FI75524C - Extruded plastic pipe with longitudinal channels in the wall. - Google Patents

Description

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Mouth 1 an extruded plastic tube with longitudinal channels in the wall

The present invention relates to an extruded plastic pipe made of thermoplastic, in particular polyvinyl chloride, in which the wall of the pipe consists of an inner wall and an outer wall connected to each other by partitions thus forming longitudinally spaced channels rounded cross1 shape.

A plastic pipe of this type, the wall of which contains longitudinal channels with a circular cross-section, is known. Said tubes are made by extruding a plasticized thermoplastic material, such as polyvinyl chloride, through an extrusion nozzle containing pins to form longitudinal channels. These longitudinal channels are distributed at regular intervals along the circumference and the distance between two adjacent channels is preferably equal to the distance of the outer surface of the pipe to the nearest channel wall.

Said known tubes have the disadvantage that when a sharp tool hits the outside of the movable tube, a rupture is formed and this rupture increases and extends over the entire length of the tube so that the tube is unusable.

Said tears are caused by first cooling the outside of the extruded plastic tube, after which, at a later stage, the inner wall, which is joined to the outer wall, shrinks due to cooling. As a result, pressure stresses are generated on the outer wall, which cause tensile stresses on the inner wall of the pipe.

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Although attempts have been made to overcome this difficulty using very specific types of plastics, these difficulties have not been eliminated by current methods.

It is an object of the present invention to provide a plastic pipe which does not have the disadvantages described above.

According to the invention, this is achieved in that the tube has the molecular structure and stresses of a tube obtained by heating a calibrated and cooled tube to a temperature range of 50-100 ° C for less than 5 minutes, which provides a molecular structure of the inner and outer wall of the tube. the stresses and the inner wall stresses are equalized so that a circumferential residual stress is present in the pipe wall, which for test purposes after axial wiring of the pipe produces a circumferential overlap between the cutting edges of the pipe of less than 5%, preferably less than 2% of the entire outer circumference of the pipe.

The invention then also comprises pipes which, after axial opening, do not overlap, but even open into the gap.

For example, it has been found that in a polyvinyl chloride pipe with a diameter of 315 mm and a wall thickness of 3 mm, after the parts adjacent the edge have been overlapped by less than 2 cm, the stress in the wall required to spread the rupture is below the critical value. An impact with a sharp tool on the outside of the pipe will not lead to an expansion or increase in the length of the pipe and will not cause the inner edge of the pipe to crack.

However, the latter phenomenon occurs in any case when the overlap is well over 20 mm in this case.

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In the pipe according to the invention, the channels may also be elliptical or their cross-sectional shape may consist of four curved surfaces, the joints of which are rounded. The cross-sectional shape of the ducts can also be flattened on the outer side of the pipe.

The tube can be heated along its entire cross-section and the inside and outside are then simultaneously cooled gradually. The above-mentioned limits, i.e. that the circumferential overlap between the cutting edges is less than 5% and preferably less than 2% of the entire outer circumference of the pipe, should be reached during said gradual cooling.

The same effect can be achieved by homogeneously cooling the still warm, extruded tube from the inside and the outside.

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Stress in the pipe can also be removed by capacitively heating the pipe.

The invention will now be described by means of an embodiment with reference to the drawings, in which: Figure 1 shows an apparatus for manufacturing a pipe according to the invention; Figure 2 is a cross-section of a pipe according to the invention; Fig. 3 is a part of the wall of a pipe according to the invention, in which the channels have an elliptical cross-section; Fig. 4 is a part of a wall of a pipe according to the invention, in which the channels have a second cross-section, and Fig. 5 shows an overlap of adjacent edge portions of the cut edges of the pipe according to Fig. 2.

According to one example, the polyvinyl chloride pipe 2 is extruded as shown in Fig. 1 by means of a press 1, said pipe having an outer diameter of 315 mm and a wall thickness of 8 mm, while the longitudinal channels 3 in the wall have a diameter of 5 mm. The distance between the two adjacent channels is 1.8 mm and the distance from the outer surface 4 of the plastic tube to the part of the wall 5 of the longitudinal channel 3 closest to it is equal to the distance between the wall 5 of the channel 3 and the peripheral wall 6 at the point where the walls are closest. The channels are equally spaced around the perimeter.

After extrusion, the tube is passed through a calibration box 7 and further cooled to ambient temperature.

Since the outer wall 8 of the pipe is first cooled by cooling the calibration box 7, said outer wall 8 receives a large 2 E modulus, for example 30,000 kg / cm, while due to the subsequent cooling of the inner wall 9, said inner wall 9 is subjected to a higher tensile stress.

When a sharp tool hits the inner wall of this type of pipe, a tear is created that rapidly grows along the entire length of the pipe.

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In order to avoid this phenomenon, it is necessary that the energy released from a given volume of plastic is less than the energy required for the expansion of the rupture.

To achieve this goal, the polyvinyl chloride pipe is now led to a heated zone 10 where only the outer surface of the outer wall of the pipe is heated. For this purpose, a surface radiation device 11 can be used, which heats the surface of the outer wall to a temperature of about 80 ° C. Thus, the average temperature of the outer wall 8 ranges from 50 to 65 ° C.

Rapid heating of the outer surface of the outer wall of the pipe is essential. Rapid is to be understood here as a period of less than 5 minutes, preferably between 0.2-2 minutes and surface heating to 75-80 ° C.

By heating the outer wall 8 of the plastic tube, the tensile stresses in the inner wall 9 of the tube are reduced so that the tensioned inner wall receives less tension (reduction of about 50-75%) and the subsequent cooling of the outer wall means that the tensile stresses are further balanced so that the tensile stress is no longer .

The result of the heat treatment is shown in the following experiment.

In an extruded tube, cooled to ambient temperature as described above and not subsequently heated, there is an overlap of 5-7 cm on the adjacent portions of the cut edges. This overlap 14 is shown in Fig. 5 and denotes the distance between the cutting edges 15a and 15b when the pipe is cut along the line 15 in Fig. 2. Under the combined notched impact effect, a crack expansion phenomenon occurs in the pipe. Such rupture expansion occurs especially when an unsupported portion of such a pipe is sawn off.

6 75524 After the heat treatment, the overlap is less than 2 cm, whereby the step of subjecting the pipe to the combined notched impact and thus causing damage no longer results in the expansion of the rupture in the inner wall of the pipe.

It should be noted that the temperature during the heating of the outer wall should preferably be such that the plasticization temperature of the plastic material is exceeded, but the temperature remains below the glass transition temperature of the plastic material.

According to another example, the tube is extruded as in the previous example and cooled on the outside by a calibration box 7 and on the inside by a cylindrical part 12 to which cooling water is fed through the tube 13. Cooling by means of the calibration box 7 and part 12 is performed simultaneously.

There is only a 2 cm overlap in the manufactured pipe and the length of the tear formed in the inner wall does not increase.

When using pipes with a diameter of 200 mm, no rupture of the rupture occurs with an overlap of 15 mm.

When using pipes with a diameter of 250 mm, no rupture of the rupture occurs with an overlap of 22 mm.

As shown in Fig. 3, the channels 3 with a rounded cross-section may have an elliptical shape or some other rounded cross-section, as shown in Fig. 4.

Claims (1)

7,75524 Claim Extruded plastic pipe made of thermoplastic, in particular polyvinyl stem, in which the wall of the pipe consists of an inner wall (9) and an outer wall (8) connected to each other by partitions thus forming longitudinal channels (3) spaced apart perimeter and having a rounded cross-sectional shape, characterized in that the tube has the molecular structure and stresses of a tube obtained by heating a calibrated and cooled o tube to a temperature range of 50-100 C for less than 5 minutes, resulting in an inner and outer wall (9, 8) a molecular structure such that the stresses of the outer wall and the stresses of the inner wall are equalized so that there is a circumferential resultant stress in the wall of the pipe (2), which for testing ), which is less than 5%, advantage less than 2% of the total circumference of the pipe.