(b) If a wheel of like size were broken only in the rim, midway between spokes, explain procedure in welding without preheating.
(c) Same sized wheel, broken only in hub;—can weld be made without preheating? Give reasons for so thinking.
(d) Were breaks (a), (b) and (c) all present in same wheel, with rim fracture on opposite side of adjoining spoke from break in hub, should welding be started at rim or hub? Why?
12. (a) In the building up of broken or missing teeth in cast-iron gears, what procedure is necessary when no carbon blocks are available for forms?
(b) If certain carbon centers from dry cell batteries are obtainable how should they be treated before allowing molten metal to come in direct contact with them?
(c) What very important point must be uppermost in mind when dental work on gears is being done?
(d) Explain precautions taken in allowing work of this nature to cool.
13. (a) Realizing that hard spots occur in most welds executed by the new welder and having learned the cause of their presence and how to overcome them, would it not be possible to utilize this process for hardening parts which were subject to much wear and little strain? Explain procedure.
(b) Why is it necessary to preheat such pieces as the following before the weld is attempted; broken water-jackets on gas-engine cylinders, usually brought about by freezing, and holes or cracks in crank cases, caused by the loosening of a connection rod; when lugs on the same cylinder, the arms on the same crank case can be welded without preheating, and ofttimes without even dismantling the motor?