| As a new practical and effective mechanical oil recovery device, PCP has uniqueadvantages including simple connfiguration, small size, low noise, low energyconsumption, and less investment. PCP is also characterized by easy use, quick installation,convenient repair and maintenance. It has the merits of both the centrifugal pump and thepositive displacement pump. Free from broken rods and tube leakage, it is well used for theinclined shaft, horizontal wells, and the operations of oil production in the marsh land andoffshore platform. The better performance and higher efficiency of PCP is achieved in thedrilling operations of high viscosity heavy oil, big oil-gas ratio oil and sand oil. At present,PCP has received widespread attention at home and abroad, and is expected to become themain method for machinery oil production. The rubber material, characterized by good oilresistance, abrasion resistance and high temperature resistance, is used as the material ofPCP’s stator. The actual working environment of oil wells is usually filled with thecorrosive medium with abrasive grain dopants, making rubber materials prone topremature fatigue wear failure in the dynamic sealing process. This tendency greatlyaffects the PCP’s stator performance and working life, and therefore becomes one of themain causes of PCP failure. To date, unfortunately, few studies has been performed on thewear mechanism of such rubber material, and no general guiding principles have beenestablished either. Research on PCP’s stator rubber wear mechanism, therefore, not onlyhas a certain value to the actual production, but is also of crucial significance to theenrichment and development of rubber tribology theory and practice.In response to inadequate research on PCP’s stator rubber wear mechanism, this paper,based on the testing of abrasive wear, abrasive grain erosion wear and corrosion wear,conducts a comprehensive study on friction-wear mechanism of oil screw pump statorrubber. To achieve this goal, rubber friction and wear tests were made. In the tests, PCP’smetal rotor and stator of metal rubber friction were used as the test subject, and the actualworking condition of PCP was simulated in the laboratory. After the stator rubber frictionand wear test analysis program was designed and the test platform was built, rubberfriction and wear tests were conducted with rubber blocks placed under oil lubricationconditions, oil and sand medium conditions and lubrication of liquid paraffin conditions.At first, on the basis of the full understanding of the characteristics of PCP, a detailedanalysis of the motion characteristics of PCP’s screw in the rubber bushing pair was made, and then the formula of the maximum slip velocity of single screw pump rotor and stator aswell as the formula of contact pressure between rotor and stator were derived. According tothe structure parameters of GLB120-27type PCP, the sliding velocity and load databetween PCP’s rotor and rubber stator were obtained through the PCP’s kinematics analysismethod and calculation formula, thus establishing the speed and load parameters of rubberwear under the simulated conditions of PCP’s actual working conditions in the laboratory.This dissertation expounds the complexity of friction and wear of rubber, discussesthe lubrication mechanism and the impact of crude oil in the screw pump stator rubberduring friction, in-depth analysis of the rubber friction and wear theory, clear the crude oilmedium in screw pump stator rubber friction and wear process, rubber friction and wearmechanism, wear type and its influencing factors. On this basis, through the analysis aboutthe screw pump stator rubber material properties and the working environment, systematicresearch the wear mechanism in crude oil screw pump stator rubber.The study finds that during the early phase of PCP’s running, the main forms of wearin the normal working of a screw pump include abrasive wear, adhesive wear, abrasivegrain erosion wear, fatigue wear and corrosive wear. To study these wear behaviors, afriction wear test was conducted on MPV-600micro-computer-controlling grain-abrasiontesting machine. NBR, FPM and45#steel pair area were tested in the conditions of crudeoil lubricating, sand-contained crude oil lubricating and liquid paraffin lubricating.Through the measuring of the friction coefficient and wear volume, the variation pattern offriction coefficient and wear volume with normal load was established. Then with the aidof SEM, EDX and FT-IR, the wear scar surface, functional group state and chemicalelement contents of rubber were measured after wear occurred. Based on the above testresults, this dessertation analyzes rubber’s friction and behavior, observes the physicalchanges of rubber in oil medium, considers the grain concentration, size, shape at differentnormal loads on the rubber wear in crude oil, and pays attention to the influence ofcorrosive medium to rubber wear. Thereby, this dessertation discovers relevance of theinteraction effect between rubber stator’s abrasive wear mechanism in oil medium, andimmersion corrosion and abrasive wear. And make improvements for the deficiencies ofthe existing rubber abrasion testing machine, set up a new rubber sand slurry abrasive weartesting device.The research in this dissertation comprehensively expounds the mechanismof wears of the PCP stator rubber and provides guiding principles for stator rubber in theactual engineering application in tribology design, material selection and performance evaluation. |
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