Side Bearer (constant contact) characteristics

[Overmod]

For those with the interest, you can spend about half an hour of the hour you got back this morning by watching this training video from a maker of CCSBs:

https://vimeo.com/175430795/a3b439ba65

[Euclid]

notkarl

Hello, I am trying to confirm if constant contact side bearers are constantly wearing against the car body wear plate whenever a rail car is going through a curved section off track. Physically I'm not clear on how this does not rapidly wear away either the cap of the side bearer, or the wear plate itself. Any clarity on the mechanics or materials that make this arrangement work are much appreciated. 

I have included links to photos of two variations I looked at recently near my house. 

karl

 

As you surmise, there are indeed issues with constant contact side bearings.  While the do prevent derailments by adding friction to the truck pivot, in order to dampen truck hunting; that friction can wear them out so they lose their effectiveness.  Then if the affected car is allowed to run without the protection of CCSBS, it can derail from truck hunting due to the loss of that protection caused by CCSB wear.  

 

Here is a TSB accident report with an excellent explanation of one such derailment caused by worn out CCSBs on an empty center beam flat car.  Such cars when empty are especially vulnerable to truck hunting.

 

DERAILMENT REPORT:

 

http://www.bst-tsb.gc.ca/eng/rapports-reports/rail/2014/r14t0180/r14t0180.pdf

 

 

 

1.6 Truck hunting

 

Truck hunting is the oscillation of the wheel set from rail to rail due to the dynamic response of the railway car truck as it travels along the track. All wheel sets hunt as they seek to achieve the optimal placement of the wheel tread conical taper on the rails. Under certain conditions, truck hunting can become excessive resulting in hard contact between the wheel flange and the rail head, in wheel lift, and in some cases, derailment. Truck hunting will typically become more severe when lightly loaded or empty cars, greater than 50 feet in length, travel at speeds in excess of 45 mph on dry tangent CWR track. Throughout North America, there are about 48 000 bulkhead and centre beam bulkhead flat cars, which are known to be more susceptible to truck hunting when empty. In addition, excessive truck hunting can be more pronounced in trucks with low warp stiffness. Certain older truck designs, such as the Barber S2, have low warp stiffness and are known to be prone to excessive hunting. While truck component and wheel wear can exacerbate the phenomenon, excessive truck hunting can also occur on cars with these components in good condition. 10 | Transportation Safety Board of Canada The presence of certain track conditions in close proximity to each other, such as narrow gauge and multiple minor track cross-level perturbations, are also known to initiate excessive truck hunting. While truck hunting is more likely to occur in track with narrow gauge, it can be more severe in track with wide gauge. However, excessive truck hunting can also occur on track in good condition. Truck hunting can cause car body lateral oscillation. The side-to-side motion of the truck as it hunts causes the car body ends to rotate about their centre of gravity. As both trucks do not hunt in unison, a torsional force along the length of the car can develop. The torsional force will load and unload in a spring-like manner. Certain cars, such as the centre beam bulkhead flat car with a torsionally flexible car body and large bulkheads at each end, have increased susceptibility to this spring-like loading. This torsional force can contribute to wheel offloading. In extreme cases, truck hunting and wheel offloading can cause the wheel flange to climb the gauge face of the rail, derailing the truck. Low spots in the rail, narrow gauge, and a lateral force caused by dynamic7 braking can also contribute to a wheel climb event.8 When a truck hunting-type derailment occurs, long flange marks may be present along the running surface of the rail. Over the years, the railway industry has become more aware of the truck hunting phenomenon. Since the 1990s, to address the tendency for trucks to hunt excessively at high speeds, railway cars have been built with CCSBs installed. The first type of CCSBs installed were the ST CCSBs. In 2002, the Association of American Railroads (AAR) Manual of Standards and Recommended Practices (MSRP) adopted Specification M-976 (Truck Performance for Rail Cars) which introduced improved truck performance requirements. Specification M-976 included testing requirements for the control of truck hunting and placed limits on the allowable lateral acceleration of the trucks. Freight car trucks built to this standard have improved warp stiffness and are less susceptible to excessive truck hunting. In 2003, new freight cars were required to be equipped with the newly developed long travel (LT) CCSBs, which provides more effective damping and further reduces the risk of excessive truck hunting. Because of this superior performance, Rule 88 in the AAR Office Manual was revised to indicate that, as of 01 January 2003, certain cars be equipped with LT CCSBs, including all new, rebuilt or modified cars, and all cars that have been given an increased gross rail load, an extended service, or increased life status.9 7 The dynamic brake is a locomotive electrical braking system that converts the locomotive traction motors into generators to provide resistance against the rotation of the locomotive axles. When the dynamic brakes are used, compressive forces are created within the train. 8 TSB Engineering Laboratory report LP 128/2004 9 D. Iler, “Understanding the Benefits of Long Travel Constant Contact Side Bearings”, Proceedings of JRC06 Joint Rail Conference of ASME Rail Transportation Division and Land Transportation Division of the IEEE Vehicular Technology Society, April 4-6, 2006, Atlanta Georgia USA. Railway Investigation Report R14T0180 | 11 In 2006, the AAR Interchange Rules were further modified to protect against wheel lift derailments due to truck twist and truck hunting. The requirement was added for LT CCSBs to be installed when converting cars from roller or block side bearings. Cars with ST CCSBs installed were not affected. The 2006 modification also prohibited the use of roller or block side bearings on bulkhead flat cars and centre beam bulkhead flat cars as of 01 January 2011.

 

 

 

1.7 Constant contact side bearings

 

CCSBs are secured to the truck bolster below the car body side bearing,10 which is secured to the underside of the car. The CCSB cap serves as the bearing surface upon which the car body side bearing is in constant contact. Resilient members beneath the cap provide the vertical force (preload) to keep the cap in constant contact with the car body side bearing. The CCSB cap displaces vertically to allow the car body to roll relative to the truck. CCSBs increase the truck’s turning resistance by placing a load between the truck and the car body side bearing thereby minimizing truck hunting. CCSBs also limit the side-to-side oscillation of the car body. 11 A known problem with CCSB arrangements is designing a resilient member with characteristics suitable for the long-term loads and stresses encountered during operation of the rail car. Resilient members are susceptible to thermal damage from the heat generated at the interface between the bearing cap and the car body side bearing. Worn, melted or deformed resilient members lessen the preload, lowering the rotational resistance of the truck.12 A 2014 Transportation Technology Center, Inc. (TTCI) study for CN concluded that “decreasing side bearing preload for ST CCSBs was also shown to increase derailment risk due to vertical wheel unloading in track with cross-level perturbations.” The installation of LT CCSBs enables the wheels to remain in contact with the rail longer thus lowering the risk of derailment. LT CCSBs allow for improved curve negotiation and better negotiation of track irregularities.13 In contrast, ST CCSBs are more prone to bottoming out and introducing wheel offloading forces into the truck during excessive truck hunting events. A 2006 TTCI study 14 concluded that LT CCSBs improve rail operations by 10 Wear plates attached to the bottom of car bodies that make contact with the truck mounted portion of the side constant contact bearings. 11 D. Iler, “Understanding the Benefits of Long Travel Constant Contact Side Bearings”, Proceedings of JRC06 Joint Rail Conference of ASME Rail Transportation Division and Land Transportation Division of the IEEE Vehicular Technology Society, April 4-6, 2006, Atlanta Georgia USA. 12 H. Tournay, R. Walker, S. Chapman, “Inspection and Maintenance of Poorly Performing Cars Identified by Hunting Detectors”, in Technology Digest, TD-07-005, April 2007. 13 B. O’Donnel, “Making the Case for Long Travel Constant Contact Side Bearings”, Interface – The Journal of Wheel/Rail Interaction, July 2005. 14 D. Iler, “Understanding the Benefits of Long Travel Constant Contact Side Bearings”, Proceedings of JRC06 Joint Rail Conference of ASME Rail Transportation Division and Land Transportation Division of the IEEE Vehicular Technology Society, April 4-6, 2006, Atlanta Georgia USA. 12 | Transportation Safety Board of Canada “maintaining better vertical wheel loads, providing high-speed stability, and providing more predictable truck turning forces.” In addition, the improved design of the resilient member and the CCSB has resulted in LT CCSBs being less susceptible to the negative effects of wear.

[notkarl]

Thank you. So under ideal conditions (no hunting), when the truck pivots on a turn, there is lighter sliding friction between the CCSB and the car body wear plate, is that an accurate way to describe the conditions?

Very helpful to understand that most of the loaded weight goes to the bolster via the  center beearing.  

[Overmod]

Keep in mind that constant-contact side bearings are not carrying a significant fraction of the loaded weight of the car.  That goes into the bolster via the center bearing (which requires careful maintenance and lubrication)

Consequently, while there is of course sliding friction (to the degree, as noted, that controls truck rotation and possibly progression to lozenging) it is not dramatically high.  The trouble Euclid mentioned is that the side bearings have the 'same' bearing pressure whether the car is loaded or unloaded, as they act on top of the bolster and not through the suspension springs in the trucks.

[Euclid]

notkarl

Hello, I am trying to confirm if constant contact side bearers are constantly wearing against the car body wear plate whenever a rail car is going through a curved section off track. Physically I'm not clear on how this does not rapidly wear away either the cap of the side bearer, or the wear plate itself. Any clarity on the mechanics or materials that make this arrangement work are much appreciated. 

I have included links to photos of two variations I looked at recently near my house. 

karl

 

Your links open as pictures for me. 

 

We had a thread on this topic of Constant Contact Side Bearings a few years ago at this link:

 

https://cs.trains.com/trn/f/111/t/254486.aspx?sortorder=desc&page=1

 

 

 

https://cs.trains.com/trn/f/111/p/293830/3428103.aspx#3428103:~:text=https%3A//cs.trains.com/trn/f/111/t/254486.aspx%3Fsortorder%3Ddesc%26page%3D1

 

 

 

 

I want to review this thread  because it was a long time ago, and also because something seems strange about the sequence of posts.  I just took a quick look at it.   

 

Also google:

 

Constant contact side bearings

 

There are many sites offering explanations, and technical details. 

 

Here is a video:

 

https://www.youtube.com/watch?v=GsFO7b93CY8

 

 

Without reviewing this, as I recall, the constant contact side bearings do have contacting friction surfaces to provide friction that is intended to restrict truck hunting.  If they can completely prevent truck hunting, there would be no wear on the friction plate surfaces, because they would be prevented by siding on each other due to the friction.  But I assume they would often be sliding on each other.  So they would wear, but presumably within an acceptable rate of wear just like the brake shoe/wheel friction wear. 

 

But as I recall, there are also downsides to them such as causing derailments due to excess truck pivot friction on relatively light, empty cars.   

[BaltACD]

notkarl

Hello, I am trying to confirm if constant contact side bearers are constantly wearing against the car body wear plate whenever a rail car is going through a curved section off track. Physically I'm not clear on how this does not rapidly wear away either the cap of the side bearer, or the wear plate itself. Any clarity on the mechanics or materials that make this arrangement work are much appreciated. 

I have included links to photos of two variations I looked at recently near my house. 

karl

Welcome!

If you want to post pictures on this forum they must be hosted on another site and the link to the pictures on the other site used to put the pictures in play on this site.

[notkarl]

Hello, I am trying to confirm if constant contact side bearers are constantly wearing against the car body wear plate whenever a rail car is going through a curved section off track. Physically I'm not clear on how this does not rapidly wear away either the cap of the side bearer, or the wear plate itself. Any clarity on the mechanics or materials that make this arrangement work are much appreciated. 

I have included links to photos of two variations I looked at recently near my house. 

karl