Lead Acid Battery Plate Locking with 2 Part Epoxy

A typical lead acid battery is susceptible to premature failure if it experiences excessive side loads - not an unusual situation to find itself under the bonnet of a car. The lead plates can dislodge or buckle and end up touching each other causing internal shorting and subsequent battery failure.

Johnson Controls in the US, a major leading battery manufacturer saw a way to improve the life expectancy of their batteries. Their approach was to lock the lead plates at the bottom of the battery by effectively anchoring them in cured epoxy resin.

In order for the plate locking operation to be a viable production process, Johnson Controls determined that each battery needed a shot of around 15 - 20 cc's of mixed 2 part epoxy in the bottom of each of the six cell chambers, and that this had to be achieved in no more than 15 seconds per battery. Furthermore, Johnson Controls needed the shot size to be repeatable for each chamber within +/- 1%.

Their initial thoughts were to assume that 6 independent metering systems were required, which would of made the whole project prohibitively expensive. In addition, the system would need to be flexible enough to allow adjustment to suit their full range of battery sizes.

What was the solution ?

Sealant Equipment & Engineering's (S.E.E.) approach was to design a single continuous flow machine with sophisticated shot controls to operate 6 individual dispense valves sequentially. Basically, one valve at a time opened and closed until all 6 cells had been dispensed. This would make the system considerably cheaper and the project financially viable.

S.E.E. adapted the SeeFlo® 582 fixed ratio meter / mix / dispense machine to continuously meter the 2 part epoxy formulation accurately without pulsation. The shot controls enabled a single metering system to supply metered material to 6 mixing dispense valves in sequence. Each valve incorporated a low cost disposable mixer nozzle removing the need for solvent flushing, which are disposed of at the end of each day's production.

S.E.E. then designed and manufactured a suitable fixture that would hold 6 valves above the battery casing and allow easy adjustment of each valve to suit all battery sizes. A lifting mechanism was also built in to raise the battery casing so that the mixer nozzles reached the bottom of the casing. This was done to prevent epoxy getting on the side walls of the casing which would affect the performance of the final product. Once dispensing had been completed, the casing would be removed and the top cover with lead plate assemblies attached would be lowered into the casing. The bottom edge of the lead plates become immersed in the rapidly curing epoxy and effectively anchoring them in place.

To ensure continuous dispensing without interruption, a drum over drum, gravity-fed material supply system was used. This involved mounting 2 off 45 gallon drums on their sides, one on to of the other on a specially designed rack. The top drum was connected to the bottom drum via a flexible hose. The bottom barrel served as a buffer stock of material and the top drum was replaced as necessary. The outlet of the bottom drum was fed into a stick pump to enable the material to be supplied to the SeeFlo® 582 under pressure. This ensured that the metering pumps never cavitated. The same material supply system was utilised for the B component.

Once the system was installed at Johnson Controls, it became evident that the casing raising & lowering feature was unnecessary and the material leaving the dispense nozzle travelled vertically to the bottom of the cell anyway. Without this feature, it became even easier to incorporate the dispense station into a conveyorised system, thereby enabling even faster automatic indexing of the battery casings and removing the need for an operator.

Since the installation of the first system nearly 5 years ago, Johnson Controls have incorporated similar SeeFlo® 582 systems in 4 other plants throughout the US and Mexico.

Recent developments include a 12 valve system capable of dosing 2 battery casings at the same time.