[audioholic]

Also the black material acts as an intermediate bonding agent between the glue and the glass. Something like a putty or a surrface preparation agent.

[a4anurag]

Thanks to all for the prompt replies and help me clear the doubts that I had from long.

Cheers,
Anurag.

[100kmph]

In our A-Star I have seen that behind the black outlines on the rear glass there are the metal and the plastic covers. IMO the black outline hides the metal,interior fittings or any wiring. From the outside it gives the appearance of a bigger glass.

[SS-Traveller]

Originally Posted by audioholic

Also the black material acts as an intermediate bonding agent between the glue and the glass. Something like a putty or a surrface preparation agent.

That's the main reason for having the black border. Windshield adhesive (usually polyurethane) will not adhere firmly to clean smooth glass. Therefore the edges of the glass are sandblasted and chemically treated for the polyurethane to form a firm bond.

How wide that black margin is, depends on the manufacturer/design team.

Why are windshields stuck on nowadays rather than being mounted with rubber beads as they used to be in older cars? Multiple reasons.

1. Better aerodynamics.

2. Greater structural strength because the bonded windscreens reduce some of the flex in the bodyshell. Notice that hatchbacks?SUVs where the hatch + windscreen is the openable component, the bonded area is wider (than in sedans) to provide better bond and increased structural strength.

3. Safer in an accident (windscreen does not separate from bodyshell).

4. Cheaper to assemble than windscreens mounted with rubber beads (labour intensive, more time consuming).

[chinkara]

Yes, as SS-traveller said.

It hides the bond area, and is made thick to increase the surface area of contact between glass and metal. It may cover some harnesses etc., but that is incidental.

In SUVs and hatches, the area would be typically higher, as the rear windshield experiences more vibration than a sedan when the boot is opened / closed.

The reason bonded windshield is preferred these days is more point (4) above than other things though.

[condor]

Originally Posted by SS-Traveller

4. Cheaper to assemble than windscreens mounted with rubber beads (labour intensive, more time consuming).

I think a beading mount would be quicker & cheaper, as can be seen in cases of replacements of the two types of windshields.

[audioholic]

Time consumption will be lesser on the assembly line with the help of robots or semi assisted machines as the process is straightforward compared to fitting a beeding all around. However it might be time consuming when it comes for replacement as it is skill dependent. When the windshield of my car broke, the only time consuming process was cleaning up of the old glass and glue. Pasting of new glass took less than ten minutes.

[SS-Traveller]

Originally Posted by condor

I think a beading mount would be quicker & cheaper, as can be seen in cases of replacements of the two types of windshields.

In case of replacements, yes (removing bits of the old windscreen is a downright headache! ). On the assembly line, no. Glued windscreens win hands down in saving time and labour.

[condor]

But the back-ground work would be more- preparing the surface, the glue, the frame, and the claddings. Pretty much will bring it to the same point.

[VaahanYogi]

Originally Posted by mpksuhas

It depends on a mix of parameters -
1. To hide the metal frame, glue used to fix the wind shield.
2. To avoid de -fogger metal strip heads being visible from outside
3. Aesthetic appeal.

Agree with parameters-1 & 3. Differ with parameter 2 as I have observed Zens and Esteems with rear defogger and the rear windshield is covered by rubber beeding.

[SS-Traveller]

Originally Posted by condor

But the back-ground work would be more- preparing the surface, the glue, the frame, and the claddings. Pretty much will bring it to the same point.

No. The surface is prepped at the glass manufacturer's end. The bodyshell has the regular paint coat. The glue is applied with a robot arm. Two workers use suction handles to position the glass on to the bodyshell. Job done in 2 minutes - even less. You've got to watch the process in a factory to know how quick it is. More importantly, you've got to have seen how the Amby's windscreens were fixed on, and how much time that took! (and of course, how frequently the beading was not fixed properly and leaked water during the next spell of rain).