CA1090087A - Investment casting method - Google Patents
Investment casting methodInfo
- Publication number
- CA1090087A CA1090087A CA282,385A CA282385A CA1090087A CA 1090087 A CA1090087 A CA 1090087A CA 282385 A CA282385 A CA 282385A CA 1090087 A CA1090087 A CA 1090087A
- Authority
- CA
- Canada
- Prior art keywords
- pattern
- mold
- thermally fusible
- investment
- refractory
- 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
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/02—Sand moulds or like moulds for shaped castings
- B22C9/04—Use of lost patterns
- B22C9/043—Removing the consumable pattern
Abstract
INVESTMENT CASTING METHOD
ABSTRACT OF THE DISCLOSURE
The specification discloses a method of manufacturing a propeller or other large casting wherein a pattern coated with a ceramic shell defining an investment mold is removed from the shell in two stages. In the first stage a sufficient amount of the material constituting the pattern is removed by the vapour of a solvent for the material to produce a small gap between the pattern and the shell. In the second stage, heat is applied to remove the rest of the pattern. Because of the gap produced in the first stage, stress on, and cracking of, portions of the shell due to expansion of the pattern are avoided in the second stage and there is thereby produced a shell mold permitting production of a casting such as a pro-peller having good surface finish and precise dimensions.
ABSTRACT OF THE DISCLOSURE
The specification discloses a method of manufacturing a propeller or other large casting wherein a pattern coated with a ceramic shell defining an investment mold is removed from the shell in two stages. In the first stage a sufficient amount of the material constituting the pattern is removed by the vapour of a solvent for the material to produce a small gap between the pattern and the shell. In the second stage, heat is applied to remove the rest of the pattern. Because of the gap produced in the first stage, stress on, and cracking of, portions of the shell due to expansion of the pattern are avoided in the second stage and there is thereby produced a shell mold permitting production of a casting such as a pro-peller having good surface finish and precise dimensions.
Description
~0~0~ 7 .
The present invention relates in general to a precision casting method and, more partlcularly, to a method of manufacturing a profiled three dimensional structure, such as a propellor, using investment or precision casting molds.
; Investment or precision casting is a process which has been used for many hundreds of years for casting parts of complex shape, and it has recently been employed for casting parts which, even if they have a comparatively simple shape, have to be cast to precise dimensions. This avoids the need for subsequent cleaning or machining processes, which cause a loss of expensive material and may also result in an alter-ation of the properties of at least the surface portions of the casting.
In the conventional process a pattern made of wax or polystyrene (or a substance having similar properties) is formed, either directly or by using a solid master-profile, and then the pattern is dipped into a slurry of a refractory material. The pattern is normally sprinkled with sand after it has been dipped, so that a refractory coating is produced on the pattern. Back up material, such as dry sand, is then poured around the pattern, whereby an investment mold is defined by the back up material. The investment mold is allowed to dry, the wax or other substance defining the pattern is melted and caused to flow out of the mold, the mold is preheated to a temperature suitable for receiving a particular molten metal or alloy, and then the molten metal is poured into the mold and allowed to solidify, and then the molten article is removed.
Since the shape of a casting is defined by an integral mold or pattern, it is possible to achieve much - ~.6~ t~
greater precision than is possible in casting processes in which different portions of the casting are defined by separatP
patterns or mold parts, and for this reason investment casting is commonly used in the aircraft industry, for example. Con-ventionally, however, it has been found extremely difficult or impossible to produce molds of sufficient strength to permit casting of large articles, and in the aircraft and other industries the investment casting process is almost entirely limited to the production of small articles.
For the precision casting of large articles such as generator turbine blades having a length of from 40 cm to 130 cm and a weight of from 1 kg to 70 kg, or marine screw pro-pellors having a diameter of the order to 200 cm and a weight of the order of 250 kg, it has been usual to employ a process `
in which a pair of molds, such as green molds, jell molds or ; ceramic shell molds, is employed over a pattern, then stripped from the pattern, fitted together again, and solidified, i.e., the shaw process or a modification thereof. However, in this process the mold comprises at least two portions which must be fitted in an exactly matching relationship and held clamped together, and apart from the fact that fitting together of mold halves constitutes an extra work step, it is found difficult to ensure that the mold halves are exactly fitted together. Cast parts are often produced with overhang pro-jections in the region where the molds fit together, there-fore usually require subsequent machining, which results in wastage of material. Furthermore, with some materials such as stainless steel, is difficult to obtain a required degree of precision during machining.
From hydrodynamic considerations, the thickness of a blade of a ship's screw propellor varies in the direction , , .
of the longitudinal axis thereof. If such a propellor is cast by a conventional process, since the green mold employed has a comparatively low heat-resistance, which imposes limits on the temperature to which the mold may be heated during the pouring process, there is likely to be inefficient filling or short-run of the mold by the poured metal, particularly when, in order to achieve improved strength and resistance to wear and corrosion, stainless steel is used instead of a copper alloy. In addition, blowholes or burning stainless steel are sometimes present on the surface of the cast part. Because of these faults, combined with the fact that good dimensional precision of a cast part cannot be guaranteedl as noted above, such castings always have unnecessary metal or other material attached thereto, which must be removed by machining which increases the cost of manufacture of a propellor.
These disadvantages are not limited to the manufac-ture of ships' propellors, and they also apply to the manu-facture of similar large articles of complex shape, for example the blades of large supercharger turbines, compressors or condenser.
In the conventional investment casting processes, because of the properties of the pattern material employed, it is necessary to employ comparatively large and complex injection molding equipment for injection of the thermally fusible material. The pattern made of a thermally fusible material may be formed manually by an artwork engraving, but for production on an industrial scale, split molds made of a metallic alloy may be used for casting a master pattern.
In this case, the mold halves must be given a correct finish by machining or a similar process, and then clamped together to define a single mold into which thermal]y fusible material 13'7 .
can be injected by an injection molding machine. However, use of an injection molding machine results in increased manu-facturing costs, since the split mold defining the required shape must be extremely strong and able to resist the high-pressure flow of injected thermally fusible material. Also, `~if the mold cavity has to contain a core, special measures must be taken to ensure that the core is not moved during the forcible injection of the thermally fusible material, and the complicated procedures necessary to ensure that the core remains correctly positioned are often the cause of delay in the manufacturing processes.
-It is accordingly a principal object of the present invention to provide an improved method for precision casting profiled members of three dimensional structure, such as propellors, impellers, diffusers, condensers, turbine blades and the like which reduces some of the problems inherent in conventional casting processes.
According to one aspect of the invention there is provided an investment casting method which comprises (a) pre-20 paring a thermally fusible pattern from a material selected -;from the group consisting of naphthalene and para-dichloro-benzene, with or without the addition of one or more polymers each having a vinyl radical, which thermally fusible pattern is substantially a replica of the article to be cast; (b) forming a refractory investment around the thermally fusible pattern by coating the pattern with a refractory slurry; (c) preliminary melting the outer parts of the thermally fusible pattexn so as to produce a small gap between said thermally fusible pattern and said refractory investment by dissolving the surface portions of said pattern by means of exposing the -pattern to the vapour of an organic solvent for the pattern 9~
material; (d) completely melting and removing the residue of the thermally fusible pattern from the refractory invest-ment by heating so as to leave the refractory investment with a cavity previously occupied by the thermally fusible pattern, said cavity having all the details of said thermally fusible pattern, whereby there is provided a rigid ceramic mold of one-piece construction; (e) preheating said refractory invest-ment constituting said mold in an oven to a temperature close to the temperature of the molten metal to be cast; (f) pouring said molten metal into the mold while the latter is heated to minimize the temperature difference between the mold and the molten metal; (g) solidifying the molten metal within the mold;
and (h) removing the solidified metal from the mold in the form of the desired casting.
According to another aspect of the invention there is provided a refractory mold of one-piece construction which is manufactured by preparing a thermally fusible pattern from a material of the group consisting of naphthalene and para-dichloro~benzene, with or without the addition of at least one polymer having a vinyl radical, which thermally fusible pattern is a substantial replica of a desired casting to be made by the use of said mold, subsequently forming a refractory invest-ment enveloping the thermally fusible pattern, preliminarily melting the thermally fusible pattern so as to produce a small gap between saicl pattern and said refractory investment by dissolving a portion of said pattern by means of contacting the pattern and investment with the vapour of an organic solvent, and then completely melting and removing all the residue of the thermally fusible pattern from said refractory investment by the heating thereof so as to leave the refractory investment having a cavity that was formerly occupied by said thermally fusible pattern, said cavity having all the details of said .
, , -` ~.C~S~ 37 `
thermally fusihle pattern.
It is an advantage of the invention, at least in preferred forms, that it can provide a method for casting large profile members which does not require the execution of complex casting procedures.
It is a further advantage of the invention, at least in preferred forms that it can provide a method for precision casting of profiled members which is not limited to casting of propellors or the like of particular size or of particular material, and which permits production of profiled members of three dimensional structure with highly precise as-cast dimensions and smooth casting surfaces.
It is yet another advantage of the invention, at least in the preferred forms, that it can provide an investment casting method in which production of investment casting patterns of profiled members of three dimensional structure is fairly easily achieved and costs of mold-making are com-paratively low.
Preferably the thermally fusible material is poured into a mold during the production of a pattern at a pouring speed in the range of from 0.1 kg/sec to 5 kg/sec.
Because of the gap produced in the preliminary melting stage" stress on, and cracking of, portions of the shell due to expansion of the pattern are avoided during the complete melting stage and a shell mold is thereby produced which enables the production of a propellor or other casting with a good surface finish and precise dimensions.
These and other advantages and features of the invention will become apparent from the following detailed description of preferred embodiments of the invention when read with reference to the attached drawings, in which like ., .
numbers refer to like parts, and:
Fig. 1 is a cross-sectional view of a thermally fusible pattern defining a ship's screw propellor coated with a ceramic shell according to one form of investment casting method of the present invention;
Fig. 2 is a cross-sectional view of a heating means for removal of the pattern-defining thermally fusible material and illustrates the preliminary removal of the thermally fusible material employed in Fig. l;
Fig. 3 is a cross-sectional view similar to Fig. 2 which illustrates the removal of the remainder of the thermally fusible material;
Fig. 4 is a cross-sectional view of a mold positioned in readiness for investment after removal of the thermally fusible material therefrom; and Fig. 5 is a cross-sectional view similar to Fig. 4, showing a mold defining the propellor positioned in a flask immediately prior to pouring of the metal.
The description below refers to the casting of a ship's screw propellor, but it should be understood that the method of the invention is equally appliable to the casting of other types of three dimensional structure, such as impellers, diffusers, condensers, turbine blades and the like.
In Fig. 1, a hot-melt or thermally fusible pattern 1 defines a screw propellor or similar element to be cast and has a coating of a ceramic forming a shell 2 of suitable thickness.
The thermally fusible pattern 1 may be made by any known pattern-making method, such as employed for example in investment casting or similar processes. Preferably, however, a split mold is employed which is made of gypsum and comprises ~ .. . . . .
'.: ~ ' , . `: .: ' ' ' two halves, and in which portions corresponding to the thin portions of a screw propeller master-mold, not shown, define cavities. The dimensions of this gypsum mold are selected bearing in mind the shrinkage of the poured metal and the material which must be removed to produce the finished part.
As a propellor must define a hole to permit mounting thereof on a drive shaft, such a hole is provided in the propellor-defining pattern, and for reasons which will be apparent later, a recessed portion corresponding to the shaft hole may be provided in the master mold.
Before the thermally fusible material of the pattern 1 is poured into the central area defined by the two halves of the split mold which are clamped together, a core 3 is positioned in the split mold which defines a hole for the propellor drive shaft and is provided with à flange 4 at the bottom.
Next, the thermally fusible material, which has a composition described later, and has been rendered fluid by being heated to 85C, is poured into the split mold. The properties of the thermally fusible material poured are such that use of an injection molding machine is unnecessary.
This does not necessarily mean that an injection molding machine is never used in this invention. However, even for the casting of comparatively large parts, an injection molding machine, if employed, need have only a simple construction.
A particularly noteworthy fea-ture of the method is the speed at which the thermally fusible material can be poured into the mold. A preferred thermally fusible material is material of the naphthalene system. Although such material has many advantages, it has been found that use thereof in conventional methods leads to surface holes and local porosity ...... .... , . _ . .. _ . _ _ .. _ .... _ . _ _ _ .. _ . _ ... .. . _ .. . .. .... _ ...
in a pattern produced. Research undertaken by the inventors showed that the principal cause of such faults was the adherence of steam produced during the pouring process to the wal]s of the mold. From the results of further research and ; tests made it became clear that this could be avoided by keeping the pouring speed in the range 0.1 kg/sec to 5 kg/sec.
When fluid material is poured into a mold at a speed greater than 5 kg/sec, swirling occurs and air is entrapped against the mold surface, leading to surface roughness in the finished pattern. In addition to this, there is a tendency for an applied release agent to be stripped off, with the result that separation of the pattern from the mold becomes difficult.
On the other hand, if the pouring speed is slower than 0.1 kg/sec there may be local porosity and, since poured material tends to cool excessively before new material is poured in, step-lines or zones are produced in the surface of the pattern, and the required dimensional precision fails to be achieved.
When the pouring speed is kept in the range 0.1 kg/sec to 5 kg/
sec, however, a pattern with precise dimensions and a smooth s-~rface finish can be obtained.
After being poured into the split mold, the thermally fusible material defining the pattern 1 is allowed to solidify and is then removed from the mold. The pattern 1 thus removed still supports the core 3.
The thermally fusible material employed for the pattern may be para-dichloro benzene or naphthalene, and, in addition, polystyrene resin or vinyl acetate may be present employed singly or as a mixture.
Preferably, however, the total weight of the B
.. . .. .. .
.~ . . . . . .
tB~
naphthalene is kept within the range of 0.5~ - 10~ if a mixture of naphthalene and polystyrene resin is employed, in the range of 1 - 5% if a mixture of naphthalene and a copolymer of ethylene acetate is employed, and in the range of 3 - 10~ if a mixture of naphthalene and polyethylene resin is employed.
The properties of naphthalene and styronaphthalene, i.e., a mixture of naphthalene and polystyrene resin, are shown in Table 1. For comparison, the properties of represen-tative conventional waxe~ are noted in Table 2. Comparingthe values in these two tables, it is seen that the addition of polystyrene increases bending strength.
."~ . ' , .
3'7 '. VC ~ ~ . . _ .~, ~ .
~ ~ CO O In O O l a I ~ ~ ~ I ~ ~
:: ~ _ __ _ ~ ~~
~n~ ~ ~ OO O O O O
~ 1~ _ ~ ~ o O o o ~'': ' ', R ~ o o ,, _ _ ,, n o o o o ~ ~ ,~ ~ a~, ~ In ~ , , ' ~
~1- ~ - ,~ ~ ~ ~r ~
~01 ~ ~ ~ .~
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' .. . .
. . .. ~ , , , . :: , . . .
,' ' : ! ' '; ',',' ''.' '. " ~, ' , ,~' ' ' ' . , ' "' ' ' ' ' ' ''. ' . ' :
~ o ~u~- o~ - - - -,~ X_, N : :
. ~ ~i -- # l ~0 ~ ~I) \a~ Cl~ L~ ~J
O ~
~ ~ U)o\~ ~
!C~ O ~ __ ~1 X Xra o~ ~co t C~ ,.~ oO _-- ' ,'~
~ U~ In ~D
~1 _ P~ ___ ~1 ---~ ~ -~ ~ . '.
~- 13 -- . .
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, .
. . . .
t8~7 When the thennally fusible pattern 1 is for~ed a refracto-ry ceramic shell 2 is formed therearound by repeating a coat-ing and sand-sprinkling processes a set number of times determined with reference to the required strength of the shell 2. For example, coating and sand-sprinkling are alternately repeated 6-7 times if :it is required to subse-quently cast a screw propellor hav:ing a diameter of 400 mm, and 10-12 times if it is required to cast a propellor hav-ing a diameter of 1,200 mm. The pattern 1 is completely enclosed in the shell 1 except for an opening 10, which for a propellor pattern is located on the opposite side of the pattern to the core 3.
Each sand-sprinkling step is designed to strength-en the ceramic chell 2, and the sand emplos~ed is suitably -a dry sand such as alumina sand or fusible silica, which -may be applied in a flow bed tray, or be blown or poured onto the shell 2.
After completion of the requisite number of cycles of coating and sand-sprinkling, the core 3 supported by the pattern 1 is held mechanically by the flange 4 to the shell 2, in order to ensure that the core 3 remains in place after the pattern 1 is subsequently melted out of the shell
The present invention relates in general to a precision casting method and, more partlcularly, to a method of manufacturing a profiled three dimensional structure, such as a propellor, using investment or precision casting molds.
; Investment or precision casting is a process which has been used for many hundreds of years for casting parts of complex shape, and it has recently been employed for casting parts which, even if they have a comparatively simple shape, have to be cast to precise dimensions. This avoids the need for subsequent cleaning or machining processes, which cause a loss of expensive material and may also result in an alter-ation of the properties of at least the surface portions of the casting.
In the conventional process a pattern made of wax or polystyrene (or a substance having similar properties) is formed, either directly or by using a solid master-profile, and then the pattern is dipped into a slurry of a refractory material. The pattern is normally sprinkled with sand after it has been dipped, so that a refractory coating is produced on the pattern. Back up material, such as dry sand, is then poured around the pattern, whereby an investment mold is defined by the back up material. The investment mold is allowed to dry, the wax or other substance defining the pattern is melted and caused to flow out of the mold, the mold is preheated to a temperature suitable for receiving a particular molten metal or alloy, and then the molten metal is poured into the mold and allowed to solidify, and then the molten article is removed.
Since the shape of a casting is defined by an integral mold or pattern, it is possible to achieve much - ~.6~ t~
greater precision than is possible in casting processes in which different portions of the casting are defined by separatP
patterns or mold parts, and for this reason investment casting is commonly used in the aircraft industry, for example. Con-ventionally, however, it has been found extremely difficult or impossible to produce molds of sufficient strength to permit casting of large articles, and in the aircraft and other industries the investment casting process is almost entirely limited to the production of small articles.
For the precision casting of large articles such as generator turbine blades having a length of from 40 cm to 130 cm and a weight of from 1 kg to 70 kg, or marine screw pro-pellors having a diameter of the order to 200 cm and a weight of the order of 250 kg, it has been usual to employ a process `
in which a pair of molds, such as green molds, jell molds or ; ceramic shell molds, is employed over a pattern, then stripped from the pattern, fitted together again, and solidified, i.e., the shaw process or a modification thereof. However, in this process the mold comprises at least two portions which must be fitted in an exactly matching relationship and held clamped together, and apart from the fact that fitting together of mold halves constitutes an extra work step, it is found difficult to ensure that the mold halves are exactly fitted together. Cast parts are often produced with overhang pro-jections in the region where the molds fit together, there-fore usually require subsequent machining, which results in wastage of material. Furthermore, with some materials such as stainless steel, is difficult to obtain a required degree of precision during machining.
From hydrodynamic considerations, the thickness of a blade of a ship's screw propellor varies in the direction , , .
of the longitudinal axis thereof. If such a propellor is cast by a conventional process, since the green mold employed has a comparatively low heat-resistance, which imposes limits on the temperature to which the mold may be heated during the pouring process, there is likely to be inefficient filling or short-run of the mold by the poured metal, particularly when, in order to achieve improved strength and resistance to wear and corrosion, stainless steel is used instead of a copper alloy. In addition, blowholes or burning stainless steel are sometimes present on the surface of the cast part. Because of these faults, combined with the fact that good dimensional precision of a cast part cannot be guaranteedl as noted above, such castings always have unnecessary metal or other material attached thereto, which must be removed by machining which increases the cost of manufacture of a propellor.
These disadvantages are not limited to the manufac-ture of ships' propellors, and they also apply to the manu-facture of similar large articles of complex shape, for example the blades of large supercharger turbines, compressors or condenser.
In the conventional investment casting processes, because of the properties of the pattern material employed, it is necessary to employ comparatively large and complex injection molding equipment for injection of the thermally fusible material. The pattern made of a thermally fusible material may be formed manually by an artwork engraving, but for production on an industrial scale, split molds made of a metallic alloy may be used for casting a master pattern.
In this case, the mold halves must be given a correct finish by machining or a similar process, and then clamped together to define a single mold into which thermal]y fusible material 13'7 .
can be injected by an injection molding machine. However, use of an injection molding machine results in increased manu-facturing costs, since the split mold defining the required shape must be extremely strong and able to resist the high-pressure flow of injected thermally fusible material. Also, `~if the mold cavity has to contain a core, special measures must be taken to ensure that the core is not moved during the forcible injection of the thermally fusible material, and the complicated procedures necessary to ensure that the core remains correctly positioned are often the cause of delay in the manufacturing processes.
-It is accordingly a principal object of the present invention to provide an improved method for precision casting profiled members of three dimensional structure, such as propellors, impellers, diffusers, condensers, turbine blades and the like which reduces some of the problems inherent in conventional casting processes.
According to one aspect of the invention there is provided an investment casting method which comprises (a) pre-20 paring a thermally fusible pattern from a material selected -;from the group consisting of naphthalene and para-dichloro-benzene, with or without the addition of one or more polymers each having a vinyl radical, which thermally fusible pattern is substantially a replica of the article to be cast; (b) forming a refractory investment around the thermally fusible pattern by coating the pattern with a refractory slurry; (c) preliminary melting the outer parts of the thermally fusible pattexn so as to produce a small gap between said thermally fusible pattern and said refractory investment by dissolving the surface portions of said pattern by means of exposing the -pattern to the vapour of an organic solvent for the pattern 9~
material; (d) completely melting and removing the residue of the thermally fusible pattern from the refractory invest-ment by heating so as to leave the refractory investment with a cavity previously occupied by the thermally fusible pattern, said cavity having all the details of said thermally fusible pattern, whereby there is provided a rigid ceramic mold of one-piece construction; (e) preheating said refractory invest-ment constituting said mold in an oven to a temperature close to the temperature of the molten metal to be cast; (f) pouring said molten metal into the mold while the latter is heated to minimize the temperature difference between the mold and the molten metal; (g) solidifying the molten metal within the mold;
and (h) removing the solidified metal from the mold in the form of the desired casting.
According to another aspect of the invention there is provided a refractory mold of one-piece construction which is manufactured by preparing a thermally fusible pattern from a material of the group consisting of naphthalene and para-dichloro~benzene, with or without the addition of at least one polymer having a vinyl radical, which thermally fusible pattern is a substantial replica of a desired casting to be made by the use of said mold, subsequently forming a refractory invest-ment enveloping the thermally fusible pattern, preliminarily melting the thermally fusible pattern so as to produce a small gap between saicl pattern and said refractory investment by dissolving a portion of said pattern by means of contacting the pattern and investment with the vapour of an organic solvent, and then completely melting and removing all the residue of the thermally fusible pattern from said refractory investment by the heating thereof so as to leave the refractory investment having a cavity that was formerly occupied by said thermally fusible pattern, said cavity having all the details of said .
, , -` ~.C~S~ 37 `
thermally fusihle pattern.
It is an advantage of the invention, at least in preferred forms, that it can provide a method for casting large profile members which does not require the execution of complex casting procedures.
It is a further advantage of the invention, at least in preferred forms that it can provide a method for precision casting of profiled members which is not limited to casting of propellors or the like of particular size or of particular material, and which permits production of profiled members of three dimensional structure with highly precise as-cast dimensions and smooth casting surfaces.
It is yet another advantage of the invention, at least in the preferred forms, that it can provide an investment casting method in which production of investment casting patterns of profiled members of three dimensional structure is fairly easily achieved and costs of mold-making are com-paratively low.
Preferably the thermally fusible material is poured into a mold during the production of a pattern at a pouring speed in the range of from 0.1 kg/sec to 5 kg/sec.
Because of the gap produced in the preliminary melting stage" stress on, and cracking of, portions of the shell due to expansion of the pattern are avoided during the complete melting stage and a shell mold is thereby produced which enables the production of a propellor or other casting with a good surface finish and precise dimensions.
These and other advantages and features of the invention will become apparent from the following detailed description of preferred embodiments of the invention when read with reference to the attached drawings, in which like ., .
numbers refer to like parts, and:
Fig. 1 is a cross-sectional view of a thermally fusible pattern defining a ship's screw propellor coated with a ceramic shell according to one form of investment casting method of the present invention;
Fig. 2 is a cross-sectional view of a heating means for removal of the pattern-defining thermally fusible material and illustrates the preliminary removal of the thermally fusible material employed in Fig. l;
Fig. 3 is a cross-sectional view similar to Fig. 2 which illustrates the removal of the remainder of the thermally fusible material;
Fig. 4 is a cross-sectional view of a mold positioned in readiness for investment after removal of the thermally fusible material therefrom; and Fig. 5 is a cross-sectional view similar to Fig. 4, showing a mold defining the propellor positioned in a flask immediately prior to pouring of the metal.
The description below refers to the casting of a ship's screw propellor, but it should be understood that the method of the invention is equally appliable to the casting of other types of three dimensional structure, such as impellers, diffusers, condensers, turbine blades and the like.
In Fig. 1, a hot-melt or thermally fusible pattern 1 defines a screw propellor or similar element to be cast and has a coating of a ceramic forming a shell 2 of suitable thickness.
The thermally fusible pattern 1 may be made by any known pattern-making method, such as employed for example in investment casting or similar processes. Preferably, however, a split mold is employed which is made of gypsum and comprises ~ .. . . . .
'.: ~ ' , . `: .: ' ' ' two halves, and in which portions corresponding to the thin portions of a screw propeller master-mold, not shown, define cavities. The dimensions of this gypsum mold are selected bearing in mind the shrinkage of the poured metal and the material which must be removed to produce the finished part.
As a propellor must define a hole to permit mounting thereof on a drive shaft, such a hole is provided in the propellor-defining pattern, and for reasons which will be apparent later, a recessed portion corresponding to the shaft hole may be provided in the master mold.
Before the thermally fusible material of the pattern 1 is poured into the central area defined by the two halves of the split mold which are clamped together, a core 3 is positioned in the split mold which defines a hole for the propellor drive shaft and is provided with à flange 4 at the bottom.
Next, the thermally fusible material, which has a composition described later, and has been rendered fluid by being heated to 85C, is poured into the split mold. The properties of the thermally fusible material poured are such that use of an injection molding machine is unnecessary.
This does not necessarily mean that an injection molding machine is never used in this invention. However, even for the casting of comparatively large parts, an injection molding machine, if employed, need have only a simple construction.
A particularly noteworthy fea-ture of the method is the speed at which the thermally fusible material can be poured into the mold. A preferred thermally fusible material is material of the naphthalene system. Although such material has many advantages, it has been found that use thereof in conventional methods leads to surface holes and local porosity ...... .... , . _ . .. _ . _ _ .. _ .... _ . _ _ _ .. _ . _ ... .. . _ .. . .. .... _ ...
in a pattern produced. Research undertaken by the inventors showed that the principal cause of such faults was the adherence of steam produced during the pouring process to the wal]s of the mold. From the results of further research and ; tests made it became clear that this could be avoided by keeping the pouring speed in the range 0.1 kg/sec to 5 kg/sec.
When fluid material is poured into a mold at a speed greater than 5 kg/sec, swirling occurs and air is entrapped against the mold surface, leading to surface roughness in the finished pattern. In addition to this, there is a tendency for an applied release agent to be stripped off, with the result that separation of the pattern from the mold becomes difficult.
On the other hand, if the pouring speed is slower than 0.1 kg/sec there may be local porosity and, since poured material tends to cool excessively before new material is poured in, step-lines or zones are produced in the surface of the pattern, and the required dimensional precision fails to be achieved.
When the pouring speed is kept in the range 0.1 kg/sec to 5 kg/
sec, however, a pattern with precise dimensions and a smooth s-~rface finish can be obtained.
After being poured into the split mold, the thermally fusible material defining the pattern 1 is allowed to solidify and is then removed from the mold. The pattern 1 thus removed still supports the core 3.
The thermally fusible material employed for the pattern may be para-dichloro benzene or naphthalene, and, in addition, polystyrene resin or vinyl acetate may be present employed singly or as a mixture.
Preferably, however, the total weight of the B
.. . .. .. .
.~ . . . . . .
tB~
naphthalene is kept within the range of 0.5~ - 10~ if a mixture of naphthalene and polystyrene resin is employed, in the range of 1 - 5% if a mixture of naphthalene and a copolymer of ethylene acetate is employed, and in the range of 3 - 10~ if a mixture of naphthalene and polyethylene resin is employed.
The properties of naphthalene and styronaphthalene, i.e., a mixture of naphthalene and polystyrene resin, are shown in Table 1. For comparison, the properties of represen-tative conventional waxe~ are noted in Table 2. Comparingthe values in these two tables, it is seen that the addition of polystyrene increases bending strength.
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t8~7 When the thennally fusible pattern 1 is for~ed a refracto-ry ceramic shell 2 is formed therearound by repeating a coat-ing and sand-sprinkling processes a set number of times determined with reference to the required strength of the shell 2. For example, coating and sand-sprinkling are alternately repeated 6-7 times if :it is required to subse-quently cast a screw propellor hav:ing a diameter of 400 mm, and 10-12 times if it is required to cast a propellor hav-ing a diameter of 1,200 mm. The pattern 1 is completely enclosed in the shell 1 except for an opening 10, which for a propellor pattern is located on the opposite side of the pattern to the core 3.
Each sand-sprinkling step is designed to strength-en the ceramic chell 2, and the sand emplos~ed is suitably -a dry sand such as alumina sand or fusible silica, which -may be applied in a flow bed tray, or be blown or poured onto the shell 2.
After completion of the requisite number of cycles of coating and sand-sprinkling, the core 3 supported by the pattern 1 is held mechanically by the flange 4 to the shell 2, in order to ensure that the core 3 remains in place after the pattern 1 is subsequently melted out of the shell
2. . :
After completion of the final coating and sand-sprinkling cycle, preliminary and completion melt-out steps are performed in order to remove the pattern 1 and leave a central hollow space in the shell 2 defining the shape of the propellor it is desired to cast. The first of these steps is perfor~ed in a preliminary melt-out oven 5 shown - 14 - .
~ . ~ .. . . .. , . _ .
' , ' . ~ , ` ' . ::
.
~.6~ a~
in Fig. 2, to which reference is now made.
A horizontally disposed partition board 6 is provided across a lower portion of the melt-out oven 5 so that a heating compartment 7 is defined in the lowermost portion of the oven S.
The heating compartment 7 is filled with a fluid medium, such as oil. An electric heater tube 8, to which power is supplied by power line 9, is mounted in a lower side-wall portion of the oven 5 and projects into the compartment 7. When power is . supplied to the heater tube 8, the fluid medium in the compart-ment 7 is heated and the partition board 6 is also heated.
The pattern 1 coated with the shell 2 is held by supports 11 in the oven 5 in such a manner that the uncoated opening 10 thereof faces downwards, so that melted material of the pattern 1 may fall onto the board 6, on which it forms a layer 12. A suitable quantity of an organic solvent is supplied into the oven 5 in the form of an alkene or chloro-hydro-carbon, for example, such as 1-1-1 trichloro-ethane tCH3:CCQ3), 1-1-2 trichloro-ethane, (CHCQ:CCQ2), or 1-1-2-2 tetrachloro-ethane . (CQ2C:CCQ2), in order to dissolve the material of the pattern 1.
; 20 The properties of various different solvents which may be used in the invention are shown in Table 3.
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To avoid the necessity of using of an unduly large amount of solvent, and also to prevent atmospheric pollution, cooler pipes 13 are provided around the upper portion of the inner walls of the oven 5. Cooling air or other fluid is constantly circulated through the pipes 13 by external con-ventionally known means (not shown). With this arrangement, as solvent vapour rises to the upper portion of the oven 5, it is cooled by the cooler pipes 13 and forms droplets 14, which, since the solvent employed is heavier than air, as indicated in Table 2, run down the inner wall of the oven 5, so that the solvent is recovered.
The thermally fusible material of the pattern 1 melts due to the effect of the latent heat`of vaporization of the solvent and is also dissolved by the vapour of the solvent.
At the same time, the solvent vapour passes through micro-pores in the ceramic shell 2, and the shell 2 is heated due to the effect of latent heat of li~uefaction of this vapour. It is undesirable to leave the pattern shell assembly in the oven for a long time once the varporization of the solvent has commenced, and after such an amount of the thermally fusible material has been melted that a gap 3a of several millimetres is provided between the outer surface of the pattern 1 and the inner surface of the shell 2, the assembly of the pattern 1 and shell 2 is removed from the preliminary melt-out oven 5 and transferred to a complete melt-out oven lS.
Referring now to Fig. 3, the pattern and shell assembly is supported in the complete melt-out oven 15 with the opening 10 facing downwards by supports 20 of the same construction as the supports 11 in the melt-out oven 5. The 30 assembly is heated by air at a temperature of 350 - 450C, which is supplied into the interior of the oven 15 via one or .. _ .. . .
'3~{?B~
more pipes 17 by a high-pressure burner unit 16. This hot air is preferably directed into the oven 15 in a direction such that it is not blown directly from the pipe or pipes 17 onto the pattern and shell assembly. The top of the oven 15 is closed, and air may leave the oven 15 via suitable ducts (not shown).
This two-stage melt-out process is very advantageous in terms of maintenance of dimensions in the cast parts. Al-though cracking of the ceramic shell can be avoided in the conventional processes for the melt-out of pattern defining material, in which a pattern and shell assembly is immersed in boiling water or in which a pattern and shell assembly is heated by an air blast at a temperature in the range 350 - 450C
without any preliminary treatment, in the first process immer-sion of the assembly for too long results in a weakening of the binder material and consequent distortion of the mold, while in the latter process it is difficult to control the path of heat transfer from the boss portion of the propellor to the blade tips or edges, and if the pattern-defining material contains a large amount of polystyrene, i.e. 3% or more, there may be breakage of large portions of the mold intended to define the blade edges since the material expands before it melts.
With the two stage method described above, however, these problems are avoided, since the first stage of the melt-out is accompanied by practically no expansion of the pattern-defining material, as it takes place at relatively low tem-perature and usually for a short time, since it is only necessary to effect production of a gap 3a of the order of 0.5 -1.0 mm between the pattern defining material and the ceramic -'0 shell interior in order to ensure that thermal expansion has no adverse effects in the subsequent complete melt-out stage.
Melt out of the thermally fusible material in the oven 15 results in the production of a hollow ceramic shell or mold 2a. To remove any water or residual pattern material which may still adhere to the inner surface of the mold 2a, and also to render the mold 2a strong and stable, the mold is -held for a set time at a temperature in the range 500 - l,100C
in a heating furnace 22 such as that shown in Fig. ~, to which reference is now made. The furnace 22 has steel walls which are lined with a refractory lining material 23, and a mold support stand 24 is provided in the centre of the lower wall. The mold 2a is supported on the stand 24 with the boss portion thereof underneath and the open portion thereof facing upwards, the upper surface of the stand 24 being flat in order to ensure stable support for the mold 2a. Nozzles 27 are defined in the support stand 24 to provide communication between the interior of the furnace 22 and a high-pressure burner 25 provided below the stand 24 outside the main body of the furnace 22, and to which gas is supplied by a line 26. Upon actuation of the burner 25, therefore, the mold 2a is subjected to a hot blast effecting complete removal therefrom of water and other residual material.
In addition to drying the mold 2a, the furnace 22 also serves to heat the mold to a temperature as close as possible to the temperature of molten metal subsequently poured thereinto.
For example, the mold 2a may be held in the furance 22 for about three hours if it is required to heat the mold to a temperature of the order of 400C to 700C.
'The mold 2a is then placed in a flask 28, such as - that shown in Fig. 5, with the opening of the mold 2a facing upwards and now constituting a sprue lOa. Steel shot, chromite sand, zircon sand, or similar dry sand material 29 is packed around the mold 2a, only the sprue lOa being left projecting PC1~7 ~ .
. .
above the level of the sand material 29. This projecting portion is suitably wrapped with insulating material 30 made of ceramic fibre, for example.
; In the condition shown in Fig. 5, the mold 2a is ready to receive the molten metal. One of the main advantages of this method is that the metal to be cast may be stainless steel. Although recently some materials such as aluminium bronze have sometimes been used in place of high tension brass (HBsC-l), which was previously the main material used for the manufacture of ships' propellors, there has previously been no equipment or methods available permitting the use of stainless steel in an economical manner. This is because, conventionally, use is made of the so-called sweeping mold methods employing C2 or green molds, and problems associated with run and other factors make it necessary to leave 2 - 3 mm of metal to be machined off after casting. This is not an excessive amount for conventional copper alloys, which are comparatively cheap and easily machinable, but is excessive for stainless steel which is very difficult to machine, as well as being expensive.
The result has been that in conventional methods, processing costs when propellors are cast in stainless steel are 3 - 5 times higher than when copper alloys are employed. With the method of the invention, however, as noted in greater detail below, an extremely good finish and close dimensional tolerances can be achieved in the casting of propellors even when stainless steel is employed, and the amount of material to be removed after the casting is only in the order of 0.3 mm. In other words, the invention offers the advantage that in terms of overall processing costs, there is very little difference between using stainless steel and copper alloys for manufacture of propellors, i.e., propellors may be easily and economically ''.' ' , , ", ' ' ~' ': ' '' ' .
~ (3~ S ~ 7 .; ' made of stainless steel, which for this purpose is far superior to copper alloy materials.
Examples of suitable types and compositions of stainless steels which may be employed for the manufacture of propellors are given in Table 4.
Table 4 .._ Material C Si Mn Cr Ni ~lo Cu (Code) __ _ .. _ . _ __ No. 1 KSP-l 0.0~ 1.4 1.2 18.8 8.5 1.0 ..__ No. 2 KSP-2 0.05 0.8 0:8 13.0 4.0 0.7 _ .
Using the method of the invention, there was found to be no difference in the casting surface regardless of whether the casting was effected by bottom pouring or by top pouring, but the latter type of pouring is preferred since it presents advantages with respect to the preparation of molds.
When a pouring well is employed, there is only a minor amount of inclusion of slag or dross in the finished casting.
From the point of view of ease of the casting process, the best process is to use a tea-spout ladle to effect prelimi-nary pouring and then to effect a top pour.
Subsequent to pouring, the castings are allowed tocool, and then the risers are cut off and machining or other finishing processes are effected in a known manner, to produce ~inished propellors.
; In contrast with the average value of surface roughness of 50 - 140 ~ of propellors cast in conventional sand molds, the surface roughness of 18-8 stainless steel propellors cast by the method of the invention is very small, and is in the range 5 ~ 15 ~. Thanks to this, only a small amount of finishing machining is necessary, and the required time and expense for producing a finished propel-S~ '7 lor are accordingly much less.
SpeciEic examples of the good results obtained by the method of the invention are given in Table 5, which notes as-cast dimensions of propellors cast by the above-described method.
Table 5 . ____ . . ........ _ . .
Size Dimensional precision __ . .~
<25 mm < ~0.2 mm .. _ . ...
25 - 75 mm ~0.15 ~ 0.5 mm 75 - 200 mm ~0.4 - 1.0 mm _ . .
200 - 400 mm ~0.8 - ].. 5 mm _ ... _ ~ 400 - 600 mm ~1.2 - 2.0 mm _ 600 - 800 mm ~1.8 - 2.4 mm ~800 mm _0.2 - 0.4 mm ' In further illustration of the advantages of the invention, Table 6 provides a comparison of the propellor blade pitch achieved by conventional green mold casting methods and by the me-thod of the invention~
; - . - . :
.
::
After completion of the final coating and sand-sprinkling cycle, preliminary and completion melt-out steps are performed in order to remove the pattern 1 and leave a central hollow space in the shell 2 defining the shape of the propellor it is desired to cast. The first of these steps is perfor~ed in a preliminary melt-out oven 5 shown - 14 - .
~ . ~ .. . . .. , . _ .
' , ' . ~ , ` ' . ::
.
~.6~ a~
in Fig. 2, to which reference is now made.
A horizontally disposed partition board 6 is provided across a lower portion of the melt-out oven 5 so that a heating compartment 7 is defined in the lowermost portion of the oven S.
The heating compartment 7 is filled with a fluid medium, such as oil. An electric heater tube 8, to which power is supplied by power line 9, is mounted in a lower side-wall portion of the oven 5 and projects into the compartment 7. When power is . supplied to the heater tube 8, the fluid medium in the compart-ment 7 is heated and the partition board 6 is also heated.
The pattern 1 coated with the shell 2 is held by supports 11 in the oven 5 in such a manner that the uncoated opening 10 thereof faces downwards, so that melted material of the pattern 1 may fall onto the board 6, on which it forms a layer 12. A suitable quantity of an organic solvent is supplied into the oven 5 in the form of an alkene or chloro-hydro-carbon, for example, such as 1-1-1 trichloro-ethane tCH3:CCQ3), 1-1-2 trichloro-ethane, (CHCQ:CCQ2), or 1-1-2-2 tetrachloro-ethane . (CQ2C:CCQ2), in order to dissolve the material of the pattern 1.
; 20 The properties of various different solvents which may be used in the invention are shown in Table 3.
.
.
, .
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, . .
To avoid the necessity of using of an unduly large amount of solvent, and also to prevent atmospheric pollution, cooler pipes 13 are provided around the upper portion of the inner walls of the oven 5. Cooling air or other fluid is constantly circulated through the pipes 13 by external con-ventionally known means (not shown). With this arrangement, as solvent vapour rises to the upper portion of the oven 5, it is cooled by the cooler pipes 13 and forms droplets 14, which, since the solvent employed is heavier than air, as indicated in Table 2, run down the inner wall of the oven 5, so that the solvent is recovered.
The thermally fusible material of the pattern 1 melts due to the effect of the latent heat`of vaporization of the solvent and is also dissolved by the vapour of the solvent.
At the same time, the solvent vapour passes through micro-pores in the ceramic shell 2, and the shell 2 is heated due to the effect of latent heat of li~uefaction of this vapour. It is undesirable to leave the pattern shell assembly in the oven for a long time once the varporization of the solvent has commenced, and after such an amount of the thermally fusible material has been melted that a gap 3a of several millimetres is provided between the outer surface of the pattern 1 and the inner surface of the shell 2, the assembly of the pattern 1 and shell 2 is removed from the preliminary melt-out oven 5 and transferred to a complete melt-out oven lS.
Referring now to Fig. 3, the pattern and shell assembly is supported in the complete melt-out oven 15 with the opening 10 facing downwards by supports 20 of the same construction as the supports 11 in the melt-out oven 5. The 30 assembly is heated by air at a temperature of 350 - 450C, which is supplied into the interior of the oven 15 via one or .. _ .. . .
'3~{?B~
more pipes 17 by a high-pressure burner unit 16. This hot air is preferably directed into the oven 15 in a direction such that it is not blown directly from the pipe or pipes 17 onto the pattern and shell assembly. The top of the oven 15 is closed, and air may leave the oven 15 via suitable ducts (not shown).
This two-stage melt-out process is very advantageous in terms of maintenance of dimensions in the cast parts. Al-though cracking of the ceramic shell can be avoided in the conventional processes for the melt-out of pattern defining material, in which a pattern and shell assembly is immersed in boiling water or in which a pattern and shell assembly is heated by an air blast at a temperature in the range 350 - 450C
without any preliminary treatment, in the first process immer-sion of the assembly for too long results in a weakening of the binder material and consequent distortion of the mold, while in the latter process it is difficult to control the path of heat transfer from the boss portion of the propellor to the blade tips or edges, and if the pattern-defining material contains a large amount of polystyrene, i.e. 3% or more, there may be breakage of large portions of the mold intended to define the blade edges since the material expands before it melts.
With the two stage method described above, however, these problems are avoided, since the first stage of the melt-out is accompanied by practically no expansion of the pattern-defining material, as it takes place at relatively low tem-perature and usually for a short time, since it is only necessary to effect production of a gap 3a of the order of 0.5 -1.0 mm between the pattern defining material and the ceramic -'0 shell interior in order to ensure that thermal expansion has no adverse effects in the subsequent complete melt-out stage.
Melt out of the thermally fusible material in the oven 15 results in the production of a hollow ceramic shell or mold 2a. To remove any water or residual pattern material which may still adhere to the inner surface of the mold 2a, and also to render the mold 2a strong and stable, the mold is -held for a set time at a temperature in the range 500 - l,100C
in a heating furnace 22 such as that shown in Fig. ~, to which reference is now made. The furnace 22 has steel walls which are lined with a refractory lining material 23, and a mold support stand 24 is provided in the centre of the lower wall. The mold 2a is supported on the stand 24 with the boss portion thereof underneath and the open portion thereof facing upwards, the upper surface of the stand 24 being flat in order to ensure stable support for the mold 2a. Nozzles 27 are defined in the support stand 24 to provide communication between the interior of the furnace 22 and a high-pressure burner 25 provided below the stand 24 outside the main body of the furnace 22, and to which gas is supplied by a line 26. Upon actuation of the burner 25, therefore, the mold 2a is subjected to a hot blast effecting complete removal therefrom of water and other residual material.
In addition to drying the mold 2a, the furnace 22 also serves to heat the mold to a temperature as close as possible to the temperature of molten metal subsequently poured thereinto.
For example, the mold 2a may be held in the furance 22 for about three hours if it is required to heat the mold to a temperature of the order of 400C to 700C.
'The mold 2a is then placed in a flask 28, such as - that shown in Fig. 5, with the opening of the mold 2a facing upwards and now constituting a sprue lOa. Steel shot, chromite sand, zircon sand, or similar dry sand material 29 is packed around the mold 2a, only the sprue lOa being left projecting PC1~7 ~ .
. .
above the level of the sand material 29. This projecting portion is suitably wrapped with insulating material 30 made of ceramic fibre, for example.
; In the condition shown in Fig. 5, the mold 2a is ready to receive the molten metal. One of the main advantages of this method is that the metal to be cast may be stainless steel. Although recently some materials such as aluminium bronze have sometimes been used in place of high tension brass (HBsC-l), which was previously the main material used for the manufacture of ships' propellors, there has previously been no equipment or methods available permitting the use of stainless steel in an economical manner. This is because, conventionally, use is made of the so-called sweeping mold methods employing C2 or green molds, and problems associated with run and other factors make it necessary to leave 2 - 3 mm of metal to be machined off after casting. This is not an excessive amount for conventional copper alloys, which are comparatively cheap and easily machinable, but is excessive for stainless steel which is very difficult to machine, as well as being expensive.
The result has been that in conventional methods, processing costs when propellors are cast in stainless steel are 3 - 5 times higher than when copper alloys are employed. With the method of the invention, however, as noted in greater detail below, an extremely good finish and close dimensional tolerances can be achieved in the casting of propellors even when stainless steel is employed, and the amount of material to be removed after the casting is only in the order of 0.3 mm. In other words, the invention offers the advantage that in terms of overall processing costs, there is very little difference between using stainless steel and copper alloys for manufacture of propellors, i.e., propellors may be easily and economically ''.' ' , , ", ' ' ~' ': ' '' ' .
~ (3~ S ~ 7 .; ' made of stainless steel, which for this purpose is far superior to copper alloy materials.
Examples of suitable types and compositions of stainless steels which may be employed for the manufacture of propellors are given in Table 4.
Table 4 .._ Material C Si Mn Cr Ni ~lo Cu (Code) __ _ .. _ . _ __ No. 1 KSP-l 0.0~ 1.4 1.2 18.8 8.5 1.0 ..__ No. 2 KSP-2 0.05 0.8 0:8 13.0 4.0 0.7 _ .
Using the method of the invention, there was found to be no difference in the casting surface regardless of whether the casting was effected by bottom pouring or by top pouring, but the latter type of pouring is preferred since it presents advantages with respect to the preparation of molds.
When a pouring well is employed, there is only a minor amount of inclusion of slag or dross in the finished casting.
From the point of view of ease of the casting process, the best process is to use a tea-spout ladle to effect prelimi-nary pouring and then to effect a top pour.
Subsequent to pouring, the castings are allowed tocool, and then the risers are cut off and machining or other finishing processes are effected in a known manner, to produce ~inished propellors.
; In contrast with the average value of surface roughness of 50 - 140 ~ of propellors cast in conventional sand molds, the surface roughness of 18-8 stainless steel propellors cast by the method of the invention is very small, and is in the range 5 ~ 15 ~. Thanks to this, only a small amount of finishing machining is necessary, and the required time and expense for producing a finished propel-S~ '7 lor are accordingly much less.
SpeciEic examples of the good results obtained by the method of the invention are given in Table 5, which notes as-cast dimensions of propellors cast by the above-described method.
Table 5 . ____ . . ........ _ . .
Size Dimensional precision __ . .~
<25 mm < ~0.2 mm .. _ . ...
25 - 75 mm ~0.15 ~ 0.5 mm 75 - 200 mm ~0.4 - 1.0 mm _ . .
200 - 400 mm ~0.8 - ].. 5 mm _ ... _ ~ 400 - 600 mm ~1.2 - 2.0 mm _ 600 - 800 mm ~1.8 - 2.4 mm ~800 mm _0.2 - 0.4 mm ' In further illustration of the advantages of the invention, Table 6 provides a comparison of the propellor blade pitch achieved by conventional green mold casting methods and by the me-thod of the invention~
; - . - . :
.
::
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Ideally, dimensions for the first to the third blades should be the same, but in practice there is inevitably some difference in the dimensions or pitch between the blades As seen from the above -table, whereas this difference is large in conventionally cast propellors, it is small in propellors cast by the method of the invention. In other words, the invention makes it possible to manufacture propellors which may be rotated at high speed but are sub-ject to little vibration.
A specific Example of manufacture of a stainless steel propellor according to one form of the method of the invention is as follows.
Example 1. Propellor dimensions Diameter 810 mm Expanded area ratio 45 ~
Weight 15 kg Number of blades 3 2. Manufacturing stages a) A gypsum mold was prepared in a size dimensioned to allow for shrinkage and the material to be removed to give a finished product of the required dimensions.
b) Napthalene was melted at a temperature of 85~C, a 1% addition of polystyrene was made thereto and melted therein, and the mixture was poured into the gypsum mold to form a pattern.
c) After the pattern had hardened, it was released from the mold and then allowed to cool to room temperature.
d~ The propellor pattern was coated by being .; : .
3~
dipped in a slurry consisting of silica flour throughly mixed in colloidal silica, and while still wet had grains ~ of silica sprinkled thereon, and was then dried. This coating and sand-sprinkling process was repeated 8 times, resulting in the formation on the pattern of a ceramic shell having an average thickness of 6 mm.
e) The pattern coated in this manner was dried for approximately 12 hours and then immersed in a trichloro-ethylene vapour bath fQr approximately 15 minutes to effect preliminary melt-off of approximately 1 mm of the outer surface of the pattern, after which the pattern and shell assembly was transferred to a hot air furnace in which it was exposed for approximately 30 minutes to a hot air blast at a temperature of 350C, to completely melt out the pattern material and produce a shell mold.
f) The shell mold thus produced was dried and hardened for approximateIy 15 minutes in a heating furnace employing high-pressure burners, and was then heated to red heat (approximately 650C).
g) The heated mold was packed in dry sand, and then 18-~ stainless steel,which had been melted in an ultrasonic electric furnace,was poured thereinto.
h) After pouring, the cast metal was allowed to cool to room temperature and was then removed from the mold.
3. As-cast dimensional precision The thickness at two places on each of 20 propellors produced by the abovedescrlbed process was measured, and it was found that the variation ln thickness for the enti.re sample of 20 propellors was no more than +0.41 mm and the standard deviation was 0.12. This is as opposed to conven-tional sand-mold casts for which the variation in thickness is +1.5 mm or more.
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~ ~ ~ ~ u~ ~
o) .~ _ ~ '~u ~ ~ ~ ~ .~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
r ~ O . ~ ~ r ~ ~ r ) t .1 f ~
E-l t~7 tJ~ ~ ~ ~
~ _~ ~ ...._ ~ ~ ~, .~, ~ . , ~ 3n~
Ideally, dimensions for the first to the third blades should be the same, but in practice there is inevitably some difference in the dimensions or pitch between the blades As seen from the above -table, whereas this difference is large in conventionally cast propellors, it is small in propellors cast by the method of the invention. In other words, the invention makes it possible to manufacture propellors which may be rotated at high speed but are sub-ject to little vibration.
A specific Example of manufacture of a stainless steel propellor according to one form of the method of the invention is as follows.
Example 1. Propellor dimensions Diameter 810 mm Expanded area ratio 45 ~
Weight 15 kg Number of blades 3 2. Manufacturing stages a) A gypsum mold was prepared in a size dimensioned to allow for shrinkage and the material to be removed to give a finished product of the required dimensions.
b) Napthalene was melted at a temperature of 85~C, a 1% addition of polystyrene was made thereto and melted therein, and the mixture was poured into the gypsum mold to form a pattern.
c) After the pattern had hardened, it was released from the mold and then allowed to cool to room temperature.
d~ The propellor pattern was coated by being .; : .
3~
dipped in a slurry consisting of silica flour throughly mixed in colloidal silica, and while still wet had grains ~ of silica sprinkled thereon, and was then dried. This coating and sand-sprinkling process was repeated 8 times, resulting in the formation on the pattern of a ceramic shell having an average thickness of 6 mm.
e) The pattern coated in this manner was dried for approximately 12 hours and then immersed in a trichloro-ethylene vapour bath fQr approximately 15 minutes to effect preliminary melt-off of approximately 1 mm of the outer surface of the pattern, after which the pattern and shell assembly was transferred to a hot air furnace in which it was exposed for approximately 30 minutes to a hot air blast at a temperature of 350C, to completely melt out the pattern material and produce a shell mold.
f) The shell mold thus produced was dried and hardened for approximateIy 15 minutes in a heating furnace employing high-pressure burners, and was then heated to red heat (approximately 650C).
g) The heated mold was packed in dry sand, and then 18-~ stainless steel,which had been melted in an ultrasonic electric furnace,was poured thereinto.
h) After pouring, the cast metal was allowed to cool to room temperature and was then removed from the mold.
3. As-cast dimensional precision The thickness at two places on each of 20 propellors produced by the abovedescrlbed process was measured, and it was found that the variation ln thickness for the enti.re sample of 20 propellors was no more than +0.41 mm and the standard deviation was 0.12. This is as opposed to conven-tional sand-mold casts for which the variation in thickness is +1.5 mm or more.
4. Cast surface roughness The surface roughness was measured at three locations on each of the 20 propellors, and the as-cast surface roughness was found to be in the range of 8 - 12 ~, which is much less than the range of 50 - 140 ~ achievable by conventional methods.
Although the present invention has fully been described in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are ap-parent to those skilled in the art. Accordingly, such changes and modifications are to be understood as included within the true scope of the present invention as defined by the appendant claims.
.~
, .
' ' : . ~ .
Although the present invention has fully been described in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are ap-parent to those skilled in the art. Accordingly, such changes and modifications are to be understood as included within the true scope of the present invention as defined by the appendant claims.
.~
, .
' ' : . ~ .
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An investment casting method which comprises:
(a) preparing a thermally fusible pattern from a material selected from the group consisting of naphthalene and para-dichloro-benzene, with or without the addition of one or more polymers each having a vinyl radical, which thermally fusible pattern is substantially a replica of the article to be cast;
(b) forming a refractory investment around the thermally fusible pattern by coating the pattern with a refractory slurry;
(c) preliminary melting the outer parts of the thermally fusible pattern so as to produce a small gap between said thermally fusible pattern and said refractory investment by dissolving the surface portions of said pattern by means of exposing the pattern to the vapour of an organic solvent for the pattern material, (d) completely melting and removing the residue of the thermally fusible pattern from the refractory investment by heating so as to leave the refractory investment with a cavity previously occupied by the thermally fusible pattern, said cavity having all the details of said thermally fusible pattern, whereby there is provided a rigid ceramic mold of one-piece construction;
(e) preheating said refractory investment constituting said mold in an oven to a temperature close to the temperature of the molten metal to be cast;
(f) pouring said molten metal into the mold while the latter is heated to minimize the temperature difference between the mold and the molten metal;
(g) solidifying the molten metal within the mold; and (h) removing the solidified metal from the mold in the form of the desired casting.
(a) preparing a thermally fusible pattern from a material selected from the group consisting of naphthalene and para-dichloro-benzene, with or without the addition of one or more polymers each having a vinyl radical, which thermally fusible pattern is substantially a replica of the article to be cast;
(b) forming a refractory investment around the thermally fusible pattern by coating the pattern with a refractory slurry;
(c) preliminary melting the outer parts of the thermally fusible pattern so as to produce a small gap between said thermally fusible pattern and said refractory investment by dissolving the surface portions of said pattern by means of exposing the pattern to the vapour of an organic solvent for the pattern material, (d) completely melting and removing the residue of the thermally fusible pattern from the refractory investment by heating so as to leave the refractory investment with a cavity previously occupied by the thermally fusible pattern, said cavity having all the details of said thermally fusible pattern, whereby there is provided a rigid ceramic mold of one-piece construction;
(e) preheating said refractory investment constituting said mold in an oven to a temperature close to the temperature of the molten metal to be cast;
(f) pouring said molten metal into the mold while the latter is heated to minimize the temperature difference between the mold and the molten metal;
(g) solidifying the molten metal within the mold; and (h) removing the solidified metal from the mold in the form of the desired casting.
2. A method as claimed in Claim 1, wherein said forming step (b) is carried out by repeating several times a cycle consisting of dipping the thermally fusible pattern into a bath containing the refractory slurry and subjecting the coated pattern to a sanding process.
3. A method as claimed in Claim 1, wherein said pre-liminary melting step (c) is carried out by using a chlorinated hydrocarbon as the organic solvent, said melting of said thermally fusible pattern being achieved by the contact of the vapour of said organic solvent with the pattern and by the effect of the latent heat evolved by the vaporized solvent.
4. A method as claimed in Claim 1, wherein said complete melting step (d) is carried out in an oven at a temperature within the range of 350 to 450°C.
5. A method as claimed in Claim 1, wherein said pre-heating step (e) is carried out in a furnace at a temperature within the range of 500 to 1,100°C.
6. A method as claimed in Claim 1, wherein the polymers in step (a) are selected from the group consisting of polystyrene resins, ethylene-vinyl acetate copolymers and polyethylene resins.
7. A method as claimed in Claim 3, wherein said chlorin-ated hydrocarbon is selected from the group consisting of 1,1,1-trichloroethane, 1,1,2-trichloroethane and 1,1,2,2-tetrachloroethane.
8. An investment casting method which comprises:
(a) forming a thermally fusible pattern of a profiled member by melting a thermally fusible substance formed of naphthalene or para-dichloro-benzene employed singly or mixed with one or more copolymers having vinyl radicals, and pouring said melted substance into a mold at a pouring speed in the range of from 0.1 kg/sec to 5 kg/sec;
(b) forming a refractory investment around said thermally fusible pattern by repeatedly coating said pattern with a refractory material and then applying thereon refractory flour materials;
(c) effecting a preliminary melt-out process to cause production of a small gap between said thermally fusible pattern and said shell by dissolving the surface portion of said pattern by means of contacting the pattern and investment with the vapour of an organic solvent for the pattern material;
(d) effecting a complete melt-out process in which the remainder of said thermally fusible pattern is subjected to heat to effect complete melting and removal thereof from said -shell, whereby there is produced a rigid ceramic mold of one-piece construction;
(e) preheating said shell mold to a temperature close to the temperature of the molten metal to be cast into the shape of said profile member and pouring said molten metal into said mold; and (f) allowing said poured metal to solidify, and then removing said solidified metal from said mold.
(a) forming a thermally fusible pattern of a profiled member by melting a thermally fusible substance formed of naphthalene or para-dichloro-benzene employed singly or mixed with one or more copolymers having vinyl radicals, and pouring said melted substance into a mold at a pouring speed in the range of from 0.1 kg/sec to 5 kg/sec;
(b) forming a refractory investment around said thermally fusible pattern by repeatedly coating said pattern with a refractory material and then applying thereon refractory flour materials;
(c) effecting a preliminary melt-out process to cause production of a small gap between said thermally fusible pattern and said shell by dissolving the surface portion of said pattern by means of contacting the pattern and investment with the vapour of an organic solvent for the pattern material;
(d) effecting a complete melt-out process in which the remainder of said thermally fusible pattern is subjected to heat to effect complete melting and removal thereof from said -shell, whereby there is produced a rigid ceramic mold of one-piece construction;
(e) preheating said shell mold to a temperature close to the temperature of the molten metal to be cast into the shape of said profile member and pouring said molten metal into said mold; and (f) allowing said poured metal to solidify, and then removing said solidified metal from said mold.
9. A refractory mold of one-piece construction which is manufactured by preparing a thermally fusible pattern from a material of the group consisting of naphthalene and para-dichloro-benzene, with or without the addition of at least one polymer having a vinyl radical, which thermally fusible pattern is a substantial replica of a desired casting to be made by the use of said mold, subsequently forming a refractory investment enveloping the thermally fusible pattern, preliminarily melting the thermally fusible pattern so as to produce a small gap between said pattern and said refractory investment by dissolving a portion of said pattern by means of contacting the pattern and investment with the vapour of an organic solvent, and then completely melting and removing all the residue of the thermally fusible pattern from said refractory investment by the heating thereof so as to leave the refractory investment having a cavity that was formerly occupied by said thermally fusible pattern, said cavity having all the details of said thermally fusible pattern.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP120666/1976 | 1976-10-05 | ||
| JP12066676A JPS5344427A (en) | 1976-10-05 | 1976-10-05 | Method to manufacture propellers by using extinguishable pattern |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090087A true CA1090087A (en) | 1980-11-25 |
Family
ID=14791893
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA282,385A Expired CA1090087A (en) | 1976-10-05 | 1977-07-08 | Investment casting method |
Country Status (19)
| Country | Link |
|---|---|
| JP (1) | JPS5344427A (en) |
| AU (1) | AU509149B2 (en) |
| BE (1) | BE856629A (en) |
| BR (1) | BR7704507A (en) |
| CA (1) | CA1090087A (en) |
| CH (1) | CH635010A5 (en) |
| DE (1) | DE2730945A1 (en) |
| DK (1) | DK308677A (en) |
| ES (2) | ES460606A1 (en) |
| FI (1) | FI772107A (en) |
| FR (1) | FR2366896A1 (en) |
| GB (1) | GB1590480A (en) |
| IT (1) | IT1083095B (en) |
| MX (1) | MX147702A (en) |
| NL (1) | NL7707591A (en) |
| NO (1) | NO772424L (en) |
| SE (1) | SE7708005L (en) |
| SU (1) | SU664539A3 (en) |
| ZA (1) | ZA774134B (en) |
Families Citing this family (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5284191A (en) * | 1975-12-30 | 1977-07-13 | Asahi Glass Co Ltd | Improved f-contg. cation exchange resin membrane |
| US4289191A (en) * | 1980-04-02 | 1981-09-15 | United Technologies Corporation | Injection molding thermoplastic patterns having ceramic cores |
| FR2493199A1 (en) * | 1980-10-30 | 1982-05-07 | Aherne Heron John | Lost wax casting of metal pieces - using refractory brick with several inlet holes for molten metal, each hole leading to one mould cavity and to common trough |
| JPS62227603A (en) * | 1986-03-31 | 1987-10-06 | 日本碍子株式会社 | Manufacture of ceramics sintered body and molding tool used for said manufacture |
| DE4244480A1 (en) * | 1992-12-30 | 1994-07-07 | Bodenseewerk Geraetetech | Sensor arrangement with cooled sensor |
| DE19939155A1 (en) * | 1999-08-20 | 2001-02-22 | Pore M Gmbh | Production of metallic lattice network structure comprises inserting foam pre-structure into container, infiltrating with refractory material, and solidifying |
| CN103878321B (en) * | 2014-03-27 | 2016-07-06 | 舟山市定海区龙叶螺旋桨制造有限公司 | Propeller formative technology |
| CN103909227A (en) * | 2014-04-04 | 2014-07-09 | 含山县荣盛机械铸造有限公司 | Processing method of common casting pieces |
| CN105436412B (en) * | 2015-11-23 | 2017-12-22 | 镇江同舟螺旋桨有限公司 | A kind of propeller casting mold Nitrogen filling system |
| CN105562644A (en) * | 2015-12-18 | 2016-05-11 | 吉林常春高氮合金研发中心有限公司 | Method for manufacturing propeller casting for high nitrogen austenite stainless steel vessel |
| US10493523B1 (en) | 2016-02-04 | 2019-12-03 | Williams International Co., L.L.C. | Method of producing a cast component |
| CN106040990B (en) * | 2016-08-11 | 2018-09-11 | 山东豪迈机械科技股份有限公司 | A kind of plaster core production method and system that large size pump vane casting uses |
| CN106077501B (en) * | 2016-08-11 | 2018-09-11 | 山东豪迈机械科技股份有限公司 | A kind of the drying bracket and drying device of pump vane casting gypsum mould |
| CN106636860B (en) * | 2016-12-02 | 2018-03-16 | 机械科学研究总院青岛分院有限公司 | A kind of method for manufacturing high-nitrogen austenitic stainless steel ships propeller casting |
| RU2733531C1 (en) * | 2019-07-03 | 2020-10-05 | Федеральное государственное автономное образовательное учреждение высшего образования "Уральский федеральный университет имени первого Президента России Б.Н. Ельцина" | Method of melting model composition with hot air |
| CN113437846B (en) * | 2021-06-08 | 2023-12-05 | 无锡胜鼎智能科技有限公司 | Manufacturing method of new energy vehicle washing motor shell |
| CN115846593B (en) * | 2022-11-28 | 2023-10-20 | 洛阳航辉新材料有限公司 | Dewaxing method for precision investment casting |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5120011B2 (en) * | 1971-10-21 | 1976-06-22 | ||
| JPS5111022B2 (en) * | 1972-12-11 | 1976-04-08 | ||
| JPS528248B2 (en) * | 1973-09-20 | 1977-03-08 | ||
| JPS5742414B2 (en) * | 1973-11-13 | 1982-09-08 | ||
| US3996991A (en) * | 1973-11-13 | 1976-12-14 | Kubota, Ltd. | Investment casting method |
| JPS5124523A (en) * | 1974-08-22 | 1976-02-27 | Kubota Ltd | SEIMITSUCHUZOYOIGATANO SHOSEIHO |
-
1976
- 1976-10-05 JP JP12066676A patent/JPS5344427A/en active Pending
-
1977
- 1977-07-05 FI FI772107A patent/FI772107A/en not_active Application Discontinuation
- 1977-07-07 NL NL7707591A patent/NL7707591A/en not_active Application Discontinuation
- 1977-07-08 GB GB28787/77A patent/GB1590480A/en not_active Expired
- 1977-07-08 ZA ZA00774134A patent/ZA774134B/en unknown
- 1977-07-08 DE DE19772730945 patent/DE2730945A1/en active Pending
- 1977-07-08 DK DK308677A patent/DK308677A/en not_active Application Discontinuation
- 1977-07-08 SE SE7708005A patent/SE7708005L/en unknown
- 1977-07-08 CA CA282,385A patent/CA1090087A/en not_active Expired
- 1977-07-08 NO NO772424A patent/NO772424L/en unknown
- 1977-07-08 IT IT68597/77A patent/IT1083095B/en active
- 1977-07-08 MX MX169795A patent/MX147702A/en unknown
- 1977-07-08 SU SU772501370A patent/SU664539A3/en active
- 1977-07-08 BE BE179195A patent/BE856629A/en not_active IP Right Cessation
- 1977-07-08 BR BR7704507A patent/BR7704507A/en unknown
- 1977-07-09 ES ES460606A patent/ES460606A1/en not_active Expired
- 1977-07-11 AU AU26912/77A patent/AU509149B2/en not_active Expired
- 1977-08-08 FR FR7724360A patent/FR2366896A1/en active Granted
- 1977-08-10 CH CH980577A patent/CH635010A5/en not_active IP Right Cessation
-
1978
- 1978-08-23 ES ES472801A patent/ES472801A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SU664539A3 (en) | 1979-05-25 |
| BR7704507A (en) | 1978-04-25 |
| ES472801A1 (en) | 1979-04-16 |
| BE856629A (en) | 1978-01-09 |
| GB1590480A (en) | 1981-06-03 |
| JPS5344427A (en) | 1978-04-21 |
| MX147702A (en) | 1983-01-06 |
| DE2730945A1 (en) | 1978-04-06 |
| ES460606A1 (en) | 1978-10-01 |
| IT1083095B (en) | 1985-05-21 |
| AU2691277A (en) | 1979-01-18 |
| NO772424L (en) | 1978-04-06 |
| AU509149B2 (en) | 1980-04-24 |
| CH635010A5 (en) | 1983-03-15 |
| ZA774134B (en) | 1978-07-26 |
| DK308677A (en) | 1978-04-06 |
| NL7707591A (en) | 1978-04-07 |
| FR2366896A1 (en) | 1978-05-05 |
| FR2366896B1 (en) | 1981-07-17 |
| SE7708005L (en) | 1978-04-06 |
| FI772107A (en) | 1978-04-06 |
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