M Golzar - Assistant professor- Manufacturing Engineering Group, Tarbiat Modarres University, Tehran, Iran
A Ghaderi - M.Sc. student - Manufacturing Engineering Group, Tarbiat Modarres University, Tehran, Iran

Cellulose sheets are usually used in electrical insulator of power transformators. For manufacturing this insulator moisturized sheet is formed by bending press in an elevated temperature. The purpose of this paper is to find the spring back of bended sheet after removing from press die and to obtaine the radius change over time. Material behavior of cellulose sheet is assumed to be viscoelastic during and after the forming process. The spring back of bending press process is obtained experimentally by various methods of radius measuring of bended sheet. The process is also simulated by Finite Element Method and the results of experimental test and FEM have been compared. The material behavior during and after process and stress relaxation and strain recovery were discuused in order to predict the final raduis.

Cellulose sheet, spring back, viscoelasticity, bending press, FEM