Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1998-06-10
1999-11-16
Sells, James
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156 731, 156251, 156515, 1565801, 1565802, B29C 6508
Patent
active
059850655
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for ultrasonically welding or cutting a moving web of material generally transversely to its the direction of movement, comprising at least one elongated ultrasonic horn and at least one anvil corresponding to said horn, the web being moved between the at least one horn and the at least one corresponding anvil. The invention also relates to a method of ultrasonic welding or cutting such a web.
TECHNICAL BACKGROUND
Many different types of apparatus for welding or cutting material ultrasonically are available commercially. A common feature of these apparatus is that they include one or more ultrasonic horns which emit high frequency sound waves, and ultrasonic anvil surfaces positioned opposite respective horns. The material is worked in the manner desired, by moving or otherwise placing said material between the ultrasonic horns and opposing anvil surfaces. It is common procedure to use ultrasound when laminating and patterning thermoplastic material. In this regard, there are often used cylinders or drums that are provided with a number of raised surfaces which function as anvils and which as the cylinder/drum rotates punctiform welds, linear welds, etc., in coaction with one or more ultrasonic horns. Desired weld patterns and weld distribution are achieved by giving the raised surfaces different positions, sizes, shapes, etc. The raised surfaces may also be replaced with comb-like elements, so as to obtain continuous welds. When wishing to make holes in the material or to clip or cut the material, this can be best achieved by increasing the power of the ultrasound generating unit. EP 0,092,866 describes apparatus for bonding together several layers of material to form a laminate structure by means of ultrasound, wherein the ultrasonic anvil surfaces may have any one of the aforesaid forms, among other things.
TECHNICAL PROBLEMS
One problem experienced with ultrasonic welding in which several different materials are joined together with the aid of cylinders provided with a plurality of ultrasonic anvils in accordance with the above, resides in the occurrence of so-called cobblestoning, i.e. hammering motion between ultrasonic horn and anvil caused by variation in the abutment pressure therebetween. In addition to resulting in a poorer weld quality, cobblestoning also increases the wear on the ultrasonic horn, primarily punctiform wear. EP 0,092,866 describes how at least one anvil surface can be held in firm abutment with the ultrasonic horn as the cylinder rotates, by relative distribution of such anvils on a rotatable cylinder. In this way, there is obtained a constant total abutment pressure between the ultrasonic horn and the anvil surfaces carried by the cylinder. Cobblestoning is counteracted in this way. Although the wear problem is alleviated to some extent it is not resolved completely, because the pressure exerted per unit area on the ultrasonic horn varies as the cylinder rotates and the anvils pass the horn. When the abutment surface between horn and anvil varies in magnitude as the cylinder rotates, the ultrasonic energy delivered per unit area will normally also vary, resulting in welds of varying quality. Even though attempts have been made to avoid this problem with the aid of electronic control units, the energy delivered is still able to increase momentarily and therewith influence the weld quality. Large variations in power outtake will occur particularly when welding or cutting transversely to the direction of web movement, wherewith anvil and horn will lie against one another during short repeated points in time along the whole of their respective lengths, i.e. with large variations in said abutment surface. One result of this variation is the necessity to restrict the speed of the web.
SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the aforesaid problems. The present invention provides an apparatus and a method of welding or cutting a moving web of material transversely to
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