Research Of Stress Analysis Theory And Strength Design Methods For Cast Iron Dryers

Cast iron dryers, which are classified to special cast iron pressure vessels, have been applied in paper drying in papering industry all over the world. In this paper, owing to the gross deficiencies of the design method and code of dryers, the stress status of dryers under the working condition is analyzed in detail and the reasonable, reliable methods of the designing calculation are studied.At first, one kind of finite element model which is more accurate than the union model used before is set up to simulate the mutual contact between head and shell flange well. The stress analysis and measurement of the most typical and common dryers are done, from that the rightness of the calculative model is verified and the stress distribution of dryers under the inner pressure is got. According to the stress calculation of bolts of all common kinds of dryers with this model, the design method of bolts is put forward. Further more, the fracture possibility is analyzed with fracture mechanics after the stress calculation of local high stress area around the bolt hole in shell flange and the measurement of fracture toughness of gray cast iron. The improving structure of bolts connected head and shell flange is brought forward.The calculation method of the utmost load of gray cast iron beam with rectangle section is obtained through the analysis of limit load behavior of the beam under the united action of bending and pulling, therefore the design method of limit load about forcing parts of cast iron pressure vessels is determined. According to the results of explosion experiment and nonlinear finite element analysis of the head of 914mm dryer, the feasibility of the theory of limit load of cast iron applying to the design of heads of dryers is studied and the designing calculation principle for heads of dryers is established.The calculating mold consisted of shell, pyramidal neck of shell with varied thickness, flange of ring with definite thickness for analytic solution is set up for the strength calculation and the design of the structure dimension of shell flange and pyramidal neck. This theoretic solution is compared with the results of finite element analysis and stress-strain measurement and is verified to be right. By use of this theoretical solution, the stress for various dryers with different pyramidal neck dimension is solved to study the influencing of dimension change on the stress level, from that the design request of the dimension of this transitional structure is put forward.For the stress analysis of dryers under the line load of supporting rollers, according to Hoff theoretical solution of thin cylindrical shell under line loads, Mangelsdorfapproximate solution is modified on the basis of the calculation analysis for 14 sets dryers' dimension by computer programming with Matlab software. The approximate formulas of the second largest hoop stress of the middle section of the shell are derived. The influence of line load width on the results of theoretical solution is studied by the way of finite element calculation of cylindrical shell under line loads with different acting width. On the basis of the results of finite element analysis and comparison with stress measurement about 2500mm dryer, the error which may produce by applying the theoretical solution derived from calculation mold of cylindrical shell to dryers is analyzed, form that veracity of using the stress calculation formulas derived in this paper to dryers under supporting rollers is conformed.After a dryer with a inner shell connected with two heads is analyzed with finite element method, the difference of stress distribution between this kind of dryer with common one is examined and the feasibility of utilizing the highest and lowest stress calculation formulas derived in this paper is studied. After the study on the characteristic of the fatigue behavior of gray cast iron dryer, the fatigue analysis on this kind of dryer is carried out so as to specify the fatigue analysis method of dryers.