Engineering update – Cylinders & valves

Cylinders and valves – Having gone through a thorough selection process, the order for the fabricated cylinder block was placed with Howco at Irvine in Scotland. Howco is part of a large Japanese owned group specialising in oil exploration equipment but given the cyclical nature of the oil business has a stated plan to diversify. They have first class fabrication facilities and a large CNC machining capability along with in house weld procedure development, heat treatment furnaces and comprehensive non-destructive testing (NDT) resources. Whilst complex, our cylinder block fabrication is quite small by their standards.  After a review by Howco, some minor design changes have been made by combining some fabricated sub assembles into fewer parts to be CNC machined from thicker plate than originally proposed in our design.

Howco wasted no time in starting work on the monobloc, here one of the cylinders is machined – Howco Engineering

Perhaps the most difficult part of the fabrication is the cruciform exhaust ports which take exhaust steam from both ends of all three cylinders to the base of the blast pipe. In order to clear the inside cylinder and the inside steam chest, these have to be curving in two directions at once. This is achieved by making each port of rectangular section from pieces of 25mm thick steel plate which is pre-bent then profiled to the required shapes. The problem here is that if each plate is profiled to the finished shape and then bent using a brake press, because the width of each plate is varying and not symmetrical, the required shape will not be achieved. To overcome this the process is to start with a rectangular plate large enough to accommodate all the curves which, being formed on a constant width piece of metal, will come out as expected. However, once we have a an “S” shaped plate it is not possible to use a CNC flame or plasma profiling machine to produce the final shape – these machines need flat plate.

It is therefore necessary to mark out the finished shape on each plate and use hand operated oxy-acetylene burning equipment to produce an approximation to the finished shape, after which the final shape including weld preparations will be achieved by hand grinding, or where applicable by CNC machining.

The problem that then came to light is that the Standard version of Solidworks which we employ in the design work on the P2 is not able to produce these developed shapes automatically, and from previous experience with the guard irons mounted on the front of the frames and the bogie frame, the only way we could produce the necessary profile was by an old fashioned and time-consuming manual method. As we had at least 16 components requiring this treatment, an approach was made to Solid Solutions, the Solidworks UK distributor we use, who said that this could be achieved with the Premium version which is several thousand pounds extra.

As luck would have it, Martin Shepherd, whom we retained initially to turn the valve gear models into manufacturing drawings, has a Premium version of Solidworks which has the additional “Flatten” button. The resultant 2D developed surface is then transferred to a drawing at 1:1 scale which is plotted on paper, the shape accurately cut round with scissors and laid out on the bent plate to enable it to be marked out for flame cutting

To check that this was actually producing the shapes required, two of them have been 3D printed at one third scale (the largest that could be accommodated on the Director of P2 Engineering’s 3D printer) and the one-third scale cut-out developed shape offered up the models to check that they would produce the required shape – they do!

1/3 scale cylinder exhaust passage component with paper developed profile overlaid – A1SLT

1/3 scale cylinder exhaust passage component with paper developed profile – A1SLT

Martin Shepherd has produced almost all the 2D manufacturing drawings for the valve gear and has now turned his attention to lubrication including oil coolers for the cam boxes and pumped lubrication of the 12 valve spindles. Martin has made further progress with the one third size 3D printed cam box being produced by Warwick University Manufacturing Group (WMG). This is nearing completion following a visit to DLW by Martin who with assistance from Daniela and David Elliott has made the various pieces of plain shaft from steel which would have been difficult to make accurately by 3D printing but is easily sawn and turned from bright bar.

Further progress has been made in tying down the precise specifications and obtaining quotes for the various cardan shafts required for the drives from the return crank gear boxes to the cam boxes and the reverser drive from the cab to the cam boxes.