The Demand Supply Steady-State Process-Based Multi-Level Spare Parts Optimization

Spare parts are one of the important components of the equipment comprehensive support system. Spare parts management plays a decisive role in achieving the desired availability with the minimum cost. With the equipment complexity increasing, the price of spare parts has risen sharply. The traditional spare parts management makes the contradiction between fund shortage and spare parts shortage increasingly prominent. Based on the analysis of the multi-echelon and multi-indenture spare parts support model VARI-METRIC (vary multi-echelon technology for recoverable item control, VARI-METRIC), which is widely used by troops and enterprises in various countries, the model is mainly used in high system availability scenarios. However, in the case of low equipment system availability, the accuracy and cost of model inventory prediction are not ideal. This paper proposed the multi-level spare parts optimization model, which is based on the demand-supply steady-state process. It is an analytical model, which is used to solve the low accuracy problem of the VARI-METRIC model in the low equipment system availability. The analytical model is based on the multi-level spare parts support process. The article deduces methods for solving demand rate, demand–supply rate, equipment system availability, and support system availability. The marginal analysis method is used in the model to analyze the spare parts inventory allocation strategy’s current based cost and availability optimal value. Finally, a simulation model is established to evaluate and verify the model. Then, the simulation results show that, when the low availability of equipment systems are 0.4, 0.6, the relative errors of the analytical model are 3.54%, 3.86%, and its costs are 0.52, 1.795 million ¥ RMB. The experiment proves that the inventory prediction accuracy of the analytical model is significantly higher than that of the VARI-METRIC model in low equipment system availability. Finally, the conclusion and future research directions are discussed.

Force parameters of metal deformation during sheet drawing

The aim of the work. The effect of the curvature of the rounding of torus surfaces during the formation of a cylindrical product (glass) is investigated, taking into account the plastic thinning of the deformable material at the end edges of the matrix and pressing punch. Methods. The existing scheme for determining the power parameters of sheet drawing is analyzed, based on the assumption of the implementation of some abstract stress state in the material; mainly conditional tensile strength. At the same time, the possibility of forming the product without destruction determines the obvious overestimation of the stress level. A mathematical model of the volumetric stress state of the metal is being developed, which makes it possible to assess the deformation and stress state during the formation of a cold-drawn product, i. e. the folding of the sheet blank along the end radius of the rounding of the pressing punch and the steady-state process of drawing the blank into the deformation zone with successive bending/straightening of the material along the edge of the matrix are considered. The level of radial stresses during folding and stretching of sheet material is estimated, taking into account its strain hardening and thinning, which determine the forming force. The obtained results will make it possible to simulate the stress-strain state of the metal during the development of sheet drawing technology: to establish the amount of thinning, to estimate the level of radial stresses in the formation of rounding of torus surfaces along the end edges of the matrix and the pressing punch, as well as to determine the power parameters of the formation, which will prevent the destruction of the pulled part, guaranteeing obtaining high-quality products and more accurately choosing the deforming equipment.

Adsorption dynamics of phenol by crab shell chitosan

The performance of crab shell chitosan (600 µm) as prospective adsorbent for phenol removal was studied in dynamics mode. The chitosan adsorbent had specific surface area of 191 m2/g and showed the surface characteristics linked to amine/amide groups. The effects of operating conditions on phenol adsorption at different concentrations (100 and 200 mg/L), flow rates (2.17 and 2.90 mL/min) and bed heights (1.75 and 3.5 cm) were evaluated. Results showed that the maximum phenol adsorption capacity by the crab shell chitosan was recorded at 190 mg/g. Thomas, Yoon–Nelson and Adam–Bohart models displayed good correlation with experimental data, hence best described the dynamics breakthrough of phenol removal. External and internal diffusion were the rate controlling mechanism, while the entire system was predominated by a simultaneous steady state process of intraparticle diffusion and ionic interactions. The crab shell chitosan shows a promising potential as adsorbent for wastewater treatment.

Adsorption dynamics of dye onto crab shell chitosan/neem leaf composite

The aim of this study was to evaluate the adsorption dynamics of crab shell chitosan/neem leaf composite against methylene blue dye at varying concentrations (50 and 200 mg/L), bed depths (2.5 and 5.0 cm), and flow rates (2.17 and 2.90 mL/min). The chitosan composite has a specific surface of 258 m2/g. Its surface is rich in amine/amide groups. The results reflect better dye adsorption at higher operating conditions. The maximum dye adsorption capacity observed was almost 77 mg/g. The kinetics models showed good correlation with the experimental data and described the breakthrough behaviour of dye removal. The Thomas model predicts external and internal diffusion as the rate controlling mechanisms, while the Adams-Bohart model indicates a simultaneous steady state process of intraparticle diffusion and ionic interaction. Chitosan composite is a promising adsorbent candidate for dye wastewater treatment.

PROSPECTS FOR USE OF THE RESERVE FORCES OF FRICTION ON CONTACT SURFACE IN DEFORMATION ZONE AT ROLLING TO INCREASE PROCESS EFFICIENCY

Rolling process is carried out due to power supplied to the center of deformation using contact friction forces. Rolling takes place in two stages – the capture stage and the steady-state process. The capture stage determines possibility of deformation in rolls. During this period, retracting forces of friction are used with maximum efficiency. The main stage of rolling is the steady-state stage of the process, where contact friction capabilities are not fully used and reserve of friction forces is created, which can increase efficiency of rolling process. To balance excessive friction forces on contact surface in deformation zone during the steady-state process, zones of advance and adhesion appear. Their length characterize amount of excessive friction forces. Theoretical dependences for determining slip and adhesion zones are given taking into account variety of rolling factors. Estimation indicator of abilities of friction forces reserve at the steady-state stage is offered as well as dependence for its definition. It is analytically established that in steady-state stage of rolling on smooth rolls with ratio α/μз = 1 it is possible to supply 1.7 – 2 times greater energy due to exis ting reserve of friction force than at the stage of capture at a lower ratio α/μз ; these numbers are even higher for rolling on grooved rolls. Dependence which determines amount of additional power provided by friction forces reserve is given. Promising directions of using friction forces reserve at the steady- state stage of rolling are provided to improve its efficiency. On the example of rolling in drive – non-drive stand, an increase in efficiency (Efficiency Ratio) of the main line of rolling mill is established with more efficient use of friction forces at the steady-state stage of rolling process. Theoretical dependences are given to determine Efficiency Ratio at usual rolling process and at more full use of friction forces reserve.