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Vacuum processes

Secondary Metallurgy

Recirculation Degassing (RH)

SMS group's RH process  is characterized by very good results in decarburization and degassing with relatively low temperature losses. It is particularly suitable for a melting operation with short cycle times. This has been demonstrated in the operation of more than 180 plants worldwide with heat sizes of up to 400 tons.

No special slag measures, no additional ladle freeboard or purge plugs in the ladle bottom are required for the RH process. Fast vessel change and efficient ladle transport concepts increase the capacity of a plant. It can be further increased by using a duplex design.

The following features characterize the RH process:

  •     Decarburization to lowest final contents
  •     Rapid removal of hydrogen
  •     Alloying and fine trimming with high accuracy and very good yield
  •     Fast addition of large quantities of alloy
  •     Rapid homogenisation of the ladle contents - even when adding large quantities of alloy
  •     Very short treatment times with the vacuum carbon deoxidation type
  •     Relatively low temperature losses (depending on the batch size)
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RH and RH-TOP units are installed in steelmaking plants with heat sizes of up to 400 tons.

There are different types of lifting systems: Fixed vessel installations use ladle lifting systems, while movable vessel installations employ vessel lifting systems.

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Multifunctional TOP lance systems are indispensable for operating RH systems efficiently and cost-effectively. The circulating liquid steel comes into direct contact with the refractory lining of the vacuum vessel, therefore the lining must be preheated to over 1,000° C. All modern RH plants today have either a simple burner lance for heating the vacuum vessel in the plant or a multifunctional TOP lance.

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Rh-Rockertype® – a boost for safety

The RH-RockerType® unit has been engineered to significantly increase the performance parameters of RH processes. This well proven yet future-oriented solution provides safe, reliable RH operation.

The origin of RH-RockerType® technology from SMS group goes back to the 1950s. Its main purpose then was to safely lower the vacuum vessel system and immerse the snorkels into the liquid steel in a simple and reliable way. The system stands out because of its user-friendly operation and maintenance.

Recently, RH-RockerType® technology has been further improved. It now smoothly lifts and lowers the ladle instead of the vacuum vessel system. Other useful features have also been added.

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Increased efficiency

To speed up your intra-logistic processes in the RH plant, the ladle lifting RH-RockerType® can use two ladle cars. One of them brings the ladle to the RH station for treatment. After treatment, another car takes it to the caster area while the first ladle car brings the next ladle.

This design supports flexible processes, since the first ladle car can be recharged while the ladle is being treated. Depending on the layout of the steel shop, this greatly improves your ladle transportation logistics. The resulting advantages can be implemented both in single treatment stations as well as in our fast vessel exchange units.

Since the alloy system and the vacuum pump are fixed directly to the vacuum vessel system, no special conveyors or moving vacuum ductwork are required.

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A key to lasting reliability

Two hydraulic cylinders are installed to operate the lifting and lowering processes of the ladle. For normal operations, they are mechanically synchronized. In the case of an electric power failure, the ladle is lowered safely onto the ladle car in a controlled way by gravity. Maintenance of the complete hydraulic system is simple and straightforward. The RH-RockerType® unit is very well protected against steel splashes and liquid steel from a ladle break-out.

In comparison to vacuum vessel lifting installations, there is much better access to the vacuum vessel platform. Similarly the automatic sampler and other auxiliary equipment are easily accessed.

For safety and efficiency reasons RH-RockerType® technology will play an important role in future RH secondary metallurgical infrastructure.

Vacuum Degassers (VD)

The tank degassing process has proven its high availability and its suitability for the production of high-quality steel grades in more than 130 units with heat sizes up to 340t. The process is characterized by slag free-tapping at the melting unit, application of ladles with a sufficient freeboard and inert gas stirring through the ladles bottom by means of porous plugs.

The application of oxygen blowing systems (VD-OB) enables forced decarburization and chemical heating by aluminium combustion.

VD and VD-OB tank degassers

SMS group’s tank degassers support EAF and BOF plants, permitting heat sizes of up to 400 t. Inert gas is introduced into the bottom of the ladle by means of porous plugs. The process is characterized by slag-free tapping at the melting unit. The plant requires an efficient vacuum pump system to meet the specific requirements of the desired metallurgical process.

Standard tank installations are fixed above or below the shop floor. Movable tank installations or twin tank installations substantially increase performance.

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Metallurgical functions

  • Hydrogen and nitrogen removal
  • Decarburization to lowest levels
  • Desulfurization by metal and slag reaction
  • Efficient alloying and fine trimming with high accuracy
  • Slag management
  • Improvement of castability
  • Homogenization of ladle contents

Additional applications using VD-OB lance systems:

  • Oxygen blowing for forced decarburization from high initial carbon levels, e.g. for the production of ultra-low carbon steel grades
  • Oxygen blowing for chemical heating by aluminum oxidation
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Vacuum ingot casting (VIC)

An alternative application for Tank Degasser technology is VIC. The basic principle is stream degassing of liquid steel poured under vacuum conditions to form an ingot situated in the vacuum tank. Beneath the removal of gases oxygen pick-up from ambient air is safely prevented.
Steel flow is controlled either by stopper rod or slide gate. Stations process ingots from 15 to 350 t.

Metallurgical functions

  • Degassing
  • Prevention of oxygen pick-up during casting
  • Prevention of re-oxidation
  • Reduction of macro inclusions
  • Significant reduction of alumina inclusions
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Vacuum Oxygen Decarburization(VOD)

The vacuum Oxygen Decarburization process has proven its economic operation and its suitability for the production of high-quality stainless steel grades with highest cleanliness in more than 75 plants with heat sizes of up to 200t.

Similar to VD, the VOD units are designed to meet the specific requirements of the plant layout as well the individual process of our customers.

VOD tank degassers

Vacuum Oxygen Decarburization units are needed in stainless steel production in order to reach extra low carbon contents in an economical way.
This advantage is due to reduced chromium oxidation that results in less reduction agent consumption. VOD is still without any alternative in the production of high-end stainless steels such as ferritic and super-ferritic grades. SMS group supplied VOD units up to 200 t.

Metallurgical functions in addition to VD-OB

  • Forced decarburization of up to 1 % [C]
  • Oxygen blowing at < 80 mbar pressure
  • Slag reduction for chromium recovery

VODs are integrated into the production line in two ways:

  • DUPLEX-line – EAF- (LF) –VOD – CCM
  • TRIPLEX-line – EAF – AOD – (LF) – VOD – CCM

Basically similar to VD-OB the VOD units feature an adapted design due to the more violent character of process

  • Additional water-cooled parts and splash shield
  • Design and control of the vacuum pump match the demanding process
  • Vacuum bag filters ensure waste gas cleaning from extra dust load

SMS group offers a sophisticated metallurgical model for operator support in achieving uniform results with complex VOD process.

  • Dynamic tracking of steel condition
  • Dynamic calculation of set point values
  • Dynamic tracking and guidance of carbon content based upon waste gas data
  • Thermal model
  • Least-cost calculation of alloy additions
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Vacuum Pumps

Vacuum pumps

High-performance vacuum pumps from SMS group are the heart of secondary metallurgical vacuum processes. For both recirculation or tank degassing processes, our vacuum pump technologies are tuned to your specific steel conditions and to your individual plant and production requirements.

Our vacuum pump systems precisely control the rate of pressure reduction from atmospheric level to low vacuum pressure. During the various treatment steps the vacuum level is accurately controlled to match the system’s metallurgical needs.

In order to deliver optimum results high suction capacity, low energy consumption and optimal reliability are essential elements of our design.

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