Ball Bearings Sealed or open bearings 6313 C3 2

[Swedishrigpig]

I ordered 6313 C3 bearings (open ones) for our electric motor.
The motor is vertically mounted and drives an hydraulic pump. The motor runs 24/7 but on very low loads.

Our dear purchase department has supplied us with the 2Z verison, i.e shielded or "sealed" otherwise same specs.

My questions are: Are they suitable to use as they are for our type of running conditions?
Can the shields be removed and used as "open" and greased as usual (albeit a risk of metal particles entering the bearing)?
Do we need to send them back and change them for opened type?

 

[GVMOGUL]

I'm trying to think of what the downside would be of just leaving the seals. You say the load is light, but don't say what the RPM's are. A seal is made of rubbery material and because there is contact, they generate a little heat, more at higher RPM's. If you don't have a heat problem, seems like it would be advantageous to leave the seals in. They contain the lube and usually don't ever need greasing as long as the seals remain intact for the life of the bearing. If you just have shields then you won't have any extra heat generation. Just pry them or the seals off if you don't want to take a chance.

 

[Swedishrigpig]

GVMOGUL

Thanks for your input.
The shields are not rubber, they are metal.
The RPM on this motor is 1775 or 1800.
That, I suppose is "normal" and not considered very high speed.
At what speed are these 2Z bearings not suitable?

 

[JJPellin]

We went through a long process to determine the best bearing configuration for our motors. Based on input from the motor manufacturers, bearing manufacturers, lubricant suppliers and our own electrical group, we determined that the best option was a single shield with the shield toward the grease cavity. We have been using this arrangement for the past 20 years and our mean time between bearing failure for motors with grease lubricated ball bearings is well over 10 years. The bearing you specified has metal shields with no rubber seals, as you already noted. The presence of the shields does not affect the speed capability of the bearing. With a little bit of care, the shields can be easily removed.

Based on our experience, I would suggest the following: Remove one shield. Hand pack the bearing with grease. Hand pack the grease cavity on the upper side of the bearing about 1/3 full of grease. Install a grease fitting and vent fitting in the same upper cavity. Leave the lower cavity below the bearing empty with no grease fittings. Install the bearing with the shield on the upper side (toward the grease). Add grease to the motor as specified by the manufacturer. Apply only the amount that they specify. Do not attempt to purge out the old grease. Do not add grease until you see fresh grease at the vent. In our plant, we would add 0.6 ounces of grease to that bearing housing every 9 months.

The shield will serve to limit the introduction of oil to the bearing. The bearing will wick in as much oil from the store of grease as it needs. If the bearing has too much grease, it can expel the excess from the open side on the bottom. I have heard it from experts and I believe it; many more motor bearings fail from over-lubrication than fail from under-lubrication.


Johnny Pellin

 

[Artisi]

Interested as to why you are using C3 bearings for a vertical instalation - from memory these are maximum clearance bearings, is the same bearing fitted both ends. I would have thought an angular contact or spherical roller bearing for 1 end and possibly the C3 or even a parallel roller at the other would be a better solution.

 

[electricpete]

C3 is standard from what I see in motors, even though officially it stands for "looser than normal".

"2Z verison, i.e shielded or "sealed""

Shielded and sealed are not the same. For SKF, 2Z means double shielded.

You may get 100 different answers from 100 different people and there are many application/situational factors that could be considered.

As a a very conservative approximation (recommended by some bearing manfacturers), the life of non-relubricatable bearing is about twice the relubrication interval. The relubrication interval gets shorter as run-time increases (24-7 worst case), but also as size and speed (D*N) go up.

If you were at 3600rpm, I would definitely lean towards removing one or both shields since high D*N bearings.... if you left it double shielded and didn't relubricate, would expect to start seeing beairng symptoms in vibration in 2 or 3 years.

At 1800 rpm, since you've already got the shields in there, it's a tougher call, I would lean towards leaving them both in there. You will most likely have a long life of the bearings 5-10 years.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[JJPellin]

I would offer one point of clarification. The shields do not prevent re-lubrication. As I recommended, I would place the single shield toward the grease and I would re-lubrication. We remove the opposite shield to help reduce the problem of over-lubrication and overheating. A bearing with rubber seals cannot be re-greased. A bearing with metal shields can be re-greased. Even if you leave both shields in place, I would still add 0.6 ounces of grease every 9 to 12 months. I would add the grease with the motor running.

Johnny Pellin

 

[Swedishrigpig]

Very interesting reading this, from all of you.

Our motors has no thrust bearings but two 6313 C3 bearings, I agree this sounds strange but they have all ran like that for 5 years without any problems, even though they are vertically mounted.

First: Is there an recognized procedure for the method of removing one of the shields (towards the grease)? I could use something in writing to make a procedure at my company, as this is news to me. I had no idea grease would penetrate the shield.

Second: How is the calculation done? D*n (mm x rev/ min) makes no sense to me; I assume the answer would be in hours.
What units should be used?

 

[Fugeguy]

Shields on modern bearings can be very close running to the inner ring. This can make getting grease into them difficult.

Since you have been using an open bearing with success I would not change a thing and just remove both shields. Wash out any grease inside the bearing to avoid any grease compatibility issues with what you are already using.

Remove the shields with a small screwdriver of dental pick working the shield up around the inner ring in about 6 to 8 places. Avoid scratching the inner ring.

 

[JJPellin]

A ball bearing does not run on grease. It runs on oil. The composition of grease is oil plus thickener. The only purpose of the thickener is to keep the oil where it needs to be. The grease does not need to pass under the shield. The heat of the bearing will wick in as much oil as it needs. The thickener will be left behind. When you re-grease the bearing, it is like you are simply dumping some fresh oil into a dried out sponge. The old thickener will absorb the oil and distribute it. As long as any of that old thickener is contacting the bearing, the oil will pass under the shield.

I have never seen a procedure for removal of the shield. I have done it myself using a process very much like the one described by Fugeguy. I simply pried up on the inside edge of the shield until I could get a grip on it with a pair of vice-grips and then pulled it off.

Fugeguy brings up another very good point. Since your bearing came with shields, it would have been pre-greased. If you don't know exactly what grease was used, you should remove it. The thickeners in grease are very often incompatible. If you added a Lithium based grease to the pre-charge of Polyurea based grease, the thickeners would have an adverse reaction with undesirable properties. Most motor manufacturers supply their motors with Polyurea based grease. But, bearing suppliers selling bearings for an unknown application may use something else.

To restate my recommendation one more time, I would install the bearing with a shield toward the grease and the opposite shield removed. As I noted above, this was confirmed with our alliance partners. At the time, those included Siemens motors, SKF bearings and Exxon-Mobil lubricants.

But, removal of both shields would not pose a problem as long as your operators do not over-grease (too often or too much).

Johnny Pellin

 

[Fugeguy]

I agree with what JJPellin is saying but please put some grease on the bearing when you install it. If it is dry the time to heat the grease and for the oil to wick under the shield might be just long enough to shorten bearing life.

In principle there is nothing wrong with leaving a shield on the bearing.

It is not a panacea for over greasing. I've seen several over greased bearings that grease pressure (a grease gun can generate thousands of psi) actually collapsed the shield into the bearings.

 

[tbuelna]

Swedishrigpig,

Your motor's lower (axial load carrying) 6313 Z single row, deep groove ball bearing should have an L10>1x10^6 hours assuming:

-grease lubrication
-normal cleanliness
-1800 rpm
-axial load <150 lbf
-150degF max operating temp

Also, regular applications of grease serves a very important function with regards to bearing life. The new, clean grease should displace the old grease which is likely contaminated with debris and moisture. Debris and moisture are the most common causes of rolling element bearing failures.

Regards,
Terry

 

[diskullman]

Pop the shields with a little screwdriver. If your original application had open bearings, that's how some engineer designed it. Too much thinking going on here.

PS Distributors rarely stock open bearings, as the shielded type will fit more varieties, they can always pull shields off, but you can't add them.

Russell Giuliano