In this research, effect of surface characteristics including restitution coefficient, cohesion factor, sliding friction and rolling resistance on the green pellet motion on the roller screen were studied numerically with the aid of discrete element method (DEM). Sensitivity analysis pertaining to integration time step and surface meshing were conducted to ensure the results accuracy. Curve fitting were applied on the numerical results to represent the critical speed versus the surface characteristics in mathematical functions. Based on the obtained results, the critical speed was increased by increasing the sliding friction however, when this coefficient exceeds a limit (around 0. 3) its impact became negligible. Moreover, it was revealed that by increasing the rolling resistance, the critical speed was reduced. Regarding the restitution coefficient, it was observed that increasing this factor increases the possibility of remaining the pellet between the rollers. Furthermore, it was concluded that cohesion can cause increasing or decreasing of the critical speed depending on the other surface characteristics.

The operational parameters of the roller screen substantially affect the efficiency and mechanical performance of its components, particularly those of the rolls. This study presents, for the first time, extensive coupled simulations employing the discrete element method-finite element method (DEM-FEM) to examine the effects of operating parameters on the mechanical behavior of rolls. This is achieved through the utilization of a realistic geometric model of the green pellets in conjunction with a hysteretic spring elastic-plastic contact model. The investigation revealed that decreasing the undersize gap from 9.75 mm to 9 mm led to increases of 20.27%, 29.71%, and 102.91% in the average force, total deformation, and equivalent stress exerted on the rolls, respectively. Furthermore, coupled DEM-FEM simulation tests of an Industrial-scale roller screen were conducted for the first time, and the results obtained were compared with those from laboratory tests. The average force acting on the rolls of the laboratory roller screen was measured at 2.43 N. In contrast, simulations of a full-scale roller screen operating at capacities of 120 t/h and 200 t/h revealed average forces of 34.46 N and 54.06 N, respectively. The average total deformation observed in the rolls of the laboratory roller screen was measured at 4.27E-05 mm. In contrast, under industrial conditions, this deformation increased significantly to 1.89E-02 mm at a processing capacity of 120 t/h, and further escalated to 2.95E-02 mm at a capacity of 200 t/h

Grading of agricultural products, especially fruits and vegetables, improves packaging, transportation and marketing processes, reduces losses, and leads to an added value of the product. It is therefore important that the appropriate technology is adopted for this purpose. In this study, performance of four onion sorting mechanism, namely sieving screen, fixed divergent rollers, expandable rollers with plate spacer and expandable roller with roller spacer were compared by both Analytical Hierarchy Process (AHP) and fuzzy analytical hierarchy process (FAHP). 8 main criteria including proper grouping of onions, machine capacity, mechanical damages, machine portability, member of outlet groups, adjustment of outlet group size range, initial price and after-sales services were considered for determining the priority of onion sorters. The results showed that among the 8 main criteria, the highest and lowest weights were allocated to mechanical damage and initial price, respectively. According to the results of the integration of different criteria and options, Both methods showing the same order determined that the expandable rollers with plate spacer with 0. 317 (AHP) and 0. 412 (FAHP) have the highest weight following by expandable roller with roller spacer with 0. 315 (AHP) and 0. 291 (FAHP), sieving screen with 0. 218 (AHP) and 0. 189 (FAHP) and fixed divergent rollers with 0. 150 (AHP) and 0. 106 (FAHP) respectively. In this way, expandable rollers with plate spacer, expandable roller with roller spacer, sieving screen and fixed divergent rollers were selected as the priority. These results showed that FAHP eliminating weak probabilities improved the decision-making ability.

Background: roller shoes (Heelys), which have one or more removable wheels embedded in each sole, allow the wearer to walk, run, or roll by shifting their weight to their heels. Objectives: The aim of this study was to analyze pediatric roller shoe injuries in Korea. Methods: Injury cases associated with roller shoes were collected from the consumer injury surveillance system of the Korea customer agency and analyzed. Results: Questionnaire survey was conducted among 300 elementary school pupils. One hundred pediatric roller shoe wearers (RSWs) were assessed regarding whether they wore protective equipment. Among the 29 injury cases, 24 were safety accidents, and most of them were caused by falls while rolling. Hand and wrist injuries were the most common (25. 0%), followed by injuries to the face, arm, and leg. Contusion was the most common type of injury (39. 1%), followed by laceration and fractures. Among the 300 children surveyed, 23. 0% had roller shoes. The minority of children (27. 5%) reported using roller shoes alone. Most of the RSWs answered that they had the experience of rolling in multiuse facilities. The most frequently visited multiuse facilities were department stores (72. 5%), followed by shopping malls, and food courts or cafes. Over half of RSWs answered that they had experienced rolling in danger zones for safety accident, and 47. 8% reported experiencing accidents. About two-thirds of RSWs answered that they did not remove the wheel while walking. Most of RSWs (82. 6%) indicated that they didn’ t wear protective equipment. Among the 100 children wearing roller shoes, 99 did not wear any kind of protective device; only one child wore a helmet, elbow protector, and knee protector. Conclusions: RSWs are recommended to wear protective equipment and to be accompanied by parents. Inside commercial facilities, signs prohibiting the wearing of roller shoes should be affixed.

Economic advantages and rapid construction of roller compacted concrete (RCC) has been considered by researchers and stakeholders of hydraulic structures with the increasing use of roller compacted concrete in dams industry and highway projects. The purpose of this experimental research is to investigate the influence of polypropylene fibers with different size and amounts on the mechanical properties of roller compacted concrete. Different type of fibers and admixtures has been suggested and in this research, cement type II from Sofian cement factory, silica fume from Azna-Lorestan factory, super plasticizer with poly carboxylic base, aggregates from Talmase factory (coarse aggregate with Dmax= 50 mm and fine aggregate with FM= 3.12), filler from Azardash factory, and poly-propylene fibers from Isfahan factory in different sizes of 6 and 12 mm by using in amounts of 0.35, 0.70 and 1.4 kg/m3. Cylindrical samples of 150´300 mm were prepared with above mentioned local materials and cured in fresh water in definite periods days of 3, 7 and 28 days in laboratory temperature and tested according to standards ASTM C39 and ASTM C496 for compressive and tensile strengths of samples. Consideration of test results showed that the Aspect Ratio of fibers is an important factor in strength of samples. Mainly for compressive strength, the best results come out by shorter fibers; and for tensile strength, the best results were with longer fibers. According to the test results, using polypropylene fibers in roller compacted concrete mix, tensile strength was increased almost 20%.

In this paper, the effects of two parameters named width of the roller and exerted force on it in direct and indirect rolling, on residual stresses in Friction Stir Welding (FSW) process of SU304 steel have been studied. FSW numerical modeling has been performed by ABAQUS. In both direct and indirect rolling, five levels have been considered for each variable. Based on the results, it has been shown that both variables have significant effects on the pattern and maximum of residual stresses. In general, in both direct and indirect rolling, by increasing the rolling force, residual stresses decrease intensely. In direct rolling, tensile residual stresses decrement happens locally by using relatively narrow rollers and increasing the rolling force. While in wide rollers, the decrement in tensile residual stresses occurs constantly. Based on the results, using direct rolling causes more decrement in welding tensile residual stresses in comparison with indirect rolling. In direct and indirect rolling, the minimum tensile residual stresses take place when the width of roller is equal to diameter and half of the diameter of welding tool, respectively. In this situation, the maximum of tensile residual stresses decreases 97. 4% for direct rolling and 57. 3% for indirect rolling.

During onion harvesting, removing leaves from the onion bulbs is a time- and energy-consuming operation that is currently done manually on most Iranian farms. roller-type toppers can be appropriate devices for onions that are already undercut and gathered. The machine parameters of rotational speed and clearance between rollers have significant impacts on machine performance. This study developed a rolling topper and evaluated the effects of rotational speed (100, 150, 200, 250 and 300 rpm) and the clearance between rollers (23, 33 and 43 mm) on the percentage of damaged bulbs, number of bulbs oriented in the appropriate direction and forward speed of the bulbs on the machine. Results showed that the greatest percentage of damaged bulbs (31.8%) occurred where clearance between rollers was set at 43 mm.Increasing the rotational speed enables movement of bulbs at higher forward speeds along the rollers; however, increasing the forward speed of bulbs increased the percentage of non-oriented bulbs to 24% at a rotational speed of 300 rpm. A rotational speed of 200 rpm and 23 mm in clearance between rollers was found to be the optimum configuration for a roller-type topper. In this case, a two blade mechanism decreased the height of remaining leaves after cutting (6.52 mm) and increased the number of onions topped at the appropriate distance from bulb base (95.5%), which was more effective than blade and idler mechanisms.