Mainland High School
Blinding Light: ISTF 06-1439
PVB and Windshield Manufacturing

The following manufacturing process is closer to that of the aftermarket, windshield replacement process. The windshields used in the production of entire automobiles are made on a much lager scale for mass volume and high speed production.

Windshield manufacturing is done in an assembly line manner which contains two components: Float Glass and Polyvinyl Butyral (PVB) Interlayer. The manufacturing company buys these components from a supplier and combines them to make a windshield in a process called laminating.

The float glass layers from the factory are curved together as matching pairs byseparately heating them to 620 degrees Celsius. The temperature is varied widely so as to formcomplex shapes, required by today's varying windshield design, through press-bending or regular gravity sagging. The shaped glass pairs are then cooled to room temperature before the PVB laminate can be sandwiched between them. This lamination process is actually forming a safety glazing that keeps the glass in place in case of breakage and affords the driver some degree of visibility in emergency situations.


Image courtesy of Answers.com


The PVB is bought in large rolls and goes to a multistage process before being combined with the float glass and placed into the furnace. PVB is refrigerated in storage or interleaved because at room temperature the polymer becomes soft and tacky, making it stick together.1 A processing line is used to manipulate the PVB into the desired shape, thickness and curvature, to cut it, and to stack it with the sheets of float glass.

If the PVB has a sunshade band along the top edge then the PVB is sent through a manipulation process to shape the PVB. A machine begins the shaping and curving process by using a moderate amount of heat to first soften and thin the PVB sheet so that it can attain a curve when it is later rolled over a conical roller while under tension to stretch one side of the film.  This is done so that the sunshade band has a proper curvature to match the roofline of the car that will receive the windshield.


Image courtesy of AYROX: PVB Treatment


The second step is to run the PVB through a relaxation unit. This step requires at least half an hour for the PVB to settle into its final shape and curvature.


Image courtesy of AYROX: PVB Treatment


The final step in this process is the cutting of the PVB into individual sheets. This machine can cut the PVB at an angle from 0 to 25 degrees to accommodate the different shapes of car models.  This process is done to reduce the amount of waste involved with cutting excess PVB from a rectangular sheet.


Image courtesy of AYROX: PVB Treatment


After the glass is bent it is put inside a vacuum bag. When under the vacuum condition the pressure holds the PVB in place between the layers of glass to remove air bubbles. The vacuum bags are then put into an oven called an autoclave which heats the vacuumed windshield. The entire setup reaches 135C to 145C, thereby melting the PVB, making it transparent, and fusing the three layers into one. The quality of lamination, or adhesiveness between the PVB and the layers of float glass, are dependent on the temperature within the autoclave and the effectiveness of the pressure on the layers of glass and PVB. A combination of vacuum packing and pressurized heated air inside the autoclave must be 175 psi for the PVB to adhere to both layers of glass. Before going into the autoclave the PVB appears opaque due to a pattern embossed on the surface that severely diffracts light.2 The autoclave uses heat and pressure to press out the embossed pattern and dissolve any trapped air. If the temperature is too low, the PVB will not melt entirely and will remain cloudy.  If it is too hot the PVB will discolor.


Image courtesy of Sean B.








Rob Vandal
  1  email correspondence 19 February 2007
  2  email correspondence 19 February 2007

AYROX: PVB Treatment
  http://www.ayrox.com/PDF/PVB%20line.pdf

How Products are Made: Automotive Windshield
  http://www.madehow.com/Volume-1/Automobile-Windshield.html

Glass Association of North America: Float Glass Manufacturing Video
  http://www.glasswebsite.com/video/fgmd.asp

Pilkington: Automotive Products Processes
  http://www.pilkington.com/Automotive+International/technology+and+processes/auto+products+processes.htm


Copyright 2006-2007
Mainland High School ISTF
Volusia County Schools

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