The Study On The Control And Annealing Process Of The Bell-type Annealing Furnace

Full hydrogen bell type furnace is a kind of the main heat treatment equipment,which is used for the cold-rolled strip annealing treatment in the hydrogen as a protective gas.Compared with hydrogen nitrogen furnace,the surface cleanliness of the annealing product is high,meanwhile,the heat transfer efficiency is greatly increased.To process the harden cold-rolled strip steel,the strip steel internal organization will be rearranged and the internal stress will be eliminated after the recrystallization annealing in the full hydrogen bell type furnace.It is helpful for the subsequent use of the products.This paper introduced the control mode of the full hydrogen bell type annealing furnace.It analyzed the annealing performance instability and surface area of carbon defects for production of steel coil,which identified the furnace temperature control is not accurate and atmosphere control purging inadequate were the main reasons for the above defects.Not only improved the furnace temperature control accuracy by heating cover points or control mode,the number of air valve and nozzle switch improvement but the effect of the purging,improve the strip surface quality by purging process improvement and wind guide plate.In process of the bell type furnace annealing,the heat goes from heating cover to internal cover by radiation,mainly because of the convection heat transfer between the internal and external cover,which is made from the ejecting of high temperature flue gas from the burner;the radiation heat transfer from the inner cover and the inner surface of outer garment;cooling on outside surfaces of heated hood and the heat conduction on the hood wall.The accuracy of the calculation model was verified by multi-point temperature test,and the influence of heating speed and heat preservation time on the temperature difference of the coil of strip was analyzed.The annealing process of stamping cracking and annealing adhesion was studied.Firstly,through the technological test of the heating speed and heat preservation time,it improved the system of heating and heat preservation and prevented the hot phenomenon of overheating and excessive temperature difference in order to ensure the uniform annealing organization and improved the stamping cracking defects.Secondly,the steel volume is reduced as well through the improvement of cooling speed and the test analysis.