Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/76

72 MODEL STEAM TURBINES. With regard to shrouding, it is an open question as to whether this is necessary in a model turbine. Mr Naylor's wheel is not so provided, and a small turbine that the writer has experimented with was also unshrouded. The function of the shrouding is to prevent the steam being thrown out of the wheel radially by centrifugal action, but in addition it prevents the steam jet expanding laterally during its passage through the wheel. A piece of tubing of an

Fig. 64. Diagram showing best form of Blade.

internal diameter equal to that of the wheel may be used as in fig. 26, but if shrouding is decided on, it is better to use very thin sheet brass. The ring may be made by taking a circular disc of brass and turning a piece of hard wood the diameter of the wheel and of thickness equal to the width of the shrouding. The brass disc should be larger than the wood, and being placed on this with the centres coinciding, the projecting metal edge should be gently and carefully hammered down or spun so as to present the appearance of a canister lid or boiler end. From the centre of the disc a circle should be