Abstract: A spindle motor comprising a bracket, a shaft member secured to the bracket, a rotor rotatively supported by the shaft member while interposing bearings a rotor magnet fastened to the rotor and a stator disposed to confront the rotor magnet, wherein the rotor has a hub portion, to which a recording disk is fastened, and a rotor portion, to which the rotor magnet is fastened, the hub portion and the rotor portion being made to be interchangeable. The hub portion has a plurality of female screw holes for fastening the retaining cap, the number of a plurality of the female screw holes being different from the number of ball members of the ball bearing by at least two.

Abstract: Undesirable deposition of polyoxymethylene onto the inner wall of a polymerization reactor and onto a stirrer, which deposition is observed in the slurry polymerization of formaldehyde carried out in an inert organic liquid medium, can be minimized by carrying out the slurry polymerization in the presence of a polymerization catalyst prepared by bringing a metal chelate compound into contact with polyoxymethylene in an inert organic liquid medium in the presence of formaldehyde. Preferably, the slurry polymerization is carried out in the presence of, in addition to the above-mentioned polymerization catalyst, at least one polyvalent metal salt of an alkylsalicylic acid or of a dialkyl ester of sulfosuccinic acid. It is also preferable to use a tubular closed loop reactor equipped with an impeller wherein gaseous formaldehyde is blown into the reactor in a position located downstream from the impeller, while the catalyst-containing slurry is circulated therethrough.

Abstract: Anhydrous magnesium chloride containing substantially no magnesium oxide is produced by a process comprising reacting magnesium chloride in the form of its hexahydrate with ammonia in the presence of ammonium chloride in an aqueous media; separating the resultant precipitated magnesium chloride hexammoniate crystals from an aqueous solution containing unreacted ammonia, magnesium chloride and ammonium chloride; washing the crystals with liquid ammonia; decomposing the washed crystals into anhydrous magnesium chloride and gaseous ammonia, and; isolating the anhydrous component from the composition mixture; which process is characterized in that a portion of the separated aqueous solution is evaporated until the concentration of ammonia in the resulting residual liquid becomes 2.

Abstract: Urea granules having a desired size are produced in a fluidized bed formed in a vertical cylindrical vessel which is partitioned into an upper compartment and a lower compartment by means of a funnel shaped partition having numerous holes through which the lower compartment is connected to the upper compartment, by: (A) feeding urea solid seed particles into the upper compartment; (B) atomizing and injecting upward a liquid containing a material to be incorporated onto the urea seed particles into the upper compartment through a nozzle having a top thereof located just above a center of the bottom of the funnel-shaped partition; (C)-(1) upwardly blowing a number of streams of an inert gas having a temperature of from 50.degree. to 98.degree. C. into the upper compartment through the holes of the funnel-shaped partition; (C)-(2) blowing upward a stream of an inert gas having a temperature of from 30.degree. to 120.degree. C.