Power assisted roller-stretch wrapping process

A process of wrapping a load encompassing irregular or crushable members with a plastic material comprising the following steps:

• a. pulling a plastic web through a pre-stretch device comprising roller means adapted to rapidly stretch the plastic material over one hundred percent and substantially over its yield point;
• said pulled plastic web at least partially driving said roller means;
• b. immediately relieving the majority of the stretching force from the plastic material after leaving the pre-stretch device by applying a positive torque to the roller means while transmitting speed changes on the load surfaces back to the roller means to keep a relatively constant force and stretch level;
• c. wrapping the load with stretched plastic material having said majority of stretch force relieved;
• and
• d. allowing stress and strain recovery of the pre-stretched plastic material to increase load holding forces and conformation of the wrap to load configuration irregularities.

A process of making a unitary package by wrapping a plurality of units with a stretched plastic film web overwrap to form a unitary packaged load comprising the steps of:

• a. placing a load having corners on a support;
• b. positioning a roll of stretchable plastic film web on a dispenser means adjacent to said support;
• c. withdrawing a leading edge of said plastic film web from said dispenser means through a plastic film web pre-stretching means;
• d. holding said plastic film web adjacent said load;
• e. stretching said film web above its yield point in said pre-stretching means by relatively rotating the load causing the film web to be pulled past at least two roller surfaces of said stretching means, said roller surfaces being interconnected so that they rotate at different speeds when partially driven by said film web, the downstream roller surface propelling the film web at a faster rate of speed than the upstream roller surface causing the film web to incur substantially all of its elongation between said roller surfaces;
• f. applying a substantially constant positive torque to the interconnected roller surfaces to partially drive and reduce the stretch force from the pre-stretching means to the load to a level below the force required to pre-stretch the film web so that the pre-stretch device speeds up and slows down with the passage of the corner of the load, and
• g. wrapping the load with more than one revolution of the previously elongated film web.

A process of making a unitary package by wrapping a plurality of units with a stretched plastic film web overwrap to form a unitary packaged load comprising the steps of:

• a. placing a load on a support;
• b. positioning a roll of stretchable plastic film web on a dispenser means adjacent to said support;
• c. withdrawing a leading edge of said plastic film web from said dispenser means through a plastic film web pre-stretching means;
• d. holding said plastic film web adjacent said load;
• e. stretching said film web in said pre-stretching means at a first force by relatively rotating the load causing the plastic film web to be pulled past and partially drive at least two roller surfaces of said stretching means, said roller surfaces being connected so that they rotate at different speeds when driven by said film web, the downstream roller surface propelling the film web at a faster rate of speed than the upstream roller surface causing the plastic film web to be substantially elongated over its yield point and incur substantially all of its elongation between said roller surfaces;
• f. pulling the stretched web from the pre-stretching means at a second force less than that of the first force by relatively rotating the pallet causing stretched material to be wrapped around said load;
• and
• g. applying a substantially constant positive torque to said pre-stretching means at least equal to the difference between said first force and said second force corrected for the friction and mechanical advantage of said pre-stretching means.