Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
On The Testing And Strength Of Railway Materials, &C.
ON THE TESTING AND STRENGTH OF RAILWAY MATERIALS , & c .
BY BRO . R . M . BANCROFT , Mem . Civil and Mechanical Engineers' Society . . MODES OF TESTING RAILS . THE usual modes of testing rails are : First , dead central weight or static test ; Secondd test b Third combination of first ancl second
, ynamic or y impact ; , a - first by the central ancl aftenvards by the falling load ; Fourth , chemical or acid test ; and Fifth , by rolling weight . To those might be added one of torsion 01 twisting . It should bo borne in mind that tests ought to be such as can at all times be easily applied , and not to cause unnecessary inconvenience to the contractor in carrying out his contract . Climate has great influence upon rails , for hi tropical countries a comparatively hard rail might be employed , ancl a greater amount of duty might probably be obtained than from a softer rail . In practise , any sleeper may be badly packed or decayed so as to offer little resistance , therefore it follows that a rail to be safe should not break or
take a permanent set under the weight of an engine ; if every other sleeper Avere taken away this would ahvays give a bearing at Avhich to test rails for different lines or gauges . A good steel rail , as used on the English Railways , will deflect about 3-16 of an inch in a span of 6 ft . Avhen a locomotive engine is passing over it . Taking the tests seriatim , it seems to me that the test by a falling Aveight is more to detect brittleness than a test of deflection ; and being a destructive one , only 1 or 2 per cent , of the quantities are
tested , and the rest of the turn is supposed to be like them . For the test of brittleness , it has been suggested that a good method Avould be to chop rails from a given heighth on to a hard platform , Avhich would certainly detect any cold short ones . To detect brittle rails is certainly most important , yet it is difficult to imagine how the loads passing over rails come with the suddenness of a MOAV from a test monkey . Some engineers say the endeavour to ascertain Avhether a rail has sufficient toughness by submitting it to the
action of a falling weight is most deceptive ; the test goes as far beyond the mark , as that by a dead Aveight faUs short of it , because it requires an amount of toughness which is cpiite unnecessary and inconsistent AA'ith a proper degree of hardness . Dead central Aveight tests determine the strength of a rail as a girder , ancl are adopted by some engineers , who consider nothing so good as the simple application gradually increasing bending stress to the centre , the deflection ancl set being noted after each successive increment of stress . These tests being usually made upon bearings , varying from 2 ft . Sin . up to 5 ft . and 6 ft „ it is a Question whether the amount of deflection
sliOAvn by so short a length of rail without being damaged by a permanent set , is no ' too small to be accurately measured ; ancl the difference of the deflection ivhich would be exhibited by a short piece of very good iron ancl a similar piece of very bad iron would , at any-rate , be very small to afford any certain gauge of its qualities . It would seem that a double test of dead wei ght and afterwards by impact is a severe and , one would think , a satisfactory one ; and , unlike a chemical test , is simple , quick , and inexineers
pensive ; it severely tests the qualities of material ancl workmanship . Some eng adopt this method , and , though these tests are not designed to represent the wear the rail would have to undergo , yet they are , combined , the safest and simplest that AVC know of at present to apply . The acid test is made by cutting off a slice from the end of a rail , and , after polishing , immersing it hi dilute acid , which eats away all ha * purities , leaving a lot of cavities and furroAvs , thus showing up the fibre or gram of tho metal very plainly . With most metals , chemical analysis is in itself a comp lete and sufficient test of quality , but not in steel . The toughness of steel may be altered hy sudden coolness ; aud , although the effect of this operation , and generally the effects of
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
On The Testing And Strength Of Railway Materials, &C.
ON THE TESTING AND STRENGTH OF RAILWAY MATERIALS , & c .
BY BRO . R . M . BANCROFT , Mem . Civil and Mechanical Engineers' Society . . MODES OF TESTING RAILS . THE usual modes of testing rails are : First , dead central weight or static test ; Secondd test b Third combination of first ancl second
, ynamic or y impact ; , a - first by the central ancl aftenvards by the falling load ; Fourth , chemical or acid test ; and Fifth , by rolling weight . To those might be added one of torsion 01 twisting . It should bo borne in mind that tests ought to be such as can at all times be easily applied , and not to cause unnecessary inconvenience to the contractor in carrying out his contract . Climate has great influence upon rails , for hi tropical countries a comparatively hard rail might be employed , ancl a greater amount of duty might probably be obtained than from a softer rail . In practise , any sleeper may be badly packed or decayed so as to offer little resistance , therefore it follows that a rail to be safe should not break or
take a permanent set under the weight of an engine ; if every other sleeper Avere taken away this would ahvays give a bearing at Avhich to test rails for different lines or gauges . A good steel rail , as used on the English Railways , will deflect about 3-16 of an inch in a span of 6 ft . Avhen a locomotive engine is passing over it . Taking the tests seriatim , it seems to me that the test by a falling Aveight is more to detect brittleness than a test of deflection ; and being a destructive one , only 1 or 2 per cent , of the quantities are
tested , and the rest of the turn is supposed to be like them . For the test of brittleness , it has been suggested that a good method Avould be to chop rails from a given heighth on to a hard platform , Avhich would certainly detect any cold short ones . To detect brittle rails is certainly most important , yet it is difficult to imagine how the loads passing over rails come with the suddenness of a MOAV from a test monkey . Some engineers say the endeavour to ascertain Avhether a rail has sufficient toughness by submitting it to the
action of a falling weight is most deceptive ; the test goes as far beyond the mark , as that by a dead Aveight faUs short of it , because it requires an amount of toughness which is cpiite unnecessary and inconsistent AA'ith a proper degree of hardness . Dead central Aveight tests determine the strength of a rail as a girder , ancl are adopted by some engineers , who consider nothing so good as the simple application gradually increasing bending stress to the centre , the deflection ancl set being noted after each successive increment of stress . These tests being usually made upon bearings , varying from 2 ft . Sin . up to 5 ft . and 6 ft „ it is a Question whether the amount of deflection
sliOAvn by so short a length of rail without being damaged by a permanent set , is no ' too small to be accurately measured ; ancl the difference of the deflection ivhich would be exhibited by a short piece of very good iron ancl a similar piece of very bad iron would , at any-rate , be very small to afford any certain gauge of its qualities . It would seem that a double test of dead wei ght and afterwards by impact is a severe and , one would think , a satisfactory one ; and , unlike a chemical test , is simple , quick , and inexineers
pensive ; it severely tests the qualities of material ancl workmanship . Some eng adopt this method , and , though these tests are not designed to represent the wear the rail would have to undergo , yet they are , combined , the safest and simplest that AVC know of at present to apply . The acid test is made by cutting off a slice from the end of a rail , and , after polishing , immersing it hi dilute acid , which eats away all ha * purities , leaving a lot of cavities and furroAvs , thus showing up the fibre or gram of tho metal very plainly . With most metals , chemical analysis is in itself a comp lete and sufficient test of quality , but not in steel . The toughness of steel may be altered hy sudden coolness ; aud , although the effect of this operation , and generally the effects of