CH688296B5 - A method of manufacturing a plastic wire wheel axis. - Google Patents

Description

1

CH 688 296G A3

2

Description

The subject of the present invention is a method of manufacturing a plastic wheel with a metal axis consisting in injection molding the plastic wheel on the metal axis, a method in which a new axis is introduced into the mold at least approximately simultaneously with ejection of the molded part.

This process is particularly intended for the manufacture of toothed wheels for watchmaking.

Document DE-A 3 135 259 discloses a process for manufacturing plastic wheels with a metal axis according to which the metal axes arrive successively in the mold by a supply device to come to be placed between an ejector and the molded part, in the extension of the axis of the molded part, so that the molded part is ejected via the new axis which takes the place, in the mold, of the axis of the ejected part, and so on . A continuous process is thus obtained in which the phase of introducing a new axis into the mold is merged with the ejection phase.

This process is certainly all-to-do valid for parts of medium dimensions, but difficult to implement and unreliable for the manufacture of very small parts such as one meets them in a watch movement, because of the small dimensions metal axes, in particular of their small diameter. Regular feeding is not guaranteed, nor is pushing from one axis to another axis.

The object of the present invention is to obviate the drawbacks of the process described above in its application to very small parts, while retaining the advantages of this process with regard to continuous manufacturing.

The method according to the invention is characterized in that a mold is used such that the metal axis of the finished part, but also in the closed mold, protrudes outside the mold, that a round metal wire is introduced into this mold unwound from a torch and previously straightened and calibrated intended to constitute the desired axis, that the plastic material is injected, that during these operations, the wire is cut to the length of the desired axis, that open the mold and eject the finished part and advance the wire through the mold at least approximately simultaneously and so on.

The wire can be cut in length simultaneously with the closing of the mold, after this closing and before injection, simultaneously with the injection or after the injection.

The very thin wire is not used as an ejector and is guided close to where it is cut.

Compared to the previous method, this eliminates the prior manufacture of the axes and their loading in a mold supply device. The axis is obtained almost simultaneously with the molding of the wheel on this axis. The wire cutting can be ensured by knives integral with the two mold shells.

The appended drawing schematically represents an example of implementation of the method according to the invention.

Fig. 1 is a sectional view of the closed mold just after the injection of the synthetic material.

Fig. 2 illustrates the sectioning of the metal wire.

Fig. 3 illustrates the phase of ejection and advance of the metal wire.

The drawing schematically represents a mold consisting of two shells 1 and 2 deviating from one another for the opening of the mold. The shell 1 consists of three parts 11, 12, 13. Likewise, the shell 2 consists of three parts 21, 22, 23. The parts 12 and 22 are intermediate parts determining the thickness of the molding wheel 3 and having the shape of its toothing 4. The mold also contains the shape of a pinion 5 associated with the toothed wheel 3. The shell 1 has an injection well 6 for injecting the plastic.

The steel wire 7 in torch, straightened and calibrated, advances in the mold of a determined length. It is guided by a guide piece 8 having a cylindrical bore. The mold is then closed and the plastic material is injected so as to form the toothed wheel 3 on the wire 7. This wire 7 ensures the sealed closure of the parts 13 and 23 of the mold.

The wire 7 is then cut in length between a knife 9 and a counter knife 10 (fig. 2).

The mold is then opened (FIG. 3) and the wheel 3 provided with its axis 30 is ejected by an ejector not shown. Simultaneously with this ejection or immediately after it, the wire 7 again advances an axis length in the mold and the operation of injection and cutting of the wire is repeated and so on.

The mold has of course been shown schematically. In general, it presents itself in a more complex way. Such molds are however well known per se. They have means allowing parts 11, 12, 13, respectively 21, 22, 23 to be separated from one another.

As soon as the mold is closed on the wire 7, this wire can be cut. Sectioning can therefore occur simultaneously with the closing of the mold or immediately after this closing. The knife 9 and the counter knife 10 could therefore be respectively secured to the two shells 1 and 2 of the mold as indicated in broken lines in FIG. 2.

Claims (1)

Claims 1. A method of manufacturing a plastic wheel (3) with a metal axis (30) comprising injection molding the plastic wheel on a metal axis, in which a new axis is introduced into the mold at least approximately simultaneously with the ejection of the molded part, characterized in that a mold (1, 2) is used such that the metal axis of the finished part, but still in the closed mold, protrudes out of the mold, which is introduced into this molds a round metal wire unwound from a torch and previously straightened and calibrated (7) 5 10 15 20 25 30 35 40 45 50 55 60 65 3 3 CH 688 296G A3 tiné to constitute the desired axis (30), which one injects the plastic material, that during these operations one cuts the wire (7) to the length of the desired axis, which one opens the mold and ejects the finished part and that the wire (7) is advanced at least approximately simultaneously in the mold and so on. 2. Method according to claim 1, characterized in that the wire (7) is cut at least approximately simultaneously with the closing of the mold. 3. Method according to claim 1, characterized in that the wire (7) is cut at least approximately simultaneously with the injection. 4. Mold for implementing the method according to claim 2, characterized in that it is equipped with a knife (9) and a counter knife (10) actuated simultaneously with the closing of the mold. 5. Mold according to claim 4, characterized in that the knife (9) and the counter-knife (10) are fixed symmetrically on two parts of the mold approaching symmetrically to the axis of the wire when the mold is closed. 5 10 15 20 25 30 35 40 45 50 55 60 65 4