A METHOD AND AN APPARATUS FOR THE PRODUCTION OF PIPES

Abstract: In the extrusion of plastic pipes, a circular mould cavity is formed of chill moulds (1, 2) which are semicircular in cross-section and the junction faces of which are pressed against each other. In order to keep the chill moulds tightly against each other, it is known to provide the edge area of the chill moulds (1, 2) with counter pieces (4) which have locking surfaces (5) whereon a press force is exerted by means of a rail of a U-shaped cross-section. In this known solution, great friction forces are created between the locking surfaces (5) and the rail, and the diameter of the mould increases in a direction perpendicular to the junction faces. These disadvantages are avoided in the present invention wherein the apparatus comprises locking means (6) which follow the movement of the chill moulds (1, 2) and grip the locking surfaces (5) of the chill moulds.

Description: A method and an apparatus for the production of pipes This invention relates to a method for the pro¬ duction of pipes, according to which method chill moulds positioned one after another are transported along two endless paths to be positioned against each other within a pipe moulding zone for the formation of a tubular mould, whereby said chill moulds transported along different paths are, adjacent to those edges thereof which are to be positioned against each other, provided with locking surfaces which are displaced at the forming stage of said tubular mould between locking means pressed against said locking surfaces, and at the latest at the disenabling stage of the mould away from between said locking means. The invention is also concerned with an apparatus for the production of pipes. German Offenlegungsschrift 1,203,940 discloses an apparatus for the extrusion of plastic pipes, in which semicircular chill moulds are pressed against each other by means of rolls which are pressed against the back sur¬ face of the chill moulds within the area of the symmetry plane thereof. In some constructions the press force can be adjusted by means of a spring load. The press force of the rolls thus acts perpendicularly to the junction face of the chill moulds. This known structure is very suitable for devices by means whereof plastic pipes having broad low ribs are manufactured, because the pressure of the plastic substance is typically below 1 bar in this kind of devices, and the chill moulds are therefore not exposed to any great forces which would tend to separate the chill moulds from each other. However, it is necessary to apply considerably higher operational pressures, typically about 30 bar and intermittently even 50 bar, when manufacturing pipes which have thin high ribs, for example, and which are made of a material of high viscosity. At such high pressures, chill moulds designed for low pressures are subjected to a transformation, whereby the radius of curvature of the chill moulds increases, i.e. the chill moulds get straighter, as a result of which the cross- section of the pipes deviates from a round form. For the prevention of this disadvantageous effect, the chill moulds of apparatuses using high pressures must be extremely massive, weighing typically 200 kg each. It is self-evident that the apparatus is thereby very heavy and expensive. A further problem of apparatuses having high opera- tional pressure is that high friction forces are often created between the chill moulds and means provided for the supportion thereof, which causes problems in the lubrication. E.g. in the apparatuses according to the abovementioned German Offenlegungsschrift, the shafts of the rolls would be exposed to an extremely high strain, wherefore their useful life would be short. Another known solution (German Offenlegungsschrift 1,233,128) comprises an assembly of locking rolls sup¬ ported on the outer surface of the chill moulds in the vicinity of those edges of the chill moulds which are to be pressed against each other. Fixed rolls having a V- shaped cross-section are provided adjacent the extruder beside the row of chill moulds. When the chill moulds are positioned against each other within the area of the pipe moulding zone, the rolls receive part of the forces caused by the pressure. At high pressures, a dis¬ advantage of this solution is the rapid wearing of the counter surfaces and the transmission of great locking forces to the frame structures of the apparatus. The application of the method is therefore limited to pipe production carried out at low pressures. The chill moulds cannot be aligned in the longitudinal direction by means of this method, and the same applies to the method described earlier. A problem with older apparatuses in particular is that one of the pair of chill mould chains tends to be left behind on account of the wearing of the operational clearances and the aligning studs provided between the chill moulds. As a result thereof the product obtained is unsatisfactory as the ribs positioned on different sides are partly out of alignment with respect to each other. The object of the present invention is to provide a method and an apparatus in which the shape of the chill moulds is maintained unchanged all the time and in which no friction occurs between the chill moulds and the supporting means pressing them' against each other. The method according to the invention is characterized in that said locking means are transported with said locking sur- faces within the pipe moulding zone. The friction between the locking surfaces and the locking means is wholly avoided when the locking means are transported with the locking surfaces as long as the chill moulds form a mould for the production of a pipe, by virtue whereof the durability of the apparatus is con¬ siderably increased, and the power demand is decreased. In addition, the lubrication, which has caused problems, becomes nearly unnecessary. The invention is also concerned with an apparatus for the production of pipes, comprising two endless paths; chill moulds positioned one after another to be trans¬ ported along said paths in such a manner that they are positioned against each other within a pipe moulding zone for the formation of a tubular mould; locking sur- faces provided on said chill moulds adjacent to those edges thereof which are to be positioned against each other; and locking means arranged to be pressed against said locking surfaces of the chill.moulds for pressing the chill moulds against each other within the moulding zone. The apparatus according to the invention is characterized in that said locking means are moveable in the direction of motion of the chill moulds so that they are displaceable with said locking means. According to one preferred embodiment of the apparatus according to the invention, the locking means are positioned one after another in two endless paths positioned in the plane of the junction face of the chill moulds. The locking means are thereby diplaced similarly as the chill moulds along endless paths which are posi¬ tioned in a plane extending perpendicularly to the plane of the chill mould paths. It is of advantage for the guiding of the locking means that the locking means are supported on a supporting rail within the area of the mould. According to one preferred embodiment of the invention, the apparatus is provided with a motor which is arranged to transport the locking means along the paths. When the locking means are transported forwards by means of the motor, an advantage is achieved in that the movements of the locking means and the chill moulds can be controlled accurately. Additionally, the locking means and the supporting surfaces of the chill moulds can be such in shape that the locking means press the chill moulds forwards so that the power demand of the main displacing chain of the chill moulds is decreased. In its simplest form, each of the locking means is formed by a material piece having an U-£>haped recess the side walls of which form a supporting surface arranged to be pressed against the locking surfaces of ■ the chill moulds. By virtue of the shape thereof, the material piece receives all opening forces exerted on the chill moulds, wherefore the friction between the piece and the supporting rail thereof is very low. The press force exerted on the locking surfaces of the chill moulds can be adjusted by a movement of the locking means in the radial direction of the chill moulds if the distance between the supporting surfaces increases towards the free edge of the side walls and if the locking surfaces of the chill moulds are substantially parallel to said supporting surfaces. The locking means are preferably formed as a locking piece having the length of the chill moulds and a U-shaped cross-section. The inventors have realized that the locking means, which exert a force on the edges of the chill moulds, are not alone able to wholly maintain the shape of the chill moulds, and therefore it is suggested according to the invention that besides the locking means, supporting means, known per se are arranged to be pressed against the sliding surface of the chill moulds in a direction perpendicular to the plane of the junction face of the chill moulds. By exposing the chill moulds to external forces both at the edges of the chill moulds and in the middle thereof, the semicircular shape of the chill moulds is maintained even at high pressures. One preferred embodiment of the invention will be described more closely below with reference to the attached drawing, wherein Figure 1 is a side view of the apparatus. Figure 2 is a section along the line II...II shown in Figure 1 , Figure 3 is a vertical section of the apparatus, Figure 4 illustrates a detail of a chill mould and the locking means, and Figure 5 is a cross-section along the line V...V shown in Figure 4. Figure 1 shows chill moulds 1 , 2 which are transported along two endless paths and which are semi¬ circular in cross-section so that a tubular mould, see Figure 3, is formed when they meet at the beginning of or before a pipe moulding zone. The pipe moulding zone means that portion of a pipe production apparatus in which the raw material is formed into a pipe and in which there usually prevails a high pressure. The outer sur¬ face of the chill moulds is provided with a sliding sur- face 3 which extends in parallel with the plane of the junction faces of the chill moulds and whereon a press force is exerted in a known manner to press the chill moulds against each other. Since the driving power and the control of the chill moulds 1 , 2 are effected in a conventional manner, these are not more closely discussed here. In order to effect the closing force of the chill moulds, a counter piece 4 is provided on the outer sur¬ face of the chill moulds close to the junction face, whereby said piece has the length of the chill mould and is provided with a locking surface 5 protruding from the outer surface of the chill mould and facing away from the junction face. According to the embodiment shown in the figures, the apparatus according to the invention comprises two endless paths along which locking means 6 having the same length as the chill moulds are displaced. Said means are formed by U-shaped locking pieces 6, the inner surface of the branches thereof forming a supporting surface 7 which is arranged to be pressed against the locking sur¬ faces 5. The locking pieces 6 are placed beside the extruder on a supporting rail 8 having a U-shaped cross-section to be transported thereon by means of rolls 9. One of the two locking piece paths is shown as a top view in Figure 2, while it appears from Figures 1 and 3 that the paths are positioned in the plane of the junction faces of the chill moulds. The locking piece paths can have their own source of driving power, whereby the locking pieces are displaced along the path by the driving power. Alternatively the locking pieces can be displaced freely along the paths. As appears from Figure 4 in particular, the supporting surfaces 7 of the locking pieces β are so formed that the distance therebetween increases towards the free end of the branches. The locking surface 5 of the counter pieces 4 is correspondingly at an angle with respect to the junction faces of the chill moulds. The surfaces 5 and 7 are preferably made parallel with each other. A wedge effect is thereby created between said surfaces, as a result whereof the force exerted on the locking surfaces 5 by the supporting surfaces 7 is adjustable by displacing the locking piece 6 in the radial direction of the chill moulds. In addition, radial forces, i.e. forces acting in the direction of the junction faces, can be exerted on the sides of the chill moulds by virtue of the position of the surfaces 5 and 7. As shown in Figures 4 and 5, the counter pieces 4 are provided with grooves 10 extending perpendicularly to the direction of motion of the pieces, and the locking pieces 6 are correspondingly provided with ribs 11 which fit the grooves for the alignment of the adjacent chill moulds 1 , 2 with respect to each other in the direction of the production line. The apparatus according to the invention operates as follows. When the chill moulds 1, 2 reach the pipe moulding zone to form a circular mould, the counter pieces 4, which protrude from the side of the chill moulds, are inserted in pairs into a space between the supporting surfaces 7 of the locking pieces 6, and are wedged in place therein. When the chill moulds are displaced forwards along the extruder, the locking pieces follow them, being displaced along the supporting rail 8 by means of the rolls 9. In order to maintain the proper shape thereof, the chill moulds are exposed to closing forces both through the sliding surfaces 3 and the locking sur- faces 5. The force exerted on the locking surfaces are perpendicular to the junction faces and possibly also parallelto the junction faces. All forces are preferably adjustable. By virtue of the structure according to the invention, no notable friction occurs between the chill moulds andthe locking means keeping them in position, onaccount whereof the power consumption of the apparatus is particularly low, and the structures can be light. The friction is especially low if no locking forces are exerted on the sliding surfaces 3 of the chill moulds, which is possible, too. After the chill moulds have passed by the pipe moulding zone, the locking pieces 6 are detached from the locking surfaces 5 of the chill moulds, as shown in Figure 2, so that the chill moulds are again able to separate from each other to follow the paths thereof. The locking means can be constructed in other ways, too. So it is possible to leave out the grooves and the ribs of the counter pieces and the locking pieces, respectively. The locking surfaces 5 can be provided on the chill moulds in some other ways than by means of pro¬ truding pieces 4, e.g. by forming a notch on the outer surface of the chill moulds, whereby one surface of the notch acts as a locking surface.

Claims: Claims 1. A method for the production of pipes, accord¬ ing to which method chill moulds (1, 2) positioned one 5 after another are transported along two endless paths Ho be positioned against each other within a pipe moulding zone for the formation of a tubular mould, whereby said chill moulds (1, 2) transported along different paths are, adjacent to those edges thereof which are 10 to be positioned against each other, provided with locking surfaces (5) which are displaced at the forming stage of the tubular mould between locking means (6) pressed against said locking surfaces, and at the latest at the disembling stage of the mould away from between T5 the locking means, c h a r a c t e r i z e d in that the locking means (6) are transported with the locking surfaces (5) within the pipe moulding zone. 2. An apparatus for the production of pipes, comprising two endless paths; chill moulds (1, 2) 20 positioned one after another to be transported along said paths in such a manner that they are positioned against each other within a pipe moulding zone for the formation of a tubular mould; locking surfaces (5) provided on the chill moulds (1, 2) adjacent to those 25 edges thereof which are to be positioned against each other; and locking means (6) arranged to be pressed against said locking surfaces (5) of the chill moulds for pressing the chill moulds against each other within the moulding zone, c h a r a c t e r i z e d in that 30 the locking means (6) are moveable in the direction of motion of the chill moulds (1, 2) so that they are dis- placeable with said locking surfaces (5) . 3. An apparatus according to claim 2, c h a r a c t e r i z e d in that the locking means (6) are positioned one after another in two endless paths which are positioned in the plane of the junction ■ face of the chill moulds (1, 2). 4. An apparatus according to claim 2, c h a r a c t e r i z e d in that the locking means (6) are supported on a supporting rail (8) within the area of the mould. 5. An apparatus according to claim 3, c h a r a c t e r i z e d in that the paths of the locking means (6) are provided with a motor which is arranged to transport said locking means along said paths. 6. An apparatus according to claim 2, c h a r a c t e r i z e d in that each one of the locking means (6) is formed by a material piece having a U-shaped recess the side walls of which form a supporting surface (7) which is arranged to be pressed against said locking surfaces (5) of the chill moulds. 7. An apparatus according to claim 6, c h a r a c t e r i z e d in that the distance between the supporting surfaces (7) increases towards the free edge of the side walls and the locking surfaces (5) of the chill moulds extend substantially in parallel with the supporting surfaces (7) . 8. An apparatus according to claim 6, c h a r a c t e r i z e d in that the locking means is formed as a locking piece (6) which has substantially the same length as a chill mould and a U-shaped cross- section. 9. An apparatus according to claim 6, c h a r a c t e r i z e d in that the locking surfaces (5) are situated on counter pieces (4) which are pro¬ vided with a groove (10) perpendicular to the direction of motion of the chill moulds (1, 2), said locking pieces (6) being provided with a rib (11) fitting said groove. 10. An apparatus according to claim 2, c h a r a c t e r i z e d in that, in addition to said locking means (6) , supporting means known per se are arranged to be pressed against the outer sur¬ face (3) of the chill moulds in a direction perpendi¬ cular to the plane of the junction face of the chill moulds.

Inventors: JAERVENKYLAE JYRI, SILLANPAEAE PAULI, JAERVENKYLAE, JYRI, SILLANPAEAE, PAULI
Applicants: UPONOR NV, UPONOR N.V.
Application year: 1987
Main classification: B29C47
IPC codes: B29C33