Pasting and its associated
activities represent the most important and critical operation in the storage
battery manufacturing plant.
The grids are designed to hold a
predetermined amount of active lead oxide material. The amount of lead oxide
has been calculated to deliver a specified amount of electrical energy. The
manufacturer must see that this combination of grid structure and active
material amount are united in a precise manner. Starting materials must comply
with rigid specifications to assure a smooth pasting operation and
satisfactory battery performance.
Most U.S. manufacturers use flat
plate technology in their positive and negative plate designs. In this
technology, PbO, H2SO4 , and water are blended in a
mixture to the approximate consistency of stiff mortar cement. This blend is
called paste. There are several different types of machines designed to
transfer this paste from the mixer and "paste" it into the grid framework. The
pasted grids are usually moved through a flash drying oven to remove some
water and dry their surfaces. This allows stacking on top of one another, if
required by the process.
Some manufacturers use tubular
positives in their cell designs. These plates employ lead oxide powder packed
around a lead core rod. The lead powder is also constrained by an inert porous
fabric tube structure on the outside of the core rod and powder aggregate.
Transferring the lead oxide powder into the fabric tube and around the core
rod is called "filling." After filling, tubular positives are soaked in
diluted H2SO4 to convert some of the lead oxide to lead
sulfate. This forms a porous pencil from the powder.
The essential raw materials
required for plate pasting include:
Many variations in the conditions
of preparing and applying the paste are possible. Experience is an important
factor in perfecting proper methods and techniques. Variations in physical and
chemical characteristics of the oxides, temperature and strength of the acid
solution, time of mixing, treatment of the plates during and after the pasting
process, and even atmospheric humidity are among the conditions that affect
the finished product. By attention to such details, control may be obtained of
the bulk of the paste. Variation in the time of setting, the hardness of the
plate, the time required for formation, the initial capacity when put in
service and, to a limited extent, the life of the plate can be
There are several different types
of mixers available from equipment suppliers. Most of them have been manually
operated, until recent years when continuous paste mixing has been developed
in some companies.
There are two popular types of
pasting machines: belt-type and beltless-type machines. With the belt-type of
pasting machine, experience has shown that the pasted plate weight varies
according to such factors as paste characteristics, the age of the pasting
belt, and a few other details. The paste consistency for such machines is
usually somewhat stiff. The pasted plate thickness is approximately the same
as the grid thickness, making the plate a "flush" pasted plate.
A beltless machine, sometimes
called a "fixed" orifice pasting machine, moves the grid mechanically through
the paste hopper. The grid moves out of the hopper through a fixed dimensional
opening or orifice which regulates the pasted plate surface and thickness.
Some machines are so designed that the grid travels horizontally. Other
machine designs carry the grid vertically from the paste hopper top through to
the orifice outlet at the bottom of the machine. The preferred paste for this
type of pasting machine has a rather soft consistency. This softer paste
permits easy entry of paste in the grid areas and less difficulties as the
pasted plate emerges from the orifice. In usual practice, the finished plate
thickness is at least 0.006" greater than the grid thickness. Thus, this plate
type may be referred to as an "overpasted" plate.