Yes, could be, but I don't see how to put a new degassing tube in the mold,
this is a very easy and simple mold. Mmmmm, As I have just said in my last
post, I will make another test tomorrow,now it's 23:00 here...:-).
I will try to add some vents to let the gass go out. I have read the plaster
is not so porous, so I will try it.
Thanks.
JRL
"jk" escribió en el mensaje
...
Could be you are not degassing?
"jr" wrote:
Mmmm, I think it would be not the problem, because the mold is an open
mould, so there is a lot of metal over it. Think it's a cylinder, so the
mold only have an entry. I will try to draw with characters:
******** *********
******** *********
******** *********
******** ********* Think in the figure as a box with a
cylinder hole in the middle.
***********************
***********************
The * are the mold, and the [spaces] the cavity of the mold. I fill it all
with melt bronze. The result piece I get is like that:
--------------------
--------------------
-------------------[]
--------------------
-------------------- Think in the figure as a Cylinder
--[]-----------------
---[]-----[]---------
--[][]----[]------[]--
Being the [] holes in the bronze resulted piece. Of course the "-" are
solid
bronze. It seems there were captured some bubbles in the piece.
I will try to make some pictures right now and post here.
Thanks
JRL
"F. George McDuffee" escribió en el mensaje
. ..
On Fri, 26 Aug 2005 16:01:50 GMT, "jr"
wrote:
Hi,
I'm just trying to make a mold with plaster + kaolin (25% + 75 %) to
hold
bronze. The mold works fine but the final piece have a lot of big
bubbles
inside the bronze , so the piece it's totaly unusable.
any idea?
Thanks
JRL
==============
That the bubbles are inside the casting indicates that these may
not be bubbles but rather voids left when the metal solidified
and shrank. Water expands when it freezes but metal shrinks by
quite a large amount in volume when it changes from liquid to
solid. In casting it is common to provide a large volume of
liquid metal in the mold above the casting [the riser] to feed
metal into the casting as it cools and solidfies. The sprues and
runners that feed the metal into the mold cavity must be large
enough so these will not solidify first so that additional liquid
metal [from the riser] can fill any voids in the mold cavity.
Design and creation of molds to allow ouring of sound castings is
an art. Lindsay books has a good selection. see
http://www.lindsaybks.com/prod/sub/foundry.html
jk