Tempered Glass Articles

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"We All Wash Our Glass and Our Hands"

Washing flat glass prior to tempering is another issue. Encouraged by experts to avoid the scratched, pockmarked and dented glass that can result from tempering unwashed glass, washing also serves the basic purpose of keeping the tempering furnace clean. Once dirt or particles from the edging process are introduced into the furnace, it can build up on the conveyance rollers, eventually damaging glass as it flows through the system. Other times, particles such as glass fines from the cutting or edging process and handling smudges that are not washed off the surface of glass before tempering will bake onto the surface, causing blemishes.

Whether from dirty rollers or debris on the glass surface, unclean furnace conditions can cause small "pimples" on the surface not visible to the casual viewer. This pimpling condition is described throughout the industry by various names, including "orange peel," "heat prickling," "seeds," "bubbles," or just plain "garbage" that was not washed off prior to the glass entering the tempering furnace. During normal window cleaning after building construction, the pimples can be scraped off and then dragged across the glass surface, causing scratches.

Dan Fields, a third-generation window cleaner and owner of Fields Window Cleaning in Livermore, CA, said he first became aware of the problem more than three years ago when he was consulted in an insurance lawsuit. Since learning about the causes of tempered glass with these pimples, Fields has become an outspoken advocate of glass washing, writing articles and traveling to industry conferences to spread the word.

He named several West Coast temperers whose glass is regularly found to be pimpled during window cleaning—companies whose windows he refuses to clean.

"I've lost jobs when I've refused to wash (blemished) glass," he said, "but I end up getting them back."

Though no standard for washing tempered glass exists, most tempering facilities do wash all glass prior to tempering as a matter of good practice. "Glass comes to the temperer with interleaving powder, sometimes a carbon-dioxide film and some handling smudges. Cutting and edging adds a little oil, chips and other smudges," explained Miles. "While there might be a reason for not washing the glass prior to tempering, I cannot imagine what it might be."

Lutz remarked, "PPG has a proprietary coating and surface protection, so washing removes this coating and any residue from the edge seaming process, as well as any cutting chips and marks left by handling."

"Foreign matter on the glass can become fused to the glass during tempering," added Aldrich. "If you don't wash the glass, you cannot control this."

Still, some resistance to washing glass before tempering remains, especially in cases where the application does not demand high-quality tempered glass or due to the expense of the glass washing system.

In particular, washing glass before tempering is imperative if there is to be any treatment after tempering. As Lyle Hill, president of MTH Industries in Chicago observed, in the case of glass to be laminated, etched or sandblasted, "If not washed first, the glass will be virtually useless." He added, "I know there is an additional cost for washing, but there needs to be some discernment as to where and how the glass will be used."

Further, evidence does not support the cost argument for not washing glass prior to tempering. According to Bob Lang, sales manager for Zelionople, PA-based Billco Manufacturing, a manufacturer of glass washers, "The cost of a glass washer is often less than ten percent of the cost of a tempering furnace. It's minuscule compared to the furnace investment and the potential cost of customer rejects."

"The tempering companies that don't wash prior to tempering just say there is no ASTM standard that requires them to, even though they should know it's bad practice not to," noted Fields.

In addition to washing glass prior to tempering, many temperers also regularly clean the surface of the rollers in the tempering furnace, a process called honing. "We clean our furnace rollers every week to prevent a buildup of contamination," said Aldrich. This practice also extends the life of the rollers, which are expensive to replace.

Despite the fact that no standard for washing tempered glass exists, most temperers do not believe the industry should adopt one.

"We don't need more regulation, especially regarding washing," said Sugano. "I can't believe there would be a temperer who wouldn't wash glass. You're ruining your most expensive piece of equipment."

"I think it's so obvious people should do it, there is no need (for standardization)," said Lutz. Miles compared it to the most basic act of cleanliness: "We all wash our glass and our hands . . ."

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