METHOD FOR CUTTING A RUBBER WEB

Abstract

The present invention concerns a method of cutting a rubber web by means of ultrasound, in which a sonotrode comes into contact with the rubber web and the rubber web and the sonotrode are moved relative to each other while the sonotrode is excited with an ultrasonic vibration. To provide a method of the kind set forth in the opening part of this specification which allows reliable cutting of a rubber web and at the same time ensures that the wear of the tool and the converter is markedly reduced according to the invention it is proposed that a sonotrode comprising steel, preferably hardened steel, is used.

Claims

1. A method of cutting a rubber web by means of ultrasound, the method comprising: contacting the rubber web with a sonotrode and moving the rubber web and the sonotrode relative to each other while the sonotrode is excited in an ultrasonic vibration, the sonotrode comprising steel.

2. A method according to claim 1 characterised in that the sonotrode has a wedge-shaped tip.

3. A method according to claim 11 characterised in that the length of the separating surface is <60 mm.

4. A method according to claim 1 characterised in that the sonotrode is coated at least at portions which are intended to come into contact with the rubber web.

5. A method according to claim 1 characterised in that the sonotrode is cooled during the cutting operation.

6. A method according to claim 1 characterised in that the sonotrode is excited with an ultrasonic frequency of less than 38 kHz.

7. A method according to claim 1 characterised in that the sonotrode is connected to a converter by way of an amplitude transformer, wherein a clamping device is used, with which a holding element can be clamped to the converter or the amplitude transformer.

8. A method according to claim 1 characterised in that the sonotrode and the converter are arranged on a tool axis, wherein the tool axis includes an angle of between 30° and 70° with a normal on the rubber web.

9. A method according to claim 1 characterised in that the longitudinal direction of the separating surface includes an angle of between 10 and 20° with the rubber web.

10. A method according to claim 1 characterised in that the method is carried out with a cutting speed of between 1.5 and 4 mm/s.

11. A method according to claim 2 characterised in that the wedge-shaped tip has a rectangular separating surface with a width and a length.

12. A method according to claim 1 wherein the sonotrode comprises hardened steel.

13. A method according to claim 3 characterised in that the length of the separating surface is between 25 and 35 mm.

14. A method according to claim 4 characterised in that the coating is Teflon.

15. A method according to claim 5 characterised in that the sonotrode is cooled by means of a cooling air flow directed onto the sonotrode.

16. A method according to claim 6 characterised in that the sonotrode is excited with an ultrasonic frequency of between 34 and 36 kHz.

17. A method according to claim 9 characterised in that the longitudinal direction of the separating surface includes an angle of between 14 and 15° with the rubber web.

18. A method according to claim 10 characterised in that the method is carried out with a cutting speed of about 2.5 mm/s.

Description

[0028] Further advantages, features and possible uses of the present invention will be apparent from the description hereinafter of a preferred embodiment and the accompanying Figures in which:

[0029] FIG. 1 shows a perspective view of a sonotrode as is used for the method according to the invention,

[0030] FIG. 2 shows a side view of the sonotrode of FIG. 1,

[0031] FIG. 3 shows an exploded view of an ultrasonic cutting installation, and

[0032] FIGS. 4 and 5 show two perspective views of the ultrasonic processing installation of FIG. 3.

[0033] FIG. 1 shows a perspective view of a sonotrode 1 which can be used in the method according to the invention. It is produced from steel, more specifically CPM 420 V. The sonotrode 1 has a threaded bore 12 at which a converter or an amplitude transformer adjoining the sonotrode 1 can be fixed. Disposed on the side of the sonotrode 1, in opposite relationship to the threaded bore 12, is the separating surface which is of a length l.

[0034] FIG. 2 shows a side view of the sonotrode 1 of FIG. 1. The sonotrode 1 has a main body 2 and an adjoining wedge-shaped portion 3, at the tip of which is arranged the separating surface which is of a width b. The wedge-shaped portion 3 has a taper angle α which is at best between 8 and 15°.

[0035] FIG. 3 shows an exploded view of an ultrasonic processing installation for cutting rubber webs 8. It is possible to see the sonotrode 1 which is shown in detail in FIGS. 1 and 2 and which is connected to a converter 5 by way of an amplitude transformer 4. The converter 5 converts an electric ac voltage into a mechanical vibration. Generally piezoelements are used for that purpose.

[0036] The mechanical vibration generated by the converter is converted in the amplitude transformer into a vibration at the same frequency, but under some circumstances of different amplitude. That is then transmitted to the sonotrode 1 so that an acoustic ultrasound wave is propagated from the converter 5 by way of the amplitude transformer 4 into the sonotrode 1. The separating surface, that is to say the tip of the wedge-shaped element 3, thus presents a vibration which supports cutting of the rubber web 8. In order to hold the ultrasonic vibration unit consisting of the converter 5, the amplitude transformer 4 and the sonotrode 1 there is a holding element 6 which however is not screwed to same. Instead the holding element 6 is connected to a hollow cylinder 7 which has an outwardly projecting flange. Arranged in the flange are a series of screws which hold on the one hand the clamping element 13 and on the other hand the holding element 6.

[0037] In this case clamping is effected in a region of the amplitude transformer, in which a vibration node of the ultrasonic vibration is formed in order to influence the ultrasonic vibration system as little as possible in its vibration characteristic by virtue of the clamping action. The amplitude transformer therefore has a holding flange 9 in that region. The clamping element 13 has a step bore (not shown), the bore portion of smaller diameter of which is of a diameter which is less than the diameter of the holding flange 9 of the amplitude transformer 4 so that in the assembled state the amplitude transformer 4 is clamped at its holding flange 9 between the clamping element 13 and the fixing flange of the hollow cylinder 7.

[0038] FIGS. 4 and 5 show two perspective views. It will be seen from FIG. 4 that the separating surface includes with the plane of the rubber web 8 a cut angle γ which should preferably be between 4 and 5°.

[0039] FIG. 5 shows that the longitudinal axis of the ultrasonic vibration system is tilted through an angle β with respect to the normal on the plane of the rubber web 8.

LIST OF REFERENCES

[0040] 1 Sonotrode [0041] 2 Main body [0042] 3 Wedge-shaped portion [0043] 4 Amplitude transformer [0044] 5 Converter [0045] 6 Holding element [0046] 7 Hollow cylinder [0047] 8 Rubber web [0048] 9 Holding flange [0049] 11 Fixing flange [0050] 12 Threaded bore [0051] 13 Clamping element