Electric heating – Metal heating – By arc
Reexamination Certificate
1998-12-14
2001-03-20
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121840
Reexamination Certificate
active
06204472
ABSTRACT:
This invention relates to a method and device for the laser-beam cutting of hollow glass articles, for example the blowing cap of blow-moulded articles such as tumblers, in accordance with the pre-characterising part of the independent claims.
In cutting methods similar to the aforesaid type, the incision is made by mechanical devices carrying grinding wheels, points or similar cutting members. With the known methods and devices of the aforesaid type, an incision of constant depth along the entire circumferential cutting line is not always obtained.
Non-uniform incision of the articles sometimes makes it impossible to cut the article by “temperature change” during the next heating stage, and at other times results in an extremely irregular cut.
Hence the article must often be either rejected or undergo costly and lengthy smoothing.
Other cutting methods and devices are also known in which a laser is used for cutting. For example, DE-OS-3546001 describes a method in which the glass region to be cut is firstly maintained at a high temperature, slightly below the softening point, after which this region is exposed several times along the division line to a laser beam, while a traction force simultaneously acts on that part of the article to be removed. This method is relatively complicated and difficult to implement, mainly for the fact that the force of gravity is generally used as the traction force, this resulting in the need to suitably position the glass to be cut. The cutting line is not sharp and precise, in that the glass is substantially cut by the effect of the laser irradiation.
U.S. Pat. No. 4,467,168 describes a method for cutting glass plates in which a laser is used to make an incision in the glass along the desired cutting line while simultaneously heating said incision region above the glass softening point, after which a gas jet is directed onto the laser focusing region, this gas jet cooperating with the laser to create a fissure in the glass.
The aforedescribed method is claimed for cutting for example brittle plates, but not hollow articles. Moreover it should be noted that the cut in the glass is not obtained by virtue of the stresses generated in the glass but by evaporation-removal, by the combined action of the laser and gas jet, through the entire glass thickness along the incision line. The cut which would be obtained in this manner in the case of hollow glass articles would not be sufficiently sharp, and would require subsequent lengthy and costly machining.
Finally, WO 94/22778 describes a method for cutting hollow glass articles in which the article is rotated at a velocity of about 1 m/sec in correspondence with the cutting line and is heated with a laser such as to generate a region of stress at the required cutting line. In addition, a small crack is made in the article in correspondence with the cutting line. The article is then cooled along the entire circumferential cutting line. This method has proved extremely deficient in the case of glass of non-uniform thickness or of particular geometrical shapes, for example conical. In such a case, as there is not an incision line along the entire circumferential cutting line, the cut is often not sharp and satisfactory.
An object of the present invention is to provide a specific method and device for cutting hollow glass articles by a laser, which obviates the aforesaid drawbacks and in particular, for equal production rates compared with the known art, results in cuts of superior quality which minimize or eliminate subsequent lengthy and costly smoothing, even in the case of articles of non-uniform thickness or of particular geometrical shapes such as conical, elliptical or polygonal.
A further object is to provide a method and device which reduce the number of rejects.
These and further objects which will be apparent to an expert of the art are attained by a method and device in accordance with the characterising part of the accompanying main claims.
REFERENCES:
patent: 3453097 (1969-07-01), Hafner
patent: 3839005 (1974-10-01), Meyer
patent: 4467168 (1984-08-01), Morgan et al.
patent: 4549066 (1985-10-01), Piccioli et al.
patent: 4682003 (1987-07-01), Minakawa et al.
patent: 5622540 (1997-04-01), Stevens
patent: 4305107 (1994-08-01), None
patent: 4411037 (1994-10-01), None
patent: 1292981 (1972-10-01), None
Cipriani Claudio
Gusti Dario
Muzzi Alessio
CALP-Cristalleria Artistica La Piana S.p.A.
Heinrich Samuel M.
Steinnberg & Raskin, P.C.
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