Shrink sleeve geometry

Purpose and scope

This calculator sizes a shrink sleeve from the container geometry and the film behavior you enter. It returns layflat width, cut height before machine-direction shrink, flat film width including seam, required transverse shrink and remaining film shrink margin. It is a geometry and screening tool, not a shrink-curve simulator. The linked equipment supplier discussion of directional shrink and process curves supports the caution that temperature and dwell affect real sleeve behavior; it does not replace converter or applicator approval.

Container and coverage inputs

Enter widest diameter the sleeve passes in inches. This is the maximum container diameter the sleeve must clear, not an average. Enter smallest diameter to grip in inches. The tool rejects a grip diameter larger than the widest diameter with an error. Finished coverage height is the final vertical coverage in inches. Seam allowance is the film seam width in inches and is used only in flat film width. All dimensional fields use inches; shrink fields use percent.

Clearance and layflat

Layflat slip clearance is added to half the widest circumference to form the starting layflat width. The model uses layflat = pi times widest diameter divided by two plus clearance. Clearance is a slip allowance, so it increases the starting tube size. A larger clearance raises flat film width and, for a fixed grip diameter, raises required transverse shrink because the starting tube has more circumference to contract. It does not model ovality, container taper or slip force.

Shrink inputs

Machine-direction shrink is the percent contraction along the film direction. The tool uses it only to set cut height: finished height divided by the retained fraction after MD shrink. Higher MD shrink increases cut height because the retained fraction in the denominator becomes smaller. Verified film transverse shrink is the percent contraction across the film that you have confirmed for the film and process. The tool compares it with required transverse shrink to report margin in percentage points. It does not infer shrink from temperature, dwell, film thickness or tunnel settings.

Reading outputs

Layflat width is the starting half-circumference plus clearance. Cut height before MD shrink is the length to cut so the finished height is reached after MD contraction. Flat film width including seam is twice layflat plus seam allowance. Required transverse shrink is the contraction needed to bring the starting tube circumference down to the grip circumference. Remaining film shrink margin is verified TD minus required TD. A positive margin means the entered TD exceeds the model requirement; a negative margin means it falls short in this screening calculation.

Worked examples

Using the starting scenario, widest diameter 2.6 in, grip diameter 2.1 in, finished height 4 in, clearance 0.12 in, MD shrink 2 percent, verified TD 65 percent and seam 0.25 in, the tool reports layflat width 4.204 in, cut height 4.082 in, flat film width 8.658 in, required transverse shrink 21.54 percent and remaining margin 43.46 percentage points. The margin is large because the entered TD is well above the model requirement.

Changing grip diameter to 1 in and verified TD to 50 percent leaves layflat, cut height and flat film width unchanged because those outputs do not depend on grip diameter or TD. Required transverse shrink rises to 62.64 percent because the sleeve must contract to a smaller grip circumference. Remaining margin becomes negative 12.64 percentage points, so the entered TD is below the model requirement. That is a screening flag, not a prediction of tunnel performance.

Validation and edge cases

The cross-field check rejects a grip diameter greater than the widest diameter. Equal diameters are allowed. A zero clearance is allowed and makes layflat equal half the widest circumference. Machine-direction shrink accepts 0 to 95 percent. Verified transverse shrink accepts 0 to 99 percent. At the upper end of the MD range, the small retained fraction makes the cut-height estimate rise sharply. Negative margin can occur when grip diameter is small, clearance is large or verified TD is low. Treat that result as a check against film data, not as a failure diagnosis.

Approval and limitations

Shrink curves depend on temperature and dwell. Maximum percentage alone cannot predict distortion, seam strength or tunnel performance. Ask the applicator and converter to approve the dimensions. Use measured film shrink from the actual process, not a generic datasheet value, when available. The calculator does not model seam orientation, film thickness, container corners, taper, ovality or application speed. Its outputs are starting dimensions for review, not production guarantees.

Questions about shrink sleeve geometry