| The rack and pinion rig is a new type of rig,and the conventional rig hoisting system and the rotating system are replaced by a rack and pinion structure and a top drive integrated device.It has the advantages of high transmission efficiency,compact structure and the ability to actively apply the weight-on-bit.The rack and pinion is one of the key components of the rack and pinion drill,and the plurality of gears repeatedly engage the rack mounted on the derrick.The rack and pinion mesh drive the up and down movement of the lifting box.After the long-term alternating load,the rack and pinion are prone to tooth root bending fatigue fracture or tooth surface fatigue wear.Therefore,improving the fatigue life of the rack and pinion is also an important design content of the rack and pinion drill.At present,the research on gear rack rigs in China is still relatively slow.The rack and pinion drilling rig has gradually become a research hotspot in the field of drilling rigs due to its high efficiency in drilling.This paper also relies on the sub-project of the national major special project "Development of high-efficiency automatic drilling unit in well factory" to carry out the research on fatigue life prediction of rack and pinion.The contact strength of the rack and pinion was calculated based on the Hertz contact strength theory.The root bending strength of the rack and pinion is calculated based on the theory of gear tooth root bending strength.The gear root bending stress is less than the gear contact strength.More attention should be paid to the damage of the meshing of the rack and pinion during the gear operation.At the same time,it is found that the gear contact strength exceeds the yield strength of the gear material,and the gear should be made of a higher strength material.A calculation model for the large hook load in vertical and horizontal wells was established.Parameter selection analysis was carried out on the main influencing factors of the large hook load.Vertical wells with well inclination angles of 0°,15°,and 30° and horizontal wells with wellbore curvatures of 6°/30 m,20°/30 m,and 60°/30 m were designed.Based on this,the large hook load in the vertical well and the horizontal well was calculated.At the same time,the frequency of the hook load acting on the gear at different drilling depths is calculated for the gear single tooth.A finite element model of contact stress of single gear rack was established.The stress distribution of the rack and pinion under different hook loads is analyzed.The gear contact stress is greater than the root bending stress.In this way,the contact stress spectrum of the vertical well and the horizontal downhole gear is obtained.The S-N curve of the rack and pinion material was obtained through experimental tests and linear fitting.Based on the miner linear fatigue damage accumulation theory,the fatigue life of multiple vertical shafts and horizontal downhole gears was calculated.In vertical wells of 0°,15°,and 30°,the greater the inclination angle of the well is,the smaller the fatigue life of the rig gear is.When the inclination angle of the well is 0°,the gear fatigue life is 263 days.Under the same working conditions,the drilling rig can continuously drill four vertical wells with 0° well angle.At the same time,the gears are in the infinite fatigue life stage before the drilling depth reaches 2520 m,2390m and 2230 m respectively.In horizontal wells of 6°/30 m,20m°/30 m,60°/30 m,the greater the radius of curvature of the wellbore,the greater the fatigue life of the gear.In horizontal wells of 6°/30 m,20m°/30 m,60°/30 m,the greater the radius of curvature of the wellbore is,the greater the fatigue life of the gear is.When the radius of curvature of the wellbore is 60°/30 m,the fatigue life of the rig gear is 2608 days.Under the same working conditions,the drilling rig can continuously drill 43 horizontal wells of 60°/30 m.At the same time,the gears are in the infinite fatigue life stage before the drilling depth reaches 2530 m,2531m and 2532 m.In this paper,the fatigue life of the rig gears in multiple vertical wells and horizontal wells is calculated separately.A method for predicting fatigue life of gear racks is formed.This provides a reference for the design and pre-maintenance of the rack and pinion rig. |
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