Case solved! Those little black dots on car windows are actually used for this...

When you are sitting in a car and enjoying the scenery outside, have you ever noticed the circle of black dots on the front windshield of the car? These dots may seem inconspicuous, but they play an important role in the design and function of the car. They are not just decorations, but also have many practical functions.

So, let’s talk about what these black spots on the edges of car glass are used for today?

What are those black spots on my car windows?

Many passengers may touch these inconspicuous black spots when they are free on the road. Their surface feels smooth. On some vehicles, you can even feel slightly raised black spots, but they are firmly attached to the glass and difficult to peel off.

In addition to these small black dots, there is also a circle of black borders around the edge of the car window. This circle of borders, called decorative borders or flower dots, is made of a ceramic-like material and is closely bonded to the glass through screen printing and high-temperature sintering . Before talking about the role of the small black dots, let's first understand the role of these black borders.

The black borders below the black dots. Copyrighted images from the gallery. Reproduction and use may cause copyright disputes.

In old movies and photos, we can see that early car windshields did not use black frames, but metal frames. Car windshields of that era were usually flat. Around the 1950s and 1960s, curved windshields began to appear . With this change, the way windshields were fixed also changed, from metal parts to glue for fixing and sealing .

This transition brought some challenges: first, how to ensure that the glass can be firmly adhered to the car body; second, how to ensure the long-term stability and durability of the glue. The emergence of the black frame just solves these problems. Since the smooth glass surface is not conducive to the adhesion of glue, the rough texture of the black frame provides better adhesion for the glue .

In addition, many organic materials, including commonly used polyurethane sealants, are susceptible to damage from ultraviolet rays, and the black frame plays a role in sun protection. At the same time, it also cleverly shields the glue that fixes the glass, avoiding direct exposure of the glue to the line of sight, and improving the overall aesthetics of the car.

Some people may be curious, since the black borders already have these functions, why do we still need to design small black dots?

Those black spots on the windshield

What is it used for?

Because the glass windows of cars are mounted on metal window frames, the edges of the glass are closely connected to the metal frames. On hot summer days, the metal frames and glass exposed to direct sunlight will experience varying degrees of temperature rise.

Glass absorbs relatively less heat, while metal frames absorb more heat, resulting in a relatively low temperature in the center of the window glass and a higher temperature at the edges and in contact with the metal frame, forming a temperature gradient inside the glass.

Additionally, since objects expand when heated, both the glass and the metal frame will expand accordingly as the temperature rises. Although the glass does not expand as much as the metal frame, in the area where the metal frame contacts, the glass not only has to deal with its own thermal expansion, but also has to be pulled by the expansion of the metal frame.

This dual effect may cause local deformation of the glass. Near the deformation area, there will be interactive internal stress between the edge and the center of the glass, that is, the edge part exerts force inward, while the center part exerts force outward. If the scope of action of this internal stress is small, its effect will be more concentrated. When the interactive force inside the glass reaches a certain level, it may cause the glass to explode.

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To prevent this, technicians designed this layer of black dots on the edge of the car window. Since black has a higher ability to absorb heat, the temperature of the area containing more black elements will be relatively high under direct sunlight. These black dots on the edge of the car window vary in size and density. The closer the black dots are to the edge of the glass, the larger they are and the more heat they absorb; while the closer the black dots are to the center of the glass, the smaller they are and the less heat they absorb.

Through this design, the temperature gradient distribution inside the car window becomes more extensive, the scope of internal stress is also expanded, and the stress effect is weakened accordingly. Such a transition layer helps to reduce the internal stress concentration caused by temperature differences, thereby reducing the risk of glass self-explosion.

The small black dots can also avoid visual distortion

In addition to reducing the risk of glass self-explosion, the black dots can also avoid visual distortion. When we look at the window frame, we will find that the gradient dots or mesh patterns play a soft transition visually, making the black frame not appear too harsh. And in places that are out of our sight, these patterns are silently guarding the safety of drivers and passengers.

This has to start with the manufacturing of the car's front windshield. The car's front windshield usually has a specific curvature, which is achieved through a shaping process at a high temperature of over 700°C. During the glass shaping process, the black frame heats up faster due to its material characteristics, while the glass heats up relatively slowly. This drastic temperature difference between the black frame and the glass may cause changes in the optical properties of the glass, which in turn causes visual distortion , which may interfere with the driver's vision and increase driving risks.

Car windshield shaping process

To solve this problem, technicians designed a gradient dot pattern in the transition area between the black frame and the glass. These patterns help heat to be transferred more evenly to the center of the glass, thereby reducing visual distortion caused by temperature differences , ensuring clear vision for the driver and improving driving safety. Through this ingenious design, the window frame is not only more harmonious visually, but also plays an important role in terms of function.

Planning and production

Source丨Like Popular Science (ID: lxkp_cstam)

Author: Luffy

Editor: Yinuo

Proofread by Xu Lai and Lin Lin

The cover image and the images in this article are from the copyright library

Reprinting may lead to copyright disputes