Testing And Inspection Of Heat Treatment





The hard parts of the

gear must be so hard that a new mill file does not bite in the

least. Having passed this file test at several points, the gears go

to the center-punch test. The inspector is equipped with a wooden

trough secured to the top of the bench to support the gear, a number

of center punches (made of 3/4-in. hex-steel having points sharpened

to an angle of 120 deg.) and a hammer weighing about 4 oz. With

these simple tools, supplemented by his skill, the inspector can

feel the depth and quality of the case and the condition of the

core. The gears are each tested in this way at several points on

the teeth and elsewhere, the scrap gear being also subjected to

the test. Finally, the scrap gear is securely clamped in the

straightening press shown in Fig. 57. With a 3-1/2-lb. hammer and

a suitable hollow-ended drift manipulated by one of Sandow's

understudies, teeth are broken out of the scrap gear at various

points. These give a record confirming the center-punch tests,

which, if the angle of the center punch is kept at 120 deg. and

the weight of the hammer and blow are uniform, is very accurate.



After passing the center-punch test the ends of the teeth are peened

lightly with a hammer. If they are too hard, small particles fly

off. Such gears are drawn in oil at a temperature of from 300 to

350 deg.F., depending on their hardness. Some builders prefer to have

the extreme outer ends of the teeth drawn somewhat lower than the

rest. This drawing is done on gas-heated red-hot plates, as shown

at A in Fig. 58.






Nickel steel, in addition to all the tests given to carbon steel,

is subjected to a Brinell test. For each steel, the temperature

and the period of treatment are specific. For some unknown reason,

apparently like material with like treatment will, in isolated

cases, not produce like results. It then remains for the treatment

to be repeated or modified, but the results obtained during inspection

form a valuable aid to the metallurgist in determining further

treatment.





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