Gearbox Oil Seal Failure

Get the equipment manufacturer involved. They will be pleased to help, so as to learn something that will improve their product. The problem may have already been seen before, and the solution tried there can also be tried here.

I am expecting engineers to come up with ideas and solutions rather than completely being dependent on manufacturer.

Manufacturers do employ engineers. They have probably seen this problem several times. Change those expectations!

Put the shaft in a heat box oven on about 2000 to 3000 deg F for a set time to raise it's resistance to scoring. (Ask the heatbox owner or manufacturer?)

http://www.charlesahones.com/oven_furnaces.htm

Possibly machine it before hardening and match it to the seals and bearings more precisely when done.

Using precision gauges is a must with fine machining.

Perhaps upgrade your bearing suppliers along with oil, seals, machinist, shaft manufacturer!

Coatings can give a much higher grade finish so that sounds ok if it's price competitive.

Beyond that employ a shaft specialist even if just by talking through it! Mainly because the material science versus mechanics is only as good as what works with what you have and can afford.

It may be helpful if we get some idea about

1) RPM

2) Shaft Diameter

3) Lubricant.

4) Are the seals failing on both Low as well as High RPM sides?

5) Seal material

In addition from your side you can check up

6) Is the oil level bathing the seals?

7) Is the greasing of the seals done?

8) What is the ambient contamination (dust etc)

In case there is dusty ambient, consider putting a dust guard/ labyrinth seal in front of the oil seal.

As a principle we do not prefer chrome plating the shafts since the chrome plating typically leaves residual surface stresses and reduces the fatique life of the shafts.

In our gear boxes (we are OEM), we never plate the shafts. We rather put a plated sleeve shrunk on the shaft (or retained on the shaft and in this case an internal O ring also is put for the sealing purpose)

However in this case you may need to re-design the seal seating portion, especially the housing bore.

The scoring on the shaft and failure of the seal almost invariably points to Dust entry, Lubrication failure or both.

The gearbox is vetrically mounted (I/P & O/P shafts both are vertical) and its used to cool the exhaust steam by air (Air cooled condenser)

the I/P shaft is sealed only at the top position while the O/P shaft has three oil seals at

bottom seal is grease seal

middle oil seal and o-ring

top oil seal

The gearbox is operating in dusty environment Since here in the gulf region.

1) RPM

input shaft=1750 RPM

output shaft=104 RPM

2) Shaft Diameter

input shaft=85 mm

output shaft=120 mm

3) Lubricant.

The lubricant used is MEROPA lube oil VG220 as per manufacturer.

4) Are the seals failing on both Low as well as High RPM sides?

Yes

5) Seal material

the seal material has been changed from nitrile rubber to viton which has higher temperature limit but leakages didnt stop.

Regading chrome plating, why its advisable for hydraulic cylinders and not for gearbox although it can have effect in increasing shaft hardness and therefore prevent shaft scoring?

Regards

The parameters seem to be OK. The VG220 is having sufficient lubricating property to lubricate the lip seals. So the Shaft on the lower side should not have any problem, theough the shaft on the top side will have problem with lubrication and hence will require regular greasing.

More or less your normal sealing is OK.

In similar surface speed our vitons lubricated with siicone grease (Molykote #33) have worked well.

We normally use 3 spring loaded lip seals- viton- back to back. All filled with grease and grease ring and grease injection point between the innermost seal (towards oil) and the two outer ones. The inner most seal spring should face inwards to stop oil and the other two should face outwards to stop dust ingress.

However we have observed scoring (rather the circular valley formation) on the shaft after a couple of years. Once this is formed, obviously the replacement of the seal will not stop the leakage. We resorted to introduction of the chrome plated sleeve (thin, may be only about 5mm wall thichmess) shrunk onto the shaft. It can be easily made from the tubes available, machined to the diameter. Interference of about 0.05 to 0.1 mm will be enough.

The chrome plating as I mentioned leaves a resifdual stress on the shaft.

You can search the net, I think I have read about this in Dieter, on the fatigue chapter.

However a few links could be seen

http://books.google.co.in/books?id=B2aAPVa1TloC&pg=PA255&lpg=PA255&dq=chrome+plating+fatigue&source=bl&ots=AvgtxYmaBx&sig=NnP-4k-CkJfc01NDTMeHhkg8cnQ&hl=en&ei=4SudSqKCNJChkAWb2PWyBg&sa=X&oi=book_result&ct=result&resnum=7#v=onepage&q=chrome%20plating%20fatigue&f=false

or

http://books.google.co.in/books?id=qoEq8ZLhPJkC&pg=PA235&lpg=PA235&dq=chrome+plating+fatigue&source=bl&ots=oBmY485iYg&sig=HBtZDwamk-qu6ezTiWa579p4n5g&hl=en&ei=iC2dSoraHMaJkQXa-O2yBg&sa=X&oi=book_result&ct=result&resnum=10#v=onepage&q=chrome%20plating%20fatigue&f=false

Anyway we do not carry out the platings on the components that are proone to fatigue loads and gear box shafts are the main ones.

Also I would prefer if you put some sort of labyrinth seal or dust guard over the lip seals.

Look at mechanical face seals- there are a few suppliers including i thhink Parker Hannifin that will supply mech seals.

Magtecta or Labtecta from AESSEALS are pretty good bearing protectors, not sure if suitable for what you are suggesting.

Thank you for your detailed response,

If we are going to introduce a shrunk fit sleeve please advice on the following

1- material of sleeve

2- min sleeve wall thickness (i think 5mm is not applicable)

3- design changes to be done for shaft

4- design changes to be done for seal housing

In addition could you provide me drawing of the back to back lip seals and whether modifications can be done for our gearbox to implent this type of sealing.

we are recently using ordinary single lip oil seals.

Regards

The sketch of the sleeve we are using is enclosed. the end 15 degree chamfers are for the seal entry.

You have to measure the shaft diameter. Since it is already for seal, it is likely to have sufficiently close tolerance. Based on this you must decide the sleeve ID.

The sleeve OD depends upon the available seals (You may refer the ISO or contact James Walker Group or parker seals or any other locally available seals corresponding)

For 85 shaft I expect the one corresponding to say dia 100 shaft seal. The seal supplier will give you the recommended housing bore and tolerance, for us it is with approx 0.25 to 0.45 interference between the seal OD and housing ID to ensure the seal do not rotate inside housing.

the assembly

Please look at this link

http://www.jameswalker.biz/docs/jwco/walkersele%20guide.pdf

James Walker are one of the better manufacturers of the seal.

BTW: study the mechanical seal aspect too. Parker Seals make both, mechanical as well as lip seals.

I forget to mention the problem of the oil seal in the middle of the output shaft.

as i mentioned earlier there are three seals for the output shaft

top oil seal (shaft end)

middle oil seal (shaft centre)

bottom oil seal (shaft end)

any idea how can we mount shrunk fit sleeve at the shaft middle position???

Is it possible to have a sketch of the arrangement? I am unable to visualise the seal in the middle of a gear box. The gear boxes are supposed to be totally enclosed only the input and output shafts are required to have the seals.

The type you are trying to signify, putting the sleeve will be a broblem. Split sleeves are there and are technically possible but had never had an opportunity to see them.

In our similar cases we go for labyrinth seals but then these are horizontal axes gearboxes.

Only option I see are the mechanical seals. They perfectly adapt to half sections.

I regret for the delay in replying

I have attached this picture of the output shaft showing the locations of oil seals.

the bottom seal actually is a grease seal since no oil present in the space above the bottom seal.

Do you have idea about the material of the shaft and hardness so that we can now how much improvement we can achive by installation of sleeves.

The material of the shaft is likely to depend on whether the gear is integral or shrunk in the shaft.

The likely candidates are if the load is not too high , one of the alloy steels (AISI4340, or BS970-2 , or in some application we have used 711M40 ie 1%CrMo steel etc, or one of the DIN 17210 steels)

Difficult to tell exactly, however these will be most likely in hardened and tempered condition to optimise its toughness and then you are unlikely to get an hardness > 300BHN or about 30-35 HRC.

The hard chrome plated surface whereas will give you a hardness of 60-62 HRC.

And it is not only the hardness, the chromeium has, as on now, best antiwear properties, and hence despite all the environmental hazards, still going stronk. In our plated surfaces, even in extremely dusty conditions, the sleeve has provided a life of 5 yrs+ (in fact we rarely sell the sleeves as spares loss of market for us )

The shaft as I can see, though the sleeve is in between, there are no collars on the other side which will obstruct its entry, so I don't see why you should not be able to insert it.

get the seal dimensions, based on that design the sleeve OD and Housing ID. Ensure to get the sleeve OD ground to a finish better than 0.8 micron. We usually get between 0.2 to 0.4 micron. ID may be finished on the lathe to a good finish, but controlled dimensions.

During assembly, especially the middle sleeve, which has to travel a long way, you have to maintain the temperature of the sleeve, else it will get stuck on the way. But since there are differences in diameters (recess) as it looks it may not be too difficult.

In your last reply you have mentioned that to design the sleeve OD and housing ID based on the available seal dimension

cant it be the other way which means to select sleeve thickness and using same housing bore then requesting a seal company for a seal which suit our sleeve and housing dimensions??

Which process can be done after chrome plating to get the desired surface finish of 0.2 to 0.4

Regards

GA-GA and GA.

BTW:

1. Welcome to the community and if you follow, quite a few of us are off the gear and most are non-human .

2. The seals have a shelf life (like any other rubber items). Check it up with the manufacturer and the storage guidelines. We normally follow 12 months from the date of manufacturer, but for us it is less critical, since as OEM, it is often hand to mouth and we have taken the least of all manufacturers and types and to avoid any confusion, kept the ceiling at that value.

3. Due to this limited shelf life, it becomes more important for you, the O&M person, to go for standard/catalogue item.

I want to give you golden card for your knowledge in so many fields.

thank you for sharing your years of valuable experience in the field with young engineers like us.

this is good solution

A basic question: was the gear box designed for the application or is it of general use?

It can happen that the choice was not done considering the environment and the solution adopted is not compatible to it. What you give as input is too limited to be able to make a thorough analysis. The solution suggested : use of a bushing has to be considered since it is a very good one. I also used it with good results in very harsh environments. there are companies selling such bushings for repair or OEM usage.

What kind of seals do you have? what kind of shafts? how is the box with horizontal or vertical shafts? can dirt accumulate on the seal? As you see the list is long.

A few pictures will help to understand better your problem and may be give a hint.

You can find by SKF wear sleeves exactly for what you need. For seals with vertical axis and able to keep dirt on it is recommendable to protect with V-seals (Timken and others).

The problem you are confronted with is often appearing so that solutions are offered by bearing manufacturers who are interested to protect their products from ingression and wear.

could you post the link for website or brochure for this type of sleeve.

I heard that this type of sleeve come as intergral unit with radial seal ?

Try the SKF catalogue and the other one I mentioned.

How is this box vented?

cloged vent will pressure the box and blow the seal.

Being in a hot zone I would say that you need to examine the internal heat saturation (infrared thermometer's are so good at tracing) and the oil pressure. Maybe you need to change the grade of oil and filling capacity due to adverse conditions. Also check that the shaft isn't heating straight off the cooling fans; therefore requiring a thermo conduction restricting coupling.

Other than that examine the play and tension created by the rig and see if a lighter fan can achieve the same goal without creating so much stress; e.g shim the fan's alignment to agree with the shaft's rotation.

Perhaps limit the exposure to the environment by running the shaft through a brush or flap like flange cover and change it as a filter at regular cycles.

AESSEAL do a vertical labyrinth with integral lipseal. They have them working on cooling tower gearboxes in refineries in the UK.

www.labtecta.com

Study the different parameter of gearbox like temparature, pressure inside the gearbox etc. while testing. What is input and output RPM?

Based on this select seal material. prefereably select double lip oil seal.