Snorkels for vacuum degassing of steel

The subject of his invention are the snorkels for recirculating vacuum-degassing of steel.

The process of vacuum degassing of steel in steel ladle has the purpose of reducing the content harmful gasses dissolved in steel as hydrogen, oxygen, nitrogen, as well as decarbourizing and raising steel purity, thus improving its mechanical properties.

Many methods of vacuum degassing of steel are known, among them the RH recirculating vacuum-degassing process consisting in metal circulation through a vacuum chamber of an RH degasser equipped with a ladle for liquid steel, provided with a metal-drawing snorkel that contains an inert gas supply pipe and a recirculating snorkel. During the steel degassing process both snorkels are inserted into liquid steel in the ladle that is situated below the chamber of the degasser unit. Besides, the RH degasser is equipped with chute for alloying additions, a burner hole and, in its upper section, a gas-suction duct and a pipe for vacuum creation in the chamber.

The vacuum-chamber throat, located in its lower section, consists of separate ceramic rings connected to the metal-drawing and recirculating snorkels, located coaxially to each other and their internal refractory lining is made of many layers of ceramic blocks arranged next to each other in one circumferential line.

Once the snorkels are inserted in molten steel, liquid steel is drawn from the ladle to the vacuum chamber of the, RH unit, whereby the steel is circulated due to inert gas, preferably argon, being supplied through metal-drawing snorkel. By raising up and expanding, the inert gas pumps liquid steel into vacuum chamber through the metal- drawing snorkel, wherefrom, after its degassing, the steel returns to the ladle through the other, recirculating snorkel. Liquid steel is drawn only up to the level of the barometric pressure column which depends on external pressure and the pressure in the vacuum chamber.

The external refractory lining of snorkels, as used in known equipment for vacuum- degassing of steel, has a relatively short service life because of concrete-dissolving chemical corrosion that takes place in their service as a result of direct contact with the liquid layer of slag and having a destructive effect on the refractory lining of snorkels. In order to reduce the corrosive wear of monolithic Al ₂ O ₃ -base concrete layer of snorkels the concrete surface is sprayed with alkaline mass during time breaks between consecutive steel melting cycles. Thus, a layer of material that protects the concrete against direct contact with liquid slag is created.

The above mentioned snorkels have a steel casing, which holds the internal and external parts of ceramic working lining. However, in case of long times of the process and short time periods between consecutive degassings, the temperature increments of that casing after each degassing add up during the sequence and the consequential excessive rise of casing temperature leads to its significant expansion and deformation. The expansion of casing as a result of high temperature causes clearly noticeable cracks j.J „&:„„+ „,, +^ ₁ .

cooperating vacuum-chamber throat rings.

The essence of the snorkels for recirculating vacuum-degassers of steel according to this invention consists in manufacturing of metal-drawing and recirculating snorkels as well as vacuum-chamber throat rings in degassers as monolithic sets, in which ceramic blocks of the internal lining are made of several layers of rings bound together with similar overlapping blocks, with perforation being made on/in external refractory concrete lining of those monolithic sets. Favorably, the steel casings of both snorkels are provided with cooling systems, preferably gas cooling systems. Connecting the throat ring with snorkel to form a single monolith in which ceramic blocks of the external lining overlap each other has caused a significant raising of mechanical strength of those monoliths compared to separate rings of throats and snorkels with ceramic blocks arranged one next to the other in several ring-shaped layers. Making of perforation on external refractory concrete lining/surface of snorkel has enlarged the contact surface for the sprayed protective mass with concrete surface thus providing the potential for applying a thicker protective layer onto external concrete lining of snorkels for vacuum degassing of steel while ensuring also good adherence and holding of sprayed alkaline mass on the external surface of the snorkel. On the other hand, introducing of cooling system into steel casing of snorkel constituting a monolith with throat ring prevented excessive temperature increments and consequential cracks of the protective mass.

The object of his invention is shown in examples of its embodiments in the drawing where fig. 1 is a perspective view of either metal-drawing or recirculating snorkel with perforated surface of external refractory lining of the recirculating vacuum-degasser of steel, fig. 2 is a perspective view of the steel casing of the snorkel shown in fig. 1 with an arrangement of cooling pipes, and fig. 3 is a perspective view of a fragment of vacuum chamber of the recirculating vacuum-degasser of steel in axial cross-section.

The throat I of the vacuum chamber 2 of the recirculating vacuum-degasser of steel is provided with metal-drawing snorkel 3 and recirculating snorkel 4. Each of these snorkels, 3 and 4, is made as the monolith, 5 and 6, consisting of steel casing 7 with refractory lining 8_ on its external surface and a sleeve element 9 of refractory ceramic blocks iO located inside of that casing, so that the sleeve element 9 covers a set of pipes of the gas cooling system JJ, mounted on the internal surface of the steel casing 7 and projecting above its upper face by a dimension L which is equal to approx. 40 % of its total height H. Besides, external refractory lining 8 of the steel casing 7 is provided with perforation 12 all over its surface, whereas the refractory ceramic blocks H) of the sleeve element 9 are arranged alternately next to each other so that they form overlaps 1_3 with the neighboring ceramic blocks jj).