Method and apparatus for metered pre-stretch film delivery

The present invention provides a method and apparatus for dispensing a predetermined substantially constant length of pre-stretched packaging material based upon load girth. Based upon the girth of the load to be wrapped, an amount of pre-stretched packaging material to be dispensed for each revolution of relative rotation between a packaging material dispenser and the load is determined. A rotational drive system used to provide the relative rotation is linked to a pre-stretch assembly portion of the packaging material dispenser. The linkage may be mechanical or electrical. The linkage controls a ratio of the rotational speed to the pre-stretch assembly dispensing speed, such that the predetermined substantially constant length of pre-stretched packaging material is dispensed for each revolution of the packaging material dispenser relative to the load regardless of the speed of the rotational drive. In the case of a mechanical linkage, the linkage also connects the rotational drive to the pre-stretch assembly portion such that the rotational drive also drives the pre-stretch assembly portion. Good wrapping performance in terms of load containment (wrap force) and optimum packaging material use is obtained by dispensing a length of pre-stretched packaging material that is between approximately 90% and approximately 120% of load girth.