Cause Analysis And Control Of Shell Defect Of Hot Rolled Strip

The quality characteristic of hot rolled strip product is mainly composed of surface quality,shape accuracy,the size and mechanical properties.With the development of steelmaking and hot rolling technology,dimensional accuracy,shape accuracy and mechanical properties are greatly improved.However,surface quality includes many kinds of defects,involved in a long process and affected by a number of factors.The control difficulty is relatively large.Only depending on the process tracking of the surface detector is not enough.It is necessary to find out the crux of the problem and make effective control through mechanism research and macro and micro analysis.The shell defect is a kind of common surface defects of hot rolled strip.The shell defect is easy to produce holes after cold rolling.It leads to broken belt or adhere to the roll which causes many defects.The research on the shell has not stopped at home and abroad.Through the improvement of steel making controlling level,the application of chamfering crystallizer technology,and the improvement and application of rolling process technology,the overall control level is improving,but it still can not completely solve the problem of skin defect.This paper focuses on the study of the causes of shell in hot rolling process from the following aspects,which provides a basis for the control of warping:(1)From the macro and micro characteristics,establish a method to distinguish the causes of shell defect which caused by slab defects or hot rolling process.(2)By measuring the slab temperature field,it is analyzed that the slab is actually rolled in the two-phase region during the rough rolling process.The reason of shell is rolling crack.The flow characteristics of hot rolled slab and the reason of shell further are verified by drilling experiment on slab.(3)The heating mode of heat load forward is established.The improved plans of the temperature increase of heat recovery section and burner control are made,and it improves the heating efficiency.(4)Controlling water leakage point of rough rolling,remodeling of descaling nozzle and edger rolls,improving the slab corner shape,and reducing slab temperature drop and local temperature drop could effectively reduce the shell defects during hot rolling process.