METHOD AND APPARATUS FOR TRIMMING THE EDGES OF A FLOAT GLASS RIBBON

Abstract

A method and apparatus for trimming the edges of a float glass ribbon whose thickness can vary between 0.4 mm and 24 mm in which a specific depth crack is generated for the respective thickness. The depth of the crack is actively influenced by energy introduced by means of a laser which is controlled as a function of the surface temperature of the float glass ribbon and by a subsequent cooling whose acting period is variable. To ensure a permanently reliable process, the severing crack and the thickness of the float glass ribbon are detected in order to initiate a new initial crack immediately in the event that the severing crack should break up and so that a cutting unit comprising the scribing device, the beam-shaping optics and the cooling nozzles is always at a constant vertical distance from the surface of the float glass ribbon. The method and apparatus are distinguished particularly by the fact that only a low laser power is required.

Description

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic drawing of an apparatus according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus according to the invention can basically be mounted at a bridge or a frame above the horizontal transporting device of a float glass installation. Two apparatuses which may share a temperature sensor 5 and a thickness sensor 6, as the case may be, are required to cut off both edges of a float glass ribbon 13 simultaneously.

As is shown in FIG. 1, an apparatus according to the invention basically comprises a laser 1, beam-shaping optics 2 which are arranged downstream of the laser 1 and which shape the emitted laser beam bundle 12 into a beam bundle with an elliptical cross section, a cooling arrangement 3 with a plurality of cooling nozzles 4 arranged one behind the other in a straight line, a temperature sensor 5 which measures in a noncontacting manner, e.g., an IR sensor, a thickness sensor 6 which measures in a noncontacting manner, e.g., an ultrasonic sensor, a crack detector 7, a control device 8 by which the laser output is controlled as a function of the detected temperature, and a regulating device 9 which regulates the vertical position of a cutting unit 11 depending on thickness. The cutting unit 11 comprises the beam-shaping optics 2, the cooling arrangement 3 with cooling nozzles 4 and a scribing device 10.

By fastening the apparatus in a prescribed manner to a bridge or a frame 11 above the transporting belt, the cutting unit 11 and therefore in particular the beam-shaping optics 2, the cooling nozzles 4 and the scribing device 10 are positioned in a defined manner vertically and laterally with respect to the transporting device arranged horizontally below them. The scribing device 10, the beam-shaping optics 2 and the cooling nozzles 4 are arranged one behind the other at selected distances relative to one another in the transporting direction of the transporting device which is the same as the drawing direction of the float glass ribbon 13. Their vertical distance is regulated by the change in thickness so that they always maintain a constant distance from the float glass ribbon 13 moving on the transporting device regardless of the thickness of the float glass ribbon.

The cooling nozzles 4, three of which are provided in the embodiment example, can be opened individually or simultaneously so that the coolant can act locally over a shorter or longer period of time and the cooling penetrates to a varying depth from the surface into the material. The depth of the crack can also be influenced in this way, which is benefited by the fact that the material core is still warm.

The crack detector 7 is provided in order to ensure that a crack is always actually generated for the permanently and continuously running process. A radiation sensor which emits a measurement beam that is reflected back into the sensor at the interfaces of the crack can be used as a crack detector 7. When the distance and the angular position of the crack detector 7 to the crack is kept constant independent from the glass thickness, it is also possible to deduce the crack depth or changes in the crack depth by way of the intensity or change in intensity of the measurement beam reflected back into the crack detector 7. The crack detector 7 could be fastened to the horizontally fixedly arranged shaft of a loose vertically movable roller which rolls in the edge area on the surface of the float glass ribbon 13. In this way, it maintains a constant distance from the crack and always directs its measurement beam at the same angle to the interfaces of the crack.

As soon as a crack is no longer detected, a signal is sent to the scribing device 10 which immediately initiates a new initial crack. The crack detector 7 can also supply a signal when the crack depth is not sufficient. The crack is made deeper by switching on another cooling nozzle 4.

Instead of the optical crack detector 7, the existing crack could also be verified by once again sensing the temperature subsequent to cooling. With knowledge of the heating temperature determined by the surface temperature immediately before the action of the laser beam, the given energy input by the laser and the temperature measured following the cooling, the generated temperature gradient can be deduced and therefore also the occurring tensile stresses which have generated a crack insofar as they have exceeded the breaking stresses. For this purpose, a second temperature sensor would be arranged following the final cooling nozzle 4.

The cutting process starts when an initial crack is made on the surface of the float glass ribbon 13 which is transported relative to the apparatus in the cutting direction identical to the drawing direction at a cutting speed identical to the drawing speed depending on the actual thickness of the float glass ribbon 13. In the cutting direction, starting with the initial crack, a specific depth crack is made in the float glass ribbon 13 comparable to a method according to U.S. Pat. No. 5,609,284 in that the float glass ribbon 13 is initially acted upon along the desired path of the crack by a laser beam having an elliptical beam cross section and is subsequently cooled. The float glass ribbon 13 is subsequently broken in a known manner along the crack that has been formed in this way.

Contrary to the teaching of U.S. Pat. No. 5,609,284 to adapt the beam geometry corresponding to thickness, the beam spot geometry, particularly the beam spot length, remains constant regardless of the thickness. In practice, a beam spot length of 120 mm, which corresponds to approximately ten-times the beam spot lengths indicated in the embodiment examples in U.S. Pat. No. 5,609,284, has proven successful for all standard thicknesses of the float glass ribbon 13.

The laser output is controlled in the method according to the invention only as a function of temperature independent of the change in thickness which can have the range of a power of ten anyway. The range of variation of the temperature of the float glass ribbon 13 directly before the action of the laser is between approximately 50° C. and 80° C. The possible temperature differences result from the material-specific and thickness-specific regime of the active cooling in the annealing oven and the passive cooling through the plant temperature which can vary appreciably particularly over the course of a year.

A laser with an output of 200 W is sufficient for an apparatus which can process the full spectrum of conventional float glass thicknesses. For float glass installations provided only for producing glass of smaller thickness, e.g., only up to 6 mm, a laser with a maximum output of 100 W would even be sufficient.

It will be apparent to a person skilled in the art that the invention is not limited to the particulars of the embodiment forms discussed above by way of example, but that the present invention can be embodied in other specific forms without departing from the scope of the invention as set forth in the appended claims.

REFERENCE NUMBERS

• 1 laser
• 2 beam-shaping optics
• 3 cooling arrangement
• 4 cooling nozzle
• 5 temperature sensor
• 6 thickness sensor
• 7 crack detector
• 8 control device
• 9 regulating device
• 10 scribing device
• 11 cutting unit
• 12 laser beam bundle
• 13 float glass ribbon

Claims

1. A method for severing two portions of a body of glass comprising the steps of: forming a depth crack with a specific depth for the thickness of the body starting from an initial crack, said depth crack extending into the body from the surface of the body and in a desired direction along the surface;guiding an elliptical laser beam bundle to the surface along the desired direction at a cutting speed;directing a stream of coolant to an area of the surface that is heated by the beam bundle at a selected distance from the beam bundle;providing that the body of glass is a float glass ribbon whose core is still warm and whose surface temperature is between 50° C. and 80° C. and which is drawn in a float glass installation at a specific drawing speed for generating specific glass thicknesses in the range of 0.4 mm to 24 mm so that the cutting speed is identical to the drawing speed and the drawing direction is identical to the desired cutting direction;measuring the surface temperature of the float glass ribbon and joining the specific depth of the crack exclusively by controlling the laser output depending on the measured surface temperature; andmeasuring the thickness of the material and using the thickness as a regulated variable to keep the radiation ratios and cooling ratios constant over changes in thickness.

2. The method according to claim 1, wherein the area acted upon by the stream of coolant is elongated in the cutting direction to bring about a heat extraction at greater depths.

3. The method according to claim 2, wherein the length of the area acted upon by the coolant can be varied in that the cooling nozzles which are arranged one behind the other are switched on and off.

4. The method according to claim 1, wherein the formation of the crack is detected optically so that in the event that the crack breaks open a new initial crack is made.

5. The method according to claim 4, wherein, when the crack is detected, the crack depth is also detected in order to lengthen the area acted upon by the stream of coolant when the crack depth is too shallow.

6. The method according to claim 1, wherein a laser of 200 W is used for generating the laser output.

7. The method according to claim 1, wherein the temperature is detected along the crack behind the cooled area in order to be able to deduce formation of a crack from this temperature in connection with the laser output and the measured temperature immediately before the impingement of the laser beam.

8. An apparatus for generating a specific depth crack induced by thermal stress in a float glass ribbon which is moved relative to the apparatus in the cutting direction, comprising: a laser which is directed to the surface of the float glass ribbon;a cutting unit which comprises beam-shaping optics arranged downstream of the laser, a cooling device and a scribing device;a control device by which the output of the laser is controlled;a temperature sensor which is connected to the control device and which measures the surface temperature of the float glass ribbon in front of the location where the laser beam impinges on the float glass ribbon and supplies this surface temperature to the control device as a control quantity;said cooling device comprising a plurality of cooling nozzles which are arranged one behind the other in a straight line and which can be opened in a variable manner to be able to change the acting period of the coolant;a thickness sensor being provided which detects the thickness of the float glass ribbon and supplies it to a regulating device as a controlled variable in order to adjust a constant vertical distance of the cutting unit relative to the float glass ribbon; anda crack detector which communicates with the scribing device in order to initiate a new initial crack in the event that the crack should break up.

9. The apparatus according to claim 8, wherein the crack detector is also connected to the cooling device so that the individual cooling nozzles are opened depending on the crack depth that is reached.