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Exhaust Steam Spider

For most of the photos on this page, you can click the image for a larger picture.

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This page is the story of the making of the exhaust steam spider. You don't see this component mentioned in locomotive books. The spider is used in outside cylinder locomotives and performs the same function as the exhaust manifold in a car in that it provides a passage for the exhaust gases from the cylinders. Like a modern car (with turbocharger), the exhaust gases are used to improve the efficiency of the engine.

In the photographs you can see the 2 main frame plates (in grey) standing vertically. The red block between the frames is the fabricated smokebox saddle/frame stretcher and cast exhaust steam spider. The spider is cast first and then it is welded into the smokebox saddle/frame stretcher.

Normally the spider would be cast in the normal way, i.e. make a wooden male pattern, pack foundry sand around it to make a female mould and finally pour in molten metal to produce the component. See the cylinder page for a fuller explanation.

A wooden pattern had been built but this had suffered from years in storage so, in late 2015, a decision was taken to explore alternative methods of producing a new one. A new technology has emerged, that of sand printing. Sand printing is similar to 3D printing in that a specialised 'printer' prints layer of sand and resin and produces the female mould directly from the CAD model.This type of casting is cheaper for one-off parts, like the exhaust steam spider. For parts like the outside cylinder, where the pattern can be re-used, conventional wooden patterns are cheaper. We believe that this is the first time any large major component has been produced, using this method, in the history of British Steam Locomotive building.

Highslide JS This is the CAD model of the exhaust steam spider. The 2 exhaust ports from one of the outside cylinder are in front. The 4 exhaust pipes combine together for the top outlet which is directly under the blastpipe. The exhaust steam goes up through the blast pipe to the chimney. Importantly, it creates a vacuum in the smokebox which draws the fire down the fire tubes from the firebox. The harder the engine is worked, the more exhaust steam is produced and the stronger the draught on the fire. The pipe to the left provides exhaust steam for the exhaust steam injector.
The gases must flow cleanly through the spider. The holes through the frame are cut at the same angles as the spider gas ways so that no sharp edges are present which could cause turbulence.
Highslide JS Computers have made significant impacts into all areas of engineering and casting is no exception. Computer modelling was used to analyse how the metal would behave during the casting process.With the need to produce a good casting right first time; Maxima Engineering (UK and ROI agents for MAGMASOFT®) were contacted to assist with the development of a suitable casting method. The original foundry method was simulated using MAGMASOFT®. This simulation indicated a large area of isolated liquid steel during solidification shown on the left hand image. This resulted is a significant risk of porosity shown on the right hand image
Highslide JS Following a review of the design it was decided to add a small pad above the rib area effected, to allow a molten metal feeder to be placed and thus allow for direct feeding ( left). This pad allowed directional solidification to the feeder and significantly reduced the predicted porosity risk (right). The area of porosity has now moved to a metal feeder which will be removed during fettling.
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The mould was printed and delivered to Boro Foundry in Lye, West Midlands.

The starting point is a casting box packed with foundry sand to give a flat surface. You can see the part of the mould in its wrapping in the top right of the photo.

Highslide JS These 2 sections are the first 2 parts of the sand printed mould and are the bottom of the exhaust steam spider. The exhaust steam services take off can be seen on the left.
It can be seen that the mould has a very clean surface.
Highslide JS The surface of the casting box is treated with a sizing compound. The first section of the mould is lowered onto the casting box.
In the top right of the photo can be seen the central core of the pattern. This will be used to produce the steam passages in the final part.
Highslide JS The second section of the mould is now added. The bottom section is now complete
Highslide JS The central core of the mould is also sand printed. This will be used to ensure that the steam passages are formed in the manifold.
Highslide JS The central core is added to the mould. You can see how the ends of the core are positively located in recesses in the bottom moulds. You can see the gap between the central core and the bottom mould where the metal will flow to form the casting.
Highslide JS Here's a view from the other side
Highslide JS The next section of the mould is carefully lowered into place
Highslide JS You can see a number of half tubes which are in place to allow the hot gasses to escape
Highslide JS The final section is lowered in and the mould is complete. Now we need to prepare for the casting process.
Highslide JS More casting boxes are added and are securely locked in place. Foundry sand is packed in the gap between the casting box and the sand printed mould. Some serious lumps of metal go on the top to keep everything in its place. The square section in the front is where the molten metal is introduced
Highslide JS The pour is complete and now we have the long wait while everything cools down
Highslide JS Here's the manifold after it has been extracted from the mould and after some of the risers and runners have been removed. You can see the pads on each of the 4 exhaust ports that were added to improve quality
Highslide JS The rest of the runners are removed and then the component is passed for NDT (Non Destructive Testing) to prove that we have a satisfactory casting. A white coating is applied as part of the testing.
Highslide JS Now we move to CTL Seal in Sheffield where the exhaust steam manifold must be incorporated into the smoke box saddle and frame stretcher. Furthest away from the camera is the smokebox saddle. It is sitting on its side on one of the vertical plates that butt against the frames. You can make out the square holes for the exhaust steam manifold. The whole assembly is sitting on the other vertical plate.
Now all of this needs to be welded into one assembly.
You can see that there has been a considerable amount of machining on the flange faces
Highslide JS The exhaust steam spider is welded into the smokebox saddle. The square brackets on the inside face of the saddle are temporary lifting brackets. Once welding is complete, we have an assembly as you will see at the top of the page.