FIELD OF THE INVENTION

The present invention relates to corrugated pipe where at least some or all of the corrugation cavities are filled with foam.

BACKGROUND OF THE INVENTION

A method for the manufacture of corrugated pipe is disclosed in our earlier US Patent 6,399,002 and a further variation of a triple wall corrugated pipe is shown in US Patent 8,820,801.

Patent 6,399,002 discloses a manufacturing method for forming corrugated pipe and in a preferred embodiment a third outer wall is applied to a previously formed two wall corrugated pipe. Two wall corrugated pipes are commonly produced using extrusion equipment having two die outlets and a series of reciprocating mold blocks which move with the plastic pipe during the manufacture thereof. The mold blocks define the outer corrugated shape of the pipe and the mold blocks also assist in cooling of the molten plastic. An inner wall is typically immediately applied to the previously formed corrugated outer wall. The inner wall is of a tubular or cylindrical shape and provides a smooth interior wall of the pipe secured to the inner edge of the corrugated outer wall. Double wall spigots and double wall bellmouth connectors (sized to receive a spigot) are commonly used to couple one pipe section to another.

The outer corrugated wall improves or reinforces the inner wall providing good strength and durability particularly with respect to collapse or crushing of the pipe.

For many applications it is desirable to manufacture this type of pipe with a spigot at one end and a bellmouth or inline female connector at an opposite end of a pipe section forming a unitary construction that allows coupling of one pipe section to another pipe section. Typically a mechanical type seal is made by inserting the spigot of one pipe section into the bellmouth or female connector of a second pipe section.

The normal practice in the manufacture of two wall corrugated pipe is to use circulating mold blocks to shape the pipe during the extrusion thereof and at selective points form a coupling between two pipe sections where the coupling is integral or unitary with the pipe. This coupling includes the bellmouth connector and the separate spigot that are preferably one after the other between adjacent pipe sections when the pipe is manufactured. At a downstream position the coupling is cut to free the bellmouth connector from the spigot such that the spigot is attached to one section of pipe and the bellmouth connector is attached to the adjacent pipe section. Typically there is a transition portion of the pipe between the bellmouth connector and the spigot which is removed from the extruded pipe during the cutting of the bellmouth connector and the spigot.

Double wall corrugated pipe is relatively strong however for some applications it is desirable to provide additional strength and/or reduce sound transmission of fluid flowing through the pipe. The size of the corrugations and the wall thicknesses can be increased to provide additional strength but thicker wall sections can adversely affect the manufacturing speed and increase the material costs. Larger corrugations require different mold blocks and the capital cost may be higher. It is also known to use a vacuum tank and a sizing die to attach an outer tubular third wall to reinforce and increase the strength of the double wall corrugated pipe.

Both double and triple wall corrugated plastic pipe are relatively strong however the maximum rating of the pipe sections is often limited by the strength of the bellmouth or female connector and spigot coupling where a spigot of one pipe section is inserted in a bellmouth or female connector of another pipe section. The rated load for these couplings can significantly reduce the rated strength of the overall pipe.

It is therefore desirable for some applications to provide a high strength corrugated pipe and coupling that can be manufactured inline with the continuous manufacture of pipe.

In other applications, the strength of double wall or triple wall corrugated pipe is satisfactory however the transmission of fluid through the pipe may generate unwanted noise. In some applications such as heating or transmission systems improved thermal insulation properties are desired.

SUMMARY OF THE INVENTION

A corrugated plastic pipe according to the present invention comprises a smooth inner wall with a corrugated reinforcing wall secured to an exterior surface of the smooth inner wall and having a series of corrugations that reinforce the inner wall. The inner wall and the series of corrugations cooperate to define a series of spaced inner cavities that alternate with a series of outer cavities defined between adjacent corrugations. At least some of the series of inner cavities are filled with a foam to alter the characteristics of the corrugated plastic pipe.

According to an aspect of the invention, the adjacent inner cavities of the series of inner cavities include connecting channels joining adjacent cavities of the inner cavities, and wherein each connecting channel extends through and is closed with respect to one of the outer cavities. According to an aspect of the invention the corrugated plastic pipe includes a bell connector at one end thereof and a spigot of a size for insertion in the bell connector capable of forming a connection therewith. The spigot has an inner wall that forms a continuation of the inner wall of the corrugated pipe.

In an aspect of the invention, the spigot includes a reinforcing corrugated wall attached to the exterior of the inner wall of the spigot.

In a further aspect of the invention, the inner wall and the reinforcing corrugated wall of the spigot have a plurality of foam filled cavities defined between the reinforcing corrugated wall and the inner wall of the spigot.

According to an aspect of the invention the bell connector includes in cross section an inner wall sized to sleeve a received spigot of a similar pipe and a corrugated wall exterior to the inner wall of the bell connector.

In a preferred aspect of the invention, the series of connecting channels include a plurality of connecting channels connecting each pair of adjacent inner cavities with the plurality of adjacent inner cavities being distributed in a circumferential manner about the corrugated pipe. Preferably the series of connecting channels on opposite sides of a respective inner cavity are angularly offset with respect to a longitudinal axis of the reinforced corrugated pipe.

In a further aspect of the invention the corrugated pipe includes an outer wall connected to the corrugated reinforcing wall at a position closing the outer cavities to form a triple wall corrugated pipe. Preferably at least some of the outer cavities are filled with reinforcing foam. In a further aspect of the invention the series of outer cavities are interconnected by outer connecting channels that pass through the series of inner cavities.

In a further aspect of the triple wall corrugated pipe a bell connector is provided at one end of the corrugated plastic pipe and a spigot of a size for insertion in the bell connector is formed at an opposite end of the pipe. The spigot has an inner wall inline with and forming a continuation of the inner wall of the corrugated pipe. Preferably, the spigot includes a reinforcing corrugated wall attached to the exterior of the inner wall of the spigot defining cavities filled with a reinforcing file.

In an aspect of the invention, the bell connector includes in cross section an inner wall sized to sleeve a received spigot of a similar pipe, a corrugated wall exterior to the inner wall of the bell connector, and an exterior wall.

In an aspect of the invention, the series of connecting channels include a plurality of connecting channels connecting each pair of adjacent inner cavities with the plurality of connecting channels are distributed in a circumferential manner about the corrugated pipe.

In yet a further aspect of the invention, the series of outer connecting channels include a plurality of outer connecting channels for each outer cavity and the outer connecting channels are distributed in a circumferential manner about the corrugated pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawings, wherein: Figure 1 is a partial view of two pipe sections with one pipe section having a bellmouth connector and the other pipe section showing the spigot connection thereof;

Figure 2 is an assembled version of the two pipe sections of Figure 1 where the spigot of one pipe section has been inserted into and couples with the bellmouth connector of the second pipe connection;

Figure 3 is a partial perspective view showing the manufacture of the triple wall pipe with the inline connection prior to the cutting of the connector adjacent a middle portion thereof to form a pipe section with a spigot at one end and a different pipe section with a bellmouth connector at an end thereof;

Figure 4 is a partial view showing two pipe sections with the connection cut at two locations such that a disposable cut out portion is removed;

Figures 5 through 8 show a particular structure and method for forming of the triple wall corrugated pipe sections with a triple wall bell connection;

Figure 9 shows representative stiffness values for a two wall bell connection, a three wall bell connection and a bell and spigot assembly of a two wall and a three wall;

Figure 10 is a sectional view of an alternate corrugated foam filled pipe that additionally shows the structure for injecting of the foam into cavities of the corrugated pipe shortly after the manufacture thereof; and

Figure 11 is a sectional view through a corrugation showing the inner and outer walls of the pipe, the corrugated wall and connecting channels that connect the inner and outer cavities of the pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1 and 2 show two pipe sections 20 and 22 and a coupling 4 that includes a bellmouth connector 8 and spigot 6 used for coupling pipe sections on a job site. These pipe sections are cut from corrugated pipe 2 shown in Figure 3.

Figure 3 shows a portion of the corrugated pipe 2 after it has been manufactured and before cutting of the corrugated pipe to form individual pipe sections. The pipe sections 20 and 22 show details of the inline coupling 4 that includes both the bellmouth connector 8 and the spigot 6 where the spigot is designed to be received in a bellmouth connector 8 of a second pipe section. The bellmouth connector 8 as shown in the drawings as an "inline" connector as the maximum diameter of the bellmouth connector is the same as the maximum diameter of the corrugated pipe. It is also possible for the bellmouth connector and spigot to be of greater diameter than the maximum diameter of the remaining portion of the pipe section. This type of oversized connection is commonly used in clay pipes and can be used with this corrugated pipe.

The corrugated pipe 2 after the manufacture thereof is cut a number of times at a central position of the inline coupling 4. A chamfer cut 40 provides a tapered finished outer edge of the connecting sleeve 8 and separates pipe section 20 from the corrugated pipe. The spigot cut 42 is typically a straight cut through the pipe between corrugations to provide a double wall thickness edge at the end of the spigot 6. In light of the chamfer cut 40 and the spigot cut 42 a scrap portion 44 is removed and is recycled. In addition, a further sleeve wall cut 46 is made to allow removal of the outer sleeve wall portion 48 from over the spigot 6.

Figure 1 shows the resulting pipe sections 20 and 22 with the pipe section 20 having the bellmouth connector 8 at the end of the pipe section with pipe section 22 having the spigot 6. Pipe section 20 would have a spigot at the opposite end of this pipe section and similarly the pipe section 22 would have a bellmouth connector 8 at an opposite end (not shown) of the pipe section.

With the present arrangement the sealing walls of the spigot (i.e. the outside walls) and the inner wall of the bellmouth connector are formed as part of the initial double wall forming step. The additional outer reinforcing wall is applied afterwards to surfaces away from the bellmouth connector/spigot interface. This arrangement is preferred as the sealing surfaces of the coupling are better controlled and the surfaces primarily contributing to the fit of the spigot in the bellmouth connector are not directly part of the additional third wall.

It is possible to have an inline coupling 4 which is two bellmouth connectors and a further inline coupling which is two spigots, however this requires additional mold blocks and the inline coupling as shown in the drawings having a spigot and a bellmouth connector is preferred.

The manufacture of double wall corrugated pipe (i.e. with an inner wall 54 of the corrugated pipe and the spigot in combination with the corrugated wall 56 of the pipe sections and the corrugated wall 58 of the spigot) is known. In addition, having such a pipe section with the outer sleeve wall 10 secured to the outside of the corrugated wall 56 of the pipe sections is also known and provides additional strength as the corrugations are bridged or traversed on the inside and outside edges of the pipe section. It is also known in such triple wall pipe to remove the scrap outer sleeve wall portion 48 from over the spigot. The particular corrugated wall structure of the bellmouth connector 8 as shown in Figures 1 through 4 is new and has improved structural properties. Advantageously this bellmouth connector when used with the spigot 6 provides a coupling of increased strength. Further improvements in the structural properties of the pipe are possible by providing a foam fill in at least some of the cavities of double wall corrugated pipe and triple wall corrugated pipe. Selective filling of cavities in the spigot and/or bellmouth and/or cavities either side of these connection components can increase the structural characteristics in what is often a limiting region. Filling more cavities or all cavities of the pipe may also be desirable, particularly for improved thermal insulating properties and acoustic dampening properties. The outer cavity above the male spigot 6 is not filled with foam to allow the male/female connection to function in the normal manner.

Double or triple wall corrugated pipe has commonly been used for drainage applications where strength and durability are a high priority. The pipes are often buried and must distribute loads from above without crushing. The additional strength of adding foam is helpful for these applications but also opens other applications where high strength may not be needed. For example, pipes used in buildings may not need high strength but thermal insulating properties and/or acoustical dampening properties are more important. The addition of foam in the cavities can provide these properties and perhaps the amount of plastic forming the walls can be reduced. The foaming of cavities in a triple wall pipe protects the foam and the pipe can be manufactured economically.

The structure and method of forming triple wall corrugated pipe will initially be described followed by the foam filling steps shown in Figures 10 and 11. The bellmouth connector 8 includes an outwardly displaced inner wall 60, a corrugated sleeve wall 62 and the outer sleeve wall 10. Adding the corrugated wall 62 and providing the corrugations in a particular manner has a number of benefits. The initial benefit is additional strength of the bellmouth connector 8 and the overall coupling when a spigot 6 is inserted in a bellmouth connector 8.

In triple wall corrugated pipe the inner wall 54, the corrugations 56 and the outer sleeve wall 10 cooperate to form enclosed inner and outer cavities. The properties of the pipe can be modified in a desired manner by filling of some or all of the cavities with an appropriate foam material. The particular structure of the spigot in combination with the corrugated wall of the bellmouth connector 8 increases the strength of the coupling and thus the rating on the pipe sections can be increased. Furthermore the bellmouth connector 8 has additional rigidity and this rigidity is advantageous given that compressible seal members are typically provided on the spigot that engage both the spigot and the inside walls of the bellmouth connector 8 to form a seal. Such a compression seal is maintained by the bellmouth connector 8 resisting outward movement and the spigot resisting inward movement.

The previous practice of a double wall non-corrugated bellmouth connector and even a triple wall non-corrugated bellmouth connector fails to provide the higher strength of the corrugated wall bellmouth connector and spigot coupling as shown in the drawings and as described in the application (assuming similar amounts of material).

It has been found that the coupling of two pipe sections as shown in Figure 2, where the bellmouth connector 8 has a corrugated wall significantly improves structural integrity and strength. The relative strength of the prior art as well as the present combination is shown in relative terms in Figure 9.

It has further been found that the foam filling of cavities of the double or triple wall corrugated pipe can further improve the product. In some applications only some of the cavities may be filled. For improved thermal insulating and/or acoustic dampening properties all of the cavities are preferably filled. Although it is preferred to include connectors formed with the pipe these need not be the case. Foam filling of inner and/or outer cavities of the corrugated pipe is also a practical embodiment of the invention.

As shown in Figures 1 and 2 the corrugated spigot 6 and the bellmouth connector 8 have a particular configuration and shape. The first corrugation 202 and the second corrugation 204 of the spigot each include a valley 206 and 208, respectively, that preferably receive a compressible ^λ 0' ring seal. These valleys 206, 208 are opposite the inwardly extending shallow corrugations 210, 212 of the bellmouth connector when the spigot is coupled to a bellmouth connector as shown in Figure 2. These corrugations 210, 212 provide an extended sealing surface as well as a reinforced sealing surface opposite the valleys for receiving the 0' ring seals. A smaller same depth corrugation is provided between corrugations 210, 212 and provides additional stiffness. The width of corrugations 210, 212 is three to four times greater than the width of corrugation 214.

Different sealing arrangements can be used for example some installers prefer to use one or more larger 0' rings located between corrugations. For some applications a single 0' ring in one of the valleys is sufficient. The free end 216 of the bellmouth connector includes a series of corrugations 218 similar to corrugator 214 and provides a stiff open end section.

The spigot includes an inner corrugation 220 that is opposite and cooperates with the series of corrugations 218.

Figures 5 through 8 illustrate the apparatus used to apply the outer sleeve wall to a previously formed two wall corrugated pipe. The die tooling 100 includes a die outlet 102 for applying the outer sleeve wall to the corrugated pipe and also includes an air pressure outlet 104. The air pressure outlet includes an air pressure channel 106 connected to a variable air pressure supply 108. In addition, the die tooling 100 includes an associated sealing arrangement 110 (applied around the pipe) that allows the die tooling and the previously formed corrugated pipe to form a chamber therebetween allowing the pressure of the chamber to be varied during the application of the outer sleeve wall to the previously formed corrugated pipe. The die tooling 100 is preferably of a length longer than the connecting sleeve 8 of the corrugated pipe to simplify sealing.

In Figure 5, the outer sleeve wall 10 is applied to and across the large corrugations of the pipe as the corrugated pipe is moved through the die tooling and through the vacuum tank and sizing bushing. The vacuum tank 120 is closed on an interior surface by the sizing bushing 122. The sizing bushing has a series of parts allowing a vacuum source to be applied to the extruded outer sleeve wall and to also assure contact of the outer sleeve wall with the corrugations. It can be seen that the space between corrugations of the pipe is subject to the air pressure that is established by the variable air pressure source 108, and this allows positive air pressure to' be introduced pressurizing the cavities between corrugations. This arrangement reduces thermal deformation (inward deflection) that occurs when the triple wall pipe is cooled. By pressurizing the cavities before the outer sleeve wall is applied, the sealed cavities and in particular the outer sleeve wall undergoes less deformation that otherwise would occur due to the cooling of the pipe after forming. By increasing the pressure, the amount of thermal deformation is decreased.

In Figure 6 it can be seen that the previously formed double wall corrugated pipe moves past the die outlet 102 and sleeve wall 10 is applied to the previously formed corrugated wall of the sleeve. Given that the corrugated sleeve wall 62 is close to the die outlet 102 the pressure is less important but it is generally maintained at the pressure for forming at the corrugations as shown in Figure 5.

It can also be seen in Figures 5, 6 and 7 that the seal arrangement 110 engages the corrugations of the pipe as the pipe is moved therepast. This allows control of the pressure with respect to the space interior to the die tooling 100. This seal limits or blocks off atmospheric pressure. In Figure 7 it can be seen that the connecting sleeve 8 is about to move past the die outlet 102 and the connecting wall 10 or the plastic coming out of the die outlet will be over the spigot portion of the inline connector. This can be appreciated from a review of Figures 7 and 8.

In Figure 8, the spigot is below the die outlet 102 and it is desirable to maintain the connecting wall against the sizing bushing 122 and away from the corrugations of the spigot. This portion of the outer wall will be cut away in a subsequent downstream step and therefore controlling of the plastic such that it does not adhere to or come into contact with the corrugations of the spigot is highly desirable. Basically the corrugations of the spigot can be accurately formed by the mold blocks in the upstream forming process and these cooperate with the interior accurate surface of the connecting sleeve to allow for connection between pipes and is not affected by the outer sleeve wall.

It has been found that it is desirable to reduce the pressure provided through the air pressure outlet 104 when the connecting wall is over the corrugations of the spigot.

The air pressure provided to the cavity of the die tooling 100 will again be increased as the next row of full corrugations of the pipe section move past the die outlet.

It has been found that this arrangement for controlling of the outer sleeve wall during the attachment to the large corrugations of the pipe and to the outside of the corrugated connecting sleeve is beneficial. In addition, maintaining this outer sleeve wall away from the corrugations of the spigot also simplifies the subsequent cutting steps.

The outer sleeve wall over the spigot is maintained out of contact with the spigot and is subsequently removed. It is also possible to divert the extruded plastic using a sliding bypass valve whereby the plastic is removed during the extrusion process.

Figure 9 shows a relative strength comparison of a pipe connector of the same wall thickness when made as a two wall corrugated pipe, the triple wall connector and the preferred arrangement where the connecting sleeve is a triple wall corrugated bellmouth connector.

The embodiment of the invention shown in Figures 10 and 11 and is directed to the partial or complete foam filling of the corrugated pipe 202 which is similar to the triple wall corrugated pipe of the earlier Figures. The foam filled corrugated pipe 202 as shown in Figure 10 has an inline connector 204 made up of the corrugated spigot 206 and the corrugated bellmouth connector 208. As in the earlier embodiment, the particular triple wall corrugated foam filled pipe 202 preferably includes an outer wall 210 which forms the outer wall of both the corrugated pipe as well as the outer wall of the connecting sleeve 208. A portion of the outer wall over the spigot will be removed in a subsequent manufacturing step to allow the spigot 206 to be received in the corrugated bellmouth connector 208 of a similar pipe.

During the manufacture of the triple wall corrugated pipe, the piercing/injection station 240 injects foam for filling some or all of the series of inner cavities 220 and the series of outer cavities 222. Both the inner and outer cavities are partially defined by the corrugated wall 256 that alternately attaches to the outer wall 210 and the inner wall 254 of the pipe 202. The outer cavities 222 are connected to one another by the outer channel connectors 228 which extend through the inner cavities 220. The inner cavities 220 are connected by the inner channel connectors 226.

The corrugations 248 also include cavities 250 that are interconnected by the spigot channel connectors 252. The various channel connectors 226, 228, and 252 allow foam to expand into and fill adjacent cavities and simplify the foam filling of the various cavities. The channel connectors are typically positioned at a series of spaced circumferential positions of the pipe as shown in Figure 11 and are preferably offset such that the inner channel connectors 226 are not radially aligned with the outer channel connectors 228.

The addition of foam to some or all of the cavities can significantly change the pipe. For example, appropriate filling of cavities of the pipe coupling and cavities adjacent thereto can improve structural integrity, acoustical and/or thermal properties. Filling of all cavities (or most cavities) may be used to significantly improve noise dampening properties caused by fluid movement through the pipes or improving thermal insulating properties. Selective filling of cavities provides a further tool for providing particular properties where required for example in a particular location where higher forces may be incurred.

In general triple wall corrugated pipe gains additional strength due to the corrugations extending between and being connected to the inner and outer walls. By offsetting and limiting the size of the inner and outer channel connectors the additional strength obtained by the corrugated wall is maintained. The subsequent filling of the cavities between the corrugated wall and the inner and outer walls together may additionally strengthen the pipe with respect to inward deformation or alternatively impart improved thermal insulating and/or acoustical dampening properties. The foaming of cavities significantly dampens sound transmission through the pipes and increases thermal insulating properties. This is advantageous in many building applications.

The injection station 240 is shown as having an inner piercing injection arrangement 236 and an outer piercing injection structure 234. Typically the pipe will be pierced at a number of points to simplify the injection of foam or a foaming agent into the various cavities. The distribution of the foam within the cavities and between the cavities is further improved by the various inner and outer channel connectors 226 and 228 which are also filled. Depending upon the diameter of the pipe and other manufacturing parameters (such as speed), the number of injection stations can significantly vary. The arrangement has also been shown as being on the inside and the outside. It is possible to merely use an outside piercing and injection station given that both the inner and outer cavities essentially extend to the outer wall 210 of the pipe. The addition of the injection station and the selective foam filling of cavities expands the use of the pipe molding tooling .

The inline connector 204 shown in the drawings includes the spigot 206 and the corrugated bellmouth connector 208 need not be limited to an inline connector where the diameter of the bellmouth connector sleeve is the same as the diameter of the corrugated pipe. This inline arrangement is preferred as it simplifies the installation of the pipe, however the traditional approach of a bellmouth connector of oversized diameter can also be used. This traditional arrangement where the female connector is oversized relative to the pipe diameter requires additional care with respect to installation. Therefore the installation of such a traditional connector requires more care during initial placement as well as perhaps in backfilling.

The additional strength or enhancement of other properties possible by foam filling the generally closed cavities or the corrugated pipe, is also preferably used to fill the cavities 250 of the corrugated spigot 248. The cavities 250 of the spigot are in communication with each other via the spigot channel connectors 252. Preferably the inner wall of the spigot shown as 254 is in line with and the same diameter as the inner wall of the long intermediate pipe section. Therefore with respect to the spigot, improved structural characteristics of the spigot can be realized by foam filling of the cavities 250 thereof. The area exterior to these cavities is not foamed.

The corrugated bellmouth connector 208 includes the series of inner sleeve cavities 266 and the series of outer sleeve cavities 268 defined by the corrugated sleeve wall 262 that alternately connects with the outwardly displaced inner wall 260 of the bellmouth connector and the outer wall of the pipe 210. The inner and outer sleeve cavities 266 and 268 are interconnected by the sleeve channel connectors 270. The bellmouth connector cavities are of much smaller volume and require less foam. The sleeve channel connectors 270 simplify the foaming of the individual cavities as foam can move between cavities during the injection process. Both the spigot channel connectors 252 and the sleeve channel connectors 270 are selectively placed at various positions about the circumference of these components.

In- the case of an over diameter bellmouth the internal cavities of the bellmouth can be enlarged to allow for higher volumes of foam helpful in increasing thermal insulating properties and/or acoustic dampening properties.

It has been found that the foaming of the cavities associated with both the corrugated pipe, the male connector shown in the preferred embodiment as a corrugated spigot and the corrugated bellmouth connector (connecting sleeve) improves the thermal insulating properties and/or the acoustic dampening properties of the corrugated pipe and/or the strength of the pipe. Preferably, the bellmouth connector or alternate female connector is the same diameter as the pipe. Furthermore, the selection of the injection foam material can be made to enhance one or more of these properties. In particular, improved acoustical dampening qualities can be achieved by foaming of the cavities and is advantageous in drainage pipes where noise transmission produced by the flow of water or liquid through the pipes is to be minimized or reduced. By foaming of the cavities of the pipe, improved acoustical dampening properties of the pipe are realized as well as thermal insulating properties. In some applications the thermal insulating and/or acoustic properties are of a high priority.

The foam filling of cavities has been described with respect to triple wall pipe but also can be used for double wall corrugated pipe. Furthermore in some applications only selected cavities may be filled where additional strength or changes in properties is desired. For example cavities in the spigot and cavities either side of or part of the pipe connection components can strengthen the pipe connection, bringing it to a level appropriate in comparison to the remaining portions of the pipe. Filling of only some of the cavities of the spigot may also be desired.

Various arrangements for foam filling of the cavities have been schematically shown and it is preferred that the walls of the pipe be pierced after the initial manufacturing thereof and the foam injected as the pipe moves away from the forming equipment. Cavities exterior to the outer wall of the spigot connector are not filled. This reduces secondary processing of the pipe and is cost effective. Selective piercing of the various corrugations to gain access to the cavities can be accomplished from the inside or the outside of the pipe or both. It is preferred to provide piercing from the outside as access is more easily obtained and the corrugations essentially extend to the outer wall such that the inner and outer cavities are both accessible at the outer wall. Connecting channels between these cavities further simplifies the foaming of the cavities without any significant reduction in the ultimate strength of the pipe. These connecting channels can reduce the number of piercing points and balance the injection fill and venting associated with the foaming of the cavities. The foaming of the cavities significantly improves the structural, acoustical and insulating properties of the product. The piercing of foaming station can be used with existing systems for producing new products and also higher strength products or products having improved acoustic or thermal insulating properties. In this way improved utilization and/or more specialized products can be produced.

Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art that variations may be made thereto without departing from the invention as defined in the appended claims .