By Jim Fitch
Machinery Lubrication Magazine
What’s life like inside a rolling element bearing? Let’s say you are a dollop of grease and you’ve just been pushed by a grease gun into the dark recesses of a bearing cavity. You are now in a combat zone. What are your orders? Maybe you are on a suicide mission. Your bearing has been screaming for reinforcements and you are it – the new recruit – all gooey and slimy.
Inside you see grease casualties all around. There’s the stench of oil oxidation on one side and the stiff lifeless remains of a soap-based thickener on the other. In an instant, the floor and walls begin to vibrate, then you hear a low rumbling sound. You are pushed deeper into the bearing cavity and suddenly you can’t move – the heat and the pressure are excruciating. Then more pressure … crack … silence.
What just happened? How could regreasing a bearing have contributed to sudden-death failure? Doesn’t fresh grease prolong bearing life and restore reliability? Not so fast. The problem here is new grease entering an old, infrequently lubricated (and overly lubricated) bearing. As the new grease enters, it must make room, and in doing so, it pushes around the crusty remnants of grease past.