AU664879B2 - Foundry mould coating compositions - Google Patents

Description

OPI DATE 05/10/93 APPLN. 10 36396/93 AOJP DATE 09/12/93 PCT NUMBER PCT/GB93/00419 AU9336396 INTERNATIONAL APPLICATION PUBLISHED UN ER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 5 (11) international Publication Number: WO 93/17815 B22C 3/00 Al (43) International Publication Date: 16 September 1993 (16.09.93) (21) International Application Number: PCT/GB93/00419 (74) Agents: GREEN, Mark, Charles et al.; Urquhart-Dykes Lord, 91 W;mpole Street, London WIM 8AH (GB).

(22) International Filing Date: 1 March 1993 (01.03.93) (81) Designated States: AU, CA, FI, JP, NZ, US, European pa- Priority data: tent (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, 9204622.6 2 MLrch 1992 (02.03.92) GB LU, MC, NL, PT, SE).

(71) Applicant (for all designated States except US): ABEL LEM- Published ON CO PTV. LIMITED [AU/AU]; 26 Fariola Street, With international search report.

Silverviater, NSW 2141 (AU).

(72) Inventors; and Inventors/Applicants (for US only) RANGUS, Scott [US/ US]; Laporte Inc., 3701 Algonquin Road, Suite 390, Rolling Meadows, IL 60008 PATTERSON, Gor- f don [GB/GB]; COHEN, Jane [GB/GB]; Laporte Indus- 7 tries Limited, P.O. Box 2, Moorfield Road, Widnes, Cheshire WA8 OJU TORCHIA, Robert (AU/AU]; Abel Lemon Co Pty Limited, 131 Grange Road, P.O.

Box 50, Fairfield, VIC (AU).

(54) itle: FOUNDRY MOULD COATING COMPOSITIONS (57) Abstract An aqueous foundry mould coating composition comprising as a suspending agent a synthetic trioctahedral mineral having the general formula: [Mg 6 .xLIxSi 8 0 20 0H 4 .yFy] Mn+ in which x may have a value of from 0 to 1.2, y may have a value of from 0 to less than 4, n- is the negative charge imbalance of the magnesium silicate lattice and M is an alkali metal, alkaline earth metal or onium cation.

^I

WO 93/17815 PCT/GB93/00419 Foundry mould coating compositions This invention relates to the manufacture of foundry castings and more particularly to compositions suitable for coating foundry moulds, cores or patterns hereafter all encompased by the term mould.

It is widespread practice in the foundry industry toform moulds, cores or patterns, by shaping.a mixture of natural or synthetic foundry sand with a suitable binder system. Such moulds can readily be removed from complex castings and the mould material recycled for further use.

Sand moulds are subject to problems in use. The surface of such moulds may not be as smooth as might be desired and may contain cracks or other imperfections which could allow penetration of the molten casting metal.

Release of the mould material from the casting may be imperfect leading to the need for a special casting finishing stage to remove traces of the casting. To alleviate these problems it is common practice to coat sand moulds with a material which is applicable by dipping, brushing or spraying and which may be caused to harden 'in situ' to give a mould surface coating of increased smoothness resulting in improved casting release and increased strength giving resistance to erosion of the mould surface by the flow of molten metal during the filling of the mould. It is also the practice to coat foam or evaporative patterns, for example of polystyrene, polymethylmethacrylate or other polymers with a coating PCT/GB93/0041 9 WO 93/17815 which bacomes part of the mould as the core is evaporated or to coat ceramic cores.

Foundry mould coatings generally comprise a liquid carrier medium, a refractory material which may be present in the composition in from 20% to 80% by weight of the composition depending on its density and a suspending/binding system together with optional additives such as dispersing agents, antifoam additives or colourants and are usually hardened by heating to remove the liquid 0i carrier and to cause the setting of any resin binder which may be present. The liquid carrier medium may be water or water mixed with a polar organic solvent such as ethanol in for example from 5% to 50% by weight. The refractory material may be selected from relatively low or moderate density materials such as graphite, kaolin, mica, talc, fused silica or magnesium oxide or from higher density material such as zirconia or other zircon-based materials.

The suspending/binding system may comprise a small proportion, say from 0.5% to 2.0% by weight, based on the whole coating composition, of a resin binder for example aqueous emulsion of a vinyl polymer such as polyvinyl alcohol or of a lignosulphonate and/or a suspending agent.

Where a clay suspending agent is used in a foundry mould coating it is usually a bentonite. In this context the term bentonite is used to refer to the class of clays referred to structurally as the montmorillonite, itself a subclass of the smectites. The montmorillonites are minerals having an anionic three layer sheet lattice comprising an alumina octahedral layer interposed between silica tetrahedral layers, some alumina being replaced by magnesium or other divalent ions. Such minerals are structurally known as dioctahedral minerals. The anionic lattice is charge-balanced by cations which are usually, in nature, mixtures of sodium, calcium and magnesium cations and it has been preferred, in certain mould coating compositions, to treat such natural minerals so as to ion exchange divalent cations for sodium and/or lithium cations by treatment with a sodium and/or lithium compound in an aqueous medium. Such ion exchanged minerals have been referred to in the content of mould coatings, as activated bentonite.

It has now been found that the performance of foundry mould coatings may be improved by replacing the dioctahedral mineral hitherto used as suspending agent by a particular range of synthetic trioctahedral minerals that is, synthetic three layer minerals of the smectite group in which the octahedral layer is mainly composed of magnesia.

Accordingly, the present invention provides a foundry mould coating composition comprising a synthetic trioctahedral mineral having the general formula [Mg 6 xLixSi 8 O- .OH 4 _yFy]n-Mn+ in which x may have a value of from 0 to 1.2, y may have a value of from 0 to less than 4, n- is the negative charge imbalance of the magnesium silicate lattice and M is an alkali metal, alkaline earth metal or onium cation as a suspending agent, having a charge n+.

The said synthetic mineral has a structure characteristic of a hectorite.

The present invention also provides a method for preparing a mould coating composition comprising including in a further quantity of water the composition of the invention.

The present invention further provides a method of casting comprising coating a mould, core or pattern with a composition of the invention and drying the coating before S* 20 pouring the molten metal.

The synthetic trioctahedral mineral disclosed above may be manufactured according to known processes. United States Patents No. 3586478 and 3671190 disclose one such process which involves the co-precipitation of magnesium and silicon values corresponding to the desired composition from a solution of a water soluble magnesium 25 salt such as magnesium sulfate or magnesium chloride, sodium silicate, a base such as sodium carbonate or hydroxide and, if appropriate, lithium and fluorine compounds and the treatment of the precipitate under hydrothermal and preferably elevated pressure conditions to achieve crystallisation. The crystalline product so obtained may be washed free of any salts, dried and ground to produce a powdered product. United States Patent No. 4049780 discloses a variation of the above process comprising precipitating silicon values onto a preformed suspension of a water-insoluble magnesium [G:\WPUSER\LIBVV]00471 :TCW 44 compound.

US-A-4 040 974 discloses a further process for the production of a trioctahedral mineral. That process involves forming a high concentration reactant gel and hydrothermally treating the gel. The product may merely be dried to form a gellant.

Naturally occuring mineral hectorite has some suspending properties but is not known in use in mould coatings. The synthetic trioctahedral smectite used according to the present invention has a different morphology to natural hectorite comprising platelets having diameters in the region of 200-300 Angstroms and a thickness in the region of 20 Angstroms, and having a high surface area and cation exchange capacity. This material has been found to equate or to provide advantages over bentonite.

The quantity of bentonite used in a mould coating composition may be from about 0.2% to 10% but more usually from about 0.5% to 5.0% by weight based in each case on the solids cdntent of the coating composition. The synthetic trioctahedral mineral according to the invention may be used in broadly similar quantities. It is also found in some formulations that a smaller quantity of the said trioctahedral mineral may be used to replace a given quantity of bentonite to obtain similar or improved properties.

It is generally found advantageous to use a mixture of the synthetic trioctahedral mineral with a peptiser selected from alkali metal salts containing polyvalent anions for example the pyro-or poly-phosphates tetrasodium pyrophosphate or sodium tri-polyphosphate. The anions are preferably capable of forming complex or insoluble salts with magnesium. Peptisation is a well known phenomenon and other suitable polyvalent anion materials may be substituted. The quantity of the peptiser may be, for 'example, from 3% to 12% of the mineral each by dry weight.

The presence of a peptiser eases the incorporation of the mineral into the coating composition and can improve its properties. Preferably the mineral is incorporated into the coating composition as a predispersed sol containing a peptiser.

AMENDED

SHEET

WO 93/17815 P~/GB93/00419 According to a further feature of the invention there is provided a solid or concentrated aqueous composition comprising solids of a foundry mould coating composition which composition includes the synthetic trioctahedral smectite. Such a composition may advantageously contain some or all of the refractory material, optionally one or more thickeners such as xanthan or other gum, the peptiser and the synthetic trioctahedral smectite in the relative proportions required in the foundry mould coating composition. Such a composition may be formulated at more near the point of use by including in it, the liquid components of the coating composition. These liquid components may be sourced locally but, advantageously, they may be included in a concentrated liquid composition which together with the solid or concentrated aqueous composition first mentioned above provides a two-pack system requiring only the addition of a suitable quantity of water. The pack containing the liquid components may include an aqueous emulsion of a resin binder, dye and a biocide if required.

The advantages of the two pack system outlined above, are reduced transport costs, extended storage life, the ability to make up only the amount required for use.

A two-pack composition comprising a dry pack containing zirconia based refractory solids, the trioctahedral synthetic mineral and a particulate gum thickener and a wet pack containing a polyvinyl emulsion, a dye and a biocide was prepared as an example. The dry pack was added to the required extra quantity of water under shear and was then mixed for 15 minutes. The wet pack was then added and mixed in for 20 minutes. The product had the desired viscosity and was apparently physically stable.

It may be desired to use a combination of the synthetic trioctahedral smectite with a cellulosic thickening agent and this is preferred in the two pack composition disclose_ above. This tends to give an initially thinner coating which thickens up in storage or use to the desired level.

The cellulose material may be any swelling cellulose WO 93/17815 PCT/GB93/00419 6 derivative such as ethyl cellulose on methyl cellulose but is preferably a cellulose ether such as, for example, carboxymethyl cellulose. Preferably the cellulose ether has a degree of substitution of from 0.7 to 1.1. The cellulose derivative is preferably present in from 5% to particularly preferably from 30% to 70% by dry weight of the synthetic trioctahedral smectite. Other thickeners, such as xanthan gum may also be included in the composition.

The invention will now be illustrated by reference to the following examples of specific embodiments thereof.

A synthetic trioctahedral mineral having a hectorite structure was produced by the process disclosed in United States Patent No. 4049780 in which a solution of magnesium and lithium salts were precipitated by the addition of base and a sodium silicate solution was added to the suspension thus obtained to precipitate silicon values. After then ageing the mixed precipitate under reflux to allow the reaction to go to completion the precipitate was subjected to hydrothermal treatment in an autoclave under an autogenous pressure until crystallisation had occurred, the product was filtered, washed with demineralised water, and ground. The present invention is particularly applicable to synthetic mineral produced by such a successive precipitation process but without being limited to mineral produced according to that process.

In the following examples quantities are stated in parts by weight unless otherwise stated.

Example 1 Mould coating composition based on zirconia An aqueous foundry mould coating containing zircon flour as the sole refractory material and sodium bentonite as a suspending agent together with small quantities of other normal ingredients such as preservatives, dyes etc.

was prepared as Composition A.

Composition B was the same as Composition A with the exception that the sodium bentonite was replaced by the same WO 93/17815 PCT/CB93/00419 7 quantity of the synthetic trioctahedral mineral according to the invention.

Composition C was formed by adding about 7% to 10% wt of water to composition B.

On standing for 7 days none of the Compositions showed separation or syneresis. However Composition A showed colour variations in the bulk of the sample which were not visible in Compositions B or C. The final viscosity of the compositions was as follows: A 17000 cps B 24300 cps C 17600 cps initially on dilution 18620 cps after further 24 hours (20 0 C, Brookfield, Spindle 5, 20 rpm) The compositions may be painted onto sand moulds followed by drying. Both compositions B and C, whun brushed onto a sand core and flame dried, gave excellent application properties with no appreciable drag, balling or dripping.

There were no blisters or pinholes and only slight mud cracking in the sections of thicker coating. When a part of .the synthetic trioctahedral mineral was replaced by a cellulose ether thickening agent as hereinbefore taught, it gave improved brushing properties and the final coating had a smoother texture.

Example 2 Mould coating composition based on Talc An aqueous foundry mould coating composition containing talc as the main refractory material, sodium bentonite as the suspending agent together with small quantities of other normal ingredients was prepared as Composition D.

Composition E was the same as Composition D with the exception that the bentonites were replaced by the same total quantity of the trioctahedral synthetic mineral according to the invention.

Composition F was the same as Composition E with the exception that the synthetic material contained 6% of its own weight of tetrasodium pyrophosphate. The viscosity of )A nfti IOi nR rr .r.nf? nf Atr9 WU Y3/1 /013 8 rL/IjDb3/uu'41 the Compositions, ascertained in the same manner as in the preceding Example was: Initial 24 hours 48 hours D 1090 cps 1130 cps 1154 cps E 1282 cps 960 cps 920 cps F 1120 cps 1144 cps 1144 cps While compositions D and E both looked slightly unstable they both gave acceptable performance in core coating.

Composition F was fully homogeneous and stable. When coated onto a core by dripping it gave a reasonable build with no significant teardrops and was adjudged to be more effective than composition E in use.

The compositions may be applied to sand moulds by dipping followed by a suitable drying regime.

v

Claims (16)

1. An aqueous foundry mould coating composition comprising one or more refractory materials and a suspending agent, characterized in that the suspending agent comprises a synthetic trioctahedral mineral having the general formula: [Mg6-xLixSi8O-00H4-yFy]n-Mn+ in which x may have a value of from 0 to 1.2, y may have a value of from 0 to less than 4, n- is the negative charge imbalance of the magnesium silicate lattice and M is an alkali metal, alkaline earth metal or onium cation having a charge n+.

2. A composition as claimed in claim 1 also comprising a binder.

3. A composition as claimed in claim 1 or 2 wherein the synthetic trioctahedral mineral has a structure characteristic of hectorite.

4. A composition as claimed in any preceding claim wherein the quantity of the synthetic trioctahedral mineral is from 0.2% to 10% of the solids content of the composition.

5. A composition as claimed in any preceding claim wherein the synthetic trioctahedral mineral is used in combination with a peptiser. e 6. A composition as claimed in claim 5 wherein the peptiser is an alkali metal salt containing polyvalent anions. S00 a *e a 0 0 0 0 [G-\WPUSER\LIBVV]00471:TCW )0

7. A composition as claimed in claim 5 or 6 wherein the peptiser is present in from 3% to 12% by weight of the synthetic trioctahedral mineral.

8. A composition as claimed in any preceding claim wherein the synthetic trioctahedral mineral is used in combination with a swelling cellulose derivative.

9. A composition as claimed in claim 8 wherein the cellulose derivative is a cellulose ether. A composition as claimed in claim 8 or 9 wherein the cellulose derivative is present in from 5% to 95% by weight of the synthetic trioctahedral mineral.

11. A composition as claimed in any preceding claim comprising a refractory material selected from graphite, kaolin, mica, talc, fused silica, magnesium oxide or zirconium oxide.

12. A composition as claimed in any preceding claim comprising a binder selected from an aqueous emulsion of a vinyl polymer or a lignosulphonate.

13. A composition as claimed in any preceding claim made up as two parts of which a first part is dry and contains refractory solids and synthetic trioctahedral mineral and the second part is wet and contains a binder resin emulsion and water, the water being present less than the total quantity required for the composition.

14. A method for preparing a mould coating composition comprising including in a further quantity of water the composition as claimed in claim 13. AMENDED SHEET 11 A method of casting comprising coating a mould, core or pattern with a composition as claimed in any preceding claim and drying the coating before pouring the molten metal.

16. An aqueous foundry mould coating composition substantially as herein described with reference to Example 1 or 2.

17. A process of preparing a mould coating composition, which process is substantially as herein described with reference to Example 1 or 2.

18. A method of casting comprising coating a mould, core or pattern with a composition as claimed in claim 16 and drying the coating before pouring the molten metal. Dated 28 August, 1995 Abel Lemon Co Pty. Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 55 5 0 *0 S U S S *0 5 o go [G:\WPUSER\LIBVV]00471:TcW INTERNATIONAL SEARCH REPORT lattradwacl A"Okactlom No PCI/GB 93/00419 L C..A5SJICATION OF SUNjZCT MATTER OIf seval dsssffktoe symbols apply, lndlktV au) Acaudlag to latera~doW patsed assmncaea MPC or to bad Nsaloaa Cauifimtom sand IC Int.Cl. 5 B22C0/00 I. FEUDS SEAIQIED Mlamm Docummtl swted Classiflmhlca Systm almi Symbols In~t.Cl. 5 822C Domation Serthud other than Minbs.. D~ocuetation to the Extent that such Doajagats ame Included In the Field Swcned 8 DOCUMENTS CONSIDERED TO U RJUZVANTS Category Ckztoa, of Docuset U1 with Indlicatiou, uberd appoprto,. Of the v.1WmD pweap12 Releant to aist No.U x USA,4 040 974 (WRIGHT ET AL) 1-16 9 August 1977 see column 3, line 7 column 4, line 11 see column 6, line 4 line 26 see column 11, line 41 column 1,2, line 9 y US,A,3 671 190 (NEUMANN) I-i6 June 1972 cited in the application see column 13, line 25 column 14, line 29 see claim 1 Y GB,A,1 194 158 (NALCO CHEMICAL COMPANY) 1-16 June 1970 see page 2, line 26 -line 100 see claims 'Spel dal sies of cited Awmasi 2 10 hrI& doom"Me Published after the latermatioeal flla dat A" datma gels~agthe d~ or rirty dte n t Isdl comfflct wtca the aspIoction but 'A doma heifa So Oec oa w sa U the priniple or theory w~~tthe earler inmout bat sabllth as or af ter nawsa or documut ofpesar relevaac the clAimed lratin Miesg date cisno be ri- .ovw 1w mas be owimiered to IV doaisent whilch my thrw douts as priorfty cams) or imolve an ievtlve Key wc~ Is shed to at h the puictu ae of 5flothUf Ir dosot of particular relevace; the calmued laintoa diution or other special Pasil(as specifieW) cmo be 03asidered to Involve an lawed top we hen the 0 dacumat reuin to an oral disodoern se, hlbltlam or docaat is combined with ose or Sm other such docs other am m S, uch Combination beang obvious to a porm shlukA IY docat published prier to the intwnaanl I IhS date butIntea. later than the priority date calmed w doceat =mber of the sae "hteeamialy 2 IV CERTffICAUhlN Date of the Aausl Couplellas of the lateratlanal Sarch Daue of Mailing of this lateatoeel Search Repor 19 MAY 1993 1waloml Searching Awthorit Sltume of Axstrzud Office rEUMOI'AN PATENT OMFCE RIBA VILAHOVA M. PCT/GB 93/00419 fizt~uerso Aeglation No UL 5O-CMI7TS COMSMEDM TO 3U WUZVANT (CON'TMD~ FROM THE SECOND SHEET) Cusp,1 Mtak~e of Doamm.st with Lndfxis wi a.piso, of the mW.vat peua RAWvut to CLMia N&~ A US,A,3 878 034 (BEVER E-1 AL) 1-16 April 1975 see column 1, line 12 line 17 A EP,A,0 088 372 (HOECHST 1-16 AKTIENGESELLSCHAFT) 14 September 1983 see page 1, 'ne 5 'ine 21 see page 6,.lne 15 'fine 21 A EP,A,0 445 653 (RHEOX INTERNATIONAL) 1-16 11 September 1991 see abstract see page 1, line 23 -line 32 see page 4, line 3 -line 19 A US,A,3 936 383 (DAIMON ET AL) 1-16 3 February 1976 see column 1, line 5 line see claims A GB,A,919 194 (THE BRITISH STEEL CASTINGS I13,14 RESEARCH ASSOCIATION) 2C February 1963 see page 2, line 78 line 103 PTMaJ21o Md 0-0107 1%4 ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL PATENT APPLICATION NO. 9300419 70f7 'Th13 a-n MU the -ai famly somober rehthg to the pbM documets cdo in the Wnmhdomw~d istorndeowd ine.h report Mwe nmabws we ceab~ui In dhe Fmpeeao PatMn Offif ED Bie *a The Eurepem Ptn 095is is.. wn aye hkfr thins pmaitwrn w ih we mm Shm for the pswpein of Wwofmim. 19/05/93 US-A-4040974 09-08-77 DE-A- FR-A, B GB-A- JP-A- JP-s- US-A- 2718576 2349541 1553127 52130499 60009068 4054537 16-08-77 10-11-77

25-11-77 19-09-79 01-11-77 07-03-85 18-10-77 US-A-367 1190 20-06-72 None GB-A-1194153 10-06-70 DE-A- 1771623 03-02-72 FR-A- 1576616 01-08-69 NL-A- 6808590 23-12-68 US-Am3878034 15-W4i75 CA-A- 947939 28-05-74 CH-Am 573366 15-03-76 DE-A- 2131665 05-01-72 GB-A- 1338631 28-11m73 SE-B- 382164 19-01-76 US-A- 3859153 07-01-75 US-A- 375 1275 07-08-73 EP-A-0088372 14-09m83 DE-A- 3207886 15-09-83 EP-A-0445653 11-09-91 US-A- 5112400 12-05-92 CA-A- 2035120 07-09-91 JP-A- 4220486 11-08-92 US-A-3936383 03-02-76 JP-Cm 943565 15-03-79 JPm- 50002698 11-01-75 JP-Bm 53020959 29-06-78 DE-A,B 2423197 28-11-74 GB-Am 1469710 06-04-77 GO-A-919194 None SFor ow ieto AM. tb ceow: m Offiia Jemal of (hi Eme. Pao Oflke No. 12)32