Glass Technology



[:Modern windshield or windscreens are generally made of laminated safety glass, a type of treated glass, which consists of two (typically) curved sheets of glass with a plastic layer laminated between them for safety, and are glued into the window frame.][1]



The term windshield is used generally throughout North America. The term windscreen is the usual term in the UK and Australia/New Zealand. Glass windshields first appeared around 1905. The first automobile windshields were a luxury, sold as optional equipment to motorists who needed something a little more dashing than goggles. With the invention of safety glass, tempered glass (tempering is a heat treatment) to make it especially hard and resistant to shattering. This type of windshield was popular well into the middle of the century, but it was eventually replaced by windshields made of laminated glass



Automakers began using laminated safety glass, also known as auto glass, for automobile windshields in 1927. To make laminated safety glass, the manufacturer sandwiches a thin layer of flexible clear plastic film called polyvinyl butyral (PV between two or more pieces of glass. The plastic film holds the glass in place when the glass breaks, helping to lessen injuries from flying glass.



PPG Industries has developed Optech clear coating, it’s made up of a single component designed to provide improved resistance to marring and environmental etch.



According to PPG, the high solids formulation, developed over a six year period, allows it to bond with an adhesive to join the windshield, backlight and sidelight windows to vehicle bodies thereby eliminating the need for a urethane primer commonly used to ensure adhesion.

Optech also meets the Federal Motor Vehicle Safety Standard for windshield retention during roll-over accidents and crashes. The technology can improve scratch and etch resistance characteristics by approximately 25 to 100 percent when compared to conventional one-component clear coats that are currently used, says PPG. Optech is currently being used in two plants in North America.



Laminated glass is a multilayer unit consisting of a plastic layer surrounded by two sheets of glass. In many countries, including the U.S., auto windshields are required by law to be made of laminated glass. Laminated glass can bend slightly under impact and is less likely to shatter than normal safety glass. This quality reduces the risk of injury to the automobile`s passengers.



After the glass is tempered and cleaned, it goes through a laminating process. In this process, two sheets of glass are bonded together with a layer of plastic (the plastic layer goes inside the two glass sheets). The lamination takes place in an autoclave, a special oven that uses both heat and pressure to form a single, strong unit that is resistant to tearing. The plastic interlayer is often tinted to act as an ultraviolet filter.



When laminated glass is broken, the broken pieces of glass remain bound to the internal tear-resistant plastic layer, and the broken sheet remains transparent. Thus, visibility remains good. Unlike traditional safety glass, laminated glass can be further processed—cut, drilled, and edge-worked, as necessary. A typical laminated windshield is very thin: each glass layer is approximately 0.03 inch (0.75 millimetres) thick, while the plastic interlayer is approximately 0.098 inch (2.5 millimetres) thick.



Types of Glass Surface Corrosion



a) Stage I Corrosion [: defined as a surface with light to moderate corrosion damage to the paint surface]



b) Stage II Corrosion [: definition when the dirt/corrosion deposits are no longer on the surface but have started to break down the molecular structure, leaving an etched or white haze on the surface after the stain has been removed, with moderate to serious stains / damage] (See also Glass Cleaning Process article)



Should I repair or replace my windshield?



Be aware the some imperfections cannot be removed (by doing so you will compromise the glass surface optics) and you may have to replace it. If you can catch your fingernail in the scratch 0.4 Mil (0 .004 –inch deep) you should consult a professional glass repair / replacement company.



A replacement windscreen can sometimes be claimed on an insurance policy without loss of no-claim bonus, dependent upon coverage (check first with insurance company).Some windscreen ‘glass’ is actually a plastic resin and will scratch easily, consult your dealer to find out what material was used for the OEM windshield.



There are various types of windshield glass; some newer cars have acoustic glass or rain sensors built in, so be sure you get the correct type of glass. Aftermarket glass is not required to meet the same Federal Motor Vehicle Safety Standards (FMVSS) regulations as OEM glass



OEM glass is usually stronger and this may be important when you realize that the windshield becomes the backing plate for your air bags in a crash. The glass windshield provides up to 60% of the cage strength in the event of a rollover accident. OEM glass is more expensive as it is more costly to make. Yet the windshield may save your life or your family`s lives in a crash. See also -http://www.bestglass.com/faq.html#faq1



Glass Polishing Pad



Groit’s Garage synthetic 6-inch glass polishing pads for use with a random orbital polisher Use these pads along with a glass polish to remove etched water marks and other tenacious surface residue. Once thoroughly cleaned they can be re- used



Alternative - Lake County - GPS PRO Glass Polishing System



Glass Polishing



Common sense dictates that if you want to remove a scratch, then you must remove some of the material (paint, glass, etc) to get down to the bottom of the scratch.



Modern automotive windshields hardness is 6/10 on the Moh’s harness scale and contains a thin plastic sheet between two layers of glass (interior and exterior). Glass is very hard and t he polishing process for the correction of scratches requires pressure, which combined with kinetic energy produces heat, if the glass surface becomes too hot the plastic sheeting can warp leading to distortion. When polishing glass use capacious amounts of water and periodically check the surface temperature



Use caution when polishing glass, especially with polishes that contain abrasives like cerium oxide (belonging to the group of elements known as rare earth) use optical grade only on auto glass and observe all necessary safety precautions (see also personal protection equipment (PPE) with regard to the dust produced. They also have the potential to damage glass by removing layers; compromising its optical clarity, strength and rigidity, necessitating replacement An airbag relies on the glass windshield as it ‘backing plate’ (i.e. it supports the inflated bag and gives it the necessary rigidity, as it is unable to arrest forward motion without some kind of strong support) so don’t do anything that would compromise it.



Once the glass surface has been washed and cleaned (detailers clay) any minor imperfections can be removed with an abrasive glass polish (Autoglym Car Class Polish or Zaino Z-12 Clear-View Glass Polish) Removes "light" scratches, acid water spots, bird and bug stains, including alkaline mineral deposits, and then smoothes out etched glass



If you can catch your fingernail in the scratch 0.4 Mil (10µ) deep, you should consult a professional glass repair / replacement company.



Methodology



• Clean glass to remove dirt, dust or road grime from surfaces



• Use masking tape to protect windscreen rubber sealing



• Apply clay (Magic Clay®) and lubricant solution (WooliteTM / Water 5:1) onto the glass surface (Do not apply to plastic as dulling may occur.)



• Apply a quarter (coin) size amounts of CarPro CeriGlass and an LC Glass polishing pad, is made of dense polyurethane foam with very small cells. The pad’s density enables it to keep the glass polish on the surface, rather than soaking into the foam. You’ll use less polish to get the job done, despite its density, the pad still has plenty of flexibility to conform to the curvature of the glass, speed #4 on a PC random orbital polisher



• Heat caused by abrasive polishing can soften and damage glass; foam pad and product used must minimize heat build-up. Since glass is a poor heat conductor any friction heat built up from polishing must be kept to a minimum by using sufficient product and regular misting of both the polishing pad and glass surface with water.



• Apply to half of the windshield, polishing first in an up and down motion then in a left-to-right motion and then repeat on the other side, proceed to other glass surfaces.



• Go over the glass several times in each direction, glass will polish virtually residue free.



• Wipe off any residue, and polish with a clean dry 100% cotton Micro fibre cloth.



• Inspect glass for clarity and smoothness. Repeat if necessary.



Alternative products / methods:



a) Apply Zaino Z-12 with a damp cotton cloth to cool glass, apply to small sections at a time and allow to completely dry, buffing with a clean dry cotton towel. If there is any smearing or residue left just use Stoner’s Invisible Glass or any good quality glass cleaner to remove excess residue.



b) Glass Technology Inc - Glass Scratch Removal & Glass Scratch Repair | Glass Technology, Inc.



Alternative pads- these 4-inch ‘Metal Polishing Pads’ are made from 600 grit nylon (Scotchbrite®) and are designed for hard / rough surfaces like aluminium diamond plate, pitted aluminium, chrome, and glass. TOL



Glass Scratch / Rock Chip Removers



This glass polishing kit comprises one 2-inch diameter felt bob mounted on a ¼-inch shaft, with a tub of abrasive optical grade Cerium powder. This will remove glass scratches that you can’t feel with your fingernail (approximately 0.004") To remove scratches that you cannot feel with your fingernail, mark them on the inside of the glass with a crayon or a piece of tape. (Deeper scratches may not be possible to completely remove.)



Tape off glass surrounds with 3M Green Tape masking tape, as it’s water-resistant whereas the 3M Blue is not. Mix up a small quantity of the abrasive powder with some water to make wet slurry, and dip the flat end of the felt bob in it and use the fastest electric drill speed available, work the slurry up and down across the scratch until it is removed, keep the surface wet - do not allow the slurry to dry out, otherwise the glass will get hot - Caswell Inc. - Glass Polishing Kit



Note - Do not use an abrasive polish on Targa ‘glass’ tops as they are actually a plastic (Lexan) and an abrasive will remove the tint Suggested product- Plexus (BTI Chemicals Plexus® Glass Polish & Cleaner)



Glass Polishing Kit for Deep Scratches - most glass polishers contain Cerium Oxide an optical polishing compound (belonging to the group of elements known as rare earth) all necessary precautions should be used with regard to the dust produced. Removes deep scratches from automotive glass and save the replacement costs, this abrasive system literally grinds away imperfections until scratches disappear, works best with a Rotary set at 1500-2000 RPM.



The Lake Country Glass Restoration Kit #2 - is for heavy duty glass polishing. This kit will polish and restore automotive glass and other glass surfaces. This machine powered system restores clarity by removing wiper tracks, light scratches, water spots and other minor defects. Designed for use on automotive windshields and Automotive Glass; most other glass surfaces. For use with rotary buffers or dual-action polishers, the kit contains enough materials to polish and seal approximately 7,200 square inches.



Warning- these systems remove glass, maintain a wet surface and keep pad moving to avoid heat build-up and optical distortion





[EDIT; added CarPro CeriGlass 12/14 ]