シェルモールドにおける測定法の研究（第5報）

―崩壊性について―

抄録

  The collapsibility is determined by measuring the time to be required to cause collapse of a test piece under constantly applied compressive load at an elevated temperature.
  The aim of this study is to obtain fundamental data on the collapsibility of shell molds, and some considerations of measuring conditions, experiments on various factors, relationship between several mechanical properties and collapsibility, etc. are reported.
  Main conclusions obtained were as follows :
  1) The collapsibility may be measured under any proper condition of compressive load and elevated tempreature, but for Fe-alloys, a measuring temperature of 800°C or more is recommendable.
  2) Collapse is caused by thermal decomposition of the resin contained in shell molds, and at a constant temperature, the rate of the thermal decomposition is considered mainly due to the air permeability of the mold, which is influenced by sand percentage, void or distance between sand particles. All those are governed by the flowability of sand-resin mixture, too. Moreover the flowability is a function of grain shape and size of the sand and resin percentage. Therefore fundamental variables of the collapsibility seem to be the grain shape, size and the resin percentage.
  3) The collapsibility is not influenced by curing temperature and time which are generally used.
  4) The collapsibility is proportional to the resin percentage in the range of its practical use.
  5) The following equations are the the relationship between the collapsibility and several mechanical properties ;
          C=a_t log σ_t+b_t
          C=a_c log σ_c+b_c
      log C=a_f log σ_f+b_f
          C=a_s σ_s+b_s
where C is the time requied to collapse, σ_t tensile strength, σ_c compressive strength, σ_f bond strength, σ_s surface strength (depth of scratch), and a and b are constants.