The Deep Drawing Process Of Low Carbon Steel Tank With Large Diameter For Water Heater

The inner tank of water heater with large volume is increasing with domestic water consumption increasing.The traditional process of inner tank with large diameter is complex and difficult.While the deep drawing process for manufacturing inner tank can reduce costs and improve product’ quality effectively.However,the crack and inner wall wrinkle often take place for the deep drawing process of inner tank.So it is difficult to deep draw the cylindrical inner tank with large diameter.In this paper,the mechanical properties,finite element analysis of forming process and parameters of drawing process of STC2 steel plate and BTC245 R steel were investigated.The tensile property of STC2 steel and BTC245 R steel were investigated by uniaxial tensile tests at room temperature.Based on the load-stroke curves of tensile tests,the n value and r value of STC2 steel and BTC245 R steel were calculated.Then the engineering stress-strain curve and true stress-strain curve of STC2 steel and BTC245 R steel were obtained.According to the requirement of water heater capacity,the inner tank’ structure was designed,then the engineering diagrams and three-dimension models were drawn.It is determined that the two steps of drawing processes for inner tank should be adopted,and drawing coefficients of the first step and second step during drawing process are also selected.Then the dimension parameters of drawing depth,drawing diameter,fillet radius and the drawing gap of the two steps of process are designed.Finite element analysis of two steps of drawing process for inner tank was carried out,then the thickness distribution of inner tank during the first step and the second step of drawing process were analyzed.The effects of lubrication state,blank holder pressure(3-7MPa)and blank holder gap(t-1.5t)on the two stages of deep drawing process were investigated,and the optimum drawing parameters were selected.Thickness distribution of the final structure was measured.The thickness reduction ratio of BTC245 R and STC2 were 14.5% and 20%,respectively.Finally,the performance tests of the complete inner tank were carried out with static-pressure test and pulsation-pressure test.The static pressure test with thepressure of 1.5MPa for 15 min showed that the irreversible permanent deformation or rupture did not take place.And the pulsation-pressure test showed that there was no permanent deformation or rupture resulting from the structural defects caused by forming process.The results showed that the performance of inner tank obtained could meet the requirements,and the optimized drawing parameters were suitable for the manufacturing of inner tank.