| Reciprocating mud pumps are widely used in energy drilling,engineering construction,and agricultural production.The piston is the most important fragile part and the core component of mud pump to realize medium pumping.When the mud pump is used in oil drilling,geological exploration,mud transportation,and river dredging,poor working conditions will result in lack of lubrication,severe friction and wear of the piston,and will also cause the friction pair temperature to rise sharply,which will lead to premature failure and short service life of the piston.The friction and wear performance and service life of piston directly affect the stability,safety and efficiency of mud pump.Frequent piston replacement will spend a lot of manpower and material resources.The pump shutdown will also seriously affect exploration and mining,urban infrastructure construction and agricultural production.Therefore,how to improve the friction and wear performance of the friction pair,slow down the temperature rise and improve the service life of the piston is an urgent problem to be solved for the mud pump.To reduce friction,wear and operating temperature of piston-cylinder liner friction pair and to improve lubrication conditions of piston surface,based on the surface structure of earthworm and leech,the bionic cylindrical pit texture array is designed and machined on the standard piston surface of BW-250 mud pump.Then,relevant researches were carried out on friction,wear,lubricant film,and thermography of bionic textured pistons.Finally,the finite element analysis and field test of bionic textured piston are carried out and its processing technology is improved.The main research contents and achievements of this paper are as follows:1.Observation of bionic prototype and preparation of bionic textured piston: Earthworms and leeches with similar working conditions as mud pump piston were selected as bionic prototypes,and morphological structure and distribution characteristics of earthworm back hole and leech pit were observed respectively by stereo microscope and scanning electron microscope.The results showed that the back hole of the earthworm presented regular arrangement distribution characteristics,and the distribution characteristics of leech pits were a combination of straight row and triangular array.Both pit-like structures can reduce their friction resistance by the way of mucus secretion.Inspired by the surface structure and distribution characteristics of earthworms and leeches,a bionic cylindrical pit texture array was designed on the surface of the piston rubber bowl of the BW-250 mud pump.The bionic textured piston is manufactured by machining without changing the original structure size of the standard piston.2.Bionic textured piston friction test: Based on the piston-cylinder liner friction pair in the body of BW-250 mud pump,a piston friction test stand was designed and built.The friction test scheme for pistons was developed by means of the test design method and 27 groups of comprehensive orthogonal tests were carried out.The friction test curve shows that the piston friction gradually stabilizes after 21 minutes of the test.The friction force of each piston in reverse and forward stroke is different,and the piston in reverse stroke has a larger friction force.The calculation results of friction mean and drag reduction ratio show that the mean friction force of bionic textured piston is less than that of standard piston and the drag reduction ratio is more than 10% no matter the reverse or forward stroke.Friction mean of reverse and forward travel decreases first and then increases with the increase of texture radius,and is the smallest when r=0.75 mm.Friction mean decreases with the increase of texture density and is the smallest when ?=10°.Friction mean has no significant regularity with the change of texture depth.Friction mean decreases with the increase of area ratio.3.Wear,lubrication and thermography test of bionic textured piston: The wear test results show that the wear amount of bionic textured piston is smaller than that of standard piston.The parameters of bionic textured piston with the best wear performance are r=0.75 mm,?=10° and h=0.5 mm.The standard piston surface has obvious plough,tear,bite and three-part wear appearance.While the bionic textured piston can supplement lubrication,store abrasive particles,improve lubrication conditions and reduce wear phenomenon.Thermographic test results show that the temperature gradually stabilizes after 40 minutes,at which time the average temperature value of bionic textured piston is lower than that of standard piston.The oil film observation test results show that the oil film length and thickness of the bionic textured piston are higher than those of the standard piston.4.Finite element analysis of bionic textured piston: A piston-cylinder liner friction pair model was established.The results of piston simulation analysis show that the piston deformation and contact pressure are distributed in a ring pattern,decreasing step by step from top to bottom.Compared with standard piston,the maximum deformation of bionic textured piston decreases,and the maximum contact pressure increases or decreases with little change.Bionic textured pistons relieve piston deformation and stress concentration.The lubricant fluid domain model was established.The finite element analysis results of the lubricant show that the bionic cylindrical pit texture can cut off the flow line,reduce the flow rate,improve the interfacial lubrication condition and reduce the piston friction.The average oil film pressure and oil film bearing capacity of the bionic textured piston are significantly increased.5.Bionic textured piston field test and process improvement: The mud pump field test results show that the wear rate of bionic textured piston is significantly reduced and the temperature of cylinder liner is significantly reduced.The service life of bionic textured piston is significantly improved and the wear of cylinder liner is also reduced.In this paper,the processing technology of bionic textured piston has been improved,and the mold of bionic textured piston has been designed and developed. |
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