Method and injection tool for making a plastic link conveyer, in particular a ball chain.

The invention relates to a method according to the preamble of claim 1, further comprising an injection tool for performing the method and a plastic link belt.

There are already known ball chains are where strung on a flexible cord at regular intervals balls. Such bead chains have a wide application area, in particular because they can deflect in any direction and thus serve in many cases for the synchronous drive, controller or as a power transmission system. Originally such ball chains of metal were produced. There are, however, well known plastic balls. Such plastic_-Ball chains have been produced in the manner that the balls separately sprayed onto a cord or a cable, and subsequently the cord or the cable has been transported further in each case by the predetermined pitch. This production method is suitable for mass production and very slow.

The simultaneous production of multiple sprayed on a cord or cable balls in a plastic injection mold failed until now because that arose due to the heat shrinkage pitch error, which was not acceptable especially when used for synchronous drives and controls. The for spraying on the individual balls leading, by a common injection ridge projecting connecting webs caused namely due to the thermal shrinkage during cooling, that is not yet fully cooled inside balls are moved along the cord or cable slightly, thereby dividing inaccuracies arose on the finished ball chain._Jwas the inaccuracy e more bullets were sprayed at the same time, the greater. This division errors are the greater the farther the balls from the center of the injection bridge.

The problem to be solved by the invention is to provide a link belt, in particular a ball chain to be able to produce efficiently in a multiple mold having a plurality of made of plastic members, in particular balls, are avoided by the or with the pitch errors.

This object is solved by the features contained in the characterizing part of claims 1, 2 and 5. FIG.

Due to the thin-walled weak connection between the molded members, in particular balls and their associated connecting webs, prior to complete cooling of the members or balls from the relatively massive injection web forth due to its material shrinkage no displacement force to the members or balls in the longitudinal direction of the cord or of the cable be exercised. The inevitable in plastics, in comparison to metals relatively large material shrinkage in the longitudinal direction of the injection web on cooling causes only a slight bending of the relatively thin connecting webs and / or the point of weakening before the member or the ball. When the members or balls, shortly after the injection process as a result of their mass in the interior are not yet completely cooled and therefore not yet been fixed surround the cord or cable, is prevented by the weak juncture that in the longitudinal direction of the cord or cable, a change in position of the members or balls can be effected.

In the drawing, embodiments of the invention items are shown. Show it:<ul><li>FIG. 1 is a view of two ball chains, which are connected to later severed connecting webs and a common injection bridge</li><li>Fig. 2 is a plan view of a mold plate of the injection molding tool</li><li>Fig. 3 is a section according to the line III-III in Fig. 2</li><li>Fig. 4 shows an embodiment of the limbs in the form of plates</li><li>Fig. 5 shows an embodiment of the limbs in the form of forks</li><li>Fig. 6 shows an embodiment of the limbs in the form of eyelets together with balls.</li></ul>

From Fig. 1, an injection molded plastic part 1 is shown in which two ball chain part lengths are available, still hanging by the spray process of connecting webs 5, which in turn are connected to a common injection web 4. The connecting webs 5 are separated after the injection process at the constriction 7 directly with the balls 2, and together with the injection web 4 waste, so that afterwards remain only the ball chain partial lengths with the cords 3 for use. The balls 2 sitting after its complete common cold alone due to the heat shrinkage of the plastic shift firmly on the cord. 3

The production takes place in the manner that such plastic molding parts 1 according to Fig l -. Which thus each comprise a plurality of balls 2 - be intermittently injected by a corresponding feed velvet drawstring 3 takes place after a first injection to injection molded parts-length, so that the length of the member band is practically determined only by the total length of the cord. 3

As is apparent from FIGS. 2 and 3, the multiple injection mold includes two mold plates 18, 20, which is in the shape of the produced injection-molded part is formed. The injection cavity 12 in the two mold plates 18, 20, into which formed from the injected plastic is the late injection web 4 of the molded part 1, extending in the longitudinal direction of the cord 3 and the cavity 13 for receiving the cord 3. To support the injection web in the longitudinal direction are spaced at intervals cylindrical recesses 16 in the injection lumen 12 is present, forming the pin 6 in the injection molded part. Each spherical recess 8 in the mold plates 18, 20 leads - from the injection cavity 12, starting - one side channel 10. These produce the molded part, the relatively thin-walled connecting webs 5. The cross sections of these approximately wedge-shaped connecting webs 5 decrease with increasing distance from the injection web 4 from. Immediately prior to the transition into the spherical Hohraum 8, the side channels 10 in the mold plates a severe narrowing 14. The task of the remaining small cross-section of the constriction 14 is during the cooling of the molded part 1 and thus to avoid the heat shrinkage of the injection web 4 that axial forces are transmitted to the ball 2 comprising a longitudinal displacement of the not yet completely cooled inner sphere 2 would bring along the cord 3 after removal.

In a practical embodiment, the diameter of the constriction 14 is less than 1/10 of the diameter of the ball 2 and its cross section is less than 1 mm², With a ball diameter of 4.5 mm, the narrowed section is still approximately 1/6 mm², The cross section of the injection web 4 is substantially larger than the cross section of the connecting web 5 in the immediately following range, for example about three times.

The second mold plate 20 which has abutted against the first similar recesses as the first mold plate 18, with the difference that the side channels 10 and the injection port 12 have a flat narrow side 21 and a - not shown in the drawing - sprue mark for supply of the supplied pressurized, liquid plastic is present.

The plastic for the balls 2, for example, polyamide, polyester or the like are suitable.

Each ball 2 is penetrated in the midst of a cord 3, preferably made of synthetic fibers. This cord 3, for example, of polyamide,_Polyster- or polypropylene fibers. For special purposes, a coated with these plastics steel cable or a metal cable can be used without cladding.

Instead of balls, the sprayed on the cord 3 or cable links can have almost any other form, such as those in the form of exemplary embodiments of Figs. 4 - emerge 6, namely the plate 21, as forks 22 or eyelets 23rd

For efficient production of such link belts not only an injection molded part 1 with two ball chain part lengths in the injection mold at the same time be injected, but it can be configured as a four- or six-cavity mold. In addition, the length is not limited to the partial length shown in FIG. 1, but this and thus the number of simultaneously sprayed on a cord 3 balls 2 or other members per molded part 1 is usually greater, and preferably 40-50 pieces per link chain.