CA1109633A - Mold assembly and method of making the same - Google Patents
Mold assembly and method of making the sameInfo
- Publication number
- CA1109633A CA1109633A CA310,081A CA310081A CA1109633A CA 1109633 A CA1109633 A CA 1109633A CA 310081 A CA310081 A CA 310081A CA 1109633 A CA1109633 A CA 1109633A
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- CA
- Canada
- Prior art keywords
- pattern
- mold
- coating
- patterns
- covering
- 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
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- 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
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
- Turbine Rotor Nozzle Sealing (AREA)
- Moulds, Cores, Or Mandrels (AREA)
Abstract
MOLD ASSEMBLY AND METHOD OF MAKING THE SAME
ABSTRACT
A segmented mold assembly is utilized to cast a turbine engine component having a relatively heavy hub from which relatively light vanes project. The mold assembly includes a plurality of sections which are formed of a ceramic mold material and are interconnected at flange joints. The mold sections are advantageously formed by repetitively dipping patterns in a slurry of liquid ceramic mold material to form wet coatings on the patterns. These wet coatings are dried and separated from the patterns to form the mold sections.
The mold sections which are used to cast the vanes retard the removal of heat from the vanes to provide time for the hub to solidify. This can be accomplished by using relatively thick walled mold sections to form the mold cavities in which vanes are east and relatively thin walled mold sections to form the cavity in which the hub is cast. This could also be accomplished by forming the vane mold section of material having a relatively low rate of heat removal and the hub mold section of a material having a relatively high rate of heat removal.
ABSTRACT
A segmented mold assembly is utilized to cast a turbine engine component having a relatively heavy hub from which relatively light vanes project. The mold assembly includes a plurality of sections which are formed of a ceramic mold material and are interconnected at flange joints. The mold sections are advantageously formed by repetitively dipping patterns in a slurry of liquid ceramic mold material to form wet coatings on the patterns. These wet coatings are dried and separated from the patterns to form the mold sections.
The mold sections which are used to cast the vanes retard the removal of heat from the vanes to provide time for the hub to solidify. This can be accomplished by using relatively thick walled mold sections to form the mold cavities in which vanes are east and relatively thin walled mold sections to form the cavity in which the hub is cast. This could also be accomplished by forming the vane mold section of material having a relatively low rate of heat removal and the hub mold section of a material having a relatively high rate of heat removal.
Description
BACKGROUND OF TEIE INVE~TIOI~
This invention relates to a new and improved mold assembly and a method by which it is made and more specifically to a segmented ceramic mold assembly-which may be advantageously utilized in casting articles having portions o different thicknesses.
When an article having relatively thick and thin portions is to be cast, difficulty may be encountered due to solidification of the relatively thin portion of the article while the relatively thick portion of the article is still molten. This can result in the formation of defects in the thick portion of the article. These defects may be detrimental to the operating characteristics of the article and could result in premature failure of the article under load. For ;example, turbine engines frequently include a rotatable hub which is integrally cast with radially projecting vanes or airfoils. The hub is relatively thick while the vanes are relatively thin. When the hub and vanes are to be integrally cast, difficulties may be encountered due to solidification of the vanes ~hile the hub is still molten.
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The present invention provides an improved method of making an improved mold assembly. The improved method could be utilized to make molds for shaping many different objects.
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:~ ~.'3~6;~3 However, the method is advantageously utilized in making a mold assembly which is utilized in the casting of a one piece turbine engine component having portions of different thicknesses.
The mold assembly includes a plurality of interconnected sections.
The section of the mold assembly in which a relatively thin portion of an article is to be cast has a lower rate of heat removal than the section of the mold assembly in which a relatively thick portion of the article is to be cast. As is well known, the heat removal rate varies as a function of the thermal conductivity, specific head and density of the mold material.
According to one aspect of the invention there is provided a method of making a mold assembly having portions of different thicknesses, said method comprising the steps of providing a plurality of separate disposable patterns each of which has a surface area with a configuration similar to a portion of a surface area of a product, at least partially coating each of !
the disposable patterns with a wet covering of ceramic mold material, drying ~; the wet covering on the patterns, repeating the coating and drying steps with a first one of the plurality of patterns a first number of times to build up a relatively thick covering of ceramic mold ma~erial on the first pattern, repeating the coating and drying steps with a second one of the plurality of patterns a second number of times which is less than the first number of times to build up a relatively thin covering of ceramic mold material on the second pattern, separating the relatively thick covering of ceramic mold material from the first pattern to provide a relatively thick walled mold section, separating the relatively thin covering of ceramic mold material from the second pattern to provide a relatively thin walled mold section, and interconnecting the relatively thick and thin walled mold sections to at least partially form the mold assembly.
According to another aspect of the invention there is provided a method of making a mold assembly comprising the steps of providing a plurality of separate disposable patterns each of which has a surface area ,`?~ ~
~9633 with a configuration similar to a portion of a surface area of a cast product, at least partially coating each of the disposable patterns with a wet covering ceramic mold material, drying the wet coverings on the patterns, repeating the coating and drying steps until coverings of ceramic mold material of desired thicknesses have built up on the patterns, said step of coating t}ie patterns includes at least partially covering a first pattern with material having a first rate of heat removal, said step of coating the patterns further includes at least partially covering a second pattern with a material having a second rate of heat removal, the second rate of heat removal being greater than the first rate of heat removal, separating the covering from the first pattern to at least partially form a f~irst mold section, separating the covering from the second pattern to at least partially form a second moId section having a rate of heat removal which is greater than the rate of heat removal of the first mold section, and interconnecting the first and second mold sections to at least partially ~-~: form a mold assembly having portions with different rates of heat removal.
- BRIEF DESCRIPTION OF THE DRAWINGS
~ The foregoing and other features of the present invention will .i become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein: :
Figure 1 is an illustration of a cast turbojet engine fan frame;
-~ Figure 2 is an illustration of a mold assembly utilized to cast the jet engine fan frame of Figure 1 and constructed in accordance with the present invention;
Figure 3 is a radial sectional view further illustrating the :~ configuration of various sections of the mold assembly of Figure 2;
Figure 4 is a fragmentary upwardly facing view of a hub portion of the mold assembly of Figure 2 with some of the mold sections removed to further illustrate the segmented construction of the mold assembly;
Figure 5 is an illustration of a pattern utilized in forming hub 5' ~? , sections of the mold assembly of Figure 2;
Figure 6 is an illustration of a turbine engine component having a relatively thick hub section and relatively thin vane sections;
- 4a -Fig. 7 is a fragmentary sectional view of a portion of a ¦ mold assembly having thick and thin walled mold sections; and I Fig. 8 is a fragmentary sectional view of a portion of a ¦ mold assembly having sections with walls of different ¦ compositions.
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DESCRIPTION OF SPECIFIC PREFERRED
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A fan frame or inlet duct 20 for a turbojet engine is illustrated in Fig. 1. The jet engine fan frame 20 has an annular central hub or wall 22 from which a plurality of struts or vanes 24 extend radially outwardly to a relatively large diameter annular outer ring or wall 26. When the fan frame 20 is installed in a turbojet engine, the inner wall or hub 22 supports one end of the compressor rotor. The struts or vanes 24 direct air flow back to the compressor through the space between the outer ring or wall 26 and hub. The hollow struts 24 are also utilized to enclose conduits and other parts (not shown) leading between the outside of the outer ring 26 and the interior of the hub 22.
Since the outer ring 26 of the jet engine fan frame 20 has a relatively large diameter, that is a diameter in excess of forty inches, and since relatively close dimensional tolerances are required to fabricate a fan frame which will function properly in a jet engine, relatively large fan frames have previously been fabricated by joining a large number of castings, sheet metal details and forgings to form a completed assembly. Although only jet engine fan frame 20 has been illustrated in Fig. 1, it should be understood that the .
1~3~633 present invention can advantageously be utilized in the ¦ -forming of other turbine engine components. Among these other turbine engine components are diffuser cases, nozzle rings, vane assemblies and bearing supports.
The jet engine fan frame 20 is cast in one piece in a segmented mold assembly 30 (see Fig. 2). The mold assembly 30 is constructed in the manner disclosed in United States Patent No. 4,066,116 and includes a plurality of sprue or pour cups 32 which are disposed within a hub portion 34 of the mold assembly. The hub portion 34 of the mold assembly 30 is connected with an annular outer ring portion 36 of the mold assembly by a plurality of radially extendlng strut portions 38 of the mold assembly.
As is perhaps best seen in Fig. 3, each of the pour cups 32 is connected in direct fluid communication with the hub portion 3~ ~f the mold assembly 30 by gating 42. The hub portion 34 of the mold assembly 30 is in turn connected in fluid communication with the outer ring 36 of the mold assembly through struts 38. Although the illustrated gating 42 onl~ connects the pour cup 32 with the hub portion 34 of the mold assembly 30, additional gating and/or pour cups could be provided in association with the outer ring portion 36 of the mold assembly if desired. Upon a pouring of molten metal into the pour cups 32 of the mold assembly 30, the metal flows into an annular hub mold cavity 46 (Fig. 3), the radially extending strut mold cavities 48 and into an annular outer ring mold cavity 50. This results in an integrally cast jet engine fan frame 20 having a one-piece construction.
The mold assemb]y 30 is formed of a plurality of mold sections which are interconnected to define the various mold cavities 46, 48 and 50. Although the ~et engine fan frame mold assembly 30 is relatively large, by forming the mold assembly 30 of a plurality of small mold sections, it is possible to accurately form each of the mold sections. These mold sections may then be placed in a jig or locating frame to accurately position them relative to each other and are cemented or otherwise interconnected to form a unitary assembly.
The various mold sections are constructed in such a manner that the surfaces which define the various mold cavities can be readily inspected prior to construction of the mold assembly 30. Of course, if any defects are noted during the inspection they are either repaired or a properly formed mold section is substituted for the defective mold section.
To this end, the hub portion 34 of the mold assembly 30 includes a circular array of hub panel mold sections 54 (see Fig. 4) having major side surfaces 56 with a configuration corresponding to the configuration of portions of an annular inner side surface 58 (see Fig. 1) of the jet engine fan frame hub 22. A second circular array of hub panel mold sections 58 are disposed radially outwardly of the hub mold panel sections 54 (see Fig. 4). The hub panel mold sections 58 have major inner side surfaces 60 of a configuration corresponding to the configuration of portions of the outside surface 64 (see Fig.
1) of the hub 22.
A plurality of top caps or end walls 68 extend between the coaxial circular arrays of hub panel mold sections 54 and 58 to close off the top of the hub mold cavity 46. Similarly, bottom caps or end walls 72 cooperate with the lower edge portions of the hub panel mold sections 54 and 58 to close off the bottom of the hub mold cavity 46 tsee Fig.s 3 and 4). The mold sections 54 and 58 may be assembled in an inverted position on a suitable jig or fixture so that the relatively large diameter portion of the hub is disposed downwardly.
The outer ring portion 36 of the mold assembly 30 is constructed in much the same manner as is the hub portion 34 h of the mold assembly 30. Th,ls, the outer ring portion 36 includes a circular array of ring panel mold sections 76 (Fig.
This invention relates to a new and improved mold assembly and a method by which it is made and more specifically to a segmented ceramic mold assembly-which may be advantageously utilized in casting articles having portions o different thicknesses.
When an article having relatively thick and thin portions is to be cast, difficulty may be encountered due to solidification of the relatively thin portion of the article while the relatively thick portion of the article is still molten. This can result in the formation of defects in the thick portion of the article. These defects may be detrimental to the operating characteristics of the article and could result in premature failure of the article under load. For ;example, turbine engines frequently include a rotatable hub which is integrally cast with radially projecting vanes or airfoils. The hub is relatively thick while the vanes are relatively thin. When the hub and vanes are to be integrally cast, difficulties may be encountered due to solidification of the vanes ~hile the hub is still molten.
~ . . , :
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The present invention provides an improved method of making an improved mold assembly. The improved method could be utilized to make molds for shaping many different objects.
.
.
:~ ~.'3~6;~3 However, the method is advantageously utilized in making a mold assembly which is utilized in the casting of a one piece turbine engine component having portions of different thicknesses.
The mold assembly includes a plurality of interconnected sections.
The section of the mold assembly in which a relatively thin portion of an article is to be cast has a lower rate of heat removal than the section of the mold assembly in which a relatively thick portion of the article is to be cast. As is well known, the heat removal rate varies as a function of the thermal conductivity, specific head and density of the mold material.
According to one aspect of the invention there is provided a method of making a mold assembly having portions of different thicknesses, said method comprising the steps of providing a plurality of separate disposable patterns each of which has a surface area with a configuration similar to a portion of a surface area of a product, at least partially coating each of !
the disposable patterns with a wet covering of ceramic mold material, drying ~; the wet covering on the patterns, repeating the coating and drying steps with a first one of the plurality of patterns a first number of times to build up a relatively thick covering of ceramic mold ma~erial on the first pattern, repeating the coating and drying steps with a second one of the plurality of patterns a second number of times which is less than the first number of times to build up a relatively thin covering of ceramic mold material on the second pattern, separating the relatively thick covering of ceramic mold material from the first pattern to provide a relatively thick walled mold section, separating the relatively thin covering of ceramic mold material from the second pattern to provide a relatively thin walled mold section, and interconnecting the relatively thick and thin walled mold sections to at least partially form the mold assembly.
According to another aspect of the invention there is provided a method of making a mold assembly comprising the steps of providing a plurality of separate disposable patterns each of which has a surface area ,`?~ ~
~9633 with a configuration similar to a portion of a surface area of a cast product, at least partially coating each of the disposable patterns with a wet covering ceramic mold material, drying the wet coverings on the patterns, repeating the coating and drying steps until coverings of ceramic mold material of desired thicknesses have built up on the patterns, said step of coating t}ie patterns includes at least partially covering a first pattern with material having a first rate of heat removal, said step of coating the patterns further includes at least partially covering a second pattern with a material having a second rate of heat removal, the second rate of heat removal being greater than the first rate of heat removal, separating the covering from the first pattern to at least partially form a f~irst mold section, separating the covering from the second pattern to at least partially form a second moId section having a rate of heat removal which is greater than the rate of heat removal of the first mold section, and interconnecting the first and second mold sections to at least partially ~-~: form a mold assembly having portions with different rates of heat removal.
- BRIEF DESCRIPTION OF THE DRAWINGS
~ The foregoing and other features of the present invention will .i become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein: :
Figure 1 is an illustration of a cast turbojet engine fan frame;
-~ Figure 2 is an illustration of a mold assembly utilized to cast the jet engine fan frame of Figure 1 and constructed in accordance with the present invention;
Figure 3 is a radial sectional view further illustrating the :~ configuration of various sections of the mold assembly of Figure 2;
Figure 4 is a fragmentary upwardly facing view of a hub portion of the mold assembly of Figure 2 with some of the mold sections removed to further illustrate the segmented construction of the mold assembly;
Figure 5 is an illustration of a pattern utilized in forming hub 5' ~? , sections of the mold assembly of Figure 2;
Figure 6 is an illustration of a turbine engine component having a relatively thick hub section and relatively thin vane sections;
- 4a -Fig. 7 is a fragmentary sectional view of a portion of a ¦ mold assembly having thick and thin walled mold sections; and I Fig. 8 is a fragmentary sectional view of a portion of a ¦ mold assembly having sections with walls of different ¦ compositions.
.
DESCRIPTION OF SPECIFIC PREFERRED
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A fan frame or inlet duct 20 for a turbojet engine is illustrated in Fig. 1. The jet engine fan frame 20 has an annular central hub or wall 22 from which a plurality of struts or vanes 24 extend radially outwardly to a relatively large diameter annular outer ring or wall 26. When the fan frame 20 is installed in a turbojet engine, the inner wall or hub 22 supports one end of the compressor rotor. The struts or vanes 24 direct air flow back to the compressor through the space between the outer ring or wall 26 and hub. The hollow struts 24 are also utilized to enclose conduits and other parts (not shown) leading between the outside of the outer ring 26 and the interior of the hub 22.
Since the outer ring 26 of the jet engine fan frame 20 has a relatively large diameter, that is a diameter in excess of forty inches, and since relatively close dimensional tolerances are required to fabricate a fan frame which will function properly in a jet engine, relatively large fan frames have previously been fabricated by joining a large number of castings, sheet metal details and forgings to form a completed assembly. Although only jet engine fan frame 20 has been illustrated in Fig. 1, it should be understood that the .
1~3~633 present invention can advantageously be utilized in the ¦ -forming of other turbine engine components. Among these other turbine engine components are diffuser cases, nozzle rings, vane assemblies and bearing supports.
The jet engine fan frame 20 is cast in one piece in a segmented mold assembly 30 (see Fig. 2). The mold assembly 30 is constructed in the manner disclosed in United States Patent No. 4,066,116 and includes a plurality of sprue or pour cups 32 which are disposed within a hub portion 34 of the mold assembly. The hub portion 34 of the mold assembly 30 is connected with an annular outer ring portion 36 of the mold assembly by a plurality of radially extendlng strut portions 38 of the mold assembly.
As is perhaps best seen in Fig. 3, each of the pour cups 32 is connected in direct fluid communication with the hub portion 3~ ~f the mold assembly 30 by gating 42. The hub portion 34 of the mold assembly 30 is in turn connected in fluid communication with the outer ring 36 of the mold assembly through struts 38. Although the illustrated gating 42 onl~ connects the pour cup 32 with the hub portion 34 of the mold assembly 30, additional gating and/or pour cups could be provided in association with the outer ring portion 36 of the mold assembly if desired. Upon a pouring of molten metal into the pour cups 32 of the mold assembly 30, the metal flows into an annular hub mold cavity 46 (Fig. 3), the radially extending strut mold cavities 48 and into an annular outer ring mold cavity 50. This results in an integrally cast jet engine fan frame 20 having a one-piece construction.
The mold assemb]y 30 is formed of a plurality of mold sections which are interconnected to define the various mold cavities 46, 48 and 50. Although the ~et engine fan frame mold assembly 30 is relatively large, by forming the mold assembly 30 of a plurality of small mold sections, it is possible to accurately form each of the mold sections. These mold sections may then be placed in a jig or locating frame to accurately position them relative to each other and are cemented or otherwise interconnected to form a unitary assembly.
The various mold sections are constructed in such a manner that the surfaces which define the various mold cavities can be readily inspected prior to construction of the mold assembly 30. Of course, if any defects are noted during the inspection they are either repaired or a properly formed mold section is substituted for the defective mold section.
To this end, the hub portion 34 of the mold assembly 30 includes a circular array of hub panel mold sections 54 (see Fig. 4) having major side surfaces 56 with a configuration corresponding to the configuration of portions of an annular inner side surface 58 (see Fig. 1) of the jet engine fan frame hub 22. A second circular array of hub panel mold sections 58 are disposed radially outwardly of the hub mold panel sections 54 (see Fig. 4). The hub panel mold sections 58 have major inner side surfaces 60 of a configuration corresponding to the configuration of portions of the outside surface 64 (see Fig.
1) of the hub 22.
A plurality of top caps or end walls 68 extend between the coaxial circular arrays of hub panel mold sections 54 and 58 to close off the top of the hub mold cavity 46. Similarly, bottom caps or end walls 72 cooperate with the lower edge portions of the hub panel mold sections 54 and 58 to close off the bottom of the hub mold cavity 46 tsee Fig.s 3 and 4). The mold sections 54 and 58 may be assembled in an inverted position on a suitable jig or fixture so that the relatively large diameter portion of the hub is disposed downwardly.
The outer ring portion 36 of the mold assembly 30 is constructed in much the same manner as is the hub portion 34 h of the mold assembly 30. Th,ls, the outer ring portion 36 includes a circular array of ring panel mold sections 76 (Fig.
2) having inner surfaces of a configuration corresponding to ~;
the configuration of portions of an annular inner side surface -78 (Fig. 1) of the jet engine fan frame 20. A second circular array of ring panel mold sections 82 (Fig. 2) is disposed outwardly of and coaxial with the inner circular array of ring panel mold sections 76. The mold sections 82 have inner or mold surfaces which correspond to the configuration of portions of the annular outer surface 84 (Fig. 1) of the outer ring section 26 of the jet engine fan frame.
The upper and lower end portlons of the outer mold sections 76 and 87 are interconnected by end caps or pane]s 88 and 90 (Fig. 3). The end caps 88 and 90 cooperate with the outer ring panel mold sections 76 and 82 to close the outer ring mold cavity 50 in the same manner as previously described in connection with the hub mold end walls or caps 68 and 72.
The circular arrays of outer ring mold sections 76 and 82 circumscribe and are disposed in a coaxial relationship with the circular arrays of hub panel mold sections 54 and 58.
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l l Both the hub portion 34 and outer ring portion 36 of the mold assembly 30 are formed by separate mold sections so that the surfaces which are utilized to form the molten metal in either the annular hub mold cavity 46 or the annular outer ring mold cavity 50 are exposed to view so that they can be , inspected. Of course, defective mold sections would be either repaired or replaced. This results in high quality castings which need little or no repair. Since the jet engine fan frame 20 is integrally cast as one piece, the extensive welding and brazing steps currently used to make large jet engine fan frames are unnecessary.
The relatively large jet engine fan frame 20 is integrally formed of a one-piece construction by a precision investment casting or lost wax process. In this process the wax patterns having configurations corresponding to the ~ :
configurations of the various mold sections are dipped in a slurry of ceramic mold material. After the wax patterns have been repetitively dipped and dried to form a covering of a desired thickness over the wax pattern, the covering and pattern are heated to a temperature sufficient to melt the wax pattern so that the covering over the wax pattern is free of the pattern. The mold could be dewaxed by many other methods including using solvents or microwave energy. At least some of the wet slurry coatings are wiped away from portions of the wax pattern so that the various mold sections can be easily separated when the wax pattern is melted. These mold sections are then assembled in a suitable jig to form the mold assembly 30 0 ~ig. 2.
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, A wax pattern (not shown) is utilized in forming of the strut mold sections in the manner disclosed in United States Patent No. 4,066,116. A wax pattern 174 (Fig 5) is utilized to form the hub panel mold sections 54 and 58 (Fig. 3) and the grating 42. Wax patterns of a configuration similar to the wax pattern 174 (Fig. 5) but without the grating, are utilized in the forming of the outer ring panel mold sections 76 and 82. It should be understood that the disposable patterns could be formed of a material other than wax, for example, a plastic pattern material such as polystyrene could be utilized, if desired.
To form the hub panel mold sections 54 and 58, the wax pattern 174 is repetitively dipped in a liquid slurry of ceramic mold material. Although many different types of slurry could be utilized, one illustrative slurry contains fused silica, zircon, or other refractory materials in combination with binders. Chemical binders such as ethyl silicate, sodium silicate and colloidal silica can be utilized. In addition, the slurry may contain suitable film formers such as alginates to control viscosity and wetting agents to control flow characteristics and pattern wetability. ~
In accordance with common practices, the initial slurry ;
coating applied to the pattern contains a very finely divided refractory material to produce an accurate surface finish. A
typical slurry for a first coat may contain approximately 29 percent colloidal silica suspension in the form of a 20 to 30 percent concentrate. Fused si]ica of a particle size of 325 me6h o small6r in an amount of 71 percent can be employe2, ---'~
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together with less than one-tenth percent by weight of a wetting agent. Generally, the specific gravity of the slurry of ceramic mold material may be on the order of 1.75 to 1.80 and have a viscosity of 40 to 60 seconds when measured with a Number 5 Zahn cup at 75 to 85F. After the application of the initial coating, the surface is stuccoed with refractory materials having particle sizes on the order of 60 to 200 mesh.
In accordance with well known procedures, each dip coating is dried before subsequent dipping. The pattern is repetitively dipped and dried enough times to build up a covering of ceramic mold material of a desired thickness. In one specific case the pattern was dipped fifteen times to build up a covering of a thickness of approximately 0.400 inches in order to prevent mold bulge. After the dewaxing, mold sections are fired at approximately 1900F. for one hour to thoroughly cure the mold sections.
To provide the de-sired mold section configuration~ the wax pattern 174 (see Fig. 5) includes a main wall or panel section 176 having an arcuate configuration with an annular extent of sixty degrees. The main wall section 176 includes a radially inner major side surface 178 having a configuration corresponding to the configuration of the radially inner surface 58 (Fig. 1) of the air frame hub 22. A radially outer major side surface 180 of the wall panel 176 has a configuration corresponding to the configuration of the outer surface 64 of the air frame hub 22. It should be noted that a projection 184 is provided on the inner side of the wall 176 to form an opening to an associated strut section. Similarly, a projection (not shown) is formed on the opposite side of the .
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wall 176 to form a root or base to which to connect the strut mold sections.
Since each of the hub panel mold sections 54 and 58 are connected with adjacent mold sections at flange joints, pattern flange panels 188 and 190 (Fig. 10) are provided at opposite ends of the main wall 176. The pattern flange panels have inwardly facing side surface areas 192 and 194 which will accurately form the flat flange surfaces of the hub panel mold sections 54. Similarly, the flange panels 188 and 190 each have a pair of facing side surface areas 198 (only one of which is shown in Fig. 5) which accurately form the flat flange surfaces on the outer hub panel mold section 58. The , flange panel 188 has a flat rectangular major outer side , surface 202 which is connected with the major side surface areas 192 and 198 by a plurality of longitudinally extending edge or minor side surfaces 204, 206, 208 and 210. Although the configuration of only the flange panel 188 is fully ~ -illustrated in Fig. 5, it should be understood that the flange panel 190 is of the same configuration. It should be noted that the major side surface 202 and the minor side surfaces 204, 206, 208 and 210 of the pattern flange panel 188 do not correspnd to any surfaces on the hub panel mold sections 54 and 58.
Since the major outer side surfaces 202 of the pattern ;~-, flange patterns 188 and 190 do not correspond to portions of the hub mold sections, the ceramic coating on these outer side panels must be separated from the,ceramic coatings on the wall surfa :s 178 and 180 and ~he inner side surface areas 192, 194 '' .
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and 197 of the flange panels. In addition, the ceramic mold material which was disposed over the inner major side surface 178 of the pattern wall 176 must be separated from the ceramic mold material which was disposed over the outer major side surface 180 of the mold wall 176.
The separating of the hardened ceramic mold material overlying the major outer side surfaces 202 of the pattern flange panels 188 and 190 from the hardened ceramic mold material overlying the major side surfaces 178 and 180 of the ,.
panel wall 176 is greatly facilitated by wiping away the wet ¦i dip coating on the minor side surfaces of the flange panels ll immediately after the pattern is dipped in the slurry of ¦¦ ceramic mold material. Similarly, the separating of the hardened ceramic mold material overlying the inner and outer major side surfaces 178 and 180 of the panel wall 176 is l~ facilitated by wiping away the wet coating of ceramic mold ¦I material from upper and lower minor edge wall areas 214 and ¦l 126 extending between the upper and lower edges of the major ¦¦ side surfaces 178 and 180 of the wall panel 176.
¦ The manner in which the wiping away of the wet coating of ¦ ceramic mold material overlying the various minor side or edge surfaces of the pattern 174 is performed is fully disclosed in I United States Patent No. 4,066,116. After the pattern 174 has ¦ been dipped in a liquid slurry of ceramic mold material, the pattern is manually supported above the liquid slurry tank by a support frame. A metal blade is utilized to wipe away the I! slurry coating overlying the edge surface 120 of the pattern flange panel 188. Of course, the other minor surfaces 204, 206 an9 ~08 of the pattern Flange panel 188 are also wiped '' ~` 1 13 with the blade to remove the wet coating of ceramic mold material overl~;ng the suxfaces. This separates the portion of the wet coating of ceramic mold ~aterial overlying the flange side surface 202 from the wet coating of ceramic mold material overlying the remainder of the pattern 174. The wet coating of ceramic material is then wiped from the minor sides of the pattern flange panel 190. This separates the portion of the coating of wet ceramic mold material overlying the major side surface of the flange 190 from the wet coating of ceramic mold material overlying the rest of the pattern 174.
The portions of the coating of wet ceramic mold material overlyinq the major side surfaces 178 and 190 are separated from each other. To this end, the wet coating of ceramic mold material overlying the minor side edge surface 126 is wiped away. Finally, the top edge surface 124 of the pattern 173 is wiped with;the blade 218 to complete the removal of the wet coating of ceramic mold material from the connect;ng surfaces of the pattern 174.
It should be noted that the foregoing wiping steps separated the wet coating of mold ceramic material overlying the pattern 174 into a plurality of discrete segments each of whcih is separated from an adjacent segment by a wiped area.
In the illustrated embodiment of the invention two of the segments of wet dip coating correspond to two mold sections.
Thus, the segment of wet dip coating overlying the inner major side surface 178 of the pattern corresponds to a hub mold section 54 and the segment of the wet dip coating overlying the ma or outer side sur~ac~ lBO of the pattern wall 176 ~: I' ~ 14 6~3 corresponds to the hub mold section 58. The segments of wet dip coating overlying the major outer side surfaces of the pattern flange panels 188 and 190 do not correspond to any of the mold sections.
As the pattern 374 is repetitively dipped, each wet coating is wiped in the manner previously explained and then dried. This results in the formation of a multi-layered covering of ceramic mold material on the pattern. This covering of ceramic mold material is sharply discontinuous at the areas overlying the wiped surfaces of the pattern. Thus the wiped minor flange surface 204 of the pattern flangè panel 188, a covering 218 of ceramic mold material overlying the flange panel side surface 202 is separated from a covering 220 overlying the inner side surface 198 of the inner flange panel 1ange 188 and the major side surface 178 of the pattern wall 176. When ;the wax pattern is disposed of by melting, the dried covering 128 of ceramic mold material overlying the pattern flange panel surface 202 is separated from the dried covering 220 of ceramic mold material overlying the pattern flange panel surface 198 and side wall surface 178.
Similarly, a covering 224 of dried ceramic mold material overlying the pattern flange surface lg8 and the outer pattern wall surface 180 is separated from the covering 128 overlying the major outer surface 202 of the pattern flange panel. r :' l 1 A turbine engine component 280 having a relatively thick . ~ hub po ion 282 from which relatively thin vanes or airfoils ~', ~ ~ I
~s6~3 284 extend radially is illustrated in Fig. 6. The hub 282 and vanes 284 are integrally cast as one piece. During the casting process, the relatively thin vanes 284 tend to solidify before the relativeIy thick hub 282 solidifies. If the hub 282 is allowed to remain molten after the vanes have solidified, defects may be formed in the hub. Of course, any defects which are formed in the hub 282 are detrimental to its strength. Although many different types of defects could develop with different metals, microporosity and inclusions are the most common defects to be eliminated. In addition, controlling the heat removal rate enables grain structure and size to be controlled.
Although the turbine engine component 280 has been illustrated in Fig. 6 as having vanes 284 which are not -associated with an outer ring or shroud similar to the outer ring 26 of the turbine engine component 20 of Fig. 1, it is contemplated that such an outer ring could be associated with the turbine engine component 280. If this were done, the ~ , outer ring could solidify after the vanes 284 solidify and before the hub 282 solidifies with the formation of defects in both the hub and outer ring.
In accordance with a feature of the present invention, the turbine engine component 280 is cast in a mold assembly 288, a portion of which is shown in Fig. 7. The mold assembly 288 is formed of a plurality sections which are interconnected to define relatively small cavities in which the vanes 284 are cast and a relatively large cavity in which the hub 282 is cast. The various sections are interconnected in the same manner as previously explained in connection with the mold assembly 30.
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, ¦ The mold assembly 288 includes sections having different l heat removal rates. Thus, a mold section 290 in which a vane or airfoil 284 is cast has a relatively low rate of heat il removal whlle a mold section 294 in which the hub 282 is cast ¦I has a high rate of heat removal~ The different rates of heat li removal result in a promoting of solidification of the ¦¦ relatively thick hub 282 and retarding of solidification of the relatively thin vanes 284. This tends to minimize any tendency for defects to form in the hub as it solidifies.
It is contemplated that the different heat removal rates -for the mold sections 290 and 294 could be obtained in several different ways. In the embodiment of the invention illustrated in Fig. 7, the vane mold section 290 has a relatively thick wall to retard removal of heat from the relatively thin vanes or airfoils 284. The hub mold sectio-n ~;i' 294 has a-relatively thin wall to enable heat to be readily ¦ removaved from the relatively thick hub 282.
¦ The different mold wall thicknesses are obtained by ¦ dipping the associated patterns a different number of times in ¦ a slurry of liquid ceramic mold material. Thus, a wax or plastic pattern having a conflguration corresponding the shape of a single vane 284 is dipped in a liquid ceramic mold material a relatively large number of times, for example twelve times, to form a relatively thick build-up of ceramic mold material over the pattern. Each time the vane pattern is dipped, it is wiped in the manner previously explained to remove the wet ceramic mold material from an area where a -joint is to be formed between the mold sections 290 and 294.
The relatively thick wall of the vane mold section 290 has a relatively low rate of heat removal and tends to maintain the vane molten while the hub is solidifying.
" ._ ~ 9633 , To promote the solidification of the hub, the mold section 294 has a relatively thin wall. The relatively thin wa]led mold section 294 was obtained by dipping a hub pattern a relatively small number of times in liquid ceramic mold material. For example, the hub pattern associated with the mold section 294 was dipped only six times to provide a relatively thin build-up of ceramic mold material. The thin walled hub mold section 294 and a plurality of thick walled vane mold sections 290 are interconnected in the manner -previously explained to form a mold assembly in which the turbine engine component 280 is cast.
The thin walled hub mold section is not as effective to insulate the hub as the relatively thick walled vane mold sections 290. Therefore, the heat transfer rate from the hub is greater than the heat transfer rate from the vanes to promote solidification of the hub contemporaneously with solidification of the vanes. The transfer of heat from the hub can be further promoted by investing the mold 288 in a container with steel shot adjacent to the hub mold section 294 to provide a heat sink.
It is also contemplated that the mold sections could be provided with different heat removal rates by forming the mold sections of different materials. Thus, the pattern for a vane mold section 298 (Fig. 8) is dipped in a slurry of colloidal silica in which Zircon is suspended. The resulting wet covering of ceramic mold material is coated with a stuccoing of fused silica having a particle size on the order of 60 to 20 mesh This wet coating is then dried. After repetitive dipping, stuccoing and drying, the resulting covering is 63~ , separated from the pattern to form a ceramic mold section in the manner previously explained.
A hub mold section 304 is formed by dipping a pattern having a configuration corresponding the configuration of the !i hub 282 in a slurry o~ colloidal si]ica having the same ¦, composition as the slurry in which the vane pattern was ¦1 dipped. However, the wet covering of ceramic mold material on ; I the hub pattern is stuccoed with zircon. The wet covering of I silica stuccoed with zircon is then dried. After repetitive ¦ dipping, stuccoing and drying, the resulting covering is ~
¦ separated from the pattern. Due to the zircon stuccoing, the resulting hub mold section has a heat removal rate which is I greater than the heat removal rate of the vane mold section 298 formed by coating a wet slurry covering of silica with a stuccoing of fused silica. Of course, other stuccoing materials having a rela,ively high heat removal rate could be utilized if desired.
~1 The two mold sections 298 and 304 are interconnected at joints in the matter previously explained in connection with the mold assembly 30. This results in a mold assembly 306 having a hub mold section 304 with a relatively high heat removal rate and a vane mold section 298 with a relatively low heat removal rate. Although the mold sections 298 and 304 have the same thickness, it is contemplated that they could be formed with different thicknesses by coating the associated ¦ patterns different numbers of times with ceramic slurry and stucco.
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It is contemplated that it may be desirable under certain circumstances to form both of the mold sections of completely different materials. This could be done by repetitively dipping the hub pattern in a s]urry of ceramic mold material having a high heat removal rate. The vane pattern would be repetitively dipped in a slurry of a different ceramic mold material having a low heat removal rate. For example, a pattern associated with a thick portion of an article could be dipped in a slurry having a zircon filler while the other pattern is dipped in a slurry having a fused silica filler.
Another way of controlling the heat removal rate of the ;-mold sections is to form the mold sections with different ~
porosities. The vane mold section wou3d be made relatively ~r porous to retard heat removal~ The hub mold section would be relatively dense to promote heat removal.
In vi~W of the foregoing, it is apparent that the present invention provides an improved method of making a mold assembly having portions with different heat removal rates.
The mold assembly includes a plurality of interconnected sections. The sections of the mold assembly in which relatively thin portions of the article are to be cast-have a.
lower rate of heat removal than the sections of the mold assembly in which relatively thick portions of the articles are to be cast. Of course if desired, the mold could be constructed to have a high heat removal rate from the thin portion of the casting and a low heat removal rate from the thick portion of the casting.
In one embodiment of the invention the different heat removal rates are obtained by forming the mold assembly 288 .
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with walls of different thicknesses. A relatively thin walled section 294 is utilized to define a mold in which the thick hub portion of the article is cast. Thick walled mold sections 290 are utilized to define the mold cavities in which the thin vane portions of the article are cast. In another embodiment of the invention the composition of the mold sections are different to provide different heat removal rates. The mold wall section 304 associated with the relatively thick hub portion of a casting is formed of a substance having a relatively high heat removal rate to promote solidification of the hub portion of the casting. The vane mold sections 298 are formea of a material having a relatively low heat removal rate to retard solidification of the vanes. .
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the configuration of portions of an annular inner side surface -78 (Fig. 1) of the jet engine fan frame 20. A second circular array of ring panel mold sections 82 (Fig. 2) is disposed outwardly of and coaxial with the inner circular array of ring panel mold sections 76. The mold sections 82 have inner or mold surfaces which correspond to the configuration of portions of the annular outer surface 84 (Fig. 1) of the outer ring section 26 of the jet engine fan frame.
The upper and lower end portlons of the outer mold sections 76 and 87 are interconnected by end caps or pane]s 88 and 90 (Fig. 3). The end caps 88 and 90 cooperate with the outer ring panel mold sections 76 and 82 to close the outer ring mold cavity 50 in the same manner as previously described in connection with the hub mold end walls or caps 68 and 72.
The circular arrays of outer ring mold sections 76 and 82 circumscribe and are disposed in a coaxial relationship with the circular arrays of hub panel mold sections 54 and 58.
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l l Both the hub portion 34 and outer ring portion 36 of the mold assembly 30 are formed by separate mold sections so that the surfaces which are utilized to form the molten metal in either the annular hub mold cavity 46 or the annular outer ring mold cavity 50 are exposed to view so that they can be , inspected. Of course, defective mold sections would be either repaired or replaced. This results in high quality castings which need little or no repair. Since the jet engine fan frame 20 is integrally cast as one piece, the extensive welding and brazing steps currently used to make large jet engine fan frames are unnecessary.
The relatively large jet engine fan frame 20 is integrally formed of a one-piece construction by a precision investment casting or lost wax process. In this process the wax patterns having configurations corresponding to the ~ :
configurations of the various mold sections are dipped in a slurry of ceramic mold material. After the wax patterns have been repetitively dipped and dried to form a covering of a desired thickness over the wax pattern, the covering and pattern are heated to a temperature sufficient to melt the wax pattern so that the covering over the wax pattern is free of the pattern. The mold could be dewaxed by many other methods including using solvents or microwave energy. At least some of the wet slurry coatings are wiped away from portions of the wax pattern so that the various mold sections can be easily separated when the wax pattern is melted. These mold sections are then assembled in a suitable jig to form the mold assembly 30 0 ~ig. 2.
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, A wax pattern (not shown) is utilized in forming of the strut mold sections in the manner disclosed in United States Patent No. 4,066,116. A wax pattern 174 (Fig 5) is utilized to form the hub panel mold sections 54 and 58 (Fig. 3) and the grating 42. Wax patterns of a configuration similar to the wax pattern 174 (Fig. 5) but without the grating, are utilized in the forming of the outer ring panel mold sections 76 and 82. It should be understood that the disposable patterns could be formed of a material other than wax, for example, a plastic pattern material such as polystyrene could be utilized, if desired.
To form the hub panel mold sections 54 and 58, the wax pattern 174 is repetitively dipped in a liquid slurry of ceramic mold material. Although many different types of slurry could be utilized, one illustrative slurry contains fused silica, zircon, or other refractory materials in combination with binders. Chemical binders such as ethyl silicate, sodium silicate and colloidal silica can be utilized. In addition, the slurry may contain suitable film formers such as alginates to control viscosity and wetting agents to control flow characteristics and pattern wetability. ~
In accordance with common practices, the initial slurry ;
coating applied to the pattern contains a very finely divided refractory material to produce an accurate surface finish. A
typical slurry for a first coat may contain approximately 29 percent colloidal silica suspension in the form of a 20 to 30 percent concentrate. Fused si]ica of a particle size of 325 me6h o small6r in an amount of 71 percent can be employe2, ---'~
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together with less than one-tenth percent by weight of a wetting agent. Generally, the specific gravity of the slurry of ceramic mold material may be on the order of 1.75 to 1.80 and have a viscosity of 40 to 60 seconds when measured with a Number 5 Zahn cup at 75 to 85F. After the application of the initial coating, the surface is stuccoed with refractory materials having particle sizes on the order of 60 to 200 mesh.
In accordance with well known procedures, each dip coating is dried before subsequent dipping. The pattern is repetitively dipped and dried enough times to build up a covering of ceramic mold material of a desired thickness. In one specific case the pattern was dipped fifteen times to build up a covering of a thickness of approximately 0.400 inches in order to prevent mold bulge. After the dewaxing, mold sections are fired at approximately 1900F. for one hour to thoroughly cure the mold sections.
To provide the de-sired mold section configuration~ the wax pattern 174 (see Fig. 5) includes a main wall or panel section 176 having an arcuate configuration with an annular extent of sixty degrees. The main wall section 176 includes a radially inner major side surface 178 having a configuration corresponding to the configuration of the radially inner surface 58 (Fig. 1) of the air frame hub 22. A radially outer major side surface 180 of the wall panel 176 has a configuration corresponding to the configuration of the outer surface 64 of the air frame hub 22. It should be noted that a projection 184 is provided on the inner side of the wall 176 to form an opening to an associated strut section. Similarly, a projection (not shown) is formed on the opposite side of the .
~ 11 ~' .
wall 176 to form a root or base to which to connect the strut mold sections.
Since each of the hub panel mold sections 54 and 58 are connected with adjacent mold sections at flange joints, pattern flange panels 188 and 190 (Fig. 10) are provided at opposite ends of the main wall 176. The pattern flange panels have inwardly facing side surface areas 192 and 194 which will accurately form the flat flange surfaces of the hub panel mold sections 54. Similarly, the flange panels 188 and 190 each have a pair of facing side surface areas 198 (only one of which is shown in Fig. 5) which accurately form the flat flange surfaces on the outer hub panel mold section 58. The , flange panel 188 has a flat rectangular major outer side , surface 202 which is connected with the major side surface areas 192 and 198 by a plurality of longitudinally extending edge or minor side surfaces 204, 206, 208 and 210. Although the configuration of only the flange panel 188 is fully ~ -illustrated in Fig. 5, it should be understood that the flange panel 190 is of the same configuration. It should be noted that the major side surface 202 and the minor side surfaces 204, 206, 208 and 210 of the pattern flange panel 188 do not correspnd to any surfaces on the hub panel mold sections 54 and 58.
Since the major outer side surfaces 202 of the pattern ;~-, flange patterns 188 and 190 do not correspond to portions of the hub mold sections, the ceramic coating on these outer side panels must be separated from the,ceramic coatings on the wall surfa :s 178 and 180 and ~he inner side surface areas 192, 194 '' .
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and 197 of the flange panels. In addition, the ceramic mold material which was disposed over the inner major side surface 178 of the pattern wall 176 must be separated from the ceramic mold material which was disposed over the outer major side surface 180 of the mold wall 176.
The separating of the hardened ceramic mold material overlying the major outer side surfaces 202 of the pattern flange panels 188 and 190 from the hardened ceramic mold material overlying the major side surfaces 178 and 180 of the ,.
panel wall 176 is greatly facilitated by wiping away the wet ¦i dip coating on the minor side surfaces of the flange panels ll immediately after the pattern is dipped in the slurry of ¦¦ ceramic mold material. Similarly, the separating of the hardened ceramic mold material overlying the inner and outer major side surfaces 178 and 180 of the panel wall 176 is l~ facilitated by wiping away the wet coating of ceramic mold ¦I material from upper and lower minor edge wall areas 214 and ¦l 126 extending between the upper and lower edges of the major ¦¦ side surfaces 178 and 180 of the wall panel 176.
¦ The manner in which the wiping away of the wet coating of ¦ ceramic mold material overlying the various minor side or edge surfaces of the pattern 174 is performed is fully disclosed in I United States Patent No. 4,066,116. After the pattern 174 has ¦ been dipped in a liquid slurry of ceramic mold material, the pattern is manually supported above the liquid slurry tank by a support frame. A metal blade is utilized to wipe away the I! slurry coating overlying the edge surface 120 of the pattern flange panel 188. Of course, the other minor surfaces 204, 206 an9 ~08 of the pattern Flange panel 188 are also wiped '' ~` 1 13 with the blade to remove the wet coating of ceramic mold material overl~;ng the suxfaces. This separates the portion of the wet coating of ceramic mold ~aterial overlying the flange side surface 202 from the wet coating of ceramic mold material overlying the remainder of the pattern 174. The wet coating of ceramic material is then wiped from the minor sides of the pattern flange panel 190. This separates the portion of the coating of wet ceramic mold material overlying the major side surface of the flange 190 from the wet coating of ceramic mold material overlying the rest of the pattern 174.
The portions of the coating of wet ceramic mold material overlyinq the major side surfaces 178 and 190 are separated from each other. To this end, the wet coating of ceramic mold material overlying the minor side edge surface 126 is wiped away. Finally, the top edge surface 124 of the pattern 173 is wiped with;the blade 218 to complete the removal of the wet coating of ceramic mold material from the connect;ng surfaces of the pattern 174.
It should be noted that the foregoing wiping steps separated the wet coating of mold ceramic material overlying the pattern 174 into a plurality of discrete segments each of whcih is separated from an adjacent segment by a wiped area.
In the illustrated embodiment of the invention two of the segments of wet dip coating correspond to two mold sections.
Thus, the segment of wet dip coating overlying the inner major side surface 178 of the pattern corresponds to a hub mold section 54 and the segment of the wet dip coating overlying the ma or outer side sur~ac~ lBO of the pattern wall 176 ~: I' ~ 14 6~3 corresponds to the hub mold section 58. The segments of wet dip coating overlying the major outer side surfaces of the pattern flange panels 188 and 190 do not correspond to any of the mold sections.
As the pattern 374 is repetitively dipped, each wet coating is wiped in the manner previously explained and then dried. This results in the formation of a multi-layered covering of ceramic mold material on the pattern. This covering of ceramic mold material is sharply discontinuous at the areas overlying the wiped surfaces of the pattern. Thus the wiped minor flange surface 204 of the pattern flangè panel 188, a covering 218 of ceramic mold material overlying the flange panel side surface 202 is separated from a covering 220 overlying the inner side surface 198 of the inner flange panel 1ange 188 and the major side surface 178 of the pattern wall 176. When ;the wax pattern is disposed of by melting, the dried covering 128 of ceramic mold material overlying the pattern flange panel surface 202 is separated from the dried covering 220 of ceramic mold material overlying the pattern flange panel surface 198 and side wall surface 178.
Similarly, a covering 224 of dried ceramic mold material overlying the pattern flange surface lg8 and the outer pattern wall surface 180 is separated from the covering 128 overlying the major outer surface 202 of the pattern flange panel. r :' l 1 A turbine engine component 280 having a relatively thick . ~ hub po ion 282 from which relatively thin vanes or airfoils ~', ~ ~ I
~s6~3 284 extend radially is illustrated in Fig. 6. The hub 282 and vanes 284 are integrally cast as one piece. During the casting process, the relatively thin vanes 284 tend to solidify before the relativeIy thick hub 282 solidifies. If the hub 282 is allowed to remain molten after the vanes have solidified, defects may be formed in the hub. Of course, any defects which are formed in the hub 282 are detrimental to its strength. Although many different types of defects could develop with different metals, microporosity and inclusions are the most common defects to be eliminated. In addition, controlling the heat removal rate enables grain structure and size to be controlled.
Although the turbine engine component 280 has been illustrated in Fig. 6 as having vanes 284 which are not -associated with an outer ring or shroud similar to the outer ring 26 of the turbine engine component 20 of Fig. 1, it is contemplated that such an outer ring could be associated with the turbine engine component 280. If this were done, the ~ , outer ring could solidify after the vanes 284 solidify and before the hub 282 solidifies with the formation of defects in both the hub and outer ring.
In accordance with a feature of the present invention, the turbine engine component 280 is cast in a mold assembly 288, a portion of which is shown in Fig. 7. The mold assembly 288 is formed of a plurality sections which are interconnected to define relatively small cavities in which the vanes 284 are cast and a relatively large cavity in which the hub 282 is cast. The various sections are interconnected in the same manner as previously explained in connection with the mold assembly 30.
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, ¦ The mold assembly 288 includes sections having different l heat removal rates. Thus, a mold section 290 in which a vane or airfoil 284 is cast has a relatively low rate of heat il removal whlle a mold section 294 in which the hub 282 is cast ¦I has a high rate of heat removal~ The different rates of heat li removal result in a promoting of solidification of the ¦¦ relatively thick hub 282 and retarding of solidification of the relatively thin vanes 284. This tends to minimize any tendency for defects to form in the hub as it solidifies.
It is contemplated that the different heat removal rates -for the mold sections 290 and 294 could be obtained in several different ways. In the embodiment of the invention illustrated in Fig. 7, the vane mold section 290 has a relatively thick wall to retard removal of heat from the relatively thin vanes or airfoils 284. The hub mold sectio-n ~;i' 294 has a-relatively thin wall to enable heat to be readily ¦ removaved from the relatively thick hub 282.
¦ The different mold wall thicknesses are obtained by ¦ dipping the associated patterns a different number of times in ¦ a slurry of liquid ceramic mold material. Thus, a wax or plastic pattern having a conflguration corresponding the shape of a single vane 284 is dipped in a liquid ceramic mold material a relatively large number of times, for example twelve times, to form a relatively thick build-up of ceramic mold material over the pattern. Each time the vane pattern is dipped, it is wiped in the manner previously explained to remove the wet ceramic mold material from an area where a -joint is to be formed between the mold sections 290 and 294.
The relatively thick wall of the vane mold section 290 has a relatively low rate of heat removal and tends to maintain the vane molten while the hub is solidifying.
" ._ ~ 9633 , To promote the solidification of the hub, the mold section 294 has a relatively thin wall. The relatively thin wa]led mold section 294 was obtained by dipping a hub pattern a relatively small number of times in liquid ceramic mold material. For example, the hub pattern associated with the mold section 294 was dipped only six times to provide a relatively thin build-up of ceramic mold material. The thin walled hub mold section 294 and a plurality of thick walled vane mold sections 290 are interconnected in the manner -previously explained to form a mold assembly in which the turbine engine component 280 is cast.
The thin walled hub mold section is not as effective to insulate the hub as the relatively thick walled vane mold sections 290. Therefore, the heat transfer rate from the hub is greater than the heat transfer rate from the vanes to promote solidification of the hub contemporaneously with solidification of the vanes. The transfer of heat from the hub can be further promoted by investing the mold 288 in a container with steel shot adjacent to the hub mold section 294 to provide a heat sink.
It is also contemplated that the mold sections could be provided with different heat removal rates by forming the mold sections of different materials. Thus, the pattern for a vane mold section 298 (Fig. 8) is dipped in a slurry of colloidal silica in which Zircon is suspended. The resulting wet covering of ceramic mold material is coated with a stuccoing of fused silica having a particle size on the order of 60 to 20 mesh This wet coating is then dried. After repetitive dipping, stuccoing and drying, the resulting covering is 63~ , separated from the pattern to form a ceramic mold section in the manner previously explained.
A hub mold section 304 is formed by dipping a pattern having a configuration corresponding the configuration of the !i hub 282 in a slurry o~ colloidal si]ica having the same ¦, composition as the slurry in which the vane pattern was ¦1 dipped. However, the wet covering of ceramic mold material on ; I the hub pattern is stuccoed with zircon. The wet covering of I silica stuccoed with zircon is then dried. After repetitive ¦ dipping, stuccoing and drying, the resulting covering is ~
¦ separated from the pattern. Due to the zircon stuccoing, the resulting hub mold section has a heat removal rate which is I greater than the heat removal rate of the vane mold section 298 formed by coating a wet slurry covering of silica with a stuccoing of fused silica. Of course, other stuccoing materials having a rela,ively high heat removal rate could be utilized if desired.
~1 The two mold sections 298 and 304 are interconnected at joints in the matter previously explained in connection with the mold assembly 30. This results in a mold assembly 306 having a hub mold section 304 with a relatively high heat removal rate and a vane mold section 298 with a relatively low heat removal rate. Although the mold sections 298 and 304 have the same thickness, it is contemplated that they could be formed with different thicknesses by coating the associated ¦ patterns different numbers of times with ceramic slurry and stucco.
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It is contemplated that it may be desirable under certain circumstances to form both of the mold sections of completely different materials. This could be done by repetitively dipping the hub pattern in a s]urry of ceramic mold material having a high heat removal rate. The vane pattern would be repetitively dipped in a slurry of a different ceramic mold material having a low heat removal rate. For example, a pattern associated with a thick portion of an article could be dipped in a slurry having a zircon filler while the other pattern is dipped in a slurry having a fused silica filler.
Another way of controlling the heat removal rate of the ;-mold sections is to form the mold sections with different ~
porosities. The vane mold section wou3d be made relatively ~r porous to retard heat removal~ The hub mold section would be relatively dense to promote heat removal.
In vi~W of the foregoing, it is apparent that the present invention provides an improved method of making a mold assembly having portions with different heat removal rates.
The mold assembly includes a plurality of interconnected sections. The sections of the mold assembly in which relatively thin portions of the article are to be cast-have a.
lower rate of heat removal than the sections of the mold assembly in which relatively thick portions of the articles are to be cast. Of course if desired, the mold could be constructed to have a high heat removal rate from the thin portion of the casting and a low heat removal rate from the thick portion of the casting.
In one embodiment of the invention the different heat removal rates are obtained by forming the mold assembly 288 .
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with walls of different thicknesses. A relatively thin walled section 294 is utilized to define a mold in which the thick hub portion of the article is cast. Thick walled mold sections 290 are utilized to define the mold cavities in which the thin vane portions of the article are cast. In another embodiment of the invention the composition of the mold sections are different to provide different heat removal rates. The mold wall section 304 associated with the relatively thick hub portion of a casting is formed of a substance having a relatively high heat removal rate to promote solidification of the hub portion of the casting. The vane mold sections 298 are formea of a material having a relatively low heat removal rate to retard solidification of the vanes. .
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Claims (8)
1. A method of making a mold assembly having portions of different thicknesses, said method comprising the steps of providing a plurality of separate disposable patterns each of which has a surface area with a configuration similar to a portion of a surface area of a product, at least partially coating each of the disposable patterns with a wet covering of ceramic mold material, drying the wet covering on the patterns, repeating the coating and drying steps with a first one of the plurality of patterns a first number of times to build up a relatively thick covering of ceramic mold material on the first pattern, repeating the coating and drying steps with a second one of the plurality of patterns a second number of times which is less than the first number of times to build up a relatively thin covering of ceramic mold material on the second pattern, separating the relatively thick covering of ceramic mold material from the first pattern to provide a relatively thick walled mold section, separating the relatively thin covering of ceramic mold material from the second pattern to provide a relatively thin walled mold section, and interconnecting the relatively thick and thin walled mold sections to at least partially form the mold assembly.
2. A method as set forth in claim 1 wherein said steps of coating the first one of the plurality of patterns includes the step of dipping the first pattern in a body of liquid ceramic mold material having a first composition, said steps of coating the second one of the plurality of patterns including the step of dipping the second pattern in a body of liquid ceramic mold material having a second composition which is different than said first composition.
3. A method as set forth in claim 1 wherein said steps of coating the first pattern includes covering at least a portion of the first pattern with a ceramic mold material having a first rate of heat removal when the mold material has dried, said steps of coating the second pattern includes covering at least a portion of the second pattern with a ceramic mold material having a second rate of heat removal when the mold material has dried, the second rate of heat removal being greater than the first rate of heat removal to promote a removal of heat through the thin walled mold section.
4. A method as set forth in claim 1 wherein said steps of coating the first pattern includes dipping the first pattern in a body of liquid ceramic mold material to form a wet coating on the first pattern and stuccoing the wet coating with a first material, said steps of coating the second pattern including dipping the second pattern in a body of liquid ceramic mold material to form a wet coating on the second pattern and stuccoing the wet coating with a second material which is different than the first material to effect the formation of coverings having different characteristics over the first and second patterns.
5. A method of making a mold assembly comprising the steps of providing a plurality of separate disposable patterns each of which has a surface area with a configuration similar to a portion of a surface area of a cast product, at least partially coating each of the disposable patterns with a wet covering ceramic mold material, drying the wet coverings on the patterns, repeating the coating and drying steps until coverings of ceramic mold material of desired thicknesses have built up on the patterns, said step of coating the patterns includes at least partially covering a first pattern with material having a first rate of heat removal, said step of coating the patterns further includes at least partially covering a second pattern with a material having a second rate of heat removal, the second rate of heat removal being greater than the first rate of heat removal, separating the covering from the first pattern to at least partially form a first mold section, separating the covering from the second pattern to at least partially form a second mold section having a rate of heat removal which is greater than the rate of heat removal of the first mold section, and interconnecting the first and second mold sections to at least partially form a mold assembly having portions with different rates of heat removal.
6. A method as set forth in claim 5 wherein said steps of coating the first and second patterns includes repeating the coating and drying steps with one of the patterns a first number of times to build up a relatively thick covering of ceramic mold material on the one pattern and repeating the coating and drying steps with the other pattern a second number of times which is less than the first number of times to build up a relatively thin covering of ceramic mold material on the other pattern, said steps of separating the coverings. of ceramic mold material from the first and second.
patterns at least partially resulting in the forming of relatively thick and thin walled mold sections.
patterns at least partially resulting in the forming of relatively thick and thin walled mold sections.
7. A method as set forth in claim 5 wherein said step of coating the first pattern includes the step of dipping the first pattern in a body of liquid ceramic mold material having a first composition, said step of coating the second pattern includes the step of dipping the second pattern in a body of liquid ceramic mold material having a second composition.
8. A method as set forth in claim 5 wherein said steps of coating the first pattern includes the step of stuccoing a wet coating of ceramic mold material on the first pattern with a material having the first rate of heat removal, said steps of coating the second pattern includes the step of stuccoing a wet coating of ceramic mold material on the second pattern with a material having the second rate of heat removal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US828,492 | 1977-08-29 | ||
| US05/828,492 US4170256A (en) | 1976-01-29 | 1977-08-29 | Mold assembly and method of making the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1109633A true CA1109633A (en) | 1981-09-29 |
Family
ID=25251965
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA310,081A Expired CA1109633A (en) | 1977-08-29 | 1978-08-25 | Mold assembly and method of making the same |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5495921A (en) |
| BE (1) | BE870003A (en) |
| CA (1) | CA1109633A (en) |
| CH (1) | CH635765A5 (en) |
| DE (1) | DE2837286C2 (en) |
| FR (1) | FR2401721A1 (en) |
| GB (1) | GB2003421B (en) |
| IL (1) | IL55283A (en) |
| IT (1) | IT1098295B (en) |
| SE (1) | SE439126B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3806987A1 (en) * | 1988-03-03 | 1989-09-14 | Thyssen Industrie | Method for the production of castings by the lost-wax method |
| DE102007014744A1 (en) * | 2007-03-28 | 2008-10-02 | Rwth Aachen | Mold and method for the casting production of a cast piece |
| WO2014093826A2 (en) | 2012-12-14 | 2014-06-19 | United Technologies Corporation | Multi-shot casting |
| CN113828734B (en) * | 2021-09-16 | 2022-09-30 | 江苏金诺炉辊有限公司 | Gating system and investment casting process of high-temperature alloy four-way flange |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3598167A (en) * | 1968-11-01 | 1971-08-10 | United Aircraft Corp | Method and means for the production of columnar-grained castings |
| US3669177A (en) * | 1969-09-08 | 1972-06-13 | Howmet Corp | Shell manufacturing method for precision casting |
| US3724531A (en) * | 1971-01-13 | 1973-04-03 | United Aircraft Corp | Mold for casting single crystal articles |
| JPS5161433A (en) * | 1974-11-27 | 1976-05-28 | Kubota Ltd | SEIMITSUCHUZOYOIGATANO SAKUSEIHO |
| GB1509298A (en) * | 1975-09-20 | 1978-05-04 | Rolls Royce | Mould insulation and a method of insulating a mould |
| US4066116A (en) * | 1976-01-29 | 1978-01-03 | Trw Inc. | Mold assembly and method of making the same |
-
1978
- 1978-08-04 IL IL55283A patent/IL55283A/en unknown
- 1978-08-24 GB GB7834432A patent/GB2003421B/en not_active Expired
- 1978-08-25 CA CA310,081A patent/CA1109633A/en not_active Expired
- 1978-08-25 DE DE2837286A patent/DE2837286C2/en not_active Expired
- 1978-08-25 CH CH902278A patent/CH635765A5/en not_active IP Right Cessation
- 1978-08-28 JP JP10480478A patent/JPS5495921A/en active Pending
- 1978-08-28 IT IT27071/78A patent/IT1098295B/en active
- 1978-08-28 SE SE7809046A patent/SE439126B/en not_active IP Right Cessation
- 1978-08-28 BE BE190093A patent/BE870003A/en not_active IP Right Cessation
- 1978-08-28 FR FR7824807A patent/FR2401721A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2401721B1 (en) | 1983-09-23 |
| DE2837286A1 (en) | 1979-03-15 |
| FR2401721A1 (en) | 1979-03-30 |
| GB2003421B (en) | 1982-02-10 |
| IT1098295B (en) | 1985-09-07 |
| IT7827071A0 (en) | 1978-08-28 |
| JPS5495921A (en) | 1979-07-28 |
| CH635765A5 (en) | 1983-04-29 |
| SE439126B (en) | 1985-06-03 |
| GB2003421A (en) | 1979-03-14 |
| DE2837286C2 (en) | 1984-05-17 |
| IL55283A (en) | 1981-01-30 |
| SE7809046L (en) | 1979-03-01 |
| BE870003A (en) | 1978-12-18 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |