RECOIL MECHANISM---15-POUNDER GUN NO. 12.
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dinal movements were observed on gauged lengths O and P, representing the movements at points on the slide directly over each trunnion. Up to this time the loads had not been above 40,000 pounds.
Now they were increased to a maximum of 60,000 pounds, and observations continued, returning over the same gauged lengths as before used, the gun remaining in firing position as before. When gauged length O was reached, observations were made on descending loads, in addition to the measurements taken under increments of ascending-stresses, and frequently thereafter readings were taken under both directions of loading. It was shown that the movements of the several places on the recoil mechanism did not follow the same paths under ascending and descending stresses. Taking for example the gauge readings on length O, it will be seen that under ascending stresses, for equal increments of load, there were fairly proportional movements of the slide, but when the loads were diminished there was a marked lag in the recovery of the slide. Increasing the load from 50,000 to 60,000 pounds, there was an increase in the total movement of "0.0141, but upon return to 50,000 pounds the recovery of the slide was only "0.0003, this lag in recovery continuing throughout the time of unloading. This behavior is attributed to frictional resistance between the moving parts of the mechanism.
Movements over the ends of the piston rod, gauged, length B, showed the same peculiar behavior as above described, pertaining to the oscillating slide. Measurements on the several gauged lengths, taken when the gun was in recoil position, showed the total and relative movements of the parts are modified according to the position of the gun. This lag in recovery is apparently not materially changed by the duration of time. Observations on gauged length D, under descending loads, in which the reduced loads are left acting for intervals of five to ten minutes, showed the recovery in total movement remained practically unchanged after the first readings were taken, until the total load had been reduced to about 22,000 pounds, when evidence appeared of increased recovery after the lapse of a short interval of time.
The test of the gun and recoil mechanism was followed by a free test of the piston, loaded over the same part of its length as when tested in the cylinder. In this free test it was found that the piston rod elongated the same amount, "0.0172, namely, under 42,800 pounds tension that it did in cylinder with the gun in recoil position, under a load of 60,000 pounds on the assembled mechanism. Deducting the initial load of 1,000 pounds in each case, and it appears that 41,800 pounds tension on the free piston rod caused the same elongation of the metal as a load of 59,000 pounds tension on the recoil mechanism, a difference of 17,200 pounds to be accounted for by the frictional resistance of the mechanism. It will be further observed that in the free test of the piston the elongation of the metal was the same under ascending and descending loads, no lag in resilience being displayed in this test.
The gun was returned to the testing machine for supplementary observations, which consisted of determining the resistance of moving the gun in the slides from firing to recoil position, and returning to firing position, the spring now being in place in the recoil cylinder. Finally, the trunnion movements were determined, measuring from fixed blocks clamped to the gun to points on the trunnions. On the