Cold setting sand for foundry moulds and cores

A cold setting sand for moulds and cores comprises a refractory filler and an acid, wherein the acid used is organic acid with the dissociation constant of 10.sup.-5 to 10.sup.1, with the components being contained therein in the following amounts, in percent by weight: ______________________________________ refractory filler from 95 to 99 organic acid from 1 to 5. ______________________________________

BACKGROUND OF THE INVENTION 
The present invention relates to foundry practice and more in particular to 
a cold setting sand for foundry moulds and cores. 
There is known a foundry sand which comprises a refractory filler 
containing magnesium and/or chromium oxides, such as chrome-magnesite or 
magnesite-chrome, and a binder such as alcohol-sulfite lye or water glass 
(A. M. Liass, "Fast Setting Foundry Sands", Mashinostroenie Publishers, 
Moscow, 1965). 
There is also known a cold setting sand which comprises a filler, 
orthophosphoric acid and a powdered material containing iron oxides. 
The prior art sands are disadvantageous in that they are difficult to shake 
out, have insufficient strength, and require heat drying. Furthermore, the 
powder material containing iron oxides requires pregrinding, which makes 
the production more complicated and expensive, and damages to cores during 
their removal from core-boxes and subsequent handling. 
DISCLOSURE OF THE INVENTION 
What is required to a cold setting sand for moulds and cores of such 
composition having high strength, and not requiring heat drying and 
pregrinding of the starting materials. 
The invention provides a cold setting sand for foundry moulds and cores, 
comprising a refractory filler and an acid, wherein the acid used is an 
organic acid with a dissociation constant of 10.sup.-5 to 10.sup.1, the 
components being contained therein in the following amounts, percent by 
weight: 
______________________________________ 
refractory filler from 95 to 99 
organic acid from 1 to 5 
______________________________________ 
A decrease in the amount of organic acid below 1.0 percent by weight will 
make it impossible to prepare a sand of the required strength, whereas an 
increase of this amount above 5.0 percent by weight will have no 
substantial effect on the sand properties. 
The foundry sand of the invention lends itself readily for the knocking-out 
operation, has high strength and rapid setting rates, and requires no heat 
drying. 
The refractory filler used in the sand of the invention is preferably 
magnesium oxides, and/or chromium oxides, and/or iron oxides, and/or 
silicon oxides, and the organic acid with the dissociation constant of 
10.sup.-5 to 10.sup.1 is preferably an aromatic sulfonic acid or 
carboxylic acid. 
Such selection of fillers and acids makes it possible to produce a cold 
setting sand of good technological properties. 
Preferably, the cold setting sand of the invention additionally comprises 
orthophosphoric acid taken in a ratio to organic acid as 0.1:1 to 4:1. 
The above organic acid/orthophosphoric and ratio of 1:0.1 to 1:4 permits 
the sand setting rates to be regulated in accordance with various 
production conditions. A lower content of orthophosphoric acid will have 
no effect on the technological properties of the sand, whereas a higher 
content will bring down the sand setting rate to an inadmissibly low 
level. 
BEST MODE FOR CARRYING OUT THE INVENTION 
According to the invention, the cold setting sand is prepared by stirring a 
mixture of the refractory filler and acid for 1-2 min. 
The acid is preferably introduced undiluted, or in solution. In the latter 
case, the total amount of solution should be increased so that the content 
of acid as calculated for the undiluted acid will be within the range of 1 
to 5.0 percent by weight. 
The sand of the invention may be prepared both with the use as the filler 
of pure oxides of magnesium, and/or chrome, and/or iron, and/or silicon, 
or materials containing these oxides, for example, magnesite, 
chrome-magnesite, magnesite-chrome or a mixture thereof. The 
above-mentioned oxides or materials containing them can be also used in 
combination with other refractory fillers, such as quartz sand, zircon, 
kyanite-sillimanite, etc. 
The aggregate content of the above-mentioned oxides in the refractory 
filler should be in the range of from 2.0 to 100 percent by weight. 
Table 1 gives, as an example, the chemical composition of chrome-magnesite, 
magnesite-chrome and chrome ironstone, which are used as the refractory 
filler in the cold setting sand of the invention. 
TABLE 1 
__________________________________________________________________________ 
Chemical composition, % 
The 
Filler 
MgO Cr.sub.2 O.sub.3 
Al.sub.2 O.sub.3 
FeO Fe.sub.2 O.sub.3 
SiO.sub.2 
CaO rest 
__________________________________________________________________________ 
Magne- 
62-71 
9-17 
3-7 -- 4-7 3-7 3-6 0.3- 
site- 8.8 
chrome 
Chrome- 
51-57 
18-22 
5-7 -- 7-10 
3-5 3-4 0.3- 
magne- 9.8 
site 
Chrome 
14-18 
52-58 
8-10 
11- -- 2-5 -- 0.9- 
iron- 14 1.1 
stone 
__________________________________________________________________________ 
The rate of setting and strength of the sand may be regulated by altering 
the granulometric composition of oxides. Therefore, the sand composition 
should include such oxides in which the amount of fractions having less 
than 0.1 mm in size ranges from 5.0 to 100.0 percent by weight. The use of 
oxides with a lower amount of such fractions adversely affects the rate of 
setting and strength of the sand. An increase in the amount of small-size 
fractions (below 0.1 mm) results in higher setting rates and strength of 
the sand. 
Table 2 gives the granulometric composition of the oxides used in the sand 
composition. 
TABLE 2 
__________________________________________________________________________ 
Mesh size 
2.5 
1.6 
1.0 
0.63 
0.4 
0.315 
0.2 
0.16 
0.1 
0.063 
0.05 
0.05 
Clay 
No. 
Filler 
Sieve residue, % component, % 
__________________________________________________________________________ 
1 Magnesite- 
1.4 
4.38 
10.96 
12.4 
15.76 
7.28 
11.2 
8.32 
10.68 
10.26 
2.86 
0.66 
3.84 
chrome 
2 Chrome- 
-- 
0.08 
2.44 
6.92 
11.0 
9.7 
6.42 
6.20 
7.85 
10.58 
5.90 
19.0 
13.44 
magnesite 
3 Chrome 
1.2 
3.16 
4.57 
8.71 
19.8 
11.42 
9.23 
7.84 
12.56 
11.66 
3.29 
5.34 
1.22 
ironstone 
__________________________________________________________________________ 
Standard samples were made from the sand by charging the latter into blocks 
and its subsequent compacting. The samples were then tested for 
compressive strength (in kg/cm.sup.2). 
The knocking-out characteristic is determined by the residual strength of 
the sand at high temperatures, found after heating and cooling the sand 
samples.

The invention is further described by the following illustrative Examples. 
EXAMPLE 1 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 99 
Formic acid 1 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler and 
formic acid for 1-2 min. 
Standard samples were made from the resultant sand by charging the latter 
into blocks and its subsequent compacting. 
The standard samples were tested for compressive strength which was 4.0 
kg/cm.sup.2 after 1 hour; 5.5 kg/cm.sup.2 after 4 hours; and 8.0 
kg/cm.sup.2 after 24 hours. 
EXAMPLE 2 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 97 
Formic acid 3 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler and 
formic acid for 1-2 min. 
The standard samples from the sand were tested for compressive strength, 
which was 14.0 kg/cm.sup.2 after 1 hour; 19 kg/cm.sup.2 after 4 hours; and 
23.5 after 24 hours. 
EXAMPLE 3 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 95 
Formic acid 5 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler and 
formic acid for 1-2 min. 
The standard samples from the resultant sand were tested for compressive 
strength, which was 16.5 kg/cm.sup.2 after 1 hour; 21.0 kg/cm.sup.2 after 
4 hours; and 26.5 kg/cm.sup.2 after 24 hours. 
EXAMPLE 4 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Magnesite-chrome 97 
Formic acid 3 
______________________________________ 
The sand was prepared by stirring the mixture of refractory filler and 
formic acid for 1-2 min. 
The standard samples from the sand were tested for compressive strength, 
which was 15.0 kg/cm.sup.2 after 1 hour; 19.0 kg/cm.sup.2 after 4 hours; 
and 23.5 kg/cm.sup.2 after 24 hours. 
EXAMPLE 5 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome ironstone 97 
Benzenesulfonic acid 3 
______________________________________ 
The sand was prepared by stirring the mixture of refractory filler and acid 
for 1-2 min. 
The standard samples from the resultant sand were tested for compressive 
strength, which was 14.5 kg/cm.sup.2 after 1; 17.0 kg/cm.sup.2 after 4 
hours; and 22.5 kg/cm.sup.2 after 24 hours. 
EXAMPLE 6 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 48.5 
Magnesite chrome 48.5 
Maleic acid 3 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler and 
acid for 1-2 min. 
The standard samples from the resultant sand were tested for compressive 
strength, which was 15.5 kg/cm.sup.2 after 1 hour; 20.0 kg/cm.sup.2 after 
4 hours; and 24.5 kg/cm.sup.2 after 24 hours. 
EXAMPLE 7 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Quartz sand 82 
Magnesium oxides 15 
Acetic acid 3 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler (a 
mixture of quartz sand and magnesium oxides) and acid for 1-2 min. 
The standard samples made from the sand were tested for compressive 
strength, which was 14.5 kg/cm.sup.2 after 1 hour; 17.0 kg/cm.sup.2 after 
4 hours; and 22.0 kg/cm.sup.2 after 24 hours. 
EXAMPLE 8 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 97 
Maleic acid 1.5 
Orthophosphoric acid 
1.5 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler and 
acids for 1-2 min. 
The standard samples made from the resultant sand were tested for 
compressive strength, which was 13.0 kg/cm.sup.2 after 1 hour; 16.5 
kg/cm.sup.2 after 4 hours; and 22.0 kg/cm.sup.2 after 24 hours. 
EXAMPLE 9 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 96.7 
Maleic acid 3.0 
Orthophosphoric acid 
0.3 
______________________________________ 
The sand was prepared by stirring the mixture of the refractory filler and 
acids for 1-2 min. 
The compressive strength of the standard samples made from the resultant 
sand was 15.0 kg/cm.sup.2 after 1 hour; 18.0 kg/cm.sup.2 after 4 hours; 
and 23.5 kg/cm.sup.2 after 24 hours. 
EXAMPLE 10 
A sand was prepared from the following components, in percent by weight: 
______________________________________ 
Chrome-magnesite 97 
Maleic acid 0.6 
Orthophosphoric acid 
2.4 
______________________________________ 
The resultant mixture of the refractory filler and acids was stirring for 
1-2 min. 
The compressive strength of the standard samples made from the resultant 
sand was 6.5 kg/cm.sup.2 after 1 hour; 11.0 kg/cm.sup.2 after 4 hours; and 
26.0 kg/cm.sup.2 after 24 hours. 
EXAMPLE 11 (COMATIVE) 
Table 3 gives the residual compressive strength data for the prior-art sand 
(comprising 94 parts by weight of quartz sand used as a filler; 6 parts by 
weight of powdered ferrous oxide; and 6 parts by weight of orthophosphoric 
acid) and for the sand according to the present invention. 
TABLE 3 
______________________________________ 
Compressive strength, 
Temperature, 
kg/cm.sup.2 
.degree.C. 
20 200 400 600 800 1000 1200 1400 
______________________________________ 
Prior-art sand 
13 5.6 5.0 4.5 2.0 1.1 11.6 13.0 
Sand according 
18 2.4 1.6 1.0 0.6 0.4 0.4 5.2 
to the invention 
as illustrated 
in Example 3 
______________________________________ 
INDUSTRIAL APPLICABILITY 
Cores and moulds from the cold setting sand of the invention may be used 
for the production of castings from steel, cast-iron and nonferrous 
alloys.