Bal-tec™ Home Closures
Aluminum balls are widely used to permanently plug up holes in manufactured parts. The aluminum is highly ductile, so it can literally be squashed or upset inside a slightly oversize hole, to permanently seal it. In addition to the excellent ductility of the aluminum balls, they are very round and have a consistent precision diameter. Precision aluminum balls lend themselves to use in automated handling and dispensing machinery for economical installation. An oversize steel ball can be press fit into an undersize hole to produce a good seal, but this requires a reasonably precision hole and the hardness of the part should not be over 35 HRC, (Hardness Rockwell “C”).
There are a number of adjustment holes required in the cases of heart pacers and defibrillators that must be sealed as a final step in the manufacturing process. The one millimeter holes in the skin of these titanium packages are permanently closed, by first press fitting high quality titanium balls in them, and then fusing the ball and the case together with the heat from a laser beam. During the laser fusion process, the whole package is held in an inert gaseous environment.
It is interesting to note that when a metal is subjected to the high compressive stress which occurs in press fitting, the melting temperature of the metals in the stressed area are substantially reduced, so the melting is restricted to the ball and a localized area surrounding the ball.