Seals protect the toolholder’s bearings from washout. Lip seals, or oil seals, hug the shaft to prevent liquid and light debris from entering the live tool. Although these seals prevent washout, the way they “hug” the shaft creates friction, which in turn creates heat. The labyrinth seal protects the bearings from the operating environment by creating a complicated path for the coolant to follow. Eppinger offers a patented double seal system, which disperses excessive heat and prevents unwanted leaks, while the tool is not only operating, but stationary as well.
Seals will commonly fail from wear. The seal is often the softest part of the tool so the continuous friction that a seal holds will eventually wear. Seal failure occurs when chip build up works its way past the seal. Seals will fail if the wrong coolant is being used and the chemicals in coolant are corrosive to the material used to make the seal. Overheating will cause a seal to warp and allow coolant and chips to pass the seal. Bearings wash out from seal failure. As the seals fail, coolant gets into the tool washing the grease out of the bearings.
Preventive maintenance can eliminate most of these issues. When the seal fails it allows washout, which can and will likely cause pitting in the gears, which will then need to be replaced. When washout occurs the tool will sound rough and when spun by hand will be notably different. This is a great time to send it in for repair since it will likely only require bearings and seals and can be returned and put back into production with relative speed.