Water & Air Ingress Into Paper Machine Circulating Oil, 19PaperCon
Water and air ingress into paper machine circulating lubrication oil can significantly reduce the operating life of the wet end and dry end bearings as well as gearbox bearings and gears and other roll bearings being supplied by this circulating oil.
Air entrained in the oil can lead to foaming and reduces the apparent viscosity of the oil which can reduce the film thickness between the rolling and stationary surfaces of the bearings. Air entrained in oil will change the oil flowmeter measurement characteristics and therefore can reduce the amount of oil being metered to the bearings. Both of these effects can lead to a reduction in the bearing life.
How does air enter the oil? Air can enter the oil through the bearing drain drop leg vents, mixing with the oil, resulting in small bubbles being entrained in the oil. Turbulence of the oil dropping down piping and returning to the oil reservoir can entrain air. Oil in gearboxes can become turbulent, also entraining air. In oil reservoirs, oil return lines as well as pressure control return lines that are not submerged below the oil surface in the tank can cause splashing and air entrainment.
How do we prevent air from entering the oil? The reduction of turbulence is the first line of defense. Drop legs need to be sloped near the oil reservoir and should not drop vertically into the reservoir. This will allow some time for entrained air to separate from the oil. The oil return line should be sealed with an “S” type pipe, which is a trap similar to the device found in a sink drain, preventing air from entering the reservoir with the oil. All oil lines returning to the tank, including pressure control return lines, need to be submerged below the oil surface in order to reduce the amount of air entrainment from oil splashing into the tank.
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Water & Air Ingress Into Paper Machine Circulating Oil, 19PaperCon