Blow Up Ratio Calculator

| Added in Construction

Understanding Blow Up Ratio

The blow up ratio (BUR) is a fundamental parameter in blown film extrusion that measures the expansion of the molten polymer tube as it is inflated with air. This dimensionless ratio directly impacts the final properties of the film.

Formula

[\text{Blow Up Ratio} = \frac{\text{Final Tube Diameter}}{\text{Die Diameter}}]

The result is a pure number without units, as it is a ratio of two measurements with the same units.

Example Calculation

If you have a final tube diameter of 7 inches and a die diameter of 4 inches:

  1. Final Tube Diameter = 7 in
  2. Die Diameter = 4 in
  3. Blow Up Ratio = 7 / 4 = 1.75

This means the tube has expanded to 1.75 times the diameter of the die.

Applications

Blow up ratio is crucial in determining:

  • Film orientation: Higher BUR increases transverse direction orientation
  • Mechanical properties: Affects tensile strength and tear resistance
  • Thickness uniformity: Impacts gauge variation across the film
  • Production stability: Higher ratios can be more challenging to control

Typical Values

  • Low BUR (1.5-2.0): Easier to control, less orientation
  • Medium BUR (2.0-3.0): Most common range for general applications
  • High BUR (3.0-4.0): Maximum orientation, improved properties, harder to stabilize

Frequently Asked Questions

Blow up ratio (BUR) is the ratio of the final tube diameter to the die diameter in blown film extrusion. It is a dimensionless value that indicates how much the film is expanded during the process.

Blow up ratio is calculated by dividing the final tube diameter by the die diameter. The formula is: BUR = Final Tube Diameter / Die Diameter.

Typical blow up ratios in blown film extrusion range from 1.5 to 4.0, depending on the material and desired film properties. Higher ratios generally improve mechanical properties but can be more difficult to control.

Blow up ratio affects film orientation, thickness uniformity, and mechanical properties. It is a critical parameter in controlling film quality and production efficiency in blown film extrusion.