Page 247 - The Jet Engine

Manufacture

Fig. 22-10 Examples of T.I.G. and E.B. welds.

design flexibility in that distortion and shrinkage are another (fig. 22-11). Faraday's law of electrolysis
reduced and dissimilar materials, to serve quite explains that the amount of chemical reaction
different functions, can be homogeneously joined produced by a current is proportional to the quantity
together. For example, the H.P. turbine stub shafts of electricity passed.
requiring a stable bearing steel welded to a material
which can expand with the mating turbine disc. 32. In chemical forming, (fig. 22-11), the tool
Automation has been enhanced by the application of electrode (the cathode) and the workpiece (the
computer numerical control (C.N.C.) to the work anode) are connected into a direct current circuit.
handling and manipulation. Seam tracking to ensure Electrolytic solution passes, under pressure, through
that the joint is accurately followed and close loop the tool electrode and metal is removed from the
under bead control to guarantee the full depth of work gap by electrolytic action. A hydraulic ram
material thickness is welded. Focus of the beam is advances the tool electrodes into the workpiece to
controlled by digital voltmeters. See fig. 22-10 for form the desired passage.
weld examples.
33. Electrolytic grinding employs a conductive
ELECTRO-CHEMICAL MACHINING (E.C.M.) wheel impregnated with abrasive particles. The
30. This type of machining employs both electrical wheel is rotated close to the surface of the
and chemical effects in the removal of metal. workpiece, in such a way that the actual metal
Chemical forming, electro-chemical drilling and elec- removal is achieved by electro-chemical means. The
trolytic grinding are techniques of electro-chemical by-products, which would inhibit the process, are
machining employed in the production of gas turbine removed by the sharp particles embodied in the
engine components. wheel.

31. The principle of the process is that when a 34. Stem drilling and capillary drilling techniques
current flows between the electrodes immersed in a are used principally in the drilling of small holes,
solution of salts, chemical reactions occur in which usually cooling holes, such as required when
metallic ions are transported from one electrode to producing turbine blades.

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