Unterschiede
Hier werden die Unterschiede zwischen zwei Versionen angezeigt.
| Beide Seiten der vorigen RevisionVorhergehende ÜberarbeitungNächste Überarbeitung | Vorhergehende Überarbeitung | ||
| en:berechnungen:druckverlauf [2024/10/17 20:07] – [Pressure curve calculation for wave screws] neelest | en:berechnungen:druckverlauf [2026/09/17 09:24] (aktuell) – gelöscht - Externe Bearbeitung (Unbekanntes Datum) 127.0.0.1 | ||
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| - | ======Pressure profile====== | ||
| - | In order to calculate the pressure profile it is necessary to fulfil the same conditions | ||
| - | as for the throughput calculation of both the throughput and the metering time | ||
| - | calculation. This also applies for all input data | ||
| - | [[en: | ||
| - | [[en: | ||
| - | and [[en: | ||
| - | Additionally, | ||
| - | profile of the screw length shall be calculated has to be defined. | ||
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| - | The pressure profile is calculated back to the point of melt pool formation (OSW). If it was not | ||
| - | possible to determine the point of melt pool formation on account of missing data, | ||
| - | REX/PSI will calculate up to the end of the feed section. The profile from the front | ||
| - | edge of the hopper to the last point calculated is reflected by a logarithmic | ||
| - | formulation. | ||
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| - | The pressure profile calculation starts with the screw tip. The calculated throughput is | ||
| - | used to determine the pressure loss between two calculation points and this is then | ||
| - | added to the previous absolute pressure. The pressure in the screw vestibule (at the | ||
| - | screw tip) results from the adjusted impact pressure. | ||
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| - | The pressure profile is calculated isothermally at the melt temperature for each step | ||
| - | and is subsequently multiplied by a correction factor. This correction factor has in | ||
| - | physical terms the effect that the calculation performed at a temperature that permits | ||
| - | the pressure and throughput behavior to coincide. This is necessary, since the | ||
| - | throughput has to be calculated on the basis of a mixed isothermal/ | ||
| - | formulation while the pressure profile has to be calculated either isothermally or nonisothermally. | ||
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| - | ==== Pressure profile calculation for the barrier section ==== | ||
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| - | In order to calculate the barrier screw in the way described a constant pressure | ||
| - | gradient has to be assumed. However, since every additional assumption increases | ||
| - | inaccuracy, the so-called " | ||
| - | assumption. Its calculation method is similar to the FEM calculation method. | ||
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| - | Here, single intervals are built for barrier flight, solid and melt channel and for each | ||
| - | section between the individual balance points, the change in the flow is described by | ||
| - | means of a linear equation. These equations form a linear system of equations. The | ||
| - | equations only describe the development of the flow in the direction of the channel, | ||
| - | which means that the mesh of the division of the geometry into the required intervals | ||
| - | corresponds to constant conditions. | ||
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| - | {{ : | ||
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| - | Before the resulting equation system can be solved with the familiar algorithms used | ||
| - | to solve linear equation systems, it is first necessary to reduce the system. This | ||
| - | reduction is achieved by allowing boundary conditions. | ||
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| - | {{ : | ||
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| - | In the closed barrier section, the mass flow towards the first node, or away from the | ||
| - | last node in the channel direction, can be taken as being equal to zero. If an open | ||
| - | barrier section is calculated, by contrast, it is sufficient to alter the boundary condition | ||
| - | in order to be able to calculate this design. Because of the lack of a geometrical | ||
| - | separation, the pressure difference between the first and last nodes of the solids and | ||
| - | melt channel is set at zero. | ||
| - | |||
| - | For a clear-cut solution of the system it is necessary to know about the mass flow. | ||
| - | Here an iterative calculation helps, i.e. in the first step, the pressure-throughput | ||
| - | behavior of the standard sections is calculated for a known pressure at the screw tip | ||
| - | without considering the barrier section. In the second step, this throughput is taken to | ||
| - | solve the equation system for the barrier section. Since the overall pressure | ||
| - | requirement for the screw is equal to the sum of the pressure requirements of the | ||
| - | individual screw sections, the calculated pressure requirement for the barrier section | ||
| - | can be added to the pressure requirement of the remaining screw sections that was | ||
| - | calculated in the first step. | ||
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| - | ==== Pressure curve calculation for wave screws ==== | ||
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| - | The content is currently being processed and will be made available shortly. Please be patient. | ||
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| - | ToDo: Anpasssen wenn MA Gödeke fertig ist | ||
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| - | ===Further topics=== | ||
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