Linear Motion Lubrication

[Tempest]

I'm talking about linear motion machines without the aid of bearings. Straight metal on metal like on ways, guns, etc.

My understanding is that the motion in rotary bearings causes an Elasto-Hydrodynamic Film (EHF) to form between the metal parts and keeps them separated. I have heard this referred to as a "wedge" of oil between the parts. The faster the bearing moves, the stronger the film thickness.

I was wondering where linear motion (LM) parts fit into this. Does a fast moving part in LM generate an EHF film as well? Is it related to speed? Would one type of oil be better than another?

Even if it does, the problem of course is that LM must accelerate and decelerate fairly often as opposed to a rotary bearing. So the EHF strength would fluctuate.

If an EHF does not form, is it simply a matter of viscosity that keeps things separated? If so, then I would image that boundary conditions are the rule, rather than the exception.

Any help would be appreciated.

 

[brian fix]

One place to start is the objects submerged in oil? or dry,speed/velocity,pressure,heat/cold,,many certain linear parts slide on a dry,say nylon, base with water,,metal is different of course,a dry lubricant as silicone (dow) would make a point in this,,simple machines would use a thiner oil,possibly water based for sanitary reasons,,for petro a thin oil would due,as a interisting suggestion 10w mineral oil or Marvel mystery oil,though immersed or saturated...BL

 

[bruce381]

if the linear motion was in the same direction it will form a wedge. but the time and/seed that make that occur may not
in a short "stroke". viscosoity of oil and sliding speed
will determin if a wedge will form.
bruce

 

[Tempest]

So would a wedge have a chance to form in a machine with ~1.5" stroke, moving an average of 300 feet per second? I'm thinking about an auto pistol slide in particular here which is constantly accelerating throughout the stroke.

So if an EHF forms, wear should be lower @ higher speeds, and greater at lower speeds?

Thanks for the info guys.

 

[bruce381]

do not know the I use my own blend of grease and additives
on my 45's. It is about a 0 or 00 grease consisitancy made with low temp PAO for a low "Break away torque".
bruce

 

[bruce381]

email me I'll send yah some.
bruce

 

[gigi riva]

Seems to me that you may have an EHD regime for the first couple of cycles, but since an auto slide is an open system with lubricant loss, you'll soon be experiencing boundary conditions.

Just thinking out loud here