Miscommunication between Kawasaki & WMATA lead to 7000 series issues

https://wtop.com/dc-transit/2022/04/man ... he-agency/

Kawasaki Rail Car, which manufactured the long-sidelined 7000 series, was asked by Metro to press wheels onto axles with more force, following failed wheelset inspections in 2017.

Kawasaki said the updated cars started going into the system in 2018. The company said it asked Metro what it wanted to do with the nearly 500 railcars that had already been made under the old specification, and that, to this day, Metro has not responded.

...Kawasaki said of 7000-series wheelsets that have fallen out of tolerance, 48 happened under the original pressure specification, while three happened under the revised spec.

Metro never had the nearly 500 7000 series railcars they already received fixed.

Kawaski had built railcars for MARC and those cars never had this problem

STrRedWolf
https://wtop.com/dc-transit/2022/04/man ... he-agency/

Kawasaki Rail Car, which manufactured the long-sidelined 7000 series, was asked by Metro to press wheels onto axles with more force, following failed wheelset inspections in 2017.

Kawasaki said the updated cars started going into the system in 2018. The company said it asked Metro what it wanted to do with the nearly 500 railcars that had already been made under the old specification, and that, to this day, Metro has not responded.

...Kawasaki said of 7000-series wheelsets that have fallen out of tolerance, 48 happened under the original pressure specification, while three happened under the revised spec.

Nothing irritates me more then when someone tries to blow smoke up my ass.

The amount of "pressure" used to press the wheels onto the axles does not make sense as the wheels are pressed to a shoulder on the axles. No amount greater force pressing the wheels to that shoulder is going to hold the wheels any tighter to axles.

What holds the wheels onto the axles is an interference fit. The inside diameter of the bore in the wheel must be smaller then outside diameter of axle by a specified number of thousands of an inch. If that specified number of thousands of an inch is to small the interference fit will not be tight enough and the wheel will slip off that axle.

The specifications for railroad wheel axles interference fits based on axle diameters and wheel cross section has been established for more then 100 years.

Isn't the axel and / or wheel tapered to resist the press on? Could be a test to the original spec passed but was not the correct spec? Maybe the dimensions were not proper, and another 1 /1000 would have met requirements.

west point
Isn't the axel and / or wheel tapered to resist the press on? Could be a test to the original spec passed but was not the correct spec? Maybe the dimensions were not proper, and another 1 /1000 would have met requirements.

If they are tapered then pressing them with greater force would make the wheelset less then 4' 8 1/2" if the difference between the dimensions are under specification.

This picture leads me to believe the wheels are pressed to a shoulder as the axle bearing journal is of a larger diameter then the diameter of the axle where the wheel is fitted.



Those orange things on either side of bearings are the bearing seals.

This picture leads me to believe the diameter of the axle is the same on both sides of the larger diameter bearing journals.

Sand Box John wrote: ↑Sat Apr 30, 2022 9:14 pm The amount of "pressure" used to press the wheels onto the axles does not make sense as the wheels are pressed to a shoulder on the axles. No amount greater force pressing the wheels to that shoulder is going to hold the wheels any tighter to axles.

The pressure or press tonnage is important because it is a function of (axle diameter and wheel bore) and provides the means of validation/verification for the integrity of the interference fit. You are correct that these dimensions are critical factors in the fit process but also *significant* factors are the surface finishes (roughness) of both wheel and axle and the application or lack of lubricant to these surfaces during the press operation. The pressure recorded by the press reflects each of these factors and is therefore the acceptance criteria for a successful fit.

When determining the dimensions, surface finishes, and choice of lubricant that will ultimately output a press tonnage, there are input factors such as the vehicle weight and the operating environment (curvature, switch types and arrangements, restraining rail, etc.) that must be considered. You are correct that is mostly straightforward 100+ year old knowledge and technology, but must be managed by competent mechanical AND diligent systems engineers to assure success.

As you know, the 7000 series cars are heavier than the 6000 series and older railcars, so that could be a factor