Loose wheels on wheelset

[Cotton Belt MP104]

Discussion has recently mentioned, loose wheels. During the assembly of two wheels to the axle, the process of axle cool/wheel heated was mentioned.

A call locally (Greenbriar) said, "We have a jig. All parts are placed in the jig. between 80 to 120 tons is used to press the wheels onto the axle @ AMBIENT temp. If pressure is below or above guideline, wheelset is scrapped.  endmrw0317231457

[bogie_engineer]

Correct, that is the standard method used for many years and today for wheels. Tapered roller bearings are also pressed on against a seat on the axle, then the tonnage raised to a specified level. Heating tires was the way it used to done for steam locos and other tired wheels. The inner races for Hyatt cylindrical roller bearings for locomotives are heated with an induction heater and slid on to the axle.

I don't believe they actually scrap them if the press tonnage is out of spec, at least with locomotive wheels, they were pressed back off, re-machined to clean the wheel bore up, and then mounted on another axle chosen to have the correct interference. The axles could be also re-ground slightly undersize and other wheels with the correct interference mounted. 

Dave

[Cotton Belt MP104]

Being a retired physics teacher/ham radio, the term interference mounting was new to me. Good luck trying to find the definition anywhere. All I could find was reference to things I already knew about (light waves were not included though)

Have any idea how the term came about? Sure have heard of the "hot-cold trick", but not the term interference. Is that term an indication that the pressing was done at ambient temperature?   endmrw0317231754

[bogie_engineer]

Cotton Belt MP104

Being a retired physics teacher/ham radio, the term interference mounting was new to me. Good luck trying to find the definition anywhere. All I could find was reference to things I already knew about (light waves were not included though)

Have any idea how the term came about? Sure have heard of the "hot-cold trick", but not the term interference. Is that term an indication that the pressing was done at ambient temperature?   endmrw0317231754

 

Google "interference fit" and there's lots of information. There is no requirement it be done at ambient temperature but that's how it's done with RR wheels.

[BaltACD]

Cotton Belt MP104

Being a retired physics teacher/ham radio, the term interference mounting was new to me. Good luck trying to find the definition anywhere. All I could find was reference to things I already knew about (light waves were not included though)

Have any idea how the term came about? Sure have heard of the "hot-cold trick", but not the term interference. Is that term an indication that the pressing was done at ambient temperature?   endmrw0317231754

Not a machinist by trade. 

Example, Axle is machined to an EXACT dimension of 10.000 inches.  Wheel cutout for the axle is machined to a exact dimension of 9.990 inches at the same temperature as the axle - a interference of 0.010 inches.

That interference can be overcome by differential heating/cooling or by pressing pressure, or a combination of all three - your choice.

[tree68]

Cotton Belt MP104

Good luck trying to find the definition anywhere.

Wikipedia didn't do too badly:

https://en.wikipedia.org/wiki/Interference_fit#:~:text=An%20interference%20fit%2C%20also%20known,the%20parts%20are%20pushed%20together.

 

It's interesting that a term most of us would know - press fit - is a part of the explanation.

Here's another take from an engineering website:

https://www.engineersedge.com/calculators/machine-design/press-fit/press-fit.htm

That one gets into some specifics of the parameters involved.

 

[Euclid]

“Interference” is a common machine building or fabrication term that typically refers to when two parts are intended to fit together but there is a mistake in the making of one part or the other that leaves metal in the way so as to prevent the parts from going together.  In that sense interference is a mistake or untended problem. 

 

So it is kind of an oxymoron to call a fit an interference fit.  If there is interference, typically the parts will not fit together.  That is the effect of interference.  But that is actually what happens with an interference fit, also called a press fit. 

 

With an interference fit of a round rod into a hole in a plate, the rod is made a larger diameter than the hole in the plate.  So the parts do not feely go together.  But if you position them as though they are ready to go together, and force them together, the hole in the plate will stretch to a larger diameter, as the pin is forced into the hole.  Typically the pin will have a small radius or chamfer to break the sharp edge around its end.  This allows the pin to enter with a wedging action to force the hole to open slightly.  

 

The stretch in the metal around the hole is elastic like a spring that has memory and wants to return to its smaller diameter before the pin was pressed in. That causes the hole to maintain an active squeeze on the pin which creates friction that prevents the pin from moving within the hole. So the pressing refers to pressing the pin into a hole, and the pin is oversize for the true free moving fit.  That oversize is actually what amounts to “interference.”   But the interference in a practical sense is overcome by the pressing that forces the pin to stretch the hole larger in order to accept the pin. 

 

Another kind of fit is when you make the parts with interference, but instead of press forcing them together, you heat up the part with hole and chill the pin.  Or you could just do one or the other.  This is typically called a shrink fit.  But it does have interference as the parts are made.

 

Here is a question:  When you heat a metal plate with a hole in it, dose the hold get larger or smaller?    

[SD60MAC9500]

 

BaltACD

 

 

Cotton Belt MP104

Being a retired physics teacher/ham radio, the term interference mounting was new to me. Good luck trying to find the definition anywhere. All I could find was reference to things I already knew about (light waves were not included though)

Have any idea how the term came about? Sure have heard of the "hot-cold trick", but not the term interference. Is that term an indication that the pressing was done at ambient temperature?   endmrw0317231754

 

 

Not a machinist by trade. 

Example, Axle is machined to an EXACT dimension of 10.000 inches.  Wheel cutout for the axle is machined to a exact dimension of 9.990 inches at the same temperature as the axle - a interference of 0.010 inches.

That interference can be overcome by differential heating/cooling or by pressing pressure, or a combination of all three - your choice.

 

A wheel mounting lube is also used in interference it has to be AAR spec. Also the bore of the wheel should be rough not smooth.

 

 

[tree68]

Euclid

Here is a question:  When you heat a metal plate with a hole in it, dose the hold get larger or smaller?    

Larger, of course.  Ask any mechanic who has applied heat to loosen a stubborn bolt...

[Cotton Belt MP104]

bogie_engineer

......another axle chosen to have the correct interference......

. 

 Thanks to all. Notice in all this chat about the subject......the term is SIMPLY "interference".....NOT intererence FIT.  I will inquire at the local plant again about dimensions of axle OD and wheel opening ID.

The "hole in the heated plate" is a trick question. It gets smaller IF the whole plate is heated. As expansion of all the metal occurs the "hole" expands getting smaller. Correct?  endmrw0317232221

[blue streak 1]

Euclid

 

Here is a question:  When you heat a metal plate with a hole in it, dose the hold get larger or smaller?    

 

 

That is a very impotant qustion that cannot be answered quickly. because due to material qualities the hole might get smaller as metal around hole tries to go to location of least resistance. Usually larger but when a bolt nut is heated it has resistance to tighten on to bolt.

[Overmod]

I have never experienced a hole in a heated piece growing 'smaller'.  Even if it is just the area around the hold being heated.

Likewise, I have always seen reference to an 'interference fit' (in those words) being a fit that is... well, with a smaller female than male dimension.  There may be tolerances given for the amount of the interference, but it is still going to be called an interference fit.