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In the process of grinding, rubbing, plowing, and cutting occur successively between abrasive grains and workpiece material as the grinding depth increases. In precision grinding of the screw rotor, small grinding depth is generally introduced, which usually results in plowing. Therefore, it is essential to predict the surface roughness caused by plowing in order to make the process controllable. In this paper, an analytical method for predicting tooth surface roughness of the screw rotor in precision grinding has been proposed. This method takes the following factors into consideration, i.e., distribution law of the grain protrusion heights, variation of grinding depth, velocities and diameters of the screw rotor and grinding wheel at different contact points, and the dressing parameters of grinding wheel. A trajectory projection method has been employed to determine the groove depth and distribution left by the abrasive grains. With the proposed model, the distribution of roughness over the screw rotor tooth surface can be calculated. Verification experiments were conducted with several screw motors produced and surface roughness measured. The comparison results reveal a good agreement between predicted results and experimental results, showing the effectiveness of the proposed method. This study could shed light on the plowing phenomena in precision grinding and could provide great potential in achieving an effective control of the surface roughness.

In the operation of positive displacement screw machine, the profile accuracy of the screw rotor has a significant effect on the meshing stability between male rotor and female rotor, which is the main factor for vibration, noise, sealing, and wear resistance. This sets extremely strict requirements of the profile accuracy of screw rotor. Therefore, in order to obtain precise screw rotor profile, form grinding is generally used as a finishing process in the manufacture of screw rotors. Unfortunately, the grinding wheel has to be frequently dressed due to inevitable grinding wheel wear. This will cause a substantial waste of time and thus lead to inefficiency. It is therefore desirable to be able to predict the profile error caused by grinding wheel wear in order to make it controllable. In this paper, the influence of installation angle, center distance, and grinding wheel wear on rotor profile error is investigated. A novel method has been proposed for prediction profile error of the screw rotor in precision form grinding. The proposed method has been employed to compensate profile error caused by grinding wheel wear and improve grinding efficiency. Verification experiments were conducted with several screw rotors produced and profile error measured. The comparison shows that the compensation results agree well with the numerical simulation results, showing the effectiveness of the proposed compensation method.

The profile accuracy of screw rotors plays a vital role in stabilizing the meshing operation between mated rotors. Such stability can minimize the vibration and noise, as well as improve the sealing performance and wear resistance. This is the main reason why form grinding is extensively applied as a finishing process to maintain high screw rotor profile accuracy. Since the installation parameters for form grinding wheels affect both the grinding wheel profile accuracy and grinding performance, it is essential to obtain reasonable installation parameters to guarantee the high precision and good grinding performance of form grinding wheels. In this paper, a novel optimization design method for form grinding wheels for screw rotors has been proposed. For the first time, the relationship between the grinding wheel installation parameters and profile accuracy is established to evaluate the grinding performance. A parameterized program has been designed based on space engagement theory. The characteristics of the contact line and profile features of form grinding wheels under different installation parameters have been investigated. Then, the proposed method was employed to select the correct range of installation parameters. To validate the proposed method, a set of experiments, including the manufacture and measurement of several screw rotors, was carried out. The results reveal that the precision of the screw profile is significantly improved compared with the empirical method, thus showing the effectiveness of the proposed method.

This paper presents a new mesoscopic transport model for describing the diffusion of chloride in cement-based materials simultaneously subjected to freeze-thaw (FT) conditions and incorporated with chloride ions (Ch-I). The model uses the concept of freeze-thaw stress (FT-S) to reflect the effect of freezing and thawing cycles on the transport of ionic concentrations in porous materials and the concentration gradient of chloride for calculating the effect of different concentrations of chloride ions. In addition to determining the effect of FT-S, the model also considers the interactional effects between environmental exchanges, namely the effects of different temperatures, Cl− concentrations (10.5 g/L, 21.0 g/L and 42.0 g/L), and pore size distributions. The mesoscopic model is validated using experimental data obtained from coupling tests of chloride corrosion and freeze-thaw cycles. Compared with the typical Fick’s results, advantageous agreement between the calculated and measured chloride concentration profiles is demonstrated. The new mesoscopic diffusion model can help compensate for the lack of research on the effect of freeze-thaw cycles on chloride diffusion.

Determining the rheological properties of cement-based materials and selecting the types and amounts of superplasticisers (SPs) that are appropriate for actual projects are important and topical issues. In this study, the rheological properties of cement pastes with different types of SP were investigated using an AR2000ex rheometer. A colour function method (CFM), in combination with the experimental data, was used to calculate and determine the rheological properties. This paper presents a new selection method (rapid determination system (RDS)) for determining the most suitable SPs. The results show that shear stress, plastic viscosity, normal stress and other mechanical properties are influenced by different volumes and types of SPs. Based on the CFM and RDS, 0·38% HW (a polycarboxylate-type SP) was determined to be the most appropriate.