Abstract of RIIS Report ( SH-1959-1 )

National Institute of Occupational Safety and Health, Japan

About the Aging Strength of the Life Lines

SH-1959-1-1

T.ANDO and T.SATO

: To find visually the aging strength of life line, we examined about the many ropes used in some lime stone mines.
The tested ropes were almost manila ropes. Result showed that there are the deviation in strength by conditions. And yet we obtained the diagram of the relation between the strength and age.

Study on Closed Type Explosion Test Apparatus

SH-1959-1-2

N.TAGUCHI, M.NAITO and F.ISHIMI

: For the explosion test of the explosion-proof electrical equipments, we designed and constructed the closed type explosion test apparatus.
    This apparatus consists of a closed explosion vessel, a pressure vessel to mix gas with air under high pressure, a measuring device of explosion pressure, a vacume pump, an air compressor, an operation panel and etc..
    In comparison with the open type, this has many excellent qualities.
That is,
  (1) It can be got easily and exactly the certain concentration of gases and air mixtures to be required,
  (2) It can be tested about the flame transmission and the durability for explosion pressure on the explosion proof electrical equipments at the same time,
  (3) It can be operated efficiently,
  (4) It can be got the explosion pressure to be required,
  (5) It can be easily studied on the explosion characteristics of the inflammable gases.

The Limits of Flammability of Butane Gas --Influence of Pressure--

SH-1959-1-3

M.NAITO

: By the closed explosion test apparatus, I studied on the limits of flammability of Butane Gas of three kinds having different component under pressures of 1 to 5 atmospheres. The result showed that the explosion range of Butane Gas spreads with rise of pressure, that is, it was approximately 2 to 8 per cent in air at normal condition and at 5 atmosphere was 2 to 15 per cent, therefore, only the upper limit was influenced by pressure.
And it was seemed that the explosive range was more influenced by pressure, when the ratio of the lighter hydrocarbons in Butane Gas component was great.

Investigation on the Accident in Construction the Kaimon Bridge

SH-1959-1-4

T.HAKAMAZUKA and K.ISHIBASHI

: In construction of the Kaimon Bridge by cable erection method, the cable towers collapsing, three workmen died and two were injured in the morning Dec. 29th. last year.
    We considered that this accident was caused by breaking in the anchor plate (section 19 mm × 230 mm) which had supported a rope-stay and main carrier cable together.
    The stress in the breaking point at the working time was calculated +26.10 kg / mm² on under edge, -5.30 kg / mm² on upper edge. Besides, we examined the material of the anchor plate as following. Appearance of fractured surface is brittle and the separation started from under edge. The composition by chemical analysis shows 0.26 % C, tr. Si, 0.51 % Mn, 0.05 % S, 0.048 % P, 0.245 % Cu. The tensile strength σt is 45. 6 - 46.9 kg / mm², the yielding strength σy is 27.8 - 30.1 kg / mm², the elongation is 36 - 33.2 %. There are no crack and other faults in bending test. Hardness test calculate Hv 190 in none heat effect area, max. Hv 301 in heat effect area by arc welding. U-notched Charpy impact test calculate 2. 7 - 3.3 kgm / cm² (at 7 °C ), V-notched is 0.9 - 1.2 kgm / cm² (at 0 °C). Observation on micro and macroscopic shows that the material is rimmed steel consist lamination in it. But this material pass in JIS standard test.
    By the above mentioned test, we surmised that anchor plate fractures was mostly result of brittleness by welding. Therefore we should especially take care for the selection of anchor plate material, its construction error and its maintenance.