Radial crashes are the most common form of air bearing and dicing spindle failures. In a dicing, back grinding or other type of air bearing the rotating shaft is “floating” on a cushion of air. This allows for super precise rotation. However, when the air supply is insufficient our when forces exceed the ability of the air cushion to support the shaft, it can contact the bearing journal. This is a crash.
These crashes damage the radial bearing surfaces and jets. They can be caused by excessive feed-rate, misalignment, improper program input and contamination in the spindle air supply. HST has developed several technics for restoring radial bearing to like new condition regardless of the cause of the crash.
When the spinning shaft contacts the radial bearing it can result in galling and damage to the bearing surface area. The crash can also cause material to fill in and damage or clog the bearing jets. Conversely, clogged jets can result in a radial crash by reducing the lift.
The photo below is a closer look at the above left photo. It shows a crash that was the result of excessive feed rate. The spinning steel shaft rubbed and galled the softer brass material. The damage is obvious.
Crashes can also occur when contamination in the spindle air results in clogged journal jets. This results in loss of lift and allows the spinning shaft to contact the bearing surface.
The journal jets on this radial bearing became clogged over time. Apparently there was some moisture in the spindle supply air that allowed mineral deposits of some type to actually grow in the jet orifices. In time the jets became so clogged that the airflow could no longer support the rotating shaft. We had to replace most of the jets.