Fig. 367.—Holzer Cabot partially wound barrel wound armature showing arrangement of coils. The core is built up of thin discs of soft annealed steel, which are slotted to allow the wire to sink below the surface, this being sometimes called iron clad construction. The discs are held by end plates, clamped without through bolts. The coils are machine formed of round ribbon or bar copper depending on the size and purpose of the machine, being without joint except at the commutator. They lie in insulated troughs, the upper layers being insulated from the lower layers by fibre.
Armature Windings.—The subject of windings has been fully treated from the theoretical point of view in chapter XVIII. It remains then to explain the different methods employed in the shop and the mechanical devices used to construct the scheme of winding adopted.
Ques. What is the construction of the inductors?
Ans. They are made of copper; the ordinary form consists of simple copper wire, insulated with a double or triple covering of cotton, and in some cases copper bars are used for large current machines.
Ques. What is the objection to copper bars?
Ans. They are liable to have eddy currents set up in them as illustrated in [fig. 291].
Fig. 368.—Holzer Cabot iron clad band wound armature complete; view showing openings for ventilation. The advantage of the form of winding adopted, is the ease with which a coil may be replaced in case of injury and the additional cooling surface. The coils are held in place by maple wedges secured by binding wires which are soldered throughout their length.
Ques. What may be said with respect to the sizes of wire used for inductors?