How hot would bearings have to get to burn the oil and leave residue on the bearing race and rollers but not discolor the bearing or rollers.
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It depends on the oil in use and the application, different oils have varying abilities to cope with temperature. We often see compressors running above 100C with synthetic lubricants in use with varnish deposits forming inside the equipment, however you can use a highly refined mineral oil and not have any varnish.
Also be aware that the bulk operating temperarure of the oil is not representative of the temperature in the meshing surfaces of bearings. Consult your bearing manufacturer to get an accurate idea what the potential increase inside the bearing may be.
Also be aware that the bulk operating temperarure of the oil is not representative of the temperature in the meshing surfaces of bearings. Consult your bearing manufacturer to get an accurate idea what the potential increase inside the bearing may be.
This is a 320 Ep Gear oil in a gear reducer on a cross country conveyor system. The shaft daimeter is 150mm and the OD of the bearing is 270mm running at 1785 RPM.
What is the ambient temp and operating temp of the gearbox? Check the oil condition with oil analysis, pay attention to the TAN to see if the oil has oxidised, if it is oxidising then it will leave varnish deposits.
Note on your original question regarding whether the oil will leave deposits without discoloring the metal, the answer is a definite yes. The temperatures required to discolor the metal are signficantly higher than any standard oil will cope with.
Another thing to do is to check the actual loading of the gearcase compared to rated capacity. Measure actual amperate draw on all three phases of the electric motor and then calculate the KW draw. Compare this to the rated KW capacity of the gearcase, often you will find in these applications the gearcase is operatiing well above rated capacity.
Note on your original question regarding whether the oil will leave deposits without discoloring the metal, the answer is a definite yes. The temperatures required to discolor the metal are signficantly higher than any standard oil will cope with.
Another thing to do is to check the actual loading of the gearcase compared to rated capacity. Measure actual amperate draw on all three phases of the electric motor and then calculate the KW draw. Compare this to the rated KW capacity of the gearcase, often you will find in these applications the gearcase is operatiing well above rated capacity.
The reducer is rated to over 2300 HP the motors are 1200 HP with a full load rating of 150 amps. When running fully loaded the current on all three phases is around 103 to 107 amps. The residue left behind is a hard carbon like substance that has to be scraped off. I have been monitoring the temperatures on the outside of the bearing housings and it runs around 155F the oil runs through a cooler and during the day ambient averages 90 to 97F and the oil going to the bearings has never been above 112F but normally runs around 94F.
JTT, what is the voltage to the electric motor? Is there more than one motor?
JTT
This could be varnishing. Give us an idea of the Lube Oil Circuit, and the oil analysis.
eg. sump,gear pump,10GPM, cooler(water/oil tube/shell) filter 3um, thermostat, flow meter, five separate flow channels to various bearings. 3 separate lines to spray nozzles for gear lube.
Oil 22/28 water 140ppm, metals ok.
This could be varnishing. Give us an idea of the Lube Oil Circuit, and the oil analysis.
eg. sump,gear pump,10GPM, cooler(water/oil tube/shell) filter 3um, thermostat, flow meter, five separate flow channels to various bearings. 3 separate lines to spray nozzles for gear lube.
Oil 22/28 water 140ppm, metals ok.
The voltage to the motor is 4160 and there is only one motor per reducer but three reducers driving the belt two drive the primary drive pulley and one drives a secondary pulley. The oil is pumped from the reducer through a water cooler at 30GPM and supplies oil only to the two high speed bearings the other two shafts are lubricated by oil splash. The last oil samples came back 26/24 no water and most of the contamination is silica, the wear metals are not very high. I am not sure of the filtration particle size but I believe it is 10um.
JTT,
Only the the High speed bearing are has that residue buil up problem?? or the the residues are all over the place (gears, bearings, shaft, etc).
When I was working at a papermill where similar temperatures were present (bearing temp was estimated to be 10 to 20°F higher than the measured on the housing), long drain intervals, brass cages and a reactive oil were believed as the root cause of the varnish.
We took a sample of the oil together with a bearing roller and put it into the oven at 80°C for 2 weeks and saw some similar discouloration and varnish on the roller. Another sample had a piece of brass and qualitativeliy the roller looked darker.
The soultion was to change to a less reactive EP oil and base drain intervals on oil analysis...
Hope this helps...
Only the the High speed bearing are has that residue buil up problem?? or the the residues are all over the place (gears, bearings, shaft, etc).
When I was working at a papermill where similar temperatures were present (bearing temp was estimated to be 10 to 20°F higher than the measured on the housing), long drain intervals, brass cages and a reactive oil were believed as the root cause of the varnish.
We took a sample of the oil together with a bearing roller and put it into the oven at 80°C for 2 weeks and saw some similar discouloration and varnish on the roller. Another sample had a piece of brass and qualitativeliy the roller looked darker.
The soultion was to change to a less reactive EP oil and base drain intervals on oil analysis...
Hope this helps...
quote:Originally posted by JTT:
How hot would bearings have to get to burn the oil and leave residue on the bearing race and rollers but not discolor the bearing or rollers.
a temperature of 160 to 180 degrees C (350 F)over a period of several weeks might be enough for leaving carbon residues as you described
