FIELD OF THE INVENTION

The present invention relates to relining of underground conduits such as storm water and sewerage pipes and its particular to plastic welding within underground conduits.

BACKGROUND

Many techniques are currently used for relining underground conduits. One method of relining conduits involves the digging of a "launch trench" into which lengths of new pipe are lowered. The pipe lengths are then slid into the host pipe and are joined together to form a continuous new pipe. Generally with this method, the conduit being relined must be dry. This is often achieved by "over pumping" (pumping the water, sewerage or other fluid above the surface so that it bypasses sections of the conduit being relined).

Methods that require "over pumping" are undesirable due to the cost and complexities involved with the over pumping process.

Another method of relining underground conduits involves placing a pipe winding machine into an access pit and then feeding an elongate plastic strip into the pit. The machine then winds the strip into an elongate helical pipe. The applicant has developed various machines and methods for winding such a helical pipe. Some of these methods do not require "over pumping" and can be carried out while a conduit being relined is in service.

In some applications, it is desirable to provide a fully welded pipe. Fully welded, or continuously welded pipes, are watertight. With such applications, it is necessary to pre-heat the plastic strip to achieve a satisfactory weld. Pre-heating is typically achieved by directing a hot air stream onto the plastic strip. Providing a high volume of high temperature air to the strip in situ underground is difficult, particularly when the distance between ground-level and the underground winding machine is large.

It is an object of the present invention to provide an improved method and apparatus that addresses or ameliorates the aforementioned problems or at least offers a useful choice. SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a plastic strip pre-heating assembly for facilitating plastic welding at a location underground, the pre-heating assembly mountable to an underground pipe winding machine, the pre-heating assembly including:

a multi-stage air heater including a first heating stage powered by compressed air and a second heating stage powered by electricity; and

a nozzle for directing heated air from the multi-stage air heater onto the plastic strip, wherein, in use, the pre-heating assembly receives compressed air via a flexible hose connected to the first heating stage and electricity via a cable connected to the second heating stage.

In one form the first heating stage includes a primary heater having a vortex generator.

In one form the second heating stage includes a secondary heater including:

a solid-to-air heat exchanger having a heat exchanger body;

and an electrical heater for heating the heat exchanger body.

In one form the heat exchanger body is shaped to provide an elongate annular space between a core and an outer body, in use, the core and the outer body transmitting heat to air passing through the annular space.

According to a second aspect of the invention there is provided a pipe winding machine for helically winding pipes from strips underground, the machine including:

a frame, the frame positionable within an underground conduit;

an multi-stage air heater mounted to the frame, the multi-stage air heater including a first heating stage powered by compressed air and a second heating stage powered by electricity; and a nozzle for directing heated air from the multi-stage air heater onto the plastic strip, wherein, in use, the pipe winding machine receives compressed air via a flexible hose connected to the first heating stage and electricity via a cable connected to the second heating stage.

According to a third aspect of the invention there is provided an machine for lining an underground conduit, the apparatus including:

an annular frame;

a strip guide disposed around and supported by the annular frame, the guide arranged to guide a strip around a helical path when the machine is in use, a drive assembly mounted to the frame for driving the strip downwards into the helical path in a winding direction so as to present an incoming first edge to an adjacent second edge of a wound convolution of the strip;

an extruder mounted to the frame, the extruder having a nozzle in use extruding a molten bead of plastic onto the incoming first edge at a bead landing position;

a multi-stage air heater including a first heating stage powered by compressed air and a second heating stage powered by electricity, the multi-stage heater for generating heated air; and

a nozzle for directing the heated air onto the plastic strip at a location adjacent the bead landing position.

In one form the machine includes a cleansing nozzle mounted to the annular frame, the cleansing nozzle arranged to assist with removal of water and or debris that may otherwise travel towards the plastic strip at a location adjacent to the position just before the overlap.

In one form the machine includes a connector for receiving a single compressed air line extending from above ground, the connector arranged to feed compressed air to both the first heating stage and the cleansing nozzle.

According to a fourth aspect of the invention there is provided a method of pre-heating a plastic strip to facilitate plastic welding at a location underground, the method including the steps of:

delivering compressed air from an air compressor remote from the location underground to a multi-stage heater;

delivering electrical power from a power supply remote from the location underground to a multi-stage air heater;

transforming, within the multi-stage air heater, cold air delivered from the compressor to hot air; and

directing the hot air onto the plastic strip.

Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying Figures. These embodiments are illustrative, and are not meant to be restrictive of the scope of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the invention is illustrated in the accompanying representations in which: Figure 1 shows a schematic cross sectional view of an underground conduit being relined using a method according to the invention.

Figure 2 is a schematic cross sectional view showing a method and apparatus that forms part of the background art.

Figure 3 a is a schematic cross sectional view showing a method and apparatus according to the invention.

Figure 3b is a perspective view of the pipe winding machine schematically illustrated in Figure 3a. Figure 3c is a similar schematic cross sectional view to that of figure 3a, but shows a shared compressed air supply arrangement.

Figure 4 is a view of the apparatus showing Figure 3a and b showing the relative positions of a weld bead and a nozzle for delevering heated air.

Figure 5 is a sectional view of a multi-stage heater acording to the invention.

Figure 5a is a cross sectional view through section lines 5a-5a of Figure 5.

Figure 6 is a magnified view of a portion of a first stage of the multi-stage heater of Figure 5.

Figure 7 shows a component of the assembly shown in Figure 6.

Figure 8a is a perspective view showing the apparatus from the invention in use delvering a weld bead. Figure 8b is a similar view to Figure 8a but also shows aditional components of a winding machine according to the invention.

Figure 9 shows a cross sectional view of a plastic composite strip (profile) used in the method and apparatus of the invention.

Figure 10 is a perspective view of a pipe produced by the method illustrated in the preceding Figures.

Referring to Figure 1 , a pipe winding apparatus 10 is shown in position within an access pit 3 adjoining a conduit 5 to be relined. The pipe winding apparatus 10 has an annular frame 40 through which liquid can flow. Thus, the conduit or pipe 5 can be rehabilitated while in service (carrying storm water or sewage for instance).

A spool 200 (illustrated schematically) positioned above ground feeds the pipe winding apparatus 10 with an elongate plastic or plastic composite strip 12 down into the pit 3. Various strips or profiles can be used. Figure 9 shows a cross sectional view of two adjacent convolutions of a composite strip that is suitable for use with the method and apparatus of the invention. Other composite strips as described in the applicant's earlier International Application PCT/AU2006/000474 and/or PCT/AU2007/001463 may also be suitable for use with the method and apparatus of the invention. A compressor 58 and a power supply 31 , also positioned aboveground, provide compressed air via a compressed line 92 and power via cables 32 and 34 to the underground pipe winding apparatus 10.

Referring now to Figure 2, a previous used (background art) arrangement is shown schematically. With this arrangement, a conduit 94 delivers hot gas from an above-ground air heater down to a pair of nozzles 97. Typically insulation around conduit 94 includes thermal blankets or other insulating material as indicated by item 94'. Even with insulation, significant heat loss occurs in transmitting air from above-ground to the nozzles 97 illustrated in Figure 2. Furthermore, insulation 94' around conduit 94 adds bulk and complexity to the machine and its operation.

Returning to Figure 3a, a pipe winding machine 10 according to the invention is shown. The machine includes a frame 40 (such as shown in figure 3b), the frame 40 positioned within an underground conduit 5. A pre-heating assembly 20 is mounted to the frame 40.

The apparatus 10 also includes a plurality of substantially parallel spaced apart rollers 41 disposed around and supported by the annular frame 40. The rollers 41 form a guide to the strip 12 around helically path when the machine is in use. The path has a zenith adjacent the crown portion 42 of the annular frame 40. A welding assembly 90 is shown in dotted outline in Figure 3b. The welding assembly 90 includes an extruder 80 and a preheating assembly 20.

Turing now to Figures 4 and 5 the pre-heating assembly 20 is shown in more detail. The pre-heating assembly 20 includes a first heating stage 50 and a second heating stage 150. The first heating stage 50, or pre heater 50 is powered by compressed air and the second heating stage 150 is powered by. electricity. Preferably AC or DC electricity is provided at relatively low voltage (for example 50volts) for safety via power cables 32 and 34 from a surface mounted power supply 31.

Referring now to Figure 5, it can be seen that the first heating stage includes a primary heater 50 having a vortex generator 130. The vortex generator 130 includes a vortex generator insert 135. Compressed air 60 is delivered from a surface mounted compressor 58 via a compressed air line 92 or a compressed air hose 92 as can be seen in Figures 1 and 5.

The path of the compressed air 60 into the vortex generator 130 as shown in Figure 5 can been seen more clearly in Figure 6. A vortex generator insert 135 has a plurality of angled channels 137 that direct the compressed air tangentially into a swirl chamber 139 A cooled air stream 64 and a hot air stream 62 is produced as is indicated by arrows 64 and 62 respectfully in Figure 6. The cooled air stream 64 can either be exhausted, preferably through a silencer to reduce noise, or alternatively can be used for other purposes.

Pre-heated air 62 enters a second heating stage 150 that is powered by electricity. As Figure 5 shows, pre-heated air 62 enters the secondary heating stage 150 through a conduit in the form of an elbow 151.

The secondary heating stage has a secondary heater 150 comprising a solid-to-air heat exchanger body 154 and an electrical heater 30 for heating the air heater exchanger body 154. The electrical heater 30 is a 900 watt heater band. The air heater exchanger body 154 is shaped to provide an elongate annular space 155 between a core 156 and an outer body 153 as is best shown in Figure 5a. Pre-heated air swirls around within the elongate annular space 155 as is illustrated by arrows 65 at the same time picking up heat from the heat exchanger body 154. By the time the air exits the secondary heater 150 at the secondary heater outlet 159, it is at a temperature of approximately 250 to 300 degrees Celsius. It is then guided to a position adjacent to a weld zone by a conduit 94 to a nozzle 95 as is shown in Figure 5.

A cleansing nozzle 99 is mounted to the frame 40 and is arranged to direct gas (in this embodiment, air) in a direction across and having components towards the zenith of the strip path and against the winding direction of the strip 12. The cleansing nozzle 99 prevents the water and debris (accretions) 9 illustrated in Figure 3a from travelling down towards the welding area.

Figure 3c shows a similar schematic cross sectional view to that of Figure 3a, but shows a shared compressed air supply arrangement where a single compressed air line 96 feeds compressed air to a line 92 for the vortex heater and to a line 98 for the cleansing nozzle 99.

Optionally, a single compressed air line may be used with cool exhaust air 64 from the pre-heater 50 supplying cleansing nozzle 99 Gases other than air may be suitable in some applications.

Various other means can be employed to prevent accretions travelling down towards the welding area. Some of these alternative means are shown in the applicant's earlier application

PCT/AU2006/000474. The winding apparatus shown in Figures 3a and 8b is driven by a hydraulic motor 60 (not shown). The hydraulic motor 60 is able to operate in harsh conditions and provides a high torque output to drive the strip 12 around the inside of the rollers 41.

Referring to Figure 3a, an extruder 80 forms part of the apparatus 10. The extruder 80 is fed with plastic pellets through a supply tube 82. The extruder 80 has a nozzle 85 that applies a molten bead of plastic to the incoming first edge 16 as is most clearly shown in Figure 4, 8a and 8b.

Polyethylene plastic can be used for both the strip 12 and as the feed stock for the extruder 80.

Polyethylene is a low cost plastic that has excellent chemical properties making it highly suitable for rehabilitating pipes. While it lacks the stiffness of PVC, when combined with a reinforcing strip such as the strip 30 illustrated in Figure 9, a stiff pipe can be wound. While the method of the invention is particularly suitable for polyethylene pipes, other plastics may be used.

After the molten bead of plastic has been applied to the incoming first edge 16, the bead is compressed between the incoming first edge 16 and the adjacent second edge 18 between a pinch roll assembly of primary drive assembly 70 having opposed rollers 71 and 72. Figure 9 shows the resultant welded seam 19. As this is a continuous process, a continuous weld is created.

While in the drawings the bead is shown being applied to the incoming first edge 16, in other embodiments of the invention, the bead may be applied to the adjacent second edge.

Referring to Figures 3a and 4, it can be seen that conduit 94 carries hot air towards the nozzle 95. The hot air exiting nozzles 95 and 97 preheats and dries the edges of the strip 12 to facilitate the welding process.

The apparatus described and illustrated in Figures 3a and 3b can be used to line an underground conduit while the conduit is in service carrying a liquid. Once the pipe winding apparatus has been positioned within an access pit adjoining the conduit to be relined, it is fed with an elongate plastic or plastic composite strip 12 down through an access pit 3 as is illustrated most clearly in Figure 1. The strip 12 is driven downwards into the cylindrical cage 40' so as to present an incoming first edge 16 to an adjacent second edge 18 of a wound convolution of the strip 12. The high velocity air directed from nozzle 99 prevents liquid and/or other accretions that have adhered to the second edge 18 from descending down towards the incoming first edge 16. Hot air from the pre-heating assembly 20 is directed to both the incoming first edge 16 and the adjacent second edge 18 in order to heat the edges before a molten beaded plastic is applied to either one of the incoming first edge 16 or adjacent second edge 18 and before compressing the bead between the incoming first edge 16 and the adjacent second edge 18.

The actual pipe 100 wound by either of the above-described methods is illustrated in the perspective view of Figure 10. This pipe is a continuously welded pipe that provides a watertight conduit of high integrity.

While the present invention has been described in terms of preferred embodiments, in order to facilitate a better understanding of the invention, it should be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope.