| The advantage of rack and pinion rigs is that they can actively be provided with pressure when drilling.The reliability of the rack and pinion fixed as the core component of this rig determined the proper operation of the rig.This paper is based on an eight-axis,four-rail symmetrical lifting box,which is based on its structure and work principle to analysis the form of rack loading and its tightness and the looseness requirements.Combined with the relevant standards for bolted fasteners,the bolt load distribution of multi-bolt connections,the structural parameters of bolted fasteners,the thread load distribution under preload,and the relaxation of bolts under reciprocating forces are studied.Based on the rack and pinion lifting test rig platform for bolt fixation experiments,the mechanical characteristics of the multi-bolt connection of the rack and pinion under no-load lifting,automatic drilling feed,high-speed drilling feed and maximum hook load conditions are investigated,and the reliability of the proposed bolt arrangement method for heavy-duty rack and pinion multi-bolt connections is verified by comparison and analysis with theoretical analysis and simulation results.The following main areas of research were carried out:The design methods for multi-bolt connections in domestic and international bolt design standards are reviewed.The analysis methods for contact problems in bolted connections,the analysis theory of material creep during bolt tightening and the analysis of load distribution in multi-bolt connections in conjunction with the linear elasticity theory of materials are described.On the basis of the accuracy and convergence of the creep model calculation,a creep composite time strengthening model of the material was chosen to study the bolt loosening problem.On the basis of a simplified rack and pinion drive mechanism,a geometrical model of the rack fastening has been developed using CAD parametric modelling methods.In conjunction with third strength theory,a method is proposed to assess the effectiveness of multi-bolt fastening of heavy-duty rack gears by means of the relative displacement between the bolts and the bolt holes,on the basis of satisfying the material strength of the rack gears.The influence of the bolt layout parameters(bolt spacing,end distance,hole diameter and derrick connection plate thickness)on the relative displacement between the bolts and the bolt holes was also investigated.Research shows that for heavy-duty rack and pinion,selected 36 mm bolt in the bolt distance of 200 mm,the greater the bolt and rack end distance,the smaller the bolt hole,derrick connection plate thickness,the better the rack tightening effect.The Sopwith and Yamamoto methods were used to analysis the load distribution of the threads,and a single-bolt fastening finite element model including the thread lift angle was established to simulate the thread load distribution.The accuracy of the established analytical model of the thread load distribution was verified by combining the load distribution photoelasticity experimental data of the threads.The influence of the thread structure parameters(number of threads engaged,small diameter,pressure angle,pitch and friction coefficient)on the bolt load distribution and the law of residual preload after bolt relaxation is investigated.The effect of transverse load amplitude,preload force and thread friction coefficient on the residual preload force of the bolt is investigated in relation to the impact load to which the drilling rig is subjected under actual working conditions.Based on the rack and pinion lifting test rig,experiments on the tightening effect of the rack and pinion have been designed to investigate the strain at the screw holes of the rack and pinion under no-load lifting,automatic drilling,high-speed drilling and maximum hook load conditions.The proposed method of using the relative displacement difference between the bolts and the bolt holes to evaluate the effect of multi-bolt fastening of heavy-duty rack is feasible. |
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