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, in finding 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.
Manufacturers of windows for buildings and structures place great emphasis on quality control standards during production. They consider the potential risks and expenses associated with creating a product that has direct interaction with customers. This is a key aspect of their professional approach toward manufacturing.
It is crucial that the seals connecting glass panes and the sashes, which are usually made of plastic or composite materials, meet rigorous 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 not tolerating substandard adhesion by knowing how to accurately predict it before a repair is needed.
Residential and industrial glass windows do not just sit in their frames. To keep the weather out and the comfort in, a strong seal needs to be created between the glass and the frame's material. Depending on the application, frames are usually made from polymeric material or an advanced composite.
For an adhesive to bond to glass with any strength, 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 ready for adhesion. But our experience has shown otherwise.
Brighton Science once visited a window manufacturer’s facility that was having reliability issues with adhesion. 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.
An IPA wipe can absolutely clean a surface, including glass, but in this case, it was not removing a contaminant on the surface, causing the failures they were experiencing.
Another company called upon Brighton Science 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 solve the problem consistently.
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 attracted 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 the slim and sometimes curved edge of a glass window, increasing the process's efficiency.
A plasma treatment system must help companies reach their quality goals by verifying and monitoring the process to ensure that the surface energy rises to the level necessary to create a strong bond.
Using contact angle measurements, 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 and creating a high contact angle.
The contact angle directly correlates with the material's surface energy and is a ruthless predictor of adhesion. What’s more, this simple test can be done directly on parts as they move through the production process, so no samples have to be used and scrapped or time wasted setting up a whole new inspection area. Contact angles can also be measured on curved surfaces, even from the side, so a pane of glass lying 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 meaningfully reducing or completely eliminating the risk of problems in the field or needed repairs.
To learn more about creating zero-defect production processes that meet the most stringent quality tolerances, download our free eBook, The Future of Manufacturing: A Guide to Intelligent Adhesive Bonding Technologies & Methodologies.