CA1128255A - Production of metal castings - Google Patents
Production of metal castingsInfo
- Publication number
- CA1128255A CA1128255A CA350,480A CA350480A CA1128255A CA 1128255 A CA1128255 A CA 1128255A CA 350480 A CA350480 A CA 350480A CA 1128255 A CA1128255 A CA 1128255A
- Authority
- CA
- Canada
- Prior art keywords
- composition
- aluminium
- pads
- refractory material
- mould
- 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
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
- B22D27/04—Influencing the temperature of the metal, e.g. by heating or cooling the mould
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/08—Features with respect to supply of molten metal, e.g. ingates, circular gates, skim gates
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D7/00—Casting ingots, e.g. from ferrous metals
- B22D7/06—Ingot moulds or their manufacture
- B22D7/10—Hot tops therefor
- B22D7/104—Hot tops therefor from exothermic material only
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Mold Materials And Core Materials (AREA)
- Curing Cements, Concrete, And Artificial Stone (AREA)
Abstract
A B S T R A S T
Sound castings (1), free from aluminium pick-up, are produced in moulds (2) in which are located at places where it is desirable to promote directional solidification lining pads (9) made from a composition which comprises particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, and which is substantially free of fluoride salts, which contains a fibrous refractory material and which has a density of 0.3 to 1.1 g/cm.
The composition may be incorporated as a preformed pad, or as a flexible mat or mouldable mixture which can be dried or hardened chemically.
Sound castings (1), free from aluminium pick-up, are produced in moulds (2) in which are located at places where it is desirable to promote directional solidification lining pads (9) made from a composition which comprises particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, and which is substantially free of fluoride salts, which contains a fibrous refractory material and which has a density of 0.3 to 1.1 g/cm.
The composition may be incorporated as a preformed pad, or as a flexible mat or mouldable mixture which can be dried or hardened chemically.
Description
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PRODUCTION OF METAL CASTINGS
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This invention relates to the production of metal castings, particularly steel castings,in sand or like mouldsO
In order to produce a sound casting in any metal or alloy it is essential that the metal contained in the feeder solidifies at least at the same time or preferably after the last part of the casting to solidify and that there is a path for liquid metal from the feeder to all parts of the casting to compensate for th~shrinkage contraction which occurs when liquid metals or alloys solidify. It ; is therefore a requirement of sound castings production to promote progressive directional solidification from the point most remote from the feeder towards the feed~r so that the feeder is the last section of the casting to solidify. Unfortunately, the required shape of many castings is such that without change to the design, directional solidification cannot be achieved.
As a result, the desired shape of many steel castings has to be altered in order to provide feed metal to those parts of the casting which are remote from feeder heads. The alteration generally takes the form of thickening up the metal at those casting sections where prerature solidification would otherwise occur and thereby cause shrinkage cavities in isolated hot spots. This alteration in casting sha~e by ihe addition of extra metal is known as metal padding.
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PRODUCTION OF METAL CASTINGS
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This invention relates to the production of metal castings, particularly steel castings,in sand or like mouldsO
In order to produce a sound casting in any metal or alloy it is essential that the metal contained in the feeder solidifies at least at the same time or preferably after the last part of the casting to solidify and that there is a path for liquid metal from the feeder to all parts of the casting to compensate for th~shrinkage contraction which occurs when liquid metals or alloys solidify. It ; is therefore a requirement of sound castings production to promote progressive directional solidification from the point most remote from the feeder towards the feed~r so that the feeder is the last section of the casting to solidify. Unfortunately, the required shape of many castings is such that without change to the design, directional solidification cannot be achieved.
As a result, the desired shape of many steel castings has to be altered in order to provide feed metal to those parts of the casting which are remote from feeder heads. The alteration generally takes the form of thickening up the metal at those casting sections where prerature solidification would otherwise occur and thereby cause shrinkage cavities in isolated hot spots. This alteration in casting sha~e by ihe addition of extra metal is known as metal padding.
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- 2 ~ FS 1144 Typical of the types of casting which must ba padded wl~h metal in order to obviata intarnal shrinkags ara gear whasl blanks, valve bodies and bonnets, H-arm whezls, idler wheels, pistons, rolls and turbinecasings. In the basic shape of thess and other castings thsre ara heavy sections which ara isolatad from sources of feed metal. Metal pads ara therefore positioned in such a way that thay promote diractional solidification throughout tha casting.
In ordar tc regain tha casting shapa originally raquired, the addad matal padding must be ramovad aftar tha casting and feeder have solidifiad. The removal of tha matal pad can involve one or more of the following operations: flame cutting, sawing, grinding and machining. These are lengthy and expensive processes and often create bottlenecks in foundry production. Padding removal therefora is uneconomic in itself and metal padding involves melting additional quantities of-metal to that-raquirad for tha matal castings themsalves.
The pro~otion of progressive directional solidification has already been achieved to some extent by replacing metal pads with pads of exothenmic compositions which, when located in the mould cavity in appropriate positionsJ ignite on contact with the molten metal and supply sufficient heat to prevent pre~ature solidification of the casting sections with which the exothermic materials are in contact, and hence their use promotes the raquirad directional solidification.
Alumino-thermic compositions which have bean usad for this purposa ara well known and are dascribad for exampla in 8ritish Patant Spacification Nos. 971 749 and 808 ~00. They ganerally consist of finely divided aluminium, one or more oxidising agents for the aluminium such as an alkali matal or alkaline earth matal nitrate or perchlorate, iron oxide or manganese oxide, a fluoride such as calcium fluoride or sodium aluminium fluoride to initiate , . .
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In ordar tc regain tha casting shapa originally raquired, the addad matal padding must be ramovad aftar tha casting and feeder have solidifiad. The removal of tha matal pad can involve one or more of the following operations: flame cutting, sawing, grinding and machining. These are lengthy and expensive processes and often create bottlenecks in foundry production. Padding removal therefora is uneconomic in itself and metal padding involves melting additional quantities of-metal to that-raquirad for tha matal castings themsalves.
The pro~otion of progressive directional solidification has already been achieved to some extent by replacing metal pads with pads of exothenmic compositions which, when located in the mould cavity in appropriate positionsJ ignite on contact with the molten metal and supply sufficient heat to prevent pre~ature solidification of the casting sections with which the exothermic materials are in contact, and hence their use promotes the raquirad directional solidification.
Alumino-thermic compositions which have bean usad for this purposa ara well known and are dascribad for exampla in 8ritish Patant Spacification Nos. 971 749 and 808 ~00. They ganerally consist of finely divided aluminium, one or more oxidising agents for the aluminium such as an alkali matal or alkaline earth matal nitrate or perchlorate, iron oxide or manganese oxide, a fluoride such as calcium fluoride or sodium aluminium fluoride to initiate , . .
, . :
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- 3 ~ FS 1144 ; and control the exothermic reaction, one or mora partioulate refractory fillers such as sand, alumina, grog, chamotte or other refractory silicate knc~nper se, and one or more binders such as starch, dextrin, sulphite lye, gum arabic, rssins such as phenol formaldehyde resin, sodium silicate and clays. The quantity of oxidising agent is usually stoichiometrically insuf-ficient to oxidise all the aluminium present.
Although pads of such sxothermic ccmpositicns if correctly applied promote progressive directional solidification, - 1û their use in its turn produces new problems. Due to the exothermic reaction, gases are evolved from the exothermic composition and these must be vented to the atmosphere outside the mould to avoid casting defects such as blow holes or pinhole porosity. Sometimes, because of the location of the exothermic pad in the mould it is difficult if not impossible to find a path from the pad to the atmosphere for the escape of gases evolved during the exothermic reaction.
It has also been observed when using exothermic padding materials that the surface of the metal casting in contact with the exothermic pad is rough and/or has been contaminated by undesirable impurities such as aluminium and silicon originating from the exothermic pad itself. Such roughness and contamination is undes-irable and whilst it may be reduced by the extra application of an inert mould coating, it cannot always be eliminated. As a result, although exothermic padding materials are well known their co~mercial application has besn restricted because of the problems described above.
It has been proposed to overcome the proble~s associated with aluminothermic or other exothermic padding compositions by the use of heat insulating pads of refractory fibrous material. British Patent Specification Nb. 1 240 301 described the usz of such padding .~ . - : .:
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material in the production of m~tal castings.
.
Such materials generally compriss a refractory mineral fibrs of, for example, alumino-silicate or calcium silicate, a particulate refractory filler as previously describe~ and a binder system such as colloidal oxide hydrosols and/or starch and/or phenol fonmaldehyde rssin.
However, although these padding materials do not contaminate ths metal casting with undesirable impurities and do not cause gas defects, suoh as blowholes and pinholes porosity, they ars not as s~ficisnt thsrmally as exothsrmic padding materials in promoting pr~gressivs directional solidification, and further-more the surface finish of that ,oart of the casting which comes into contact with the heat insulating pad is noticeably poorer than that in cDntact with the r~st of the mould. Heat insulat~ng pads therefore have only a limited application in conmercial castings production.
It has now been found that the merits of both typBS
of padding material can be combined in a single padding composition which is 6ufficiuntly exothermic to overcome the thenmal inefficiency 2û of a purely heat insulating padding composition but which surorisingly does not contaminate the metal casting with undesirable impurities such as aluminium, providing that the padding composition does not contain any fluoride salts and is within c~rtain limits of density.
According to the present invsntion thsre i5 providæd a process for the casting of noltsn metal in a sand or like mDwld in which thers are provided at one or mors loGations in the mould where it is dPsirable to p~omote progressivæ directional solidificatio-n, lining pads located either to constitute or to support the metal ~ contacting surface of the sand mould and to provids with the remainder :' .
~,~
. - . , ,. . : ,.. -.
~L~a28Z~i5 ~ 5 ~ FS 1144 of the sand mould a cavity of the desired shape and dirnensions, the pads being formed of a composition comprising particulate r~Practory material, finely divided aluminiumJ an oxidising agent -For khe aluminium and a binder, characterised in that the composition is substantially free of fluoride salts and contains a fibrous refractory material known E~ se and the pads have a density of 0.3 to1.1 g/cm3.
According to a further feature of the invention there is provided a process for the production of a sand or like mould f~r ca~ting molten metal in accordance with the above process in which a padding composition comprising particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder is applied to those portions of a pattern at which it is desired to promote progressive directional solidification in a casting of the shape of the pattern, moulding sand is applied around the pattern and the composition, the composition is hardened to produce pads, and the resulting mould and pads are stripped from the pattern, characterised in that the composition is substantially free of fluoride salts and contains a fibrous refractory material known E~ se and the pads have a density of 0.3 to 1.1 g/cm3.
According to a further feature of the invention there is provided a oadding material, comprising particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, for promoting progressive directional solidification in a metal casting, characterised in that the material - 25 is substantially free of fluoride salts, contains a fibrous refractory material known ~ se and has a density in the range of 0.3 to 1.1 g/cm .
The pads may be preformed and dried before being located in a mould or next to a pattern or they may be produced from a composition in the form of a flexible mat which can be placed in position in a mould or around a pattern or in the form of a mouldable .
~9~Z~55 mixturs which can be raTmed into position around a patt~rn or into a cavity in a mould. The fl~xible mat or the mouldable mixturs may be dried by the action of heat or hardened by ch0mical means. A
flexible mat or mouldable mixtur~ which can be hardened ch~mically is preferred, Suitable fibmus refractory materials include alumina fibres, alumino-silicate fibres and calcium silicats fibres such as slag wool, rock wool or mineral wool.
Suitable particulate refractory materials include alumina, 10 mullite, sillimanite, chamDtte, grog, calcined fireclay, calcined flint clay, silica, expanded venmiculite, exoanded perlite, calcined rice husks and crushed coks. It is important that the particulate refractory material contains no more than traces of fluoride salts, as oiherwise metal castings produced using the pads are likely to be 1~ contaminated with aluminium.
Suitable oxidising agents include alkali metal nitrates, alkaline earth metal nitrates, alkali mPtal perchlorates, iron oxide and mangansse oxide.
Suitable binders include o~ganic binders ~uch as resins, 2~ dsxtrin, starch, sulphite lye, gum arabic and/or inor~anic binders such as alkali metal silicates, colloidal oxide hydrosol~ and clays such as kaolin clays or ball clays.
The composition may also cont3in a sm311 proportion of organic fibre, such as rayon fibre, par~icularly when the composition is to be used in the fonm of a flsxible mat.
The preferræd pad com,oositions are (percentages by weight~.-~z~zss Fibrous refractory material 5 - 7a Particulate refrac~ory material 5 - 70 Aluminium 4 - 30 Oxidising Agent 1 - 20 Binder tsolids content) 2 - 20 In order to achieve good thermal insulation properties it is desirable that the density o-f the pads is as low as possible and in practice pads having a density of 0.3 - 1.1 g/cm are satis-factory. Within this range the optimum density -For a particular material will depend on the composition of the material because with most compositions refractoriness also decreases as density decreases.
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As mentioned earlier the pads according to the invention may be manufactured and used in one of a number of ways. For example, the individual ingredients may be mixed in one of a number of suitable mixing machines and moistened with water until a ramrable consistency is achieved. The mixture may then be ra~med into a cavity in a sand mould or core or laid against a casting pattern or co~pacted in a core box and hardened chemically or dried by the application of heat in, for example, an oven or by gentle application of a gas flame.
Alternatively, the ingredients may be mixed with water into a slurry which is then dewatered by connecting to vacuum a suitable shaped mesh former i~mersed in the slurry in order to produce the required shape, in general as taught by British Patent Specification No. 1 204 7~2. It may be desirable to include a dispersion agent such as aluminium sulphate to aid in the dispersion of the ingredients in the slurry. The green shape may be dried in, for example, an oven or hardened chemically,either separately or as an integral part of a core or mould. Pads made by the manufacturing method described, have a density when dried in the range ~.3 to ~LZ~;2S5 1.1` ~cm3 and usually in the range 0.45 to 0.95 g/om3.
- When pads are produced from a flexible mat or a mould-able mixture by chemical hardening the preferred method is to apply an alkaline substance to a few points on the surface of the mat or moulded mixture as described in British Patents 775 360 and B08 400.
Suitable alkaline m3terials include hydroxides, carbonates and alum-inates of alkali metals such as sodium and the materials are preferably applied to the pads as aqueous solutions. For the chemical hardening procass to take place the presence of a water-soluble nitrate such as an alkali metal nitrate is essential. The alkali metal nitrate may he dissolv~d in the aqueous solution of the alkaline matsrial or included in the CQmpOSitiOn of the flexible mat or mDuld-able mixture as at least a proportion of the oxidising agent pressnt in the composition.
In order to delay commencement of the che~ical hardening reaction it may be desirable to include in the coTposition fonming the flexible mat or mouldable material a small proportion of a compound such as boric acid which will passivate the aluminium as described in British Patsnt 775 3~0.
The invsntion is illustratsd by way of exampls with rsference to the accompanyin~ drawings in which Figures 1 to 3 are each a sectional view of a castin~ mould according to known practice and Figures 4 and 5 are according to the invention.
Referring to the drswings:
:~ .
~ In Figure 1 a stsel casting 1 having dimensions 11û ~m x ; 25 110 mm x 110 mm is produced in a sand mculd 2. The eastin~ 1 is separated from a cylindrical feeoer 3, 1ûO mm in diameter and 150 mm high by a plats 4, 220 mm high, 110 mm wide and 55 mm thick. The cylindrical feeder is lined by a refractory insulating sle~ve 5.
, :
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~Z8Z55i Without the use of mstal padding as traditionally practised or with-out the use of some other fonm of padding material the casting 1 is unsound in the area 6.
Figure Z illustrates t,he traditional steel -Poundry practice of utilising metal padding and the portion 7 of the plate 4 indicates the minimum possible additional metal needed to make casting 1 sound.
The dotted lines indicate the amount of cutting and machining which would be needed to produce the required casting shape. The use of metal padding also requires an increase in the diameter of the feeder 3 from 100 mm to 125 mm.
Figure 3 illustrates an alternative prior art method of applying metal padding and the portion 8 of the plate 4 indicates the minimum metal needed in order to make casting 1 sound. Again it is necessary to increase the diameter of the feeder from 100 mm to 125 mm, and to remove a considerable quantity of metal in order to produce a casting of the required shape.
Figure 4 illustrates the use of a preforméd and dried pad according to the invention. ~n the production of the mould 2 a preformed and dried pad 9 was placed against the pattern in the position indicated. The composition of the pad was:
Percent by weight Aluminium silicate fibre 26.0 Aluminium powder 10.0 Calcined alumina 38.0 Iron oxide 2.0 Colloidal silica sol (solids content) 12,0 Phenol-formaldehyde resin 10.0 Aluminium sulphate 2.0 :, ~2~3255 and the pad had a density of 0.47 g/cm3.
The casting 1 produced using the pad 9 was sound and was not contaminated by aluminium.
Figure 5 illustrates the use of a pad formed from a mouldable mixtura according to the invent~on.
A composition was produced as follows:
Alumino-silicate fibre 50.9 Aluminium powder 23.0 Colloidal silica sol ~solids content) 2.0 Sodium nitrate 12.0 Calcined chamotte 9.0 Ball clay 3.0 Boric acid 0.1 60 parts by weight of water were added to 100 parts by weight of the composition to produce a mouldable mixture, and the mixture was rammed into a cavity in the mould 2 at the position indicated 10. After removal of the pattern a few spots of an alkaline solution were applied to the exposed face of the moulded `~ 20 mixture. The composition of the alkaline solution was:
Percent by weight Sodium nitrate 10 Sodium hydroxide 10 Water 80 As a result of the ensuing chemical reaction the moulded '" ` `~
112~2~i5 mixture hard~ned to form a pad. Previous tests using the same composition had proouced pads having a density of 0.90 g/cm3.
Two hours after application of ths alkalin~ solution molten steel was poured into the mould 2 and the resulting steel casting 1 was sound and was not contaminated by aluminium.
As a further illustration of the invention the Following compositions were com,oared using preformed pads and sand moulds as shown in Figure 4.
~ 1i An exothermic composition according to British 1û Patent No. 971749 containing sillimanite as refractory filler, 1% by weight potassium cryolite and 1% by weight sodium fluoride.
(2) An exothermic/heat-insulating composition consisting of 97.0% by weight of the composition shown on page 10 and 3.0% by weight calcium fluoride.
(3) A composition exactly as stated on page 10, i.e.
containing no fluoride salts.
The density of each of~the pads was recorded and casting soundness and aluminium pick-up in the casting face in contact with the pad were determined.
The following results were obtained:
~ .
PAD DENSITY CASTINGALUMINIUM
COMPOSITION ~cm ) SOUNDNESSPICK-UP
,~
1 1.51 SOUNO 0.063%
2 0.47 SOUNO 0.070%
25 3 0.47 SOUND 0.002%
, : .
~Z~ 55 As the table shows the pad according to ths invention made from composition 3 was sufficiently exothermic even in the absence of fluoride and had sufficiently good heat insulation properties to produce a sound casting and did not cause the casting to pick up aluminium. In contrast the use of the exothsrmic composition 1 and the exothermic/heat-insulating composition 2, both of which contained fluoride, resulted in aluminium pick-up by the casting.
Although pads of such sxothermic ccmpositicns if correctly applied promote progressive directional solidification, - 1û their use in its turn produces new problems. Due to the exothermic reaction, gases are evolved from the exothermic composition and these must be vented to the atmosphere outside the mould to avoid casting defects such as blow holes or pinhole porosity. Sometimes, because of the location of the exothermic pad in the mould it is difficult if not impossible to find a path from the pad to the atmosphere for the escape of gases evolved during the exothermic reaction.
It has also been observed when using exothermic padding materials that the surface of the metal casting in contact with the exothermic pad is rough and/or has been contaminated by undesirable impurities such as aluminium and silicon originating from the exothermic pad itself. Such roughness and contamination is undes-irable and whilst it may be reduced by the extra application of an inert mould coating, it cannot always be eliminated. As a result, although exothermic padding materials are well known their co~mercial application has besn restricted because of the problems described above.
It has been proposed to overcome the proble~s associated with aluminothermic or other exothermic padding compositions by the use of heat insulating pads of refractory fibrous material. British Patent Specification Nb. 1 240 301 described the usz of such padding .~ . - : .:
:: .. .. . . .
~8;2SS
material in the production of m~tal castings.
.
Such materials generally compriss a refractory mineral fibrs of, for example, alumino-silicate or calcium silicate, a particulate refractory filler as previously describe~ and a binder system such as colloidal oxide hydrosols and/or starch and/or phenol fonmaldehyde rssin.
However, although these padding materials do not contaminate ths metal casting with undesirable impurities and do not cause gas defects, suoh as blowholes and pinholes porosity, they ars not as s~ficisnt thsrmally as exothsrmic padding materials in promoting pr~gressivs directional solidification, and further-more the surface finish of that ,oart of the casting which comes into contact with the heat insulating pad is noticeably poorer than that in cDntact with the r~st of the mould. Heat insulat~ng pads therefore have only a limited application in conmercial castings production.
It has now been found that the merits of both typBS
of padding material can be combined in a single padding composition which is 6ufficiuntly exothermic to overcome the thenmal inefficiency 2û of a purely heat insulating padding composition but which surorisingly does not contaminate the metal casting with undesirable impurities such as aluminium, providing that the padding composition does not contain any fluoride salts and is within c~rtain limits of density.
According to the present invsntion thsre i5 providæd a process for the casting of noltsn metal in a sand or like mDwld in which thers are provided at one or mors loGations in the mould where it is dPsirable to p~omote progressivæ directional solidificatio-n, lining pads located either to constitute or to support the metal ~ contacting surface of the sand mould and to provids with the remainder :' .
~,~
. - . , ,. . : ,.. -.
~L~a28Z~i5 ~ 5 ~ FS 1144 of the sand mould a cavity of the desired shape and dirnensions, the pads being formed of a composition comprising particulate r~Practory material, finely divided aluminiumJ an oxidising agent -For khe aluminium and a binder, characterised in that the composition is substantially free of fluoride salts and contains a fibrous refractory material known E~ se and the pads have a density of 0.3 to1.1 g/cm3.
According to a further feature of the invention there is provided a process for the production of a sand or like mould f~r ca~ting molten metal in accordance with the above process in which a padding composition comprising particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder is applied to those portions of a pattern at which it is desired to promote progressive directional solidification in a casting of the shape of the pattern, moulding sand is applied around the pattern and the composition, the composition is hardened to produce pads, and the resulting mould and pads are stripped from the pattern, characterised in that the composition is substantially free of fluoride salts and contains a fibrous refractory material known E~ se and the pads have a density of 0.3 to 1.1 g/cm3.
According to a further feature of the invention there is provided a oadding material, comprising particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, for promoting progressive directional solidification in a metal casting, characterised in that the material - 25 is substantially free of fluoride salts, contains a fibrous refractory material known ~ se and has a density in the range of 0.3 to 1.1 g/cm .
The pads may be preformed and dried before being located in a mould or next to a pattern or they may be produced from a composition in the form of a flexible mat which can be placed in position in a mould or around a pattern or in the form of a mouldable .
~9~Z~55 mixturs which can be raTmed into position around a patt~rn or into a cavity in a mould. The fl~xible mat or the mouldable mixturs may be dried by the action of heat or hardened by ch0mical means. A
flexible mat or mouldable mixtur~ which can be hardened ch~mically is preferred, Suitable fibmus refractory materials include alumina fibres, alumino-silicate fibres and calcium silicats fibres such as slag wool, rock wool or mineral wool.
Suitable particulate refractory materials include alumina, 10 mullite, sillimanite, chamDtte, grog, calcined fireclay, calcined flint clay, silica, expanded venmiculite, exoanded perlite, calcined rice husks and crushed coks. It is important that the particulate refractory material contains no more than traces of fluoride salts, as oiherwise metal castings produced using the pads are likely to be 1~ contaminated with aluminium.
Suitable oxidising agents include alkali metal nitrates, alkaline earth metal nitrates, alkali mPtal perchlorates, iron oxide and mangansse oxide.
Suitable binders include o~ganic binders ~uch as resins, 2~ dsxtrin, starch, sulphite lye, gum arabic and/or inor~anic binders such as alkali metal silicates, colloidal oxide hydrosol~ and clays such as kaolin clays or ball clays.
The composition may also cont3in a sm311 proportion of organic fibre, such as rayon fibre, par~icularly when the composition is to be used in the fonm of a flsxible mat.
The preferræd pad com,oositions are (percentages by weight~.-~z~zss Fibrous refractory material 5 - 7a Particulate refrac~ory material 5 - 70 Aluminium 4 - 30 Oxidising Agent 1 - 20 Binder tsolids content) 2 - 20 In order to achieve good thermal insulation properties it is desirable that the density o-f the pads is as low as possible and in practice pads having a density of 0.3 - 1.1 g/cm are satis-factory. Within this range the optimum density -For a particular material will depend on the composition of the material because with most compositions refractoriness also decreases as density decreases.
.
As mentioned earlier the pads according to the invention may be manufactured and used in one of a number of ways. For example, the individual ingredients may be mixed in one of a number of suitable mixing machines and moistened with water until a ramrable consistency is achieved. The mixture may then be ra~med into a cavity in a sand mould or core or laid against a casting pattern or co~pacted in a core box and hardened chemically or dried by the application of heat in, for example, an oven or by gentle application of a gas flame.
Alternatively, the ingredients may be mixed with water into a slurry which is then dewatered by connecting to vacuum a suitable shaped mesh former i~mersed in the slurry in order to produce the required shape, in general as taught by British Patent Specification No. 1 204 7~2. It may be desirable to include a dispersion agent such as aluminium sulphate to aid in the dispersion of the ingredients in the slurry. The green shape may be dried in, for example, an oven or hardened chemically,either separately or as an integral part of a core or mould. Pads made by the manufacturing method described, have a density when dried in the range ~.3 to ~LZ~;2S5 1.1` ~cm3 and usually in the range 0.45 to 0.95 g/om3.
- When pads are produced from a flexible mat or a mould-able mixture by chemical hardening the preferred method is to apply an alkaline substance to a few points on the surface of the mat or moulded mixture as described in British Patents 775 360 and B08 400.
Suitable alkaline m3terials include hydroxides, carbonates and alum-inates of alkali metals such as sodium and the materials are preferably applied to the pads as aqueous solutions. For the chemical hardening procass to take place the presence of a water-soluble nitrate such as an alkali metal nitrate is essential. The alkali metal nitrate may he dissolv~d in the aqueous solution of the alkaline matsrial or included in the CQmpOSitiOn of the flexible mat or mDuld-able mixture as at least a proportion of the oxidising agent pressnt in the composition.
In order to delay commencement of the che~ical hardening reaction it may be desirable to include in the coTposition fonming the flexible mat or mouldable material a small proportion of a compound such as boric acid which will passivate the aluminium as described in British Patsnt 775 3~0.
The invsntion is illustratsd by way of exampls with rsference to the accompanyin~ drawings in which Figures 1 to 3 are each a sectional view of a castin~ mould according to known practice and Figures 4 and 5 are according to the invention.
Referring to the drswings:
:~ .
~ In Figure 1 a stsel casting 1 having dimensions 11û ~m x ; 25 110 mm x 110 mm is produced in a sand mculd 2. The eastin~ 1 is separated from a cylindrical feeoer 3, 1ûO mm in diameter and 150 mm high by a plats 4, 220 mm high, 110 mm wide and 55 mm thick. The cylindrical feeder is lined by a refractory insulating sle~ve 5.
, :
.~ .
.. .. :
~Z8Z55i Without the use of mstal padding as traditionally practised or with-out the use of some other fonm of padding material the casting 1 is unsound in the area 6.
Figure Z illustrates t,he traditional steel -Poundry practice of utilising metal padding and the portion 7 of the plate 4 indicates the minimum possible additional metal needed to make casting 1 sound.
The dotted lines indicate the amount of cutting and machining which would be needed to produce the required casting shape. The use of metal padding also requires an increase in the diameter of the feeder 3 from 100 mm to 125 mm.
Figure 3 illustrates an alternative prior art method of applying metal padding and the portion 8 of the plate 4 indicates the minimum metal needed in order to make casting 1 sound. Again it is necessary to increase the diameter of the feeder from 100 mm to 125 mm, and to remove a considerable quantity of metal in order to produce a casting of the required shape.
Figure 4 illustrates the use of a preforméd and dried pad according to the invention. ~n the production of the mould 2 a preformed and dried pad 9 was placed against the pattern in the position indicated. The composition of the pad was:
Percent by weight Aluminium silicate fibre 26.0 Aluminium powder 10.0 Calcined alumina 38.0 Iron oxide 2.0 Colloidal silica sol (solids content) 12,0 Phenol-formaldehyde resin 10.0 Aluminium sulphate 2.0 :, ~2~3255 and the pad had a density of 0.47 g/cm3.
The casting 1 produced using the pad 9 was sound and was not contaminated by aluminium.
Figure 5 illustrates the use of a pad formed from a mouldable mixtura according to the invent~on.
A composition was produced as follows:
Alumino-silicate fibre 50.9 Aluminium powder 23.0 Colloidal silica sol ~solids content) 2.0 Sodium nitrate 12.0 Calcined chamotte 9.0 Ball clay 3.0 Boric acid 0.1 60 parts by weight of water were added to 100 parts by weight of the composition to produce a mouldable mixture, and the mixture was rammed into a cavity in the mould 2 at the position indicated 10. After removal of the pattern a few spots of an alkaline solution were applied to the exposed face of the moulded `~ 20 mixture. The composition of the alkaline solution was:
Percent by weight Sodium nitrate 10 Sodium hydroxide 10 Water 80 As a result of the ensuing chemical reaction the moulded '" ` `~
112~2~i5 mixture hard~ned to form a pad. Previous tests using the same composition had proouced pads having a density of 0.90 g/cm3.
Two hours after application of ths alkalin~ solution molten steel was poured into the mould 2 and the resulting steel casting 1 was sound and was not contaminated by aluminium.
As a further illustration of the invention the Following compositions were com,oared using preformed pads and sand moulds as shown in Figure 4.
~ 1i An exothermic composition according to British 1û Patent No. 971749 containing sillimanite as refractory filler, 1% by weight potassium cryolite and 1% by weight sodium fluoride.
(2) An exothermic/heat-insulating composition consisting of 97.0% by weight of the composition shown on page 10 and 3.0% by weight calcium fluoride.
(3) A composition exactly as stated on page 10, i.e.
containing no fluoride salts.
The density of each of~the pads was recorded and casting soundness and aluminium pick-up in the casting face in contact with the pad were determined.
The following results were obtained:
~ .
PAD DENSITY CASTINGALUMINIUM
COMPOSITION ~cm ) SOUNDNESSPICK-UP
,~
1 1.51 SOUNO 0.063%
2 0.47 SOUNO 0.070%
25 3 0.47 SOUND 0.002%
, : .
~Z~ 55 As the table shows the pad according to ths invention made from composition 3 was sufficiently exothermic even in the absence of fluoride and had sufficiently good heat insulation properties to produce a sound casting and did not cause the casting to pick up aluminium. In contrast the use of the exothsrmic composition 1 and the exothermic/heat-insulating composition 2, both of which contained fluoride, resulted in aluminium pick-up by the casting.
Claims (7)
1. A process for the casting of molten metal in a sand or like mould in which there are provided at one or more locations in the mould at positions where it is desirable to promote progressive directional solidification, lining pads located either to constit-ute or to support the metal contacting surface of the sand mould and to provide with the remainder of the sand mould a cavity of the desired shape and dimensions, the said pads being formed of a composition comprising fibrous refractory material, particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, said composition being substant-ially free of fluoride salts and said pads having a density of 0.3 to 1.1 g/cm3.
2. A process for the production of a sand or like mould for casting molten metal in accordance with the process of claim 1 in which a padding composition is applied to those portions of a pattern at which it is desired to promote progressive directional solidification in a casting of the shape of the pattern, moulding sand is applied around the pattern and the composition, the composition is hardened to produce pads and the resulting mould and pads are stripped from the pattern, said composition comprising fibrous refractory material, particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, and being substantially free of fluoride salts, and said pads having a density of 0.3 to 1.1 g/cm3.
3. A process according to claim 2 wherein the composition is in the form of a flexible mat or a mouldable mixture.
4. A process according to claim 3 wherein the composition is dried by heating or hardened chemically.
5. A process according to claim 4 wherein the composition contains a water-soluble nitrate and is hardened by applying an alkaline substance to the surface of the flexible mat or mouldable mixtures.
6. A padding material for use in the process of claim 1 comprising fibrous refractory material, particulate refractory material, finely divided aluminium, an oxidising agent for the aluminium and a binder, said material being substantially free of fluoride salts and having a density in the range of 0.3 to 1.1 g/cm3.
7. A padding material according to claim 6 comprising by weight:-Fibrous refractory material 5 - 70%
Particulate refractory material 5 - 70%
Aluminium 4 - 30%
Oxidising Agent 1 - 20%
Binder (solids content) 2 - 20%
Particulate refractory material 5 - 70%
Aluminium 4 - 30%
Oxidising Agent 1 - 20%
Binder (solids content) 2 - 20%
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7920757 | 1979-06-14 | ||
| GB7920757 | 1979-06-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128255A true CA1128255A (en) | 1982-07-27 |
Family
ID=10505851
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA350,480A Expired CA1128255A (en) | 1979-06-14 | 1980-04-23 | Production of metal castings |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0030940B1 (en) |
| JP (1) | JPS56500681A (en) |
| KR (1) | KR840000602B1 (en) |
| BR (1) | BR8008710A (en) |
| CA (1) | CA1128255A (en) |
| ES (1) | ES492411A0 (en) |
| GB (1) | GB2063126B (en) |
| IT (1) | IT8067928A0 (en) |
| WO (1) | WO1980002811A1 (en) |
| ZA (1) | ZA802394B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10179364B2 (en) | 2012-04-12 | 2019-01-15 | Rel, Inc. | Thermal isolation for casting articles |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3122597C2 (en) * | 1981-06-06 | 1987-04-30 | Mannesmann Rexroth GmbH, 8770 Lohr | Feeder model for a casting |
| GB9522741D0 (en) * | 1995-11-07 | 1996-01-10 | Firth Vickers Centrispinning L | Making a metal shape by casting |
| GB9618216D0 (en) * | 1996-08-30 | 1996-10-09 | Triplex Lloyd Plc | Method of making fine grained castings |
| US6298900B1 (en) | 1998-07-06 | 2001-10-09 | Ford Global Technologies, Inc. | Method of integrating wear plates into a spray formed rapid tool |
| DE19920570B4 (en) * | 1999-05-04 | 2008-01-10 | Chemex Gmbh | Moldable exothermic compositions and feed therefrom |
| DE19925167A1 (en) * | 1999-06-01 | 2000-12-14 | Luengen Gmbh & Co Kg As | Exothermic feeder mass |
| DE19953402A1 (en) * | 1999-11-06 | 2001-05-10 | Wagner Heinrich Sinto Masch | Method and device for producing and casting a casting mold consisting of two mold halves |
| JP5347077B1 (en) * | 2013-03-19 | 2013-11-20 | テクノメタル株式会社 | Sand mold casting method |
| RU2691826C1 (en) * | 2018-03-26 | 2019-06-18 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский Томский государственный университет" (НИ ТГУ) | Method of producing casts from dispersed-hard alloys based on aluminum or magnesium |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1084449B (en) * | 1953-08-05 | 1960-06-30 | Fachanstalt Fuer Giessereiwese | Heat-developing, moldable and hardenable compound for risers and funnels of molds and for block heads |
| GB769719A (en) * | 1954-01-26 | 1957-03-13 | Georges Lemoine | Improvements in or relating to exothermic mixtures |
| GB880868A (en) * | 1958-11-28 | 1961-10-25 | Foundry Services Int Ltd | Improvements in or relating to heat producing compositions |
| US3025153A (en) * | 1959-01-21 | 1962-03-13 | Foundry Services Int Ltd | Heat-producing mixtures |
-
1980
- 1980-04-18 WO PCT/GB1980/000067 patent/WO1980002811A1/en active IP Right Grant
- 1980-04-18 GB GB8040649A patent/GB2063126B/en not_active Expired
- 1980-04-18 JP JP50076880A patent/JPS56500681A/ja active Pending
- 1980-04-18 BR BR8008710A patent/BR8008710A/en unknown
- 1980-04-21 ZA ZA00802394A patent/ZA802394B/en unknown
- 1980-04-23 CA CA350,480A patent/CA1128255A/en not_active Expired
- 1980-06-11 KR KR1019800002292A patent/KR840000602B1/en active
- 1980-06-13 IT IT8067928A patent/IT8067928A0/en unknown
- 1980-06-13 ES ES492411A patent/ES492411A0/en active Granted
- 1980-12-30 EP EP80900667A patent/EP0030940B1/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10179364B2 (en) | 2012-04-12 | 2019-01-15 | Rel, Inc. | Thermal isolation for casting articles |
| US10434568B2 (en) | 2012-04-12 | 2019-10-08 | Loukus Technologies, Inc. | Thermal isolation spray for casting articles |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2063126A (en) | 1981-06-03 |
| ES8101943A1 (en) | 1980-12-16 |
| JPS56500681A (en) | 1981-05-21 |
| ZA802394B (en) | 1981-04-29 |
| WO1980002811A1 (en) | 1980-12-24 |
| KR840000602B1 (en) | 1984-04-28 |
| BR8008710A (en) | 1981-04-28 |
| EP0030940B1 (en) | 1984-01-11 |
| EP0030940A1 (en) | 1981-07-01 |
| IT8067928A0 (en) | 1980-06-13 |
| GB2063126B (en) | 1983-01-26 |
| ES492411A0 (en) | 1980-12-16 |
| KR830002549A (en) | 1983-05-30 |
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