RH Vacuum Degassing Technology Oct07

RH Vacuum Degassing Technology...

RH Vacuum Degassing Technology Vacuum degassing is an important secondary steel making process. This process was originally used for hydrogen removal from the liquid steel but presently it is also being used for secondary refining and has become increasingly important process of secondary steel making. Pressure dependent reactions are the reason for the treatment of liquid steel in this process.  There are many vacuum degassing systems but RH type degassers are very popular. The RH process has been named after Ruhrstahl and Heraeus where this process was initially developed. The RH degassing technology was first introduced in the late 1950s and presently it has become an important tool of secondary metallurgy in most of the modern steel plants. The RH circulation degassing process has proved its vast suitability in large number of shops worldwide, for operation with short tap to tap times covering heat sizes up to 400 tons. The vacuum treatment in RH plants produces steel which fulfills the demand of high steel qualities. To achieve this, the liquid steel is allowed to circulate in a vacuum chamber where a considerable drop in pressure causes it to disintegrate into the smallest of the parts. The increase in the surface area allows the liquid steel to degas to the best possible extent. The process needs reliable vacuum units since it should be able to suck off very large flow rates under very difficult conditions of dusty atmosphere and high temperatures. The mechanism of the vacuum treatment of liquid steel in RH process is shown in Fig 1. Fig 1 Mechanism of the vacuum treatment of liquid steel in the RH process RH degassing process The process mainly consists of a refractory lined cylindrical reaction vessel with two steel pipes attached to the bottom of...

CAS-OB Process of Secondary Steelmaking Oct03

CAS-OB Process of Secondary Steelmaking...

CAS-OB Process of Secondary Steelmaking The CAS-OB process consists of Composition Adjustment by Sealed argon bubbling with Oxygen Blowing. It was developed by Nippon Steel Corporation. Typical schematic diagram of a CAS-OB installation is shown in Fig 1. Fig 1 Schematic diagram of a CAS-OB installation The process allows alloy additions to be made under an inert argon environment. It allows simultaneous addition of Al and O2 gas blown through a top lance. These react to form Al2O3 and generate a considerable amount of heat due to exothermic nature of the reaction. The CAS-OB process, therefore results into chemical heating of the liquid steel. The Equipment Liquid steel processing is carried out in ladles, equipped with slide gates and a porous plug for blowing argon. Equipment for the process consists of a snorkel or bell fixed to the movable bracket. To the top of the bell, a port is provided, which serves the purpose of feeding of ferro alloys into the bell and for removal of gases to the gas cleaning system. The design of the bell has provision for lowering of oxygen lance and process and instrument (PI) lance for sampling, measuring of the temperature and for measuring of the dissolved oxygen as well as a lance for injecting a metal powder, desulphurizing compound and CaSi wire. Bell consists of two parts. The upper part is lined only from the inside, while bottom is lined both inside and outside. Lining of the bell is usually done with of high-alumina castables reinforced with 2 % stainless steel needles. These castables are also used for the lining of the oxygen lance and lance for blowing argon into the liquid steel, which is used when argon cannot be supplied to the liquid steel through the bottom porous plug. Chrome magnesite bricks...