JPH0227933B2 - NETSUSHUSHUKUCHUUBUNOSEIZOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Background and Objectives of the Invention The present invention relates to a semi-continuous manufacturing method for heat-shrinkable tubes by vacuum evacuation.

Conventionally, as a method of expanding heat-recoverable pipes such as cross-linked polyethylene (XLPE) by evacuation, the inside of the vacuum container is evacuated as shown in Figure 2, and
A method is adopted in which the tube is expanded to the inner surface of the inner tube and this is done continuously. However, it was extended to the inner surface of the inner tube.
As shown in FIG. 3, the XLPE pipe bulges outward in the shape of a bowl at the suction hole, and in this state it is difficult to move the expanded pipe in the longitudinal direction. This tendency increases as the outer diameter of the pipe after expansion, that is, the inner diameter of the vacuum container, increases, as the surface pressure pressing against the inner surface of the inner pipe increases.Even if the pipe does not expand into a bowl shape at the suction hole, the surface pressure increases. It becomes extremely difficult to move the expanded pipe in the longitudinal direction. If an attempt is made to forcibly move the pipe in this state, scratches may occur on the outer peripheral surface of the pipe, and elongation in the longitudinal direction will increase, greatly impairing its function as a heat-shrinkable tube.

The present invention has been made in view of the above points, and eliminates the drawbacks of the prior art by providing a vacuum chamber with a pressurizing function and making the connectors at both ends of the vacuum container into halves. The purpose of this invention is to provide a method for manufacturing a heat-shrinkable tube that can be expanded.

(2) Summary of the invention The gist of the present invention is to provide a molding inner tube of any length having a large number of holes on its outer peripheral surface, and a molding inner tube of an arbitrary length that is arranged concentrically with the inner tube and of the same length as the inner tube. An arbitrary number of vacuum exhaust ports are provided on the outer circumferential surface of a vacuum container with half-shaped connectors attached to both ends of an outer tube having a A pipe made of a heat-recoverable resin such as cross-linked polyethylene heated above its softening point is inserted into the vacuum container of the tube expansion molding device formed by piping through the tube, and the pipe is expanded by evacuation and pressurization. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

(3) Embodiment FIG. 1 is a longitudinal cross-sectional view of a vertical tube expansion forming apparatus in which the present invention is practiced. An inner tube 6 with a hole in its outer circumferential surface is arranged concentrically with the outer tube 5 by a spacer 3, and a half-split plug 2 is attached to both ends of the outer tube 5. 5 means O-ring 4
It is sealed with. The mating surface of the plug 2 is flat-finished with high precision, and the sealing effect is improved by applying vacuum grease, etc.
A similar effect can be obtained by forming a groove on the mating surface and attaching a string-like sealing material. A plurality of vacuum exhaust ports 7 are provided on the outer peripheral surface of the outer tube 5, and piping 8
It is not only connected to a vacuum pump 10 via a solenoid valve 9', but also to a pressure tank 11 via a solenoid valve 9. The pressure (degree of vacuum) between the outer tube 5 and the inner tube 6 is measured by a pressure gauge 13.

Next, to explain the working process of pipe expansion using the above-mentioned device, first, a raw pipe such as XLPF is heated to a temperature higher than its softening temperature (approximately 170°C). At this time, the half-split plugs at both ends of the inner tube 6 and the outer tube 5 are left open, and the heated original pipe 1 is inserted therein from below upward. Next, the vacuum pump 10 and buffer tank 15 create a low vacuum of about 530 mmHg in the space between the outer tube and the inner tube, and the pressurized raw pipe 1 expands in the radial direction. After the tube has been expanded to the inner surface of the inner tube, the solenoid valve 9' is closed, the other solenoid valve 9 is opened, the pressurized gas is sealed between the inner tube 6 and the outer tube 5, and the expanded tube is pressed against the inner surface of the inner tube. Peel off the tube. At this time, the pressurized gas is heat exchanged to a constant temperature (approximately 10° C. or less) in the heat exchanger 12, which also has the effect of cooling the tube. The tube expansion molding is thus completed, and then the half-split plugs 2 at both ends of the outer and inner tubes are opened, the tube expansion tube is moved upward, and the same process is repeated. Although not shown, a heating tank for the original pipe is disposed below the tube expansion forming device, and a tube take-off device for the tube expansion tube is disposed above the tube expansion forming device, so that the above steps can be carried out almost continuously. Furthermore, in the above example, a "vertical" device was used to hold the original pipe and the inner pipe concentrically, but a "horizontal" device could also be used as long as it could maintain the above state. be. Further, it is preferable that the pressurized gas sealed after the pipe expansion is kept at a relatively constant low temperature (10 to 15° C.) by passing it through a heat exchanger or the like.

(4) Effects of the invention As described above, according to the present invention, it is possible to expand an original pipe almost continuously, and its industrial value is extremely large.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a vertical tube expansion forming apparatus showing a state in which the present invention is practiced; The figure is an enlarged longitudinal sectional view of the main part showing the bulge of the expanded pipe that occurs when the conventional method is carried out. 1... Original pipe, 2... Half-split plug, 3... Spacer, 4... O-ring, 5... Outer tube, 6... Inner tube, 7... Vacuum exhaust port, 8... Arrangement, 9,9'...
... Solenoid valve, 10 ... Vacuum pump, 11 ... Pressure tank, 12 ... Heat exchanger, 13 ... Pressure gauge, 14
...Connection fixing fitting, 15 ...Buffer tank, 1
6... Expanded pipe, 17... Suction hole.

Claims (1)

[Claims] 1. A molding inner tube of arbitrary length having numerous holes on its outer peripheral surface, and an outer tube arranged concentrically with the inner tube and having the same length as the inner tube, with half-split connections at both ends. An arbitrary number of vacuum exhaust ports are provided on the outer peripheral surface of a vacuum container with a stopper attached thereto, and the vacuum exhaust ports are piped to a vacuum pump and a pressure tank via a switching valve or the like in the vacuum container of a tube expansion molding apparatus. A method for manufacturing a heat-shrinkable tube, which comprises inserting a heat-recoverable resin pipe heated above its softening point into a tube, and expanding the tube by vacuuming and applying pressure.