Advancing material of indeterminate length – By orbitally traveling material-engaging surface – Comprising rotary pinch pair
Reexamination Certificate
2001-04-18
2003-05-06
Matecki, Kathy (Department: 3654)
Advancing material of indeterminate length
By orbitally traveling material-engaging surface
Comprising rotary pinch pair
C226S177000, C226S193000
Reexamination Certificate
active
06557742
ABSTRACT:
BACKGROUND OF THE INVENTION
The subject invention relates to the art of wire feeding mechanisms and more particularly to drive rollers in wire feeding mechanisms that are used to driveably advance welding wire.
Wire feeding mechanisms have been provided heretofore, and generally, as shown in Seufer for example, have a wire pathway through which a continuous length of wire is advanced. Positioned on opposing sides of the wire pathway is at least one steel drive roller. Each steel drive roller is mounted on a roller support, and all of the roller supports are driveably engaged with one another. Accordingly, all of the steel drive rollers rotate in response to the movement of the corresponding roller support and thereby act to driveably advance the continuous length of wire. In order to impart an advancing force and motion to the wire, the opposing steel drive rollers are positioned sufficiently close to, one another so that the wire extending along the pathway is compressed between the opposing rollers. The compressive force in combination with the coefficient of friction, between the material of the wire and the steel roller, produces a frictional force along the wire which is greater than the force required to advance the continuous length of wire. As a result, the wire is advanced in a generally smooth and continuous motion in response to the rotation of the steel drive rollers.
Wire feeding mechanisms of the foregoing nature are utilized in a variety of applications. In many such applications, including welding operations, the advancing wire is subjected to a variety of non-uniform radial and axial impact loads. These loads normally react back through the wire to the feeding mechanism, at which point one of three results will normally occur. One result may be that the impact load will be absorbed by the system creating a minimal amount of slippage between the drive rollers and the wire causing only a brief change in wire feed speed (WFS). It will be appreciated that a consistent wire feed speed is critical to a high quality welding operation, and that anything more than a momentary deviation from the set WFS will result in low quality or failed welding operations. A second result is that the impact force reacting back to the feeding mechanism through the wire will exceed the frictional force between the steel drive rollers and the wire, and cause the drive rollers to slide against the surface of the wire causing the wire to become galled and deformed, and resulting in an extended deviation of the WFS from that desired. As previously indicated this may cause a significant reduction in the quality of the welding operation. What's more, this causes additional impact loads to be created as the galled and deformed section of wire travels along the wire pathway. These additional impact loads react back to the wire feeding mechanism potentially initiating the cycle over and over again. Furthermore, the galled and deformed wire section will not melt uniformly during the welding operation resulting in inconsistent and lower quality welds. A third result is that the impact force will not exceed the frictional force between the drive rollers and the wire, but will exceed the column strength of the wire causing the wire to bend out of the pathway and become caught inside the wire feeding mechanism, resulting in a “bird nest” inside the wire feeder. Once the wire is bent out of the wire pathway the wire cannot be advanced along the pathway. Likewise, the wire being fed behind the bent wire portion cannot advance along the pathway and therefore becomes bent itself. In just a few seconds, a large number of bent wire segments have piled up adjacent the wire feeding device. At this point, production must be stopped and the wire feeding mechanism disassembled so that the “bird nest” can be cut out. The wire feeder can then be reassembled and production resumed. This creates a significant loss in production time, wire and other materials.
As can be appreciated from the foregoing discussion, a wire feeding mechanism can be made to function quite well if the wire being fed has a high column strength value. In such case, the compression force from the steel drive rollers can be set very high, creating a high friction force which resists sliding of the wire against the drive rollers in reaction to impact loads. Since the wire will not slide against the steel drive rollers, the impact loads will act as a column load on the advancing wire. However, if the column strength of the wire is high, then the wire will not be bent by the column load and the wire will continue to be fed to the downstream welding operation.
It will be further appreciated that the column strength of a length of round wire is dependent upon the diameter of the wire, and the material from which the wire is made. Steel wire can be made to work well in wire feeding mechanisms of the foregoing description. However, many nonferrous metals, such as aluminum, for example, are soft and do not possess sufficient column strength to permit problem-free operation of a wire feeding mechanism. As a result, if the compressive force from the steel drive rollers is low enough to avoid exceeding the column strength of the wire as impact loads react back to the wire feeding mechanism, then the resulting frictional force will be low enough to allow the wire to slide against the steel drive rollers and become galled and deformed. Furthermore, if the compressive force from the steel drive rollers is high enough to prevent sliding, the impact loads will often exceed the column strength of the nonferrous wire and cause a “bird nest.” Additionally, the steel drive rollers of the wire feeding mechanism tend to deform the relatively soft nonferrous wires regardless of the value of the compressive forces used. This further increases the likelihood of impact loads, and also reduces the consistency of the melt of the wire causing low quality welding of nonferrous metals. It will be appreciated for the foregoing reasons that the compressive forces cannot simply be reduced to minimize the deformation. As a result, traditional wire feeding mechanisms cannot provide the desired trouble-free operation when feeding nonferrous wires.
SUMMARY OF THE INVENTION
In accordance with the present invention, a drive roller is provided for a wire feeding mechanism which enables avoiding or minimizing the problems and difficulties encountered with the use of feed devices of the foregoing character, while promoting and maintaining the desired trouble-free operation, simplicity of structure, and economy of manufacture thereof. More particularly in this respect, a drive roller in accordance with the present invention includes a hub and a flexible outer cover, and a wire feeding mechanism incorporating drive rollers according to the present invention includes a wire pathway along which a continuous length of wire extends, and at least two drive rollers mounted on opposite sides of the wire pathway, each having a hub and a flexible outer cover. The drive rollers on one side of the wire pathway are radially adjustable relative to the opposing drive rollers. By changing the radial position of the adjustable drive rollers, the compressive force of the drive rollers on the wire extending therebetween is increased or decreased. With nonferrous wire, the traditional steel drive rollers of existing wire feeding mechanisms would increasingly deform the wire as the compression force was increased. The flexible covers of the drive rollers of the subject invention, however, deform as the compression force between the drive rollers is increased while the nonferrous wire does not. As a result, without damaging or deforming the nonferrous wire, significantly higher compressive forces can be maintained between the subject drive rollers and nonferrous wire than could be maintained between traditional steel drive rollers and nonferrous wire. This results in the ability to create a higher frictional force between the drive rollers and the wire, and this in turn provides increased ability to w
Bobeczko James D.
Kasiewicz Thaddeus A.
Fay Sharpe Fagan Minnich & McKee
Lincoln Global Inc.
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