GB1574445A

GB1574445A - Process and apparatus for the manufacture of pipe bends of thermoplastic material

Info

Publication number: GB1574445A
Application number: GB1912/77A
Authority: GB
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1976-01-20
Filing date: 1977-01-18
Publication date: 1980-09-10
Also published as: NO770150L; SE7700524L; NL7700383A; CH617385A5; IN144926B; FR2338782B1; DD128268A5; AT365970B; FR2338782A1; AU2143477A; IT1077591B; ATA28077A; SE417799B; AU508830B2; FI770143A

Abstract

In the process a straight pipe piece is heated to thermoforming temperature. A core built up from thin steel lamina (1) is pushed into the heated pipe piece (7). The lamina can be held together at one end by a bush (2) provided with a cover (3) and a lug (4). The pipe piece is placed in the holding device (8) and bent about a bending piece (9) whose radius corresponds to the radius of curvature of the pipe bend. Then the core is pulled out of the pipe bend by means of the lug (4). The disadvantages of known processes are avoided in a cost-saving manner. <IMAGE>

Description

(54) PROCESS AND APPARATUS FOR THE MANUFACTURE OF PIPE BENDS OF THERMOPLASTIC MATERIAL (71) We, HOECHST AKENGSELL- SCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process and apparatus for the manufacture of pipe bends of thermoplastic materials.

Known processes for the manufacture of pipe bends start from sheets of plastics material; these sheets are shaped into shells of semi-circular cross section which are then welded together. The welded seam is often considered as a disadvantage, and this process is very complex and time consuming.

Other processes adapted from the metal working industry yield crinkle pipe bends or they are applicable to thermoplastic pipes having only a limited range of dimensions. Such processes involve, for example, hot bending of pipes after filling with sand and cold bending.

However, it has been found that, when using sand, sand particles adhere in the interior of the pipe bend and must be removed. In addition, filling and removing the sand are quite expensive. With cold bending, there is the disadvantage that the pipe legs do not retain the bending angle and that completed pipe lines incorporating them are under a bending stress.

It has also been proposed to bend pipes of plastics material over an elastic bending body 'which is provided with a locking groove for the pipe, and inserting, during bending, an elastic counter body, especially a coil spring, into the interior of the pipe (see Austrian Patent No. 222,875).

Furthermore, it has been proposed to bend pipes of large diameter and large wall thickness over a template, by filling the pipe with sand and carrying a steel band along the exterior of the pipe (see German Auslegeschrift No. 1,268,815).

It has also been proposed to bend pipes with the aid of an internal template and a fixed counter-template (see German Democratic Republic Patent No. 57,954).

Finally, there has been proposed in Specification No. 1237416 a bending process for pipes of thermoplastic material in which a pipe section closed at one end is heated and forced into a pipe bend mould by means of a pressure member acting against a flexible core comprising a multiplicity of longitudinal sections within the pipe section. The mould is formed in two parts to enable the pipe bend to be removed from it. This process is also very expensive, since a different mould must be used for each different pipe diameter and for each different type of bend.

The present invention is based on the observation that a pipe bend of thermoplastic materials can be manufactured by providing the straight length of pipe of circular cross-section with a flexible supporting core of appropriate circular cross-section and bending at the optimum theremoforming temperature around a curved template, the curved surface of which forms part of a right circular cylinder.

The present invention therefore provides a process for the manufacturing of a pipe bend which comprises heating a straight length of the pipe of circular cross-section of a thermoplastic material to a temperature in the optimum thermoforming range of the thermoplastic material, introducing into the interior of the pipe a supporting core of appropriate circular cross-section and consisting of a plurality of parallel flexible rods or lamellae which can slide against each other, and bending the pipe around a curved template the curved surface of which forms part of a right circular cylinder, the radius of which corresponds to the desired bending radius of the pipe bend.

The present invention also provides apparatus for the manufacture of a pipe bend of a thermoplastic material, comprising a suporting core of circular cross-section of radius equal to the internal radius of the pipe to be bent and consisting of a plurality of parallel flexible rods or lamellae which can slide against each other and, in combination, a clamp for securing one end of the pipe to be bent, a curved template the curved surface of which forms part of a right circular cylinder, the radius of which corresponds to the desired bending radius of the pipe bend, and means for applying a bending force to the free end of the pipe to bend the pipe around the template.

By "optimum thermo-forming temperature", there is to be understood the temperature range, which is desired in most thermo-forming processes, at which the plastics material gives way to the forming forces, but still has sufficient cohesion that it does not break under these forces. With some thermoplastic materials, this range is less distinct. Some plastic materials show a rubber-elastic behaviour or start to flow plastically at a temperature above the curing range; they may not be subjected to a thermo-forming process of the above kind.

Before insertion into the bending apparatus, the pipe length is heated to the optimum thermoforming temperature by an appropriate heating device, for example a circulating air furnace, electric heater or bath of heated liquid. Then the supporting core is inserted into the pipe.

The present invention will now be described in greater detail by way of example only with reference to the accompanying drawings, in which Figure 1 is a longitudinal section of a first form of supporting core for use in the process; Figure 2 is a cross-section along line A A of Figure 1; Figure 3 is a side view of a second form of supporting core; Figure 4 is a top view of a pipe during bending, using the supporting core of Figures 1 and 2; Figure 5 is a top view of one form of apparatus according to the invention; Figure 6 is a side view, partly in section, along line B-B of Figure 5; Figure 7 is a longitudinal section of a third form of suporting core; Figure 8 is a top view of the supporting core of Figure 7; and Figure 9 is a cross-section of the core of Figures 7 and 8.

Referring first to Figures 1 and 2 of the drawings, the supporting core consists of a plurality of lamellae 1 which can slide against each other and which are connected together at one end by a short length of pipe 2 of circular cross-section and a circular plate 3, which serve also as a stopper during insertion of the core into the length of pipe to be bent. In addition, the core is provided at this end with a device which facilitates extraction of the core from the bent pipe, for example an eye 4.

Figure 3 shows another method of connecting the individual lamellae, i.e. by a pin 5 and a shackle 6. The lamellae 1 may consist of thin metal strips or alternate metal and plastics strips.

The supporting core shown in Figures 7, 8 and 9 also consists of lamellae 1. To facilitate handling, the lamellae are held together by a length of tube 17 of circular cross-section which is movable along the lamellae. In order to remove the core more easily from the pipe bend, the lamellae are provided adjacent one end with a slot 16 into which a hook or similar device can be inserted. The size of this slot and its distance from the end of the lamellae depend on the nature of the material of the lamellae and its strength. In metal lamellae the hole may be larger and may be closer to the end of the lamellae, whereas with plastics lamellae it must be smaller and farther from the end of the lamellae.

It is preferred to manufacture the whole supporting core from plastics material, especially from a polyolefin. The thickness of the individual lamellae may be from 0.5 to 10 mm. With smaller nominal widths and with smaller bending radii, thinner lamellae are preferred. For the manufacture of pipes bends with small bending radii it is of advantage to replace the lamellae by flexible rods.

With references to Figure 4, the hot length of pipe 7 of circular cross-section provided with the supporting core is placed into the bending apparatus in such a manner that the end at which the lamellae of the core are fixed to one another is adjacent the holding device 8. The other end is bent by the application of pressure around a template 9, which is part of a right circular cylinder, the radius of which corresponds to the desired bending radius of the pipe bend. After the pipe bend has been allowed to cool in the bending apparatus, it is removed and the core is withdrawn. The pipe bend is utilizable immediately without further treatment.

The curved surface of the template forms part of a right circular cylinder. The template differs in this respect from the templates of conventional pipe bending mach- ines which have a groove with which the pipe mates in their curved surface, so that for each different pipe diameter there must be used a template having a groove of the appropriate size. In contrast, the template used according to the present invention can be used to bend pipes of virtually any diameter. The template may be a sector of a cylinder or a segment, depending on the magnitude of the bending radius of the pipe bend. With suitable guiding of the movable pipe leg, bending angles of up to 360" and more can be obtained.

Thermoplastic pipes which can be bent according to the present invention, are, for example, pipes of polyvinyl chloride, polyethylene and polypropylene. Especially suitable are pipes of low-pressure polyethylene and polypropylene.

The apparatus of the present invention is shown in Figures 5 and 6 and consists of a clamp 8 for the end of the pipe to be bent, a template 9 which is part of a cylinder, the radius of which corresponds to the desired bending radius of the pipe bend, and a pressing device 10 with which the movable end of the pipe is bent around the template. The clamp may consist of clamping jaws which are operated mechanically, pneumatically or hydraulically; however, especially for pipes having a nominal diameter of up to about 160 mm, it may consist of two simple rails between which the pipe leg to be clamped is inserted. The pressing device 10 may also be designed in different ways, for example a rail which can be rotated around a pivot at one end, a punch or a pressure roll which can move along the pipe leg to be moved.

The apparatus shown in Figures 5 and 6 is suitable for the manufacture of rectangular pipe bends having a nominal diameter of up to about 160 mm. On a plate 11, is arranged a clamp in the form of two parallel rails 8, 8'. Next to the clamp is a template 9 in the form of a quarter of a cylinder whose curved surface 12 is a continuation of the surface 13 of the rail 8.

The surface 12 in its turn is continued in the surface 14 of a rail 15 which is arranged at right angles to the rails 8 and 8'. The free leg of the pipe to be bent is pressed against the rail 15 by a rotatable rail 10 and is kept in this position until curing by a catch (not shown).

The bending apparatus described above consists entirely of low-pressure polyethylene. The apparatus may also be made of wood or of metal, for example in the case of pipes whose nominal diameter exceeds 160 mm. Combinations of all three materials are also possible.

According to the process of the present invention, there can be manufactured not only pipe bends having a small or large bending radius, but also pipes in which different bends follow one another, for example Utubes with straight lengths between the bends, siphon traps, extension bends, and the like.

WHAT WE CLAIM IS: 1. A process for the manufacture of a pipe bend which comprises heating a straight length of pipe of circular crosssection of a thermoplastic material to a temperature in the optimum thermoforming range of the thermoplastic material, introducing into the interior of the pipe a supporting core of appropriate circular crosssection and consisting of a plurality of parallel flexible rods or lamellae which can slide aganist each other, and bending the pipe around a curved template the curved surface of which forms part of a right circular cylinder the radius of which corresponds to the desired bending radius of the pipe bend.

2. A process as claimed in claim 1, wherein the lamellae of the supporting core are slotted adjacent one end of the core.

3. A process as claimed in claim 1 carried out substantially as hereinbefore described.

4. A pipe bend of a thermoplastic material whenever manufactured by a process as claimed in any one of claims 1 to 3.

5. Apparatus for the manufacture of a pipe bend of a thermoplastic material, comprising a supporting core of circular crosssection of radius equal to the internal radius of the pipe to be bent and consisting of a plurality of parallel flexible rods or lamellae which can slide against each other and, in combination, a clamp for securing one end of the pipe to be bent, a curved template the curved surface of which forms part of a right circular cylinder, the radius of which corresponds to the desired bending radius of the pipe bend, and means for applying a bending force to the free end of the pipe to bend the pipe around the template.

6. Apparatus as claimed in claim 5, substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. be used a template having a groove of the appropriate size. In contrast, the template used according to the present invention can be used to bend pipes of virtually any diameter. The template may be a sector of a cylinder or a segment, depending on the magnitude of the bending radius of the pipe bend. With suitable guiding of the movable pipe leg, bending angles of up to 360" and more can be obtained. Thermoplastic pipes which can be bent according to the present invention, are, for example, pipes of polyvinyl chloride, polyethylene and polypropylene. Especially suitable are pipes of low-pressure polyethylene and polypropylene. The apparatus of the present invention is shown in Figures 5 and 6 and consists of a clamp 8 for the end of the pipe to be bent, a template 9 which is part of a cylinder, the radius of which corresponds to the desired bending radius of the pipe bend, and a pressing device 10 with which the movable end of the pipe is bent around the template. The clamp may consist of clamping jaws which are operated mechanically, pneumatically or hydraulically; however, especially for pipes having a nominal diameter of up to about 160 mm, it may consist of two simple rails between which the pipe leg to be clamped is inserted. The pressing device 10 may also be designed in different ways, for example a rail which can be rotated around a pivot at one end, a punch or a pressure roll which can move along the pipe leg to be moved. The apparatus shown in Figures 5 and 6 is suitable for the manufacture of rectangular pipe bends having a nominal diameter of up to about 160 mm. On a plate 11, is arranged a clamp in the form of two parallel rails 8, 8'. Next to the clamp is a template 9 in the form of a quarter of a cylinder whose curved surface 12 is a continuation of the surface 13 of the rail 8. The surface 12 in its turn is continued in the surface 14 of a rail 15 which is arranged at right angles to the rails 8 and 8'. The free leg of the pipe to be bent is pressed against the rail 15 by a rotatable rail 10 and is kept in this position until curing by a catch (not shown). The bending apparatus described above consists entirely of low-pressure polyethylene. The apparatus may also be made of wood or of metal, for example in the case of pipes whose nominal diameter exceeds 160 mm. Combinations of all three materials are also possible. According to the process of the present invention, there can be manufactured not only pipe bends having a small or large bending radius, but also pipes in which different bends follow one another, for example Utubes with straight lengths between the bends, siphon traps, extension bends, and the like. WHAT WE CLAIM IS:

1. A process for the manufacture of a pipe bend which comprises heating a straight length of pipe of circular crosssection of a thermoplastic material to a temperature in the optimum thermoforming range of the thermoplastic material, introducing into the interior of the pipe a supporting core of appropriate circular crosssection and consisting of a plurality of parallel flexible rods or lamellae which can slide aganist each other, and bending the pipe around a curved template the curved surface of which forms part of a right circular cylinder the radius of which corresponds to the desired bending radius of the pipe bend.

6. Apparatus as claimed in claim 5, substantially as hereinbefore described.