In REX, the following ratios are differentiated between different screw zones:

The compression ratio of a compression or decompression zone is calculated from the channel depths at the beginning and end of the zone:

$CR = \frac{h_{E}}{h_{M}}$

with the channel depth of the feed zone $h_E$ and the channel depth of the metre zone $h_M$

As the ratio of the channel depths does not allow a meaningful comparison between two screw concepts, the volume compression ratio is used for a more precise description. It relates the channel cross-section of the feed zone to the channel cross-section of the metering zone. In REX, the screw clearance is also taken into account.

$VCR=\frac{[(h_E+s)*(t_E-i_E*e_E)]*(D-(h_E+s))}{[(h_M+s)*(t_M-i_M*e_M)]*(D-(h_M+s))}$

with the channel depth $h$, the side clearance $s$, the pitch $t$, the number of webs $i$, the web width $e$ and the diameter $D$. With the indices $E$ for the feed zone and $M$ for the metering zone.

For barrier screws, the volume-compression ratio is also calculated from the ratio of the channel cross-section of the feed zone to the added channel cross-section of the solids and melt channel at the end of the barrier zone:

$VCR = \frac{B_E*h_E}{B_S*h_S+B_F*h_F}$

With the channel width $B$ and the channel height $h$ for the indices $E$ for the feed zone, $S$ for the melt channel and $F$ for the solid channel of the barrier zone.

The Pump Ratio indicates the ratio of the channel depth of the metering zone after degassing $h_{M,2}$ in relation to the channel depth of the metering zone before degassing $h_{M,1}$.

$PR = \frac{h_{M,2}}{h_{M,1}}$

Typically, a value of 1.5 to 1.6 is realised.

There is also a typical ratio for the channel depth of the degassing zone. This is typically 2.0 to 2.5 times the channel depth of the metering zone after degassing. In most cases, this successfully prevents the degassing opening from flooding.

• Regular calculation
• Throughput
• Pressure profile
• Melting profile
• Temperature profile
• Power and wall shear stress
• Residence time
• Mixed indicators
• Material degradation
• Fiber length degradation
• Degassing index calculation
• Stress Analysis
• Drag pressure flow
• Solids conveying
• Processing of mixtures
• Wall-slipping Materials
• Grooved bush
• Compression ratio & Pumping ratio