The invention relates to a device, in particular for the treatment of low-viscosity polymer melts, containing a vessel (1) with a stirrer element, the stirrer element (6) essentially comprising a support structure which passes through the vessel and on which surface formers (8) are arranged. According to the invention, the support structure is designed as a cage-like rod frame (7). This results in the following advantages: 1. Owing to the now possible continuous wetting or wiping of the surfaces, encrustations and inhomogeneities are avoided. 2. Due to enhanced cascading with weir plates, the residence time spectrum can be controlled, which likewise improves the product quality. 3. The flexing of the stirrer element is reduced.

High strength polyester multifilament yarn of improved dimensional stability, which has the proper combination of an intrinsic viscosity of at least 0.90, relatively low work loss and a high degree of toughness, is incorporated as tire cord into a rubber tire for reinforcement to provide an important improvement in fatigue life and retained fatigue strength. The continuous melt-spin process comprises the steps of feeding prepolymer to a first finisher vessel to achieve at least 0.4 intrinsic viscosity transferring polymer to a second finisher vessel for a period sufficient to achieve an intrinsic viscosity of at least 0.95, and supplying this polymer to an extrusion spinnerette.

A continuous reactor for viscous materials that give off volatile matter during operation has two rows of agitation rotors mounted staggeredly and with a phase angle of 90.degree. to each other on a parallel pair of shafts. Each of the agitation rotors consists of a pair of annular brackets arranged symmetrically across the axis of one shaft in a figure eight pattern, and a pair of scraper plates attached edgewise to the free ends of the brackets, one for each, at right angles to the brackets and in parallel with the shaft. The shafts are spaced apart so that the rotors on each shaft can revolve with their free ends passing close by the other shaft as well as part of the surrounding wall of the casing.

In an essentially horizontal totally enclosed cylindrical wiped-wall polymer reactor having an essentially horizontal polymer flow, a pool of polymer in its lower portion, and driven wheels to create high surface area in the polymer to facilitate evaporation of volatiles from the polymer, the improvement comprising a freewheeling drag wheel driven by the driven wheels, with a wiping means mounted on the driven wheels and actuated by the drag wheel to wipe the entire internal circumference of the cylindrical reactor. The drag wheel generates a force to urge the wiping means outward against the internal circumference of the reactor. The force is generated by the drag of the pool of polymer on the drag wheel. This keeps the wall of the reactor wiped with a fresh film of polymer. The process and apparatus is particularly adaptable to driven wheels and drag wheels eccentrically mounted in the reactor.

An apparatus for continuously producing polyester comprises three single reactors, i.e. a single esterification reactor (first reactor), a single initial polymerization reactor (second reactor) and a single final polymerization reactor (third reactor or final polymerizer), where at least one of the first reactor and the second reactor is free from an external stirring power source, or the third reactor is a horizontal, one-shaft-type, low speed rotation type reactor. Necessary number of reactors for the esterification and polycondensation reactions can be a minimum and necessary stirring power consumption for the reaction can be a minimum, and thus polyester polymers of good quality can be efficiently produced at a minimum energy cost in a necessary minimum reactor structure.