Structural Considerations in Lead-Acid Stationary Cell Design

The classical deficiencies of the lead-acid system which lead to eventual failure are examined from a structural engineering perspective. The fundamental low tensile strength of lead in conjunction with the formation of oxide films as it relates to the creep of the metal and the resultant growth of the positive electrode is discussed. The high mass of lead combined with its low tensile strength resulting in mechanical failures and creep in other structual elements (non-positive plate) is examined. The various ways in which the above mentioned problems manifest themselves in eventual failure are considered. The effects of plate growth when not accommodated result in electrical short circuits, breakage of grid members, loss of contact between the active material and the current collector, movement of the positive posts resulting in post seal failure or breakage of the cover, and breakage of the jar walls due to contact with the growing positive plate is examined. The low tensile strength of lead and its alloys as a structural material leads to susceptibility to shipping damage, gradual collapse of the element due to creep, downward movement of the post seals due to creep resulting in post seal failure or breakage of the cover, and buckling of the element. Various means of overcoming the shortcomings of both lead as a structural material and the traditional means of constructuring lead-acid stationary cells are examined. Improved positive grid designs, which accommodate growth of the grid members, are discussed.