Study On Rolling The Driven Rotor Of The Screw Compressor

Screw rotor is the component of the screw compressor. Profile of the screw rotor comprised of varieties of curves is characterized by complexity and asymmetry, and the spiral teeth have obvious feature of big pitch, big helix angle and big tooth height. Now screw rotor is manufactured by machining. The utmost issues of present production are high material costs, low material utilization and production efficiency, in which more than60%materials of preform are removed. The reaserch of the big spiral teeth shafts like screw rotor manufactured by plastic forming process was seldom reported.In order to improve the process technology of the screw rotor, a new process of forming screw rotor by fixed cross rolling was put forward. In a rolling process, the screw rotor with asymmetric spiral teeth and steps is directly formed, which obviously enhance the production efficiency and material utilization of the production process. Due to the good mechanical property, SAE1141free-cutting steel is used in this process, convient for machining. By means of the theoretical analysis, finite element simulation and rolling experiment, the process of rolling the driven rotor with fixed cross rolling was carried out.Under the different deformation condition, hot deformation behaviors of SAE1141free-cutting steel was investigated by meas of the thermal deformation experiment. Based on the experimental results, an Arrhenius constitutive equation of SAE1141coupled strain, strain rate and temperature was established to achieve a good prediction of the hot deformation behaviors.According to the engagement theory and matrix theory, a general parametric equation of the roll profile curves was established, which shows that the shape of the profile is mainly affected by the dynamic relationship between the mould and the workpiece. The comparison of the obtained workpiece profile and the original profile of the screw rotor shows that the two profiles cannot be completely consistent. Then the corresponding roll profile of the finishing stage was rebuilt to accommodate to the meshing condition.Based on the rolling process of the big spiral teeth, two forming schemes of spiral teeth called invariant angle increase and variable angle increase were proposed. Then the two corresponding strategies of the mould profile named floated node method and fixed node method were revealed. Furthermore, the simulations of forming the spiral teeth by fixed cross rolling were carried out to analysis the proposed strategies of the mould profile and the blank. The results demonstrate the proposed condition of the blank length determined by the length of the spiral teeth and the mould profile designed by fixed node method, which is suitable for use in conjunction with the cross wedge rolling, makes the metal flow uniformly and raises the growth of teeth height. On the basis of the characteristic of forming the big spiral teeth, design method of the spiral mould with the gradual change of the tooth height and profile was present to ensure the good meshing between mould and workpiece. The mould consists of several grooves which have the features of variable lead, variable helix angle and increased height. Meawhile, the grooves height stays the same along the mould axis.The fixed cross rolling processes of forming the spiral teeth were simulated using finite element software DEFORM, which is used to analysis the law of metal flow. Furthermore, rotation direction of rolling the driven rotor is opposite to the direction of the screw rotor at work which provides the benefit that the metal in compressed zone flows along the radial direction.Based on the above theory researches, the spiral mould of forming the driven rotor was manufactured through the NC programming using UG software. The first asymmetric spiral teeth with helix angle45°20’and propotion of the tooth height45.5%and steps had been directly formed in a rolling process. That the formed driven rotor has a satisfied profile shape and good central quality was demonstrated by experiments. It verifies the validity of the research conclusions put forward firstly in this paper and the feasibility of forming the driven rotor by fixed cross rolling. The fixed cross rolling has material saving rate as high as39%and5-8s of the rolling time in comparison with classical process, which presents an application value for engineering.