Abstract: A burner for producing glass fine particles provided with an intermediate passage between a central passage and an outer passage for surrounding the periphery of the central passage characterized by that the end of the intermediate passage is disposed inner side from the end of the outer passage and the end of the central passage is disposed between the end of the intermediate passage and the end of the outer passage. Thus, the burner can stably fabricate porous glass base material having GI type or triangular refractive index distribution and yet can suppress the production of bubbles.

Abstract: A method of fabricating a porous glass rod having a reaction vessel including an elevational passage from an exhaust port of the vessel side and the top of the vessel over the interior and a burner mounted at the end in the vessel for forming glass fine particles, and a target elevationally movable and rotatably inserted from the passage into the vessel which has injecting to accumulate glass fine particles produced through the burner to form the porous glass rod at the lower end of the target rotated at a predetermined position in the reactor, and drawing the target in response to the growing velocity of the porous glass rod, wherein downward gas stream is produced along the outer periphery of the conduit in the vessel. The method is conducted by an apparatus for fabricating the glass rod. The method and apparatus can stabilize the fluidity in a reaction vessel to stabilize the outer diameter and the refractive index distribution of the glass rod in the longitudinal direction.

Abstract: An infinitesimal gas flow regulator has a valve seat member having a valve seat provided at a gas inlet thereof, and a valve body including a hemispheric portion seated on the valve seat so that said valve body is rollingly movable about the center of the hemispheric portion while the valve body is kept on said valve seat. The valve body has an orifice in the form of a notch provided in the hemispheric portion of said valve body. An adjusting screw is provided to adjust the position of the valve body about the center of the hemispheric portion whereby a predetermined degree of opening is provided to the orifice in the valve body.

Abstract: This invention generally pertains to a process for producing a foamed thermoplastic resin article by utilizing the phenomenon that a solid thermoplastic resin sorbs a gas under pressure, and more particularly to a process for producing a foamed thermoplastic resin article comprising the steps of making a solid thermoplastic resin containing a nucleating agent quickly sorb a gas under a high pressure P.sub.1, lowering said gas pressure to a low pressure P.sub.2 (P.sub.1 > P.sub.2 > the atmospheric pressure) when the gas sorption quantity reaches a predetermined value so as to equilibrate or stabilize said predetermined gas sorption quantity, feeding said gas sorbed thermoplastic resin into an extruder while said gas pressure is maintained at said low pressure P.sub.2 and extruding the resultant resin to thereby produce a foamed thermoplastic resin article. In this invention, the gas sorbed by the thermoplastic resin contributes to foam in the thermoplastic resin.

Abstract: An apparatus for producing a foamed thermoplastic resin comprising an extruder including a barrel through which a thermoplastic resin is fed while being melted and a head to extrude said molten resin from said barrel, and gas injector means to inject a gas into said molten resin in said barrel through a gas injecting port in said barrel whereby said foamed thermoplastic resin article is formed by extruding said gas containing molten resin, said gas injector means characterized by comprising a gas metering means or gas flow rate setting means disposed adjacent and connected to said gas injecting port to conduct said gas therethrough while a constant flow rate is maintained, and a volume of a gas passage from said gas flow rate setting means to said gas injecting port in said barrel being sufficiently set for the gas pressure in said gas passage to respond to variation in the pressure of said molten resin in said barrel.