Automotive glass

May 28, 2024

Date: 28 April 2023

Author: Luc Moeyersons

This information corresponds to our current knowledge on this subject. It is offered solely to provide possible suggestions for your own experimentations. It is not intended, however, to substitute for any testing you may need to conduct to determine for yourself the suitability of our advice for your particular purposes.

This information may be subject to revision as new knowledge and experience become available. Since we cannot anticipate all variations in actual end-use conditions, LAMI-Solutions makes no warranties and assumes no liability in connection with any use of this information.

Nothing in this publication is to be considered as a license to operate under or a recommendation to infringe any patent right.

TABLE OF CONTENTS

1. Introduction1.1. Stages of production1.2. Comments

2. Preparation of glass2.1. Stages of production2.2. The glass2.3. Unloading the glass2.4. Cutting the glass2.5. Breaking out of the glass2.6. Seaming2.7. Washing2.8. Separating Agent2.9. Ceramic band2.10. Coated glass

3. Bending the glass3.1. Sag bending3.2. Press bending3.3. Press assisted bending

4. PVB Preparation4.1. Stages of preparation4.2. Interleaved – Refrigerated4.3. Packaging4.4. Unwinding the roll4.5. Adhesion & Moisture control4.6. Stretching

5. Assembly5.1. Preparation of glass5.2. Assembly room

6. Prepressing6.1. A look at different processes6.2. vacuum ring process6.3. vacuum bag process6.4. Roller process6.5. Ovens in use6.6. Edge sealants6.7. Use of clips6.8. Windscreen stacking

7. Autoclaving7.1. A look at different autoclaves7.2. The purpose of autoclaving7.3. Operational parameters7.4. Risk of volatiles evaporation & autoclave fires7.5. The ideal “practical” autoclave cycle7.6. Possible autoclave cycle improvements7.7. Recommended precautions

8. Windscreen finishing8.1. Encapsulation8.2. Trimming of excess PVB

9. Inspection9.1. Defects in the glass9.2. Defects in the PVB9.3. Defects in the laminated glass9.4. the shape of the windscreen9.5. Laboratory testing

10. Lamination Defects10.1. Bubbles10.2. Bubbles: Rule of thumb on root cause10.3. Delamination

7.1. A look at different autoclaves

◦ All autoclave designs can be different:

7.2. The purpose of autoclaving

◦ To dissolve the residual air and moisture in the PVB.◦ The air moves by diffusion:

◦ The solubility of the air in the PVB is 6.4 x 10 -4 cm 3 /cm 3 PVB/cm Hg (normal temperature and pressure)◦ The air is highly soluble in the PVB.◦ Bonding of the PVB to the glass:

◦ Temperature:

◦ Pressure:

◦ Time:

◦ Note: during the autoclave cycle, compressed air diffuses into PVB-edge and needs app. 96 hours, at room temperature, to diffuse out.

7.3. Operational parameters

◦ Temperature: 135 to 145 deg C◦ Pressure: 8 to 15 Atm (Bar)◦ Time: 30 min. to 4 hrs.◦ Air turbulence:

 “Hot points” PVB flow Poor heat exchange.

7.4. Risk of volatiles evaporation & autoclave fires

◦ The plasticizer evaporates during the autoclave cycle.◦ Plasticizer condenses in the insulation, forming a good fuel. (see also “Architectural Glass – Laminating Guide part 5 chapter K – Autoclave cleaning/purging cycle)◦ Dowanol® TPM.

7.5. The ideal “practical” autoclave cycle

7.6. Possible autoclave cycle improvements

To reduce the risk of edge defects, one could decide to modify the autoclave cycle into a “Olson-Fitzgerald-cycle”.

The autoclave is heated without pressure.Pressure is added from 60° C onwards, till 3.5 bar.This way one obtains a 3rd nip, improving the edge sealing.The 3.5 bar pressure is maintained for at least 20 minutes while heating still continues.After (minimum) 20 minutes the pressure is increased.The goal is to reach maximum temperature and pressure at the same time (energy efficiency).Maximum temperature and pressure are held in line with advised time.(minimum 20 minutes).When the cooling is started, one would expect an automatic reduction of pressure (adiabatic pressure drop) of app. 2 bar. Some autoclaves are set to compensate for this pressure drop.If the autoclave is equipped with an automatic pressure compensation, one could program a 2-bar pressure drop over the cooling step.Maintaining pressure (at its maximum setting) is not really needed and is rather costly (high pressure step).Pressure should drop when 40° C autoclave air temperature is reached (over a longer time > 5 minutes).

7.7. Recommended precautions

◦ Accumulation of plasticizer (and Dowanol®) on the inside of the autoclave should be avoided.◦ Regular steam cleaning or heating up to maximum processing tempearture with pressure release valve open and pressure setting at 0.5 Bar.◦ Avoid all possibility if liquid collection:

◦ Avoid all other sources of ignition:

8.1. Encapsulation

 Polyurethane rim around the windscreen.(injection moulding) Perfect bending is necessary

8.2. Trimming of excess PVB

9.1. Defects in the glass

◦ Scratches◦ Inclusions◦ Chips◦ Glass mismatch

9.2. Defects in the PVB

◦ Inclusions (high intensity illumination)◦ Optical distortion

9.3. Defects in the laminated glass

◦ Bubbles-recuperation◦ Edge defects:

9.4. The Shape of the Windscreen

9.5. Laboratory testing

(see also architectural Glass – Laminating Guide – Part 7: Most Common Laminating Defects and Origin).

10.1. Bubbles

10.1.1. Inside the windscreen:

There is no opening towards the edges.

Causes:

Repair:

o Large bubbles - Noo Bubbles away from the edge - Noo Small bubbles close to the edges:

10.1.2. On the edge of the windscreen:

 Causes:

 Prevention:

 Repair:

10.2. Bubbles: Rule of thumb on root cause

10.3 Delamination

◦ 10.3.1. Inside the windscreen:

◦ 10.3.2. At the edge of the windscreen:

Several causes:* Edge pinching (with clips) (during autoclaving)* Poor adhesion and bending mismatch.* Solvent or moisture attack.