Fixture used for the heat sealing of foils using a plasma jet

Details Fixture used for the heat sealing of foils using a plasma jet Fixture used for the heat sealing of foils using a plasma jet

1999-06-21

2000-09-19

Paschall, Mark

Electric heating

Metal heating

By arc

21912145, 21912146, 21912137, B23K 1000

Patent

active

061215724

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention concerns a procedure and a fixture for the heat sealing (jig welding) of foils along a weld joint or seal.
2. Description of the Background Art
Common fixtures of this kind, which are used in the packing industry to close foil bags, for example, are usually equipped with a sealing jaw that can be raised and lowered, extending crosswise over a conveying path on which the foil bags that are to be sealed are moved forward gradually. During each step of the process, the sealing jaw is lowered briefly onto the overlapping foil sheets that are to be sealed, and with the help of a resistance wire, or similar component, that runs in the sealing jaw in a longitudinal direction, the foils are heated briefly on the weld joint so that they are welded together or heat-sealed and, if desired, separated at the same time.
One disadvantage of these common fixtures consists of the fact that both the movable sealing jaws and the conveying device for the foil bag have to be moved gradually in cycle sequences that are adjusted to each other. With every work cycle a considerable amount of inert mass has to be accelerated and then slowed down again. This requires complex drive and control mechanisms. The dimensions of this fixture, overall mass of the movable parts, minimum lift of stroke of the sealing jaw and step size of the conveying device all increase with increasing packing size so that great design efforts are required, particularly when packaging larger size items, and only low productivity levels can be achieved due to correspondingly long cycle times.
Another disadvantage of common fixtures is the direct contact of resistance wires with the foil, easily causing operating failures due to contamination or the caking of foil material onto the sealing jaw. Particularly in the case of relatively long weld seams it is also very difficult to ensure even temperatures and contact pressures over the entire length of the sealing jaw and to obtain a weld joint of consistently good quality.


SUMMARY OF THE INVENTION

Therefore the object of the invention consists in creating a procedure and a fixture for heat-sealing foils, especially plastic foils, which excel due to their low susceptibility to interference and low design efforts and which enable high productivity.
This object is realized with a procedure of the kind described above by heat-sealing the foils with the help of a plasma jet. A fixture suited for this process is equipped with a plasma nozzle and a conveying device that generates a relative movement between the plasma nozzle and the foil layers along the weld joint. Thus, the fixture is equipped for executing a procedure during which the foil layers are heat-sealed with each other with the help of a plasma jet that moves along the weld joint.
Since the sealing process occurs without contact, i.e. without direct contact between the foil sheets and the plasma nozzle, the fixture is not prone to failures, and the sealing process is relatively tolerant towards slight changes in the distance between the foil layers and the plasma nozzle. This makes it possible to achieve high weld joint quality, even in the case of longer weld joints.
Since the plasma jet can be very hot and therefore needs to act on the foil material only for a very short period, the plasma nozzle can be moved along the weld joint at high speed, thus achieving high productivity. The plasma nozzle itself is of a very compact and very simple design as well as being lightweight, so that it can be moved along the weld joint without difficulty.
Advantageous designs and versions of the invention are described below.
When a straight weld joint needs to be generated, the plasma nozzle is preferably stationary and the foils that are to be sealed are moved by the plasma nozzle with a conveying device, thus generating a weld joint that runs parallel to the conveying device. The conveying device can therefore be driven at a constant speed so that practically no moveable parts have to be shifted bac

REFERENCES:
patent: 2975263 (1961-03-01), Green et al.
patent: 3959567 (1976-05-01), Bradley
patent: 4282418 (1981-08-01), Wuestner
patent: 4345137 (1982-08-01), Mignier et al.

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