Improvements in or relating to the production of stretch yarns

850,079. Spinning and crimping yarns; twist tubes. BRITISH NYLON SPINNERS Ltd. Feb. 6, 1958 [Feb. 14, 1957], No. 5034/57. Addition to 797,051 Classes 120(2) and 120(3). In a process for crimping and doubling yarn, two thermoplastic e.g. nylon yarns are drawn through heating means and through one each of two twist tubes of the kind described in the parent Specification so that the yarns are given opposite twists, and doubling the crimped yarns. The yarns 5, 7 are drawn from packages 1, 3 over magnetic hysteresis tensioning devices 9, 11 to a heater 17, which may be a multizone radiation heater as described in Specification 850,080. An elliptical infra-red heater as described in the parent Specification or a pressure steam heater. A vertical arm 19 with thread guides at either end moves laterally to insert the yarn through a threading slot which extends the length of the heater and acts as an insulating closure for the slot. The yarns then pass through rubber lived twist tubes 13, 15 rotated in opposite senses by an endless band 43 which is tensioned by a spring loaded pulley and driven by a roll 45 mounted coaxially with a draw roll 39. The yarns are wrapped twice round the roll 39 and its separator roll 51, pass over an oil roll 53, are twisted by ring and traveller means and wound on a cone-shaped bobbin 41. Drive may be transmitted between the draw roll and twist tubes by gearing, or by two endless bands, or the tubes may comprise the roter and stator of an electric motor or fluid-driven turbines. The bushes or lips of the twist tubes may be natural, polyester or polyurethene rubber. Specification 801,335 also is referred to.