Complimentary Slide Rule ca. 1976
Single Roll Cutoff with Wand
If you are shrink wrapping cases, you are a converter. You buy film by the kilogram and cut it off into sleeves before it goes into the shrink tunnel.
If you buy 55.88 cm X 50.8 μm sheeting and have one ply on top & bottom, for practical purposes, you are making a bag. Multiply the weight per 1,000 packages by the price per kilogram to derive the cost per 1,000 cases.
If you cutoff one sheet at a time - simple. Just imagine a bag by folding either the width or length of the cutoff so there are two plys.
Half of the web width or ½ of 55.88: 27.94 cm X 86.36 cm X 50.8 μm÷.0001849 = 22.66 kg / 1,000 packages
Half of the web cutoff or ½ of 86.36: 43.18 cm X 55.88 cm X 50.8 μm ÷.0001849 = 22.66 kg / 1,000 packages
Example: Here is an example of film which is 7% "heavy" and well within the ± 10% industry tolerances. However, the film is produced "heavy" adding cost to the packages without the customer realizing the additional cost:
|Step 1||measured cutoff = 55.88 cm|
|Step 2||1,443 packages from 1 roll of film|
|Step 3||weight per 1,000 packages = 22.66 kg / 1,000|
|Step 4||34.93 kg ÷ 22.66 kg /1,000 = 1541 "theoretical yield" from 34.93 kg film|
|Step 5||compare actual (1,443) to theoretical (1,541)|
In this example, the real cost per 1,000,000 cases assuming a price of $1 per pound is $53,350 not $49,860.
Heat Seal Pass Through: Roll on Top / Roll on Bottom
Here is a nearly perfect scenario:
|Step 1||measured cutoff = 73.66 cm|
|Step 2||3,309 packages from 63.5 kg of film (2 rolls x 31.75 kg / roll)|
|Step 3||weight per 1,000 packages = 19.331 kg / 1,000|
|Step 4||63.5 kg ÷ 19.331 kg /1,000 = 3284 "theoretical yield" from 63.5 kg film|
|Step 5||compare actual (3,309) to theoretical (3,285)|