Extrusion Die Swell Calculator

Calculate die swell ratio from material elasticity, L/D ratio, shear rate, and melt temperature. Determine required die dimensions to achieve target extrudate size.

Inputs

Die opening diameter (mm)

Target extrudate OD (mm)

Die land length (mm)

Apparent wall shear rate (1/s)

Material elasticity (1-5)

Melt temperature (°C)

Reference temperature (°C)

Tab to move between fields

Results

Die swell ratio (B)

2.5

Required die diameter (mm)

Diameter swell (%)150

Predicted extrudate OD (mm)62.5

Area swell ratio6.25

Area swell (%)525

Size error if uncompensated (mm)32.5

Size error (%)108.3

L/D ratio2

Recommended L/D10.3

How to Use This Calculator

Enter Die opening diameter (mm), Target extrudate OD (mm), and Die land length (mm).
Set Apparent wall shear rate (1/s), Material elasticity (1-5), and Melt temperature (°C).
Adjust Reference temperature (°C) as needed.
Review Die swell ratio (B) and Required die diameter (mm).
Use Diameter swell (%) and Predicted extrudate OD (mm) to inform your decision.

How the result changes with Die land length (mm)

Die land length (mm)	Die swell ratio (B)	Required die diameter (mm)
50	2.5	12
175	1.34	22.45
325	0.98	30.59
450	0.83	36

What each input means

Die opening diameter (mm): Current die opening diameter.
Target extrudate OD (mm): Desired outer diameter of the extrudate after swell.
Die land length (mm): Length of the parallel (land) section of the die. Longer = less swell.
Apparent wall shear rate (1/s): Apparent shear rate at the die wall. Higher rates increase swell.
Material elasticity (1-5): 1=PVC (low), 2=PS, 3=PP, 4=HDPE, 5=LDPE (highest swell).
Melt temperature (°C): Actual melt temperature at the die exit.
Reference temperature (°C): Standard processing temperature for this material. Used for temperature correction.

What each result means

Die swell ratio (B): Ratio of extrudate diameter to die diameter (B = D_ext / D_die).
Diameter swell (%): Percentage increase in diameter from die to extrudate.
Predicted extrudate OD (mm): Predicted extrudate diameter from the current die.
Required die diameter (mm): Die diameter needed to achieve the target extrudate size.
Area swell ratio: Cross-sectional area increase (swell ratio squared).
Area swell (%): Percentage increase in cross-sectional area.
Size error if uncompensated (mm): Dimensional error vs target if die is not compensated for swell.
Size error (%): Percentage error vs target.
L/D ratio: Die land length-to-diameter ratio.
Recommended L/D: L/D ratio needed to reduce swell below 10%.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Die opening diameter (mm) = 25, Target extrudate OD (mm) = 30, Die land length (mm) = 50, Apparent wall shear rate (1/s) = 100 = 7 input(s) provided
Calculate Die swell ratio
Die swell ratio = baseSwell * ldFactor * shearFactor * max(0.7, min(1.3, tempFactor))
2.5 = 2.5
Calculate Required die diameter
Required die diameter = targetDiameter / swellRatio
12 = 12
Calculate Diameter swell
Diameter swell = (swellRatio - 1) * 100
150 = 150
Calculate Predicted extrudate OD
Predicted extrudate OD = dieDiameter * swellRatio
62.5 = 62.5