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99-491: It can be used to destroy bunkers and other fortifications during assault operations; it can also destroy other designated targets using the dual mode rocket, and main battle tanks using the high-explosive anti-tank rocket. Operations in Afghanistan and Iraq saw a thermobaric rocket added (described as a "novel explosive" (NE)), which can collapse a building. The SMAW system (launcher, ammunition and logistics support)

198-440: A copolymer with polyfunctional curatives or hardeners . This curing is what produces the qualities of the substance such as resistance, durability, versatility, and adhesion. In principle, any molecule containing a reactive hydrogen may react with the epoxide groups of the epoxy resin. Common classes of hardeners for epoxy resins include amines, acids, acid anhydrides, phenols, alcohols and thiols. Relative reactivity (lowest first)

297-472: A pillbox can be killed with flamethrowers . Complex, well-built and well-protected fortifications are often vulnerable to attacks on access points. If the exits to the surface can be closed off, those manning the facility can be trapped. The fortification can then be bypassed. Famous bunkers include the post-World War I Maginot Line on the French eastern border and Czechoslovak border fortifications mainly on

396-456: A calculated amount of bisphenol A and then a catalyst is added and the reaction heated to circa 160 °C (320 °F). This process is known as "advancement". As the molecular weight of the resin increases, the epoxide content reduces and the material behaves more and more like a thermoplastic . Very high molecular weight polycondensates (ca. 30,000–70,000 g/mol) form a class known as phenoxy resins and contain virtually no epoxide groups (since

495-418: A catalyst. The resulting material has ether linkages and displays higher chemical and oxidation resistance than typically obtained by curing with amines or anhydrides. Since many novolacs are solids, this class of hardeners is often employed for powder coatings . Also known as mercaptans, thiols contain a sulfur which reacts very readily with the epoxide group, even at ambient or sub-ambient temperatures. While

594-578: A cured network. This process is known as catalytic homopolymerisation. The resulting network contains only ether bridges, and exhibits high thermal and chemical resistance, but is brittle and often requires elevated temperature for the curing process, so finds only niche applications industrially. Epoxy homopolymerisation is often used when there is a requirement for UV curing, since cationic UV catalysts may be employed (e.g. for UV coatings ). Polyfunctional primary amines form an important class of epoxy hardeners. Primary amines undergo an addition reaction with

693-453: A house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with fiber-reinforced plastic shells. Bunkers deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and block radiation . A bunker's door must be at least as strong as

792-401: A house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with large cabinets. One common design approach uses fibre-reinforced plastic shells. Compressive protection may be provided by inexpensive earth arching. The overburden is designed to shield from radiation. To prevent the shelter from floating to the surface in high groundwater, some designs have

891-402: A hydroxy group, also the nitrogen atom of an amine or amide can be reacted with epichlorohydrin. The other production route for epoxy resins is the conversion of aliphatic or cycloaliphatic alkenes with peracids : In contrast to glycidyl-based epoxy resins, this production of such epoxy monomers does not require an acidic hydrogen atom but an aliphatic double bond. The epoxide group

990-424: A large extent as secondary plasticizers and cost stabilizers for PVC . Aliphatic glycidyl epoxy resins of low molar mass (mono-, bi- or polyfunctional) are formed by the reaction of epichlorohydrin with aliphatic alcohols or polyols (glycidyl ethers are formed) or with aliphatic carboxylic acids (glycidyl esters are formed). The reaction is carried out in the presence of a base such as sodium hydroxide, analogous to

1089-399: A lesser extent, monoanhydrides, non-stoichiometric, empirical determinations are often used to optimize dosing levels. In some cases, blends of dianhydrides and monoanhydrides can improve metering and mixing with liquid epoxy resins. Polyphenols, such as bisphenol A or novolacs can react with epoxy resins at elevated temperatures (130–180 °C, 266–356 °F), normally in the presence of

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1188-911: A low surface tension, it is added as a wetting agent (surfactant) for contact with glass fibres. Its reactivity to hardeners is comparable to that of bisphenol A. When cured, the epoxy resin leads to a thermosetting plastic with high chemical resistance and low water absorption. However, the commercial use of fluorinated epoxy resins is limited by their high cost and low T g . Epoxy resins diluents are typically formed by glycidylation of aliphatic alcohols or polyols and also aromatic alcohols. The resulting materials may be monofunctional (e.g. dodecanol glycidyl ether), difunctional ( 1,4-Butanediol diglycidyl ether ), or higher functionality (e.g. trimethylolpropane triglycidyl ether ). These resins typically display low viscosity at room temperature (10–200 mPa.s) and are often referred to as reactive diluents. They are rarely used alone, but are rather employed to modify (reduce)

1287-414: A lower electron density than aromatics, cycloaliphatic epoxies react less readily with nucleophiles than bisphenol A-based epoxy resins (which have aromatic ether groups). This means that conventional nucleophilic hardeners such as amines are hardly suitable for crosslinking. Cycloaliphatic epoxides are therefore usually homopolymerized thermally or UV-initiated in an electrophilic or cationic reaction. Due to

1386-452: A mount for the Mk 42 Mod 0 day sight or AN/PVS-4 or AN/PVS-17 B night sights . The launch tube is made of fiberglass - epoxy composite material with a gelcoat on the bore. The spotting rifle is mounted on the right side of the launch tube. It functions semi-automatically by primer actuation, meaning that when fired the primer sets back and unlocks the breech of the spotting rifle, ejecting

1485-400: A narrow, 1–2-metre (3.5–6.5 ft), flexible tent of thin wood is placed in a deep trench, and then covered with cloth or plastic, and then covered with 1–2 m (3.5–6.5 feet) of tamped earth. A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings to protect inhabitants from

1584-610: A network with incomplete polymerisation, and thus reduced mechanical, chemical and heat resistance. Cure temperature should typically attain the glass transition temperature (T g ) of the fully cured network in order to achieve maximum properties. Temperature is sometimes increased in a step-wise fashion to control the rate of curing and prevent excessive heat build-up from the exothermic reaction. Hardeners which show only low or limited reactivity at ambient temperature, but which react with epoxy resins at elevated temperature are referred to as latent hardeners . When using latent hardeners,

1683-515: A part of a trench system. Such bunkers give the defending soldiers better protection than the open trench and also include top protection against aerial attack. They also provide shelter against the weather. Some bunkers may have partially open tops to allow weapons to be discharged with the muzzle pointing upwards (e.g., mortars and anti-aircraft weapons). Many artillery installations, especially for coastal artillery , have historically been protected by extensive bunker systems. These usually housed

1782-628: A reinforced concrete shelter" is first recorded on 13 October 1939, in "A Nazi field gun hidden in a cemented 'bunker' on the Western front". All the early references to its usage in the Oxford English Dictionary are to German fortifications. However, in the Far East the term was also applied to the earth and log positions built by the Japanese, the term appearing in a 1943 instruction manual issued by

1881-579: A shoulder-launched enhanced-blast warhead in 2003. It was used in combat during both the first and second offensives in Fallujah , in 2004. Bunker A bunker is a defensive military fortification designed to protect people and valued materials from falling bombs, artillery, or other attacks. Bunkers are almost always underground, in contrast to blockhouses which are mostly above ground. They were used extensively in World War I , World War II , and

1980-522: A skirt held down with the overburden. It may also serve the purpose of a safe room . Large bunkers are often bought by super rich individuals in case of political instability , and usually store or access large amounts of energy for use. They are sometimes refereed to as "luxury bunkers," and their locations are often documented. Munitions storage bunkers are designed to securely store explosive ordnance and contain any internal explosions. The most common configuration for high explosives storage

2079-634: A standoff rod on the detonator, allowing the explosive force to be focused on a small point and for maximum damage against targets. The HEAA round can penetrate up to the equivalent of 600 mm of rolled homogeneous steel. The unit cost of the Mk 6 HEAA round is $ 25,000. The Mk 80 Mod 0 Encased Novel Explosive (SMAW-NE) Rocket is effective against caves and bunkers. The SMAW-NE has a 4 lb (1.8 kg) charge of PBXIH-135, an enhanced-blast warhead. The Indian Head Naval Surface Warfare Center teamed with Marine Corps Systems Command and Talley Defense Systems to respond to an urgent U.S. Marine Corps need for

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2178-566: A variety of ways, including reacting with fatty acids derived from oils to yield epoxy esters, which were cured the same way as alkyds. Typical ones were L8 (80% linseed) and D4 (40% dehydrated castor oil). These were often reacted with styrene to make styrenated epoxy esters, used as primers. Curing with phenolics to make drum linings, curing esters with amine resins and pre-curing epoxies with amino resins to make resistant top coats. Organic chains maybe used to hydrophobically modify epoxy resins and change their properties. The effect of chain length of

2277-581: A wide range of applications, including metal coatings , composites, use in electronics, electrical components (e.g. for chips on board ), LEDs, high-tension electrical insulators , paintbrush manufacturing, fiber-reinforced plastic materials, and adhesives for structural and other purposes. The health risks associated with exposure to epoxy resin compounds include contact dermatitis and allergic reactions, as well as respiratory problems from breathing vapor and sanding dust, especially from compounds not fully cured. Condensation of epoxides and amines

2376-494: A wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides ), phenols, alcohols and thiols (sometimes called mercaptans). These co-reactants are often referred to as hardeners or curatives, and the cross-linking reaction is commonly referred to as curing . Reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer , often with favorable mechanical properties and high thermal and chemical resistance. Epoxy has

2475-542: Is a common phenomenon for epoxy materials and is often of concern in art and conservation applications. Epoxy resins yellow with time, even when not exposed to UV radiation. Significant advances in understanding yellowing of epoxies were achieved by Down first in 1984 (natural dark aging) and later in 1986 (high-intensity light aging). Down investigated various room-temperature-cure epoxy resin adhesives suitable for use in glass conservation, testing their tendency to yellow. A fundamental molecular understanding of epoxy yellowing

2574-421: Is a highly effective and widely used accelerator, but is now increasingly replaced due to health concerns with this substance. The most widely used accelerator is 2,4,6-Tris(dimethylaminomethyl)phenol . Epoxy resin may be reacted with itself in the presence of an anionic catalyst (a Lewis base such as tertiary amines or imidazoles) or a cationic catalyst (a Lewis acid such as a boron trifluoride complex) to form

2673-806: Is a key technology used for toughening. Two part epoxy coatings were developed for heavy duty service on metal substrates and use less energy than heat-cured powder coatings . These systems provide a tough, protective coating with excellent hardness. One part epoxy coatings are formulated as an emulsion in water, and can be cleaned up without solvents. Epoxy coatings are often used in industrial and automotive applications since they are more heat resistant than latex-based and alkyd-based paints. Epoxy paints tend to deteriorate, known as "chalking out", due to UV exposure. Epoxy coatings have also been used in drinking water applications. Epoxy coatings find much use to protect mild and other steels due to their excellent protective properties. Change in color, known as yellowing,

2772-489: Is also sometimes referred to as an oxirane group. The most common epoxy resins are based on reacting epichlorohydrin (ECH) with bisphenol A ,  resulting in a different chemical substance known as bisphenol A diglycidyl ether (commonly known as BADGE or DGEBA). Bisphenol A-based resins are the most widely commercialised resins but also other bisphenols are analogously reacted with epichlorohydrin, for example Bisphenol F . In this two-stage reaction, epichlorohydrin

2871-417: Is an unusually large number of bunkers because of a law requiring protective shelters to be constructed for all new buildings since 1963, as well as a number of bunkers built as part of its National Redoubt military defense plan. Some of Switzerland's bunkers have since become tourist attractions housing hotels and museums such as Sasso San Gottardo Museum. The Soviet Union maintained huge bunkers (one of

2970-406: Is approximately in the order: phenol < anhydride < aromatic amine < cycloaliphatic amine < aliphatic amine < thiol. While some epoxy resin/ hardener combinations will cure at ambient temperature, many require heat, with temperatures up to 150 °C (302 °F) being common, and up to 200 °C (392 °F) for some specialist systems. Insufficient heat during cure will result in

3069-453: Is called prepolymerization: A product comprising a few repeat units ( n = 1 to 2) is a viscous, clear liquid; this is called a liquid epoxy resin. A product comprising more repeating units ( n = 2 to 30) is at room temperature a colourless solid, which is correspondingly referred to as solid epoxy resin. Instead of bisphenol A, other bisphenols (especially bisphenol F ) or brominated bisphenols (e. g. tetrabromobisphenol A ) can be used for

Mk 153 Shoulder-Launched Multipurpose Assault Weapon - Misplaced Pages Continue

3168-573: Is common to achieve the desired processing or final properties, or to reduce cost. Use of blending, additives and fillers is often referred to as formulating . All quantities of mix generate their own heat because the reaction is exothermic. Large quantities will generate more heat and thus greatly increase the rate of the reaction and so reduce working time (pot-life). So it is good practice to mix smaller amounts which can be used quickly to avoid waste and to be safer. There are various methods of toughening them, as they can be brittle. Rubber toughening

3267-406: Is connected to the epoxide group content. This is expressed as the " epoxide equivalent weight ", which is the ratio between the molecular weight of the monomer and the number of epoxide groups. This parameter is used to calculate the mass of co-reactant (hardener) to use when curing epoxy resins. Epoxies are typically cured with stoichiometric or near-stoichiometric quantities of hardener to achieve

3366-424: Is created when it is fired is a primary safety concern. When the rocket is fired, the rocket propellant is expended entirely within the rocket encasement. This is the cause of the extremely loud and violent backblast. This backblast extends in a 90-meter, 60° cone to the rear of the weapon. The backblast is lethal out to 30 metres (98 ft) and still extremely dangerous to 90 metres (300 ft). An assistant gunner

3465-475: Is degraded at temperatures above 350 °F (177 °C). Some epoxies are cured by exposure to ultraviolet light. Such epoxies are commonly used in optics , fiber optics , and optoelectronics . Epoxy systems are used in industrial tooling applications to produce molds , master models, laminates , castings , fixtures , and other industrial production aids. This "plastic tooling" replaces metal, wood and other traditional materials, and generally improves

3564-570: Is effective against bunkers, masonry and concrete walls and light armor. Initiated by a crush switch in its nose, the HEDP rocket is able to distinguish between hard and soft targets resulting in greater penetration into soft targets for increased damage potential. The HEDP round can penetrate 20 centimetres (7.9 in) of concrete, 30 centimetres (12 in) of brick, or up to 210 centimetres (6.9 ft) of wood-reinforced sandbags. The Mk 4 Mod 0 Encased High-Explosive, Anti-Armor, Practice (HEAAP) Rocket

3663-433: Is first added to bisphenol A (bis(3-chloro-2-hydroxy-propoxy)bisphenol A is formed), then a bisepoxide is formed in a condensation reaction with a stoichiometric amount of sodium hydroxide. The chlorine atom is released as sodium chloride (NaCl) and the hydrogen atom as water. Higher molecular weight diglycidyl ethers (n ≥ 1) are formed by the reaction of the bisphenol A diglycidyl ether formed with further bisphenol A, this

3762-663: Is not present in these materials as it is in Bisphenol A and F resins, the UV stability is considerably improved. Halogenated epoxy resins are admixed for special properties, in particular brominated and fluorinated epoxy resins are used. Brominated bisphenol A is used when flame retardant properties are required, such as in some electrical applications (e.g. printed circuit boards ). The tetrabrominated bisphenol A (TBBPA, 2,2-bis(3,5-dibromophenyl)propane) or its diglycidyl ether, 2,2-bis[3,5-dibromo-4-(2,3-epoxypropoxy)phenyl]propane, can be added to

3861-406: Is often used during employment of the weapon system to monitor the backblast area and clear it of fellow troops, or to notify the gunner of obstructions that could reflect the force of the backblast back at the gun team. The gunner is only cleared to launch a rocket when he hears the command "Backblast area secure" from his assistant gunner. Rounds are under development that would enable a user to fire

3960-490: Is the igloo shaped bunker. They are often built into a hillside in order to provide additional containment mass. A specialized version of the munitions bunker called a Gravel Gertie is designed to contain radioactive debris from an explosive accident while assembling or disassembling nuclear warheads . They are installed at all facilities in the United States and United Kingdom which do warhead assembly and disassembly,

4059-448: Is the family of basic components or cured end products of epoxy resins . Epoxy resins, also known as polyepoxides , are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also collectively called epoxy . The IUPAC name for an epoxide group is an oxirane . Epoxy resins may be reacted ( cross-linked ) either with themselves through catalytic homo polymerisation , or with

Mk 153 Shoulder-Launched Multipurpose Assault Weapon - Misplaced Pages Continue

4158-429: Is used in training. The warhead consists of a blue plastic projectile attached to a rocket motor similar to the HEDP rocket. The rocket contains no explosive. It does not damage a target except by kinetic energy. On impact, the plastic warhead ruptures, dispensing an inert white spotting powder. The Mk 6 Mod 0 Encased High-Explosive, Anti-Armor (HEAA) Rocket is effective against current tanks without added armor, and uses

4257-628: The British Indian Army and quickly gaining wide currency. By 1947 the word was familiar enough in English that Hugh Trevor-Roper in The Last Days of Hitler was describing Hitler's underground complex near the Reich Chancellery as "Hitler's own bunker" without quotes around the word bunker. This type of bunker is a small concrete structure, partly dug into the ground, which is usually

4356-542: The Cold War for weapons facilities, command and control centers, and storage facilities. Bunkers can also be used as protection from tornadoes . Trench bunkers are small concrete structures, partly dug into the ground. Many artillery installations, especially for coastal artillery , have historically been protected by extensive bunker systems. Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. When

4455-729: The East Wing of the White House serves as a secure shelter and communications center for the President of the United States in case of an emergency. 1. abmm.org : Australian Bunker And Military Museum 2. BunkerBlog : All about German fortifications 1933-1945 3. Bunkersite.com : About bunkers built by the Germans during 1933–1945 in the whole of Europe 4. German bunkers in Poland : Fortified Front Odra-Warta rivers, Boryszyn Loop Epoxy Epoxy

4554-593: The Germans to describe permanent structures both large ( blockhouses ), and small ( pillboxes ), and bombproof shelters both above ground (as in Hochbunker ) and below ground (such as the Führerbunker ). The military sense of the word was imported into English during World War II, at first in reference to specifically German dug-outs; according to the Oxford English Dictionary , the sense of "military dug-out;

4653-423: The Mk 3 Mod 0 Encased High-Explosive, Dual-Purpose (HEDP) Rocket, the Mk 6 Mod 0 Encased High-Explosive, Anti-Armor (HEAA) Rocket, the Mk 7 Mod 0 Common Encased Practice Rocket, the Mk 80 Mod 0 Encased Novel Explosive (NE) Rocket, and the Mk 217 Mod 0 spotting rifle cartridge. The launcher consists of the launch tube, spotting rifle, electro-mechanical firing mechanism, mounting brackets, open battle sights and

4752-508: The SMAW has slower projectile velocities, it and its ammunition are both heavier, and it takes a second crew member to keep up with the B-300's rate-of-fire, but some of its projectile options have longer ranges than the B-300. The Mk 153 SMAW has an 83.5-millimetre (3.29 in) diameter tube and fires 83-millimetre (3.3 in) rockets. It is a man-portable weapon system consisting of the Mk 153 launcher,

4851-401: The amino groups may react as slowly as some of the aromatic amines. Slower reactivity allows longer working times for processors. Temperature resistance generally increases in the same order, since aromatic amines form much more rigid structures than aliphatic amines. Aromatic amines were widely used as epoxy resin hardeners, due to the excellent end properties when mixed with a parent resin. Over

4950-489: The best physical properties. Novolaks are produced by reacting phenol with methanal ( formaldehyde ). The reaction of epichlorohydrin and novolaks produces novolaks with glycidyl residues , such as epoxyphenol novolak (EPN) or epoxycresol novolak (ECN). These highly viscous to solid resins typically carry 2 to 6 epoxy groups per molecule. By curing, highly cross-linked polymers with high temperature and chemical resistance but low mechanical flexibility are formed due to

5049-452: The blast wave or a reflection cannot lift the edge. A bunker should have two doors. Door shafts may double as ventilation shafts to reduce digging. In bunkers inhabited for prolonged periods, large amounts of ventilation or air conditioning must be provided in order to prevent ill effects of heat. In bunkers designed for war-time use, manually operated ventilators must be provided because supplies of electricity or gas are unreliable. One of

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5148-577: The cargo of a ship". In the 19th century the word came to describe a coal store in a house, or below decks in a ship. It was also used for a sand-filled depression installed on a golf course as a hazard. In the First World War the belligerents built underground shelters, called dugouts in English , while the Germans used the term Bunker . By the Second World War the term came to be used by

5247-717: The commercially used epoxy monomers are produced by the reaction of a compound with acidic hydroxy groups and epichlorohydrin . First a hydroxy group reacts in a coupling reaction with epichlorohydrin, followed by dehydrohalogenation . Epoxy resins produced from such epoxy monomers are called glycidyl -based epoxy resins. The hydroxy group may be derived from aliphatic diols , polyols (polyether polyols), phenolic compounds or dicarboxylic acids . Phenols can be compounds such as bisphenol A and novolak . Polyols can be compounds such as 1,4-butanediol . Di- and polyols lead to glycidyl ethers . Dicarboxylic acids such as hexahydrophthalic acid are used for diglycide ester resins. Instead of

5346-428: The crews serving the weapons, protected the ammunition against counter-battery fire, and in numerous examples also protected the guns themselves, though this was usually a trade-off reducing their fields of fire. Artillery bunkers are some of the largest individual pre-Cold War bunkers. The walls of the ' Batterie Todt ' gun installation in northern France were up to 3.5 metres (11 ft) thick, and an underground bunker

5445-405: The efficiency and either lowers the overall cost or shortens the lead-time for many industrial processes. Epoxies are also used in producing fiber-reinforced or composite parts. They are more expensive than polyester resins and vinyl ester resins , but usually produce stronger and more temperature-resistant thermoset polymer matrix composite parts. Machine bedding to overcome vibrations is a use in

5544-475: The enhanced FGM-172 SRAW . In combat operations, it was ultimately used to augment, rather than replace, the SMAW system. In 2008, a replacement program was again initiated and titled the SMAW II. It was developed in tandem with a round capable of being fired from an enclosed area without ill effects on the environment and personnel. Its combined weight is 13.5 kilograms (29.7 lb) — 5.3 kg (11.7 lb) for

5643-511: The epoxide group to form a hydroxyl group and a secondary amine. The secondary amine can further react with an epoxide to form a tertiary amine and an additional hydroxyl group. Kinetic studies have shown the reactivity of the primary amine to be approximately double that of the secondary amine. Use of a difunctional or polyfunctional amine forms a three-dimensional cross-linked network. Aliphatic, cycloaliphatic and aromatic amines are all employed as epoxy hardeners. Amine type hardeners will alter both

5742-462: The epoxy formulation . The formulation may then be reacted in the same way as pure bisphenol A. Some (non-crosslinked) epoxy resins with very high molar mass are added to engineering thermoplastics, again to achieve flame retardant properties. Fluorinated epoxy resins have been investigated for some high performance applications , such as the fluorinated diglycidether 5-heptafluoropropyl-1,3-bis[2-(2,3-epoxypropoxy)hexafluoro-2-propyl]benzene. As it has

5841-672: The epoxy resin and hardener may be mixed and stored for some time prior to use, which is advantageous for many industrial processes. Very latent hardeners enable one-component (1K) products to be produced, whereby the resin and hardener are supplied pre-mixed to the end user and only require heat to initiate curing. One-component products generally have shorter shelf-lives than standard 2-component systems, and products may require cooled storage and transport. The epoxy curing reaction may be accelerated by addition of small quantities of accelerators . Tertiary amines, carboxylic acids and alcohols (especially phenols) are effective accelerators. Bisphenol A

5940-449: The formation of bisphenol A-diglycidyl ether. Also aliphatic glycidyl epoxy resins usually have a low viscosity compared to aromatic epoxy resins. They are therefore added to other epoxy resins as reactive diluents or as adhesion promoters . Epoxy resins made of (long-chain) polyols are also added to improve tensile strength and impact strength. A related class is cycloaliphatic epoxy resin, which contains one or more cycloaliphatic rings in

6039-401: The high functionality, and hence high crosslink density of these resins. There are two common types of aliphatic epoxy resins: those obtained by epoxidation of double bonds (cycloaliphatic epoxides and epoxidized vegetable oils ) and those formed by reaction with epichlorohydrin (glycidyl ethers and esters). Cycloaliphatic epoxides contain one or more aliphatic rings in the molecule on which

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6138-535: The high-explosive anti-armor (HEAA) rocket to be used effectively against moving armor targets. The U.S. Armed Forces fielded boresight bracket kits which correct the loss of accurate boresight issues between the launch tube and spotting rifle. During Operation Desert Storm , 150 launchers and 5,000 rockets were deployed by the United States Army . Initially the Army showed interest in the system but ultimately returned

6237-554: The largest being the Pantex plant in Amarillo, Texas , which has 12 Gravel Gerties. Bunkers deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as 21  kPa (3  psi ; 0.21  bar ) of overpressure , bunkers are regularly constructed to survive over 1,000 kPa (150 psi; 10 bar). This substantially decreases

6336-471: The launcher is enclosed in a unique protective cage, which is also a carry handle. The development reduced the over-all weight by four and a half pounds (2.0 kg) from the older SMAW launcher. The Serpent fires the same rounds as the standard SMAW and supports new and improved/enhanced rounds. Compared to the Israel Military Industries' ( IMI Systems ) B-300 weapon that it was developed from,

6435-500: The launcher, 8.2 kg (18 lb) for the rocket. The contract was worth up to US$ 51.7 million . In 2012, Raytheon Missile Systems developed a SMAW II launcher named Serpent , and Nammo Talley developed new rounds for the Serpent. The Serpent is similar in many respects to the first SMAW launcher, except that it replaces the standard SMAW launcher's spotting gun with more sophisticated fire control electronics. The sighting unit on

6534-525: The launcher. While the Mod 0 weighs 7.5 kg (16.5 lb), the Mod 2 weighs 5.9 kg (13 lb) with the MBS attached, and 3.9 kg (8.5 lb) with the MBS detached. Other improvements include increased pad size on the forward grip and foldable backup iron sights. The Mod 2 systems were expected to replace the existing inventory by October 2020. The Mk 3 Mod 0 Encased High-Explosive, Dual Purpose (HEDP) Rocket

6633-572: The launchers and any unused rockets to the Marine Corps. Later, the U.S. Army developed the SMAW-D ("disposable"), designated by the Army as the M141 Bunker Defeat Munition . In 2002, the corps began a program to develop a successor to the SMAW system, tentatively titled "Follow-On To SMAW". The contract was awarded to Lockheed Martin and Israel Military Industries (IMI); this resulted in

6732-513: The likelihood that a bomb (other than a bunker buster ) can harm the structure. The basic plan is to provide a structure that is very strong in physical compression . The most common purpose-built structure is a buried, steel reinforced concrete vault or arch . Most expedient blast shelters are civil engineering structures that contain large, buried tubes or pipes such as sewage or rapid transit tunnels. Improvised purpose-built blast shelters normally use earthen arches or vaults. To form these,

6831-549: The linear epoxy resin with suitable curatives to form three-dimensional cross-linked thermoset structures. This process is commonly referred to as curing or gelation process. Curing of epoxy resins is an exothermic reaction and in some cases produces sufficient heat to cause thermal degradation if not controlled. Curing does induce residual stress in epoxy systems which have been studied. The induced stresses may be alleviated with flexibilisers. Curing may be achieved by reacting an epoxy with itself (homopolymerisation) or by forming

6930-435: The low dielectric constants and the absence of chlorine, cycloaliphatic epoxides are often used to encapsulate electronic systems, such as microchips or LEDs. They are also used for radiation-cured paints and varnishes. Due to their high price, however, their use has so far been limited to such applications. Epoxidized vegetable oils are formed by epoxidation of unsaturated fatty acids by reaction with peracids. In this case,

7029-923: The modifiers has been studied. Epoxy adhesives are a major part of the class of adhesives called "structural adhesives" or "engineering adhesives" (that includes polyurethane , acrylic , cyanoacrylate , and other chemistries.) These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. Epoxy adhesives can be developed to suit almost any application. They can be used as adhesives for wood, metal, glass, stone, and some plastics. They can be made flexible or rigid, transparent or opaque /colored, fast setting or slow setting. Epoxy adhesives are better in heat and chemical resistance than other common adhesives. In general, epoxy adhesives cured with heat will be more heat- and chemical-resistant than those cured at room temperature. The strength of epoxy adhesives

7128-400: The molecule (e.g. 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate). This class also displays lower viscosity at room temperature, but offers significantly higher temperature resistance than the aliphatic epoxy diluents. However, reactivity is rather low compared to other classes of epoxy resin, and high temperature curing using suitable accelerators is normally required. As aromaticity

7227-504: The most efficient manual ventilator designs is the Kearny Air Pump . Ventilation openings in a bunker must be protected by blast valves . A blast valve is closed by a shock wave, but otherwise remains open. One form of expedient blast valve is worn flat rubber tire treads nailed or bolted to frames strong enough to resist the maximum overpressure. Bunkers can be destroyed with powerful explosives and bunkerbusting warheads. The crew of

7326-962: The northern Czech border facing Germany (but to lesser extent all around), Fort Eben-Emael in Belgium, Alpine Wall on the north of Italy, World War II Führerbunker and in Italy, industrial Marnate's Bunker , the V-weapon installations in Germany ( Mittelwerk ) & France ( La Coupole , and the Blockhaus d'Éperlecques ) and the Cold War installations in the United States ( Cheyenne Mountain Complex , Site R , and The Greenbrier ), United Kingdom ( Burlington ), Sweden ( Boden Fortress ) and Canada ( Diefenbunker ). In Switzerland, there

7425-594: The oil and gas industry, potable water transmission pipelines (steel), and concrete reinforcing rebar . Epoxy coatings are also widely used as primers to improve the adhesion of automotive and marine paints especially on metal surfaces where corrosion (rusting) resistance is important. Metal cans and containers are often coated with epoxy to prevent rusting, especially for foods like tomatoes that are acidic . Epoxy resins are also used for decorative flooring applications such as terrazzo flooring, chip flooring, and colored aggregate flooring. Epoxies have been modified in

7524-602: The oxirane ring is contained (e.g. 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate ). They are produced by the reaction of a cyclic alkene with a peracid (see above). Cycloaliphatic epoxides are characterised by their aliphatic structure, high oxirane content and the absence of chlorine, which results in low viscosity and (once cured) good weather resistance, low dielectric constants and high T g . However, aliphatic epoxy resins polymerize very slowly at room temperature, so higher temperatures and suitable accelerators are usually required. Because aliphatic epoxies have

7623-400: The past few decades concern about the possible adverse health effects of many aromatic amines has led to increased use of aliphatic or cycloaliphatic amine alternatives. Amines are also blended, adducted and reacted to alter properties and these amine resins are more often used to cure epoxy resins than a pure amine such as TETA. Increasingly, water-based polyamines are also used to help reduce

7722-444: The peracids can also be formed in situ by reacting carboxylic acids with hydrogen peroxide. Compared with LERs (liquid epoxy resins) they have very low viscosities. If, however, they are used in larger proportions as reactive diluents , this often leads to reduced chemical and thermal resistance and to poorer mechanical properties of the cured epoxides. Large scale epoxidized vegetable oils such as epoxidized soy and lens oils are used to

7821-449: The polymerisation reaction used to produce them. High purity grades can be produced for certain applications, e.g. using a distillation purification process. One downside of high purity liquid grades is their tendency to form crystalline solids due to their highly regular structure, which then require melting to enable processing. An important criterion for epoxy resins is the Epoxy value which

7920-418: The processing properties (viscosity, reactivity) and the final properties (mechanical, temperature and heat resistance) of the cured copolymer network. Thus amine structure is normally selected according to the application. Overall reactivity potential for different hardeners can roughly be ordered; aliphatic amines > cycloaliphatic amines > aromatic amines, though aliphatic amines with steric hindrance near

8019-871: The range of commercially available variations allows cure polymers to be produced with a very broad range of properties. They have been extensively used with concrete and cementitious systems. In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. Many properties of epoxies can be modified (for example silver -filled epoxies with good electrical conductivity are available, although epoxies are typically electrically insulating). Variations offering high thermal insulation , or thermal conductivity combined with high electrical resistance for electronics applications, are available. As with other classes of thermoset polymer materials, blending different grades of epoxy resin, as well as use of additives, plasticizers or fillers

8118-417: The ratio of bisphenol A to epichlorohydrin during manufacture produces higher molecular weight linear polyethers with glycidyl end groups, which are semi-solid to hard crystalline materials at room temperature depending on the molecular weight achieved. This route of synthesis is known as the "taffy" process. The usual route to higher molecular weight epoxy resins is to start with liquid epoxy resin (LER) and add

8217-491: The resulting cured network makes them important materials for aerospace composite applications. There are several dozen chemicals that can be used to cure epoxy, including amines , imidazoles, anhydrides and photosensitive chemicals. The study of epoxy curing is usually carried out by using differential scanning calorimetry . In general, uncured epoxy resins have only poor mechanical, chemical and heat resistance properties. However, good properties are obtained by reacting

8316-784: The resulting network does not typically display high temperature or chemical resistance, the high reactivity of the thiol group makes it useful for applications where heated curing is not possible, or very fast cure is required e.g. for domestic DIY adhesives and chemical rock bolt anchors . Thiols have a characteristic odour, which can be detected in many two-component household adhesives. The applications for epoxy-based materials are extensive and they are considered very versatile. The applications include coatings, adhesives and composite materials such as those using carbon fiber and fiberglass reinforcements (although polyester , vinyl ester , and other thermosetting resins are also used for glass-reinforced plastic). The chemistry of epoxies and

8415-463: The rocket and serves to increase the gunner's first-round hit probability. Each round consists of a special 9 mm projectile which contains a tracer compound, crimped into a 7.62×51mm NATO casing with a .22 Hornet primer. The system can be used in conjunction with the AN/PEQ-2 aiming light in place of the spotting rifle. As with all of these types of recoilless rocket weapons, the backblast that

8514-442: The rocket from an enclosed building without risk of injury. The Mk 153 Mod 2 is an enhanced variant, featuring an electronic modular ballistic sight (MBS) in place of the 9 mm spotting system. The MBS has a laser rangefinder and thermal weapon sight to provide a firing solution using a displaced reticle, where crosshairs are adjusted for distance and environmental factors; it is lighter, more reliable, and can be detached from

8613-444: The said epoxidation and prepolymerisation. Bisphenol F may undergo epoxy resin formation in a similar fashion to bisphenol A. These resins typically have lower viscosity and a higher mean epoxy content per gram than bisphenol A resins, which (once cured) gives them increased chemical resistance. Important epoxy resins are produced from combining epichlorohydrin and bisphenol A to give bisphenol A diglycidyl ethers . Increasing

8712-632: The secondary uses of the very deeply dug Moscow Metro and Kyiv metro systems was as nuclear shelters). A number of facilities were constructed in China, such as Beijing 's Underground City and Underground Project 131 in Hubei ; in Albania , Enver Hoxha dotted the country with hundreds of thousands of bunkers . In the United States, the Presidential Emergency Operations Center underneath

8811-425: The spent round. The firing mechanism mechanically fires the spotting rifle and uses a magnet to fire the rocket. The mounting brackets connect the components and provide the means for boresighting the weapon, while the encased rockets are loaded at the rear of the launcher. The spotting cartridges are stored in a magazine in the cap of the encased rocket. The 9×51mm Mk 217 spotting round is ballistically matched to

8910-430: The terminal epoxy groups are insignificant compared to the total size of the molecule). These resins do however contain hydroxyl groups throughout the backbone, which may also undergo other cross-linking reactions, e.g. with aminoplasts, phenoplasts and isocyanates . Epoxy resins are polymeric or semi-polymeric materials or an oligomer , and as such rarely exist as pure substances, since variable chain length results from

9009-706: The toxicity profile among other reasons. Epoxy resins may be thermally cured with anhydrides to create polymers with significant property retention at elevated temperatures for extended periods of time. Reaction and subsequent crosslinking occur only after opening of the anhydride ring, e.g. by secondary hydroxyl groups in the epoxy resin. Homopolymerization may also occur between epoxide and hydroxyl groups. The high latency of anhydride hardeners makes them suitable for processing systems which require addition of mineral fillers prior to curing, e.g. for high voltage electrical insulators. Cure speed may be improved by matching anhydrides with suitable accelerators. For dianhydrides, and to

9108-891: The viscosity of other epoxy resins. This has led to the term modified epoxy resin to denote those containing viscosity-lowering reactive diluents. The use of the diluent does effect mechanical properties and microstructure of epoxy resins. Mechanical properties of epoxy resins are generally not improved by use of diluents. Biobased epoxy diluents are also available. Glycidylamine epoxy resins are higher functionality epoxies which are formed when aromatic amines are reacted with epichlorohydrin . Important industrial grades are triglycidyl- p -aminophenol (functionality 3) and N , N , N ′, N ′-tetraglycidyl-bis-(4-aminophenyl)-methane (functionality 4). The resins are low to medium viscosity at room temperature, which makes them easier to process than EPN or ECN resins. This coupled with high reactivity, plus high temperature resistance and mechanical properties of

9207-409: The walls and floors. Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and block radiation . Usually, these features are easy to provide. The overburden ( soil ) and structure provide substantial radiation shielding, and the negative pressure is usually only 1 ⁄ 3 of the overpressure. The doors must be at least as strong as

9306-437: The walls. In bunkers inhabited for prolonged periods, large amounts of ventilation or air conditioning must be provided. Bunkers can be destroyed with powerful explosives and bunker-busting warheads . The word bunker originates as a Scots word for "bench, seat" recorded 1758, alongside shortened bunk "sleeping berth". The word possibly has a Scandinavian origin: Old Swedish bunke means "boards used to protect

9405-407: The walls. The usual design is now starting to incorporate vault doors . To reduce the weight, the door is normally constructed of steel, with a fitted steel lintel and frame. Very thick wood also serves and is more resistant to heat because it chars rather than melts. If the door is on the surface and will be exposed to the blast wave, the edge of the door is normally counter-sunk in the frame so that

9504-555: Was achieved, when Krauklis and Echtermeyer discovered the mechanistic origin of yellowing in a commonly used amine epoxy resin, published in 2018. They found that the molecular reason for epoxy yellowing was a thermo-oxidative evolution of carbonyl groups in the polymeric carbon–carbon backbone via a nucleophilic radical attack. Polyester epoxies are used as powder coatings for washers, driers and other "white goods". Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in

9603-653: Was constructed for the V-3 cannon . Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. They were built mainly by nations like Germany during World War II to protect important industries from aerial bombardment . Industrial bunkers are also built for control rooms of dangerous activities, such as tests of rocket engines or explosive experiments. They are also built in order to perform dangerous experiments in them or to store radioactive or explosive goods. Such bunkers also exist on non-military facilities. When

9702-432: Was fielded in 1984 as a United States Marine Corps –unique system. The Mod 0 demonstrated several shortcomings, resulting in a series of modifications in the mid-2000s. These modifications included a re-sleeving process for bubbled launch tubes, rewriting and drafting operator and technical manuals, and a kit to reduce environmental intrusion into the trigger mechanism. This also includes an optical sight modification to allow

9801-537: Was first reported and patented by Paul Schlack of Germany in 1934. Claims of discovery of bisphenol-A -based epoxy resins include Pierre Castan in 1943. Castan's work was licensed by Ciba , Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. In 1946, Sylvan Greenlee, working for the Devoe ;& Raynolds Company (now part of Hexion Inc. ), patented resin derived from bisphenol-A and epichlorohydrin . Most of

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