service, the worst thing is, technical issues regarding the difficulty of cleanup wax pattern. Due to low strength nature of wax, the machine will add automatically wax supports which wll not be easy to get rid of. Maybe I'm talking about an old machine, not the case of yours. What about resin pattern ? if used directly for investment casting, you must be very careful because resin expands when heating, so it tends to break the ceramic shell.

Quite disappointed, laser based RP technology. I prefer traditional wax molding method.

[skyfrog]

Sorry for hijacking your thread about your turbine wheel with all this casting stuff.

Not at all, I welcome any comments, discussions, even insults that are instructive :-)

Glad to hear instances of casting big parts using lost wax casting methods.

[skyfrog]

Bloody expensive, those Inconel 713 raw materials. But well, I have completed sourcing those ingots, however. Top graded ingots will be used in casting the turbine wheels, vacuum melted, vacuum casting.

When tryout the casting, I'll use SUS304 first, since it is much cheaper with no fear of failure. So if possible, I wish to show you guys the casting parts in SS304 this week.