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Polyurethane Flush Sealing Dramatically Reduces Automotive-Glass Scrap

Image: Dariia/Adobe Stock car interior with sunroof
Consumer preference for panoramic windows and roofs in cars sent reject rates soaring for glass suppliers and glass processors. Technology developed by BBG offered a remedy.

Mold-encapsulated glass for automotive applications based on a polyurethane (PUR) flush sealing technique is less prone to breakage than conventional processes, according to BBG GmbH, a mold maker and developer of plastics processing machinery that developed the technology. PUR encapsulation results in a noticeable reduction in reject rates and improves precision, according to the company. Customers using the technology reportedly have reduced rework by 25%. PUR flush sealing is suitable for single-pane tempered glass, laminated glass, and more fragile semi-tempered glass.

The adoption of ncreasingly thinner and larger automotive glass panels, as well as the integration of features in switchable smart glass, present suppliers with new challenges. “People are moving away from the classic sliding/tilting sunroof and are choosing panoramic windows and roofs,” explained Bernhard Satzger, BBG Senior Sales and Project Manager. The reason is simple, he added: “[They] allow more light into the interior of a car. Customers currently appreciate a bright ambience that creates a feeling of open space around them," said Satzger.

It is also worth noting that panoramic sunroofs allow car manufacturers to reduce the overall weight of the vehicle. In extreme cases, the entire roof can be designed as a glass panel, resulting in considerable weight and cost savings. "This trend is very strong at the moment,” said Satzger, “but it presents glass suppliers and glass processors with new challenges."

According to Tier 1 supplier Continental, the average car has about five square meters (53.8 square feet) of glass. A large panoramic sunroof adds another 2.5 square meters of glass. Before automotive glass is installed in vehicles, it is placed in a PUR frame.

Glass panel encapsulation challenges.

Large-format glass panels may have wavy edges and bending deviations up to 5 mm (0.19 in.), making them difficult to handle and encapsulate.

Bent glass panels that are several square meters in size and with complex geometries are usually made of multi-layer laminated glass. Glass panels have a total thickness of 4.8 to 6 mm and are prone to develop cracks during PUR encapsulation. Since the glass panels sometimes are very wavy, polyurethane can leak onto the inside of the panel during the encapsulation process. The leakage "causes imprecise edges and has to be removed by hand," said Satzger. "This can take five minutes per panel."

Satzger was not prepared to accept that larger glass formats would automatically lead to more breakage and rework. He spent more than a year studying ways to improve the PUR encapsulation process, an effort that ultimately proved successful.

Good enough from the first shot.

Satzger's results got rave reviews from BBG customers. "We had no glass breakage! Normally, some glass panels break when a new glass encapsulation mold is run,” said one customer. “With our mold based on the new PUR flush sealing concept, we got it right from the very beginning. All further shots were equally successful."

The PUR-glass flush result also was successful. "The new concept completely avoids any unwanted leakage of the polyurethane on the inside of the glass panel,” said Satzger. “Instead, a precise boundary is formed between the glass and plastic when it is encapsulated with PUR. If the glass panel comes with wavy edges, there might be some minimal film residue, but this can be easily removed with a pumice sponge."

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Polyurethane (PUR) encapsulation of a large panoramic sunroof made of laminated glass is shown in a mold without (top) and with the new BBG PUR flush sealing concept.

Dramatic decrease in reject rates.

"Glass breakage has decreased dramatically and rework times have dropped from four to one minute per panel in a benchmark comparison," said Satzger. The number of OK-quality parts has increased dramatically, and manufacturing times have been reduced. The customer, who is a glass supplier to the automotive industry, is very satisfied with the result, according to Satzger. The cost to redesign the existing mold to include the new BBG PUR flush sealing concept has “already paid off within in a short period of time,” he said.

Another glass supplier to the automotive industry, who experienced an up to 50% reject rate for 10,000 panoramic glass panels, was able to slash scrap to less than 1% by using a PUR flush sealing mold.

In addition to end-to-end production lines, BBG designs, develops, and manufactures molds for processing PUR, PVC, TPE, and other elastomers, as well as a range of composite materials. The company has expertise in PUR composite spray molding, long fiber injection), resin transfer molding, sheet molding compounds, and glass mat reinforced thermoplastics. The family-owned business in Mindelheim/Allgau, German, also focuses on solutions for lightweight construction, composites processing, and the production of fiber-composite components for various sectors. In 2020, BBG broke new ground with the development and construction of packaging machines for pharmaceutical products and food supplements.

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