Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-11-27
2003-02-11
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S229000, C156S494000, C156S580000
Reexamination Certificate
active
06517652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device of friction welding of two thermoplastic elements, and more particularly to the field of friction welding of overlapping sections of a thermoplastic strip.
2. Description of Related Art
German Patent No. 44 22 147 C2 describes a device suitable for carrying out a method, whereby a strip is first passed around a package to form a loop and tightened, and then secured by at least one clamping plate pressing the strip against an abutment plate. Overlapping sections are pressed against one another and against an abutment plate by a vibrating plate driven by a vibrating drive and thus welded together. The connecting device has two clamping plates. The first of the clamping plates presses the free end section against an abutment plate after the loop has been formed, and thus securing it. The second of these two plates secures the initial section of the loop, which is still connected to the strip supply, by pressing it against an abutment plate after the strip is tightened by a tension drive. The initial section is then cut from the strip supply. The two overlapping strip sections are superimposed between the clamping plates and a vibrating plate arranged between the clamping plates pressing the two strip sections against one another and against an abutment plate. Due to the vibrating movements of the vibrating plate, heat generated by friction between the strip sections is sufficient to melt and weld the two strip sections together.
This known joining method has proven successful in practical use. However, it has some weaknesses that can lead to an inadequate bond between the two sections of strip. Since the two clamping plates are provided only for clamping one of the two strip sections, the end stop for the free end of the strip forming the loop is provided between the clamping plate for the initial section of the strip and the vibrating plate. The distance between the end stop and the vibrating plate is only a few millimeters. Since the end of the strip made of elastic plastic moves at a high speed against the end stop, a certain rebounding of the end of the strip can be observed. In an unfavorable case, the free end of the strip may rebound several millimeters, so that it rests in the area of the weld to be produced by the vibrating plate when the end section of the strip is secured by the first clamping plate. This reduces the length of the resulting weld. This reduction in length of the weld can lead to an unacceptable weakening of the joint. Thus, there is the risk of opening of the loop of strip surrounding the package under tension.
Thus, it may be advantagous and desirous to increase the reliability and stability of the welds.
SUMMARY OF THE INVENTION
The reliability and stability of the welds may be increased according to the invention by producing at least two separate welds one behind the other in the longitudinal direction of the strip, separated by an unwelded area. According to the invention a device for friction welding has incorporated means for producing such welds.
The reliability of the joint is greatly increased by producing multiple welds. Although each individual weld has approximately only the same strength as the weld known from the related art cited above, the tensile force from each end of the loop is applied only to the adjacent weld. If there are more than two welds, essentially the two outer welds absorb the tensile force. The stress on the two stressed welds is reduced approximately in half in comparison with the individual weld from the related art. If one weld is nevertheless destroyed by the tension forces, cohesion of the two strip sections is nevertheless ensured by at least one remaining weld which is still fully functional.
The proposed method of producing at least two welds separated by an unwelded area also has some major advantages in comparison with simple extension of one weld. The welds produce the highest holding force in their edge areas. As soon as a first tear has begun at one edge area of a weld, only a relatively small force need be applied for a progressive tear to result in the weld in the plane between the strip sections and thus a complete separation of the two strip sections from one another. Due to the arrangement of at least two welds separated by an unwelded area, at least one separate weld is thus created which is fully functional in the event of failure of the first weld. Paring of the first weld cannot propagate into the second weld because of their spatial separation.
An embodiment of the invention may also include more than two welds. In order to produce a sufficiently secure joint with the least possible effort and the lowest cost, two welds seem to be an optimum number in practice.
In the simplest case, the two welds may be produced by having an interruption of several millimeters in length at the center of the surface of the vibrating plate between the two clamping plates. In the area of this interruption, no compressive force is produced perpendicular to the plane of the strip, so that no welding takes place here. The two welds may be produced by two vibrating plates arranged with a distance between them. These vibrating plates can preferably be pressed independently of one another against the strip sections to be welded.
In accordance with another aspect the invention is a method for friction welding of two overlapping sections of a thermoplastic strip with a system wrapping the strip around a package. According to this method, the strip is passed around the package to form a loop whereby sections are arranged at each end of the loop. The strip is then tightened and secured by at least one clamping plate of the system in which the strip is pressed against an abutment plate of the system. Moreover, the overlapping sections are pressed together by and against the abutment plate by a vibrating plate of the system. With vibration caused by the vibrating plate, the overlapping sections are welded whereby at least two welds are produced one behind each other in longitudinal direction of the strip and separated from one another by an unwelded area of the strip.
The two vibrating plates may be arranged with a distance between them and are pressed against the strip to produce the welds.
In one embodiment of the method according to the present invention, before forming the loop, the free end of the strip is first conveyed consecutively past a first vibrating plate and a combined clamping and vibrating plate in the direction of feed, and to a strip guidance device (strip guiding frame) which guides the strip in the form of a loop around the package. After forming the loop, the free end of the strip is conveyed past a first clamping plate, past the above-mentioned vibrating plate arranged next to the first clamping plate and past the combined clamping and vibrating plate next to it, coming to rest at an end stop. Thus, after forming the loop, the free end of the strip moves between the abutment plate and the plates covered by the initial section which is connected to the strip supply, namely the first vibrating plate and the combined clamping and vibrating plate. A strip detection signal is delivered when the strip comes in contact with an end stop. This signal causes the above-mentioned first clamping plate to move toward the abutment plate in the direction perpendicular to the plane of the strip, so that the end section of the strip is clamped between the surfaces of the first clamping plate and the abutment plate. The loop is then tightened around the package by a tension force acting against the original direction of feed and is secured by the combined clamping and vibrating plate in combination with the abutment plate, with the two overlapping strip sections being clamped between the combined clamping and vibrating plate and the abutment plate.
After securing the initial section of the loop which is still connected to the strip supply, this section may be cut off close to the first clamping plate. The first vibrati
Choate Hall & Stewart
Maschinenfabrik Gerd Mosca AG
Sells James
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