December 2005

Volume 6 Issue 11 December 2005

IG Instructions

Concealed Damage:
Preventing Edge Damage Before Installation
by Mike Burk

Many of the items we purchase for business or personal use come with the warning “Check for concealed damage.”

Receiving invoices and shipping instructions inform the buyer of the sellers’ lack of responsibility for any hidden damage and warn us “to notify the carrier” or “contact the freight agent immediately.” Concealed damage is often defined as “Damage to the contents in a package without the apparent damage to the package itself.”

But with insulating glass (IG), once the IG unit is glazed into the sash, any glass-edge damage caused during the manufacturing process is hidden from view. The next opportunity to inspect this damage is after the unit has cracked or failed. With the emphasis on lean manufacturing and the continual push to reduce the amount of work in process, the time period in which glass edges may be inspected is minimal. This makes proper glass cutting, handling and inspection critical.

In many cases the glass-edge damage may appear to be minor and inconsequential. However most industry experts agree that edge damage may eventually cause the glass to fracture. It may happen as the IG unit is assembled, during glazing, during transportation, at window installation, or it may wait until the first hot afternoon or first cold night. Eventually the unit will fail.

Strategies for Prevention
Although the opportunity for inspection is brief, the opportunity for edge damage is great. It is important that operators understand the basic theories of glass cutting. They need to understand the effects of pressure and speed, along with cutting wheel angles and diameters. This training will assist in understanding the reasons for replacing worn cutting wheels and avoiding excessive cutting pressure.

Inaccuracies and poor maintenance of the cutting systems may lead to flares, edge bevel or hackle. The operators should perform regular autonomous operator maintenance on the cutting system. This includes checking the accuracy of the scores, lubrication, pressures, the squareness of the lites and the accuracy of intersecting scores.

Poor break-out techniques may also create glass-edge damage. Associates who break out glass should be instructed on how to minimize the lifting and separation of the lites. Excessive lifting prior to breakout may cause compression damage at the score. Operators should only handle one lite at a time and should not stack or deal the lites as they are sorted. Glass edge-to-glass edge impact must be avoided.

Contact with metal surfaces on slot sorting racks, carts, tables and conveyors may damage the edge of the glass. Check all glass handling equipment for exposed metal which may contact the glass edge and cause impact damage.
The entire process should be reviewed to locate any opportunity for impact damage. This may be caused by inconsistent conveyor speeds, limit switches, uneven transport systems or operator loading techniques.

Learning from Others Mistakes
One manufacturer experienced hundreds of unit failures in the first cold period in December. All the failures involved units that had been installed recently. The majority of the cracks appeared to originate in the corner of the units with a run to the edge. The manufacturer immediately set out to repair and adjust the corner cleaners and welders believing that a raised weld surface was the cause of the excess stress and resulting fracture. Inspection of returned units indicated otherwise. The fractures actually began at a point of impact damage and ran to the corner. The cause of the edge damage was traced back to a production issue and corrected.

Take the time to review your IG process and eliminate the causes of edge damage. Increase the time allowed to inspect finished units to prevent obvious damage from becoming concealed damage.

Mike Burk serves as training manager for GED Integrated Solutions in Twinsburg, Ohio. He can be reached at MBURK@gedusa.com.