Can I cast aluminium using the lost wax process?

The investment process has been used with great success for precision castings in aluminum, and magnesium as well. Many of the castings used in the Sergeant missile program were so cast, along with permanent mold castings. The process works, but I have no idea what type of equipment you may need to do the melting.

Harold

"Harold & Susan Vordos" wrote in message news:3f917cd4 snipped-for-privacy@newspeer2.tds.net...

Pretty simple, though time-consuming in burnout. I did it a few weeks ago, came out nice if not for some shrinkage from uneven heating.

In a (large) nutshell: Make a wax pattern in the exact same shape of the wanted piece, although a few % larger (in all dimensions) if you need it. Add sprues, gates and vents as necessary. Select a flask which will hold the pattern plus an inch or two. This can be a soup can for real small stuff, or a chunk of pipe, piece of rolled up sheet metal... Weld the wax to a bottom plate which fits reasonably well against the flask. Don't forget to include a pouring basin... Mix investment. Use 1:2 plaster of paris/sand (finer the sand, finer the details in the casting) mixture if doing this from scratch, or pick up some commercial stuff for like $10 per 50lbs. bag. (Check jeweler's supply.) If you didn't get instructions with it, or are using your own recipie (as above), then mix it to a creamy consistency (as with normal plaster) and pour in around the pattern. You *will* have bubbles, so a lot of vibration and poking with sticks will help settle. If you have access to a vacuum chamber, that's even better! You get about 10 minutes of working time, so be fast. After half an hour it should be hardened enough to move, I'd wait a day before burning it out. Burnout: if you have (or have access to) a kiln that will do 1200°F for up to maybe 6 hours, you're set. Burnout is complete when there are no more flames coming out of the sprue - the wax residue has evaporated. BTW it helps to steam the mold beforehand to drain out the wax, that way you won't get so much dripping out in the kiln and charring stuff. Ideally you should normalize (I guess that's a good word) the mold, say cook it at 800°F for a good number of hours to ensure it's the same temp all the way through. Nothing worse than going through all this just to discover that the mold was still red-hot in the very center, and that caused a shrinkage defect rendering the casting useless.

Melt and pour metal.. normal pouring temps somewhere around 1400°F. When the glow (dark surroundings) has left the sprue, it's cool enough to quench. Drop the mold into a bucket of water, sit back and wait for it to blast itself to bits! The steam causes the plaster to bubble and spall (don't worry, it's trapped underwater), which makes for a very easy job later on, picking out the rest of the investment. Congrats on one new casting, and celebrate with a beer...

If you're picky and can't throw away anything, the investment can be reused. Bake at 500°F for maybe 1/2 hour to drive off moisture, then grind back to original consistency. Will harden when water is added (store in a dry place!).

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

One thing to help with bubble problems is to paint the wax with the POP mix (do a single batch for this) and let it cure first. This tends to insure that there are no air bubbles up against the part.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!