The strange Hollow Ball Phenomenon

Problem: Your pump has failed. You disassemble it and lo and behold, you find broken, hollow bearing balls amongst the wreckage.

Solution: Don’t chew out your supplier for selling you faulty bearings. You are looking at something that occasionally happens when a pump, typically a process pump operating at high RPM, fails, according to Jennifer Moritz, training manager, SKF Canada.

“This is not a quality control problem. Bearing steel has oxygen inclusions. For some unrelated reason, the bearing begins to fail. The temperature gets so high, as high as 350°C, that the oxygen [inside the bearing] expands and the ball diameter increases. The ball material laps on the raceway, the inclusion grows, the ball grows and laps some more, until the wall of the hollow ball becomes so thin that it bursts. Upon inspection, the ball is seen to be hollow,” Moritz explains.

In the absence of manufacturers’ steel specifications that might allow end-users to compare the number of oxygen inclusions and their maximum size, the best bet is to buy from one of the bearing companies that have high requirements for their bearing steel, Moritz advises. “We have really tight control on the allowable number of inclusions and their maximum size.”

Mr. O thanks Jennifer Moritz of SKF Canada for this tip!