Lost Wax Castings

[Woodie]

I've got to ask, cause I'm yet to work it out. It's one of those things you're expected to know, and might look silly if ya don't. So I'm gunna look silly. sign1

Brass Lost Wax Castings for detailing bits.

I know what the brass is, but what's lost about them, and where's the wax?

 

[LongIslandTom]

How lost wax casting works:

1- You sculpt the object first in wax.

2- You encase the wax object in plaster.

3- You put the whole schmeer in an oven, and the oven will burn out the wax encased inside the plaster, leaving an empty cavity inside the plaster that is the shape of the object. (the wax becomes "lost.")

4- You pour molten brass into the plaster, and the brass will flow into that empty cavity. Once the molten brass cools and solidifies, you break open the hunk of plaster and recover the solid brass casting.

I've done quite a few of these in my professional capacity as a dentist back when solid gold crowns were common. :thumb:

 

[Woodie]

So do they have to do this process every time? Especially if they break the plaster cast to get the solidified brass out, and they don't have the original sculpted wax object cause it got "lost"? i.e. resculpt the wax object every time? Or do they mould the object from molten wax, in a cast of some sort each time, then encase in plaster, then pour molten brass etc?

 

[LongIslandTom]

Yep, you can mould many of the wax patterns en masse if you are going to mass-produce that particular brass casting shape.

The gold crowns I casted are custom-fit to a particular patient of course, so each one is unique and I never needed to mass-produce them. But for making many identical objects, there are probably industrial casting machines out there that can automatically repeat the process from beginning to end very quickly and without human intervention (from making the wax pattern to final break-out) to mass produce a particular casting.

Hope this helps!

 

[Woodie]

ahhhhh. Thanks for that Tom, who is form Long Island. (I presume).

 

[zedob]

If you want more info on the production set ups, check out jewelry making. Same thing, different product.

Hey LITom, I still use the process for making teeth(Lab Tech), I just end up fusing porcelain to it. I don't think anyone makes plain gold teeth anymore and if they keep perfecting the pressed porcelain, or milled zirconium, there may not even be a need for cast framework.

Hmmm, come to think of it, there's a Canadian company the is actually growing replacement teeth. Freeky Sci-Fi stuff.

 

[ezdays]

So do they have to do this process every time? Especially if they break the plaster cast to get the solidified brass out, and they don't have the original sculpted wax object cause it got "lost"? i.e. resculpt the wax object every time? Or do they mould the object from molten wax, in a cast of some sort each time, then encase in plaster, then pour molten brass etc?

There was a show on TV recently that took you through the process. I think it was John Ratzenberger's "Made in America", but don't hold me to that . They took an original object and made one or more rubber molds of it, then they took these molds and created the wax castings. They then took them and used wax to glue them to a trunk made also of wax. It was this way that they were able to create the plaster mold for multiple objects if they were small enough.

 

[LongIslandTom]

Hey Zedob,

Nice to see someone else in the dental field here. :thumb:

Yeah making those gold crowns were very distant in my past... These days only some of my very "grey" patients ask for those and it's once in a blue moon (if that), and even then I don't cast them myself anymore.. I still have my old equipment stored away somewhere though.. Blowtorch, crucible, casting ring, etc.. One of these days if there is a locomotive detail part I can't find, maybe I'll whip it out and cast my own.

Yep the vast majority of my fixed prostho cases these days are PFMs, and I depend on guys like you to uphold my reputation to my patients, so if any of your dentist clients who utilize your lab hasn't told you lately, thank you!

 

[zedob]

Hi Tom,

IF it weren't for MRRing, I probably wouldn't have entered the field. I used to work in the precision sheetmetal working industry when I was approached by a dentist to change careers. The dentist knows me pretty well (she's my sister) and knew of my modeling and metalworking background and talked me into making the change and I love it. Every crown is different.

 

[MadModeler]

How lost wax casting works:

1- You sculpt the object first in wax.

2- You encase the wax object in plaster.

3- You put the whole schmeer in an oven, and the oven will burn out the wax encased inside the plaster, leaving an empty cavity inside the plaster that is the shape of the object. (the wax becomes "lost.")

4- You pour molten brass into the plaster, and the brass will flow into that empty cavity. Once the molten brass cools and solidifies, you break open the hunk of plaster and recover the solid brass casting.

I've done quite a few of these in my professional capacity as a dentist back when solid gold crowns were common. :thumb:

Thank you! I just learned something new today!:thumb:

 

[zedob]

Yep the vast majority of my fixed prostho cases these days are PFMs, and I depend on guys like you to uphold my reputation to my patients, so if any of your dentist clients who utilize your lab hasn't told you lately, thank you!

Thank you for the thank you, but I'm a captive lab tech. I only do my sister's work, at the present time. She keeps me quite busy and it works out well for her because she can have me add a contact or adjust staining without sending it back to an outside lab and having to wait another 2 weeks.:curse:

I never really knew what went into crowns, where the dentist was/is concerned. I can say this, all new lab techs should work for a dentist for at least a year to see first hand what the dentist has to deal with. They may not complain about cruddy margins again.