MAIN INJECTOR WITH INCREASED TENSIONING FORCE FOR AIRJET LOOMS

Abstract: Main injector with increased tensioning force, of the type where the actual injector consists of an injector tube whose diameter is mainly constant, with the characteristic that symmetrically-positioned air outlet openings (6) are arranged along the length of said main injector tube (2) at different sections of the nozzle.

Description: This invention concerns a main injector with increased tensioning force, for use on airjet weaving machines. Such a main injector is mounted in front of the shed, with the purpose of injecting the pick into the shed with as high a velocity as possible. More particularly, this invention concerns a main injector of the type that consists of a main injector tube, a hollow threading needle, a mixing zone and a compressed air supply. The aim of this invention is to achieve as great a weft thread force as possible. This is normally done by increasing the pressure and/or increasing the length of the tube and/or decreasing the tube diameter. However, all these methods have disadvantages caused by phenomena associated with the flow of air in the tube. Thus regions of turbulence are caused in the tube due to friction between the fluid medium and the tube wall and/or internal friction within the medium itself and/or friction between the medium and the thread. This turbulence, which mainly occurs in the region of the tube wall, has the effect of reducing the effective tube diameter, ie. the diameter of the region in which there is a well-defined airflow. Another phenomen associated with main injectors is that the airflow is forced to follow the same path as that of the thread, so that the tensioning force exerted on the thread is greater than would be the case if no tube was used. This favourable phenenon can be accentuated by increasing the length of the tube. Since however the amount of friction increases with the length of the tube, so also does the amount of turbulence, thus unfavourably affecting the tensioning force and cancelling out the advantage which might be obtained by having a longer tube. Another known phenomenen associated with main injectors is that transmission of force to the thread is greater with a smaller tube diameter than with a larger diameter. Since this favourable effect also disappears when the tube diameter becomes so small that friction with the tube occurs and/or the thread enters a region of turbulence, the minimum tube diameter is determined by the size of the turbulent regions and the thickness of the thickest weft thread to be inserted. It is therefore very important for the thread to be positioned as centrally as possible within the tube and for there to be as little turbulence as possible, in order to be able to increase the length of the tube and decrease the diameter without negative effects, in order to obtain greater tensioning force with the main injector. Finally, the length of the main injector tube on airjet machines is normally determined by the amount of space available within the construction. In the present invention, use is made of the above-mentioned phenomena by having a main injector tube which, within the space available, has a mainly constant diameter; is as long as possible; has as small an internal diameter as possible in relation to the yarn thickness used; and which has openings to let the turbulent escape while at the same time keeping the weft thread as centrally positioned as possible in order to limit friction between the thread and the tube. These openings are positioned so that the escaping air flows away symmetrically, with the same amount of air escaping from each opening, so that the escape of air does not affect the central position of the thread within the injector tube. The various aspects should preferably be designed so as to favourably affect the escape of air. In order to explain the characteristics of the invention, by way of example only and without being limitative in any way, the following preferred embodiments of such a main injector according to the invention are described with reference to the accompanying drawings, where: - fig. 1 is a perspective drawing showing the positioning of the various components; - fig. 2 is a schematic cross-section of a main injector with a main injector tube according to the invention; - fig. 3 shows the portion of fig. 2 indicated by F3, drawn to a greater scale; - fig. 4 is a cross-section along the line IV-IV in fig. 3; - fig. 5 shows a variant of fig. 3; - fig. 6 is a cross-section along the line VI-VI in fig. 5; - figs. 7 to 12 are equivalent to fig. 3, but for other variants of the invention; - fig. 13 shows a configuration with two main injector tubes mounted one above the other ("over-and-under" configuration). Fig. 1 shows in a very schematic way a main injector 1 with a main injector tube 2 according to the invention, mounted on the sley 3, on which the reed 4 is also mounted. The injector 1 is supplied from a bobbin 5. Fig. 2 is a schematic drawing of a main injector 1 with an injector tube 2 which has symmetrically-positioned air outlet holes 6 at regular distances from each other, through which unwanted air can escape while the main injector is operating. In this embodiment, as shown in figs. 3 and 4, along the length of the tube 3 there are four symmetrically-positioned round openings per cross section. Figs. 5 and 6 show another embodiment in which the openings 6 have greater length than width, with their length perpendicular to the longitudinal axis of the tube 2. Fig. 7 shows an embodiment in which the openings 6 are long and narrow, extending in the length of the tube 2 and placed in oblique formation. Fig. 8 shows an embodiment in which the diameter of the openings 6 becomes smaller with each successive cross section of the tube, while fig. 9 shows an embodiment in which the diameter of the openings becomes larger with each successive tube section. Fig. 10 shows a similar arrangement, but with slit-shaped opening 6. Fig. 11 shows an embodiment in which the openings 6 are positioned at an angle of less than 90° with respect to the tube axis in order to facilitate the escape of air, while fig. 12 shows an embodiment in which the openings 6 are placed in groups. Although the openings 6 as shown in the accompanying drawings are all placed at regular intervals from one another, the intervals can of course be progressively larger or smaller, starting from the main injector 1. Finally, fig. 13 represents a configuration with two main injectors placed one above the other (over-and-under configuration). Here it is clearly shown that the tubes are arranged with respect to each other in such a way that the air escaping through the openings 6 is not obstructed in any way by their environment; in other words the tubes must not impede each other. In general, the most suitable position, number and shape of the openings 6 will be determined experimentally to suit the yarn to be inserted into the shed. Clearly, the present invention is in no way restricted to the embodiments described by way of example and shown in the accompanying drawings; in the contrary, such a main injector tube and the openings 6 in it can be made in all sorts of forms and dimensions while still remaining within the scope of the invention.

Claims: 1. Main injector with increased tensioning force, of the type where the actual injector consists of an airjet tube whose diameter is mainly constant, with the characteristic that symmetrically-positioned air outlet openings (6) are arranged along the length of said main injector tube (2) at different sections of the tube. 2. Main injector as in claim 1, with the characteristic that said opening (6) are circular in shape. 3. Main injector as in claim 1, with the characteristic that said openings (6) are slit-shaped. 4. Main injector as in claim 3, with the characteristic that the length of the slit-shaped openings (6) is perpendicular to the longitudinal axis of the tube (2). 5. Main injector as in claim 3, with the characteristic that the length of the slit-shaped openings (6) is parallel to the longitudinal axis of the tube (2). 6. Main injector as in claim 2, with the characteristic that the diameter of the openings (6) increases in stages with each successive section of the tube. 7. Main injector as in claim 2, with the characteristic that the diameter of the openings (6) decreases in stages with each successive section of the tube. 8. Main injector as in claim 2 or 3, with the characteristic that the openings (6) are positioned at an angle of less than 90° relative to the longitudinal of the main injector tube (2). 9. Main injector as in claim 2 or 3, with the characteristic that the openings (6) at each section consist of two or more adjacent rows of openings. 10. Main injector as in claim 2 or 3, with the characteristic that the interval between openings (6) at successive sections decreases in stages starting from the main injector 1. 11. Main injector as in claim 2 or 3, with the characteristic that the interval between openings (6) at successive sections increases in stages starting from the main injector 1. 12. Main injector as in claim 3, with the characteristic that the width of the slit-shaped openings (6) or the length of the slit-shaped openings (6) increases progressively starting from the main injector 1. 13. Main injector as in claim 3, with the characteristic that the width of the slit-shaped openings (6) or the length of the slit-shaped openings (6) decreases progressively starting from the main injector 1. 14. Main injector with increased tensioning force, in principle as described above and represented in the accompanying drawings.

Inventors: VERHULST, JOZEF
Applicants: PICANOL N.V.
Application year: 1987
Main classification: D03D47
IPC codes: D03D47