A manual transmission known as a manual gearbox, a standard transmission or colloquially in some countries as a stick shift, is a type of transmission used in motor vehicle applications. It uses a driver-operated clutch engaged and disengaged by a foot pedal or hand lever, for regulating torque transfer from the engine to the transmission. A conventional 5-speed manual transmission is the standard equipment in a base-model vehicle, while more expensive manual vehicles are equipped with a 6-speed transmission instead; the number of forward gear ratios is expressed for automatic transmissions as well. Manual transmissions feature a driver-operated clutch and a movable gear stick. Most automobile manual transmissions allow the driver to select any forward gear ratio at any time, but some, such as those mounted on motorcycles and some types of racing cars, only allow the driver to select the next-higher or next-lower gear; this type of transmission is sometimes called a sequential manual transmission.
In a manual transmission, the flywheel is attached to the engine's crankshaft and spins along with it. The clutch disc is in between the pressure plate and the flywheel, is held against the flywheel under pressure from the pressure plate; when the engine is running and the clutch is engaged, the flywheel spins the clutch plate and hence the transmission. As the clutch pedal is depressed, the throw out bearing is activated, which causes the pressure plate to stop applying pressure to the clutch disk; this makes the clutch plate stop receiving power from the engine, so that the gear can be shifted without damaging the transmission. When the clutch pedal is released, the throw out bearing is deactivated, the clutch disk is again held against the flywheel, allowing it to start receiving power from the engine. Manual transmissions are characterized by gear ratios that are selectable by locking selected gear pairs to the output shaft inside the transmission. Conversely, most automatic transmissions feature epicyclic gearing controlled by brake bands and/or clutch packs to select gear ratio.
Automatic transmissions that allow the driver to manually select the current gear are called manumatics. A manual-style transmission operated by computer is called an automated transmission rather than an automatic though no distinction between the two terms need be made. Contemporary automobile manual transmissions use four to six forward gear ratios and one reverse gear, although consumer automobile manual transmissions have been built with as few as two and as many as seven gears. Transmissions for heavy trucks and other heavy equipment have 8 to 25 gears so the transmission can offer both a wide range of gears and close gear ratios to keep the engine running in the power band. Operating aforementioned transmissions use the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gear selection. French inventors Louis-Rene Panhard and Emile Levassor are credited with the development of the first modern manual transmission, they demonstrated their three-speed transmission in 1894 and the basic design is still the starting point for most contemporary manual transmissions.
This type of transmission offered multiple gear ratios and, in most cases, reverse. The gears were engaged by sliding them on their shafts, which required careful timing and throttle manipulation when shifting, so the gears would be spinning at the same speed when engaged; these transmissions are called sliding mesh transmissions or sometimes crash boxes, because of the difficulty in changing gears and the loud grinding sound that accompanied. Newer manual transmissions on 4+-wheeled vehicles have all gears mesh at all times and are referred to as constant-mesh transmissions, with "synchro-mesh" being a further refinement of the constant mesh principle. In both types, a particular gear combination can only be engaged when the two parts to engage are at the same speed. To shift to a higher gear, the transmission is put in neutral and the engine allowed to slow down until the transmission parts for the next gear are at a proper speed to engage; the vehicle slows while in neutral and that slows other transmission parts, so the time in neutral depends on the grade and other such factors.
To shift to a lower gear, the transmission is put in neutral and the throttle is used to speed up the engine and thus the relevant transmission parts, to match speeds for engaging the next lower gear. For both upshifts and downshifts, the clutch is released; some drivers use the clutch only for starting from a stop, shifts are done without the clutch. Other drivers will depress the clutch, shift to neutral engage the clutch momentarily to force transmission parts to match the engine speed depress the clutch again to shift to the next gear, a process called double clutching. Double clutching is easier to get smooth, as speeds that are close but not quite matched need to speed up or slow down only transmission parts, whereas with the clutch engaged to the engine, mismatched speeds are fighting the rotational inertia and power of the engine. Though automobile and light truck transmissions are now universally synchronized, transmissions for heavy trucks and machinery, motor
The United Kingdom the United Kingdom of Great Britain and Northern Ireland, sometimes referred to as Britain, is a sovereign country located off the north-western coast of the European mainland. The United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland, many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state, the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to the east, the English Channel to the south and the Celtic Sea to the south-west, giving it the 12th-longest coastline in the world; the Irish Sea lies between Great Ireland. With an area of 242,500 square kilometres, the United Kingdom is the 78th-largest sovereign state in the world, it is the 22nd-most populous country, with an estimated 66.0 million inhabitants in 2017. The UK is constitutional monarchy; the current monarch is Queen Elizabeth II, who has reigned since 1952, making her the longest-serving current head of state.
The United Kingdom's capital and largest city is London, a global city and financial centre with an urban area population of 10.3 million. Other major urban areas in the UK include Greater Manchester, the West Midlands and West Yorkshire conurbations, Greater Glasgow and the Liverpool Built-up Area; the United Kingdom consists of four constituent countries: England, Scotland and Northern Ireland. Their capitals are London, Edinburgh and Belfast, respectively. Apart from England, the countries have their own devolved governments, each with varying powers, but such power is delegated by the Parliament of the United Kingdom, which may enact laws unilaterally altering or abolishing devolution; the nearby Isle of Man, Bailiwick of Guernsey and Bailiwick of Jersey are not part of the UK, being Crown dependencies with the British Government responsible for defence and international representation. The medieval conquest and subsequent annexation of Wales by the Kingdom of England, followed by the union between England and Scotland in 1707 to form the Kingdom of Great Britain, the union in 1801 of Great Britain with the Kingdom of Ireland created the United Kingdom of Great Britain and Ireland.
Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain and Northern Ireland. There are fourteen British Overseas Territories, the remnants of the British Empire which, at its height in the 1920s, encompassed a quarter of the world's land mass and was the largest empire in history. British influence can be observed in the language and political systems of many of its former colonies; the United Kingdom is a developed country and has the world's fifth-largest economy by nominal GDP and ninth-largest economy by purchasing power parity. It has a high-income economy and has a high Human Development Index rating, ranking 14th in the world, it was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries. The UK remains a great power, with considerable economic, military and political influence internationally, it is sixth in military expenditure in the world. It has been a permanent member of the United Nations Security Council since its first session in 1946.
It has been a leading member state of the European Union and its predecessor, the European Economic Community, since 1973. The United Kingdom is a member of the Commonwealth of Nations, the Council of Europe, the G7, the G20, NATO, the Organisation for Economic Co-operation and Development and the World Trade Organization; the 1707 Acts of Union declared that the kingdoms of England and Scotland were "United into One Kingdom by the Name of Great Britain". The term "United Kingdom" has been used as a description for the former kingdom of Great Britain, although its official name from 1707 to 1800 was "Great Britain"; the Acts of Union 1800 united the kingdom of Great Britain and the kingdom of Ireland in 1801, forming the United Kingdom of Great Britain and Ireland. Following the partition of Ireland and the independence of the Irish Free State in 1922, which left Northern Ireland as the only part of the island of Ireland within the United Kingdom, the name was changed to the "United Kingdom of Great Britain and Northern Ireland".
Although the United Kingdom is a sovereign country, Scotland and Northern Ireland are widely referred to as countries. The UK Prime Minister's website has used the phrase "countries within a country" to describe the United Kingdom; some statistical summaries, such as those for the twelve NUTS 1 regions of the United Kingdom refer to Scotland and Northern Ireland as "regions". Northern Ireland is referred to as a "province". With regard to Northern Ireland, the descriptive name used "can be controversial, with the choice revealing one's political preferences"; the term "Great Britain" conventionally refers to the island of Great Britain, or politically to England and Wales in combination. However, it is sometimes used as a loose synonym for the United Kingdom as a whole; the term "Britain" is used both as a synonym for Great Britain, as a synonym for the United Kingdom. Usage is mixed, with the BBC preferring to use Britain as shorthand only for Great Britain and the UK Government, while accepting that both terms refer to the United K
Automotive design is the process of developing the appearance, to some extent the ergonomics, of motor vehicles, including automobiles, trucks, buses and vans. The functional design and development of a modern motor vehicle is done by a large team from many different disciplines included within automotive engineering, design roles are not associated with requirements for Professional or Chartered-Engineer qualifications. Automotive design in this context is concerned with developing the visual appearance or aesthetics of the vehicle, though it is involved in the creation of the product concept. Automotive design as a professional vocation is practiced by designers who may have an art background and a degree in industrial design or transportation design. Terminology used in the field is found in the glossary of automotive design; the task of the design team is split into three main aspects: exterior design, interior design, color and trim design. Graphic design is an aspect of automotive design.
Design focuses not only on the isolated outer shape of automobile parts, but concentrates on the combination of form and function, starting from the vehicle package. The aesthetic value will need to correspond to ergonomic utility features as well. In particular, vehicular electronic components and parts will give more challenges to automotive designers who are required to update on the latest information and knowledge associated with emerging vehicular gadgetry dashtop mobile devices, like GPS navigation, satellite radio, HD radio, mobile TV, MP3 players, video playback, smartphone interfaces. Though not all the new vehicular gadgets are to be designated as factory standard items, some of them may be integral to determining the future course of any specific vehicular models; the designer responsible for the exterior of the vehicle develops the proportions and surfaces of the vehicle. Exterior design is first done by a series of manual drawings. Progressively, drawings that are more detailed are executed and approved by appropriate layers of management.
Industrial plasticine and or digital models are developed from, along with the drawings. The data from these models are used to create a full-sized mock-up of the final design. With three- and five-axis CNC milling machines, the clay model is first designed in a computer program and "carved" using the machine and large amounts of clay. In times of high-class 3d software and virtual models on power walls, the clay model is still the most important tool to evaluate the design of a car and, therefore, is used throughout the industry; the designer responsible for the vehicles' interior develops the proportions, shape and surfaces for the instrument panel, door trim panels, pillar trims, etc. Here the emphasis is on the comfort of the passengers; the procedure here is the same as with exterior design. The color and trim designer is responsible for the research and development of all interior and exterior colors and materials used on a vehicle; these include paints, fabric designs, grains, headliner, wood trim, so on.
Color, contrast and pattern must be combined to give the vehicle a unique interior environment experience. Designers work with the exterior and interior designers. Designers draw inspiration from other design disciplines such as: industrial design, home furnishing and sometimes product design. Specific research is done into global trends to design for projects two to three model years in the future. Trend boards are created from this research in order to keep track of design influences as they relate to the automotive industry; the designer uses this information to develop themes and concepts that are further refined and tested on the vehicle models. The design team develops graphics for items such as: badges, dials, kick or tread strips, liveries; the sketches and rendering are transformed into 3D Digital surface modelling and rendering for real-time evaluation with Math data in initial stages. During the development process succeeding phases will require the 3D model developed to meet the aesthetic requirements of a designer and well as all engineering and manufacturing requirements.
The developed CAS digital model will be re-developed for manufacturing meeting the Class-A surface standards that involves both technical as well as aesthetics. This data will be further developed by Product Engineering team; these modelers have a background in Industrial design or sometimes tooling engineering in case of some Class-A modelers. Autodesk Alias and ICEM Surf are the two most used software tools for Class-A development. Several manufacturers have varied development cycles for designing an Automobile, but in practice these are the following. Design and User Research Concept Development sketching CAS Clay modeling Interior Buck Model Vehicle ergonomics Class-A Surface Development Colour and Trim Vehicle GraphicsThe design process occurs concurrently with other product Engineers who will be engineering the styling data for meeting performance and safety regulations. From mid-phase and forth interactions between the designers and product engineers culminates into a finished product be manufacturing ready.
Apart from this the Engineering team parallelly works in the following areas. Product Engineering, NVH Development team, Prototype
A brand is an overall experience of a customer that distinguishes an organization or product from its rivals in the eyes of the customer. Brands are used in business and advertising. Name brands are sometimes distinguished from generic or store brands; the practice of branding is thought to have begun with the ancient Egyptians, who were known to have engaged in livestock branding as early as 2,700 BCE. Branding was used to differentiate one person’s cattle from another's by means of a distinctive symbol burned into the animal’s skin with a hot branding iron. If a person stole any of the cattle, anyone else who saw the symbol could deduce the actual owner. However, the term has been extended to mean a strategic personality for a product or company, so that ‘brand’ now suggests the values and promises that a consumer may perceive and buy into. Over time, the practice of branding objects extended to a broader range of packaging and goods offered for sale including oil, wine and fish sauce. Branding in terms of painting a cow with symbols or colors at flea markets was considered to be one of the oldest forms of the practice.
Branding is a set of marketing and communication methods that help to distinguish a company or products from competitors, aiming to create a lasting impression in the minds of customers. The key components that form a brand's toolbox include a brand’s identity, brand communication, brand awareness, brand loyalty, various branding strategies. Many companies believe that there is little to differentiate between several types of products in the 21st century, therefore branding is one of a few remaining forms of product differentiation. Brand equity is the measurable totality of a brand's worth and is validated by assessing the effectiveness of these branding components; as markets become dynamic and fluctuating, brand equity is a marketing technique to increase customer satisfaction and customer loyalty, with side effects like reduced price sensitivity. A brand is, in essence, a promise to its customers of what they can expect from products and may include emotional as well as functional benefits.
When a customer is familiar with a brand, or favours it incomparably to its competitors, this is when a corporation has reached a high level of brand equity. Special accounting standards have been devised to assess brand equity. In accounting, a brand defined as an intangible asset, is the most valuable asset on a corporation’s balance sheet. Brand owners manage their brands to create shareholder value, brand valuation is an important management technique that ascribes a monetary value to a brand, allows marketing investment to be managed to maximize shareholder value. Although only acquired brands appear on a company's balance sheet, the notion of putting a value on a brand forces marketing leaders to be focused on long term stewardship of the brand and managing for value; the word ‘brand’ is used as a metonym referring to the company, identified with a brand. Marque or make are used to denote a brand of motor vehicle, which may be distinguished from a car model. A concept brand is a brand, associated with an abstract concept, like breast cancer awareness or environmentalism, rather than a specific product, service, or business.
A commodity brand is a brand associated with a commodity. The word, derives from its original and current meaning as a firebrand, a burning piece of wood; that word comes from the Old High German and Old English byrnan and brinnan via Middle English as birnan and brond. Torches were used to indelibly mark items such as furniture and pottery, to permanently burn identifying marks into the skin of slaves and livestock; the firebrands were replaced with branding irons. The marks themselves took on the term and came to be associated with craftsmen's products. Through that association, the term acquired its current meaning. Branding and labelling have an ancient history. Branding began with the practice of branding livestock in order to deter theft. Images of the branding of cattle occur in ancient Egyptian tombs dating to around 2,700 BCE. Over time, purchasers realised that the brand provided information about origin as well as about ownership, could serve as a guide to quality. Branding was adapted by farmers and traders for use on other types of goods such as pottery and ceramics.
Forms of branding or proto-branding emerged spontaneously and independently throughout Africa and Europe at different times, depending on local conditions. Seals, which acted as quasi-brands, have been found on early Chinese products of the Qin Dynasty. Identity marks, such as stamps on ceramics, were used in ancient Egypt. Diana Twede has argued that the "consumer packaging functions of protection and communication have been necessary whenever packages were the object of transactions", she has shown that amphorae used in Mediterranean trade between 1,500 and 500 BCE exhibited a wide variety of shapes and markings, which consumers used to glean information about the type of goods and the quality. Systematic use of stamped labels dates from around the fourth century BCE. In a pre-literate society, the shape of the amphora and its pictorial markings conveyed information about the contents, region of o
A tire or tyre is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface traveled over. Most tires, such as those for automobiles and bicycles, are pneumatically inflated structures, which provide a flexible cushion that absorbs shock as the tire rolls over rough features on the surface. Tires provide a footprint, designed to match the weight of the vehicle with the bearing strength of the surface that it rolls over by providing a bearing pressure that will not deform the surface excessively; the materials of modern pneumatic tires are synthetic rubber, natural rubber and wire, along with carbon black and other chemical compounds. They consist of a body; the tread provides traction. Before rubber was developed, the first versions of tires were bands of metal fitted around wooden wheels to prevent wear and tear. Early rubber tires were solid. Pneumatic tires are used on many types of vehicles, including cars, motorcycles, trucks, heavy equipment, aircraft.
Metal tires are still used on locomotives and railcars, solid rubber tires are still used in various non-automotive applications, such as some casters, carts and wheelbarrows. The word tire is a short form of attire, from the idea; the spelling tyre does not appear until the 1840s when the English began shrink fitting railway car wheels with malleable iron. Traditional publishers continued using tire; the Times newspaper in Britain was still using tire as late as 1905. The spelling tyre began to be used in the 19th century for pneumatic tires in the UK; the 1911 edition of the Encyclopædia Britannica states that "he spelling'tyre' is not now accepted by the best English authorities, is unrecognized in the US", while Fowler's Modern English Usage of 1926 says that "there is nothing to be said for'tyre', etymologically wrong, as well as needlessly divergent from our own older & the present American usage". However, over the course of the 20th century, tyre became established as the standard British spelling.
The earliest tires were bands of leather iron placed on wooden wheels used on carts and wagons. The tire would be heated in a forge fire, placed over the wheel and quenched, causing the metal to contract and fit on the wheel. A skilled worker, known as a wheelwright, carried out this work; the first patent for what appears to be a standard pneumatic tire appeared in 1847 lodged by the Scottish inventor Robert William Thomson. However, this never went into production; the first practical pneumatic tire was made in 1888 on May Street, Belfast, by Scots-born John Boyd Dunlop, owner of one of Ireland's most prosperous veterinary practices. It was an effort to prevent the headaches of his 10-year-old son Johnnie, while riding his tricycle on rough pavements, his doctor, John Sir John Fagan, had prescribed cycling as an exercise for the boy, was a regular visitor. Fagan participated in designing the first pneumatic tires. Cyclist Willie Hume demonstrated the supremacy of Dunlop's tires in 1889, winning the tire's first-ever races in Ireland and England.
In Dunlop's tire patent specification dated 31 October 1888, his interest is only in its use in cycles and light vehicles. In September 1890, he was made aware of an earlier development but the company kept the information to itself. In 1892, Dunlop's patent was declared invalid because of prior art by forgotten fellow Scot Robert William Thomson of London, although Dunlop is credited with "realizing rubber could withstand the wear and tear of being a tire while retaining its resilience". John Boyd Dunlop and Harvey du Cros together worked through the ensuing considerable difficulties, they employed inventor Charles Kingston Welch and acquired other rights and patents which allowed them some limited protection of their Pneumatic Tyre business's position. Pneumatic Tyre would become Dunlop Tyres; the development of this technology hinged on myriad engineering advances, including the vulcanization of natural rubber using sulfur, as well as by the development of the "clincher" rim for holding the tire in place laterally on the wheel rim.
Synthetic rubbers were invented in the laboratories of Bayer in the 1920s. In 1946, Michelin developed the radial tire method of construction. Michelin had bought the bankrupt Citroën automobile company in 1934, so it was able to fit this new technology immediately; because of its superiority in handling and fuel economy, use of this technology spread throughout Europe and Asia. In the U. S. the outdated bias-ply tire construction persisted, with market share of 87% as late as 1967. Delay was caused by tire and automobile manufacturers in America "concerned about transition costs." In 1968, Consumer Reports, an influential American magazine, acknowledged the superiority of radial construction, setting off a rapid decline in Michelin's competitor technology. In the U. S. the radial tire now has a market share of 100% in automobiles. Today, over 1 billion tires are produced annually in over 400 tire factories. There are 2 aspects to. First, tension in the cords pull on the bead uniformly around the wheel, except where it is reduced above the contact patch.
Second, the bead transfers that net force to the rim. Air pressure, via the ply cords, exerts tensile force on the entire bead surrounding th
Targa top, or targa for short, is a semi-convertible car body style with a removable roof section and a full width roll bar behind the seats. The term was first used on the 1966 Porsche 911 Targa, it remains a registered trademark of Porsche AG; the rear window is fixed, but on some targa models, it is removable or foldable, making it a convertible-type vehicle. Any piece of fixed metal or trim which rises up from one side, over the roof and down the other side is sometimes called a targa band, targa bar, or a wrapover band. Targa tops are different from T-tops, which have a solid, non-removable bar running between the top of the windscreen and the rear roll-bar, have two separate roof panels above the seats that fit between the window and central t-bar; the word targa first came into use from the 1965 Porsche 911 Targa, though it was not the first to use the removable roof panel system. The system first appeared in 1957 on the limited-production Fiat 1200 “Wonderful” by Vignale, designed by Giovanni Michelotti.
The Triumph TR4 from 1961, another Michelotti design featured a similar system, defined by Triumph as a surrey top. The 1964 SAAB Catherina prototype and the 1965 Toyota Sports 800 both used similar systems before the 1966 Porsche 911 Targa; the targa style roof opening became popular in the 1960s and 1970s, when there were fears that the Department of Transportation in the United States would ban convertibles, due to concerns over the safety of occupants when a car overturns. As a result, manufacturers adopted Targa T-tops; as Porsche helped to popularise this body style, they took out a trademark for the Targa name and manufacturers sought for alternative names for their removable tops. Porsche got the name "Targa" from the Targa Florio, the road race in Sicily where Porsche was successful. Targa means "plate" in Italian. Targa and T-top numbers have declined as manufacturers discontinued them in favour of full convertibles with retractable hardtops and folding metal roofs such as the Mercedes-Benz SLK, by better structural engineering with pop-up roll over bars behind the seats and front roll-over bar incorporated into the front windscreen, 1996 saw the debut of a retractable glass roof in the Porsche 993 Targa, a design continued on the 996 and 997 Targa.
The glass roof retracted underneath the rear window revealing a large opening. A shade was there to help prevent the greenhouse effect of the closed roof; this system was a complete redesign, as previous Targa models had a removable roof section and a wide B-pillar functioning as a roll bar. The new glass roof design allowed the 993 Targa to retain nearly the same side-on profile as the other 911 Carrera variants and eliminated the inconvenience of storing the removed top of the old system; the Targa had the body of the Cabriolet with the Targa glass roof replacing the fabric roof. The 911 Targa gained a lifting hatchback glass window. This, in turn, was used on the 997 model of 911. With the introduction and production of the latest 911, the Type 991, Porsche decided to take the latest Targa in a different direction from that of the previous water-cooled Type 996/997 cars; the latest Targa was introduced in 2014 and unlike the Type 993/996/997 Targas, the new car has somewhat returned to its earliest Targa roots by the utilizing of a solid roof panel spanning over the front seats.
However unlike the manual lift-out panels of earlier 911s, the Type 991 Targa's roof panel is mechanized for automated lift-away and storage under the rear glass roof, which itself is mechanized to lift up and out of the way as the roof panel is placed into its stowed position. The Type 991 Targa brings back the styling feature of the'Targa bar', the most obvious and overt design cue of the air-cooled generation Targas, but unlike the previous Targa hoops, the one used on the Type 991 is in sections, where the horizontal span member is a physically separate piece that itself is mechanized to lift off of its vertical supports in order to allow the solid roof panel and its motorized components to slide rearwards as the panel is being stored within the car. Ferrari introduced a hybrid variation of the targa roof and folding metal roof with the 180 degree rotating roof featured on the 2005 Ferrari 575M Maranello Superamerica; the concept was used in the 2010 Renault Wind. T-top Hardtop Bimini top Dodger
Poly known as acrylic, acrylic glass, or plexiglass as well as by the trade names Crylux, Acrylite and Perspex among several others, is a transparent thermoplastic used in sheet form as a lightweight or shatter-resistant alternative to glass. The same material can be used as a casting resin, in inks and coatings, has many other uses. Although not a type of familiar silica-based glass, the substance, like many thermoplastics, is technically classified as a type of glass hence its occasional historical designation as acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate; the material was developed in 1928 in several different laboratories by many chemists, such as William Chalmers, Otto Röhm, Walter Bauer, was first brought to market in 1933 by German Röhm & Haas AG and its partner and former U. S. affiliate Rohm and Haas Company under the trademark Plexiglas. PMMA is an economical alternative to polycarbonate when tensile strength, flexural strength, polishability, UV tolerance are more important than impact strength, chemical resistance and heat resistance.
Additionally, PMMA does not contain the harmful bisphenol-A subunits found in polycarbonate. It is preferred because of its moderate properties, easy handling and processing, low cost. Non-modified PMMA behaves in a brittle manner when under load under an impact force, is more prone to scratching than conventional inorganic glass, but modified PMMA is sometimes able to achieve high scratch and impact resistance; the first acrylic acid was created in 1843. Methacrylic acid, derived from acrylic acid, was formulated in 1865; the reaction between methacrylic acid and methanol results in the ester methyl methacrylate. Polymethyl methacrylate was discovered in the early 1930s by British chemists Rowland Hill and John Crawford at Imperial Chemical Industries in England. ICI registered the product under the trademark Perspex. About the same time and industrialist Otto Röhm of Rohm and Haas AG in Germany attempted to produce safety glass by polymerizing methyl methacrylate between two layers of glass.
The polymer separated from the glass as a clear plastic sheet, which Röhm gave the trademarked name Plexiglas in 1933. Both Perspex and Plexiglas were commercialized in the late 1930s. In the United States, E. I. du Pont de Nemours & Company subsequently introduced its own product under the trademark Lucite. In 1936 ICI Acrylics began the first commercially viable production of acrylic safety glass. During World War II both Allied and Axis forces used acrylic glass for submarine periscopes and aircraft windshields and gun turrets. Airplane pilots whose eyes were damaged by flying shards of PMMA fared much better than those injured by standard glass, demonstrating better compatibility between human tissue and PMMA than glass. Civilian applications followed after the war. Common orthographic stylings include polymethyl polymethylmethacrylate; the full IUPAC chemical name is poly. Although PMMA is called "acrylic", acrylic can refer to other polymers or copolymers containing polyacrylonitrile. Notable trade names include Acrylite, Lucite, R-Cast, Optix, Oroglas, Altuglas and Sumipex.
PMMA is produced by emulsion polymerization, solution polymerization, bulk polymerization. Radical initiation is used, but anionic polymerization of PMMA can be performed. To produce 1 kg of PMMA, about 2 kg of petroleum is needed. PMMA produced by radical polymerization is atactic and amorphous; the glass transition temperature of atactic PMMA is 105 °C. The Tg values of commercial grades of PMMA range from 85 to 165 °C. PMMA is thus an organic glass at room temperature; the forming temperature goes up from there. All common molding processes may be used, including injection molding, compression molding, extrusion; the highest quality PMMA sheets are produced by cell casting, but in this case, the polymerization and molding steps occur concurrently. The strength of the material is higher than molding grades owing to its high molecular mass. Rubber toughening has been used to increase the toughness of PMMA to overcome its brittle behavior in response to applied loads. PMMA can be joined using cyanoacrylate cement, with heat, or by using chlorinated solvents such as dichloromethane or trichloromethane to dissolve the plastic at the joint, which fuses and sets, forming an invisible weld.
Scratches may be removed by polishing or by heating the surface of the material. Laser cutting may be used to form intricate designs from PMMA sheets. PMMA vaporizes to gaseous compounds upon laser cutting, so a clean cut is made, cutting is performed easily. However, the pulsed lasercutting introduces high internal stresses along the cut edge, which on exposure to solvents produce undesirable "stress-crazing" at the cut edge and several millimetres deep. Ammonium-based glass-cleaner and everything short of soap-and-water produces similar undesirable crazing, sometimes over the entire surface of th