Investigation On The Friction And Lubrication Properties Of Bionic Hexagonal-Textured Surface For Pumpjack Plunger

As a non-renewable natural resource,petroleum has important economic value and strategic significance.Currently,oil extraction is mainly based on mechanical extraction and rod-pumpjack is still the main mechanical tool for oil production in China,of which the pumpjack plunger is a core component.The frictional resistance during plunger movement will cause the wear on the surface under various working conditions,affecting the output and profitability of oil fields.It remains a grand challenge to prolong the service life of the plunger and increase the working efficiency of the pump in the mechanical extraction.In order to adapt to the long-term sand-wearing lifestyle in the desert,Eryx tataricus has evolved the scales with excellent tribological properties.It is envisioned that the investigation on the bio-mechanism of drag-resistance and wear-resistance for such scales can afford inspiration to the design of anti-friction and anti-wear surface for plunger,which has both theoretical value and promising application.To solve the problems of serious friction and wear on the surface of pumpjack plunger,this work explores the mechanism of friction reduction and wear resistance about Eryx tataricus scale.Then,the properties of friction and lubrication for bionic hexagonal texture are studied based on the morphology of hexagonal scales.First,this work studies the macro-morphology and micro-morphology features for scale surface and explores the mechanical properties for the scales using microscopy,simulation,nanoindentation and nanotribometer,which reveals the mechanism of friction reduction and wear resistance.The results show that Eryx tataricus is covered with hexagonal scales on the skin and the single scale has a non-smooth composite structure with micron-scales and nanometer-pits.The scales form a gradient material with continuous change of an elastic modulus/hardness and have a frictional anisotropy characteristic.Compared with dorsal and lateral scales,the ventral scales express the lower surface roughness but higher elastic modulus,hardness and friction coefficient.That shows the interaction between the complex surface morphology and gradient material can improve the performance of anti-friction and anti-wear for the scales,which form the multi-coupling effects of mechanism for friction reduction and wear resistance.Then,this work designed and obtained bionic-coupled specimens by laser quenching,based on the morphology of hexagonal texture and gradient materials of the scale.The examination of dry friction on the surface reveals the coupled biomimetic drag reduction and wear mechanism.The test results show that the grooves on the surface of bionic-coupled specimen can reduce the contact area,disperse the surface stress,store wear debris and reduce secondary wear.In addition,the surface hardness gradient material of the sample has the effect of relieving the stress impact on the sample,which achieves a stable motion during the friction.Furthermore,it can reduce the spalling of the material and thus decreases the wear more effectively,resulting in a bionic coupling mechanism of friction reduction and wear resistance.Next,this paper sets up a laser processing device for bionic surface and explores the effect on lubrication for bionic hexagonal-textured surface.Compared with the other shape-textured surface(equilateral triangles,square,and round),the bionic hexagonal-textured specimens exhibit lower friction coefficient under the same conditions and the lubricating effects on its surface is more pronounced as the loads decrease and the rotational speeds increase.Then,ANSYS software is used to simulate the oil film pressure and contact pressure on the surface.The simulation results show that bionic hexagonal-textured surface has good hydrodynamic lubrication and minimal contact stress at the same area.Therefore due to the coupling effects of them,the bionic coupling specimens have a better advantage of lubrication.Subsequently,this work establishes the model of mathematical geometry and fluid mechanics for the bionic hexagonal-textured unit and analyzes numerical results by MATLAB software,which explores the lubrication performance of the bionic hexagonal-textured units with varieties of geometries under various working conditions.For the geometric parameters,the theoretical results show that both the surface density and the groove depth can affect the friction coefficients and the orientation has a significant effect on the friction coefficients under the condition of low surface density and deep groove.For working conditions,the friction coefficient decreases with the increase of speeds and loads,which indicates that the relative movement speed and external load can increase the dynamic pressure and bearing capacity of oil film.Thus,many factors will affect the lubrication of the bionic hexagonal-textured unit.Finally,the work examined the frictional and lubricating properties for the bionic hexagonal-textured units under working conditions by a reformed device for friction and wear test.The test results are well consistent with the theoretical results previously described.Then,a reasonable parameter was selected to fabricate bionic pumpjack plunger specimens and the leakage test was conducted.The obtained results are in good agreement with the previous theoretical results.According to the leakage results,the bionic hexagonal plunger maintains the original leakage of the plunger and may even improve the seal of plunger under a certain pressure.