Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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  #1   Report Post  
jr
 
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Default question

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


  #2   Report Post  
Wayne Lundberg
 
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Default


"jr" wrote in message
s...
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
JR



  #3   Report Post  
F. George McDuffee
 
Posts: n/a
Default

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



  #4   Report Post  
jr
 
Posts: n/a
Default

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





  #5   Report Post  
F. George McDuffee
 
Posts: n/a
Default

Consulting my US Navy Foundry Manual pages 221-222 [see #20072 in
http://www.lindsaybks.com/bks/foundry/index.html ] indicates two
possible problems. [I highly recommend this book -- it is low
cost and filled with practical information.]

(1) Your ladle and/or mold may not be completely dry allowing
the melt to pick up hydrogen from the water vapor.

(2) Your melting procedure is allowing the metal to pick up
excessive hydrogen from somewhere. This can be caused by too
slow/long a melt or by a reducing [hydrogen rich] atmosphere.
Manual suggests an oxidizing atmosphere. In addition, your melt
might be at too high a temperature when you are making the pour.

You may need to degas your melt before pouring, especially if you
are using scrap/salvage metal. If the top of your casting is
domed or convex when it has cooled this is an indication of
excessively gassy metal. There should be a pronounced dent or
dip [called a pipe] on the top when the casting cools with good
metal.

Which bronze alloy are you using? There are several cheap things
you can try to degas the melt depending on the composition.

You may also need to add more vents to the mold to allow the air
to escape. As my foundry teacher hammered home to me "if the air
can't get out, the metal can't get in."

=======================
On Fri, 26 Aug 2005 18:46:33 GMT, "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







  #6   Report Post  
jk
 
Posts: n/a
Default


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
  #7   Report Post  
jr
 
Posts: n/a
Default

Yes, this could be the answer, maybe one or both.

I will try tomorrow to make another new mold and to heat to 800 ºC before
fill with melt bronze, to be sure it's completely dry. Besides, I will melt
the bronze at 1000 ºC instead the 1100 ºC I used last times.

I will tell you the result.....


Thanks
JRL

"F. George McDuffee" escribió en el mensaje
news
Consulting my US Navy Foundry Manual pages 221-222 [see #20072 in
http://www.lindsaybks.com/bks/foundry/index.html ] indicates two
possible problems. [I highly recommend this book -- it is low
cost and filled with practical information.]

(1) Your ladle and/or mold may not be completely dry allowing
the melt to pick up hydrogen from the water vapor.

(2) Your melting procedure is allowing the metal to pick up
excessive hydrogen from somewhere. This can be caused by too
slow/long a melt or by a reducing [hydrogen rich] atmosphere.
Manual suggests an oxidizing atmosphere. In addition, your melt
might be at too high a temperature when you are making the pour.

You may need to degas your melt before pouring, especially if you
are using scrap/salvage metal. If the top of your casting is
domed or convex when it has cooled this is an indication of
excessively gassy metal. There should be a pronounced dent or
dip [called a pipe] on the top when the casting cools with good
metal.

Which bronze alloy are you using? There are several cheap things
you can try to degas the melt depending on the composition.

You may also need to add more vents to the mold to allow the air
to escape. As my foundry teacher hammered home to me "if the air
can't get out, the metal can't get in."

=======================
On Fri, 26 Aug 2005 18:46:33 GMT, "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







  #8   Report Post  
jr
 
Posts: n/a
Default

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



  #9   Report Post  
jr
 
Posts: n/a
Default

I don't know which bronze alloy I'm using, this come from a garden piece I
have melted....

The top of the casting is horizontal, so no domed or convex.....

hu? How to know the alloy I'm using?

JRL


"F. George McDuffee" escribió en el mensaje
news
Consulting my US Navy Foundry Manual pages 221-222 [see #20072 in
http://www.lindsaybks.com/bks/foundry/index.html ] indicates two
possible problems. [I highly recommend this book -- it is low
cost and filled with practical information.]

(1) Your ladle and/or mold may not be completely dry allowing
the melt to pick up hydrogen from the water vapor.

(2) Your melting procedure is allowing the metal to pick up
excessive hydrogen from somewhere. This can be caused by too
slow/long a melt or by a reducing [hydrogen rich] atmosphere.
Manual suggests an oxidizing atmosphere. In addition, your melt
might be at too high a temperature when you are making the pour.

You may need to degas your melt before pouring, especially if you
are using scrap/salvage metal. If the top of your casting is
domed or convex when it has cooled this is an indication of
excessively gassy metal. There should be a pronounced dent or
dip [called a pipe] on the top when the casting cools with good
metal.

Which bronze alloy are you using? There are several cheap things
you can try to degas the melt depending on the composition.

You may also need to add more vents to the mold to allow the air
to escape. As my foundry teacher hammered home to me "if the air
can't get out, the metal can't get in."

=======================
On Fri, 26 Aug 2005 18:46:33 GMT, "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







  #10   Report Post  
F. George McDuffee
 
Posts: n/a
Default

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





  #11   Report Post  
jr
 
Posts: n/a
Default

Ok. I have the tablets available now in my home. First I must check if the
sodium hypochlorite I have is pure.The tablets are of 20 gr, will need to
cut in smallest pieces. I will try it tomorrow.

Many test to do together....:-)

Thanks. I will post the results after the test. Thanks also for the
translation, but I understand better the english..:-)

I'm able better to read and understand than to speak/write, this is the
result of being reading english text all the day..:-)

As far as I see, the server has still not forward the images I posted 1 hour
ago....:-(, surely they will took more time, even though it is only 100 Kb
in size (both together).

see you all tmw.

Thanks
Greetings from Spain
JRL


"F. George McDuffee" escribió en el mensaje
...
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
m...
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





  #12   Report Post  
jr
 
Posts: n/a
Default

it have still moisture....


  #13   Report Post  
F. George McDuffee
 
Posts: n/a
Default

I would not worry about "pure" sodium hypochlorite or grinding up
the tablets.

Test with a very small piece of the tablet in the molten metal to
make sure you don't have something strange that may explode. If
this works ok, use a half tablet to start. Use tongs to get it
to the bottom of the metal so the chlorine will bubble through
the metal and combine with the hydrogen. This will boil out as
white smoke. The chlorine and other noxious gasses are colorless
and as these are poisonous, you must not inhale.

There are better degas and flux materials available than the
swimming pool additives, but these are harder to get and more
expensive. Unless you are a commercial foundry, the extra price
for the specific degas/flux compounds will not be offset by the
lower metal loss and lower [minor] sodium contamination of the
melt caused by using sodium hypochlorite.

If your feed metal is dirty or heavily corroded, you can try
adding regular salt to the charge before you melt it. This will
add sodium to the melt, which is not generally a concern for a
home foundry, and will selectively deplete certain alloying
elements such as zinc. It will however separate the dirt/oxide,
and float it to the to where you can skim it off. It is
generally helpful to keep a layer of flux/slag on top of the
molten metal until just before you pour to protect it from the
oxygen and hydrogen in the air. As mentioned before a layer of
crushed charcoal on top of the metal will also help. I have
never tried it but some people use crushed glass as a flux which
melts and forms a protective film. I know of no reason you can't
use crushed charcoal and salt at the same time.

The slag/flux you skim will be a noxious material and should be
disposed of properly, such that animals and small children can't
get to it as it can cause chemical burns and eye/skin irritation.

see
http://members.chello.se/vikingbronze/casting.htm
http://budgetcastingsupply.com/Metals.htm
http://ww2.cowtown.net/mikefirth/metalctr.htm

for more information and info about proper pouring temperatures.

Good luck and let us know how everything turns out.




On Fri, 26 Aug 2005 22:17:54 GMT, "jr"
wrote:

Ok. I have the tablets available now in my home. First I must check if the
sodium hypochlorite I have is pure.The tablets are of 20 gr, will need to
cut in smallest pieces. I will try it tomorrow.

Many test to do together....:-)

Thanks. I will post the results after the test. Thanks also for the
translation, but I understand better the english..:-)

I'm able better to read and understand than to speak/write, this is the
result of being reading english text all the day..:-)

As far as I see, the server has still not forward the images I posted 1 hour
ago....:-(, surely they will took more time, even though it is only 100 Kb
in size (both together).

see you all tmw.

Thanks
Greetings from Spain
JRL


"F. George McDuffee" escribió en el mensaje
.. .
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
om...
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




  #14   Report Post  
Mark Rand
 
Posts: n/a
Default

On Fri, 26 Aug 2005 22:17:54 GMT, "jr"
wrote:

Ok. I have the tablets available now in my home. First I must check if the
sodium hypochlorite I have is pure.The tablets are of 20 gr, will need to
cut in smallest pieces. I will try it tomorrow.

Many test to do together....:-)

Thanks. I will post the results after the test. Thanks also for the
translation, but I understand better the english..:-)

I'm able better to read and understand than to speak/write, this is the
result of being reading english text all the day..:-)

As far as I see, the server has still not forward the images I posted 1 hour
ago....:-(, surely they will took more time, even though it is only 100 Kb
in size (both together).

see you all tmw.

Thanks
Greetings from Spain
JRL



The news servers will not forward pictures for this newsgroup! Use the dropbox
at:-
http://www.metalworking.com/

There are instructions at the "Using the Dropbox" link.

Good luck with the casting.


Mark Rand
RTFM
  #15   Report Post  
jr
 
Posts: n/a
Default

Thanks Mark,

Images already sent. The links sould be:

http://www.metalworking.com/DropBox/base.jpg
http://www.metalworking.com/DropBox/lado.jpg

And the images correspond to the base and the border of the cilynder. Note
that I have still not try the George's ideas. My new mold it's still not
dry.

JRL



The news servers will not forward pictures for this newsgroup! Use the
dropbox
at:-
http://www.metalworking.com/

There are instructions at the "Using the Dropbox" link.

Good luck with the casting.


Mark Rand
RTFM





  #16   Report Post  
jr
 
Posts: n/a
Default

The images has been renamed, follow this link instead the old:

http://www.metalworking.com/DropBox/last_cast_base.jpg
http://www.metalworking.com/DropBox/last_cast_lado.jpg

JRL


  #17   Report Post  
jr
 
Posts: n/a
Default

George,

I have tried the sodium hypoclorite, but no better result got. I also tried
Borax, and got better results. Although there are also some bubbles. Maybe
few, but bugger than before.

The links you sent to me are great (many thanks). I have found something
relevant (at least for me). I have read that the mold must have no "black "
traces, because it indicates organic rests. The molds I tried, all of them
have small rest of "black" powder.

I preheat my molds only for 10 minutes, mybe this was not enough. Besides, I
was using a torch to do it. Maybe it's not the best way to do it.

I have done 3 more molds and they are now drying. I will try to make a small
furnace to let heat my molds for more time (using charcoal). Maybe it's
better to buy a resistance.....will go tomorrow to the shop.

Of the 3 molds, one have an especial vent hole in the side. Will try when
dry. Will post the result.

JRL


"F. George McDuffee" escribió en el mensaje
...
I would not worry about "pure" sodium hypochlorite or grinding up
the tablets.

Test with a very small piece of the tablet in the molten metal to
make sure you don't have something strange that may explode. If
this works ok, use a half tablet to start. Use tongs to get it
to the bottom of the metal so the chlorine will bubble through
the metal and combine with the hydrogen. This will boil out as
white smoke. The chlorine and other noxious gasses are colorless
and as these are poisonous, you must not inhale.

There are better degas and flux materials available than the
swimming pool additives, but these are harder to get and more
expensive. Unless you are a commercial foundry, the extra price
for the specific degas/flux compounds will not be offset by the
lower metal loss and lower [minor] sodium contamination of the
melt caused by using sodium hypochlorite.

If your feed metal is dirty or heavily corroded, you can try
adding regular salt to the charge before you melt it. This will
add sodium to the melt, which is not generally a concern for a
home foundry, and will selectively deplete certain alloying
elements such as zinc. It will however separate the dirt/oxide,
and float it to the to where you can skim it off. It is
generally helpful to keep a layer of flux/slag on top of the
molten metal until just before you pour to protect it from the
oxygen and hydrogen in the air. As mentioned before a layer of
crushed charcoal on top of the metal will also help. I have
never tried it but some people use crushed glass as a flux which
melts and forms a protective film. I know of no reason you can't
use crushed charcoal and salt at the same time.

The slag/flux you skim will be a noxious material and should be
disposed of properly, such that animals and small children can't
get to it as it can cause chemical burns and eye/skin irritation.

see
http://members.chello.se/vikingbronze/casting.htm
http://budgetcastingsupply.com/Metals.htm
http://ww2.cowtown.net/mikefirth/metalctr.htm

for more information and info about proper pouring temperatures.

Good luck and let us know how everything turns out.




On Fri, 26 Aug 2005 22:17:54 GMT, "jr"
wrote:

Ok. I have the tablets available now in my home. First I must check if the
sodium hypochlorite I have is pure.The tablets are of 20 gr, will need to
cut in smallest pieces. I will try it tomorrow.

Many test to do together....:-)

Thanks. I will post the results after the test. Thanks also for the
translation, but I understand better the english..:-)

I'm able better to read and understand than to speak/write, this is the
result of being reading english text all the day..:-)

As far as I see, the server has still not forward the images I posted 1
hour
ago....:-(, surely they will took more time, even though it is only 100 Kb
in size (both together).

see you all tmw.

Thanks
Greetings from Spain
JRL


"F. George McDuffee" escribió en el mensaje
. ..
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
m...

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
news:tsnug11fnni5qdctg4s2ucgo3o37pshogt@4ax. com...
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






  #18   Report Post  
James Waldby
 
Posts: n/a
Default

jr wrote on 26 Aug 2005:
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.

and on 28 Aug 2005:
The images has been renamed, follow this link instead the old:

http://www.metalworking.com/DropBox/last_cast_base.jpg
http://www.metalworking.com/DropBox/last_cast_lado.jpg


Is that 2nd image a side view, a different try, or what?

Anyhow, from the 'base' picture I imagine the mold
was wet. Plaster molds used for lost-wax casting are
heated to about red heat (to cook out all organics)
over a period of four to eight hours, and are poured
into almost immediately upon coming out of the furnace.
Also, such molds are made with "investment plaster",
which is not the same as "plaster of paris".

Where did you get your "plaster + kaolin (25% + 75%)"
recipe? I don't see how that would work, because AIUI
kaolin is a clay, so your mold would not have adequate
porosity to allow gases to escape when you pour. For
the simple cylinder you are making, perhaps you should
try a "green sand" mold. Green sand is fine sand mixed
with perhaps 10% clay and 5% moisture, although some
recipes use half or twice as much. The main idea is to
use just enough clay and water so the mold holds its
shape. Too much clay will decrease porosity and cause
bubbles; too much water gives a wet mold and bubbles.

-jiw
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