Investment casting shell binders and compositions

Abstract

Investment casting shell composition binders comprising hydrophilic fibrils having an average diameter between about 1 nm and about less than 1 ?m can be used for the preparation of investment casting shell compositions or slurries. The investment casting shell binders and compositions can be used in an investment casting process to produce investment casting shells with improved shell build thickness and strength.

Claims

1. An investment casting shell composition comprising a refractory component and a binder, the binder comprising hydrophilic fibrils having an average diameter greater than 1 nm and less than 1 ?m, wherein the hydrophilic fibrils comprise microfibrillated cellulose (MFC).

2. The composition according to claim 1, wherein the hydrophilic fibrils have an average diameter between 10 nm to less than 1 ?m.

3. The composition according to claim 1, wherein the hydrophilic fibrils are present in an amount from about 0.1 wt % to about 20 wt % based on the total mass of the binder.

4. The composition according to claim 1 further comprising at least one additional polymer, wherein the at least one additional polymer comprises one or more monomers selected from: acrylic acid, acrylic esters, methacrylic acid, methacrylic esters, styrene, butadiene, vinyl chloride, vinyl acetate, and combinations thereof.

5. The composition according to claim 1, wherein the hydrophilic fibrils in the binder are present in an amount from about 0.01 wt % to about 1 wt % based on the total mass of the composition.

6. The composition according to claim 1, wherein the refractory component comprises fused silica selected from: fused silica mesh 120, fused silica mesh 140, fused silica mesh 170, fused silica mesh 200, fused silica mesh 270, fused silica mesh 325, and combinations thereof.

7. The composition according to claim 1, wherein the refractory component comprises a wide distribution fused silica, wherein the wide distribution fused silica comprises a combination of 85% fused silica 50-80 mesh and 15% fused silica 120 mesh.

8. An investment casting shell prepared from the composition according to claim 1.

9. An investment casting method for creating an article, the method comprising coating an expendable preform with at least one coat of an investment casting shell slurry, wherein at least one of the slurry coats comprises the investment casting shell composition according to claim 1.

10. The investment casting method according to claim 9, wherein the slurry coats in the second layer and above comprise the investment casting shell composition.

11. The investment casting method according to claim 9, further comprising stuccoing one or more of the at least one slurry coats, wherein a slurry coat and a stucco coat produced by the stuccoing create a shell layer, wherein each shell layer once dried is at least 1 mm thick.

12. A kit for preparing an investment casting shell composition comprising: the compositionaccording to claim 1.

13. The binder according to claim 1, wherein the hydrophilic fibrils have an average diameter between 1 nm to less than 900 nm.

14. The binder according to claim 1, wherein the hydrophilic fibrils have an average diameter between 10 nm to less than 900 nm.

Description

(1) The invention is described with reference to the accompanying drawings which:

(2) FIG. 1 is a graph showing modulus of rupture (MOR) results for shells prepared from slurries comprising 0.1% and 0.2% MFC as binder at two different viscosities, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(3) FIG. 2 is a graph comparing the shell thicknesses of shells prepared from slurries comprising 0.1% and 0.2% MFC as binder compared to conventional shells prepared from slurries comprising no MFC [n=10].

(4) FIG. 3 is a graph showing force of break results for shells prepared from slurries comprising 0.1% and 0.2% MFC as binder compared to conventional shells prepared from slurries comprising no MFC [n=10];

(5) FIG. 4 is a graph showing modulus of rupture (MOR) results for shells comprising 6 or 9 shell layers prepared from slurries comprising 0.3% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(6) FIG. 5 is a graph comparing the shell thicknesses of shells comprising 6 or 9 shell layers prepared from slurries comprising 0.3% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(7) FIG. 6 is a graph showing force of break results for shells comprising 6 or 9 shell layers prepared from slurries comprising 0.3% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(8) FIG. 7 is a graph comparing the shell thickness of shells fired at 1000? C., comprising 3 or 4 shell layers prepared form slurries comprising 0.4% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=4];

(9) FIG. 8A is a graph showing the permeability of hot shells prepared from slurries comprising 0.1%, 0.2% and 0.3% MFC as binder at 1000? C., compared to conventional shells prepared from slurries comprising no MFC [n=5];

(10) FIG. 8B is a graph showing permeability of cold shells prepared from slurries comprising 0.1%, 0.2% and 0.3% MFC as binder at room temperature after firing at 1000? C., compared to conventional shells prepared from slurries comprising no MFC [n=5];

(11) FIG. 9 is a graph showing the modulus of rupture (MOR) results for shells prepared from slurries having binder systems with 0% MFC, 0.3% MFC and 0.3% nylon fibre [n=10];

(12) FIG. 10 is a graph showing the shell thicknesses of shells prepared from slurries having binder systems with 0% MFC, 0.3% MFC and 0.3% nylon fibre [n=10];

(13) FIG. 11 is a graph showing the force of break results for shells prepared from slurries having binder systems with 0% MFC, 0.3% MFC and 0.3% nylon fibre [n=10]:

(14) FIG. 12 is a graph showing modulus of rupture (MOR) results for shells prepared from slurries having binder systems with 0.3% MFC, in addition to 12%, 6%, 3% and 0% styrene polymer respectively [n=10];

(15) FIG. 13 is a graph comparing the shell thicknesses of shells prepared from slurries having binder systems with 0.3% MFC, in addition to 12%, 6%, 3% and 0% styrene polymer respectively [n=10];

(16) FIG. 14 is a graph showing force of break results for shells prepared from slurries having binder systems with 0.3% MFC, in addition to 12%, 6%, 3% and 0% styrene polymer respectively [n=10];

(17) FIG. 15 shows a comparison of the particle size distributions for various fused silica refractories: 200 mesh, 270 mesh and a wide distribution fused silica refractory:

(18) FIG. 16 shows the effect of the refractory material on the modulus of rupture (MOR) results for shells prepared from slurries comprising 0.3% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(19) FIG. 17 shows the effect of the refractory material on shell thickness for shells prepared from slurries comprising 0.3% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(20) FIG. 18 shows the effect of the refractory material on the force of break results for shells prepared from slurries comprising 0.3% MFC as binder, compared to conventional shells prepared from slurries comprising no MFC [n=10];

(21) FIG. 19 shows the effect of MFC on the viscosity of various binder systems;

(22) FIG. 20 shows the effect of MFC on the rheology of various binder systems;

(23) FIG. 21 is a graph comparing the shell thicknesses of shells prepared from slurries comprising binder systems with different styrene polymers compared to conventional shells prepared from slurries comprising no MFC [n=10];

(24) FIG. 22 is a graph showing force of break results for shells prepared from slurries comprising binder systems with different styrene polymers compared to conventional shells prepared from slurries comprising no MFC [n=10];

(25) FIG. 23 shows the MOR results for shells made with no fibrils slurry, MFC slurry and fHDPE slurry [n=10];

(26) FIG. 24 shows the thickness results for shells made with no fibrils slurry, MFC slurry and fHDPE slurry [n=10];

(27) FIG. 25 shows the break force results for shells made with no fibrils slurry, MFC slurry and fHDPE slurry [n=10];

(28) FIG. 26 shows the effect of addition of fHDPE or MFC on the shear rate-dependent viscosities of various binder systems; and

(29) FIG. 27 shows the effect of addition of fHDPE or MFC on the relationship between shear stress and shear rate for various binder systems.

EXAMPLES

Example 1Investment Casting Shell Composition Formulations

1.1 Formulations for Shell Room Trials

(30) TABLE-US-00001 TABLE 1 Example Example formulation 1 formulation 2 Conventional (0.1% (0.2% Ingredients (no MFC)/kg MFC)/kg MFC)/kg 200 mesh fused silica 91 91 91 (Imerys Fused Minerals) Colloidal silica (Remasol? 45.5 45.5 45.5 SP-30; Grace GMBH) Styrene butadiene 6.5 6.5 6.5 copolymer (Lipaton SB 5843; Synthomer plc) * Wetting agent, ethoxylated 0.113 0.113 0.113 akyl acid phosphate (Victawet? 12, ILCO Chemie) Anti-foaming agent, 0.091 0.091 0.091 polysiloxane dispersion (Burst 100; Remet Corporation) {circumflex over ()} Microfibrillated cellulose 0 0.552 1.104 (Exilva? P 01-V, 10% aqueous dispersion; Borregaard) * Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation). {circumflex over ()} Burst 100 may be replaced with an equal amount of Funnexol? (Huntsman Textile Effect).

1.2 Formulations for Lab Scale Trials

1.2.1200 Mesh Fused Silica as Refractory

(31) TABLE-US-00002 TABLE 2 Conventional Example formulation 3 Ingredients (no MFC)/kg (0.3% MFC)/kg 200 mesh fused silica (Imerys 700 700 Fused Minerals) Colloidal silica (Remasol? 350 350 SP-30; Grace GMBH) Styrene butadiene copolymer 50 50 (Lipaton SB 5843; Synthomer plc)* Wetting agent (Wet-in?; 10 10 Remet Corporation) # Anti-foaming agent (Burst 2.5 2.5 100; Remet Corporation) {circumflex over ()} Microfibrillated cellulose 0 12.4 (Exilval? P 01-V, 10% concentration; Borregaard) *Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation). {circumflex over ()} Burst- 100 may be replaced with an equal amount of Fumexol? (Huntsman Textile Effect). # Wet-in? may be replaced with an equal amount of Victawet? 12 (ILCO Chemie).

1.2.2 Wide Distribution Silica (WDS) as Refractory

(32) TABLE-US-00003 TABLE 3 Example Conventional formulation 4 (no MFC, (03% MFC; Ingredients WDS)/kg WDS)/kg Fused silica (EZ Cast?; 700 700 Remet UK Ltd) Colloidal silica (Remasol? 350 350 SP-30; Grace GMBH) Styrene butadiene copolymer 50 50 (Lipaton SB 5843; Synthomer plc) * Wetting agent (Wet-in?: 10 10 Remet Corporation) # Arni-foaming agent (Burst 2.5 2.5 100; Remet Corporation) {circumflex over ()} Microfibrillated cellulose 0 12.4 (Exilva? P 01-V, 10% concentration; Borregaard) * Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation). {circumflex over ()} Burst 100 may he replaced with an equal amount of Fumexol? (Huntsman Textile Effect). # Wet-int may be replaced with an equal amount of Victawet? 12 (TECO Chemie),
1.3 Binder Formulation for Warehouse Scale Trials

(33) TABLE-US-00004 TABLE 4 Example formulation 5 Ingredients (0.3% MFC)/kg Colloidal silica (Remasol? 192 SP-30; Grace GMBH) Styrene butadiene copolymer 19.2 (Lipaton SB 5843; Synthomer plc)* Deionised water 19.2 Biocide (Acticide? MBS 1.2 50:501,2-Benzisothiazol- 3(2H)-one:2-methyl-2H- isothiazol-3-one; Thor Specialities) Anti-foaming agent (Burst 1.2 100; Remet Corporation) Microfibrillated cellulose 7.2 (Exilva? P 01-V, 10% concentration; Borregaard) *Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation). {circumflex over ()} Burst 100 may he replaced with an equal amount of Fumexol? (Huntsman Textile Effect).

1.4 Viscosity Adjustments

(34) The viscosity of each test slurry was measured used a Zahn cup (#4). Timing was commenced as the sampling end of the cup broke the surface of the sample after dipping, and stopped when the first definitive break in the stream of slurry was observed at the base of the sampling cup.

(35) Before testing, the viscosity of each slurry was adjusted to 25 seconds (unless otherwise specified). Viscosity adjustments were carried out by adding deionised water (to lower viscosity) or allowing water to evaporate from the slurry (to increase viscosity).

Example 2Modulus of Rupture (MOR) Shell Build Thickness and Force of Break

2.1 Shell Room Trials (0.1% and 0.2% MFC Binder)

2.1.1 Sample Preparation

(36) Example slurry formulations 1 and 2 were prepared as set out in Table 1. Each slurry was tested at a viscosity of 25 seconds and 30 seconds respectively.

(37) Five wax bars (25 mm?150 mm) were dipped in pattern wash, rinsed with water and left to dry in a temperature controlled room (airflow 0.6 m/s; humidity 45% RH; temperature 25? C.). Each bar was then dipped in the test slurry composition following the dipping protocol set out in Table 5 to form a shell. A total of 9 slurry coats were applied to each wax bar. The first 8 coats were each followed by a stucco coat. Each layer (slurry+stucco) was left to dry for approximately 1 hour before applying a further coat on top. A prime coat was not applied to the wax patterns for shell testing.

(38) TABLE-US-00005 TABLE 5 Type of dip Stucco used Coats Backup coat Calcined kaolin 8 aluminosilicate, 48% alumina (Remasil? 50; 16-30 mesh; Remet UK Ltd) Seal coat None 1

(39) MOR, thickness and force of break measurements were carried out on each coated wax bar when green (air dried), hot (immediately after firing at 1000? C.) and cold (once cooled to room temperature after firing).

2.1.2 Method

(40) Testing was carried out in accordance with BSI BS 1902-4.4:1995 and BS EN 993-6:1995.

(41) A flat, rectangular shell sample from the top or bottom of each wax bar was removed and used for MOR testing. The width was measured in two places and an average taken. Samples of the shell were tested to rupture in a three point bending test by placing the shell sample between on two support beams (fixed span), and applying a load uniformly from above the sample. The load at fracture was recorded and the surface area of the fracture was measured in two places and an average taken. MOR was calculated as follows: MOR=3?(load at rupture)?span)/(2?(width)?(thickness).sup.2 and the results are shown in FIG. 1. The shell thickness of each sample was measured and the results are shown in FIG. 2.

(42) Force of break testing was carried out on a Lloyd Instruments LRX tensile testing device (model TG18) fitted with a calibrated 2500N load cell. The force of break results are shown in FIG. 3.

(43) The results show that the strengths for shells made from slurries comprising 0.1% and 0.2% MFC in the binder exhibited some improvement compared to the conventional slurry formulations with no MFC. In view of the results, further tests were carried out on slurry formulations comprising 0.3% of MFC.

2.2 Lab Scale Trials (0.3% MFC in Binder)

2.2.1 Sample Preparation

(44) Example formulation 3 was prepared as set out in Table 2 to a viscosity of 25 seconds.

(45) Five wax bars (25 mm?150 mm) were dipped in pattern wash, rinsed with water and left to dry in a temperature controlled room (airflow 0.6 m/s; humidity 45% RH; temperature 25? C.). Each bar was then dipped in the test slurry composition comprising 0.3% MFC (see Table 2) following the dipping protocol set out in Table 6 below to form a shell.

(46) TABLE-US-00006 TABLE 6 Example Example Conventional Conventional formulation 3 formulation 3 Type of dip Stucco used (no MFC) (no MFC) (0.3% MFC) (0.3% MFC) Backup coat Calcined kaolin 8 5 8 5 aluminosilicate, 48% alumina (Remasil? 50; 16-30 mesh; Remet UK Ltd) Seal coat None 1 1 1 1

(47) The tests were carried out on each coated wax bar when green (air dried), hot (immediately after firing at 1000? C.) and cold (once cooled to room temperature after firing).

2.2.2 Results

(48) The MOR, thickness and force of break results are shown in FIGS. 4-6.

(49) The results show a significant increase in shell thickness for the same number of coats for slurry compositions comprising 0.3% MFC, compared to the conventional slurry composition. For example, an average of about 30% increase in shell thickness for 9 coats, and about 16% increase in shell thickness for 6 coats.

(50) The force of break is also significantly improved for shells made from slurries comprising 0.3% MFC in the binder, compared to shells made from conventional slurries. For example, on average 40% more force is required to break a green shell having 8 back up coats and 1 seal coat prepared from a slurry comprising 0.3% MFC in the binder compared to a conventional slurry that does not comprise MFC in the binder. For a hot shell, on average 23% more force is required to break the shell.

2.3 Compositions Comprising 0.4% MFC in Binder

(51) The investment casting shell formulation of Example formulation 3 was prepared, except with 0.4% MFC in the binder. The slurry produced investment casting shells with a significantly increased shell build compared to the conventional slurry, e.g. around 68% increase for 3 coats and around 76% increase for 4 coats (see FIG. 7). However, the slurry was found to have inconsistent working characteristics and did not cover the wax bars as effectively as compositions comprising 0.3% MFC in the binder.

Example 3Permeability Testing

3.1 Sample Preparation

(52) Example formulations 1.2 and 3 were prepared according to Table 1. Slurries of Example formulations 1 and 2 were tested at viscosities of 25 seconds and 30 seconds respectively. A conventional slurry and a slurry comprising Example formulation 3 (Table 2) was also prepared to a viscosity of 25 seconds.

(53) The BSI (BS 1902: Section 10.2:1994) approved method for permeability testing was followed.

(54) Five plastic ping-pong balls were attached to hollow glass rods (impervious mullite) and the junction between rod and ball sealed with wax. The ping-pong balls were then dipped in the test slurry following the dipping protocol set out in Table 7 below to form a shell and left to dry in a temperature controlled room (airflow 0.6 m/s; humidity 45% RH; temperature 25? C.).

(55) TABLE-US-00007 TABLE 7 Type of dip Stucco used Coats Backup coat Calcined kaolin 4 aluminosilicate, 48% alumina (Remasil 50; 16-30 mesh; Remet UK Ltd) Seal coat None 1

(56) Each coated ball was fired up to a temperature of 1000? C., to burn out the ping-pong ball from the shell. To minimise shell cracking during the firing process, the temperature was increased using the heating ramp rate shown in Table 8.

(57) Permeability of each shell was measured by passing nitrogen gas (1.05 PSI) through the glass rod and through the shell sample, and the flow rate was calculated in ml/min. The sample was then broken and the average thickness measured. The permeability constant (K) was calculated as follows: K=dV/ptA, where d is the shell thickness (cm). V is the volume of gas (ml), p is the pressure drop across the shell (cmH2O), t is time (seconds) and A is the internal area of the ball, minus the area of rod inserted (cm.sup.2).

(58) Permeability was tested immediately after firing at 1000? C. (hot). After firing, the balls were allowed to cool for 24 hours at room temperature and permeability was retested (cold).

(59) TABLE-US-00008 TABLE 8 Temperature (? C.) Hold time minutes 250 60 350 60 500 60 750 60 1000 60

3.2. Results

(60) The results of the permeability tests for the shell room trials for slurries comprising 0.1%, 0.2% and 0.3% MFC in the binder (Example formulations 1-3) compared to conventional slurries are shown in FIGS. 8A (hot) and 8B (cold).

(61) The results show an increase in permeability for slurries of the same viscosity as the concentration of MFC increases. This result may be explained by the fact that MFC is an organic material which burns out at elevated temperatures, thus leaving voids in the shell matrix and increasing permeability in the hot and cold shells.

Example 4Comparison with Slurries Comprising Fibres Having a Diameter on the Micron Scale

(62) A slurry was prepared according to formulation 3, except that instead of 0.3% MFC, 0.3% of nylon fibre (12.4 kg) having an average diameter of 52 ?m and an average length 0.5 mm was used. MOR, thickness and force of break measurements were taken according to the methods described in Example 2. The results are shown in FIGS. 9-11. The results show that in contrast to MFC, the addition of fibres having a diameter in the micron range does not significantly improve shell build or break strength.

Example 5Analysis of Slurry Properties

(63) Example formulation 3 and a conventional slurry comprising no MFC were prepared according to Table 2, and the properties of the slurries were evaluated using the protocols described below. The results are shown in Table 9.

5.1. Slurry Analysis

(64) % total solidsa measure of all active ingredients in the slurry, i.e. all the slurry components with the water removed. The total solids in the slurry was determined using a moisture balance (Mettler MJ33). A sample of slurry was dried at 140? C., until a stable weight was achieved and the percentage of solids calculated. Alternatively, this measurement may be taken by oven drying the sample at 140? C., for around an hour and calculating the percentage solids.

(65) Slurry densitydefined as the specific gravity (SG) of the slurry, i.e. the ratio of the density of the slurry material compared to water. SG was measured using a hydrometer or by weighing a sample of slurry and comparing to a sample of water.

5.2 Binder Analysis

(66) To test the properties of the binder in the slurry, a slurry sample was centrifuged at 4600 rpm for around 30 minutes, decanted into a fresh vial and centrifuged again at 4600 rpm for around 30 minutes. The supernatant binder was retrieved from the top of the vial. The binder properties were evaluated using the protocols described below.

(67) % binder solidsmeasured in the same way as described for the % total solids but using a sample of the binder supernatant.

(68) % silicameasured by loss on ignition. A sample of binder supernatant was fired at 980? C., for 60 minutes and calculating the percentage of silica residue directly. Alternatively, the percentage silica can be found by measuring the specific gravity (SG) of the binder supernatant, e.g. using a volumetric flask and a precision balance, and the SG measurement can be converted to percentage silica by looking up the conversion in the appropriate table.

(69) % polymer solidscalculated as the difference between the binder solids at 140? C., and the percentage silica measured by loss on ignition. The % polymer concentrate is twice the percentage of polymer solids.

(70) Bacteria countmeasured by taking a sample of the supernatant binder, pipetting onto a culture slide and incubating at 30? C., for 48 hours. Bacterial infection, if present, would have shown on the culture slides as stains which can be compared to a standard control slide.

(71) Binder viscositymeasured using a Brookfield Viscometer (60 rpm, 23-25? C.).

(72) Accelerated gel testa test to simulate accelerated aging of the slurry and therefore gelation. The binder supernatant was held at 60? C., for 48 hours in an air tight bottle (equivalent to around 1 month at room temperature). A pass was recorded if there was no significant change in viscosity.

(73) 5.3 Results

(74) TABLE-US-00009 TABLE 9 Conventional Example formulation 3 Test Slurry (0.3% MFC) Difference pH 9.81 9.88 0.07 Silica (%) 27.39 26.81 0.17 Binder solids (%) 30.51 30.68 1.5 Polymer solids (%) 3.12 3.87 3.69 Polymer concentrate 6.24 7.74 0.62 (%) Viscosity Zahn #4 19.09 22.78 3.69 (seconds) Slurry solids (%) 75.37 74.75 0.62 Slurry density (g/cc) 1.6364 1.6358 0.001 Binder viscosity 60 5.07 4.85 0.22 rpm Accelerated gel test Pass Pass Bacteria count Nil Nil

(75) The results show that the presence of MFC in the binder increases the viscosity of the slurry significantly, with a difference of nearly 4 seconds between Example formulation 3 and the conventional slurry.

(76) The results from the binder viscosity tests indicate that MFC material is not present in the binder after centrifugation. In contrast, casting shell binders comprising fibres having diameters on the micro to milli scale are not removed by centrifugation, thus impacting slurry testing and preventing accurate measurements.

Example 6Warehouse Scale Method

6.1 Binder Preparation

(77) The binder used for the preparation of Example formulation 5 (see Table 4) was prepared in the warehouse as follows.

(78) 7.2 kg of MFC was blended into deionised water (19.2 kg) using a homogeniser (SilversonX, L4RT). The blend was then decanted into two containers. A 240 kg drum was placed on a pump truck with electronic scales and 192 kg of colloidal silica (Remasol? SP30, Grace GMBH) was decanted into the drum. Using an electric stirrer (Bosch? Professional. GRW12E), the blend of MFC and deionised water was added slowly to the colloidal silica in the drum and stirred for 10-15 minutes. Adbond? BV polymer (Remet Corporation) or Lipaton SB 5843 (Synthomer plc) was then added slowly to the drum and stirring continued for a further 15-20 minutes. 1.2 kg of the anti-foaming agent, (Fumexol? 100, Huntsman Textile Effect, or Burst 100. Remet Corporation) was added and the mixture stirred for a further 5 minutes. 1.2 kg of biocide (Acticide? MBS 50:50 1,2-Benzisothiazol-3(2H)-one:2-methyl-2H-isothiazol-3-one; Thor Specialities) was then added and the mixture stirred for a further 5 minutes. Stirring was continued for another 15 minutes until the slurry was completely mixed. A sample of the binder was taken for testing.

6.2 Binder Analysis

(79) The properties of the slurry were evaluated using the protocols described in Example 5 and the results are shown in Table 10.

(80) TABLE-US-00010 TABLE 10 Test Example formulation 5 pH 10.24 Silica (A) 23.12 Binder solids (%) 28.74 Polymer solids (%) 5.62 Polymer concentrate (%) 11.24 Binder density (g/cc) 1.157 Accelerated gel test Pass Bacteria count Nil

Example 7Effect of Polymer Concentration

(81) To assess the effect of the polymer concentration on shell build thickness, slurries were prepared having 6% 3% and 0% styrene butadiene polymer (Adbond? BV, Remet Corporation or Lipaton SB 5843, Synthomer plc) in the binder. MOR, shell thickness and force of break testing was carried out at green and hot (1000? C.)see Example 2 for sample preparation and test protocols. The results are shown in FIGS. 12-14.

(82) The results show an increase in shell thickness when the concentration of polymer is increased from 0% to 12%. The green shell force of break strength is also increased when the concentration of polymer in the binder is increased from 0% to 12%.

Example 8Effect of the Refractory Material

(83) To assess the effect of the refractory material on the shell build thickness, casting shell slurries were prepared using a wide distribution silica refractory (EZ Cast?; Remet UK Ltd). The particle size distributions of fused silica 200 mesh, fused silica 270 mesh and the wide distribution fused silica are shown in FIG. 15. Particle size distributions were measured on a Malvern Mastersizer 3000.

(84) MOR, shell thickness and force of break testing was carried out at green and hot (1000? C.)see Example 2 for sample preparation and test protocols. The results are shown in FIGS. 16-18.

(85) The results show that using a wide distribution silica refractory in combination with 0.3% MFC in the binder increases the shell build by over 40% compared to a conventional slurry. The force required to break the shell is also increased by up to 30% for the green shell, and up to 10/o for the hot shell.

Example 9Binder Viscosity Testing

(86) Binder viscosity tests were carried out to compare binders comprising varying concentrations of MFC in the binder (0%, 0.225%, 0.25% and 0.275%). The tests were repeated 5 times for each binder system and the results are shown in FIG. 19. The results show that the viscosity of the binder increases proportionally with increased concentration of MFC.

Example 10Slurry Rheology

(87) The effect of MFC on the rheology of investment casting shell binders was investigated. Five different binder systems were prepared as set out in Table 11.

(88) TABLE-US-00011 TABLE 11 Percentage Binder system Binder components amount (%) Binder system 1 Colloidal silica (Remasol? SP-30, Grace 100 GMBH) Binder system 2 Colloidal silica (Remasol? SP-30, Grace 97 GMBH) MFC (Exilva?, P 01-V; 10%; Borregaard) 3 Binder system 3 Colloidal silica (Remasol? SP-30, Grace 88 GMBH) Styrene butadiene copolymer (Lipaton SB 12 5843; Synthomer plc) * Binder system 4 Colloidal silica (Remasol? SP-30, Grace 85 GMBH) MFC (Exilva?, P 01-V, 10%; Borregaard) 3 Styrene butadiene copolymer (Lipaton SB 12 5843; Synthomer plc) * Binder system 5 Colloidal silica (Remasol? SP-30, Grace 82 GMBH) MFC (Exilva?, P 01-V, 10%; Borregaard) 3 Styrene butadiene copolymer (Lipaton SB 12 5843; Synthomer plc) * Wetting agent (Wet-in?; Remet 2.4 Corporation) # Anti-foaming agent (Burst 100; Remet 0.6 Corporation) {circumflex over ()} * Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation). {circumflex over ()} Burst 100 may he replaced with an equal amount of Fumexol? (Huntsman Textile Effect). # Wet-in? may be replaced with an equal amount of Victawet? 12 (ILCO Chemie).

(89) The viscosity of the binder systems as a function of shear rate was tested using an MCR 92 rheometer (Anton-Paar GmbH). The results are shown in FIG. 20.

(90) All of the binder systems which did not include MFC showed Newtonian or almost Newtonian behaviour. On the other hand, binder systems that included MFC showed a shear dependent drop in viscosity.

Example 11Stability

(91) The chemical stability of the binder used for formulation 3 comprising 0.3% MFC was compared to an equivalent binder instead comprising 0.3% of nylon fibre (average diameter 52 m; average length 0.5 mm).

(92) The binders were subjected to an accelerated gel test, wherein the supernatant binder was placed in an air tight bottle and held at 60? C., in an oven.

(93) The results are shown in Table 12 below.

(94) TABLE-US-00012 TABLE 12 Binder Observations Binder of formulation 3 (0.3% MFC) No gelation after 71 days; no fibre drop out Binder of formulation 3 (0.3% MFC No gelation after 41 days; replaced with 0.3% nylon fibre) fibres drop out of suspension after a few hours

Example 12Polymer Type

(95) Casting shell slurries of Example formulation 3 (see Example 1) were prepared with binder systems having two different styrene polymers.

(96) The thickness and force of break results are shown in FIGS. 21 and 22. Polymer is styrene acrylate polymer (Ravasol SA-1; Ravago? Chemicals Ltd). Polymer 2 is a styrene butadiene polymer (Adbond? BV Remet Corporation or Lipaton SB 5843, Synthomer plc). Both binder systems demonstrated an improvement in shell thickness and strength compared to the conventional slurry formulation with no MFC.

Example 13Comparison of MFC with Fibrillated High-Density Polyethylene (fHDPE)

(97) A series of three casting shell slurries were Compared. The tested slurries are those setout in Table 13.

(98) TABLE-US-00013 TABLE 13 No fibrils MFC fHDPE Ingredients slurry (g) slurry (g) slurry (g) 200 mesh fused silica (Imerys 700 700 700 Fused Minerals) Colloidal silica (Remasol? 350 350 350 SP-30; Grace GMBH) Styrene butadiene copolymer 50 50 50 (Lipaton SB 5843; Synthomer plc)* Wetting agent (Victawet? 12; 10 10 10 ILCO Chemie) Anti-foaming agent 2.5 2.5 2.5 (Burst 100; Remet Corporation) Fibrils None 12.4 (MFC) 1.24 (fHDPE) MFC refers to Exilva? P 01-V, 10% concentration obtained from Borregaard. *Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation). # Victawet? 12 may be replaced with an equal amount of Wet-in? (Remet Corporation).
fHDFP refers to Short Stuff? Fibrillated HDPE fibres (#ESS50F) obtained from Minifibers Inc. Johnson City TN, USA. Short Stuff? fibres (#ESS50F) have an average fibre length of ?0.1 mm and a diameter of 5 ?m. Also available are Short Stuff? fibres (#ESS5F), which also have an average fibre length of ?0.1 mm and a diameter of 5 ?m, which are said to have reduced dispersion in low shear aqueous systems.

(99) MOR testing was carried according to Example 2, section 2.1. The MOR, thickness and force of break results are shown in FIGS. 23-25.

(100) Results from the MOR testing demonstrated that there was no improvement on MOR strength when fHDPE was added to the slurry without fibrils. A small increase in the thickness of the shell build can be seen with a slurry with fHDPE compared to a slurry without fibrils, but this increase is not as significant as the increase seen with the slurry with MFC.

(101) The properties of the three slurries were analysed according to Example 5. The results are shown in Table 14.

(102) TABLE-US-00014 TABLE 14 Test No fibrils slurry MFC slurry fHDPE slurry pH 9.81 9.88 10.09 Silica % 27.39 26.81 27.47 Binder solids (%) 30.51 30.68 31.06 Polymer Solids (%) 3.12 3.87 3.59 Polymer Concentrate 6.24 7.74 7.18 (%) Viscosity (Seconds) 19.09 22.78 20.97 Zahn #4 Slurry Solids (%) 75.37 74.75 75.02 Slurry Density (g/cc) 1.6364 1.6358 1.6102 Accelerated Gel Test Pass Pass Pass Bacteria Count Nil Nil Nil

(103) The results suggest that the MFCs are centrifuged out along with the refractory material. This can be seen as the binder results between the no fibrils slurry and the MFC slurry were consistent. The MFC and fHDPE fibres both increased the viscosity providing a difference of nearly 4 seconds between the no fibrils slurry and the MFC slurry, and nearly 2 seconds between the no fibrils slurry and the fHDPE slurry.

(104) FIG. 26 illustrates the viscosities of the binder samples prepared as a function of shear rate. Binders 1-5 are as set out in Table 11. Binders 6-9 are as set out in Table 15.

(105) TABLE-US-00015 TABLE 15 Percentage Binder system Binder components amount (%) Binder system 6 Colloidal silica (Remasol? SP-30, 99.7 Grace GMBH) fHDPE (Short Stuff? Fibrillated 0.3 HDPE fibres; # ESS5F; Minifibers, Inc) Binder system 7 Colloidal silica (Remasol? SP-30, 99.7 Grace GMBH) fHDPE (Short Stuff? Fibrillated 0.3 HDPE fibres; # ESS50F; Minifibers, Inc) Binder system 8 Colloidal silica (Remasol? SP-30, 87.7 Grace GMBH) Styrene butadiene copolymer (Lipaton 12 SB 5843; Synthomer plc) * fHDPE (Short Stuff? Fibrillated 0.3 HDPE fibres; # ESS5F; Minifibers, Inc) Binder system 9 Colloidal silica (Remasol? SP-30, 87.7 Grace GMBH) Styrene butadiene copolymer (Lipaton 12 SB 5843; Synthomer plc) * fHDPE (Short Stuff? Fibrillated 0.3 HDPE fibres; # ESS50F; Minifibers, Inc) * Lipaton SB 5843 may be replaced with an equal amount of Adbond? BV (Remet Corporation).

(106) FIG. 26 shows that the addition of fHDPE fibres to SP30 results in a limited increase in viscosity at very low shear rates. However, this effect is not nearly as apparent when compared to the addition of MFC to SP30, where the binder mixture showed obvious shear thinning behaviour. Furthermore, the addition of styrene butadiene copolymer to the mixtures containing fHDPE seemed to eliminate the viscosity-modifying effect contributed by the fHSPE fibres, whereas SP30 mixtures containing MFC and styrene butadiene copolymer are able to retain their shear thinning properties.

(107) FIG. 27 shows plots of shear stress vs shear rate for the binder samples. The data show that all the samples containing fHSPE fibres exhibited Newtonian or almost Newtonian behaviour, whereas samples with MFC exhibited a more pseudoplastic or shear thinning behaviour.