Volume Eleven - Pre-Victorian to the Present Day - some more aspects - Large Testing Machines in South Wales, 1829-1906 . . .

It will take anchors 17 ft. in the stem, and 7 ft. 6 in. wide across the palms. It will impose the statutory breaking strain on stud links made of 4½ in. diameter iron, and in doing so has 40 tons of power to spare. This margin of power is, however, quite necessary to meet the excess strength with which chain cables are now made beyond the statutory minimum.

The scheme of the machine is set forth in Fig. 5, which shows a horizontal hydraulic cylinder in section with a ram having a 5 ft. stroke. This ram pushes out a sliding bed at the end of which a cast-steel anvil is carried, against which the palms of the anchor bear. The stem of the anchor is shackled on the anti-friction rollers and made with a cross-head C at the back which delivers the pull on to the lever system.

In testing links the one link is attached to fork A, the other end to the fork B, and as the hydraulic ram pushes out the sliding bed, it carries with it one end of the link while the other is held from the fork B on the weighbridge, which delivers the pull as before on to the steelyard. The steelyard carries not only a travelling poise weight but also a suspended rod, on the end of which standard weights can be dropped. By this means the scale unit is sufficiently large for testing ¼-in. diameter iron as accurately as large cables with 350 tons of load.

But to make the same machine available for testing heavy and light loads with an equal percentage of accuracy, it is necessary, besides having a larger scale unit, to so construct the machine that the knife-edged fulera may distribute the heavy load over such a length of bearing as to allow the fulera to be brought to a keen edge to give sensibility for light work and still not to crush in doing heavy work.

Fig. 5 shows the main fulcrum, which is 6 ft. long, and it will be seen how rigidly both the knife-edge and the bearing plate are supported throughout their length, so that they cannot spring apart in the middle and thus bring more pressure on one portion of the bearing than another.

The regulation of the Board of Trade, with which these fulcra comply, is that the pressure shall not exceed 5 tons per lineal inch of knife-edge. By using very hard steel it is found that the fulcra will stand endless repetitions of this pressure statically applied, but if they are allowed to chatter by reactions of the machine when the rupture of the specimen occurs, they are liable to serious damage.