Production of plaster of paris
Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. “plaster” usually means a material used for the interiors of buildings, while “render” commonly refers to external applications. Another imprecise term used for the material is stucco, which is also often used for plasterwork that is worked in some way to produce relief decoration, rather than flat surfaces.
Gypsum is the basic raw material required to manufacture Plaster of Paris. These are cleaned and washed for removal of impurities, dried in sunlight and then pulverized. Gypsum powders are calcined in a rotary drum calcinatory using light diesel oil/firewood/coal as fuel. The low pressure burner is sufficient to reach the calcinations temp. ranges from 1600C to 1800C. The process of calcinations is done over a period of about 2 hours, so that 1½ molecule of water is removed to obtain the required properties. After cooling the calcined powder.
Preparation of lime cement
Since long, Lime has been used to make things like plaster and mortar. Lime is usually made by burning of limestone. Chemically; lime itself is calcium oxide (CaO) and is made by roasting calcite (CaCO3) to remove carbon dioxide (CO2). Lime is also called calx or quicklime. Quick Lime is very caustic and can even dissolve human bodies.
When lime is mixed with water, lime slowly turns into the mineral portlandite(dense) in the reaction CaO + H2O = Ca (OH)2. Lime is mixed with an excess of water so it stays fluid, this is called slaking and the lime resulting is called slaked lime. Slaked lime continues to harden over a period of weeks. Lime has to be mixed with sand and other ingredients to take form of slaked lime cement, that can be used as mortar between stones or bricks in a wall or spread over the surface of a wall There, over the next several weeks or longer, it reacts with CO2 in the air to form calcite again(artificial limestone).
Concrete made with lime cement is well known from more than 5000 years old. It was widely used in all over the world. Sign of its usage can be found easily after surveying different archaeological sites. In dry conditions, it works extremely well.
The main ingredient of this concrete is slaked lime as binding material. The slaked lime is obtained in various forms as hydrated lime powder, lime putty, slaked lime slurry that is prepared by grinding in suitable Grinding Mills. Slaked lime is first mixed with sand to prepare lime mortar which is then further mixed with coarse aggregates, in suitable proportion. For preparation of lime concrete, first hard impervious level base is prepared by stones or brick pitching.
Then quantity of sand is spread as the horizontal base. Generally lime & sand are taken in ratio of 1:1 to 1:3 by volume. Measured quantity of slaked lime is then added to sand and then mixing is done. In this mixing, water is sprinkled continuously to make the whole mass plastic.
Then the whole mass is allowed to mature for 1 to 3 days. After that coarse aggregates of desired type are used to lay on the prepared hard impervious level surface. After that lime mortar which is made with sand & lime is introduced into the base. Sufficient water is sprinkled over the base and it is cut into the layers and then is turned upside down with the help of spade or shovel until the whole assembly has become uniform.
Preparation of glass
It consists of the following steps:
Melting & Refining
Fine grained ingredients closely controlled for quality, are mixed to make a batch, which flows into the furnace, which is heated up to 1500 degree Celsius.
The raw materials that go into the manufacturing of clear float glass are:
SiO2 – Silica Sand
Na2O – Sodium Oxide from Soda Ash
CaO – Calcium oxide from Limestone / Dolomite
MgO – Dolomite
Al2O3 – Feldspar
Apart from the above basic raw material, broken glass aka cullet, is added to the mixture to the tune of nearly 25% ~ 30% which acts primarily as flux. The flux in a batch helps in reducing the melting point of the batch thus reducing the energy consumed to carry out the process.
Float Bath
Glass from the furnace gently flows over the refractory spout on to the mirror-like surface of molten tin, starting at 1100 deg Celsius and leaving the float bath as solid ribbon at 600 deg Celsius.
Coating (for making reflective glasses)
Coatings that make profound changes in optical properties can be applied by advanced high temperature technology to the cooling ribbon of glass. Online Chemical Vapour Deposition (CVD) is the most significant advance in the float process since it was invented. CVD can be used to lay down a variety of coatings, a few microns thick, for reflect visible and infra-red radiance for instance. Multiple coatings can be deposited in the few seconds available as the glass flows beneath the coater (e.g. Sunergy).
Annealing
Despite the tranquillity with which the glass is formed, considerable stresses are developed in the ribbon as the glass cools. The glass is made to move through the annealing lehr where such internal stresses are removed, as the glass is cooled gradually, to make the glass more prone to cutting.
Inspection
To ensure the highest quality inspection takes place at every stage. Occasionally a bubble that is not removed during refining, a sand grain that refuses to melt or a tremor in the tin puts ripples in the glass ribbon. Automated online inspection does two things. It reveals process faults upstream that can be corrected. And it enables computers downstream to steer round the flaws. Inspection technology now allows 100 million inspections per second to be made across the ribbon, locating flaws the unaided eye would be unable to see.
Cutting to Order
Diamond steels trim off selvedge – stressed edges- and cut ribbon to size dictated by the computer. Glass is finally sold only in square meters.
Preparation of steel
Steelmaking is the process for producing steel from iron ore and scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon are removed from pig iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce different grades of steel. Limiting dissolved gases such as nitrogen and oxygen, and entrained impurities (termed “inclusions”) in the steel is also important to ensure the quality of the products cast from the liquid steel.
Basic oxygen steelmaking is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into steel. The process is known as basic due to the chemical nature of the refractories—calcium oxide and magnesium oxide—that line the vessel to withstand the high temperature and corrosive nature of the molten metal and slag in the vessel. The slag chemistry of the process is also controlled to ensure that impurities such as silicon and phosphorus are removed from the metal.
The process was developed in 1948 by Robert Durrer and commercialized in 1952–53 by Austrian VOEST and ÖAMG. The LD converter, named after the Austrian towns of Linz and Donawitz (a district of Leoben) is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen. It reduced capital cost of the plants, time of smelting, and increased labor productivity. Between 1920 and 2000, labour requirements in the industry decreased by a factor of 1,000, from more than 3 worker-hours per tonne to just 0.003. The vast majority of steel manufactured in the world is produced using the basic oxygen furnace; in 2011, it accounted for 70% of global steel output. Modern furnaces will take a charge of iron of up to 350 tons and convert it into steel in less than 40 minutes, compared to 10–12 hours in an open hearth furnace.
Secondary steelmaking is most commonly performed in ladles and often referred to as ladle (metallurgy). Some of the operations performed in ladles include de-oxidation (or “killing”), vacuum degassing, alloy addition, inclusion removal, inclusion chemistry modification, de-sulphurisation and homogenisation. It is now common to perform ladle metallurgical operations in gas stirred ladles with electric arc heating in the lid of the furnace. Tight control of ladle metallurgy is associated with producing high grades of steel in which the tolerances in chemistry and consistency are narrow.
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