The Analysis Of Flow Field In T-Curtain Coater On The Basis Of Fluent Software

Curtain coating is developed in recent years,it is a non-contact coating technology,can reduce the paper broken,save paint,reduce costs,improve the effect of coating cover,and realize high speed in low quantitative coating.In curtain coating process,the uniform and stability of the curtain is very important to get good coating.The formation of the curtain is linked to the die head geometric shape,operating process,and the rheological properties of coating.This subject adopt the different coatings to study the internal flow field on the die head,to analysis the influence factors of coating effect and look for ways to improve the effect of coating.This topic using Fluent software to explores the internal flow field of the die.The paper respectively analysis the flow field in the die head of heat transfer paper coating,pigment coating and the pre coating of thermal paper.Firstly,I tested the rheological properties of the three different coatings in different solid content and temperature,within the scope of 1s^-1 to20000s^-1.And adopted Carreau model to fit the rheological properties of the three kinds of coatings.Heat transfer paper coating viscosity change slow with shear rate,with a relatively low viscosity under low shear rate,a relatively high viscosity under high shear rate.Heat transfer paper coating is easy produce eddy on the die head manifold,and the eddy would decrease as the heat transfer paper coating’s solids increase,temperature decrease and coating speed decrease.The pressure drop within the die head is large,and the pressure drop increase with the heat transfer paper coating solids increase,the temperature drop and coating rate increases.Under different conditions,the curtain on the die head exit always very uniform.Pigment coating have a relatively obvious rheological properties,with a relatively high viscosity under low shear rate,a relatively low viscosity under high shear rate.There no eddy current in the die head manifold.The head pressure drop is small within the die head,and it’s pressure drop will increases with the increase of solid content and the decrease of temperature.Pigment coating’s velocity transverse distribution in the die exit easy to appear uneven phenomenon due to its large fluid rheological property.In some case,the velocity uniformity index r is greater than 5%,it can not meet the requirements of the quality of coating.The pre coating of thermal paper is also the fluid with obvious rheological property.But its low viscosity under low shear rate and high shear rate.The eddy always current in manifold,and will increase with temperature increase and coating speedincrease.The pressure drop within the die head is small.All uniform index is less than 5%,can satisfy the requirement of the coating quality.Through the numerical simulation experiment of the three kinds of coating in the die,we find that the die head is easy produce eddy,easy appear uneven transverse distribution of flow velocity,and the pressure drop is too large.Through increase the chamfering radius to 10 mm,change the constant slit gap is 0.4 mm to clearance by the shape of the 0.4 mm to 0.6 mm gradient,and increase pipe radius from 10 mm to 12 mm.Simulation results show that the manifold eddy current decreases,the pressure drop significantly reduced in the die,and transverse distribution of the velocity at the exit are uniform.Finally I had did the verified experiment.The pressure change is consistent in the production and in the numerical simulation experiment.It is show that he numerical simulation results have certain reference value.