FI78891C - Apparatus for removing powdery material collected in the tubular rear part in the manufacture of an optical fiber blank - Google Patents

Description

1 78891

The present invention relates to an apparatus for removing an abrasive substance which accumulates in the tubular back of its optical fiber, comprising a screw structure following the inner surface of this tubular back.

When manufacturing an optical fiber preform 10 by an MCVD process or the like in which the preform is grown inside a quartz tube, it is absolutely essential to ensure that the tubular attachment associated with the back of the preform cannot become clogged during accumulation by the powdered material (Soot). Conventionally, this task is carried out completely manually, for example by means of a glass rod, with which during the manufacturing process the so-called the powdery substance accumulating in the soot tube is the so-called called off to prevent clogging of this soot tube. Namely, such a blockage would lead to an increase in pressure inside the blank and to its damage. Since the blank is rotated during its manufacture, the so-called in lathes, for example, 10 to 100 revolutions per minute, a screw-type cleaner can be used as one of the drainage structures, which, placed in the soot tube and rotating 25, pulls the extra soot out of the soot tube. However, such a screw structure has various shortcomings. First, the broom tends to accumulate only at the bottom of the tube due to gravity, so it cannot be moved very efficiently with such a screw. On the other hand, such a screw, if made too closely to follow the inner surface of the soot tube or if too much soot has adhered to it, may have caused mechanical effects on the soot tube, which may have resulted in damage to the blank.

The object of the present invention is to provide 2 78891 devices for removing a powdery substance accumulating in the tubular rear part during the manufacture of an optical fiber preform, which do not have the problems of the above-known structural solutions and which can automatically and reliably maintain this so-called soot tube open.

The above object is achieved by a device according to the invention, which is characterized in that the screw structure has a gas channel provided with nozzle openings opening in the direction of the open end of the tubular rear. When a dry gas, such as N2 gas, is fed into the gas channel of the screw structure, the nozzle openings of which open in the direction of the open end of the soot tube, the soot in the soot tube is subjected to a flow of gas. This effect of the gas flow is further enhanced by the use of a screw structure following the inner surface of the soot tube, which is also in relative motion relative to the soot tube as the blank rotates. A further significant advantage is that the soot tube is now filled with dry gas, which prevents moisture from entering the preform and, on the other hand, cools the screw structure, thus preventing the soot from melting on its surface.

Preferred structural solutions for the screw structure are a helically wound pipe or a hollow fin in the form of a screw thread arranged around a central axis, such as a base pipe. In this way, a gas channel is automatically formed in the screw structure, into which the necessary nozzle openings for gas supply can be formed simply by drilling.

In order to further enhance the operation of the device according to the invention, the screw structure may comprise a rotating joint which allows the screw structure to be rotated relative to the soot pipe. If this rotation takes place in the opposite direction to the rotation of the blank itself at a speed substantially lower than that of the blank, an effect promoting the emptying of the soot tube is obtained.

In the following, the device according to the invention will be described in more detail with reference to the accompanying drawing, in which Figure 5 shows the basic structure and operating principle of the device according to the invention.

The figure shows, for example, an optical fiber blank 1 produced by the MCVD process, to which a tubular back part 2, the so-called the exhaust tube. The preform 1-10 manufactured appropriate, this preform 1 while the exhaust tube 2 is rotated in the direction of arrow A shown in Figure 1 in the direction generally at a rate of about 10 - 100 rpm. In this manufacturing process, gases are fed into the interior of the blank, which is deposited on its inner surface as glass forming the optical sheath of the blank and the core.

Some of these reactive gases and vapors enter the soot tube 2, into which they tend to accumulate. In order to keep this soot tube open, a screw structure 3 according to the invention is fitted. In the embodiment 20 shown in the figure, this screw structure comprises a helically wound tube 3 with nozzle holes 5 opening towards the open end of the soot tube 2, in particular at its blank side 1. When the screw structure 3 is formed from the pipe, a gas hub 4 is automatically formed inside it, to which dry gas or a gas mixture, such as nitrogen, is now fed in accordance with the invention. The amount of this gas flow can be, for example, 2 to 10 liters per minute. By means of this gas supply, the soot tending to accumulate in the soot tube 2 is effectively moved towards and out of the open end of the soot tube 2. Furthermore, the ingress of moisture into the blank 1 is prevented, which can also be considered an essential advantage of the invention. As shown in the figure, the screw structure 3 may be associated with a rotating joint 6, which enables the screw structure to be rotated with respect to its suction pipe 2. This rotation of which the TA-4 78 891 takes place in the direction of the arrow shown in Figure B is opposite to the one direction of rotation of the blank. The screw structure 3 to rotate in the direction of arrow B in transmission rates are to be quite low, such as for example one revolution per minute. Since the aim of this rotation is to increase the removal of the solder, this rotational speed can be increased if the formation of the solder is abundant. Conventional means known per se, such as an electric motor, for example by means of a belt, can be used to rotate the screw structure 3. An example of such a rotation structure which is completely obvious to a person skilled in the art is not shown in the figure. Likewise, the figure does not show the gas source from which the gas is fed into the gas channel 4 of the screw structure 3. As such a gas source, for example, a gas cylinder filled with pressurized gas provided with suitable valves 15 can be used.

The device according to the invention has been described above on the basis of only one exemplary embodiment and it is understood that several structural changes can be made without departing from the basic principles of the invention, i.e. dry gas gas flow and relative rotational motion between descaler and blank.

Claims (4)

5 78891 Apparatus for removing a powdery substance accumulating in its tubular rear part (2) during manufacture of an optical fiber blank (1), comprising a screw structure (3) following the inner surface of said tubular rear part (2), characterized in that the screw structure (3) has a gas channel (3). 4) provided with nozzle openings (5) opening in the direction of the open end of the tubular rear part (2). Device according to Claim 1, characterized in that the screw structure is a helically wound tube (3). Device according to claim 1, characterized in that the screw structure comprises a helical fin in the form of a screw thread arranged around the central shaft 15. Device according to Claim 1, 2 or 3, characterized in that the screw structure (3) comprises a rotating joint (6) for enabling the screw structure (3) to rotate.