CA1267266A - Casting of metal articles - Google Patents
Casting of metal articlesInfo
- Publication number
- CA1267266A CA1267266A CA000496516A CA496516A CA1267266A CA 1267266 A CA1267266 A CA 1267266A CA 000496516 A CA000496516 A CA 000496516A CA 496516 A CA496516 A CA 496516A CA 1267266 A CA1267266 A CA 1267266A
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- Canada
- Prior art keywords
- metal
- casting
- mould
- cavity
- reservoir
- Prior art date
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- Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Structures Of Non-Positive Displacement Pumps (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
Abstract
ABSTRACT
"Casting of Metal Articles"
A method of casting metal articles comprises feeding molten metal upwardly against the force of gravity from the source of molten metal into a mould cavity, the metal is permitted to solidify within the cavity then the feed of the metal is interrupted and the casting is removed from the cavity.
The mould cavity is made by embedding an in situ detroyable pattern in particulate moulding material to form a mold cavity. The pattern may be destroyed in situ by the heat of the metal as it is fed into the mould cavity orby applying heat prior to feeding the metal into the cavity. The source of metal may be a reservoir located at a level below the level of the cavity with a pump to pump metal upwardly into the cavity through a riser tube. The metal to be cast may be supplied to the reservoir in molten state or in solid state and melted in the reservoir.
"Casting of Metal Articles"
A method of casting metal articles comprises feeding molten metal upwardly against the force of gravity from the source of molten metal into a mould cavity, the metal is permitted to solidify within the cavity then the feed of the metal is interrupted and the casting is removed from the cavity.
The mould cavity is made by embedding an in situ detroyable pattern in particulate moulding material to form a mold cavity. The pattern may be destroyed in situ by the heat of the metal as it is fed into the mould cavity orby applying heat prior to feeding the metal into the cavity. The source of metal may be a reservoir located at a level below the level of the cavity with a pump to pump metal upwardly into the cavity through a riser tube. The metal to be cast may be supplied to the reservoir in molten state or in solid state and melted in the reservoir.
Description
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This invention relates to the casting of metal artiales. More particularly, it relates to the casting of metal articles in which molten rnetalis poured into a mould cavity formed in particulate material by destroying a pattern in situ.
One well known example oF such a costing method comprises embedding a pattern of foam plastics material, e.g. expanded polystyrene, in binder-free foundry sand, consolidating the sand to form a mould, pouring rnolten metal into the mould to destroy the pattern by burning or vaporising the pattern so that the metal replaces the paitern and an article corresponding to the original shape of the pattern is cast in the mould cavity previously occupied by the pattern.
Such a method has a number of advantages which include:-1. the ability to produce castings without joint lines and thus withreduced flash thereby requiring less fettling than with conven-tional moulds comprising cope and drag parts;
This invention relates to the casting of metal artiales. More particularly, it relates to the casting of metal articles in which molten rnetalis poured into a mould cavity formed in particulate material by destroying a pattern in situ.
One well known example oF such a costing method comprises embedding a pattern of foam plastics material, e.g. expanded polystyrene, in binder-free foundry sand, consolidating the sand to form a mould, pouring rnolten metal into the mould to destroy the pattern by burning or vaporising the pattern so that the metal replaces the paitern and an article corresponding to the original shape of the pattern is cast in the mould cavity previously occupied by the pattern.
Such a method has a number of advantages which include:-1. the ability to produce castings without joint lines and thus withreduced flash thereby requiring less fettling than with conven-tional moulds comprising cope and drag parts;
2. the process is relatively easy to automate since moulding involves simple filling of particulate material around the pattern using dry binder-free particulate material such as foundry sand;
3. knock-out and de-coring are easy since the unbonded particulate material simply runs off ~md out of the casting.
However1 it suffers from the disadvantage of sporadic filling defects which are Jnacceptable in castings which are safety critical, such as suspension and steering components for automobiles.
It is accordingly an object of the present invention to provide a method of casting metal articles whereby the above mentioned problem is overcome or is reduced.
According to the broadest aspect of the present invention we provide a method of casting metal articles comprising the steps of embedding an in situ destroyabie pottern in particulate moulding material to form a mould cavity therein, then feeding molten metal into the mould cavity generally upwardly against the force of gravity from a source of molten metal which is at a level which is below the level of the cavity3 then permitting the metai to solidify within the cavity and interrupting the feed of said metal and removing the casting from the mould.
The metal may be fed into the mould cavity through a passage having one end surrounded by the molten metal and an opposite end which is connected to the mould cavity and an intermediate part which extends through the free surface of the molten metal.
, The pattern may be destroyed in sit~J by the heat oF the metal as if is fed into the mould cavity.
Alternatively the pattern may be destroyed in situ prior to feeding the metal into the mould cavity.
The pattern may comprise a casting part to provide a casting portion of the cavity and an ingate part to provide a casting ingate portion of the cavity.
The pattern may also be provided with a runner system part to provide a rJnner system portion of the cavity and a rJnner ingate part to provide a runner ingate portion of the cavity.
Metal may be fed from the source into the mould through an oriftce in a mould base on which the mould is supported~
The casting ingate part of the pattern may be disposed in casting relationship with the orifice in the mould base and then the particulate material is introduced around the casting part and casting ingate parf to embed the pattern within the particulate material.
The runner ingate part of the pattern may be disposed in casting relationship with an orifice in the mould base through which metal is fed from the source into the mould and then the particulate material is introduced around the casting part and runner system and runner ing2te parts to embed the pqttern within the particJlate material.
The pattern may be supported within a container, by means of an ingate part which is mounted within the container, the particulate materia! may be introduced into the container to embed the pattern therein, and said metal may be fed, through a cavity provided by the ingate part, into the casting portion of the mould cavity.
The pattern may be coated with one or more washes, for example an aqueous cerarnic slurry, to SIJpport the mould during the casting process, followed by drying.
The particulate material in which the pattern is embedded may be compacted by vibration or the application of a vacwm~ or by other means, or by a combination of such means.
The source of metal may be a reservoir of metal and a pump may be provided to pump metal upwardly from the reservoir into the cavity.
The metal may be pumped through a passage having one end surroJnded by the molten metal in the reservoir and an opposite end which is connected to the mould CQVity and an intermediate part which extends through the free surface of the molten metal, the pump being formed separately from the reservoir to draw metal from the reservoir into the pump and discharge metal from the pump into the mould cavity.
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;7 The metal may be pumped into the cav;ty at the bottom thereof.
The metal to be cast may be supplied to the reservoir by feeding rnetal in solid state therein to, and melting the metal in the reservoir.
The reservoir may have a feed region whereat said metal i5 fed into the reservoir in solid state, and a casting region from which metal, in IjqJ;d state, is drawn by said PUrnP.
The reservoir may have a heating region, between the feed region and the casting region in which heat is applied to the metal in tlle reservoir.
Alternatively, the rnetal to be cast may be supplied to the reservoir in molten state from a source of molten metal separate from the reservoir.
The metal may be supplied to the reservoir by means of a ladle.
The metal may be supplied to the reservoir by means of a 1aunder.
The metal may be supplied to the reservoir from a melting furnace separate from the reservoir.
The metai may be pumped by an electro-magnetic pump or by a fluid pressure pump.
Alternqtively the metal may be pumped by providing the reservoir within a sealed housing and pressurisina the interior of the housing to force metal upwardly through a riser tube extending throJgh the housing.
After the metal has solidified, the level of metal may be lowered below the level of the entry to the mould and thereafter the mould and casting are removed from casting reiationship with the source of metal, together with the mould base.
The casting may be removed from the mould by tipping out the particulate material or by fluidising the particlJlq~e material or by any other desired means.
After removal of the casting from the mould, the ingate and any other running system and feeding system~ if present, may be removed from the casting.
The mould may be made of particulate moulding material which comprises any one or a number of a variety of foundry sands, including silica, olivine, chromite, zircon, chamotte, quartz, or synthetic material such as silicon carbide or iron or steel shot.
The mould may be made of particulate moulding material which may comprise a ferro-magnetic material and the pqrticuiate material is compacted by the use of a magnetic field.
A pressure below atmospheric preSsJre may be applied to the mould during casting to assist consolidation and/or removal of vapour OF other decomposition products of the pcttern.
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The mo~ld c~vity may be filled by a flow of metal generally up~ardly against the force of gravity throughout the mould cavity.
The mould cavity rnay be filled without any substantial flow of the metal downwardly under the influence of gravity within the mould cavity.
The metal may be fed into the mould cavity by a low pressure delivery system, which causes a differential pressure to exist between the pressure in the mould cavity and the pressure in the source of molten metal.
Said differential pressure may be in the range O.i to 1.0 atmospheres and preferably 0~2û to 0.7û atn ospheres.
The mould cavity may comprise at least one casting portion, in whiçh a final casting is produced, and metal is fed to the casting portion at a single location and the casting portion is designed so that no part thereof is fed from another part of the casting portion along a path having any substantial flow downwardly under the influence of gravity.
The mould cavity may comprise at least one casting portion, in which a final casting is produced, and metal is fed into the casting portion at a plurality of locations so that the casting portion is filled by generally upwardflow of metal from a plurality of locations against the force of gravity without any substantial fiow of metal downwardly under the influence of gravity.
The mould cavity may include a casting ingate portion which communicates directly with the casting portion.
The cqsting ingate portion of the cavity may communicate with a runner system portion of the cavity which is provided with a runner ingate portion oF the cavity which communicates with the source of metal.
The casting ingate portion may communicate with a source of metal without any runner system.
The ingate may be placed in casting relationship with an orifice in the mould base, thorugh which the molten metal is fed from the source of molten metal, by inserting a portion of the ingate part of the pattern into close fitting engagement within the orifice.
The orifice may be lined with, or integrally formed in, thermally insulated refractory material capable of withstanding the liquid metal to be c~st .
The orifice may be reused for a plurality of castings.
Alternatively the orifice may be disposed after each casting operation.
The orifice may be forrned as an insert in the mould base.
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The orifice may be placed in casting reiationship with the source of metal and a feed is effected by the use of a ceramic Fibre gasket between a riser tube extending between the source of metal and the member in which the orifice is formed.
Said feeding of rnolten metal generally upwardly against the force of gravity from the source of molten metal into the mould cavity may be performed without any substantial fiow of metal downwardly Jnder the influence of gravity between the source (md the entry into the cavity.
The molten metal may comprise aluminiurn or magneSilJm or copper or alloy based thereon.
The filling defects encountered with the previously known process mentioned above arise because of the action of the liquid metal whilst it falls downwards under gravity. The uncontrolled tumbiing, splashing, surging etc., introduces and entraps oxides, gases and decomposition products from the pattern and mould materials into the metal. Even when the flow is more gentle, cool streams of metal develop a carbon deposit from decomposing styrene vapour9 which prevents two such streams from effectively mergina in parts of the casting.
8y feeding metal upwardly against the influence of gravity as called for by Applicant's invention, we have Found that the above mentioned problem is overcome or reduced because the gentle rise of the substantially horizontal metal surface keeps the metal separate from and unmixed with the decomposable pattern anci its decomposition products since decomposition of the pattern occurs progressively ahead of the advancing metal surface.
By an "in situ destroyable pattern", we mean a pattern which, when in a solid state, is suFficiently strong to enable the particJlate rnaterial to be formed therearound and which can be destroyed in sit~ so as to leqve a mould cavityu For example, the pattern may be destroyed in situ by being at least substantially completely transformed to the gaseous state, whilst within the particulate material, by subjecting the pattern to heat to cause it to vaporise and/or burn and/or Jndergo some other heat or otherwise intitiated chemical reactionO One example of a suitable destroyable pattern is a pattern made of expanded poiystyrene which is decomposed by combustion substantially to the gaseous state on heating. Of course some of the decomposition products may be small solid particles such as soot but these can leave the mould cavity together with the gaseous products of combustion, for example by passing through the pores between the particles of the particulate material.
Although it is preferred that the pattern is destroyed in Sit'J by atilising theheat of the molten metal as it is cast into the mould, if desired, the pclttern .:
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may be pre-destroyed in situ, for example, by spplying heat to the pattern prior t~ casting.
Two embodiments~of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:-FIGURE I is a diqgrammatic cross-sectional view through part oF an apparatus for performing the method embodying the present invention;
FIGURE 2 is a perspective view of the pattern for the castina and ingate shown in Figure l;
FIGURE 3 is a diagrammatic cross-section to a reduced scale through a low pressure casting machine for use with the apparatus shown in Figure l;
and FIGURE 4 is a diagrarnmatic cross-section, to a reduced scale, through a melter/holder furnace for use with the ~pparatus and pattern of Figures I
and 2 in a second embodiment of the invention.
Referring to the drawings, a pattern made of expanded polystyrene is indicated at lû and comprises two parts namely a casting part 11 of a desired shape of the final casting to be produced, and a casting ingate part 12. The pattern 10 is made in conventional manner by introducing polystyrene granules into a moulding maehine where they are injected into a die of the desired configuration. Steam is then injected which causes the granules to expand and fuse together. The resultant expanded polystyrene pattern is then water cooled and ejected from the die.
Although in the example illustrated the pattern is a one-piece moulding with the c~sting parts 11 and 12 integral with each other, depending upon the shape of the final casting and ingate or ingate and runner system, the pattern may be rnoulded in two or more separate parts bonded together by a suitable adhesive or other rnenns.
The pattern is then stored so that the normal pattern shrinkage occurs prior to use of the pattern. Of course, the die in which the pattern is made is correspondingly larger size to nllow for the shrinkage both of the pattern and of the final casting.
The pattern is then cocted with an aqueous refractory slurry by dipping or spraying and allowing to dry.
The pattern 10 is then positioned so that the ingate part i2 is in close fi~ting engagement with a cylindrical orifice 13 formed in an insert 14 made of suitable insulating refractory material such as o lightweight refractory cement, removably mounted by plates 15 secured in position by bolts 16 in an ~7;2~j~
aperture 17 of a mould bcse board 18. An open battomed cnd topped container 19 is then positioned on top of the mould bqse 18 and particu1ate moulding materia1 20 poured into the container 19 around the pattern 10 so as to embed the pattern 10 in t1-e particulate material 20 and form a mouid cavity C thereinO
In the present examp1e, the particu1ate material comprises zircon sand but may be any other suitable particulate materi~19 such as silica, olivine, chromite, chamotte, quartz sand or synthetic material such as silicon carbide or iron or steel shot.
In the present exarnple, the particu1ate material is then consolidGted around the pattern 10 by vibrating the assemb1y of mould base 18, container 19 etc., but it may be conso1idated by any other suitable means such as the cpp1ication of suction to the interior of the mould materi~1, or by other means or by a combinatio7 thereof.
The rnould base 18 carrying the mouldin~ materia1 20 and pattern 1û
therein is then positioned in casting re1~tionship with a conventional 1OW
pressure cas7ing machine M so that a riser tube 21 of the m~chine is p1aced in sealing engcgement with the insert 14 with a cer~mic fibre gasket 22 therebe!tween to provide a 1i4uid-tight seal.
The lo~ pressure die casting machine M comprises a furnace 23 havinc~ electrical heating elements 23 containing a sealed reservoir 25, to which molten metal is fed from a separate melting furnace by means of, for example, a ladle. ~he riser tube 21 provides a passage whlch has a lower end immersed in the molten metal, an upper end for sealing engagement with the insert 14 and an intermediate portion which extends through the free upper surface of the molten metal. If desired the molten metal may be fed to the reservoir 24 by other means such as a launder. After filling with molten metal the reservoir 25 is sealed and the machine M is then operated by pressurisin~ the reservoir 25 in conventional manner by applying gas, e.g. air or nitrogen, under pressure, e.g. 0.2 to 0.7 atmospheres, so as to force metal up the riser tube 21 to cast molten metal into the mould cavity C.
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Ç~j 8a If desired, mçtal may be fed from a holding furnace which is not sealed from the atmosphere by using a pump separate from the reservoir such as an electromagnetic pump or a fluid pressure pump.
In the present exampie, the metal is Gn aluminium alloy, but may be other metal such as aluminium, magnesium, copper and alloys based on such metals, cast iron or steel. The molten metal is fed by the casting machine ~ ,~
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g through the riser tube 21 and into the orifice in the insert 14 where the heat of the metcll cavses progressive decomposition of the ingate part 1~ and casting part 11 so that the pattern 10 is destroyed by being decomposed into gas and/or smqll solid or liquid particles which escape from the resultant cavity through the pores between the particles of particulate material 20 Thus, the molten metal occupies the rnould cavity C in the granular material 2û which wqs previously occupied by the pattern lO.The refractory coating provided by the slurry supports the mouldina material during casting and provides the cavity with a good surface finish.
If desired, a partial vacuum may be applied to the mould during at least the initial stages of Feeding metal into the mould to assist with consolidation and/or removal of vapour or other decomposition products of the pattern.
After the mould cavity C has been filled with liquid metal, the metal Ts allowed to solidify, or at least solidify to the extent so as to be self-supporting. Pressure is then released or partially released to allow the rnetal to fall back or partially fall back from the level of the ingate down the riser tube into the reservoir, Gnd then the mould and the casting therein are removed out of casting relationship with the casting machine M together with the mould base 18 and thereafter the casting is removed from the moulding material, either by tipping the moulding material out of contact with the casting or by fluidising the moulding material to permit it to flow or by other means.
The ingate is then removed from the castingO
Although in the present example, the orifice 13 is formed in a removable insert 14, if desired, the orifice may be formed in other material than insulcting refractory material but be lined with ;nsulating refractory material~ For example the orifice may be defined in q sleeve of the insulating refractory rnaterial provided in an opening in an aluminium plate mounted on, or which itself forms the mould base 18. The insert 14 may be used for a considerable number of casts or replaced after each cast or a small nurnber of casts depending upon the metal being cast and the materiai of which the orifice is made.
In the present example, the casting ingate is placed dTrectlv in casting relationship with the riser tube. If desired, however, in any particular castingwhere feeding is required to a plurality of locations to ensure that the castingis fed by movement of metal upwardly against the influence of gravity, a plurality of cast;ng ingates may be provided interconnected to a runner .
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system along which the molter- metal passes against the force of gravity without any subst~ntial flow downwardly under the influence of gravity, and the runner system itself having a runner ingate which is placed directly in casting relationship with ~he riser tube.
Alternatively, a plurality of separate castings may be made at the same time by feeding molten metal thereto by a similar feeder system extending from the feeder ingate to a casting ingate of the cavity for each casting.
A!ternatively, more than one riser tube may be provided to feed the metsl to feeder ingates corresponding to the number of riser tubes. Each feeder ingate may comprise also a casting ingate or each feeder inyate may be connected to a plurality of casting ingates by a runner system.
in the second embodiment of the invention the metal, method, pattern and apparatus are as described in connection with the first embodiment9 except that, instead of feeding molten metal into the moulds using the mGchine shown in Figure 3, there is used the apparatus shown in Figure 4.
In this embodiment, referring particularly to Figure 4, there is provided a melter/holder furnace 30 comprising a refractory lined vessel 31 having a generally rectangular base 32, and vertical side and end walls 33, 34 respectively. A roof 35 extends across the whole width of the vessel 31 but stops short of the end walls 34 to provide a charging well 36 and a pump well 37 at opposite ends of the vessel.
The roof 35 comprises a generally horizontal rectangular top part 38 and verticai side and end walls 39, 4û respectively. The roof 38 comprises suitable refractory materiai and within the roof are provided electrical radiant heaters 41.
The temperature of the heaters 41 and the number thereof and the area of the top par~ 38 of the roof are arranged so as to provide sufficient heat to melt ingots fed into the vessel 31 at the charging well 36 and to maintain the metal molten in the remainder af the vessel. A downwardly depending refractory wall 42 is provided at the charging well end of the vessel 31 to separate the charging well from Jhe main heating part of the vessel whilst downwardly depending and upwardly extending refractory walis 43, 44 are provided at the pump well end of the vessel to define a casting vessel region 45 within which a pump 46, separate from the reservoir, is provided~ In the present example the pump 46 is an electro-magnetic pump which pumps metal from the region 45 through a riser tube 47 which is connected to the ,............................... .
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;72~i6 mo~l1d base 18 in exac~ly the same way as the riser tube 21 shown in Figure 1. If desired a filter 48 may be provided between the walls 43 and 44 to filter metal entering the casting vessel 45. Ihe riser tube 47 and pump 46 provide a passage which ha~ a lower end imnersed in the molten meta1, an upper end for sealing eng~gelrRnt with the insert 14 and an intermediate portion which exter~s through the free upper surface of the molten meta1. If desired, other types of p~nl?, separate from the furnace, may be used, such as a fluid pressure P~.
AIthoush it is preferred that the melterJholder furr;ace an~ pump shown in Figure 4 are used to feed metal to G mould which has been made using an in sitv destroyabIe pattern, if desired the apparatus shown in Figure 4 may be used to feed metal generally upwardly against the force of gravity into a mould cavity made in any other way and of any other suitcbIe material. In all other respects the method ancl apparatus wilI be the same as described hereinbef ore.
The features disclosed in the foregoing description, or the accompany-ing drawings, expressed in their specific forms or in terms cf a means for performing the discIosed function, or a method or process for attaining the disclosed resuIt, may, separately or in any combination of such features, be utitised for realising the invention in diverse forms thereof.
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However1 it suffers from the disadvantage of sporadic filling defects which are Jnacceptable in castings which are safety critical, such as suspension and steering components for automobiles.
It is accordingly an object of the present invention to provide a method of casting metal articles whereby the above mentioned problem is overcome or is reduced.
According to the broadest aspect of the present invention we provide a method of casting metal articles comprising the steps of embedding an in situ destroyabie pottern in particulate moulding material to form a mould cavity therein, then feeding molten metal into the mould cavity generally upwardly against the force of gravity from a source of molten metal which is at a level which is below the level of the cavity3 then permitting the metai to solidify within the cavity and interrupting the feed of said metal and removing the casting from the mould.
The metal may be fed into the mould cavity through a passage having one end surrounded by the molten metal and an opposite end which is connected to the mould cavity and an intermediate part which extends through the free surface of the molten metal.
, The pattern may be destroyed in sit~J by the heat oF the metal as if is fed into the mould cavity.
Alternatively the pattern may be destroyed in situ prior to feeding the metal into the mould cavity.
The pattern may comprise a casting part to provide a casting portion of the cavity and an ingate part to provide a casting ingate portion of the cavity.
The pattern may also be provided with a runner system part to provide a rJnner system portion of the cavity and a rJnner ingate part to provide a runner ingate portion of the cavity.
Metal may be fed from the source into the mould through an oriftce in a mould base on which the mould is supported~
The casting ingate part of the pattern may be disposed in casting relationship with the orifice in the mould base and then the particulate material is introduced around the casting part and casting ingate parf to embed the pattern within the particulate material.
The runner ingate part of the pattern may be disposed in casting relationship with an orifice in the mould base through which metal is fed from the source into the mould and then the particulate material is introduced around the casting part and runner system and runner ing2te parts to embed the pqttern within the particJlate material.
The pattern may be supported within a container, by means of an ingate part which is mounted within the container, the particulate materia! may be introduced into the container to embed the pattern therein, and said metal may be fed, through a cavity provided by the ingate part, into the casting portion of the mould cavity.
The pattern may be coated with one or more washes, for example an aqueous cerarnic slurry, to SIJpport the mould during the casting process, followed by drying.
The particulate material in which the pattern is embedded may be compacted by vibration or the application of a vacwm~ or by other means, or by a combination of such means.
The source of metal may be a reservoir of metal and a pump may be provided to pump metal upwardly from the reservoir into the cavity.
The metal may be pumped through a passage having one end surroJnded by the molten metal in the reservoir and an opposite end which is connected to the mould CQVity and an intermediate part which extends through the free surface of the molten metal, the pump being formed separately from the reservoir to draw metal from the reservoir into the pump and discharge metal from the pump into the mould cavity.
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;7 The metal may be pumped into the cav;ty at the bottom thereof.
The metal to be cast may be supplied to the reservoir by feeding rnetal in solid state therein to, and melting the metal in the reservoir.
The reservoir may have a feed region whereat said metal i5 fed into the reservoir in solid state, and a casting region from which metal, in IjqJ;d state, is drawn by said PUrnP.
The reservoir may have a heating region, between the feed region and the casting region in which heat is applied to the metal in tlle reservoir.
Alternatively, the rnetal to be cast may be supplied to the reservoir in molten state from a source of molten metal separate from the reservoir.
The metal may be supplied to the reservoir by means of a ladle.
The metal may be supplied to the reservoir by means of a 1aunder.
The metal may be supplied to the reservoir from a melting furnace separate from the reservoir.
The metai may be pumped by an electro-magnetic pump or by a fluid pressure pump.
Alternqtively the metal may be pumped by providing the reservoir within a sealed housing and pressurisina the interior of the housing to force metal upwardly through a riser tube extending throJgh the housing.
After the metal has solidified, the level of metal may be lowered below the level of the entry to the mould and thereafter the mould and casting are removed from casting reiationship with the source of metal, together with the mould base.
The casting may be removed from the mould by tipping out the particulate material or by fluidising the particlJlq~e material or by any other desired means.
After removal of the casting from the mould, the ingate and any other running system and feeding system~ if present, may be removed from the casting.
The mould may be made of particulate moulding material which comprises any one or a number of a variety of foundry sands, including silica, olivine, chromite, zircon, chamotte, quartz, or synthetic material such as silicon carbide or iron or steel shot.
The mould may be made of particulate moulding material which may comprise a ferro-magnetic material and the pqrticuiate material is compacted by the use of a magnetic field.
A pressure below atmospheric preSsJre may be applied to the mould during casting to assist consolidation and/or removal of vapour OF other decomposition products of the pcttern.
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The mo~ld c~vity may be filled by a flow of metal generally up~ardly against the force of gravity throughout the mould cavity.
The mould cavity rnay be filled without any substantial flow of the metal downwardly under the influence of gravity within the mould cavity.
The metal may be fed into the mould cavity by a low pressure delivery system, which causes a differential pressure to exist between the pressure in the mould cavity and the pressure in the source of molten metal.
Said differential pressure may be in the range O.i to 1.0 atmospheres and preferably 0~2û to 0.7û atn ospheres.
The mould cavity may comprise at least one casting portion, in whiçh a final casting is produced, and metal is fed to the casting portion at a single location and the casting portion is designed so that no part thereof is fed from another part of the casting portion along a path having any substantial flow downwardly under the influence of gravity.
The mould cavity may comprise at least one casting portion, in which a final casting is produced, and metal is fed into the casting portion at a plurality of locations so that the casting portion is filled by generally upwardflow of metal from a plurality of locations against the force of gravity without any substantial fiow of metal downwardly under the influence of gravity.
The mould cavity may include a casting ingate portion which communicates directly with the casting portion.
The cqsting ingate portion of the cavity may communicate with a runner system portion of the cavity which is provided with a runner ingate portion oF the cavity which communicates with the source of metal.
The casting ingate portion may communicate with a source of metal without any runner system.
The ingate may be placed in casting relationship with an orifice in the mould base, thorugh which the molten metal is fed from the source of molten metal, by inserting a portion of the ingate part of the pattern into close fitting engagement within the orifice.
The orifice may be lined with, or integrally formed in, thermally insulated refractory material capable of withstanding the liquid metal to be c~st .
The orifice may be reused for a plurality of castings.
Alternatively the orifice may be disposed after each casting operation.
The orifice may be forrned as an insert in the mould base.
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The orifice may be placed in casting reiationship with the source of metal and a feed is effected by the use of a ceramic Fibre gasket between a riser tube extending between the source of metal and the member in which the orifice is formed.
Said feeding of rnolten metal generally upwardly against the force of gravity from the source of molten metal into the mould cavity may be performed without any substantial fiow of metal downwardly Jnder the influence of gravity between the source (md the entry into the cavity.
The molten metal may comprise aluminiurn or magneSilJm or copper or alloy based thereon.
The filling defects encountered with the previously known process mentioned above arise because of the action of the liquid metal whilst it falls downwards under gravity. The uncontrolled tumbiing, splashing, surging etc., introduces and entraps oxides, gases and decomposition products from the pattern and mould materials into the metal. Even when the flow is more gentle, cool streams of metal develop a carbon deposit from decomposing styrene vapour9 which prevents two such streams from effectively mergina in parts of the casting.
8y feeding metal upwardly against the influence of gravity as called for by Applicant's invention, we have Found that the above mentioned problem is overcome or reduced because the gentle rise of the substantially horizontal metal surface keeps the metal separate from and unmixed with the decomposable pattern anci its decomposition products since decomposition of the pattern occurs progressively ahead of the advancing metal surface.
By an "in situ destroyable pattern", we mean a pattern which, when in a solid state, is suFficiently strong to enable the particJlate rnaterial to be formed therearound and which can be destroyed in sit~ so as to leqve a mould cavityu For example, the pattern may be destroyed in situ by being at least substantially completely transformed to the gaseous state, whilst within the particulate material, by subjecting the pattern to heat to cause it to vaporise and/or burn and/or Jndergo some other heat or otherwise intitiated chemical reactionO One example of a suitable destroyable pattern is a pattern made of expanded poiystyrene which is decomposed by combustion substantially to the gaseous state on heating. Of course some of the decomposition products may be small solid particles such as soot but these can leave the mould cavity together with the gaseous products of combustion, for example by passing through the pores between the particles of the particulate material.
Although it is preferred that the pattern is destroyed in Sit'J by atilising theheat of the molten metal as it is cast into the mould, if desired, the pclttern .:
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.
. . .
may be pre-destroyed in situ, for example, by spplying heat to the pattern prior t~ casting.
Two embodiments~of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:-FIGURE I is a diqgrammatic cross-sectional view through part oF an apparatus for performing the method embodying the present invention;
FIGURE 2 is a perspective view of the pattern for the castina and ingate shown in Figure l;
FIGURE 3 is a diagrammatic cross-section to a reduced scale through a low pressure casting machine for use with the apparatus shown in Figure l;
and FIGURE 4 is a diagrarnmatic cross-section, to a reduced scale, through a melter/holder furnace for use with the ~pparatus and pattern of Figures I
and 2 in a second embodiment of the invention.
Referring to the drawings, a pattern made of expanded polystyrene is indicated at lû and comprises two parts namely a casting part 11 of a desired shape of the final casting to be produced, and a casting ingate part 12. The pattern 10 is made in conventional manner by introducing polystyrene granules into a moulding maehine where they are injected into a die of the desired configuration. Steam is then injected which causes the granules to expand and fuse together. The resultant expanded polystyrene pattern is then water cooled and ejected from the die.
Although in the example illustrated the pattern is a one-piece moulding with the c~sting parts 11 and 12 integral with each other, depending upon the shape of the final casting and ingate or ingate and runner system, the pattern may be rnoulded in two or more separate parts bonded together by a suitable adhesive or other rnenns.
The pattern is then stored so that the normal pattern shrinkage occurs prior to use of the pattern. Of course, the die in which the pattern is made is correspondingly larger size to nllow for the shrinkage both of the pattern and of the final casting.
The pattern is then cocted with an aqueous refractory slurry by dipping or spraying and allowing to dry.
The pattern 10 is then positioned so that the ingate part i2 is in close fi~ting engagement with a cylindrical orifice 13 formed in an insert 14 made of suitable insulating refractory material such as o lightweight refractory cement, removably mounted by plates 15 secured in position by bolts 16 in an ~7;2~j~
aperture 17 of a mould bcse board 18. An open battomed cnd topped container 19 is then positioned on top of the mould bqse 18 and particu1ate moulding materia1 20 poured into the container 19 around the pattern 10 so as to embed the pattern 10 in t1-e particulate material 20 and form a mouid cavity C thereinO
In the present examp1e, the particu1ate material comprises zircon sand but may be any other suitable particulate materi~19 such as silica, olivine, chromite, chamotte, quartz sand or synthetic material such as silicon carbide or iron or steel shot.
In the present exarnple, the particu1ate material is then consolidGted around the pattern 10 by vibrating the assemb1y of mould base 18, container 19 etc., but it may be conso1idated by any other suitable means such as the cpp1ication of suction to the interior of the mould materi~1, or by other means or by a combinatio7 thereof.
The rnould base 18 carrying the mouldin~ materia1 20 and pattern 1û
therein is then positioned in casting re1~tionship with a conventional 1OW
pressure cas7ing machine M so that a riser tube 21 of the m~chine is p1aced in sealing engcgement with the insert 14 with a cer~mic fibre gasket 22 therebe!tween to provide a 1i4uid-tight seal.
The lo~ pressure die casting machine M comprises a furnace 23 havinc~ electrical heating elements 23 containing a sealed reservoir 25, to which molten metal is fed from a separate melting furnace by means of, for example, a ladle. ~he riser tube 21 provides a passage whlch has a lower end immersed in the molten metal, an upper end for sealing engagement with the insert 14 and an intermediate portion which extends through the free upper surface of the molten metal. If desired the molten metal may be fed to the reservoir 24 by other means such as a launder. After filling with molten metal the reservoir 25 is sealed and the machine M is then operated by pressurisin~ the reservoir 25 in conventional manner by applying gas, e.g. air or nitrogen, under pressure, e.g. 0.2 to 0.7 atmospheres, so as to force metal up the riser tube 21 to cast molten metal into the mould cavity C.
- " ::
.
.
.
Ç~j 8a If desired, mçtal may be fed from a holding furnace which is not sealed from the atmosphere by using a pump separate from the reservoir such as an electromagnetic pump or a fluid pressure pump.
In the present exampie, the metal is Gn aluminium alloy, but may be other metal such as aluminium, magnesium, copper and alloys based on such metals, cast iron or steel. The molten metal is fed by the casting machine ~ ,~
. .
. :, ..
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g through the riser tube 21 and into the orifice in the insert 14 where the heat of the metcll cavses progressive decomposition of the ingate part 1~ and casting part 11 so that the pattern 10 is destroyed by being decomposed into gas and/or smqll solid or liquid particles which escape from the resultant cavity through the pores between the particles of particulate material 20 Thus, the molten metal occupies the rnould cavity C in the granular material 2û which wqs previously occupied by the pattern lO.The refractory coating provided by the slurry supports the mouldina material during casting and provides the cavity with a good surface finish.
If desired, a partial vacuum may be applied to the mould during at least the initial stages of Feeding metal into the mould to assist with consolidation and/or removal of vapour or other decomposition products of the pattern.
After the mould cavity C has been filled with liquid metal, the metal Ts allowed to solidify, or at least solidify to the extent so as to be self-supporting. Pressure is then released or partially released to allow the rnetal to fall back or partially fall back from the level of the ingate down the riser tube into the reservoir, Gnd then the mould and the casting therein are removed out of casting relationship with the casting machine M together with the mould base 18 and thereafter the casting is removed from the moulding material, either by tipping the moulding material out of contact with the casting or by fluidising the moulding material to permit it to flow or by other means.
The ingate is then removed from the castingO
Although in the present example, the orifice 13 is formed in a removable insert 14, if desired, the orifice may be formed in other material than insulcting refractory material but be lined with ;nsulating refractory material~ For example the orifice may be defined in q sleeve of the insulating refractory rnaterial provided in an opening in an aluminium plate mounted on, or which itself forms the mould base 18. The insert 14 may be used for a considerable number of casts or replaced after each cast or a small nurnber of casts depending upon the metal being cast and the materiai of which the orifice is made.
In the present example, the casting ingate is placed dTrectlv in casting relationship with the riser tube. If desired, however, in any particular castingwhere feeding is required to a plurality of locations to ensure that the castingis fed by movement of metal upwardly against the influence of gravity, a plurality of cast;ng ingates may be provided interconnected to a runner .
- ~ .,, . :
: : , ' ~
' : ' ~ ', : .
system along which the molter- metal passes against the force of gravity without any subst~ntial flow downwardly under the influence of gravity, and the runner system itself having a runner ingate which is placed directly in casting relationship with ~he riser tube.
Alternatively, a plurality of separate castings may be made at the same time by feeding molten metal thereto by a similar feeder system extending from the feeder ingate to a casting ingate of the cavity for each casting.
A!ternatively, more than one riser tube may be provided to feed the metsl to feeder ingates corresponding to the number of riser tubes. Each feeder ingate may comprise also a casting ingate or each feeder inyate may be connected to a plurality of casting ingates by a runner system.
in the second embodiment of the invention the metal, method, pattern and apparatus are as described in connection with the first embodiment9 except that, instead of feeding molten metal into the moulds using the mGchine shown in Figure 3, there is used the apparatus shown in Figure 4.
In this embodiment, referring particularly to Figure 4, there is provided a melter/holder furnace 30 comprising a refractory lined vessel 31 having a generally rectangular base 32, and vertical side and end walls 33, 34 respectively. A roof 35 extends across the whole width of the vessel 31 but stops short of the end walls 34 to provide a charging well 36 and a pump well 37 at opposite ends of the vessel.
The roof 35 comprises a generally horizontal rectangular top part 38 and verticai side and end walls 39, 4û respectively. The roof 38 comprises suitable refractory materiai and within the roof are provided electrical radiant heaters 41.
The temperature of the heaters 41 and the number thereof and the area of the top par~ 38 of the roof are arranged so as to provide sufficient heat to melt ingots fed into the vessel 31 at the charging well 36 and to maintain the metal molten in the remainder af the vessel. A downwardly depending refractory wall 42 is provided at the charging well end of the vessel 31 to separate the charging well from Jhe main heating part of the vessel whilst downwardly depending and upwardly extending refractory walis 43, 44 are provided at the pump well end of the vessel to define a casting vessel region 45 within which a pump 46, separate from the reservoir, is provided~ In the present example the pump 46 is an electro-magnetic pump which pumps metal from the region 45 through a riser tube 47 which is connected to the ,............................... .
~.
.
.. ..
::
;72~i6 mo~l1d base 18 in exac~ly the same way as the riser tube 21 shown in Figure 1. If desired a filter 48 may be provided between the walls 43 and 44 to filter metal entering the casting vessel 45. Ihe riser tube 47 and pump 46 provide a passage which ha~ a lower end imnersed in the molten meta1, an upper end for sealing eng~gelrRnt with the insert 14 and an intermediate portion which exter~s through the free upper surface of the molten meta1. If desired, other types of p~nl?, separate from the furnace, may be used, such as a fluid pressure P~.
AIthoush it is preferred that the melterJholder furr;ace an~ pump shown in Figure 4 are used to feed metal to G mould which has been made using an in sitv destroyabIe pattern, if desired the apparatus shown in Figure 4 may be used to feed metal generally upwardly against the force of gravity into a mould cavity made in any other way and of any other suitcbIe material. In all other respects the method ancl apparatus wilI be the same as described hereinbef ore.
The features disclosed in the foregoing description, or the accompany-ing drawings, expressed in their specific forms or in terms cf a means for performing the discIosed function, or a method or process for attaining the disclosed resuIt, may, separately or in any combination of such features, be utitised for realising the invention in diverse forms thereof.
~ . ~
' ' ~`" ` `
Claims (53)
1. A method of casting metal articles comprising the steps of embedding an in situ destroyable pattern in particulate moulding material to form a mould cavity therein, then feeding molten metal into the mould cavity generally upwardly against the force of gravity from a source of molten metal which is at a level which is below the level of the cavity, then permitting the metal to solidify within the cavity and interrupting the feed of said metal and removing the casting from the mould.
2. A method according to Claim 1 wherein the metal is fed into the mould cavity through a passage having one end surrounded by the molten metal and an opposite end which is connected to the mould cavity and an intermediate part which extends through the free surface of the molten metal.
3. A method according to Claim 1 wherein the pattern is destroyed in situ by the heat of the metal as it is fed into the mould cavity.
4. A method according to Claim 1 wherein the pattern is destroyed in situ prior to feeding the metal into the mould cavity.
5. A method according to Claim 1 wherein the pattern comprises a casting part to provide a casting portion of the cavity and an ingate part to provide a casting ingate portion of the cavity.
6. A method according to Claim 5 wherein the pattern is also provided with a runner system part to provide a runner system portion of the cavity and a runner ingate part to provide a runner ingate portion of the cavity.
7. A method according to Claim 5 wherein metal is fed from the source into the mould through an orifice in a mould base on which the mould is supported.
8. A method according to Claim 7 wherein the casting ingate part of the pattern is disposed in casting relationship with the orifice in the mould base and then the particulate material is introduced around the casting part and casting ingate part to embed the pattern within the particulate material.
9. A method according to Claim 6 wherein the runner ingate part of the pattern is disposed in casting relationship with an orifice in the mould base through which metal is fed from the source into the mould and then the particulate material is introduced around the casting part and runner system and runner ingate parts to embed the pattern within the particulate material.
10. A method according to Claim 1 wherein the pattern is supported within a container, by means of an ingate part which is mounted within the container, the particulate material is introduced into the container to embed the pattern therein, and said metal is fed, through a cavity provided by the ingate part, into the casting portion of the mould cavity.
11. A method according to Claim 1 wherein the pattern is coated with one or more washes to support the mould during the casting process, followed by drying.
12. A method according to Claim 1 wherein the particulate material in which the pattern is embedded is compacted by vibration.
13. A method according to Claim 1 wherein the particulate material in which the pattern is embedded is compacted by the application of a vacuum.
14. A method according to Claim 1 wherein the particulate material in which the pattern is embedded is compacted by vibration and the application of a vacuum.
15. A method according to Claim 1 wherein the source of metal is a reservoir of metal and a pump is provided to pump metal upwardly from the reservoir into the cavity.
16. A method according to Claim 15 wherein the metal is pumped through a passage having one end surrounded by the molten metal in the reservoir and an opposite end which is connected to the mould cavity and an intermediate part which extends through the free surface of the molten metal, the pump being formed separately from the reservoir to draw metal from the reservoir into the pump and discharge metal from the pump into the mould cavity.
17. A method according to Claim 15 wherein the metal is pumped into the cavity at the bottom thereof.
18. A method according to Claim 15 wherein the metal to be cast is supplied to the reservoir by feeding metal in solid state therein to, and melting the metal in the reservoir.
19. A method according to Claim 18 wherein the reservoir has a feed region whereat said metal is fed into the reservoir in solid state, and a casting region from which metal, in liquid state, is drawn by said pump.
20. A method according to Claim 19 wherein the reservoir has a heating region, between the feed region and the casting region in which heat is applied to the metal in the reservoir.
21. A method according to Claim 15 wherein the metal to be cast is supplied to the reservoir in molten state from a source of molten metal separate from the reservoir.
22. A method according to Claim 21 wherein the metal is supplied to the reservoir by means of a ladle.
23. A method according to Claim 21 wherein the metal is supplied to the reservoir by means of a launder.
24. A method according to Claim 21 wherein the metal is supplied to the reservoir from a melting furnace separate from the reservoir.
25. A method according to Claim 15 wherein the metal is pumped by an electro-magnetic pump.
26. A method according to Claim 15 wherein the metal is pumped by a fluid pressure pump.
27. A method according to Claim 15 wherein the metal is pumped by providing the reservoir within a sealed housing and pressurising the interior ofthe housing to force metal upwardly through a riser tube which extends through the housing.
28. A method according to Claim 15 wherein, after the metal has solidified, the level of metal is lowered below the level of the entry to the mould and thereafter the mould and casting are removed from casting relationship with the source of metal, together with the mould base.
29. A method according to Claim 1 wherein the casting is removed from the mould by tipping out the particulate material.
30. A method according to Claim 1 wherein the casting is removed from the mould by fluidising the particulate material.
31. A method according to Claim 1 wherein, after removal of the casting from the mould, the ingate and any other running system and feeding system, if present, is removed from the casting.
32. A method according to Claim 1 wherein the mould is made of particulate moulding material which comprises any one or a number of a variety of foundry sands, including silica, olivine, chromite, zircon, chamotte,quartz, or synthetic material including silicon carbide, or iron or steel shot.
33. A method according to Claim 1 wherein the mould is made of particulate moulding material which comprises a ferro-magnetic material and the particulate material is compacted by the use of a magnetic field.
34. A method according to Claim 1 wherein a pressure below atmospheric pressure is applied to the mould during casting.
35. A method according to Claim 1 wherein the mould cavity is filled by a flow of metal generally upwardly against the force of gravity throughout the mould cavity.
36. A method according to Claim 35 wherein the mould cavity is filled without any substantial flow of the metal downwardly under the influence of gravity within the mould cavity.
37. A method according to Claim 27 wherein the metal is fed into the mould cavity by a low pressure delivery system, which causes a differential pressure to exist between the pressure in the mould cavity and the pressure in the source of molten metal.
38. A method according to Claim 37 wherein said differential pressure lies in the range 0.1 to 1.0 atmospheres.
39. A method according to Claim 1 wherein the mould cavity comprises at least one casting portion, in which a final casting is produced, and metal is fed to the casting portion at a single location and the casting portion is designed so that no part thereof is fed from another part of the casting portion along a path having any substantial flow downwardly under the influence of gravity.
40. A method according to Claim 1 wherein the mould cavity comprises at least one casting portion, in which a final casting is produced, and metal is fed into the casting portion at a plurality of locations so that the casting portion is filled by generally upward flow of metal from a plurality of locations against the force of gravity without any substantial flow of metal downwardly under the influence of gravity.
41. A method according to Claim 1 wherein the mould cavity includes a casting ingate portion which communicates directly with the casting portion.
42. A method according to Claim 41 wherein the casting ingate portion of the cavity communicates with a runner system portion of the cavity which is provided with a runner ingate portion of the cavity which communicates with the source of metal.
43. A method according to Claim I wherein the casting ingate portion communicates with a source of metal without any runner system.
44. A method according to Claim 41 wherein the ingate is placed in casting relationship with an orifice in the mould base, through which the molten metal is fed from the source into the mould,by inserting a portion of the ingate part of the pattern into close fitting engagement within the orifice.
45. A method according to Claim 7 wherein the orifice is lined with, or integrally formed in, thermally insulated refractory material capable of withstanding the liquid metal to be cast.
46. A method according to Claim 7 wherein the orifice is re-used for a plurality of castings.
47. A method according to Claim 7 wherein the orifice is disposed of after each casting operation.
48. A method according to Claim 7 wherein the orifice is formed as an insert in the mould base.
49. A method according to Claim 7 wherein the orifice is placed in casting relationship with the source of metal and a feed is effected by the use of a ceramic fibre gasket between a riser tube extending between the source of metal and the member in which the orifice is formed.
50. A method according to Claim 1 wherein said feeding of molten metal generally upwardly against the force of gravity from the source of molten metal into the mould cavity, is performed without any substantial flow of metal downwardly under the influence of gravity between the source and the entry into the cavity.
51. A method according to Claim 1 wherein the molten metal comprises at least one of aluminium, magnesium, copper and an alloy based thereon.
52. An apparatus for casting metal articles comprising a container for an in-situ destroyable pattern embedded in particulate moulding material to form within the container a mould cavity having a casting portion and means to feed molten metal into the container generally upwardly against the force of gravity from a reservoir of molten metal which is at a level which is below the level of the container.
53. An apparatus for casting metal articles as claimed in Claim 52 wherein said means comprises a pump to pump molten metal into the container through a passage having one end to be surrounded, in use, by the molten metal in the reservoir and an opposite end which is connected, in use, to the mould cavity and an intermediate part which extends, in use, to the free surface of the molten metal in the reservoir, the pump being formed separately from the reservoir to draw metal from the reservoir into the pump and discharge metal from the pump into the container.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8513810 | 1985-05-31 | ||
| GB08513810A GB2159445B (en) | 1984-06-02 | 1985-05-31 | Casting of metal articles |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1267266A true CA1267266A (en) | 1990-04-03 |
Family
ID=10579994
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000496516A Expired - Lifetime CA1267266A (en) | 1985-05-31 | 1985-11-29 | Casting of metal articles |
Country Status (6)
| Country | Link |
|---|---|
| AU (2) | AU5053785A (en) |
| BR (1) | BR8505995A (en) |
| CA (1) | CA1267266A (en) |
| ES (1) | ES8701553A1 (en) |
| MX (1) | MX167695B (en) |
| PT (1) | PT81579B (en) |
-
1985
- 1985-11-29 AU AU50537/85A patent/AU5053785A/en not_active Abandoned
- 1985-11-29 BR BR8505995A patent/BR8505995A/en not_active IP Right Cessation
- 1985-11-29 PT PT8157985A patent/PT81579B/en unknown
- 1985-11-29 MX MX78185A patent/MX167695B/en unknown
- 1985-11-29 CA CA000496516A patent/CA1267266A/en not_active Expired - Lifetime
- 1985-11-29 ES ES549439A patent/ES8701553A1/en not_active Expired
- 1985-11-29 AU AU50536/85A patent/AU579907B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| BR8505995A (en) | 1986-12-09 |
| AU5053685A (en) | 1986-12-04 |
| AU579907B2 (en) | 1988-12-15 |
| PT81579A (en) | 1985-12-01 |
| AU5053785A (en) | 1986-12-04 |
| ES549439A0 (en) | 1986-12-01 |
| ES8701553A1 (en) | 1986-12-01 |
| PT81579B (en) | 1987-09-30 |
| MX167695B (en) | 1993-04-06 |
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