Channelled plastic pipe with channel ends closed and method of producing the same.

The present invention relates to a channeled plastic pipe having a number of air channels continuously axially extending through the wall thereof and particularly to such a pipe wherein at least one of the respective ends of said air channels are closed and the inner and outer surfaces of the closed region are finished as smooth surface, and to a method of producing the same.

Description of the Prior Art

There has heretofore been proposed a channeled pipe having a number of air channels continuously axially extending through the wall thereof as a means for saving raw material and increasing the flattening rigidity of the pipe. Particularly, channeled plastic pipes, such as are made of rigid polyvinyl chloride, can stand comparison with ordinary, non-channeled plastic pipes in regard to the surface conditions and basic physical properties, e.g., tensile strength. Thus, the technique for production of channeled plastic pipes has been established.

Because of their high flattening rigidity, such channeled plastic pipes are utilized as underground sewage pipes, in which case the manner of connecting them together is, e.g., as illustrated in Fig. 1. The lefthand end of each pipe 1 is a socket end la increased in diameter by being subjected to secondary processing and the right-hand end is a spigot end lb not subjected to secondary processing. Thus, these pipes are of the so- called socket-spigot type. Therefore, a continuous line .of pipe can be formed by inserting the spigot end lb of each pipe 1 into the socket end la of the adjacent pipe 1 at its right, and it is buried in the ground. 2. Fig. '2 is an enlarged section showing details of the socket-spigot joint. Air channels ld continuously axially extend through the pipe wall. In addition, the line III-III section is shown in Fig. 3(A) and (B), the former referring to an oval (in cross-section) pipe lA and the latter to a round (in cross-section) pipe 1B. In each case, a number of air channels ld are formed in the pipe wall. Besides these cross-sectional shapes, there are many others, each presenting similar problems. Thus, if the pipeline is buried in the ground in the illustrated condition, rainwater, underground water or the like may flow in, as indicated by an arrow P, through the air channels ld and out at the spigot end, as indicated by an arrow Q, into the pipeline or the water flowing through the pipeline may leak out through the air channels in the reverse direction. In such channeled plastic pipes, it becomes necessary to close the air channels ld at the socket or spigot ends thereof. In addition, the socket end shown in Figs. 1 and 2 has a first diameter-increased portion lc and a second diameter-increased portion le, the latter having a plastic or metal retainer ring 3 set in the inner surface thereof for retaining a packing 4 having an annular groove shaped complementary to the exposed portion of the retainer ring 3. The formation of such air channels is not limited to the pipe having the socket end shown in Fig. 2. Such air channels are often formed in various pipe constructions, including a simple extruded pipe with no secondary processing applied to either end thereof and a socket-spigot pipe with a single diameter-increased portion having a packing receiving annular groove 5 as shown in Fig. 4. Of course, there are similar problems also with them.

Therefore, it has been thought necessary to close such air channels at either the socket end or the spigot end thereof to prevent entry of outside water or leakage of inside water. For example, European Patent Specification Nos. 13,457 and 13,458 disclose means for applying a force which tends to squeeze or expand the pipe wall to thereby press the outer wall surface against the inner. wall surface or the latter against the former, or force- fitting a blind plate to the pipe end surface. The portion thus processed, however, is formed with a constriction, which is a structural defect, on the outer or inner surface thereof, possibly leading to damage to the pipe unless special measures for reinforcement are taken. Further, since the pipe wall is only crimped under pressure, the resulting end-closing effect is insufficient, requiring the application of an auxiliary part in the form of a blind plate. However, such blind plate applied to the pipe end cannot be said to be sufficient since it could be easily removed by external forces unless it is held under adequate pressure.

Japanese Patent Specifications Nos. 52222/1977, 127481/1979, 37344/1980, 73514/1980, 10658/1979, and 103480/1979 disclose means for crimping the end edge or end portion of pipe over a given length; however, the sealing quality of the crimped portion cannot always be said to be satisfactory, and water could pass therethrough. Further, Japanese Patent Specification No. 73512/1980 and Japanese Utility Model Specifications Nos. 83024/1979 and 114812/1979 disclose means for fitting a plug into the end of each air channel, however, it is very difficult to ensure satisfactory positioning between the air channels and plugs. Another drawback is that the plugs tend to come off the air channels when subjected to a high outward force produced as the wster pressure in the pipe builds up. Further, Japanese Patent Specification No. 123180/1979 discloses a method of closing air channels by injecting a foamable material into the air channels and then causing it to foam. However, it is very troublesome to inject such material individually into the air channels. Since it is difficult to uniformly control the amount of injection and the degree of foaming, the sealing quality differs in different air channels and some air channels are insufficiently closed while others are overfilled with said material, detracting from economy. There have been many other suggestions but none has been known which is satisfactory from the standpoint of easiness of operation, reliability and uniformity of closure, economy, external appearance, etc.

Summary of the Invention

The present invention has been accomplished with the above in mind and has .for its object the provision of an air-channeled pipe with the air channels closed at their ends uniformly and positively.

A plastic pipe with channel end closed according to the invention comprises an annular slotted channel-closure (hereinafter referred to as U-cross-sectioned annular channel-closure) having two projecting walls adapted to clamp the inner and outer wall surfaces of the pipe end throughout the circumference thereof, at least one end of the pipe having said channel-closure fitted thereon, with a caulking material (the term "caulking material" as used herein includes those materials called "sealing material") filling a space extending from the slot bottom to the inlets of said channels. A method of forming such channel closing section with simplicity and reliability comprises the steps of filling the U-slot of the U-cross-sectioned annular channel-closure with a caulking material, fitting said channel-closure on the end of the plastic pipe heated and softened, pressing them against each other while holding the fitting section between inner and outer mold parts, forcing a fluid into the channels of the plastic pipe to press the inner and outer surfaces of said fitting section against said inner and outer mold parts so as to smooth the inner and outer surfaces, removing said fitting section from said inner mold, and cooling the same.

Thus, the closing material in the present invention is a caulking material, which, unlike the conventional solid plug, is capable of plastic deformation, so that even if there is some error of accuracy in the size and shape of the channels, the material will deform itself to accommodate said error. Thus, it has very high sealing quality and its adhesion to the plastic pipe is satisfactory. Unlike foaming materials, it does not require secondary processing, thereby avoiding increases in the number of production steps and in production time. Further, in the case of a foaming material, it tends to be injected deep into the channels, resulting in increased material cost. In contrast thereto, caulking materials used in the invention are relatively inexpensive.

According to the invention, the caulking material is charged in advance into the U-slot of the U-cross-sectioned annular channel-closure and the latter is fitted on the pipe end, so that the caulking material can be uniformly charged circumferentially of the pipe. Therefore, there is no variation in the sealing effect, nor is local overcharging. Thus, uniform and reliable sealing effect can be obtained. In addition, the side to be closed is usually heated for secondary processing. Particularly where the plastic pipe end is increased in diameter to form a socket, a diameter-increasing force acts outwardly of the inner mold part 6 as indicated by arrows M in Fig. 5, so that hoop stresses τ_x, τ_y, τ_z are produced as indicated by arrows, respectively. Since the stresses τ_x and T_z are produced in a region of relatively small cross-sectional area while the stress τ_y is produced in a region of relatively large cross-sectional area, τ_x and τ_zper unit area are larger than τ_y per unit area, with the result that pipe wall regions land 1 acted upon τ_xand τ_z, respectively, are circumferentially stretched, thereby forming small undulations 7, as shown in Fig. 6, in the pipe cross-section after heat-processing. The formation of such undulations is undesirable since they detract from the external appearance and, moreover, they cause variations in the circumferential sealing effect when the pipe is connected to another pipe, particularly where a packing is interposed therebetween. Therefore, according to the invention, this relevant portion is held between the inner and outer mold parts and then a fluid is forced into the channels ld to expand the latter, thereby successfully avoiding formation of undulations. Further, since the caulking material is pressed against the U-slot by the pressurized fluid, as described above, it is spread onto the inner surfaces of the channels ld to fill the channels, so that there is no danger of a clearance being formed between the inner surfaces of the-channels ld and the caulking material.

While the invention has been generally described so far, concrete examples of the arrangement of the invention and its merits will become apparent from the following detailed description of the invention.

Brief Description of the Drawings

<ul id="ul0001" list-style="none"><li>Fig. 1 is a sectional view showing a pipelinge buried in the ground; .</li><li>Fig. 2 is an enlarged sectional view of a pipe joint section;</li><li>Fig. 3 is a section taken along the line III-III of Fig. 2;</li><li>Fig. 4 is an enlarged sectional view showing another pipe;</li><li>Fig. 5 is a schematic view illustrating pressure developing condiitons during hot diameter-increasing process;</li><li>Fig. 6 is an end view showing small undulations formed on the peripheral surfaces of the pipe;</li><li>Figs. 7 through 12 are sectional views showing a production procedure step by step;</li><li>Fig. 13 is a sectional view of a channel closing section;</li><li>Fig. 14 is a sectional view of a channel closing section at the spigot end;</li><li>Fig. 15 and 16 are sectional views illustrating a process for closing the channels at both ends in a double- spigot joint; and</li><li>Fig. 17 is a sectional view showing an application of the invention to an adhesive agent type joint.</li></ul>

Detailed Description of the Preferred Embodiments

In Fig. 7, an inner mold part 8 is formed with 5 steps 8a, 8b, 8c, 8d and 8e, said step 8c having a rubber form or split form 9 and a packing engaging ring 3 fitted thereon so that the packing engaging ring 3 abuts against the back surface of said step, and said step 8e having a U-cross-sectioned annular channel-closure 10 fitted thereon so that it abuts against the back surface of said step, with a caulking material charged into the U-slot. The annular channel-closure 10 has outer and inner peripheral projecting walls 10a and 10b having their front ends taper-chamfered, as shown. The taper 10a^l of the outer peripheral projecting wall 10a is formed to face away from the U-slot and the taper lOb' of the inner peripheral projecting wall 10b is formed to face toward the U-slot. The material of the annular channel-closure is not limited in particular. Preferably, it is the same plastic as that of the pipe, but rigid rubber or stainless steel may be used as needed.

The caulking material is a soft material which is used for caulking and sealing purposes. Since it must be soft and capable of deforming to enter the channels through the open ends thereof, it is desired that it be plastic and flowable to a great degree and yet it must set as quickly as possible after entry. Materials which meet all these requirements include two-liquid type thermosetting resins, e.g., epoxy resins, and thermosetting resins, whether one-liquid or two-liquid type, such as silicone resins and butyral resins. Sometimes, thermoplastic resins (acrylic resin) and butyl rubber may be used. Typical of them are epoxy resins. To illustrate concrete examples of composition, it is preferable to use epoxy resins having a polyamide type setting agent incorporated therein in amounts greater than the theoretical amount or epoxy resins having incorporated therein a plasticizer or non-reactive diluent, such as DBP, coal tar, polyethylene glycol, and polypropylene glycol.

Such caulking material is charged into the U-slot of the annular channel-closure and the latter is fitted on the innermost region of the step 8d of the inner mold part 8 which is heated.

The channeled pipe-1 is slid along the guide portion (the step 8a) of the inner mold part after it has been heated to its plasticizing temperature. Therefore, it is successively increased in diameter by the tapering portions and the step 8c and moved over the rubber form 9 and the packing engaging ring 3 toward the annular channel-closure 10, as shown in Fig. 8. Since the inner peripheral projecting wall 10b of the channel-closure 10 is formed with the taper surface 10b', as described above, the front end of the channeled pipe 1 is smmothly inserted into the U-slot of the channel-closure 10. Since the caulking material in the channel-closure cannot escape, it is pressed between the slot bottom surface of the channel-closure and the non-channeled surface region of the pipe to be uniformly squeezed into the channels ld, as shown in Fig. 9. Subsequently, the outer mold part 11, divided into 3 or 4 pieces, is radially inwardly clamped to establish the Fig. 9 state. In the illustrated example the outer mold part 11 has been clamped later, but it may be clamped in advance and then the channeled pipe 1 may be pushed into an annular clearance defined between the outer mold part 11 and the inner mold part 8. When the Fig. 9 state is established, a blowing jig 12 adapted to cover the spigot end surface, as shown at right in Fig. 9, is fitted in position and a fluid is blown in from a nozzle 13 in the direction of arrow, whereby the fluid is forced into the channels ld. This eliminates small undulations described in Figs. 5 and 6. Further, the charging density of the caulking material in the channels is increased. In addition, 14a and 14b in Fig. 9 denote packings. Since the taper surface 10a' of the outer peripheral projecting wall of the channel-closure 10 supports the radially inward pressure from the outer mold part 11-on its entire area, as shown in Fig. 9, an even and beautiful appearance is presented.

With the first stage of the molding operation thus completed, cooling means is applied as by introducing a coolant between the outer and inner mold parts 11 and 8 or releasing the outer mold part 11 from the clamping force and feeding cool air or cold water. The molded pipe and the inner mold part 8 are then separated from each other, as shown in Fig. 10, and the molded pipe is further cooled. In the case of the rubber form 9, it is pulled out by being deformed as shown in Fig. 11 and in the case of the split form, it is pulled out by being disassembled. Fig. 12 is a sectional view showing the finished socket portion, with the packing engaging ring 3 being set in the inner surface of the socekt portion, the annular channel-closure 10 being fitted on the front end surface, and the channels ld being filled with the caulking material 11. In this manner, the channels ld are closed and the socket having a beautiful appearance is formed. In the inner surface of the socket, the inner peripheral projecting wall 10b is flush with the inner surface of the pipe, while in the outer surface of the socket the taper surface 10a' of the outer peripheral projecting wall 10a is smoothly continuous with the outer surface of the pipe. Thus, even if the channel-closure 10 is caught by something, it is prevented from coming off since the projecting walls 10a and 10b provide nothing which functions as a hook. After the caulking material 11 has fully set, the adhesion between the caulking material 11 and the channels ld provides strong binding therebetween. Before it fully sets, however, there would be a danger of the channel-closure coming off. If necessary, therefore, a force F may be applied in the direction of arrow as shown in'Fig. 13 to recess the outer peripheral wall surface lk of the pipe 1 at suitable places or throughout the circumference thereof so as to prevent coming off; this is also included in the scope of the invention.

Fig. 14 shows an example in which the invention is applied to the spigot end. Since the outer surface of the spigot is rubbed against a seal packing when being inserted into the socket, it woule be inconvenient to have the outer peripheral projecting wall 10a extending beyond the outer surface of the pipe as in the case of Fig. 12. Therefore, the outer peripheral projecting wall 10a in Fig. 14 is formed with a taper surface l0a" facing toward the U-slot. As a result, both the inner and outer surfaces are even.

Figs. 15 and 16 are sectional view showing a procedure for closing the channels at both ends of a double- spigot pipe. The right-hand side (R) is closed in the same procedure as described above, and then the lefthand side (L) is closed. Fig. 15 is a sectional view corresponding to Fig. 9, but unlike the latter the side R has already been closed. Therefore, in preventing formation of small undulation on the side L, it is impossible to blow in a pressurized fluid from the side R.

Therefore, in Fig. 15, a fluid blowing jig 15 whose fit- ing portion has the same shape as the channel-closure is fitted on the front end of the side L and a pressurized fluid is blown in from a nozzle 16. Since the channels ld are completely sealed, the undulations on the side L are pressed between the inner mold part 8 and the outer mold part 11, so that a beautiful appearance is presented as in the case of Fig. 9. After the socket has been cooled to the extent that it will not deform, the mold is released from the clamping force, a channel-closure 10 filled with a caulking material 11 similar to that used in the preceding examples is fitted on the processed socket end, and it is heated, as needed, to accelerate setting, thereby completing the double-end closing operation.

In addition, as shown in Fig. 17, the invention is also applicable to the closing of channels in a simple diameter-increased socket of the adhesive bond type.

With the invention arranged in the manner described above, the channels in a channeled pipe can be uniformly and reliably closed each at one or both ends thereof by simple means and at the same time formation of small undulations, which otherwise would easily form, on the inner and outer surfaces of the pipe can be prevented.