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Volume 6   Issue 5                June 2005

IG Instructions

Investigating Scratched Glass
And Finding a Solution for IG Remakes
by Mike Burk

For many window manufacturers, “scratched glass” is the highest reported reason code for remaking insulating glass units. Determining the cause of the scratches is often perceived as too time consuming or too difficult. Many times the investigation is never completed because it’s “much easier and faster to remake the entire unit.” We can use the advice of Sherlock Holmes in the story A Study in Scarlet to make this task easier and to begin the process of reducing remakes and improving productivity. 

“In solving a problem of this sort, the grand thing is to reason backwards. That is a very useful accomplishment, and a very easy one, but people don’t practice it much. In the everyday affairs of life it is more useful to reason forward, as so the other comes to be neglected.” 

The majority of scratch damage in insulating glass units is not detected until the units are completed and glazed in the finished window. Detecting scratched units earlier in the process, before each value added step, can improve the profitability of the insulating glass department dramatically. Using Holmes’ advice we can work our way backwards from the point of detection until we locate the source of the damage. 

A Variety of Culprits
Scratches in glass may be caused in any of the manufacturing steps. However, it appears that a large number of scratches occur as a result of common, preventable handling and process operations. Most damage is caused when the glass is moved against a fixed or non-moving object or when the glass contacts an object moving at a different speed or in a different direction. Preventive maintenance programs, proper equipment set-up, scheduled cleaning and vacuuming and operator training are the best methods to prevent scratching. Once scratch damage has been detected, an attempt should be made to determine the cause immediately. The shape, length and spacing of the scratches can provide us with the clues needed to discover the source of the damage. 

Straight scratches often match the direction of glass travel. Long single scratch marks may be caused by a single point of contact. If the damage starts and stops, the spacing of the marks may match the circumference of a pinch roll, conveyor wheel or oven roll. If the scratch marks are parallel, the spacing may match the spacing of conveyor drive wheels. 

Curved scratches indicate that the glass is spinning or turning. Curved scratch marks may be a result of handling as the lites and units are loaded and unloaded in the process. They may be an indication of worn washer brushes, misaligned conveyors or non-parallel rolls. 

Some random or multiple scratches may be caused as the lites or units are dragged or pushed across conveyors and roller tables. Other damage may be caused by worn or deteriorated breakout table surfaces or edges. 

A Thorough Inspection
Investigation requires clean glass and good lighting. As the inspection moves backwards through the process, it may be necessary to hand clean the lites. Scratches that are incurred prior to the washer may not be detected due to the dirt and interleaving on the glass. Again, begin the search for clues at the point where the scratches are first detected. 

Once the section or process causing the scratches is determined, begin looking for the source. Look for any object that contacts the glass. Make sure that this contact with the glass is planned and required. Look for contamination, worn components, incorrect adjustments and mismatched speeds. Inspect conveyor wheels, positioning devices, pinch rolls, press rolls and drive belts. Ensure that the glass exiting any operation or process is oriented the same way in which it entered. If the glass has rotated, look for the cause of this unnecessary movement.

In another Sherlock Holmes story, Holmes scolds his associate, “On the contrary, Watson, you can see everything. You fail, however, to reason from what you see.” 

Take the time to closely examine the scratches. Investigate backwards through the process, and by gathering clues from what you observe, “reason from what you see.” 

Mike Burk serves as training manager for GED Integrated Solutions in Twinsburg, Ohio. 

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