 INDEX

FORMS FOR CALCULATION OF REQUIRED KILOGRAMS

 PROCEDURE EXPLANATION

Example for the case of a packing in folded film covering a product of regular form.

In order to determinate the amount of Kg of required material for packing a product, we should know first:

1. Amount of required packages.
2. Dimension of the product to pack, and consequently, the dimensions (long, wide and thickness) of the material required for each package.
3. Material that is going to be used in the packing (PVC, PEAD, PEBD, PP, CELOFAN, etc.), therefore, its density or specific gravity, this means, its weight per volume unit of the material in question.

For the calculation, will use the following formula:

D = M/V

where:

D = density of the packing material, in g/cm3.
M = Mass (weight) of the packing material, in g.
V = Volume of the packing material(long x wide x height (thickness)), in cm3.

therefore:

M=DV

or what it is the same:

Amount of required material for packing a product  =  Required packages number X Length of packing material X Width of packing material  X Height of packing material (Thickness) X Density of packing material Figure 1. Usual form of Shrink film: Rolls of center folded film.

We must remember that in order to obtain appropriate results, we should use the same units in whole formula, consequently, adapting the previous formula to the units normally used and to the commonly used form of presentation of the film (see figure 1), it remains in the following form:

K = ( N x L x A x C x (2.54/100,000) x 2 x D )/ 1000

where:

K = Amount of required Kg for packing a product.
N = Number of required packages.
L = Length of packing material, in cm.
A = Width of required material for each package, in cm (don't forget add the waste upon sealing and the tolerance of production).
C = Gauge or thickness of packing material, normally specified in 0.00001" (hundred thousandths of a inch).
(2.54/100,000) = conversion of 0.00001" to cm.
2 = duplication of the volume of used wide A film; this is because we are using a folded film that cover top and bottom parts of the product (see figure 3).
D = Density of packing material, in g/cm3. (For PVC=1.35, PEBD=0.92, PEAD=0.96, etc.)
1000 = conversion of used material, g to Kg.

 CALCULATION EXAMPLE

Calculating the amount of PVC shrink film required in order to pack 10,000 packages with the dimensions shown in the following figure: Figure 2. Measures of the product to packing

DATA:

1. N = 10,000 packages.
2. Dimensions of the product = 40 x 30 x 10 cm, consequently the dimensions of each packing will be (see figure 3): Figure 3. Dimensions of the film used in each package.

Note. In case of having a product with different dimensions in both ends, you will use the average value of both ends, for example, if one side measure 8 cm and the other side 10 cm, the value that will take for calculation will be 9 cm.

3. L = 42 cm.
4. A = 54 cm. = nominal measure of the utilized roll, include the looseness of the packing before the shrinking, that avoid breaks in the seal at the moment of closing the sealer jaws, as well as the amount of waste required for a comfortable seal job (2 or preferentially 3 cm).
Including the tolerance added in manufacturing (2.5 cm.), the total width is 57.5 cm.
5. C = 100 hundred thousandths of inch (recommended for most of applications).

Note. Preferentially, the product to pack will make comfortable according to the previous figure in order to facilitate the packing and diminish the waste, that is, the minor dimension will correspond to the height, for diminishing the dog ears and the wrinkles in corners; from the other two dimensions the longer will correspond to the roll width, for the lower amount of waste (in this case 30 cm instead of 40 cm), but this is not advisable for small measures (widths lower to 15 cm), because its manufacturing is hindered. Figure 4. Product packed showing the waste.

6. Used material = PVC
7. Density = 1.35 g/cm3

Minimum amount of kilograms required by the customer (you will be suppose to add the material that considered as waste in the packing process and 10% additional for possible variations in width and gauge of the packing material):

K = ((10,000 x 42 x 57.5 x 100 x (2.54/100,000) x 2 x 1.35)/ 1000)*1.1 = 182 Kg of folded PVC shrink film of 54 cm, gauge 100

07/09/2005   