THE WORLD'S LARGEST TESTING MACHINE

Dominion, Volume 20, Issue 136, 5 March 1927, Page 24

THE WORLD'S LARGEST TESTING MACHINE

When steel bridges are built, it is highly desirable that the metal used should be tested to find out its tensile strength. The most dependable results are obtained when full-sized bars are pulled apart, rather than small test pieces. Valuable information is also obtained by testing full-sized built-up beams for transverse strength, and compression constituents for the load they will bear without distortion (says a writer in "Chamber’s Journal”). It may even be thought necessary to test complete models of large-scale size. Until recently the biggest testing machine lor these purposes has been that at the Birmingham University, which has a pull oi a push of 300 tons. A 1250-ton machine is. however, now available, having been built by tne famous weighing-machine makers of Birmingham, 'W. and T. Avery Ltd. for Dorman. Long and Co’. Ltd of Middlesborough. The latter firm is bunding the huge bridge that is to span Sydney Harbour, and the new testing machine is being employed in testing bars and other components for this structure. Measuring just ever I°o feet in length and 13} feet in height; this testing machine is easily the largest tn existence. It will test to destruction a column or a compression component 50 feet long ami having a cross section 45 inches square. Bound bars C inches in diameter or flat bars 12 inches wide and 3 inches thick, can be stretched until they break. Lattice girders up to 42 inches in width and of any depth may be subjected to a transverse test over a span of 20 feet. Tn all eases the strains or the loads are measured to within onetenth of a ton. The measuring is done by a series of links and lovers with knife-edge joints which terminate in on enormous steel-yard with a movable poise of 1 ton. Knife edges for a load up to 1250 tons offered som- difficulty, since each inch of length will fake only 5 tons. This difficulty has been overcome by sharing the null .among four main levers, each with load end fulcrum knife edges 02 inches long. Tho-e leverreduce the load in the proportion of 0 to 1. Their small ends are linked up to a bell-crank lever with a ratio of 5 tn 1. which transmits the load, now reduced to one-thirtieth of the original pull, to the overhead «<ccl'’.nrd. The poise is traversed along the steelyard by a screw which is turned bv a hand wheel. A graduated scale shows the effect of the poise from zero to 1250 tons in tenths of a ton. the scale being read by means of a vernier. No loose weights are used, a great advantage. as they would involve delays while they wore being placed in position by means of lifting tackle. The load on the specimen being tested is imposed by a hvdraulic ram 32 inches in diameter, which has a water pressure of 2 tons per square inch behind it. An important feature of the machine is a long frame with massive square crossheads at the ends, which are connected together at the corners by forged steel bars. One crosshead, that used for tensile tests, is connected with the four main levers of the measuring system, and the frame with the levers is "floated” on knife edges. =o as to. allow the slight movement needed io t'n the steelvard without any friction. The hydraulic ram *s attached bv tension bars to intermediate crossheads. between which and the frame crosshead* the testloads are imposed. T' ,n machine is of very missive con'l ruction. ?«•• weigh o about 350 fans. Tt is installed in a special building with a 30-ton overhead crane for lifting the specimens to be tested.

riso to the present Rugby Union-code, which has become almost universal at public schools. Eighty-,'i-side was not uncommon in a “Big Side” game, and the present fifteen-a-side game was once commonly played twenty-a-side. The idea of playing. Rugby at Harrow is not, of course, a new one. Inter-school matches have necessitated the playing of a limited amount of Rugby and Association for many years, Init the new and more sweeping proposal is hound to rouse the opposition of the very strong forces of tradition.