Battery is an essential requirement to start electrically operating equipments, especially in electrically operated vehicles. And also, in case of mains failures or interruptions in power supply, a standby or backup power is necessary for critical applications. Therefore a battery provides the necessary power to startup as well as standby depending on the type of application. Some of the applications of the batteries include automobiles, railways, airlines, defense, telecommunication, power stations, industries, and so on. The battery manufacturing process of each company has its own special technical patented and secret processes, which are not bound to be revealed to masses.
Introduction to Lead-Acid Batteries
Therefore, this article is intended to give a brief idea of lead acid battery manufacturing process. A lead-acid battery is commonly used in automobile applications and UPS systems. These batteries provide sufficient energy to start engines, and are maintenance free, and durable. Mainly 98 percent of these batteries are recyclable, and therefore, they minimize environmental impact while being disposed off.
The lead battery is manufactured by using lead alloy ingots and lead oxide It comprises two chemically dissimilar leads based plates immersed in sulphuric acid solution. The positive plate is made up of lead dioxide PbO2 and the negative plate with pure lead. The nominal electric potential between these two plates is 2 volts when these plates are immersed in dilute sulfuric acid. This potential is universal for all lead acid batteries. Therefore, a 12 volt lead acid battery is made up of six cells that are connected in series are enclosed in a durable plastic casing, as shown in the figure.
The capacity of the battery depends on the amount of lead dioxide on the positive plate; sulfuric acid present in the battery; and, the amount of spongy lead on the negative plate. During discharging process, the suphate ions in the electrolyte interact with the positive and negative plates and form lead sulfate on them. This result in the reduction of specific gravity of the electrolyte in proportion to the charge delivered to the load.
During the charging process, the cycle is reversed, that is, lead sulphate and water are converted to lead, lead oxide and electrolyte of sulphuric acid by an external charging source. This process is reversible, which means lead acid battery can be discharged or recharged many times. The chemical formulas of charging and discharging process of the lead acid batteries is given above.
The main parts of the battery are plates, i.e., anode and cathode plates, separators, electrolyte or sulphuric acid, case, cell connectors and terminals, as shown in the above figure.
Manufacturing Steps of Lead-Acid Batteries
Batteries are manufactured using careful maintenance of equipments in an automated controlled environment. The Manufacturing processes can be divided into several stages like Oxide and grid production process, pasting and curing, assembly process, formation, filling, charge-discharge process, final assembly, inspection and dispatch. These manufacturing steps are briefly explained below.
1. Oxide and Grid Production Process
- Lead oxide is obtained by masses of lead from melting furnaces either by Milling or Barton Pot process methods. In the milling process, the tumbling action generated by the rotating mill on solid lead generates heat and then the surface of the lead gets oxidized. The surface layers of the oxide are removed while the lead particles roll in the drum. In Barton Pot process a fine stream of lead droplets is produced by blowing air on molten lead. These droplets are reacted with oxygen and produce lead oxide.
- Casting and stamping methods are generally used for making battery grids. In casting method, the lead alloy slabs are melted in melting pot and this molted lead is poured into the patterns of battery grids whereas stamping operation produces on battery grids based on stamping on lead sheets. When these grids are cooled after casting operation, these are passed to trimming machine where rough edges and casting gates are trimmed.
2. Pasting and Curing
- Manufacturers consider the pasting material as a trade secret,and therefore not reveal this to public. However, this paste material in general is made with oxide of lead, red lead, litharge, water and dilutes sulphuric acid. These pastes are used to fill the grids, i.e., positive and negative grids; but, for both, the pastes are not exactly filled with the same material, some expander materials are added for making negative paste.
- The paste is then forced or pressed on the interstices of the grids by a machine or by hand, and then these are turned as plates. These pasted plates are cured in ovens under certain conditions of temperature near 32 degree centigrade for about 48 hours, with humidity nearing about 90 percent and are finally allowed to dry condition at ambient temperatures.
3. Assembling the Elements
- In this process, all the parts are assembled into a battery case and covered with the plastic moulds plastic molding plant. This step involves the formation of positive and negative plate stacks, insertion of separators, inter-cell connector and plate burning. In this step positive and negative plates are formed like groups which are strapped to a suitable rack, slipped together and a separator is inserted in-between them. This separator is made up of non-conductive material such as paper, plastic or a glass fiber.
- During the burning operation each positive and negative plate tab is welded to lead to produce an element and these are then welded to respective positive and negative posts on the battery’s case top. After keeping this element in the jar or case, sealing compound is applied to make the space leak proof between the battery jar and cover.
4. Filling and Formation
- After the assembling, battery jar is filled with required amount of electrolyte through a filling or vent tube. Then, it is ready for initial charging, which may require several hours of charging depending on the battery size. Low charging rate is generally employed that may be nearly one day to several days. This charge formation may either be dry or wet. In a dry-formation method, batteries are shipped as dry after the positive and negative elements are fully charged or formed and dried in tanks or as an individual plates and are connected to positive and negative terminals of the battery.
- In a wet-formation method, a battery undergoes initial charging for several hours after plates are immersed in an electrolyte battery case. And, in some cases, this acid is dumped and fresh acid is added after forming it.
5. Charging and Discharging
- After the formation, batteries are subjected to high-rate discharge test for short duration to rule out any defects before sending them out to the final charge. After discharging and recharging batteries for several times to attain best working condition, these are inspected and tested with some measuring instruments.
- Then finally these are recharged for certain backup hours and sent to the next level where additional connections, labeling and caps are inserted to battery with sealed-cotton packing. At last, these are dispatched to ordered places.
This is all about the lead-acid battery manufacturing process carried out in several battery production industries. We hope that the given content might have been helpful for the readers. Furthermore, for any information like electronic circuits for charging batteries, battery capacity selection and battery safety methods you can contact us by commenting below.
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