It is called centrifugal (spelling?) casting. It is usally done on investment type castings. I have done it using lead and lead alloys. The molds are round with a center sprue hole with runners going out. Sort of like a wagon wheel. Building one is rather easy, I used a blower motor with a 6" pulley attached to the shaft. Mount the motor so the shaft sits vertical. The mold is sandwiched between a piece of plywood and the pulley, held in place with a series of staybolts around the perimeter. The plywood has a hole in the center that lines up with the center of the mold. The staybolts are just snugged down, this allows the air to escape out of the mold when pouring. Here is a secret that I had to find out the hard way. Mount the assembly in a cut off metal trash can or 55 gallon barrel with the top of the mold at least 12" below the top edge. It is amazing what flying molten metal can do to a pair of jeans when you mis the sprue hole much less to your skin, ouch doesn't even cover it.
If it's not nailed down, it's mine.
If I can pry it loose, it's not nailed down.