Dies ist eine alte Version des Dokuments!
Power and wall shear stress
The same conditions have to be filled for the calculation of the power and wall shear stress as for the calculation of the melting profile.
Realization of the theoretical principles
In the power calculation a distinction is drawn between the incipient fusing and the melting section. In the incipient fusing section, i. e. from the start of the first heating section through to the point of melt pool formation, the power can be established via an average melt layer thickness, assuming a pure drag flow in the melt film. The power conversion in the pure solids section between the hopper and the first heating section is neglected, since no pressure has built up till then and the frictional forces of the solids at the barrel wall are negligibly small compared to the frictional forces of the melt film.
The calculation for the other sections results in an addition of the wall shear stresses at the barrel. Similar to the calculation of the pressure throughput approximation equations are used, which are based on numeric examinations. A distinction is drawn between the melting section, where high wall shear stresses in the melt film occur and the pure melt conveying.
The overall drive power required (without transmission losses) and the overall torque is calculated from the local power requirement.
The heating/cooling power consists of components from the melt film and the melt pool. The temperature gradient at the barrel wall is established for both sections and from this the necessary heating/cooling power is determined via a temperature balance. The power at each single calculation point is added up for the heating section in question. The heating/cooling power calculation only allows for the heating flow between the band heater and the melt, but not for any heat losses (of any type) towards the outside.