CA1170848A - Plastic underdrainage tube - Google Patents
Plastic underdrainage tubeInfo
- Publication number
- CA1170848A CA1170848A CA000412438A CA412438A CA1170848A CA 1170848 A CA1170848 A CA 1170848A CA 000412438 A CA000412438 A CA 000412438A CA 412438 A CA412438 A CA 412438A CA 1170848 A CA1170848 A CA 1170848A
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- Canada
- Prior art keywords
- strands
- tube
- annular bands
- longitudinal
- plastic
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
A plastic underdrainage tube of generally reticular configuration formed by extruded plastic material is disclosed.
The tube is comprised axially spaced relatively thick annular bands to reinforce or impart to the tube a high stability against surrounding pressures, and circumferentially disposed longitudinal strands in thicknesses less than those of said annular bands. These longitudinal strands are closely spaced along the circumference of the tube to form drainage openings between the circumferentially adjacent strands, the openings being disposed across the entire periphery and length-wise of the tube to allow water inflow over the entire wall portion thereof. Each of said strands is blended into or in-tegrally joined at its intersections to the annular bands so as to be mechanically supported by said annular bands of reinforcing members, thus improving the overall strength of the tube to withstand the surrounding pressure while requiring the amount of plastic material to be used at a low level.
In another embodiment, longitudinal strands are formed in sinuously corrugated configuration and blend at their valley portions into the annular bands to define the drainage openings between the ridge portions of the adjacent strands. The external forces acting on the ridge portions can be spread or decentralized by the corrugation of the strands and supported by the adjacent annular bands of reinforcing member.
A plastic underdrainage tube of generally reticular configuration formed by extruded plastic material is disclosed.
The tube is comprised axially spaced relatively thick annular bands to reinforce or impart to the tube a high stability against surrounding pressures, and circumferentially disposed longitudinal strands in thicknesses less than those of said annular bands. These longitudinal strands are closely spaced along the circumference of the tube to form drainage openings between the circumferentially adjacent strands, the openings being disposed across the entire periphery and length-wise of the tube to allow water inflow over the entire wall portion thereof. Each of said strands is blended into or in-tegrally joined at its intersections to the annular bands so as to be mechanically supported by said annular bands of reinforcing members, thus improving the overall strength of the tube to withstand the surrounding pressure while requiring the amount of plastic material to be used at a low level.
In another embodiment, longitudinal strands are formed in sinuously corrugated configuration and blend at their valley portions into the annular bands to define the drainage openings between the ridge portions of the adjacent strands. The external forces acting on the ridge portions can be spread or decentralized by the corrugation of the strands and supported by the adjacent annular bands of reinforcing member.
Description
I 1 7~84~
The present invention relates to plastic underdrain-age tube of the type buried in the soil to remove excess `~ ground water from the soil, more particularly to a plastic underdrainage tube of generally reticular configuration in which longitudinal strands are closely spaced apart to define the drainage openings therebetween.
The present invention will be illustrated by way of the accompanying drawings, in which:-FigO 1 is a schematic illustration of a convention-al plastic underdrainage tube;
Fig. 2 is a longitudinal section of the plastic underdrainage tube with an inner plastic film removed in accordance with a preferred embodiment of the present inven-tion;
Fig. 3 is a transverse section taken along the line A-A in Fig. 2;
Fig. 4 is a lonyitudinal section of a plastic under-drainage tube in accordance with another embodiment of the present invention;
Fig. 5 :is a transverse section taken along the line B-B in Fig. 4;
Fig. 6 is a schematic illustration showing how the loads acting on the ridge portions of the tube shown in Fig.
4 are spread and supported by the annular bands of greater thicknesses; and Fig. 7 is a partial schematic sectional view illus-trating a modification of the tube shown in Fig. ~.
Underdrainage t~bes, being subject to a high pres-sure or rorce by the surrounding soil, requires a high mech-anical strength of withstanding such pressures. For this reason, conventional plastic underdrainage tubes, as illus-trated in Fig. 1, have been thick-wall tubes with a large .. , ~
I J ~848 number of minute pores ~ through the wall 9 thereof. However, such thick-wall type plastic tubes are disadvantageous from economic and resource-saving standpoints, because of the amount of material required in their manufacture. Further-more, because excess numbers of the pores will weaken the tube against the surrounding pressures, the tube has to be made with a limited number of pores or openings. Accordingly, plastic tubes of higher drainage capacity have been difficult to produce.
The present invention provides a plastic underdrain-age tube which, in spite of a smaller amount of the plastic material being required for its manufacture, has higher sta-bility and sufficient mechanical strength to withstand the surrounding pressures and at the same time provides a higher drainage capacity.
According to the present invention there is provided a plastic underdrainage tube comprising a plurality of axial-ly spaced apart annular bands, a plurality of longitudinally parallel bars each joining integrally at its intersections with said annular bands to form a reticular tube body, and a plurality of circumferentially disposed longitudinal strands of thicknesses less than those of said annular bands, said strands joining integrally substantial portions of outer peripheries of said annular bands and being closely spaced along the circumference of said tube body to define drainage openings therebetween in mesh portions defined by the annular bands and longitudinal bars, and said openings being dispersed over the entire surface of the tube.
Thus in accordance with the present invention, there are provided plastic tubes comprising a plurality of longitudinal strands having relatively smaller thicknesses and a plurality of annular bands in thicknesses greater than
The present invention relates to plastic underdrain-age tube of the type buried in the soil to remove excess `~ ground water from the soil, more particularly to a plastic underdrainage tube of generally reticular configuration in which longitudinal strands are closely spaced apart to define the drainage openings therebetween.
The present invention will be illustrated by way of the accompanying drawings, in which:-FigO 1 is a schematic illustration of a convention-al plastic underdrainage tube;
Fig. 2 is a longitudinal section of the plastic underdrainage tube with an inner plastic film removed in accordance with a preferred embodiment of the present inven-tion;
Fig. 3 is a transverse section taken along the line A-A in Fig. 2;
Fig. 4 is a lonyitudinal section of a plastic under-drainage tube in accordance with another embodiment of the present invention;
Fig. 5 :is a transverse section taken along the line B-B in Fig. 4;
Fig. 6 is a schematic illustration showing how the loads acting on the ridge portions of the tube shown in Fig.
4 are spread and supported by the annular bands of greater thicknesses; and Fig. 7 is a partial schematic sectional view illus-trating a modification of the tube shown in Fig. ~.
Underdrainage t~bes, being subject to a high pres-sure or rorce by the surrounding soil, requires a high mech-anical strength of withstanding such pressures. For this reason, conventional plastic underdrainage tubes, as illus-trated in Fig. 1, have been thick-wall tubes with a large .. , ~
I J ~848 number of minute pores ~ through the wall 9 thereof. However, such thick-wall type plastic tubes are disadvantageous from economic and resource-saving standpoints, because of the amount of material required in their manufacture. Further-more, because excess numbers of the pores will weaken the tube against the surrounding pressures, the tube has to be made with a limited number of pores or openings. Accordingly, plastic tubes of higher drainage capacity have been difficult to produce.
The present invention provides a plastic underdrain-age tube which, in spite of a smaller amount of the plastic material being required for its manufacture, has higher sta-bility and sufficient mechanical strength to withstand the surrounding pressures and at the same time provides a higher drainage capacity.
According to the present invention there is provided a plastic underdrainage tube comprising a plurality of axial-ly spaced apart annular bands, a plurality of longitudinally parallel bars each joining integrally at its intersections with said annular bands to form a reticular tube body, and a plurality of circumferentially disposed longitudinal strands of thicknesses less than those of said annular bands, said strands joining integrally substantial portions of outer peripheries of said annular bands and being closely spaced along the circumference of said tube body to define drainage openings therebetween in mesh portions defined by the annular bands and longitudinal bars, and said openings being dispersed over the entire surface of the tube.
Thus in accordance with the present invention, there are provided plastic tubes comprising a plurality of longitudinal strands having relatively smaller thicknesses and a plurality of annular bands in thicknesses greater than
- 2 -, ~
`` I ~ 7~8~
those of the strands, the longitudinal strands being closelyspaced in circumferentially arrangement to define therebetween the drainage openings which are small enough to block the entry of gravel or pebbles from the surrounding soil, and the annular bands blending into or incorporating with each of the longitudinal strands at their intersections to support the external forces acting on the longitudinal strands from the surrounding soil so as to make the tube strong enough to withstand such forces without being bent or buckled.
In preferred embodiments of the present invention, there are two basic types of the plastic underdrainage tube of the invention. In one such tube each of the longitudinal relatively thin strands is sinuously corrugated and blends at its ridge portions into outer peripheries of the relative-ly thick annular bands to form the drainage openings between the valley portions of the adjacent strands and longitudinal bars having thicknesses greater than those of the strands are incorporated into the annular bands at its intersections.
With this type configuration, the longitudinal bars of thick elements, together with the annular bands also of thick ele-ments forms generally rectangular lattices to strengthen the whole tube and particularly to reinforce the valley portions formed in the corrugated wall of the tube. Therefore the tube constructed can be prevented from being bent or buckled at these valley portions. In the other such tube each of longitudinal strands is sinuously corrugatcd and blends at its valley portions into the outer peripheries of the annular bands so as to form the drainage openings bctween the ridge portions of the adjacent strands. With this type configura-tion, the external forces acting on the ridge portions of thelongitudinal strands of thin elements will be supported by
`` I ~ 7~8~
those of the strands, the longitudinal strands being closelyspaced in circumferentially arrangement to define therebetween the drainage openings which are small enough to block the entry of gravel or pebbles from the surrounding soil, and the annular bands blending into or incorporating with each of the longitudinal strands at their intersections to support the external forces acting on the longitudinal strands from the surrounding soil so as to make the tube strong enough to withstand such forces without being bent or buckled.
In preferred embodiments of the present invention, there are two basic types of the plastic underdrainage tube of the invention. In one such tube each of the longitudinal relatively thin strands is sinuously corrugated and blends at its ridge portions into outer peripheries of the relative-ly thick annular bands to form the drainage openings between the valley portions of the adjacent strands and longitudinal bars having thicknesses greater than those of the strands are incorporated into the annular bands at its intersections.
With this type configuration, the longitudinal bars of thick elements, together with the annular bands also of thick ele-ments forms generally rectangular lattices to strengthen the whole tube and particularly to reinforce the valley portions formed in the corrugated wall of the tube. Therefore the tube constructed can be prevented from being bent or buckled at these valley portions. In the other such tube each of longitudinal strands is sinuously corrugatcd and blends at its valley portions into the outer peripheries of the annular bands so as to form the drainage openings bctween the ridge portions of the adjacent strands. With this type configura-tion, the external forces acting on the ridge portions of thelongitudinal strands of thin elements will be supported by
3 -~ 1 7~84~
the annular bands of thick ele~ents to assure enough strength against hending or buckling.
The present invention also provides a further ad-vantageous configuration of the plastic underdrainage tube in which a thin plastic film covers the inner surface in the lower circumferential half of the reticular tube so as to allow the flow of water in the tube without being disturbed by the inwardly protruding bands and strands, increasing flow effi-ciency of the water flowing in the tube. Thus, the present invention provides a plastic underdrainage tube that is capable of allowing water to flow smoothly in the tube to enhance drainage capacity.
The present invention further provides a plastic underdrainage tube of the type which is easily formed to shape using smaller amounts of plastic material with the lowest production costs.
Referring now to Figs. 2 and 3, there is shown a plastic underdrainage tube of generally reticular construction comprising a plurality of relatively thick annular plastic bands 1, a plurality of relatively thic~ longitudinal plastic bars 2 and a plurality of longitudinal plastic strands 3 in thicknesses less than those of each of the bands 1 and bars 2.
The plastic material may be any thermoplastic material, for example, high density solid polyethylene or foamed polyethy-lene with a density of the order of two-thirds to one-fifth, preferably of the order of one-half to one-third that of the solid polyethylene.
The tube is formed by a continuous extruding method employing two coaxial die members, one of which is stationary and the othex is reciprocated in axial direction to separate the contacting surfaces between two uie me.lbers. In this method, a plurality of said longitudinal bars 2 and strands 3 _ ~ _ ~ 1 7~8~8 are continuousli~ extruded through the openings of different diameters which are circumferentially spaced along the contact-ing surfaces, and a plurality of said annular bands 1 are extruded through the gap formed between the contacting sur-faces of the two die members ~hen separated to intersect with or join integrally the bars 2 and strands 3 at right angles to form a generally reticular structure.
Each extruded annular band 1 is generally elliptical in longitudinal cross section with its major axis extending substantially radîally, as shown in Fig. 2. Into each annular band 1 said longitudinal bars 2 are blended at substantially regular distances along the circumference thereof to provide substantially parallel relationship therebetween. Also each longitudinal bar 2 has a generally elliptical cross section with its major axis extending in the circumferential direction of the resulting tube. Each annular band 1 is extruded to have a greater minor axis than that of each longitudinal bar 2, which in turn has a greater minor axis than the diameter of each longitudinal strand 3. For tubes 10 to 15 cm in dia-meter, for example, the ma~or axis, which can be regarded asthe thickness, or the diameter of the band 1, the bar 2 and the strand 3 are set to be of the order of 0.7 to 2.0, 0.3 to 1.0 and 0.1 to 0.5 cm respectively, the annular bands 1 being evenly spaced at a distance of 0.5 to 2.0 cm in longitudinal direction. Three to twelve longitudinal bars 2 are disposed in evenly spaced relationsllip along the inner periphery of the bands 1, and 50 to 150 longitudinal strands 3 are disposed along the outer periphery of the bands 1.
Each longitudinal bar 2 is extruded in a lengthwise direction with its partial portions folded back at the inter-sections with the annular bands 1 to form a generally straight I ~ 7~8~
element. The longitudinal strands 3 are extruded in circum-ferentially closely spaced relationship and join integrally the outer periphery of the annular bands 1 at their inter-sections to define therebetween drainage openings 4 which are dimensioned to allow water flow from the surrounding soil into the tube while blocking the entrance of gravel or pebbles from the soil. The openings 4 thus formed are generally in the form of substantially longitudinally elongated slots hav-ing widths less than that of the longitudinal bar 2 with some possible exceptions. As illustrated in Fig. 2, each longitu-dinal strand 3 is sinuously corrugated and intersect with or blends into the annular bands 1 at their ridge portions to define the openings between some valley portions of the ad-jacent strands 3. These strands 3 of corrugated configuration are formed by loosening the tension forces applied on the extruded strands 3 in its longitudinal direction during drawing the strands from the die members. Thus corrugated strands 3, due to their residual plasticity, suffer in some segments thereof circumferential staggers to join or interlace with each other, with the result that in some regions the adjacently disposed strands 3 compact and form mechanical con-nections therebetween so as to reinforce the valley portions, while at the same time leaving in other regions said openings
the annular bands of thick ele~ents to assure enough strength against hending or buckling.
The present invention also provides a further ad-vantageous configuration of the plastic underdrainage tube in which a thin plastic film covers the inner surface in the lower circumferential half of the reticular tube so as to allow the flow of water in the tube without being disturbed by the inwardly protruding bands and strands, increasing flow effi-ciency of the water flowing in the tube. Thus, the present invention provides a plastic underdrainage tube that is capable of allowing water to flow smoothly in the tube to enhance drainage capacity.
The present invention further provides a plastic underdrainage tube of the type which is easily formed to shape using smaller amounts of plastic material with the lowest production costs.
Referring now to Figs. 2 and 3, there is shown a plastic underdrainage tube of generally reticular construction comprising a plurality of relatively thick annular plastic bands 1, a plurality of relatively thic~ longitudinal plastic bars 2 and a plurality of longitudinal plastic strands 3 in thicknesses less than those of each of the bands 1 and bars 2.
The plastic material may be any thermoplastic material, for example, high density solid polyethylene or foamed polyethy-lene with a density of the order of two-thirds to one-fifth, preferably of the order of one-half to one-third that of the solid polyethylene.
The tube is formed by a continuous extruding method employing two coaxial die members, one of which is stationary and the othex is reciprocated in axial direction to separate the contacting surfaces between two uie me.lbers. In this method, a plurality of said longitudinal bars 2 and strands 3 _ ~ _ ~ 1 7~8~8 are continuousli~ extruded through the openings of different diameters which are circumferentially spaced along the contact-ing surfaces, and a plurality of said annular bands 1 are extruded through the gap formed between the contacting sur-faces of the two die members ~hen separated to intersect with or join integrally the bars 2 and strands 3 at right angles to form a generally reticular structure.
Each extruded annular band 1 is generally elliptical in longitudinal cross section with its major axis extending substantially radîally, as shown in Fig. 2. Into each annular band 1 said longitudinal bars 2 are blended at substantially regular distances along the circumference thereof to provide substantially parallel relationship therebetween. Also each longitudinal bar 2 has a generally elliptical cross section with its major axis extending in the circumferential direction of the resulting tube. Each annular band 1 is extruded to have a greater minor axis than that of each longitudinal bar 2, which in turn has a greater minor axis than the diameter of each longitudinal strand 3. For tubes 10 to 15 cm in dia-meter, for example, the ma~or axis, which can be regarded asthe thickness, or the diameter of the band 1, the bar 2 and the strand 3 are set to be of the order of 0.7 to 2.0, 0.3 to 1.0 and 0.1 to 0.5 cm respectively, the annular bands 1 being evenly spaced at a distance of 0.5 to 2.0 cm in longitudinal direction. Three to twelve longitudinal bars 2 are disposed in evenly spaced relationsllip along the inner periphery of the bands 1, and 50 to 150 longitudinal strands 3 are disposed along the outer periphery of the bands 1.
Each longitudinal bar 2 is extruded in a lengthwise direction with its partial portions folded back at the inter-sections with the annular bands 1 to form a generally straight I ~ 7~8~
element. The longitudinal strands 3 are extruded in circum-ferentially closely spaced relationship and join integrally the outer periphery of the annular bands 1 at their inter-sections to define therebetween drainage openings 4 which are dimensioned to allow water flow from the surrounding soil into the tube while blocking the entrance of gravel or pebbles from the soil. The openings 4 thus formed are generally in the form of substantially longitudinally elongated slots hav-ing widths less than that of the longitudinal bar 2 with some possible exceptions. As illustrated in Fig. 2, each longitu-dinal strand 3 is sinuously corrugated and intersect with or blends into the annular bands 1 at their ridge portions to define the openings between some valley portions of the ad-jacent strands 3. These strands 3 of corrugated configuration are formed by loosening the tension forces applied on the extruded strands 3 in its longitudinal direction during drawing the strands from the die members. Thus corrugated strands 3, due to their residual plasticity, suffer in some segments thereof circumferential staggers to join or interlace with each other, with the result that in some regions the adjacently disposed strands 3 compact and form mechanical con-nections therebetween so as to reinforce the valley portions, while at the same time leaving in other regions said openings
4 defined by the circumferentially closely spaced adjacent strands 1. Such openings 4 occur mainly at the positions ad-jacent to the longitudinal bars 2, therefore they are dispos-ed at substantially regular distances in the circumferential direction as well as in the longitudinal direction.
The straight longitudinal strands may be used in the present invention, provided that the strands are circumferen-tially spaced closely enough to allow tne formation of the openings of like dimensions as above. Such straight strands _ ~ _ I ~ 7~84~
are obtained by drawing the strands at a speed equal to the extrusîon speed, in contrast to the above-described procedure.
In this case, there are possible staggers in the strands as occurs in the above corrugated strands 3 to cause a similar distribution of the openings 4 in both longitudinal and cir-cumferential directions. However, it is more effective to use the corrugated strands 3 than to use the straight strands because the configuration including the corrugated strands 3 will cause a greater number of the openirlgs and therefore has a wall of hi`gher porosity than a tube with the straight strands.
The stands 3, irrespective of being corrugated or straight, are normally made of the same material as the rest of the tube and preferably made of semi-hard or relatively soft plastic materials that have a higher tensile strength as well as a higher impact value for strengthening purposes of the wall portion of the tube.
In the above embodiments, the circumferentially spaced apart strands 3 form a single wall of the tube. How-ever, it is also effectlve to provide construc-tions of more than one wall wherein each strand in one wall is in a stagger-ed relationship with the strand in other walls so as to de-fine the openings 4 among the radially and circumferentially adjacent disposed strands.
In the lower circurnferential half of the tube, there is provided a plastic thin film 6 adhered to the inner surface of the tube to cover the roughened inner surface contoured by the partially appear ng annular bands 1, bars 2 and the strands 3 which are exposed in the mesh portions of the bands 1 and bars 2, so that the water will flow smoothly along this film 6 in the lower portion of the tube witl;out being disturb-ed by such roughened inner surface.
~ ~ 7~84~
In accordance with the present invention the longi-tudinal strands 3 and bars 2 blend into or join integrally respectively the annular bands 1 so as to provide a unique configurationwhich a plurality of the longitudinal strands 3 having smaller thicknesses are circumferentially disposed in close relationship with each other to form a wall with open-ings 4 defined between the adjacent strands 3 and the wall so formed is integrally supported or reinforced by the lattice construction defined by the annular bands 1 and the longitu-dinal bars 2 both having greater thicknesses than those ofthe strands 3. Accordingly, the tube of this configuration, in addition to having a higher porosity due to the formation of the openings 4 between the adjacently disposed strands 3, is capable of exhibiting improved strength against the ex-ternal pressures as high as a conventional plastic thick-wall tube having the same thickness as that of the annular bands 1.
This enables the plastic tube of the present invention to be manufactured with lower consumption of plastic material and therefore at lower cost. I'he reinforcing effect will be further improved by the annular bands 1 having an elliptical cross section with its major axis extending substantially radially. Further, for the tube with sinuously corrugated longitudinal strands 3, the openings 4 are formed between the valley portions of the adjacently disposed strands 3 so that water in the surrounding soil will be collected in the va]ley portions and then smoothly passes through such openings 4 into the tube, which will assure a higher drainage capacity.
Also, with this construction of the tube, the valley portions extending circumferentially have along their peripheries some 3Q regions in which the adjacent strands are closely packed to form an integrally joined bunch, so that the wall maue of a 1 1 7~8~
plurality of the circumferentially disposed strands 3 of thin elements is strengthened at its valley portions, which would otherwise ~e weaker against bending forces. Therefore the whole tube is reinforced, in addition to the longitudinal bars 2 of thick elements making a lattice construction with the annular bands 1, in such a way as to impart to the result-- ing tube a higher strength against the external pressures acting on the tube from the surrounding soil.
Referring now to Figs. 4, 5 and 6, the plastic under-drainage tube comprises a plurality of relatively thick axial-ly spaced apart annular bands 11 and a plurality of circum-ferentially disposed longitudinal strands 13 having thickness-es less than those of the annular bands 11. This tube also includes a plurality of circumferentially disposed longitudin-al bars having the same thicknesses as the strands 13. There is no distinguishable configuration between the bars and the strands except for their behaviox in the extruding process in that the annular bands 11 are periodically extruded con-tinuously with the bars while the strands 13 are extruded from the ports other than those for the bars and bands to overlap the annular bands 11 immediately after being extruded, so that the bars and strands 13 are toyether referred to as the strands 13. These bands 11 and strands 13 are extruded to have generally circular cross sections. Each band 11 has a cross sectional area 5 to 30 times that of the longitudinal strands 13, which are extruded in sinuously corrugated shape along the full length thereof whilst maintaining a generally parallel relationship. In this embodiment, the tube is ex-truded to form a double-wall construction of inner and outer walls each ~eing made of a plurality of the strands arranged along the circumference of a circle. The strands 13 forming the inner wall intersect with and blend into the outer peri-) I 7~84~
; pheries of the annular bands 11 at their valley portions, while the strands 13 forming the outer wall blend into the strands 13 of the inner wall and/or the annular bands 11 a~
their valley portions, thus forming a tube wherein the strands 13 and the bands 11 are integrally joined with each other and leaving drainage openings 14 in the ridge portions of the adjacently disposed strands 13. As best illustrated in Fig. 5, the strands 13 forming the inner wall are circumfer-entially spaced apart along the annular bands 11 at distances less than the diameters of the strands 13. The strands 13 forming the outer wall are also closely spaced in the vicinity of the annular bands 11 to constitute such circumferential spacing of the strands 13 that one strand 13 in the inner wall lies between the circumferentially adjacent disposed strands 13 in the outer wall. The strands 13 however are spaced in their ridge portions at greater distances than in their valley portions such that said openings 14 are formed among the ridge portions of circumferentially and radially adjacent strands 13.
The tube of this configuration is obtained by con-tinuously extruding the strands while at the same time period-ically extruding the annular bands from the contacting surfaces of two die members constructed in the same manner as describ-ed in the embodiment of Figs. 1 and 2. In the extruding pro-cess of the tube of this embodiment, the strands are extruded through the ports of same diameters at a higher extruding speed than the drawing speed in such a way as to be staggered or corrugated along the ]ength thereof as well as to be joined in their valley portions to the just extruded annular bands, 3a with the result that each strand thus formed at regular in-tervals along its length by annular bands will cause no sub-- stantial warp or distortion in the directions other than the 1 1 7~
radial direction to have regularly corrugated configuration wherein each strand of substantially same pitch and amplitude extends longitudinally. In this sense, the annular bands 11 not only work as reinforcing ring members of the tube but also cause each strand to regularly corrugate along the length thereof at the time of extruding to ensure the formation of the openings among the ridge portions of the adjacently dis-posed strands.
According to this embodiment, in addition to the tube being regarded as having a wall as thick as the amplitude - W of the sinuously corrugated strands 13, the tube exhibits the behavior when buried in the soil such that the external pressures of forces F applied fromthe surrounding soil on the ridge portions of the strands 13 will be, as schematically shown in Fig. 6, spread along their sides so as to be receiv-ed by the annular bands 11 of greater thicknesses. Consequent-ly, there will be no concentration of stress in the ridge portions of the strands 13 t assuring a higher strength against the surrounding pressures. Also, the tube of double-wall type has a unique configuration in that the strands 13 are arranged such that one strand in each wall lies between the circumferentially adjacent strands in the radially adjacent disposed wall, so that one strand in one of the walls extends across the gap formed between the ridge portions of the cir-cumferentially adjacent strands in the other wall to reduce the dimension of the opening, which improves the filtering effect of blocking the entrance of smaller gravel or pebbles from the surrounding soil. This arrangement is particular]y effective when the gap between the circurnferentially adjacent strands in one of the walls is accidentally made much greater than a prescribed dimension on solidification.
1 ~ 7 (~
The valley portions of the corrugated strands are referred to as the portions below the line L bisecting the thickness of the wall, tfiat is, the amplitude W of the cor-rugation as indicated in Fig. 7, which shows the modification in which each corrugated strand 13 integrally forms the annular bands 11 at its side portions in juxtaposition with the bottom of the valley.
Further, the size of the opening formed among the . ridge portions of the adjacent strands, the thickness of the - 10 tube wall (i.e., the amplitude of the corrugated strands) and the strength can be varied by simply controlling the spacing of the annular bands 11, that is, by varying the extrusion interval of the annular bands 11 in the longitudinal direction.
In the above embodiment, only the double-wall con-struction wherein each of inner and outer wall is defined by a plurality of the strands arranged along the circumference of a circle is disclosed, however, the present invention should not be limited to this embodiment and may include the provision of the tube with a si.ngle wall or may, or course, 20 include the embocliment wherein more than two walls are provid-ed for. In multi-wall construction of the strands, the strands may preferably, as described hereinbefore, be arranged such that one strand in each wall lies between the circumferential-ly adjacent strands in the radially adjacently disposed wall of the strands. With this arrangement, the above filtering effect of the strands will be.increased with the increasing numbers of walls. Still in the above embodiments, only the tubes having the cross section in circular are disclosed, however, the present invention may apply to the tubes having any desired cross section, for e~ample, triangular, rectangu-lar, or semi circular.
The straight longitudinal strands may be used in the present invention, provided that the strands are circumferen-tially spaced closely enough to allow tne formation of the openings of like dimensions as above. Such straight strands _ ~ _ I ~ 7~84~
are obtained by drawing the strands at a speed equal to the extrusîon speed, in contrast to the above-described procedure.
In this case, there are possible staggers in the strands as occurs in the above corrugated strands 3 to cause a similar distribution of the openings 4 in both longitudinal and cir-cumferential directions. However, it is more effective to use the corrugated strands 3 than to use the straight strands because the configuration including the corrugated strands 3 will cause a greater number of the openirlgs and therefore has a wall of hi`gher porosity than a tube with the straight strands.
The stands 3, irrespective of being corrugated or straight, are normally made of the same material as the rest of the tube and preferably made of semi-hard or relatively soft plastic materials that have a higher tensile strength as well as a higher impact value for strengthening purposes of the wall portion of the tube.
In the above embodiments, the circumferentially spaced apart strands 3 form a single wall of the tube. How-ever, it is also effectlve to provide construc-tions of more than one wall wherein each strand in one wall is in a stagger-ed relationship with the strand in other walls so as to de-fine the openings 4 among the radially and circumferentially adjacent disposed strands.
In the lower circurnferential half of the tube, there is provided a plastic thin film 6 adhered to the inner surface of the tube to cover the roughened inner surface contoured by the partially appear ng annular bands 1, bars 2 and the strands 3 which are exposed in the mesh portions of the bands 1 and bars 2, so that the water will flow smoothly along this film 6 in the lower portion of the tube witl;out being disturb-ed by such roughened inner surface.
~ ~ 7~84~
In accordance with the present invention the longi-tudinal strands 3 and bars 2 blend into or join integrally respectively the annular bands 1 so as to provide a unique configurationwhich a plurality of the longitudinal strands 3 having smaller thicknesses are circumferentially disposed in close relationship with each other to form a wall with open-ings 4 defined between the adjacent strands 3 and the wall so formed is integrally supported or reinforced by the lattice construction defined by the annular bands 1 and the longitu-dinal bars 2 both having greater thicknesses than those ofthe strands 3. Accordingly, the tube of this configuration, in addition to having a higher porosity due to the formation of the openings 4 between the adjacently disposed strands 3, is capable of exhibiting improved strength against the ex-ternal pressures as high as a conventional plastic thick-wall tube having the same thickness as that of the annular bands 1.
This enables the plastic tube of the present invention to be manufactured with lower consumption of plastic material and therefore at lower cost. I'he reinforcing effect will be further improved by the annular bands 1 having an elliptical cross section with its major axis extending substantially radially. Further, for the tube with sinuously corrugated longitudinal strands 3, the openings 4 are formed between the valley portions of the adjacently disposed strands 3 so that water in the surrounding soil will be collected in the va]ley portions and then smoothly passes through such openings 4 into the tube, which will assure a higher drainage capacity.
Also, with this construction of the tube, the valley portions extending circumferentially have along their peripheries some 3Q regions in which the adjacent strands are closely packed to form an integrally joined bunch, so that the wall maue of a 1 1 7~8~
plurality of the circumferentially disposed strands 3 of thin elements is strengthened at its valley portions, which would otherwise ~e weaker against bending forces. Therefore the whole tube is reinforced, in addition to the longitudinal bars 2 of thick elements making a lattice construction with the annular bands 1, in such a way as to impart to the result-- ing tube a higher strength against the external pressures acting on the tube from the surrounding soil.
Referring now to Figs. 4, 5 and 6, the plastic under-drainage tube comprises a plurality of relatively thick axial-ly spaced apart annular bands 11 and a plurality of circum-ferentially disposed longitudinal strands 13 having thickness-es less than those of the annular bands 11. This tube also includes a plurality of circumferentially disposed longitudin-al bars having the same thicknesses as the strands 13. There is no distinguishable configuration between the bars and the strands except for their behaviox in the extruding process in that the annular bands 11 are periodically extruded con-tinuously with the bars while the strands 13 are extruded from the ports other than those for the bars and bands to overlap the annular bands 11 immediately after being extruded, so that the bars and strands 13 are toyether referred to as the strands 13. These bands 11 and strands 13 are extruded to have generally circular cross sections. Each band 11 has a cross sectional area 5 to 30 times that of the longitudinal strands 13, which are extruded in sinuously corrugated shape along the full length thereof whilst maintaining a generally parallel relationship. In this embodiment, the tube is ex-truded to form a double-wall construction of inner and outer walls each ~eing made of a plurality of the strands arranged along the circumference of a circle. The strands 13 forming the inner wall intersect with and blend into the outer peri-) I 7~84~
; pheries of the annular bands 11 at their valley portions, while the strands 13 forming the outer wall blend into the strands 13 of the inner wall and/or the annular bands 11 a~
their valley portions, thus forming a tube wherein the strands 13 and the bands 11 are integrally joined with each other and leaving drainage openings 14 in the ridge portions of the adjacently disposed strands 13. As best illustrated in Fig. 5, the strands 13 forming the inner wall are circumfer-entially spaced apart along the annular bands 11 at distances less than the diameters of the strands 13. The strands 13 forming the outer wall are also closely spaced in the vicinity of the annular bands 11 to constitute such circumferential spacing of the strands 13 that one strand 13 in the inner wall lies between the circumferentially adjacent disposed strands 13 in the outer wall. The strands 13 however are spaced in their ridge portions at greater distances than in their valley portions such that said openings 14 are formed among the ridge portions of circumferentially and radially adjacent strands 13.
The tube of this configuration is obtained by con-tinuously extruding the strands while at the same time period-ically extruding the annular bands from the contacting surfaces of two die members constructed in the same manner as describ-ed in the embodiment of Figs. 1 and 2. In the extruding pro-cess of the tube of this embodiment, the strands are extruded through the ports of same diameters at a higher extruding speed than the drawing speed in such a way as to be staggered or corrugated along the ]ength thereof as well as to be joined in their valley portions to the just extruded annular bands, 3a with the result that each strand thus formed at regular in-tervals along its length by annular bands will cause no sub-- stantial warp or distortion in the directions other than the 1 1 7~
radial direction to have regularly corrugated configuration wherein each strand of substantially same pitch and amplitude extends longitudinally. In this sense, the annular bands 11 not only work as reinforcing ring members of the tube but also cause each strand to regularly corrugate along the length thereof at the time of extruding to ensure the formation of the openings among the ridge portions of the adjacently dis-posed strands.
According to this embodiment, in addition to the tube being regarded as having a wall as thick as the amplitude - W of the sinuously corrugated strands 13, the tube exhibits the behavior when buried in the soil such that the external pressures of forces F applied fromthe surrounding soil on the ridge portions of the strands 13 will be, as schematically shown in Fig. 6, spread along their sides so as to be receiv-ed by the annular bands 11 of greater thicknesses. Consequent-ly, there will be no concentration of stress in the ridge portions of the strands 13 t assuring a higher strength against the surrounding pressures. Also, the tube of double-wall type has a unique configuration in that the strands 13 are arranged such that one strand in each wall lies between the circumferentially adjacent strands in the radially adjacent disposed wall, so that one strand in one of the walls extends across the gap formed between the ridge portions of the cir-cumferentially adjacent strands in the other wall to reduce the dimension of the opening, which improves the filtering effect of blocking the entrance of smaller gravel or pebbles from the surrounding soil. This arrangement is particular]y effective when the gap between the circurnferentially adjacent strands in one of the walls is accidentally made much greater than a prescribed dimension on solidification.
1 ~ 7 (~
The valley portions of the corrugated strands are referred to as the portions below the line L bisecting the thickness of the wall, tfiat is, the amplitude W of the cor-rugation as indicated in Fig. 7, which shows the modification in which each corrugated strand 13 integrally forms the annular bands 11 at its side portions in juxtaposition with the bottom of the valley.
Further, the size of the opening formed among the . ridge portions of the adjacent strands, the thickness of the - 10 tube wall (i.e., the amplitude of the corrugated strands) and the strength can be varied by simply controlling the spacing of the annular bands 11, that is, by varying the extrusion interval of the annular bands 11 in the longitudinal direction.
In the above embodiment, only the double-wall con-struction wherein each of inner and outer wall is defined by a plurality of the strands arranged along the circumference of a circle is disclosed, however, the present invention should not be limited to this embodiment and may include the provision of the tube with a si.ngle wall or may, or course, 20 include the embocliment wherein more than two walls are provid-ed for. In multi-wall construction of the strands, the strands may preferably, as described hereinbefore, be arranged such that one strand in each wall lies between the circumferential-ly adjacent strands in the radially adjacently disposed wall of the strands. With this arrangement, the above filtering effect of the strands will be.increased with the increasing numbers of walls. Still in the above embodiments, only the tubes having the cross section in circular are disclosed, however, the present invention may apply to the tubes having any desired cross section, for e~ample, triangular, rectangu-lar, or semi circular.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A plastic underdrainage tube comprising a plural-ity of axially spaced apart annular bands, a plurality of longitudinally parallel bars each joining integrally at its intersections with said annular bands to form a reticular tube body, and a plurality of circumferentially disposed longitud-inal strands of thicknesses less than those of said annular bands, said strands joining integrally substantial portions of outer peripheries of said annular bands and being closely spaced along the circumference of said tube body to define drainage openings therebetween in mesh portions defined by the annular bands and longitudinal bars, and said openings being dispersed over the entire surface of the tube.
2. A plastic underdrainage tube as set forth in claim 1, wherein each of said longitudinal strands is sinuously corrugated in the longitudinal direction and integrally joins at its ridge portions with said annular bands to define said openings between the valley portions of the adjacently dispos-ed strands, and said longitudinally parallel bars have greater thicknesses than the longitudinal strands.
3. A plastic underdrainage tube as set forth in claim 1, wherein each of said longitudinal strands is sinuous-ly corrugated in the longitudinal direction and integrally join at its valley portions with said annular bands to define said openings between the ridge portions of the adjacently disposed strands, and said longitudinally parallel bars have substan-tially the same thicknesses as the longitudinal strands.
4. A plastic underdrainage tube as set forth in claim 1, 2 or 3, in which a thin plastic film covers the inner surface in the lower circumferential half of the reticular tube so as to allow the flow of water in the tube without being disturbed by the inwardly protruding hands and strands, increas-ing flow efficiency of the water flowing in the tube.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000412438A CA1170848A (en) | 1982-09-29 | 1982-09-29 | Plastic underdrainage tube |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000412438A CA1170848A (en) | 1982-09-29 | 1982-09-29 | Plastic underdrainage tube |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1170848A true CA1170848A (en) | 1984-07-17 |
Family
ID=4123683
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000412438A Expired CA1170848A (en) | 1982-09-29 | 1982-09-29 | Plastic underdrainage tube |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1170848A (en) |
-
1982
- 1982-09-29 CA CA000412438A patent/CA1170848A/en not_active Expired
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