Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a method and
apparatus for the production of branched junctions for
joining lengths o corrugated pipe.
Single walled corrugated tube and double
walled corrugated tube are both used, or example~ for
conduit for electrical wiring, sewer or drainage
purposes. Frequently, in use, it is necessary to join
a length of pipe into another length of pipe at an
angle which often a right angle. Junctions for such
joints are especially difficult to make for corrugated
pipe bec~use of the necessity of making a continuous
surace between the corrugations. The situation is
also difficult in the case of double walled corrugated
pipe since it is necessary to consider the provision
of a fluid tight surface at both the outer corrugated
wall and ~he smooth inner wall.
It is possible to make T junctions for
corrugated pipe as separate integral items by blow
~ moldislg techniques. The term "T junction as used
2~ herein is intended to include Y junctions and other
junctions including a plurality of branches. Such
~ ~ T junctions for large pipes are very expensive to
; produce since a separate mold must be provided for
~ each shape and size of the junction. The total number
-~ ~ of junctions of each shape and size which are produced
need not~necessarily be very many. Therefore the mold
costs may be excessive.
Moreover, there may be a problem in matching
~he diameters of the junctions produced with the
diameters of a pipe. This problem may be accentuated
when a pipe of one diameter is to be joined into a
pipe of a different diameter.
The actual joint of the T junction with the
pipes which intersect may, itself, cause problems.
The material and thickness of the pipe wall are such
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as to give it at least semi-rigid construction. Thus,
it is not thought practicable to joint the pipes by
force fitting onto a T junction. The T junctions,
themselves, at their free end, may be provided with
bells for easy connection with the end of the tubes
which they are to connect. The bells may be provided
by conventional methods or by a smooth walled node in
the corrugator face and by apparatus such as those
disclosed and claimed in U.S. Patent Nos. 4,534,923 to
Lupke issued August 13, 1985 and 4,500,284 to Lupke
issued February 19, 1985.
When pipe of small diameter is to be joined,
it may be possible to use conventional smooth walled
T junctions, especially when the pipe has smooth
walled ends adapted for joining with the smooth walled ~-
T junctions. However, such junctions are not only not
suitable for use ~lth large diameter pipe but also
such large diameter smooth wall T junctions are not
generally available.
While the use of smooth walled T junctions
having an internal fit into double walled corrugated
pipe might be possible, it is not suitable for single ~-
walled corrugated pipe unless a bell is provided at
the ends of the pipes which are to be connected. When
; the T junction and the associated belled ends of the
pipe have very short lengths, there may be little
deterioration of strength in the pipe. However, ~ -
should it be convenient or desirable to use a
T junction having relatively long legs, strength
deterioration may~be e~pected. ~-~
Moreover, if smooth walled tube T junctions
are used with their legs inserted into the ends of
double walled corrugated tube, there will be no
physical connection of the corrugated walls unless
smooth walled end portions of tube are provided. It
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will be necessary to provide a wrapping or other
sleeve around the joint. If this is not done, there
is a risk of liquid penetration between the smooth and
corrugated walls of each tube and, moreover, any rough
edges of the corrugated outer tube may be at risk of
tearing.
An attempt has been made to provide an
economically viable corrugated T junction which may be
easily matched with the diameter of tubing with which
it is to be used.
According to the invention, there is
provided a method of forming a junction from tube of
semi-resilient plastics material, the tube having
ridged outer surface, comprising molding continuous
tube in a travelling mold tunnel comprising mold
blocks having mold faces adapted to mold the ridged
tube and cooperating in pairs to form the tunnel.
Selected mold blocks ha~te mold faces adapted to mold
smooth regions of tube at axially spaced apart
locations of the tube, to provide lengths of the tube
adapted to form of the junction. Each length which is
adapted to form two aligned or substantially aligned
branches includes at least a first of said smooth
regions between its ends and each length adapted to
form a Ieg angled to the aligned branches includes a
second smooth region at at least one end thereof. An
orifice is formed in the first smooth region adapted
for connection with an open end of the leg length and
~' the second smooth region of the leg tube end is shaped
to fit snugly about the orifice. The leg tube end is
then fitted snugly about the orifice, and aligned
branch tube length and leg tube length are sealed
together. Herein after it will be assumed that the
aligned branch tube length forms a bar of the T, but
it is emphasiz:ed that Y configurations are possible.
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The tube may be corrugated tube, either
single walled or double walled or it may be ribbed
tube, or indeed, any other type of tube having a
roughened or ridged outer surface.
Selected mold blocks for providing lengths
of tube to form bar lengths, may have faces adapted to
mold a saddle shaped smooth region of tube each the
saddle-shaped region sized for forming said orifice
therein. Preferably, the saddle shaped smooth region
in is sized to allow a smooth margin about the orifice.
When such a margin is provided, a
corresponding leg tube length may be fitted to the bar
tube to fit snugly against the margin, to which it may
be sealed securely.
When double walled tube is used it may be
convenient to form the smooth walled regions as a
laminate of the walls.
Selected mold blocks for forming the leg
portion may have faces adapted to mold a pair of
diametrically opposed, axially extending, similarly
shaped, smooth walled regions having corresponding
edges shaped to correspond to the contour of the
smooth walled region of the bar tube length, and in
which the axially extending smooth walled regions are - ~;
cut out to adapt the leg tube length to fit ayainst
the bar tube length about the orifice.
Conveniently, bar tube lengths and leg tube
lengths may be molded alternately in a continuously
molded tube.
The invention also includes a~mold block
having a face having concavities and convexities
adapted to mold the surface of a molded article, in
combination with a mold face modifying insert having a
front mold fac:e of the mold block and a rear face
engaging the concavities and conve~ities of the mold
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face of the mold block through engagement means.
Such a mold block may be one forming part of
a travelling mold tunnel for molding tube. In that
case, the mold block may have a mold face having
alternating troughs and creæts adapted to form annular
corrugations or ribs in the resulting tube, and the
insert may have a rear face having valleys and ridges
to engage the troughs and crests of the mold block and
a smooth front face.
The insert may be generally saddle shaped
for the formulation of a saddle shaped smooth tube
section rom which an orifice may be cut.
Alternatively, a pair of diametrically locatable
inserts may be provided to form diametrically located
smooth tube portions which may be cut to fit against
the corresponding bar portion.
Embodiments of the invention will now be
described by way of example with reference to the
drawings in which:
Figure 1 shows a continuous length of pipe
which may be cut into sections to
form T junctions according to the
invention;
Figure 2 shows a pair of secti.ons cut from
the pipe of Figure 1 and located
ready for T junction formation;
Figure 3 illustrates a slightly differently
configured pipe from that of
; Figure l;
Figure 4 shows a pair of sections cut from
the pipe of Figure 3 located ready
for formation of the T junction;
Figure 5 illustrates the interior surface
of a mold block of the type
commonly used in travelling mold
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tunnel apparatus modified or the
formation of one configuration of -~
Figure l;
Figure 6 illustrates an insert for a
conventional mold block for ~he
formation of corrugated pipe to
modify it in one configuration;
Figure 7 shows a T junction ormed from the
pipe illustrated in Figures 1 and
2;
Fiyure ~ shows a T junction formed from the
pipe illustrated in Figures 3 and :
4; and
Figure 9 shows an interior surface of a
mold block modified for the
formation of another configuration
~:~ of Figure 1.
In the drawings corrugated or ribbed tube 10
as shown in Figures 1 and 3 may be continuously
:20 extruded in apparatus of the type forming a travelling
: mold tunnel.
Corrugated tube 10 is formed with spacect
apart regions 14~and 16 whi;ch are not corrugated or
ribbed in any manner. The region 14 is a generally
~:: saddle shaped~smooth area of the tube of a size and
shape to correspond with an end of a projecting leg of
: a T region 16 comprises:a pair of opposed, smooth ::
axially extending, symmetrical undulations having a :
curvature corresponding to that of the saddle shaped
are 14.
: To form a T junction 20, the tube 10 is
severed into lengths, one of~which, including a saddle
: shaped area 14 forms the bar 22 of the T junction 20
~- and the other of which, having a cut out 24 from
: region 16 forms the leg 26 of the T junction 20.
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In practice it may be convenient to mold
tube lO having alternating regions 14 and 16.
However, tube lO may be formed w;th a plurality of
spaced-apart saddle shaped regions 14 and no
undulating regions 16 which may be molded in a
separate tube. When the regions 16 and 14 are formed
in separate tubes, the tubes need not necessarily be
of the same diameter. While modification or these
lines are clearly within the scope of the invention,
the formation of the T-junction will be specifically
described with reference, in the first instance to
tube lO of Figure 1.
Tube 10 of Figure 1 comprises only two
lengths, one including region 14 and one having region
16 at its end. The tube lO is cut into these two
lengths at the smooth walled portion of region 16
indicated by broken line 17. Line 17 may allocate all
the region 16 to the leg length 26, or it may allocate
a short cylindrical smooth walled portion to the bar
length 22 for the purpose of forming a coupling region
with another length of tube.
After cutting tube lO into the two lengths
26 and 22, each of these lengths is trimmed for
securing them together in T configuration. Saddle
shaped, smooth walled region 14 of bar tube length 22
is trimmed to make an access~aperture 28 into the
interior of tube length 22. The aperture 28 is
surrounded by a margin 30 of the saddle shaped region
14 which extends such that a close fit with the
abutting leg tube length 26 is possible.
Somewhat similarly the smooth walled portion
of leg tube length 26 is trimmed. In this case the
trimming closely conform to the shape of the
undulation such that the resulting trimmed leg tube
length 26 has an end 32 adapted to abut closely
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against smooth walled margin 30 of bar tube length
22. It is, of course, not necessary for the end 32 to
ahout the margin 30; it may alternatively project
slightly into the aperture 28, in which case it is
desirable to provide a smooth walled margin at end 30
so as to provide an abutment surface for the edge of
aperture 28.
In any event, once tube lengths 22 and 26
are fitted together in T configuration, they may be
secured in this configuration by butt welding, stick
welding or other conventional means. When the tube
lengths 22 and 26 are ~ormed form polyvinyl chloride, ~ -
they may be glued together.
- The smooth walled saddle shaped region 14
and the smooth walled undulations 16 may be formed by,
for example, modifying certain of the mold blocks in
molding apparatus forming an advancing mold tunnel.
In such apparatus mold blocks move in at least one
continuous path to form a closed mold tunnel in a
forward run. Mold blocks from the forward end of the
mold tunnel, after releasing formed tube are
recirculated to the beginning of the tunnel.
Conventionally, either two circulating paths for mold
blocks are provided, the mold blocks of each run
cooperating to form the tunnel on the forward run.
Alternatively a single circulating path of mold blocks
is provided. In this case the mold blocks may
comprise halves which are hingably connected to form
the mold tunnel in a forward run and open to release
the formed tube before the return run. In either case
the mold blocks may be generally of the form shown in
Figures 5 and 5 which also shows means for forming
saddle region 14. In fact, Figure 5 shows mold blocks
34, 34', 35, 35' and Figure 6 shows mold blocks 36,
36', 37, 37' for use in two circulating paths, but if
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the upper mold blocks 35 were hinged to the lower mold
blocks 36 only one circulating path would be necessary.
Mold blocks such as mold blocks 34, 35 may
be shaped to form corrugated or ribbed tube. When
ribbed tube is to be molded, rib forming troughs of
the mold block are often deeper and sharper than those
required for corrugated tube. When double walled
corrugated tube is to be molded an inner wall is
extruded within the outer corrugated wall formed in
crests and troughs of the mold blocks.
In order to form the saddle region 14 or the
region 16 having symmetrical undulations 17, a mold
block, or a pair of mold blocks cooperating to form a
tunnel section, or two or more axially adjacent mold
blocks, may be modified to form these regions.
Examples of mold blocks cooperating to form a tunnel
section are 34, 34' and 35, 35' and 36, 36' and 37,
37'. Examples of two axially adjacent mold blocks are
34, 35 and 34', 35' and 36, 37 and 36' and 37'.
The modification may be the provision of a
region 42 of the appropriate mold block or blocks to
mold a smooth walled section of tube level with the
base of the valleys 38 between corrugations or ribs 40
of the resulting tube. The region 42 as shown in
Figure 5 is designed to mold an appropriate saddle
region 14 and extends over two axially adjacent mold
blocks 34, 35. Mold blocks may be customed machined
to incorporate a suitable region 42. It may be
envisaged that saddle region 14 is not necessarily
always of the same dimensions. For example, saddle
region 14 may be small when it is envisaged forming a
. .
T junction with a diameter leg 26. Thus a large
number of customized mold blocks may be necessary to
form a full range of T junctions. Moreover, it is
necessary to physically change the conventional mold
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block for the modified mold block when it is desired
to provide a smooth walled region 14 or 16.
The modification of the mold blocks may
alternatively be achieved by means of an insert 44 as
shown in Figure 7. The insert 44 of Figure 7 is
depicted to form a saddle region 14 but it will be
appreciated that inserts for the undulations 17 might
equally well be provided. An insert 44, which ever
region it is intended to mold, comprising a front
molding face and rear surface abutting the respective
mold block or mold blocks. The rear face may be
formed with ribs 46 and valley 47 complementary to the
troughs and crests 48, 50 of the mold blocks. The
insert 44, may then be engaged in its desired position
in the mold tunnel by engagement of its ribs 44 and
valleys 47 with respective troughs 45 and crests 50 of
the mold blocks 34, 35.
When, as shown, the insert e~tends over more
than one axially adjacent mold blocks 34, 35 it will
automatically disengage from one of them at the
forward end of the mold tunnel. As the leading mold
block, say 35, ends its forward run and either moves
away from the alignment of the forward run, or hinges
away from it, to release formed tube, it will
: disengage from insert 44. Insert 44 will still be
:~ carried by the other mold block 34 of the pair. If
the return run is straight there may be automatic
re-engagement with both mold blocks 34, 35. The
insert 44 may be removed entirely during the return
3~ run and replaced with a different mold block, if
desired.
Figure 6 shows mold blocks 36, 36', 37, 37'
modified to mold the smooth walled undulations 17 and
a short section of smooth walled cylindrical tube. In
this case modifications are made to both upper and
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lower blocks. Conveniently, the undulations 17 are
formed by modified mold regions 52 and the smooth
walled cylindrical tube is formed by mold regions 54.
As described the mold regions may be machined or
provided by inserts.
It is important to not that when double
walled corrugated tube is being ormed, the two walls
may form a laminate in the smooth walled regions
referred to. Not only may this be advantageous in
overcoming some of the difficulties encountered in
joining double walled corrugated tube in that it
avoids a separated double wall at the joint, but it
also may provide some strength advantages which would
not be present in a non-laminated true single wall.
Figures 3 and 4 of the drawings illustrate a
slightly different embodiment in that the end 32' of
leg tube length 26 is provided with an outwardly
extending flange 56 to make a good seal with margin 30
of the bar tuhe length. Flange 56 may be molded by
means of troughs 58 of modified mold regions 52. Such
a flange 56 may suitably have an end face 58
orthogonal to the tube axis and a following face 60
which merges into the next adjacent valley of the
corrugated tube 10.
Figure 9 shows an assembled T junction form
tube of Figures 1 and 2 and Figure 10 shows an
assembled T junction from tube of Figure 3.
Other modifications will be apparent to one
skilled in the art.
9276b~
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