The objective of the staybolt of conodial shaft profile is to distribute bending stress along the entire length of the shaft rather than concentrate it near the sheets. In a sense, the staybolt is actually more rigid at any specific point for a given bending stress, because all cross-sections of the shaft are more engaged in elastically bending to the load rather than one cross-section plastically bending. Plastic deformation causes damage to the material, and propagates corrosion. Dr. Greenslade of Flannery translated Tross's work better than I did and there was a Master Boilermaker's task group looking at the staybolt design data - but it was too late in the game to be seriously considered. Rather than answer more questions with second-hand information, I will work on getting the MM material posted.

I really like the U-shaped mudring that eliminates a joint that usually grooves. It looks so much easier to clean, too. I also like American-type foundation rings. I don't see why one can't have both.

There is a lot to learn from everybody. That is why Mr. Chapelon surveyed the steam locomotives of the World at least twice. Perhaps someday all of this data will be put to a constructive use.

Hi Mr. Jansen

Mr. Anderson Of “the Burg” posted info on a D&H locomotive with both a US type mud ring with a trough so there was at least an attempt to do both out there.

Robby Peartree

A little more elaboration from what I have learned so far:

The reason German wartime boilers are built very lightly is because they needed horsepower to pull trains and could not afford the weight from a materials standpoint and restrictions placed by infrastructure. The larger locomotives are very lightly built, with the extreme example being the Class 52 - which do not even have much wheel counterbalance. A lot of the Class 52's were re-boilered as material supply and infrastructure improved. 52 8055 is a good example.

The 141R's had the same weight problem. Chapelon wanted robust American locomotives with French thermodynamics, but the environment at the time precluded both being fully realized. From my experience, the 141R boiler seems to hold together pretty well.

The German boilers with Tross's bracing seem to work at high outputs. I think when tonnage was decreased post-wartime they were less necessary as John Rimmasch pointed out. But, if one takes a boiler with a lightly built mudring up to a high specific evaporation rate, one is going to encounter problems.

I am a firm believer that everyone does the best they can in the situation they are given. I have been to Meiningen and they are good people and I know they are working with the best intents. I think a lot of the elements of design and construction are superior.

Meiningen is an "East German" shop and installs straight shaft staybolts as per Russian practice. West German boilers used Tross bolts, bracing, etc. With reunification, all steam work and tooling was relocated to Meiningen, who was building new locomotives well into the '80's. It seemed a good idea, but now there seems to be problems with "German" boilers.

I hear good reports about ŽOS České Velenice's boiler work.

I'm glad to see people reading this material. Hopefully, good things will happen.

OK, having mulled this over for a while and thinking as a practical wrench......

Two cases:

I'm replacing the firebox in an old style US built boiler and can spec any style of stay I want. this boiler has a history of the common staybolt trouble, breaking of the rigid stays at the wrapper sheet or real close to it. Would substituting a Tross design where the bending stress is distributed rather than concentrated help solve the problem without compounding other problems? Any reason for concern about the Tross bolts being "more flexible" or maybe leading to greater corrugation of the side sheets as referenced in another thread?

I'm building a new boiler to fit onto an old frame and running gear. Since the carrying hardware was built for a US style heavy mud ring I'm going to stick with that foundation rather than try to make it adapt to a flexible mud ring German design. How can I design the best most resilient and robust boiler for tourist line or intermittent museum service - using very traditional methods, modern methods, European or Asian methods, or a hybrid?

Loaded questions without a specific instance to use for calculation, I know, just trying to get a better sense of differing design ideas comparative strengths and weaknesses. We can use an Army 0-6-0T boiler as an example if you like, there's a lot of documentary stuff out there about them and the boilers are of a good size for museum and light tourist duty.

dave

More Tross Info Posted:

http://vaporlocomotive.com/site/wp-content/uploads/VLC_Data/Manuals_and_Archives/Steam_Locomotives/MBMA_Tross_Staybolts.pdf

Dave,

I believe a better way to think of the Tross-Henschel BTH-28 rigid staybolt is that it has re-enforced heads. In general, the re-enforcing allows the component to withstand greater stress before becoming damaged and/or breaking, as the profile encourages the bending stress to be distributed across the shaft rather than concentrated near the sheets. So, as a component, the BTH-28 is not less resistant to bending stress, but can handle more bending stress without becoming damaged than a plain shaft staybolt of a diameter equivalent to the BTH's minimum cross-section.

As per your question, what I and others have concluded is that the BTH-28 profile has to be compromised to fit American design practices. I think it is still a great advantage, and superior over early American designs where the transition was much more crude (however, these made a positive difference, too.) I think to find the expertise you need for design and manufacture for your application, you only need to look at the individuals and firms posting in this thread and similar previous ones as a number of them have done this work and manufactured double conodial staybolts and other custom designs.

Sincerely,

Matt

You are right, Matt, I should have said "differently flexible" rather than "more flexible". My problem is, I can mentally envision both scenarios of how having stays that don't pull as hard at the interface of the stay and sheet either "kink" the sheet less and make the waviness less pravelent, or allow the sheet to move more which could increase the waviness - and I can also envision the third scenario in which it doesn't matter. I'm not skilled as a theoretician or trained in mechanical engineering to do more than mentally envision it, however. That's why I'm asking - I don't have an application since I left the business a few years back, just want to understand it in specific conceptual terms. Sure, i can hire an expert if I have a boiler to rebuild, but I don't, and I'd learn nothing apart from what an expert costs if I did so, so I'm nowhere ahead in comprehension following that advice.

If you know this stuff please share it. if not, say so and maybe somebody who does will chime in, say the other Matt for example. You risk losing nothing since there's no work under bid behind my inquiry, but may gain future business if you show your ability in answering these kinds of questions completely.

dave

Dave,

Thanks for your comments. The design I have come up with is basically proportioning the staybolt cross-sections and transitions of the BTH 28 to achieve the desired tension stress (minimum shaft diameter) and maximum allowable head diameter for a given application. Mine is an Excel-based spreadsheet. I have compared notes with others who have developed different approaches with nearly identical results. As the exact proportions are application specific, there is no exact design, just the most BTH-28-like possible given what you have to work with. It is not rocket-science, and you can likely come up with the same results from reading Tross's papers and understanding your jurisdictional requirements.

Sincerely,

Matt

And thank you again Matt; I'm going to see if I can get somebody who is a mechanical engineer to translate this for the rest of us.

dave

Since Staybolts fail due to a number of causes the first step would be to determine why they are failing. After determining this then I think the biggest issues are how do you want your boiler to behave when subject to heat and stress? How do you want it to search for a lower stress level while subject to operating conditions? What life and what type of repairs do you want to do? It strikes me that Tross was trying to deal with issues that were caused by the switch from a copper box to a steel firebox with no change in design to compensate for the difference in material properties. For me how the boiler is built is an individual one for each organization and who builds the boiler and the respective governing organizations. That being said I think the life of the boiler will be determined more by the way it is treated than by how it is constructed. Proper maintenance, good water and a diligent crew will help a boiler live a long time.

Robby Peartree