Over-thread tension device on the head of a sewing machine

摘要

The application relates to an over-tension device on sewing machines, having two tension discs which are axially displaceable counter to the pressure of a tension spring on a bar-shaped carrier and between which the over-thread is guided. To maintain the tension during the change of thread, the tension discs can be blocked alternately on the carrier against axial displacement. For this purpose, the carrier is designed as a sleeve 14 which possesses for each of the two tension discs 5, 6 a group of radial bores 5c, 6c in which blocking balls 5b, 6b are radially displaceable, which blocking balls, in a position pushed radially outwards, block the respective tension disc 5, 6 against axial displacement. For the radial displacement of the blocking balls 5b, 6b, two cones 5d, 6d directed axially towards one another are displaceable axially in the sleeve counter to spring force. <IMAGE>