Preparing for Backhead Stay Installation

During the last week of January Continental Fabricators began installation of the 1385’s backhead diagonal braces. The backhead is the end of the boiler located within the cab and is a large, flat plate or sheet of steel that has been flanged and then welded to the wrapper sheet.  Flanging is the process of very carefully curling the edges of a sheet to meet the next piece it will be mated to.  The flanging process has been covered in previous update posts.

Much of the boiler is round, a naturally strong shape.  With areas that are flat or nearly flat the forces of nature (including steam pressure) are constantly trying to force them round and thus they require support or “staying”. Staybolts, or “stays” and braces are thus used to reinforce the area and prevent the backhead as well as the other flat areas from bowing outward when the boiler is under pressure.

firebox diagram

While installing these braces, crews at Continental Fabricators flipped the wrapper sheet/backhead assembly upside-down to facilitate easier working conditions. The first photo below shows the assembly as of the last week of January 2019 as the braces are being fitted and tack welded in place.  The tack welds are just enough to hold the braces in place so this assembly can be righted and lowered onto the firebox/mud ring assembly to check for proper clearance between the braces and the firebox.  Once Continental is satisfied with the fit-up between the pieces the wrapper assembly will once again be pulled off the firebox, inverted and the braces will receive the final welds.

upside-down wrapper sheet and backhead

Much of the backhead will be supported via staybolts connected between it and the firebox door sheet. The pictured diagonal braces are used to support the part of the backhead that does not line up with the door sheet and is instead connected to the wrapper sheet for support. This picture was taken during the last week of Jan. 2019. Photo courtesy Continental Fabricators.

A few days later during this the first full week of February, Continental’s crews had flipped the backhead/wrapper sheet assembly right-side-up again and placed it over top the firebox/mud ring assembly. The purpose of doing this is to test fit for any contact between the backhead braces and the firebox crown sheet before final welding of the braces and before the wrapper sheet/backhead assembly is welded to the firebox/mud ring assembly.  Once the two assemblies become one the installation of the staybolts can begin.

Lots and Lots of Staybolts

A brief update to yesterday’s discussion on staybolts:

SPEC has received the stock to be used for C&NW No. 1385’s rigid staybolts and is cutting it to the length, engraving the heat number and drilling the tell-tale holes per Continental Fabricator’s specifications. There will be over 1000 new rigid staybolts created in all, cut to five different lengths as required by 1385’s boiler.

Staybolts Help 1385’s Boiler Keep in Shape

The Flannery Bolt Company is long gone but their products live on as their staybolt and staybolt accessories are reproduced today for projects like the Mid-Continent’s Chicago & North Western No. 1385.  In the steam era staybolt production and replacement were a regular occurrence and such parts were readily available in large quantities. Even in 2018 there are at least two shops readily producing them as a specialty item, but for the 1385 project Mid-Continent has opted to keep it local, producing them in-house at SPEC Machine where the bulk of the locomotive’s overhaul and assembly is taking place.

1385 project volunteer Pete Deets explains, “We decided to have Steve Roudebush [owner of SPEC Machine] make them as the best way to control the cost and delivery schedule.” He adds, “The bolts to go with the sleeves and caps are on the way… there are 72 flexible staybolts on the 1385 but there are also a few hundred rigid stays that will go into the boiler.”

diagram of boiler showing staybolts

The majority of the boiler is cylindrical, a naturally strong shape, but there are also some flat and irregular surfaces within the boiler too, especially around the firebox. With the intense pressures up to 250 psi inside 1385’s boiler, these surfaces would weaken, bow, and eventually fail without staybolts to support them.

The flexability afforded by a flexible staybolt is critical to maintaining the boiler’s strength while still allowing for the expansion and contraction that occurs as temperatures change from one extreme to another within the boiler.  Deets explains:

A flexible staybolt has a ball shape on one end and is threaded on the other.  The ball end fits into and will be held by the cup shape of the inside of the sleeve.  The sleeve will be welded on the outside or wrapper sheet of the boiler above the firebox. The bolt is then dropped into the sleeve and the threaded end is screwed into a threaded hole in the firebox.  The bolt is hammered or “upset” to cause it to swell into the threads and form a steam tight seal and a copper gasket is applied with the cap to seal the sleeve end.  The ball end of the bolt can actually swivel in the cup shape of the cap and it allows the firebox to move in relation to the wrapper sheet of the boiler as the engine goes down the road.  [Locomotive designers] found that allowing that slight bit of movement was better overall for the boiler than trying to hold every bit very stiff and rigid. If things were too rigid the boiler would break the staybolts anyway.  It was also noted there were fairly specific areas of a boiler that were prone to breaking stays so the Railroad Master Mechanics Committee came out with recommended patterns of placement for the flexi’s to alleviate or at least minimize the breakage.

The photos of the staybolt caps reveal a series of numbers stamped on each one. The number represents the part’s “heat number.”  That is a jargon from the steel industry as they refer to every batch of iron or steel (or any metal) that comes out of a furnace as a “heat.”

Deets elaborates on the importance of heat numbers:

That number is vital because every piece of metal that goes into the pressure retaining portion of the boiler must meet very specific requirements of physical strength, mechanical properties and chemical properties and we have to be able to prove the materials we use meet those specs.  Every batch of steel made is tested for chemistry and physical properties and is assigned a unique number.  The records of those batches made for specific applications such as boiler plate follow the steel through the finishing process of the mill and each piece is marked with the heat number and other information.  Those records are the certification that this particular batch or heat number meets this specific set of requirements and we must get a copy of and keep on file the material certifications or “certs” for short.  That heat number represents the “pedigree” of each of those parts.

The below YouTube video produced by Wasatch Railroad Contractors while working on a different locomotive restoration provides a good illustration and explanation of how flexible staybolts work.

Last but not least, SPEC Machine has also been busy finishing up more work on 1385’s brake equipment. Brand new brake heads were cast last summer (see post from Sept. 1, 2017) and are now being machined in preparation for installation.

break head machining

One of the newly cast brake heads is machined to specification. Each brake head supports one of 1385’s brake shoes.

Drilling Guide

Bob Ristow devised a drilling guide to ensure alignment of the replacement staybolts in the crownsheet patch. Here are a few pictures of Bob and Dave Lee drilling pilot holes for the staybolts.

May 14-15, 2005 Work Session Results

Doug Crary reports:

“Is it Denver Gardner or Gardner Denver? What ever! Doug Klitzke into Boo to get gas, Jason and Bob Jackson on R-1 to remove bell. Jason, Doug Klitzke and Bob Jackson finished the staybolts on the wrapper sheet. Dave B. and Ed Ripp started work on the firebox supports for the heat treating. Some parts by Petebone, other parts on track one south of the house. Diesel work was essentially completed. Future work ID’d and scheduled. 2 small bottles of acetylene MT. We had to use Ricks large bottle.”

Jason Sobczynski photos.