Abstract: An apparatus is provided for grinding a semiconductor wafer, which includes a table having a work stage on which a semiconductor wafer to be ground is placed, at least the work stage being rotatable about an axis, and a grinding wheel which is movable in a direction perpendicular to or parallel to the work stage while being rotated about an axis parallel to the rotational axis of the work stage. In this apparatus, a semiconductor wafer is cooled during grinding. In order to perform cooling, the apparatus has an inlet flow path for guiding cooling liquid to a grinding surface of the grinding wheel, and an outlet flow path for collecting the cooling liquid which flows onto the work stage. The apparatus also includes a temperature detector, disposed in the outlet flow path, for detecting a temperature of the recovered cooling liquid. A rotational speed of the grinding wheel or the rotary table is controlled based on the temperature of the cooling liquid detected by the temperature detector.

Abstract: A crude polyacetal polymer obtained by polymerization or copolymerization and having as a principal component thereof connected oxymethylene radicals in a main chain is treated in a non-soluble liquid medium at temperatures higher than 80.degree. C. but lower than the melting point of the polymer and at heterogeneous equilibrium, moving the crude polymer and the non-soluble medium in opposite directions relative to each other.