Question about investment casting

[44-henry]

I've been playing around with small investment castings using a vacuum casting table. The other day I acquired a Sorvall Superspeed centrifuge that came out of the Biology department here at UND. It looks like everything works and the dial will adjust the speed anywhere from about 300 on up to 25000 rpm. The chamber is covered with stainless steel and is about 2' in diameter. My question is have any of you worked with centrifugal machines in the investment casting process. I have seen the spring arms, but have not had any experience using them.  I would assume that this machine could be made to work in essentially the same way, but I'm wondering if it would offer any real advantages over the vacuum process that I have been using.

Alex Johnson

[smart dog]

Hi Alex,
It is my understanding that the centrifugal force method works just as well as a vacuum but can be more dangerous and requires more space (for the swing arm that is). It also is more limited with respect to the size of the casting that can be spun. I do not believe, however, that there is any advantage to the method over using a vacuum (except maybe price). I think vacuum systems are the method of choice by most investment casters.

dave

[davec2]

Alex,

I have been doing both types of casting for about 45 years.  Most of my casting is centrifugal with a spring arm machine.  However, the larger the casting, the easier it is to do with vacuum.  I started out doing dental casting for my Dad in his lab and, when making small, precision castings like dental crowns with very fine detail like knife edge thin margins, the centrifugal machine (electric motor driven or spring arm) works best.  For larger jewelry items or gun parts, the vacuum system is easier, safer, and produces excellent parts.  If the vacuum casting rig you are using is making good castings, there is no real advantage to using the centrifugal method.  It would also probably be much more trouble than it is worth to convert a biological centrifuge to a casting machine.

[jerrywh]

 I agree with Dave2.  Also--- nothing takes the place of plenty of sprew. Lots or weight to force the metal into the mold.  Trying to Save metal by making small sprews , runners and etc is a big mistake.

[davec2]

44 Henry,

I have been making a bunch of sterling silver castings lately (the sterling silver flint charms).  I just ran a dozzen centrifugal investment castings like this one that include some 19 or 20 small items per cast.  Thought I would post a picture before I cut them all off the sprue and finished them.  The ring gate the charms are sprued to is about 3 inches in diameter.  Thought you might be interested in seeing this.



Dave C

[jerrywh]

Dave2.
  did you vacume cast that or just pour it?? There's plent of sprue there to just pour.

[davec2]

Jerry,

This was centrifugally cast in a spring arm machine.  I will take a picture of the machine tomorrow.

DC

[jerrywh]

I thought I had a big swing arm but it's not that big.

[davec2]

Jerry,

Forgot to take a picture of the casting machine, but here are the wax patterns in the investment ring.  This ring is 4 inches in diameter and about 4 tall.  The machine can swing a 4 inch diameter ring up to 7 inches tall.

[jerrywh]

Dave. What kind of wax are you using??

[davec2]

Aqua !

Sorry....wise guy answer.  I'm not sure Jerry, I will look it up and get back to you.

Dave C

[jerrywh]

Maybe it is aqua wax. I think Rio Grande has some stuff called that.

[davec2]

Jerry,

Here is the photo of my casting machine.  The empty flask in the cradle is 4 inches by 6 1/2 inches to give you some idea of scale.  Not very elaborate, but it does a good job.  I will check on the wax type.  I like it - it doesn't shrink very much and comes out of the vulvanized molds fairly easily.

Dave C

[jerrywh]

Dave. That's the same machine I have only I don't have any crucibles that big.  How much silver can you melt in your biggest crucible??

[davec2]

About 10 ounces - about 14 ounces of 14K gold.  There is a bigger machine available from Gesswein.