CA1181223A - Centrifugal casting - Google Patents
Centrifugal castingInfo
- Publication number
- CA1181223A CA1181223A CA000378623A CA378623A CA1181223A CA 1181223 A CA1181223 A CA 1181223A CA 000378623 A CA000378623 A CA 000378623A CA 378623 A CA378623 A CA 378623A CA 1181223 A CA1181223 A CA 1181223A
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- CA
- Canada
- Prior art keywords
- metal
- mold
- zone
- easily oxidized
- less dense
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D19/00—Casting in, on, or around objects which form part of the product
- B22D19/16—Casting in, on, or around objects which form part of the product for making compound objects cast of two or more different metals, e.g. for making rolls for rolling mills
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D13/00—Centrifugal casting; Casting by using centrifugal force
- B22D13/02—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
Abstract
IGOR Y. KHANDROS
For: CENTRIFUGAL CASTING
Abstract of the Disclosure A centrifugal casting high in an easily oxidized element achieved by casting a high melting point metal on to an easily oxidized metal of lower melting point. The desirable distribution of the oxidizable element through the cross section of a casting is achieved relying on the basic effect of centrifugal separation.
For: CENTRIFUGAL CASTING
Abstract of the Disclosure A centrifugal casting high in an easily oxidized element achieved by casting a high melting point metal on to an easily oxidized metal of lower melting point. The desirable distribution of the oxidizable element through the cross section of a casting is achieved relying on the basic effect of centrifugal separation.
Description
This invention relates to centrifugal casting and in particular casting centrifugally alloys containing a sub-stantial amount of a light, easily oxidized element, either as a pure metal or a light alloy itself.
Castings employed under oxidation, carburization or corrosion conditions at elevated temperatures are usually cast from an ailoy containing a high percentage of chromium. In view of the price and the potential shortage o~ chromium as a strategic metal, -the problems of chromium substitution, lower chromium content or increase oE the service life of a chromium-containing alloy are of great importance. One of the.main alternatives for chromium as an element providing oxidation-corrosion resistance is aluminum, but unfortunately high aluminum steels case in air are generally unacceptable due to poor castability and the large amounts of dross and oxides present in the metal.
. . .
According to a method aspect of this invention there is provided a method of centrifugally casting a metal tube comprising: pouring an easily oxidized metal onto~
the inside diameter of a rota-ting centrifugal mold and allowing the easily oxidized metal to solidify in the mold so that it has a thick section at one end of the mold !
tapering to a thinner section; pouring a denser metal ini-tially onto the thick section of the solidi~ied metal while rotating the mold, the denser metal having a higher melting point than the easily oxidized metal thereby gradually re-melting the easily oxidized metal and progressing down the length thereoE as a protectiye blanket :Eor preventing oxi-dation of the easily oxidized metal at the pouring tempera-. ture of the denser metal; continuing rotation oE the centri-Eugal mold until the easily oxiclized metal is en-tirely covered by the blanket and also until the easily oxidized .. ~
mab/1-LZ~3 metal has moved radially inward through the denser metal -to reach the inside surface of the tube, whereby -the easily oxidized metal has been prevented from undergoing objectionable oxidation; an~ allowing the metals to solidify to complete a centrifugally cast. tube of both metals characterized b~ a centrifugal casting having at and near the outside surface a first zone having a high concentra-tion of the denser metal alloyed with a l~w concentration of the easily oxidized metal; a second zone having a h.igher concentration of the easily oxidized metal, higher than in the first zone, alloyed wi-th a lower concentration of the denser metal, lawer than in the first zone, located at and near the inside surfacei and a -transition zone between the other two zones where the concentration of the easily oxidized metal is continuously increasing radially in the direction of the inside surface.
According to a product aspect of this invention there is provided a cen-trifugal casting having at and near the outside surface a first zone having a high concentration of a dense ~etal alloyed with a low concentration of a less dense metal; a second zone having a higher concentration of the less dense ~etal, higher than in the first - zone! alloyed with a lower concentration of the dense me-tal! lower than in the first zone, at and near the inside surface, and a transition zone between the other two zones where the concentration of the less dense metal is continuously increasing radially in the d.irection of the inside sur~ace.
According to a further product aspect of this .invention there is provided a tubular centrifugal casting having a low concentration of a less dense metal and a high concentration of a dense metal combined in a zone at and near the outside; having a lower concentration oE the dense metal, compared to the outside zone, and a higher concentration of the less dense metal, also compared to the outside zone, combi.ned in a zone near the inside of the castiny; and having a transitlon zone be-tween the other two zones where the less dense metal exhibits a continuosly in-creasing concentration rad:ially inward in the direction of the inside zone.
Castings employed under oxidation, carburization or corrosion conditions at elevated temperatures are usually cast from an ailoy containing a high percentage of chromium. In view of the price and the potential shortage o~ chromium as a strategic metal, -the problems of chromium substitution, lower chromium content or increase oE the service life of a chromium-containing alloy are of great importance. One of the.main alternatives for chromium as an element providing oxidation-corrosion resistance is aluminum, but unfortunately high aluminum steels case in air are generally unacceptable due to poor castability and the large amounts of dross and oxides present in the metal.
. . .
According to a method aspect of this invention there is provided a method of centrifugally casting a metal tube comprising: pouring an easily oxidized metal onto~
the inside diameter of a rota-ting centrifugal mold and allowing the easily oxidized metal to solidify in the mold so that it has a thick section at one end of the mold !
tapering to a thinner section; pouring a denser metal ini-tially onto the thick section of the solidi~ied metal while rotating the mold, the denser metal having a higher melting point than the easily oxidized metal thereby gradually re-melting the easily oxidized metal and progressing down the length thereoE as a protectiye blanket :Eor preventing oxi-dation of the easily oxidized metal at the pouring tempera-. ture of the denser metal; continuing rotation oE the centri-Eugal mold until the easily oxiclized metal is en-tirely covered by the blanket and also until the easily oxidized .. ~
mab/1-LZ~3 metal has moved radially inward through the denser metal -to reach the inside surface of the tube, whereby -the easily oxidized metal has been prevented from undergoing objectionable oxidation; an~ allowing the metals to solidify to complete a centrifugally cast. tube of both metals characterized b~ a centrifugal casting having at and near the outside surface a first zone having a high concentra-tion of the denser metal alloyed with a l~w concentration of the easily oxidized metal; a second zone having a h.igher concentration of the easily oxidized metal, higher than in the first zone, alloyed wi-th a lower concentration of the denser metal, lawer than in the first zone, located at and near the inside surfacei and a -transition zone between the other two zones where the concentration of the easily oxidized metal is continuously increasing radially in the direction of the inside surface.
According to a product aspect of this invention there is provided a cen-trifugal casting having at and near the outside surface a first zone having a high concentration of a dense ~etal alloyed with a low concentration of a less dense metal; a second zone having a higher concentration of the less dense ~etal, higher than in the first - zone! alloyed with a lower concentration of the dense me-tal! lower than in the first zone, at and near the inside surface, and a transition zone between the other two zones where the concentration of the less dense metal is continuously increasing radially in the d.irection of the inside sur~ace.
According to a further product aspect of this .invention there is provided a tubular centrifugal casting having a low concentration of a less dense metal and a high concentration of a dense metal combined in a zone at and near the outside; having a lower concentration oE the dense metal, compared to the outside zone, and a higher concentration of the less dense metal, also compared to the outside zone, combi.ned in a zone near the inside of the castiny; and having a transitlon zone be-tween the other two zones where the less dense metal exhibits a continuosly in-creasing concentration rad:ially inward in the direction of the inside zone.
- 2 -mab/.
In the drawing:
Figs. 1, lA and lB are sectional views, partly sche-matic, of a centrifugal mold in several stages of producing a casting and wherein, for convenience, the ordinary end caps for the mold are omitted;
Fig. 2 is a photomicrograph (magnification 6X) of a cross section of a tube cast centrifugally in accordance with the present invention;
Fig. 2A is a graph showing distributions of elements in the casting Fig. 3 is a photomicrograph of the casting of Fig. 2 at a magnification of 40X; and Figs. 4 and 4A are views similar to Fig. 1 showing several stages of casting centrifugally under another embodiment of the invention.
Typical centrifugal mold apparatus is shown in Fig. 1 comprising a centrifugal mold 10. The molten metal for the cast-ing pours from the end of a spout 13A which is part of a pouring vessel 13. Because of the rotating mold the entrant metal, what-ever its kind, spirals down the ID of the mold, as the molten metal will act like any other free body of liquid seeking its own level, especially with the force of the reservoir (vessel 13) behind it.
Earlier in the process, a light, low melting point metal 12 was deposited in the same way on the ID of the mold, having solidiied, and as shown in Fig. 1 a heavier metal 14 having a much higher melting point is being deposited on the previous layer of lighter metal 12.
The first portions of heavier metal 14, therefore, will remelt outer layers of the lighter metal 12 and will spirally slip across the partially remelted substrate of the lighter metal like a skate on ice. The oncoming streams of the high melting point metal gradually remelt remaining light metal and the rest of the heavier metal eventually slips over the molten alloy con-taining both heavier and lighter metal. At these moments thelighter metal is dissolved only in the O.D. adjustment zone of the molten tube and, therefore, this zone is lighter than the rest of the metal. Because of centrifugal force, the heavier metal 14 will gravitate in the direction of the outside tOD) dia-meter of the centrifugal mold, or stated in other words, the lighter metal will be at the ID of the resultant cast tube T.
Essentially, there are four stages in principle although in actual practice they may by no means exhibit the distinctive-ness shown in the drawing. The first stage is solidification of the light metal followed next by the occurrence of the heavier, high melting point spiralling across the earlier deposited light metal, Fig. 1. The taper shown for the lighter metal in Fig. 1 ~8~2~3 is actual, and is desirable in some cases for the achieving of a uniform ID alloyed layer t especially when a lower rotating speed of the mold is employed. In the third stage the melted metals attain uniform wall thickness with the heavier metal at the ID, but because the mold continues to rotate the heavier metal moves to the OD/ Fig. lB, where it remains while the casting cools to the solid state during the last stage.
More specifically, a No. 356 aluminum alloy (6.5 to 7.0~ silicon) was poured at 1450F into the rotating mold which had been preheated to 400F. Afterwards, a heat-resistant alloy (HRA alloy) of 35% nickel, 19% chromium, 0.42% carbon, 1.2~ silicon and 1.2~ manganese (balance iron except for impurities) is poured at 2900F onto the earlier formed, thin aluminum "tube" 12 from the same end of the mold.
The resultant centrifugally cast tube is found to con-tain three zones of metal:
(1) an ordinary HRA zone at the outside diameter with some residual Al dissolved in it, (2) a transition zone, and
In the drawing:
Figs. 1, lA and lB are sectional views, partly sche-matic, of a centrifugal mold in several stages of producing a casting and wherein, for convenience, the ordinary end caps for the mold are omitted;
Fig. 2 is a photomicrograph (magnification 6X) of a cross section of a tube cast centrifugally in accordance with the present invention;
Fig. 2A is a graph showing distributions of elements in the casting Fig. 3 is a photomicrograph of the casting of Fig. 2 at a magnification of 40X; and Figs. 4 and 4A are views similar to Fig. 1 showing several stages of casting centrifugally under another embodiment of the invention.
Typical centrifugal mold apparatus is shown in Fig. 1 comprising a centrifugal mold 10. The molten metal for the cast-ing pours from the end of a spout 13A which is part of a pouring vessel 13. Because of the rotating mold the entrant metal, what-ever its kind, spirals down the ID of the mold, as the molten metal will act like any other free body of liquid seeking its own level, especially with the force of the reservoir (vessel 13) behind it.
Earlier in the process, a light, low melting point metal 12 was deposited in the same way on the ID of the mold, having solidiied, and as shown in Fig. 1 a heavier metal 14 having a much higher melting point is being deposited on the previous layer of lighter metal 12.
The first portions of heavier metal 14, therefore, will remelt outer layers of the lighter metal 12 and will spirally slip across the partially remelted substrate of the lighter metal like a skate on ice. The oncoming streams of the high melting point metal gradually remelt remaining light metal and the rest of the heavier metal eventually slips over the molten alloy con-taining both heavier and lighter metal. At these moments thelighter metal is dissolved only in the O.D. adjustment zone of the molten tube and, therefore, this zone is lighter than the rest of the metal. Because of centrifugal force, the heavier metal 14 will gravitate in the direction of the outside tOD) dia-meter of the centrifugal mold, or stated in other words, the lighter metal will be at the ID of the resultant cast tube T.
Essentially, there are four stages in principle although in actual practice they may by no means exhibit the distinctive-ness shown in the drawing. The first stage is solidification of the light metal followed next by the occurrence of the heavier, high melting point spiralling across the earlier deposited light metal, Fig. 1. The taper shown for the lighter metal in Fig. 1 ~8~2~3 is actual, and is desirable in some cases for the achieving of a uniform ID alloyed layer t especially when a lower rotating speed of the mold is employed. In the third stage the melted metals attain uniform wall thickness with the heavier metal at the ID, but because the mold continues to rotate the heavier metal moves to the OD/ Fig. lB, where it remains while the casting cools to the solid state during the last stage.
More specifically, a No. 356 aluminum alloy (6.5 to 7.0~ silicon) was poured at 1450F into the rotating mold which had been preheated to 400F. Afterwards, a heat-resistant alloy (HRA alloy) of 35% nickel, 19% chromium, 0.42% carbon, 1.2~ silicon and 1.2~ manganese (balance iron except for impurities) is poured at 2900F onto the earlier formed, thin aluminum "tube" 12 from the same end of the mold.
The resultant centrifugally cast tube is found to con-tain three zones of metal:
(1) an ordinary HRA zone at the outside diameter with some residual Al dissolved in it, (2) a transition zone, and
(3) an aluminum-rich alloy zone at the inside diameter, all zones being shown in Figs. 2 and 3, as will be ex~
plained in more detail below.
Aluminum oxide clusters were observed only near the inside diameter (ID) surface of the tube, and in surprisingly small quantities for an air-melted heat containing so much aluminum.
The three zones (1), (2), and (3) are designated in Figs. 2 and 3. The OD for the most part is the HRA alloy identi-fied above but containing evenly distributed aluminum nitrides while the aluminum-rich alloy at the ID contains Fe-Ni-~l with some chromium carbides precipated in intermetallic phases pre-cipitated in lnterdendritic areas.
Clearly, when the heavier metal 14, Fig. 1, was poured the standard HR~ melt covered and remelted the aluminum alloy which was then shifted toward the inside diameter durin~ continued rotation of the mold. However, some aluminum is dissolved in the HRA alloy during the shift, lowering the melting point of the alloy at the OD. The greater alloying with aluminum occurs at the ID, lowering the melting point of that alloy sti]l further.
The ID may be covered by an aluminum-rich oxide film providing protection against further oxidation. Those light oxide inclu-sions which get underneath the film do not propagate deeply intothe metal owing to their light weight and the centrifugal force.
Because of the increase in aluminum content a tube cast centrifugally in the manner of the present invention will exhibit higher corrosion, oxidation and carburization resistance compared to the corresponding HRA alloy having no aluminum. Also, the aluminum-rich layer at the ~D, having heavy precipitation of intermetallic phases and carbides will be harder and will exhibit improved abrasion resistance for those applications where hardness is a controlling factor. The hardness measured at the ID surface ~0 of several tubular products produced according to the present invention was up to 430 BHN.
~ n any event, the process of the present invention may permit reduction in chromium content relying on aluminum substi-tution, especially for those applications where high temperature corrosion and oxidation resistance are most needed.
The HR~ alloy specified above is only one o a whole host to which the invention may be applied. A family of HRA alloys to which the present invention may be applied is given in U.S.
Patent No. 4,077,801, issued March 7, 1978 to applicant:
Z~3 Carbon 0.25 to 0.8 ) Nickel 8 to 62 ) balance iron Chromium 12 to 32 ) except for Silicon Up to 3.5 ) impurities and Manganese Up to 3 ~ tramp elements Most of aluminum alloys may be employed without diffi-culty, depending on the final composition of metal required.
Additions of other easily oxidi~ed elements, such as titanium or boron, can be placed into the metal 12 in the form of a coarse powder of their low melting temperature alloys.
When additions of surface active elements such as boron are employed the time of solidification of the casting is apparently reduced due to lowering of the surface tension between the solid state nuclei and liquid phase. As a consequence, less centrifugal separation was observed and almost uniform distribution of aluminum through the wall of the casting resulted.
The principles of the invention would be equally appli-cable when replacing the HRA alloy with any steel such as a stain-less steel, any other HRA alloy, or a nickel or cobalt base alloy;
indeed the replacement can be any alloy meltlng appreciably higher and which is appreciably heavier than the light weight alloy and which is advantaged or improved by having the light weight, low melting point metal move therethrough while both are in the molten state.
Preferably the mold will be preheated at 350F-400F
to avoid premature solidification when the lower melting point metal is first introduced to the mold cavity. Since the mold in most instances will have a mold wash lining (e.g. one sixteenth of an inch thick) on the inside diameter derived from a mixture of silica and watier, h~eating the mold to drive off the water will also aford all, if not the major part of the preheat L22~
For any given amount of lighter, low melting point metal initially poured the distribution of the lighter element through the cross section of the casting will be proportional to the following major influences:
(1) The rotational speed of the mold over the time period required for solidification to be attained because a higher speed means higher degree of centrifugal separation and more of the heavier metal moving radially outside; higher rotational speed will also result in higher longitudinal velocity of the heavier metal, so that less heat is lost during this period of the process and, therefore, more time is available for the centri-fugal separation;
(2) The pouring temperature of the heavier metal, because when the metal is poured "hotter, 7r the total time of solidification is increased and more centrifugal separation occurs; and because metal possesses higher fluidity at higher temperatures it will move more quickly in the longitudinal direction in the first moments of the process;
(3) The thickness of the mold wash, because it also influences the total time of metal solidifications.
It will be recognized that alloying between the light and heavy metals takes place inside the mold. At all times the light metal~ if easily oxidi2ed, is prevented from doing so to any objectionable degree. The objectionable oxidation is that which ordinarily occurs when an HRA metal, combined with aluminum, is poured into the mold from a vessel as 13, at or above the melt-ing point of the HRA-aluminum alloy. Objectionable oxidation does not occur when merely pouring the aluminum alloy at its melt-ing point into a preheated mold, say when pouring at 1400F into a mold at 400F. Now then, when the HRA metal 14, not yet alloyed with aluminum 12, is poured at say 2900F, the aluminum, though melting on contact, Fig. 1, is covered by the molten HRA metal which induces the melting, and hence the easily oxidized metal is blanketed against oxidation. In comparison, an HRA-aluminum alloy of the proportion specified above, when poured all at once, will exhibit a drossyl porous, heavily oxidized ID which can be rendered acceptable only at an exhorbitant machining cost to reduce the wall thickness to a radius of sound metal; the loss in yield is prohibitive in most instances.
A further advantage is the ability to pour the HRA metal 14 at a temperature lower than hereto~ore. Thus, the HRA metal or the high melting point metal is usually poured at a temperature considerably above the liquidus so it will not be solidified too quickly by the much cooler mold. Such is not necessary under the present invention, especially when the lighter metal is aluminum because in that case the aluminum not only melts, becoming a "lubri-cant~" it is dissolved in the HRA molten metal at the same time and heat or solution is generated, meaning the HRA metal need not be poured at the higher temperature to assure sustained 1uidity.
The lower temperature results in a finer grain size which usually means (and in the case of HR~-aluminum) does mean a stronger casting.
In accordance with the broader objective of the inven-tion it is possible to reduce further the ~ormation of nonmetallic inclusions and improve the surface quality of the castings even at the ID. This is made possible by displacing air from the mold, after the light metal has solidified, with a confined body of non-oxidizing gas which itself is afterwards displaced as an inci-dent to casting the heavy metal or alloy. Thus, referring to Fig. 4, a centrifugal mold 20 is provided with the usual end caps, but in this instance one end cap 22 is provided with one or more ~8~2;~3 vent openings 24 and the other end cap 26 has a central aperture 26A of a size to admit a lance 28 which feeds a non-oxidizing gas such as argon into the mold interior after the light metal has solidified. Argon displaces air out the vent hole, which is continued until the body of gas inside the mold is the non-oxidizing gas. The lance is withdrawn and the openings in the end caps are temporarily sealed with a displaceable plug or ruptur-able diaphragm (not shown) which may be nothing more than a piece of plastic film.
When the casting is to be completed, the pouring spout 30 of a pouring vessel 32 is positioned in aperture 26~ incidental to allowing molten metal 34 (heavy metal) to pour onto the pre-viously poured light alloy at the inside diameter of the mold, which is being rotated.
The molten metal expands the gas (NG) which is forced from the mold at the vent 24 and at the annular venting space presented by aperture 26A~
The non-oxidizing gas continues to be displaced as the molten metal spirals down the mold, seeking its own level as any other fluid body.
Since the mold was and remains air-free ~rom the incep-tion of pouring the heavier metal there can be no appreciable oxidation of the molten metal, nor formation of nonmetallic inclu-sions at the ID.
plained in more detail below.
Aluminum oxide clusters were observed only near the inside diameter (ID) surface of the tube, and in surprisingly small quantities for an air-melted heat containing so much aluminum.
The three zones (1), (2), and (3) are designated in Figs. 2 and 3. The OD for the most part is the HRA alloy identi-fied above but containing evenly distributed aluminum nitrides while the aluminum-rich alloy at the ID contains Fe-Ni-~l with some chromium carbides precipated in intermetallic phases pre-cipitated in lnterdendritic areas.
Clearly, when the heavier metal 14, Fig. 1, was poured the standard HR~ melt covered and remelted the aluminum alloy which was then shifted toward the inside diameter durin~ continued rotation of the mold. However, some aluminum is dissolved in the HRA alloy during the shift, lowering the melting point of the alloy at the OD. The greater alloying with aluminum occurs at the ID, lowering the melting point of that alloy sti]l further.
The ID may be covered by an aluminum-rich oxide film providing protection against further oxidation. Those light oxide inclu-sions which get underneath the film do not propagate deeply intothe metal owing to their light weight and the centrifugal force.
Because of the increase in aluminum content a tube cast centrifugally in the manner of the present invention will exhibit higher corrosion, oxidation and carburization resistance compared to the corresponding HRA alloy having no aluminum. Also, the aluminum-rich layer at the ~D, having heavy precipitation of intermetallic phases and carbides will be harder and will exhibit improved abrasion resistance for those applications where hardness is a controlling factor. The hardness measured at the ID surface ~0 of several tubular products produced according to the present invention was up to 430 BHN.
~ n any event, the process of the present invention may permit reduction in chromium content relying on aluminum substi-tution, especially for those applications where high temperature corrosion and oxidation resistance are most needed.
The HR~ alloy specified above is only one o a whole host to which the invention may be applied. A family of HRA alloys to which the present invention may be applied is given in U.S.
Patent No. 4,077,801, issued March 7, 1978 to applicant:
Z~3 Carbon 0.25 to 0.8 ) Nickel 8 to 62 ) balance iron Chromium 12 to 32 ) except for Silicon Up to 3.5 ) impurities and Manganese Up to 3 ~ tramp elements Most of aluminum alloys may be employed without diffi-culty, depending on the final composition of metal required.
Additions of other easily oxidi~ed elements, such as titanium or boron, can be placed into the metal 12 in the form of a coarse powder of their low melting temperature alloys.
When additions of surface active elements such as boron are employed the time of solidification of the casting is apparently reduced due to lowering of the surface tension between the solid state nuclei and liquid phase. As a consequence, less centrifugal separation was observed and almost uniform distribution of aluminum through the wall of the casting resulted.
The principles of the invention would be equally appli-cable when replacing the HRA alloy with any steel such as a stain-less steel, any other HRA alloy, or a nickel or cobalt base alloy;
indeed the replacement can be any alloy meltlng appreciably higher and which is appreciably heavier than the light weight alloy and which is advantaged or improved by having the light weight, low melting point metal move therethrough while both are in the molten state.
Preferably the mold will be preheated at 350F-400F
to avoid premature solidification when the lower melting point metal is first introduced to the mold cavity. Since the mold in most instances will have a mold wash lining (e.g. one sixteenth of an inch thick) on the inside diameter derived from a mixture of silica and watier, h~eating the mold to drive off the water will also aford all, if not the major part of the preheat L22~
For any given amount of lighter, low melting point metal initially poured the distribution of the lighter element through the cross section of the casting will be proportional to the following major influences:
(1) The rotational speed of the mold over the time period required for solidification to be attained because a higher speed means higher degree of centrifugal separation and more of the heavier metal moving radially outside; higher rotational speed will also result in higher longitudinal velocity of the heavier metal, so that less heat is lost during this period of the process and, therefore, more time is available for the centri-fugal separation;
(2) The pouring temperature of the heavier metal, because when the metal is poured "hotter, 7r the total time of solidification is increased and more centrifugal separation occurs; and because metal possesses higher fluidity at higher temperatures it will move more quickly in the longitudinal direction in the first moments of the process;
(3) The thickness of the mold wash, because it also influences the total time of metal solidifications.
It will be recognized that alloying between the light and heavy metals takes place inside the mold. At all times the light metal~ if easily oxidi2ed, is prevented from doing so to any objectionable degree. The objectionable oxidation is that which ordinarily occurs when an HRA metal, combined with aluminum, is poured into the mold from a vessel as 13, at or above the melt-ing point of the HRA-aluminum alloy. Objectionable oxidation does not occur when merely pouring the aluminum alloy at its melt-ing point into a preheated mold, say when pouring at 1400F into a mold at 400F. Now then, when the HRA metal 14, not yet alloyed with aluminum 12, is poured at say 2900F, the aluminum, though melting on contact, Fig. 1, is covered by the molten HRA metal which induces the melting, and hence the easily oxidized metal is blanketed against oxidation. In comparison, an HRA-aluminum alloy of the proportion specified above, when poured all at once, will exhibit a drossyl porous, heavily oxidized ID which can be rendered acceptable only at an exhorbitant machining cost to reduce the wall thickness to a radius of sound metal; the loss in yield is prohibitive in most instances.
A further advantage is the ability to pour the HRA metal 14 at a temperature lower than hereto~ore. Thus, the HRA metal or the high melting point metal is usually poured at a temperature considerably above the liquidus so it will not be solidified too quickly by the much cooler mold. Such is not necessary under the present invention, especially when the lighter metal is aluminum because in that case the aluminum not only melts, becoming a "lubri-cant~" it is dissolved in the HRA molten metal at the same time and heat or solution is generated, meaning the HRA metal need not be poured at the higher temperature to assure sustained 1uidity.
The lower temperature results in a finer grain size which usually means (and in the case of HR~-aluminum) does mean a stronger casting.
In accordance with the broader objective of the inven-tion it is possible to reduce further the ~ormation of nonmetallic inclusions and improve the surface quality of the castings even at the ID. This is made possible by displacing air from the mold, after the light metal has solidified, with a confined body of non-oxidizing gas which itself is afterwards displaced as an inci-dent to casting the heavy metal or alloy. Thus, referring to Fig. 4, a centrifugal mold 20 is provided with the usual end caps, but in this instance one end cap 22 is provided with one or more ~8~2;~3 vent openings 24 and the other end cap 26 has a central aperture 26A of a size to admit a lance 28 which feeds a non-oxidizing gas such as argon into the mold interior after the light metal has solidified. Argon displaces air out the vent hole, which is continued until the body of gas inside the mold is the non-oxidizing gas. The lance is withdrawn and the openings in the end caps are temporarily sealed with a displaceable plug or ruptur-able diaphragm (not shown) which may be nothing more than a piece of plastic film.
When the casting is to be completed, the pouring spout 30 of a pouring vessel 32 is positioned in aperture 26~ incidental to allowing molten metal 34 (heavy metal) to pour onto the pre-viously poured light alloy at the inside diameter of the mold, which is being rotated.
The molten metal expands the gas (NG) which is forced from the mold at the vent 24 and at the annular venting space presented by aperture 26A~
The non-oxidizing gas continues to be displaced as the molten metal spirals down the mold, seeking its own level as any other fluid body.
Since the mold was and remains air-free ~rom the incep-tion of pouring the heavier metal there can be no appreciable oxidation of the molten metal, nor formation of nonmetallic inclu-sions at the ID.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of centrifugally casting a metal tube comprising:
pouring an easily oxidized metal onto the inside diameter of a rotating centrifugal mold and allowing the easily oxidized metal to solidify in the mold so that it has a thick section at one end of the mold, tapering to a thinner section;
pouring a denser metal initially onto the thick section of the solidified metal while rotating the mold, the denser metal having a higher melting point than the easily oxidized metal thereby gradually remelting the easily oxidized metal and progressing down the length thereof as a protective blanket for preventing oxidation of the easily oxidized metal at the pouring temperature of the denser metal;
continuing rotation of the centrifugal mold until the easily oxidized metal is entirely covered by the blanket and also until the easily oxidized metal has moved radially inward through the denser metal to reach the inside surface of the tube, whereby the easily oxidized metal has been prevented from undergoing objectionable oxidation; and allowing the metals to solidify to complete a centrifugally cast tube of both metals characterized by a centrifugal casting haying at and near the outside surface a first zone having a high concentration of the denser metal alloyed with a low concentration of the easily oxidized metal; a second zone having a higher concentration of the easily oxidized metal, higher than in the first zone, alloyed with a lower concentration of the denser metal, lower than in the first zone, located at and near the inside surface;
and a transition zone between the other two zones where the concentration of the easily oxidized metal is continuously increasing radially in the direction of the inside surface.
pouring an easily oxidized metal onto the inside diameter of a rotating centrifugal mold and allowing the easily oxidized metal to solidify in the mold so that it has a thick section at one end of the mold, tapering to a thinner section;
pouring a denser metal initially onto the thick section of the solidified metal while rotating the mold, the denser metal having a higher melting point than the easily oxidized metal thereby gradually remelting the easily oxidized metal and progressing down the length thereof as a protective blanket for preventing oxidation of the easily oxidized metal at the pouring temperature of the denser metal;
continuing rotation of the centrifugal mold until the easily oxidized metal is entirely covered by the blanket and also until the easily oxidized metal has moved radially inward through the denser metal to reach the inside surface of the tube, whereby the easily oxidized metal has been prevented from undergoing objectionable oxidation; and allowing the metals to solidify to complete a centrifugally cast tube of both metals characterized by a centrifugal casting haying at and near the outside surface a first zone having a high concentration of the denser metal alloyed with a low concentration of the easily oxidized metal; a second zone having a higher concentration of the easily oxidized metal, higher than in the first zone, alloyed with a lower concentration of the denser metal, lower than in the first zone, located at and near the inside surface;
and a transition zone between the other two zones where the concentration of the easily oxidized metal is continuously increasing radially in the direction of the inside surface.
2. A method according to claim 1 in which the easily oxidized metal is aluminum or an aluminum alloy.
3. A method according to claim 1 in which the easily oxidized metal is principally aluminum and in which the denser metal is a heat-resistant alloy consisting in percent by weight essentially of:
4. A method according to claim 1 in which the denser metal is selected from the group consisting of steel, cobalt base alloys, nickel base alloys, and heat-resistant alloys containing both nickel and chromium.
5, A method according to claim 1 including the step between pouring the easily oxidized metal and pouring the denser metal of displacing air from the interior of the mold with a nonoxidizing gas, confining the body of non-oxidizing gas to the interior of the mold, and providing for escape of the body of nonoxidizing gas when pouring the denser metal.
6. A method according to claim 5 in which the mold has end caps of which at least one is provided with a vent route for the escape of nonoxidizing gas and including the step of sealing that vent route to confine the body of nonoxidizing gas until the denser metal is poured.
7. A centrifugal casting having at and near the outside surface a first zone having a high concentration of a dense metal alloyed with a low concentration of a less dense metal; a second zone having A higher concentration of the less dense metal, higher than in the first zone, alloyed with a lower concentration of the dense metal, lower than in the first zone, at and near the inside surface; and a transition zone between the other two zones where the con-centration of the less dense metal is continuously increas-ing radially in the direction of the inside surface.
8. A centrifugal casting according to claim 7 of tubular form in which the less dense metal is principally aluminum and in which the dense metal consists essentially of:
carbon 0.25 to 0.8 nickel 8 to 62 balance iron except for chromium 12 to 32 ? impurities and tramp elements.
silicon up to 3.5 manganese up to 3
carbon 0.25 to 0.8 nickel 8 to 62 balance iron except for chromium 12 to 32 ? impurities and tramp elements.
silicon up to 3.5 manganese up to 3
9. A casting according to claim 7 achieved by pouring the less dense metal into a rotating centrifugal mold and allowing it to solidify while rotating the mold, and afterwards pouring the dense metal into the mold atop the less dense metal to melt it while rotating the mold until the melted less dense metal has attained the inside of the casting.
10. A tubular centrifugal casting having a low concentration of a less dense metal and a high concentration of a dense metal combined in a zone at and near the outside;
having a lower concentration of the dense metal, compared to the outside zone, and a higher concentration of the less dense metal, also compared to the outside zones, combined in a zone near the inside of the casting; and having a transition zone between the other two zones where the less dense metal exhibits a continuously increasing concentration radially inward in the direction of the inside zone.
having a lower concentration of the dense metal, compared to the outside zone, and a higher concentration of the less dense metal, also compared to the outside zones, combined in a zone near the inside of the casting; and having a transition zone between the other two zones where the less dense metal exhibits a continuously increasing concentration radially inward in the direction of the inside zone.
11. A centrifugal casting according to claim 10 in which the less dense metal is principally aluminum and in which the dense metal consists essentially of:
carbon 0.25 to 0.8 nickel 8 to 62 balance iron except for chromium 12 to 32 ? impurities and tramp elements.
silicon up to 3.5 manganese up to 3
carbon 0.25 to 0.8 nickel 8 to 62 balance iron except for chromium 12 to 32 ? impurities and tramp elements.
silicon up to 3.5 manganese up to 3
12. A centrifugal casting according to claim 10 or 11 achieved by pouring the less dense metal into a rotating centrifugal mold and allowing it to solidify while rotating the mold, and afterwards pouring the dense metal into the mold atop the less dense metal to melt it while rotating the mold until the melted less dense metal combined with the dense metal has attained the inside of the casting.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16872880A | 1980-07-14 | 1980-07-14 | |
| US168,728 | 1980-07-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1181223A true CA1181223A (en) | 1985-01-22 |
Family
ID=22612701
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000378623A Expired CA1181223A (en) | 1980-07-14 | 1981-05-29 | Centrifugal casting |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0043999B1 (en) |
| JP (2) | JPS5846384B2 (en) |
| AU (1) | AU539855B2 (en) |
| BR (1) | BR8104464A (en) |
| CA (1) | CA1181223A (en) |
| DE (1) | DE3173614D1 (en) |
| MX (1) | MX155723A (en) |
| ZA (1) | ZA813806B (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE566714C (en) * | 1931-03-19 | 1932-12-20 | Peter Otto | Process for producing blanks |
| FR1304956A (en) * | 1961-11-03 | 1962-09-28 | Deutsche Edelstahlwerke Ag | Method and apparatus for the centrifugal molding of metal materials sensitive to oxidation |
| FR2149294A1 (en) * | 1971-08-18 | 1973-03-30 | Apv Paramount Ltd | Bi metallic tubes - with specified properties of inner or outer layers |
| JPS4918696A (en) * | 1972-06-15 | 1974-02-19 | ||
| JPS5550961A (en) * | 1978-10-05 | 1980-04-14 | Kubota Ltd | Production of composite casting by centrifugal casting |
-
1981
- 1981-05-29 CA CA000378623A patent/CA1181223A/en not_active Expired
- 1981-06-08 ZA ZA00813806A patent/ZA813806B/en unknown
- 1981-06-24 MX MX187980A patent/MX155723A/en unknown
- 1981-07-02 EP EP81105149A patent/EP0043999B1/en not_active Expired
- 1981-07-02 DE DE8181105149T patent/DE3173614D1/en not_active Expired
- 1981-07-13 JP JP56108333A patent/JPS5846384B2/en not_active Expired
- 1981-07-13 AU AU72789/81A patent/AU539855B2/en not_active Ceased
- 1981-07-13 BR BR8104464A patent/BR8104464A/en unknown
-
1982
- 1982-11-19 JP JP57202187A patent/JPS58154448A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5846384B2 (en) | 1983-10-15 |
| JPS5747564A (en) | 1982-03-18 |
| JPS58154448A (en) | 1983-09-13 |
| EP0043999A1 (en) | 1982-01-20 |
| ZA813806B (en) | 1982-06-30 |
| AU539855B2 (en) | 1984-10-18 |
| DE3173614D1 (en) | 1986-03-13 |
| MX155723A (en) | 1988-04-20 |
| BR8104464A (en) | 1982-03-30 |
| EP0043999B1 (en) | 1986-01-29 |
| AU7278981A (en) | 1982-01-21 |
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