Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1995-12-13
1998-05-12
Simmons, David A.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156 731, 156358, 1565801, B32B 3100
Patent
active
057499870
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of controlling the power of a welding unit when ultrasonic welding webs of material which pass between an ultrasonic horn of the welding unit and an anvil holder equipped with anvils. The invention also relates to a welding arrangement for carrying out the method.
In ultrasonic welding, the materials to be joined together are worked mechanically by moving the end of an ultrasonic horn up and down in the material at a frequency which lies within the ultrasonic frequency band. This mechanical working of the material results in an internal friction which generates heat in the material, therewith causing the material to melt in the region worked by the ultrasonic horn and the materials located between horn and anvil to fuse together. The amount of heat generated in the material will, of course, depend on the extent to which work is carried out and when this work is too low, the weld between the materials will be weak or non-existent, whereas when the work is excessively high, the materials are perforated.
In recent times, the use of ultrasonic welding for joining together the outer sheets of absorbent articles has become progressively more usual. When an ultrasonic welding unit is used to this end, problems are encountered in obtaining continuously high-quality weld joins. This is because a number of factors which influence the welding conditions vary during the continuous operation of an absorbent article process line. Examples of these factors include thermal expansion of the welding unit or the anvil as a result of variations in ambient temperatures, variations in the thickness of the materials to be joined, wear primarily on the ultrasonic horn, and variations in the speeds of the webs passing between the ultrasonic horn and the anvil.
An object of the present invention is to solve this problem.
This object is achieved in accordance with the invention by means of a method of the kind defined in the introduction which is characterized by controlling the mean distance of the ultrasonic horn from the anvil in a manner such that the power of the welding unit will coincide with a predetermined control value. Surprisingly, it has been found that such power regulation results in high-quality weld joins when the welding unit is operated continuously.
According to one preferred embodiment of the invention, the control value is varied as a function of the web speeds, and in one variant of this embodiment, the control value is determined as a function of the web speeds by determining experimentally the constants of and the break points between three consecutive linear functions.
The invention also relates to an ultrasonic welding arrangement for joining together webs of material which pass between an ultrasonic horn of an ultrasonic welding unit and an anvil holder equipped with anvils. The arrangement is characterized by means for measuring and indicating the power input to the welding unit, means for moving the ultrasonic horn so as to change its mean distance from the anvil, and means for comparing the measured power input with a control value and controlling the ultrasonic horn-moving means in accordance with the difference between the measured power and the control value.
A preferred embodiment of the invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 illustrates schematically and from one side an ultrasonic welding arrangement according to one preferred embodiment of the invention; and
FIG. 2 is a curve of the control value as a function of the speed at which the webs of material move.
The ultrasonic welding arrangement illustrated in FIG. 1 includes an ultrasonic welding unit 1 which is comprised typically of an electric high-frequency generator G, a transductor T, which converts the high-frequency electric energy to mechanical energy, an amplifier B which increases the amplitude of the mechanical oscillations, and an ultrasonic horn 2 which is connected to the amplifier B so that its mechanical oscillations are
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patent: 3666599 (1972-05-01), Obeda
patent: 4087297 (1978-05-01), Johnson
patent: 4313778 (1982-02-01), Mims
patent: 4373982 (1983-02-01), Kreager et al.
patent: 4823713 (1989-04-01), Ogawa et al.
Molnlycke AB
Rivard Paul M.
Simmons David A.
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