GB2399694A

GB2399694A - A conduit unit formed of two identical parts

Info

Publication number: GB2399694A
Application number: GB0306427A
Authority: GB
Inventors: Russell Darling Currie
Original assignee: Johnston Pipes Ltd
Current assignee: Johnston Pipes Ltd
Priority date: 2003-03-20
Filing date: 2003-03-20
Publication date: 2004-09-22
Anticipated expiration: 2023-03-20
Also published as: GB0306427D0; WO2004084369A1; GB2399694B

Abstract

A conduit unit (10, 10A) has a channel defined by a base portion (13, 13A) and a pair of spaced apart walls (11, 11A, 12, 12A) extending away from the base portion (13, 13A) and one wall (12, 12A) having male locating means (14, 14A) and the other wall (11, 11a) having female locating means (15, 15A). The conduit unit (10, 10A) can be assembled with an identical inverted conduit unit (10, 10A) with the male locating means (14, 14a) co-operating with female locating means (15, 15A) of the inverted unit and with the female locating means (15, 15A) co-operating with male locating means (14, 14A) of the inverted unit (10, 10A). Thus, one conduit unit (10, 10A) is securely seated on the other (10, 10A).

Description

A CONDUIT UNIT FOR USE AS CABLE TROUGHING

CABLE TROUGHING COMPRISING AT LEAST TWO CONDUIT

UNITS, A METHOD OF MANUFACTURE OF AN ANGLED JOINT CONDUIT UNIT, A METHOD OF MANUFACTURE OF A T-JUNCTION CONDUIT UNIT,

A METHOD OF MANUFACTURE OF CABLE TROUGHING

AND A GANG MOULD FOR USE IN THE METHOD

The present invention relates to a conduit unit suitable for use in the formation of cable "roughing for locating cables, in particular for locating cables alongside railway tracks or motorways. The present invention also relates to cable "roughing formed from a plurality of conduit units of the invention, to a method of manufacture of an angled joint conduit unit, to a method of manufacture of a T-junction conduit unit, to a method of manufacture of cable "roughing from a plurality of the conduit units and to a gang mould for use in the method.

Cable "roughing is well known in the art for locating cables together in a known, safe and usually visible location. It typically carries power cables, electrical cables for carrying signals (e.g. telecommunication signals or signals to operate railside or roadside indicators) and fibre optic cables, particularly alongside railway tracks and motorways. Typically cable "roughing comprises a U-shaped trough with a planar lid which may be locked in place. Cable "roughing is typically mass produced using semi- dry concrete. It is used either surface mounted, i.e. above ground, buried below ground or partially buried. It is typical to leave at least the top surface of cable "roughing exposed to allow access.

Known cable "roughing has several disadvantages. The troughs and lids must be manufactured separately, and the - 2 - correct number of each must be transported to the site.

Each trough is usually considerably heavier than the lid, ; and can weigh over 5Okg. This can cause problems when manhandling or carrying of the trough is required. For instance health and safely regulations dictate than anything heavier than 25kg should not be lifted by one person.

In order to carry cables alongside a curved railway line or motorway or over bridges, known cable "roughing requires compatible fittings such as bends and junctions which are usually manufactured individually using wet cast concrete cast in moulds individual to the particular bend or junction. Such moulds are typically made of timber and the cast components usually take one day to manufacture. It has not been possible to arrange for mass production of the bends and junctions. ; Another problem faced by the prior art cable troughs is the issue of security. Cable "roughing typically carries copper cable which has a high scrap value and is liable to theft.

The present invention provides, in a first aspect, a conduit unit for use in assembly of cable "roughing, the conduit unit having a channel defined by a base portion and a pair of spaced apart walls extending away from the base portion and one wall having male locating means and the other wall having female locating means whereby the conduit unit can be assembled with an identical inverted conduit unit with the male locating means co-operating with female locating means of the inverted unit and with the female locating means co-operating with male locating means of the inverted unit in order that one conduit unit is securely seated on the other to form a part of the cable trough. - 3 -

This has the advantage that only one unit has to be manufactured, rather than the U-shaped unit and planar lid of the known art. Additionally, the weight of the lower unit is smaller and so facilitates manhandling and carrying. The weight of the upper unit is heavier than the conventional lid, which reduces the risk of it being dislodged by wind or vandals and discourages thieves.

However, it is envisaged that each unit could be made light enough to be handled by a single individual, provided it was the right size and length (however, for all sizes and lengths the conduit unit of the present invention will be lighter than a known base unit of the same size and length).

The present invention provides, in a second aspect, cable "roughing comprising at least two conduit units, each having a channel defined by a base portion and a pair of spaced apart walls extending away from the base portion, the cable "roughing being assembled with one conduit unit inverted with respect to the other conduit unit and with the walls of one conduit unit seated on the walls of the other conduit unit.

The present invention provides, in a third aspect, a method of manufacture of an angled joint conduit unit comprising the steps of: forming a plurality of conduit units of the type described above; joining at least two pairs of the conduit units together to form two cable trough units each comprising a lower conduit unit with an upper conduit unit seated thereon, the upper conduit unit being inverted relative to the lower conduit unit; cutting at least two of the formed cable trough units each along a plane angled with respect to a plane extending transversely across the cable trough unit; and joining along the cut planes at least one cut part of one - 4 - trough unit with a cut part of the other trough unit.

The present invention provides, in a fourth aspect, a method of manufacture of an angled joint conduit unit comprising the steps of: forming a plurality of conduit units of the type described above; joining at least one pair of the conduit units together to form a cable trough unit comprising a lower conduit unit with an upper conduit unit seated thereon, the upper conduit unit being inverted relative to the lower conduit unit; cutting the formed cable trough units along at least two cut planes each angled with respect to a plane extending transversely across the cable trough unit; and joining along the cut planes at least one cut part of the trough unit with another cut part of the trough unit.

The present invention provides, in a fifth aspect, a method of manufacture of a T-junction conduit unit comprising the steps of: forming a plurality of conduit units of the type described above; joining a plurality of the conduit units together to form a plurality of cable trough units each comprising a lower conduit unit with an upper conduit unit seated thereon, the upper conduit unit being inverted relative to the lower conduit unit; cutting a W-shaped notch in one side of a first cable trough unit; cutting from one or more additional trough units at least two swept junction sections and a side branch section; fixing the swept junction sections in the W-shaped notch of the first cable trough unit to form a swept junction; and fixing the side branch section to the formed swept junction to complete the T-junction conduit unit. - 5 -

The present invention, in a sixth aspect, provides a method of manufacture of cable "roughing of the type described above, the method comprising the steps of: casting in concrete in a gang mould a plurality of straight conduit units, each having a channel defined by a base portion and a pair of spaced apart walls extending away from the base portion; removing the cast straight conduit units from the gang mould; transporting the cast straight conduit units to a site where they are needed; and on site assembling the cable "roughing from the plurality of straight conduit units by laying them end to end with some of the straight conduit units forming a lower part of the cable trough and other straight conduit units forming an upper part of the cable trough, the straight conduit units of the upper part being inverted with respect to the straight conduit units of the lower part and the walls of the straight conduit units of the upper part being seated on walls of the straight conduit units of the lower part.

The present invention, in a seventh aspect, provides a gang mould comprising a plurality of moulds, a majority of which are used for casting of straight conduit units to be used in formation of cable troughs of the type described above and a minority of which are used in casting of joint sections for the formation of angled joint conduit units for use with the said cable troughs, wherein the minority of the moulds used for the casting of the joint sections are provided with one or more former(s) to define the features of the joint sections.

Preferred embodiments of conduit units according to the present invention will now be described, with reference to the accompanying drawings, in which: - 6 - Figure 1 is a perspective view of a pair of straight conduit units according to the present invention; Figure 2 is a side elevation showing facing ends of two pairs of joined straight conduit units according to the present invention, with a first end configuration; Figure 2a is a plan view of conduit units of the type shown in Figure 1 with a variant end configuration; Figure 3 is a side elevation showing facing ends of lO two pairs of straight joined conduit units according to the present invention, with a second end configuration; Figure 3a is a plan view of the conduit units of Figure 3; Figure 4 is a side elevation showing facing ends of two pairs of straight joined conduit units according to the present invention, with a third end configuration; Figure 5 is a plan view of two of the straight conduit units shown in figure 3 joined end to end; Figure 6 is a side view of the joined straight conduit units of figure 5 with a bridging straight conduit unit (again of the type illustrated in figure 3) shown in dotted lines set across a lower joint; Figure 7 is a cross-section through the joined straight conduit units of figure 6 taken along the line A-A' of figure 6, in the direction of the illustrated arrows (again the upper conduit unit is shown in dotted lines) ; Figure 8 is an side view of two of the figure 3 straight conduit units joined end to end and in dotted lines an upper straight conduit unit forming a matched coterminous pair with one of the lower straight conduit -units; Figure 9 is a side elevation view of two joint conduit units according to the present invention, prior to connection, the joint units forming together a vertical bend with one an uphill unit and the other a return unit; - 7 - Figure 10 is a plan view of a lower T-joint conduit unit according to the present invention; Figure 11 is a plan view of a first lower corner conduit unit for a horizontal plane bend according to the present invention; Figure 12 is a plan view of a second lower corner conduit unit for a horizontal plane bend according to the present invention; Figures 13 to 16 illustrate a method of construction of the lower T-joint conduit unit of figure 10, figure 13 being a plan view of the finished unit illustrating different sections of the unit, figure 14 being a side elevation view of the figure 13 finished unit, figure 15 being a plan view of a straight conduit unit cut or moulded in sections and figure 16 being a plan view of a further straight conduit unit cut or moulded in sections; Figure 17 is a plan view of a mould used to manufacture the conduit units of the present invention; and Figure 18 is a cross-section of a part of the figure 17 mould, taken along the line A-A' on the direction of the arrows shown in figure 17.

Referring to Figure 1, there are shown two straight conduit units 10 and lOA, both identical to each other, which provide respectively lower and upper portions of cable "roughing formed when the two units are joined together, one above the other.

The cross-section of each straight conduit unit 10, lOA is constant and is substantially U-shaped having two side walls 11,12 and llA,12A extending away from a base 13,13A. The walls 12,12A both have an end surface 14,14A which is convex when viewed in transverse cross-section and the walls ll,llA both have an end surface 15,15A which is concave when viewed in transverse cross- section.

The surfaces 14,15,14A and 15A all have the same radius - 8 - of curvature and all match each other. Preferably each unit is lm long. The choice of length is dictated by a need to make each unit light enough to be manhandled and also short enough that offset forces on the unit do not result in significant bending moments on the unit.

When the straight conduit units 10 and lOA are assembled to form cable "roughing, the straight conduit unit lOA is placed vertically above the straight conduit unit 10, the unit lOA being inverted having regard to the unit 10.

When they are brought into contact a section of cable "roughing is formed. The convex surface 14 acts as a male connecting feature of the unit 10 and abuts and engages the concave surface 15A which acts as a female connecting feature of the unit lOA. Similarly the convex surface 14A acts as a male connecting feature of the unit lOA and abuts and engages the concave surface 15 of the unit 10. By shaping of the surfaces 14,15,14A,15A the interaction between the abutting surfaces acts to prevent relative transverse movement of the two units lO,lOA.

This is very important since cable "roughing located next to railways and motorways experiences a considerable degree of vibration and must be able to withstand the vibrational forces without the upper unit lOA slipping off the lower unit 10.

A plurality of matched straight conduit units lO,lOA are arranged end to end to form cable "roughing. In order to increase theresistance of the cable "roughing to lateral forces, it may be desirable to stagger the upper conduit units lOA from the lower conduit units 10, so that a single upper conduit unit lOA bridges two lower conduit units 10, with each half of each upper conduit unit lOA engaging a half of each of two lower conduit units 10.

At each end of the cable "roughing a half length of upper straight conduit unit lOA would be used to finish the run of upper straight conduit units lOA. The half length 9 - conduit units lOA could be factory made and delivered to the location of installation or the assembler of the cable "roughing could simply cut a whole unit in half during assembly of the cable "roughing.

In the figure 1 it can be that the straight conduit unit has a 'knockout' section 16. This is formed by a rebate in the external surface of the wall 15 which forms a section in the wall 15 of reduced thickness. An installer installing a cable trough using the conduit units 10, lOA can knock through the preformed knock-out section 16, e.g. with a hammer, to provide an aperture through which cables can be led into and out of the cable "roughing. The rebate in the external wall surface makes the 'knock-out' section immediately visible to the installer. The lack of a corresponding rebate (aligned with rebate 16) on the internal surface of wall 11 is deliberate in order to avoid sharp edges which might damage cables dragged through the cable trough. The edges of the rebate 16 are also preferably radiussed again to minimise wear of cables passing through an aperture left when the rebate is knocked through. The straight conduit unit lOA, being identical to the straight conduit unit 10, also has a 'knock-out' section formed by a rebate in the external surface of the wall llA. Since the conduit unit lOA is inverted with respect to conduit unit 10 the 'knock-out' section of the unit lOA faces in the opposite direction to the 'knock-out' section of the unit 10 (and at a higher level) and thus conveniently provides the installer with the possibility of leading cables into and out of the cable trough from both sides of the "roughing (and at two different heights).

Each straight conduit unit lO,lOA is manufactured out of cast concrete by a method which will be described later

in this specification. - 10

In figure 1 each straight conduit unit is shown with a planar end surface with no provision for end to end attachment to another conduit unit. Variations of end surface designs are shown in figures 2 to 4. In figure 2 each end surface of each lower straight conduit unit 30 is provided with a pair of blind horizontal bores, two such bores 31,32 being shown in dotted lines in the figure. During assembly of a cable trough from the units 30 an assembler would insert one end of a dowel horizontally into one of the bores e.g. 31 and then insert the other end of the dowel into the other bore e.g. 32 (and the assembler would use a second dowel to link the other bores of the two units 30, not shown in the figures). The dowels used could be of the 'fir tree' design or could be serrated pins. If the assembler wishes to ensure that the assembled units remain in strict straight alignment then steel pins could be used.

This would be the case, for instance if the straight conduit units are assembled with the upper conduit units each bridging two lower conduit units. If the assembler wishes to allow a degree of articulation between conduit units assembled end to end then plastic connectors could be used which would flex to allow one unit to be out of alignment with the next, e.g. to accommodate formation of gradual bends in the cable trough and/or slight inclines.

This assumes that the upper conduit units are laid coterminously with the lower conduit units.

Figure 2a shows a variant of the Figure 2 end configuration designed to minimise intrusion of debris into the joint between two conduit units. One end face 34 of each unit 33 is angled so that the wall end faces are inclined and extend longitudinally outwardly from the base section and the other end face 35 of each unit 33 is angled so that the wall end faces are inclined and extend longitudinally inwardly from the base section. Thus in - 11 - the formed joint there are two opposed surfaces extending transversely of the cable "roughing and two pairs of facing inclined surfaces inclined to the transversely extending surfaces.

The figure 2 and 2a conduit end configurations allow only a limited degree of articulation between adjacent conduit units. A much greater degree of articulation (at least within a horizontal plane common to the units) is provided by the end configuration illustrated in figures 3, 3a and 5. In the configuration one end face of each unit 40 is provided with a semi-circular horizontally extending protrusion 41 and the other end face is provided with a matching horizontally extending semi circular recess 42 (see Figure 3a). As with the figure 2 embodiment, each end face of each unit is also provided with a pair of blind bores 43, 44,45,46. When the units are brought together end to end then the protrusion 41 extends into the recess 42 and dowels are used to connect the blind bore 43 with the blind bore 44 and the blind bore 45 with the blind bore 46. The dowels used will typically be flexible in nature so that the units can easily be articulated about a vertical axis defined by interaction of the semi-circular protrusion 41 with the semi-circular recess 42. Alternatively the assembler may decide not to use interconnecting dowels at all. The prime use of the dowels is to ensure that there is no step between conduit units which might damage the cables.

Such a step could occur if the units are not laid on an even gravel bed and/or the units have base regions which vary in thickness due to manufacturing tolerances.

Figure 4 shows conduit units 50 with another variation of configuration of end surfaces. In this configuration each conduit unit 50 has a horizontally extending semi- circular protrusion 51 and a horizontally semi-circular recess 52, as with the figure 3 embodiment. Also each - 12 conduit can have in each end face a pair of blind bores e.g. 53,54 as with the embodiments of figures 2 and 3.

Additionally each conduit unit has a curved vertically extending end face (55 in figure 4) which with a matching coterminous straight conduit unit defines a convex end face for the matched pair of conduit units. The convex end face is curved about an axis extending perpendicularly to the walls of the conduit unit 50.

Furthermore each conduit unit has a curved face (56 in figure 4) which with a matching coterminous straight conduit unit defines a concave end face for the matched pair of conduit units. The concave end face is curved about an axis extending perpendicularly to the walls of the conduit unit 50. The abutting convex and concave end surfaces of matched pairs of conduit units allow for articulation of one matched pair relative to the other about a horizontal axis defined by the interaction of the convex and concave surfaces. This will be the case if either flexible dowels are used to interconnect the blind bores in the end surfaces or use of interconnecting dowels is omitted altogether.

Whilst the conduit units 40 and 50 of figures 3 and 4 are provided with features which allow articulation and interconnection, it is not necessary for an assembler to use these features each time he assembles together the units. The features are there if needed, but may be need; only occasionally. As an example in figure 6 it can be seen that the conduit units of figures 3 and 5 are used in a way which permits no or very little articulation between the conduit units 40 and in a which removes the need for dowels interconnecting the blind bores.

In figure 6 there is a view of the figure 3 conduit units 40 and 40A (the units 4OA are identical to the units 40, save that they are inverted) connected together to form cable "roughing without the use of horizontal dowels. - 13

Instead each of the upper conduit units 40A (one example is shown in dotted lines in the figure) is used to bridge two lower conduit units 40. Mechanical fasteners or vertical dowels (not shown) will be used to secure each upper straight conduit unit to two lower straight conduit units, with the mechanical fasteners or vertical dowels extending through vertically extending open-ended passages 60 provided in each conduit unit 40,40A. From the figure 7 cross-section it can be seen that the passages 60 are provided in each conduit unit 40,40A in transversely aligned pairs. Each unit 40,40A is provided with two pairs of transversely aligned passages and the pairs are spaced longitudinally by a spacing chosen such that passages in an upper unit 40A align with passages in each of two lower units 40 laid end to end when the upper unit 4OA is located above the lower units 40 with one half of the upper unit 4OA located above one of the lower units and the other half of the upper unit 40A located above the other lower unit. The mechanical fasteners used could be nuts and bolts, but they are more likely to be fixings of the type that can be hammered into place from the top surface of the cable "roughing, e.g. the fir tree' or expanding type of fixing. Since each upper unit 40A is fixed to two lower units 40 the need for end to-end fixings, such as the horizontal dowels described previously, is removed. However, with the staggered arrangement of upper 4OA and lower 40 units shown in figure 6 it will not be possible to provide the degrees of articulation possible in arrangements where the units 40,4OA are coterminous, although limited articulation could be provided by each convex surface being formed such that it is not an exact match for each concave surface, but of slightly smaller dimensions so that some play between the abutting surfaces is deliberately provided for.

When the upper 40A and lower 40 straight conduit units - 14 are laid in matched pairs coterminously as seen in figure 8 (in which one example of an upper unit 40A is shown in dotted lines) then the four vertical passages in each upper unit 40A Will align with the four lower vertical passages in each lower unit 40.

The use of fixings extending vertically through the units 40,4OA has the advantage of preventing lateral movements between the upper 40A and lower 40 conduit unit. The fixings will also prevent easy removal of the upper conduit units 40A by vandals or thieves or dislocation by vibration or wind.

Figure 9 shows in side elevation two joint conduit units 70,70A according to the present invention. They are designed to provide a vertical shift upward/downward in the cable "roughing, e.g. to allow the "roughing to bridge an obstacle. Each unit 70,70A is simply formed from the straight conduit units described previously.

This is done by: taking, for instance, two pairs of the figure 3 conduit units 40,40A; fixing the units of each pair together coterminously as upper 40A and lower 40 parts of a cable trough unit with the upper unit 4OA inverted with respect to the lower unit 40 and thereby forming a pair of cable trough units; cutting through each formed cable trough unit in a diagonal plane lying at a chosen angle to a plane perpendicular to the axis of the trough unit, with the same magnitude of angle chosen in each case, but with one unit cut so that the distance between the end of the unit which has the protrusion and the cut line is greater at the bottom of the unit than at the top and with the other unit cut so that the distance between the end of the unit which has the protrusion and the cut line is greater at the top of the unit than at the bottom; taking from each trough unit a cut part having an end with a protrusion and fixing it to a cut part of the other trough unit which has an end with a - 15 recess; and thereby forming two angled joint conduit units 70,70A as illustrated in figure 9. The units 70,70A can be arranged end to end with each other or with straight conduit units 40,40A in the manner described above for the straight conduit units 40,40A.

Figures ll and 12 show in plan view two different angled conduit units 90 and 100, angled in the horizontal plane.

Each can be formed easily by cutting trough units made up of pairs of the conduit units 40. For instance the angled corner conduit unit 90 comprises two parts 91 and 92 each formed from a cut section of a previously assembled trough unit. The angled corner unit 100 comprises three parts 101, 102 and 103 each formed from a cut section of a previously manufactured trough unit.

The angled joint conduit units and the junction units are typically made to be the same length or shorter than the straight units bearing in mind the bending moments which will be applied to them in use.

Figure 10 shows a swept/T-shaped joint 80, which is formed from straight conduit units 40,40A in a manner which will now be described, with reference to figures 13 to 16. In figure 16 it can be seen that a first trough unit, formed from a pair of conduit units 40,40A fixed together, is cut with a W-shaped recess 81 to form a part 82 of the finished T-shaped joint 80. Then a second trough unit, formed form a pair of conduit units 40,40A fixed together, is cut to provide the three parts 83,84 and 85 of the finished T-shaped joint. Then the cut parts 83,84 and 85 are fixed together in the manner shown in figure 13 to form the completed joint. The cut parts are fixed together e.g. by use of epoxy adhesive. It is preferred that the trough units formed from straight conduit units 40,40A are cut and then reassembled to form the T- shaped joint unit at a factory rather than on site. - 16

The T-shaped joint unit will typically be connected to three straight conduit units 40,40A in the manner described above for the straight conduit units 40,4OA. A I side view of the formed unit 80 can be seen in figure 14. I It is advantageous that the sections 84 and 85 provide a swept bend transition zone as illustrated since if the part 83 branched directly off the part 82 then the cables in the unit would have to be turned past a single sharp degree corner (with associated difficulty of routing and wear problems) rather than past two roughly 45 degree corners.

The straight conduit units (all types) are cast in concrete in a multiple mould or gang mould (typically 4m by 2m approximately) which is shown in plan view in figure 17 and in cross-section in figure 18. In a tray there are provided a plurality of moulds 201 each shaped (see figure 18) to produce a straight conduit unit 40. Semi-dry concrete will be delivered to all of the; moulds and then a bar/brush (depending on whether a smooth or rough finish is required) will pass over the I top of each mould to ensure a level filling of the I moulds. Then a flat plate is brought over the back of the multiple mould and the plate and the multiple mould areinverted together. The plate is then lowered with respect to the multiple mould to release the conduit units cast in semi-dry concrete. The plate is then moved to a storage location in which the conduit units are allowed to set hard. The process is designed to be fast ' with the multiple mould refilled every 10 minutes.

The rebates on the exterior surfaces of the conduit units are provided by farmers attached to the surfaces on the moulds 201. The edges of the rebates will typically be radiussed to ease the removal of the cast units from the moulds and also to remove (in the finished product) sharp; edges which could damages cables. In conduit designs - 17 which have blind bores in the end surfaces it will be necessary to provide each mould with movable cores, initially extended to form the blind bores and then retracted to allow release of the formed units from the moulds. Alternatively farmers could be used which are released with the cast units then removed from the released units.

In the figure 17 it can be seen that the majority of the moulds 201 are located close together. However, two moulds 202 and 203 are spaced apart on their own at one end of the array of moulds. It is envisaged that the steel used in the part of the multiple mould in the vicinity of the moulds 202 and 203 will be of thicker gauge than the steel used in the rest of the multiple mould. This will facilitate the attachment of farmers to the interior surface of the moulds 202 and 203 by allowing for e.g. the provision of tapped drillings in the mould surface. It is envisaged that farmers could be (perhaps) releasably attached to the interior surfaces of the moulds 202 and 203 to allow the formation of parts for angled joint conduit units in a one step process without a need for cutting operations. For instance a wooden former with a W-shape could be included in the mould 202 so that the casting formed in the mould has the shape of the part 82 shown in figures 13 and 16.

Then a shaped wooden former could be included in the mould 203 to enable the formation of the three parts 83;84 and 85 of the T-shaped junction 80 without the need for any cutting operations. In this way for every forty eight straight conduit units produced there would also be produced the parts necessary for the manufacture of a T shaped junction 80. Of course, the moulds 202 and 203 could be set up to produce other specially shaped parts, for instance the parts 91 and 92 of the angled joint 90 could be made one each in the moulds 202 and 203. Half length straight conduit units could also be formed in the - 18 moulds 202 and 203.

An additional option would be to include a cast-in plastic liner in each unit. A liner sheet would be laid covering a part of each mould (e.g. the part 210 shown in figure 18) and then the concrete poured in on top of the liner. Typically the liner would have an array of keys protruding from the sheet across the surface which is in contact with the concrete so that the sheet is secured firmly to the concrete when it sets. The liner sheet would typically be 2mm thick so that it could easily bend around the corners in the mould. The use of a liner sheet would increase the smoothness of the interior surface of each conduit unit, reducing cable damage and decreasing cable friction during cable pulling.

In a further variant each straight conduit unit could be provided with a plurality of vertically extending rebates positioned along the sides of the U-shaped channel which would allow an assembler to insert vertically extending pegs during assembly of a cable trough from the units.

This would mean that the assembler could lay cables above the height of the U-shaped channel in the lower straight conduit unit before enclosing the cables be the laying of an upper straight conduit unit above the previously laid lower unit. Thus this would maximise the use of the space of the void in the formed cable trough. It is possible that free standing rods could be used.

Whilst above the conduit units are made from cast concrete and this is greatly preferred for reasons of cost, fire resistance, ease of manufacture and durability the units could be made from other materials. One possibility would be to preform fibrous bodies and then spray them with cement to form the conduit units. - 19

Claims

Claims 1. A conduit unit for use in the assembly of a cable trough, the

conduit unit having a channel defined by a base portion and a pair of spaced apart walls extending away from the base portion and one wall having male locating means and the other wall having female locating means whereby the conduit unit can be assembled with an identical inverted conduit unit with the male locating means co-operating with female locating means of the inverted unit and with the female locating means cooperating with male locating means of the inverted unit in order that one conduit unit is securely seated on the other to form a part of the cable trough.
2. A conduit unit as claimed in claim 1 which is a cast concrete unit in which the male and female locating means are integral features of the conduit unit formed during casting thereof.
3. A conduit unit as claimed in claim 1 or claim 2 wherein the male locating means comprises a convex upper surface of one wall and the female locating means comprises a matching concave surface on the other wall.
4. A conduit unit as claimed in any one of claims 1 to 3 wherein a rebate is provided in an external surface of one wall to provide a wall region of decreased thickness visible to the exterior of the conduit unit which can be punched through to provide a shaped aperture through which cables may pass.
5. A conduit unit as claimed in any one of claims 1 to 4, wherein the end surfaces of both ends of the base portion extend transversely of the unit and the end surfaces of the walls are inclined relative to the end surfaces of the base portion. -
6. A conduit unit as claimed in any one of claims 1 to 4 wherein the base portion is provided at one end with a shaped protrusion and at the other end with a recess of matching shape whereby the unit can be assembled end to end with two identical conduit units with the shaped protrusion extending into a recess in one of the adjacent conduit units and with the shaped recess receiving a protrusion of the other adjacent conduit unit.
7. A conduit unit as claimed in claim 6 wherein the protrusion and the recess are semi-circular when viewed in plan view in order to facilitate, during assembly of the cable trough, pivoting between conduit units joined end to end about an axis parallel to the walls.
8. A conduit as claimed in any one of claims 1 to 4 or 6 and 7 in which each end surface of the conduit unit is curved to facilitate, during assembly of the cable trough, pivoting between conduit units joined end to end about an axis perpendicular to the walls.
9. A conduit unit as claimed in any one of the preceding claims having a plurality of preformed passages therethrough into which can be inserted mechanical fastening means used to secure the conduit unit to the inverted conduit unit assembled therewith.

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10. A conduit unit as claimed in any one of the preceding claims wherein each end face of the conduit unit is provided with a plurality of blind bores into which mechanical fasteners can be inserted to secure the conduit unit end to end with an adjacent conduit unit.
11. A conduit unit as claimed in any one of the preceding means wherein along side edges of the channel of a plurality of vertically extending rods extending - 21 above the channel.
12. A conduit unit as claimed in claim 11 wherein the installation means are provided along side edges of the channel to permit installation of the rods, the installation means comprising a plurality of rebates in side surfaces of the channel.
13. Cable "roughing comprising at least two conduit units, each having a channel defined by a base portion and a pair of spaced apart walls extending away from the; base portion, the cable tough being assembled with one conduit unit inverted with respect to the other conduit unit and with the walls of one conduit unit seated on the walls of the other conduit unit.
14. Cable "roughing as claimed in claim 13 wherein the two conduit units are identical to each other, at least when initially formed.
15. Cable "roughing as claimed in claim 13 or claim 14 assembled with the inverted conduit unit coterminous with the conduit unit on which it is seated.
16. Cable "roughing as claimed in claim 13 or claim 14 in which at least three conduit units are assembled with I the one conduit unit inverted with respect to the other two conduit units and with the inverted conduit unit bridging the other two conduit units and with the walls of the inverted conduit unit seated partly on the walls of a first of the other two conduit units and partly on a second of the other two conduit units.
17. Cable "roughing as claimed in any one of claims 13 to 16 in which each conduit unit has male locating means provided on one wall and female locating means provided on the other wall whereby when the cable trough unit is - 22 assembled the male locating means of a first conduit unit cooperate with female locating means of at least a second conduit unit inverted with respect thereto and the female locating means of the first conduit unit co operate with male locating means of at least the second inverted conduit unit in order that the second inverted conduit unit is securely seated on the first conduit unit.
18. Cable "roughing as claimed in claim 17 wherein each of the conduit units is a cast concrete unit in which the male and female locating means are integral features of the conduit unit formed during casting thereof.
19. Cable "roughing as claimed in any one of claims 13 to 18 wherein each of the conduit units has a rebate provided in an external surface of only one wall to provide a wall region of decreased thickness visible to the exterior of the conduit unit which can be punched through to provide a shaped aperture through which cables may smoothly pass, whereby the cable trough has a wall region of decreased thickness provided on a first side a first level by a first conduit unit and a wall region of decreased thickness provided on a second side at a second higher level by a second conduit unit inverted with respect to the first conduit unit.
20. Cable "roughing as claimed in any one of the preceding claims wherein a length of the cable "roughing is formed by assembly end to end of a lower plurality of the conduit units to form a lower part of the cable "roughing and by assembly end to end of an upper plurality of the conduit units inverted with respect to and seated on the lower plurality of conduit units to form an upper part of the cable "roughing, and wherein the base portion of each of the conduit units is provided at one end with a shaped protrusion and at the other end - 23 with a recess of matching shape whereby the shaped protrusion of each conduit unit extends into a recess in an adjacent conduit unit and the shaped recess of each conduit unit receives a protrusion of an adjacent conduit unit.
21. Cable "roughing as claimed in claim 20 wherein the base portion of each conduit unit has end surfaces which; extend transversely across the unit and each wall has end surfaces inclined relative to the base portion.
22. Cable "roughing as claimed in claim 20 wherein in each conduit unit the protrusion and the recess are semi- circular when viewed in plan view in order to facilitate, during assembly of the cable "roughing, pivoting between conduit units joined end to end about an axis parallel to the walls.
23. Cable "roughing as claimed in any one of claims 13 to 20 in which each end surface of each of the conduit units is curved to facilitate, during assembly of the cable "roughing, pivoting between conduit units joined end to end about an axis perpendicular to the walls.
24. Cable "roughing as claimed in any one of claims 13 to 20 having a plurality of mechanical fasteners which extend through passages preformed in each of the plurality of conduit units to secure each conduit unit to at least one inverted conduit unit 'sedated thereon.
25. Cable "roughing as claimed in any one of claims 13 to 24 wherein each end face of each conduit unit is provided with a plurality of blind bores and mechanical fasteners are inserted in to the blind bores to secure each conduit unit end to end with an adjacent conduit unit. - 24
26. Cable "roughing as claimed in any one of claims 13 to 25 wherein each conduit unit is provided with a plurality of vertically extending rods each extend above the channel.
27. Cable "roughing as claimed in claim 26 wherein in each conduit unit installation means is provide along the side edges of the channel for securing the rods, the installation means comprising a plurality of rebates in side surfaces of the channel.
28. A method of manufacture of an angled joint conduit unit comprising the steps of: forming a plurality of conduit units of the type claimed in any one of claims 1 to 12; joining at least two pairs of the conduit units together to form two cable trough units each comprising a lower conduit unit with an upper conduit unit seated thereon, the upper conduit unit being inverted relative to the lower conduit unit; cutting at least two of the formed cable trough units each along a plane angled with respect to a plane extending transversely across the cable trough unit; and joining along the cut planes at least one cut part of one trough unit with a cut part of the other trough unit.
29. A method of manufacture of an angled joint conduit unit comprising the steps of: forming a plurality of conduit units of the type claimed in any one of claims 1 to 12; joining at least one pair of the conduit units together to form a cable trough unit comprising a lower conduit unit with an upper conduit unit seated thereon, the upper conduit unit being inverted relative to the lower conduit unit; cutting the formed cable trough unit along at least two cut planes each angled with respect to a plane extending - 25 transversely across the cable trough unit; and joining along the cut planes at least one cut part of the trough unit with another cut part of the trough unit.
30. A method of manufacture of a T-junction conduit unit comprising the steps of: forming a plurality of conduit units of the type claimed in any one of claims 1 to 12; joining a plurality of the conduit units together to form a plurality of cable trough units each comprising a lower conduit unit with an upper conduit unit seated thereon, the upper conduit unit being inverted relative to the lower conduit unit; cutting a W-shaped notch in one side of a first cable trough unit; cutting from one or more additional trough units at least two swept junction sections and a side branch section; fixing the swept junction sections in the W-shaped notch of the first cable trough unit to form a swept junction; and fixing the side branch section to the formed swept junction to complete the Tjunction conduit unit.
31. A method of manufacture of cable "roughing of the type claimed in any one of claims 13 to 27, the method comprising the steps of: casting in concrete in a gang mould a plurality of straight conduit units, each having a channel defined by a base portion and a pair of spaced apart walls extending away from the base portion; removing the cast straight conduit units from the gang mould; transporting the cast straight conduit units to a site where they are needed; and on site assembling the cable "roughing from the plurality of straight conduit units by laying them end to end with some of the straight conduit units forming a lower part - 26 of the cable "roughing and other straight conduit units forming an upper part of the cable "roughing, the straight conduit units of the upper part being inverted with respect to the straight conduit units of the lower part and the walls of the straight conduit units of the upper part being seated on walls of the straight conduit units of the lower part.
32. A method as claimed in claim 31 wherein the straight conduit units are cast in semi dry concrete.
33. A method as claimed in claim 31 or claim 32 wherein in at least one mould of the gang mould a former is provided to define a rebate in an external surface of a cast straight conduit unit.
34. A method as claimed in any one of claims 31 to 33 wherein joint sections for forming angled joint conduit units are cast in concrete in at least one mould of the gang mould, with one or more former(s) being provided in the said mould(s) to define features of the joint sections.
35. A method as claimed in claim 34 wherein the joint sections are assembled to form the angled joint conduit units before the angled joint conduit units are transported to the site of installation.
36. A gang mould comprising a plurality of moulds, a majority of which are used for casting of straight conduit units to be used in formation of cable troughs of the type described in any one of claims 13 to 25 and a minority of which are used in casting of joint sections for the formation of angled joint conduit units for use with the said cable troughs, wherein the minority of the moulds used for the casting of the joint sections are provided with one or more former(s) to define the features of the joint sections.
37. A gang mould as claimed in claim 36 which is made out of metals and wherein the walls of the moulds used in the casting of straight conduit units are thinner than the walls of the moulds used in the casting of the joint sections.
38. A conduit unit substantially as hereinbefore described with reference to and as shown in the accompanying drawing figures 1 to 4.
39. Cable "roughing substantially as hereinbefore described with reference to and as shown in the accompanying drawing figures 5 to 8.
40. An angled joint conduit unit substantially as hereinbefore described with reference to and as shown in the accompanying drawing figures 9,11 and 12.
41. A T-shaped junction unit substantially as hereinbefore described with reference to and as shown in the accompanying drawing figures 10 and 13 to 16.
42. A gang mould substantially as hereinbefore described with reference to and as shown in the accompanying drawing figures 17 and 18.

447956: AM: AM: LONDOCS