Starting In Lost Wax/ Investment Casting

[Harold_V]

I stand corrected. I should have referenced the bible instead of trusting the scant information I had at my disposal. In doing so, here's what I learned, from Metal's Handbook, Ninth Edition, Volume 2 - page 416

There is no mention of 87300, but there is mention of 87200, 87500 and 87800

87200 is referenced as Everdur, Herculoy or Navy Tombasil, ingot code 500, with 87500 and 87800 referenced as Tombasil, ingot code 500T

87200:

89% min copper
1% maximum tin
½% maximum lead
5% maximum zinc
2½% maximum iron
1½% maximim aluminum
1½% maximum mangansese
1-5% silicon


87500:

79% minimun copper
½% maximum lead
12-16% zinc
½% maximum aluminum
3-5% silicon

87800:

80-83% copper
¼% maximum tin
.15% maximum lead
.15% maximum iron
.15% maximum manganese
.15% maximum aluminum
3.75-4.25% silicon
.01% maximum magnesium
balance zinc (with the potential for a 15% zinc content)

All are reputed to cast well. At best, they offer 50% of the machinability of C36000, with 87800 only 40%.

Harold

[FLtenwheeler]

The information below is from the Material Data Web Page. The only way to make sure you are getting what you think you are getting is by using the UNS code.

UNS C87300 has very little Zinc.

Tim

UNS C87300, Formerly C87200, Silicon Bronze, Everdur, Copper Casting Alloy
Copper, Cu >= 94 %
Iron, Fe <= 0.20 %
Lead, Pb <= 0.20 %
Manganese, Mn 0.80 - 1.5 %
Silicon, Si 3.5 - 4.5 %
Zinc, Zn <= 0.25 %
Machinability 50 %
Casting shrinkage allowance is 1.8 - 2.0%

UNS C87400, Copper Casting Alloy
Copper, Cu 83 %
Silicon, Si 3.0 %
Zinc, Zn 14 %
Machinability 50 %

UNS C87500, Tombasil, Copper Casting Alloy
Aluminum, Al <= 0.50 %
Copper, Cu <= 79 %
Lead, Pb <= 0.50 %
Silicon, Si 3.0 - 5.0 %
Zinc, Zn 12 - 16 %
Machinability 50 %
Casting shrinkage allowance is 1.9%

UNS C87600, Low-Zinc Silicon Brass, Copper Casting Alloy
Copper, Cu >= 88 %
Iron, Fe <= 0.20 %
Lead, Pb <= 0.50 %
Manganese, Mn <= 0.25 %
Silicon, Si 3.5 - 5.5 %
Zinc, Zn 4.0 - 7.0 %
Machinability 40 %

UNS C87610, Silicone Bronze, Herculoy Regular, Copper Casting Alloy
Copper, Cu >= 90 %
Iron, Fe <= 0.20 %
Lead, Pb <= 0.20 %
Manganese, Mn <= 0.25 %
Other, total <= 0.50 %
Silicon, Si 3.0 - 5.0 %
Zinc, Zn 3.0 - 5.0 %
Machinability 40 %
Casting shrinkage allowance is 1.8 - 2.0%

UNS C87800, Tombasil, Copper Casting Alloy
Aluminum, Al <= 0.15 %
Copper, Cu 80 - 83 %
Iron, Fe <= 0.15 %
Lead, Pb <= 0.15 %
Magnesium, Mg <= 0.010 %
Manganese, Mn <= 0.15 %
Other <= 0.25 %
Silicon, Si 3.75 - 4.25 %
Tin, Sn <= 0.25 %
Zinc, Zn 14 %
Machinability 40 %
Casting shrinkage allowance is 1.9%

UNS C87900, Silicon Yellow Brass, Copper Casting Alloy
Aluminum, Al <= 0.15 %
Antimony, Sb <= 0.050 %
Arsenic, As <= 0.050 %
Copper, Cu >= 63 %
Iron, Fe <= 0.40 %
Lead, Pb <= 0.25 %
Manganese, Mn <= 0.15 %
Nickel, Ni <= 0.50 %
Phosphorous, P <= 0.010 %
Silicon, Si 0.80 - 1.2 %
Sulfur, S <= 0.050 %
Tin, Sn <= 0.25 %
Zinc, Zn 30 - 36 %
Machinability 80 %

UNS C99700, White Manganese Brass, Copper Casting Alloy
Aluminum, Al 0.50 - 3.0 %
Copper, Cu >= 54 %
Iron, Fe <= 1.0 %
Lead, Pb <= 2.0 %
Manganese, Mn 11 - 15 %
Nickel, Ni 4.0 - 6.0 %
Tin, Sn <= 1.0 %
Zinc, Zn 19 - 25 %
Machinability 80 %
Casting shrinkage allowance is 2.0%

[Harold_V]

Thanks for that, Tim. The analysis is in support of the information I had on 87300, and makes it clear that there is a wide variation in the content, depending on its designation.

Frankly, I'm a little surprised that my book doesn't include the 87300, but it most likely reflects the fact that there was no such alloy when the book was copyrighted (1979).

It pays to have up-to-date literature.

Harold

[FLtenwheeler]

Now that I have some ideal on casting alloys I would like to look at building the silicone molds. I will be using plastic RPs for most of the items I am thinking about casting. So I will be using RTV.

How much distance should be left between the mold and the mold frame?

Looking at the picture should the spur be on the large end or the small end? How about gating? The part is 1-3/4" tall

I know that this will have to be played with some times.

Again thanks for every ones help.

Tim

[RONALD]

Tim, first question. How many of that particular part do you need? If it is less then four, I would go to the direct investment of the RP part; forget RTV molds, you will save time and $$.

Second question. Have you found a Wax Injector to buy? You will need that to get the wax into the RTV mold. Also be sure you buy Injector Wax, some waxes may not flow right.

Third question. You will need to vacuum all the air out of the RTV before pouring it over the RP part. Do you have access to a small vacuum pump and container?

In the attached photo, is one the largest RTV molds I made. I first made the original pattern, a wooden box to fit it in and a base and sprue to support it.

I then mixed the RTV, vacuumed it, and when it stopped bubbling under vacuum, poured it over the pattern. I did this as a two part mold, by RTVing the lower part, and then later the upper (In the first pour, I used clay as the upper)

When the RTV mold was ready to go, I fired up the injector, and using a piece of wood on the top and bottom, pressed it against the injector. If I had the right wax temp and pressure, I got what you see on the left, if not the wax goes back into the pot.

The distance the wax should be from the edge depends on the wax temperature, pressure and how tightly you clamp the mold. If hot wax gets all over your hands, you did not leave enough space.

[FLtenwheeler]

Hi Ron

I am purchasing a wax pot and a programmable burnout oven from the same gentleman that I purchased the furnace from. I have a vacuum pump I just need to make the chambers, one for degassing and one for casting.

I see some people use a dewaxing steamer. Is this a nicety?

I also would like recommendations on injection waxes.

Thanks

Tim

[RONALD]

A Steam Dewaxer will be quickly recognized as needed, when you fill the house with the smell of burning wax, and your wife threatens to move out of the house!

Even after steam dewaxing, there is always some residual wax left in the mold, so it would be wise to run a vent pipe from the burn-out oven to the outside, using a little fan in line, as I did.

Steam dewaxers come in several sizes, I bought one as on the site below, but not from Rio Grande. They are mostly made in asia, and most Lost Wax equipment sites on the Internet sell the same models; find the best price.

http://www.riogrande.com/Product/Standa ... 0677?Pos=1

http://www.riogrande.com/Search/Dewaxer

Using a double boiler as Grantham did in his You Tube video, may be a short term solution, but long term a dewaxer is the way to go.

For Injection Wax, just type that into the Rio Grande site, and you will see that there are too many choices, read thru them, and pick one that looks good. One of the advantages of the kind of dewaxer I have, is that most of the wax ends up a a sheet of hard wax floating on top of the water in the dewaxer, and can be broken up and used again.

I bought 50lbs of a wax called NYC Wax, but don't remember from who. Also when they closed out that foundry class I got two different kinds of injector wax that my friend had been using.

[FLtenwheeler]

Degassing Silicone

I poured my fist mold today.

Can you use to much vacuum when degassing silicon? My chamber will pull 29".

Tim

[Harold_V]

Degassing Silicone

I poured my fist mold today.

Can you use to much vacuum when degassing silicon? My chamber will pull 29".

Tim

Strictly my opinion--not based on experience.

No, you can't. The objective is to remove air----and that's what happens. I would assume that greater vacuum will accomplish the task faster, though, but even that is speculation.

I've observed investment in the vacuum chamber. My memory recalls that it becomes very tranquil once the air is removed. I'd expect that would be true of most, if not all, substances.

I would think that so long as the end result is bubble free, it doesn't really matter.

Any chance we could see the mold?

Harold

[jkimberln]

Degassing Silicone

I poured my fist mold today.

Can you use to much vacuum when degassing silicon? My chamber will pull 29".

Tim

Remember that when you lower the air pressure, you also lower the boiling point of the material in the vacuum. I have sucked 29" in my dessicater with RTV in it and got frothing. I thought it was just air coming out. Then I realized that I had lowered the boiling point so much that part of the RTV or the catalyst was boiling out as well as the air.

I would suggest that you reduce the air pressure by about 5" Hg slowly. You will see what happens as you move down to 29". You don't want to boil out the curing peroxide component. Going down to 29" will make the air come out faster, but the usual advice is to only hold it there about 15 seconds. Also, if you aren't careful you will froth the RTV out of the container you put it in and cause a mess The froth is not caused by air coming out.

JerryK

[FLtenwheeler]

Here are some pictures of my first mold. There where some problems. I tore a chuck out between the part and the sprue. I mixed up some silicone and glued it back in. I need to slow down and not pull so hard when I am cutting. Once I receive my wax pot I will see how it works.

Tim

[Harold_V]

Degassing Silicone

I poured my fist mold today.

Can you use to much vacuum when degassing silicon? My chamber will pull 29".

Tim

Remember that when you lower the air pressure, you also lower the boiling point of the material in the vacuum. I have sucked 29" in my dessicater with RTV in it and got frothing. I thought it was just air coming out. Then I realized that I had lowered the boiling point so much that part of the RTV or the catalyst was boiling out as well as the air.

I would suggest that you reduce the air pressure by about 5" Hg slowly. You will see what happens as you move down to 29". You don't want to boil out the curing peroxide component. Going down to 29" will make the air come out faster, but the usual advice is to only hold it there about 15 seconds. Also, if you aren't careful you will froth the RTV out of the container you put it in and cause a mess The froth is not caused by air coming out.

JerryK

Wow! Thanks for the very informative post. I hadn't considered the boiling situation.

Harold