Ultrasonic welding device with preheating unit

Abstract

The present invention concerns an apparatus for ultrasonic welding of at least two material webs comprising a processing sonotrode which can be excited with an ultrasonic vibration, a processing counterpart tool and a material web guide which is so designed that the material web can be passed through between the processing sonotrode and the processing counterpart tool, in which there is provided a device for heating at least one material web prior to the welding operation. To provide an ultrasonic welding apparatus which avoids the stated disadvantages and which nonetheless provides a high processing speed it is proposed according to the invention that the device for preheating at least one material web has a preheating sonotrode which can be excited with an ultrasonic vibration.

Claims

1. Apparatus for ultrasonic welding of at least two material webs comprising a processing sonotrode which can be excited with an ultrasonic vibration, a processing counterpart tool and a material web guide which is so designed that the material web can be passed through between the processing sonotrode and the processing counterpart tool, in which there is provided a device for heating at least one material web prior to the welding operation, wherein the device for preheating at least one material web has a preheating sonotrode which can be excited with an ultrasonic vibration, characterised in that the processing sonotrode has a welding surface with a welding surface width a and the preheating sonotrode has a welding surface with a welding surface width b, wherein b is greater than a.

2. Apparatus as set forth in claim 1 characterised in that there is provided a preheating counterpart tool which is associated with the preheating sonotrode, wherein the material web is so adapted that at least one material web, can be passed through between the preheating sonotrode and the preheating counterpart tool.

3. Apparatus as set forth in claim 2 characterised in that the processing counterpart tool is also associated with the preheating sonotrode and the material web guide means is so adapted that the material web can firstly be passed through between the preheating sonotrode and the processing counterpart tool for preheating and then between the processing sonotrode and the processing counterpart tool for welding.

4. Apparatus as set forth in claim 1 characterised in that at least the processing sonotrode is in the form of a rotational sonotrode having a welding surface which is substantially in the form of a cylindrical surface.

5. Apparatus as set forth in claim 4 characterised in that at least the processing counterpart tool is rotatable and has a welding surface which is substantially in the form of a cylindrical surface.

6. Apparatus as set forth in claim 1 characterised in that the processing counterpart tool is in the form of a further processing sonotrode which can be excited with an ultrasonic vibration.

7. Apparatus as set forth in claim 5 characterised in that there is provided a device for rotating the preheating sonotrode and for rotating the processing sonotrode, wherein the device is so adapted that the peripheral speed of the processing sonotrode is greater than the peripheral speed of the preheating sonotrode.

8. Apparatus as set forth in claim 1 wherein b is greater than a by more than 50%.

9. Apparatus as set forth in claim 1 wherein b is approximately twice as great as a.

10. Apparatus as set forth in claim 2 wherein both material webs can be passed through between the preheating sonotrode and the preheating counterpart tool.

11. Apparatus as set forth in claim 4 wherein the preheating sonotrode is in the form of a rotational sonotrode having a welding surface which is substantially in the form of a cylindrical surface.

12. Apparatus as set forth in claim 5 wherein the preheating counterpart tool is rotatable and has a welding surface which is substantially in the form of a cylindrical surface.

13. Apparatus as set forth in claim 6 wherein the processing sonotrode and the further processing sonotrode have different natural frequencies.

Description

(1) Further advantages, features and possible uses of the present invention will be clearly apparent from the description hereinafter of a preferred embodiment and the accompanying FIGURE in which:

(2) FIG. 1 shows a perspective view of a preferred embodiment of the invention.

(3) FIG. 1 shows an embodiment of an ultrasonic welding apparatus 1 according to the invention. It serves to weld two material webs 2 together.

(4) Welding is effected by means of a processing sonotrode 3 and a processing counterpart tool 4. Both the processing sonotrode 3 and also the processing counterpart tool 4 have welding surfaces in the form of cylindrical surfaces and are rotated about their longitudinal axis by means of the drives 7, 8. In the illustrated embodiment the axis of rotation of the processing counterpart tool 4 is connected to the machine support frame structure while the processing sonotrode 3 can be moved in a vertical direction relative to the holder 5 by means of the carriage 6. Thus the desired welding gap can be adjusted by means of the carriage 6 between the processing sonotrode 3 and the processing counterpart tool 4. The processing sonotrode 3 is caused to perform an ultrasonic vibration by means of a converter (not shown) so that the material webs 2 which are moved through the apparatus in the direction of the arrow are welded between the processing sonotrode 3 and the counterpart tool 4. In that case the peripheral speed of the processing sonotrode 3 and the counterpart tool 4 is equal to the speed of movement of the material webs 2.

(5) It will be appreciated that the speed of movement of the material webs cannot be increased just as desired as, during processing of the material web by the processing sonotrode 3, sufficient energy has to be introduced into the material webs 2 to guarantee welding of the two material webs.

(6) To increase the advance speed of the material webs the embodiment, in accordance with the invention, has a preheating sonotrode 9 and a preheating counterpart tool 10. The preheating sonotrode 9 and the preheating counterpart tool 10 also have welding surfaces in the form of cylindrical surfaces and are rotatable about their axis of rotation by means of the drives 11, 12. When the material webs 2 are being transported through the ultrasonic welding apparatus in the direction indicated by the arrow therefore the material webs are firstly processed by the preheating sonotrode 9 and the preheating counterpart tool 10 and thereafter by the processing sonotrode 3 and the processing counterpart tool 4. The preheating sonotrode 9 can also be moved in the vertical direction relative to the holder 13 by means of the carriage 14 while the preheating counterpart tool 10 cannot be moved in the vertical direction.

(7) The preheating sonotrode 9 and the preheating counterpart tool 10 are intended to preheat the material webs 2 in the region which is to be ultrasound-welded by the processing sonotrode 3 and the processing counterpart tool 4. The preheating sonotrode 9 which is also acted upon with an ultrasonic vibration therefore delivers vibration energy to the material webs 2 in the material processing operation so that as a result the two material webs 2 are preheated in a strip-shaped region, the width of which is determined by the welding surface width of the preheating sonotrode 9 and the preheating counterpart tool 10 respectively and which extends in the material advance direction.

(8) In that respect for example when processing polyethylene (PE) temperatures of about 80° C. are reached. What is essential in that respect is that the melting temperature of the material is not exceeded as otherwise welding would already be effected.

(9) The preheating sonotrode 9 and the preheating counterpart tool 10 are only intended for preheating the material webs 2. The actual welding operation is then effected by means of the processing sonotrode 3 and the counterpart tool 4 which carry out the welding operation exactly within the preheated line-shaped region. As the material webs are already preheated in that line-shaped region less vibration energy has to be introduced into the material webs 2 for welding thereof so that overall it is possible to operate with a higher material advance speed without reducing the weld quality.

(10) While the processing sonotrode and/or the processing counterpart tool which are responsible for the welding operation can have a welding surface which is contoured with projections, it is rather of advantage for the preheating sonotrode and the preheating counterpart tool to have a contour which is constant in the peripheral direction in order to achieve uniform preheating.

(11) By way of example the preheating sonotrode in a section extending perpendicularly to the material web could be of a bell-shaped or ridge-like or bulging cross-section.

LIST OF REFERENCES

(12) 1 ultrasonic welding apparatus 2 material webs 3 processing sonotrode 4 processing counterpart tool 5, 13 holder 6, 14 carriage 7, 8, 11, 12 drive 9 preheating sonotrode 10 preheating counterpart tool