JPS597061Y2 - ``Kinzoku Kanhi Fukuyou Plastics Obizhiyotaino Atsuchi Yakusouchi'' - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an apparatus for continuously crimping a semi-molten plastic strip which is continuously extruded from an extruder and wound helically around a metal tube such as a steel tube.

Conventionally, the method of forming a plastic coating on the outer surface of a metal tube is to continuously extrude semi-molten plastic strips from a T-shaped die of an extruder so that a portion of the strips in the width direction overlap each other. Wrap it spirally around the outer circumferential surface of a metal tube,
A method is known in which the semi-molten plastic strip is crimped in the vicinity of the starting point of winding contact over its entire length using a flat roll 6 having the same diameter, as shown in FIG.

However, when crimping is performed using the flat roll 6, there is a step between the first layer strip 1A and the second layer strip 1B in the wound plastic strip. The upper surface of the strip 1A is a flat roll 6
Since the flat roll 6 applies strong pressure only to the upper surface of the second layer strip 1B without crimping, the air bubbles 7 and 8 generated inside the first layer strip 1A are transferred to the second layer strip 1B. Due to the crimping of 1B, the length will be increased to some extent.

As a result, not only does the adhesion between the metal tube 2 and the plastic strip become poor, but also the external shape becomes extremely poor.

The object of this invention is to provide an apparatus for crimping plastic strips for covering metal pipes, which eliminates the above-mentioned drawbacks.

Next, this invention will be explained in detail using illustrated examples.

Figure 2 shows an embodiment of this invention, in which a semi-molten plastic strip 1 is continuously extruded from an extruder.
A large-diameter front cylindrical body having an axis parallel to the axis of the metal tube 2, in which 3, a small-diameter rear cylindrical body 4 disposed on the same straight line as the axis of the large-diameter front cylindrical body 3, and a tapered portion 9 that integrally connects each cylinder 3, 4. The semi-molten plastic strip 1 is placed in opposition to the vicinity of the winding contact start point, and the first layer strip 1A is strongly pressed by the large diameter front cylindrical body 3, and the second layer strip IB is placed near the small diameter rear cylindrical body 3. It is strongly pressed by the cylindrical body 4, and the stepped portion of the plastic strip is configured to be crimped by the tapered portion 9.

The width of the large-diameter front cylindrical body 3 and the small-diameter rear cylindrical body 4 needs to be about 1/2 of the wrapping width of the semi-molten plastic strip 1, and the large-diameter front cylindrical body 3 and the small-diameter rear cylindrical body 4 is preferably slightly smaller than the wrapping thickness of the plastic strip, for example, the difference in radius is 1.8 mm.
It is possible to press a semi-molten plastic strip having a thickness of 2 to 3 mm even if the thickness is only about 2 to 3 mm.

A plane perpendicular to the axes of the large-diameter front cylinder 3 and the small-diameter rear cylinder 4 may be formed between the circumferential edges of the opposite ends of the cylinders, however, as in the embodiments described above, A tapered portion 9 is interposed at the peripheral edge of the opposing ends of the large-diameter front cylindrical body 3 and the small-diameter rear cylindrical body 4, and the tapered portion 9 forms a stepped portion of the wrapped semi-molten plastic strip. By crimping the steps, it is possible to prevent air bubbles from forming at the stepped portions.

The taper amount of the tapered portion 9 varies depending on the shape of the stepped portion of the wrapped semi-molten plastic strip, but is generally about 1.8/10 to 1.8/30.

When the semi-molten plastic 1 is wound spirally around the outer peripheral surface of the metal tube 2, for example, it is sufficient to fix the T-shaped die of the extruder and move it in the tube axis direction while rotating the metal tube 2. A belt-shaped body is wound in a fusion shape so that two-thirds of the widthwise direction of the body overlaps each other to form a three-dimensional structure consisting of three cylindrical bodies with different diameters and two tapered portions interposed between the cylindrical bodies. The crimping may be performed using a stepped crimping roll.

According to this invention, in an apparatus for spirally attaching semi-molten plastic strips 1 continuously extruded from an extruder to the outer circumferential surface of a metal tube 2 so that parts of the strips in the width direction overlap each other, A multi-stage crimping roll 5 having a large-diameter front cylindrical body 3 and a small-diameter rear cylindrical body 4 is disposed opposite to the semi-molten plastic strip 1 near the winding contact start point, so that the multi-stage crimping roll 5 is provided with a large diameter front cylindrical body 3 and a small diameter rear cylindrical body 4. The large-diameter front cylindrical body 3 of the roll 5 reliably presses the first layer strip 1A, and the small-diameter rear cylindrical body 4 reliably presses the second layer diaphragm 1B. In addition to improving the adhesion between the outer peripheral surface and the plastic strip, the plastic strips can be reliably fused to each other, and a high quality and strong plastic coating can therefore be formed.

[Brief explanation of the drawing]

FIG. 1 is a vertical side view showing a state in which a plastic strip is being crimped by a conventional crimping device, and FIG. 2 is a longitudinal side view showing a state in which a plastic strip is being crimped by a crimping device according to an embodiment of the present invention. FIG. In the figure, 1 is a semi-molten plastic strip, 1A is a first layer strip, 1B is a second layer strip, 2 is a metal tube, and 3
4 is a large-diameter front cylindrical body, 4 is a small-diameter rear cylindrical body, 5 is a multi-stage pressure roll, and 9 is a tapered portion.

Claims (1)

[Scope of utility model registration request] In an apparatus for spirally wrapping a semi-molten plastic strip 1 continuously extruded from an extruder around the outer peripheral surface of a metal tube 2 so that a portion of the strip in the width direction overlaps each other, a large-diameter front cylinder is used. A plastic strip for coating a metal pipe, characterized in that a multi-stage pressure roll 5 comprising a body 3 and a small-diameter rear cylindrical body 4 is disposed opposite to the semi-molten plastic strip 1 near the winding contact start point. Body crimping device.