CS257550B1 - Graphite nozzle with lining and method of its production - Google Patents

Abstract

The graphite nozzle with liner is uniform and the liner is boron nitride. Way its production lies in the fact that it is hot compresses turbostratic boron nitride, characterized hexagonality index Ijj> 30, in a graphite molding tool at the same time becoming part of the body of the nozzle, at temperature 1800 to 1900 ° C and a pressure of 20 to 400 MPa and after cooling with mechanical treatment creates a nozzle opening. The nozzle is usable for mold making for continuous metal casting high in Fe, Co, Ni and high resistant to erosion by hot gases.

Description

The invention relates to graphite nozzles with lining suitable for the manufacture of ingot molds for the continuous and / or semi-continuous casting of metals with a high content of cobalt, nickel and iron elements.

In demanding working conditions, graphite nozzles are used which have a number of advantageous properties, such as the ability to withstand high temperatures and temperature shocks, high thermal conductivity, good machinability, abrasion and erosion resistance, dimensional stability even at high temperatures, low coefficient of linear expansion However, the disadvantage is that at temperatures above 1,300 ° C, graphite oxidizes rapidly and also reacts with carbide-forming elements such as Ni, Ti, Fe, Co, etc.

An example of limiting conditions is the use of graphite ingot molds for the continuous casting of alloys containing the above elements in a higher concentration. Recently, devices for casting alloyed steel, nickel, cobalt and their alloys have been put into operation in the world. These devices have crystallizer nozzles composed of several parts of different materials, most often zirconia, hexagonal boron nitride, beryllium bronze and graphite. All these parts are mechanically interconnected in various ways, eg by screwing, wedges, gluing, etc. and cooled by water.

The disadvantages of such a construction are high demands on the accuracy and alignment of the assembly, easy vulnerability, difficult joining of materials with considerably different dilatations, high cost and low efficiency of heat transfer from the cast metal to the cooling medium, There is also a danger of melting or even melting the bronze part of the nozzle, and thus of the entire device. The most difficult part to manufacture, ie the lining, has to be produced with a dimensional excess, which creates a risk of inhomogeneity, cracks and increases the cost of the equipment.

The above-mentioned drawbacks are overcome by the graphite nozzle with the lining according to the invention, which is characterized in that it is monolithic and the lining is formed by boron nitride. The process for the production of this graphite nozzle according to the invention is characterized in that turbostratic boron nitride, characterized by a hexagonal index of I > 30, of a vibration band width in the IR range of 1 375 cm

-1 ^H and an antipase between 810 and 830 cm, hot-pressed in a graphite die, which also becomes part of the nozzle body, at a temperature of 1,800 to 1,900 ° C and a pressure of 20 to 400 MPa upon cooling, a nozzle hole is formed by mechanical machining.

The mechanical properties of boron nitride, ie hardness, ability to withstand thermal shocks, dilatations, allow easy mechanical working together with the graphite part. By hot pressing of turbostratic boron nitride into a graphite tube, a semi-finished product was produced, which by mechanical processing produces compact, non-detachable graphite nozzles with a homogeneous lining of perfectly hexagonal boron nitride.

Indeed, from the close connection of the boron nitride liner to the graphite nozzle itself, the nozzle's ability to dissipate heat from the interior of the nozzle to its cooled surface is dependent on the nozzle to determine its usability.

The manufacturing process is simple, inexpensive and the nozzles are resistant to higher working temperatures, the heat dissipation ability is not reduced by air gaps. The boron nitride lining is not unnecessarily large, it is very tightly bonded to the graphite (a diffusion joint with a boron carbide interlayer is also possible) and the combined nozzle can be produced with ideal alignment. The nozzle is highly resistant to dissolution in the carbide forming environment. It is applicable, for example, to the manufacture of nozzles for the continuous casting of metals with a high content of Fe, Co, Ni and as a nozzle it is highly resistant to erosion by glowing gases.

An exemplary embodiment of a graphite nozzle is shown in Figures 1 and 2 of the drawing.

Example

In the graphite die 2 ' of FIG. 1, with a bore 2 made of graphite, cold pre-compressed tablets of turbostratic boron nitride were inserted. The actual hot pressing was carried out at a temperature of 1,900 ° C and a pressure on the piston of 40 MPa for 120 minutes, while the graphite pressing tool 2 was electrically resistively heated by passing the current and the pressure on the piston was applied throughout the heating. The die formed from this result was made by mechanical machining of the die - die for continuous casting of metals upwards of shapes according to Fig. 2. The die 2 consists of a graphite body and a boron nitride lining in hole 2. This die was used for continuous casting of Cu70Ni30 alloy; the service life of this ingot mold was 15 hours of operation.

Claims (2)

Graphite nozzle with lining, characterized in that it is monolithic and the lining consists of boron nitride. 2. A process for producing a graphite nozzle according to claim 1, characterized in that the turbostratic boron nitride, characterized by a hexagonal index I _R > 30, is hot-pressed in a graphite die which becomes part of the nozzle body at a temperature of 1800 to 1900C. and a pressure of 20 to 400 MPa, and after cooling, a nozzle opening is formed by mechanical machining.