'Sandblasted' windscreen

[Westheath]

Ok .................Lets simplify this.

Bang your door glass window with your hand as hard as you can.

Then I dare you to do same to your windscreen.

But seriously don't do this you will break your windscreen as it much weaker glass.

 

[Craiglxviii]

Ok .................Lets simplify this.

Bang your door glass window with your hand as hard as you can.

Then I dare you to do same to your windscreen.

But seriously don't do this you will break your windscreen as it much weaker glass.

You have that the wrong way around.

Take a window glass and rest it on 4 bricks. Stand on it and it'll shatter.

Do the same with a windscreen. You can jump up and down on it as long as you don't catch the edge.

Believe me, a windscreen is significantly tougher than a side window.

 

[Westheath]

You have that the wrong way around.

Take a window glass and rest it on 4 bricks. Stand on it and it'll shatter.

Do the same with a windscreen. You can jump up and down on it as long as you don't catch the edge.

Believe me, a windscreen is significantly tougher than a side window.

Errrm nope....

 

[Craiglxviii]

Errrm nope....

You know I work in Body Design for a carmaker, right, and windscreen is one of my areas of responsibility?

 

[Westheath]

Well you know I work in the automotive world as well actually repairing cars at workshop level.

Windscreen glass can be cut with a glass cutter if the roof been chopped and you need to make the screen smaller, cut both sides heat up the laminate and trim off with a modelling knife.

You cant do that to tempered/toughened glass because its many times harder.

The weakest point of tempered/toughened glass used in doors and rear screen is the edge, its where thieves push a screwdriver against the door frame and lever against the edge of the glass to shatter it.



http://www.autoglass-atlanta.com/tempered-laminated/

 

[Craiglxviii]

Well you know I work in the automotive world as well actually repairing cars at workshop level.

Windscreen glass can be cut with a glass cutter if the roof been chopped and you need to make the screen smaller, cut both sides heat up the laminate and trim off with a modelling knife.

You cant do that to tempered/toughened glass because its many times harder.

The weakest point of tempered/toughened glass used in doors and rear screen is the edge, its where thieves push a screwdriver against the door frame and lever against the edge of the glass to shatter it.



http://www.autoglass-atlanta.com/tempered-laminated/

So you don't work with design and test standards then... and yes I know, we have our own pro thief.

Side door glass is so strong that it can (and does) shatter after having a small handful of granite gravel thrown at it 3-4 times. Your windscreen will stand that on a daily basis for years.

There's a big difference between hardness and toughness (and resilience for that matter). Windscreens are designed to absorb and dissipate impact energy both via the PVB interlayer, which allows for elastic deformation, and the continuous edge bonding which transmits impact energy into the pillars/ cowl top/ roof bow. As the glass is fully supported it is very strong.

Side door glass is just a piece of tempered float glass. Same for the rear screen.

 

[Westheath]

You have that the wrong way around.

Take a window glass and rest it on 4 bricks. Stand on it and it'll shatter.

Do the same with a windscreen. You can jump up and down on it as long as you don't catch the edge.

Believe me, a windscreen is significantly tougher than a side window.

The above is statement is completely wrong (back to front).

Your summary of how automotive glass actually performs in the real world is wrong as well.

I suggest going to a windscreen installation company and trying to convince them of your opinions on what they work with every day.

Don't be too offended when they tear you a new one

 

[Craiglxviii]

The above is statement is completely wrong (back to front).

Your summary of how automotive glass actually performs in the real world is wrong as well.

I suggest going to a windscreen installation company and trying to convince them of your opinions on what they work with every day.

Don't be too offended when they tear you a new one

I'll ask the bloke who designs them, then the bloke who tests them, in the morning eh?

 

[craigdm]

Had mine changed a few weeks ago. Called Autoglass out as I thought I had a chip. The guy kindly pointed out that it was a chip which had already been repaired, but also spotted just how badly the windscreen was pitted. Said he's seen quite a few Mercs in the same state. Certainly never seen this before in any of the 50+ cars I have previously owned.

Anyway I rung the dealer who wanted £700 to replace the screen, so I decided to risk Autoglass. Apart from the inconvenience of having to drop the car off (as the ILS needed calibrating), I can't fault the work they did. It's even a proper MB screen with the signature.

 

[Man in Black]

Had mine changed a few weeks ago. Called Autoglass out as I thought I had a chip. The guy kindly pointed out that it was a chip which had already been repaired, but also spotted just how badly the windscreen was pitted. Said he's seen quite a few Mercs in the same state. Certainly never seen this before in any of the 50+ cars I have previously owned.

Anyway I rung the dealer who wanted £700 to replace the screen, so I decided to risk Autoglass. Apart from the inconvenience of having to drop the car off (as the ILS needed calibrating), I can't fault the work they did. It's even a proper MB screen with the signature.

Thanks, craigdm. That is the feedback I have been receiving from other Merc owners. Strangely, not so many from this site. May I ask how much Autoglass charged for the complete job?
Many thanks.
Man in Black

 

[V6Matty]

It's not really a Mercedes problem but I do know where your coming from, my 211 had this but I didn't notice it unoversell over 120k, my brothers previous Volvo V50 used to suffer the same again around 70k he started to notice it. On the other hand my wife's 169 at around 70k now hasn't a sign of this so I'd say it could be generally a work conditions thing rather than a bad design with mercs

While I think about it, I'd almost wager that people notice it more on cars that ae a few years old that haven't had a windscreen replacement, I know with my 211 I had 3 windscreens in 2 years all due to stone hits that couldn't be repaired

 

[LostKiwi]

I think it most likely a problem for vehicles doing high numbers of motorway miles at high speeds.
Also car aerodynamics may come into play as well with respect to the way the particles are directed over the roof or into the glass.

I've not really noticed it any worse on MBs compared to other vehicles per se.
I do remember my 1995 Saab 900 as being quite bad though!

 

[Rory]

Sorry to disabuse, but replacement screens (even Autoglass labelled or whatever) branded come direct from the same factory as the OEM screen. Ask me how I know this.

Hmmm...even Autoglass's own website says they use glass from OEM or "other suppliers".

 

[V6Matty]

Hmmm...even Autoglass's own website says they use glass from OEM or "other suppliers".

There's only about 3 manufacturers in the world these days I think

 

[C350Carl]

The above is statement is completely wrong (back to front).

Your summary of how automotive glass actually performs in the real world is wrong as well.

I suggest going to a windscreen installation company and trying to convince them of your opinions on what they work with every day.

Don't be too offended when they tear you a new one

I’m fairly certain (although no expert) that the windscreen provides structural integrity to most cars.

So I would expect it to be tougher than side windows.

One thing to prove this (and I’ve done this recently on a demonstration for a different reason than just to break some glass)

Take an ordinary spark plug and hit the spark plug on the ceramic bit so it breaks. Take a small piece of the ceramic and flick it at a side window. The glass will shatter into hundreds of pieces and fall out the door. Mostly on first go but certainly within 2-3 attempts.

Do it with a windscreen and it will just bounce off.

 

[C350Carl]

This video should help as well. I have this rescue tool (which I was also using in the demonstration)

Watch what happens to the side window vs to windscreen.

 

[LostKiwi]

I’m fairly certain (although no expert) that the windscreen provides structural integrity to most cars.

So I would expect it to be tougher than side windows.

One thing to prove this (and I’ve done this recently on a demonstration for a different reason than just to break some glass)

Take an ordinary spark plug and hit the spark plug on the ceramic bit so it breaks. Take a small piece of the ceramic and flick it at a side window. The glass will shatter into hundreds of pieces and fall out the door. Mostly on first go but certainly within 2-3 attempts.

Do it with a windscreen and it will just bounce off.

That's due to the treatment on the glass.
Toughened glass has a heat treatment applied which puts the outer skin of the glass under tension. If this is scratched then the tension imbalance causes the glass to shatter.
Laminated glass has no such tensions built into the glass and is simply 'normal' glass bonded to a tough plastic inner core.

Spark plug ceramic is incredibly hard so will scratch the skin of toughened glass very easily resulting in the shattering.

 

[C350Carl]

Agreed. My point being that the windscreen is far more resilient (or can withstand more) than a side window.

Unless of course it’s bulletproof.

 

[MalcQV]

Interesting. The windscreen in my CLK is the worst I have ever seen for pitted marks. I assume it is the original and somebody earlier mentioned Northwest and road chippings. I wonder. That said I have never seen a windscreen so bad as this on 25 cars I have had in my driving time.
It does have two small chips that could probably be repaired but I am seriously thinking about a replacement windscreen.

Debate regarding side glass and windscreen. As an engineer logically I expect the windscreen to be far stronger than a side window. Would like to hear the outcome of Craiglxviii's discussion with the designer.

 

[Craiglxviii]

Right, OK. I didn't get the chance to post this yesterday. Carl is correct, windscreens (frontal) are indeed structural members (in a way) in their own right, dependent on the car. They are designed to, and thus are strong enough to carry some transverse force loading as they contribute to roof stiffness.

Car windscreens are designed to withstand impacts from certain objects, ranging from chickens (to simulate bird strikes- think of the infamous Space Shuttle tests) to gravel chippings, to test chippings of various sizes to represent stone impacts.

Side door and rear door glass are designed to fill a hole, with the thickness being determined by whichever OEM's engineering design standards manual.

I'll go back to my point about the gravel. Take a parked car. Flick a slack handful of gravel that you've collected from the road into a door side window. It'll bounce off. Repeat in the same spot 2-3 times. The window will shatter and fall into itself. Almost noiseless. It's one of the tea-leaves' most favourite methods of breaking into a car; if they're caught by the police all they have on them is a pocked full of gravel so they can't be done for Going Prepared.

The following is quite interesting, it's always good to look at fact and data so here's some. Page 12 has the test results.

https://www.google.fr/url?sa=t&rct=...?la=en&usg=AFQjCNEWA8t1YZp0DMvi05IlV8SfJWOy9g

For a 5mm thick car windscreen, to get full penetration a 25mm concrete ball needs to hit the car square on at 58m/s, equivalent to the car doing 204km/h with that 25mm ball being thrown off the overpass at it. For a 50mm dia ball that drops to 118km/h. Substitute for steel balls and the respective velocities required roughly halve.

By the way, the impact energy of the 25mm concrete and steel balls are almost identical: 35 and 33J respectively. To put into context a standard test .22LR round has 168J, 5.56NATO has 1,800J and 7.62NATO 3,255J.

Now for float glass. Glass that is categorized as "attack resistant" is tested with a 100mm dia steel ball dropped from 1,500mm. That gives an impact energy of 58J. To withstand this, the glass must be able to take 3 strikes dropped in a triangular pattern 100mm on a side without collapsing. The minimum single thickness of float glass that achieves this is 12mm. Car side door glass are not made to this test standard or anything like it.

Now ask yourself how fast a 25mm concrete ball would need to go to completely penetrate a 3mm thick piece of tempered float glass.