1. Field of the Invention
This invention relates to a method of and an apparatus for intitating a damage-free score e.g. a subsurface and/or psuedosubsurface score in a piece of refractory material.
2. Discussion of the Prior Art and Technical Problems.
U.S. Pat. Nos. 3,865,293; 3,865,673; and 4,057,184 teach techniques of imposing scores that are free of surface damage in refractory material such as ceramics, glass and/or glass ceramics. These types of scores are known as subsurface scores and/or psuedosubsurface scores. The term "subsurface score" as used herein is defined in U.S. Pat. No. 3,865,673 which, in general, defines a subsurface score as an essentially spall or wing-free discontinuity or fissure such as an intentionally induced crack or score respectively that is within the thickness of a refractory piece and extends substantially perpendicular to its major surfaces but does not extend to or connect either major surface of the piece. The term "psuedosubsurface score" as used herein is defined in U.S. Pat. No. 3,865,673 which, in general, defines a psuedosubsurface score as an intentionally induced discontinuity or fissure in a piece of refractory material that extends substantially perpendicular to its major surfaces, that does not appear itself to extend or connect to either major surface of the piece but which is accompanied by a microscopic zone of damage essentially spall or wing-free material which is disposed between or extends between its tip and the major surface of the piece. For purposes of simplicity, the term "damage-free score" is used herein to refer to a subsurface score and/or a psuedosubsurface score.
The advantage of imposing a damage-free score in a refractory piece to sever same is that the resultant severed edge is essentially in a pristine condition i.e., has essentially maximum edge strength. U.S. Pat. No. 3,979,243 in Column 6, lines 23-49 teaches that a damage-free score is initiated at a zone of damage. The zone of damage as taught therein is imposed in the refractory piece by applying an initial force to the scoring wheel approximately 20% greater than the selected scoring force or initially impacting the surface of the piece to be scored with a force of about 20% greater than the selected scoring force. U.S. Pat. No. 4,057,184 in Column 6, lines 47-59 teaches that the zone of damage is generated by tapping the surface of the piece to be scored with a rigid object; impacting the surface of the piece with a scoring wheel; or rotatably urging the scoring wheel against the surface of the piece.
Limitations of the prior art techniques of initiating a damage-free score are for practical purposes non-existent when the piece of refractory material is stationary. When a piece of refractory material, e.g., a glass ribbon is continually moving the prior art techniques are not acceptable. This is because the prior art technique for initiating a damage-free score teaches that the scoring wheel be tapped or rotated to initiate the damage-free score. As can be appreciated, acting on a wheel as it is powered by a glass ribbon moving at speeds of up to 600 inches per minute (15 meters per minute) is hazardous. Further the prior art suggests that a zone of damage be imposed in a glass piece but is silient as to the equipment or manner employed to accomplish this result on a moving glass ribbon. It would be advantageous, therefore, to provide techniques of initiating damage-free scores in a moving ribbon.