CA2013666A1 - T-junction for double-walled corrugated tube - Google Patents

Abstract

ABSTRACT

This invention concerns branched connectors for joining single walled corrugated or double walled corrugated pipe. A method of forming a branched junction comprises forming tube of the type to be joined with smooth patches which are later excised so that sections of the tube may be fitted and sealed together to form the connectors. The invention includes special mold blocks for use in a travelling mold tunnel to form the smooth regions and/or special inserts for standard mold blocks to adapt them for forming smooth walled regions.

Description

2~3~

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 i, - ~ .:. ~ ~

.~. 2~3~

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 ~, .. . . . . .

2 ~

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.

~ 21~3~
, 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 21~:d 36~

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 2~3~

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.
`:

} ~ s ~

2 ~

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 2~3~

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 ~,,,., - - I

- 2~3~

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 .~ ç~ 3 ~.~ r,~ ~

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 ,............. . .

~'~
2 ~

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~

:

Claims (14)

1. A method of forming a branched 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 ridiged tube and cooperating in pairs to form the tunnel, selected mold blocks having mold faces adapted to mold smooth regions of tube at axially space apart locations of the tube:
the method comprising molding bar and leg lengths of the tube adapted respectively to aligned branches and branches to be angled thereto, each length adapted to form aligned branches including at least a first of said smooth regions between its ends and each length adapted to form a branch angled thereto including a second smooth region at least one end thereof;
forming an orifice in the first smooth region adapted for connection with the leg length;
fitting an end of said leg length snugly about the orifice; and sealing the bar length and the leg length together about the orifice.

2. A method of forming a branched junction as claimed in claim 1, in which the tube is corrugated tube.

3. A method of forming a branched junction as claimed in claim 2, in which the tube is double walled tube.

4. A method of forming a branched junction as claimed in claim 1, in which selected mold blocks are adapted to mold a saddle shaped first smooth region of tube sized for forming said orifice therein.

5. A method of forming a branched junction as claimed in claim 4, in which the saddle shaped first smooth region in is sized to allow a smooth margin about the orifice.

6. A method of forming a branched junction as claimed in claim 5, in which said end of the leg length is fitted snuggly against the margin.

7. A method of forming a branched junction as claimed in claim 6, in which selected mold blocks are adapted to mold a saddle-shaped first region in which the two walls are laminated together, the smooth walled first region being sized for forming said orifice therein.

8. A method of forming a branched junction as claimed in claim 7, in which the saddle shaped first smooth region in is sized to allow a smooth margin about the orifice.

9. A method of forming a branched junction as claimed in claim 8, in which said end of the leg length is fitted snuggly against the margin.

10. A method of forming a branched junction as claimed in claim 1, in which selected mold blocks are adapted to mold a pair of diametrically opposed axially extending similarly shaped smooth walled first regions having corresponding edges shaped to correspond to the contour of the smooth walled second region of the bar length, and in which the axially extending smooth walled regions are cut out to adapt the leg length to fit against the bar length about the orifice.

11. A method of forming a branched junction as claimed in claim 3, in which selected mold blocks are adapted to mold a pair of diametrically opposed axially extending similarly shaped smooth walled first regions having corresponding edges shaped to correspond to the contour of the smooth walled second region of the bar length, and in which the axially extending smooth walled regions are cut out to adapt the leg length to fit against the bar length about the orifice.

12. A method of forming a branched junction as claimed in claim 1, in which bar lengths and leg tube lengths are molded alternately in a continuously molded.

13. A mold block having a mold 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 face of the mold block and a rear face engaging the concavities and convexities of the mold face of the mold block through engagement means.

14. A mold block as claimed in claim 13, which forms part of a travelling mold tunnel and has a mold face adapted to form annularly ridged tube, the insert having a rear face contoured in mirror image to that of the mold face of the mold block whereby the contoured rear face is engagable with the mold face of the mold block.