Claims
- 1. A process of making a unitary package by wrapping a plurality of units with a stretched plastic material overwrap forming a unitary load comprising the steps of:
- a. placing a load on a support;
- b. positioning a roll of stretchable plastic material on a dispenser means adjacent to said support;
- c. withdrawing a leading end of said plastic material from said dispenser means and passing said plastic material through a powered prestretch device adapted to drive the plastic material at a proportional speed with respect to the surface speed of the load, said prestretch device comprising a powered roller assembly with at least one rotationally restrictive roller assembly, said rotationally restrictive roller assembly being retarded to a substantially constant relative speed with respect to the rotationally powered roller assembly so that the plastic material is elongated substantially above its yield point between the roller assemblies, thereby changing strength characteristics and cross-sectional area of the plastic material;
- d. holding said plastic material adjacent said load and simultaneously prestretching said plastic material substantially above the yield point by driving said prestretch device and causing relative rotation between said load and said dispenser means at a predetermined speed;
- e. substantially reducing the force on the plastic material while maintaining the majority of the elongation incurred in said powered prestretch device through inelastic strain recovery after it leaves the powered prestretch device; and
- f. covering the load with previously elongated plastic material so that the units of the load are held under a compressive force.
- 2. A process for spirally wrapping a web of stretched film on a load comprising a plurality of units to form a unitary package, which process is repeated in a commercial environment comprising the steps of:
- a. withdrawing film from a film roll through a powered prestretch means comprising a powered roller assembly and at least one restrictive roller assembly interconnected by speed control means and retarded to maintain a substantially fixed relative speed, the speed of the restrictive roller assembly being less than said powered roller assembly, and holding the film adjacent to the load;
- b. activating the powered prestretch means to drive the film at a downstream speed increased from its upstream speed to produce film elongation above one hundred percent and the yield point of the film;
- c. forming a spiral wrap around the load by causing relative rotation of the load and the powered prestretch means while substantially reducing film stress and maintaining a majority of film elongation incurred in said powered prestretch means through inelastic strain recovery between the load and the powered prestretch means;
- d. forming a fastened web section by fastening a leading film portion of the wrap to a trailing film portion of the wrap; and
- e. severing said film between the film roll and the fastened web section.
- 3. A process for spirally wrapping a stretched plastic film web on an angular load comprising a plurality of units to form a unitary package comprising the steps of:
- a. withdrawing the film web from a film web roll through a powered prestretch device comprising a positively rotationally powered downstream roller assembly and a rotational restricted upstream roller means, and holding the film web adjacent a load;
- b. activating the prestretch device to drive the film web at a downstream speed on the powered roller assembly which is substantially greater than an initial upstream film web speed on the retarded upstream roller means sufficient to produce a film web elongation above one hundred percent and substantially above the yield point of the film web;
- c. simultaneously initiating relative rotation of the load and the film web roll to achieve a force on the film web from the roller assembly to the load which is less than the force on the film web in the prestretch device while maintaining a majority of the elongation incurred in said prestretch device to produce inelastic strain recovery of the film web as it is wrapped around the load;
- d. spirally wrapping the load;
- e. fastening a trailing end of the film web to an underlying film web layer; and
- f. severing the film web from the load.
- 4. A process of making a unitary load by wrapping a plurality of units with a stretched plastic film web overwrap forming a unitary load comprising the steps of:
- a. elongating the film web in a prestretching means at least fifty percent over the yield point while obtaining elongation of the film web over one hundred percent by subjecting the film web to differential surface speeds through engagement of a powered roller and a restricted roller, said restricted roller being retarded thereby causing said film web to elongate and gain substantially in strength per corss-sectional area and modulus;
- b. wrapping the load with prestretched film web by causing relative movement between said prestretching means and said load while reducing the force on the film web from the prestretching means to the load substantially below the force applied to stretch the film web in the prestretching means and retaining the majority of the elongation through inelastic strain recovery between the prestretching means and the load.
Parent Case Info
This is a continuation application of Ser. No. 074,786, filed Sept. 12, 1979.
US Referenced Citations (8)
Foreign Referenced Citations (2)
Number |
Date |
Country |
2750780 |
May 1979 |
DEX |
2281275 |
Apr 1976 |
FRX |
Continuations (1)
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Number |
Date |
Country |
Parent |
74786 |
Sep 1979 |
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