Method for intermittent ultrasonic processing of a length of material

Abstract

The present invention relates to a method for intermittent ultrasonic processing of a length of material, wherein a length of material is moved through between a sonotrode and a counter-tool and the length of material is processed intermittently. In order to specify a method for intermittent ultrasonic processing of a length of material by which the disadvantages of the prior art can be avoided or at least reduced, according to the invention it is suggested that in a processing interval the sonotrode is stimulated by an ultrasonic oscillation with an oscillation amplitude A and in a movement interval the sonotrode is stimulated with an oscillation amplitude B, wherein B<A and during the processing interval and during the movement interval the length of material touches both the sonotrode and also the counter-tool.

Claims

1. Method for intermittent ultrasonic processing of a length of material, wherein a length of material is moved with a web velocity through between a sonotrode with a cylindrical surface and a counter-tool with a cylindrical surface, a circumferential velocity of the sonotrode and of the counter-tool corresponding to the web velocity of the length of material which is to be processed and the length of material is processed intermittently, stimulating the sonotrode by an ultrasonic oscillation with an oscillation amplitude A in a processing interval and stimulating the sonotrode with an oscillation amplitude B in a movement interval, wherein B<A, and during the processing interval and during the movement interval the length of material touches both the sonotrode and also the counter-tool.

2. Method according to claim 1, wherein the oscillation amplitude B>0.

3. Method according to claim 2, wherein the oscillation amplitude B during the movement interval amounts to between 10% and 30% of the oscillation amplitude A during the processing interval.

4. Method according to claim 1, wherein a rotary sonotrode with cylindrical sealing surface is selected as sonotrode and the sonotrode is rotated around the axis of rotation through an angle of rotation both during the processing interval and also during the movement interval.

5. Method according to claim 4, wherein the angle of rotation of the rotary sonotrode is detected and the beginning and end of the processing interval and the movement interval are determined, depending on the detected angle of rotation.

6. Method according to claim 1, wherein the sonotrode or counter-tool is pressed onto the length of material with a predetermined force F.sub.A during a welding interval.

7. Method according to claim 6, wherein the sonotrode or counter-tool is pressed onto the length of material with a predetermined force F.sub.B during a standby interval, wherein the force F.sub.B<F.sub.A.

8. Method according to claim 6, wherein the welding interval is shorter than the processing interval.

9. Method according to claim 6, wherein the welding interval lies within the processing interval, wherein the processing interval begins before the welding interval.

10. Method according to claim 1, wherein a ramp interval is provided between the movement interval and the processing interval in which the oscillation amplitude of the ultrasonic oscillation of the sonotrode is increased from the oscillation amplitude B to the oscillation amplitude A, continuously.

11. Method according to claim 10, wherein, during the processing interval, the movement interval and the ramp interval the length of material is moved through between the sonotrode and counter-tool with a constant web velocity v, wherein the length of the ramp interval is selected such that between 0.5 and 10 cm of the length of material is moved through between the sonotrode and counter-tool during the ramp interval.

12. Method according to claim 9 wherein the welding interval ends before the processing interval.

13. Method according to claim 1, wherein a ramp interval is provided between the movement interval and the processing interval in which the oscillation amplitude of the ultrasonic oscillation of the sonotrode is increased from the oscillation amplitude B to the oscillation amplitude A, in several steps.

14. Method according to claim 10, wherein, during the processing interval, the movement interval and the ramp interval, the length of material is moved through between the sonotrode and counter-tool with a constant web velocity v, wherein the length of the ramp interval is selected such that between 1 and 5 cm of the length of material is moved through between the sonotrode and counter-tool during the ramp interval.

15. Method according to claim 4, wherein the angle of rotation of the rotary sonotrode is detected and the beginning and end of the processing interval or the movement interval is determined, depending on the detected angle of rotation.

16. A method according to claim 1, wherein during the movement interval the length of material is moved through between the sonotrode and the counter-tool.

Description

(1) Further advantages, features and possible applications of the present invention become clear from the following description of a preferred embodiment together with the associated figures, wherein:

(2) FIG. 1 shows a schematic representation of a device for carrying out the method and

(3) FIG. 2 shows a schematic representation of the time dependency of oscillation amplitude and force.

(4) FIG. 1 shows a schematic representation of a device for carrying out a method for intermittent ultrasonic processing of a length of material. The length of material 1 is moved through, in the direction of the arrow, between a sonotrode 2 and a counter-tool 3. Both the sonotrode 2 and the counter-tool 3 are configured in the form of rollers in this embodiment. The sonotrode 2 is pressed in the direction of the counter-tool 3 with a force F, so that the length of material 1 is compressed between the sonotrode 2 and the counter-tool 3.

(5) A processing of the length of material 1 takes place if the sonotrode 2 is pressed onto the length of material with the suitable welding force F.sub.A and the sonotrode oscillates with a suitable oscillation amplitude A.

(6) However, there are applications in which the entire length of material 1 does not need to be processed, but rather only sections thereof require processing.

(7) According to the invention, the oscillation amplitude of the ultrasonic oscillation of the sonotrode is therefore always reduced if no processing is to take place. While the length of material is still moved through between sonotrode and counter-tool, due to the reduced oscillation amplitude of the ultrasonic oscillation no processing takes place.

(8) This is represented schematically in FIG. 2. In the diagram, both the oscillation amplitude (continuous line) and also the welding force (dotted line) with which the sonotrode is pressed in the direction of the counter-tool are plotted, in random units. It can be seen that in an interval I the oscillation amplitude assumes the value A and the force with which the sonotrode is moved in the direction of the counter-tool assumes the value F.sub.A. The actual processing takes place in the interval I. Therefore, in this example the interval I corresponds to both the processing interval and also the welding interval. As already explained above, the processing interval and welding interval do not necessarily need to be identical.

(9) Before and after the processing interval I, during a movement interval II both the oscillation amplitude is reduced to the value B and the force with which the sonotrode is pressed in the direction of the counter-tool is reduced to the value F.sub.B.

(10) No processing takes place during the movement interval II. A ramp interval III, in which the oscillation amplitude is continuously increased or reduced, is drawn in here between the movement interval II and the processing interval I. Even though, in the example shown, the oscillation amplitude is changed in a linear manner in the ramp interval, non-linear changes, for example a stepped increase or reduction in the oscillation amplitude, are also possible.

(11) Even though an abrupt increase in force from the force F.sub.B to the force F.sub.A and an abrupt decrease in force from the force F.sub.A to the force F.sub.B is shown in the figure, this does not as a rule need to be realised completely. As a rule, on closer inspection the change in force will also take place not abruptly, but gradually.

(12) In the embodiment shown, only the sonotrode 2 is excited with an ultrasonic oscillation. Alternatively however, it is also possible to use a second sonotrode as counter-tool, so that the length of material is passed through between two sonotrodes. In this case the oscillation amplitude of the ultrasonic oscillation of at least one of the two sonotrodes should be reduced in the movement interval, whereby it is best if the oscillation amplitudes of both sonotrodes are reduced.

LIST OF REFERENCE SYMBOLS

(13) 1 length of material 2 sonotrode 3 counter-tool A oscillation amplitude F force F.sub.A welding force I processing interval II movement interval III ramp interval