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Computer-controlled dual-rotor polishing, as the final step to correct the optical part surfaces, plays an important role in improving the quality and service life of the surfaces. However, in previous study, the material removal model of dual-rotor polishing was fixed-point polishing model, which could not continuously polish the workpiece. Herein, a novel material removal model of dual-rotor polishing is proposed according to the removal profile orthogonal to the tool path. Firstly, the material removal function per unit time is developed, which is further converted into the material removal function per unit length of the tool path. Secondly, for obtaining the removal profile of dual-rotor polishing, the above function is integrated along the tool path in the polishing area. Then, to verify the effectiveness of the material removal model, the polished profile is studied experimentally and the effects of parameters, such as eccentricity, speed ratio, and main motion feed rate, on material removal of dual-rotor polishing are theoretically analyzed. It is demonstrated that the experimental material removal profiles are in good agreement with the theoretical results; besides, the stable and efficient polishing process can be obtained by optimizing parameters, which have different effects on the material removal depth. This work is of great significance for correcting the optical surface.

As the final step to fabricate the optical parts, the deterministic polishing process is usually used to reduce the roughness and correct the surface form. In this article, a new compensation metho...

Electrorheological (ER) polishing, as a new ultra-precision super-effect polishing method, provides little damage to the workpiece surface and is suitable for polishing all kinds of small and complex curved surface workpieces. In this paper, an ER polishing tool with an annular integrated electrode is developed. The orthogonal experiments are carried out on the six influencing factors of ER polishing which include the applied voltage, the abrasive particle size, the abrasive concentration, the polishing gap, the polishing time and the tool spindle speed. The influence order of these six factors on the ER polishing is obtained. On this basis, the effect of a single process parameter of ER polishing on surface roughness is studied experimentally.

Strength retrogression of cement stone is one of the major challenges in oil well cementing under high temperatures. Nano-SiO2 exhibits the potential to mitigate this problem, but there is lack of reports about the role of nano-SiO2 playing within cement stone under high temperatures. Therefore, in this study, we experimentally determined the effect of nano-SiO2 sol on the compressive strength of Class-G oil well cement stone cured under high temperature (150 °C/35 MPa). Then we provided the explanations for the cement strength variation by analyzing the mineral compositions and microstructures of cement. The experimental results are summarized as follows: (1) The cement stone with 2% nano-SiO2 sol does not perform a strength reduction after cured for 5 days, and its XRD patterns indicate that low-dose nano-SiO2 sol will yield little effect on the cement hydration products; (2) While with a high dose, nano-SiO2 can react with calcium hydroxide, resulting in microstructure change of cement and the generation of a novel honeycomb calcium silicate hydrate gel (Ca/Si ratio is about 1.5); (3) Nano-SiO2 particles make the microstructure of cement stone more compact through impaction and filling into the pore among cement hydration products, which helps to prevent cement stone from strength retrogression under high temperatures. Generally, this study lays a theoretical foundation for the nano-SiO2 used as cement additive and sheds light on the design of high-temperature cement slurry system. Keywords: Nano-SiO2 sol, High temperature, Class-G oil well cement, Cement stone, Compressive strength, Strength retrogression, Hydration product, Microstructure

The viscosity of cement slurry decreases when the temperature rises, resulting in bleeding and sedimentation issues caused by high temperatures. The available viscosity modifying admixtures (VMAs) usually thicken cement slurry under low temperatures but their performances deteriorate under higher temperatures. This study proposes a novel thermo-thickening VMA (i.e., a thermo-thickening polymer with strong hydrophobicity, HTP); its thickening ability will become stronger with an increase in temperature. HTP helps to compensate for the consecutive viscosity reduction of cement slurry due to temperature increases and yields a constant-consistency cement slurry over a wide temperature range (up to 165 °C). Most importantly, HTP is able to slash the bleeding water exuded from cement slurry and eliminate the compressive-strength/density differences among the upper-middle-lower hardened cement paste segments, resulting in a significant improvement in the settlement stability of cement slurry. Microscopic observations reveal that the HTP molecules may fully stretch in the cement slurry and integrate with cement hydration products, contributing to the uniform micromorphology of hardened cement paste. The novel thermo-thickening VMA imposes a limited impact on the compressive strength, fluid loss and thickening time of cement slurry and is very compatible with various cement additives. Finally, the high-temperature high-density cement slurry system containing HTP exhibits a constant consistency until rapid setting behavior, which suggests that it has good potential for field applications.

The current research on the removal mechanism of ultra-precision polishing lacks various microscopic understandings of material removal and the process of surface material migration, which hinders the development of ultra-precision polishing technology, especially field constrained abrasive polishing. In order to clarify effects of abrasives at the atomic level on material removal in the field constrained abrasive polishing, a three-dimensional molecular dynamics model is conducted to study the mechanics of ultra-precision polishing on an aluminum (Al) specimen with a diamond abrasive. In order to simulate the real polishing environment, a double abrasive polishing system is designed. The mechanism of material removal was studied by observing the surface topography, surface damage, and coordination number of the working area during polishing. The influence factors of material removal were also investigated by changing the initial velocity, incidence angle, initial force, and relative position of the double abrasives. The results show that the transverse distance and the longitudinal distance between the double abrasives make a slight difference to the number of phase transformation atoms in the double abrasive polishing system, which is directly proportional to the initial velocity, the initial force, the distance between the specimen and its closest abrasive in the Z direction, and the distance between the double abrasives in the Z direction and inversely proportional to the incident angle of the double abrasives. Finally, it is found that the force on the abrasives is the main factor that determines the removal efficiency of the field constrained abrasive polishing.