CS240887B1 - Refractory graphite-fireclay material with mixed chemical binders, especially for the production of crucible - Google Patents

Abstract

The invention relates to the field of ceramics. A conventional graphite-fireclay refractory mass is bonded with a mixed chemical binder formed by a mixture of 0.5 wt. % to 6.0 wt. % of colloidal silica, based on a 30% solution, and 0.1 wt. % to 0.6 wt. % of oxidized syntan.

Description

BACKGROUND OF THE INVENTION The present invention relates to a refractory graphite-chamotte compound with a mixed chemical binder, in particular for the production of corrosion-resistant melting crucibles with a mixed chemical binder.

In the foundry industry, graphite-fireclay crucibles having an aluminum oxide content of 30% by weight, a refractoriness of 165 and a compressive strength of 4.5 MPa are still used. These crucibles are universal for all types of non-ferrous metals and their alloys, melting temperatures and total melting time.

When melting non-ferrous metals and their alloys, these crucibles significantly reduce the lifetime of the burn-out process by using graphite on the outer surface of the crucibles. The graphite burn-out results in high shrinkage of the burnt-through layer, cracks and scratches on the surface of the crucibles, dropping of different thickness of the shards and weakening of the walls up to the point of rupture. For this reason, the melts are degraded, the consumption of crucibles increases and, above all, the health of workers is endangered.

The above-mentioned deficiencies are eliminated by a refractory graphite-grout compound with a mixed binder, consisting of a mixture of graphite, refractory clay and ceramic grit in which

240 887 the mixed chemical binder consists of a mixture of 0.5 wt. % to 6.0 wt. % colloidal 30% silica solution; and 0.1 wt. % to 0.6 wt. oxidized synthane.

The mixed binder forms a bond in the mass, allowing to reduce the addition of mixing water having an effect on the dimensional stability of the products, accelerating the drying cycle and achieving gelation within a suitable time interval of the manufacturing section when handling the products.

The advantage of the refractory composition according to the invention is the increased plasticity, the bondability and the considerable green strength of the products, the formation of water-insensitive bonds which resist high temperatures with minimal extraction at firing.

The advantage of the crucibles made of the refractory mass according to the invention is, in comparison with the crucibles of conventional production, higher compressive strength values, less water absorption and an increase in the crucible durability, which represents a significant increase in the crucible life. These advantages are due to the bonds formed in the refractory material and to the reduction of the amount of mixing water.

The refractory composition of the invention will be further exemplified.

Example 1

1.5 hours of colloidal SiOg silica solution containing 30% SiOg and 0.20 hours of oxidized synthane were added to a graphite-fireclay mass of 37 hours graphite, 7 hours dump refractory slag and 26 hours d refractory clays.

Melting crucibles were formed from this mass and fired in a muffle furnace at 850 ° C. The crucibles were used to melt copper.

240 807

During the verification of the graphite crucibles, a total of 14,759 kg of copper with an average weight of 2,108 kg per crucible were melted, with a melting point of 1,090 1,270 ° C at an average melting time of 818 minutes per crucible. The melting was trouble-free and compared to conventional pots the pot life was increased by 77%.

The crucible values were as follows:

for rovzdornost content ¹ ₂ 3 ° compression strength nasákavos t

165

31.80% 5.99 MPa

17,20%

Example 2

To the graphite-fireclay mass of the composition of Example 1 were added 3 hd of a 30% SiO ₂ colloidal SiO ₂ solution and 0.32 hd of the oxidized synthane.

The crucibles produced after firing in a muffle furnace at 850 ° C were used to melt bronze and brass in an amount of 3,500 kg with an average weight of 1,710 kg per crucible, with a melting temperature of 1,120 1,260 ° C and an average melting time of 590 minutes based on per cup. No metal leakage occurred during melting, graphite burn-out was minimal and in particular absolute safety of work was ensured.

The crucible values were refractory content Al 2 ° 3 compressive strength absorbency t as follows:

165

32.05% 6.22 MPa

16,40%

Example 3

A 4 h. D. Colloidal solution was added to the graphite-fireclay mass of 19 h. D., Graphite, 45 h. Dump refractory slag and 64 h. D. Refractory clays.

240,887 SiO 2 silica having a SiO 8 content of 30% and 0.4 h, d. Of oxidized synthane.

Plugs were made from this mass to close the outlets of the ladle nozzles. The pressed plugs showed the following values after firing at 960 ° C in a reducing atmosphere:

heat resistance crushing capacity content ΑΙ ,, Ο ^ water absorption

167/169 590.02 MPa

33,90% 13,93%

The plugs were used in casting steel with 12% Mn in a 5t ladle. The plugs were very well sealed compared to the conventional ones, the casting process was controllable, the plugs had a low melting rate. ·

Example 4

With the graphite-refractory material having the composition of Example 3 was added 2.6 HD silica sol Si0 ₂ content of Si0 ₂ 30% and 0.3 HD oxidized Syntan. Stoppers were pressed from the mass and fired in a reducing atmosphere to 960 ° C. The defectoscopic examination by irradiation eliminated structural defects in comparison with plugs. The casting plugs of manganese steels showed inertia to the molten metal. The weight loss of the plugs was 4%.

Claims (1)

SUBJECT OF THE INVENTION 240 887 Refractory graphite-chamotte compound with a mixed chemical binder, in particular for the manufacture of crucibles, composed of a mixture of graphite, refractory clay and ceramic grit, characterized in that the mixed chemical binder is a mixture of 0.5% by weight. % to 0.0 wt. % colloidal 30% silica solution and 0.1 wt. % to 0.6 wt. oxidized synthane.