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Nächste Überarbeitung		Vorhergehende Überarbeitung
en:berechnungen:aufschmelzverlauf [2025/06/26 12:33] – cschallen:berechnungen:aufschmelzverlauf [2025/07/03 13:34] (aktuell) – cschall
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 The melting process is divided into three sections. \\ The melting process is divided into three sections. \\
-  - First the location of the melt vortex formation (OSW) is calculated +  - First the location of the melt pool formation (OSW) is calculated 
-  - ‘Conventional’ melting begins from the location of the melt vortex formation+  - ‘Conventional’ melting begins from the location of the melt pool formation
   - From a certain switching point, conventional melting **can** change to disperse melting   - From a certain switching point, conventional melting **can** change to disperse melting
  
 The three sections are described below. The three sections are described below.
  
-===== Calculation of melt vortex formation location =====+===== Calculation of melt pool formation location =====
  
-The location of the melt vortex formation describes the distance from the start of the channel to the position where the melt vortex forms. For calculating the melting length, it is assumed that the melt film between the barrel and the solid bed gradually increases. The required melt film thickness for the formation of the melt vortex corresponds to the average melt film thickness as determined by the conventional melting calculation. Due to the porous structure of the solid bed, the initial heat flux from the barrel is reduced. The lower the barrel temperature and the bulk density of the material in the channel, the further downstream the location of melt vortex formation will be.+The location of the melt pool formation describes the distance from the start of the channel to the position where the melt pool forms. For calculating the melting length, it is assumed that the melt film between the barrel and the solid bed gradually increases. The required melt film thickness for the formation of the melt pool corresponds to the average melt film thickness as determined by the conventional melting calculation. Due to the porous structure of the solid bed, the initial heat flux from the barrel is reduced. The lower the barrel temperature and the bulk density of the material in the channel, the further downstream the location of melt pool formation will be.
  
 ===== Conventional melting ===== ===== Conventional melting =====
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 {{ :berechnungen:aufschmelzverlauf:abb_konv_aufschmelzen_01_en.svg?nolink&500 |}} {{ :berechnungen:aufschmelzverlauf:abb_konv_aufschmelzen_01_en.svg?nolink&500 |}}
  
-The solid bed is deposited on the non-driving (passive) flank of the screw channel. As the plastic melts, it is carried away to the active flank of the screw channel by the relative movement between the screw and barrel and by the ‘scraping’ by the screw flights. This creates a melt vortex, which simultaneously presses the solid bed against the non-driving flank. \\ +The solid bed is deposited on the non-driving (passive) flank of the screw channel. As the plastic melts, it is carried away to the active flank of the screw channel by the relative movement between the screw and barrel and by the ‘scraping’ by the screw flights. This creates a melt pool, which simultaneously presses the solid bed against the non-driving flank. \\ 
-As the melting process continues, the solids bed becomes narrower, but retains its height due to the pressure of the melt vortex. The solid bed width therefore decreases as a result of the melting process. If the channel geometry remains constant, the solids bed width decreases continuously. If the channel volume is reduced (lower channel depth, bigger flights, multi-flight section, lower channel pitch, restriction to the solid channel in barrier screws), the solids bed width increases, as the solids volume flow remains constant.+As the melting process continues, the solids bed becomes narrower, but retains its height due to the pressure of the melt pool. The solid bed width therefore decreases as a result of the melting process. If the channel geometry remains constant, the solids bed width decreases continuously. If the channel volume is reduced (lower channel depth, bigger flights, multi-flight section, lower channel pitch, restriction to the solid channel in barrier screws), the solids bed width increases, as the solids volume flow remains constant.
 The dimensionless solids bed width $y$ shown in REX is normalised to the channel width: $y = \frac{solids bed width}{channel width}$ The dimensionless solids bed width $y$ shown in REX is normalised to the channel width: $y = \frac{solids bed width}{channel width}$
  
-==== Clogging of the screw ====+==== Plugging of the screw ====
  
 Excessive compression of the screw channel can lead to plugging of the screw. Excessive compression of the screw channel can lead to plugging of the screw.
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 If a degassing extruder is calculated, there are three options in the event that the plastic has not yet completely melted at the start of degassing (s. [[en:berechnungen:einfache_berechnung|regular calculation]]): If a degassing extruder is calculated, there are three options in the event that the plastic has not yet completely melted at the start of degassing (s. [[en:berechnungen:einfache_berechnung|regular calculation]]):
-  - **Melting up to degassing zone**: The melting calculation is cancelled at the start of the degassing zone +  - **Melting up to degassing zone**: The melting calculation is cancelled at the start of the degassing section 
-  - **Melting from degassing zone conventional**: After the start of the degassing zone, the melting process continues to be calculated using the conventional melting model. +  - **Melting from degassing zone conventional**: After the start of the degassing section, the melting process continues to be calculated using the conventional melting model. 
-  - **Melting from degassing zone dispersed**: After the start of the degassing zone, the melting process is calculated further using the dispersed melting model.+  - **Melting from degassing zone dispersed**: After the start of the degassing section, the melting process is calculated further using the dispersed melting model.
  
 ==== Special features in PSI ==== ==== Special features in PSI ====
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 <dl> <dl>
-<dd>$\text{Number of downtimes} = \frac{\text{Channel volume of the leg}}{\text{Dosing volume}}$\\ \\ +<dd>$\text{Number of downtimes} = \frac{\text{Channel volume of the screw}}{\text{Dosing volume}}$\\ \\ 
-$\text{Total downtime}= \text{Number of downtimes} * \text{Total downtime}$\\ \\ +$\text{Total downtime}= \text{Number of downtimes} * \text{downtime}$\\ \\ 
-$\text{Normalised standstill time} = \frac{\text{Total standstill time}}{\text{Total throughput time}_{\text{Screw}}}$\\ \\ +$\text{Normalised downtime} = \frac{\text{Total downtime}}{\text{Residence time}_{\text{Screw}}}$\\ \\ 
-$\text{downtime in interval}=\text{leadtime}_{\text{interval}}*\text{standardised downtime}$</dd>+$\text{downtime in interval}=\text{Residence time}_{\text{interval}}*\text{Normalised downtime}$</dd>
 </dl> </dl>
  
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 ==== Calculation of the melt fraction ==== ==== Calculation of the melt fraction ====
  
-The melt fraction is calculated from the current normalised solids bed width $y$, the current channel width $b$, channel height $h$, number of passes $i$, and the current solids bed velocity $v_{fz}$ in relation to the channel geometry at the location of the melt vortex formation and the solids bed velocity $v_{fz,OSW}$ present there+The melt fraction is calculated from the current normalised solids bed width $y$, the current channel width $b$, channel height $h$, number of channels $i$, and the current solids bed velocity $v_{fz}$ in relation to the channel geometry at the location of the melt pool formation and the solids bed velocity $v_{fz,OSW}$ present there
 <dl> <dl>
 <dd>$\text{melt fraction} = 1 - y * \frac{h*b*i*v_{fz}}{(h*b*i*v_{fz})_{OSW}}$</dd> <dd>$\text{melt fraction} = 1 - y * \frac{h*b*i*v_{fz}}{(h*b*i*v_{fz})_{OSW}}$</dd>
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   * [[en:berechnungen:temperaturverlauf|]]   * [[en:berechnungen:temperaturverlauf|]]
   * [[en:berechnungen:leistung_und_schubspannungen|]]   * [[en:berechnungen:leistung_und_schubspannungen|]]
 +  * [[en:berechnungen:schergeschwindigkeit]]
   * [[en:berechnungen:verweilzeit|]]   * [[en:berechnungen:verweilzeit|]]
   * [[en:berechnungen:verweilzeitverteilung|]]   * [[en:berechnungen:verweilzeitverteilung|]]