The main purpose of strip annealing is to eliminate work hardening of cold rolling, reduce deformation resistance, restore plasticity, and improve the deep drawing performance of strip. The main forms of steel strip annealing include bell annealing and continuous annealing. Bell annealing is divided into nitrogen-hydrogen bell annealing and full-hydrogen bell annealing according to the type of protective gas.
The annealing process system of the bell annealing furnace mainly includes heating speed, heating temperature, holding time, cooling speed, discharge temperature, etc.
The main disadvantages of the annealing process include:
1. Bonding:
There are some forms of stickiness, strip stickiness, and surface stickiness. When the bonding is severe, there will be a protruding feeling when touching, mostly distributed on the edges or in the middle of the strip; severe surface bonding will be torn or holes will appear when uncoiling, or even The book cannot be opened and becomes a "dead book".
cause:
(1) The tension is too large. Tension is one of the main reasons for the bonding of steel coils. Tension includes rolling tension and coiling tension of the rolling mill. When the tension is too high, the air flow circulation of the protective gas will be poor and thermal blockage will occur, causing the steel plate to bond.
(2) Poor plate shape. Poor plate shape will cause the strip to be thick on both sides, thin in the middle or thin on both sides, thick in the middle or have edge waves, middle waves, multiple waves and peripheral local waves, etc. After high temperature annealing, bonding can occur.
(3) Uneven overflow edges appear during coiling, and the strip coiling is uneven, especially for thinner plates, which are prone to adhesion.
(4) The emulsion is impure, and there are impurities in the emulsion that remain between the steel plates after annealing and evaporation. If they are not blown away, adhesion will also occur.
(5) Overtemperature, no matter what the cause is, if there is serious overtemperature in the furnace, it will inevitably cause bonding.
(6) Poor gas circulation. Because the furnace stacking does not meet the requirements, the protective gas circulates poorly in the furnace, resulting in uneven furnace temperature. Severe thermal blockage occurs in individual parts, and large temperature differences cause adhesion.
(7) The surface roughness of the strip steel is too small.
(8) The steel is too soft, the carbon and silicon content in the steel is low, and the bonding tendency is high.
(9) The cooling rate is too fast.
Prevention and elimination methods:
(1) Correctly select the curling tension.
(2) Control the roughness of the work roll.
(3) Control the plate shape and roll shape.
(4) Stack according to the stacking principle, place the tower-shaped rolls and overflow side rolls on the upper part of the steel stack.
(5) Comply with operating procedures and control annealing temperature and time.
(6) Ensure the integrity of the annealing equipment, accurate detection instruments, and insertion of thermocouples in place, etc.
