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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
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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
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"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
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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
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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
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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
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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
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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
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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
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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
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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
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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 |
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it have still moisture....
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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 |
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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 |
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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 |
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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 |
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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 |
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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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