29-08-2014, 03:45 PM
It is basically manufacturing of lead oxide batteries which involves casting of grids,pasting of battery plates,charging of batteries. These batteries are used as inverter batteries and also used in automobiles.
Construction of lead oxide battery
• One –piece cover • Terminal-post cover • Cell connector • Terminal post • Vent plugs underneath the cover plate • Plate strap • Case • Bottom mounting rail • Positive plates inserted into envelope type separators Construction of battery Plates The principle of the lead acid cell can be demonstrated with simple sheet lead plates for the two electrodes. However such a construction would only produce around one ampere for roughly postcard sized plates, and it would not produce such a current for more than a few minutes. Gaston Plante realized that a plate construction was required that gave a much larger effective surface area. Plante’s method of producing the plates has remained largely unchanged and is still used in stationary applications. The Faure pasted-plate construction is typical of automotive batteries. Each plate consists of a rectangular lead grid alloyed with antimony or calcium to improve the mechanical characteristics. The holes of the grid are filled with a mixture of red lead and 33% dilute sulfuric acid. (Different manufacturers have modified the mixture). The paste is pressed into the holes in the plates which are slightly tapered on both sides to assist in retention of the paste. This porous paste allows the acid to react with the lead inside the plate, increasing the surface area many fold. At this stage the positive and negative plates are similar , however expanders and additives vary their internal chemistry to assist in operation when in use. Once dry, the plates are then stacked together with suitable separators and inserted in the battery container. An odd number of plates is usually used, with one more positive plate than negative. Each alternate plate is connected together. After the acid has been added to the cell, the cell is given its first forming charge. The positive plates gradually turn the chocolate brown color of lead dioxide, and the negative turn the slate gray of 'spongy' lead. Such a cell is ready to be used. Modern manufacturing methods invariably produce the positive and negative plates ready formed, so that it is only necessary to add the sulfuric acid and the battery is ready for use. One of the problems with the plates is that the plates increase in size as the active material absorbs sulfate from the acid during discharge, and decrease as they give up the sulfate during charging. This causes the plates to gradually shed the paste during their life. It is important that there is plenty of room underneath the plates to catch this shed material. If this material reaches the plates a shorted cell will occur. The paste material used to make battery plates also contains carbon black, blow fixe (barium sulfate) and lignosulfonate. The blanch fixe acts as a seed crystal for the lead to lead sulfate reaction. The blanc fixe must be fully dispersed in the paste in order for it to be effective. The lignosulfonate prevents the negative plate from forming a solid mass of lead sulfate during the discharge cycle. It enables the formation of long needle like crystals. The long crystals have more surface area and are easily converted back to the original state on charging. Carbon black counteracts the effect of inhibiting formation caused by the lignosulfonates. It has been found that sulfonated naphthalene condensate dispersant is a more effective expander than lignosulfonate and can be used to speed up the formation of the battery plate. This dispersant is believed to function to improve dispersion of barium sulfate in the paste, reduce hydro set time, produce a stronger plate which is resistant to plate breakage, to reduce fine lead particles and thereby improve handling and pasting characteristics. It extends the life of the battery by increasing the end of charge voltage. The sulfonated naphthalene condensate polymer dispersant can be used in about one-half to one-third the amount of lignosulfonate and is stable to higher temperatures than lignosulfonate About 60% of the weight of an automotive-type lead-acid battery rated around 60 Ah (8.7 kg of a 14.5 kg battery) is lead or internal parts made of lead; the balance is electrolyte, separators, and the case. Conventional batteries Battery case •Sediment chambers which serve to accumulate the solid material which is sloughed off from the plates and falls to the bottom of the case. The sediment accumulates in the sediment chambers without contacting the plates. Short-circuits are thus avoided. •Partitions subdivide the battery case into cells, the basic battery assemblies. They contain the elements (9,10) with positive and negative plates, as well as separators inserted between them. •The cells are connected in series using cell connectors (3), which provide the connection' through openings in the cell walls One-piece cover •The cells are all covered and sealed with a one-piece cover (1), which is provided with an opening above each cell for filling with electrolyte and for servicing. •The opening is closed by a screw-in plug with vent opening (5). On 100% maintenance-free batteries, although these vent plugs are no longer accessible they are also provided with vent openings although these are not visible. Lead-antimony alloy (PbSb) •Antimony is added to the lead used for the grid to improve the cast ability of the thin lead grids • The antimony acts as a hardener, this is where the term "hard lead" •Antimony is increasingly separated out due to positive-grid corrosion. It wanders to the negative plate, these increase the negative plate's self-discharge and reduce the voltage at which gassing starts •The 4... 5 % antimony content formerly used in the grid lead led to self-discharge of the negative plate, one of the main reasons for starter-battery failure. Active material •The active mass is that part of the battery plates which changes chemically when current flows, that is, during the charging and discharging processess (see DIN 40 729). • The electrochemical conversion of the active material which usually takes place at the manufacturer. Separators •Separators are used between the positive and negative plates of a lead acid battery to prevent short circuit through physical contact, mostly through dendrites (`treeing'), but also through shedding of the active material. •Separators obstruct the flow of ions between the plates and increase the internal resistance of the cell. •Various materials have been used to make separators Wood Rubber Glass fiber mat Cellulose Sintered PVC Micro porous PVC/polyethylene An effective separator must possess a number of mechanical properties; applicable considerations include permeability, porosity, pore size distribution, specific surface area, mechanical design and strength, electrical resistance, ionic conductivity, and chemical compatibility with the electrolyte. In service, the separator must have good resistance to acid and oxidation. The area of the separator must be a little larger than the area of the plates to prevent material shorting between the plates. The separators must remain stable over the operating temperature range of the battery. Wooden separators were originally used, but deteriorated in the acid electrolyte. Rubber separators were stable in the battery acid. Cell connectors •The battery's individual cells (elements) are connected in series by the cell connectors (Fig. I). •To decrease the battery's internal resistance and weight, direct cell connectors are used in modern batteries. •The plate straps of individual cells are connected by the shortest path, that is directly through the cell partition. This also reduces the danger of short-circuits due to external influences. Terminal posts •The plate strap for the positive plates of the first cell is connected to the positive terminal post, and that from the negative plates of the last cell to the negative terminal post. • The terminal voltage is then available between these two terminal posts (in other words approx. 12 V). • The positive post is thicker than the negative post Lead Lead is bright and silvery when freshly cut but the surface rapidly tarnishes in air to produce the more commonly observed dull luster normally associated with lead. It is a dense, ductile, very soft, highly malleable, bluish-white metal that has poor electrical conductivity. This true metal is highly resistant to corrosion, and because of this property, it is used to contain corrosive liquids (e.g., sulfuric acid). Because lead is very malleable and resistant to corrosion it is extensively used in building construction, e.g., external coverings of roofing joints. Lead can be toughened by addition of a small amount of antimony or other metals. All lead, except 204Pb, is the end product of a complex radioactive decay. Lead is also poisonous, as are its compounds, and therefore is dangerous to human health and use as a food containment device is not recommended. Lead is a chemical element in the carbon group with symbol Pb and atomic number 82. Lead is a soft and malleable metal, which is regarded as a heavy metal and an other metal. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid. It is also the heaviest non-radioactive element. Lead is used in building construction, lead-acid batteries, bullets and shot, weights, as part of solders, pewters, fusible alloys, and as a radiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has ahalf-life that is so long (over one billion times the estimated age of the universe) that it can be considered stable. Its four stableisotopes have 82 protons, a magic number in the nuclear shell model of atomic nuclei. The isotope 208Pb is double magic. If ingested, lead is poisonous to animals, including humans. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury, another heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China Characterstics Lead is a bright and silvery metal with a very slight shade of blue in a dry atmosphere. Upon contact with air, it begins to tarnish by forming a complex mixture of compounds depending on the conditions. The color of the compounds can vary. The tarnish layer can contain significant amounts of carbonates and hydroxycarbonates. Its characteristic properties include high density, softness, ductility and malleability, poor electrical conductivity compared to other metals, high resistance to corrosion, and ability to react with organic chemicals. Various traces of other metals change its properties significantly: the addition of small amounts ofantimony or copper to lead increases the alloy's hardness and improves corrosion resistance fromsulfuric acid. Some other metals, such as cadmium, tin, and tellurium, also improve hardness and fight metal fatigue. Sodium and calcium also have this ability, but they reduce the alloy's chemical stability .Finally, zinc and bismuth simply impair the corrosion resistance (0.1% bismuth content is the industrial usage threshold). Conversely, lead impurities mostly worsen the quality of industrial materials, although there are exceptions: for example, small amounts of lead improve the ductility of steel. Lead has only one common allotrope, which is face-centered cubic, with the lead–lead distance being 349 pm At 327.5 °C (621.5 °F),lead melts; the melting point is above that of tin (232 °C, 449.5 °F), but significantly below that of germanium (938 °C, 1721 °F). The boiling point of lead is 1749 °C (3180 °F), which is below those of both tin (2602 °C, 4716 °F) and germanium (2833 °C, 5131 °F). Densities increase down the group: the Ge and Sn values (5.23 and 7.29 g•cm−3, respectively) are significantly below that of lead: 11.32 g•cm−3. A lead atom has 82 electrons, having an electronic configuration of [Xe] 4f145d106s26p2. In its compounds, lead (unlike the othergroup 14 elements) most commonly loses its two and not four outermost electrons, becoming lead(II) ions, Pb2+. Such unusual behavior is rationalized by considering the inert pair effect, which occurs because of the stabilization of the 6s-orbital due to relativistic effects, which are stronger closer to the bottom of the periodic table. Tin shows a weaker such effect: tin(II) is still areducer. The figures for electrode potential show that lead is only slightly easier to oxidize than hydrogen. Lead thus can dissolve in acids, but this is often impossible due to specific problems (such as the formation of insoluble salts).Powdered lead burns with a bluish-white flame. As with many metals, finely divided powdered lead exhibits pyrophoricity.Toxic fumes are released when lead is burned Production and recycling Production and consumption of lead is icreasing worldwide. Total annual production is about 8 million tonnes; about half is produced from recycled scrap. The top lead producing countries, as of 2008, are Australia, China, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea , Australia, China and the United States account for more than half of primary production. In 2010, 9.6 million tonnes of lead were produced, of which 4.1 million tonnes came from mining. At current use rates, the supply of lead is estimated to run out in 42 years. Environmental analyst Lester Brown has suggested lead could run out within 18 years based on an extrapolation of 2% growth per year. This may need to be reviewed to take account of renewed interest in recycling, and rapid progress in fuel cell technology. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of lead in use in society is 8 kg. Much of this is in more-developed countries (20–150 kg per capita) rather than less-developed countries (1–4 kg per capita) The industry obtain it from two ways 1.Fresh lead is purchased from market. 2. Recycling of lead from dead batteries. Recycling of lead Recycling process •The lead obtained from dead batteries is put into furnace. •Lead is put in furnace along with coal. •Temperature upto 350-400 degree is reached inside the furnace. •The lead comes out in the molten form. Recycling Process •When molten lead gets cool it is put in refinery plant. •In refinery plant a chemical is mixed with it and again heating process is started. •The impurities are deposited on top and removed manually. •Now this lead from any impurities and used for further process. Smoke Filter System •The smoke which is evolved from the furnace and recycling process is passed through the smoke filter system. •Thesmoke filter system contains filter pads which filter the smoke and absorbed the harmful leads particles or precipitates and stops them to enter in environment.