WO1997043061A1 - Investment casting composition - Google Patents

Investment casting composition Download PDF

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Publication number
WO1997043061A1
WO1997043061A1 PCT/GB1997/001289 GB9701289W WO9743061A1 WO 1997043061 A1 WO1997043061 A1 WO 1997043061A1 GB 9701289 W GB9701289 W GB 9701289W WO 9743061 A1 WO9743061 A1 WO 9743061A1
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WO
WIPO (PCT)
Prior art keywords
investment casting
casting composition
composition
thermoplastic pattern
wax
Prior art date
Application number
PCT/GB1997/001289
Other languages
French (fr)
Inventor
Michael Anthony Stradling
Original Assignee
Dussek Campbell Limited
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Dussek Campbell Limited filed Critical Dussek Campbell Limited
Priority to AU27823/97A priority Critical patent/AU2782397A/en
Publication of WO1997043061A1 publication Critical patent/WO1997043061A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes
    • B22C7/02—Lost patterns
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/08—Copolymers of ethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L45/00—Compositions of homopolymers or copolymers of compounds having no unsaturated aliphatic radicals in side chain, and having one or more carbon-to-carbon double bonds in a carbocyclic or in a heterocyclic ring system; Compositions of derivatives of such polymers

Definitions

  • This invention relates to investment casting compositions used to produce disposable thermoplastic patterns in investment casting processes.
  • a disposable thermoplastic pattern is usually formed by heating and melting an investment casting composition, introducing the molten material into a mold and then cooling the material until it solidifies to form a disposable thermoplastic pattern.
  • the disposable thermoplastic pattern is then removed from the mold and encased in a mold-forming material, usually a ceramic material, and the mold-forming material is caused or allowed to form a shell or cast around the disposable thermoplastic pattern.
  • a major portion of the disposable thermoplastic pattern is then removed from the shell by melting the thermoplastic composition at a moderately elevated temperature, such as 150 °C.
  • thermoplastic composition remaining on the shell after this step is removed by a substantially higher temperature, such as 950 °C, which causes vaporization, burning or both, so that, except for any ash residue, the inner surface of the shell is clean.
  • the shell can then be used for forming an investment cast part. This process allows the surface characteristics of the disposable thermoplastic pattern to be transferred to the final casting via the ceramic shell.
  • the quality of an investment casting depends on the quality of the disposable thermoplastic pattern, which in turn depends on the quality of the investment casting composition from which the disposable thermoplastic pattern is molded.
  • GB-A-1 403 112 teaches the use of a pattern-forming composition comprising a mixture of at least one waxy material such as paraffin wax and from 5-50% of a polyhydric alcohol such as pentaerythritol.
  • GB-A-1 , 509, 814 teaches the use of a specific pattern-forming composition comprising: 50% of a stearic acid/ palmitic acid mixture; 33% of an alkyl aromatic resin; 10% of a microcrystalline wax such as paraffin wax; 3% stearamide; 2.5% aluminium tristearate; and 1.5% magnesium distearate.
  • JP 55-117541 teaches the use of a pattern-forming composition comprising 0.5-75 wt% of wax such as paraffin wax and a higher alcohol such as cetyl alcohol.
  • the present invention is concerned with providing an improved thermoplastic pattern.
  • the present invention is also concerned with reducing the amount of shrinkage that occurs when an investment casting composition solidifies to produce a thermoplastic pattern.
  • the present invention is also concerned with: increasing rigidity and toughness of a thermoplastic pattern; increasing dimentional stability of a thermoplastic pattern; reducing the amount of wax left in a shell after dewaxing; increasing surface energy of a thermoplastic pattern; improving surface finish of a thermoplastic pattern; reducing total ash content produced by a thermoplastic pattern; and producing an environmentally friendlier thermoplastic pattern.
  • an investment casting composition comprising a polar waxy material such as stearic acid and being substantially free from a non-polar wax such as paraffin wax.
  • a polar waxy material such as stearic acid
  • a non-polar wax such as paraffin wax
  • an investment casting process comprising the steps of: a) preparing a disposable thermoplastic pattern; b) encasing the disposable thermoplastic pattern in a mold forming material such as a ceramic, and allowing or causing the mold forming material to form a shell or cast around the disposable thermoplastic pattern; and c) removing the disposable thermoplastic pattern from the shell or cast; characterised in that the disposable thermoplastic pattern is prepared from the investment casting composition defined above.
  • the polar waxy material is present in an amount from 15 to 60 % by total weight of the composition.
  • substantially free 1 in relation to the non-polar wax we mean that a non-polar wax is not intentionally added to the pattern-forming composition; however, trace amounts of a non-polar wax may unintentionally be present in the pattern-forming composition.
  • polar waxy material we mean a hydrocarbon compound that has a polar group such as an alcohol, a carboxylic acid, a glycol, a ketone, an aldehyde or a nitrogen-containing group such as an amine or amide attached thereto.
  • the hydrocarbon compound preferably has a carbon chain length of 14 to 60 carbon atoms.
  • the polar waxy material preferably has a melting point of 40-150 °C.
  • Suitable polar waxy materials are stearic acid, arachidic acid, behenic acid, palmitic acid, octadecanol, eicosanol and docosanol.
  • the preferred polar waxy material is stearic acid.
  • non-polar wax we mean a hydrocarbon compound that does not have any polar groups attached thereto.
  • the non-polar wax is preferably a hydrocarbon compound comprising long chain alkanes, with or without branching, and with or without cyclic groups.
  • the non-polar wax material preferably has a melting point of 40-150 °C.
  • non-polar waxes examples include paraffin waxes, microcrystalline waxes, Fischer-Tropsch waxes and polyethylene waxes.
  • the most common non-polar wax is paraffin wax.
  • stearic acid was only used as an additive in a thermoplastic pattern-forming composition, and its use was in addition to a non-polar wax such as paraffin wax.
  • Stearic acid was added to investment casting compositions for the purpose of improving the flow of the wax and improving the adhesion of waterborne refractory materials. In the present invention, however, the stearic acid is added to the investment composition as a replacement for the paraffin wax
  • the investment casting composition may also contain a selection of additives from the following list: polyethylene waxes modified with a polar component such as vinyl acetate or acrylic acid, ethylene bis-stearamide, stearamide waxes, erucamide waxes, acrylic resins, urea, pentaerythritol, isophthahc acid, terephthahc acid, cross linked poly methyl methacrylate, crosslinked polystyrene, phthalic anhydride, pentaerythritol esters of rosin, glycol esters of rosin, aliphatic and aromatic hydrocarbon resins, terpene resins, limonene resins, hydrogenated hydrocarbon resins, pentadiene resins, natural waxes such as carnauba, candelilla, spermaceti, bees wax and esparto, gum rosin, refined rosin, hydrogenated rosin, hydrolysed rosin, dime ⁇ sed
  • thermoplastic composition comprising paraffin wax produces hydrocarbons as an environmentally unfriendly by-product
  • Replacing paraffin wax with a polar waxy material such as stearic acid will produce an environmentally friendlier product because heating stearic acid to 950°C produces carbon dioxide and water
  • Example 1 Two investment casting compositions, designated Example 1 and Comparative Example 1 , having the above mentioned compositions, were prepared by the following method:
  • a steam heated vessel was charged with the wax components and they were melted. When a minimum temperature of 120 °C had been reached, the blend was stirred and the ethylene vinyl acetate copolymer was added to the mixture. The mixture was stirred until the vinyl acetate copolymer was completely dissolved After the vinyl acetate copolymer had been completely dissolved, pentaerythritol rosin ester was added to the mixture while stirring, and the mixture was stirred until the pentaerythritol rosin ester had completely dissolved. After the pentaerythritol rosin ester had been completely dissolved, the aromatic hydrocarbon resin was added to the mixture and the mixture was stirred until the aromatic hydrocarbon resin had been completely dissolved. The molten blend was then decanted from the mixing vessel and filtered through a 100 micron mesh.
  • Bars having dimensions of 100mm by 20mm by 5 mm were prepared. A small weight of 5.86g ⁇ 0.02g was attached to one end of each bar. The other end of each bar was firmly clamped in a clamp in a horizontal position so that 80mm of the bar (including the weight) was exposed. The assembly of clamp, bar and weight was placed in a circulating water bath at 40°C for approximately 48 hours.
  • the bars were removed from the bath, the weights removed and the bars dried.
  • a measurement was made of the vertical distance dropped by the bars. The measurement was made by lining the 20mm length of bar that was clamped in the clamp with a horizontal line and measuring the vertical distance between the end of the bar that was not in the clamp and the horizontal line.
  • Method Bars having the following dimensions were poured from molten wax at a temperature of 80°C into dies measuring 9mm by 9mm by 90mm. The bars were allowed to set and then removed from the dies. The bars were then left for 48 hours. After 48 hours, the bars were placed in a water bath at 23°C for thirty minutes. The bars were then tested on a Lloyd instrument LRX materials testing machine fitted with a three point bend jig. The test parameters were:
  • Example 1 Ten bars were prepared for both of the investment casting compositions designated Example 1 and Comparative Example 1. The average test results were as follows:
  • Example 1 The waxes designated Example 1 and Comparative Example 2 were each injected separately into a test die under identical conditions of injection time, injection pressure, wax temperature, platen temperature, clamping pressure and flow rate.
  • the linear contractions of ten pieces of each of the two waxes were measured with a micrometer on a straight section of the pattern. The average linear contraction was calculated and is quoted as the linear free contraction.
  • the volume contraction was evaluated subjectively as sinkage in heavy sections of the pattern.
  • Example 1 was taken to be the standard reference.
  • Example 1 which does not comprise paraffin wax, gives reduced shrinkage when compared to the investment casting composition designated Comparative Example 2, which comprises paraffin wax.
  • a polar waxy material such as stearic acid can therefore be used as a replacement for a non-polar wax such as paraffin wax in an investment casting composition in order to reduce the shrinkage of a thermoplastic pattern produced from the investment casting composition.
  • Example 1 Thin walled boxes having a wall thickness of approximately 1.6mm were injected with the waxes designated Example 1 and Comparative Example 2. The boxes were then invested in a refractory ceramic material and dewaxed in an autoclave. By visual inspection of the dewaxed boxes, it was clear that less wax remained in the box into which the wax designated
  • Example 1 had been injected.
  • a polar waxy material such as stearic acid can therefore be used as a replacement for a non-polar wax such as paraffin wax in an investment casting composition in order to reduce the amount of wax left in a shell or cast after dewaxing of a thermoplastic pattern produced from the investment casting composition.
  • the advantage of reducing the amount of wax left in a shell or cast after dewaxing is that when the shell or cast is fired at elevated temperatures, such as 950°C, less shell or cast cracking is likely to occur. Also, contamination of the shell or cast is reduced so there is a reduction in the presence of large deposits of inorganic ash within the shell or cast, which reduces the likelihood of inclusions occurring on the cast part.
  • Example 1 and Comparative Example 2 were measured using surface energy pens.
  • Surface energy test pens contain a mixture of solvents that produce an ink with a chosen known surface tension When the ink is applied to a surface, the ink will reticulate if the surface has a lower surface energy that the surface energy of the ink
  • the surface energy of the substrate is preferably in the region of 36 to 40 dynes/cm, to ensure that the ink wets the substrate and adheres well If the surface energy of the film is less than 36 dynes/cm, it is difficult to obtain adhesion of the ink to the substrate
  • a polar wax based investment casting composition that has a higher surface energy than a paraffin wax based investment casting composition gives increased adhesion and wetting of a primary coat of a refractory material when the pattern is invested
  • the polar wax based investment casting composition wets the surface of a die more effectively during the injection process Improved wetting of the die leads to superior reproduction of the surface characteristics of the die and to a generally superior surface finish
  • Example 1 The total ash content of Example 1 and Comparative Example 2 were measure according to ASTM D482
  • Example 1 0.002% Comparative Example 1 0.015%
  • Example 1 gives a reduced total ash when compared to Comparative Example 2.
  • Ash is undesirable in an investment casting process because any ash remaining in a shell or cast may cause inclusions or holes in a cast part. Furthermore, some metals, such as titanium, may react violently with any metallic ash contained in a shell or cast.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)

Abstract

An investment casting composition comprising a polar waxy material such as stearic acid and being substantially free form a non-polar wax such as paraffin wax.

Description

INVESTMENT CASTING COMPOSITION
This invention relates to investment casting compositions used to produce disposable thermoplastic patterns in investment casting processes.
Investment casting processes, which are also known as 'lost-wax' processes, have been known for many years. In an investment casting process a disposable thermoplastic pattern is usually formed by heating and melting an investment casting composition, introducing the molten material into a mold and then cooling the material until it solidifies to form a disposable thermoplastic pattern. The disposable thermoplastic pattern is then removed from the mold and encased in a mold-forming material, usually a ceramic material, and the mold-forming material is caused or allowed to form a shell or cast around the disposable thermoplastic pattern. A major portion of the disposable thermoplastic pattern is then removed from the shell by melting the thermoplastic composition at a moderately elevated temperature, such as 150 °C. Any thermoplastic composition remaining on the shell after this step is removed by a substantially higher temperature, such as 950 °C, which causes vaporization, burning or both, so that, except for any ash residue, the inner surface of the shell is clean. The shell can then be used for forming an investment cast part. This process allows the surface characteristics of the disposable thermoplastic pattern to be transferred to the final casting via the ceramic shell.
The quality of an investment casting depends on the quality of the disposable thermoplastic pattern, which in turn depends on the quality of the investment casting composition from which the disposable thermoplastic pattern is molded. GB-A-1 403 112 teaches the use of a pattern-forming composition comprising a mixture of at least one waxy material such as paraffin wax and from 5-50% of a polyhydric alcohol such as pentaerythritol.
GB-A-1 , 509, 814 teaches the use of a specific pattern-forming composition comprising: 50% of a stearic acid/ palmitic acid mixture; 33% of an alkyl aromatic resin; 10% of a microcrystalline wax such as paraffin wax; 3% stearamide; 2.5% aluminium tristearate; and 1.5% magnesium distearate.
JP 55-117541 teaches the use of a pattern-forming composition comprising 0.5-75 wt% of wax such as paraffin wax and a higher alcohol such as cetyl alcohol.
The present invention is concerned with providing an improved thermoplastic pattern. The present invention is also concerned with reducing the amount of shrinkage that occurs when an investment casting composition solidifies to produce a thermoplastic pattern. The present invention is also concerned with: increasing rigidity and toughness of a thermoplastic pattern; increasing dimentional stability of a thermoplastic pattern; reducing the amount of wax left in a shell after dewaxing; increasing surface energy of a thermoplastic pattern; improving surface finish of a thermoplastic pattern; reducing total ash content produced by a thermoplastic pattern; and producing an environmentally friendlier thermoplastic pattern.
In accordance with the present invention there is provided an investment casting composition comprising a polar waxy material such as stearic acid and being substantially free from a non-polar wax such as paraffin wax. In accordance with the present invention there is also provided use of a polar waxy material such as stearic acid as a replacement for a non-polar wax such as paraffin wax in an investment casting composition.
In accordance with the present invention there is also provided use of the investment casting composition defined above to reduce shrinkage of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
In accordance with the present invention there is also provided use of the investment casting composition defined above to increase rigidity or toughness of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
In accordance with the present invention there is also provided use of the investment casting composition defined above to increase dimentional stability of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
In accordance with the present invention there is also provided use of the investment casting composition defined above to reduce the amount of wax left in a shell or cast after dewaxing of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
In accordance with the present invention there is also provided use of the investment casting composition defined above to increase surface energy of a thermoplastic pattern produced from the investment casting composition in an investment casting process. In accordance with the present invention there is also provided use of the investment casting composition defined above to increase surface finish of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
In accordance with the present invention there is also provided use of the investment casting composition defined above to reduce total ash content during removal of a thermoplastic pattern produced from the investment casting composition from a shell or cast in an investment casting process.
In accordance with the present invention there is also provided use of the investment casting composition defined above to produce an environmentally friendlier thermoplastic pattern.
In accordance with the present invention there is also provided an investment casting process comprising the steps of: a) preparing a disposable thermoplastic pattern; b) encasing the disposable thermoplastic pattern in a mold forming material such as a ceramic, and allowing or causing the mold forming material to form a shell or cast around the disposable thermoplastic pattern; and c) removing the disposable thermoplastic pattern from the shell or cast; characterised in that the disposable thermoplastic pattern is prepared from the investment casting composition defined above.
Preferably the polar waxy material is present in an amount from 15 to 60 % by total weight of the composition.
By the term 'substantially free1 in relation to the non-polar wax, we mean that a non-polar wax is not intentionally added to the pattern-forming composition; however, trace amounts of a non-polar wax may unintentionally be present in the pattern-forming composition.
By the term 'polar waxy material' we mean a hydrocarbon compound that has a polar group such as an alcohol, a carboxylic acid, a glycol, a ketone, an aldehyde or a nitrogen-containing group such as an amine or amide attached thereto. The hydrocarbon compound preferably has a carbon chain length of 14 to 60 carbon atoms. The polar waxy material preferably has a melting point of 40-150 °C.
Examples of suitable polar waxy materials are stearic acid, arachidic acid, behenic acid, palmitic acid, octadecanol, eicosanol and docosanol.
The preferred polar waxy material is stearic acid.
By the term 'non-polar wax' we mean a hydrocarbon compound that does not have any polar groups attached thereto. The non-polar wax is preferably a hydrocarbon compound comprising long chain alkanes, with or without branching, and with or without cyclic groups. The non-polar wax material preferably has a melting point of 40-150 °C.
Examples of non-polar waxes are paraffin waxes, microcrystalline waxes, Fischer-Tropsch waxes and polyethylene waxes.
The most common non-polar wax is paraffin wax.
Until the present invention, stearic acid was only used as an additive in a thermoplastic pattern-forming composition, and its use was in addition to a non-polar wax such as paraffin wax. Stearic acid was added to investment casting compositions for the purpose of improving the flow of the wax and improving the adhesion of waterborne refractory materials. In the present invention, however, the stearic acid is added to the investment composition as a replacement for the paraffin wax
The investment casting composition may also contain a selection of additives from the following list: polyethylene waxes modified with a polar component such as vinyl acetate or acrylic acid, ethylene bis-stearamide, stearamide waxes, erucamide waxes, acrylic resins, urea, pentaerythritol, isophthahc acid, terephthahc acid, cross linked poly methyl methacrylate, crosslinked polystyrene, phthalic anhydride, pentaerythritol esters of rosin, glycol esters of rosin, aliphatic and aromatic hydrocarbon resins, terpene resins, limonene resins, hydrogenated hydrocarbon resins, pentadiene resins, natural waxes such as carnauba, candelilla, spermaceti, bees wax and esparto, gum rosin, refined rosin, hydrogenated rosin, hydrolysed rosin, dimeπsed rosin, disproportionated rosin, styrenated acrylic resins, polyamide resins, oxidised polyethylene waxes, polyalpha-olefins, tall oil rosin, Bisphenol A, alpha methyl styrene, gum damar, hardened rapeseed oil, hardened castor oil, rice oil wax, rice bran wax, maleic modified rosin, phenolic modified rosin, phenolic resin, oxidised alpha-olefins, isocyanate modified alpha-olefins, water, ketone resin, Montan wax and its derivatives and other similar materials
During removal of a thermoplastic composition from a shell using an elevated temperature such as 950°C, a thermoplastic composition comprising paraffin wax produces hydrocarbons as an environmentally unfriendly by-product Replacing paraffin wax with a polar waxy material such as stearic acid will produce an environmentally friendlier product because heating stearic acid to 950°C produces carbon dioxide and water
Replacing a non-polar wax such as paraffin wax with a polar waxy material such as stearic acid therefore produces a more environmentally friendly thermoplastic pattern The invention will now be described by reference to the following examples:
EXAMPLES
Figure imgf000009_0001
* ASTM D127 ** ASTM E-28 Λ Melt index 150g/mιn @ 190°C, vinyi acetate incorporation 19%w/w
Two investment casting compositions, designated Example 1 and Comparative Example 1 , having the above mentioned compositions, were prepared by the following method:
A steam heated vessel was charged with the wax components and they were melted. When a minimum temperature of 120 °C had been reached, the blend was stirred and the ethylene vinyl acetate copolymer was added to the mixture. The mixture was stirred until the vinyl acetate copolymer was completely dissolved After the vinyl acetate copolymer had been completely dissolved, pentaerythritol rosin ester was added to the mixture while stirring, and the mixture was stirred until the pentaerythritol rosin ester had completely dissolved. After the pentaerythritol rosin ester had been completely dissolved, the aromatic hydrocarbon resin was added to the mixture and the mixture was stirred until the aromatic hydrocarbon resin had been completely dissolved. The molten blend was then decanted from the mixing vessel and filtered through a 100 micron mesh.
The investment casting composition below, designated Comparative Example 2, was prepared in the same way as the investment casting compositions designated Example 1 and Comparative Example 1.
Figure imgf000010_0001
TESTS
The following tests were carried out:
Distortion at Elevated Temperatures
Method
Bars having dimensions of 100mm by 20mm by 5 mm were prepared. A small weight of 5.86g ± 0.02g was attached to one end of each bar. The other end of each bar was firmly clamped in a clamp in a horizontal position so that 80mm of the bar (including the weight) was exposed. The assembly of clamp, bar and weight was placed in a circulating water bath at 40°C for approximately 48 hours.
After approximately 48 hours, the bars were removed from the bath, the weights removed and the bars dried. A measurement was made of the vertical distance dropped by the bars. The measurement was made by lining the 20mm length of bar that was clamped in the clamp with a horizontal line and measuring the vertical distance between the end of the bar that was not in the clamp and the horizontal line.
Results
Distance dropped Example 1 4.5mm
Comparative Example 1 10.5mm
It can be clearly seen from the above results that even a very small amount of paraffin wax has an adverse effect on the high temperature distortion properties of an investment casting composition. This means that the investment casting composition of Example 1 is subject to less post die deformation than the investment casting composition of Comparative Example 1. A polar waxy material such as stearic acid can therefore be used as a replacement for a non-polar wax such as paraffin wax in an investment casting composition in order to increase the dimentional stability of a thermoplastic pattern produced from the investment casting composition.
Three Point Bend Characteristics
Method Bars having the following dimensions were poured from molten wax at a temperature of 80°C into dies measuring 9mm by 9mm by 90mm. The bars were allowed to set and then removed from the dies. The bars were then left for 48 hours. After 48 hours, the bars were placed in a water bath at 23°C for thirty minutes. The bars were then tested on a Lloyd instrument LRX materials testing machine fitted with a three point bend jig. The test parameters were:
Test speed 40mm per minute Gauge length 9mm Span 65mm
Ten bars were prepared for both of the investment casting compositions designated Example 1 and Comparative Example 1. The average test results were as follows:
Example 1 Comparative Example 1 Maximum load 77.2N 64.2N
Load at break 77.2N 63.5N Strain at break 16.6% 14.3% Three point bend 10.3Nmrτv2 8.6Nmπr2
It can be clearly seen from the above results that the presence of paraffin wax has as adverse effect on maximum load, load at break, strain at break and three point bend. These results show that the investment casting composition of Comparative Example 1 , the investment casting composition comprising paraffin wax, is considerably weaker than the investment casting composition of Example 1 , and thus it is more likely to break during handling of the composition. The test for three point bend conforms to ASTM D790/BS2782, Part 3, Method A. A polar waxy material such as stearic acid can therefore be used as a replacement for a non-polar wax such as paraffin wax in an investment casting composition in order to increase the rigidity and toughness of a thermoplastic pattern produced from the investment casting composition.
Linear and Volume Contraction
Method
The waxes designated Example 1 and Comparative Example 2 were each injected separately into a test die under identical conditions of injection time, injection pressure, wax temperature, platen temperature, clamping pressure and flow rate. The linear contractions of ten pieces of each of the two waxes were measured with a micrometer on a straight section of the pattern. The average linear contraction was calculated and is quoted as the linear free contraction. The volume contraction was evaluated subjectively as sinkage in heavy sections of the pattern. Example 1 was taken to be the standard reference.
Results
Example 1 Comparative Example 2
Linear free contraction 0.7% 0.9%
Volume contraction standard inferior
(approximately 50% increase in sinkage)
These results show that the investment casting composition designated Example 1 , which does not comprise paraffin wax, gives reduced shrinkage when compared to the investment casting composition designated Comparative Example 2, which comprises paraffin wax. A polar waxy material such as stearic acid can therefore be used as a replacement for a non-polar wax such as paraffin wax in an investment casting composition in order to reduce the shrinkage of a thermoplastic pattern produced from the investment casting composition.
Dewaxing of Thin-walled boxes
Methpd
Thin walled boxes having a wall thickness of approximately 1.6mm were injected with the waxes designated Example 1 and Comparative Example 2. The boxes were then invested in a refractory ceramic material and dewaxed in an autoclave. By visual inspection of the dewaxed boxes, it was clear that less wax remained in the box into which the wax designated
Example 1 had been injected. A polar waxy material such as stearic acid can therefore be used as a replacement for a non-polar wax such as paraffin wax in an investment casting composition in order to reduce the amount of wax left in a shell or cast after dewaxing of a thermoplastic pattern produced from the investment casting composition. The advantage of reducing the amount of wax left in a shell or cast after dewaxing is that when the shell or cast is fired at elevated temperatures, such as 950°C, less shell or cast cracking is likely to occur. Also, contamination of the shell or cast is reduced so there is a reduction in the presence of large deposits of inorganic ash within the shell or cast, which reduces the likelihood of inclusions occurring on the cast part.
Surface Energy
Method
The surface energy of the waxes designated Example 1 and Comparative Example 2 were measured using surface energy pens. Surface energy test pens contain a mixture of solvents that produce an ink with a chosen known surface tension When the ink is applied to a surface, the ink will reticulate if the surface has a lower surface energy that the surface energy of the ink
When the pens were applied to the surface of an injected pattern formed from Comparative Example 2, it was found that the surface energy was approximately 31 dynes/cm When the same test was performed on the surface of an injected pattern formed from Example 1 , it was found that the surface energy was between 37 and 40 dynes/cm
In a process for printing polyolefin films such as polyethylene, the surface energy of the substrate is preferably in the region of 36 to 40 dynes/cm, to ensure that the ink wets the substrate and adheres well If the surface energy of the film is less than 36 dynes/cm, it is difficult to obtain adhesion of the ink to the substrate A polar wax based investment casting composition that has a higher surface energy than a paraffin wax based investment casting composition gives increased adhesion and wetting of a primary coat of a refractory material when the pattern is invested Also, the polar wax based investment casting composition wets the surface of a die more effectively during the injection process Improved wetting of the die leads to superior reproduction of the surface characteristics of the die and to a generally superior surface finish
Total Ash Content
Method
The total ash content of Example 1 and Comparative Example 2 were measure according to ASTM D482
Results Total Ash Content
Example 1 0.002% Comparative Example 1 0.015%
These results show that Example 1 gives a reduced total ash when compared to Comparative Example 2.
Ash is undesirable in an investment casting process because any ash remaining in a shell or cast may cause inclusions or holes in a cast part. Furthermore, some metals, such as titanium, may react violently with any metallic ash contained in a shell or cast.

Claims

15Claims
1. An investment casting composition comprising a polar waxy material such as stearic acid and being substantially free from a non-polar wax such as paraffin wax.
2. Use of a polar waxy material such as stearic acid as a replacement for a non-polar wax such as paraffin wax in an investment casting composition.
3. Use of the investment casting composition claimed in claim 1 to reduce shrinkage of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
4. Use of the investment casting composition claimed in claim 1 to increase rigidity or toughness of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
5. Use of the investment casting composition claimed in claim 1 to increase dimentional stability of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
6. Use of the investment casting composition claimed in claim 1 to reduce the amount of wax left in a shell or cast after dewaxing of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
7. Use of the investment casting composition claimed in claim 1 to increase the surface energy of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
8. Use of the investment casting composition claimed in claim 1 to increase surface finish of a thermoplastic pattern produced from the investment casting composition in an investment casting process.
9. Use of the investment casting composition claimed in claim 1 to reduce total ash content during removal of a thermoplastic pattern produced from the investment casting composition from a shell or cast in an investment casting process.
10. Use of the investment casting composition claimed in claim 1 to produce an environmentally friendly thermoplastic pattern.
11. The composition or use as claimed in any one of the preceding claims, wherein the polar waxy material is present in an amount from 15 to 60 by total weight of the composition.
12. An investment casting process comprising the steps of: a) preparing a disposable thermoplastic pattern; b) encasing the disposable thermoplastic pattern in a mold forming material such as a ceramic, and allowing or causing the mold forming material to form a shell or cast around the disposable thermoplastic pattern; and c) removing the disposable thermoplastic pattern from the shell or cast; characterised in that the disposable thermoplastic pattern is prepared from the investment casting composition defined in claims 1 or 11.
PCT/GB1997/001289 1996-05-13 1997-05-12 Investment casting composition WO1997043061A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU27823/97A AU2782397A (en) 1996-05-13 1997-05-12 Investment casting composition

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9609933.8A GB9609933D0 (en) 1996-05-13 1996-05-13 Pattern-forming thermoplastic compositions
GB9609933.8 1996-05-13

Publications (1)

Publication Number Publication Date
WO1997043061A1 true WO1997043061A1 (en) 1997-11-20

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1997/001289 WO1997043061A1 (en) 1996-05-13 1997-05-12 Investment casting composition

Country Status (3)

Country Link
AU (1) AU2782397A (en)
GB (1) GB9609933D0 (en)
WO (1) WO1997043061A1 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE29919100U1 (en) 1999-10-30 2001-03-08 Agrodyn Hochspannungstechnik GmbH, 33803 Steinhagen Test ink container
EA022719B1 (en) * 2012-03-21 2016-02-29 Открытое Акционерное Общество "Завод Горного Воска" Precision casting pattern compound and method for production thereof
TWI552849B (en) * 2013-01-25 2016-10-11 瑩信工業股份有限公司 Method of manufacturing composite wheel rim
CN112920611A (en) * 2021-01-13 2021-06-08 苏州泰尔航空材料有限公司 Filling type investment casting mold material with high filler content and preparation method thereof
US11993004B2 (en) 2019-09-27 2024-05-28 3M Innovative Properties Company Molding process and compositions therefor

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1583556A1 (en) * 1966-11-25 1970-08-13 Reichhold Albert Chemie Ag Homogeneous and isotropic samples or models for making a shape and using the same
GB1338808A (en) * 1970-12-14 1973-11-28 Trw Inc Thermoplastic compositions
US3964915A (en) * 1974-12-26 1976-06-22 Trw Inc. Investment wax
US4064083A (en) * 1976-06-28 1977-12-20 Precision Metalsmiths, Inc. Pattern material composition

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1583556A1 (en) * 1966-11-25 1970-08-13 Reichhold Albert Chemie Ag Homogeneous and isotropic samples or models for making a shape and using the same
GB1338808A (en) * 1970-12-14 1973-11-28 Trw Inc Thermoplastic compositions
US3964915A (en) * 1974-12-26 1976-06-22 Trw Inc. Investment wax
US4064083A (en) * 1976-06-28 1977-12-20 Precision Metalsmiths, Inc. Pattern material composition

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE29919100U1 (en) 1999-10-30 2001-03-08 Agrodyn Hochspannungstechnik GmbH, 33803 Steinhagen Test ink container
EA022719B1 (en) * 2012-03-21 2016-02-29 Открытое Акционерное Общество "Завод Горного Воска" Precision casting pattern compound and method for production thereof
TWI552849B (en) * 2013-01-25 2016-10-11 瑩信工業股份有限公司 Method of manufacturing composite wheel rim
US11993004B2 (en) 2019-09-27 2024-05-28 3M Innovative Properties Company Molding process and compositions therefor
CN112920611A (en) * 2021-01-13 2021-06-08 苏州泰尔航空材料有限公司 Filling type investment casting mold material with high filler content and preparation method thereof

Also Published As

Publication number Publication date
AU2782397A (en) 1997-12-05
GB9609933D0 (en) 1996-07-17

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