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Volume 6   Issue 2                March 2005


Edge Deletion
"That Is a Very Nice Way to Go"
By Mike Burk

In the movie “The Wizard of Oz,” when Dorothy was lost and needed directions she sought advice from the scarecrow. His response: “That way is a very nice way to go. It’s pleasant down that way too. Of course, people do go both ways.” This exchange is similar to the response many insulating glass (IG) manufacturers receive when investigating edge-deletion requirements.

The debate regarding edge deletion of low-E coatings (soft-coat) continues. The response to the edge-deletion requirement question is often “yes, you do” and “no, you don’t” from the same source. Despite all the recommendations, opinions and advice, I have not been able to locate anyone willing to take on the liability for “no, you don’t.” Although I have serious concerns for those who don’t, I also have some concerns for those who do.

The manual edge-deletion process can be a time consuming bottleneck in the production of insulating glass. In some cases the damage caused by the manual edge-deletion process can outweigh the benefits of deletion. Scratching, edge damage and excessive glass removal can all lead to premature seal failure, stress cracks and increased warranty claims. Applying the five W’s and one H developed by Masaji Tajiri and Fumio Gotoh may identify edge-deletion issues in your facility. Review the who, what, where, when, why and how of your process.

Answer the Five W’s
Who does the edge deletion in your glass department? Who should be doing it? In most cases manual edge deletion is completed by the washer loader.
What is done? A rotating abrasive wheel removes the low-E coating as the lite is moved beneath the wheel manually. The lite is then rotated 90 degrees and the process repeated for the remaining sides.
Where is it done? In order to minimize handling, many manufacturers have located the manual edge-deletion equipment near the washer entrance. Edge deletion near the glass washer may increase the amount of contaminates entering the washer’s water system. In addition floor space is usually limited in this area making handling for edge deletion and washer loading difficult.
When is it done? As mentioned previously, the deletion is often completed just prior to the lite being washed. This may reduce a step in handling but may cause interruptions and delays.
Why should it be done? Proponents of edge deletion believe that, over the life of an IG unit, the low-E coating may react with the sealant or delaminate from the glass resulting in unit failure. By removing the coating, the sealant is applied directly to the glass ensuring adhesion. 
How is it done? Removing the low-E coating by using an abrasive wheel is acceptable when done properly. Problems begin to occur when the equipment is maintained poorly or set up incorrectly. If the pressure on the abrasive wheel is too high, a layer of glass will be removed along with the coating. If the pressure is too low, the coating may not be removed completely. In some cases the glass at the corners of the lite is deleted twice, which may lead to stress cracks. If the deletion wheel begins to travel against the glass before the lite is completely squared, a curved or rounded path is deleted. 

Some Final Questions
Analyze your edge-deletion process and ask the following questions. Have you trained your operator on edge deletion requirements? Does he fully understand why deletion is required? Are the deletion quality control standards clearly defined? Is the operator taking the correct amount of time to ensure that the low-E coating is removed completely without damaging the glass? Is the operator handling the glass by the edges to avoid scratching? Does the operator have the correct safety equipment? 

Finally, as I always recommend, talk with the operators. Don’t send them down the wrong road. Give them the directions they need. 

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


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