Hi,

currently our workshop have rewinded a motor which spec are:

Power: 60 Hp
Voltage: 220V to 460V
Frequency: 60Hz
Maker: Marathon Electric

But the main problem is we have detected a high temperature at the DE side especially at the shaft area. the temperature reach 70 Celcius. We suspected the problem is due to the oil seal, because when we remove it, and again do the solo run, the temperature was dropped to 49 Celcius. What is the main problem? Basically, the oil seal is to avoid any oil to enter the inner side of the motor which can cause short circuit.

We replace the same type of oil seal as before rewinding which is 471372, brand National Mexico. Anyone to help me. Thank You.

Fazli Sham
Malaysia

Fazli:

Not uncommon. When I was in the motor repair industry, we would do our bearing temperatures before adding any oil seals. The friction of the lip of the oil seal on the shaft of the motor is what causes the temperature to increase (also found with machine tools and cooling tower motors). As long as it stabalizes, it should be OK (if it is actually exposed to oil, the oil will cool it also).

The only two cautions are: Ensure that the lip (oil) seal is not too tight on the shaft, and, if you have disassembled the motor, that the seal surface of the shaft is 'cleaned up' so that any rough spots will not damage the seal.

You may also have to make sure that the bearing fit on the inner race of that bearing is towards the loose side of tolerance (inner race will have additional stress as the motor, shaft and bearing come up to temperature) if the motor is started and stopped often.

The bearing temperature (at the bearing) should be, under load, about 80C for standard grease and 100C for synthetic grease.

Howard

Sincerely,
Howard

Dear Mr Howard,

Thank you for your reply. I have few other question regarding this matter.

1. can u explain more on ' we would do our bearing temperatures before adding any oil seals'. Is that mean to run the motor without oil seal and check the temperature?

2. in what condition did you consider it stabilize?

3. As for the shaft whereby the lip of old oil seal located, it have some effect on the shaft surface. did it need to be metal sprayed?

4. What temperature that is suitable for the bearing? as per your reply, you mention 80C for standard grease and 100C for synthetic grease but as requirement by our client (an oil and gas industry), it should be not more that 50C. is there any guideline for it.

Further info for my case, we use 6312 C3 type of bearing.

Thank you for your attention.

quote:

1. can u explain more on ' we would do our bearing temperatures before adding any oil seals'. Is that mean to run the motor without oil seal and check the temperature?

Yes. The contact surfaces of the oil seal will cause the temperature to increase due to friction.

quote:

2. in what condition did you consider it stabilize?

Once the temperature remains constant for 2-3 minutes. I have seen recommendations for up to 10 minutes. In effect, if there is a problem with a bearing, such as too tight a fit, the temperature will 'run away' and continue to increase.

quote:

3. As for the shaft whereby the lip of old oil seal located, it have some effect on the shaft surface. did it need to be metal sprayed?

In my experience, metal spray does not perform very well as a seal surface. If not properly prepared, it may raise and destroy the seal. Same type of problem with welding and turning. Surface may be too rough.

Best way is to either clean-cut the shaft, if there is enough meat, or sleeve the shaft.

quote:

4. What temperature that is suitable for the bearing? as per your reply, you mention 80C for standard grease and 100C for synthetic grease but as requirement by our client (an oil and gas industry), it should be not more that 50C. is there any guideline for it.

There is no clear-cut standard. With good bearing fits and no load, 50C is do-able. However, with the seal added, the friction causes additional heat. Items, such as this, are not always addressed in standards.

I do have several items that I have referenced for a similar item. One is from US Electrical Motors and one is from Reliance. I used these, combined with a military standard, in response to a similar question in another string.

Howard

IEEE841 is a purchase spec for devere duty motors for the Petrochem industries. It mentions a bearing housing external surface temperature limit of 45C rise above ambient (50C for 2-pole motors). Considering a 35C ambient temperature, that would correspond to a 80C or 85C total temperature on the bearing housing. No mention of shaft temp. These temperatures are based on limiting the temperature of the lubricant in the bearing (note the bearing and lubricant would likely be 10C-15C hotter than the external surface of the housing). If the area has explosive gases than other limits may apply to limit the possibility of explosion, but I don't know them.

We had a similar situation of higher temperatures on the shaft than housing noted by infrared. In that case it was a greased bearing and we found excessive grease in the bearing was pushing the lip seal into abnormal contact (suface contact rather than line contact). Condition of the seal and shaft are also important as Howard said.

This message has been edited. Last edited by: electricpete,

Dear Mr Howard,

There is another info that i did not to mention. As for the DE side (the one which recorded high temp) we have done metal spray on the bearing housing. The reason why we did the metal spray is when we dissemble the motor at the fisrt place, we detected that the old bearing is easy to be removed. as for that, we decided to do the metal spray on the bearing housing, which afterthat, we did some machining on it to get the size slightly bigger that the bearing size (0.01mm). then we reassemble the motor and after that, we detected the high temperature (70C). basically, since the motor is very urgent (the plant need it by next morning) and the machining workshop is closed (it's already past midnight), we remove the cover (DE side) and by using sand paper (its very conventional way and very improper way), we 'enlarge' the bearing housing side. reassemble it and tested it again. the temp dropped to 58C. again we redo it again and tested, the temp dropped to 49C. Basically, what has answered is the temperature is not due to oil seal. But, why did the bearing housing size did contribute for the rise in temp.

My second findings is, some motor are equiped with housing cap, which goes for this motor. and what we find is, the bearing housing size is not as tight as (for insertion of bearing) for the motor that not with it. does the fabrication of these kind of motor are purposely designed like that.

Thank You.

Dear Mr Howard,

There is another info that i did not to mention. As for the DE side (the one which recorded high temp) we have done metal spray on the bearing housing. The reason why we did the metal spray is when we dissemble the motor at the fisrt place, we detected that the old bearing is easy to be removed. as for that, we decided to do the metal spray on the bearing housing, which afterthat, we did some machining on it to get the size slightly bigger that the bearing size (0.01mm). then we reassemble the motor and after that, we detected the high temperature (70C). basically, since the motor is very urgent (the plant need it by next morning) and the machining workshop is closed (it's already past midnight), we remove the cover (DE side) and by using sand paper (its very conventional way and very improper way), we 'enlarge' the bearing housing side. reassemble it and tested it again. the temp dropped to 58C. again we redo it again and tested, the temp dropped to 49C. Basically, what has answered is the temperature is not due to oil seal. But, why did the bearing housing size did contribute for the rise in temp.

My second findings is, some motor are equiped with housing cap, which goes for this motor. and what we find is, the bearing housing size is not as tight as (for insertion of bearing) for the motor that not with it. does the fabrication of these kind of motor are purposely designed like that.

Thank You.

Dear Mr Howard,

There is another info that i did not to mention. As for the DE side (the one which recorded high temp) we have done metal spray on the bearing housing. The reason why we did the metal spray is when we dissemble the motor at the fisrt place, we detected that the old bearing is easy to be removed. as for that, we decided to do the metal spray on the bearing housing, which afterthat, we did some machining on it to get the size slightly bigger that the bearing size (0.01mm). then we reassemble the motor and after that, we detected the high temperature (70C). basically, since the motor is very urgent (the plant need it by next morning) and the machining workshop is closed (it's already past midnight), we remove the cover (DE side) and by using sand paper (its very conventional way and very improper way), we 'enlarge' the bearing housing side. reassemble it and tested it again. the temp dropped to 58C. again we redo it again and tested, the temp dropped to 49C. Basically, what has answered is the temperature is not due to oil seal. But, why did the bearing housing size did contribute for the rise in temp.

My second findings is, some motor are equiped with housing cap, which goes for this motor. and what we find is, the bearing housing size is not as tight as (for insertion of bearing) for the motor that not with it. does the fabrication of these kind of motor are purposely designed like that.

Thank You.

Dear Mr Howard,

There is another info that i did not to mention. As for the DE side (the one which recorded high temp) we have done metal spray on the bearing housing. The reason why we did the metal spray is when we dissemble the motor at the fisrt place, we detected that the old bearing is easy to be removed. as for that, we decided to do the metal spray on the bearing housing, which afterthat, we did some machining on it to get the size slightly bigger that the bearing size (0.01mm). then we reassemble the motor and after that, we detected the high temperature (70C). basically, since the motor is very urgent (the plant need it by next morning) and the machining workshop is closed (it's already past midnight), we remove the cover (DE side) and by using sand paper (its very conventional way and very improper way), we 'enlarge' the bearing housing side. reassemble it and tested it again. the temp dropped to 58C. again we redo it again and tested, the temp dropped to 49C. Basically, what has answered is the temperature is not due to oil seal. But, why did the bearing housing size did contribute for the rise in temp.

My second findings is, some motor are equiped with housing cap, which goes for this motor. and what we find is, the bearing housing size is not as tight as (for insertion of bearing) for the motor that not with it. does the fabrication of these kind of motor are purposely designed like that.

Thank You.

I have never heard of metal spray to "build up" a housing. Our shops always bore/sleeve the housing if it is undersized. Metal spray the shaft if it is undersized. I don't know the reason why one technique is used for one applicaiton and the another technique for the other application. Anyone else know why? (maybe there is some good reason why metal spray is not typically applied to housing and that reason might shed light on the high temperature).

If you had repeated experience where enlarging the bearing housing decreased the temperature, I can think of two explanations:

1 - IF this is a greased bearing (it seems we have talked about both grease and oil in this thread so I'm not sure), it may have something to do with the way the grease was handled during the evolution. In particular if you packed the bearing itself full initially and then never repacked, then you are giving the grease an oppotunity to move out of the bearing each time you start/stop, resulting in decreased temp. We have one set of pumps with greased bearings that often run hot after bearing replacement. Our standard procedure is to start/stabilize/stop several times until stabililized temperature is acceptable. Our theory is that over time the running/starting/stopping pushes FROM the ball path (where it creates friction heat) TO other parts of the bearing/housing where it does not create heat.

2 - There is some degree of internal clearance or interference in the bearing during operation. It is affected by the unounted internal clearance (i.e. C3, C4 etc), the pressure acting inwards from interference to housing and outwards form interference to shaft, and the temperature of the bearing which causes it to expand compared to ambient conditions. In most cases there should be no inteference between housing and outer ring, but instead a little clearance (for example H5 fit). But if for some reason due to housing dimension, bearing dimension (there is some small variation) and operating temperature there was an interference between outer ring and bearing at operating temperature, than that inteference could contribute to reduction in internal clearance which could increase operating temperature. When you enlarged the bearing housing you would have reduced that effect. If you really did have interference between housing and bearing to begin with (after metal spray and before sanding), I would have thought someone might have noticed it was unusually difficult to mount the housing onto the bearing.

Just some thoughts. Interested to hear Howard and others' thoughts.

Pisemude - can you clarify greased or oiled? Also can you expand a little on your 2nd finding. I didn't understand what you were saying.

This message has been edited. Last edited by: electricpete,

ElectricPete is correct on the second point. If the fit is too tight, the internal clearances of the bearing will be reduced. The additional friction will cause the bearing to heat up. Whether using metalizing or a sleeve, polishing the housing can be an effective method to ensure the fit is correct. It is important to remember that the outer and inner races of the bearing also have tolerances - how good those tolerances are depends upon the manufacturer.

Metalizing housings is a very precise procedure with errors potentially causing the metalizing to 'lift' from the prepared surface. I am also assuming that you are using one of the newer metalizing spray systems. The preparation for a housing requires an oil-free surface (for the process) then a course then fine thread made within the housing (usually, the thickness of the metalizing must be at least 10 Mils (0.010 inch) after machining. Oil, even from fingertips (body oils), that comes into contact with the surface can also cause it to lift.

If the housing was not machined straight, then 'cocking' of the bearing within the housing can occur. In this case, polishing will allow movement of the bearing to reduce friction during operation by allowing the outer race to 'twist' in the housing. This will reduce the life of the machined surfaces and the bearing.

As to the second point. The housing clearance is not determined by the bearing cap. Some happen to be 'loose' as far as the lip of the bearing cap fitting into the bearing housing. As long as there are mating surfaces (and possibly a gasket - very important as the lack of a gasket, if required, can increase pressure on the bearing), then grease should not escape into the motor. The bearing fit tolerance of the outer race exists to prevent torsional movement of the outer race of the bearing in the housing which can cause damage to the bearing, but will wear down the housing very quickly. The 'pinching' of the bearing housing with a bearing cap will only be effective until the components of the endshied, bearing housing, bearing and shaft begin to change due to heat (thermal changes).

Also noted by ElectricPete, the best method for machining a housing, if there is enough 'meat' (metal), is to bore the housing and add a sleeve, which is then turned to size. While metalizing (housing or shaft) is an inexpensive method of returning fits, it can cause problems, such as belted applications in which the uneven radial pressure can cause the metalizing to lift, as well. [at least that is my opinion]

Hope this helps.

Howard

Dear electricpete,

bearing is using grease.

regarding the bearing cap, (as mention in the 2nd findings), inside the bearing, there is a bearing cap (that is what we call it here), which the function is to hold the bearing and maybe to avoid the grease from entering the inner part of the motor. some motors are equipped with it, but some are not. what did we found, if the motor is equipped wit5h this bearing cap, we found that, to remove the bearing from the bearing housing is much easier compared with the one without it. in other word, it is not as tight to the one that without it. my question is, is the bearing housing diameter is on purposely made a little bit larger compared to the one that without it (the different is maybe in milimeter, but still, it does gives some effect on it).


Best Regard,

Fazli Sham.
Perwaja Steel Sdn. Bhd.

The biggest concern for a housing too large would be vibration and movement. I don't think there would be significant heat associated with change in housing fit except in very extreme cases (especially since you say the high temperature was on the shaft, right?).

I think the most likely scenario is that you had high bearing temperature initially after repacking the bearing itself (between the balls) with grease. Then through multiple starts and stops, the grease worked its way from the bearing itself into the housing and the temperature decreased (provided you did not repack the bearing itself when you went back and adjusted the housing). We have seen the same scenario many times (initial high temperature after hand repack of bearing itself which stabilizes at a lower value on each subsequent start). Does this scenario sound reasonable to you?