Sabtu, 28 Mei 2011

andes

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Andes (Quechua: Anti(s/kuna))
Range
Aerial photo of a portion of the Andes between Argentina and Chile
Countries Argentina, Bolivia, Chile, Colombia, Ecuador, Peru, Venezuela

Cities Bogotá, Santiago, Medellín, La Paz, Cali, Quito, Pasto, Bucaramanga, Arequipa, Mendoza, Cuenca, Cochabamba, Pereira, Ibagué, Salta, Manizales

Highest point Mt. Aconcagua
 - location Las Heras Department, Mendoza, Argentina
 - elevation 6,962 m (22,841 ft)
 - coordinates 32°39′10″S 70°0′40″W / 32.65278°S 70.01111°W / -32.65278; -70.01111

Length 7,000 km (4,350 mi)
Width 500 km (311 mi)

Composite satellite image of the southern Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about 7,000 km (4,300 mi) long, about 200 km (120 mi) to 700 km (430 mi) wide (widest between 18 degrees South and 20 degrees South latitude), and of an average height of about 4,000 m (13,000 ft).
Along its length, the Andes is split into several ranges, which are separated by intermediate depressions. The Andes is the location of several high plateaux – some of which host major cities such as Quito, Bogotá, Arequipa, Medellín, Sucre, and La Paz.
The so-called Altiplano plateau is the world's second-highest plateau following the Tibetan plateau. The Andes extends to seven countries, in alphabetical order: Argentina, Bolivia, Chile, Colombia, Ecuador, Peru, and Venezuela, some of which are known as the Andean States.
The Andes range is the world's highest mountain range outside of the continent of Asia. The highest peak, Mt. Aconcagua, rises to an elevation of about 6,962 m (22,841 ft) above sea level. The peak of Mt. Chimborazo in the Ecuadorean Andes is located at the point on the surface of the Earth that is the most distant one from its centre. This is because of the Earth's equatorial bulge that results from its rotation. The world's highest volcanos are in the Andes, including Ojos del Salado on the Chile-Argentina frontier which rises to 6,893 m (22,615 ft), and over 50 other volcanos that rise above 6,000 m.

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[edit] Name

The etymology of the word Andes has been debated. The major consensus is that it derives from the Quechua word anti, which means "high crest". Others believe that Andes comes from Anti Suyu, one of the four regions of the Inca empire. It is more likely however that the word Antisuyo derives from the use of Anti to designate mountain chains. Derivation from the Spanish andén (in the sense of cultivation terrace) has also been proposed, yet considered very unlikely.

[edit] Geography

Aerial view of Aconcagua.
The Andes can be divided into three sections:
I. The Southern Andes in Argentina and Chile;
II. The Central Andes, including the Chilean and Peruvian cordilleras and parts of Bolivia;
III. The Northern Andes in Venezuela, Colombia, and Ecuador that consists of two parallel ranges, the Cordillera Occidental and the Cordillera Oriental. In Colombia, north its the border with Ecuador, the Andes split in three parallel ranges, the western, central, and eastern ranges. (The cordillera occidental, central, and oriental).
In the northern part of the Andes, the isolated Sierra Nevada de Santa Marta range is often considered to be part of the Andes. The eastern range of Colombia is the only one that extends to Venezuela.[1] The term cordillera comes from the Spanish word meaning "cuerda", meaning "rope". The Andes range is about 200 km (124 mi) wide throughout its length, except in the Bolivian flexure where it is about 640 kilometres (398 mi) wide. The islands of the Dutch Caribbean Aruba, Bonaire, and Curaçao, which lie in the Caribbean Sea off the coast of Venezuela, were thought to represent the submerged peaks of the extreme northern edge of the Andes range, but ongoing geological studies indicate that such a simplification does not do justice to the complex tectonic boundary between the South-American and Caribbean plates. [2]

[edit] Geology

Geology of the Andes
The Andes
Orogenies
Pampean orogeny
Famatinian orogeny
Gondwanide orogeny
Andean orogeny
Fold-thrust belts
Central Andean | Patagonian
Batholiths
Peruvian Coastal | North Patagonian | South Patagonian
Subducted structures
Antarctic Plate | Carnegie Ridge | Chile Rise | Farallon Plate (formerly) | Juan Fernández Ridge | Nazca Plate | Nazca Ridge
Faults
Gastre | Liquiñe-Ofqui | Magallanes-Fagnano
Andean Volcanic Belt
Northern Zone| Peruvian flat-slab | Central Zone | Pampean flat-slab | Southern Zone | Patagonian Gap | Austral Zone
Paleogeographic terminology
Arequipa-Antofalla Terrane | Chilenia | Chiloé Block | Cuyania | Iapetus Ocean | Madre de Dios Terrane | Mejillonia | Pampia
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The Andes are a MesozoicTertiary orogenic belt of mountains along the Pacific Ring of Fire, a zone of volcanic activity that encompasses the Pacific rim of the Americas as well as the Asia-Pacific region. The Andes are the result of plate tectonics processes, caused by the subduction of oceanic crust beneath the South American plate. The main cause of the rise of the Andes is the compression of western rim of the South American Plate due to the subduction of the Nazca Plate and the Antarctic Plate. To the east, the Andes range is bounded by several sedimentary basins such as Orinoco, Amazon Basin, Madre de Dios and Gran Chaco which separates the Andes from the ancient cratons in eastern South America. In the south the Andes shares a long boundary with the former Patagonia Terrane. To the west the Andes ends at the Pacific Ocean, although the Peru-Chile trench can be considerated its ultimate western limit. From a geographical approach the Andes are considered to have their western boundaries marked by the appearance of coastal lowlands and a less rugged topography.

[edit] Orogeny

The western rim of the South American Plate has been the place of several pre-Andean orogenies since at least the of the late Proterozoic and early Paleozoic when several terranes and microcontinents collided and amalgamated with the ancient cratons of eastern South America, by then the South American part of Gondwana.
The formation of the modern Andes began with the events of the Triassic when Pangea begun to break up and several rifts developed. It continued through the Jurassic Period. It was during the Cretaceous Period that the Andes began to take its present form, by the uplifting, faulting and folding of sedimentary and metamorphic rocks of the ancient cratons to the east. The rise of the Andes has not been constant and different regions have had different degrees of tectonic stress, uplift, and erosion.
Tectonic forces above the subduction zone along the entire west coast of South America where the Nazca Plate and a part of the Antarctic Plate are sliding beneath the South American Plate continue to produce an ongoing orogenic event resulting in minor to major earthquakes and volcanic eruptions to this day. In the extreme south a major transform fault separates Tierra del Fuego from the small Scotia Plate. Across the 1,000 km (620 mi) wide Drake Passage lie the mountains of the Antarctic Peninsula south of the Scotia Plate which appear to be a continuation of the Andes chain.[citation needed]

[edit] Volcanism

Selasa, 24 Mei 2011

potal geography

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Geography is the study of the location, extent, distribution, frequency and interaction of all significant elements of the human and physical environment on or near the Earth's surface, particularly its features and of the distribution of life on the earth, including human life and the effects of human activity. The word geography derives from the Greek γη (ge) or γαια (gaia) ("Earth") and γραφειν (graphein) ("to inscribe"). Physical geography focuses on the physical, meteorological and ecological patterns and processes on Earth. Human geography focuses on economic, political and cultural processes and features in their spatial dimensions. In addition to studying human and natural features of Earth, Geographers also study Earth's place in the Solar System and the Universe and how this affects the Earth features (e.g. climate, sea currents and tides), as well as physical processes on other planets.

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Trafford Park is an area of the Metropolitan Borough of Trafford, in Greater Manchester, England. Located opposite Salford Quays, on the southern side of the Manchester Ship Canal, it is 3.4 miles (5.5 km) west-southwest of Manchester city centre, and 1.3 miles (2.1 km) north of Stretford. Until the late 19th century it was the ancestral home of the Trafford family, who sold it to financier Ernest Terah Hooley in 1896. Occupying an area of 4.7 square miles (12 km2), it was the first planned industrial estate in the world, and remains the largest in Europe. Trafford Park is almost entirely surrounded by water; the Bridgewater Canal forms its southeastern and southwestern boundaries, and the Manchester Ship Canal, which opened in 1894, its northeastern and northwestern boundaries. Hooley's plan was to develop the Ship Canal frontage, but the canal was slow to generate the predicted volume of traffic, therefore in the early days the park was largely used for leisure activities such as golf, polo, and boating. British Westinghouse was the first major company to move in, and by 1903 it was employing about half of the 12,000 workers then employed in the park, becoming one of the most important engineering facilities in Britain.

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Antelope Canyon
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Image credit: Luca Galuzzi

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Ponds in the Upper Harz Water Regale near Buntenbock

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Sabtu, 07 Mei 2011

injection molding

Dari Wikipedia bahasa Indonesia, ensiklopedia bebas
Injection molding adalah metode material termoplastik dimana material yang meleleh karena pemanasan diinjeksikan oleh plunger ke dalam cetakan yang didinginkan oleh air dimana material tersebut akan menjadi dingin dan mengeras sehingga bisa dikeluarkan dari cetakan.
Meskipun banyak variasi dari proses dasar ini, 90 persen injection molding adalah memproses material termoplastik. Injection molding mengambil porsi sepertiga dari keseluruhan resin yang dikonsumsi dalam pemrosesan termoplastik. Sekarang ini bisa dipastikan bahwa setiap kantor, kendaraan, rumah, pabrik terdapat barang-barang dari plastik yang dibuat dengan cara injection molding, misalnya pesawat telepon, printer, keyboard, mouse, rumah lampu mobil ,dashboard, reflektor, roda gigi, helm, televisi, sisir, roda furnitur, telepon seluler, dan masih banyak lagi yang lain.

Daftar isi

[sembunyikan]

[sunting] Sejarah

Mesin injection molding tercatat telah dipatenkan pertama kali pada tahun 1872 di Amerika Serikat untuk memproses celluloid. Berikutnya pada tahun 1920-an di Jerman mulai dikembangkan mesin injection molding namun masih dioperasikan secara manual dimana pencekaman mold masih menggunakan tuas. Tahun 1930-an ketika berbagai macam resin tersedia dikembangkan mesin injection molding yang dioperasikan secara hidrolik. Pada era ini kebanyakan mesin injection moldingnya masih bertipe single stage plunger. Pada tahun 1946 James Hendry membuat mesin injection molding tipe single-stage reciprocating screw yang pertama. Mulai tahun 1950-an relay dan timer mulai digunakan untuk pengontrolan proses injeksi.
Mesin injection molding ukuran kecil, tampak hopper, nozzle dan clamping unit

[sunting] Proses

Termoplastik dalam bentuk butiran atau bubuk ditampung dalam sebuah hopper kemudian turun ke dalam barrel secara otomatis (karena gaya gravitasi) dimana ia dilelehkan oleh pemanas yang terdapat di dinding barrel dan oleh gesekan akibat perputaran sekrup injeksi. Plastik yang sudah meleleh diinjeksikan oleh sekrup injeksi (yang juga berfungsi sebagai plunger) melalui nozzle ke dalam cetakan yang didinginkan oleh air. Produk yang sudah dingin dan mengeras dikeluarkan dari cetakan oleh pendorong hidrolik yang tertanam dalam rumah cetakan selanjutnya diambil oleh manusia atau menggunakan robot. Pada saat proses pendinginan produk secara bersamaan di dalam barrel terjadi proses pelelehan plastik sehingga begitu produk dikeluarkan dari cetakan dan cetakan menutup, plastik leleh bisa langsung diinjeksikan.

[sunting] Jendela proses

Molding area diagram
Jendela proses atau juga disebut Molding Area Diagram adalah sebuah indikator seberapa jauh kita bisa memvariasikan proses dan masih bisa membuat produk yang memenuhi syarat. Idealnya jendela proses cukup lebar sehingga bisa mengakomodasi variasi alami yang terjadi selama proses injeksi. Jika jendela proses terlalu sempit maka ada risiko menghasilkan produk yang cacat akibat variasi proses injeksi berada di luar jendela. Jendela proses berbeda-beda untuk tiap resin karena masing-masing resin memiliki titik leleh (temperatur transisi gelas, Tg) yang berbeda-beda.
Jika temperatur proses terlalu rendah maka ada kemungkinan material tidak meleleh dan jika meleleh maka viskositasnya sangat tinggi sehingga memerlukan tekanan injeksi yang sangat tinggi. Jika tekanan injeksi terlalu tinggi maka akan menimbulkan flash atau burr pada garis pemisah cetakan akibat gaya pencekaman lebih kecili dari tekanan injeksi. Dan jika temperatur proses terlalu tinggi maka material akan mengalami kerusakan atau terbakar.

[sunting] Gas Assisted Injection Molding

Gas Assisted Injection Molding
Gas Assisted Injection Molding melibatkan penggunaan gas bertekanan tinggi dalam proses injeksi. Ketika mold baru terisi sebagian material plastik leleh (1), gas bertekanan tinggi diinjeksikan. Gas ini akan mendorong plastik leleh ke arah dinding-dinding cetakan (2). Tekanan gas tetap dipertahankan untuk memberikan tekanan pemadatan sementara produk mengalami pendinginan (3). Gas yang biasa dipakai adalah gas Nitrogen karena bersifat inert.
Perbedaan tekanan di dalam mold
Keuntungan[1]:
  1. Leluasa dalam mendesain bentuk-bentuk produk berongga, berdinding tipis ataupun tebal dan berbentuk batang atau pipa
  2. Kekakuan produk lebih tinggi akibat adanya ruang kosong (momen inersia polar lebih tinggi)
  3. Memerlukan jumlah gate lebih sedikit sehingga mengurangi weldline
  4. Tidak ada cacat sinkmark pada produk-produk yang tebal
  5. Tekanan injeksi dan pemadatan yang lebih rendah
  6. Distribusi tekanan pemadatan lebih merata
  7. Siklus injeksi lebih cepat akibat waktu pendinginan yang lebih singkat.
  8. Produk yang lebih ringan

[sunting] Mesin injection molding

[sunting] Komponen utama

  1. Unit injeksi - bagian dari mesin injection molding yang berfungsi untuk melelehkan material plastik, terdiri dari hopper, barrel dan screw.
  2. Mold - bagian dari mesin injection molding dimana plastik leleh dicetak dan didinginkan
  3. Unit pencekam - bagian dari mesin injection yang berfungsi untuk mencekam mold pada saat penginjeksian material ke dalam cetakan sekaligus menyediakan mekanisme pengeluaran produk dari mold
Sebuah mold akan dipasang ke mesin injection molding

[sunting] Jenis-jenis mesin injection molding

  1. Berdasarkan metode pencekaman cetakan
    1. pencekam toggle
    2. pencekam hidrolik
  2. Berdasarkan proses pelelehan bijih plastik
    1. single-stage plunger
    2. two-stage screw-plunger
    3. single-stage reciprocating-screw
  3. Berdasarkan tonase - Mesin injection molding dibedakan berdasarkan besarnya gaya pencekaman maksimum yang bisa diberikan. Kisarannya mulai dari 5 ton untuk menghasilkan produk seberat 10 gram sampai dengan 5000 ton untuk menghasilkan produk seberat 50 kilogram.[1]
Mesin injection molding 1300 ton dengan tambahan robot di bagian atas mesin untuk pengambilan produk dari mold

[sunting] Referensi

  1. ^ a b Anonymous (2002). The Injection Molding of Quality Parts - Process Engineering Alternatives and Process Selection (edisi ke-1st). Bayer AG - Plastics Business Group, D-51368 Leverkusen.. p. 18.

[sunting] Daftar pustaka

  • (Inggris) Strong, A. Brent (2006). "Plastics: Materials and Processing". Pearson Prentice Hall ISBN 0-13-114558-4
  • (Inggris) R.J. Crawford (2002). “Plastic Engineering”. Buttenworth-Heinemann ISBN 0-7506-3764-1
  • (Inggris) Anonym (1995). “The Wordsworth Dictionary of Science & Technology”. Wordsworth Reference ISBN 1-85326-351-6
  • (Inggris) Charles A. Harper (2000). “Modern Plastic Handbook”. McGraw-Hill, ISBN 0-07-026714-6

[sunting] Pranala luar

Selasa, 03 Mei 2011

injection molding machine

From Wikipedia, the free encyclopedia

Paper clip mold opened in molding machine; the nozzle is visible at right

An Injection molding machine, also known as an injection press, is a machine for manufacturing plastic products by the injection molding process. It consists of two main parts, aninjection unit and a clamping unit.
Injection molding machines can fasten the molds in either a horizontal or vertical position. The majority of machines are horizontally oriented, but vertical machines are used in some niche applications such as insert molding, allowing the machine to take advantage of gravity. There are many ways to fasten the tools to the platens, the most common being manual clamps (both halves are bolted to the platens); however hydraulic clamps (chocks are used to hold the tool in place) and magnetic clamps are also used. The magnetic and hydraulic clamps are used where fast tool changes are required.

[edit]Types of injection molding machines

Machines are classified primarily by the type of driving systems they use: hydraulic,mechanical, electric, or hybrid. Hydraulic presses have historically been the only option available to molders until Nissei Plastic Industrial Co., LTD introduced the first all-electric injection molding machine in 1983. The electric press, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have a higher accuracy, however the machines are more expensive.Mechanical type machines use the toggle system for building up tonnage on the clamp side of the machine. Tonnage is required on all machines so that the clamp side of the machine does not open (i.e. tool half mounted on the platen) due to the injection pressure.If the tool half opens up it will create flash in the plastic product. Reliability of mechanical type of machines is more as tonnage built during each cycle is the same as compared to hydraulic machines. Hybrid injection molding machines claim to take advantage of the best features of both hydraulic and electric systems, but in actuality use almost the same amount of electricity to operate as a standard hydraulic. Hydraulic machines, although not nearly as precise, are the predominant type in most of the world, with the exception of Japan.
robotic arm is often used to remove the molded components; either by side or top entry, but it is more common for parts to drop out of the mold, through a chute and into a container.

[edit]References