Study On Wear- And Heat-resistant Materials For Over-lining Of Pump Rod Joints

Rod-tube eccentric wear of rod pumping well shortens the well repairing cycle, and restricts the normal production of oil field. The working life of a rod and a tube could be significantly enhanced by over-lining of wear-resistant materials on the pump rod joints. In this thesis, SiO2 nanosphere/PTFE (SNS/PTFE) composites and fiber-reinforced PA66 composites were developed to meet the requirement of preventing the eccentric wear between rods and tubes as well as the physical and chemical environments in rod pumping wells. This is designed to solve the problem of rode-tube eccentric wear and thus to extend working life of oil wells.1. Synthesis and characterization of SiO2 nanospheres for polymer fillingsThe SiO2 nanospheres were prepared by a sol-gel method. In the reaction system, the effect of TEOS concentrations, solvent species, catalyst types and concentrations, deionized water concentrations as well as reaction temperatures on the morphologies and structures of SiO2 was investigated by SEM, FT-IR and XRD. Ammonia catalyzed hydrolysis, crystallization and polymerization of TEOS, which generated SiO2 nanospheres with narrow a size distribution and a high sphericity. The sizes of synthesized SiO2 nanospheres increased with concentrations of TEOS, carbon chain length of solvent alcohols, concentrations of ammonia and temperatures of reaction. They also increased with an increase of a water concentration at a relatively low concentration,but a high concentration of water will lead to a decrease. All of the synthesized SiO2 presented amorphous structures and the surfaces rich in hydroxyl functional groups under the different preparation conditions.2. Preparation of SiO2 nanosphere/PTFE composites by an in-situ chemical synthesis and their tribological performancesSiO2 nanosphere/PTFE (SNS/PTFE) composites were prepared by an in-situ chemical synthesis and a heat molding process. The microscopic structures of the composites were characterized by FT-IR, XRD and SEM. The hydrophobic properties, mechanical properties and thermal properties were determined by a video optical contact angle measuring instrument,a universal testing machine, a Rockwell hardmeter, a DSC and a TMA. The friction coefficients and wear resistant performances were tested by an MRH-3 high-speed wear tester and an oil-sand slurry apparatus with an oil bath, and the morphologies of friction surfaces were analyzed by a 3D laser microscope. The sizes of SiO2 nanospheres, which were highly dispersed in the matrix material, generated by the in-situ chemical synthesis in PTFE were 50?70 nm. The filled SiO2 nanospheres interacted with PTFE resin via hydrogen bonding. The hydrophobic properties of the prepared composites have been improved significantly compared with that of PTFE. The elasticity modulus of composites increased obviously with the increases of the contents of SiO2 nanospheres in spite of a slight decline in their tensile strength and elongation at break. The Rockwell hardness of the synthesized SNS/PTFE composites increased with a SiO2 nanosphere filling, and reaches maximum at a concentration of 2.0%, which was 12.5% higher than that of PTFE. The average linear expansion coefficients of composites filled with SiO2 nanospheres exhibited a decrease trend at a filling concentration up to 2.0%, and the glass transition temperatures of all SNS/PTFE composites increased.The friction coefficients and volume wear rates of SNS/PTFE composites prepared by an in-situ chemical synthesis significantly decreased with respect to PTFE under dry friction conditions. The volume wear rates of SNS/PTFE composites at a filling concentration of 2.0%decreased to 1.8% of the pure PTFE, and the friction coefficients were 14.3% lower than that of the matrix. Furthermore, the composites filled with SiO2 nanospheres exhibited high wear- and erosion-resistant performances at enhanced temperatures.3. Preparation of fibers reinforced Nylon 66 composites and their tribological performancesThe composites of glass fibers (GF) and carbon fibers (CF) reinforced PA66 were prepared by a two-screw extrusion followed by a granulation, and the resulting composite particles were molded by an injection process. The microscopic structures of the resultant composites were characterized by FT-IR and XRD. The mechanical properties, thermal properties and swelling properties were examined by a universal testing machine, a Cantilever beam impact testing machine, a Rockwell hardmeter, a DSC, a TMA, a Vicat temperature meter and a hydrothermal kettle. And the morphologies of tensile fractures were observed by a scanning electron microscopy. The friction coefficients and wear resistant performances were tested by an MRH-3 high-speed wear tester, and the morphologies of friction surfaces were analyzed by a 2D laser microscope. The filled fibers interacted with PA66 resin via hydrogen bonding,and achieved a high dispersion in PA66. Carbon fibers played a heterogeneous nucleation role in PA66, and led 9to an increase of the crystallinity of composites. Although elongation at break and impact strength of PA66 composites modified by different fibers decreased, their elasticity modulus,tensile strength, flexural modulus,flexural strength and Rockwell hardness improved. The melting points and Vicat softening temperatures of PA66 composites filled with two kinds of fiber were elevated, which showed that the heat resistance of PA66 composites was enhanced,and their linear expansion coefficients had a reduction to some extent. Meanwhile, their swelling properties of composites in water and oil improved.The average friction coefficients of PA66 composites filled with glass fibers and carbon fibers showed different degrees of declines under both dry and water friction conditions. The volume wear rates of composites filled with carbon fibers under dry friction conditions were only 1/3 of that of the raw material. Under the conditions of water lubrication, the volume wear rates of composite filled with glass fibers decreased an order of magnitude, and that filled with carbon fibers can gain a decrease of two orders of magnitude.In summary, based on the detailed studies on the conditions and mechanisms of preparations for SiO2 nanospheres by a sol-gel method, the prepared SNS/PTFE composites by an in-situ chemical synthesis in this thesis can realize the high dispersion of SiO2 nanospheres in PTFE. The filled SiO2 nanospheres play a role of filling enhancement, and significantly enhanced their performances in anti-wear and friction reducing and other properties. The prepared SNS/PTFE composites can be applied to sucker rod couplings by a heat compression molding method to realize friction-, wear-, corrosion- and swelling-resistance under a relatively high temperature.In addition, PA66 was promoted by glass fibers and carbon fibers in this thesis, and the mechanical properties, thermal properties and tribological properties of the CF/PA66 composites were significantly improved. The obtained composites were outer-lined to sucker rod couplings by an injection molding process to meet wear-, friction-, corrosion- and swelling-resistance. The injection molding can significantly improve processing efficiency and reduce costs.In one word, the developed SNS/PTFE and CF/PA66 composites can be used as over-lining materials for sucker rod couplings,and play a crucial role against friction,wear,corrosion and swelling. Comparatively speaking, the main advantage of SNS/PTFE composites is high temperature resistance,but the molding efficiency is relatively low by a heat compression processing method. PA66 composites can be molded by injection processing with a high efficiency in spite of relatively low usage temperatures and some extent of swelling.