The lead grid is the supporting structural element of the electrode of the EDCON lead-acid battery and simultaneously performs the functions of the mechanical frame of the active mass and the current-carrying conductor. The internal resistance of the battery, the cold-scroll current, the cyclic resource, the corrosion resistance in the sulfuric acid environment and the tendency to self-discharge directly depend on its geometry, alloy and manufacturing method.
In the manufacture of batteries, a complex of technological processes is used based on a combination of gravity casting, expanded stamping and continuous rolling with subsequent cutting, which ensures the optimization of grids for specific operational scenarios. The production processes comply with industry requirements for starter lead-acid batteries, as well as environmental restrictions on the content of hazardous substances.
Alloys for the manufacture of gratings
The base material is refined lead with a purity of at least 99.985%. Pure lead has insufficient mechanical strength and high creep at battery operating temperatures, so alloying elements are introduced into the production alloy.
An alloy of the Pb–Ca–Sn–Al system with a calcium content of 0.06–0.09%, tin 0.8–1.5% and aluminum 0.015–0.025% is used for positive gratings. Calcium increases mechanical strength and ensures maintenance-free operation by eliminating the gas emission characteristic of antimony alloys. Tin improves casting properties, reduces the surface resistance of the passivating layer PBO₂/pbso₄ at the “grid — active mass” boundary, and suppresses the effect of premature loss of capacity. Aluminum performs the function of a protective component, preventing the combustion of calcium in the melt.
For negative gratings, a similar alloy with a reduced content of tin (0.2–0.4%) and calcium (0.08–0.12%) is used, which provides sufficient strength at a lower cost of alloying components, since the negative electrode is not susceptible to anodic corrosion.
Melt preparation
Lead pellets are loaded into an induction or gas type melting furnace with a melt temperature in the range of 480-520 °C. Temperature control is carried out by K-type thermocouples with an accuracy of ± 3 °C, which is critical for stabilizing the chemical composition.: overheating leads to accelerated carbon monoxide of calcium and aluminum, and insufficient temperature leads to deterioration of melt fluidity and formation of shrinkage defects.
The melt is refined by flotation using caustic soda and charcoal to remove oxides and non-metallic inclusions. After refining, a sample is taken for spectral analysis on an optical emission spectrometer. If the composition deviates from the range, an adjustment is made by introducing Pb-Ca ligatures (a master alloy with a calcium content of 4%) or pure tin grade Sn 99.90.
Gravity casting method
Gravity casting in stationary molds is used for the manufacture of large battery grids with a thickness of 1.8 mm and above. The melt is fed into a carousel type casting machine with a capacity of up to 20 gratings per minute. The mold is made of grey cast iron with a water-based cork slurry coating on the working surface, which performs the functions of a heat insulator and a separation layer.
The temperature regime of the mold is maintained in the range of 150-180 °C, which ensures directional solidification of the melt: the peripheral sections of the frame crystallize first, followed by the inner cells. This eliminates the formation of shrinkage shells in the current collector areas. The cycle time is 4-6 seconds. After extraction, the grate is fed to a cut-off stamp to remove the spigots and debris, after which the geometry is monitored on an optical measuring system with a tolerance of ± 0.05 mm in core width and ± 0.1 mm in dimensions.
The advantage of gravity casting is the possibility of obtaining a complex geometry of the grid with a radial core structure optimized to reduce internal resistance. A defect is a relatively large granular metal structure that increases the tendency to intercrystalline corrosion. To compensate for this effect, cast gratings are artificially aged at 80 °C for 24 hours in order to stabilize the phase composition of Pb₃ca and Pb–Sn precipitates.
Expanded technology
For the manufacture of thin gratings (0.8–1.4 mm) used in standard and Ca/Ca-version batteries, the expansion method is used — stretching perforated lead tape. The alloy is cast as a continuous strip 130-280 mm wide by semi-continuous casting on a cooled roll or rolled from an ingot on a multicellular mill.
The resulting 1.0–1.5 mm thick tape passes through a die-cut die forming diamond-shaped staggered perforations. Then the tape enters the expander, where the lateral grippers with reciprocating motion stretch it in the transverse direction, turning the perforations into open rhombic cells.
Expanded gratings have a fine-grained textured metal structure oriented in the direction of rolling. This increases the strength characteristics and reduces the rate of corrosion by 1.5–2 times compared to cast analogues. However, the geometry of the cores in expanded sockets is limited by rectilinear elements, which slightly increases the internal resistance compared to the radial cast structure.
Technology of cutting and drawing production
For specialized grids, including those used in AGM batteries, Punched Grid technology is used – die—cutting of rolled tape without subsequent expansion. The 0.9–1.2 mm thick tape passes through a progressive multi-position die, in which current-carrying tires, longitudinal and transverse cores, and mounting lugs are sequentially formed.
This technology makes it possible to implement arbitrary grid geometry, including an alternating core section optimized for current density. Grilles made by die-cutting demonstrate the lowest internal resistance and the maximum cycling life, which is critical for execution with Start-Stop and regenerative braking modes.
Finishing and quality control
After the grating is formed, a calibration operation is performed on a hydraulic press with a force of 50-100 tc to eliminate residual deformations and ensure flatness with a tolerance of no more than 0.3 mm along the length of the grate. The surface is degreased and an adhesive coating based on carbon modifiers is applied, which improves adhesion to the lead paste when applied.
Quality control includes: visual inspection for cracks, spills and debris; measurement of the mass of each lattice with a tolerance of ± 2% of the nominal value; selective metallographic analysis of the microstructure on an optical microscope at magnification ×200-500; tensile testing of samples to determine the ultimate strength (at least 35 MPa for Pb-of Ca–Sn alloys) and elongation (not less than 8%).
Environmental and regulatory aspects
The production cycle at the enterprise is organized in accordance with the current requirements for limiting emissions of lead and its compounds. All technological operations related to lead smelting and processing are equipped with local exhaust ventilation systems and fine filters that ensure a safe concentration of lead in the air of the work area. Lead production waste is sent for recycling within the framework of the current requirements for the handling of accumulators and industrial responsibility.
EDCON’s lead grid manufacturing technology is a complex process in which the choice of alloy, forming method, and finishing modes is determined by the target performance characteristics of a particular battery series. The use of Pb-Ca–Sn–Ag alloys in combination with modern expansion and die–cutting methods ensures the achievement of high cold-rolling current, cyclic service life and corrosion resistance while maintaining a maintenance-free battery architecture. Multi-stage control of chemical composition, geometry and microstructure at all stages of production guarantees stable characteristics of finished products and compliance with current technical and environmental requirements.
