Misplaced Pages

#831168

89-431: Fifteen masked gunmen stormed the studio and transmission complex and destroyed the main control room of the group on 6 January 2009. Investigations revealed that a Claymore mine was used for the attack. Critics and observers linked the attack to the controversial reporting that was adopted in relation to the capture of Kilinochchi by Government Forces. Opposition political parties and associated media organizations accused

178-440: 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)

267-703: A thermosetting polymer , often with favorable mechanical properties and high thermal and chemical resistance. Epoxy has 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

356-595: A 60° arc in front of the device. It is used primarily in ambushes and as an anti-infiltration device against enemy infantry . It is also used against unarmored vehicles . Many countries have developed and used mines like the Claymore. Examples include models MON-50 , MON-90 , MON-100 , and MON-200 introduced by the Soviet Union and used by its successor Russia, as well as MRUD (Serbia), MAPED F1 (France), and Mini MS-803 (South Africa). The M18A1 Claymore mine has

445-454: A battery pack, which had been used with the M18. This was found to be undesirable for a number of reasons. Bill Kincheloe came up with the idea of using a "Tiny Tim" toggle generator, of the type used with a number of Navy rockets. Originally an aluminum box was used to hold the generator. Later a Philadelphia company, Molded Plastic Insulation Company, took over the manufacture of the firing device for

534-456: 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

623-418: 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

712-578: 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

801-427: A heavy backing surface (for example, a metal plate), the resulting blast is primarily directed away from the surface in a single direction. Schardin spent some time developing the discovery as a side-attack anti-tank weapon, but development was incomplete at the end of the war. Schardin also spent time researching a "trench mine" that used a directional fragmentation effect. Following the massed Chinese attacks during

890-432: A hit probability of around 10% on a prone man-sized 1.3-square-foot (0.12 m ) target. The fragments can travel up to 250 m (270 yd). The optimum effective range is 50 m (55 yd), at which the optimal balance is achieved between lethality and area coverage, with a hit probability of 30% on a man-sized target. The weapon and all its accessories are carried in an M7 bandolier ("Claymore bag"). The mine

979-434: A horizontally convex gray-green plastic case (inert training versions are light blue or green with a light blue band). The shape was developed through experimentation to deliver the optimum distribution of fragments at 50 m (55 yd) range. The case has the words "FRONT TOWARD ENEMY" embossed on the front of the mine. A simple open sight on the top surface allows for aiming the mine. Two pairs of scissor legs attached to

SECTION 10

#1733085240832

1068-402: 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

1157-424: 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

1246-399: 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

1335-911: 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)

1424-414: 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

1513-618: A maximum effective range of only 20 to 30 yards (about 20 to 30 meters). Around 1952 Norman MacLeod, at his company the Calord Corporation, began working on a small directional mine for use by infantry. It is not clear if the United States Picatinny Arsenal took the concept from the Canadian weapon and asked Norman MacLeod to develop it, or if he developed the design independently and presented it to them. MacLeod designed

1602-610: 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,

1691-445: A number of experiments, the engineers settled on Devcon-S steel-filled epoxy to hold the balls in place. With this change, the velocity improved to 3,995 feet per second (1,218 m/s). Technical challenges to overcome included developing a case to contain the corrosive C-3 explosive that would be durable enough to withstand months of field handling in wide temperature ranges. Using dyes to test various plastics for leaks, they found

1780-428: A relieving unit. The 100-foot (30 m) M4 electric firing wire on a green plastic spool is provided in each bandolier. The M57 firing device (colloquially referred to as the "clacker") is included with each mine. An M40 circuit test set is packed in each case of six mines. When the mines are daisy-chained together, one firing device can detonate several mines. The mine can be detonated by any mechanism that activates

1869-496: A suitable plastic called Durex 1661½, which could be easily molded into a case. By the spring of 1956, Aerojet had a near-final design. It was awarded a pre-production contract for 1,000 M18A1 Claymores, designated T-48E1 during testing. The initial versions of the mine used two pairs of wire legs produced from number 9 (3 mm) wire. Later when production was ramped up, the design was changed to flat steel scissor, folding-type legs. Early pre-production mines were triggered using

SECTION 20

#1733085240832

1958-566: 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

2047-664: A weapon called the T-48; broadly similar to the final M18A1, it lacked a number of the design details that made the M18A1 effective. Through Picatinny, the United States Army accepted the weapon into service as the M18 Claymore and approximately 10,000 were produced. It was used in small numbers in Vietnam from around 1961. It was not until the improved M18A1 was developed that the Claymore became

2136-402: A widely used weapon. The M18 was 9.25-inch (235 mm) long and 3.27-inch (83 mm) high, held in a plastic case with three folding spike legs on the bottom. An electrical blasting cap for triggering the mine was inserted through a small hole in the side. Internally the mine consisted of a layer of 12-ounce (340 g) of C-3 explosive (the forerunner of C-4 explosive ) in front of which

2225-542: 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

2314-607: Is a directional anti-personnel mine developed for the United States Armed Forces . Its inventor, Norman MacLeod, named the mine after a large medieval Scottish sword . Unlike a conventional land mine, the Claymore may be command-detonated (fired by remote-control), and is directional, shooting a wide pattern of metal balls into a kill zone . The Claymore can also be activated by a booby-trap tripwire firing system for use in area denial operations . The Claymore fires steel balls out to about 100 m (110 yd) within

2403-421: 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

2492-806: 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,

2581-489: 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

2670-509: Is an oxirane . Epoxy resins may be reacted ( cross-linked ) either with themselves through catalytic homo polymerisation , or with 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

2759-406: 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

Sirasa TV - Misplaced Pages Continue

2848-453: 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

2937-573: 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

3026-406: 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

3115-475: 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

3204-430: Is detonated as the enemy personnel approaches the killing zone. Controlled detonation may be accomplished by use of either an electrical or non-electrical firing system . When mines are employed in the controlled role, they are treated as individual weapons and are reported in the unit fire plan . They are not reported as mines; however, the emplacing unit must ensure that the mines are removed, detonated, or turned over to

3293-433: 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

3382-663: 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

3471-522: Is packed in a Claymore bag with inert M10 simulated detonator cap wire, an M57 "clacker" firing control, and an M40 circuit test kit. In early 2015, the U.S. Army began testing a smaller version of the Claymore called the Mini-Multi-Purpose Infantry Munition (M-MPIMS). It weighs 2 lb (0.91 kg) and has a 50 m (160 ft) effective range, similar to the full-size Claymore. At its optimized range of 30 m (98 ft),

3560-503: Is poured rather than packed for more uniform distribution results in more consistent blast pattern. Rear-safety distance has been decreased to 15 m (49 ft) and shelf life has been increased to 25 years. PADMINE is an anti-personnel directional fragmentation mine produced by the United Kingdom, similar to the Claymore in cosmetic design with two swivelling legs, inserted into soft-ground. Its lethality out to 50 meters arrives in

3649-499: Is similar to the Claymore mine. A number of licensed and unlicensed copies of the mine have been produced. Epoxy resin Epoxy 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

Sirasa TV - Misplaced Pages Continue

3738-593: The Korean War , Canada and the United States began to develop projects to counter them. Canada fielded a weapon called the "Phoenix" landmine, which used the Misnay–Schardin effect to project a spray of 0.25-inch (6.4 mm) steel cubes towards the enemy. The cubes were embedded in 5 pounds (2.3 kg) of Composition B explosive. It was too large to be a practical infantry weapon and was relatively ineffective, with

3827-553: The Army, and Aerojet, which further developed the Claymore design. MacLeod's case collapsed when photographs of the German Trenchmine prototype were produced as evidence of prior art . In 1954 Picatinny Arsenal issued a request for proposals (RFP) to improve the M18 as a more effective weapon. At Aerojet in the early 1950s, Guy C. Throner had independently come up with a design for a Claymore-like mine. He worked with Don Kennedy and

3916-452: The ability to aim the mine with an accuracy of around two feet (0.61 m) at the center of the target zone. The team at Aerojet were given access to all previous research into directional mines, including the M18 and the Phoenix, as well as German research. Dr. John Bledsoe led the initial project. The original M18 mine fell far short of Picatinny's requirements. One of the first improvements

4005-401: 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

4094-489: 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

4183-404: The blasting cap. There are field-expedient methods of detonating the mine by tripwire, or by a timer, but these are rarely used. The development of the M18A1 mine dates back to work done during World War II . The Misnay–Schardin effect was independently discovered during that war by József Misnay, a Hungarian , and Hubert Schardin , a German. When a sheet of explosive detonates in contact with

4272-449: The bottom support the mine and allow it to be aimed vertically. On both sides of the sight are fuse wells set at 45 degrees. Internally the mine contains a layer of C-4 explosive behind a matrix of about seven hundred 1 ⁄ 8 -inch-diameter (3.2 mm) steel balls set into an epoxy resin . When the M18A1 is detonated, the explosion drives the matrix forward, out of the mine at a velocity of 1,200 m/s (3,937 ft/s), at

4361-717: 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

4450-405: 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

4539-511: 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

SECTION 50

#1733085240832

4628-462: 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

4717-672: 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

4806-451: The first large-scale production run producing a plastic device. The sighting for the device was originally intended to be a cheap pentaprism device, which would allow the user to look down from above and see the sight picture. After locating a suitably low-cost device, the engineers found that fumes from either the C-3 explosive or the cement used to glue the sight to the top of the mine corroded

4895-538: The form of 650 steel balls and it is activated by remote control or trip wire. The M18 directional fragmentation anti-personnel mine, developed by Cardoen of Chile, contains 626 grams of explosives, surrounded by 607 AP fragmentation units providing a 60 degree arc of fire, with a 50-250 meters lethal range. Italy produces the DAF M6 and DAF M7 directional fragmentation mines, weighing 18 and 10 kilograms respectively, with trip wire or remote control detonation. Their appearance

4984-449: 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

5073-418: The fragmentation zone is 23 m (75 ft) wide and 2 m (6.6 ft) high, with a minimum of five hits per 1 m (11 sq ft). It has the surface space of an average smartphone and includes a Picatinny rail for camera, laser, or other attachments. The M-MPIMS is designed to be more controllable than the Claymore with less collateral damage, using an insensitive munitions explosive that

5162-1034: The government of being responsible for the attack. Sinhala : කියා දෙන්න ආදරේ තරම් Sinhala : දාම් Sinhala : සකූගේ ලෝකය Sinhala : සල් මල් ආරාමය Sinhala : සද තරු මල් Sinhala : Wow මැඩම් Sinhala : හිත ලග හිනැහුනා Sinhala : අපි අපේ Sinhala : රැස් Sinhala : හේලන්කඩ Sinhala : සූර්‍ය වංශය Sinhala : සක්කාරං Sinhala : නීල පබළු Sinhala : මිනි ගං දෑල Sinhala : අඩෝ Sinhala : ඔබ නිසා Sinhala : සල් සපුනා Sinhala : සර්කස්කාරයෝ Sinhala : උතුම් පැතුම් Sinhala : පැහැසරා Sinhala : යස් බොස් Sinhala : නෝනාවරුනි මහත්වරුනි Sinhala : චන්දෝලි Sinhala : ඉම්ලි Sinhala : අග්‍රා Sinhala : හිමන්තරා Sinhala : සුජාත Sinhala : ස්වප්නා Sinhala : ප්‍රේමායුධ Sinhala : අනන්තයෙන් ආ තරු කුමරා Sinhala : ප්‍රේම දඩයම Sinhala : ඉක්කයි මායි Sinhala : යවෙස් ලූ කුමරා Sinhala : මේ ආදරයයි Claymore mine The Claymore mine

5251-401: 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

5340-549: 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

5429-435: 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,

SECTION 60

#1733085240832

5518-510: The mine. The M68 kit is designed to familiarize personnel with the placement and arming of a real M18 directional mine. It comes with all the components of a real Claymore kit packed in an M7 bandolier. The light blue or black plastic M33 Inert Anti-Personnel Mine is the training and practice version of the M18A1 Claymore. Some inert mines were green with a light blue band. It does not contain an explosive or pyrotechnic filler of any kind. It

5607-923: 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

5696-400: 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

5785-594: 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

5874-602: 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

5963-400: 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

6052-444: 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

6141-528: The plastic mirrors, rendering them unusable. They adopted simple peep sights, which were later replaced by a knife blade sight . Testing concluded that the mine was effective out to approximately 110 yards (100 m), being capable of hitting 10% of the attacking force. At 55 yards (50 m), this increased to 30%. The development project completed, the Aerojet team sent the project back to Picatinny. The Arsenal bid it out to various component suppliers. In 1960 it

6230-449: 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

6319-418: 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

6408-871: 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

6497-417: 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

6586-491: 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

6675-784: 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

6764-444: 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

6853-427: The same time breaking it into individual fragments. The steel balls are projected in a 60° fan-shaped pattern that is 2.0 metres (6.6 ft) high and 50 m (55 yd) wide at a range of 50 m (55 yd). The force of the explosion deforms the relatively soft steel balls into a shape similar to a .22 rimfire projectile. These fragments are moderately effective up to a range of 100 m (110 yd), with

6942-399: The shock of the explosive, but deformed into a useful aerodynamic shape similar to a .22 rimfire projectile. Using a homemade chronograph , the engineers clocked the balls at 3,775 feet per second (1,151 m/s). The second change was to use a poured plastic matrix to briefly contain the blast from the explosive, so that more of the blast energy was converted into projectile velocity. After

7031-430: 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

7120-706: 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

7209-442: The two men submitted a 30-page proposal in response to Picatinny's RFP. They were awarded a $ 375,000 development contract to improve the Claymore design. The Picatinny criteria for the weapon were as follows: The requirement for kinetic energy was based on the fact that 58-foot pounds is required to deliver a potentially lethal injury. Given the requirements of weight and fragment density, approximately 700 fragments were needed, with

7298-891: 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

7387-555: 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

7476-537: 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

7565-425: Was laid an array of 0.25-inch (6.4 mm) steel cubes. In total the mine weighed about 2.43-pound (1.10 kg), and could be fitted with an optional peep sight for aiming. It lacked the later version's iconic "FRONT TOWARD ENEMY" marking. The mine was planted in the ground, using its three sharp legs, and aimed in the direction of enemy approach; at that point, it was fitted with an electrical blasting cap. The mine

7654-469: Was the curvature of the mine. This was determined experimentally by Bledsoe, through a large number of test firings. After Bledsoe left the project to work at the Rheem corporation, William Kincheloe, another engineer, came onto the Claymore project. Kincheloe immediately suggested using softer 1 ⁄ 8 -inch (3.2 mm) steel "gingle" balls, which were used in the foundry process. They did not spall from

7743-427: Was to replace the steel cubes with 7 ⁄ 32 -inch (5.6 mm) hardened 52100 alloy ball bearings. These performed poorly for two reasons. Firstly, the hardened steel balls spalled into fragments when hit by the shock of the explosion; the fragments were neither aerodynamic enough nor large enough to perform effectively. Secondly, the blast "leaked" between the balls, reducing their velocity. A second problem

7832-463: Was triggered from a safe position, preferably to the side and rear. The mine was barely more than a prototype and was not considered a "reliable casualty producer"; like the Phoenix it had an effective range of only 90 feet (27 m). MacLeod applied for a patent for the mine on 18 January 1956, and was granted it in February 1961. The patent was later the subject of a civil court case between MacLeod,

7921-486: Was type standardized as the M18A1. It was first used in Vietnam in the spring or early summer 1966. Minor modifications were made to the mine during its service. A layer of tinfoil was added between the fragmentation matrix and the explosive. This slightly improves the fragment velocity, and protects the steel fragments from the corrosive explosive. A ferrite choke was added to prevent RF signals and lightning from triggering

#831168