• They must be porous—high porosity gives a high rate of flow of ions.
• Pore size must be small enough to restrict the flow of colloid particles but not restrict the ions.
• They must be as thin as possible.
• Electrical resistance must be very high.
• They are a little larger than the plates to prevent material shorting the plates.

To balance these criteria, the choice of separator shifted from wood to rubber to glass mat to cellulose based separators to sintered PVC separator to micro porous PVC/polyethylene separator. An effective separator must meet a number of mechanical properties. 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.

Description:

The paste used in an industrial battery’s “plates” is one of the most critical aspects of the manufacturing process. There are many formulas for pastes, which are later converted into active material, and each is considered a trade secret by the manufacturer using it. The basis of all, however, is oxide of lead, either Red Lead (Pb₃0₄), Litharge (PbO), or a mixture of the two, made into a paste with a liquid, such as dilute sulphuric acid. The object of mixing the oxides with the liquid is to form a paste of the proper consistency for application to the grids, and at the same time introduce the proper amount of binding, or setting agent which will give porosity, and which will bind together the active material, especially in the positive plate. Red lead usually predominates in the positive paste, and litharge in the negative, as this combination requires the least energy in forming the oxides to active material.

The oxides of lead used in preparing the pastes which are applied to the grids are powders, and in their dry condition could not be applied to the grids, as they would fall out. Mixing them with a liquid to make a paste gives them greater coherence and enables them to be applied to the grids. Sulphuric acid puts the oxides in the desired pasty condition, but has the disadvantage of causing a chemical action to take place which changes a considerable portion of the oxides to lead sulphate, the presence of which makes the paste stiff and impossible to apply to the grids. When acid is used, it is therefore necessary to work fast after the oxides are mixed with sulphuric acid to form the paste.

In addition to the lead oxides, the pastes may contain some binding material such as ammonium or magnesium sulphate, which tends to bind the particles of the active material together. The paste used for the negatives may contain lamp black to give porosity.

Applying the Paste to the Grid: After the oxides are mixed to a paste they are applied to the grids. In the hand pasting process, the pastes are applied from each face of the grid by means of a wooden paddle or trowel, and are smoothed off flush with the surface of the ribs of the grid. This work is done quickly in order that the pastes may not stiffen before they are applied.

Typically, plates that are pasted in a machine which applies the paste to the grid, subjecting it at the same time to a pressure which forces it thoroughly into the grid, and packs it in a dense mass.

Drying the Paste: The freshly pasted plates are now allowed to dry in the air, or are dried by blowing air over them. In any case, the pastes set to a hard mass, in which condition the pastes adhere firmly to the grids. The plates may then be handled without a loss of paste from the grids.

12 Volt / 6 Cells

24 Volt / 12 Cells

48 Volt / 24 Cells