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Arch Bar Trucks -- Arch Bar Replacement Question
https://rypn.org/forums/viewtopic.php?f=1&t=26923		 Page 1 of 1
Author:  california [ Mon Jan 12, 2009 3:31 am ]
Post subject:  Arch Bar Trucks -- Arch Bar Replacement Question
The Ventura County #2 Prairie type steam engine at OERM is currently in service and running well, but the tender truck frames are sagging badly. When the locomotive was received from the VCRy the tender trucks were undersized for the tender and had stiffener plates welded onto the sides of the arch bars in order to stiffen the trucks to carry the load.

Image

After the locomotive was received by the museum, the tender trucks were replaced with a set of arch bar trucks from a side dump gon.

Image

The trucks were designed for a max load of 25+ tons. The current tender puts a max load of about 20 tons on a truck, yet still they sag. The best conclusion is that the arch bars themselves are simply fatigued and worn out and need to be replaced. Note in the picture of the tender below, the top arch bar on the rear truck is almost flat.

Attachment:
tender.JPG
tender.JPG [ 128.24 KiB | Viewed 7478 times ]


The questions for the knowledgeable members of this forum are
(1) Is the conclusion presented above reasonable?
(2) What material would be best suited for this application?
(3) Do the bends need to be cold formed or can they be heated and bent?

Thanks in advance for the information
Author:  Kelly Anderson [ Mon Jan 12, 2009 3:09 pm ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
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Author:  Dave [ Mon Jan 12, 2009 3:19 pm ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
Can't help but notice the trucks in the side dump picture have a pack of coil springs, while the same trucks under the tender have a highly compressed set of leaf springs. It may be worthwhile to compare the combined spring rate for the coil pack to that of the leaf spring replacing it - if the coil pack has more total compression resistance, swap them out and see what happens. In either case, I'd certainly recommend the inspection procedure Kelly recommends.

dave
Author:  SZuiderveen [ Mon Jan 12, 2009 5:58 pm ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
Dave wrote:
Can't help but notice the trucks in the side dump picture have a pack of coil springs, while the same trucks under the tender have a highly compressed set of leaf springs. It may be worthwhile to compare the combined spring rate for the coil pack to that of the leaf spring replacing it - if the coil pack has more total compression resistance, swap them out and see what happens. In either case, I'd certainly recommend the inspection procedure Kelly recommends.

dave


Are the origninal leaf springs installed in the dump car trucks? While the space between the bolster and trck frame may be ok, is the tender loaded or light in the photo? The leaf springs look way too long for the truck,which makes me wonder if they were taken out of a six wheel passenger car (Pullman) truck. Note the shortness of the springs in the enclosed drawing of a tender truck from the '22 Cyc.

Steve

Attachments:
tender truck.jpg
tender truck.jpg [ 19.07 KiB | Viewed 6989 times ]
Author:  SouPac [ Tue Jan 13, 2009 12:22 pm ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
Hey Jeff,

Hope all is well down in So Cal. As for the trucks can you see any evidence (rust, dust, etc.) that would indicate the bars are moving? Try hammer testing all the bolts to see if anything is loose. Kelly's previous discourse I think is very much on the money here. There is one other thing I would ask which is it appears as if one truck under the side dump car had a much lower upper bar than the other. Could part of this problem actually be something that has nothing to do with fatigue and instead is a remnant of the manufacturing process. Best of luck.

Stathi Pappas

PS: Hope you like that waterglass.
Author:  Frisco1522 [ Tue Jan 13, 2009 12:45 pm ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
Is it an optical illusion or is there a great difference in wheel diameter between the front and rear truck on the tender? Looks significant.
Author:  california [ Wed Jan 14, 2009 1:15 am ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
Thank you all for your excellent comments. I will try to address them here and see if we can work towards a solution.

Yes, the springs are sagging badly. The springs are obviously not original. The coil springs were replaced with leaf springs at some time after the trucks were put into service under the tender. The tender is significantly lighter than the loaded weight of the side dump, and so I am told that the tender rode very hard with the coil spring installed, and so they were replaced. While the springs are flat, they are not bottoming out. Regardless of the spring constant, the loads on the truck are the same.

As for the loads on the axles, I do not believe them to be overloaded. If allowable per axle weight is 32k, then the allowable 4 axle weight would be 128k, or 64 tons. The tender weight is no where near 64 tons.

There is no visible cracking around the bolt holes that is visible to external inspection, but the trucks have not been disassembled and penetrant tested.

I don't think the image of the tender trucks tells the whole story. As that picture was taken over 2 years ago, I can't be sure if the tender was light or loaded at the time, but looking at the bars, it looks like its at least partially loaded. The tender carries 4000 gallons total fuel and water for and approximately liquid weight of about 32k lbs. When fully loaded the rear arch bar is almost flat, not arched as in the attached image. I don't think I quite understand how that can be caused by loose bolts in ovalled holes. Is the idea that the ovalled holes allow the axle centers to move farther apart with respect to one another, thus allowing the top arch bar to flatten out?

One last thing, don't take too much stock in comparing the trucks under the tender to the trucks under the side dump. The trucks under the tender were from a sister car to that side dump, and so are not shown in that picture, rather an identically designed pair is.

Once again thanks for the comments and Stathi, the water glass looks great.
Author:  Kelly Anderson [ Wed Jan 14, 2009 10:24 am ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
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Author:  Dennis Storzek [ Wed Jan 14, 2009 11:46 am ]
Post subject:  Re: Arch Bar Trucks -- Arch Bar Replacement Question
Or, another way of looking at it is the side frame is a truss (which it is) and relies on the triangles maintaining their geometry to support the load. If loose fitting bolts allow the bars to slide past each other, then the geometry of the truss changes, and so does the angle of the bars. The journal bolts need to come out… actually all the bolts need to come out and the bars need to be re-bent to their proper geometry. If no cracks, I should think that welding the ID of the holes and boring them to size on location would be a viable fix. Likewise, if the bolts have worn so they look like crankshafts, they will need replacement also.
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