GB885513A - Hot stretching of fibres - Google Patents

Abstract

<PICT:0885513/IV (a)/1> <PICT:0885513/IV (a)/2> The temperature of a continuous artificial thermoplastic fibre such as nylon is changed during the operations associated with hotstretching thereof by passing the fibre through a bed of a fluidized solid which is at a temperature different from that of the fibre entering the bed. The bed may be heated to a temperature at which the fibre softens and the fibre may be simultaneously stretched. The fibre may be annealed by passing it through the bed while in the stretched condition. The fibre may be cooled after hot stretching by passing it through a second bed which is cooled. The fibres may be in the form of yarns, threads, cords or fabrics. The fibre may be a string for tennis rackets comprising a continuous filament core yarn having at least one yarn wrapped thereon and adhesively bonded thereto. Both yarns may be of nylon. As shown in Fig. 1, nylon cord or fabric 18 is fed into the apparatus and travels in the direction shown by the arrows through the first pair of nip rolls 7, 8 over the guide roll 9 and over the idler roll 14 situated vertically above the fluidized bed 1 of small particles of sand or small glass spheres held in a container 2 provided with a porous tile 3 near the base thereof. Air to keep the bed in a fluidized condition is introduced into the chamber 5 below the tile through a duct 4. The container 2 is provided with a heating element 6. The cord or fabric then passes from the roll 14 down into and through the heated bed 1, round the idler roll 13, situated within the bed, up through the bed, over a second guide roll 12 and through a second pair of nip rolls 10, 11 driven at a higher peripheral speed than the nip rolls 7, 8. Idler rolls 13 and 14 are connected together by a framework 15 suspended from a bracket 16 which is arranged to slide vertically on a guide rod 17 so that the rolls can be raised to a position 13a, 14a, 15a and 16a for threading up of the cord 18 or if the feeding of the fibre ceases due to failure of the feed rolls. Overheating of the fibre is thus prevented. The raising of the idler rolls may be effected automatically if the machine stops. The apparatus may comprise a double heated fluid bed in the first portion of which the cord is hot stretched and in the second portion of which it is annealed. As shown in Fig. 3, the apparatus may comprise a double bed 32, 33 for hot stretching and cooling, the bed being divided into two by a heat insulating partition 34, the upper part of which is situated immediately above an idler roll 35 positioned in the fluid bed and arranged so that it can be raised by means of framework 36 until it is above the level of the bed. As the roll 35 is raised, the partition 34 is also raised and the lower portion of the partition 34 previously situated in a housing 37 rises through a seal 38 at the base of the beds to maintain the division between the two beds 32, 33. The cord or fabric is fed through the nip rolls 39, 40, down through the hot stretch bed 32, round the roll 35, and up through the cooling bed 33. It is then taken off by the nip rolls 41, 42, which run at a higher peripheral speed than the nip rolls 39, 40. The idler roll situated in the fluid bed may be perforated in order that it should not interfere with the fluidization of the portion of the bed situated above the roll. In order to avoid the risk that the bearings of the idler roll situated within the fluid bed might be damaged by particles of the bed, the roll bearings may be mounted in the external surfaces of two plates arranged to slide on opposite faces of the fluid bed container and each covering slots formed in the sides of the container of a width sufficient for the bearings to travel vertically therein a distance such that the idler roll can be raised from a position near the base of the bed to a position immediately above the bed. The plates are longer than the slots and, when the roll is raised, cover the slots and prevent particles of the bed from falling out of the container. Owing to the efficient heat transfer obtained with a fluidized bed, the period of residence of the cord or fabric in the heated bed may be greatly reduced compared with heating by means of a hot air oven, and danger of degradation of the fibre material is reduced even if the bed is maintained at a temperature only a little below the melting point of the fibre material.