Monday, May 31, 2010

Baja Stainless Steel

Baja stainless

Baja stainless merupakan baja paduan yang mengandung minimal 10,5% Cr. Sedikit baja stainless mengandung lebih dari 30% Cr atau kurang dari 50% Fe. Karakteristik khusus baja stainless adalah pembentukan lapisan film kromium oksida (Cr2O3). Lapisan ini berkarakter kuat,tidak mudah pecah dan tidak terlihat secara kasat mata. Lapisan kromium oksida dapat membentuk kembali jika lapisan rusak dengan kehadiran oksigen. Pemilihan baja stainless didasarkan dengan sifat-sifat materialnya antara lain ketahanan korosi, fabrikasi, mekanik, dan biaya produk. Penambahan unsur-unsur tertentu kedalam baja stainless dilakukan dengan tujuan sebagai berikut :

1. Penambahan Molibdenum (Mo) bertujuan untuk memperbaiki ketahanan korosi pitting dan korosi celah

2. Unsur karbon rendah dan penambahan unsur penstabil karbida (titanium atau niobium) bertujuan menekan korosi batas butir pada material yang mengalami proses sensitasi.

3. Penambahan kromium (Cr) bertujuan meningkatkan ketahanan korosi dengan membentuk lapisan oksida (Cr2O3) dan ketahanan terhadap oksidasi temperatur tinggi.

4. Penambahan nikel (Ni) bertujuan untuk meningkatkan ketahanan korosi dalam media pengkorosi netral atau lemah. Nikel juga meningkatkan keuletan dan mampu bentuk logam. Penambahan nikel meningkatkan ketahanan korosi tegangan.

5. Penambahan unsur molybdenum (Mo) untuk meningkatkan ketahanan korosi pitting di lingkungan klorida.

6. Unsur aluminium (Al) meningkatkan pembentukan lapisan oksida pada temperature tinggi.

Umumnya berdasarkan paduan unsur kimia dan presentasibaja stainless dibagi menjadi lima katagori[4]. Lima katagori tersebut yaitu :

Baja stainless martensitik.

Baja ini merupakan paduan kromium dan karbon yang memiliki struktur martensit body-centered cubic (bcc) terdistorsi saat kondisi bahan dikeraskan. Baja ini merupakan ferromagnetic, bersifat dapat dikeraskan dan umumnya tahan korosi di lingkungan kurang korosif. Kandungan kromium umumnya berkisar antara 10,5 – 18%, dan karbon melebihi 1,2%. Kandungan kromium dan karbon dijaga agar mendaptkan struktur martensit saat proses pengerasan. Karbida berlebih meningkatkan ketahanan aus. Unsur niobium, silicon,tungsten dan vanadium ditambah untuk memperbaiki proses temper setelah proses pengerasan. Sedikit kandungan nikel meningkatkan ketahan korosi dan ketangguhan.

Baja stainless Ferritik

Baja jenis ini mempunyai struktur body centered cubic (bcc). Unsur kromium ditambahkan ke paduan sebagai penstabil ferrit. Kandungan kromium umumnya kisaran 10,5 – 30%. Beberapa tipe baja mengandung unsur molybdenum, silicon, aluminium, titanium dan niobium. Unsur sulfur ditambahkan untuk memperbaiki sifat mesin. Paduan ini merupakan ferromagnetic dan mempunyai sifat ulet dan mampu bentuk baik namun kekuatan di lingkungan suhu tinggi lebih rendah dibandingkan baja stainless austenitic. Kandungan karbon rendah pada baja ferritik tidak dapat dikeraskan dengan perlakuan panas.

Tingkat kekerasan beberapa tipe baja stainless ferritik dapat ditingkatkan dengan cara celup cepat. Metode celup cepat merupakan proses pencelupan banda kerja secara cepat dari keadaan temperature tinggi ke temperature ruang. Sifat mampu las, keuletan, ketahanan korosi dapat ditingktakan dengan mengatur kandungan tertentu unsur karbon dan nitrogen.

Baja Stainless austenitik

Baja Stainless austenititk merupakan paduan logam besi-krom-nikel yang mengandung 16-20% kromium, 7-22%wt nikel, dan nitrogen. Logam paduan ini merupakan paduan berbasis ferrous dan struktur kristal face centered cubic (fcc). Struktur kristal akan tetap berfasa austenit bila unsur nikel dalampaduan diganti mangan (Mn) karena kedua unsur merupakan penstabil fasa austenit. Fasa austenitic tidak akan berubah saat perlakuan panas anil kemudian didinginkan pada temperatur ruang. Baja stainless austenitik tidak dapat dikeraskan melalui perlakuan celup cepat (quenching). Umumnya jenis baja ini dapat tetap menjaga sifat asutenitik pada temperature ruang, lebih bersifat ulet dan memiliki ketahanan korosi lebih baik dibandingkan baja stainless ferritik dan martensit. Setiap jenis baja stainless austenitic memiliki karakteristik khusus tergantung dari penambahan unsur pemadunya terlihat pada Gambar 1. baja stainless steel austenitik hanya bisa dikeraskan melalui pengerjaan dingin. Material ini mempunyai kekuatan tinggi di lingkungan suhu tinggi dan bersifat cryogenic. Tipe 2xx mengandung nitrogen, mangan 4-15,5%wt, dan kandungan 7%wt nikel. Tipe 3xx mengandung unsur nikel tinggi dan maksimal kandungan mangan 2%wt. Unsur molybdenum, tembaga, silicon, aluminium,titanium dan niobium ditambah dengan karakter material tertentu seperti ketahanan korosi sumuran atau oksidasi. Sulfur ditambah pada tipe tertentu untuk memperbaiki sifat mampu mesin.

Salah satu jenis baja stainless austenitic adalah AISI 304. Baja austenitic ini mempunyai struktur kubus satuan bidang (face center cubic) dan merupakan baja dengan ketahanan korosi tinggi. Komposisi unsur – unsur pemadu yang terkandung dalam AISI 304 akan menentukan sifat mekanik dan ketahanan korosi. Baja AISI 304 mempunyai kadar karbon sangat rendah 0,08%wt. Kadar kromium berkisar 18-20%wt dan nikel 8-10,5%wt yang terlihat pada Tabel 1. Kadar kromium cukup tinggi membentuk lapisan Cr2O3 yang protektif untuk meningkatkan ketahanan korosi. Komposisi karbon rendah untuk meminimalisai sensitasi akibat proses pengelasan.

Tabel 1. Komposisi kimia baja AISI 304[4]

Unsur

C Mn P S Si Cr Ni Mo Ni Cu Fe
%wt 0.08 2 0.45 0.03 0.75 18-20 8-10.5 0 0.10 0 Balance

Komposisi kandungan unsure dalam baja AISI 304 tersebut diperoleh sifat mekanik material yang ditunjukan pada Tabel 2.

Tabel 2. Sifat mekanik AISI 304 [4]

Poison 0.27-0.30

Tensile 515

Yield 205

Elong 40

Hard 88

Mod 193

Density 8

Keterangan :

Poison : Rasio Poison

Tensile : Tensile strength (MPa)

Yield : Yield Strength (MPa)

Elong : elongation %

Hard : Kekerasan (HVN)

Mod : Modulus elastisitas (GPa)

Density : berat jenis (Kg/m3)

Tabel 3. Sifat fisik dan listrik AISI 304 pada kondisi annealed[4]

Thermal ekspansi (10-6/ºC) 17.2

Thermal konduktivitas (W/m-K) 16.2

Spesific heat (J/kg-K) 500

Resistivitas (10-9W-m) 720

Baja stainless dupleks

Jenis baja ini merupakan paduan campuran struktur ferrite (bcc) dan austenit. Umumnya paduan-paduan didesain mengandung kadar seimbang tiap fasa saat kondisi anil. Paduan utama material adalah kromium dan nikel, tapi nitrogen, molybdenum,tembaga,silicon dan tungsten ditambah untuk menstabilkan struktur dan memperbaiki sifat tahan korosi. Ketahanan korosi baja stainless dupleks hampir sama dengan baja stainless austenitik. Kelebihan baja stainless dupleks yaitu nilai tegangan tarik dan luluh tinggi dan ketahanan korosi retak tegang lebih baik dari pada baja stainless austenitik. Ketangguhan baja stainless dupleks antara baja austenitic dan ferritik.

Baja stainless pengerasan endapan

Jenis baja ini merupakan paduan unsure utama kromium-nikel yang mengandung unsur precipitation-hardening antara lain tembaga, aluminium, atau titanium. Baja ini berstruktur austenitic atau martensitik dalam kondisi anil. Kondisi baja berfasa austenitic dalam keadaan anil dapat diubah menjadi fasa martensit melalui perlakuan panas. Kekuatan material melalui pengerasan endapan pada struktur martensit.

Thursday, May 27, 2010

cara melacak ip

Cara Melacak IP Address Orang Lain

Banyak temen yang bertanya gimana caranya biar kita bisa tau ipaddress lawan chatting, atau ipaddress situs. Nih tipsnya :)

1. Melacak alamat IP suatu situs

Untuk mengetahui alamat IP suatu situs, kita dapat melakukan PING terhadap situs tersebut. Caranya: Masuk ke command Prompt dan ketikan PING www.situs-yang-ingin-diketahui.com lalu tekan enter. Maka akan muncul alamat Ip situs tersebut.

2. Melacak Lokasi server (real address) suatu situs

Kita dapat melacak lokasi server suatu situs hanya dengan mengetahui alamat situsnya saja. Coba anda buka www.domainwhitepages.com Tinggal masukkan IP address situs tadi atau masukkan alamat situsnya dan anda akan mendapatkan info lengkap tentang server dari situs tersebut diantaranya adalah lokasi negara dan kota.

3. Melacak IP address lawan chatting kita

Saat kita menggunakan Yahoo messenger, sebenarnya kita bisa mengetahui alamat IP dari lawan chatting kita. Caranya:

:: Kirimkan suatu file pada lawan chat kita.

:: Lalu masuklah ke Command Prompt (MSDOS) dan ketikkan NETSTAT -N lalu tekan enter, maka alamat IP lawan chatting anda (yang telah anda kirimi file tadi) akan muncul beserta port yang digunakan untuk pengiriman file

Well, selamat mencoba....

kisah sawunggaling

Sawunggaling ternyata juga ada di Lidah Wetan, jaraknya memang tidak lebih dua kilometer dari Wiyung, namun sosok legendaris ini memiliki cerita hidup yang berbeda jauh di mata warga Lidah Wetan dibanding warga Wiyung.

Jika di Wiyung mengklaim makam Sawunggaling di kampungnya, di Lidah Wetan juga tidak mau kalah. Sebuah kompleks pemakaman kuno di daerah ini diyakini sebagai makam Sawunggaling dan kerabatnya.

Ada lima batu nisan di kompleks ini. Yang pertama makam Sawunggaling, empat lainnya bertuliskan Raden Ayu Dewi Sangkrah (Ibu Sawunggaling. Mbah Buyut Suruh (neneknya). Raden Karyosentono (kakeknya). Raden Ayu Pandansari. Siapa Pandansari? masih simpang siur

Ada yang yakin dia mahluk yang mengawal Sawunggaling. Puteri kesayangan raja jin penguasa hutan Lidah dan Wiyung kala itu masih belantara. Namun ada warga yang menduga pandansari adalah istri Sawunggaling. Padahal kisah yang dikenal selama ini menyebutkan Sawunggaling bujangan sampai akhir hayatnya.

Seorang ningrat Mataram Raden Ayu Dewi Sangkrah yang minggat dari keraton diangkat anak oleh sesepuh adat Lidah Karyosentono dan Buyut Suruh. Gadis yang digambarkan cantik ini sempat menarik perhatian raja Surabaya, Jayengrono yang gemar berburu di kawasan ini.

Kisah perkenalan, hingga perkawinan ini sama dengan versi Wiyung, Namun di versi Lidah dijelaskan jika Jayengrono sempat berpesan kepada Sangkrah jika kelak Sawunggaling dewasa, beritahu jika ayahnya adalah Jayengrono, penguasa kerajaan Surabaya. Sang Raja meninggalkan selendang yang dikenal dengan sebutan cinde. Kain inilah yang akan menjadi penghantar Sawunggaling dewasa menemui ayahnya. kelak.

Singkat cerita, Dewi yang sudah nikah lagi dan dikaruniai dua anak harus membuka rahasia selama belasan tahun ketika Sawunggaling berpamitan ingin merantau ke kota kerajaan Surabaya. Sawunggaling berniat berangkat bersama kakek angkatnya Karyosentono ke keraton. Upaya penggagalan rencana Sawunggaling itu juga dilakukan dua adik tirinya, Sawungrono dan Sawungsari.

Perjalanan melelahkan menembus hutan itu akhirnya sampai ke kota kerajaan. Dia mengubah namanya dengan sebutan Joko Berek karena nama Sawunggaling sudah dikenal sebagai jago adu ayam. Diduga ini sebagai upaya agar dirinya tidak dikenal.

Namun dikisahkan Sawunggaling ternyata justru tidak bisa masuk dalam tembok keraton meskipun membawa cinde. Tidak ada yang bisa meyakinkan penjagaan dengan sehelai kain yang dibawa lelaki ceking dari pedalaman Surabaya ini.

Sampai beberapa lama dia menggelandang. Menjadi orang yang gemar berkelahi, sosoknya kian terkenal, sampai suatu hari sang raja yang sudah uzur berkeliling kerajaan. Sawunggaling berniat mencegatnya, namun sempat pula dihalang-halangti.

Namun ketika sang raja sedang lewat menunggang gajah, dan setiap orang di kota kerajaan menunduk, Sawunggaling malah memperlihatkan bkepala tegak, dai memancing perhatian, dia kemudian justru melempar cinde. Para pengawalpun sigap menangkap.

"Saya dititipi kain ini oleh ibu," teriaknya. Sang raja sontak kaget langsung berhenti dan menemui anaknya. Dia memeluk haru. Semua bengong, pengawal juga demikian. Tidak ada yang bisa menghalangi pertemuan bapak anak yang belasan tahun berpisah ini.

Saturday, April 24, 2010

Pembuatan Pencils

One of the oldest and most widely used writing utensils, the pencil originated in pre-historic times when chalky rocks and charred sticks were used to draw on surfaces as varied as animal hides and cave walls. The Greeks and Romans used flat pieces of lead to draw faint lines on papyrus, but it was not until the late 1400s that the earliest direct ancestor of today's pencil was developed. About one hundred years later graphite, a common mineral occurring as soft, lustrous veins in rocks, was discovered near Borrowdale in northwestern England. The Borrowdale mine supplied Europe with graphite for several hundred years; however, because people could not then differentiate between graphite and lead, they referred to the former as "black lead." Cut into rods or strips, graphite was heavily wrapped in twine to provide strength and a comfortable handle. The finished product, called a lead pencil, was quite popular. In the late sixteenth century, a method for gluing strips of wood around graphite was discovered in Germany, and the modern pencil began to take form. In 1779, scientists determined that the material they had previously thought was lead was actually a form of microcrystalline carbon that they named graphite (from the Greek "graphein" meaning "to write"). Graphite is one of the three natural forms of pure carbon—the others are coal and diamond.
In the late eighteenth century the Borrowdale mine was depleted, and, as graphite was now less plentiful, other materials had to be mixed with it to create pencils. A Frenchman chemist, Nicolas Jacques Conte, discovered that when powdered graphite, powdered clay, and water were mixed, molded, and baked, the finished product wrote as smoothly as pure graphite. Conte also discovered that a harder or softer writing core could be produced by varying the proportion of clay and graphite—the more graphite, the blacker and softer the pencil. In 1839, Lothar von Faber of Germany developed a method of making graphite paste into rods of the same thickness. He later invented a machine to cut and groove the pencil wood. Following the depletion of the once-abundant graphite source at Borrowdale, other graphite mines were gradually established around the world.
A number of these mines were set up in the United States, and the first American pencils were manufactured in 1812, after the War of 1812 ended English imports. William Monroe, a cabinet maker in Concord, Massachusetts, invented a machine that cut and grooved wood slats precisely enough to make pencils. Around that time, American inventor Joseph Dixon developed a method of cutting single cedar cylinders in half, placing the graphite core in one of the halves, and then gluing the two halves back together. In 1861, Eberhard Faber built the United States' first pencil-making factory in New York City.
Today, the hardness of a pencil is designated by numbers or letters. Most manufacturers use the numbers 1 to 4, with 1 being the softest and making the darkest mark. Number 2 pencils (medium soft) are used for normal writing. Pencils are also sometimes graded by letters, from 6B, the softest, to 9H, the hardest. The idea of attaching an eraser to a pencil is traced to Hyman W. Lipman, an American whose 1858 U.S. patent was bought by Joseph Rechendorfer in 1872 for a reported $100,000.

The first step in pencil manufacture involves making the graphite core. One method of doing this is extrusion, in which the graphite mixture is forced through a die opening of the proper size.
In addition to the conventional wood pencil, a number of other pencils are widely used. In the early 1880s, the search for a pencil that didn't require sharpening led to the invention of what has variously been termed the automatic, propelling, or repeating pencil. These instruments have a metal or plastic case and use leads similar to those found in wood cased pencils. The lead, lodged in a metal spiral inside the case, is held in place by a rod with a metal stud fastened to it. When the cap is twisted, the rod and stud move downward in the spiral, forcing the lead toward the point. The early twentieth century saw the development of colored pencils in which the graphite core was replaced by a combination of pigments or dyes and a binder. Today, colored pencils are available in more than 70 colors, with 7 different yellows and 12 different blues. However, the cedar-casing lead pencil—manufactured at a pace of 6 billion per year in 40 different countries—continues to outsell all of its competitors, including the ballpoint pen.
Raw Materials
The most important ingredient in a pencil is the graphite, which most people continue to call lead. Conté's method of combining graphite with clay is still used, and wax or other chemicals are sometimes added as well. Virtually all graphite used today is a manufactured mixture of natural graphite and chemicals.
The wood used to manufacture pencils must be able to withstand repeated sharpening and cut easily without splintering. Most pencils are made from cedar (specifically, California cedar), the choice wood for many years. Cedar has a pleasant odor, does not warp or lose its shape, and is readily available. Some pencils have erasers, which are held on with a ferrule, a metal case that is either glued or held on with metal prongs. The erasers themselves consist of pumice and rubber.
The Manufacturing
Process
Now that most commercially used graphite is made in factories rather than mined, manufacturers are able to easily control its density. The graphite is mixed with clay according to the type of pencil being made—the more graphite used, the softer the pencil, and the darker its line. For colored pencils, pigments are added to the clay, and virtually no graphite is used.
Processing the graphite
• 1 Two methods are used to form the graphite into its finished state. The first is an extrusion method in which the graphite and wax mixture is forced through a mold to create a spaghetti-like string, which is then cut to precise measurements and dried in ovens. In the second method, the graphite and clay mixture is poured into a machine called a billet press. A plug is placed over the top of the press, and a metal ram ascends from the bottom to squash the mixture into a hard, solid cylinder called a "billet." The billet is then removed from the top of the machine and placed into an extrusion press that forces it through a mold, slicing off strips the

To make the wood casings for the pencils, square slats are formed, and then grooves are cut into the slats. Next, graphite sticks are inserted into the grooves on one slat, and then a second slat with empty grooves is glued on top of the graphite-filled slot. Correctly sized pencils are cut out of the sandwich, and the eraser and metal ferrule are attached.
size of the pencil core. After being cut to size, the cores pass along a conveyor belt and are collected in a trough to await insertion in the pencil wood.
Making the wood casings
• 2 The cedar usually arrives at the factory already dried, stained, and waxed, to prevent warping. Logs are then sawed into narrow strips called "slats"; these are about 7.25 inches (18.4 centimeters) long, .25 inch (.635 centimeter) thick, and 2.75 inches (6.98 centimeters) wide. The slats are placed into a feeder and dropped, one-by-one, onto a conveyor belt which moves them along at a constant rate.
• 3 The slats are then planed to give them a flat surface. Next, they pass under a cutter head that makes parallel semicircular grooves—one half as deep as the graphite is thick—along the length of one side of each slat. Continuing along the conveyor belt, half of the slats are coated with a layer of glue, and the cut graphite is laid in the grooves of these slats.
• 4 The slats without glue—and without graphite in the grooves—are placed on another belt that carries them to a machine that picks them up and turns them over, so they are laying on the belt with the grooves facing down. The two conveyor belts then meet, and each unglued slat is placed over a slat with glue and graphite, forming a sandwich. After the sandwiches have been removed from the conveyor belt, they are placed into a metal clamp and squeezed by a hydraulic press and left clamped together until the glue is dried. When the pencils are dried, the ends are trimmed to remove excess glue.
Shaping the pencils
• 5 The next step is shaping, when the sandwiches actually become pencils. The sandwiches are placed on a conveyor belt and moved through two sets of cutters, one above and one below the belt. The cutters above the sandwiches cut around the top half, while the lower set cuts around the bottom half and separates the finished pencils. The majority of pencils are hexagonal, so designed to keep the pencils from rolling off surfaces; a single sandwich yields six to nine hexagonal pencils.
Final steps
• 6 After the pencils have been cut, their surfaces are smoothed by sanders, and varnish is applied and dried. This is done with varnishing machines, in which the pencils are immersed in a vat of varnish and then passed through a felt disk, which removes the excess varnish. After drying, the pencils are put through the process again and again until the desired color is achieved. Finally, the pencils receive a finishing coat.
• 7 The pencils once again are sent on a conveyor belt through shaping machines, which remove any excess varnish that has accumulated on the ends of the pencils. This step also ensures that all of the pencils are the same length.
• 8 Erasers are then attached, held to the pencil by a round, metal case called a "ferrule." The ferrule first attaches to the pencil either with glue or with small metal prongs, and then the eraser is inserted and the ferrule clamped around it. In the final step, a heated steel die presses the company logo onto each pencil.
Colored pencils
Colored pencils are produced in much the same way as black-writing pencils, except that their cores contain coloring materials such as dyes and pigments instead of graphite. First, clay and gum are added to pigment as bonding agents, and then the mixture is soaked in wax to give the pencils smoothness. When the pencils have been formed, the outsides are painted according to the color of the center mixture.
Quaility Control
Because they travel along a conveyor belt during the manufacturing process, pencils are thoroughly scrutinized before they are distributed to the public. Workers are trained to discard pencils that appear dysfunctional, and a select number are sharpened and tested when the process is complete. A common problem is that the glue of the sandwiches sometimes doesn't adhere, but this nuisance is usually caught when the sandwiches are being cut.
Where To Learn More
Books
Fischler, George. Fountain Pens and Pencils. Schiffer Publishing, 1990.
Petroski, Henry. The Pencil: A History of Design and Circumstance. Knopf, 1990.
Thomson, Ruth. Making Pencils. Franklin Watts, 1987.
Periodicals
Leibson, Beth. "A Low-Tech Wonder." Reader's Digest. July, 1992, p. 92.
Lord, Lewis J. "The Little Artifact that Could." U.S. News & World Report. January 22, 1990, p. 63.
Sprout, Alison. "Recycled Pencil." Fortune. June 15, 1992, p. 113.
Urbanski, Al. "Eberhard Faber: the Man, the Pencil, the Born-Again Marketing Company." Sales & Marketing Management. November, 1986, p. 44.
— Jim Acton