Theoretical And Experimental Study Of Pressure Screw Pairs Micro-Size Behavior

The pressure screw pairs are important parts of modern high intensity mill to meetthe demanding of large stroke adjusting, whose service life and stability is closely relativewith the normal running of mill. And the short service lives limit the mill development.The pressure screw pairs are similar with threaded and coupled in outline. Presentstudy of pressure screw pairs stays on static design in relative books. The pressure screwpairs need to meet the demanding of intensity, rigidity, abradability and stability. Inpractice, pressure screw pairs abrade heavily. Some even broke up in several weeks. Nowpressure screw pairs of 2800mm and 3500mm plate mill are brought from abroad tomaintain the normal running of mill. It is urgent to know why the pressure screw pairsabrade heavily. It is a great chance to enter the sub-project of "Ten-five" National Science andTechnology named "Improve the capability of bending roll and reliability of the pressdown system for 3500 plate mill". After practical testing, numerical analysis, modelexperiment and thinking, it is found the medium diameter orientation is unreliable. It isthe micro-size behavior makes the pressure screw pairs with short service life. In the endof paper, a new screw pairs with long service life is presented.The paper has six chapters. The first chapter is introduction of the developmenthistory of heavy and medium plate mill and problems existing in the pressure screw pairsof present plate mill. In the second chapter, 3-D traction and displacement field MultipoleBEM analysis are given out, including the axial pressure distribution between threadlayers, radial pressure distribution along teeth surface and pressure distributions under theinterference of outer couple. The third chapter is about the one-third model experiment.Electrometric method is adopted. It can be seen from the testing results the micro-sizebehavior is the main reason for the uneven pressure distribution. In the fourth chapter, thepressure screw pairs are checked with traditional design theory. The traditional theory cannot explain why the pressure screw pairs abrade heavily. Impact load is used to analyzethe forming reason of the teeth bulge. The fifth chapter is focus on the dynamic charactercomputing of the pressure screw pairs, including the natural modes and frequencies ofscrew under compound and normal nut constraints, dynamic response under impact load.One-eighth model experiment is done to verify the analysis results. In the sixth chapter, anew pressure screw pairs is given out.The micro-size behavior explains why the pressure screw pairs abrade heavily andlays experimental and theoretical basement for the design of new pressure screw pairswith long service life. The research results have both theoretical and economic value.