The present invention relates to a method of producing a low-shrinkage synthetic flat yarn, as well as an apparatus for carrying out the method. 
High-strength flat yarns, which are used, for example, for producing PVC-coated tarps, conveyor belts, or V-belts, are required to exhibit only little shrinkage by the action of heat, when being further processed. 
Therefore, in the production of these flat yarns, one subjects the yarn after the melt spinning and drawing steps one more time to an increased temperature and reduced tension, so that the yarn is able to relax.  Such a method is described in EP 0 164 624 B1. 
It has been found that the parameters low yarn tension, temperature, and time are important for the shrinkage of the yarn during relaxation.  The apparatus disclosed in EP 0 164 624 B1 does simply not permit adjusting the parameters yarn tension, time, and temperature, as desired.  On the one hand, it is necessary to maintain a minimum yarn tension for a satisfactory yarn advance.  On the other hand, a long dwelling time would require at high yarn speeds a great distance to cover, which may easily lead in addition to an unstable yarn advance under a very low yarn tension.  A removal of the shrinkage in the yarn on the finished package may result in that after winding, such high forces are active in the yarn package that the package can no longer be removed from the mandrel. 
It is therefore an object of the invention to extend the known method and the known apparatus, so that long dwelling times are obtained during a relaxation, while keeping the yarn tension as low as possible.