"Cat Scratch" cord has been a significant problem in the glass industry for perhaps 70 years or so. It is a common problem in tableware and containers but can also be present in rolled plate flat glass and tubing. "Cat scratch" cord is caused by a viscous glass enriched in alumina and zirconia which settles out on the bottom of furnaces, distributors and forhearths. This glass eventually travels along the bottom of the forehearths, is present in the surface of the gob and appears as a line or series of lines in the surface of the bottle or article being manufactured. One of the most effective ways of dealing with this defect is by the operation of correctly configured stirrers to lift and disperse this viscous glass into the body of the base glass so that it is then present in the centre of the gob and distributed throughout the base and side walls of the article so that it is no longer readily visible. This paper describes the application of stirrers in a proven cord dispersal system. It is based on the observations and experiences of Parkinson-Spencer Refractories (PSR) in supplying refractory stirrers and complete cord dispersal stirrer systems to the glass industry worldwide.
