Editor's note: The following article is based on Briese’s presentation, Preventing Insulating Glass Failures: Glass Washing & Cutting Techniques,” delivered Sept. 11 during the Insulating Glass Manufacturers Alliance’s annual IGMA Performance and Innovation in Insulating Glass Educational Seminar. In November, IGMA will be launching an online education center that will include Briese’s full presentation.
Fabricating insulating glass is a multi-dimensional process that requires communication between a number of suppliers. All of the players— from the glass, sealant and spacer providers; to the equipment manufacturer; to the IG fabricator— need to work as a team to build a successful IGU. Any mistake at any stage of the fabrication process can lead to failures in the field. This article specifically identifies dos and don’ts for the glass washing stage of the IG fabrication process.
General glass cutting and washing considerations
1. Consult the glass supplier, glass washer supplier and sealant manufacturer for proper glass cleaning process recommendations, including detergent, brush type and rinse water quality.
2. Consult the glass supplier on the care and handling of low-emissivity or other coated glasses.Glass suppliers are constantly developing new low-E coatings, which mean new procedures.Some coatings are soft and fragile. The way you have been handling glass might not be the best way to handle these new coatings.
3. When working with low-E glass products, follow several steps to maintain the integrity of the glass coating prior to IGU fabrication:
- Keep inventory dry and ventilated.
- Keep glass racks out of sunlight, away from dock doors and at least 50 feet away from the glass washer or other humid processes.
- Make sure glass is stabilized to room temperature before processing. This usually takes about 72 hours, but can vary depending on the season.
- Rotate the stock—first in, first out.
- Take ambient changes between seasons into consideration.
4. Don’t use spray lubricants near the glass washer or in the IG manufacturing area. Spray lubricants can disrupt adhesion. In the case of IGU, atomized particles from silicone and Teflon lubricants, for example, can get between the spacer edge seal and glass at the bond line, compromising adhesion. Particulate can travel even long distances through ventilation systems, so the products should be banned in areas where concern for adhesion is present.
Residual sealant on the glass can transfer to other lites, if put through the washer.
5. Don’t wash glass with residual sealant or residue on the surface or edges, as it could result in transfer contamination to the next glass lites. This could include adhesive/sticker residue or sealant residue. The glass washer isn’t designed to remove those materials, and the contaminants will transfer onto the glass washer drive components (brushes and rolls) and will create a printing press effect.
1. Make sure the washer is functioning properly. Seek assistance from the equipment manufacturer,and use the instruction manual and other technical resources to ensure proper setup. For example, check to make sure your brushes are set up correctly: only the bristle tip should be in contact with the glass. Contaminants can build up on the bristle strands, and excessive bristle contact can scratch/scrape glass. Most brushes are set between 5/8-inch to 1-inch contact flat with the glass.
Temperature monitors notify employees if the washer temperature falls outside of the specified range.
2. Use hot wash water, as it is more difficult to dissolve oil and debris in cold water. Temperatures should range between about 130 degrees Fahrenheit to 140°F; however, avoid excessive heat, as temperatures above 160°F can damage glass coatings and machine components. Make sure your glass washing equipment controls and monitors wash tank temperatures, and check temperatures hourly.
3. Ensure that glass coatings are placed face upon a horizontal washer or face out on a vertical washer. A low-E or surface coating validation device on your glass washer can ensure proper loading direction. Additionally, make sure back-to-back lites are spaced sufficiently to prevent edge contact as they travel through the washer. Do not carry two lites stacked on top of each other to the washer, and for horizontal washers, stagger feed the lites if possible to maximize brush life.
Feed lites at an angle to the air knives onthe washer.
4. Feed the lite of glass at an angle to the air knives on a horizontal washer. A glass washer includes a drying section typically equipped with a high velocity air knife system. Feeding glass at an angle to the air knives allows the final rinse water to roll smoothly off the glass edge. When the glass edge is perpendicular to the air knife, all the water on the trailing edge must peel off simultaneously, which creates turbulence. Water droplets can fly in any direction and can remain on the glass edge, which creates potential for water spotting and adhesion issues with the spacer.
Re-circulating water purification(de-ionizing) treatment system.
5. Use clear, fresh water rinse for final rinse, or de-ionized when required. Change water frequently, preferably every shift. Tap water, at about $0.0019 per gallon, might work in some locations. Reverse osmosis water, at $0.049 pergallon, is a better option, and de-ionized water, at $0.076 per gallon, is the best option for many facilities. Glass suppliers might recommend or require de-ionized water for some coated glass types. Regardless of glass type, de-ionized water offers the best opportunity for maximum spacer adhesion and minimum risk of water spotting.
6. Have your water analyzed. A water treatment specialist or your glass washer manufacturer can provide guidance with water treatment options. Hard water can create problems with the glass and equipment:
- Water/mineral residue on glass (evenmicroscopic) is the enemy of adhesion.
- Water/mineral residue on glass cancause water spots and visual defects.
- Hard water can build up inside theglass washer and compromise its ability to effectively clean glass.
- Hard water can prematurely fail components inside your glass washer.
Use adequate water in the final rinse.
7. Use enough fresh water to flood the lite of glass in the final rinse. Adequate water flow is necessary to ensure a good flushing and shedding of contaminants from the glass surfaces. In other words, don’t just push dirt around; have enough water to rinse it away. Additionally, washer bristles are typically made from nylon, which is a hygroscopic material. It will absorb about 10 percent of its weight in water, making the bristles slightly softer and less likely to scratch glass. Because of this, it is good practice to start the washer ahead of production by about 15 minutes.
8. Inspect glass to ensure it is completely clean and dry. Daylighting or specific indoor lighting will show these defects easier. Plant lighting, if it is poor, might mask visual defects.
9. Don’t stop glass lites in the glass washer. Low-E glass can “burn” if left stationary under rotating washer brushes. Make certain your washer doesn’t permit glass to be left standing inside. Additionally, ensure that you have adequate run-out at the washer exit to prevent glass edges from hitting each other.
10. Don’t use recycled rinse water unless it is properly treated with a carbon filter or other treatment. A closed-loop treatment and filtration of rinse water will:
- Remove dissolved solids, chlorine and residual soap from the water
- Help to achieve water quality requirements, especially for low-Ecoatings
- Reduce water consumption demand from about 3,000 gallons per shift to about 300 gallons per shift
- Extend the life of the glass washer.
The pictured operator is touching the surface opposite of what will eventually become the IGU seal bonding surface. If you handle both surfaces, re-wash prior to assembling the unit.
11. Don’t touch the surface of the glass lite that will contact the sealant. If you have to handle the glass on both surfaces, re-wash it prior to assembling the IGU.