A pressure-resistant helical corrugated pipe comprises a helical corrugated pipe wall having a top portion, opposite side wall portions extending from the top portion and a bottom portion extending from the side wall portions and disposed closed to the axis of the pipe; and belt plates which are formed separately from each other and made of a thin metal. The belt plates are disposed respectively at the side of the top portion and the side of the bottom portion as constituent elements for the pipe wall. The opposite edges of the two metal belt plates are disposed in abutted relation or in spaced opposed relation at the opposite side wall portions. The two metal belt plates are interconnected by connective portions which are made of a synthetic resin or rubber.

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure-resistant helical corrugated 
pipe adapted to be buried in the ground, so that telecommunication cables 
such as an electric cable and a telephone cable can be installed in such 
corrugated pipe for the purpose of protecting such cables. Also, such a 
corrugated pipe is used as a water main pipe, a sewer pipe, or a liquid 
transport pipe used in a plant or a factory. 
Among such conventional pressure-resistant helical corrugated pipes, the 
pipes adapted for underground use have been required to be 
pressure-resistant in order to withstand a great ground pressure. An 
underground pressure-resistant pipe as shown in FIGS. 16 and 17 is 
conventionally known (see, for example, Japanese Laid-Open Utility Model 
Application No. 141889/86 filed by the Applicant of the present 
application). In this conventional pressure-resistant pipe, a continuous 
reinforcing belt plate 06 made of a thin metal plate is embedded in a pipe 
wall 01 and extends over a top portion 02 of the helical corrugation, 
opposite side wall portions 03 and 04 extending from the top portion 02, 
and part of a bottom portion 05. 
However, since the metal reinforcing belt plate 06 to be thus embedded in 
the pipe wall 01 is of such a unitary construction that this plate is 
disposed in the top portion 02 and the opposite side wall portions 03and 
04, with its oppositely-projecting side edge portions disposed in part of 
the bottom portion 05 as described above, the thin metal plate, when 
helically wound, is liable to be subjected to deformation due to strain 
because of variations in diameter of the thus helically-wound thin metal 
plate. This results in a problem that it is difficult to produce a helical 
pipe having a good appearance, and for this reason it has been necessary 
for the thin metal plate to be subjected to a special processing or 
working. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a pipe 
overcoming the problems encountered with the conventional pipe, in which 
belt plates each made of a thin metal plate are embedded in a pipe wall 
completely or generally over the entire periphery of the pipe wall in such 
a manner that the belt plates are not disposed in overlapping relation to 
each other, and in some cases, the metal belt plates are exposed at the 
surface of the pipe wall. The pipe can be easily manufactured, and can 
have a good appearance. The amount of a covering resin material can be 
reduced as compared with the amount used in the conventional pipe so that 
the overall weight of the pipe is reduced, and the pipe is excellent in 
pressure-resistance. 
According to the present invention, there is provided a pressure-resistant 
helical corrugated pipe having a helical corrugated pipe wall formed by a 
top portion, opposite side wall portions extending from the top portion 
and a bottom portion extending from said side wall portions and disposed 
close to the axis of the pipe, wherein belt plates formed separately from 
each other and made of a thin metal plate are disposed respectively at the 
side of the top portion and at the side of the bottom portion as 
constituent elements for the pipe wall, the opposite side edges of the two 
metal belt plates are disposed in abutted relation or in spaced opposed 
relation at the opposite side wall portions, and the opposite side edge 
portions of the two metal belt plates are interconnected by connective 
portions which are made of a synthetic resin or rubber. 
When the pipe of this construction is, for example, to be buried in the 
ground, a groove is dug in the ground at a required depth at the 
installation site, and the pipe is installed along the groove. When this 
pipe is used as a protective pipe for a cable, an electric cable or a 
telephone cable is passed through the pipe using a leading wire, and then 
the dug soil is applied to the pipe to cover it. In the case of such a 
cable-protective pipe, preferably, the pipe is not provided with the inner 
pipe wall, so that the pipe offers a less contact resistance when the 
cable is installed in the pipe. In the case where the pipe is used as a 
water mains pipe or a sewer pipe, preferably the pipe is provided with the 
inner pipe wall, so that a less water flow resistance is encountered.

DETAILED DESCRIPTION OF THE INVENTION 
Preferred embodiments of the present invention will now be described with 
reference to the drawings. 
FIGS. 1 to 3 show one preferred embodiment of the invention (hereinafter 
referred to as "first embodiment"). A helical corrugated pipe A shown in 
FIG. 1 includes two kinds of belt plates 6 and 7 each made of a steel 
plate. As best shown in FIG. 3, the belt plate 6 has a downwardly-opening 
trapezoidal cross-section having a relatively small depth, and the belt 
plate 7 has a cross-section inverse to the cross-section of the belt plate 
6, that is, an upwardly-opening trapezoidal cross-section having a 
relatively small depth. As shown in FIG. 2, the two belt plates 6 and 7 
are so arranged as to be disposed at the side of a top portion 2 of a pipe 
wall 1 and at the side of a bottom portion 5, respectively, and the two 
belt plates 6 and 7 are sandwiched between synthetic resin materials so 
that the entire inner and outer peripheral surfaces of the two metal belt 
plates are covered with these synthetic resin materials. These synthetic 
resin materials are fused to be integrally joined to the two belt plates 6 
and 7. Thus, the upper and lower metal belt plates 6 and 7 are disposed or 
embedded in the synthetic resin material constituting the pipe wall 1. 
For forming the helical corrugated pipe A of this embodiment, as shown in 
FIG. 3, a belt member 11 of a synthetic resin, which has a generally 
downwardly-opening trapezoidal cross-section having lower end or edge 
portions (projections) 11a and 11b directed laterally horizontally away 
from each other, is gradually wound helically with its opposite horizontal 
projections 11a and 11b overlapping each other, and the thus overlapped 
projections 11a and 11b are fused together to form an inner resin wall 
portion of the pipe wall 1. Then, the two kinds of steel belt plates 6 and 
7 are helically wound on this inner resin wall portion in such a manner 
that the plates 6 and 7 are arranged at the top portion side and the 
bottom portion side, respectively. Another belt member 12 of a synthetic 
resin, which is inverse in cross-section to the belt member 11 and hence 
has a generally trapezoidal cross-section, is helically wound on the two 
metal belt plates 6 and 7 on the inner resin wall portion in such a manner 
that its opposite horizontal projections 12a and 12b overlap each other. 
The thus overlapped horizontal projections 12a and 12b are fused together 
integrally to form an outer resin wall portion of the pipe wall 1. Thus, 
the belt members 11 and 12 are fusingly joined to the metal belt plates 6 
and 7, so that the metal belt plates 6 and 7 are disposed integrally in 
the fusingly joined belt members 11 and 12, thereby providing the helical 
corrugated construction shown in FIG. 2. 
In this embodiment, connective portions 3a and 4a made solely of the 
synthetic resin are provided respectively at generally central portions of 
opposite side wall portions 3 and 4 of the pipe wall 1. The metal belt 
plates 6 and 7 are absent in the connective portions 3a and 4a. 
FIG. 4 shows another method of producing a helical corrugated pipe similar 
in construction to the helical corrugated pipe A of the first embodiment 
shown in FIGS. 1 and 2. In this embodiment, two kinds of stainless steel 
belt plates 6 and 7, which respectively have downwardly-opening and 
upwardly-opening trapezoidal cross-sections as described above in the 
first embodiment, are passed through a synthetic resin extruder (not 
shown), so that the synthetic resin is fused onto the belt plate 6, 7 over 
the entire inner and outer peripheral surfaces thereof to form a molded 
belt member 6A, 7A. The belt member 7A of an upwardly-opening 
cross-section is precedingly wound helically, and subsequently the belt 
member 6A of a downwardly-opening cross-section is disposed above the belt 
member 7A and is helically wound in such a manner that the opposite lower 
ends or side edges of the belt member 6A abut respectively against the 
upper ends of the adjacent turns of the precedingly-wound belt member 7A. 
The thus abutted ends formed of the molded resin are fused to be joined 
together to form connective portions 3a and 4a. In this manner, the 
continuous helical pipe is formed step by step. Further, a synthetic resin 
belt member 12, which is similar to that shown in FIG. 3 and has a 
generally upwardly-opening, inverted trapezoidal cross-section, is 
helically wound on the outer periphery of the wall constituted by the belt 
members 6A and 7A, with its opposite side portions or projections fused 
together, and also the belt member 12 is fusingly joined integrally to the 
molded resin of the belt members 6A and 7A. 
In this embodiment, the synthetic resin is beforehand fused to and 
integrally formed with each of the metal belt plates 6 and 7 over the 
entire inner and outer surfaces thereof. Thus, each metal belt plate is 
embedded in the synthetic resin material from the beginning, and the 
connective portions 3a and 4a made solely of the synthetic resin 
interconnect the opposed ends or edges of the belt plates 6 and 7 to form 
the helical pipe, as shown in FIG. 2. The metal belt plates 6 and 7 are 
not present in the connective portions 3a and 4a. 
In this embodiment, although the belt members to be first wound are the 
resin molded belt members 6A and 7A having the synthetic resin applied 
integrally over the entire inner and outer peripheral surfaces of the 
metal belt members 6 and 7, the pipe wall may be formed by first winding 
the inner belt member 11, made solely of a synthetic resin, to form the 
inner resin wall portion of the pipe wall as in the first embodiment and 
then by winding the molded belt members 6A and 7A around this inner resin 
wall portion and fusing them to be integrally joined together. Further, an 
outer layer or wall of a synthetic resin may be formed on the outer 
periphery of such a construction to cover the same. Although not shown in 
the drawings, connective-purpose belt or extension portions made solely of 
the synthetic resin may be formed respectively on the lower ends or edges 
of the upper resin molded belt member 6A of a downwardly-opening 
cross-section, in which case these extension portions are fused to be 
integrally joined to the outer surface of the lower resin molded belt 
member 7A of an upwardly-opening cross-section, thereby interconnecting 
the two molded belt members 6A and 7A. 
The metal belt plates 6 and 7 are not limited to a flat plate, and they can 
be made by a so-called perforated metal plate having a number of small 
perforations or punched holes formed therethrough. When synthetic resin 
layers are applied to such a metal plate having a number of small 
perforations, the synthetic resin layers on the opposite sides of the 
perforated metal plate flow through the perforations and are integrally 
joined together, so that the metal belt plate is firmly joined to the 
inner and outer resin layers. However, as described above in the above 
embodiments, the metal belt plates 6 and 7 used in the present invention 
are not necessarily limited to such a plate having the small perforations. 
A method of manufacturing the resin molded belt members 6A and 7A is not 
limited to the above-mentioned method in which the synthetic resin is 
extruded from the die together with the metal belt plate 6, 7 to cover the 
same. For example, there can be used a covering method in which the metal 
belt plate 6, 7 is dipped in a molten resin, and also other coating and 
resin-application methods can be used. 
In the helical corrugated pipes of the above embodiments, the pipe wall 1 
is not provided with an inner pipe wall and therefore the inner peripheral 
surface of the pipe has a corrugated configuration. Such a pipe which is a 
so-called single-wall type helical pipe is used mainly as a 
cable-protective pipe into which a cable such as an electric cable and a 
telephone cable is inserted. In this case, the cable, when inserted into 
the pipe, comes into contact only with the corrugation of the inner 
peripheral surface of the pipe, and therefore the cable can be inserted 
into the pipe with a less frictional resistance. 
Next, pipes of other embodiments having an inner pipe wall will now be 
described. 
An embodiment shown in FIGS. 5 and 6 relates to a helical corrugated pipe A 
in which metal belt plates 6 and 7, respectively having a 
downwardly-opening trapezoidal cross-section and an upwardly-opening 
trapezoidal cross-section, are embedded in a pipe wall 1 as described 
above in the preceding embodiments, and in which an inner pipe wall 8 of a 
cylindrical shape is provided in the pipe wall. As shown in FIG. 6, a 
synthetic resin belt member 11 of a trapezoidal cross-section for forming 
an inner resin wall portion or layer of the pipe wall has a raised central 
portion and lower end or edge portions projecting laterally outwardly away 
from each other. Another synthetic resin belt member 12 for forming an 
outer resin layer of the pipe wall has a cross-section generally similar 
to but inverse to that of the belt member 11, that is, an inverted 
trapezoidal cross-section having a central portion recessed downwardly. 
The metal belt plates 6 and 7 are sandwiched between the two belt members 
11 and 12 to form the helical corrugated pipe wall 1. A flat belt member 
13 for forming the inner pipe wall 8 is applied to the inner peripheral 
surface of the helical corrugated pipe wall 1 in such a manner that the 
belt member 13 is integrally joined by fusion to a bottom portion 5 of the 
pipe wall 1. 
The pipe having the inner pipe wall 8 provided in the helical corrugated 
pipe wall 1 is mainly used as a water main pipe, a sewer pipe, a pipe for 
transporting various chemicals or the like in a plant, and a pipe for the 
airborne transport of particles such as grain. In this case, because of 
the provision of the inner pipe wall 8, the flowing fluid in the pipe 
undergoes a less resistance, and therefore the fluid can be transported 
smoothly. 
Next, modifications of the helical corrugated pipe wall 1 and the metal 
belt plates 6 and 7 will now be described. 
In the above embodiments, although the corrugation of the pipe wall 1 as 
well as the belt plates 6 and 7 has a trapezoidal cross-section, the metal 
belt plates 6 and 7 may have, for example, an arcuate cross-section as 
shown in FIG. 7, in which case the pipe wall 1 has an arcuate corrugated 
cross section so as to match the shape of the metal belt plates 6 and 7. 
Also, for example, a channel-shaped corrugated cross-section or a 
triangular corrugated cross-section may be employed. 
The metal belt plates 6 and 7 are not always required to have the same 
size, the same shape and the same thickness. The thickness of the resin 
constituting the pipe wall 1 does not always need to be uniform over the 
entire region thereof. Specifically, for example, as shown in FIG. 8, one 
belt plate 6 may have a greater width whereas the other belt plate 7 may 
have a smaller width. Also, as shown in FIG. 9, one belt plate 6 may be of 
a trapezoidal shape whereas the other belt plate 7 may be of a different 
shape such as an arcuate shape. In FIG. 9, the metal belt plates 6 and 7 
are embedded in the pipe wall 1 in such a manner that the opposite side 
edges of metal belt plate 6 are almost abutted against the opposite side 
edges of the metal belt plate 7, respectively, at the respective 
connective portions 3a and 4a of the side wall portions 3 and 4 of the 
pipe wall 1. 
In an embodiment of the invention shown in FIG. 10, a pipe has a pipe wall 
1 having a uniform thickness over the entire region thereof. Metal belt 
plates 6 and 7 are embedded in the pipe wall 1 in such a manner that the 
metal belt plate 6 is offset in the direction of the thickness of the pipe 
wall 1 toward one side of the pipe wall 1 whereas the metal belt plate 7 
is offset in the direction of the thickness of the pipe wall 1 toward the 
other side of the pipe wall 1. With this arrangement, a thickened resin 
portion 9 is provided at the outer section of a top portion 2 of the pipe 
wall, and a thickened resin portion 10 is provided at the inner section of 
a bottom portion 5 of the pipe wall 1. 
However, the thickened resin portions 9 and 10 do not always need to be 
provided over the entire widths of the top and bottom portions 2 and 5, 
respectively, and may be partially provided. 
In the case where such thickened resin portion is provided at the inner 
side of the bottom portion 5, even when wear develops due to the 
frictional contact of a cable or the like, the wear does not reach the 
metal belt plate 7, so that the metal belt plate 7 will not become bare, 
thus positively preventing this metal belt plate from being subjected to 
rust. In the case where such thickened resin portion is thus provided at 
the outer side of the top portion, even when the pipe is dragged at the 
time of installation thereof, and is brought into contact with a sharp 
corner of a stone or a rock so that the pipe is damaged, the metal belt 
plate 6, advantageously, will not be exposed immediately. 
In an embodiment of the invention shown in FIG. 11, one belt plate 6 is 
formed using a metal belt material having a greater thickness than that of 
the other metal belt plate 7. Thus, the metal belt plates 6 and 7 may be 
made respectively of the materials having different thicknesses. Also, the 
two metal belt plates may be made of different materials. For example, one 
may be made of steel, and the other may be made of iron. 
In the above embodiments, the pipes include the metal belt plates 6 and 7 
which are covered with the covering or coating materials of a synthetic 
resin or the like over the entire inner and outer peripheral surfaces 
thereof. In other words, the pipes are of such a construction that the 
metal belt plates 6 and 7 are embedded in the pipe wall forming material 
of a synthetic resin or the like. However, in the present invention, the 
metal belt plates 6 and 7 are not always required to be covered with a 
synthetic resin or the like over the entire peripheral surfaces thereof. 
In the case where the metal belt plates 6 and 7 are made of a rust 
resistant material or a material which has been subjected to a 
rust-prevention treatment such as plating, electrophoretic deposition, 
metallic coating and resin baking finish, the pipe can be of such a 
construction that the metal belt plates 6 and 7 are partially exposed at 
the surface of the pipe wall, as in those embodiments mentioned below. 
In an embodiment of the invention shown in FIG. 12, two kinds of metal belt 
plates 6 and 7 are arranged in such a manner that the opposite side edges 
of the belt plate 6 abut respectively against the opposite side edges of 
the belt plate 7 at opposite side wall portions 3 and 4 of a pipe wall 1. 
The outer surface of a top portion 2 of the pipe wall 1 and the inner 
surface of a bottom portion 5 are covered with resin materials 12 and 11, 
respectively, in such a manner that the resin materials 11 and 12 also 
cover the opposite sides of the belt plates 6 and 7 at connective portions 
3a and 4 interconnecting there two belt plates. Thus, the inner side of 
the top portion 2 is exposed at the inner surface of the pipe wall 1, and 
the outer side of the bottom portion 5 is exposed at the outer surface of 
the pipe wall 1. 
In an embodiment of the invention shown in FIG. 13, two kinds of metal belt 
plates 6 and 7 are arranged in such a manner that the opposite side edges 
of the belt plate 6 are disposed in spaced opposed relation to the 
opposite side edges of the belt plate 7, respectively, at opposite side 
wall portions 3 and 4 of a pipe wall 1. The other features of the 
construction are similar to those of the embodiment of FIG. 12. 
In an embodiment of the invention shown in FIG. 14, inner and outer 
surfaces of one metal belt plate 7, which is disposed at the side of a 
bottom portion 5 of a pipe wall 1, are covered with resin materials 11 and 
12, respectively. The resin materials 11 and 12 also cover the opposite 
side edge portions of the other metal belt plate 6 at connective portions 
3a and 4a interconnecting the two belt plates 6 and 7. The metal plate 6 
disposed at the side of a top portion 2 of the pipe wall 1 remains bare at 
its inner and outer surfaces except for its opposite side edge portions 
covered respectively by the connective portions 3a and 4a. 
In an embodiment of the invention shown in FIG. 15, two kinds of metal belt 
plates 6 and 7 are abutted against each other at their side edges, and the 
inner and outer surfaces of the two metal belt plates 6 and 7 are covered 
at their abutted side edge portions with resin materials 11 and 12, 
respectively. Thus, in this case, the resin materials 11 and 12 serve as 
connective portions 3a and 4a interconnecting the two metal belt plates 6 
and 7. In this embodiment, the inner surface of a bottom portions 6 of a 
pipe wall 1 is covered with a resin material 14, and the outer surface of 
a top portion 2 is covered with a resin material 15. 
As to the material of the metal belt plates 6 and 7, in addition to a thin 
stainless steel plate or a steel plate, an iron plate may be used. Also, 
other metal may be used. When forming the above-mentioned punched holes, 
the shape, size and density of such holes can be suitably determined. 
As to the synthetic resin materials forming the pipe wall and the 
connective portions, a polyolefin such as polyethylene, polypropylene or 
the like, and a vinyl chloride can be mainly used, but other synthetic 
resins may be used. Also, rubber or a rubber-type resin such as synthetic 
rubber may be used. 
While the representative embodiments of the invention have been described 
herein, the invention itself is not to be restricted to such embodiments, 
and suitable modifications can be made so long as they have the essential 
features of the invention, achieve the object of the invention, and 
achieve the advantageous effects of the invention mentioned below. 
As described above in detail with reference to the preferred embodiments, 
in the present invention, the wide thin metal belt plates are used as 
constituent elements for the pipe wall. These metal belt plates are 
suitably processed and deformed, and one of the metal belt plates 
continuously extends over the entire top portion of a helical corrugated 
shape and part of the opposite side wall portions extending from the top 
portion. The other metal belt plate continuously extends over the entire 
bottom portion and part of the opposite side wall portions extending from 
the bottom portion. In the helical corrugated pipe, the two metal belt 
plates, disposed respectively at the side of the top portion of the pipe 
wall and the side of the bottom portion, are arranged in such a manner 
that their opposite side edges are disposed in opposed relation. With this 
construction, the two metal belt plates will not be displaced away from 
each other in the direction of the thickness of the pipe wall, thus 
maintaining a stable posture. Therefore, even if the metal belt plates are 
considerably thin, the resultant pipe has a sufficient pressure-resistant 
strength withstanding a flattening force. Therefore, even when the metal 
belt plates are covered with the synthetic resin material over the entire 
inner and outer peripheral surfaces thereof, such covering synthetic resin 
layers can be considerably reduced in thickness. This achieves such 
advantages as the reduction of the overwall weight of the pipe, easier 
transport and handling of the pipe, and the reduction of the amount of the 
synthetic resin to be used. As to the manufacture, the metal belt plate 
which is rather difficult to be formed into a wound shape is divided into 
the two kinds of metal belt plates adapted to be disposed respectively on 
the side of the top portion of the pipe wall and the side of the bottom 
portion, and these two kinds of metal belt plates can be wound 
independently from each other when manufacturing the pipe. Therefore, the 
pipe can be easily manufactured. Moreover, the metal belt plates are 
hardly subjected to wrinkles, and therefore the pipe having a good 
appearance can be manufactured. Further, the thin metal belt plates can be 
made of a relatively thick plate. Further, the two kinds of metal belt 
plates can have different thicknesses and hardnesses, and also can be made 
respectively of different materials.