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Environmental Hazards and Their Management
Published in Danny D. Reible, Fundamentals of Environmental Engineering, 2017
Even the best pollution prevention cannot eliminate all waste from any engineering activity. Some waste will be generated and discharged to the environment. The next consideration in the management strategy is then to consider recycling this material to avoid its treatment and disposal. Much of the same creativity applied to the pollution prevention effort must also be applied to the investigation of opportunities for waste minimization. Recycling paper and aluminum cans and other metals are well known and comparatively easy to implement. Similarly segregation of wastes can ensure that the recycled materials are of the highest quality and retain as much value as possible. More difficult is recognizing what is generally considered to be waste as a valuable product. Since recycling is process- and product-dependent, we will not focus on it in this text, but examples will be provided where appropriate.
To cast or not to cast
Published in M.A. Jaurrieta, A. Alonso, J.A. Chica, Tubular Structures X, 2017
Pieter C. Glijnis, Joost Crommentuyn
In case of use in critical (fatigue) loaded situations the casting process is also critical. During the solidifying a thickening layer is formed from the outsides and the heat has to be dissipated through this layer. In this process the volume of the cast steel decreases (volumetric contraction). This volumetric contraction has to be compensated by liquid from the heavier sections or from a riser that acts as a feed metal reservoir, which is placed on the heavier section. In case there is not enough feed metal to compensate this shrinkage cavities (sometimes cracks) will be formed. Also segregation can be a problem. Segregation is a concentration of certain alloying elements at specific regions, usually as a result of the primary crystallization of one phase with the subsequent concentration of other element in the remaining liquid. To determine that the cast part is suitable for its task testing is mandatory. With rising quality demands, the costs (testing and rejected parts) will grow exponentially.
Contact Materials
Published in Milenko Braunovic, Valery V. Konchits, Nikolai K. Myshkin, Electrical Contacts, 2017
Milenko Braunovic, Valery V. Konchits, Nikolai K. Myshkin
Although not as widely documented as in the case of ferrous alloys, thermal treatments were also used to modify the surface properties of electric contact materials. This is achieved by provoking an intensive surface segregation of impurities or solute at the free surface. Segregation can be defined as the enrichment of a material constituent at a surface or internal interface of material. This segregation may intensify or moderate the tendency of surfaces to absorb active species from the environment with consequent modification of the segregation of impurities from within the body.107–112
Fluidization of forest biomass-sand mixtures: experimental evaluation of minimum fluidization velocity and CFD modeling
Published in Particulate Science and Technology, 2021
Florencia Toschi, Mariana T. Zambon, Julio Sandoval, Andrés Reyes-Urrutia, Germán D. Mazza
The results of the pressure drop versus velocity for the sawdust are shown in Figure 3. The bed behavior differs from that observed in sand-air systems. At low gas velocities, the bed remains at rest, and the pressure drop increases linearly, but beyond 0.12 m s−1, small channels begin to occur at the center of the bed tube and along the walls. With further increments in the gas velocity, the observed channeling increases in number and size. At a gas velocity of 0.174 m s−1, the maximum pressure drop is observed, and any velocity increments beyond this point result in particle rearrangement, in addition to a slight decrease in the pressure drop. The particles in the upper zone of the bed are fluidized, while those in the lower zone remain static. This behavior, typical of segregated systems, is attributed to the size distribution of the biomass sample. Segregation occurs in systems where particles have different densities and/or different sizes. The particles with a higher density tend to sink in the bed, while the particles with a lower density tend to float. In systems where there is no density difference, the larger particles tend to remain at the bottom (Di Maio, Di Renzo, and Vivacqua 2012). With subsequent increments in the gas velocity, the number of particles moving within the bed increased, and at a velocity of 0.314 m s−1, all the particles were fluidized.
Recent progress and scientific challenges in multi-material additive manufacturing via laser-based powder bed fusion
Published in Virtual and Physical Prototyping, 2021
The considerable difference between the melting points of the two materials causes the evaporation of the material with a low melting point during the melting process. In contrast, the material with a high melting point insufficiently melts. This can cause defects, such as element segregation (Zhang et al. 2018), pores (Liu et al. 2015), and powder infusibility (Brueckner et al. 2018), which can eventually reduce the mechanical properties of processed parts (Taheri Andani et al. 2017). Element segregation can be reduced by homogenisation heat treatment (Simonelli et al. 2018). Moreover, the simultaneous use of laser power in the medium range and high scanning speed can suppress the evaporation of metal elements with low meting point and reduce segregation (Vora et al. 2015). Researchers attempted to reduce the defects caused by the lack of fusion by optimising laser processing parameters (e.g. scanning speed (Kuo et al. 2020; Huang et al. 2021), hatch distance (Kuo et al. 2020), and laser power (Huang et al. 2021), optimising scanning strategies (Nadammal et al. 2021; Sing and Yeong 2020), and using a top-hat laser profile (Huang et al. 2021)). If the melting points of the two materials are similar, the above measures are suitable for suppressing the occurrence of defects due to the lack of fusion. However, if the difference between their melting points is extremely large, the effectiveness of the above strategy may be limited (Wei, Gu, Li, Sun, Liu, et al. 2020).
A Swedish case study of reprocessing of fashion products
Published in International Journal of Fashion Design, Technology and Education, 2023
It is a process of collection, categorisation, and processing of products for material recovery (Gobbi, 2011). The product lost its original functionality in the recycling process, and it is a low-value process (Thierry et al., 1995). Recycling is only profitable for precious materials (Fleischmann et al., 2004). Segregation of material is complex, and in the absence of mixed or blended material, the recycling yields inferior quality material (Alkazam, 2013). There is also a considerable cost associated with the recycling process. Therefore, recycling is not a feasible option in high wage countries (Carlsson, Torstensson, Pal, & Paras, 2015). Recycling on an international scale requires transportation that is also unsustainable and costly (Dervojeda et al., 2014).