COMPOSITION, CORE AND MOULD FOR CASTING AND MOULDING PROCESSES

Abstract

A composition for making a core for use in a moulding or casting process, a core comprising said composition, and a mould for producing an article by high pressure die casting or semi-solid casting. The composition comprises a particulate refractory material, a binder composition comprising at least one hydrophilic polymer, comprising at least one polysaccharide or polysaccharide derivative; and at least one pozzolanic additive. The mould comprises a core for defining an internal cavity of the article and the core comprises a solidified core composition. The solidified core composition comprises a particulate refractory material and a binder composition, degrades in water such that a cylinder of the solidified core composition having a maximum height of 80 mm and a maximum diameter of 50 mm disintegrates in no more than 10 minutes when immersed in water at a temperature of 20° C. and stirred at a speed of 60 rpm, and has a flexural strength of at least 300 N/cm.sup.2. The invention also resides in a method for producing an article by high pressure die casting or semi-solid casting.

Claims

1. A composition for making a core for use in a molding or metal casting process, the composition comprising: a particulate refractory material; a binder composition comprising at least one hydrophilic polymer, wherein the at least one hydrophilic polymer comprises at least one polysaccharide or polysaccharide derivative; and at least one pozzolanic additive.

2. The composition of claim 1, wherein the composition comprises at least 1 wt % of the binder composition, and at least 1 wt % of the pozzolanic additive, relative to the weight of the refractory material.

3. The composition of either claim 1, wherein the at least one hydrophilic polymer comprises at least one synthetic polymer having a molecular weight of no more than 1,000,000 g/mol and/or selected from the group consisting of polyacrylates, polymethacrylates, polyphosphates, polymetaphosphates, polyvinyl alcohol, alkali polyacrylate salts, alkali polyphosphate salts, and mixtures thereof.

4-5. (canceled)

6. The composition of claim 1, wherein the at least one polysaccharide or polysaccharide derivative is selected from the group consisting of: starches, starch derivatives, potato starch, dextrin cellulose, cellulose derivatives, carboxymethyl cellulose, and mixtures thereof.

7-9. (canceled)

10. The composition of claim 1, wherein the at least one hydrophilic polymer does not undergo cross-linking when the composition is heated to a temperature from 200 to 350° C.

11. The composition of claim 1, wherein the binder composition further comprises at least one plasticiser plasticizer comprising at least one polyol or polyol derivative.

12. (canceled)

13. The composition of claim 1, further comprising at least one surfactant selected from the group consisting of: anionic, cationic, non-ionic and amphoteric surfactants, sulphates, methosulphates, linear alcohol sulphates, sulphonates, sulphosuccinates, phosphate esters, glucosides, 2-ethylhexyl sulphosuccinate, 2-ethylhexyl sulphate, dodecylbenzene sulphonate, nonylphenol sulphate, sodium laureth sulphate, 3-ethylhexyl phosphate ester, undecyl amido propyl trimethyl ammonium methosulphate, alkyl polyglycol ether ammonium methosulphate, 2-ethylhexyl glucoside, hexyl glucoside, and mixtures thereof.

14-15. (canceled)

16. The composition of claim 1, wherein the at least one pozzolanic additive comprises spherical particles and/or cenospheres, and/or has a D50 particle diameter of no more than 20 μm and/or is selected from the group consisting of silica fume, fly ash, rice husk ash, diatomaceous earth, volcanic ash, metakaolin, and mixtures thereof.

17-18. (canceled)

19. The composition of claim 1, wherein the particulate refractory material has a D50 particle diameter of at least 50 μm and/or comprises one or more of: sand; quartz sand; spherical particles and/or cenospheres; and fly ash.

20. (canceled)

21. A core comprising the composition of claim 1.

22. The core of claim 21, wherein the core is coated with a surface coating comprising boron nitride, silicate, titania, alumina, zirconia, or mixtures thereof.

23. A mold comprising the core claim 21, wherein the mold is for producing an article by metal casting and the core is for defining an internal cavity of the article, wherein the mold is for high pressure die casting or semi-solid casting.

24. (canceled)

25. The mold according to claim 23, wherein the solidified core composition degrades in water such that a cylinder of the solidified core composition having a maximum height of 80 mm and a maximum diameter of 50 mm disintegrates in less than 10 minutes when immersed in water at a temperature of 20° C. and stirred at a speed of 60 rpm, and wherein the solidified core composition has a flexural strength of at least 300 N/cm.sup.2.

26. The mold of claim 25, wherein the cylinder of solidified core composition disintegrates in water in less than 10 minutes after being heated to a temperature from 200 to 350° C.

27. A method for producing an article by high pressure die casting or semi-solid casting, the method comprising the steps of: (i) mixing a composition according to claim 1 to form a mixture; (ii) molding and hardening the mixture to produce a core in the shape of an internal cavity of the article; (iii) assembling the core with a mold for high pressure die casting or semi-solid casting, such that the mold and the core together define a casting cavity; (iv) injecting molten or semi-solid metal into the casting cavity until the cavity is filled; (v) cooling and solidifying the molten or semi-molten metal to form the article, the core being contained within the internal cavity of the article; (vi) removing the article containing the core from the mold; and (vii) removing the core from the internal cavity by flushing out with water.

28. The method of claim 27, further comprising a step of coating the core with a surface coating prior to assembling the core with the mold.

29. The method of claim 27, wherein the step of molding and hardening the mixture includes drying the mixture; and/or includes compacting the mixture into a core mold; and/or is performed using a core-shooting apparatus; and/or includes producing the core by an additive manufacturing or 3D printing process.

30-32. (canceled)

33. Use of a composition according to claim 1 in a molding process or a metal casting process.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0119] FIG. 1a is a schematic view of a high pressure die casting mould in accordance with an embodiment of the present invention, in an open position;

[0120] FIG. 1b is a schematic view of the high pressure die casting mould shown in FIG. 1a, in a closed position.

DETAILED DESCRIPTION

[0121] FIG. 1a shows an example of a high pressure die casting mould 100 according to an embodiment of the present invention, in an open position. The mould 100 comprises a first die 2 mounted on a fixed plate 4 and a second die 3 mounted on a movable plate 6. A core 8 in accordance with the present invention is assembled on the first die 2. In use, the movable plate 6 is moved towards the fixed plate 4, bringing the dies 2, 3 together into a closed position (shown in FIG. 1b). A casting cavity 10 is defined between the dies 2, 3 and the core 8.

[0122] The mould 100 also comprises an injection system 12 for injecting molten metal 14 into the casting cavity 10. The injection system 12 comprises a chamber 16 for holding the molten metal 14 and a piston 18 for pushing the molten metal 14 through the chamber 16 and into the casting cavity 10, via a gate 20 defined between the first and second dies 2, 3. Molten metal may be supplied to the injection system by any appropriate means, e.g. by immersing in a basin or crucible of molten metal. In the embodiment illustrated in FIGS. 1a and 1b, molten metal 14 is supplied to the injection system 12 by pouring molten metal 14 from a ladle or pouring cup 22 into the chamber 16, via an opening 24 in the chamber 16.

[0123] The injection system 12 fills the casting cavity 10 extremely quickly, within seconds or even milliseconds, and continues to apply pressure to the metal until the metal has solidified. The metal may be rapidly cooled by a water cooling system, which comprises a series or network of water cooling pipes 26 extending through the dies 2, 3, in order to accelerate solidification of the metal. Once the metal has solidified, the movable plate 6 is retracted, separating the dies 2, 3 and opening the mould 100. The solidified casting may then be ejected from the mould by ejector pins 28, which push the casting out of the die 3.

[0124] At this stage, the core 8 will still be contained within the casting. In accordance with the present invention, the core 8 is made from a composition which disintegrates in water and can be readily removed from the casting by simply flushing out with water.

EXAMPLES

Example 1

[0125] The following example compositions were initially prepared:

TABLE-US-00001 TABLE 1 Composition 1 2 3 4 5 Sand Quartz Quartz Quartz Quartz Quartz Binder composition Water .sup.a 29.6 50.9 43.6 43.5 Sucrose .sup.a 62.7 Sodium 4- 0.1 (methoxycarbonyl) phenolate .sup.a Sodium 21.8 29.1 29.1 polyphosphate .sup.a,c (Budit 4H) Sodium 69.65 polyacrylate .sup.a,d (Dispex AA4135) Dextrin .sup.a,d 29.85 (P623/4) Carboxymethyl 7.6 13.65 13.65 13.65 cellulose ª Potato Starch .sup.a 13.65 13.65 13.65 (Honig) Dodecylbenzene 0.1 sulphonate .sup.a (Sermul EA88) 2-Ethylhexyl 0.50 sulphosuccinate ª (Serwet WH175) Total .sup.b 3.03 11.00 11.00 11.00 5.00 Pozzolanic additive Fly ash .sup.b 2.00 (Microsit H10) .sup.a wt % relative to total weight of binder composition, .sup.b wt % relative to weight of sand, .sup.c polymer chain length 30, .sup.d aqueous solution, 40% w/v solids content

[0126] A Laempe L1 laboratory-type core-shooting apparatus was used to produce hardened cores from each of example compositions 1-5. The core-shooting apparatus was set with a shooting time of 1-2 seconds and shooting pressure of 4 bar. If needed, the cores were purged with heated air at 120° C. for 60-300 seconds. The core box temperature was set at 140° C. The cores were produced in a generally cylindrical shape having a maximum diameter of 50 mm and a total height of 80 mm, with a 30 mm frustonical portion at one end tapering to a minimum diameter of 40 mm. The example compositions were also used to make transverse bars having dimensions of 180×22.4×22.4 mm, for bending strength measurements.

[0127] The cylindrical cores and transverse bars made using example compositions 1-5 were tested for bending strength and water solubility both immediately after production (as received) and after heating for 2 hours at 120, 140, 160, 180, 200, 220 or 240° C., to simulate a range of temperatures that the core might be exposed to in use.

[0128] The bending strength of the transverse bars was measured with a three-point bending test at room temperature.

[0129] The water solubility of the cores was determined qualitatively by suspending a core inside a box, filling the box with water at room temperature until the core was fully immersed in the water, then draining the water from the box and observing how much of the suspended core material had disintegrated.

[0130] Example compositions 3-5 were also tested for flowability using a Brookfield Powder Flow Tester. The unconfined failure strength of the composition was measured at 0.60, 1.13, 2.19, 4.35 and 8.70 kPa.

[0131] The results are shown in Table 2:

TABLE-US-00002 TABLE 2 Composition 1 2 3 4 5 Bending strength N/cm.sup.2 As received 120-140 270 304 269 372 120° C. 60 225 183 225 278 140° C. 20 215 143 177 297 160° C. 10 200 149 204 228 180° C. 100 175 136 208 261 200° C. 120 230 124 192 286 220° C. n/a n/a 119 196 238 240° C. n/a n/a 95 182 260 Water solubility As received excellent excellent excellent excellent excellent 120° C. excellent excellent excellent excellent excellent 140° C. excellent excellent excellent excellent excellent 160° C. good excellent excellent excellent excellent 180 ºC bad excellent excellent excellent excellent 200° C. bad excellent excellent excellent excellent 220° C. bad excellent excellent excellent excellent 240° C. bad excellent excellent excellent excellent Flowability 0.60 kPa n/a n/a 0.613 0.485 0.304 1.13 kPa n/a n/a 0.976 0.691 0.413 2.19 kPa n/a n/a 1.574 1.047 0.535 4.35 kPa n/a n/a 2.335 1.47 0.671 8.70 kPa n/a n/a 3.392 2.2 0.9075 Environmentally yes no no no yes friendly

[0132] Example composition 1, comprising sucrose and carboxymethyl cellulose as hydrophilic polymers, achieved good water solubility up to 160° C. However, the sucrose caramelised above 160° C., drastically reducing the water solubility, and the cores were relatively weak, with flexural bending strengths significantly lower than 200 N/cm.sup.2.

[0133] Cores made using the polyphosphate-based compositions, example compositions 2-4, achieved excellent water solubility even after heating at temperatures up to 240° C. for 2 hours, and good flexural strength. Example composition 4, which comprised a small amount of surfactant but was otherwise identical to example composition 3, showed improved flexural strength after heat treatment, as well as improved flowability.

[0134] Example composition 5, comprising sodium polyacrylate and dextrin as hydrophilic polymers together with a small amount of surfactant, achieved good flexural strength, water solubility and flowability—even after heating at up to 240° C. for 2 hours—as well as being environmentally friendly. This composition was therefore selected as a basis for further tests.

Example 2

[0135] Further compositions were prepared based on example composition 5, comprising the same components and in the same quantities, but with varying proportions of sodium polyacrylate and dextrin.

[0136] Cores made using these compositions were tested for bending strength and flowability using the same procedures as described in Example 1.

[0137] Water solubility was measured semi-quantitatively using a similar procedure to the procedure described in Example 1. A core was suspended inside a box and the box was filled with water at room temperature until the core was fully immersed. The core was then gently shaken and the time taken for the core to completely disintegrate was observed.

[0138] The results are shown in Tables 3a and 3b:

TABLE-US-00003 TABLE 3a Composition 6 7 8 9 10 Sodium 0 10 20 30 40 polyacrylate .sup.a, b Dextrin .sup.a, b 100 90 80 70 60 Bending strength N/cm.sup.2 As received 228 ± 19 235 ± 12 268 ± 9 310 ± 7 295 ± 6 Water solubility seconds As received  5-10  5-10  5-10  5-10  5-10 140° C. 20-30 15-25 10-15 10-15 15-25 200° C. 150-180 n/a n/a n/a n/a Flowability 0.60 kPa 0.450 0.429 0.388 0.411 0.384 1.13 kPa 0.627 0.600 0.579 0.570 0.564 2.19 kPa 0.841 0.800 0.803 0.748 0.732 4.35 kPa 1.112 1.021 1.021 0.959 0.923 8.70 kPa 1.371 1.359 1.334 1.142 1.136 .sup.a wt % relative to total weight of sodium polyacrylate and dextrin, .sup.b aqueous solution, 40% w/v solids content

TABLE-US-00004 TABLE 3b Composition 11 12 13 14 15 16 Sodium 50 60 70 80 90 100 polyacrylate .sup.a, b Dextrin .sup.a, b 50 40 30 20 10 0 Bending strength N/cm.sup.2 As received 316 ± 9   391 ± 26  410 ± 19  374 ± 38  313 ± 9  264 ± 40  Water solubility seconds As received 5-10 10-15 10-15 20-25 10-15 20-30 140° C. 5-10  5-10 20-30 20-30 20-25 20-25 200° C. n/a 50-60 15-25 30-40 30-40 30-40 Flowability 0.60 kPa 0.403 0.42 0.413 0.423 0.402 0.395 1.13 kPa 0.567 0.561 0.556 0.574 0.555 0.558 2.19 kPa 0.729 0.708 0.717 0.722 0.713 0.721 4.35 kPa 0.9 0.861 0.871 0.874 0.886 0.889 8.70 kPa 1.089 1.033 1.053 1.055 1.061 1.076 .sup.a wt % relative to total weight of sodium polyacrylate and dextrin, .sup.b aqueous solution, 40% w/v solids content

[0139] Each of the cores made with example compositions 6-16 showed reasonable flexural strength of at least 200 N/cm.sup.2. The cores comprising 30-100 wt % sodium polyacrylate showed good flexural strength of around ≥300 N/cm.sup.2, while the cores comprising 60-80 wt % sodium polyacrylate in particular showed very good flexural strength of around ≥400 N/cm.sup.2.

[0140] Each of the cores showed very good water solubility as received. However, after heating for 2 hours at 200° C. the cores comprising 10-50 wt % sodium polyacrylate only weakened in water and did not disintegrate, so these compositions would only be suitable for lower temperature applications. The cores comprising 60-100 wt % sodium polyacrylate showed good water solubility even after heating for 2 hours at 200° C., with the core comprising 70 wt % sodium polyacrylate showing particularly good water solubility.

[0141] Each of the compositions showed acceptable flowability, with the compositions comprising 50-100 wt % sodium polyacrylate showing particular good flowability.

[0142] The composition comprising 70 wt % sodium polyacrylate (corresponding to example compositions 5 and 13) was selected as a basis for further testing against several other binder combinations.

Example 3

[0143] Cores were prepared using the following compositions and tested for flexural strength and water solubility on the cores as received (without exposure to heat). Flexural strength was tested using the same methodology described in Example 1.

[0144] Water solubility was measured quantitatively. A large beaker was placed on a set of scales and the scales were tared. The core was mounted onto the end of a rotor shaft and lowered into the beaker such that the core was suspended above the base of beaker and did not weigh on the scales. The container was then filled with water to fully immerse the core, and the core was rotated on the rotor shaft to stir the water. The weight displayed on the scales was observed to determine the time taken for the core to completely disintegrate and fall into the container. This experiment was performed under two different conditions: 1) stirring rotation speed 60 rpm and water temperature 20° C.; and 2) stirring rotation speed 150 rpm and water temperature 65° C.

[0145] The results are shown in Table 4:

TABLE-US-00005 TABLE 4 Composition 17 18 19 20 21 Sand Quartz Quartz Quartz Quartz Quartz Binder composition Water .sup.a 4.5 Sodium polyacrylate .sup.a,d 69.65 (Dispex AA4135) Dextrin .sup.a,d 29.85 (P623/4) Sodium silicate/lithium 90.0 silicate .sup.a,f (ZSE 874) Potassium silicate .sup.a,f 5.0 (K-silicate 42/43) Phenol formaldehyde .sup.a 50.0 (Politec E 6010) Isocyanic acid, 50.0 polymethylene polyphenylene ester ª (Politec E 9030) Acid catalyst .sup.a 23.1 (Cataset ST2) Furfuryl alcohol ª 76.9 (Eshanol U1N) Polyvinyl alcohol .sup.a,e 74.1 (P118/2) Glycerol ª 1.5 (Glysorb 14) Sorbitol .sup.a,d 5.9 (Glysorb 14) Potato Starch .sup.a 18.5 2-Ethylhexyl sodium 0.5 sulfate ª (DSK 40) 2-Ethylhexyl 0.50 sulphosuccinate .sup.a (Serwet WH175) Total .sup.b 10.0 4.0 1.6 2.16 10.8 Pozzolanic additive Silica fume .sup.c 100.0 68.0 100.0 (Cofermin silica fume A) Aluminium silicate .sup.c 6.8 (Eurocell 150H) Carbon black .sup.c 0.2 Silica/kaolinite .sup.c 25.0 (Aktisil EM) Total .sup.b 8.0 0.8 0.0 0.0 8.0 Bending strength N/cm.sup.2 As received 829 ± 27 794 ± 18 335 ± 9 287 ± 1 798 ± 8 Water solubility seconds 20° C., 60 rpm 20-40 n/a n/a n/a 240-260 (>60 (>60 (>60 min) min) min) 65° C., 150 rpm  5-15 n/a n/a n/a 15-45 (>60 (>60 (>60 min) min) min) .sup.a wt % relative to total weight of binder composition, .sup.b wt % relative to weight of sand, .sup.c wt % relative to total weight of pozzolanic additive, .sup.d aqueous solution, 40% w/v solids content, .sup.e aqueous solution, 20% w/v solids content, .sup.f aqueous solution, 35-45% w/v solids content

[0146] Cores made using compositions 17, 18 and 21 showed excellent flexural strength of around 800 N/cm.sup.2.

[0147] Cores made using compositions 18-20 did not show any water solubility even when stirred at 65° C. and 150 rpm, so these compositions were deemed not suitable for use in the present invention. Composition 21 showed acceptable water solubility, while composition 17 showed excellent water solubility.

[0148] Composition 17 was based on compositions 5 and 13, with silica fume used instead of fly ash and an increased amount of binder composition and pozzolanic additive used. These changes resulted in a doubling of the flexural strength compared with compositions 5 and 13, without any significant loss of water solubility or flowability. Cores made using composition 17 were free from defects and showed excellent, homogenous compaction.

[0149] The water solubility of compositions 17 and 21 was further tested after heating the cores for 30 minutes at 200, 300 and 400° C., with a water temperature of 65° C. and rotation speed of 150 rpm. The results are shown in Table 5:

TABLE-US-00006 TABLE 5 Composition As received 200° C. 300° C. 400° C. 17  5-15 s  5-15 s 5-15 s 20-120 s 21 15-45 s 30-240 s n/a n/a (>300 s) (>300 s)

[0150] Cores made using composition 17 showed good water solubility even after heating up to 400° C. Cores made using composition 21 showed good water solubility after heating up to 200° C., but cores heated up to 300 and 400° C. did not show signs of significant disintegration after 300 s of stirring in water.

Example 4

[0151] The effect of varying the relative binder and pozzolanic additive content on the strength of the cores was investigated. Cores were prepared using the following compositions and tested for flexural strength and water solubility on the cores as received (without exposure to heat). Flexural strength was tested using the same methodology described in Example 1.

[0152] The binder used in each of the compositions below was as described in Composition 17 above: 69.65% sodium polyacrylate (Dispex AA4135); 29.85% dextrin (P623/4); and 0.5% 2-ethylhexyl sulphosuccinate (Serwet WH175). Percentages are wt % relative to total weight of binder composition. The results are shown in Tables 6a and 6b (Composition 26 has been listed twice for ease of comparison).

[0153] Table 6a shows the effect of varying the pozzolanic content. It has been found that increasing the pozzolanic additive content lead to cores with greater bending strength. Composition 23, containing no pozzolanic additive, was significantly weaker than even a 2% pozzolanic additive relative to the weight of sand. Compositions 22 and 26 show that specific pozzolanic additive choice effects the bending strength, but that desirable strength is not limited to a sole pozzolanic additive.

TABLE-US-00007 TABLE 6a Composition 22 23 24 25 26 Refractory material Quartz sand (H33) Binder content ª 6 6 6 6 6 Pozzolanic additive Fly ash — Silica Silica Silica Fume A Fume A Fume A Pozzolanic content ª 6 0 2 4 6 Bending Strength N/cm.sup.2 As received 547 ± 22 110 ± 7 694 ± 20 1040 ± 41 1332 ± 29 .sup.a wt % relative to weight of refractory material

TABLE-US-00008 TABLE 6b Composition 27 28 29 30 26 Refractory material Quartz sand (H33) Binder content ª 2 3 4 5 6 Pozzolanic content .sup.a, b 6 6 6 6 6 Bending Strength N/cm.sup.2 As received 71 ± 4 435 ± 15 809 ± 22 1056 ± 37 1332 ± 29 .sup.a wt % relative to weight of refractory material; .sup.b Silica Fume A

[0154] Table 6b shows that increasing the binder content (e.g. the hydrophilic polymer content), relative to the weight of refractory material, lead to an increase in bending strength of the cores. Compositions having very low binder content were found to be significantly weaker, despite a relatively high content of pozzolanic additive. All of the compositions 22 to 30 were found to have acceptable water solubility.