Lubrication for tight clearance steel bushings

I have seen this situation before, the problem is not only the grease groove but the amount of pressure and relubrication intervals. You can put a standard grease in and it will immediately get squeezed out and therefore need re-application on a continuous basis. Ideally you need something which has a very high base oil viscosity but that is still pumpable and will stay in place. We have fitted automatic lubrication systems to this type of application working on the "little bit often" principle. If an autolube is not suitable then i would look for an open gear type lubricant which is designed for extreme loads plus staying in place under slow speed sliding motion. You can also get OGL's which have a diluent which will allow you to apply easily then the diluent will evaporate under the load leaving a very tenacious thick lube film. Link attached to LE5180, it is a NLGI 0 at application then turns into an NLGI 2.

http://www.le-international.com/productdisplay.aspx?id=24

Regards,

Rodney Fitzpatrick.

Thank you very much for your reply. You have been very helpful. It is apparent that this situation called for much more than a simple squirt of 'whatever was laying around' out of a grease gun. You say you would expect a slip/stick event to occur? Would you expect damage to the pin (4140 material) if this condition was occuring for a short time (2 months-ish)? Can the ferrogram help identify potential damage?

Regards,
Tim

You need a High solids anti sieze Moly grease I would think >10% moly grease perhaps a 1 or 2 grade on a routine grease interval whatever it WAS go half or more
bruce

Have you considered your material choices?

You say you have a 4140 pin and a hardened steel bushing.

Could you replace the pins with ones clad with another material, perhaps Carpenter 40, Stellite, etc?

Or even berrylium bronze? (IIRC from my fuel moving days)

An auto lube system was mentioned and in this particular instance you have to be very careful adding something like that. Most auto lube systems tend to have problems moving any lubricant with a very high "moly" content. The moly if higher than 4% it can separate in the system, then you have other issues.

However if the system was set up to dispense while the equipment was in movement, the lubricant under pressure, and the movement of the pin / bushing assembly, the lubricant will flow into the clearance easier than if applied while static. We have set systems up in similar applications and it is quite amazing how well it does work. It is almost like the pin and bushing while moving will dynamically draw the lubricant into itself. You also don't need a lot of lubricant, but a small amount often will provide a much more even film, than loading it up, then letting it run towards the dry side, causing wear.

[QUOTE]Originally posted by Dean Maier:
The moly if higher than 4% it can separate in the system, then you have other issues. /QUOTE]

Dean, is there any literature about this problem of separation of high moly content greases? We are working with systems in long lines, sometimes 30 feet, and the grease has 5% moly. We are looking for documented experiences with that high moly content. Thanks

I haven't seen any documentation, but have seen the results. The systems i have experienced this usually are an injector style with main lines that are 150 feet plus. With lines this big you generally have to pressurize the system to 2200 - 2500 psi to make sure the injectors at the far end dispense. This cycling over and over I suspect is part of it.

I also suspect that the problem is caused by cheaper greases that can include a certain percentage of graphite as a moly substitute that also can separate easier. I was just wanting to give a heads up.

Otto 34,

We never recommend using moly in autolube systems, there are two main reasons. The first is that the moly will drop out in bends and build up inside injectors and ends of pistons. This has been visually identified in many cases. The second is that greases with high content moly tend to be abrasive to the seals and tight clearances found in the pumps and valves of the lubrication systems.

Regards,

Rodney Fitzpatrick

Try a grease with a low viscosity oil and Boron Nitride, ask Acheson

We have similar application of Memolub Automatic Lubricator in a tobacco impregnator. A 12inch 100kg pin in steady position inside in 2 copper bushing inside a housing that is connected to a 18 tons stainless cover of impregnator. The lube point was not in the pin but on the housing drilled in the center where the bushing location. We put one unit of Memolub with 2 outlet distributor block, we used NLGI 2 grease Castrol LT2 but I think NLGI 3 LT3 grease is better.