TEST OF CONICAL AND CYLINDRICAL BREECH BLOCKS
Bethlehem Steel Company, January, 1900
HYDRAULIC TESTS OF CONICAL AND CYLINDRICAL BREECH PLUGS
First test Length Diameter Threaded Weight of threaded
rear front area portion in pounds
Conical Plug 1.5” 3” 2” 11.78 2.12
Cylindrical Plug 2.0” 3” 3” 9.4 4.
A load of 350,000 pounds corresponding to 112,500 pounds per square inch of powder pressure was applied without injury to either plug.
Second Test Length Diameter Threaded Weight of threaded
rear front area portion in pounds
Conical Plug 1.5 3” 2” 11.78 12.12
Cylindrical Plug 1.5 3” 3” 7.05 3.
The conical plug was again subjected to the load of 35,000 pounds without injury, while the cylindrical thread sheared under a load of 340,000 pounds corresponding to a pressure of 108,000 pounds per square inch in powder chamber.
ANALYSIS OF REPORT OF FEBRUARY, 1900
March 6, 1900
MR. R. W. DAVENPORT, General Superintendent.
Dear Sir:
I send you two copies of the report of the test of conical and cylindrical breech blocks, undertaken to determine the value of the new Bethlehem conical continuously threaded breech block, compared with the breech blocks of the existing types of interrupted cylindrical threads; the claims for the new breech block being, that it is stronger and will open and close with greater ease than a cylindrical block of the same weight.
Photograph: Housings and Blocks Before Testing.
Photograph: Housings and Blocks After Testing.
(Housing for cylindrical block cut through to show shearing of thread.)
The plugs tested were the standard plug for the 5-inch U. S. Army gun, a plug of more than ordinary strength and the conical plug of the Bethlehem 5-inch gun. These plugs were first tested as far as the strength of the gun would allow, then one half of the threaded area was removed from each plug, as shown on photograph and the test continued to destruction. In the table of this latter test there is first a column of actual pressure and then a column of estimated pressures, which would have strained the full original thread to the same extent. This latter column I have added to show the full strength of the respective plugs in comparison to that of the gun as expressed in pressure per square inch of powder chamber. The table will show some upsetting of the threads of both plugs early in the test. This I consider due to unavoidable imperfection in workmanship, such as roughness of surfaces, and an inaccurate fit. The elastic strength of the gun under hydraulic pressure is about 40,000, while that of the cylindrical plug seems to be about 60,000, and that of the conical plug is between 70,000 and 80,000. The superiority of the conical plug is due to its greater threaded area. The greater ultimate strength of the cylindrical plug (125,000 as against 110,000 for the conical plug) is not very important, as no gun (certainly not a light gun like the 5-inch army gun) could be subjected to a pressure of over 100,000 pounds per square inch without bursting and the cylindrical plug was made useless under a pressure, which the conical plug stood without having its quality of ease of opening and closing materially impaired. It should further be remembered that the threaded portion engaged on the conical plug weighs about 53 pounds while the corresponding part of the cylindrical plug weighs 74 pounds and that consequently weight for weight, the conical plug has 12 per cent greater ultimate strength and fully 70 per cent greater elastic strength than the cylindrical plug.
Yours truly,
J. F. MEIGS.