The modern day lead acid battery would be very different — both more expensive and less efficient — were it not for the contribution of David Prengaman, one of the world’s top specialists in the metallurgy of lead alloys and related energy storage.

The Lead Pope

R David Prengaman of Dallas, Texas is one of the top specialists in the fields of metallurgy of lead alloys and lead acid batteries, in particular the innovation of lead anodes for electrowinning metals and recycling processes for lead acid batteries to produce high quality lead and lead alloys. The German company, Metallgesellschaft, once aptly nicknamed him “The Lead Pope”.

A crucial moment for him happened when he was 14 years old. Prengaman was selected to attend the Joe Berg Science seminars. These involved visits to many company facilities and laboratories in the Pittsburgh area to see scientists or engineers at work. The first factory they visited was Pittsburgh Steel Company’s metallurgical laboratory. When it was his turn to look into the microscope at the various steel samples, he said: “It was as though I had looked at them all my life. I knew then that I wanted to be a metallurgical engineer.”

Prengerman attended the Carnegie Institute of Technology, graduating with his BS degree in 1965 and in 1967 his Masters in metallurgy and materials science. His research was into the development of rolling textures in high chromium, high nickel stainless steels and the properties and corrosion resistance of these materials.

R David Prengaman

R David Prengaman

He was accepted to do a PhD but Carl Long, director of research for St Joe Lead Company, convinced him to join the firm as a researcher.

Prengaman’s work at St Joe involved the development of rolled lead calcium tin alloys. The rolling process developed structures and rolling textures which made the material very resistant to corrosion. Delco was interested in the new material because they had such severe cracking in their cast lead antimony alloys that they were scrapping as many as a third of their battery grids. The new rolled expanded metal material did not crack and grids could be produced at 10 times the speed.

One of the benefits of the change in grid material was the fact that it did not contain antimony, which was not transferred to the negative plate to cause gassing — thus maintenance-free batteries.

In 1973, Prengaman moved to Atlanta to join Evans Metal. While he was there, the chief engineer from Delco visited Atlanta to meet him and the owner of Taracorp. They made a proposal that they would build a lead rolling plant which would supply all five Delco factories with strip if Prengaman would operate the plant. He refused because at that time all the metal for the rolled grids came from primary lead, and the lead calcium alloy-rolled expanded metal grids would make the lead antimony alloys which the smelter produced obsolete.

“When they turned down the offer from Delco, I was ready to look for another position. Within a week I saw an ad in a trade magazine that RSR, a major battery-recycling company, was looking for a chief engineer. Replying to the ad, I indicated that I was not interested in the chief engineer’s position, but I thought that RSR would be interested in talking to me.”

R&D at RSR 

Prengaman was hired to start an R&D group and provide technical assistance to battery customers. He spent most of the first year working with Delco to build their new rolling plant and expand battery grid production lines.

“The main problem of the lead recycling process at that time was the production of pure lead which could be used as an active material in the battery. The impurities were too high and the refining, as well as the analytical techniques to remove and analyze the impurities in the lead, were not developed.”

So Prengaman and his colleagues set about developing new refining practices to remove the major gassing elements in pure lead to make it suitable for battery oxide. In addition, with only AA instruments available at the time, they developed new techniques to analyze these elements in the lead at very low levels.

Necessity is the mother of invention. To extract the newly solidified lead strip from the aluminium mould, they adapted the wringer part of an old washing machine because it had rubber rolls which could grip the lead and pull it out of the mould continuously. “We called the original casting machine Maytag 1 after the most famous washing machine in the 1960s in the US,” he said.

By 1975, the RSR team had developed and introduced the first low antimony maintenance-free battery grid alloy, which could be cast on conventional grid casting equipment without cracking. It is called R275.

“In the late 1970s we set up a pilot plant to recycle the active materials in the battery by leaching and electro-winning the lead. This produced pure lead, but improvements made to the smelting process at RSR recycling plants made the process economical.”

In the early 1980s the Environmental Protection Agency declared that the slag from the battery recycling was hazardous waste. So Prengaman and his team developed an improved recycling process using an electric furnace to clean the slag and produce a non-hazardous product.

Towards the ALABC 

In the mid-1980s Prengaman was part of a team which looked for acquisitions in Europe, primarily battery recycling factories. They would acquire factories in the UK, France, Italy, Germany, Austria, South Africa and Saudi Arabia in the mid and late 1990s. Prengaman worked to make these factories profitable and environmentally ahead of the regulations.

During the same period, Prengaman went on to develop rolled lead anodes for copper and zinc electrowinning. The anodes were based on the rolled lead calcium tin alloys which he had developed for battery grids. These anodes have become the dominant anodes for copper mines worldwide. About 95% of mines use these anodes for the recovery of copper in low-cost operations by RSR and the affiliated companies of the Ecobat group which produce anodes.

“In the mid-1990s the vehicle profiles changed with the air now flowing over the vehicle instead of through the front grill. This caused the engine compartment to become very hot and battery life to become much shorter. In 1999 I developed an alloy called 007, which had silver added to a lead calcium tin alloy. The alloy was called 007 because the active material would “bond” to this grid compared to other alloys with silver, which had to be specially treated to accept the paste.”

In 1996, Prengaman became president of RSR Technologies, Inc which provides research and development services to RSR Corporation, the European and South African Eco-Bat Group, and their customers for battery recycling.

Alongside his innovative work at RSR, Prengaman has chaired a number of committees, published extensively on these subjects, served in various positions in the industry and received a galaxy of awards. He is now retired but an active participant in the industry.

According to John Devitt, a key figure in the development of the first VRLA battery and who has known Prengaman for many years: “Dave is undoubtedly the world’s expert on lead metallurgy, plus many other metals. And he is uniquely accessible to all battery folk. He is the pioneer on many of our best alloys, so essential to a really good battery.”