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The Melt Flow Index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures.
The most significant parameter for controlling the fiber diameter is the flow rate of the polymer to the spinneret - in general, the higher the flow rate, the larger the fiber diameter. While reported flow rates are low, all of the fluid electrospun is collected, unlike solution electrospinning where a great part of the solvent is evaporated.
These processes include planar flow casting, twin roll melt spinning, and auto ejection melt spinning. Originating with Robert Pond in a series of related patents from 1958 to 1961 (US Patent Nos. 2825108, 2910744, and 2976590), the current concept of the melt spinner was outlined by Pond and Maddin in 1969.
Melt rheology has shown to be an accurate method in determining the polymer's molecular structure. [3] This is beneficial in determining weld compatibility between materials; as materials with drastically different flow characteristics will be more difficult to join compared to those with more closely matched viscosity and melting temperature ...
In this phase the melting rate of the material matches the flow of material extruded at the lateral surfaces. The material flow and thickness of the melt layer become constant. This is the step that determines the quality of the weld. This step is maintained until the desired ‘melt down’ thickness (thickness of the molten material) is achieved.
At low shear rate (˙ /) a Carreau fluid behaves as a Newtonian fluid with viscosity .At intermediate shear rates (˙ /), a Carreau fluid behaves as a Power-law fluid.At high shear rate, which depends on the power index and the infinite shear-rate viscosity , a Carreau fluid behaves as a Newtonian fluid again with viscosity .
Ideally, the melt rate stays constant throughout the process cycle, but monitoring and control of the vacuum arc remelting process is not simple. [5] This is because there is a complex heat transfer occurring involving conduction, radiation, convection within the liquid metal, and advection caused by the Lorentz force .
Melt expulsion occurs when the vapor pressure is applied on the liquid free surface which in turn pushes the melt away in the radial direction. In order to achieve fine melt expulsion, the melt flow pattern needs to be predicted very precisely, especially the melt flow velocity at the hole's edge.