Abstract: A flame detector comprising a flame sensor, a storing section for storing a predetermined reference value, a comparing section for comparing a value of a signal from the flame sensor which changes in amplitude corresponding to a change in flickering of flames with said reference value and adapted to detect flames when the value of said signal exceeds the reference value, and a flame determining section which comprises a computing section for computing a ratio of an amplitude value of a minus change component to an amplitude value of a plus change component of changes in flickering of flames. The storing section stores a preset first threshold value and a preset second threshold value higher than said first threshold value, and the flame determining section signifies the presence of flames is when the ratio of the amplitude values of the signals is larger than the first threshold value and lower than the second threshold value.

Abstract: Apparatus for monitoring the fire extinguishing condition of automatic fire extinguishing equipment which is adapted to detect flames and spray a fire extinguisher liquid from a nozzle to extinguish a fire. The apparatus comprises a detector for generating a signal corresponding to the light energy radiated by the flames and a fire determination circuit for determining that the fire extinguisher liquid is hitting the flames when the detector signal has a DC component but has no AC component, since the AC component corresponds to flicker of the flame and ceases when the fire is sprayed with the fire extinguisher liquid.

Abstract: A process for preparing a mold by preparing a slurry of refractory powder in a binder solution comprising silica sol and monomethyl triethanol ammonium silicate or tetraethanol ammonium silicate at a mole ratio of SiO.sub.2 /M.sub.2 O of 10 to 22 and a mole ratio of SiO.sub.2 /NR of 9 to 28 wherein M represents Li or Na and NR represents monoethyl triethanol ammonium hydroxide or tetraethanol ammonium hydroxide, and repeating an overcoating of said slurry and a refractory powder by coating said slurry on a pattern, sanding said refractory powder on the coated pattern and drying it to form a green mold, separating said green mold from said pattern and calcining said green mold.