That your casting was flat on top and did not have a pronounced
"pipe" appears to indicate a significant amount of gas [hydrogen]
is dissolved in the melt.

Your ISP [telofonica.net] indicates you are located in Spain. In
the United States, home swimming pools are very common, and thus
the chemicals needed to prevent the growth of algae and bacteria
are widely sold. Assuming swimming pools and the necessary
maintenance chemicals are also widely used in Spain, you should
be able to buy sodium hypocholorite, as this is the active
ingredient in most swimming pool powder and tablet treatments.

Note that this is the dry powder and adding a water solution of
sodium hypochlorite to molten metal will result in a steam
explosion with the likelihood of serious personal injury.

In the United States, swimming pool treatments are commonly
available in both powder and tablet form. The tablets tend to be
considerably higher in cost on the weight basis and offer no
benefit when used to degas metal.

Buy the smallest possible bag of powder pool treatment that
indicates sodium hypochlorite as the major active ingredient for
this test. You will need a short piece [50 m/m / 2 inches long]
of one-half inch [13 mm] nominal i.d. pipe. This should be what
is called black iron pipe in the US meaning it is not plated and
has a black oxide finish. This is commonly used here for gas
pipe.

To degas your metal, put a wad of soft paper such as newspaper in
one end of the piece of pipe, tamp the pipe full of the sodium
hypochlorite powder and put another wad of soft paper in the
other end of the pipe. When your melt is up to full pouring
temperature or slightly hotter, and wearing face mask, apron,
gloves and other protective clothing, thrust the pipe and powder
to the bottom of the crucible using tongs or a welded handle, and
gently stir. The powder will decompose, liberating chlorine gas
that will combine with any hydrogen in the molten metal. Be sure
not to breathe any of the smoke that comes off the melt when you
do this, as it is poisonous. This will also create a quantity of
slag or residue that will float to the top of the molten metal.
It may be helpful to cover the molten metal with a layer of
powdered charcoal to protect it while melting and after
degassing. You will need to skim this off before pouring the
casting. Stir the metal when you degas and skim off the slag to
insure you have a good mixture of the metals as these may want to
separate.

If this helps but does not eliminate the bubbles in your casting,
get a bigger piece of pipe and use more powder. Be advised that
the chlorine will also combine with any zinc in your brass/bronze
and will lose excessive amounts of metal if you over-degas.

[computer translation follows/la traducción de la computadora
sigue]

Que su echada era llana en cima y no tenía que una "cañería"
pronunciada parece indicar una cantidad significante de gas [el
hidrógeno] se disuelve en la fusión.

Su ISP [telofonica.net] indica usted se localiza en España. En
los Estados Unidos, casa las piscinas que nada son muy comúnes, y
así se venden los químicos necesitados prevenir el crecimiento de
algas y bacterias ampliamente. También se usan ampliamente
piscinas de la natación arrogantes y los químicos de
mantenimiento necesarios en España, usted debe poder comprar
hypocholorite de sodio, como esto el ingrediente activo está en
la mayoría el polvo de la piscina que nada y tratamientos de la
lápida.

Note que éste es el polvo seco y agregando una solución de agua
de hypochlorite de sodio al metal fundido producirán una
explosión de vapor con la probabilidad de lesión personal seria.

En los Estados Unidos, los tratamientos de la piscina que nada
están normalmente disponibles en los dos el polvo y forma de la
lápida. Las lápidas tienden ser considerablemente más alto en
costo en la base de peso y no ofrecer beneficio cuando acostumbró
a metal del degas.

Compre la posible bolsa más pequeña de tratamiento de piscina de
polvo que indica hypochlorite de sodio como el ingrediente activo
mayor para esta prueba. Usted necesitará un pedazo corto [50 m/m
/ 2 inches] de media pulgada [13 mm] i.d nominal. Esto debe ser
lo que se llama cañería de hierro negra en el significado
americano él no se chapa y tiene un acabado del óxido negro.
Esto normalmente se usa aquí para la cañería de gas.

Al degas su metal, ponga un taco de papel suave como periódico en
un extremo del pedazo de cañería, tamp la cañería lleno del polvo
del hypochlorite de sodio y puso otro taco de papel suave en el
otro extremo de la cañería. Cuando su fusión es a abatanar
vertiendo temperatura o máscara de la cara ligeramente más
caliente, y desgastado, delantal, guantes y otra ropa de la
protección, empujó la cañería y empolva al fondo del crisol que
usa tenazases o una asa soldada, y suavemente el movimiento. El
polvo descompondrá y liberará gas del cloro que combinará con
cualquier hidrógeno en el metal fundido. Está seguro no respirar
nada del humo que se cae la fusión cuando usted hace esto, cuando
es venenoso. Esto también creará una cantidad de slag o residuo
que flotarán a la cima del metal fundido. Puede ser útil cubrir
el metal fundido con una capa de carbón de leña empolvado
protegerlo mientras fundiendo y después del degassing. Usted
necesitará desnatar esto fuera de antes de verter la echada.
Revuelva el metal cuando usted el degas y desnata fuera del slag
para asegurarlo tiene una mezcla buena de los metales como éstos
puede querer separar.

Si esto ayuda pero no elimina las burbujas en su echada, consiga
un pedazo más grande de cañería y usa más polvo. Se aconsejado
que el cloro también combinará con cualquier cinc en su
brass/bronze y perderá cantidades excesivas de metal si usted
encima de-degas.
============================
On Fri, 26 Aug 2005 20:53:40 GMT, "jr"
wrote:

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