Quality control isn’t about preventing just the most egregious failure possibilities. It’s about setting high standards so that products are reliable for years. Control of quality standards for adhesive bonding of dissimilar materials plays a massive role in not only ensuring recalls and warranty claims are minimized but, more importantly, to find the sweet spot of quality that indicates an efficient and optimized process while also reducing costs due to scrap, rework, costly repairs and time spent trying to solve problems.
For businesses manufacturing windows for structures and buildings, quality control standards play a large role in manufacturing due to the risk and cost involved in creating a product that interacts so closely with consumers.
The seals between glass panes and the often plastic or composite sashes they are set into need to meet hefty standards. Weak seals at these interfaces can lead to recalls and brand damage related to higher heating and cooling costs for the manufacturer’s customers, or even a high risk failure such as the glass panel detaching.
The key to ensuring this never occurs is to not tolerate substandard adhesion, by knowing how to accurately predict it before a repair is needed.
How to Seal a Glass Pane to a Composite Frame
Residential and industrial glass windows do not just sit in their frames. In order to keep the weather out and the comfort in, a strong seal needs to be created between the glass and the material the frame is made out of. Depending on the application, frames are usually made from a polymeric material or an advanced composite.
For an adhesive to bond to glass with any strength at all, the glass needs to be thoroughly cleaned. There are many ways to do this, but the most common is a manual wipe with isopropyl alcohol (IPA). A cloth dampened with IPA is run along the edge of the glass panel to remove contaminants and create a surface that is ready for adhesion. But, our experience has shown otherwise.
BTG Labs once made a visit to a window manufacturer’s facility who was having reliability issues with adhesion and in response, the manufacturer added this exact hand wiping process.
In order to gain more knowledge of what was actually happening on the glass surfaces, we conducted a test of cleanliness on glass that hadn’t been wiped down yet and compared it to glass that had been wiped down by a team member using their standard process. The test revealed that the ‘unprepared’ surface was the exact same as the ‘prepared’ surface. This additional step the manufacturer added was not having the intended effect.
To learn more about how to create zero defect production processes, download our free eBook: Predictable Adhesion in Manufacturing Through Process Veriﬁcation
An IPA wipe can absolutely clean a surface, including glass, but in this case it was not removing a contaminant that was on the surface which was causing the failures they were experiencing.
Another company called upon BTG Labs to help them reduce costly field repairs due to poor bonding of their windows. Now, these weren’t windows falling out of ten story buildings, but the quality of these seals was not meeting the required thresholds and nothing the company did was able to consistently solve the problem.
Both of these companies decided to implement a plasma treatment process to activate the glass surface and make it bondable. Plasma treatment is an automatable process that activates a material surface by bombarding it with an energized gas, creating a highly reactive and bondable surface. A reactive surface is what materials scientists call a high energy surface. Surface energy is a way of talking about how attractive the molecules on a surface are to other molecules it comes in contact with. An optimized and monitored plasma treatment system is an excellent way to achieve a high energy surface.
One of the benefits of an atmospheric pressure plasma treatment system is that it can target a slim and sometimes curved edge of a glass window, increasing the efficiency of the process.
How to Measure Surface Energy in an Automated Process
For a plasma treatment system to help companies reach their quality goals, the process needs to be verified and monitored to ensure that the surface energy is rising to the level necessary to create a strong bond.
Using a simple contact angle measurement through an in-line, automated inspection system both companies were able to quantitatively assess the cleanliness of the glass before and after plasma treatment, guaranteeing that the surface met the new surface quality standards. A contact angle measurement deposits a drop of liquid on a surface and measures the extent to which that drop beads up or wets out on the surface. A clean surface with high surface energy will attract that drop and it will wet out, spreading over the surface and producing a low contact angle. A low energy surface will repel the drop causing it to bead up, creating a high contact angle.
The contact angle directly correlates with the amount of surface energy a material has and is a ruthless predictor of adhesion. What’s more is, this simple test is able to be done directly on parts as they move through the production process so there don’t have to be any samples used and scrapped or time wasted setting up a whole new inspection area. Contact angles are also able to be measured on curved surfaces, even from the side, so a pane of glass laying horizontally can have each edge measured without any loss of accuracy or time.
Rapid and reliable surface quality tests that are sensitive to the molecular changes that directly affect the strength of an adhesive bond are critical to having a meaningful impact on reducing or completely removing the risk of problems in the field or repairs needed.
To learn more about how to create zero defect production processes that meet the most stringent quality tolerances, download our free eBook: Predictable Adhesion in Manufacturing Through Process Veriﬁcation.