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The windshield or windscreen (some commonwealth countries) of an aircraft, car, bus, motorbike or tram is the front window. Modern windshields 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 bonded into the window frame. Motorbike windshields are often made of high-impact acrylic plastic.
Windshields protect the vehicle's occupants from wind and flying debris such as dust, insects, and rocks, and provide an aerodynamically formed window towards the front. UV coating may be applied to screen out harmful ultraviolet radiation. However, this is usually unnecessary since most auto windshields are made from laminated safety glass. The majority of UV-B is absorbed by the glass itself, and any remaining UV-B together with most of the UV-A is absorbed by the PVB bonding layer.
On motorbikes their main function is to shield the rider from wind, though not as completely as in a car, whereas on sports and racing motorcycles the main function is reducing drag when the rider assumes the optimal aerodynamic configuration with his or her body in unison with the machine, and does not shield the rider from wind when sitting upright.
Early windshields were made of ordinary window glass, but that could lead to serious injuries in the event of a crash. A series of lawsuits led up to the development of stronger windshields. The most notable example of this is the Pane vs. Ford case of 1917 that decided against Pane in that he was only injured through reckless driving. They were replaced with windshields made of toughened glass and were fitted in the frame using a rubber or neoprene seal. The hardened glass shattered into many mostly harmless fragments when the windshield broke. These windshields, however, could shatter from a simple stone chip. In 1919, Henry Ford solved the problem of flying debris by using the new French technology of glass laminating. Windshields made using this process were two layers of glass with a cellulose inner layer. This inner layer held the glass together when it fractured. Between 1919 and 1929, Ford ordered the use of laminated glass on all of his vehicles.
Modern, glued-in windshields contribute to the vehicle's rigidity, but the main force for innovation has historically been the need to prevent injury from sharp glass fragments. Almost all nations now require windshields to stay in one piece even if broken, except if pierced by a strong force. Properly installed automobile windshields are also essential to safety; along with the roof of the car, they provide protection to the vehicle's occupants in the case of a roll-over accident.
Today’s windshields are a safety device just like seat belts and airbags. The installation of the auto glass is done with an automotive grade urethane designed specifically for automobiles. The adhesive creates a molecular bond between the glass and the vehicle. If the adhesive bond fails at any point on the glass it can reduce the effectiveness of the air bag and substantially compromise the structural integrity of the roof.
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In many places, laws restrict the use of heavily tinted glass in vehicle windshields; generally, laws specify the maximum level of tint permitted. Some vehicles have noticeably more tint in the uppermost part of the windshield to block sunglare.
In aircraft windshields, an electric current is applied through a conducting layer of tin(IV) oxide to generate heat to prevent icing. A similar system for automobile windshields, introduced on Ford vehicles as "Quickclear" in Europe ("InstaClear" in North America) in the 1980s and through the early 1990s, used this conductive metallic coating applied to the inboard side of the outer layer of glass. Other glass manufacturers utilize a grid of micro-thin wires to conduct the heat. These systems are more typically utilized by European auto manufacturers such as Jaguar and Porsche.
Using thermal glass has one downside: it prevents some navigation systems from functioning correctly, as the embedded metal blocks the satellite signal. This can be resolved by using an external antenna. Even mobile-phones can have problems, typically thermal glass will only allow one (1) per mille/‰ (0.0001) of the signal to pass.. compared to a concrete wall with rebars that allows up to 10% of the signal to pass (per mille/‰ 0.0100).
|This section does not cite any references or sources. (December 2013)|
The term windshield is used generally throughout North America. The term windscreen is the usual term in the British Isles and Australasia for all vehicles. In the US windscreen refers to the mesh or foam placed over a microphone to minimize wind noise, while a windshield refers to the front window of a car. In the UK, the terms are reversed, although generally, the foam screen is referred to as a microphone shield, and not a windshield.
Auto windshields less than 20 cm (8 in) in height are sometimes known as aeroscreens since they only deflect the wind. The twin aeroscreen setup (often called Brooklands) was popular among older sports and modern cars in vintage style.
A wiperless windshield is a windshield that uses a mechanism other than wipers to remove snow and rain from the windshield. The concept car Acura TL features a wiperless windshield using a series of jet nozzles in the cowl to blow pressurized air onto the windshield.
Repair of stone-chip and crack damage
According to the US National Windshield Repair Association many types of stone damage can be successfully repaired. Whether the windshield can be repaired always depends upon four factors: the size, type, depth, and location of the damage.
Size and depth
Repair of cracks up to 61 cm (24 in) is within permissible limits, auto glass with more severe damage needs to be replaced.
Circular Bullseyes, linear cracks, crack chips, dings, pits, and star-shaped breaks can be repaired without removing the glass, eliminating the risk of leaking or bonding problems sometimes associated with replacement.
If the damage is in the driver’s line of sight or very near the windshield’s edge, usually it cannot be repaired.
Some damages are very difficult to repair, or cannot be repaired:
- on inside of the windshield
- deep damage on both layers of glass
- damage over rain sensor or internal radio antenna
- damages that reach into the driver’s critical viewing area
- complex multiple cracks
- very long cracks (i.e. over 18 - 24 inches long)
- contaminated cracks
- edge cracks and chips
In cracked windshield repair, air is removed from the damaged area on the windshield with a specified vacuum injection pump. Then using the injection pump, clear adhesive resin is injected to replace the air in the windshield crack. The resin is then cured with an ultraviolet light. When done properly, the damaged area’s strength is restored, as is 90–95% of the clarity. Auto glass chip repair usually take about 15–20 minutes.
Windshields that cannot be repaired have to be replaced. Replacement of a windshield typically takes less than 1 hour. To ensure the vehicle is safe to drive, time values called the Safe Drive Away Time have been established. Windshields which have been replaced must cure or bond sufficiently until they are able to withstand the forces of a crash. Knowing the minimum time needed to cure the glass bonding adhesives is therefore important. This safe drive away time (SDAT) or minimum drive away time (MDAT) refers to the time required until a windshield installation or glass replacement is considered safe to drive again. Criteria are speified in U.S. Federal Motor Vehicle Safety Standards 212/208 (see FMVSS) to ensure the reliability of adhesive systems. Typically the SDAT is verified with crash tests as well as with high speed laboratory test methods.
Consumers may be unaware that the MDAT or SDAT time is focused on safety and not necessarily on the quality, durability, or warranty of the installation. Care must be taken not to drive the vehicle prior to the SDAT/MDAT.
Airbags deploy at speeds up to 89 m/s (200 mph) and in some cases exert tremendous force on the windshield. Occupants can impact the airbag just 50 ms after initial deployment. Depending on vehicle design, airbag deployment and/or occupant impact into the airbag may increase forces on the windshield, dramatically in some cases. Forces of occupants on the airbags - and hence the potential forces on the windshield - are lower for belted occupants. As consequence, adhesive suppliers usually inform their customers about the level of security achieved:
1) Example: Security exceeding FMVSS 212/208 belted
2) Example: Security exceeding FMVSS 212/208 unbelted
With the advent of quick cure adhesives, mobile windshield replacements have become more prevalent. Often the temperature and humidity cannot be controlled for mobile installations. For most common glass adhesives the ideal environment is 70 degrees fahrenheit and 50% humidity. Variations from the ideal curing environment can increase the time needed for a sufficiently safe bond to form. A controlled environment always ensures the performance and safety of the windshield installation.
If not properly cured, the adhesive bond could fail during a crash, allowing occupants to be injured, ejected, or causing other harm. Because of the variables and difficulties involved in mobile windshield replacement, many vehicle manufacturers do not recommend this method of installation.
Waste disposal of laminated glass is no longer permitted in landfill in most European countries as the End of Life Vehicles Directive (ELV) is implemented. A study by Surrey University and Pilkington Glass proposes that waste laminated glass is placed into a separating device such as a rolling mill where the glass is fragmented and the larger cullet is mechanically detached from the inner film. The application of heat then melts the laminating plastic, usually Polyvinyl Butyral "PVB" enabling both the glass and the interior film to be recycled. The PVB recycling process is a simple procedure of melting and reshaping it. A Yorkshire consortium of CO2Sense and Ecofillers Ltd estimate that in the UK the potential market for recycled PVB in 2020 may reach a value of around £5,000.
- Automotive head-up display
- BS 857
- Driver visibility
- Car glass
- Motorcycle windshield
- Windscreen wiper
- Windshield visor
- Glass run channel
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- "Your Windshield is Not Just a "Wind-Shield" Any More". National Glass Association. Archived from the original on 2 August 2009.
- "Is Your Windshield Repairable?". Car Windshield Info. Retrieved 22 February 2014.
- "Windshield Repair FAQ's". Patsco windshield repair. Retrieved 14 December 2013.
- Cognard, Philippe (2006). Handbook of Adhesives and Sealants. Elsevier. ISBN 978-0080447087.
- Bob Stenzel: Determining SDAT, AGRR Magazine, March/April 2012, page 29-30
- Exposing Industry Shortcuts to SDAT Recommendations, http://www.sika.com/en/solutions_products/Sika%20Industry%20Business/01a001/noshortcutstosafety/nsts_4.html
- Premium Adhesive Systems, AGRR Magazine, March/April 2012, Page 15
- "Laminated Car Windscreen Recycling" (pdf). Archived from the original on 2008-10-31.
Manufacturing Processes Reference Guide: Robert H. Todd, Dell K. Allen, and Leo Alting How It's Made: Windshields
- UNECE Reg. 43 Safety glazing material
- BS 857:1967 Specification for safety glass for land transport
- National Glass Association
- Auto Glass Replacement Safety Standards Council
- How It's Made: Windshields
- Repair of Laminated Automotive Glass Standard
- Windsor, H. H., Jr., ed. (September 1933). "Shatter Proof Glass Found In Laboratory Accident". Popular Mechanics (Chicago, IL ISA: Popular Mechanics) 60 (3): 337. Retrieved 2013-12-02.