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The windshield (
North American English North American English (NAmE, NAE) is the most generalized variety of the English language as spoken in the United States and Canada. Because of their related histories and cultures, plus the similarities between the pronunciations (accents), v ...
) or windscreen (
Commonwealth English The use of the English language in current and former Member states of the Commonwealth of Nations, member countries of the Commonwealth of Nations was largely inherited from British Empire, British colonisation, with some exceptions. English s ...
) of an
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
, car,
bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
,
motorbike A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruisin ...
,
truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...
,
train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and Passenger train, transport people or Rail freight transport, freight. Trains are typically pul ...
,
boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats. Small boats are typically found on inl ...
or
streetcar A tram (called a streetcar or trolley in North America) is a rail vehicle that travels on tramway tracks on public urban streets; some include segments on segregated right-of-way. The tramlines or networks operated as public transport are ...
is the front
window A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent materia ...
, which provides visibility while protecting occupants from the elements. Modern windshields are generally made of
laminated safety glass Laminated glass (LG) is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by a thin polymer interlayer, typically of polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), lonoplast polymer ...
, a type of treated glass, which consists of, typically, two curved sheets of
glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
with a
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
layer laminated between them for safety, and bonded into the window frame. Motorcycle windshields are often made of high-impact
polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
or
acrylic Acrylic may refer to: Chemicals and materials * Acrylic acid, the simplest acrylic compound * Acrylate polymer, a group of polymers (plastics) noted for transparency and elasticity * Acrylic resin, a group of related thermoplastic or thermosett ...
plastic.


Usage

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 Laminated glass (LG) is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by a thin polymer interlayer, typically of polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), lonoplast polymer ...
. 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 their body in unison with the machine and does not shield the rider from wind when sitting upright.


Safety

Early windshields were made of ordinary window glass, but that could lead to serious injuries in the event of a crash. A series of crashes 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 Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tens ...
and were fitted in the frame using a
rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...
or
neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion R ...
seal Seal may refer to any of the following: Common uses * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impr ...
. The hardened glass shattered into many mostly harmless fragments when the windshield broke. These windshields, however, could shatter from a simple stone chip. "Triplex" glass laminating, however, had been available for windshields in France from 1911 and in Britain from 1912; it was adopted as an accessory by some high-end American auto manufacturers beginning in 1913, and from 1919 to 1929
Henry Ford Henry Ford (July 30, 1863 – April 7, 1947) was an American industrialist, business magnate, founder of the Ford Motor Company, and chief developer of the assembly line technique of mass production. By creating the first automobile that mi ...
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. The urethane sealant is protected from UV in sunlight by a band of dark dots called a ''
frit A frit is a ceramic composition that has been fused, quenched, and granulated. Frits form an important part of the batches used in compounding enamels and ceramic glazes; the purpose of this pre-fusion is to render any soluble and/or toxic compo ...
'' around the edge of the windshield. The darkened edge transitions to the clear windshield with smaller dots to minimize thermal stress in manufacturing. The same band of darkened dots is often expanded around the rearview mirror to act as a sunshade.


Other aspects

In many places, laws restrict the use of heavily
tinted glass Window film (tint) is a thin laminate film that can be installed to the interior or exterior of glass surfaces in automobiles and boats and also to the interior or exterior of glass in homes and buildings. It is usually made from polyethylene te ...
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 Tin(IV) oxide, also known as stannic oxide, is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin. With many other names, this oxide of tin is an important material in tin ...
to generate
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
to prevent icing. A similar system for automobile windshields, introduced on
Ford Ford commonly refers to: * Ford Motor Company, an automobile manufacturer founded by Henry Ford * Ford (crossing), a shallow crossing on a river Ford may also refer to: Ford Motor Company * Henry Ford, founder of the Ford Motor Company * Ford F ...
vehicles as "
Quickclear Quickclear is a European trademark used by the Ford Motor Company for its electrically heated windshield technology. Instaclear was the name used sometimes in the United States. First seen on the Rolls-Royce in 1969 then the 1985 Ford Scorpio/G ...
" 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 especially on the later European Ford Transit vans. These systems are more typically utilized by European auto manufacturers such as
Jaguar The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus '' Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the th ...
and Porsche. The use of thermal glass prevents some navigation systems from functioning correctly, as the embedded metal blocks the satellite signal. The RF signal tends to flow along the metal wires or layer so very little radiation can pass. This can be resolved by using an external antenna. Mobile telephones can also have problems; thermal glass typically allows only 0.001 (1‰, or one per mille or 1 ppt) of the signal to pass, whereas a concrete wall with rebars allows up to 0.100 (10%, or 100‰) of the signal to pass.


Terminology

The term ''windshield'' is used generally throughout North America. The term ''windscreen'' is the usual term in the
British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, ...
and
Australasia Australasia is a region that comprises Australia, New Zealand and some neighbouring islands in the Pacific Ocean. The term is used in a number of different contexts, including geopolitically, physiogeographically, philologically, and ecologica ...
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. Sports or racing cars would sometimes have aero screens, which were small semi-circular or rectangular windshields. These were often mounted in pairs behind a foldable flat windshield. Aero screens are usually less than in height. They are known as aero screens because they only deflect the wind. The twin aeroscreen setup (often called
Brooklands Brooklands was a motor racing circuit and aerodrome built near Weybridge in Surrey, England, United Kingdom. It opened in 1907 and was the world's first purpose-built 'banked' motor racing circuit as well as one of Britain's first airfields, ...
) 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 A cowl is an item of clothing consisting of a long, hooded garment with wide sleeves, often worn by monks. Originally it may have referred simply to the hooded portion of a cloak. In contemporary usage, however, it is distinguished from a clo ...
to blow
pressurized air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and ...
onto the windshield. Also several glass manufacturers have experimented with nano type coatings designed to repel external contaminants with varying degrees of success but to date none of these have made it to commercial applications.


Certification

Certification of a windshield is necessary to ensure safety. Different counties have made different set of rule that all windshield manufacturers need to comply under Motor Vehicle Acts. Some of the most know certifications are US DOT, EU ECE, Chinese CCC, South African SABS and Indian BIS standards. These certification ensures safety, reliability and quality of a product as per respective legal requirements.


Repair of stone-chip and crack damage

According to the US National Windshield Repair Association, many types of
stone damage Stone damage, or stone-chip, is the damage that gravel and small stones can make to a vehicle. Stone damage is most common on roads on which the allowed speed exceeds , since stones stuck in the tires come loose at that speed and fly away with s ...
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 is within permissible limits; automobile glass with more severe damage needs to be replaced. However, this is dependent on local laws. If a crack extends to the edge of the panel then this would compromise the structural integrity of the windshield. Aircraft windshields are designed in such a way that even if a crack were to extend all the way across the panel, the structural integrity is maintained via multiple failsafe methods in both frame and the glass plies. A sacrificial outer layer that cracks rather than devitrifies is the first failsafe.


Type

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.


Location

Some damages are very difficult to repair, or cannot be repaired: * on inside of the windshield * deep damage on both layers of glass due to solar absorption or oxidation. * damage over rain sensor or internal radio antenna * complex multiple cracks * very long cracks (i.e. over long) * contaminated cracks * edge cracks 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, the 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.


Replacement

Windshields that cannot be repaired have to be replaced. Replacement of a windshield typically takes less than an 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 specified in U.S. Federal Motor Vehicle Safety Standards 212/208 (see
FMVSS The Federal Motor Vehicle Safety Standards (FMVSS) are U.S. federal vehicle regulations specifying design, construction, performance, and durability requirements for motor vehicles and regulated automobile safety-related components, systems, and ...
) to ensure the reliability of adhesive systems. Typically the SDAT is verified with
crash test A crash test is a form of destructive testing usually performed in order to ensure safe design standards in crashworthiness and crash compatibility for various modes of transportation (see automobile safety) or related systems and comp ...
s 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 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 Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...
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 and 50%
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...
. Variations from the ideal curing environment can increase the time needed for a sufficiently safe bond to form. Because of the variables and difficulties involved in mobile windshield replacement, many vehicle manufacturers do not recommend this method of installations.


Disposal

Waste disposal Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment and disposal of waste, together with monitoring ...
of
laminated glass Laminated glass (LG) is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by a thin polymer interlayer, typically of polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), lonoplast polyme ...
is no longer permitted in a landfill in most European countries as the
End of Life Vehicles Directive The End of Life Vehicles Directive is a Directive of the European Union addressing the end of life for automotive products. Every year, motor vehicles which have reached the end of their useful lives create between 8 and 9 million tonnes of ...
(ELV) is implemented. A study by Surrey University and
Pilkington Glass Pilkington is a Japanese-owned glass-manufacturing company which is based in Lathom, Lancashire, United Kingdom. In the UK it includes several legal entities and is a subsidiary of Japanese company NSG Group. Prior to its acquisition by NSG ...
proposes that waste laminated glass be placed into a separating device such as a rolling mill where the glass is fragmented and the larger
cullet Glass recycling is the processing of waste glass into usable products. Glass that is crushed or imploded and ready to be remelted is called cullet. There are two types of cullet: internal and external. Internal cullet is composed of defective p ...
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. One possible method of recycling of simple automotive laminated windshields could involve heating the windshield to above the melting point of the PVB interlayer and then separating the glass plies. This depends chiefly on the differential melting points of PVB and glass and is not suitable for other interlayer materials such as silicone based materials.


See also

* Automotive head-up display *
BS 857 BS 857:1967 is a currently in-use British Standard British Standards (BS) are the standards produced by the BSI Group which is incorporated under a royal charter and which is formally designated as the national standards body (NSB) for the UK. ...
*
Driver visibility A blind spot in a vehicle or vehicle blind spot is an area around the vehicle that cannot be directly seen by the driver while at the controls, under existing circumstances. In transport, driver visibility is the maximum distance at which the dr ...
*
Glass run channel A glass run channel is a groove, normally made of rubber or plastic, that is found around windows (most commonly car windows). The primary purpose of a glass run channel is to provide a seal Seal may refer to any of the following: Common u ...
* Motorcycle windshield *
Windscreen wiper A windscreen wiper, windshield wiper, wiper blade (American English), or simply wiper, is a device used to remove rain, snow, ice, washer fluid, water, or debris from a vehicle's front window. Almost all motor vehicles, including cars, truc ...
*
Windshield sun shade Windshield sun shades (also known as sun-screen shades, sunscreens, sun car shades, sun shields, heat shields, or UV shields) are protective shields attached to a car's windshield or side window to keep the sun from reaching the interior and help re ...


References


Further reading

* How it's made. Series six, Windshields, English saddles, butter, and post clocks * Manufacturing Processes Reference Guide: Robert H. Todd, Dell K. Allen, and Leo Alting *


External links


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
{{Authority control Vehicle parts Glass applications Glass coating and surface modification Vehicle safety technologies Automotive safety Car windows