1,721,082 research outputs found
Influence of the technological route andof the associated thermo-mechanical processeson the realization of thick cylindrical componentsin 2.25%Cr-1%Mo steel
No full textThis study is focused on a critical evaluation
of the features and properties of thick ferrule
usually applied for construction of reactors and
realized through different technological routes.
At the present these pieces can be obtained
through three different technological routes:
forging, hot rolling and cold bending. The
characterization of the analysed ferrules has
been performed through the coupling
of results coming from metallographic optical
observations, mechanical tests, texture
crystallographic analysis performed by
SEM-EBSD. The obtained results allow defining
the mechanical performances as a function
of the applied technology and they permit
comprehending these results on the basis
of the particular micro-structural modifications
induced by the investigated processes and
the examined production systems
Application of electromagnetic stirring for the homogenization of aluminium billet cast in a semi-continuous machine
No full textSeveral billets have been cast at different levels of current induced in the stirrer coil, they have been
characterized under the microstructural aspects and their features have been compared with the characteristics
of the as-cast billets and of the thermally homogenized ones, because these last ones are used
in the typical and traditional technological route. The coupling of the computational simulations – performed
by a multiphysic platform – allows us to estimate the flow patterns induced by the different
current levels applied in the stirrer coil. The homogenization of the electromagnetically treated billet has
certainly taken place implying a finer distribution of the intermetallic phases. The thermal homogenizing
is always associated with a softening of the metal alloys whereas the electromagnetically refined structure
shows a hardening phenomenon caused by the induced finest grain size. The flow pattern imposed
by the electromagnetic stirrer is strongly dependent on the current intensity that is pointed out as the
ruling variable conditioning the velocity field of the liquid pool. Thus, an electromagnetic stirring working
at low frequency and a correct modulation of current intensity can be useful for improving the technological
route finalized to the extrusion of the aluminium alloys, taking into account that such a route
involves the use of extrusion machines featured by a higher power level
Analysis of the factors involved in failure of a brass sleeve mounted onan electro-valve
No full textSeveral electro-valves have failed because of the fracture occurred on the internal sleeve
made in a typical free cutting leaded brass CW614 N (UNS 36000). The morphology of
the observed fracture surface clearly indicates that the failure phenomenon has been ruled
by a stress corrosion cracking mechanism. On the other hand, all the electro-valves operate
in an environment featured by potable water that does not justify an alchaline concentration
able to induce the SCC phenomenon. The analysis of the observed surface and the comparison
of the stress that can induce SCC clearly point out that the failure has been induced
by the application of excessive torque on the threaded sleeves to grant their fixing. The performed
investigation allows us to indicate the correct procedure in order to avoid the failure
of the sleeves and also the change of the applied alloy or an excessive increase of the
resistant thickness of such a component
Caratterizzazione microstrutturale di scorie da forno ad arco elettrico e aspetti associati al rilascio di specie chimiche inquinanti
No full text
Influence of the residual stresses induced by tool wear on the failure of brass electro-valves
No full textFailure analysis was performed on different brass electro-valves body affected by unexpected phenomena of cracking. Through the application of optical and scanning electron
microscopy, micro hardness Vickers test and X-ray diffraction, the causes of damage were identified. The study showed the dependence between roughness and residual stress associated to the tool wear. A solution to avoid the failure is finally proposed, based on the use combination of a tool with controlled wear and stress relieving heat treatment
Critical evaluation of role of viscosity and gas flowrate on slag foaming
No full textSlag foaming is a fundamental aspect in both electric arc furnace and oxygen converter steelmaking. In the latter, the unstable foaming can cause the undesired phenomenon of slopping, which implies significant blow-up of the material contained in the converter. The foaming has been studied on the basis of different approaches; theoretical studies usually based on a dimensional physical analysis and experimental studies. In all the cases, strong non-linear relations among the involved factors of influence have been highlighted, but some lack of consistency among the different results has emerged, especially about the role of the surface gas velocities and the viscosities of the slag and foam. Therefore, in this study the discussion about the foaming phenomenon has been evaluated through experimental trials developed using oil at different temperatures in order to take into account the effect of the change of the viscosity. The study has permitted the clarification of the reason of the collapse of the foam at a high gas flowrate; this phenomenon being associated to the increase in the average bubble size provided to the already formed structure of the foam. Via the experimental observations made at different gas flowrates and the development of simple analytical relationships, the viscosity has been confirmed to be an important stabilising factor, because it does not favour the liquid drainage, and low temperatures favour foam stabilisation, increasing its height
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