Annealing and coating

Annealing and coating lines
for silicon steels

An annealing and coating line (ACL) is used for recrystallization, texture formation and grain size adjustment of the silicon steel by heating the strip up to the annealing temperature. After cooling of the strip it applies onto its surface a varnish thanks to a coating machine.

The main goal of this line is to deliver a final product that can be used to manufacture electrical motors or small transformers.

Drever International furnaces allow to heat the strip in a controlled atmosphere to keep a clean surface suitable for the coating process. They also have a perfect control of the heating and of the cooling rate requested to perform the heat treatment of the most advanced steel grades.

ACL for silicon steels

After the cold rolling mill, the strip is delivered to the annealing and coating line. The steel strip coming from the cold rolling is very hard, as it has been extensively work hardened. It must be reheated to a temperature in the range of 850°C – 1150°C: this is the annealing. The annealing temperature is held for some time: this is the soaking. Then the strip is cooled down first slowly then at higher rate to a temperature low enough so that it can be coated. In order to avoid the oxidation of the strip, the complete furnace is filled by a non-oxidizing HNx atmosphere, a mixture of hydrogen and nitrogen.

Our mathematical model as well as our dedicated control system drive the temperature of the different zones of the furnace to reach the requested microstructure and properties at the end of the line.

Configuration

The usual configuration for the annealing and coating lines is horizontal.

Heating

Drever International supplies a combination of three technologies to reach the desired annealing temperature:

• The radiant tube furnace (RTF)
• Induction heating with longitudinal flux at lower temperature, or with transversal flux at higher temperature
• Electrical heating elements

Cooling

After the annealing and soaking, the strip must be cooled down to the exit temperature. A slow cooling is followed by a quicker cooling provided by HNx jets.

• Cooling tube section that can be equipped with electrical heating
• Slow cooling with plenums blowing hot HNx. This section can also be equipped with electrical heating
• Fast cooling with plenums blowing cold HNx

Coating

After annealing, the strip can be coated with a dielectric solution of three different types:

• Fully organic
• Fully inorganic
• Semi organic 

Drever International delivers

• The annealing furnace and the cooling section 
• The control system and a mathematical model of the furnace 

Our parent company, SMS group and its affiliates deliver all the other equipment of the line.
More information on SMS group offer