Research On Friction And Wear Performance Of NBR As The Stator Of Progressing Cavity Pump

Recent years in our country, technology of oil well using progressing cavity pump isexpanded rapidly in LiaoHe, ShengLi and BoHai sea oils, which has made outstandingcontributions for the country's energy development. Compared with the plunger typepumping unit, electric submersible centrifugal pump etc, progressing cavity pump issuitable for mining crude oil with high viscosity, high sand content, and deviated well,horizontal well, marshland, and operation of oil production in offshore platform. It is alsono break and pipe leakage failure, low energy consumption under the same oil recovery.Screw pump is mainly composed of stator and rotor (screw) components. Rotor is aspecially processed spiral metal rod, which is coated corrosion resistant layer outside, andthe stator is metal tube with rubber in the internal. In the process of the work, the statorrubber is impacted and slidded by metal rotor. Rubber of screw pump stator often appearthe phenomenon such as degumming, tearing and peptizing in the corrosive medium ofcrude oil, which lead to reducing the wear resistance, then the equipment overall failure,so screw pump stator rubber wear severely restrict the service life of screw pump. Atpresent, the research on the performance of the stator rubber at home and abroad havemade certain progress, which direction is more on the physical and chemical properties ofthe rubber material. But it is rarely reported on friction and wear behavior between therubber and metal pair in the working condition of screw pump, still in the stage oftheoretical analysis. Research work in this area, on the one hand, offer help for reasonableselection of screw pump stator rubber materials under different working conditions. Onthe other hand also contribute to the development of rubber tribology.There are many types of the stator rubber, comprehensive considering the materialperformance, cost-effective, oil well conditions and other factors, people mainly choosenitrile rubber (NBR). Nitrile rubber performance is affected mainly by acrylonitrile andcarbon black content.So in this paper the friction and wear behavior of commonly usedNBR and metals was studied, aimed at offering help to select screw pump stator rubbermaterials for different working conditions. By comparing the test results, friction and wear rule of NBR is summed up underdifferent working condition. Under dry friction, the higher the carbon black content, thebetter the dispersion degree, the better the wear resistance of NBR. But carbon blackcontents are too high, composition of masterbatch decreased, physical and chemicalproperties of the NBR reduced, wear resistance increase with the increase of carbonnumber. With increase of the acrylonitrile content, the polarity between the molecularchains is bigger, the higher the acrylonitrile content, the better the wear resistance ofNBR. The wear mechanism of NBR under dry friction mainly adhesive wear and lagwear; Under water medium, because of the cooling water, reduce the influence oftemperature on the friction and wear, content of carbon black has very little effect onamount of wear and tear. Smaller hardness of NBR, the higher the acrylonitrile content,the stronger the polarity, the better resistance to wear; Low acrylonitrile content of NBR,carbon black content is larger, due to low-C?N keys, molecular polarity is poor, thepacking is more conducive to form a flexible network structure, to improve the wearresistance of NBR, wear mechanism is abrasive wear in the water. Wear loss under crudeoil medium is slightly larger than the water, the higher the carbon black is leaked,resistance to wear of NBR is better. At low load, due to the oil film thicker, wear mainlyoccurs between rubber and crude oil, so the carbon black content has a little influence onthe wear properties of the NBR; High load, the dynamic pressure lubrication formedbetween NBR and metal wheels, erosion rate decreases with the increase of the carbonblack was leaked. Smaller hardness, the higher the acrylonitrile content, the stronger thepolarity, resistance to wear is better, acrylonitrile affects the quantity of abrasion wearrules consistent with the water, the main wear mechanism is corrosion and wear.Based on research of the friction and wear behavior of NBR under dry frictioncondition, friction and wear mechanism is proposed.Under the action of shear force inwear process, carbon black particles to overcome molecular inter-atomic forces fall offfrom the rubber matrix, by forming a lubrication film extrusion on the friction surface,reduce the substrate, direct contact with the dual surface friction by rubber and metal tomake dual surfaces into carbon black of lubricant and metal friction, the friction coefficient decreases, and reduce the wear of rubber. However, this layer of lubricationfilm combined with the weak, very easy to damage and wear off, rubber wear, has beengiven to the inside of the carbon black and debonding from matrix to form the lubricationfilm, the cycle form a circle.In the screw pump working process, the choice of the stator rubber need variesaccording to the working conditions, this paper realized the optimal selection of NBRbased on the production condition of acrylonitrile and carbon black content. Based on thefriction and wear test results under different carbon black and acrylonitrile content, thequalitative relationship is determined which between production conditions, acrylonitrilecontent, carbon black content and rubber abrasion resistance, it provides theoreticalsupports for screw pump rubber material selection.