CPC Definition - Subclass C21B

Last Updated Version: 2026.05
MANUFACTURE OF IRON OR STEEL (preliminary treatment of ferrous ores or scrap C22B 1/00)
Definition statement

This place covers:

  • The production of iron or steel starting from iron ores, e.g. the production of pig-iron;
  • The recovery of by-products, e.g. slag from these production methods;
  • Apparatus specially adapted therefore, e.g. blast furnaces or air heaters.
Relationships with other classification places

General metallurgical processes for obtaining metal from ores, and non-ferrous ores in particular, are treated in C22B.

Details of the apparatus which are of general interest to the group of installations, e.g. shaft furnaces, are also to be classified in F27B or F27D.

C21B 2100/40 concerns the specific purification and reuse of exhaust gases in metallurgical processes, while B01D 2258/025 concerns only the purification process in general of waste gases from metallurgy plants.

References
Limiting references

This place does not cover:

Preliminary treatment of ferrous ores or scrap

C22B 1/00

Informative references

Attention is drawn to the following places, which may be of interest for search:

Filters comprising loose filtering material

B01D 24/00

Filtering devices having features not specifically covered by groups B01D 24/00 - B01D 33/00, or for applications not specifically covered by groups B01D 24/00 - B01D 33/00

B01D 35/00

Separating solid materials using liquids or using pneumatic tables or jigs

B03B

Lift inclined, e.g. serving with blast furnaces

B66B 9/06

Manufacture or shaping of glass, or of mineral or slag wool; Supplementary processes in the manufacture or shaping of glass, or of mineral or slag wool

C03B

Lime; Magnesia; Slag; Cements; Compositions thereof, e.g. mortars, concrete or like building materials; Artificial stone; Ceramics; Refractories; Treatment of natural stone

C04B

Destructive distillation of carbonaceous materials for production of gas, coke, tar or similar materials, e.g. coke ovens

C10B

General processes of reducing to metals

C22B 5/00

Valves

F16K

Furnaces, kilns, ovens or retorts in general

F27B

Details or accessories of furnaces, kilns, ovens or retorts in general

F27D

Details of heat exchange or heat-transfer apparatus, of general application

F28F

Electric heating

H05B

Special rules of classification

In the group C21B 2100/22, reforming is based on a reaction with other hydrocarbon containing gases. In the group C21B 2100/24, shift reactions involve steam, water vapor or water.

Glossary of terms

In this place, the following terms or expressions are used with the meaning indicated:

pig iron

intermediate product of smelting iron ore with a high-carbon fuel, e.g. coke or charcoal

slag

partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction

tuyères

tubes, nozzles or pipes through which air is blown into a furnace

by applying additives, e.g. fluxing agents
Definition statement

This place covers:

Processes in which the additives can be added to dry products (e.g. pellets, briquettes), a metal melt or a slag.

Special rules of classification

The group overlaps with C21B 5/008, C21B 5/02, C21B 5/04, C21B 13/008: depending on whether the additives are generally applicable or related to a specific process either in the Blast Furnace (C21B 5/00) or in Direct Reduction process (C21B 13/00), double or single classification will apply.

Recovery of by-products, e.g. slag
Relationships with other classification places

Treatment of (metallurgical) slag is also classified in C04B 5/00 when artificial stone, cement, road material or like building materials are obtained therefrom.

Treatment of liquid slag
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Processes or devices for granulating material

B01J 2/00

Manufacture or shaping glass, or of mineral or slag wool; Supplementary processes in the manufacture or shaping of glass, or of mineral or slag wool

C03B

Lime; Magnesia; Slag; Cements; Compositions thereof, e.g. mortars, concrete or like building materials; Artificial stone; Ceramics; Refractories; Treatment of natural stone

C04B

Cooling slag
Definition statement

This place covers:

Cooling covers both dry and wet methods of cooling.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

General arrangements of separating plants

B03B 9/04

Ingredients other than water added to the molten slag; Treatment with gases or gas generating material

C04B 5/06

Handling or treating discharged material in furnaces

F27D 15/00

Making pig-iron in the blast furnace
Definition statement

This place covers:

Also the injection of additional (pure) oxygen and additional fuel; automatic control of the process; condition of the cokes or their characterisation; composition and distribution of the charge.

using top gas in the blast furnace process
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

In coke ovens

C10B

Production of fuel gases by carburetting air or other gases without pyrolysis or of combustible gases containing carbon monoxide from solid carbonaceous fuels

C10J

Purifying or modifying the chemical composition of combustible gases containing carbon monoxide

C10K

Special rules of classification

In case the top gas is treated before being sent back into the furnace, this aspect is also classified : either by the relevant class in another field (specific, e.g. C10K 1/02, dust removal).

Blast furnaces
Definition statement

This place covers:

Features which relate to the lay-out of the blast furnace area or to repair.

Evacuation and treatment of exhaust gases and the control and regulation of the top pressure.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Filtering material for liquid or gaseous fluids

B01D 39/00

Separating dispersed particles from gases or vapours by gravity, inertia or centrifugal forces

B01D 45/00

Separation of gases or vapours; Recovery vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases or aerosols

B01D 53/00

Centrifuges

B04B

Apparatus using free vortex flow, e.g. cyclones

B04C

Purifying or modifying the chemical composition of combustible gases containing carbon monoxide

C10K

Special rules of classification

Groups C21B 7/002 and C21B 7/005 concern evacuating and treating of exhaust gases from blast furnaces in general. Further classification is mandatory in indexing codes C21B 2100/00 - C21B 2100/80.

with special refractories
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Refractory materials

C04B

Linings for furnaces
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Arrangements of linings in shaft furnaces

F27B 1/14

Linings or walls for metallurgical furnaces in general

F27D 1/00

Cooling; Devices therefor
Definition statement

This place covers:

Cooling devices for the walls and bottom including staves, plates, pipes, etc; also leakage detection.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Cooling of linings of combustion chambers

F23M 5/08

Shaft furnaces with cooling arrangements

F27B 1/24

Linings or walls incorporating cooling arrangements

F27D 1/12

Cooling of furnaces or of charges therein

F27D 9/00

Heat exchange apparatus in which heat exchange media do not come into direct contact

F28D

Details of heat exchange apparatus of general application

F28F

Opening or sealing the tap holes
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Details or accessories of converters

C21C 5/46

Tapping equipment; Equipment for removing slag

F27D 3/15

Discharging devices, e.g. for slag
Definition statement

This place covers:

Runners and their accessories (roofs, heating etc); also equipment for transporting said runners.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Charging or discharging liquid or molten material

F27D 3/14

Tuyéres
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Arrangements of tuyeres

F27B 1/16

with appliances for distributing the burden
Definition statement

This place covers:

All distribution means different from bell-and-hopper, i.e. including revolving chute.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Transport or storage devices, including chutes, conveyor belts etc

B65G

Arrangements of devices for charging of shaft furnaces

F27B 1/20

Charging of particulate material

F27D 3/00

Charging directly from hoppers or chutes

F27D 3/10

Dust arresters
References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Open-topped filter housing

B01D 35/34

Filtering material for liquid or gaseous fluids

B01D 39/00

Separating dispersed particles from gases or vapours by gravity, inertia or centrifugal forces

B01D 45/00

Removal of waste gases or dust from converter

C21C 5/38

Offtakes or separating apparatus for converter waste gases or dust

C21C 5/40

Test rods or other checking devices
Definition statement

This place covers:

Any measuring, controlling or observation devices.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Arrangements of monitoring devices, of indicators, of alarm devices for shaft furnaces

F27B 1/28

Arrangements of controlling devices of furnaces, kilns, ovens or retorts

F27D 19/00

Arrangements of monitoring devices in furnaces, kilns, ovens or retorts

F27D 21/00

Specific investigation or analysing means of materials by determining their chemical or physical properties

G01N

Making spongy iron or liquid steel, by direct processes
Definition statement

This place covers:

Direct reduction processes obtaining either sponge iron or molten iron or steel.

Inventions which concern the treatment of the reducing gases, the solid reductant, the ores, the reduced iron or the addition of fluxes or the treatment of the ores in a fluidised bed or lead to attainment of molten iron or steel.

References
Informative references

Attention is drawn to the following places, which may be of interest for search:

Chemical or physical processes according to "fluidised-bed" technique

B01J 8/24

General methods of reducing to metals by solid carbonaceous reducing agents

C22B 5/10

General methods of reducing to metals, by gases

C22B 5/12

Fluidised bed furnaces

F27B 15/00

in hearth-type furnaces
Definition statement

This place covers:

Also rotary-hearth furnaces.

in electric furnaces
Definition statement

This place covers:

Also using a plasma.

Multi-stage processes {processes carried out in different vessels or furnaces}
Definition statement

This place covers:

Inventions in which different types of installations are used in sequence to arrive either at a solid or a molten product.

Other processes for the manufacture of iron from iron compounds (by electrolysis C25C 1/06)
Definition statement

This place covers:

Any other processes for the manufacture of iron from iron compounds not covered by other groups in C21B 13/00, e.g. processes involving nuclear energy or a chloride process.

References
Limiting references

This place does not cover:

Electrolytic production, recovery or refining of iron group metals

C25C 1/06

Informative references

Attention is drawn to the following places, which may be of interest for search:

General methods of reducing to metals

C22B 5/00