Another noob question- delicate/thin part removal from mold

He's right, cast aluminum doesn't anodize very well, the uptake of colour tends to be quite uneven giving a blotchy appearance

 

I've had no problems anodizing cast aluminium AA601/LM-25/A356 7% aluminium by burnishing the surface with a wire wheel first: it seems to get rid the the surface silicon and smear the surface aluminium. This was for red, blue, purple and orange dyes.

 

Will You make your own investment? Lots of people do.... I had at least three good mixtures all with plaster of paris as the base. Some with sands some with cements some with water mixed with refractory cement. LOL Now I buy investment. Do you have a way to de-gas/vacuum the investment (get the air/bubbles out) It's best if it pours into the flask without the bubbles. Your casting can have defects like the wax piece in the earlier picture. With all of that said one thing to keep in mind. Whatever that piece of wax (the model) looks like IE: finger prints, scuffs, scratches, dust and dirt. All of that will be in your final cast piece. Of course with my optimism I may be over looking any defects that may cover up any prior undesirable marks on the original model.

Once you have a piece of wax for casting you can use an old pantyhose (hopefully not yours) to polish the wax to a shine. Soft waxes will not polish as well as the harder waxes but, they will shine up. The better finish on the model/wax the better the finish on the casting. Less finishing work later.

I cant really help much with aluminum other than do not over heat it, stay in the pouring temp range. The few times I have cast aluminum, over heating was always my issue. LOL I use copper and copper alloys mostly. Silver from time to time.

Keep us updated.

 

Does that come from the sand??? Absorbed gasses binding with the surface crystals, prior to solidification and grain structure???

 

That particular alloy has 7% silicon to increase the fluidity of the molten metal amongst other things.

 

Ahhh I get it.

 

My memory isn't that good so If you have a particular metal you use i have forgotten. Is that silicon brass/bronze??? It seems to be a favorite...

 

That was six posts ago in this thread that I mentioned AA601/A356 aluminium alloy. It's what alloy car wheels are mostly made of.

 

Thanks. Someday I will start using more aluminum and that sounds like a good place to start.

I work in a commercial printing plant (retirement job) and we have about 6000 pounds of used aluminum printing plates for scrap. LOL Almost free, I can buy it super cheap. A lot of dross though.

 

I've seen printing plates for a MAN newspaper press, they had fairly thin sheet coated on photoresist chemicals, you could cut them into ingot length and roll them up tightly to minimize dross I suppose. Well worth the experiment.

 

It’s a rifle, so I’ll just tell everyone the trigger guard isn’t blotchy, it’s camouflage!

 

I’ll be using a custom alloy comprised of beer cans, rain gutters, and old aircraft parts. ;-)

 

Care to share the plaster of Paris recipe? I just happen to have a bag laying around.
I built a small Vacuum chamber, but don’t own a vacuum pump. I tried using the vacuum port from a 66 VW...ingenious, but a failed attempt, as it only pulls about 20Hg and everything I read says I need about 29Hg. Maybe try a small block Chevy...lol.

 

Your boss would be wise to wait for scrap to spike again (who knows when). Those are near the top of the scale in scrap value as long as they're clean. They're wrought though, so not the best for casting. Metal doesn't flow into fine tight areas as well as alloy with more silicon content. If you were to use them you could stack them a 1/2" high or more and cut into 2 or 3" square stacks on a bandsaw that would fit in the crucible compactly.


Pete

 

First of all if you have the money I wouldn't do any of this stuff with plaster. Too much work. LOL The real deal isn't that much but, you may have to wait a day or so.

But these were what made me know I could do it. I had two types of POP (Plaster of Paris) so I followed the mixing ratio that was on the directions to start. They were different. Didn't matter which one I used.

1st recipe) I added 20% ROCKITE Anchor Cement by weight to the dry plaster, mix well. (DONT BREATH THIS STUFF). Then used the appropriate amount of water. I always add the powder to the water. Use water on the colder side of 70°F I use a hand mixer to mix the investment. This can and will introduce a lot of air so don't whip it. This recipe sets up quick, beware. Even faster with vacuum. Over vacuum and it will start to pour like waffle batter...not good.... throw it away and start over don't waste the wax and sprue setup. JMO

I really need to see a picture of that.....

Much better than nothing. It will make a difference.

Here was my first one



2nd recipe) I removed 20% of the plaster by weight and added that amount of grams of whatever 2200-2400°F refractory cement I had here at the house. I bought some 20 years ago for the fire place. So if I needed 100 grams of investment I would use 80 grams of POP and add 20 grams of cement to the water. Mix this well, it will have the viscosity of 2% milk. Then add the POP to that.

 

That's why we have 6000lbs.... HaHa

And they still have ink on them. So not real clean.

 

First of all if you have the money I wouldn't do any of this stuff with plaster. Too much work.

Well...by the time I go out shopping for refractory cement, and/or anchor cement, I’d probably be better off just ordering some real investment. I’d probably save money in the long run because we all know you can never walk out of the hardware store with only the one thing you came in for...

 

This is true.
Since I already had that stuff it was a good place to start.

When I used home made investment I didn't have any way to vacuum the castings so I cant speak for the porosity of the mold. I also did not have any way to do a proper burnout at the required investment temperature.