Grafil Injection
Hall of Fame
Francis William Gower was the lead author of the patents. He was joined by Hugh James Owen and Robert John Nash. All three lived in Birmingham, and were presumably associates/engineers/workers of/at Birmal.
I don't know why they didn't try to build a frame using aluminum tubing, as some of their contemporaries did (and likely produced better-playing racquets because of that choice).
The earliest aluminum racquet to reach the market was actually a tubular Wright & Ditson, launched in 1920, which had a boxy aluminum head that was mated to a wooden lower shaft/grip, just like on steel frames that came out decades earlier (as seen in @Henry Hub 's magnum opus of a thread). While the Wright & Ditson predates the Birmal by a few years, the latter was the first (and only) frame of that period to be made entirely out of aluminum, with no structural wooden components.
To my knowledge, Wright & Ditson did not patent their aluminum design, at least not successfully. Instead, Spalding became the first to patent a tubular aluminum racquet in 1927, authored by William Reach. The initial Spalding product, marketed as the "Metalite", looked very similar to the much earlier Wright & Ditson effort (perhaps they were related?), and may have been the first metal frame to exhibit 'better-than-wood' playing properties, such as combining lightness with increased stiffness. This is especially true of the second generation "Metallite", marketed in the 1930s, which departed dramatically from the earlier boxy profile to sport an art-deco-esque oval beam that was even more modern-looking than some of the designs from the 1960s, notwithstanding its wooden lower half. The Gen II example I have weighs 362g strung, has a 330 swing weight thanks to its 4 pt HL balance, and has a measured flex of 66 RA. These specs are nearly identical to those I got out of a Prince Magnesium Pro 90, and are very much in the goldilocks' zone of modern 'player's frames'!
Below is a photo of a Gen I "Metalite" (borrowed from a 'sold' listing on the Schotten Sport Antiques site) and a Gen II unit from the original Rolf Jaeger collection now residing in an Australian museum:
The later Birmals with wooden handles look cool too. Probably better for vibration absorption given the steel strings!