SK115494A3 - Piping part from polyethylene plastic made by extruding and method of its manufacture - Google Patents

Abstract

Extruded pipe end made from polyethylene, which has a moulded-on socket. The extruded pipe end has a wall thickness of over 5 mm. The moulded-on socket has at least the same wall thickness. The wall has in cross-section a highly crystalline inner region (4) and a weakly crystalline outer region (5). The highly crystalline inner region (4) forms a peripheral crystalline supporting shroud. This is designed for the virtually deformation-free supporting of the weakly crystalline outer region when shrinkage stresses occur. A method for producing such a pipe end is also specified. <IMAGE>

Description

Technical field

BACKGROUND OF THE INVENTION The present invention relates to an extruded polyethylene plastic pipe part having at least one insertion throat. The invention further relates to a process for the manufacture of this pipe part.

The wall of the pipe part may consist of a single layer, but it may also consist of several layers when the pipe part is made by coextrusion. It is preferably a pipe part made of uniform polyethylene plastic, although the pipe part has various microstructures spaced along its length or circumferentially. The polyethylene plastics used in the present invention are the polyethylene plastics customary for pipelines, especially those laid in the ground. Polyethylene plastics consist of many disordered long chains that are formed by joining C atoms and CH 2 groups. The strings can be arranged linear or branched. There are weak intermolecular binding forces between the chains that determine the properties of the material. Obviously, these binding forces are particularly pronounced when the individual pieces of the chains in the polyethylene bundle get very close together. Arranged areas of this kind, in which the chains run together in a bundle, are called crystals, unlike the surrounding disordered area. A disordered portion is also referred to as an amorphous portion. Obviously, other forces, which include less or more pronounced crosslinking, act in addition to the binding force described above. At very low temperatures, all parts of the macromolecules are almost frozen. The introduction of thermal energy initially stimulates the movement of lighter and later heavier moving molecules. The aggregation state of the plastic hardly varies with such heating. Above a certain temperature, however, the movement energy of the macromolecules will be so great that the plastic begins to soften. It passes from a solid to a softer state, referred to as viscoelastic. In the viscoelastic state, the cohesiveness of the macromolecules is already very relaxed with one another, but is not yet completely abolished. If the temperature rises further, the viscoelastic state becomes viscous. Due to the existence of crystallites formed as a result of the described bundling phenomenon, the extent of softening is also associated with the extent of melting of the crystallites at higher temperatures. First, the crystallites are cohesive beyond the extent of softening of the amorphous fractions. The number or quantity of crystallites per unit volume determines the strength. Polyethylene plastics, which in principle have been formed in the manner described, have a so-called memory effect due to the described embodiment and the associated thermodynamics. This term refers to a particular diminishing phenomenon. Polyethylene plastics can change their shape in a reversible manner, depending on the temperature, depending on the temperature. When the deformation of the polyethylene plastic, for example by elongation or expansion, is carried out in the viscoelastic range and this condition is frozen by temperature change, in which virtually no movement of the molecules occurs, the stress is relaxed under sudden heating and the deformed state is evident returns to its original dimensions.

BACKGROUND OF THE INVENTION Polyethylene-molded insertion parts

With known new plastic pipes with at least one spigot, this spigot is realized regularly in a virtually viscoelastic state, pipe pieces preformed before use, or when using shrinks, for example when a pre-formed insertion neck

In this way, unwanted piping parts can be deposited after the throat insertion process and at the same time they are exposed to thermal influences, but this can also occur in the installed or laid condition of the piping parts. Dimensional changes that occur may cause malfunctions. These failures are all the more pronounced, the thicker the wall of the pipework. In the case of duct pieces having at least one shaped insertion neck which consists of polyvinyl chloride, it is possible without difficulty to ensure that the wall of the duct pieces having a thickness of greater than 4 mm, for example about 6 mm or more, is not subject to disturbing diminishing effects. In this case, the shaped insertion neck usually has the same wall thickness as the pipe part itself, since the insertion neck is tamped in the axial direction in order to increase the wall thickness reduced by shaping the insertion neck. In the case of duct pieces with at least one shaped insertion throat which consist of polyethylene plastic and have a large wall thickness, this does not occur without disturbing diminishing effects.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a pipe part with a molded insertion neck made of polyethylene plastic by extrusion, which does not cause disturbances to be reduced at the back of the neck during re-heating. Another object of the invention is to provide a method of manufacturing such a pipe part.

SUMMARY OF THE INVENTION

This task is accomplished by an extruded polyethylene plastic pipe part having a molded push-in throat with

(a) the extruded pipe part has a wall thickness of more than 5 mm;

(b) the shaped male throat has at least the same wall thickness, and with the indication that the wall has a high-crystalline inner region and a low-crystalline outer region in cross-section, and with further data that the high-crystalline inner region still forms a crystalline supporting arch over time and this supporting arch is dimensioned practically Supporting the low-crystalline outer region at reduced stresses.

Particularly stable ratios with a view to avoiding the occurrence of disturbing diminishing effects are achieved according to a preferred embodiment of the invention by a further indication that the wall of the male throat has a tufted structure. Within the scope of the invention, the wall of the pipe part and the insertion neck may have a thickness of greater than 6 mm. However, the measures according to the invention have also proved to be effective in the case of pipe components in which the wall has a thickness greater than 10 mm. A preferred embodiment according to the invention relates to a pipe part of the described basic embodiment, in which the insertion neck has at least one region with a shaped circumferential bearing groove for an inserted sealing ring and a sealing chamber, this region being realized as described in the highly crystalline inner region.

This object is further accomplished by a method of forming a push-in throat on a pipe part by extrusion of polyethylene plastic with the following operations:

(a) the pipe part is heated to the extent of softening at the end at which the male connector is to be shaped;

b) the end of the pipe work heated to the softening range is inserted into a mold in which the heated mandrel is provided and which is unheated or cooled from the outside,

c) in this case or thereafter, the heated end is compressed pneumatically, hydraulically and / or mechanically with an extension towards the inner wall of the molding space of the mold, taking into account the reduction of the wall thickness of the pipe part in the region of the insertion throat.

(d) the end of the pipe part, extended to the width of the male socket, is moved from the female socket opening as the wall thickness reduced according to (c) increases, to the male socket geometry predetermined by the male socket shape and thereby being pressed against the unheated or cooled internal the mold forming space wall,

(e) the temperature of the heated mandrel, taking into account the external temperature of the mold, is selected such that a temperature within the melting range is set in the inner cross-sectional area of the male throat which decreases to a temperature within the softening range on the male mold wall; as well as the cooling rate of the shaped male throat in the interior or exterior of the mold is selected such that a high crystalline inner region and a low crystalline outer cross-sectional area are formed and the inner cross-sectional area still forms a crystalline support arch that is dimensioned for virtually non-deformable support a low-crystalline outer region at emerging mechanical reducing voltages.

The process according to the invention can start from piping parts which, after being extruded and routinely calibrated, are first cooled and then stored. According to a preferred embodiment of the invention, which allows very short times for the insertion neck to be formed in the process according to the invention, after the extrusion and calibrating the end of the pipe part which still contains residual heat after extrusion or after preheating is introduced into the insertion sleeve. . This method makes it possible to work with very short time cycles in the production of pipe components.

The numerical parameters which must be taken into account in the process according to the invention can be readily determined by experiment. In the case of conventional polyethylene plastics, very good results are obtained regularly if the temperature of the heated mandrel is maintained at a temperature of more than 125 ° C inside the insertion throat and a temperature clearly below 125 ° C on the outside of the insertion throat. The residence time in minutes of the molded insertion neck in the mold should correspond to approximately half the wall thickness in millimeters of the insertion neck formed. This rule applies up to a wall thickness of about 10 mm. For larger wall thicknesses, the dwell time may be shorter than this rule. In the method according to the invention, the wall thickness of the pipe part and therefore of the insertion neck formed can be, for example, 4 mm. However, the method according to the invention is particularly suitable for the production of pipe parts having a shaped, virtually non-reducible insertion neck having a thickness of 6 mm, 8 mm and 10 mm.

The invention is based on the finding that by means of suitable temperature conduction for expanding the insertion throat on a pipe part previously made of polyethylene plastic, as well as suitable temperature conduction for cooling after the insertion throat is formed, the described vault can be formed. This means that it no longer interferes with the dimensions of the insertion throat formed due to subsequent reduction effects. The measures necessary to form the load-bearing arch are readily detectable experimentally, the numerical parameters varying according to the diameters, wall thickness, but also to the particular polyethylene plastics used.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail by way of example with reference to the accompanying drawing, in which: FIG. 1 is a longitudinal sectional view of a portion of a pipe part having a shaped insertion neck; FIG. 2 is a substantially enlarged scale compared to FIG.

detail A of FIG. 1, and FIG. 3 at the same scale as FIG. 2 shows a section along line B-B in FIG. First

Examples of embodiments of the invention

The pipe part 7 shown in FIG. 1, has been made by extrusion and is made of polyethylene plastic. It has a wall 2 which, according to the initial definition, is a single or multilayer and which has been made by extruding one material or by simultaneously extruding several materials. The pipe part 1 is provided with a shaped insertion neck

3. The layers of the multilayer formation are not shown.

The extruded tubular member 1 has a wall thickness of greater than 5 mm. The shaped insertion neck 2 has at least the same wall thickness 2. When comparing FIG. 1 to 3, and in particular FIG. 3 it can be seen that the wall 2 has a highly crystalline inner region 4 in cross-section and a crystalline outer region 5 therethrough. One or both of these regions 4, 5 or both may consist of several layers. The term highly crystalline refers to the fact that many crystallites are present which directly or indirectly support each other, such as building blocks in the arch. The term low crystalline means that only a few crystallites have been formed. It can further be seen that the high crystalline inner region 4 still forms a crystalline supporting arch over and over. This supporting arch is dimensioned such that, under the occurrence of mechanical reducing stresses, the low-crystalline outer region 2 results in virtually non-deformable support of the low-crystalline outer region 5.

The wall 2 of the insertion neck 2 has a tamped structure, since not only the expansion but also the tamping has been realized in the formation of the insertion neck 2. The wall thickness 2 may be greater than 6 mm or even greater than 10 mm. In the illustrated embodiment and according to a preferred embodiment of the invention, the insertion throat 3 has a part with a circumferential receiving groove 6 on the inserted sealing ring 7 and a so-called sealing chamber 8 on which the sealing lip 9 of the sealing ring 7 rests. and the male throat 3 is realized as a supporting arch.

It will be appreciated that the described single-layer or multilayer pipe part 1 with the insertion neck 3 formed can also form an almost self-supporting core of the pipe part, which can be provided with an additional outer plastic layer or a layer with a different function.

Claims (10)

PATENT CLAIMS Pipe part (1) of polyethylene plastic, made by extrusion, having a wall thickness (2) of more than 5 mm and having a male insertion neck (3) having at least the same wall thickness (2), characterized in that the wall ( 2) has a high-crystalline inner region (4) and a low-crystalline outer region (5) in cross-section, and that the high-crystalline inner region (4) forms a crystalline supporting arch around and this supporting arch is designed to substantially support the low crystalline external shrinkage stresses. non-deformable regions (5) when formed and blown 2. Pipe part by providing a wall structure. according to claim 1, (2) a male insertion n ( 3) has pecho3. Pipework characterized by greater than 6 mm. According to one of the claims, the wall 1 or 2, (2) has a thickness 4. Pipework characterized by greater than 10 mm. According to one of the claims, the wall (2) has a thickness 1 or 2, Pipe part according to one of Claims 1 to 4, characterized in that the insertion neck (3) has at least one part with a circumferential receiving groove (6) for the inserted sealing ring (7) and the sealing chamber (8) and also the part is designed as a supporting arch. Method for forming an insertion sleeve on a pipe part according to one of Claims 1 to 5, in which the pipe part is heated to the softening range at the end at which the insertion neck is to be shaped, the end of the pipe part heated to the softening range is inserted into a mold. in which a heated mandrel is provided and which is unheated or cooled externally, wherein or thereafter the heated end is compressed pneumatically, hydraulically and / or mechanically with an extension towards the inner wall of the mold forming space, reducing the wall thickness of the pipe part in the region of the insertion throat, characterized in that the end of the pipe part extended to the width of the insertion throat differs from the mouth of the insertion throat as the wall thickness increases on the insertion throat geometry predetermined by the shape of the insertion throat and thereby is pressed against unheated or cooled inner wall of the molding space f and that the temperature of the heated mandrel is selected, taking into account the external temperature of the mold, such that a temperature in the melting range is set in the inner cross-sectional area of the male throat, which decreases to a temperature within the plasticizing range on the outer mold wall; the mold, as well as the cooling rate of the shaped male throat inside or outside the mold, is selected such that a high crystalline inner region is formed and a low crystalline cross-sectional outer region forms a crystalline supporting arch around the non-deformable support or reinforcement of the low crystalline region. under the occurrence of mechanical shrinkage stresses. Method according to claim 6, characterized in that the pipe part cooled after extrusion and calibration is heated to the softening range at the end at which the insertion neck is to be shaped. - / 3 - Method according to claim 6, characterized in that the end of the pipe part, which, after extrusion and calibration, still contains residual heat or intermediate heating, is inserted into the insertion throat mold. Method according to one of Claims 6 to 8, characterized in that the temperature of the heated mandrel maintains a temperature greater than 125 ° C inside the insertion throat and a temperature clearly below 125 ° C on the outside of the insertion throat. Method according to any one of Claims 6 to 9, characterized in that the residence time in minutes of the molded throat formed corresponds to approximately half the wall thickness in millimeters of the molded throat.