LARGE TESTING MACHINE.

Putaruru Press, Volume V, Issue 177, 24 March 1927, Page 3

LARGE TESTING MACHINE.

Whetti steel bridges are built, it is highly desirable that the metal used shoujJ tb tested to find out its te-ns'ile strength. The most dependable results aire obta'ned when full-sized taks are pulled apart, rather than small teat p’eects. Va:.liable mrorinaticn i s also -c-i: t-ained by i '-sting fullsized built-up teams for Transverse strength, and compression qpnsti'tuents for the loa.l they will tek.r without d'lstoriiton (slays r a wtr’ter in Oh amber's Journal), it may even be •thought necessary to test complete mod-els of large-s-c-ai'e s'ize. Until re--1 c.ently the biggest testing machine for these purposes has teen that at the Biirm University, wh'ic-h has a pull c-r a piJsh of SOO toms. A y 250 ton machine is. however, now available, having been -built ty the famous wteigning-machine makers of Birmangham, W. and T. Avery Ltd., fdr Dorman, Long and Co., Ltd., of Miiddleborough. The -latter firm is building -the huge bridge thc.t is to s-pan Sydney Harbour, and the new tje-sting tars a.n d other components for this stlru-ctuire. Measuring just over 120 fe-st in length and 13£. feet in height, this testing m-a Line is easily the' 'la«r:):st in existence. It w'U test to destruction a column or a compression component 50 feet iong and having crests section of 45 inches square. Round bc.rs 6 inches in diameter or flat bars 12 inches wide and 3 inch-sis*thick, can te stret;Ked until tlhey break. Lattice s up to 42 inches in width and of any depth may ■be (subjected to a transverse test over a span of 20 fef=t. ,In all cases the strains or the loads are measured to wHth'-n one-tenth of a ton. Tb:a measuring is done Iby a serie>s of links and levers with knife-edged joints which terminate in an enormous steelyard with a movable poise of 1 ton. Knife edge s (for a load up/ to 1250 tons oci >:id isoms -difficulty, since each inch of length will thake only 5 tons. Th:i S difficulty has been overcome by sharing the pull among four main levers, each with load and fulcrum kn'ife ed-g-es 62 inches long. . These levers reduce the load in the proportion of '6 to 1. Thei/r small 1 ends are linked up to a .Teill-cralnk levfer with a .ratio of 5 to 1, which transmits the load, now reduced to one-thirtieth of the original pull,, to the overhead •steelyard. . Thla poise is tlraversed along (Jhe steelyard by a screw which is turned by a hand wheie!l. A gradti- 1 ated sr.ale -shows the effect of the poise from zero to 1250 ton's in tejnths 1 of ia ton ‘the scale being read by ' means of a vernielr. No loose weights 1 are used, a great advantage, as they ! would involve delayts wlhi'le thiey were being placed in position by means of 1 lifting tackle. Th© load on the spe- 1 oilmen being tested is imposed by a ■ hydraulic ram 32 inches in diameter, 1 which has a water pressure of 2 tons -per squ'are inch behind it. An impctrta.nt feature of the machine is a long 'frame with massive square croslsheads at the ends which are connected together at the corners by forged steel <1 arfe. One 'crosshead, that used far -tensile tests, is connected with the four main levfers of the measuring system, and the frame with the levers is “floated.” on klni-fe edgeb, so as to allow the slight movement needed to tip tflilei steelyard without any friction Thte' hydraulic ram is attached by tein'sion balrs to intermediate Crossheadis, between which and the frame crossheads the teist loads are impos-ed. Tlhe macilne i s of very massive construction, and weighs about 350 tons. It is* installed ifi a special building with a 30 ton overhead arane for Qi»fltiiig the apecim>:tas to he f . &