HK1072231B - Ultrasonic welding apparatus - Google Patents

Description

Technical field

The invention relates to an ultrasonic welding device as defined in claim 1.

Such ultrasonic welding devices have an ultrasonic sonotrode which presses the flat workpieces to be welded against a counter plate, preferably as part of a closing unit for a belting machine welding a loop of a belt.

State of the art

Such ultrasonic welding devices for belts are known from the publications DE 39 11 634 A1 and DE 39 34 560 A1, DE 196 14 634 and EP 0 551 244 A1.

In the case of the EP 0 551 244 A1, the surface of the counter plate is also fitted with protrusions. The protrusions are, for example, formed as triangular ribs in cross-section. Each rib produces a strong local pressure at the beginning of each ultrasonic welding operation. This ensures that in the area of the sonotrode's protrusion a high proportion of the ultrasonic energy is introduced into the workpieces to be welded and the material of the workpiece to be welded, continuously running, is in a thermotropic ribbon, which is successfully melted in this area.

Printed matter EP-A 1 253 557 shows a welding device as defined in the general term of claim 1. Here, in a first embodiment, as shown in Figure 1, only one of the band sections to be welded is held by a rifle profile of the counter plate (here called an amboss) and the other band section is against a smooth surface section.

Such welding devices are now being used with great success as fasteners for belting machines, but they are also suitable for other applications where flat plastic sections must be joined together.

In the case of welding of belts, the tensile strength of the welding point is generally less than that of the plastic belt itself and there is a large variation in the tensile strength of the welding points.

One of the tasks of the present invention is to create an ultrasonic welding device which ensures more reliable welding.

A further task of the present invention is to create an ultrasonic welding device which is effective in creating the progressive formation of the weld joint between two workpiece sections.

The invention is further applied to create an ultrasonic welding device suitable for the production of welded joints of greater homogeneity.

Finally, another task of the invention is to create a closing device for a belting machine for welding a loop of a belt, which has an ultrasonic welding device according to the invention.

Description of the invention

According to the principles of the present invention, the above and other tasks are solved by a welding device having the characteristics of claim 1.

This ultrasonic welding device incorporates an ultrasonic sonotrode, which is capable of pressing flat sections of the workpiece to be welded against a counter plate. The ultrasonic sonotrode and the counter plate have opposite surfaces which are in contact with the workpiece surface when the workpieces are clamped together. Each of these surfaces has at least one protruding section and one smooth section.

It should be noted that each of the surfaces of the ultrasonic sonotrode on the one hand and the counter plate on the other hand may also have a number of profiled, i.e. protruding, and/or a number of smooth sections.

The fact that the protrusions which ensure the reliable formation of the molten area between the workpieces to be joined are partly located on one side of the surface of the sonotrode and partly on the surface of the counter plate, enables the protrusions which change the structure and contour of the workpiece during welding to be placed in such a way as to minimise the impact on the strength of the weld. In particular, the protrusions may be essentially so arranged that they enter the weld at the point of entry into the final band, which is only hidden under low mechanical stress. This ensures that the high tensile strength of the weld is not affected by the steepness of the welded band and this greatly increases the structural strength of the welded band.

As already mentioned, the welding device of the invention may in a practical embodiment be a component of a locking unit for a belting machine which welds a loop of a belting tape, e.g. around one or more objects to be belted.

According to the invention, in practice the protruding part of the ultrasonic sonotrode surface is opposite and vice versa to a smooth part of the counter plate surface, which ensures that in areas where one surface of the welded part is deformed by the protrusions, the other surface remains undistorted, so that only one of the two workpieces cut against each other at the weld point is deformed while the surface of the other workpiece is unaffected.

The smooth part of a surface may in practice, when welding, press against the part of the workpiece through which the forces are introduced into the weld, thus limiting the deformation of the workpiece material to the areas which, due to the protrusions of the surfaces of the welding device, absorb a small part of the load on the weld joint.

The protruding part of the sonotrode surface is near the intersection of the band pressing against the sonotrode. The protruding part of the counter plate surface is also near the intersection of the band pressing against the counter plate. Each nearby intersection does not exert its forces on the bands. The forces of traction are exerted in the band itself and are exerted over the bands in the intersection.

The height of the protrusions cannot in practice be greater than the thickness of one of the two flat workpieces to be welded; in the case of the embodiment in which the protrusions each push into the workpiece material near the cutting edge, this ensures that only the unstressed band is actually deformed by the protrusions and the stressed band is not substantially affected in its shape.

In practice, the protruding part of the sonotrode and the counter plate can cover essentially half of the total surface, while the other half of the surface remains free of protrusions.

An embodiment of the invention is described below with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 shows a schematic front view of a belts machine according to the invention which has a welding device according to the invention and Figure 2 shows a schematic representation of the welding device according to the invention used on the machine according to Figure 1.

Embodiments of the invention

The band 2 is fed from a retractor 4 to a band magazine 5 and is then fed by a band conveyor 6 through a tensioner 8 through a band conductor in a B-guide frame 9 so that the band loop around the pack 7; the end of the band is held by an unmarked band holder and then the drive of the band conveyor 6 is reversed; the band loop is then removed from the conveyor frame 9 and placed at the end of the pack 7; the tensioner 8 is then activated so that the band loop is moved with a high force forward of the pack 7; the end of the pack 10 is then moved in a direction opposite to the direction of the band 10 which is then pulled out of the pack 10 by an ultrasonic transverse force.

A motor 23 is located below the locking unit 10; the motor 23 drives a shaft 24. The shaft 24 is equipped with a number of cams, one of which is located in the middle area of the locking unit 10; this cam 25 serves as the actuator for moving the ultrasonic sonotrode of the locking unit 10, which is described in more detail by reference to Fig. 2.

It is apparent that the closing unit 10 includes an ultrasonic welding device according to the invention, although its use is also possible in other applications where plastic materials such as foil are welded together.

The ultrasonic welding device used in the closing unit 10 of the machine shown in Figure 1 comprises an ultrasonic sonotrode 11 and a counter plate 12 against which the ultrasonic sonotrode 11 can be pressed with interlaced welding of flat workpiece sections.

The reference marks 13 and 14 in Fig. 2 therefore refer to the ends of the belt 2 which are located for welding between the sonotrode 11 and the counter plate 12.

Both sonotrode 11 and counter plate 12 have at least one profiled section 15.17 on which several protrusions are arranged 16.18 The profiled section 15.17 of the surface of sonotrode 11 and counter plate 12 essentially covers half of the contact surface with the welding tape 2 The second half of the surface of sonotrode 11 is formed by a smooth section 19 Similarly, counter plate 12 has a smooth section 20 in the second half of the contact surface with the band 2 to be welded This means that the profiled section 15 of the surface of sonotrode 11 is arranged opposite to the smooth section 20 of the surface of the counter plate 12 and is similar to the profiled section 20 of the surface of the frontal surface of the sonotrode 11 which is opposite to the surface of the counter plate 11

It can be seen from Fig. 2 that the profile design of sonotrode 11 and counter plate 12 described above ensures that the protrusions 16,18 of the protruded sections 15,17 of the opposite surfaces of sonotrode 11 and counter plate 12 deform the respective bands 13,14 of the loop of the band 2 only in the area close to their intersection 21,22 over which no forces are introduced into the weld, thus ensuring that the protrusions in the band 2 do not have a significant effect on the tensile strength of the welding connection produced by the welding direction.

It is also apparent from Fig. 2 that the height of the 16th and 18th protrusions is less than the thickness of the band 2. For this reason, the protrusions 16, 18 and 16 produce only deformations of the band ends 13, 14 in the area adjacent to their respective intersection 21. 22.

The lower deformation of the bands in the welding area into which the tensile force is introduced gives the welding an overall higher strength. It was also found that the strength values are less diffused from one welding to another, so that a welding device of the invention can produce a large number of welds of relatively high and constant strength. To examine the foregoing aspects in some detail, the fact that the protrusions which ensure reliable formation of the structural area between the welding surface sections to be welded are placed partly on the upper part of the sonotrode and partly on the upper part of the final welding platform, which is a solid solid surface, means that they can only be placed in a position where the welding surface is significantly displaced. This is particularly true in the case of the welding of the bands, which is not possible to change significantly the position of the protrusions.

It should be noted that the above embodiments of the ultrasonic welding device and the closing unit of a belting machine have been provided only as examples and that the principles of the invention and various other variations and modifications shown may be made without departing from the spirit and scope of the invention.

List of references:

1Tyring machine2Tape3Storage roll4Tire-pulling device5Tape magazine6Tape conveyor device7Package 8Tape tensioner9Tape guide frame10Tape connector11Ultrasonic ultrasonic nozzle12Counter plate13Workpiece,Tape end14Workpiece,Tape end15Profiled section16Predecessor17Profiled section18Predecessor19Smooth section20Smooth section21Sectionallet22Sectionallet23Motor24Wave25 Knots

Claims (5)

1. A welding apparatus for welding by means of ultrasound, comprising an ultrasonic sonotrode (11), a backing plate (12) in opposite relationship to the ultrasonic sonotrode (11), and actuating means (25) for displacement of the ultrasonic sonotrode (11) and the backing plate (12) relative to each other for pressing flat workpiece portions between mutually facing surfaces of the ultrasonic sonotrode (11) and the backing plate (12) for welding thereof, wherein each of the respective surfaces have at least one portion (15,17) provided with projections (16) and one smooth portion (19,20), characterized in that the portion (15) of the surface of the ultrasonic sonotrode (11), which is provided with projections (16), is disposed in opposite relationship to a smooth portion (20) of the surface of the backing plate (12) and that the portion (17) of the surface of the backing plate (12), which is provided with projections (18), is disposed in opposite relationship to a smooth portion (19) of the surface of the ultrasonic sonotrode (11).
2. Apparatus of claim 1, characterized in that when carrying out a welding operation the smooth portion (19,20) of a surface presses against the part of the workpiece portion (13,14), by way of which forces are applied to the weld.
3. Apparatus of one of the preceding claims, characterized in that the portion (17;15) of the surface of the backing plate (12) and/or the sonotrode (11), which is provided with projections (18; 16), extends in a longitudinal direction of the workpiece (2) to be welded over approximately half the total length of the surface of the backing plate (12) and/or the sonotrode (11).
4. A closure assembly (10) comprising a welding apparatus of one of the preceding claims.
5. A strapping machine for strapping packages (7) with loops of a strapping tape (2), comprising a closure assembly (10) of claim 4 for welding of said loops of strapping tape.