Quality control

Dos and don’ts for the handling and cutting stage of the IG fabrication process
By Bill Briese
November 30, 2012
FABRICATION

The following article is the second of a two-part series based on Briese’s presentation, “Preventing Insulating Glass Failures: Glass Washing & Cutting Techniques,” delivered during the Insulating Glass Manufacturers Alliance’s annual IGMA Performance and Innovation in Insulating Glass Educational Seminar. See Page 38 of the November 2012 issue for the first article, which addresses the glass washing stage of the IG fabrication process. You can also visit www.igmaonline.org to view Briese’s full presentation in the IGMA online education center.

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Wear proper glass handling/safety equipment when handling glass. Make sure you have a documented Personal Protective Equipment system, and that operators are properly trained. Protective equipment should include: safety glasses with shields; steel toe shoes; wrist guards, aprons and neck guards; and gloves. Keep up to date with new PPE products, and make sure that new operators are properly trained.

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Use a water soluble or evaporating cutting fluid, as it plays a vital role in glass edge quality. Never use kerosene or a similar-type solvent unless specifically recommended by the glass and equipment manufacturer. Using improper solvent-based fluids will leave residue on the glass, resulting in IG seal adhesion issues. Also, don’t flood the glass with cutting fluid; 1 millimeter to 2 mm on each side of the score line is adequate. Consult the glass supplier for cutting fluid recommendations for coated glass. Cutting fluids can be specifically formulated for:

  • Glass end use and type, such as automotive, residential, coated, laminated, mirror glass, etc.
  • Evaporation properties versus breakout processing time
  • Elimination of residues that can cause poor adhesion
  • Hand cutting, shape cutting or thick glass cutting
  • Elimination of splinters and chips that can cause surface damage.

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Maintain sharp cutting wheels on the glass cutter, and change wheels as frequently as recommended. As a rule of thumb, you can expect  wheel life of about 5 miles, depending on glass type and thickness. Wheel life and cut quality depend on many factors, however, so check with your glass and equipment suppliers. Factors affecting wheel life include glass thickness and type, cutting speed, cutting force, lubrication amount and type, whether the cuts are for arcs and non-rectangular shapes, wheel diameter and angle, wheel material and finish, and whether or not the glass is laminated.

To achieve the best cut, use as little down force as necessary, noting that increased speed leads to increased down force. Cutting glass shapes requires smaller diameter wheels, which require less down force. Shapes use smaller diameter, and smaller diameter wheels require less down force as well.

Finally, break-out the glass immediately after cutting.

4

Keep a clean cutting table. Vacuum tables; do not blow them. Blowing tables will also blow glass bits into the air. Also, inspect tables for worn carpeting. Wearing can lead to uneven score depth due to the varying cushion.

5

Check for accurate cuts, dimensions and glass damage. Make sure the glass is square by measuring diagonals, and be sure that an interrupted score stops short of the cross score. The thicker the glass, the sooner the score should stop. In addition, don’t allow out-of-specification or tolerance product to proceed downstream.

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Ensure the glass edge is free of chips, nicks, flaws and other irregularities along the break line. Edge damage can lead to stress cracking and IGU failure, even after a window has been in service. A change in seasonal temperature can create a stress crack failure due to edge defects.

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Use proper glass separators when stacking glass. Consult with glass manufacturers for recommendations for stacking and separating, especially for coated or treated glass types. Some common interleaving/separating materials include lucor powder, paper, and foam and cork pads.

8

Edge delete glass coating when recommended by the glass and/or sealant manufacturers. Pyrolitic (hard) coat low-E typically does not require edge deletion, while soft coat might require edge deletion. Edge deleting is not a costly process but does require some level of equipment and/or automation. The glass supplier can provide guidance and requirements for specific products.

Edge deletion dust can become airborne and compromise wash water quality, especially for machines in close proximity to the glass washer. Automated edge deletion can reduce handling and scratch damage.

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Don’t handle glass with bare hands. Different gloves serve different purposes for fabrication; one type does not fit each manufacturing process. In addition to being necessary for safety, gloves prevent glass contamination. Require employees to change gloves often to prevent the transfer of oils to glass.

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Don’t allow contaminated glass to be sealed in an IGU. Have a system in place to look for haze, film, fingerprints, smudges, suction cup marks and other visual defects on the glass. Lighting the glass can help draw attention to contamination and imperfections. Automated systems can help with lighting conditions, and quantify defects or contamination.

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Don’t nip the glass. This will lead to irregular and poor edge quality. Make sure you have sufficient trim-cut: at minimum, this should be four times the glass thickness. The typical trim cut is eight times the glass thickness. If the score line cannot be broken in a single smooth action, then you have insufficient trim stock. Additionally, do not try to re-cut glass that is too small.

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Don’t allow out-of-tolerance or damaged glass to be fabricated. Wrong size glass can create improper glazing support leading to increased edge stress when glazed. Small surface scratches can also lead to glass fracture, especially on tightly clamped IGU glazing.

13

Don’t put glass on racks that can damage the bottom edge of the lite. Small glass fragments and debris can become lodged in the slots, and sliding glass over this debris can damage the glass edge. Harp racks can accumulate dust via static attraction and other contaminants. Ensure the rack and cart is clean prior to loading glass.

Put only one lite per slot in the rack. For coated glass, a slight tilt in the rack can help the glass lean to the uncoated face of the glass.

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