Refractory materials

A refractory shape is molded on a pattern by pouring over the pattern a mixture of two slurries each of which is stable but which together react to gell. The mixture is formed by merging two slurry streams immediately above the pattern.

This invention relates to a method for the preparation of moulds and cores 
for the casting of liquids such as molten metals and/or alloys. When used 
with metals the invention is applicable to the casting of both ferrous and 
non-ferrous materials. 
The present invention provides a method of preparing a mould or core for 
casting liquids such as molten metals, such method comprising the steps of 
coating a pattern with a mixture of two slurries each of which is 
substantially stable but which together gell to form a rigid coherent 
shape wherein each slurry is discharged as a stream onto the pattern, the 
two streams converging adjacent the pattern to mix the slurries. 
The following systems are specifically envisaged: 
A. The zirconium salt/magnesia dispersion systems of copending Patent 
Application Ser. No. 561,245 now U.S. Pat. No. 4,018,858 assigned to 
Zirconal Processes Limited. The preferred system includes in one slurry a 
zirconium salt and a gellation-delaying agent and in the other slurry the 
special magnesia dispersion. 
B. The acidic zirconium salt/gellation-delaying agent/gellation-inducing 
agent system of copending patent application Ser. No. 561,347 now U.S. 
Pat. No. 4,025,350 (assigned to Zirconal Processes Limited) the salt and 
delaying agent being in the one slurry and the inducing agent in the 
other. 
C. The basic zirconium salt/gellation-delaying agent/gellation-inducing 
agent system of the divisional application from application Ser. No. 
561,347 filed on Dec. 8, 1976, now U.S. Pat. No. 4,025,350, the salt 
delaying agent being in one slurry and the inducing agent in the other 
slurry. 
D. A silica aquasol, a silical alcosol or a hydrolysed alkyl silicate and 
the gellation inducing agent is the magnesia dispersion specified in 
application Ser. No. 561,245 now U.S. Pat. No. 4,018,858. One slurry 
contains the silica derivative and the other slurry the magnesia 
dispersion. 
A powdered refractory material is advantageously applied to the mixture of 
slurries during gelling. 
The pattern may be a non-expendable pattern or an expendable pattern. 
Non-expendable patterns may be made from wood, metal or plastic. 
Expendable patterns may be wax or a plastic material. Preferably the 
pattern is coated by spraying the two slurries on to the pattern either 
consecutively or by means of a spraying apparatus in which the two 
slurries are mixed just prior to spraying. 
The powdered refractory material forms the surface of the mould on to which 
the molten metal (or allow is cast. To obtain good definition and good 
surface finish on the material being cast, the refractory material must 
have a small particle size and must not react with the material being 
cast. Desirably, the major part of the refractory material should pass a 
200 mesh B.S. 410 sieve. Among examples of suitable refractory materials 
are alumina and the aluminosilicates, zircon, zirconia, fused silica and 
spinel materials. 
The preferred magnesia is a light magnesia. The preparation of dispersions 
of light magnesia in a mixture of water and polyhydric alcohols is 
described in British Patent 1,356,247. This Patent also describes the 
preparation of gellable mixtures of refractory powders dispersed in a 
silica aquasol or a silica alcosol, with dispersions of light magnesia in 
water and polyhydric alcohol systems. The preparation of gellable mixtures 
of dispersions of light magnesia in water and polyhydric alcohol systems 
with dispersions of refractory powders in aqueous solutions of a zirconium 
salt is described in copending application Ser. No. 561,347 now U.S. Pat. 
No. 4,025,350. 
Silica aquasols and silica alcosols are well known. For a description of 
properties and methods of preparation, see R. K. Iler, "The Colloid 
Chemistry of Silica and Silicates" (Ithaca, N.Y. Cornell University Press, 
1955). 
As prepared, the silica aquasols are almost always alkaline. Alkaline 
silica aquasols must be made acid before they are suitable for use in the 
present process. 
The hydrolysed alkyl silicate solution is preferably an acid hydrolysed 
alkyl silicate solution. Methods for the preparation of acid hydrolysates 
of alkyl silicates are well known. The term acid hydrolysed alkyl silicate 
solution includes mixed acid hydrolysates of alkyl silicates and metal 
salts, which may be prepared as described in British Pat. No. 1,356,248, 
also acid hydrolysates of organic silicates, particularly ethyl silicate 
prepared as described in British Specification No. 898,103, and acid 
hydrolysates of organic silicates (particularly ethyl silicate), prepared 
using a silica aquasol as described in British Specifications Nos. 768,232 
and 1,309,915 together with the acid hydrolysates of ethyl silicate 
prepared using a silica alcosol. Other methods for the preparation of 
hydrolysed alkyl silicate solutions are described in U.K. Pat. 
Specification No. 1,459,786 which also describes the preparation of 
gellable mixtures of refractory powders dispersed in hydrolysed alkyl 
silicate solution, with dispersion of light magnesia in water and 
polyhydric alcohol systems. 
When the gellable mixture used to coat the pattern has gelled, a powdered 
refractory and a binder which is subsequently caused or allowed to harden 
is applied to the gelled coating to complete the preparation of the mould 
or core. If the pattern is non-expendable, one suitable powdered 
refractory and binder is a mixture of silica sand and sodium silicate 
solution. The silica sand should be slightly dampened with the sodium 
silicate solution. Carbon dioxide gas may be used for hardening. Other 
methods of hardening silica sand and sodium silicate systems are known and 
may be used. Details of these procedures are given in `Foundry Year Book`, 
1975, Table 14, P. 209. Silica sands bonded with a synthetic resin may 
also be used. Methods of hardening these sands are given in `Foundry Year 
Book`, 1975, Table 14, P. 210. Mixtures of zircon and silica sand may also 
be used with sodium silicate solution and hardened by carbon dioxide gas. 
Mixtures of fireclay grog and sodium silicate solution may also be used, 
being hardened by carbon dioxide gas. Alternatively, the powdered 
refractory and binder applied to the gelled coating may be as described in 
British Patent Specification No. 716,394. This powdered refractory and 
binder may be hardened as described in British Pat. Specification No. 
716,394 and the mould or core ignited as described in British Pat. 
Specification No. 716,394. 
If the pattern is an expendable pattern, examples of suitable powdered 
refractory and binder systems are given in British Pat. Specifications 
Nos. 768,232 and 650,532. These specifications also give methods for 
hardening the refractory and binder systems. 
The following are examples of combinations of slurries which may be used in 
the present invention. 
SLURRY NO. 1.A 
400 grams of refractory powder comprising 90 parts by weight of Molochite 
(120 grade) and 10 parts by weight of ball clay grade TWVD, supplied by 
Watts Blake Bearne & Co. Ltd. are dispersed in 210 ml of a solution of one 
volume of Zetabond 10 and one volume water. The Molochite and the grade 
numbers refer to British Standard 410 sieves. Flow time through a B-4 cup, 
B.S. 3900 was 65 seconds. Zetabond 10 is a formulation containing 100 ml 
of zirconium acetate solution (ZrO.sub.2 content 22% w/w) in which are 
dissolved 10 gm of magnesium acetate 4H.sub.2 O crystals. The 10 in 
Zetabond 10 designates the number of grams of magnesium acetate. Thus 
Zetabond 20 contains 20 gm of magnesium acetate. Molochite is a Registered 
Trade Mark denoting a china clay calcination product. 
SLURRY NO. 1B 
To 100 ml of water was added 5.0 grams of light magnesia (grade LMO/262) 
followed by 150 grams of Molochite (120 grade). Flow time through a B-4 
cup, B.S. 3900 was 50 seconds. One volume of Slurry No. 1.A + One volume 
Slurry No. 1B - set in 30 seconds. Two volumes of Slurry No. 1.A + One 
volume Slurry No.1.B - set in 45 seconds. In each case strength 
development was good. 
SLURRY NO. 2A 
As Slurry No. 1.A 
SLURRY NO. 2B 
To 100 ml of a mixture of glycerol and water (10 parts by volume of glycols 
with 90 parts by volume of water) was added 5.0 grams of light magnesia 
(grade LMO/262) followed by 150 grams of Molochite (120 grade). Flow time 
through a B-4 cup, B.S. 3900 was 40 seconds. 
One volume of Slurry No. 2.A + One volume Slurry No. 2. B - set in 30 
seconds. Strength development was satisfactory. 
SLURRY NO. 3.A 
1.2 kg of Molochite (200 grade) and 1.2 kg of Molochite (30/80 grade) are 
dispersed in 1.0 litre of Zetabond C. 
SLURRY NO. 3.B 
1.2 kg of Molochite (200 grade) and 1.2 kg of Molochite (30/80 grade) are 
dispersed in a mixture of 500 ml water and 500 ml pure triethanolamine. 
One volume of slurry No. 3.A + One volume Slurry No. 3.B - set in 15 
seconds. 
SLURRY NO. 4.A 
200 grams of refractory powder comprising 90 parts by weight of Molochite 
(120 grade) and 10 parts by weight of ball clay grade TWVD are dispersed 
in 105 ml of Zetabond C. 
SLURRY NO. 4.B 
200 grams of Molochite (120 grade) are dispersed in a mixture of 50 ml 
water and 50 ml technical grade triethanolamine. The composition of the 
technical grade triethanolamine used was (percentages are by weight) 
Triethanolamine -- 80% min 
Diethanolamine -- 15% max 
Monoethanolamine -- 4% max 
Water -- to 100% 
1 volume of Slurry No. 4.A + 1 volume Slurry No. 4.B - viscous in 15 
seconds, set in 60 seconds. 
2 volumes of Slurry No. 4.A + 3 volumes Slurry No. 4.B - viscous in 30 
seconds, set in 55 seconds. 
2 volumes of Slurry No. 4.A + 1 volume Slurry No. 4.B - set in 5 seconds. 
Optionally, when the first slurry is a dispersion of a refractory powder in 
a solution of a zirconium salt containing at least one of the 
gel-controlling additives described in British Pat. Application No. 
35610/74, it may be used with a solution of a gel-inducing agent described 
in British Pat. Application No. 35610/74. The following are examples of 
this procedure, to be used in the first step of the present invention. 
British Pat. Application No. 35610/74 is the equivalent of U.S. 
Application No. 561,347 now Pat. No. 4,025,350. 
PREATION OF SLURRY 
200 grams of refractory powder comprising 90 parts by weight of Molochite 
(120 grade) and 10 parts by weight of ball clay (grade TWVD) are dispersed 
in 105 ml of Zetabond 20. 
SOLUTION OF GEL-INDUCING AGENT 
SOLUTION NO. 1 
Water 75% v/v : Techanical grade triethanolamine 25% v/v 
SOLUTION NO. 2 
Water 50% v/v : Technical grade triethanolamine 50% v/v 
2 volumes of slurry + 1 volume Solution No.1 - set in 20 secs. 
1 volume of slurry + 1 volume Solution No.1 - set in 15 secs. 
2 volumes of slurry + 3 volumes Solution No.1 - set in 15 secs. 
2 volumes of slurry + 1 volume Solution No.2 - set in 20 secs. The 
composition of the technical grade of triethanolamine used is given in 
Slurry No. 4. B.

EXAMPLE 1 
This example illustrates a procedure for spraying a mixed slurry. The 
slurries which make up the mixture are as follows: 
SLURRY NO. 1 
Zetabond 10 is mixed with Molochite (120 grade) to form a relatively mobile 
slurry of the general consistency of commercially sold emulsion paint. 
Such a mobile slurry can be made by mixing weight for weight Zetabond 10 
and Molochite (120 grade). To this mixture is further added a suitable 
suspension aid. There are several possible materials. One suitable 
material has between 5% and 10% of ball clay which has a similar chemical 
composition to that of Molochite. 
SLURRY NO. 2 
Consists of water with a similar weight of Molochite (120 grade) with a 
percentage of suitable magnesium oxide (gellation inducing agent) which 
will result in a gel time suitable for the job. In the method now 
described, it is desirable to provide a gel time for approximately 30 - 40 
seconds, from the moment that the two slurries meet each other and are 
mixed. In order to obtain this type of gel time, without adverse effect on 
the refractory properties subsequently, a grade of light magnesia is used 
in excess of 0.01%, and less than 1% by weight of the refractory material 
used. It should be noted that each of these two slurries with occasional 
stirring will maintain a stable condition in an enclosed space, such as a 
sealed drum more or less indefinitely. It should also be noted that if 
these two slurries are added together in approximately equal proportions 
they will set to a hard gel in approximately 40 seconds. 
Apparatus for conducing the spraying operation is illustrated in FIG. 1. 
The spraying head 1 schematically indicated comprises separate pipe lines 2 
and 3 each connected to a pressurised pot containing a mixing motor (not 
shown). Each pot and motor is of the type used in the paint industry and 
is pressurised to approximately 40 p.s.i. The pipes 2 and 3 diverge and 
each terminate in an inwardly inclined nozzle 4. Thus in use the two 
slurry steams 5, one containing Slurry 1 and the other containing Slurry 
2, from the nozzle 4 converge and mix immediately above a pattern 6 being 
coated. The pattern 6 is contained on a base 7 between walls 8. 
An apparatus is thus provided together with two reactive slurries capable 
of being sprayed, having in admixture a fast setting time. This being the 
case, if a pattern suitable for precision casting is taken and treated 
with a suitable parting agent for Zetabond compositions, the pattern may 
be sprayed with the combined slurries to form a thin film 9 of refractory 
slurry in which a high degree of control of overall thickness can be 
obtained, depending upon the length of time the spray gun is in operation. 
By way of example, a layer of approximately 1/16 - 1/8 inch thick can be 
evenly coated all over the pattern. It should be noted that because the 
material will gel in approximately 40 seconds, there will be little or no 
tendency for the slurry to run off the high spots and flow into the low 
spots and create uneven thickness. However, immediately after spraying a 
coating of CO.sub.2 sand (foundry sand and sodium silicate) is preferably 
applied. 
When the CO.sub.2 sand has been hardened, the pattern can be stripped from 
the mould, and one of several procedures may now be followed prior to the 
casting of the metal. By way of example, one might heat with a powerful 
torch flame the face of the mould to dry out the water, and also to create 
crazing (provided that suitable refractory material has been used, being 
selected to allow micro-crazing without gross cracking under these 
circumstances, also to withstand thermal shock). If dimensional tolerances 
were not particularly important, the mould could be dried carefully in a 
warm oven for a period of some hours in order to drive out the residual 
water. The preferred method described here would be to use a high velocity 
combustion system designed to provide a copious supply of gaseous 
combustion products at approximately 300.degree. C, and induce rapid 
evaporation from the surface of the gelled slurry in order (a) to drive 
out the water, and (b) to induce the desirable micro-crazed cracking. The 
mould could then be dried to 100.degree. C as is common practice, but the 
preferred method is to do the whole operation in a conventional foundry 
sand box or a mechanised sand box in order to enhance the strength of the 
mould, and to ensure that the evaporation of the liquids in the gelled 
slurry is carried on for long enough to ensure that no residual water 
remains in the mould prior to casting metal. 
The methods described above can be used to spray other slurry mixtures. The 
use of silica sols or ethyl silicates, or sodium or potassium silicate is 
envisaged. 
EXAMPLE 2 
Preparation of Mould Dressing for the technique set out above. 
A mould dressing is prepared as follows: 
STAGE 1 
Zetabond 10 is diluted with isopropanol in the proportion of two volumes 
Zetabond 10 to one volume of isopropanol. 
STAGE 2 
Graphite powder is added to the liquid prepared in Stage 1, in the 
proportion of 40% v/v. The graphite powder desirably contains magnesium 
oxide to cause the composition to set. Sardamag DP52 is suitable; up to 2% 
by weight, based on the weight of graphite, may be used. The composition 
is preferably applied by spraying, but may also be applied by brushing.